JPS6262520A - Pattern forming method - Google Patents

Abstract

PURPOSE:To form an ultrafine and accurate pattern and a pattern having high alignment accuracy by forming a perfluoroalkyl polyester film or perfluoroalkylamine film or their mixture film on a resist. CONSTITUTION:A perfluoroalkyl polyether film, a perfluoroalkylamine film or their mixture film (perfluoroalkyl compound) is formed on a resist before exposing, and the perfluoroalkyl compound film is removed after exposing. The perfluoroalkyl compound film is transparent and its refractive index is approx. 1.3. Therefore, it serves as a resist reflection preventive film. Reflected light on the resist surface is reduced without loss of the incident light amount by the transparent reflection preventive film to prevent the pattern dimension accuracy from decreasing owing to the multiple interference of light in the resist film. It also reduces the deterioration of a pattern detection signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a microfabrication method that can be used for manufacturing semiconductor devices, magnetic bubble devices, superconducting devices, etc., and relates to a pattern forming method in photolithography and X-ray lithography.

[Background of the invention]

The degree of integration of semiconductor circuits, magnetic bubble memory circuits, etc. is improving year by year. In order to improve the degree of integration, miniaturization of patterns is required, as well as higher precision of pattern dimensions and higher precision of alignment. However, optical lithography has a problem in that dimensional accuracy and alignment accuracy are reduced due to the influence of optical interference.

First, the decrease in dimensional accuracy will be explained. High resolution;
The reduction projection exposure method is used as the mainstream method for forming fine patterns because it has a low defect occurrence rate due to foreign particles and can correct wafer distortion using a step-and-repeat mechanism. In the reduction projection exposure method, monochromatic light is used due to limitations of lenses and optical systems, and light interference occurs within the resist. Due to optical interference, the effective amount of light absorbed by the resist varies, resulting in variations in pattern dimensions. As shown in FIG. 2, as the film thickness of the resist changes, the pattern line width changes periodically, and the amount of change is about 0.3 μm in the case of a Si substrate. The minimum line width is required to be approximately 1 .mu.m or less, and a decrease in dimensional accuracy due to this dimensional variation is a major problem.

A multilayer resist method, an ARC method, and the like have been proposed as methods for reducing the decrease in dimensional accuracy due to optical interference. However, the multilayer resist method involves forming three or two resist layers and then performing pattern transfer to form one resist pattern that serves as a mask, so there is a problem in that the number of steps is large and the throughput is low. Furthermore, the improvement in dimensional accuracy is not necessarily sufficient due to the reflected light from the intermediate layer. In the ARC method, since the antireflection film formed under the resist is wet-etched by development, the amount of side etching is large, which causes a problem in that the dimensional accuracy is greatly reduced. In addition,
Multilayer resists are described in Japanese Patent Application Laid-Open No. 51-10775. Also, as an ARC method,
No. 9-93448.

Next, I will explain the matching problem.

“The alignment method using monochromatic light is TTL (Through).
hthe Lsnse) method can be used, which is advantageous in terms of throughput and offset fluctuation.
This is advantageous for chip-by-chip alignment (hereinafter referred to as chip alignment) that can correct asymmetric wafer distortion. Similarly, in the case of a Fresnel zone alignment method that uses monochromatic light and utilizes its optical interference, the focus position and pattern alignment can be performed simultaneously, which is very effective. However, due to the following problems, sufficient butterfly detection accuracy could not be obtained.

When detecting a pattern by irradiating monochromatic or quasi-monochromatic light onto a mating target pattern formed on a substrate and using the reflected light from the target pattern, conventional pattern detection methods detect light on the surface of a resist formed on a substrate. The pattern detection light causes optical interference within the resist film because it is reflected. As a result, the reflected light (detected light) is also affected,
The light intensity and phase change as the resist film thickness changes. For this reason, the pattern detection signal is disturbed and alignment accuracy is reduced. For example, if a resist is applied with a film thickness asymmetrical to the target pattern, the target position will be detected at a position shifted from the actual position. In other words, it is falsely detected. Also, depending on the thickness of the resist, the intensity of reflected light between the target pattern and other parts becomes almost equal, resulting in a marked reduction in the contrast of the target pattern.
In other words, detection of the target pattern may become extremely difficult. Such a problem existed in the alignment method using monochromatic light.

