JP2012531053A - Method for removing photoresist and etching residues from vias - Google Patents

Abstract

An excellent method for removing a photoresist is provided.
A method for removing photoresist simultaneously with veil removal is provided. This method uses a plasma formed from a gas species including a fluorine-containing gas such as O ₂ , NH ₃ and CF ₄ . This method is particularly suitable for use in MEMS fabrication processes such as inkjet printhead fabrication.
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Description

  The present invention relates to the field of printers, and in particular to the field of MEMS inkjet printheads. Although the present invention has been developed primarily to improve the fabrication of MEMS inkjet printheads, the present invention is equally applicable to any MEMS fabrication process.

  Many different types of printing have been invented, many of which are still in use today. Known printing forms have various methods for marking print media with suitable marking media. Commonly used printing forms include offset printing, laser printing and copying devices, dot matrix impact printers, thermal paper printers, film recorders, thermal transfer printers, sublimation printers, and drop-on-demand and continuous There are both flow type inkjet printers. Every type of printer has its own advantages and problems in terms of cost, speed, quality, reliability, structure and simplicity of operation.

  In recent years, the field of ink jet printing, where each individual ink pixel originated from one or more ink nozzles, has become increasingly popular, mainly due to its low cost and versatility.

  Many different techniques for ink jet printing have been invented. To obtain an overview of this field, see the article by J Moore, “Non-Impact Printing: Introduction and Historical Perspective” (Output Hard Copy Devices, Editors R Dubeck and S Scher, 207, page 207). .

  Ink jet printers are of many different types. The continuous use of ink flow for ink-jet printing dates back to at least 1929, when a simple form of continuous-flow electrostatic ink-jet printing was disclosed in Hansell U.S. Pat. No. 194,001.

  US Pat. No. 3,596,275 to Sweet et al. Also discloses a continuous ink jet printing process that includes the step of modulating the ink jet stream by a high frequency electrostatic field to produce droplet separation. This technology is still used by several manufacturers, including Elmjet and Scitetex (see US Pat. No. 3,373,437 to Sweet et al.).

  A piezoelectric ink jet printer is one form of a commonly used ink jet printing device. Piezoelectric systems include Kyser et al. US Pat. No. 3,946,398 (1970), which utilizes a diaphragm operating mode, and Zolten US Pat. No. 3,683,212, which disclosed a piezoelectric crystal squeeze operating mode. 1970), Stemme, US Pat. No. 3,747,120 (1972), which disclosed a bend mode of piezoelectric operation, and Hawkins, US Pat. No. 4,459,601, which disclosed piezoelectric push mode operation of an ink jet stream. And Fischbeck, U.S. Pat. No. 4,584,590, which discloses a shear mode type piezoelectric transducer element.

  Recently, thermal ink jet printing has become a widely used form of ink jet printing. Inkjet printing techniques include those disclosed in Endo et al., British Patent No. 200700712 (1979) and Vaught et al., US Pat. No. 4,490,728. Both of the above-mentioned references include an ink jet printing technique that relies on the operation of an electrothermal actuator that ejects ink onto an appropriate print medium from an opening connected to a limited space by generating bubbles in a confined space such as a nozzle. It is disclosed. Printing devices that use electrothermal actuators are manufactured by manufacturers such as Canon (registered trademark) and Hewlett Packard (registered trademark).

  As can be seen from the foregoing, many different types of printing techniques are available. Ideally, the printing technology should have a number of desired attributes. These attributes include inexpensive structure and operation, high speed operation, safety and continuous long-term operation. Each technology may have its own advantages and disadvantages in terms of cost, speed, quality, reliability, power usage, ease of assembly operation, durability and consumable parts.

  The applicant has developed a number of inkjet printheads made by MEMS technology. Typically, MEMS fabrication uses multiple photoresist deposition and removal steps. Typically, removal of a relatively thin photoresist layer (approximately 1 micron or less) used as a photolithography mask is easy. Standard conditions use an oxygen plasma that oxidatively removes any photoresist in a process known in the art under the name “ashing”.

  In making inkjet nozzle assemblies, Applicants have used photoresist as a sacrificial scaffold on which other materials (eg, heater materials, roof structures, etc.) can be deposited. This technique allows for the assembly of relatively complex nozzle assemblies. However, it is required to deposit a relatively thick photoresist layer that is viscous and heat resistant. As described in more detail below, a photoresist layer or plug of up to 30 microns may be required. Furthermore, the photoresist must be completely hardbake and UV cured so that it does not flow back during subsequent high temperature deposition steps, for example, while depositing metal or ceramic material on the photoresist.

