JPH08220777A - Pattern forming method - Google Patents

Abstract

PURPOSE: To form a resist pattern having a fine satisfactory shape and a high aspect ratio through relatively simple processes even in the case of exposure using far UV, soft X-rays or electron beams which are largely absorbed in a resist. CONSTITUTION: Desired positions on a resist film 4 formed by coating on a substrate 5 to be worked are irradiated with energy beams 1 to form an acid or base donor/acceptor distribution on the surface of the resist film. The resist film is then immersed in or brought into contact with a soln. 6 of a compd. having such a property as to cause deposition from the soln. by a pH change to selectively form an etching mask 7 in the unexposed region or the exposed region 3 of the resist film and the resist film is developed with plasma 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fine pattern forming method in the production of solid-state elements such as semiconductors, magnetic materials, superconductors, and dielectrics.

[0002]

2. Description of the Related Art A reduced projection exposure method is widely used for forming a circuit pattern of an LSI or the like. In recent years, in the exposure method, the resolution is being improved by shortening the wavelength of exposure light. It is considered that a 0.25 μm level pattern can be processed by a KrF excimer laser (wavelength 248 nm) and a 0.2 μm level processing can be performed by an ArF excimer laser (wavelength 193 nm) instead of a mercury lamp which has been widely used from the past. There is.

For exposure using g rays or i rays of a mercury lamp, a novolak-naphthoquinonediazide type resist has been widely used. However, as the wavelength of the light source becomes shorter, the absorption of the exposure light by the resist becomes stronger, and the resolution and the resist pattern shape deteriorate.

Therefore, a surface reaction resist process is being studied as one of the methods for solving this problem. For example, in a silylation process, which is a typical surface reaction process, after silicon-containing molecules are selectively introduced into a non-exposed region or an exposed region of a resist film, dry development (etching) using oxygen plasma is performed using this as a mask.
Since a vertical cross-sectional shape can be obtained by using anisotropic plasma during development, it is considered that a resist pattern having a high aspect ratio and a good shape can be obtained even in the exposure to the deep ultraviolet region where the light absorption by the resist is large.

Such a silylation process is known as DESI.
Various processes have been proposed, including a process called RE. For example, Digest of Technical Papers, 1987 Symposium on VLSI.
Technology, pp. 7-8, (1987 Symposium o
n VLSI Technology, Digest of Technical Papers, pp7-
8 (1987)).

The first proposed silylation process was to introduce a silylating agent into the resist after exposure in the gas phase, but recently, a liquid-phase silylation which can simplify the apparatus and temperature control. Processes are being studied, for example, Journal of Vacuum Science and Technology B, Vol. 9, No. 6, pages 3399-340.
P. 5, 1991 (Journal of Vacuum Science and Te
chnology B, Vol.9, No.6, pp3399-3405 (1991)).

As a process of introducing a substance other than a silicon compound as an etching mask on the same principle as the silylation process, a germanylation process using a germanium compound is being studied. For example, Journal of Photopolymer Science and Technology. Volume 4, Issue 3, 497-507, 1991 (Journal of Science and Technology vol.4, No. 3,
pp.497-507 (1991)).

[0008]

In order to explain the problems to be solved by the present invention, problems of the conventional positive type silylation process using a silicon compound as an etching mask will be described with reference to FIG.

In the positive type silylation process, the resist film 10 applied as a base film on the substrate 5 to be processed is first crosslinked as indicated by 11 by exposure or heat treatment performed subsequent to the exposure. Next, as shown in (b), the resist film is exposed to the silylating agent vapor, which is a silicon-containing molecule, or immersed in the silylating agent solution. As a result, the silylating agent is diffused in the unexposed portion that is not crosslinked, and the silylated diffusion region 13 so-called silylated layer is formed.
Next, as shown in (c), the resist film is dry-developed by oxygen plasma 9 using the silylated layer 13 as an etching mask to form a resist pattern as shown in (d).

