JP4050534B2 - Laser processing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser processing method used for cutting a semiconductor substrate such as a silicon wafer.
[0002]
[Prior art]
As a method of obtaining a semiconductor chip by cutting a semiconductor substrate such as a silicon wafer in a lattice shape in a semiconductor device manufacturing process, a scribe line is provided in a lattice shape on the surface of the semiconductor substrate with a diamond point tool or the like. A method is known in which a knife edge is pressed against the back surface of the semiconductor substrate along the surface, and the semiconductor substrate is broken and cut (braking).
[0003]
In this semiconductor substrate braking, it is common to cut a semiconductor substrate into a strip shape along a scribe line in one direction, and then cut the semiconductor substrate cut into a strip shape at the same time along a scribe line in another direction. Is.
[0004]
It should be noted that in order to cut the semiconductor substrate with high accuracy while suppressing the occurrence of chipping and cracking, it is necessary to determine extremely severe conditions such as keeping the pressing force of the knife edge to the minimum necessary level.
[0005]
[Problems to be solved by the invention]
However, compared with the case where the semiconductor substrate is cut into strips along one direction of the scribe line, the case where the semiconductor substrate cut into strips at the same time along the scribe line in the other direction requires a larger cutting force. Therefore, in order to realize cutting of the semiconductor substrate with high accuracy by braking, it is necessary to perform the extremely severe condition described above every time the direction of the scribe line is changed.
[0006]
Therefore, the present invention has been made in view of such circumstances, and provides a laser processing method capable of forming a scheduled cutting portion on a semiconductor substrate that can maintain a constant cutting force for cutting the semiconductor substrate. For the purpose.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a laser processing method according to the present invention forms a modified region by multiphoton absorption inside a semiconductor substrate by irradiating a laser beam with a focusing point inside the semiconductor substrate. Then, a step of forming the first cut portion in the first direction in the modified region and a laser beam with a converging point aligned inside the semiconductor substrate are used to increase the number of the inside of the semiconductor substrate. Forming a modified region by photon absorption and forming a second planned cutting portion in a second direction intersecting the first direction with the modified region, and along the first planned cutting portion So that the first cutting force for cutting the semiconductor substrate is equal to the second cutting force for cutting the semiconductor substrate along the second cutting scheduled portion. The formation state of the modified region and the modification in the second scheduled cutting portion And wherein varying the formation conditions of the band together.
[0008]
According to this laser processing method, a laser beam is irradiated with a focusing point inside the semiconductor substrate, and a modified region is formed by generating a phenomenon called multiphoton absorption inside the semiconductor substrate. Accordingly, a first planned cutting portion and a second planned cutting portion are formed in a first direction and a second direction that intersect each other. When a modified region is formed inside the semiconductor substrate, cracks occur in the thickness direction of the semiconductor substrate starting from the modified region. Therefore, the semiconductor substrate is broken along the planned cutting portion with a relatively small cutting force. Can be cut. And the magnitude | size of this cutting force changes with the formation state of the modification area | region in the scheduled cutting part. Therefore, the semiconductor substrate is cut along the first scheduled cutting portion by making the modified region forming state in the first scheduled cutting portion different from the modified region forming state in the second scheduled cutting portion. Therefore, it is possible to control so that the first cutting force for cutting is equal to the second cutting force for cutting the semiconductor substrate along the second scheduled cutting portion. That is, it is possible to form a planned cutting portion on the semiconductor substrate that can make the cutting force for cutting the semiconductor substrate constant.
[0009]
The cutting force refers to, for example, a semiconductor substrate that generates bending stress or shear stress in the semiconductor substrate along a planned cutting portion of the semiconductor substrate, or generates thermal stress by giving a temperature difference to the semiconductor substrate. This is the force required to cut the substrate. Moreover, a condensing point is a location which the laser beam condensed. Then, the scheduled cutting portion may be formed by continuously forming the modified region, or may be formed by intermittently forming the modified region.
[0010]
Examples of the formation state of the modified region in the planned cutting portion described above include the formation density of the modified region, the size of the modified region, and the distance from the surface of the semiconductor substrate to the modified region as described below. .
[0011]
That is, in the laser processing method described above, if the formation state of the modified region in the first scheduled cutting portion and the formation state of the modified region in the second scheduled cutting portion are equal, the first cutting force is greater than the first cutting force. When the cutting force of 2 is larger, it is preferable that the formation density of the modified region in the second scheduled cutting portion is higher than the formation density of the modified region in the first scheduled cutting portion.
[0012]
This is because, inside the semiconductor substrate, cracks occur in the thickness direction of the semiconductor substrate starting from the modified region. Therefore, if the formation density of the modified region in the planned cutting portion is increased, along the planned cutting portion This is because the cutting force for cutting the semiconductor substrate can be reduced. The formation density of the modified region in the planned cutting portion means the ratio of the modified region to the semiconductor substrate in the planned cutting portion.
[0013]
Further, in the above laser processing method, when the formation state of the modified region in the first scheduled cutting portion and the formation state of the modified region in the second scheduled cutting portion are equal, the first cutting force is greater than the first cutting force. When the cutting force of 2 is larger, it is preferable to increase the size of the modified region in the second scheduled cutting portion than the size of the modified region in the first planned cutting portion.
[0014]
This is because, inside the semiconductor substrate, cracks occur in the thickness direction of the semiconductor substrate starting from the modified region. Therefore, if the size of the modified region in the planned cutting part is increased, along the planned cutting part This is because the cutting force for cutting the semiconductor substrate can be reduced. Note that the size of the modified region mainly means the length of the modified region in the thickness direction of the semiconductor substrate.
[0015]
Furthermore, in the above laser processing method, the first cutting force and the second cutting force cause bending stress in the semiconductor substrate, and the formation state of the modified region in the first scheduled cutting portion and the first cutting force are the same. If the second cutting force is larger than the first cutting force when the modified region formed in the planned cutting portion 2 is equal, the side pulled by the bending stress due to the first cutting force Compared to the distance from the surface of the semiconductor substrate to the modified region in the first scheduled cutting portion, the modified region in the second scheduled cutting portion from the surface of the semiconductor substrate pulled by the bending stress due to the second cutting force It is preferable to reduce the distance up to.