For this reason, for example, in the Fresnel zone pattern detection method, optimization of the target pattern shape has been studied as discussed in SPIE, Vol. 470, pp. 122-135 (1984). ing. Further, dual wavelength detection is being studied as shown in Japanese Patent Publication No. 58-30736. However, in either case, it is sufficient to prevent deterioration of the pattern detection signal due to optical interference, and improvements are desired.

[Purpose of the invention]

An object of the present invention is to solve the above-mentioned conventional problems and to provide a method for forming fine and highly accurate patterns and patterns with high alignment accuracy using a simple method.

[Summary of the invention]

In order to achieve the above object, the present invention forms a perfluoroalkyl polyether film, a perfluoroalkylamine film, or a mixture film thereof (hereinafter collectively referred to as perfluoroalkyl compound film) on a photoresist film or an X-ray resist film. The perfluoroalkyl compound film is transparent and has a refractive index of approximately 1.3, so it serves as an anti-reflection film for the above resist.The transparent anti-reflection film allows it to coat the resist surface without loss of incident light. This reduces reflected light at the resist film and prevents deterioration in pattern dimensional accuracy due to optical multiple interference within the resist film.

It also reduces deterioration of the pattern detection signal.

The principle of the present invention will be explained in detail below.

First, the principle of improving dimensional accuracy will be explained.

Interference between lights traveling in opposite directions, such as interference between light reflected from the substrate and incident light, changes the light intensity distribution in the resist film thickness direction, creating a "standing wave" that makes the cross-sectional shape of the resist ripple. However, the total amount of light absorbed by the resist does not change and the effect on dimensional accuracy is small.On the other hand,
Considering the case of light traveling in the same direction, such as the light reflected from the top surface of the resist and the incident light, the phase difference between the lights changes as the resist film thickness changes. The light intensity of the interference light of these lights increases and decreases. In other words, overexposure or underexposure occurs depending on the resist film thickness, resulting in a decrease in dimensional accuracy.

In order to improve the dimensional accuracy, it is sufficient to reduce the reflected light traveling in the same direction, that is, it is sufficient to reduce the reflected light on the upper surface of the resist. In order to reduce the reflected light from the upper surface of the resist without attenuating the exposure light, a transparent anti-reflection film is formed on the resist, which uses light interference with a small absorption coefficient. That is, as shown in FIG. 3, reflection prevention 11 of light 31 directed from the substrate to the resist surface! l! /Reflected light 34 from the resist interface 32a and the atmosphere/antireflection film interface 3
The reflected light 35 from 2b is interfered with to make the reflected light sufficiently small. In this case, the amount of transmitted light 36 approaches the amount of incident light 31, and when no reflection occurs, the amount of transmitted light 36 is completely transmitted without loss of amount of light.

From the principle of anti-reflection, if the refractive index of the resist with respect to exposure light is n and the wavelength of the exposure light is λ, then the refractive index of the anti-reflection film is n'
5, the reflectance (amplitude ratio) of this antireflection decreases as the film thickness approaches an odd multiple of λ/4n'. The refractive index of a phenol novolak resist is about 1.7, and the optimum refractive index required for an antireflection film is about 1.30.

The refractive index of perfluoroalkyl polyethers or perfluoroalkyl amines or mixtures thereof is approximately 1.
31, and when this film is used as an antireflection film, it becomes possible to significantly reduce the reflectance of the upper surface of the resist, and the dimensional accuracy can be improved.

Next, the principle of improving alignment accuracy will be explained.

