JPH0799730B2 - Pattern formation method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a microfabrication method in the production of semiconductor elements, magnetic bubble elements, superconducting elements, etc., and 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, and it is also necessary to improve the accuracy of pattern dimensions and the accuracy of alignment. However, optical lithography has a problem that dimensional accuracy and alignment accuracy are degraded due to the influence of optical interference.

The decrease in dimensional accuracy will be described recently.

The reduction projection exposure method, which has a high resolution, a low defect occurrence rate due to foreign matter, and is capable of correcting the distortion of a wafer by a step-and-repeat mechanism, is used as a mainstream of fine pattern formation. In the reduction projection exposure method, monochromatic light is used due to restrictions of the lens and optical system, and optical interference occurs in the resist. Due to optical interference, the effective amount of light absorbed by the resist fluctuates, so that the pattern dimension fluctuates. As shown in Fig. 2, as the resist film thickness changes, the pattern line width fluctuates periodically, and the fluctuation amount is about 0.3 for the Si substrate.
μm. The minimum line width is required to be about 1 μm or less, and the decrease in dimensional accuracy due to this dimensional variation is a serious problem.

Multi-layer resist method or ARC (Anti-Reflective Coating) is a method to reduce the deterioration of dimensional accuracy due to optical interference.
Laws have been proposed. However, the multi-layer resist method has a problem that the number of steps is large and the throughput is low because three or two resist layers are formed and then a pattern is transferred to form a resist pattern serving as a mask. AR
The method C has a problem that the amount of side etching is large because the antireflection film formed under the resist is wet-etched by the development, and thus the dimensional accuracy is greatly reduced. Regarding the multilayer resist, JP-A-51-10775
No. etc. Further, as the ARC method, Japanese Patent Laid-Open No.
9-93448 and the like.

Next, the problem of alignment will be described.

The matching method using monochromatic light is TTL (Through the Lens
The method e) can be used and is advantageous in terms of fluctuations in throughput and offset, which is advantageous in chip-by-chip alignment (hereinafter referred to as chip alignment) capable of correcting asymmetrical wafer distortion. Similarly, in the case of the Fresnel zone alignment method using monochromatic light and utilizing the optical interference, it is very effective because the focus position and the pattern alignment can be performed at the same time. However, there were problems due to the following causes, and sufficient pattern detection accuracy could not be obtained.

When monochromatic light or quasi-monochromatic light is applied to the matching target pattern formed on the substrate and pattern detection is performed using the reflected light from the target pattern, the conventional pattern detection method uses the resist surface formed on the substrate to detect light. Are reflected, the pattern detection light causes optical interference in the resist film. As a result, the reflected light (detection light) is also affected,
The light intensity and the phase change as the resist film thickness changes. As a result, the pattern detection signal is disturbed and the alignment accuracy is reduced. For example, when the resist is applied asymmetrically with respect to the target pattern, the target position is detected at a position shifted from the actual position. That is, false detection is performed.
Also, depending on the film thickness of the resist, the reflected light intensities of the target pattern part and other parts become almost equal, the contrast of the target pattern becomes equal, and the contrast of the target pattern decreases significantly, that is, it is extremely difficult to detect the target pattern. May become. Such a problem has been encountered in the alignment method using monochromatic light.

For this reason, for example, in the Fresnel zone pattern detection method, SPIE Volume 470, Volume 122
~ 135 (1984), optimization of the target pattern has been studied. In addition, Japanese Patent Publication Sho 58-30
Dual wavelength detection is being considered, as shown in 736. However, in either case, prevention of deterioration of the pattern detection signal due to optical interference is incomplete.

Although the problems of the optical lithography have been described above, the pattern detection method using monochromatic light is mainly used for alignment in the X-ray lithography, and the above problems occur.

[Object of the Invention]

An object of the present invention is to solve the above conventional problems and provide a method for forming a fine and highly precise pattern and a pattern with high alignment precision by a simple method.

