JPH0289315A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To prevent surface pollution and internal defect formation by etching a silicon substrate or a silicon layer, with a mixed liquid of hydrofluoric acid, nitric acid, acetic acid, and water to form a trench in the periphery of an opening utilizing a silicon oxide film as a mask. CONSTITUTION:A silicon oxide film 2 with a thickness of 0.6mum is formed on an n-type silicon substrate 1 with a resistance of 10 to 20OMEGAcm by thermal oxidation. A negative resist is deposited on the silicon oxide film 2, and a negative-type resist pattern 3 having a square opening 41 whose side is 100mum is formed by electron beam exposure. After an opening 42 is formed by etching the silicon oxide film 2 through the opening 41 utilizing dilute hydrofluoric acid, the negative resist pattern 3 is removed. The silicon substrate 1 is etched in an etchant bubbled by nitrogen utilizing the silicon oxide film with the opening 42 as a mask 21, for about three minutes. Thus, a trench 5 having a width of about 20mum and a depth of about 3mum is formed in the silicon substrate 1 in the periphery of the opening 42.

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a method of manufacturing a semiconductor device, and particularly to a method of forming a trench in a silicon substrate or a silicon layer.

In order to shorten the time required to form a mask pattern and improve the controllability of the trench shape, a silicon oxide film is formed on a silicon substrate or a silicon layer, and a negative resist pattern having openings is formed on the silicon oxide film. a step of etching the silicon oxide film from the opening to form an opening in the silicon oxide film and then removing the negative resist pattern; using the silicon oxide film having the opening as a mask, The semiconductor device manufacturing method includes a step of etching the silicon substrate or the silicon layer with a mixed solution of hydrofluoric acid, nitric acid, acetic acid, and water to form a trench around the opening.

[Industrial application field]

The present invention relates to a method of manufacturing a semiconductor device, and particularly to a method of forming a trench in a silicon substrate or a silicon layer.

Trenches are often formed in a silicon substrate or a silicon layer in order to isolate an element formation region or to fabricate a capacitor. Therefore, it is required to form trenches with good controllability, and it is also required to save cost and time.

[Conventional technology]

Conventionally, reactive ion etching (RIB) has been used as a method for forming trenches in semiconductor substrates.However, the substrate may become contaminated with heavy metals or organic substances, requiring a cleaning process for the substrate surface or inside the trench. Become. Contamination sources include impurities contained in the electrode metal, the metal constituting the chamber, or the etching gas, but cleaning the inside of the trench is complicated.

In addition, radiation damage caused by anil after the reactive ion etching process is generated that cannot be removed at low temperatures, and new defects are generated due to residual heavy metals at high temperatures, inhibiting the reproducibility of device characteristics and reducing yield. Cause.

Wet etching avoids the contamination and damage problems discussed above. The present invention relates to a method of forming trenches using wet etching.

When forming the trench, a corresponding photoresist mask is formed. There are two methods for exposing a desired portion to light: a method in which a photomask is manufactured and placed on top of the photoresist layer, and a method in which the photoresist layer is directly exposed to light using an electron beam or the like. It takes a lot of cost and time to produce a photomask, but
This is advantageous when copying a large number of identical patterns. On the other hand, direct electron beam exposure is often more advantageous for small-volume products such as custom LSIs.

The time it takes to draw a mask pattern on a photoresist layer by direct electron beam exposure becomes longer if the drawing area is wide, and various efforts have been made to shorten the drawing time. One of the objects of the present invention is to shorten the time required to write a mask pattern on a photoresist layer by direct electron beam exposure.

A conventional example of exposure for forming trenches using a negative resist is shown in FIG. In FIG. 5, the trench forming portion is left as an unexposed area 72, and the remaining exposed area 62.6 is left as an unexposed area 72.
Exposure to 3. When developed, the unexposed area 72 is removed,
Using this negative resist pattern as a mask, silicon is etched to form a trench.

Incidentally, in the electron beam direct exposure, for example, the hatched exposure areas 62 and 63 in FIG. 5 are exposed by a hector scanning method using a rectangular shaped beam, but since the area is large, a long drawing time is required.

[Problems to be Solved by the Invention] The present invention provides a method for significantly shortening the drawing time. Another object of the present invention is to provide a method that avoids contamination of the surface of a silicon substrate or silicon layer and the generation of defects inside it, and also allows good control over the shape of the trench to be formed.

