JPH02219229A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To improve the adhesion between a thin film and resist, and obtain a semiconductor element provided with a fine pattern by a method wherein, before a resist pattern is formed on a thin film, pretreatment is performed by sulfuric acid boiling. CONSTITUTION:By developing with a specified developer, photoresist 3 of a part irradiated with light is eliminated, and a resist pattern 5 is formed. In this case, a wafer 1 before the resist pattern 5 is formed is processed with sulfuric acid boil. That is, the wafer 1 is dipped in solution whose main component is sulfuric acid, and subjected to heat treatment in sulfuric acid, thereby eliminating coating film component of impurity existing on an interface between an SiO2 film 2 and a resist pattern 5. Thereby, the under-cut dimension at the time of etching is reduced, and a fine pattern of high precision can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to a method for manufacturing a semiconductor device using an etching technique.

In the manufacturing process of semiconductor devices, etching technology has traditionally been used for microfabrication of semiconductors.

This etching processing technique includes a wet etching method using a liquid and a dry etching method using a gas.

The wet etching method refers to a wafer (silicon substrate) on which a resist pattern 51 is formed, as shown in FIG.
In this method, the resist film 52 is immersed in an etching solution 53, and the thin film 54 on which the resist is not attached is chemically dissolved and removed by the etching solution 53, thereby forming a fine pattern.

In this wet etching method, since the wafer 52 on which the resist pattern 51 is formed as described above is immersed in the etching solution 53, the etching rate is uniform.

Therefore, as shown in FIG. 5, the etching direction advances not only in the vertical direction (depth direction) as shown by the arrow X, but also in the horizontal direction as shown by the arrow Y.
Etching progresses to the part of the thin film 54 covered by the etchant, resulting in undercut (indicated by Z in the figure).
. Therefore, a window 55 (hereinafter, this window will be referred to as a "contact hole") formed by etching the thin layer 1i54.
Since the opening end portion 56 of the opening end portion 56 becomes larger than the design value, it is disadvantageous in terms of design rules, and there is a limit to forming a highly accurate fine pattern.

On the other hand, the dry etching method is a method in which a radical reaction is caused in an etching gas by applying a high frequency electric field, etc., and etching is performed using ion species generated by the radical reaction.

This dry etching method has few drawbacks such as the above-mentioned undercut, and allows for extremely precise microfabrication.

However, this dry etching method has the following drawbacks because the opening end of the contact hole is formed in a substantially right-angled shape.

That is, as shown in FIG. 6, when a conductive thin film 57 made of a metal such as Aj2-3i is formed on the entire surface of the wafer 52 by vacuum evaporation or the like after forming the contact hole 55, the wafer 52 and the conductive thin film 57 are In order to electrically connect the thin film 57, a portion of metal such as AJ2-Si is flowed into the contact hole 55. Therefore, there is a drawback that the thickness T of the conductive thin film 57 near the contact hole 55 is thinner than the thickness T2 of the conductive thin film 57 in other parts.

Further, when a current is passed through the conductive thin film 57, there is a possibility that the conductive thin film 57 may be cut at the thin open end portion 56 during the current flow.

Therefore, recently, contact holes are frequently formed by using both wet etching and dry etching.

That is, in order to prevent the opening end of the contact hole from having a substantially right-angled shape, wet etching is first performed to give the opening end a rounded shape such as a chamfered shape or an R shape, and then dry etching is performed. Etching is used to obtain the desired fine contact holes.

Problems that Akira is trying to address In forming fine patterns by using both wet etching and dry etching, it is important to control the line width by wet etching. In particular, as fine pattern processing is required, its importance increases. That is, in the wet etching method, the thin film 54 is undercut as described above, but if the dimension of the undercut is too large, the opening end 56 becomes large and the area occupied by the thin film 54 becomes small, so that the gate There was a problem that the distance between the electrode and the contact hole, etc. could not be formed as designed values.

Furthermore, when designing with a large undercut dimension, the chip size must be increased, making it difficult to miniaturize the semiconductor element.

The present invention was invented in view of these problems, and by reducing the occurrence of undercuts in the wet etching method, it is suitable for forming fine patterns and can achieve further miniaturization. An object of the present invention is to provide a method for manufacturing a semiconductor device.

