JPH0831714A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To narrow an effective exposure region, and to reduce the diameter of a minimum hole pattern capable of being formed through photolithography further by neutralizing an acid in the vicinity of a substrate in the peripheral section of the exposure region by bringing a substrate surface to an extremely weak basic state immediately before a process, in to which the substrate surface is coated with a positive resist. CONSTITUTION:A weak basic layer 3 is formed on the surface of a substrate 1, on which a desired thin-film 2 is formed. The layer 3 is exposed by ultraviolet rays 6 by using a photo-mask 7. An acid H<+> is generated in a resist exposure section 5. On the other hand, the weak basic layer on the surface of the substrate is distributed uniformly on the whole surface. Accordingly, an effect by the base of the substrate is difficult to be generated because a large quantity of the acid are generated from a resist at a central section at a fixed basic level, but the acid concentration of the resist is inhibited by neutralization by the base of the substrate surface in the peripheral section of a hole pattern.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to resist pattern formation in a photolithography process for semiconductor devices.

In response to the recent trend of higher integration and higher density of semiconductor devices, in the photolithography process using light as an exposure source, use of an excimer stepper using far ultraviolet light of less than 300 nm as a light source has become mainstream. Came. Also,
At the same time, a chemically amplified resist having a high transmittance for far-ultraviolet light and a high sensitivity is drawing attention.

However, 64 prototypes are currently being developed.
In the MDRAM and 256MDRAM, the minimum hole diameter required for patterning has reached 0.25 μm, which is said to be the resolution limit of optical lithography.

The present invention relates to the formation of a fine hole pattern by photolithography using a chemically amplified resist.

[0005]

2. Description of the Related Art In conventional optical lithography technology, 248
Even with a KrF excimer stepper using a short wavelength of nm, it was difficult to form a fine hole pattern having a size close to 0.25 μm. Therefore, in order to form a pattern of this size, it was necessary to use electron beam exposure instead of light exposure. However, electron beam exposure has the drawbacks that batch transfer is difficult, the drawing speed is slow, and the throughput is poor.

Therefore, when forming a device composed of a multi-layered film, in order to increase the throughput, it is said that the pattern formation which can be produced by optical lithography uses optical exposure, and other fine patterns use electron beam exposure. As described above, each layer may be used properly, and in this case, it is necessary to consider the problem of alignment matching.

[0007]

In the semiconductor device forming process which requires the formation of a minute hole pattern having a diameter of 0.25 μm, it is not possible to form the whole process only by photolithography, so that the productivity is improved. I couldn't. It is desired to be able to form the entire process only by photolithography without using electron beam exposure.

An object of the present invention is to further reduce the diameter of the minimum hole pattern that can be formed by photolithography.

[0009]

The present invention is an optical lithography process in which an acid-catalyzed chemically amplified positive resist is used to perform patterning by light exposure, immediately before the step of applying the positive resist to the substrate surface. The substrate surface is made extremely weakly basic.

[0010]

The exposure intensity is high in the central portion of the exposed area of the resist, but is reduced in the peripheral portion. Therefore, the acid concentration generated by exposure is high in the center and low in the periphery. By preliminarily applying a base to the surface of the substrate, the acid in the vicinity of the substrate can be neutralized in the peripheral portion of the exposure area. As a result, the effective exposure area becomes narrow.

[0011]

EXAMPLE An acid-catalyzed chemically amplified resist generates an acid in an exposed portion by light exposure in an ultraviolet region of less than 300 nm such as an excimer stepper. This acid removes the dissolution inhibitor bonded to the resin of the resist by heat treatment after exposure. Therefore, the resist in the exposed portion can be dissolved in the developing solution.

Conventionally, it has been often pointed out that the pattern edge of the resist is skirted when the resist is used to form a pattern by photolithography. FIG. 2 shows an example showing the tailing of a resist pattern manufactured by a conventional method.
They are shown in (a) and (b), respectively.

In FIG. 2 (a), a SiO ₂ thin film 2 is formed on a substrate. After a chemically amplified resist film 4 is spin-coated, it is exposed and developed by a KrF excimer stepper using a photomask pattern, It is an enlarged cross-sectional photograph of a hole pattern of a resist formed. The edge of the resist pattern in the vicinity of the interface between the resist film 4 and the thin film SiO ₂ 2 is bottomed.