[Means to solve the problem]

FIG. 1 shows Example 1 of the present invention. FIG. 2 shows Example (2).

I will now explain means for solving the problem with reference to FIGS. 1 and 2.

The above-mentioned problems include a step of forming a silicon oxide film 2 on a silicon substrate 1 or a silicon oxide layer 12, and forming a negative resist pattern 3 having an opening 41 on the silicon oxide film 2; A step of etching the silicon oxide film 2 to form an opening 42 in the silicon oxide film 2 and then removing the negative resist pattern 3;
A step of etching the silicon substrate 1 or the silicon layer 12 with a mixed solution of hydrofluoric acid, nitric acid, acetic acid, and water using the silicon oxide film having the oxide as a mask 21 to form a trench 5 around the opening 42. The problem is solved by a method of manufacturing a semiconductor device including.

[Operation] According to the present invention, when a silicon substrate or a silicon layer is wet-etched using a silicon oxide film as a mask, the entire opening is not uniformly etched, but the silicon substrate or the silicon layer near the step of the mask around the opening is etched. It is based on a new experimental fact that the etch rate of the silicon layer increases and trenches are formed.

FIG. 3 shows the exposure of the present invention. According to the method of the invention,
A trench is formed in the silicon substrate or silicon layer below the trench forming portion 51 near the boundary between the exposed region 61 and the unexposed region 71 of the negative resist.

According to the method of the present invention, there is no need to expose the interior surrounded by the trench forming portion. Therefore, the drawing time is significantly reduced.

FIG. 4 shows an example of a cross section of a trench formed by the method of the present invention. The silicon substrate 1 is excessively etched to form a trench 5 around the opening where the silicon oxide film mask 21 forms a step. The element forming region 8 surrounded by the trench 5 is also etched to some extent, but the degree of etching can be controlled to be much smaller than the etching of the trench 5.

It is not yet clear why such a difference in machining and notching occurs between the periphery and the inside of the hole, but it is closely related to the use of a mask with a silicon oxide film.1For example, when using a mask with a silicon nitride film, If so, no such effect will occur. Silicon oxide film mask 2 with etchant
Some of the holes were also etched and notched, which is presumed to be related to increasing the etch rate of silicon near the step.

〔Example〕

FIGS. 1(a) to 1(d) are diagrams illustrating the process of separating element formation regions by trenches in a silicon substrate in Example I. The following description will be given with reference to these figures.

FIG. 1(a) A silicon oxide film 2 having a thickness of 0.6 μm is formed by thermal oxidation on an n-type (100) silicon substrate 1 having a reference resistance of 10 to 20 Ωcffl.

Referring to FIG. 1(b), a negative resist is applied onto the silicon oxide film 2, and a negative resist pattern 3 having square openings 41 each side of which is 100 μm is formed by electron beam exposure.

Refer to FIG. 1(c) After etching the silicon oxide film 2 with dilute hydrofluoric acid through the opening 41 to form the opening 42, the negative resist pattern 3 is removed.

Referring to FIG. 1(d), using a silicon oxide film having openings 42 as a mask 21, the silicon substrate 1 is etched for about 3 minutes in an etchant bubbled with nitrogen.

The composition of the etchant is as follows.

HF 50% aqueous solution 1 volume HNO361%
Aqueous solution 3 volume CI! , C00I+ 7 volumes of 99.5% aqueous solution H20□ 1 volume of 31% aqueous solution Thus, a trench 5 having a width of approximately 20 μm and a depth of approximately 3 μm was formed in the silicon substrate 1 around the opening 42 .

The element formation region surrounded by the trench was etched by about 0.1 μm.

FIGS. 2(a) to (e) show Example 2, in which the pasting Sol
FIG. 3 is a diagram illustrating a process of forming element formation regions separated by trenches in the silicon layer of FIG.

The following description will be given with reference to these figures.

Refer to FIG. 2(a). Two (100) silicon substrates on which 11 insulating layers of SiO2 have been formed are attached together with the insulating films. The upper silicon substrate is polished to a thickness of 0.9 μm. A paste Sol with layer 12 formed thereon is prepared.

Referring to FIG. 2(b), a silicon oxide film 2 having a thickness of 0.2 μm is formed on the silicon layer 12 by thermal oxidation. The thickness of the silicon layer 12 is approximately 0.8 μm.

