Resin film forming method

A resin film forming method for forming a resin film on a substrate includes forming an intermediate layer on the substrate which includes an inorganic composition as a main component to chemically bond the resin film to be formed on the substrate to the substrate, carrying out a treatment on the substrate to remove an edge of the intermediate layer from an edge of the substrate, forming the resin film on the substrate by spin coating, chemically bonding the resin film to the substrate and hardening the resin film, and removing an edge of the resin film from the edge of the substrate by applying vibrations to the hardened resin film.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority of prior Japanese Patent Application No. 2010-136386, filed on Jun. 15, 2010, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a resin film forming method.

BACKGROUND

In the field of photolithography or nanoimprint lithography, a spin coating method is used to form a thin film on a substrate. In the spin coating method, a thin film is formed in an almost uniform thickness by dropping a solution containing film components onto a substrate while rotating the substrate at a certain speed.

However, the resin thickens in the width of several mm at the edge of the substrate due to the surface tension of the dropping solution. The thick resin on the edge of the substrate is called an edge bead.

When a resin film having an edge bead is used for photolithography or nanoimprint lithography, contact between the resin film and a photomask or mold that may be large relative to the substrate becomes insufficient as illustrated inFIG. 6B, thus affecting patterning accuracy.

Japanese Laid-open Patent Publication No. 2006-80298 discloses the step of dropping a photoresist onto a substrate and spin coating the photoresist while rotating the substrate, the step of removing the photoresist from the circumferential edge of the substrate by supplying a solvent to the circumferential edge of the substrate while rotating the substrate, and the step of drying the surface of the photoresist while rotating the substrate.

In Japanese Laid-open Patent Publication No. 6-163389, a polyimide precursor composition at an end of the surface of a semiconductor substrate is removed with a scraper tool and the semiconductor substrate is successively rotated while the polyimide precursor composition is being spin coated on the surface of the substrate.

In Japanese Laid-open Patent Publication No. 2006-80298, since the photoresist is removed from the circumferential edge of the substrate by supplying the solvent, a portion of the photoresist other than at the circumferential edge of the substrate is also removed. Thus, the thickness of the photoresist becomes non-uniform.

In Japanese Laid-open Patent Publication No. 6-163389, the polyimide precursor composition is physically removed with a scraper tool, and therefore the film thickness of the polyimide precursor composition becomes non-uniform.

SUMMARY

According to an embodiment, a resin film forming method for forming a resin film on a substrate includes forming an intermediate layer on the substrate which includes an inorganic composition as a main component to chemically bond the resin film to be formed on the substrate to the substrate, carrying out a treatment on the substrate to remove an edge of the intermediate layer from an edge of the substrate, forming the resin film on the substrate by spin coating, chemically bonding the resin film to the substrate and hardening the resin film, and removing an edge of the resin film from the edge of the substrate by applying vibrations to the hardened resin film.

The object and advantages of the invention will be realized and attained by at least the features, elements, and combinations particularly pointed out in the claims.

DESCRIPTION OF EMBODIMENTS

FIGS. 1A and 1Billustrate a resin film-formed substrate10formed by a resin film forming method of an embodiment.FIG. 1Ais a cross sectional view of the resin film-formed substrate10, andFIG. 1Bis the top view thereof.

The resin film-formed substrate10includes a substrate12, a resin film14, an adhesion aid layer16, and a masking material deposited layer18.

The substrate12may be a substrate mainly made of an inorganic composition such as quartz, glass, ceramics and metal, for example. The thickness of the substrate may be, for example, 0.5 to 6.5 mm. The substrate12may be rectangular, but the shape of the substrate is not limited thereto. For example, the substrate12may be circular or polygonal.

The resin film14is formed on the adhesion aid layer16on the substrate12. The resin film14may be made of, for instance, a resin material including a phenolnovolak resin, a photosensitive agent, a perfluoroalkyl-containing oligomer, 2-heptanone and 1,4-dioxane as components, or a resin including a phenolnovolak resin, a photosensitive agent, a perfluoroalkyl-containing oligomer, butyl acetate and ethyl lactate as components. The photosensitive agent may include, for instance, a naphthoquinone diazide compound as photosensitive groups.

The adhesion aid layer16chemically bonds the resin film14to the substrate12. For the adhesion aid layer16, a silane coupling agent may be used such as hexamethyldisilazane, 3-methacryloxypropyltrimethoxysilane and 3-acryloxypropyltrimethoxysilane. The silane coupling agent has reactive groups that bond to the resin film14, and reactive groups that bond to the substrate12in one molecule. The reactive groups that bond to the resin film14include, for example, a vinyl group, an epoxy group, an amino group, a methacrylic group, a mercapto group, and the like. On the other hand, the reactive groups that bond to the substrate12include a methoxy group, an ethoxy group, and the like.

The adhesion aid layer16may be thin and may also be thinner than, for instance, 10 nm. The adhesion aid layer16is preferably about the thickness of one molecular layer. The adhesion aid layer16is made thin so as to chemically bond the resin film14to the substrate12.

The masking material deposited layer18is provided so as not to chemically bond to the composition of the resin film14. The masking material deposited layer18is a layer made of masking components that are deposited by partially ashing the adhesion aid layer16. The masking material deposited layer18does not chemically bond to the resin film14on the edge of the substrate12. Therefore, the resin film14on the edge can be removed by physically applying external force such as ultrasonic vibrations to the resin film14on the edge, for example.

When the resin film14on the edge of the substrate12is removed, the resin film-formed substrate10has no edge bead. Accordingly, a resin film is stably formed at a substantially constant thickness.

The resin film forming method of the embodiment illustrated inFIGS. 1A and 1Bwill be explained below.FIGS. 2A to 2DandFIGS. 3A to 3Dillustrate the resin film forming method.FIG. 4is a flow chart of the resin film forming method of the embodiment.

First, the substrate12made of an inorganic composition such as quartz is provided, and the adhesion aid layer16is formed thereon by a spin coating method (Step S10). The thickness of the substrate12may be in the range of, for instance, 0.5 to 6.35 mm. On a spin coater22, a solution including hexamethyldisilazane (HMDS) as an adhesion aid is dropped at, for instance, 0.1 to 1 cc, onto the substrate12and is spin coated for 60 seconds by the spin coater at, for example, 3000 rpm. Accordingly, the adhesion aid layer16may be formed at a thickness of several nm as illustrated inFIG. 2A.

As illustrated inFIG. 2B, a mask20is provided on top of adhesion aid layer16in a region which does not include the edge of adhesion aid layer16. Plasma ashing is then carried out (Step S20).

The mask20is, for instance, made of a fluorine rubber or a silicone rubber. The mask20may be in contact with the adhesion aide layer16at 0.1 to 10 mm from the edge of the substrate12. The mask20may have a thickness of 1 to 5 mm, for example.

A parallel flat plate electrode type plasma generating apparatus may be used for plasma ashing. More specifically, for plasma ashing, argon gas and oxygen gas are mixed at a pressure ratio of, for instance, 1:5, and plasma is generated by applying electrical power of 0.3 kW under the pressure of e.g., 45 Pa. The edge of the adhesion aid layer16is oxidized by using oxygen radicals generated by the plasma, thus oxidizing the edge of the adhesion aid layer16. Substantially the same effects are also obtained solely from argon gas, so that the treatment is not limited to oxidation with oxygen radicals. The plasma ashing period is, for example, 0.5 to 1 minute.

In the plasma ashing, a portion of the mask20is sputtered with plasma and is deposited at the edge of the substrate12. Accordingly, the masking material deposited layer18is formed as illustrated inFIG. 2C. The masking material deposited layer18may be formed on the remaining adhesion aid layer16before the edge of the adhesion aid layer16is completely removed by ashing.

Subsequently, the mask20is removed and the resin film14is formed on the adhesion aid layer16(Step S30). Specifically, the substrate12is placed on a spin coater22as illustrated inFIG. 2D, and a resin is dropped onto the substrate12, thus forming the resin film14by a spin coating method.

When the resin film14is made of a resin material including a phenolnovolak resin, a photosensitive agent, a perfluoroalkyl-containing oligomer, 2-heptanone, and 1,4-dioxane as components, a solution including the phenolnovolak resin at 5 to 45 mass % is dropped onto the adhesion aid layer16at 0.3 to 6 cc and is spin coated at 2000 to 5000 rpm for 20 seconds, for example. Accordingly, the resin film14may be formed at a thickness of 1.5 to 2.5 μm.