[0016]
This is because when a bending stress is generated in the semiconductor substrate, the closer the modified region is to the surface of the semiconductor substrate pulled by the bending stress (that is, the smaller the distance from the surface to the modified region), the modified the substrate. This is because a larger tensile stress acts on the region, so that the cutting force that generates the bending stress can be reduced.
[0017]
In the above laser processing method, the condition for irradiating the semiconductor substrate with the laser beam is set such that the peak power density at the laser beam focusing point is 1 × 10⁸(W / cm²) By setting the pulse width to 1 μs or less, a modified region including a melt processing region can be formed inside the semiconductor substrate. That is, the inside of the semiconductor substrate is locally heated by multiphoton absorption, and this heating forms a melt processing region only inside the semiconductor substrate. This melting processing region is an example of the above-described reforming region.
[0018]
In the laser processing method according to the present invention, a modified region is formed inside the semiconductor substrate by irradiating a laser beam with a condensing point inside the semiconductor substrate. And forming a modified region in the semiconductor substrate by irradiating a laser beam with a converging point aligned inside the semiconductor substrate, and forming the modified region in the semiconductor substrate. And a step of forming the second scheduled cutting portion in the second direction intersecting the first direction, and the modified region forming state in the first scheduled cutting portion and the modification in the second scheduled cutting portion. The formation states of the quality regions are different from each other. The modified region may be a melt-processed region.
[0019]
According to this laser processing method, a modified region is formed inside the semiconductor substrate by irradiating a laser beam with a converging point inside the semiconductor substrate, and the first direction intersecting with each other in the modified region. And a second cutting planned portion are formed in the first direction and the second direction, respectively. Therefore, by changing the formation state of the modified region in the first scheduled cutting portion and the modified region formation state in the second scheduled cutting portion, for example, the semiconductor substrate along the first scheduled cutting portion Various controls are possible, such as making the first cutting force for cutting equal to the second cutting force for cutting the semiconductor substrate along the second scheduled cutting portion. However, the formation of the modified region may be caused by multiphoton absorption or may be caused by others.
[0020]
That is, in the laser processing method, the first cutting force for cutting the semiconductor substrate along the first scheduled cutting portion and the second cutting force for cutting the semiconductor substrate along the second scheduled cutting portion. The formation state of the modified region in the first scheduled cutting portion and the formation state of the modified region in the second scheduled cutting portion can be made different from each other so that the cutting force becomes equal.
[0021]
In the laser processing method described above, the formation density of the modified region in the first scheduled cutting part may be different from the formation density of the modified region in the second scheduled cutting part.
[0022]
Furthermore, in the above laser processing method, the size of the modified region in the first planned cutting portion may be different from the size of the modified region in the second planned cutting portion.
[0023]
In the laser processing method according to the present invention, the second scheduled cutting portion is for simultaneously cutting the cut semiconductor substrate after cutting the semiconductor substrate along the first scheduled cutting portion. It is preferable. This is because a larger cutting force is required when simultaneously cutting the cut semiconductor substrates than when cutting an uncut semiconductor substrate.
[0024]
Moreover, in the laser processing method according to the present invention, the orientation flat is formed on the semiconductor substrate, the first direction is parallel to the longitudinal direction of the orientation flat, and the second direction is the longitudinal direction of the orientation flat. It is preferable to be perpendicular to. This is because a larger cutting force is required when cutting perpendicular to the longitudinal direction of the orientation flat than when cutting parallel to the longitudinal direction of the orientation flat.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the laser processing method according to the present embodiment, a laser beam is irradiated with a condensing point inside the semiconductor substrate, and a modified region by multiphoton absorption is formed inside the semiconductor substrate to form a planned cutting portion. . This laser processing method, particularly multiphoton absorption, will be described first.
[0026]
Band gap E of material absorption_GIf the photon energy hv is smaller than that, it becomes optically transparent. Therefore, the condition for absorption in the material is hν> E_GIt is. However, even if it is optically transparent, if the intensity of the laser beam is made very large, nhν> E_GUnder these conditions (n = 2, 3, 4,...), Absorption occurs in the material. This phenomenon is called multiphoton absorption. In the case of a pulse wave, the intensity of the laser beam is the peak power density (W / cm at the condensing point of the laser beam).²), For example, the peak power density is 1 × 10⁸(W / cm²) Multiphoton absorption occurs under the above conditions. The peak power density is determined by (energy per pulse of laser light at the condensing point) / (laser beam cross-sectional area of laser light × pulse width). In the case of a continuous wave, the intensity of the laser beam is the electric field intensity (W / cm at the focal point of the laser beam).²)
[0027]
The principle of laser processing according to this embodiment using such multiphoton absorption will be described with reference to FIGS. FIG. 1 is a plan view of the semiconductor substrate 1 during laser processing, FIG. 2 is a cross-sectional view taken along the line II-II of the semiconductor substrate 1 shown in FIG. 1, and FIG. 3 shows the semiconductor substrate 1 after laser processing. 4 is a cross-sectional view taken along line IV-IV of the semiconductor substrate 1 shown in FIG. 3, and FIG. 5 is a cross-sectional view taken along line V-V of the semiconductor substrate 1 shown in FIG. FIG. 6 is a plan view of the cut semiconductor substrate 1.
[0028]
As shown in FIGS. 1 and 2, there is a desired cutting line 5 on the surface 3 of the semiconductor substrate 1 where the semiconductor substrate 1 is to be cut. The planned cutting line 5 is a virtual line extending in a straight line (the actual cutting line 5 may be used as the planned cutting line 5 on the semiconductor substrate 1). In the laser processing according to the present embodiment, the modified region 7 is formed by irradiating the semiconductor substrate 1 with the laser beam L while aligning the condensing point P inside the semiconductor substrate 1 under the condition that multiphoton absorption occurs. In addition, a condensing point is a location where the laser beam L is condensed.
[0029]
The condensing point P is moved along the planned cutting line 5 by relatively moving the laser light L along the planned cutting line 5 (that is, along the direction of the arrow A). Thereby, as shown in FIGS. 3 to 5, the modified region 7 is formed only inside the semiconductor substrate 1 along the planned cutting line 5, and the planned cutting portion 9 is formed by the modified region 7. In the laser processing method according to the present embodiment, the modified region 7 is not formed by causing the semiconductor substrate 1 to generate heat when the semiconductor substrate 1 absorbs the laser light L. The modified region 7 is formed by transmitting the laser beam L through the semiconductor substrate 1 and generating multiphoton absorption inside the semiconductor substrate 1. Therefore, since the laser beam L is hardly absorbed by the surface 3 of the semiconductor substrate 1, the surface 3 of the semiconductor substrate 1 is not melted.