[Outline of Invention]

In order to achieve the above object, the present invention provides an alginate, sodium alginate, potassium alginate, tetraethylammonium alginate, tetramethylammonium alginate, soluble starch, amylose, imarin, lichenin on a photoresist film or an X-ray resist film. It forms at least one polysaccharide film selected from the group consisting of glycogen and pullulan. Since the polysaccharide film is transparent and has a refractive index smaller than that of the resist, it serves as an antireflection film for the resist. The transparent antireflection film reduces the reflected light on the resist surface without loss of the incident light amount, and prevents the pattern dimensional accuracy from deteriorating due to optical multiple interference in the resist film. Also, the deterioration of the pattern detection signal is reduced.

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

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

Interference between light 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, and is called a “standing wave” that causes the resist cross section to wavy. This causes the phenomenon of exposure, but the total amount of light absorbed by the resist does not change and has little effect on dimensional accuracy. on the other hand,
Considering the case of light reflected from the top surface of the resist and light traveling in the same direction such as incident light, the phase difference between the lights changes according to the change in the resist film thickness. The light intensity of the interference light of these lights increases or decreases. That is, overexposure or underexposure occurs depending on the resist film thickness, and as a result, the dimensional accuracy decreases.

In order to improve the dimensional accuracy, the reflected light traveling in the same direction may be reduced. 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 attenuation of each exposure, a transparent antireflection film utilizing light interference with a small absorption coefficient is formed on the resist. That is, as shown in FIG. 3, an antireflection film / resist interface 33 for the light 34 traveling from the substrate 31 to the surface of the resist 32.
The reflected light 35 from a and the reflected light 36 from the atmosphere / antireflection film interface 33b are interfered with each other to make the reflected light sufficiently small. In this case, the light quantity of the transmitted light 37 approaches the light quantity of the light 34, and when it becomes non-reflecting, it is completely transmitted without loss of the light quantity.

From the principle of antireflection, assuming that the refractive index of the resist for exposure light is n and the wavelength of each exposure is λ, the refractive index of the antireflection film is n ′.
But The reflectance of this antireflection film decreases as the film thickness approaches an odd multiple of λ '/ 4n'. A film made of a polysaccharide has a refractive index lower than that of a resist due to its structure, and serves as an antireflection film. By forming a film made of a polysaccharide on the resist, it is possible to reduce the reflectance on the upper surface of the resist and improve the dimensional accuracy. Since the polysaccharide is water-soluble, it does not deteriorate the resist. Anti-reflection film (polysaccharide)
Can be shared with the developing step, so there is no process problem and it is simple.

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

When light interferes in the resist film multiple times, the reflected light reflected from the substrate is also affected, and the pattern detection accuracy deteriorates as described above. In order to solve this problem, the antireflection film made of the above-mentioned polysaccharide is formed on the resist to reduce the reflected light at the interface between the outside air and the resist and make it a completely transparent surface. The optimum thickness of the antireflection film (polysaccharide) at the time of pattern detection is 1 / 4n 'of the wavelength λ'of the pattern detection light, that is, λ' / 4n. By overcoating the polysaccharide film on the resist, the alignment detection signal becomes good with little influence of optical interference in the resist film, and the alignment accuracy is improved.

Example of Invention

 Hereinafter, the present invention will be described in detail with reference to examples.

Example 1 As shown in FIG. 1 (a), a resist was spin-coated on a Si substrate 1 having a step, followed by baking at 90 ° C. for 10 minutes to evaporate the solvent and form a resist film 2. The pattern on the Si substrate is a lattice pattern, a concave pattern, a convex pattern or the like, and the height of the pattern is about 0.1 to 0.6 μm. MP1300 (trade name of Shipley Co., Ltd.) was used as the resist, and the film thickness was set to about 1.0 μm on the flat surface. However, the film thickness of the resist need not be limited to 1.0 μm as long as the film thickness can sufficiently cover the substrate step. Also, the step is 0.1 to 0.6
It is not necessary to limit to μm. No need to limit to Si substrate,
For example, PSG (phosphorus glass), SiO ₂ , W, Al, polyimide, SiN, G
There is no problem with aAs. For resist, OFPR800, ONPR8
30, OFPR5000 (TOKYO OHKA CO., LTD. Product name), AZ1350J
(Microposit Co., Ltd. product name), HPR204 (Hunt Co., Ltd. product name) and other phenol novolak resists, RD200N, R
Cyclization of U100N (Hitachi Chemical Co., Ltd. product name), MP23 (Situpray company product name), and other polyvinylphenol-based resists, KTFR (Kodak company product name), CBR (Nippon Synthetic Rubber Co., Ltd. product), etc. Any photo resist such as a rubber-based resist can be used. Then, Fig. 1 (b)
As shown in (1), a tetramethylammonium alginate salt was applied and formed on the resist film 2 in a thickness of about 60 to 95 nm to form an antireflection film 3. Then, as shown in FIG. 1 (c), ordinary exposure was performed using light having a wavelength of 436 nm. Thereafter, as shown in FIG. 1 (d), development was performed using a developer MF312 (trade name of Shipley Corporation) to form a resist pattern 2'on the Si substrate. The antireflection film 3 made of tetramethylammonium alginate was removed during development. The antireflection film 3 can be removed by washing with water before the development. Although MF314 is used as the developing solution, it is not limited to this developing solution.

The pattern dimensional accuracy without the antireflection film 3 made of tetramethylammonium alginate (conventional method) is about ±
Although it was 0.15 μm, the dimensional accuracy was approximately ±
A highly accurate resist pattern 2'having a thickness of 0.1 μm could be formed on the Si substrate.

In addition, although alginic acid tetramethylammonium salt is used as the antireflection film 3 in the above-mentioned embodiment, the invention is not limited to this.
Alginic acid sodium salt, Alginic acid ammonium salt,
Polysaccharides such as alginic acid tetraethylammonium salt, pullulan, soluble starch, amylose, inulin, lichenin and glycogen can be used.

Further, in the above embodiment, the case where the exposures with the wavelength of 436 nm are used is shown, but in the case of the exposures with the wavelength of 405 nm, the thickness of the antireflection film 3 made of tetramethylammonium alginate is about 55 to 85 nm. Approximately 50-80 nm when the wavelength is 365 nm
As a result, the dimensional accuracy is about ± 0.
It could be 1 μm.

Example 2 In Example 1, mask alignment was performed using light having the same wavelength as that for each exposure. At this time, the target pattern on the substrate was a concave pattern, a convex pattern, a double slit pattern, a grid pattern, a dot pattern, and a hole pattern, and the pattern detection signal was observed for each and the alignment accuracy was evaluated. As a result, the asymmetry of the signal waveform due to the uneven coating of the resist and the decrease in the signal strength due to the optical interference and the decrease in the contrast can be suppressed, and the alignment accuracy is improved.

Example 3 A resist was applied on a flat Si wafer to a thickness of about 1.0 μm.
The variation in the film thickness of the resist was about ± 0.05 μm. Wafers are not limited to Si, GaAs can be used, and the substrate surface can be Si.
Not only SiO _2, SiN, polyimide, Al, W, WSi _2, there is no problem even in such as MoSi. After that, one substrate was exposed as it was, and on the other substrate, a sodium alginate film was formed on the resist, and then exposed. The exposure wavelength is 436 nm. The thickness of the sodium alginate salt film was varied from 0 to 160 nm for each substrate. Then, development was performed to form a pattern.
Alginic acid sodium salt is removed by development,
It is also possible to remove it by washing with water before development.

As a result of forming the pattern by the above method, the dimensional variation of about ± 0.15 μm in the conventional method was reduced as shown in FIG. Especially the thickness of sodium alginate film is λ / 4n
When (λ: exposure wavelength 436 nm, n: refractive index of sodium alginate about 1.35), which is about 80 nm, the dimensional variation is minimized, and it can be reduced to about ± 0.04 μm. In this embodiment, the resist film thickness is about 1.0 μm, but the resist film thickness is not limited to this. Also, the exposure wavelength is not limited to 436 nm. For example, 405 nm or 365 nm can be used, and multiple wavelengths may be used.

As in Example 1, the antireflection film is not limited to sodium alginate, but a film made of a polysaccharide can be used.

Example 4 As shown in FIG. 5A, 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 three-layer resist lower layer resist 52. The pattern on the Si substrate is a grid pattern, a concave pattern, a convex pattern, etc., and various steps were formed up to a step of about 1.5 μm at the maximum. MP1300 (trade name of Shipley Co., Ltd.) was used as the resist, and the film thickness was about 2.0 μm on the flat surface. The heat treatment at 200 ° C. for 30 minutes alleviated the step on the surface of the lower resist 52. The material and the film thickness of the lower layer resist 52 are not limited to the above examples, and those generally used for the lower layer resist can be used without any problem. The substrate step is not limited to the above example. There is no problem if the substrate is coated with a metal film such as Al, an insulating film such as SiO ₂ , an organic film such as polyimide, or a semiconductor film such as Ge.

SOG then as a three-layer resist of the intermediate layer 53 (S pin o n
G lass) was formed to a thickness of about 0.18 .mu.m. OCD of Tokyo Ohka Co., Ltd. was used for SOG. The material of the intermediate layer 53 is not limited to the above example, but a material generally used for the intermediate layer, for example, Si
Insulating films such as O ₂ and SiN, metal compounds such as organic Ti, metals such as W, and semiconductors such as Si can also be used. Film thickness is 0.1
Not limited to 8 μm.

After that, a resist layer 54 was formed for pattern formation.
Although MP1300 was used as the resist, all resists can be used as in Example 1.

Next, as shown in FIG. 5B, an antireflection film 55 made of tetramethylammonium alginate was formed on the resist layer 54. Its film thickness is about 65 nm.

Then, the desired pattern was exposed using light with a wavelength of 365 nm. Thereafter, development was performed to form a pattern 54 'on the resist layer as shown in FIG. 5 (c). After that, as shown in FIG. 5 (d), a pattern 5 is formed by dry etching.
4 ′ was transferred to the intermediate layer 53, and a transfer pattern 53 ′ was formed on the intermediate layer. Then, as shown in FIG. 5 (e), the pattern 53 'was used as a mask to transfer the pattern to the lower layer resist to form a pattern 52', that is, a three-layer resist pattern.

As a result, in the case of a normal three-layer resist, the variation in size of about ± 0.04 μm is about ± 0 due to the formation of the antireflection film.
It was reduced to 03 μm.

In the above-mentioned embodiment, the wavelength is 365 nm, but the wavelength is not limited to this. The case of a three-layer resist is shown, but the same effect is obtained in the case of a two-layer resist.

Example 5 In Example 2, e-rays of mercury (54
6 nm), d-line (577 nm), and HeNe laser light (633 nm) were used for mask alignment. 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 tetramethylammonium alginate antireflection film is set to 1 / wavelength λ'of the pattern detection light.
4n (where n is the bending ratio of tetramethylammonium alginate is about 1.45), that is, the alignment detection signal is the best when e-line, d-line, and HeNe light are set to approximately 95 nm, 100 nm, and 110 nm, respectively, and alignment accuracy is improved did.

Although e-line, d-line, and HeNe light were used in the examples, other monochromatic light or polychromatic light was also effective. Further, when the light is used for the alignment using the X-ray resist, the detection signal becomes good by this method, and the alignment accuracy is improved.

Example 6 In Example 4, mask alignment was performed using e-line, d-line, and HeNe light of mercury. As the target pattern, a concave pattern, a convex pattern, a double slit pattern, a grid pattern, a dot pattern and a hole pattern were used as in Example 2, and each case was examined. Even in the case of a multi-layered resist, the pattern detection light intensity was sufficient by performing the pattern detection using holes of different wavelengths during each exposure, and the antireflection film could reduce the asymmetry of the pattern detection signal and the deterioration of the contrast. . In particular, in the case of a multi-layer resist, the flatness of the upper surface of the resist was high, so that the film thickness of the antireflection film was uniform, and as a result, the reduction effect was large compared with the single-layer resist.

Although e-line, d-line, and HeNe light were used in the examples, light of other wavelengths can be similarly used as long as the light is transmitted through the lower layer resist.

