TW201343296A - Laser scribing system and method with extended depth affectation into a workpiece - Google Patents

Abstract

Systems and methods for laser scribing provide extended depth affectation into a substrate or workpiece by focusing a laser beam such that the beam passes into the workpiece using a waveguide, self-focusing effect to cause internal crystal damage along a channel extending into the workpiece. Different optical effects may be used to facilitate the waveguide, self-focusing effect, such as multi-photon absorption in the material of the workpiece, transparency of the material of the workpiece, and aberrations of the focused laser. The laser beam may have a wavelength, pulse duration, and pulse energy, for example, to provide transmission through the material and multi-photon absorption in the material. An aberrated, focused laser beam may also be used to provide a longitudinal spherical aberration range sufficient to extend the effective depth of field (DOF) into the workpiece.

Description

Laser cutting system and method for extending depth in a workpiece [Cross-application for related applications]

This application is a continuation-in-part application of U.S. Patent Application Serial No. 12/962,050, filed on Dec. 7, 2010, which is incorporated herein by reference. The right of the present application is hereby incorporated by reference.

This invention relates to laser processing, and more particularly to laser cutting having an extended depth illusion in a workpiece.

Lasers are commonly used to cut or scribe a workpiece (such as a substrate or semiconductor wafer). For example, in semiconductor fabrication, a laser is often used to cut a semiconductor wafer to separate individual devices (or die) made from the semiconductor wafer. Each die on the wafer is separated by a street and the wafer can be cut along the via using a laser. The wafer can be completely cut using a laser, or the wafer can be completely cut and the remainder of the wafer separated by breaking the wafer at the point of perforation. For example, when a light emitting diode (LED) is fabricated, each die on the wafer corresponds to an LED.

As semiconductor devices are becoming smaller in size, the number of such devices that can be fabricated on a single wafer is increased. An increase in device density per wafer increases throughput and similarly reduces the cost of manufacturing each device. To increase this density, it is desirable to manufacture such devices as closely as possible. The tighter the device is positioned on the semiconductor wafer, the narrower the barrier between the devices. Thus, the laser beam is accurately positioned within the narrower channel and the wafer should be cut with minimal or no damage to the device.

According to one technique, a laser can be focused onto one of the substrate or wafer The surface is ablated and a partial cut is achieved. Laser cutting can be performed on a semiconductor wafer, for example, on the front side of the wafer on which the device is formed (referred to as front-side scribing (FSS)), or on the back side of the wafer (called For back-side scribing (BSS). Although these techniques are effective, they also have disadvantages. This two process often results in a large amount of debris generation and often requires a coating and rinsing process to remove or reduce debris. Backside cutting often uses a wider slit and a wider heat affected zone (HAZ), which can cause heat generation, which can cause epitaxial damage and light loss.

According to another technique, often referred to as stealth scribing, a laser can be focused on a wafer by a high numerical aperture (NA) lens (eg, NA > 0.8). Multiphoton absorption is caused within the material. The high NA lens provides a very short working distance and a very small depth of field (DOF). This process also has several drawbacks. In particular, invisible dicing may limit the thickness of the wafer, may be difficult to perform on warped wafers, and may be much slower when performed on thicker wafers, as it may take several passes to achieve separation. Invisible dicing also provides a relatively large spot size on the surface of the wafer, which can prevent frontal dicing in narrow channels between dies or require less crystal on each wafer. grain. Stealth cutting technology also has problems in processing wafers with DBR or metal reflective films because of the inability to achieve the desired focus inside the wafer. Invisible cutting also requires expensive lenses and tight focus tolerances, and invisible cutting equipment typically has higher equipment costs and annual maintenance costs.