[0030]
In the cutting of the semiconductor substrate 1, if there is a starting point at the cutting position, the semiconductor substrate 1 breaks from the starting point, so that the semiconductor substrate 1 can be cut with a relatively small force as shown in FIG. 6. Therefore, the semiconductor substrate 1 can be cut without causing unnecessary cracks in the surface 3 of the semiconductor substrate 1.
[0031]
The following two methods can be considered for cutting the semiconductor substrate starting from the planned cutting portion. One is a case where after the formation of the planned cutting portion, an artificial force is applied to the semiconductor substrate, whereby the semiconductor substrate is cracked starting from the planned cutting portion, and the semiconductor substrate is cut. This is cutting when the thickness of the semiconductor substrate is large, for example. The artificial force is applied, for example, by applying bending stress or shear stress to the semiconductor substrate along the planned cutting portion of the semiconductor substrate, or generating thermal stress by applying a temperature difference to the semiconductor substrate. That is. The other one is a case where by forming the planned cutting portion, the semiconductor substrate is naturally cracked from the planned cutting portion toward the cross-sectional direction (thickness direction) of the semiconductor substrate, and as a result, the semiconductor substrate is cut. . For example, when the thickness of the semiconductor substrate is small, this is possible by forming the planned cutting portion by one row of the modified region. When the thickness of the semiconductor substrate is large, a plurality of portions are arranged in the thickness direction. This is made possible by forming the planned cutting portion by the modified region formed in a row. In addition, even when this breaks naturally, in the part to be cut, the part corresponding to the part where the part to be cut is formed without cracking on the surface of the part corresponding to the part where the part to be cut is not formed Since it is possible to cleave only, the cleaving can be controlled well. In recent years, since the thickness of a semiconductor substrate such as a silicon wafer tends to be thin, such a cleaving method with good controllability is very effective.
[0032]
Now, as the modified region formed by multiphoton absorption in the present embodiment, there is a melting processing region described below.
[0033]
The focusing point is set inside the semiconductor substrate, and the electric field intensity at the focusing point is 1 × 10.⁸(W / cm²) Irradiation with laser light is performed under the above conditions with a pulse width of 1 μs or less. As a result, the inside of the semiconductor substrate is locally heated by multiphoton absorption. By this heating, a melt processing region is formed inside the semiconductor substrate. The melt treatment region is a region once solidified after melting, a region in a molten state, or a region re-solidified from a molten state, and can also be referred to as a phase-changed region or a region in which the crystal structure has changed. The melt treatment region can also be said to be a region in which one structure is changed to another structure in a single crystal structure, an amorphous structure, or a polycrystalline structure. In other words, for example, a region changed from a single crystal structure to an amorphous structure, a region changed from a single crystal structure to a polycrystalline structure, or a region changed from a single crystal structure to a structure including an amorphous structure and a polycrystalline structure. To do. When the semiconductor substrate has a silicon single crystal structure, the melt processing region has, for example, an amorphous silicon structure. As an upper limit value of the electric field strength, for example, 1 × 10¹²(W / cm²). The pulse width is preferably 1 ns to 200 ns, for example.
[0034]
The inventor has confirmed through experiments that a melt-processed region is formed inside a silicon wafer. The experimental conditions are as follows.
[0035]
(A) Semiconductor substrate: silicon wafer (thickness 350 μm, outer diameter 4 inches)
(B) Laser
Light source: Semiconductor laser pumped Nd: YAG laser
Wavelength: 1064nm
Laser beam spot cross-sectional area: 3.14 × 10^-8cm²
Oscillation form: Q switch pulse
Repeat frequency: 100 kHz
Pulse width: 30ns
Output: 20μJ / pulse
Laser light quality: TEM₀₀
Polarization characteristics: linearly polarized light
(C) Condensing lens
Magnification: 50 times
N. A. : 0.55
Transmittance to laser light wavelength: 60 percent
(D) Moving speed of the mounting table on which the semiconductor substrate is mounted: 100 mm / second
[0036]
FIG. 7 is a view showing a photograph of a cross section of a part of a silicon wafer cut by laser processing under the above conditions. A melt processing region 13 is formed inside the silicon wafer 11. The size in the thickness direction of the melt processing region 13 formed under the above conditions is about 100 μm.
[0037]
The fact that the melt processing region 13 is formed by multiphoton absorption will be described. FIG. 8 is a graph showing the relationship between the wavelength of the laser beam and the transmittance inside the silicon substrate. However, the reflection components on the front side and the back side of the silicon substrate are removed to show the transmittance only inside. The above relationship was shown for each of the thickness t of the silicon substrate of 50 μm, 100 μm, 200 μm, 500 μm, and 1000 μm.
[0038]
For example, when the thickness of the silicon substrate is 500 μm or less at the wavelength of the Nd: YAG laser of 1064 nm, it can be seen that the laser light is transmitted by 80% or more inside the silicon substrate. Since the thickness of the silicon wafer 11 shown in FIG. 7 is 350 μm, the melt processing region 13 by multiphoton absorption is formed near the center of the silicon wafer, that is, at a portion of 175 μm from the surface. In this case, the transmittance is 90% or more with reference to a silicon wafer having a thickness of 200 μm. Therefore, the laser beam is hardly absorbed inside the silicon wafer 11 and almost all is transmitted. This is not because the laser beam is absorbed inside the silicon wafer 11 and the melt processing region 13 is formed inside the silicon wafer 11 (that is, the melt processing region is formed by normal heating with laser light) It means that the melt processing region 13 is formed by multiphoton absorption. The formation of the melt-processed region by multiphoton absorption is described in, for example, “Evaluation of processing characteristics of silicon by picosecond pulse laser” on pages 72 to 73 of the 66th Annual Meeting of the Japan Welding Society (April 2000). Are listed.
[0039]
Silicon wafers are cracked in the cross-sectional direction starting from the planned cutting portion formed in the melt processing region, and the cracks reach the front and back surfaces of the silicon wafer, resulting in cutting. Is done. The cracks that reach the front and back surfaces of the silicon wafer may grow naturally or may grow by applying force to the silicon wafer. In addition, when a crack naturally grows from the planned cutting part to the front and back surfaces of the silicon wafer, the crack grows from a state where the melt treatment region forming the planned cutting part is melted, and the planned cutting part. There are both cases where cracks grow when the solidified region is melted from the molten state. However, in both cases, the melt processing region is formed only inside the silicon wafer, and the melt processing region is formed only inside the cut surface after cutting as shown in FIG. When the planned cutting portion is formed in the semiconductor substrate in the melt processing region, unnecessary cracks that are off the planned cutting portion line are less likely to occur at the time of cleaving, so that cleaving control is facilitated.
[0040]
Here, the relationship between the formation state of the melt processing region in the planned cutting portion and the cutting force for cutting the semiconductor substrate along the planned cutting portion (hereinafter referred to as “cutting force along the planned cutting portion”) will be described. To do.
[0041]
As the formation state of the melt processing region in the planned cutting portion, for example, there are the following formation density of the melt processing region, the size of the melt processing region, and the distance from the surface of the semiconductor substrate to the melt processing region. Here, the laser beam used for forming the melt processing region will be described as a pulsed laser beam. Further, a melting processing region formed by one pulse of laser light is particularly referred to as a “melting processing spot”. In addition, since the melting treatment area is an example of the reforming area, it is needless to say that the following description also applies to the reforming area.
[0042]
The relationship between the formation density of the melt processing region and the cutting force will be described with reference to FIGS. FIG. 9 is a diagram showing the planned cutting portion 9 where the melting treatment spots 15 are intermittently formed, and FIG. 10 is a diagram showing the planned cutting portion 9 where the melting processing spots 15 are continuously formed.
[0043]
Inside the semiconductor substrate 1, cracks occur in the thickness direction of the semiconductor substrate 1 starting from each melting processing spot 15, so that the melting processing spot 15 is intermittently formed as shown in FIG. 9. As shown in FIG. 10, the cutting force along the planned cutting portion 9 is smaller when the melt processing spots 15 are continuously formed. Therefore, if the formation density of the melt processing region 13 in the planned cutting portion 9 is increased, the cutting force along the planned cutting portion 9 can be reduced.
[0044]
The formation density of the melt processing region 13 in the planned cutting portion 9 is, for example, of the repetition frequency f (Hz) of the laser beam and the moving speed v (mm / sec) of the condensing point of the laser beam with respect to the semiconductor substrate 1. It can be controlled by adjusting at least one. The formation density of the melt processing region 13 in the planned cutting portion 9 can be regarded as the number of melting processing spots formed per unit length of the planned cutting portion 9, where n is the number of the melting processing spots. This is because it can be expressed as “= f / v”. Therefore, in order to increase the formation density of the melt processing region 13, the repetition frequency of the laser light may be increased, or the moving speed of the condensing point of the laser light with respect to the semiconductor substrate 1 may be decreased.
[0045]
The relationship between the size of the melting treatment area and the cutting force will be described with reference to FIG.
[0046]
Inside the semiconductor substrate 1, cracks occur in the thickness direction of the semiconductor substrate 1 starting from each melting processing spot 15. However, when the melting processing spot 15 shown in FIG. Since the distance traveled by the crack to the front surface 3 or the rear surface 17 is reduced, the cutting force along the planned cutting portion 9 is reduced. Therefore, if the size of the melting region 13 in the planned cutting part 9 is increased, the cutting force along the planned cutting part 9 can be reduced.
[0047]
The size of the melt processing region 13 in the planned cutting portion 9 can be controlled by adjusting the power of the laser beam (ie, energy per pulse of the laser beam), for example. FIG. 11 is a cross-sectional view of the semiconductor substrate 1 on which laser light L having a predetermined power is condensed, and FIG. 12 is a semiconductor including a melt processing spot 15 formed by irradiation with the laser light L shown in FIG. 1 is a cross-sectional view of a substrate 1. A region 19 shown in FIG. 11 is a region having an electric field strength equal to or higher than a threshold at which multiphoton absorption occurs due to the irradiation of the laser beam L, and the size of the melting treatment spot 15 depends on the size of the region 19. On the other hand, FIG. 13 is a cross-sectional view of the semiconductor substrate 1 in which the laser light L having a higher power than that in FIG. 11 is condensed, and FIG. 14 is formed by irradiation with the laser light L shown in FIG. 2 is a cross-sectional view of a semiconductor substrate 1 including a molten processing spot 15. FIG. Since the power of the laser beam L is increased, the size of the region 19 shown in FIG. 13 is larger than the size of the region 19 shown in FIG. 11, and accordingly, the size of the melting spot 15 shown in FIG. Further, it is larger than the size of the melt processing spot 15 shown in FIG. Therefore, in order to increase the size of the melt processing region 13, the power of the laser beam may be increased.
[0048]
The relationship between the distance from the surface of the semiconductor substrate to the melt processing region and the cutting force will be described with reference to FIG. FIG. 15 is a diagram schematically showing a state in which the cutting force F is acting on the back surface 17 of the semiconductor substrate 1.
[0049]
As shown in FIG. 15, when a cutting force F acts on the back surface 17 from the back surface 17 of the semiconductor substrate 1 toward the front surface 3, bending stress acts on the semiconductor substrate 1. Although the surface 3 of the semiconductor substrate 1 is pulled by the cutting force F, the melting spot 15b having a small distance from the surface 3 is larger than the melting spot 15a having a large distance from the surface 3. A tensile stress will act. Therefore, when the cutting force F that generates a bending stress on the semiconductor substrate 1 acts as described above, the surface 3 on the pulled side of the semiconductor substrate 1 to the modified region 15 in the planned cutting portion 9. If the distance is reduced, the cutting force F along the planned cutting portion 9 can be reduced.
[0050]
The distance from the surface 3 of the semiconductor substrate 1 to the melt processing region 13 can be controlled by adjusting the position of the condensing point of the laser beam inside the semiconductor substrate 1.
[0051]
Next, a laser processing apparatus used in the laser processing method described above will be described with reference to FIG. FIG. 16 is a schematic configuration diagram of the laser processing apparatus 100.
[0052]
The laser processing apparatus 100 includes a laser light source 101 that generates laser light L, a laser light source control unit 102 that controls the laser light source 101 to adjust the power and repetition frequency of the laser light L, and a reflection function of the laser light L. And a dichroic mirror 103 arranged to change the direction of the optical axis of the laser light L by 90 °, a condensing lens 105 for condensing the laser light L reflected by the dichroic mirror 103, and a condensing lens The mounting table 107 on which the semiconductor substrate 1 irradiated with the laser beam L condensed by the lens 105 is mounted, the θ stage 108 for rotating the mounting table 107, and the mounting table 107 are moved in the X-axis direction. An X-axis stage 109, a Y-axis stage 111 for moving the mounting table 107 in the Y-axis direction orthogonal to the X-axis direction, and the mounting table 107 in the X-axis and Y-axis directions. A Z-axis stage 113 for moving in the Z-axis direction orthogonal to the axial direction and a stage controller 115 for controlling the movement of these four stages 108, 109, 111, 113 are provided.
[0053]
Since the Z-axis direction is a direction orthogonal to the surface 3 of the semiconductor substrate 1, it is the direction of the focal depth of the laser light L incident on the semiconductor substrate 1. Therefore, by moving the Z-axis stage 113 in the Z-axis direction, the condensing point P of the laser light L can be aligned with the surface 3 of the semiconductor substrate 1 or a desired position inside the semiconductor substrate 1. Further, the converging point P is moved in the X (Y) axis direction by moving the semiconductor substrate 1 in the X (Y) axis direction by the X (Y) axis stage 109 (111).
[0054]
The laser light source 101 is an Nd: YAG laser that generates pulsed laser light. Other lasers that can be used for the laser light source 101 include Nd: YVO._FourThere are lasers, Nd: YLF lasers, and titanium sapphire lasers. Nd: YAG laser, Nd: YVO are used to form the melt processing region._FourIt is preferable to use a laser, Nd: YLF laser. In this embodiment, pulsed laser light is used for processing the semiconductor substrate 1, but continuous wave laser light may be used as long as multiphoton absorption can be caused.
[0055]
The laser processing apparatus 100 further includes an observation light source 117 that generates visible light to illuminate the semiconductor substrate 1 mounted on the mounting table 107 with visible light, and the same optical axis as the dichroic mirror 103 and the condensing lens 105. And a visible light beam splitter 119 disposed above. A dichroic mirror 103 is disposed between the beam splitter 119 and the condensing lens 105. The beam splitter 119 has a function of reflecting about half of visible light and transmitting the other half, and is arranged so as to change the direction of the optical axis of visible light by 90 °. About half of the visible light generated from the observation light source 117 is reflected by the beam splitter 119, and the reflected visible light passes through the dichroic mirror 103 and the condensing lens 105, and passes through the planned cutting line 5 of the semiconductor substrate 1. Illuminate the containing surface 3.
[0056]
The laser processing apparatus 100 further includes an imaging element 121 and an imaging lens 123 disposed on the same optical axis as the beam splitter 119, the dichroic mirror 103, and the condensing lens 105. An example of the image sensor 121 is a CCD camera. The reflected light of the visible light that illuminates the surface 3 including the planned cutting line 5 passes through the condensing lens 105, the dichroic mirror 103, and the beam splitter 119, is imaged by the imaging lens 123, and is imaged by the imaging device 121. And becomes imaging data.
[0057]
The laser processing apparatus 100 further includes an imaging data processing unit 125 to which imaging data output from the imaging element 121 is input, an overall control unit 127 that controls the entire laser processing apparatus 100, and a monitor 129. The imaging data processing unit 125 calculates focus data for focusing the visible light generated by the observation light source 117 on the surface 3 based on the imaging data. The stage control unit 115 controls the movement of the Z-axis stage 113 based on the focus data so that the visible light is focused on the surface 3. Therefore, the imaging data processing unit 125 functions as an autofocus unit. The imaging data processing unit 125 calculates image data such as an enlarged image of the surface 3 based on the imaging data. This image data is sent to the overall control unit 127, where various processes are performed by the overall control unit, and sent to the monitor 129. Thereby, an enlarged image or the like is displayed on the monitor 129.
[0058]
Data from the stage controller 115, image data from the imaging data processor 125, and the like are input to the overall controller 127. Based on these data, the laser light source controller 102, the observation light source 117, and the stage controller By controlling 115, the entire laser processing apparatus 100 is controlled. Therefore, the overall control unit 127 functions as a computer unit.
[0059]
Hereinafter, the laser processing method according to the present embodiment when the laser processing apparatus 100 is used will be described.
[0060]
In the laser processing method according to the present embodiment, the condensing point is aligned inside the semiconductor substrate 1, and the peak power density at the condensing point is 1 × 10.⁸(W / cm²) By irradiating laser light under the above conditions with a pulse width of 1 μs or less and forming a melt processing region inside the semiconductor substrate 1, a plurality of cutting planned portions are formed in each of the first direction and the second direction. To do.
[0061]
Here, as shown in FIG. 17, the semiconductor substrate 1 is a silicon wafer (thickness: 625 μm, outer diameter: 6 inches) having an orientation flat (hereinafter referred to as “OF”) 21, and the surface 3 is a (100) plane. The plane parallel to the OF 21 and the plane perpendicular to the OF 21 are (110) planes, that is, cleavage planes.
[0062]
In the present embodiment, the first direction is a direction parallel to the longitudinal direction of the OF 21, and the second direction is a direction perpendicular to the longitudinal direction of the OF 21. Further, a plurality of cutting scheduled portions (hereinafter referred to as “parallel cutting scheduled portions”) formed in the first direction are formed at intervals of 2 mm, and are for cutting the semiconductor substrate 1 first during braking. The plurality of planned cut portions (hereinafter referred to as “vertical cut planned portions”) formed in the second direction are formed at intervals of 2 mm, and the semiconductor substrate 1 cut along the parallel cut planned portions at the time of braking is formed. It is for cutting at the same time.
[0063]
Then, the laser processing method according to the present embodiment is such that the cutting force along the parallel cutting scheduled portion and the cutting force along the vertical cutting scheduled portion are equal to each other, the formation density of the melt processing region in the parallel cutting planned portion As compared with the above, the formation density of the melt processing region in the vertical cutting scheduled portion is increased.