When the resin film14is made of a resin material including a phenolnovolak resin, a photosensitive agent, a perfluoroalkyl-containing oligomer, 2-heptanone, and 1,4-dioxane as components, a solution including the phenolnovolak resin at 5 to 40 mass % is dropped onto the adhesion aid layer16at 0.3 to 6 cc and is spin coated at 2000 to 5000 rpm for 20 seconds, for example. Thus, the resin film14may be formed at a thickness of 1.5 to 2.5 μm.

Subsequently, the resin film14is hardened (Step S40). More specifically, the substrate12formed with the resin film14is placed on a heater base24as illustrated inFIG. 3B, and is heated at, for instance, 90° C. for 1.5 minutes and is then cooled to room temperature. The resin film14is solidified as the solvent is removed from the film. The resin film14that is in contact with the adhesion aid layer16in a region which does not include the edge of the adhesion aid layer is chemically bonded to the substrate12through the reactive groups of the adhesion aid layer16.

The resin film14formed thereby has an edge bead along the edge of the substrate12as illustrated inFIG. 3B.

Then, vibrations may be applied to the resin film14formed on the substrate12, thereby removing the edge of the resin film14(Step S50). It is preferable to apply ultrasonic vibrations of 28 to 100 kHz to the resin film, for example. It is more preferable to repeatedly apply the vibrations at a plurality of frequencies.

More specifically, ultrasonic waves may be applied to the resin film14while the whole substrate12is dipped in a liquid26, such as water, as illustrated inFIG. 3C, thus physically removing the edge of the resin film14that is not chemically bonded to substrate12.

For example, the substrate12may be dipped in a liquid in an ultrasonic cleaner, and ultrasonic waves applied at certain frequencies. The frequencies may be, for instance, a plurality of frequencies. When ultrasonic waves are applied, frequencies thereof are changed sequentially per a certain period and the application is repeated. For instance, ultrasonic waves at frequencies such as 28 kHz, 45 kHz, and 100 kHz may be sequentially applied every 10 seconds repeatedly to the resin film14. The ultrasonic waves may be applied for a total of 10 minutes, for example. More specifically, the ultrasonic waves of 28 kHz may be applied at 0 to 10 seconds; the ultrasonic waves of 45 kHz are applied at 10 to 20 seconds; the ultrasonic waves of 100 kHz may be applied at 20 to 30 seconds; the ultrasonic waves of 28 kHz may be applied at 30 to 40 seconds; and the ultrasonic waves of 45 kHz may be applied at 40 to 50 seconds. This process may be repeated. Thus, the resin film14can be completely removed from the edge of substrate12as the ultrasonic waves of a plurality of frequencies are sequentially applied repeatedly.

After removing the resin film14from the edge of resin film-formed substrate10, the resin film-formed substrate10is taken out from the liquid26for drying.

As illustrated inFIG. 3D, the resin film14, having no edge bead, may thus formed on the substrate12.

In this resin film forming method, the masking material deposited layer18is formed, thus forming a region at the edge of the substrate12where the resin film14will physically deposit. Additionally, the adhesion aid layer16is formed at a region which does not include the edge of substrate12, thereby forming the region where the resin film14will chemically bond to the substrate12. The resin film14deposited on the edge of the substrate12may thus be removed by applying vibrations to the film.

A material that does not chemically bond to the resin film14may preferably used for the mask20. In the embodiment, a fluorine rubber or a silicone rubber is used as an example of the material. When HMDS is used as an adhesion aid, a fluorine rubber is more preferable. In the above-mentioned method, the resin film-formed substrate10illustrated inFIG. 1is formed.

A resin film-formed substrate10was prepared so as to test the effects of the resin film forming method described above.

The substrate12was a quartz plate of 14.5 mm in length×14.5 mm in width×6.35 mm in thickness.

For the adhesion aid layer16, HMDS solution was dropped at 0.3 cc and was spin coated for 60 seconds at 3000 rpm by a spin coater. Then, the adhesion aid layer16was formed at a thickness of several nm.