100‧‧‧Laser processing system

102‧‧‧Workpiece

104‧‧‧ Surface

106‧‧‧Ablative area

108‧‧‧Internal position

110‧‧‧Laser

112‧‧‧Original laser beam

114‧‧‧Expanded beam

116‧‧‧Focused laser beam

120‧‧‧beam delivery system

122‧‧‧beam expander

124‧‧‧focus lens

202‧‧‧Workpiece

204‧‧‧ surface

212‧‧‧Original laser beam

213‧‧‧Light

214‧‧‧Expanded laser beam

215‧‧‧Light

216‧‧‧ Focused laser beam

222‧‧‧beam expander

223‧‧‧Diffraction restricted area

224‧‧‧focus lens/lens

226‧‧‧ paraxial focal plane

228‧‧‧effective DOF

δ _f ‧‧‧Focus offset

802‧‧‧ sapphire substrate

805‧‧‧Laser area

806‧‧‧ ablative holes

808‧‧‧Extended depth imaginary channel

1000‧‧‧Laser processing system

1001‧‧ plane

1002‧‧‧Workpiece

1003‧‧‧ side

1005‧‧‧ opposite side

1016‧‧‧ Focused laser beam

1020‧‧•Laser beam delivery system

1030‧‧‧Air-floating X-Y positioning table/X-Y positioning table

1034‧‧‧Workpiece support

1040‧‧‧ opposite side camera

1044‧‧‧Front camera

1050‧‧‧ Motion Control System

1101‧‧‧Semiconductor wafer

1102‧‧‧Substrate

1103‧‧‧ positive

1104‧‧ layer

1105‧‧‧Back

1106‧‧‧Ablative area

1107‧‧‧way

1108‧‧‧Extended depth illusion

1109‧‧‧Grain section/section

1116‧‧‧Laser beam

1140‧‧‧ opposite side camera

1201‧‧‧Semiconductor Wafer

1203‧‧‧ positive

1205‧‧‧Back

1206a‧‧‧Back cutting line

1206b‧‧‧ front cutting line

1207‧‧‧way

1208‧‧‧Extended depth illusion

Section 1209‧‧‧

1216‧‧‧Laser beam

1240‧‧‧ opposite side camera

1244‧‧‧Processing side camera

1300‧‧ ‧ laser processing system

1302‧‧‧Workpiece

1304‧‧‧ surface

1306‧‧‧Ablative area

1308‧‧‧Internal position

1310‧‧‧Super fast laser

1316‧‧‧Linear beam

1320‧‧‧beam delivery system

1321‧‧‧Original laser beam

1322‧‧‧beam expander

1323‧‧‧Expanded beam

1324‧‧‧focus lens

1325‧‧‧Oval beam

1326a‧‧‧Cylindrical plano-concave lens

1326b‧‧‧Cylindrical plano-lens lens

1328‧‧‧ reflector

The above and other features and advantages of the present invention will become more apparent from the written description of the appended <RTI A schematic diagram of one of the laser cutting systems; and FIG. 2 is a schematic diagram of one of the focusing lenses for focusing a laser beam and locating the spherical aberration in a diffraction limited region according to an embodiment of the invention 3A is a schematic diagram of a lens providing a paraxially focused laser beam with a spherical aberration; FIG. 3B is a lens being overfilled beyond a diffraction limited region to provide an aberration A schematic diagram of a focused laser beam having a range of longitudinal spherical aberrations sufficient to extend depth of field into a workpiece and a limited range of lateral spherical aberration; FIG. 3C is a lens overfilled Further extending beyond a diffraction-limited region to provide a schematic image of a focused laser beam having aberrations having a larger range of longitudinal and lateral spherical aberration; FIGS. 4A through 4C are images having an image A schematic diagram of a poorly focused laser beam at a different focus offset position relative to a surface of a workpiece; 5A to 5D are a focused laser beam with different focus offsets and different spherical aberrations from one A schematic diagram of a ternary lens having a focal length of 60 millimeters (mm) into a sapphire of 250 micrometers thick; and FIGS. 6A to 6D are diagrams of a focused laser beam with different focus offsets and different spherical aberration amounts from one to 54 The binary lens of the rice focal length enters the schematic diagram of the sapphire of 250 micrometers thick; the 7A to 7D are the ternary of a focused laser beam with different focal offsets and different spherical aberrations from a focal length of 25 mm. A schematic view of a lens entering a 120 micrometer thick sapphire; Fig. 8 is a photograph showing a surface of a sapphire substrate having a series of ablation holes by an embodiment in accordance with the invention Formed by a method; FIG. 9 is a photograph showing one of the sides of a sapphire substrate, the side having a series of extended embossments extending from the ablation holes, the extended embossed by an embodiment according to the present invention One of the methods is formed; FIGS. 10A and 10B are schematic views of a laser processing system having a workpiece positioning table according to an embodiment of the present invention, the workpiece positioning table being respectively located at an aligned position and a laser processing position; Figure 11 is a side elevational view of a backside cut in accordance with an embodiment of the present invention, wherein a laser beam is aligned with the opposite side of a channel on a semiconductor wafer; Figures 12A and 12B are based on A side view of a double-sided cut of an embodiment of the invention in which a laser beam is aligned on the opposite side from a shallow back scratch; and FIG. 13 is an extension for use in accordance with another embodiment of the present invention. A schematic diagram of a laser cutting system with deep illusion and a slender beam spot for cutting.

In accordance with an embodiment of the present invention, a system and method for laser cutting provides an extended depth imaginary in a substrate or workpiece by focusing a laser beam and causing the beam to enter using a waveguide self-focusing effect. In the workpiece, internal crystal damage is caused by a passage extending into the workpiece. Different optical effects (eg, multiphoton absorption in the workpiece material, transparency of the workpiece material, and optical aberrations of the focused laser beam) can be utilized to promote the waveguide self-focusing effect. The laser beam can have a wavelength, pulse duration, and pulse energy, for example, to at least partially transmit the material and provide multiphoton absorption in the material. A focused laser beam with aberrations can also be used to provide a range of longitudinal spherical aberrations sufficient to extend the effective depth of field (DOF) into the workpiece.

Laser cutting that produces extended depth illusions can be used to cut a workpiece, such as a substrate or a semiconductor wafer, for example to separate the dies. According to one application, the laser processing systems and methods described herein can be used to process semiconductor wafers to separate crystal grains for forming light emitting diodes (LEDs). Laser cutting that produces extended depth illusions can be used for backside cutting and/or frontal cutting of semiconductor wafers of different thicknesses. The different materials can be cut in an extended depth imaginary by selecting laser parameters and optical parameters that enable at least partial transmission of the material and multi-photon absorption in the material. In particular, the methods described herein can be used to cut sapphire, tantalum, glass, and other substrates or materials that enable a laser beam to at least partially penetrate the material while being sufficiently absorbed to cause crystal damage. A laser cut that produces an extended depth imaginary can also be preferably used, for example, on a workpiece having an opaque coating. The initial ablation can cut through the opaque coating.

As used herein, the term "machining" refers to any action that uses a laser energy to change a workpiece, and "cutting" refers to the action of machining a workpiece by scanning a laser over the workpiece. Processing may include, but is not limited to, material ablation of the surface of the workpiece and/or damage to the material crystals within the workpiece. Cutting can include a series of ablated or crystal damaged regions without the need for a continuous row of ablation or crystal damage. As used herein, the term "extended depth illusion" refers to crystal damage occurring along a passage extending inside the workpiece due to the energy of the laser and the interaction of photons and material within the workpiece.

A laser cut that produces an extended depth imaginary cut can be external to one of the ablative materials and then focus the beam inside to cause internal cracking or crystal damage (ie, extended depth illusion), thereby causing or facilitating cutting or dicing For example, to separate wafer grains. Initial ablation can cause a change in refractive index that promotes the waveguide or self-focusing effect of the laser into the slit to create a convergence within the crystal structure of the material, effectively focusing the high electric field energy to a point where it occurs. Crystal damage. The laser parameters can be optimized to provide a clean ablation (i.e., with minimal debris) to promote self-focusing effects, as will be explained in more detail below. In other embodiments, a laser cut that produces an extended depth illusion can also be performed without ablating the surface of the workpiece.

The extended depth imaginary can be achieved by adjusting the laser parameters (eg, wavelength, pulse duration, and pulse energy) such that it is at least partially transmissive to the material and provides multiphoton absorption sufficient to disrupt the crystal structure of the material. In particular, the laser beam may have a wavelength that is transmissive to the workpiece material (eg, infrared, green, or ultraviolet wavelengths) and may include an ultrashort pulse (eg, less than 1 nanosecond) Or a short pulse (eg, less than 200 nanoseconds) one of the pulsed laser beams, thereby providing one of the peak powers that can cause multiphoton absorption. Thus, by using a substantially transparent target and a high energy ultrafast laser, the balance of irradiance and extended depth of field (DOF) allows for deep volume range interaction with the target.

The laser wavelength may be in the infrared (IR) range and may be from one to five harmonics, more specifically, for example from about 1.04 micron to 1.06 micron (IR), from 514 nm to 532 nm (green light) ), from 342 nm to 355 nm (UV), or from 261 nm to 266 nm (UV). In sapphire, for example by UV Cutting by one of the laser wavelengths (for example, 266 nm, 343 nm, or 355 nm) is achieved by extending the depth illusion. In the crucible, the cutting by the extended depth imaginary can be achieved by a laser wavelength in the IR range, for example longer than 1.2 microns (where the enthalpy begins to transmit), more particularly about 1.5 microns. The glass can be cut using a laser wavelength in the visible range to extend the depth illusion. As disclosed herein, the dicing by extending the depth imaginary can also be used for semiconductor and dielectric materials having a band gap by using a laser wavelength that is transmissive to materials that include Not limited to GaAs and other III-V materials, SiC, Si, GaN, AIN, and diamond.

Using a longer wavelength (e.g., compared to conventional cutting techniques) with a shorter pulse wave results in better coupling efficiency and absorption of the laser energy, particularly in highly transparent materials such as sapphire. The pulse duration can be shorter than the thermal diffusion time, which in turn causes rapid evaporation of the material (ie, evaporative ablation with a solid to vapor transition). To minimize melting of certain materials, for example, the pulse duration can be sub-picoseconds. When processing sapphire, for example, an ultrashort pulse duration of less than about 10 picoseconds (ps) can be used. In other examples, longer pulse durations greater than 1 nanosecond or even greater than 100 nanoseconds may also be used (eg, 150 nanoseconds to 200 nanoseconds of pulse waves may be used in the sputum).

For example, ultra-fast lasers can be used to generate ultra-short pulses of picosecond or femtosecond. In some embodiments, ultrafast lasers can be capable of producing different wavelengths (eg, about 0.35 micrometers, 0.5 micrometers, 1 micrometer, 1.3 micrometers, 1.5 micrometers, 2 micrometers, or any increment therebetween) and different ultrashort pulses. The original laser beam with a wave duration (eg, less than about 10 picoseconds). An example of an ultrafast laser includes one of the TruMicro series 5000 picosecond lasers available from TRUMPF. The laser can also provide a pulse energy in the range of about 1 microjoule (μJ) to 1000 microjoules at a repetition rate in the range of about 10 kilohertz (kHz) to 1000 kilohertz.