[0064]
This requires a larger cutting force when cutting perpendicular to the longitudinal direction of the OF 21 than when cutting parallel to the longitudinal direction of the OF 21 and cutting compared to cutting the semiconductor substrate 1 that has not been cut. This is because a larger cutting force is required when simultaneously cutting the semiconductor substrate 1. That is, if the formation density of the melt processing region in the parallel cutting scheduled portion is equal to the formation density of the melt processing region in the vertical cutting scheduled portion, the cutting along the vertical cutting planned portion is compared to the cutting force along the parallel cutting planned portion. This is because power is greater. As described above, when the formation density of the melt processing region in the planned cutting portion is increased, the cutting force along the planned cutting portion is reduced.
[0065]
In this embodiment, since the pulse laser beam is used as the laser beam, the repetition frequency of the laser beam is increased, so that the formation of the melt treatment region in the vertical cutting scheduled portion is higher than the formation density of the melt treatment region in the parallel cutting planned portion. The density is increased so that the cutting force along the parallel cutting scheduled portion is equal to the cutting force along the vertical cutting planned portion. The repetition frequency of the laser beam for forming the parallel cutting scheduled portion and the repetition frequency of the laser beam for forming the vertical cutting scheduled portion are determined in advance in consideration of various conditions.
[0066]
A specific example of the laser processing method according to the present embodiment will be described with reference to FIGS. 16 and 18. FIG. 18 is a flowchart for explaining the laser processing method according to the present embodiment.
[0067]
First, the light absorption characteristics of the semiconductor substrate 1 are measured with a spectrophotometer or the like (not shown). Based on the measurement result, a laser light source 101 that generates laser light L having a wavelength transparent to the semiconductor substrate 1 or a wavelength with little absorption is selected (S101).
[0068]
Then, the thickness of the semiconductor substrate 1 is measured, the amount of movement of the semiconductor substrate 1 in the Z-axis direction is determined based on the measurement result of the thickness and the refractive index of the semiconductor substrate 1, and the above-described parallel cut scheduled portion is formed. The repetition frequency of the laser beam for performing and the repetition frequency of the laser beam for forming the vertical cutting scheduled portion are determined (S103). Note that the amount of movement of the semiconductor substrate 1 in the Z-axis direction is determined so that the condensing point P of the laser light L having a wavelength transparent to the semiconductor substrate 1 or a wavelength with little absorption is located inside the semiconductor substrate 1. This is the amount of movement of the semiconductor substrate 1 in the Z-axis direction with reference to the condensing point P of the laser beam L located on the surface 3 of the substrate 1. The movement amount data and the repetition frequency data determined in step S103 are input to the overall control unit 127.
[0069]
Thereafter, the semiconductor substrate 1 is mounted on the mounting table 107 of the laser processing apparatus 100, and visible light is generated from the observation light source 117 to illuminate the semiconductor substrate 1 (S105). The surface 3 of the illuminated semiconductor substrate 1 is imaged by the image sensor 121. Imaging data captured by the imaging element 121 is sent to the imaging data processing unit 125. Based on this imaging data, the imaging data processing unit 125 calculates focus data such that the visible light focus of the observation light source 117 is located on the surface 3 (S107).
[0070]
This focus data is sent to the stage controller 115. The stage controller 115 moves the Z-axis stage 113 in the Z-axis direction based on the focus data (S109). Thereby, the focal point of the visible light of the observation light source 117 is positioned on the surface 3 of the semiconductor substrate 1. The imaging data processing unit 125 calculates enlarged image data of the surface 3 of the semiconductor substrate 1 based on the imaging data. This enlarged image data is sent to the monitor 129 via the overall control unit 127, whereby an enlarged image of the surface 3 of the semiconductor substrate 1 is displayed on the monitor 129.
[0071]
Subsequently, the semiconductor substrate 1 is rotated by the θ stage 108 so that the direction parallel to the longitudinal direction of the OF 21 of the semiconductor substrate 1 coincides with the stroke direction of the Y stage 111 (S111). Then, the movement amount data determined in step S103 and input in advance to the overall control unit 127 is sent to the stage control unit 115. The stage control unit 115 moves the semiconductor substrate 1 in the Z-axis direction by the Z-axis stage 113 to a position where the condensing point P of the laser light L is inside the semiconductor substrate 1 based on the movement amount data (S113). .
[0072]
After that, the repetition frequency of the laser light for forming the parallel cutting scheduled portion determined in step S 103 and input in advance to the overall control unit 127 is sent to the laser light source control unit 102. The laser light source control unit 102 generates laser light L from the laser light source 101 based on the repetition frequency data, and irradiates the semiconductor substrate 1 with the laser light L. Since the condensing point P of the laser beam L is located inside the semiconductor substrate 1, the melting processing region is formed only inside the semiconductor substrate 1. Then, the semiconductor substrate 1 is moved by the X-axis stage 109 and the Y-axis stage 111 to form a plurality of parallel cutting scheduled portions inside the semiconductor substrate 1 at intervals of 2 mm (S115).
[0073]
Subsequently, the semiconductor substrate 1 is rotated by the θ stage 108 so that the direction perpendicular to the longitudinal direction of the OF 21 of the semiconductor substrate 1 coincides with the stroke direction of the Y stage 111 (S117). Then, the laser light repetition frequency for forming the vertical cutting scheduled portion determined in step S <b> 103 and input in advance to the overall control unit 127 is sent to the laser light source control unit 102. The laser light source control unit 102 generates laser light L from the laser light source 101 based on the repetition frequency data, and irradiates the semiconductor substrate 1 with the laser light L. Since the condensing point P of the laser beam L is located inside the semiconductor substrate 1, the melting processing region is formed only inside the semiconductor substrate 1. Then, the semiconductor substrate 1 is moved by the X-axis stage 109 and the Y-axis stage 111, and a plurality of vertical cutting scheduled portions are formed inside the semiconductor substrate 1 at intervals of 2 mm (S119).