In a typical MEMS printhead fabrication process, the final ashing step removes all residual photoresist in the nozzle assembly, including the photoresist scaffold and photoresist plug used during the fabrication process. In the past, conventional O ₂ plasma ashing techniques have been used to remove the photoresist in a final or subsequent stage.

However, hard-baked (hardbake; hard bake) and a thick photoresist layer that is UV cured, resistant to the ashing is high, is relatively slowly removed by conventional O ₂ ashing. This means that the ashing time needs to be extended and / or the ashing temperature needs to be raised. Extending the ashing time and / or increasing the ashing temperature is undesirable because it increases the risk of damage to other MEMS structures (eg, nozzle chambers, actuators) during the ashing process. In addition, it is generally necessary to increase the efficiency of each MEMS processing step to reduce processing time and ultimately reduce the cost of each printhead.

In order to increase the ashing rate, a combination of O ₂ and a fluorinated gas (eg, CF ₄ ) is known. However, Applicants have found that O ₂ / CF ₄ gas species require large amounts of CF ₄ (> 10%) to increase the ashing rate. At higher concentrations of CF _4, the ashing conditions adversely affects the silicon nitride nozzle structure of the applicant of the print head. Thus, it has been found that O ₂ / CF ₄ is not at a satisfactory level for removing hardbake photoresist from Applicant's printhead.

It is also known to use O ₂ / N ₂ to increase the ashing rate, but the addition of N ₂ is pure to remove hard-baked photoresist. Although improved over O ₂ , the degree is moderate.

  Accordingly, it should be recognized from the foregoing that the photoresist removal efficiency needs to be increased in MEMS fabrication techniques.

It is further desirable to remove the “veil” from the etched via simultaneously with the removal of the photoresist. Post etch residues or “veils” are formed along the via sidewalls as a byproduct of an anisotropic etch process (eg, the Bosch process). Veil is a well-recognized problem in the art and is also known to be difficult to remove. The veil typically contains a potential species of etched material and is generally a silicon oxycarbide compound. The anisotropic etch species that form the polymer (eg, the Bosch process) typically results in veils that are only removed using aggressive wet chemical solvents. Furthermore, conventional ashing using O ₂ at high temperatures typically exacerbates the veil problem and makes it more difficult to remove the veil. Therefore, there is a need for a dry veil removal process that is reliable and does not require aggressive wet species that can damage the wafer.

  While the above-described demand exists in printhead fabrication, any MEMS fabrication process, particularly a MEMS fabrication process that uses a relatively thick sacrificial photoresist layer that is hardbake and / or UV cured, It should be appreciated that benefits from improved techniques of photoresist removal and / or veil removal can be obtained.

US Patent No. 194001 US Pat. No. 3,596,275 U.S. Pat. No. 3,373,437 U.S. Pat. No. 3,946,398 US Pat. No. 3,683,212 US Pat. No. 3,747,120 U.S. Pat. No. 4,459,601 U.S. Pat. No. 4,584,590 British Patent No. 2007162 U.S. Pat.No. 4,490,728

J Moore, literature "Non-Impact Printing: Introduction and Historical Perspective", Output Hard Copy Devices, Editors: R Dubeck and S Sherr, pages 207-220 (198-220).

In a first aspect, a method is provided for removing a photoresist from a substrate using a plasma formed from a gas species including O ₂ , NH ₃ and a fluorine-containing gas. The method according to the invention surprisingly beneficially increases the ashing rate by at least 20%, at least 50% or at least 100% compared to the ashing rate using conventional O ₂ plasma or O ₂ / N ₂ plasma.

The method according to the present invention simultaneously removes the veil of the etched via in the substrate, as opposed to a conventional O ₂ or O ₂ / N ₂ ashing plasma.

Optionally, a fluorine-containing gas is CF _4.

  Optionally, a fluorine-containing gas is present in the gas species at a concentration of less than 5% by volume. The amount of fluorine-containing gas is typically kept low so as to avoid damage to any silicon nitride printhead structure on the substrate.

  Optionally, the fluorine-containing gas is present in the gas species at a concentration of less than 3% by volume.

Optionally, the O ₂ : NH ₃ ratio is in the range of 20: 1 to 5: 1.

Optionally, the O ₂ : CF ₄ ratio is in the range of 40: 1 to 20: 1.

Optionally, the gas species consists only of O ₂ , NH ₃ and CF ₄ . However, if necessary, an inert gas such as He or Ar may be present in the gas species.

Optionally, the photoresist is a hardbake photoresist and / or a UV-cured photoresist, and in particular is removed using a conventional O ₂ or O ₂ / N ₂ ashing plasma. Is difficult. In addition, the use of conventional ashing plasmas typically leaves a problematic residue ("veil").