Example 7 A resist was applied and formed on a Si substrate on which a full-nel zone pattern was formed, and then a film made of pullulan was formed on the resist. Its film thickness is about 110 nm. After that, the pattern position and the focus position were detected using HeNe laser light. By forming the anti-reflection film made of pullulan, the pattern position detection and focus position detection signals became sharp and the detection accuracy was improved.

The detection light is not limited to HeNe laser light, and other monochromatic light can be used. A multi-layer resist may be used instead of the single-layer resist. Further, when the pattern detection is performed by using not only the Fresnel zone pattern but also the matching target pattern utilizing interference or diffraction like the diffraction pattern, the present method of overcoating pullulan on the resist is extremely effective.

In this example, pullulan was used as the antireflection film, but Example 1 was used.
Similar to the above, not only pullulan but also a membrane composed of a polysaccharide can be used.

〔The invention's effect〕

As described above, according to the present invention, a pattern with high dimensional accuracy can be formed by a simple method. Further, since the alignment pattern can be detected with high accuracy, the alignment accuracy is improved.

Since the dimensional accuracy and the alignment accuracy can be improved, the circuit can be highly integrated and the chip area can be reduced, and a high-quality element with stable electric characteristics can be obtained with a high yield.

[Brief description of drawings]

FIG. 1 is a process drawing showing an embodiment of the present invention. FIG. 2 is a diagram for explaining a conventional problem. Third
The figure is a figure for demonstrating the principle of this invention. FIG. 4 is a curve diagram showing the effect of the present invention. FIG. 5 is a process drawing showing an embodiment of the present invention. 1 ... Si substrate, 2 ... resist, 3 ... antireflection film, 4
...... Mask, 5 ... UV light, 2 '... resist pattern,
31 ... Substrate, 32 ... Resist, 33 ... Antireflection film, 33a
...... Interface between antireflection film and resist, 33b ...... Interface between outside air and antireflection film, 34 ...... Light traveling from substrate to antireflection film, 35 ...... Reflected light traveling from antireflection film / resist interface to substrate , 36 …… Reflected light from the outside air / antireflection film interface toward the substrate, 37 …… Transmitted light toward the outside air, 51 …… Si substrate, 52
...... Lower layer resist, 52 '…… Pattern transferred to lower layer resist, 53 …… Intermediate layer, 53 ′ …… Pattern transferred to intermediate layer, 54 …… Resist, 54 ′ …… Resist pattern, 55 …… Anti-reflection coating of tetramethylammonium alginate.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Norio Hasegawa 1-280 Higashi Koigakubo, Kokubunji, Tokyo Inside Central Research Laboratory, Hitachi, Ltd. (72) Inventor Tetsuya Hayashida 1-280 Higashi Koigakubo, Kokubunji, Tokyo Hitachi Ltd. (56) References JP-A-60-138922 (JP, A) JP-A-60-223121 (JP, A)

Claims (5)

[Claims] 1. A step of forming a resist film on a substrate, and alginate, sodium alginate, potassium alginate, tetraethylammonium alginate, tetramethylammonium alginate, soluble starch, amylose, imalin, lichenin, glycogen and pullulan. Forming a transparent film composed of at least one type of polysaccharide selected from the group consisting of on the resist film, exposing the resist film to a predetermined pattern using a projection exposure method, and then developing And a step of developing the resist film by using. 2. A pattern for alignment is formed on the substrate, and a step of aligning using the alignment pattern is provided before the exposing step. The method for forming a pattern according to item 1. 3. The wavelength of the exposure light in the exposing step is λ,
3. The pattern forming method according to claim 1, wherein the transparent film has a film thickness of an odd multiple of λ / 4n, where n is the refractive index of the transparent film. 4. The film thickness of the transparent film is an odd multiple of approximately λ '/ 4n, where λ'is the wavelength of the pattern detection light in the alignment step and n is the refractive index of the transparent film. The pattern forming method according to claim 2, wherein 5. The pattern forming method according to claim 1, further comprising a step of removing the transparent film by washing with water before the developing step. .