[0074]
In this way, the parallel cutting scheduled portions 9a and the vertical cutting scheduled portions 9b are formed in a lattice shape in the semiconductor substrate 1 shown in FIG. 17, as shown in FIG. 20 and FIG. 21, the formation density of the fusion processing spot 15 in the vertical cutting scheduled portion 9b shown in FIG. 21 is compared with the formation density of the fusion processing spot 15 in the parallel cutting scheduled portion 9a shown in FIG. It is high. As a result, the cutting force along the vertical cutting scheduled portion 9b, which requires a large cutting force when the formation density of the melt processing region is made equal, is reduced, and the cutting force and the vertical cutting along the parallel cutting planned portion 9a are reduced. The cutting force along the planned portion 9b is equivalent.
[0075]
Therefore, when the semiconductor substrate 1 is braked, the semiconductor substrate 1 is cut into strips along each parallel cutting scheduled portion 9a by pressing the knife edge against the back surface 17 of the semiconductor substrate 1. Later, the semiconductor substrate 1 cut into strips is simultaneously cut along the respective vertical cutting scheduled portions 9b. The cutting force along the parallel cutting planned portions 9a and the cutting force along the vertical cutting planned portions 9b Therefore, even if the direction of the planned cutting portion changes, it is not necessary to re-execute extremely severe conditions such as keeping the pressing force of the knife edge to the minimum necessary level. Therefore, it is possible to cut the semiconductor substrate 1 with high accuracy while suppressing the occurrence of chipping and cracking while keeping the braking conditions constant, and to obtain a semiconductor chip having a highly accurate cut surface.
[0076]
As mentioned above, although embodiment of this invention was described in detail, it cannot be overemphasized that this invention is not limited to the said embodiment.
[0077]
The above embodiment is a case where the formation density of the melt processing region is changed as the formation state of the melt processing region in the parallel cutting scheduled portion 9a and the vertical cutting scheduled portion 9b of the semiconductor substrate 1, As the forming state, the cutting force along the parallel cutting scheduled portion 9a and the cutting force along the vertical cutting planned portion 9b are varied by changing the size of the melting processing region and the distance from the surface 3 of the semiconductor substrate 1 to the melting processing region. May be equivalent to each other. Furthermore, these forming states may be combined so that the cutting force along the parallel cutting scheduled portion 9a and the cutting force along the vertical cutting planned portion 9b are equal.
[0078]
Moreover, although the said embodiment was a case where a square (1 side is 2 mm) semiconductor chip was cut out from the semiconductor substrate 1, For example, also when cutting out a rectangular semiconductor chip, it is the long side direction of the said rectangle. Since the cutting force for cutting the semiconductor substrate is different from that in the short side direction, the present invention is extremely effective even in such a case.
[0079]
Furthermore, in the present invention, the modified region is set to 1 by the one-point spot laser processing (the laser beam condensing point is aligned in the thickness direction) as described above in the planned cutting portion formed in the first direction. The modified region is formed by multi-point spot laser processing (a plurality of laser beam condensing points are aligned in the thickness direction), which will be described later, in a portion to be cut that is formed in a row and formed in a second direction that intersects the first direction. It is also possible to make the formation states of the modified regions different from each other by forming them in a plurality of rows. FIG. 22 is a diagram showing a first example of multi-point spot laser processing, and FIG. 23 is a diagram showing a second example of multi-point spot laser processing.
[0080]
As shown in FIG. 22, by using a two-point spot lens 131, the condensing points P <b> 1 and P <b> 2 of the laser light L aligned in the thickness direction of the semiconductor substrate 1 are simultaneously aligned with the inside of the semiconductor substrate 1. Two rows of modified regions 7 are formed inside, and the planned cutting portions 9 can be formed with the two rows of modified regions 7. Specific conditions are as follows.
Semiconductor substrate: silicon wafer (thickness 300 μm)
Laser light source wavelength: 1064 nm
Beam diameter: φ5mm
Beam profile: TEM₀₀
Short focal depth position: 60 μm
Long focal depth position: 240 μm
Long focus N.E. A. : 0.6
Short focus N.E. A. : 0.8
Lens material: BK7
[0081]
Further, as shown in FIG. 23, the condensing point P1 of the laser light L1 is aligned with the front surface 3 side inside the semiconductor substrate 1 by the condensing lens 105, and another concentrating point is arranged on the back surface 17 side inside the semiconductor substrate 1. By aligning the condensing point P2 of the laser beam L2 with the light lens 105, two rows of modified regions 7 are formed inside the semiconductor substrate 1, and the planned cutting portions 9 are formed by the two rows of modified regions 7. You can also
[0082]
【The invention's effect】
As described above, according to the laser processing method of the present invention, the semiconductor substrate is irradiated with the laser beam with the focal point aligned, and the phenomenon of multiphoton absorption is generated inside the semiconductor substrate. A region is formed, and in this modified region, a first planned cutting portion and a second planned cutting portion are formed in a first direction and a second direction crossing each other, respectively. When a modified region is formed inside the semiconductor substrate, cracks occur in the thickness direction of the semiconductor substrate starting from the modified region. Therefore, the semiconductor substrate is broken along the planned cutting portion with a relatively small cutting force. Can be cut. And the magnitude | size of this cutting force changes with the formation state of the modification area | region in the scheduled cutting part. Therefore, the semiconductor substrate is cut along the first scheduled cutting portion by making the modified region forming state in the first scheduled cutting portion different from the modified region forming state in the second scheduled cutting portion. Therefore, it is possible to control so that the first cutting force for cutting is equal to the second cutting force for cutting the semiconductor substrate along the second scheduled cutting portion. That is, it is possible to form a planned cutting portion on the semiconductor substrate that can make the cutting force for cutting the semiconductor substrate constant.
[Brief description of the drawings]
FIG. 1 is a plan view of a semiconductor substrate during laser processing by a laser processing method according to an embodiment.
2 is a cross-sectional view taken along the line II-II of the semiconductor substrate shown in FIG.
FIG. 3 is a plan view of the semiconductor substrate after laser processing by the laser processing method according to the embodiment.
4 is a sectional view taken along line IV-IV of the semiconductor substrate shown in FIG. 3;
5 is a cross-sectional view taken along line VV of the semiconductor substrate shown in FIG.
FIG. 6 is a plan view of a semiconductor substrate cut by the laser processing method according to the present embodiment.
FIG. 7 is a view showing a photograph of a cross section of a part of a silicon wafer cut by the laser processing method according to the embodiment.
FIG. 8 is a graph showing the relationship between the wavelength of laser light and the transmittance inside the silicon substrate in the laser processing method according to the present embodiment.