  Optionally, the photoresist thickness is at least 5 microns, such as a photoresist used as a sacrificial scaffold in MEMS structure formation (eg, an inkjet nozzle assembly).

  Optionally, the substrate is attached to a chuck and the chuck is cooled to a temperature in the range of −5 to −30 ° C.

  Optionally, the method is a step in a MEMS fabrication process, such as a printhead fabrication process.

  Optionally, photoresist is included in the inkjet nozzle chamber and / or ink supply channel.

  Optionally, the photoresist is a protective coating for an inkjet nozzle assembly and / or a mask for an anisotropic deep reactive ion etching (DRIE) process.

In a second aspect, a method for producing an inkjet printhead comprising:
Forming inkjet nozzle chambers each having a corresponding ink inlet plugged with photoresist on the front side of the wafer substrate;
Etching the ink supply channel from the back side of the wafer substrate so that the photoresist meets the plug-filled ink inlet;
By exposing the back side to a first plasma formed from a first gas species comprising O ₂ , NH ₃ and a fluorine-containing gas, at least a portion of the photoresist is removed and at the same time the ink supply channel bale is removed. And a removing step is provided.

Optionally, this method
Removing additional photoresist by exposing the front side to a second plasma formed from a second gas species comprising O ₂ and NH ₃ .

  In the following, any embodiment of the present invention will be described by way of example with reference to the accompanying drawings.

2 is a partial perspective view of an array of nozzle assemblies for a thermal inkjet printhead. FIG. It is a side view of the nozzle assembly unit cell shown in FIG. FIG. 3 is a perspective view of the nozzle assembly shown in FIG. 2. FIG. 6 shows a partially formed nozzle assembly after depositing sidewall and roof material on a sacrificial photoresist layer. FIG. 5 is a perspective view of the nozzle assembly shown in FIG. 4. It is a mask relevant to the nozzle rim etching shown in FIG. Figure 5 shows the etching of the roof layer to form a nozzle opening rim. FIG. 8 is a perspective view of the nozzle assembly shown in FIG. 7. It is a mask relevant to the nozzle opening etching shown in FIG. FIG. 5 illustrates etching the roof material to form an oval nozzle opening. It is a perspective view of the nozzle assembly shown in FIG. Fig. 5 shows the nozzle assembly after thinning the backside wafer. FIG. 13 is a perspective view of the nozzle assembly shown in FIG. 12. It is a mask relevant to the back side etching shown in FIG. Fig. 4 shows backside etching of an ink supply channel to a wafer. FIG. 16 is a perspective view of the nozzle assembly shown in FIG. 15. The nozzle assembly after back side ashing is shown. FIG. 18 is a perspective view of the nozzle assembly shown in FIG. 17.

  As noted above, the present invention may be used with any process that requires photoresist removal. However, the invention is illustrated with examples of fabrication of MEMS inkjet printheads. Applicants have described above the fabrication of a plurality of inkjet printheads for which the present invention is suitable. It is not necessary to describe all such printheads herein to facilitate an understanding of the present invention. However, the present invention will be described in the context of thermal bubble forming ink jet printheads and mechanical thermal bend actuated ink jet printheads. The advantages of the present invention will be readily apparent from the following description.

  Referring to FIG. 1, a printhead component including a plurality of nozzle assemblies is shown. 2 and 3 show a side cross-sectional view and a cutaway perspective view of one of these nozzle assemblies.

  Each nozzle assembly includes a nozzle chamber 24 formed on the silicon wafer substrate 2 by a MEMS fabrication technique. The nozzle chamber 24 is defined by a roof 21 and side walls 22 extending from the roof 21 to the silicon substrate 2. As shown in FIG. 1, each roof is defined by a portion of a nozzle plate 56 that extends across the printhead ejection surface. The nozzle plate 56 and the sidewall 22 are formed of the same material, which is deposited by PECVD over the sacrificial scaffold of photoresist during MEMS fabrication. Typically, nozzle plate 56 and sidewall 21 are formed of a ceramic material such as silicon dioxide or silicon nitride. These rigid materials have excellent print head robustness properties, and the inherently hydrophilic nature is beneficial for supplying ink to the nozzle chamber 24 by capillary action.