Laser cutting that produces extended depth illusions typically uses optics that have a long working distance (eg, a lower NA lens compared to a high NA lens for stealth dicing). Optics with longer working distance and lower NA can be packaged A focusing lens having, for example, an NA of less than 0.8, more particularly less than 0.5 or less than 0.4 is included. A laser cut that produces an extended depth illusion may also introduce a spherical aberration having a range of longitudinal spherical aberrations sufficient to extend the effective DOF into a workpiece. Lenses with longer working distances and lower NA typically have a longer DOF than lenses with higher NA. The use of a lens incorporating spherical aberration further extends the effective DOF so that the waveguide self-focusing effect adds energy to an extension in the workpiece.

As will be explained in more detail below, by adjusting laser parameters (eg, wavelength, pulse duration, and pulse energy), processing parameters (eg, pulse spacing), and optical parameters (eg, working NA and Depth of focus) to control the depth of the extended depth illusion.

Referring to Fig. 1, an embodiment of a laser processing system 100 for laser cutting by extending depth imaginary can be used to cut a workpiece 102 (e.g., a sapphire substrate of a semiconductor wafer). This embodiment of the laser processing system 100 includes a laser 110 for generating an original laser beam and a beam delivery system 120 for focusing the laser beam and focusing the laser beam. The beam is directed to one of the surfaces 104 of the workpiece 102. The beam delivery system 120 includes a beam expander 122 and a focusing lens 124 for expanding an original laser beam 112 from the laser 110 to form an expanded beam 114, the focusing lens 124 being used The dilated beam 114 is focused to provide a focused laser beam 116. Beam delivery system 120 may also include an autofocus system (not shown), although this need not be the case.

In the illustrated embodiment, the laser processing system 100 focuses the dilated laser beam 114 such that one of the focused laser beams 116 has an energy density sufficient to ablate the surface 104 of the workpiece 102 in an ablation region 106 and The beam penetrates the ablated region 106 and enters the workpiece 102 using a waveguide self-focusing effect. Thus, the waveguide self-focusing effect directs the focused laser beam 116 from the ablation zone 106 to an internal location 108 extending within the workpiece 102 where the crystal is damaged by vibration, electric field and/or pressure. Each pulse of the focused laser beam 116 forms a beam spot on the workpiece 102 and extends into the workpiece 102 using a waveguide self-focusing effect to provide high energy over an extended depth and along the channel at an internal location 108. Causing crystal Body damage. Although it may be sufficient to use only a single pulsed focused laser beam 116 at each location, a multi-pulse process may be used in which subsequent pulses provide deeper or stronger material cracking.

The focused laser beam 116 can be scanned over the workpiece 102, and a series of ablation zones 106 and crystal damage internal locations 108 (i.e., extended embossments) are formed along a cutting line by a series of laser pulses. For example, the laser beam 116 can be scanned in a single pass or multiple passes to achieve various depths and spacings. For example, workpiece 102 can be moved relative to focused laser beam 116 to form a series of ablation zones 106 and crystal damage internal locations 108. The ablation zone 106 and the crystal damage internal location 108 may thereafter facilitate separation of the workpiece 102 along the cutting line. Although the illustrated embodiment shows front side cuts on a semiconductor wafer having LED dies, the laser processing system 100 can also be used for back side or double sided cut, as will be explained in more detail below.

Depending on the type of material, the laser 110 can be capable of emitting short pulses (eg, less than about 200 nanoseconds) or ultrashort pulses (eg, less than about 1 nanosecond) that are at least partially transparent to the material of the workpiece 102. ). According to one example of cutting sapphire by extending the depth imaginary, the laser 110 is an ultra-fast laser that emits an original laser beam having a wavelength in the UV range (eg, about 266 nm) , 343 nm, or 355 nm) and have a pulse duration of less than about 10 picoseconds and a pulse energy of about 60 microjoules. Such a laser provides a wavelength that can penetrate the sapphire and a peak power that is high enough to damage the crystal at the internal location within the sapphire. The laser 110 can be operated at a repetition rate to achieve a desired cut at a particular scan speed. According to an example of a processed sapphire, it can operate at a repetition rate of about 33.3 kHz and at a scanning speed of about one of a range of about 70 mm/sec (mm/s) to 90 mm/sec (mm/s) with about 60 microjoules. A UV laser with pulse energy. In another example, the repetition rate can be about 100 kHz and a scan speed is about 100 mm/sec to 300 mm/sec. In other embodiments, a lower power laser (eg, about 8 watts (W) can be used with a reduced pulse energy (eg, about 40 microjoules) and a higher repetition rate (eg, about 200 kilohertz). )).

The beam expander 122 can be a 2×expanding telescope, and the focusing lens 124 can be a 60 mm ternary lens for A focal depth of about 400 microns (μm) and a desired kerf width of about 3 microns achieve an effective focusability. The beam expander 122 can be, for example, a beam expander telescope comprising a combination of an uncoated negative lens (e.g., f = -100 mm) and a positive lens (e.g., f = 200 mm). Focusing lens 124 can have an NA of less than 0.8, more specifically less than 0.5 or less than 0.4, which provides a longer working distance and a longer DOF. The focusing lens 124 can also introduce spherical aberration to provide a focused laser beam 116 having aberrations, and the focused laser beam 116 having aberrations has a range of longitudinal spherical aberrations sufficient to further effective DOF Extending into the workpiece 102 will be explained in more detail below.

The combination of a focused laser beam with an ultrashort pulse or a short pulse causes enhanced focus performance (with lower NA optics) to cause crystal damage at the internal location 108 of the workpiece 102 while simultaneously causing the workpiece surface 104 to be The amount of material removed (eg, debris) is minimized. Laser 110 and beam delivery system 120 may be configured with laser processing parameters (eg, wavelength, pulse duration, pulse energy, peak power, repetition rate, scan speed, and beam length and width), such laser processing The parameters enable surface ablation and self-focusing effects on the material to be cut and the desired slit width.

As shown in more detail in FIG. 2, the extended depth imaginary can be promoted by extending the effective DOF of a focused laser beam 216 having aberrations using the lens aberration of a focusing lens 224. Lens aberration is the deviation of light from a perfect path after passing through a lens, which is predicted by the paraxial optics. In particular, spherical aberration is produced by the deviation of light passing through a lens further from the optical axis of the lens.

In this embodiment, a portion of the focusing lens 224 typically includes a diffraction limited region 223 that provides diffraction substantially free of aberrations (i.e., diffraction effects over performance that exceed the effects of aberrations on performance). Limited performance. The ray 213 of a laser beam 214 that illuminates the lens 224 within the diffraction limited region 223 is focused at the paraxial focal plane 226, thereby producing a high resolution focused beam spot in this region of the focused laser beam 216. . Outside the diffraction limited region 223, Focusing lens 224 introduces spherical aberration into the focused laser beam 216 with aberrations. The ray 215 that illuminates the lens 224 outside the diffraction limited region 223 is offset from the paraxial focus and is focused (ie, across the optical axis of the lens 224) at an extended focus behind the paraxial focal plane 226. Therefore, the spherical aberration effectively effectively extends the focus of the focused laser beam 216 having aberrations from the paraxial focus.