FIG. 2B is an enlarged cross-sectional photograph of the SiO ₂ film 2 under the resist film 4 which is etched using the bottomed resist pattern shown in FIG. 2A. A hole having a diameter smaller than that of the photomask pattern is formed by the hem of the resist.

The generation of such a resist pattern is said to be due to the fact that the substrate surface immediately before spin coating the resist adsorbs basic components in the atmosphere.
The present invention aims to form a resist bottoming pattern that has been conventionally generated with good reproducibility by positively imparting basicity to the substrate surface, and to make the minimum hole pattern that can be produced by optical lithography smaller. is there.

A basic embodiment of the present invention will be described with reference to FIG. FIG. 1 shows a resist patterning process. As shown in FIG. 1A, a weak basic layer 3 is provided on the surface of a substrate 1 on which a desired thin film 2 is formed. In order to improve the adhesion between the resist and the substrate, the substrate is exposed to a gas containing HMDS (hexamethyldisilane). Furthermore, FIG.
As shown in (b), an acid catalyst type chemically amplified resist film 4 is spin-coated thereon.

As shown in FIG. 1B, the photomask 7
Is used to expose the ultraviolet ray 6. Acid H on the resist exposed area 5
⁺ Occurs. The intensity distribution of exposure applied to the resist during exposure is shown in the lower part of FIG. The vertical axis is the exposure intensity,
The horizontal axis represents the exposure position. The area indicated by A corresponds to the hole pattern diameter on the mask. The exposure intensity is highest in the center of the hole pattern, and has a weaker distribution in the vicinity of the pattern edge than in the center. Since the amount of acid H ⁺ generated depends on the exposure intensity, it shows a similar distribution.

On the other hand, the weak base layer on the substrate surface has a uniform distribution over the entire surface. Therefore, at a certain level of basicity, the acid generation of the resist is large in the central part, so it is less likely to be affected by the base of the substrate. Since it is suppressed by, the trailing edge B can be formed in the resist pattern after development. Further, the degree of tailing can be determined by adjusting the basic amount of the substrate surface.

FIG. 1C shows a step of etching the thin film 2 using the resist patterned by the above method as a mask. With this bottoming pattern of the resist, it is possible to obtain a smaller hole diameter pattern as compared with the hole pattern diameter obtained in the original photolithography process.

Next, various examples of making the substrate surface basic will be described. The first example is a method of immersing a substrate in a basic solution. The Si wafer before resist film coating and formation is diluted with NH ₄ OH aqueous solution diluted to about 5% molar concentration.
Soak for a minute. After that, the wafer is washed with pure water and dried. As the basic solution, NMP (N-methylpyrrolidone) or DMA (dimethylacetamide) may be used.

FIG. 4A shows an example of the structure of a resist coating apparatus according to the first embodiment. FIG. 4 (a) shows an apparatus for immersing a substrate in the above-mentioned basic solution, which is provided with a base-resistant tank, for example, a tank made of fluororesin, and a pump for circulating the solution therein. . Is a heating device for drying the substrate, CT is a resist spin coater, AD is a device for applying HMDS, which is a resist adhesion material, with vapor, HP is a heating device with a hot plate, and CP is a cooling plate with a cooling plate. Each device is shown.

As shown in FIG. 4A, as shown in FIG. 4A, the first column in which three devices CT, CT are connected in this order, AD, HP,
2nd connection of 5 devices CP, HP, CP in this order
The rows are assembled in parallel, and one end of each row is connected to a common wafer indexer IDX having a function of carrying and distributing substrates. The substrate is automatically transferred between the above devices without exposing it to the outside.

The second embodiment is a method of exposing the substrate to a basic gas. FIG. 3 shows an apparatus diagram of the embodiment. The tank 11 contains an NH ₄ OH aqueous solution 10 diluted to a molar concentration of about 5%, and a basic gas is introduced into the chamber 12 by bubbling with an N ₂ gas 9. The introduced gas flows on the surface of the substrate 8 installed in the chamber and is exhausted to the outside from the exhaust port 13 by the pump connected to the chamber. For example, the inside of the chamber is set to an atmosphere of NH ₄ OH concentration of 50 ppb, and the substrate is exposed for 30 seconds.