  Returning to the details of the nozzle chambers 24, it can be seen that nozzle openings 26 are defined in the roof of each nozzle chamber 24. Each nozzle opening 26 is generally oval and has an associated nozzle rim 25. The nozzle rim 25 assists the directionality of droplets during printing and reduces ink overflow from the nozzle openings 26 at least to some extent. The actuator for ejecting ink from the nozzle chamber 24 is a heater element 29 disposed below the nozzle opening 26 and suspended over the pit 8. A current is supplied to the heater element 29 via the electrode 9 connected to the drive circuit in the underlying CMOS layer of the substrate 2. When a current is passed through the heater element 29, the heater element 29 rapidly heats the surrounding ink to form bubbles, and the bubbles push ink out of the nozzle openings. By suspending the heater element 29, when the ink is injected into the nozzle chamber 24, the heater element 29 is completely immersed in the ink. Thereby, less heat is dissipated into the underlying substrate 2 and more input energy is used to generate bubbles, thus improving the efficiency of the printhead.

  As most clearly shown in FIG. 1, the nozzles are arranged in multiple rows, and ink supply channels 27 extending longitudinally along the rows supply ink to each nozzle in the row. The ink supply channel 27 delivers ink to the ink inlet passage 15 of each nozzle, and the ink inlet passage 15 supplies ink into the nozzle chamber 24 from the side of the nozzle opening 26 through the ink conduit 23.

  A complete MEMS fabrication process for manufacturing such a printhead is described in detail in US patent application Ser. No. 11 / 246,684, filed on Oct. 11, 2005, already filed by the applicant. The entire contents of which are described and incorporated herein by reference. In order to illustrate one embodiment of the present invention, the later stages of this fabrication process will now be briefly described.

  4 and 5 show a partially fabricated printhead with a nozzle chamber 24 that contains a sacrificial photoresist 16. During nozzle fabrication, the photoresist 16 is used first to plug the ink inlet 15 (shown in FIG. 2) and secondly deposits heater material to form a suspended heater element 29. And, third, it was used as a scaffold to deposit the sidewalls 22 and the roof 21 (defines a portion of the nozzle plate 56). The depth of the photoresist that plugs the ink inlet 15 is about 20 microns, whereas the thickness of the photoresist used as a scaffold in the nozzle chamber has a thickness of at least 5 microns. In addition, all of the photoresist 16 must be hardbake and UV cured and later removed in the fabrication process.

  With reference to FIGS. 6-8, the next stage of MEMS fabrication defines an oval nozzle rim 25 in the roof 21 by etching 2 microns from the roof material 20. This etch is defined using a photoresist layer (not shown) exposed by the dark tone rim mask shown in FIG. The ellipse rim 25 includes two coaxial rim lips 25a and 25b, each positioned over a thermal actuator 29.

  Referring to FIGS. 9-11, the next step is to define an oval nozzle opening 26 in the roof 21 by etching through the remaining roof material 20 bounded by the rim 25. This etch is defined using a photoresist layer (not shown) exposed by the dark tone roof mask shown in FIG. As shown in FIG. 11, the oval nozzle opening 26 is disposed over the thermal actuator 29.

  Once the front side MEMS processing of the wafer is complete, the wafer is thinned by grinding the back side and etching to a thickness of about 150 microns (FIGS. 12 and 13). After wafer thinning, the ink supply channel 27 is etched from the back side of the wafer to meet the ink inlet 15 using standard anisotropic DRIE (FIGS. 14-16). This backside etch is defined using a hardbake photoresist layer 50 exposed by the dark tone mask shown in FIG. The ink supply channel 27 establishes a fluid connection between the back side of the wafer and the ink inlet 15 after removing all of the sacrificial photoresist 16 used in the fabrication of the front side MEMS nozzle assembly.

  Photoresist removal begins with backside ashing, removes the backside hardbake photoresist layer 50, and plugs the front side ink inlet 15 (FIGS. 17 and 18). A part of the plug of the photoresist 16 to be removed is removed. Backside ashing uses a continuous three-stage ashing process and utilizes the ashing conditions described in the examples below.

In a conventional ashing process, O ₂ plasma is used to ash the photoresist 16. However, according to the present invention, the ashing plasma is formed using a gas species that includes O ₂ , NH _3, and CF ₄ . When the plasma is formed from a gas species including this gas species, excellent ashing is achieved in terms of increasing the ashing rate and reducing damage to the nozzle structure. Furthermore, the bale obtained from the back side anisotropic etching of the ink supply channel 27 is removed using this gas species, thereby eliminating the need for aggressive wet chemical removal of the bale. Experimental details of ashing conditions are described in more detail in the Examples section below.

Finally, front side ashing removes the remainder of the photoresist 16 to provide the completed printhead shown in FIGS. Front side ashing may utilize O ₂ / NH ₃ / CF ₄ gas species according to the present invention. Alternatively, front side ashing may utilize an O ₂ / NH ₃ gas species as described in Applicant's US Patent Application Publication No. 2009/0078675, the entire contents of which are referred to Is incorporated herein by reference.