However, in the silylation process, since the silylating agent itself does not polymerize so much, sufficient etching resistance cannot be obtained and there is a problem that the etching selectivity is low. Therefore, a silylated layer with a thickness of the submicron order is required, but in the positive silylated process,
Since the silylated layer is formed faithfully to the cross-linking rate of the resist polymer, the silylation selectivity was not very good. That is, since the cross-linking rate of the resist faithfully reflects the optical image,
In a fine region (exposure wavelength level) where the contrast of the optical image is poor, the cross-sectional shape of the silylated layer becomes a bowl shape, and the dimensional controllability after development and the mask dimensional fidelity (mask linearity) were poor.

Further, the vapor-phase silylation process has a drawback that the thickness of the silylation layer changes greatly due to a minute temperature distribution, and in addition, since a vacuum system is required, the apparatus becomes complicated. . On the other hand, the liquid phase silylation process is
It has the advantage that the processing equipment is simple and the temperature control is easy, but since the organic silylating agent and solvent are used, evaporation of the silylation solution is likely to occur during silylation, and the uniformity of silylation on the wafer surface And the reproducibility tended to deteriorate. Furthermore, since the silylating agent and the solvent diffuse into the resist, the expansion of the resist is caused, and the deformation and movement of the pattern caused by this also poses a problem.

The object of the present invention is to improve the selectivity between the exposed area / unexposed area during the formation of an etching mask and during the etching in the surface reaction resist process, and to form a fine pattern of a good shape with good mask linearity.
It is to provide a method for forming a pattern without causing deformation or movement of the pattern.

[0013]

Means for Solving the Problems The above object is to use, as a base film on which a pattern is formed, a film in which the donating / accepting property of a film-forming substance to an acid / base is changed by irradiation of exposure light. A solution in which a compound having etching resistance is deposited due to a change in (pH) is brought into contact with a base film irradiated with energy rays at a desired position, and the compound layer having etching resistance is exposed in a non-exposed region or an exposed region of the base film. This is achieved by selectively forming on the surface.

As the above compound, silicate ions, metasilicic acid precipitated from a silicate hydrofluoric acid ion solution, aluminum hydroxide precipitated from an aluminum ion solution, or the like can be used.

[0015]

The function of the present invention is obtained by using a resist film containing an acid accepting group and an acid generator as a base film and changing the acidic solution of the forming element as a compound to be an etching mask to neutral or basic. An example of selecting a substance to be deposited will be described with reference to FIG. A far ultraviolet ray 1 is irradiated onto a resist film 4 formed as a base film on a substrate 5 to be processed through an exposure mask 2 and an appropriate optical system (not shown), and a far ultraviolet ray irradiation section (hereinafter referred to as an exposure section). Generate acid in 3.

Then, as shown in (b), it is dipped in the etching mask-forming element-containing solution 6 whose pH is adjusted to permeate the solution into the resist film surface. In the vicinity of the resist surface in the unexposed portion, the protons in the solution are trapped by the acid accepting groups in the resist, and the pH of the solution locally moves to the base side, so that the compound serving as an etching mask is deposited. On the other hand, on the resist surface in the exposed area, the acid acceptor group is deactivated by the acid, or the acid strengthens the acidity of the solution in the vicinity of the resist, so that the compound does not precipitate. That is, the etching mask 7 is provided only in the vicinity of the surface of the unexposed portion.
Is formed. Then, anisotropic etching is performed with oxygen plasma 9 as shown in (c) to form a fine pattern shown in (d).

According to this method, since the compound layer can be formed as an inorganic polymer-like precipitate, the atomic density can be increased and the etching resistance at the time of processing a base (resist) film is increased. Therefore, it is not necessary to form the compound layer thick as in the case of the silylated layer in the silylated process. Therefore, since the compound layer formation region is determined only by a certain threshold value of the hydrogen ion concentration near the surface of the base film, high selectivity can be obtained in the unexposed portion / exposed portion, and even in an optical image with low contrast. Resolution is possible, and a fine pattern can be formed with a good shape.