To speed up Lesson 1, "1. In order to achieve the above object, the method for manufacturing a semiconductor device according to the present invention includes a step of forming a thin film on a wafer, a step of subjecting the wafer to a sulfuric acid foil treatment, and a step of applying a sulfuric acid foil treatment to the thin film. A process of applying photoresist to the photoresist. A process of exposing and developing the photoresist by irradiating light through a mask member on which a pattern is formed to form a pattern. Wet etching is performed using the patterned photoresist as a mask. It is characterized in that it includes a process of applying it to a thin film.

■ After forming a thin film (insulating film such as S iO This improves the adhesion between the thin film and the resist coated on the thin film.

Therefore, according to the above manufacturing method, before forming a resist pattern on the thin film, pretreatment is performed with sulfuric acid foil, so that the adhesion between the thin film and the resist can be improved, and wet etching is performed on the thin film. However, the undercut dimensions are reduced, and a semiconductor device having a highly accurate fine pattern can be manufactured.

Embodiments of the method for manufacturing a semiconductor device according to the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a process diagram showing an example of a photoetching step included in the method of manufacturing a semiconductor device according to the present invention.

First, by thermal oxidation etc., as shown in FIG. 1(I),
A SiO□ film 2 as an example of a thin film is formed on the surface of a wafer (silicon substrate) 1. This SiO□ film 2 has a thickness of 1μ
m or less.

Next, the wafer 1 is subjected to a sulfuric acid foil treatment in which the wafer 1 is immersed in a solution containing sulfuric acid as a main component and heated.

Next, as shown in Figure 1, a photoresist 3 is applied to the surface of this SiO□ film 2. When the photoresist 3 is irradiated with light, that part polymerizes and is difficult to chemically remove. There are two types: a negative type photoresist, and a positive type photoresist, in which the portion irradiated with light decomposes and dissolves in a developing solution. In this embodiment, a positive type photoresist is used.

Next, as shown in FIG. 1 (III), after masking the photoresist 3 with a mask member 4 on which a predetermined pattern is formed, the photoresist 3 is exposed by irradiating light from six directions of arrows.

After this, it is developed with a prescribed developer and shown in Figure 1 (1■).
As shown, the photoresist 3 in the area irradiated with light
is removed to form a resist pattern 5.

Next, as shown in FIG. 1(V), the wafer 1 is immersed in an etching solution 7, and the SiO□ film 2 is etched using the resist pattern 5 as a mask.
The portions of the SiO□ film 2 that are not covered are removed. Here, as the etching solution 7, for example, an HF-NH,F aqueous solution is used as a solution suitable for etching the SiO□ film 2.

Next, the resist pattern 5 is removed using a predetermined stripping solution, and as shown in FIG. 1 (Vl), a contact hole 8 is formed on the wafer 1, and the photoetching process is completed.

In the method of the present invention, at the stage shown in FIG. 1(I), the wafer 1 before the resist pattern 5 is formed is treated with sulfuric acid foil. That is, the wafer 1 is immersed in a solution containing sulfuric acid as a main component, and heat treated with sulfuric acid to form SiO□.
Impure film components existing at the interface between the film 2 and the resist pattern 5 are removed, and the adhesion between the 5102 film 2 and the resist pattern 5 is improved. That is, after forming the SiO□ film 2 on the surface of the wafer l as described above,
Before coating the photoresist 3 on the O□ film 2 (Fig. 1 (
1) (see (II)), since a film such as an impure oxide film is formed on the surface of the pure SiO□ film 2, conventionally, when wet etching described later is performed, the resist pattern 5 and the SiO□ The adhesion with the film 2 deteriorated, and the portion of the 5102 film 2 covered with the resist pattern 5 was etched, resulting in an undercut. Therefore, in this embodiment, wet etching was performed after pretreatment with a chemical agent containing sulfuric acid as a main component to improve the adhesion between the resist pattern 5 and the SiO□ film 2. Table 1 shows the conditions for sulfuric acid foil.

The reason why the liquid was used was because the hydrogen peroxide had an accelerating effect on the sulfuric acid foil treatment.

Therefore, there is no problem even if the sulfuric acid foil treatment is performed using only a sulfuric acid solution, although the treatment time is slightly longer.

FIG. 2 is an enlarged sectional view of the main part of the semiconductor element after etching with the etching solution 7, and FIG. 3 is an enlarged view of the main part of the semiconductor element when no sulfuric acid foil treatment was performed (conventional example) as a comparative example. It shows a cross-sectional view. t,
is the line width, t2 and t3 are undercut dimensions, t4 is the thickness of the resist pattern 5, and t5 is the thickness of the SiO□ film 2.