The distance of the focus of the ray 215 having aberrations extending along the optical axis of the lens 224 beyond the paraxial focal plane 226 is a longitudinal spherical aberration (LSA) range, and the ray 215 having aberrations is along the paraxial focal plane. The distance extended by 226 is the transverse spherical aberration (TSA) range. The LSA range extends the effective DOF 228 of the focused laser beam 216 beyond the paraxial focal plane 226 and facilitates the creation of extended depth artifacts in a workpiece, as will be explained in more detail below.

Thus, embodiments of the present invention utilize a focus lens in a manner contrary to conventional knowledge. In lens systems for laser cutting, it is often desirable to avoid or correct lens aberrations to provide a well focused beam spot. However, in accordance with an embodiment of the present invention, lens aberrations are intentionally utilized to form an optical effect capable of extending the DOF to cut a workpiece by extending the depth smear. Moreover, as described herein, a lens for laser cutting by extending depth imaginary can be less expensive than a high NA lens required for stealth cutting.

Focusing lens 224 may comprise a multi-element lens (eg, a binary lens or a ternary lens) that corrects aberrations within diffraction-limited region 223 rather than across the entire aperture of lens 224. Focusing lens 224 can also provide a relatively long working distance and a low NA of less than about 0.8, more specifically less than about 0.5 or less than about 0.4. Different substrate materials and thicknesses may have different optimal parameter combinations for cutting by extending the depth imaginary, including wavelength, pulse duration, working NA, longitudinal spherical aberration range, and defocus. Therefore, the exact optical parameters of the lens will depend on the type of material being cut.

As shown in Figures 3A through 3C, the focusing lens 224 can be designed and/or illuminated to introduce a range of longitudinal spherical aberrations sufficient to extend the effective DOF while limiting the range of lateral spherical aberration. For example, the operation or operation of the lens 224 is NA (or F#) may be selected to provide a range of longitudinal spherical aberrations that will provide a desired extended imaginary within a workpiece 202 while limiting the range of lateral spherical aberration such that the spot beam spot size on one of the surfaces 204 of the workpiece 202 is not It will be too big. The desired beam spot size on the workpiece surface 204 depends on the particular application and can be less than about 20 microns for dicing the semiconductor wafer and grain separation.

In this embodiment, the operation or operation NA of the lens 224 can be adjusted by expanding a raw laser beam 212 using a beam expander 222 to produce a dilated laser beam 214 that dilates the laser beam 214 to illuminate the lens. One of the variable apertures of the 224 clear aperture. When the dilated laser beam 214 illuminates the aperture of the lens 224 only within the diffraction limited region 223, as shown in FIG. 3A, the focused beam 216 includes only paraxial rays that are focused to the paraxial focal plane, which is shown in On the surface 204 of the workpiece 202. This does not provide for extending the depth of the effective DOF into one of the longitudinal spherical aberration ranges within the workpiece 202 to provide an extended depth illusion.

When the expanded laser beam 214 just illuminates the aperture of the lens 224 beyond the diffraction limited region 223, as shown in FIG. 3B, the focused beam 216 also includes light having aberrations that are capable of extending the DOF 228 into the workpiece. One of the longitudinal spherical aberration ranges in 202 is focused outside of the paraxial focal plane. Since the longitudinal spherical aberration is dominant when the diffraction is not very limited when the lens is working in the vicinity, the range of the lateral spherical aberration of the light having the aberration of the focused beam 216 can be limited. Therefore, the longitudinal spherical aberration range extends the DOF while still maintaining the lateral spot size under control.

When the expanded laser beam 214 illuminates the entire aperture of the lens 224, as shown in FIG. 3C, the focused beam 216 contains light having aberrations that further extend the lateral spherical aberration range and further increase the workpiece. The beam spot size on surface 204 of 202. In this example, the increased range of lateral spherical aberration can invalidate the extended DOF effect provided by the longitudinal spherical aberration.

Thus, the lens 224 can be illuminated by a working NA such that the longitudinal spherical aberration range is sufficient to extend the DOF into the workpiece to create the desired extended depth illusion while limiting the range of lateral spherical aberration. The beam size can be gradually increased at lens 224 (eg, increasing the working NA) until it is found inside the material of workpiece 202 Produce the best size for the extended depth illusion. Limiting the lateral spherical phase difference range enables the beam spot size on the surface of the workpiece to be reduced, the laser region to be smaller, and the ablation region to be smaller, while still achieving a range of longitudinal spherical aberration sufficient to extend the effective DOF. In one embodiment, the range of lateral spherical aberration can be substantially limited to produce one of less than about 20 microns, more particularly one to 10 microns to 20 microns, and less than about 10 microns, more specifically about 5 microns. Ablation zone.

For a given material, wavelength, and pulse duration, the optimum NA and pulse energy will depend on the material thickness. For thin materials (eg, sapphire from 90 microns to 110 microns), a desired depth of extension can be achieved by a working NA of about 0.15 to 0.2 and a pulse wave energy in the range of about 10 microjoules to about 50 microjoules. Faux depth. When a ternary lens having a focal length of 25 mm and an aperture of 18 mm is used, for example, one of a range of longitudinal spherical aberration can be achieved by irradiating about 8 mm of the 18 mm aperture of the 25 mm ternary lens. Suitable for the spot size, the longitudinal spherical aberration range is sufficient to achieve an extended depth illusion in a material thickness of 90 microns to 110 microns. To process a thin sapphire by a picosecond 355 nm laser, for example, a ternary lens with a 25 mm focal length can be operated at about 0.16 NA to achieve an extended depth imaginary of a desired depth. In this example, according to a Zemax analysis, the longitudinal aberration coefficient is about 0.0133, and the lateral aberration coefficient is about 0.0024.

For thicker materials (eg, sapphire from 250 microns to 500 microns), a lower pulsed energy of about 0.05 to 0.1 and a higher pulse energy of about 30 to 61 microjoules can be used. A desired extended depth illusion is achieved that matches the thicker material. To process a thick sapphire by a picosecond 355 nm laser, a ternary lens with a focal length of 60 mm can be operated at about 0.07 NA to achieve an extended depth illusion of a desired depth. The pulse energy can be higher or lower depending on the pulse spacing to achieve a desired depth. For example, a lower pulse energy can be used with a shorter pulse spacing, and a longer pulse spacing can require a higher pulse energy.

Other techniques can also be used to reduce or eliminate excessive lateral spherical aberration. For example, an aperture can be placed in front of the lens 224 to limit penetration. The maximum beam diameter 214 in mirror 224, thereby limiting the maximum NA.

As noted above, different laser parameters and optics can be utilized to cut different materials by varying depths of various depths. In sapphire, for example, a ternary lens with a focal length of 25 mm can be used with an ultra-fast UV laser to achieve an extended depth of more than 100 microns. In the crucible, a deeper extended depth imaginary (for example, 300 microns) can be achieved with a longer lens and an IR laser with higher power.

As shown in FIGS. 4A-4C, a focus offset of the focused laser beam 216 with respect to one surface 204 of a workpiece 202 can also be selected or adjusted, for example, to change into the workpiece 202. A beam spot size and energy density on the surface 204 of the extended DOF 228 and/or workpiece 202. The focus offset can be selected, for example, to optimize depth depth of one of the extended depth imaginary features entering the workpiece 202 and to minimize surface damage or debris. Adjustable depth control of the extended depth imaginary can thus be achieved by adjusting the focus offset and other laser and optical parameters, such as laser pulse energy. The amount of focus shift can be adjusted, for example, by adjusting the position of the focus lens 224 relative to the workpiece 202.

4A shows that the focused laser beam 216 with aberrations is focused on one surface 204 of the workpiece 202 with paraxial rays without a focus shift, i.e., the paraxial focal plane 226 substantially coincides with the surface 204. 4B shows that the focused laser beam 216 with aberrations is focused below the surface 204 of the workpiece 202 with a paraxial ray and has a focus offset δ _f between the surface 204 and the paraxial focusing surface 226, thereby making the effective DOF 228 more Extending into the workpiece 202. 4C shows that the focused laser beam 216 with aberrations is focused below the surface 204 of the workpiece 202 with paraxial rays and a greater focus offset δ _f between the surface 204 and the paraxial focal plane 226, thereby effectively The DOF extends further into the workpiece 202.

The optimum focus offset may vary depending on the substrate material (e.g., the refractive index at the dicing wavelength) and the thickness of the material, and may vary depending on the lens operation NA and the resulting aberration coefficient under lens operating conditions. The focus offset can also depend on the type of process (for example, front or back). Cutting a 90- to 110-micron sapphire with a 25 mm ternary lens at 0.16 NA with a 10 picosecond 355 nm laser In the case of a substrate, for example, the optimum focus shift for backside cutting can be in the range of 20 microns to 40 microns.

Figures 5A-5D show the ray geometry of a laser beam focused on a 250 micron thick sapphire using a 60 mm focal length ternary lens with different spherical aberrations and different focal points in increments of 20 microns. Offset. Figures 6A-6D show the ray geometry of a laser beam focused on a 250 micron thick sapphire using a 54 mm focal length binocular lens with different spherical aberrations and different focal points in increments of 15 microns. Offset. Figures 7A-7D show the ray geometry of a laser beam focused on a 120 micron thick sapphire using a 25 mm focal length ternary lens with different spherical aberrations and different focal points in increments of 10 microns. Offset.

An ideal lens will provide the paraxial ray geometry as shown in Figures 5A, 6A, and 7A. According to various embodiments described herein, an actual lens having one of the diffraction limited regions introduces spherical aberration as shown in Figures 5B-5D, 6B-6D, and 7B-7D. Figures 5B, 6B, and 7B illustrate the ray geometry of the rays with aberrations provided by a uniform laser beam illuminating an actual lens across the aperture. Figures 5C, 6C, and 7C illustrate the ray geometry of the rays with aberrations provided by a Gaussian laser beam that illuminates an actual lens across the aperture. 5D, 6D, and 7C illustrate the ray geometry of the rays with aberrations provided by a Gaussian laser beam illuminating an actual lens at a portion of the aperture.

In the illustrated example, when the aperture is too large (Figs. 5B, 5C, 6B, 6C, 7B, and 7C), the lateral spherical aberration range is too large, and the aberration has the focus. The beam will be amplified. In the partial apertures (5D, 6D, and 7D), the focused beam with aberration has a relative ratio to the paraxial or ideal lens (Fig. 5A, Fig. 6A, and Fig. 7A). Compact focus and an extended effective DOF. Thus, according to one example, for a particular substrate material and thickness, the desired combination of lens and NA produces a nearly diffraction-limited lateral spot size, but at the same time produces a longitudinal direction sufficient to extend the effective DOF to match the thickness of the material. Spherical aberration range.

Although specific examples are described by lenses having focal lengths of 25 mm, 54 mm, and 60 mm, lenses having other focal lengths can also be used to provide the desired NA and spherical aberration. For example, the focal length can be less than 25 mm or greater than 60 mm.

Figures 8 and 9 show a photograph of a sapphire substrate 802 cut by a series of laser pulses and having an extended depth smear in the sapphire substrate 802. Each of the laser pulses forms a laser into the ablation region or aperture 806 of the sapphire substrate 802, wherein the ablation aperture 806 is surrounded by a laser region 805, and an extended depth imaginary channel 808 extends from the ablation aperture 806. Into the material of the substrate 802. Thus, the substrate 802 can be separated along a cutting line formed by the series of ablation holes 806 and the extended depth embossed channels 808.

In the illustrated embodiment, the ablation via 806 is about 5 microns wide and has a 20 micron laser region 805 and a pitch of about 15 microns, and the extended depth imaginary channel 808 extends into the 150 micron thick sapphire substrate 802. About 100 microns. Thus, according to embodiments described herein, the cutting by extended depth imaginary allows the cutting site to be less than 20 microns. Therefore, when cutting a semiconductor wafer with LEDs, the smaller the cut portion (for example, compared to stealth dicing), the narrower the allowable channel (for example, less than 25 microns) and the smaller the grain pitch, without Causes significant damage and debris. Even when the distance between the cutting portions is large, the depth of the extended depth embossed channel 808 can improve the break along the cutting line. Extending the depth of the imaginary channel 808 also enables the cutting of thicker substrates without the need to perform multiple passes of the laser at different focal points within the substrate, as required, for example, for invisible dicing. For example, the distance between the cutting sites allows for faster cutting by using a single pulse for each cutting site as compared to using overlapping pulse waves.

Other cutting site sizes, depths, and spacings can be achieved by varying laser parameters (eg, by controlling pulse spacing and depth). Although a single pulse wave can be used for each portion, it is also possible to use a plurality of pulse waves for each cutting portion to control the depth, for example, by scanning the laser multiple times. Although the illustrated embodiment exhibits a pitch of about 15 microns and a depth of about 100 microns, the pitch can be controlled to overlap from each other to 20 microns or more, and the depth can be controlled to be less than 100 microns to greater than 200 microns.

In other variations, different depths may be used for different pulse waves in a pulse train sequence. A pulse sequence may, for example, comprise a series of shallower pulses of higher frequency (eg, 10 micrometers to 20 micrometers spaced apart from 5 micrometers to 10 micrometers) and a lower spacing frequency (eg, every 15 micrometers to 50 micrometers) Deeper pulse waves (eg, 50 microns to 100 microns). In other words, a series of deeper pulse waves can be spaced apart over longer distances and the shallower pulse waves are located between the deeper pulse waves to enhance the break characteristics. Therefore, by improving the breaking characteristics and breaking the yield, the cutting of the extended depth imaginary and the controllable depth and spacing can be particularly advantageous when producing the LED, because the light propagation effect from the LED can reach the bottom of the sapphire sidewall. Or in the middle. In situations where less attention is paid to light loss (eg, in germanium wafers), tighter and deeper spacing can be used.

Referring to FIGS. 10A and 10B, according to another embodiment, a laser processing system 1000 includes an air bearing XY positioning table 1030 for supporting and positioning a workpiece 1002, thereby extending the depth of the workpiece. Cut. Laser processing system 1000 includes a laser beam delivery system 1020 mounted on one side (eg, a top side or a front side) and an opposite side camera 1040 mounted on an opposite side (eg, a bottom side or a back side). At least one workpiece support portion 1034 of the positioning table 1030 is configured to position the opposite side camera 1040 toward one of the workpieces 1002 (Fig. 10A) and the laser beam delivery system 1020 to one of the workpieces 1002 (Fig. 10B) Between the slides. The laser beam delivery system 1020 is higher than one of the planes 1001 of one of the workpiece support surfaces on the support portion 1034, and the opposite side camera 1040 is lower than the plane 1001 of the workpiece support surface on the support portion 1034. An example of an airfloating X-Y locating station is described in more detail in U.S. Patent Application Serial No. 12/962,050, the disclosure of which is incorporated herein in its entirety.