Further, in this pattern forming method, the step of forming the etching mask can be performed in an aqueous solution. When water is used as the solvent, the vapor pressure is lower and the diffusion to the resist is smaller than that of the organic solvent mainly used in the conventional liquid phase silylation process, so that there is no unevenness in the wafer and the difference between the wafers. It is possible to form a pattern with good reproducibility. Further, this method is a method of forming a positive type pattern, and is advantageous in reducing defects in forming a hole pattern at the time of manufacturing an LSI. This is because most of the exposure mask serves as a light-shielding portion, so that defects on the mask are less likely to be transferred.

Although a combination of an acidic solution of an etching mask forming element and a base film containing an acid accepting group and an acid generator has been described here, various combinations of solutions and base films are possible. For example, it is possible to form a negative pattern by combining an underlying film having the same properties as in the above case with a basic solution. The negative pattern forming method is advantageous when a wiring pattern is formed by using the Levenson type phase shift method. A positive type pattern can also be obtained by combining a base film containing an acid-donating group and a base generator with a basic solution.

In addition, when an ampholyte is applied as a compound, it is dissolved in both an acid and a basic solution, and a p
Since it is precipitated only in the solution of H, the compound layer is not formed in the vicinity of the exposed or unexposed portion surface inclined to the acid or base, and the compound layer is formed at the exposed / unexposed portion boundary where the pH changes. That is, the pattern can be formed only on the contour portion of the exposure mask pattern. Therefore, for example, when a line and space pattern is exposed, the pitch of the formed pattern is ½ of the exposure pattern.

For the base film, a resin or resist whose main component is novolac, polyhydroxystyrene, polyimide, polysiloxane, polymethacrylate acetate or the like can be used. Further, in order to impart an acid or base donating / accepting property to the resist film, it is possible to chemically modify the base film with an acid or a basic functional group or add an acid or a base to the base film. As the substance that forms an acid or base distribution in the undercoat film, a naphthoquinone-based photosensitizer, an onium salt-based or sulfonate-based acid generator, or a base generator such as a triarylmethane leuco body is used. be able to.

By incorporating a crosslinking agent such as azide into the base film and exposing the entire surface of the base film after applying the base film, it is possible to prevent the base film from dissolving in the solution for forming the etching mask.

Although all the explanations so far have been made with respect to optical lithography, particularly the case of using deep ultraviolet light, exposure with ultraviolet light using an ordinary mercury lamp and other energy rays such as electron beams and X-rays are performed. The same applies to the exposure used.

[0024]

【Example】

Example 1 A resist having a polymer having an amino group as a base resin and a sulfonic acid ester as an acid generator added thereto was spin-coated on a silicon substrate and then soft-baked at 80 ° C. to form a resist layer having a thickness of 1 μm. Formed. Then K
rF excimer laser reduction projection exposure system (NA = 0.45)
Then, the resist layer was exposed using the desired mask pattern. Then, the silicon substrate was immersed at room temperature for 2 minutes in a solution in which ammonia water was added to a silicic acid-hydrofluoric acid (H ₂ SiF ₆ ) aqueous solution to obtain metasilicic acid ((SiO ₂ · H ₂ O)
n) layers were formed. Next, after baking the substrate at 200 ° C., anisotropic dry etching by oxygen RIE was performed by a usual method.

As a result of observing the resist pattern formed by the above process with a scanning electron microscope,
It was confirmed that the resist pattern remained in the portion corresponding to the light shielding portion of the mask pattern, while the positive image in which the resist was etched was obtained in the portion corresponding to the exposed portion.
The etching rate ratio between the formed etching mask and the resist film was the same as that when SOG was used as the etching mask, and was twice or more that in the case of the usual silylation process. As a result, fine patterns with a size of 0.25 μm, including the 0.25 μm line and space, were formed in good shape. These patterns had better mask linearity as compared with the case of using the silylation process, and neither dimensional variation in the substrate nor pattern movement was observed.