FIG. 4B shows an example of the structure of a resist film coating apparatus according to the second embodiment. As shown in FIG.
It is an apparatus for exposing a substrate to a basic gas atmosphere, and is an apparatus equipped with a chamber, an exhaust pump, and a means for supplying a basic gas. As shown in FIG. 4B, the device and the first column in which two CTs are connected in this order, AD, H
A second row in which five devices P, CP, HP and CP are connected in this order is assembled in parallel and one end is connected to a common wafer indexer IDX. The substrate is automatically transferred between the above devices without exposing it to the outside.

The third embodiment is a method of forming an inorganic film which is known to easily adsorb a basic gas on the surface of a substrate. BP as an inorganic film that easily adsorbs basic gas
SG (borophosphosilicate glass) or S
There are OG (spin on glass) films and the like.

The BPSG film is a gas source formed by an atmospheric pressure CVD method.
To O₂, SiH_Four, PH₃, B₂H ₆Thickness of about 1
It is sufficient to form about 000Å. After this, expose the substrate to the atmosphere
The substrate surface becomes weakly basic, but it is preferable
Is immersed in the basic solution of Example 1 or of Example 2
Exposure to basic gas creates a controlled basic surface
To achieve.

The SOG film is formed by using a commercially available solution containing organic silanol, such as O produced by Tokyo Applied Chemistry Co., Ltd.
Using a CD (Type 7 6000R), spinner applied to 1000Å substrate and then 270 on hot plate
Heat to ° C. Preferably, the same basicity imparting step as described above is performed.

The present invention has been described with reference to the above embodiments.
The present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0029]

As described above, according to the present invention, the minimum diameter of the fine hole pattern that can be formed by photolithography can be further reduced.

Therefore, it is possible to form a fine hole of 0.25 μm or less by only the photolithography using the KrF excimer stepper without using the electron beam exposure process, and increase the throughput of the device process that requires the formation of the fine hole. Is possible.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a basic pattern forming process of the present invention.

FIG. 2 is an enlarged photograph of a cross section of a thin film manufactured by a conventional method.

FIG. 3 is a diagram showing a manufacturing method according to the second embodiment of the present invention.

FIG. 4 is a configuration diagram of a manufacturing apparatus according to an embodiment of the present invention.

[Explanation of symbols]

1 Substrate 2 Thin Film 3 Basically Treated Layer 4 Resist Film 5 Resist Exposure Section 6 UV Light 7 Resist Pattern Hemming Section 8 Substrate 9 N ₂ 10 Basic Solution 11 Tank 12 Chamber 13 Exhaust Port A Hole Pattern Area B Resist Pattern Hemming part Device for immersing substrate in basic solution Drying device Device for exposing substrate to basic gas CT Resist coating device AD Adhesive coating device HP Hot plate CP Cooling plate IDX Wafer indexer

Claims (6)

[Claims] 1. A step of imparting an extremely weak basicity to a substrate surface, a step of immediately thereafter applying an acid catalyst type chemically amplified positive resist to the substrate surface, and a step of selectively irradiating the positive resist with ultraviolet rays. A step of generating an acid in the exposed portion, wherein the basicity and the exposure amount are selected so that the extremely weak basicity neutralizes the acid generated around the exposed portion. Production method. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the basicity imparting step includes immersing the substrate in an extremely weak basic solution. 3. The method of manufacturing a semiconductor device according to claim 1, wherein the basicity imparting step includes exposing the substrate to an extremely weak basic gas. 4. The method for manufacturing a semiconductor device according to claim 1, wherein the basicity imparting step includes forming an inorganic film that adsorbs basic molecules on the substrate surface. 5. The method for manufacturing a semiconductor device according to claim 4, wherein the inorganic film is formed by using a CVD (Chemical Vapor Deposition) method. 6. The method of manufacturing a semiconductor device according to claim 4, wherein the inorganic film is formed by spin coating.