In the aligned position, the opposite side camera 1040 images a feature on the side 1005 of the workpiece 1002 that faces the camera 1040 and produces image material representative of the feature. The image data produced by the opposite side camera 1040 can be used to position the workpiece 1002 such that the laser beam delivery system 1020 is opposite the opposite side of the workpiece 1002, for example, using machine vision systems and alignment techniques known to those skilled in the art. The features imaged on the 1005 are aligned. In the processing position, the laser beam is delivered The delivery system 1020 directs a focused laser beam 1016 (e.g., a focused laser beam having an extended DOF with aberrations) toward one side 1003 of the workpiece 1002 facing the beam delivery system 1020 and using the extended depth virtual as described above The cut is performed to machine the workpiece 1002.

The laser processing system 1000 also includes a motion control system 1050 for controlling the motion of the positioning stage 1030 during alignment and/or processing of the workpiece 1002. Motion control system 1050 can generate alignment data based on image data generated by opposite side camera 1040 and control the motion of positioning stage 1030 as appropriate.

The laser beam delivery system 1020 can include lenses and other optical components for modifying and focusing, for example, one of the original laser beams produced by a laser as described above. A laser (not shown) may be positioned, for example, on one of the laser processing systems 1000, and the original laser beam produced by the laser may be directed into the laser beam delivery system 1020.

The laser processing system 1000 can also include a front camera 1044 for imaging the workpiece 1002 on the front side. Front camera 1044 can be mounted to beam delivery system 1020 or other suitable location. The front camera 1044 can be similarly coupled to the motion control system 1050 such that the motion control system 1050 can use the image data generated from the front camera 1044 to provide alignment. Thus, the laser processing system 1000 can be allowed to align with the back side opposite the laser beam or from the front side or the same side as the laser beam. The opposite side camera 1040 and front side camera 1044 can be high resolution cameras well known to those skilled in the art for aligning semiconductor wafers in laser processing applications.

Thus, the laser processing system 1000 can be used to align the beam delivery system 1020 and the focused laser beam 1016 with the channels between the various dies on a semiconductor wafer. When properly aligned, the XY positioning stage 1030 can move the workpiece 1002 to scan the laser beam on the workpiece 1002, such that a series of pulse waves, for example, along one of the wafers on a wafer or along the wafer The track cuts the workpiece 1002 on one side. The X-Y positioning stage 1030 can then move the workpiece to index to another lane for cutting. The alignment process can be repeated as needed to cut in other channels or along other channels.

Referring to Figure 11, the relative side alignment can be used to facilitate a semiconductor crystal. The back side of the circle 1101 is diced, thereby separating a plurality of semiconductor dies (eg, LEDs). The semiconductor wafer 1101 can include a substrate 1102 (eg, sapphire) and one or more layers of semiconductor material (eg, GaN) formed in the segment 1109 separated by the via 1107. The side of the semiconductor wafer 1101 having the section 1109 is referred to as the front side 1103, and the opposite side is referred to as the back side 1105. Substrate 1102 can also have one or more layers 1104 (eg, metal) on back side 1105 opposite section 1109.

A laser processing system (e.g., the laser processing system described above) can be used to diced the semiconductor wafer 1101 along the via 1107 between the die segments 1109 to divide the semiconductor wafer 1101 into individual dies. Thus, the semiconductor wafer 1101 is aligned such that a laser beam 1116 is incident on the semiconductor wafer 1101 between the vias 1107, thereby aligning the die segments 1109 with the laser beam 1116. As described above, the semiconductor wafer 1101 can be diced by forming a series of ablated regions 1106 having an extended depth imaginary 1108. The formation of the extended depth smear and ablation cut is particularly advantageous when the layer 1104 is opaque because the ablation can remove the layer 1104 and enable the laser beam 1116 to enter the substrate 1102. In another variation, one of the first passes of a laser can be used to ablate and remove layer 1104, and a second pass of one of the lasers provides an extended depth illusion.

When laser processing the back side 1105 of the semiconductor wafer 1101, the semiconductor wafer 1101 can be positioned such that the die segments 1109 on the front side 1103 of the wafer 1101 face the opposite side camera 1140. Thus, the opposite side camera 1140 can be used to view the channel 1107 between the segments 1109 and align the channel 1107 with respect to one of the laser beams 1116. It is especially advantageous when the alignment of the opposite side camera 1140 is opaque (e.g., metal) on the backside layer 1104 and interferes with alignment from the machine side. To provide such alignment, the wafer 1101 is positioned along the Y-axis relative to the laser beam delivery system (not shown) such that the cutting line formed by the laser beam 1116 on the back side 1105 of the wafer 1101 is located on the front side 1103. Within the width of the corridor 1107.

Referring to Figures 12A and 12B, relative side alignment can be used to facilitate double-sided cutting. In general, double-sided cutting involves forming relatively shallow cutting lines on both sides of a workpiece, and one of the cutting lines is substantially aligned with respect to the other of the cutting lines. Forming shallow cutting lines minimizes or avoids damage that can be caused by deeper cutting lines, while having cut lines on both sides improves the break yield. Cracks are more likely to propagate between the cutting lines.

In accordance with an exemplary method, a semiconductor wafer 1201 can be first positioned (e.g., positioned on a workpiece support) such that a back surface 1205 faces a laser beam delivery system (not shown) and a front surface 1203 faces a relative Side camera 1240 (Fig. 4A). When the wafer 1201 is in this position, one of the channels 1207 between the segments 1209 can be imaged using the opposite side camera 1240 such that the wafer 1201 can be positioned such that the laser beam 1216 on the back surface 1205 is The channels 1207 on the front side 1203 are aligned. When the semiconductor wafer 1201 has been aligned, the back side 1205 can be cut using the laser beam 1216 to form a relatively shallow back cut line 1206a (eg, 20 microns or less).

The semiconductor wafer 1201 can then be flipped such that the front side 1203 faces the laser beam delivery system and the back side 1205 faces the opposite side camera 1240 (Fig. 4B). When the wafer 1201 is in this position, the backside cut line 1206a can be imaged using the opposite side camera 1240 such that the wafer 1201 can be positioned to align the laser beam 1216 with the back cut line 1206a. When the semiconductor wafer 1201 has been aligned, the laser beam 1216 can be used to cut the front side 1203 in the channel 1207 between the segments 1209 to form a front cut line 1206b that is substantially aligned with the back cut line 1206a. For example, as described above, the front cut line 1206b can comprise a series of ablated regions having an extended depth imaginary 1208. Additionally or alternatively to providing alignment by the opposite side camera 1240, a processing side camera 1244 can image the channel 1207 to align the laser beam 1216 with the channel 1207.

Subsequently, the wafer 1201 can be divided into individual dies by breaking along the locations of the dicing lines 1206a, 1206b such that the crack propagates between the dicing lines 1206a and 1206b with the aid of the extended depth imaginary 1208. When each segment 1209 corresponds to each LED, for example, the front cut line 1206b will more preferably define the edge of the LED, making the LED more uniform and increasing the break yield (eg, shallower than on only one side) The case of the cutting line). In addition, the possibility of adversely affecting the LED light and electrical characteristics is less likely because the depth of the cut lines 1206a, 1206b is insufficient to cause significant thermal damage.