The material of the base film is not limited to that shown in this embodiment, but a phenol-based material chemically modified with a basic functional group,
A polyimide-based resin, a siloxane-based resin, a resist, or the like can be used. Further, various amines, polyhydric alcohols, etc. may be added to the base film. In order to form a local acid donating / accepting distribution in the undercoating film, not only the one shown in this example but also another acid generator or a dissolution inhibitor such as naphthoquinonediazide can be applied. Met.

Also based on acid donating polymers,
Alternatively, a negative image in which the unexposed area is developed can be obtained by performing the same process by adding an acidic additive and using a base film having a structure that generates a base upon exposure instead of the acid generator. Was also possible.

Although KrF excimer laser reduction exposure was used for pattern exposure in this embodiment, other methods may be used. For example, electron beam exposure, ArF excimer laser contact exposure or reduction projection exposure, step-and-scan reflection type reduction projection exposure using deep ultraviolet light as a light source, or soft X-ray can be used. Needless to say, the NA is not limited to this.

Example 2 A partially protected polyhydroxystyrene base resin, an additive phenylenediamine for imparting basicity (acid acceptability) to a film, and an onium salt as an acid generator were formed on a silicon substrate. After forming a coating film on the wafer, soft-bak it at 80 ℃ and film thickness is 1μm.
Underlayer was formed. Next, the underlayer was contact-exposed using an ArF excimer laser exposure device and a desired mask pattern. Then, the silicon substrate was immersed for 2 minutes at room temperature in a solution in which ammonia water was added to a 1% aqueous solution of aluminum nitrate to form an aluminum hydroxide layer. Next, after baking the substrate at 200 ° C., oxygen RIE is performed.
Anisotropic etching was performed.

As a result of observing the underlayer pattern formed by the above process with a scanning electron microscope, the underlayer pattern remained at the portion corresponding to the boundary between the light-shielding portion and the exposure portion of the mask pattern. In the case of the line-and-space pattern, it was confirmed that the pattern could be formed at a pitch of 1/2 of the exposure pattern. The etching rate ratio between the formed etching mask and the base film was similar to that when SOG was used as the etching mask.

The compound serving as an etching mask is made of another amphoteric electrolyte metal (for example, Be, Zn, Sn, Pb, Cr,
As, etc., nitrates, sulfates, chlorides, oxides, hydroxides and the like may be applied. Also, even if an undercoating film based on an acid-donating polymer or added with an acidic additive and a structure for generating a base upon exposure instead of the acid generator is used, a similar pattern is obtained by the same process. Can be formed. Further, by adjusting the concentration of the additive so that the base donation in the unexposed area is neutralized to the solution in the vicinity of the unexposed area, a positive type or negative type faithful to the mask pattern can be obtained as in the first embodiment. A pattern of molds was obtained. One of the features of this method is that in addition to the usual positive or negative pattern formation, the pattern formation in which the contour portion is extracted is possible by adjusting the additive concentration.

The additives for the base film are not limited to those shown in this embodiment, and various amines, polyhydric alcohols, organic acids and the like can be applied. Various compounds can be applied to the material of the base film and the substance forming a local acid donating / accepting distribution in the base film, as in Example 1. Although KrF excimer laser reduction exposure was used for pattern exposure in this embodiment, other exposure methods may be used as in the first embodiment.

[0033]

According to the present invention, the contrast of an optical image when using light or an electron beam in a wavelength range in which light absorption is extremely large for a normal resist and does not reach the bottom of the resist, or when exposed is Even if it is low, an underlying pattern having an extremely fine and good shape and a large aspect ratio can be formed by a relatively simple process.

[Brief description of drawings]

FIG. 1 is an explanatory view of a process schematically showing the principle of the present invention.

FIG. 2 is an explanatory view showing steps of a conventional liquid phase silylation process.

[Explanation of symbols]

1 ... Deep UV rays, 2 ... Mask, 3 ... Exposure (acidic) region, 4
... acid-accepting underlayer (resist) film, 5 ... substrate to be processed, 6 ...
Etching mask forming element-containing solution, 7 ... Compound layer (etching mask), 8 ... Surface reaction chamber, 9 ... Oxygen plasma.

Claims (10)

[Claims] 1. A step of forming a base film on a substrate to be processed,
A step of irradiating the desired position of the underlayer film with energy rays, a step of selectively forming a compound layer having etching resistance on the surface of the underexposed region or the exposed region of the underlayer film, and using the compound layer as an etching mask In the pattern forming method including the step of dry-developing the undercoat film, as the undercoat film, a film in which the donation / acceptability of a film-forming substance to an acid / base is changed by irradiation of exposure light is used, By contacting the underlayer film irradiated with energy rays at a desired location with a solution in which a compound having etching resistance is deposited, the compound layer having the above etching resistance is selectively applied to the surface of the underexposed region or the exposed region of the underlayer film. A pattern forming method comprising: forming. 2. The film according to claim 1, wherein the base film is a film containing an acid-accepting group and an acid generator that generates an acid upon exposure light irradiation, and the base film is acidic or medium after the exposure light irradiation step. By dipping or contacting with the above-prepared solution, a compound to be an etching mask is selectively formed in the exposure light non-irradiation area, and then the undercoat film in the exposure light irradiation area is removed by dry development, A pattern forming method for forming a pattern of a mold. 3. The compound according to claim 1, wherein the compound is metasilicic acid ((H ₂ SiO ₃ ) n = (SiO ₂ .H ₂ O) n).
And the solution is a solution of silicate ions (SiO ₃ ²⁻ ) or silicate hydrofluoric acid ions (SiF ₆ ²⁻ ). 4. The exposure light irradiation according to claim 1, wherein the compound is an amphoteric electrolyte which has a property of being dissolved in an acidic or basic solution and being precipitated in a solution having a hydrogen ion concentration in between. A compound serving as an etching mask only at the boundary between the exposure light irradiation area and the non-irradiation area by immersing or contacting the undercoating film on which the acid / base donating / accepting distribution is formed with the solution of the ampholyte. Is selectively formed, and then the underlying film in the exposure light irradiation region is removed by dry development to form a pattern on the contour portion of the exposure pattern. 5. The compound according to claim 1, wherein the compound is Be, Zn, Al, Sn, Pb, Cr, As, Sb.
A pattern forming method which is an amphoteric hydroxide of an element such as. 6. The method according to claim 1, 2, 3, 4 or 5.
A pattern forming method, wherein the main component of the base film is a resin or a resist having a structure of novolac, polyhydroxystyrene, polyimide, polysiloxane, polymethacrylate acetate or the like. 7. The functional group according to claim 1, 2, 3, 4, 5 or 6, wherein an alcoholic hydroxyl group, an amino group or the like is a functional group which imparts an acid accepting property to the base film, and a phenol is a functional group which imparts an acid donating property. A pattern forming method in which a base hydroxyl group, a carboxyl group, a sulfonyl group, or the like is contained in the base film structure, or an additive having such a functional group is contained in the base film component. 8. The method according to claim 1, 2, 3, 4 or 5.
A method for forming a pattern, wherein the undercoating film contains a substance or structure such as a naphthoquinone-based photosensitizer, an onium salt-based photosensitizer, or a sulfonate ester-based substance that changes into an acid upon exposure. 9. The method according to claim 1, 2, 3, 4 or 5.
A method of forming a pattern, wherein the underlayer film contains a substance or structure that changes into a base upon exposure, such as a leuco form of triarylmethane. 10. The surface of the undercoating film according to claim 1, 2, 3, 4, 5 or 6, wherein the undercoating film contains a crosslinking agent, and after the undercoating film is applied, the entire surface of the undercoating film is exposed. A pattern forming method in which a compound forming an etching mask is insolubilized in a solution.