If a large amount of light interferes within the resist film, the reflected light reflected from the substrate will also be affected, resulting in a decrease in pattern detection accuracy, as described above. In order to solve this problem, the above-mentioned antireflection film is formed on the resist to reduce the reflected light at the outside air/resist interface and create a completely transparent surface. Perfluoroalkyl polyether perfluoroalkyl amines and mixtures thereof are transparent, and their refractive index (approximately 1.31) allows the top surface of the resist to be almost completely transparent. The optimum thickness of the perfluoroalkyl polyether film for pattern detection is 174 n' of the wavelength λ' of the pattern detection light.
That is, approximately λ' 15.2. Similarly, when the antireflection film is made of perfluoroalkylamine or a mixture of perfluoroalkylamine and perfluoroalkyl polyether, the optimal film thickness is approximately λ' 15.2.

By overcoating the resist with perfluoroalkyl polyether, perfluoroalkyl amine, or a mixture thereof, the alignment detection signal becomes a good one without being disturbed by noise caused by optical interference within the resist film, and the alignment accuracy is improved.

[Embodiments of the invention]

The present invention will be explained below using examples.

Example 1 As shown in FIG. 1(a), a resist 2 was spin-coated on a Si substrate 1 having a step, and then subjected to beta treatment at 90° C. for 10 minutes to volatilize the solvent and form a resist film. Si
The pattern on the substrate is a lattice pattern, concave pattern, convex pattern, etc., and the height of the pattern is about 0.1 to 0.6
It was set as μm. MP1300 (trade name, Silapray Co., Ltd.) was used as the resist, and its film thickness was about 1.0 μm on a flat surface. However, the film thickness on the resist 1 does not need to be limited to 1.0 μm as long as the film thickness can sufficiently cover the substrate level difference.

Also, it is not necessary to limit the level difference to 0.1 to 0.6 μm.
Also, there is no problem with shapes other than those mentioned above, and there is no need to limit it to Si substrates, such as PSG (phosphorus glass), SiO□,
W, Aα, polyimide, SiN.

There is no problem with G a A s etc. Also, the resist has 0
Phenol novolak resists such as FPR800, 0NPR830, 0FPR5000 (Tokyo Ohka Co., Ltd. product names) A Z1350J (Microposit Co., Ltd. product name), HPR204 (Hunt Co., Ltd. product name), RD
Polyvinylphenol resists such as 200ON, RUlooON (trade name manufactured by Hitachi Chemical Co., Ltd.), MP23 (trade name manufactured by Shipley Co., Ltd.), KTF
Any photoresist such as a cyclized rubber resist such as CBR (trade name, manufactured by Nippon Gosei Rubber Co., Ltd.) can be used. Thereafter, as shown in FIG. 1(b), perfluoroalkyl polyether was coated on the resist 2 to a thickness of about 65 to 1100 nm. Examples of perfluoroalkyl polyethers include Montageson (7) FOMBLIN and KRyr from DuPont.
There are such things as ox'n. In addition, the solution was diluted in order to control the coating film thickness, and low molecular weight perfluoroalkyl polyether, Freon R (trade name of DuPont), or the like was used as the diluted solution. It is generally known that a compound obtained by replacing hydrogen in an organic compound with fluorine has a lower refractive index than the original organic compound. Therefore, in addition to the commercially available perfluoroalkyl polyethers mentioned above, alkyl polyethers in which a considerable number of hydrogen atoms are replaced with fluorine may also be used.

After the antireflection film 3 made of perfluoroalkyl polyether was formed on the resist 2 in this manner, normal exposure was performed using light having a wavelength of 436 μm, as shown in FIG. 1(c). Thereafter, as shown in FIG. 1(d), the antireflection film 3 was removed using Freon'α. Freon did not melt the resist or cause any deterioration. As a remover for the antireflection film 3, in addition to fluorol-substituted hydrocarbons such as Freon (2), low molecular weight perfluoroalkyl polyethers such as GALDEN 9 (trade name of Montegisson) can also be used.

Thereafter, as shown in FIG. 1(e), development was performed to form a resist pattern 2' on the Si substrate.

The pattern dimensional accuracy without the antireflection film 3 made of perfluoroalkyl polyether was approximately 0.15 μm, but due to the above process, the amount of dimensional variation was approximately 0.0 μm.
A highly accurate resist pattern 2' of 5 μm or less could be formed on the Si substrate.