FIG. 9 is a diagram showing a planned cutting portion in which melting processing spots are intermittently formed by the laser processing method according to the present embodiment.
FIG. 10 is a diagram showing a planned cutting portion where melt processing spots are continuously formed by the laser processing method according to the present embodiment.
FIG. 11 is a cross-sectional view of a semiconductor substrate on which a laser beam with a predetermined power is condensed by the laser processing method according to the present embodiment.
12 is a cross-sectional view of a semiconductor substrate including a melting spot formed by laser beam irradiation shown in FIG.
13 is a cross-sectional view of a semiconductor substrate on which a laser beam having a higher power than that in the case of FIG. 11 is condensed.
14 is a cross-sectional view of a semiconductor substrate including a melting spot formed by laser light irradiation shown in FIG.
FIG. 15 is a diagram schematically showing a state in which a cutting force is acting on the back surface of the semiconductor substrate according to the embodiment.
FIG. 16 is a schematic configuration diagram of a laser processing apparatus according to the present embodiment.
FIG. 17 is a perspective view of a semiconductor substrate according to the present embodiment.
FIG. 18 is a flowchart for explaining a laser processing method according to the present embodiment.
19 is a sectional view taken along line IXX-IXX of the semiconductor substrate shown in FIG. 17;
20 is a cross-sectional view taken along line XX-XX of the semiconductor substrate shown in FIG.
21 is a sectional view taken along line XXI-XXI of the semiconductor substrate shown in FIG. 19;
FIG. 22 is a diagram showing a first example of multipoint spot laser processing.
FIG. 23 is a diagram showing a second example of multi-point spot laser processing.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Semiconductor substrate, 3 ... Surface, 5 ... Planned cutting line, 7 ... Modified area | region, 9 ... Planned cutting part, 9a ... Parallel cutting planned part, 9b ... Vertical cutting planned part, 11 ... Silicon wafer, 13 ... Melting process 15 ... Melting spot, 17 ... Back surface, 19 ... Area, 21 ... Orientation flat, 100 ... Laser processing device, 101 ... Laser light source, 105 ... Condensing lens, 108 ... θ stage, 109 ... X-axis stage, 111 ... Y-axis stage, 113 ... Z-axis stage, F ... cutting force, L, L1, L2 ... laser beam, P, P1, P2 ... condensing point.

Claims (11)

By irradiating the semiconductor substrate with a laser beam with a converging point aligned, a modified region by multiphoton absorption is formed inside the semiconductor substrate, and the modified region has a first direction in the first direction. Forming a portion to be cut;
By irradiating the semiconductor substrate with a laser beam with a condensing point aligned, a modified region by multiphoton absorption is formed inside the semiconductor substrate, and the modified region intersects the first direction. Forming a second cutting scheduled portion in the second direction;
With
A first cutting force for cutting the semiconductor substrate along the first planned cutting portion and a second cutting force for cutting the semiconductor substrate along the second planned cutting portion The formation state of the modified region in the first scheduled cutting portion and the modified region formation state in the second scheduled cutting portion are different from each other so as to be equivalent.
The laser processing method characterized by the above-mentioned. When the formation state of the modified region in the first scheduled cutting portion and the modified region formation state in the second scheduled cutting portion are equalized, the second cutting force is greater than the first cutting force. If it becomes larger,
Increasing the formation density of the modified region in the second scheduled cutting portion as compared with the formation density of the modified region in the first planned cutting portion,
The laser processing method according to claim 1. When the formation state of the modified region in the first scheduled cutting portion and the modified region formation state in the second scheduled cutting portion are equalized, the second cutting force is greater than the first cutting force. If it becomes larger,
Increasing the size of the modified region in the second planned cutting portion compared to the size of the modified region in the first planned cutting portion,
The laser processing method according to claim 1 or 2, wherein The first cutting force and the second cutting force cause bending stress in the semiconductor substrate,
When the formation state of the modified region in the first scheduled cutting portion and the modified region formation state in the second scheduled cutting portion are equalized, the second cutting force is greater than the first cutting force. If it becomes larger,
The side pulled by the bending stress due to the second cutting force compared to the distance from the surface of the semiconductor substrate on the side pulled by the bending stress due to the first cutting force to the modified region in the first scheduled cutting portion Reducing the distance from the surface of the semiconductor substrate to the modified region in the second scheduled cutting portion,
The laser processing method according to any one of claims 1 to 3. The conditions for irradiating the semiconductor substrate with laser light are such that the peak power density at the laser light condensing point is 1 × 10 ⁸ (W / cm ² ) or more and the pulse width is 1 μs or less. The laser processing method according to claim 1, wherein the modified region including a melt processing region is formed inside. A modified region is formed in the semiconductor substrate by irradiating a laser beam with a condensing point inside the semiconductor substrate, and a first scheduled cutting portion is formed in the first direction in the modified region. Forming, and
A modified region is formed in the semiconductor substrate by irradiating a laser beam with a focusing point inside the semiconductor substrate, and a second direction intersecting the first direction in the modified region. Forming a second scheduled cutting portion in
With
A first cutting force for cutting the semiconductor substrate along the first planned cutting portion and a second cutting force for cutting the semiconductor substrate along the second planned cutting portion The formation state of the modified region in the first scheduled cutting portion and the modified region formation state in the second scheduled cutting portion are different from each other so as to be equivalent .
The laser processing method characterized by the above-mentioned. The laser processing method according to claim 6 , wherein the formation density of the modified region in the first planned cutting portion is different from the formation density of the modified region in the second planned cutting portion. The laser processing method according to claim 6 , wherein a size of the modified region in the first planned cutting portion is different from a size of the modified region in the second planned cutting portion. The laser processing method according to any one of claims 6 to 8 , wherein the modified region is a melt-processed region. Cutting the semiconductor substrate along the first scheduled cutting portion;
Cutting the semiconductor substrate cut along the first scheduled cutting portion simultaneously along the second scheduled cutting portion;
The laser processing method according to claim 1 , comprising: An orientation flat is formed on the semiconductor substrate,
The first direction is parallel to the longitudinal direction of the orientation flat, and the second direction is perpendicular to the longitudinal direction of the orientation flat.
The laser processing method according to claim 1 , wherein:

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