Referring to FIG. 2(C), a negative resist is applied onto the silicon oxide substrate n12, and a negative resist pattern 3 having square openings 41 each side of which is 30 μm is formed by electron beam exposure.

Refer to FIG. 2(d) After etching the silicon oxide film 2 with dilute hydrofluoric acid through the opening 41 to form the opening 42 in the silicon oxide film, the negative resist pattern 3 is removed.

Referring to FIG. 10(e), using a silicon oxide film having openings 42 as a mask 21, the silicon substrate 1 is etched for about 1 minute in an etchant bubbled with nitrogen.

The composition of the etchant is as follows.

HF 50% aqueous solution 1 volume HNO361%
Aqueous solution 3 volumes C ■ 3 COOI + 99.5% aqueous solution 7 volumes 120 □ 31% aqueous solution 1 volume Thus 2 The trench 5 has a width of about 2 μm and a depth of one layer of the lower insulating layer, which is the silicon around the opening 42. 1112, and the element formation region surrounded by this trench could be separated from the surrounding silicon layer.

The element formation region surrounded by the trench was etched by about 0.04 μm.

A negative resist is used as the resist deposited on the silicon oxide film 2. The negative resist has good adhesion to the silicon oxide film. When using a positive resist, the silicon oxide layer 1
It is not preferable because it has poor adhesion to the resin and easily peels off.

According to the experimental results, HNO3 (61% aqueous solution)
When the mixing ratio (volume ratio) to F (50% aqueous solution) is 4 or more, the silicon etholyte 1- increases and the controllability of the trench depth deteriorates. That is, the width of the trench becomes more than 10 times the depth of the trench, the one isolation region becomes wider, the element formation area surrounded by the trench becomes narrower, and the silicon layer in the element formation area becomes 1/1/2 the depth of the trench. 3 or more are also etched, and the difference in level from the silicon layer under the mask becomes large. On the other hand, when the mixing ratio (volume ratio) becomes 2 or less, S
The etch rate of iO□ to silicon becomes ⅓ or more, making it difficult to use a mask that covers silicon oxide.

C113COOI+ is a diluent that is added to control the etch rate, but CIl, C00I+
If the mixing ratio (volume ratio) of (99.5% aqueous solution) to HF (50% aqueous solution) exceeds 10, a black residue will be formed on the etched surface and etching will not proceed uniformly. On the other hand, if the mixing ratio (volume ratio) is less than 5, wavy irregularities of 0.2 μrn or more will occur on the surface, which is not desirable.

1120□ is added to alleviate changes in the etch rate due to changes in the composition of the etchant as etching progresses, and does not necessarily change the etched shape, so it does not necessarily have to be added.

〔Effect of the invention〕

As explained above, according to the second aspect of the present invention, the electron beam exposure time for trench formation can be significantly shortened, thereby increasing the turnaround time.

Furthermore, by selecting the composition of the etchant so as to increase the etching selectivity between silicon and SiO2, it is possible to form a trench and control its shape without causing scratches or contamination on the silicon substrate or silicon layer. .

[Brief explanation of drawings]

Figure 1 shows Example I Figure 2 is an example ■ FIG. 3 shows exposure according to the present invention. Figure 4 is an example of a trench cross section. Figure 5 shows conventional exposure It is. In fig. 1 is a silicon substrate, 11 is an insulating layer. 12 is a silicon layer. is a silicon oxide film. 1 is a mask. is a negative resist pattern. l, 42 is in bloom. is a trench. l is a trench forming part. 1.62.63 is the exposure area. 1.72 is the unexposed area. is the element formation area (b> (c) (e) Implementation 4y'l L v-2 listening (α) Implementation A 1) 1 Cow 1 Father ji T mi departure yo n ρ] filtration 3; Police 32 δte1 of one side of Tren÷] Half 11 ■ Unprecedented exposure 5 forces each

Claims (1)

[Claims] A silicon oxide film (2) is formed on a silicon substrate (1) or a silicon layer (12), and the silicon oxide film (2)
Negative resist pattern (3) with openings (41) on top
forming a hole (42) in the silicon oxide film (2) by etching the silicon oxide film (2) from the hole (41), and then removing the negative resist pattern (3); The silicon oxide film having the openings (42) is covered with a mask (21).
), etching the silicon substrate (1) or the silicon layer (12) with a mixture of hydrofluoric acid, nitric acid, acetic acid, and water to form a trench (5) around the opening (42); A method for manufacturing a semiconductor device, comprising: