JPH0334425A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To eliminate the necessity of excessive light etching which is performed before dry etching of polycrystalline semiconductor, by a method wherein the crystal grain diameter of a polycrystalline semiconductor film is specified by selectively eliminating an oxidation resistant film, a second semiconductor oxide film, and a part of the film thickness direction of the polycrystalline semiconductor film, and performing heat treatment. CONSTITUTION:After an SiO2 film 2 of, e. g. about 50mum in thickness is formed on the surface of an Si substrate 1 by thermal oxidation method, a polycrystalline Si film 3 of, e. g. about 480Angstrom in thickness is formed on the whole surface by, e. g. low pressure CVD method. By ionimplanting, e. g. Si, in the whole surface, the polycrystalline Si film 3 is turned into an amorphous state. One example of Si ion implantation condition is as follows; dosage is 1X10<15>cm<-2>, and energy is 40keV. After that, e. g. in a nitrogen (N2) atmosphere, heat treatment is performed at a low temperature of, e.g. about 700 deg.C for about 20 hours. By this heat treatment, the amorphous Si film formed by turning the ion-implanted polycrystalline Si film 3 into an amorphous state is subjected to solid-phase growth, and as the result, the polycrystalline Si film 3 whose crystal grain diameter is 0.5-10mum is formed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a semiconductor device, and is particularly suitable for application to isolation between elements in a semiconductor integrated circuit device with high integration density. be.

[Summary of the invention]

The present invention provides a method for manufacturing a semiconductor device in which a semiconductor substrate is selectively oxidized.
a step of sequentially forming a semiconductor oxide film, a polycrystalline semiconductor film, a second semiconductor oxide film, and an oxidation-resistant film; By selectively removing at least a portion and performing heat treatment, the crystal grain size of the polycrystalline semiconductor film is reduced to 0.
5 to 10 μm. This eliminates the need to perform excessive light etching on the rows before dry etching to remove the polycrystalline semiconductor film.

[Conventional technology]

Interelement isolation regions in semiconductor integrated circuit devices are usually formed by a selective oxidation method (LOCO3 method). However, as is well known, in the conventional LOCO3 method, the length of the bird's beak formed at the end of the field oxide film is large, which is a factor that prevents high integration density of devices.

In order to solve this problem, the present applicant has proposed a selective oxidation method that can form a field oxide film with a smaller bird's beak length (for example, Japanese Patent Application No. 220209/1982). Figures 2A to 2C show the method, and silicon nitride (silicon nitride) is used as an oxidation-resistant film.
Selective oxidation is performed using an oxidation mask with a multilayer structure including a polycrystalline silicon (St 2 ) film below the 5i3N4) film.

According to this method, as shown in FIG. 2A, first a Si0g film (pad Sin, film) 102 is formed on the surface of a Si substrate 101 by a thermal oxidation method, for example, with a thickness of about 50 mm, and then this SiO A polycrystalline Si film 103 is formed on the entire surface of the film 102 by, for example, a low-pressure CVD method to a thickness of about 480 nm. The grain size of the crystal grains 103a of this polycrystalline St film 103 is, for example, about 500 to 1000, although it depends on the growth temperature. After forming a 5iOz film 104 with a thickness of, for example, about 80 mm on the surface of this polycrystalline Si film 103 by thermal oxidation, the entire surface of this Sing film 104 is formed with a thickness of about 1000 mm by low pressure CVD, for example. ,N.

A film 105 is formed. Next, a resist pattern 106 having a predetermined shape is formed on this 5i3Na film 105 by lithography. Next, this resist pattern 106
Using as a mask, the Si3Ng film 105, the SiO□ film 10, and the crystalline St film 103 are sequentially etched to the middle of the polycrystalline St film 103 in the film thickness direction, and then the resist pattern 106 is removed. By this, these Si,
N, film 105.5iOz film 104 and polycrystalline St film 10
3 is patterned into a shape as shown in FIG. 2B.

Next, thermal oxidation is performed in this state. As a result, as shown in FIG. 2C, a field S is formed on the surface of the Si substrate 101.
In, a film 107 is selectively formed to provide isolation between elements. During this thermal oxidation, the polycrystalline Si film 103 below both ends of the 5i3N4 film 105 is also oxidized, so the length of the bird's beak formed at the end of the field 5int film 107 must be reduced. I can do it.

Next, first, 5L of hot phosphoric acid (H, PO2) etc.
3N, and after removing the film 105 by etching, 5i02 is etched by light etching using a hydrofluoric acid-based etching solution.
The film 104 is removed by etching.

Thereafter, the polycrystalline Si film 103 is removed by dry etching.

[Problem to be solved by the invention]

However, in the conventional selective oxidation method shown in FIGS. 2A to 2C, as shown in FIG. 2C, the field Sin at the boundary with the polycrystalline Si film 103,
There was a problem in that the crystal grains 103a were buried in the bird's beak portion without being oxidized. This is polycrystalline S
This is due to the progress of oxidation along the grain boundaries of the i-film 103. Since the crystal grains 103a embedded in the bird's beak portion of the field 5iO1 film 107 cause deterioration of the shape of the field Sing film 107, they are removed by etching at the same time as dry etching for removing the polycrystalline Si film 103. There is a need to.

By the way, the dry etching for removing this polycrystalline Si film 103 is performed using a Si film in order to selectively remove only this polycrystalline Si film 103.

The process is carried out under conditions such that the selectivity of polycrystalline St to polycrystalline St is high. Therefore, if even a small amount of the 5i02 film 104 remains before etching the polycrystalline St film 103, the etching of the polycrystalline St film 103 will not proceed. Therefore, it is necessary to remove this 5i02 film 104 without fail before etching the polycrystalline Si film 103. Furthermore, during dry etching of this polycrystalline St film 103, field 5 is
In order to simultaneously remove the crystal grains 103a buried in the bird's beak portion of the iCh film 107 by etching, it is necessary to expose the crystal grains 103a buried in the bird's beak portion before this dry etching.

Therefore, conventionally, before dry etching the polycrystalline Si film 103, this polycrystalline St film 103 and the field 5i are etched.
Crystal grains 1 embedded in the bird's beak part of the O1 film 107
In order to ensure that 03a is exposed, light etching using a hydrofluoric acid etching solution or the like is performed in excess to the extent that, for example, a 600 mm thick film is etched.

However, if the light etching is performed excessively in this way, the film thickness of the field 5iOt )li L O7 will be considerably reduced. In this case, it is necessary to form this field 5i0z film 107 to be quite thick in advance by selective oxidation. However, due to selective oxidation, the field Sin, film 10
If 7 is formed thickly, there are problems such as an increase in the bird's beak length and an increase in the stress generated around the bird's beak during selective oxidation, making crystal defects more likely to occur.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for manufacturing a semiconductor device that eliminates the need to perform excessive light etching before dry etching a polycrystalline semiconductor film.

[Means for Solving the Problems] As a result of various studies, the inventor has determined that
In the conventional selective oxidation method shown in Figure C, the field Sin
It has been recognized that the reason why the crystal grains 103a are buried unoxidized in the bird's beak portion of the g film 107 is that the grain size of the crystal grains 103a is small.

The present invention was devised based on this recognition.

That is, in order to achieve the above object, the present invention provides a method for manufacturing a semiconductor device in which a semiconductor substrate (1) is selectively oxidized. ), a step of sequentially forming a polycrystalline semiconductor film (3), a second semiconductor oxide film (4), and an oxidation-resistant film (5); a step of selectively removing at least a portion of the polycrystalline semiconductor film (3) in the film thickness direction; and a step of making the crystal grain size of the polycrystalline semiconductor film (3) 0.5 to 10 μm by performing heat treatment. Equipped with.

Here, the lower limit of the crystal grain size of the polycrystalline semiconductor film (3) of 0.5 μm means that if the crystal grain size is 0.5 μm or more, the edge of the oxide film (7) formed by selective oxidation The polycrystalline semiconductor film (3) at the boundary with the bird's beak to be formed is completely oxidized, and therefore crystal grains (
This is because 3a) is prevented from being buried unoxidized. On the other hand, polycrystalline semiconductor film (
The upper limit of the crystal grain size in 3), 10 μm, means that the crystal grain size is 1
Even if the crystal grain size is 0 μm or more, the advantages of increasing the crystal grain size are almost the same as those when the crystal grain size is 10 μm or less, and although the crystal grain size can be increased by increasing the heat treatment time, This is because, from the viewpoint of productivity, it is preferable that the time for this heat treatment be as short as possible.

The crystal grain size of this polycrystalline semiconductor film (3) is from 1 to 5.
More preferably, it is μm.

[Effect]

According to the above-described means, since the crystal grain size of the polycrystalline semiconductor film (3) is increased to 0.5 to 10 μm before selective oxidation, the bird's beak portion of the oxide film (7) formed by selective oxidation The polycrystalline semiconductor film (3) at the boundary with the oxide film (3) is easily and completely oxidized, thus preventing the crystal grains (3a) from being buried unoxidized in the bird's beak part of the oxide film (7). Therefore, the light etching performed before the dry etching of the polycrystalline semiconductor film (3) is sufficient to remove the second semiconductor oxide film (4), and is not performed excessively as in the conventional method. There will be no need. As a result, the amount of reduction in the thickness of the oxide film (7) due to this light etching is reduced, so there is no need to form this oxide film (7) thickly in advance, which may increase the bird's beak length or Problems such as increased stress generated around the bird's beak during oxidation, which makes crystal defects more likely to occur, are eliminated.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

1A to 1F show a method of manufacturing a semiconductor device according to an embodiment of the present invention.

In this embodiment, as shown in FIG.
After forming a 5iOz film (pad Sin, film) 2 with a thickness of, for example, about 50mm on the surface of the t-substrate 1 by thermal oxidation method, a film of about 480mm thick is formed on the entire surface of this 5iOz#2 by low pressure CVD, for example. A polycrystalline Si film 3 is formed. The grain size of the crystal grains 3a of the polycrystalline St film 3 is, for example, 500 to 1
There are about oooo people.

Next, the polycrystalline St film 3 is made amorphous by ion-implanting, for example, St into the entire surface of the polycrystalline Si film 3. An example of the conditions for this St ion implantation is: dose t I x 10 lScm-'', energy 40
keV. Thereafter, heat treatment is performed at a low temperature of, for example, about 700° C. for about 20 hours in a nitrogen (Nt) atmosphere, for example. By this heat treatment, the amorphous St formed by amorphizing the polycrystalline Si film 3 by the above-mentioned ion implantation.
A film (not shown) grows in a solid phase, and as a result, as shown in FIG. 1B, a polycrystalline Si film 3 having a crystal grain size of, for example, about 5 μm is formed.

Next, as shown in FIG.
After forming the film 4, the entire surface of the film 4 is exposed to low pressure C, for example.
By VD method, for example, about 5 N4 for about 1,000 yen per membrane
A film 5 is formed. Next, a resist pattern 6 having a predetermined shape is formed on this Si*N4 film 5 by lithography.

Next, using this resist pattern 6 as a mask, 5isN
After sequentially etching the a film 5, the Sin film 4, and the polycrystalline St film 3 to the middle of the film thickness direction of the polycrystalline St film 3,
The resist pattern 6 is removed. As a result, the Si3N film 5, the Sing film 4, and the polycrystalline Si film 3 are patterned into the shape shown in Figure 1.

Next, thermal oxidation is performed in this state. As a result, as shown in FIG. 1, a field S'x is formed on the surface of the St substrate l.
02 film 7 is selectively formed to provide isolation between elements.

In this case, as mentioned above, the crystal grain size of the polycrystalline Si film 3 is 5.
Since it is extremely large, about μm, this field is 5iOz
The polycrystalline St film 3 at the boundary with the bird's beak part of the film 7 is completely oxidized, and as a result, this field 5ift film 6
This prevents the crystal grains 3a of the polycrystalline St film 3 from being buried in the bird's beak portion in an unoxidized state.

Next, first, S i 2 N by hot H, PO, etc.
After removing the SiO□ film 4 by etching, the SiO□ film 4 is etched away by light etching using a hydrofluoric acid-based etching solution or the like. Thereafter, the polycrystalline Si film 3 is removed by dry etching to obtain the state shown in FIG. 1F. Field Sin in this state, film 7
The film thickness is, for example, about 35,001 mm.

After performing the isolation between elements as described above, the steps are performed according to the manufacturing process of the target semiconductor integrated circuit device, and the semiconductor integrated circuit device is charged.

Ru.

As described above, according to this embodiment, the grain size of the crystal grains 3a of the polycrystalline Si film 3 is increased to about 5 μm by solid phase growth through heat treatment before performing selective oxidation. The crystal grains 3a of the polycrystalline Si film 3 are prevented from being buried in the bird's beak portion of the film 7 without being oxidized, and therefore the light etching performed before the dry etching of the polycrystalline Si film 3 is not performed excessively as in the conventional method. There is no need to do so. Therefore, by selective oxidation, field 5
Since it is no longer necessary to form the iOz film 7 thickly in advance, the bird's beak length can be made smaller than before, and the stress generated around the bird's beak portion during selective oxidation can be reduced, thereby reducing the occurrence of crystal defects. can be suppressed.

The selective oxidation method according to this embodiment is suitable for performing isolation between elements of a semiconductor integrated circuit device with high integration density, and can be applied to manufacturing various semiconductor devices such as MO5LSI, bipolar-CMO3LSI, and bipolar LSI. It is possible. More specifically, the selective oxidation method according to this embodiment is applied to, for example, a 1M bit static RAM (R
andom AccessMemory).

Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications can be made based on the technical idea of the present invention.

For example, it is also possible to use ion species other than Si' to make the polycrystalline Si film 3 amorphous.

Also, heat treatment conditions for solid phase growth (atmosphere, temperature,
time) can also be selected as appropriate.

Furthermore, the method for increasing the crystal grain size of the polycrystalline Si film 3 is not necessarily limited to the method described in the above embodiment, and other methods may also be used.

It goes without saying that the film thicknesses of the 5iO1 film 2, the polycrystalline St film 3.5int film 4, and the 5izN4 film 5 are not limited to the values described in the above embodiments, and may be appropriately selected as necessary. is possible.

〔Effect of the invention〕

As explained above, according to the present invention, the crystal grain size of the polycrystalline semiconductor film is reduced to 0°5 to 10 μm by heat treatment.
This prevents the crystal grains of the polycrystalline semiconductor film from being buried unoxidized in the bird's beak part of the oxide film formed by selective oxidation. There is no need to overdo it. This eliminates the need to previously form a thick oxide film through selective oxidation, making it possible to reduce the bird's beak length of this oxide film and reducing stress generated around the bird's beak during selective oxidation. .

[Brief explanation of drawings]

1A to 1F are cross-sectional views for explaining a method for manufacturing a semiconductor device according to an embodiment of the present invention in order of steps, and FIGS. 2A to 2C are sectional views for explaining a conventional selective oxidation method in order of steps. It is a sectional view for explanation. Explanation of main symbols in the drawings 1: Si substrate, 2,4: 5iO=film, 3: Polycrystalline Si film, 3a: Crystal grain, 7: Field Sin. film.

Claims (1)

[Claims] A method of manufacturing a semiconductor device in which a semiconductor substrate is selectively oxidized, wherein a first semiconductor oxide film, a polycrystalline semiconductor film, a second semiconductor oxide film, and an oxidation-resistant film are provided on the semiconductor substrate. a step of sequentially forming films, a step of selectively removing at least a portion of the oxidation-resistant film, the second semiconductor oxide film, and the polycrystalline semiconductor film in the film thickness direction; A method for manufacturing a semiconductor device, comprising a step of adjusting the crystal grain size of a crystalline semiconductor film to 0.5 to 10 μm.