A fluorine rubber mask was placed on the adhesion aid layer16, 1.2 mm apart from the edge of the substrate12, and ashing was then carried out with a plasma asher (parallel flat plate electrode type plasma generating apparatus). Argon gas and oxygen gas were mixed at the pressure ratio of 1:5, and plasma was generated by applying electric power of 0.3 kW under a pressure of 45 Pa. The treatment period was 0.5 minutes. A masking material deposited layer18was formed at the edge of the substrate12.

Subsequently, the mask20was removed. The substrate12was then placed on the spin coater22, and a resin was dropped on the substrate12so that the resin film14was formed by a spin coating method. The resin was a resin material including a phenolnovolak resin, a photosensitive agent, a perfluoroalkyl-containing oligomer, 2-heptanone, and 1,4-dioxane as components. A solution including the phenolnovolak resin at 38 mass % was dropped onto the substrate12at 0.3 cc and was spin coated at 4000 rpm for 20 seconds. Thus, the resin film14was formed at a thickness of about 2 μm.

Then, the substrate12formed with the resin film14was placed on the heater base24, and was heated at 90° C. for 1.5 minutes and was then cooled to room temperature. Thus, the resin film14that was in contact with the adhesion aid layer16at a region which did not include the edge of the adhesion aid layer was chemically bonded to the substrate12through the reactive groups of the adhesion aid layer16.

The substrate12which was chemically bonded to the resin film14was then dipped in water, and the edge of the resin film14was removed by applying ultrasonic waves. Ultrasonic waves at frequencies of 28 kHz, 45 kHz, and 100 kHz were sequentially applied every 10 seconds repeatedly to the resin film14for a total of 20 minutes.

Subsequently, the substrate12was removed from the water for drying.

FIG. 5Ais a graph illustrating the measurement of surface flatness of the resin film14formed by the resin film forming method described above.FIG. 5Bis a graph illustrating the measurement of surface flatness of a resin film formed on a substrate by a conventional method that does not remove an edge bead. For both measurements, the P22 Automated Surface Profiler manufactured by KLA-TENCOR Corporation was used.

As seen inFIGS. 5A and 5B, the resin film formed by the embodiment of the method described above was removed at the edge of the substrate12and had no edge bead. Additionally, the resin film14was approximately at a constant thickness. On the contrary,FIG. 5Bindicates that an edge bead was formed at a height of about 5 μm at the edge of the substrate using the conventional method.

The resin film14formed thereby may be used for e.g., forming a pattern. Specifically, the resin film14may be pressed on a mold, and the mold pattern may then be transferred onto the resin film14, thus forming a pattern on the resin film14. Alternatively, a pattern may be formed on the resin film14by adhering an exposure mask to the resin film14and then exposing the resin film14.

In the conventional method described above in which an edge bead is not removed, a mold or an exposure mask is not fully in contact with the resin film because of the edge bead as illustrated inFIGS. 7A and 7B, so that a pattern is not accurately transferred on the resin film14. It is also difficult to expose the resin film14with accuracy.

FIGS. 6A and 6Billustrate the differences in pattern resolution when the resin films illustrated inFIGS. 5A and 5Bare used as a resist in photolithography.

FIG. 6Aillustrates a pattern when the resin film formed by the resin film forming method described above is used as a resist.FIG. 6Billustrates a pattern when the resin film formed by the conventional method that does not remove an edge bead, is used as a resist.

As seen fromFIGS. 6A and 6B, pattern resolution, in other words, accuracy, is insufficient at regions A inFIG. 6B. That is, due to the edge bead described above, an exposure mask does not adhere to the resin film and a gap is partially formed between the resin film and the exposure mask, lowering the resolution of an exposure pattern on the surface of the resin film.

In the resin film forming method of the embodiment mentioned above, vibrations are applied to remove an edge bead of a resin film, so that a resin film of an even thickness can be formed. In addition, since the edge of the resin film14having an edge bead is removed after hardening the film, the film can be stably formed at a uniform thickness.

Moreover, when the resin film is used as a resist in photolithography, the film adheres well to an exposure mask, so that a pattern can be formed with high resolution and accuracy. When the resin film is used as a base material for nanoimprint lithography, the film is well in contact with a mold, so that a pattern can be accurately formed.

Furthermore, the adhesion aid layer16is removed from the edge by applying the mask20, so that the shape of the substrate12is not limited to a circle or a rectangle. Thus, the substrate12may be of any shape.