According to another alternative, the front side of the extended depth imaginary 1208 The cutting line 1206b can be formed first on the front side 1203 (eg, using the machine side camera 1244 to provide alignment relative to the shroud 1207). The wafer 1201 can then be flipped over and a back cut line 1206a can be formed on the back side 1205 (eg, using the opposing side camera 1240 to provide alignment with respect to the front cut line 1206b and/or the channel 1207). One of the cutting lines can be shallower than the other. For example, a shallower cut line (eg, 20 microns or less) may be formed first, and a second deeper cut line may be aligned with the shallower cut line. According to another variation of a double-sided cutting method, the back cut line 1206a can be formed with an extended depth imaginary 1208.

Referring to Figure 13, another embodiment of a laser processing system 1300 for cutting a workpiece 1302 (e.g., one of the sapphire substrates of a semiconductor wafer) by extending the depth imaginary will be described in greater detail below. The laser processing system 1300 can include an ultrafast laser 1310 and a beam delivery system 1320 that can emit ultrashort pulses (eg, less than one nanosecond) at a wavelength that is at least partially penetrating the material. Beam delivery system 1320 is capable of providing a well focused linear beam 1316. One embodiment of beam delivery system 1320 includes a beam expander 1322 for expanding the original laser beam 1321 from ultrafast laser 1310 to form an expanded beam 1323; a beam shaper 1326 for dilating the beam 1323 is shaped to form an elliptical beam 1325; and a focusing lens 1324 is used to focus the elliptical beam 1325 to provide a well-focused linear beam 1316 that forms a linear beam spot on the workpiece 1302 and at the workpiece 1302 There is an extended DOF in it. Beam delivery system 1320 can also include one or more reflectors 1328 to reflect and redirect the laser beam as desired.

As previously described, the extended depth imaginary cut involves ablating the material in the ablated region 1306 on the surface 1304 of the workpiece 1302 and directing the laser beam 1316 from the ablated region 1306 into the workpiece 1302 using a waveguide self-focusing effect. One of the internal positions 1308 is extended, causing crystal damage at internal position 1308 due to vibration, electric field, and/or pressure. Focusing lens 1324 can introduce spherical aberration as described above, with a range of longitudinal spherical aberrations sufficient to extend the effective DOF into workpiece 1302.

Beam delivery system 1320, for example, can include a variable elongated astigmatic focal beam spot capable of forming a variable elongated astigmatic focal beam spot The beam shaping optics are described in more detail in U.S. Patent No. 7,388,172, the disclosure of which is incorporated herein in its entirety by reference. The length of the elongated astigmatic focused beam spot along one of the astigmatism axes is greater than the width along one of the focus axes. Such a beam delivery system is capable of controlling the energy density of the variable astigmatic focused beam spot as the length of the spot changes. The beam shaper 1326 can, for example, comprise an anamorphic lens system comprising a cylindrical plano-concave lens 1326a and a cylindrical plano-convex lens 1326b. A distance between the lenses can change the beam spot length and energy density on the workpiece.

The laser processing system 1300 can further modify the beam depending on the particular application to improve the quality of the cutting line. To avoid epitaxial delamination problems in certain applications (eg, backside dicing), for example, laser processing system 1300 can provide spatial filtering at the edges of the beam to clean up the beam in a narrow direction. Point spread function.

Thus, beam shaper 1326 can be used to vary the energy density of the beam spot on workpiece 1302 to optimize the fluence and coupling efficiency for a particular material or cutting operation. When performing double-sided cutting on a GaN-coated sapphire substrate, for example, the energy density of the beam spot can be adjusted to be higher to optimize the cutting of the bare sapphire (ie, the back side cutting), and the beam light can be The energy density of the dots is adjusted lower to optimize the cutting of the GaN-coated sapphire (ie, front cut). In other words, the side can be cut using a laser beam spot optimized for one side of the workpiece, the workpiece can be flipped, and the other side can be cut using a laser beam spot optimized for the other side. Thus, beam shaper 1326 does not need to adjust the laser power to change the energy density and optimize the fluence.

In other embodiments, a nonlinear optical crystal (e.g., BBO crystal or β-BaB ₂ O ₄ ) can be used as a beam shaper. BBO crystals are known to be used together with a laser as a frequency-doubling crystal. Since the BBO crystal provides a greater walk-off effect than other crystals (e.g., CLBO), the substantially circular beam entering the crystal can become an elliptical beam as it leaves the crystal. While it may not be desirable to have a walk-off effect in many applications, such characteristics of BBO crystals offer unique advantages in applications where it is desirable to have an elliptical beam.

Thus, laser processing systems and methods for cutting by extending depth smudges provide several advantages over conventional ablation cutting and stealth cutting techniques. In particular, cutting by extended depth imaginary can cut a workpiece (eg, one sapphire substrate of a semiconductor wafer) with minimal or significantly reduced heat and debris. By reducing or minimizing the heat and debris generated, LEDs can be fabricated with low electrical damage and light loss without the need for additional coating and cleaning processes. Cutting by extending the depth imaginary also facilitates the cutting of thicker workpieces and workpieces having opaque coatings or films. The cutting by extending the depth illusion also eliminates the need for complex and expensive high NA lenses and focusing systems in conventional stealth cutting systems. As described herein, dicing by extending depth imaginary can be achieved in various types of materials by adjusting processing parameters (eg, wavelength, pulse duration, pulse energy) and optics.

According to one embodiment, a method for laser cutting a workpiece includes: generating a laser beam having a plurality of ultrashort pulse waves having a pulse duration of less than 1 nanosecond; Focusing the laser beam such that an energy density is sufficient to ablate one surface of the substrate at an ablation region and is sufficient to change a refractive index of the workpiece, wherein the beam penetrates the ablation using a waveguide self-focusing effect The zone reaches an internal location within the workpiece such that the interior location causes crystal damage to the material of the workpiece.

In accordance with another embodiment, a method for laser cutting a workpiece includes: generating a laser beam having a wavelength sufficient to provide nonlinear multiphoton absorption within the material of the workpiece, a pulse lasting Time, and a pulse energy; focusing the laser beam with a lens that introduces a spherical aberration having a range of longitudinal spherical aberrations sufficient to provide an extended depth of field (DOF) within the workpiece Causing a single pulse of the laser beam to create an extended depth imaginary within the workpiece; and scanning the workpiece by the laser beam to cause a series of pulses to produce a series of positions along the workpiece at a series of locations Extend the depth of the illusion.

According to still another embodiment, a laser processing system includes: a laser for generating a laser beam having a wavelength sufficient to provide nonlinear multiphoton absorption in a material of the workpiece, a pulse wave Duration, and a pulse energy; And a beam delivery system for focusing the laser beam and directing the laser beam toward a workpiece. The beam delivery system includes a beam expander for expanding the laser beam, and a lens for introducing a spherical aberration having a range of longitudinal spherical aberrations, the longitudinal spherical aberration range being sufficient for the beam An extended depth of field (DOF) is provided within the workpiece such that a single pulse of the laser beam creates an extended embossment within the workpiece. The laser processing system further includes a workpiece positioning stage for moving the workpiece to scan the laser beam on the workpiece to form a series of pulse waves forming a series of extended embossments in the workpiece.

Although the principles of the invention have been described herein, it is understood by those skilled in the art that Other embodiments are also encompassed within the scope of the invention in addition to the exemplary embodiments shown and described herein. The refinement and replacement of the present invention by those skilled in the art are considered to be within the scope of the invention, and the scope of the invention is limited only by the scope of the accompanying claims.