In addition, although the above example shows the case where exposure light with a wavelength of 436 nm is used, in the case of exposure light with a wavelength of 405 nm, the film thickness of the perfluoroalkyl polyether antireflection film 3 is approximately 60 to 85 nm + the wavelength is 365 nm. In this case, by setting the film thickness to about 55 to 85 nm, it was possible to reduce the dimensional variation to ±0.05 μm or less, as in the above embodiment.

Example 2 In Example 1, mask alignment was performed using light of the same wavelength as the exposure light. At this time, a concave pattern, a convex pattern, a double slit pattern, a lattice pattern, a dot pattern, and a hole pattern were used as target patterns on the substrate, and pattern detection signals were observed for each pattern, and alignment accuracy was evaluated. As a result, it was possible to reduce the asymmetry of the signal waveform due to uneven resist coating, the decrease in signal strength and the decrease in contrast due to optical interference, and the alignment accuracy was improved.

Example 3 Nodist was applied to a thickness of about 1.0 μm on a flat Si wafer. The variation in resist film thickness was approximately ±0.05 μm. The wafer is not limited to Si but can also be GaAs, and the substrate surface is not only Si but also 5jOa, SiN polymide, A Q , W, WS i2, Mo Si
.

There is no problem with that. Thereafter, one substrate was exposed as it was, and a perfluoroalkyl polyether film was formed on the resist for the other substrates, and then exposed. , the exposure wavelength is “
The film thickness of the perfluoroalkyl polyether film was varied from 0 to 160 nm for each substrate.

After exposure, remove the perfluoroalkyl polyether film,
Thereafter, development was performed to form a pattern. the result,
The dimensional variation, which was approximately ±0.16 μm in the conventional method, was reduced as shown in FIG. 4. In particular, the film thickness of the perfluoroalkyl polyether film is 436 nm and 15.2 cm.
At 4 nm, the dimensional variation is minimum, approximately ±0.01
It was possible to reduce the thickness to 5 μm. Although this example shows a case where the resist film thickness is 1.0 μm, the film thickness is not limited to this, and the exposure wavelength is not limited to 436 nm. For example, 405 nm or 365 nm can also be used, or multiple wavelengths may be used. .

Example 4 As shown in FIG. 5(a), a resist was spin-coated on a Si substrate 51 having a step, and then baked at about 200° C. for 30 minutes to form a lower resist 52 of a three-layer resist. The patterns on the Si substrate were a lattice pattern, a concave pattern, a convex pattern, etc., and various steps were formed up to a maximum of about 1.5 μm. MP130 for resist
0 (trade name, Silapray Co., Ltd.) was used, and the film thickness was about 2.0 μm on a flat surface. By heat treatment at 200° C. for 30 minutes, the level difference on the surface of the lower resist 52 was alleviated. Note that the material and film thickness of the lower resist 52 are not limited to the above example.
Those generally used for lower layer resists can be used without any problem. The substrate level difference is also not limited to the above example. There is no problem even if a metal film such as Aα, an insulating film such as SjO, an organic film such as polyimide, or a semiconductor film such as Go is deposited on the substrate.

Then, as the middle layer 53 of the three-layer resist, 5OG (danpi
nεn Glass) was formed with a film thickness of about 0.18 μm. ○CD manufactured by Tokyo Ohka Co., Ltd. was used as the SOG.

The material of the intermediate layer 53 is not limited to the above-mentioned examples, but also materials commonly used for intermediate layers, such as insulating films such as SiO2 and 3iN, metal compounds such as organic Ti, metals such as W, and semiconductors such as Si. I can do it. Film thickness is also 0.18μm
Not limited to.

Thereafter, a resist layer 54 was formed for pattern formation. M P 1300 was used as a resist, but Example 1
Similarly, all registers 1- can be used.

Next, as shown in FIG. 5(b), an antireflection film 55 made of perfluoroalkyl polyether is applied to the resist layer 54.
formed on top. The film thickness is approximately 7 nm, m.