As mentioned in the "Prior Art" section, the undercut dimension t2 is side-etched because the etching speed is isotropic, and is unavoidable as long as the wet etching method is used. However, in the present invention, by performing the sulfuric acid foil treatment, the undercut dimension t3 is reduced, which is convenient for forming a fine pattern with high precision.

Table 2 shows the measurement results of the undercut dimensions t2 and t3 of the present invention and the conventional example when the line width t1 is set to t1=3 μm and t=4 μm. In addition, in these experiments, the film thickness t4 of the resist pattern 5 was set to t 4 =
1.2 μm, the film thickness t of the Sight film 2 is ts=
The thickness was set at 0.5 μm.

As is clear from this Table 2, undercut dimension t
2, since the etching rate is isotropic, in both the present invention and the conventional example, the side etching is approximately the same as the film thickness t5 (=0.5 μm) of the SiO□ film 2, but the undercut dimension It can be seen that t3 is significantly reduced.

As described above, the semiconductor device manufactured by the manufacturing method according to the present invention is pretreated with sulfuric acid foil prior to the formation of the resist pattern in the photoetching process.
Since it was applied to the O□ film 2, the resist pattern 5 and the SiO□
Adhesion at the interface with the film 2 is improved and undercuts are reduced. That is, in the case of the wet etching method, as mentioned above, the etching speed is isotropic, so it is unavoidable that some undercutting will occur, but by using the manufacturing method of the present invention, it is possible to reduce the undercutting. Can be done. Therefore, even if etching is performed using the wet etching method, it is possible to form fine patterns with higher precision than in the past. Moreover, since the opening end of the contact hole is rounded, even if a conductive thin film such as AI2 is deposited on the surface of the wafer l, the conductive thin film will not be cut as if the contact hole was formed using only the dry etching method. You no longer have to worry about being rejected.

Furthermore, even when forming the contact hole 8 by combining the wet etching method and the dry etching method, wet etching reduces the undercut dimension, which is advantageous in terms of design rules. It becomes possible to form a pattern.

The semiconductor device is manufactured after the above-mentioned photoetching process is completed (or after the dry etching process that is performed after the above-mentioned photoetching process is completed).
Further, the photo-etching process is repeated a plurality of times, and predetermined bit lines, gate electrodes, etc. are formed on the wafer 1, and the process is completed.

It goes without saying that the present invention is not limited to the above-mentioned embodiments, and can be modified without departing from the scope of the invention. Furthermore, the thin film (insulating film) formed on the wafer 1 is not limited to the SiO□ film 2, and may be a thin film such as a nitride film or a metal film. Furthermore, it goes without saying that the photoresist 3 is not limited to the positive type but may also be of the negative type.

As detailed above, the method for manufacturing a semiconductor device according to the present invention includes performing a sulfuric acid foil treatment on a wafer after forming a thin film in the photoetching process to remove impurities present in the thin film on the wafer. Therefore, the adhesion between the insulating film and the resist is improved. Therefore, the dimensions that are undercut during wet etching are reduced, making it possible to form fine patterns with higher precision than in the past.

Therefore, high integration can be achieved without adversely affecting the performance of the semiconductor element, and the size of the semiconductor element can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a process diagram of the photoetching step included in the manufacturing method of a semiconductor device according to the present invention, and FIG. 2 is an enlarged cross-sectional view of a main part showing the etching state when wet etching is performed by the manufacturing method according to the present invention. , FIG. 3 is an enlarged sectional view of a main part of a semiconductor element etched by the conventional method shown as a comparative example of FIG. 2, and FIGS. FIG. 6 is a cross-sectional view of a main part of a semiconductor element for explaining problems in the dry etching method. l...Wafer, 2...SiO□ film (thin film), 3...
- Photoresist l-, 4...Mask member.

Claims (1)

[Claims] (1) A step of forming a thin film on a wafer, a step of subjecting the wafer to a sulfuric acid foil treatment, a step of applying a photoresist on the thin film, and irradiating the photoresist with light through a mask member on which a pattern is formed. 1. A method for manufacturing a semiconductor device, comprising: exposing and developing the thin film to form a pattern; and performing wet etching on the thin film using a patterned photoresist as a mask.