  FIG. 1 shows, in a cut-away perspective view, three adjacent rows of nozzles of a completed printhead integrated circuit. Each row of nozzles has an ink supply channel 27 that extends along the length of the row and supplies ink to a plurality of ink inlets 15 in each row. The ink inlet supplies ink to each row of ink conduits 23 and each nozzle chamber receives ink from an ink conduit common to that row.

  It will be appreciated by those skilled in the art that the exact order of post-stage MEMS fabrication steps may be changed. For example, the wafer may be subjected to only back side ashing or only front side ashing. In any event, it will be appreciated that either front side ashing and / or backside ashing must be applied to the wafer in order to remove the photoresist 16 to provide the printhead.

The backside ashing of the wafers shown in FIGS. 17 and 18 was performed in an ashing furnace using the optimized ashing sequence shown in Table 1. After using recipe 1 for 15 minutes, recipe 2 was used for 5 minutes and then recipe 3 was used for 10 minutes. The temperatures in Table 1 refer to the chuck temperature cooled using helium.

An excellent photoresist removal rate was observed under the continuous ashing conditions shown in Table 1. Furthermore, as confirmed by SEM, the ink supply channel 27 and the ink inlet bale were completely removed. By comparison, conventional O ₂ ashing or O ₂ / N ₂ ashing requires about 70-90 minutes of ashing time to remove the same photoresist, and the bale that needs to be removed by a subsequent wet chemical treatment A large amount remains.

As expected, excellent ashing rates and bale removal were observed in front ashing experiments using O ₂ / NH ₃ / CF ₄ gas species.

From these experiments, it was concluded that gas species including O ₂ / NH ₃ / CF ₄ provide superior ashing rates and surprising bale removal efficiency compared to conventional ashing conditions.

  Those skilled in the art will recognize that numerous variations and / or modifications may be made to the invention shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The Accordingly, the embodiments of the invention are to be considered in all respects only as illustrative and not restrictive.

Claims (20)

A method of removing photoresist from a substrate,
Using a plasma formed from a gas species comprising O ₂ , NH ₃ and a fluorine-containing gas.   The method of claim 1, wherein a veil of etched vias in the substrate is removed simultaneously. The method of claim 1, wherein the fluorine-containing gas is CF ₄ .   The method of claim 1, wherein the fluorine-containing gas is present in the gas species at a concentration of less than 5% by volume.   The method of claim 1, wherein the fluorine-containing gas is present in the gas species at a concentration of less than 3% by volume. The method of claim 1, wherein the O ₂ : NH ₃ ratio is in the range of 20: 1 to 5: 1. The method of claim 1, wherein the O ₂ : CF ₄ ratio is in the range of 40: 1 to 20: 1. The method of claim 1, wherein the gas species consists solely of O ₂ , NH ₃ and CF ₄ . The method of claim 1, wherein the photoresist removal rate is at least 20% faster than the photoresist removal rate using O ₂ plasma.   The method of claim 1, wherein the photoresist is a hard baked photoresist.   The method of claim 1, wherein the photoresist is an ultraviolet cured photoresist.   The method of claim 1, wherein the photoresist thickness is at least 5 microns.   The method of claim 1, wherein the substrate is attached to a chunk and the chunk is cooled to a temperature in the range of −5 to −30 ° C.   The method of claim 1, wherein the method is a step in a MEMS fabrication process.   The method of claim 1, wherein the method is a step in a printhead fabrication process.   The method of claim 15, wherein the photoresist is included in at least one of an inkjet nozzle chamber and an ink supply channel.   The method of claim 15, wherein the photoresist is a protective coating for an inkjet nozzle assembly and / or a mask for an anisotropic deep reactive ion etching (DRIE) process. A method for producing an inkjet printhead, comprising:
Forming inkjet nozzle chambers each having a corresponding ink inlet plugged with photoresist on the front side of the wafer substrate;
Etching an ink supply channel from the back side of the wafer substrate to meet the ink inlet into which a photoresist is plugged; and
Removing the photoresist and simultaneously exposing the backside to a first plasma formed from a first gas species comprising O ₂ , NH ₃ and a fluorine-containing gas; Removing the veil of
Including methods. The method of claim 18, further comprising removing additional photoresist by exposing the front side to a second plasma formed from a second gas species comprising O ₂ and NH ₃ . The method of claim 18, wherein the second gas species comprises O ₂ , NH ₃ and a fluorine-containing gas.

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