Thereafter, patterning was performed using light with a wavelength of 365 nm, and then the perfluoroalkyl polyether film was removed. Thereafter, development was carried out to form a pattern 54' in the resist layer as shown in FIG. 5(C). Then the fifth
As shown in Figure (d), the pattern 54' is transferred to the intermediate layer 53 by dry etching, and the transferred pattern 5 is transferred to the intermediate layer.
3' was formed. Thereafter, as shown in FIG. 5(e), pattern 53' was used as a mask to transfer the pattern to the lower resist layer to form pattern 52', that is, a three-layer resist pattern was formed.

As a result, perfluoroalkyl polyether reflection
For normal three-layer resist without VJ stopper film, the ladle is 0.04μ.
By forming the anti-reflection film, the dimensional variation, which was 1.5 m, was reduced to 0.01 μm or less.

In addition, although the above example is a case where the wavelength is 365 nm,
It is not limited to this wavelength. Furthermore, although the case of a three-layer resist is shown, the same effect was obtained in the case of a two-layer resist.

Example 5 In Example 2, mercury e-line (5
Mask alignment was performed using d-line (577 nm), HeNe laser light (633 nm), etc. The pattern detection signal was better than that without the antireflection film, and the alignment accuracy was also improved. In particular, the film thickness of the perfluoroalkyl polyether antireflection film is set to 115.2 of the wavelength λ' of the pattern detection light, that is, approximately 1105 nm and 110 nm for e-line, d-line, and HeNe light, respectively.
The alignment detection signal was the best when the wavelength was set to m and 120 nm, and the alignment accuracy was improved.

In addition, in the example, e-line, d-line, ! Although 1aNe light was used, other monochromatic light or polychromatic light had similar effects. In addition, when it comes to mask alignment, RE-500
A resist sensitive to X-rays such as 0P (trade name, manufactured by Hitachi Chemical Co., Ltd.) can also be used.

Example 6 In Example 4, mask alignment was performed using mercury e-line, d-line, and HeNe light. The target patterns used were a concave pattern, a convex pattern, a double slit pattern, a lattice pattern, a dot pattern, and a hole pattern as in Example 2, and each case was examined. Even in multilayer resists, the pattern detection light intensity was sufficient by performing pattern detection using light of a different wavelength from the exposure light, and the anti-reflection coating was able to reduce asymmetry of the pattern detection signal and decrease in contrast. . In particular, in the case of a multilayer resist, the flatness of the upper surface of the resist is high, so the thickness of the antireflection film is uniform, and as a result, the reduction effect is greater than that of a single layer resist. Furthermore, the film thickness of the perfluoroalkyl polyether film was increased to 11% of the wavelength λ' of the pattern detection light.
5.2, that is, when the wavelengths are set to approximately 1105n, 110nm, and 120nm for A4@, d-line, and HeNe light, respectively, the pattern detection signal waveform is almost the same as that when directly detecting the board (without register). This made it possible to eliminate the influence of optical interference caused by the resist. As a result, the alignment accuracy has improved from about 0.3μm to about 0.2μm.
m, and was able to improve the alignment accuracy on top of the alignment accuracy caused by the Habo device.

Note that although e-line, d-line, and HeNe light were used in the embodiment, light of other wavelengths can be similarly effective as long as the light passes through the underlying resist.

Example 7 A resist was applied and formed on a Si substrate on which a Fresnel zone pattern was formed, and then a perfluoroalkyl polyether film was formed on the resist. The film thickness is about 120 nm. Thereafter, a pattern position and a focal point position were detected using a HeNe laser beam. By forming an antireflection film made of perfluoroalkyl polyether, pattern position detection and focused point position detection signals became sharper, improving detection accuracy.

Note that the detection light is not limited to HeNe laser light, but other monochromatic light can be used. Moreover, a multilayer resist can also be used instead of a single layer resist. Furthermore, as a result of experiments using not only Fresnel zone patterns but also alignment target patterns that utilize interference or diffraction, such as diffraction grating patterns, we found that this method of overcoating a perfluoroalkyl polyether film on a resist is extremely effective. Ta.