100‧‧‧Laser processing system

102‧‧‧Workpiece

104‧‧‧ Surface

106‧‧‧Ablative area

108‧‧‧Internal position

110‧‧‧Laser

112‧‧‧Original laser beam

114‧‧‧Expanded beam

116‧‧‧Focused laser beam

120‧‧‧beam delivery system

122‧‧‧beam expander

124‧‧‧focus lens

Claims (43)

A method for laser cutting a workpiece, the method comprising: generating a laser beam having a plurality of ultrashort pulse waves having a pulse duration of less than 1 nanosecond (ns); And focusing the laser beam such that an energy density is sufficient to ablate one surface of the substrate at an ablation region and is sufficient to change a refractive index of the workpiece, wherein the beam utilizes a waveguide self-focusing effect (waveguide self- The focusing effect penetrates the ablation zone to an internal location within the workpiece to cause crystal damage to the material of the workpiece at the interior location. The method of claim 1 wherein focusing the laser beam is performed using a lens having a numerical aperture of less than 0.8. The method of claim 2, wherein the lens is a lens triplet. The method of claim 2, wherein the lens has a focal length of at least 25 millimeters (mm). The method of claim 2, wherein the lens provides an effective focusability with a focal depth of about 400 micrometers (μm) and a kerf width of about 3 micrometers. The method of claim 1 wherein the laser beam has a wavelength to provide nonlinear multiphoton absorption within the material of the workpiece. The method of claim 6, wherein the material is sapphire and the wavelength is in the ultraviolet (UV) range. The method of claim 7, wherein generating the laser beam comprises generating at least one pulse wave having a pulse wave energy of about 60 microjoules (μJ) and a less than about 10 picoseconds (ps) The duration of the pulse wave. The method of claim 8 wherein the generating the laser beam comprises an approx. 33.3 The repetition rate of kilohertz (kHz) produces a plurality of pulses, and further includes scanning the laser beam on the workpiece at a scan speed in the range of about 70 mm/sec (mm/s) to 90 mm/sec. The method of claim 6, wherein the wavelength is in the infrared (IR) range. The method of claim 6, wherein the material is sapphire, the wavelength is about 355 nanometers (nm), and focusing the laser beam is performed using a 25 mm ternary lens, the 25 mm three The element lens has a working numerical aperture in the range of about 0.15 to 0.2. The method of claim 6, wherein the material is sapphire, the wavelength is about 355 nm, and focusing the laser beam is performed using a 60 mm ternary lens having a 60 mm ternary lens The working numerical aperture is in the range of about 0.05 to 0.1. The method of claim 1, further comprising scanning the laser beam on the workpiece at a scanning speed, so that a series of pulse waves of the laser beam form a series of ablation zones along a cutting line and the crystal is damaged. Internal location. The method of claim 1 wherein focusing the laser beam is performed using a lens having a numerical aperture of less than about 0.5. The method of claim 1 wherein focusing the laser beam provides an extended depth of field for entering a depth of at least about 100 microns within the workpiece to cause crystal damage. The method of claim 1 wherein the laser beam is focused on the surface of the workpiece with an extended depth of field entering the workpiece. The method of claim 1, wherein the laser beam is focused at a focus offset below the surface of the workpiece by further entering an extended depth of field within the workpiece. The method of claim 1, wherein focusing the laser beam introduces a spherical aberration having a range of longitudinal spherical aberrations sufficient to extend the depth of field into the depth of field In the workpiece. The method of claim 18, wherein the laser beam is focused at a focus offset below the surface of the workpiece. The method of claim 18, wherein focusing the laser beam comprises: overfilling one of the lenses having one of the diffraction-limited regions, such that the spherical aberration is introduced outside the diffraction-limited region. The method of claim 20, wherein the lens is sufficiently overfilled to provide the range of longitudinal spherical aberration that extends the depth of field into the workpiece while limiting a range of lateral spherical aberration. The method of claim 18, wherein the spot size of the laser beam on the surface of the workpiece has a width of less than about 20 microns. The method of claim 1, wherein the laser beam provides a laser region at the surface of the workpiece at a size in the range of about 10 microns to 20 microns, and the ablation at the surface of the workpiece The area is less than about 10 microns. The method of claim 1, further comprising: shaping the laser beam to form a variable elongated focused beam spot on the surface of the substrate. A method for laser cutting a workpiece, the method comprising: generating a laser beam having a wavelength sufficient to provide nonlinear multiphoton absorption in a material of the workpiece, a pulse duration, and a pulse wave energy; focusing the laser beam with a lens that introduces a spherical aberration having a range of longitudinal spherical aberrations sufficient to provide an extended depth of field (DOF) within the workpiece And causing a single pulse of the laser beam to generate an extended depth affectation in the workpiece; and scanning the workpiece by the laser beam, causing a series of pulse waves to follow the workpiece A series of extended depth illusions are produced at a range of locations. The method of claim 25, wherein the laser beam comprises a plurality of ultrashort pulse waves having a pulse duration of less than 1 nanosecond. The method of claim 25, wherein the lens comprises a diffraction limited region, and focusing the laser beam comprises overfilling an aperture of the lens such that the spherical aberration is introduced outside the diffraction limited region . The method of claim 27, wherein the lens is sufficiently overfilled to provide the range of longitudinal spherical aberration that extends the depth of field into the workpiece while limiting a range of lateral spherical aberration. The method of claim 27, wherein the spot size of the laser beam on the surface of the workpiece has a width of less than about 20 microns. The method of claim 29, wherein the extended embossing extends into the workpiece by at least 100 microns. The method of claim 25, wherein the lens has a numerical aperture of less than about 0.5. The method of claim 25, wherein the laser beam is focused on the surface of the workpiece at a paraxial focal point. The method of claim 25, wherein the laser beam is focused at a focus offset below the surface of the workpiece with a paraxial focus. The method of claim 25, wherein the laser beam is focused such that an energy density is sufficient to ablate one surface of the workpiece at an ablation zone. The method of claim 25, wherein the laser beam provides a laser region at the surface of the workpiece at a dimension in the range of about 10 microns to 20 microns, and the surface is at the surface of the workpiece. The etched area is less than about 10 microns. The method of claim 25, wherein the material is sapphire and the wavelength is in the ultraviolet (UV) range. The method of claim 25, wherein the material is germanium and the wavelength is in the infrared (IR) range. The method of claim 25, wherein the material is glass and the wavelength is Is in the visible range. The method of claim 25, wherein the workpiece is scanned by the laser beam such that the series of individual pulse waves produce the series of extended depth swashes at respective locations. A laser processing system comprising: a laser for generating a laser beam having a wavelength sufficient for providing nonlinear multiphoton absorption in a material of the workpiece, a pulse duration, and a Pulse wave energy; a beam delivery system for focusing the laser beam and directing the laser beam toward a workpiece, the beam delivery system comprising a beam expander and a lens for expanding the mine a beam for introducing a spherical aberration having a range of longitudinal spherical aberrations sufficient to provide an extended depth of field (DOF) within the workpiece, such that a single pulse of the laser beam is An extension embossing is generated in the workpiece; and a workpiece positioning table is configured to move the workpiece to scan the laser beam on the workpiece, so that a series of pulse waves form a series of extended embossments in the workpiece. The laser processing system of claim 40, wherein the laser is for generating a laser beam having a plurality of ultrashort pulse waves having a pulse duration of less than one nanosecond. The laser processing system of claim 40, wherein the lens has a numerical aperture of less than about 0.5. The laser processing system of claim 40, wherein the lens comprises a ternary lens having a focal length of at least about 25 millimeters and a numerical aperture of less than about 0.5.