Example 8 After forming the perfluoroalkyl polyether film on the resist in Examples 1 to 7 above, heat treatment was performed at about 90° C. for 10 minutes. The heat treatment reduced the change in film thickness of the perfluoroalkyl polyether film over time, and increased the latitude for leaving time for the treatment after forming the perfluoroalkyl polyether film. Note that the heat treatment conditions are not limited to the above examples, and any tube circumference that does not deteriorate the photosensitive characteristics and development characteristics of the resist may be used. However, similar effects were obtained by using a perfluoroalkyl compound such as perfluoroalkylamine or perfluoroalkylamine and perfluoroalkyl polyether instead of perfluoroalkyl polyether. Examples of perfluoroalkyl amines include Fluorinert (trade name, manufactured by Jujutsu 3M Co., Ltd.).

〔Effect of the invention〕

21, according to the present invention, a pattern with high dimensional accuracy can be formed by a simple method. Furthermore, since highly accurate alignment pattern detection can be performed, alignment accuracy is improved.

Since dimensional accuracy and precision can be improved, it is possible to increase circuit integration and reduce chip area, and it is also possible to obtain high-quality elements with stable electrical characteristics at a high yield. .

[Brief explanation of the drawing]

FIG. 1 is a process diagram showing an embodiment of the present invention. FIG. 2 is a diagram explaining the problems of the conventional method. FIG. 3 is a diagram for explaining the present invention in detail. FIG. 4 is a curve diagram showing the effect of the present invention. FIG. 5 is a process diagram showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Si substrate, 2... Resist, 3... Antireflection film, 4... Mask, 5... UV light, 2'... Resist pattern, 31... Substrate, 32... ...Resist, 33...Anti-reflective film, 33a...Interface between anti-reflective film and resist, 33b...Interface between outside air and anti-reflective film, 34...Light traveling from substrate to anti-reflective film, 35・・・
・Reflected light from the anti-reflection film/resist interface toward the substrate,
36... Reflected light heading from outside air/anti-reflection film interface to substrate, 37... Transmitted light heading towards outside air, 51... Si substrate, 52... Lower layer resist, 52'... Transferred to lower layer resist pattern, 53...middle layer, 53'.
...Pattern transferred to intermediate layer, 54...Resist, 54'...Resist pattern, 55...Perfluoro grass 1 Figure (a-small (thin (d) (Q) 7iz cyst thickness [P-] Rod 30 Kaya 4 eyes 0-Fluoroalyl base Lugol anti-octopus n stop d#4 imitation L
)B S Figure (a-) (C) (d-) (e)

Claims (1)

[Scope of Claims] 1. A pattern forming method including a step of forming a resist film on a substrate, a step of exposing the resist film with a predetermined pattern, and a step of developing the resist after the exposure, a step of forming a perfluoroalkyl polyether film, a perfluoroalkyl amine film, or a mixture film thereof (hereinafter collectively referred to as perfluoroalkyl compound) on the resist, and removing the perfluoroalkyl compound film after exposure. A pattern forming method characterized by comprising: 2. In the pattern forming method according to claim 1, an alignment pattern is formed on the substrate, and the substrate is irradiated with light for detecting the alignment pattern, and the reflected light is emitted from the substrate. 1. A pattern forming method comprising a step of detecting a pattern and aligning a desired pattern, the method comprising forming a perfluoroalkyl compound film on the resist before detecting the pattern. 3. In the pattern forming method according to claim 1, where the wavelength of the exposure light is λ, the thickness of the perfluoroalkyl compound film is approximately an odd multiple of λ/5.2. A pattern forming method. 4. In the pattern forming method according to claim 2, when the wavelength of the pattern detection light is λ', the thickness of the perfluoroalkyl compound film is approximately λ'/5.
A pattern forming method characterized in that the pattern is an odd multiple of 2. 5. A pattern forming method according to claim 1 or 2, characterized in that a heat treatment is applied after the perfluoroalkyl compound film is formed.