JPH04326576A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To obtain a semiconductor device which has a gate oxide film with a uniform thickness and a superior quality by transforming a silicon layer to a silicon oxide film by the thermal oxidation method to form a gate oxide film after new silicon layer is piled up and adhered on the silicon surface. CONSTITUTION:After a field oxide film 2 for insulating isolation is selectively formed on a silicon substrate 1, a single-crystalline silicon layer 3 having about half in thickness of desired silicon oxide film is piled up on the substrate 1. At this time, a single crystal silicon film is formed on the substrate 1 and a polycrystalline silicon film on the film 2, respectively. Next, the layer 3 is transformed to a silicon oxide film by the thermal oxidation method to form a gate oxide film 4. Then a gate electrode, etc., composed of the polycrystalline silicon are formed on the film 4. Therefore, the gate oxide film, which has the uniform film thickness even in the area adjacent to the film 2 or so far away from it and the film quality equivalent to that of the silicon oxide film through thermal oxidation of the silicon surface, can be obtained easily.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of forming a gate oxide film of a semiconductor device having a MOS type semiconductor element.

0002

2. Description of the Related Art Semiconductor devices having MOS type semiconductor elements, as typified by dynamic RAM, have become more sophisticated and highly integrated. Films are becoming thinner.

Conventionally, as shown in FIG. 4(a), the method for manufacturing a gate oxide film involves forming a field oxide film 2 on a silicon substrate 1, and then subjecting the exposed silicon substrate 1 to an oxidizing agent such as water vapor. The method was to perform heat treatment in an atmosphere, oxidize the surface of the silicon substrate 1 to a desired thickness, and convert it into a gate oxide film 4B as shown in FIG. 4(b). It is known that the quality of the silicon oxide film obtained in this way is affected by the quality of the surface of the silicon crystal to be oxidized, and prior to the thermal oxidation to form the gate oxide film 4B, a heat treatment process called so-called sacrificial oxidation is carried out. It is common to add This is because, among the oxygen normally contained in a silicon substrate, oxygen near the surface diffuses out of the silicon substrate due to heat treatment, its concentration decreases, and oxygen no longer precipitates on the silicon surface, forming a gate oxide film. Since no oxygen precipitates are present in the silicon oxide film, its quality is improved.

Furthermore, as a method for forming this type of gate oxide film, after selectively exposing the silicon substrate, CVD is performed.
There is also a method of depositing a silicon oxide film by a method such as a method or a sputtering method.

[0005]

However, all of the above-described conventional methods for forming a gate oxide film in the manufacturing process of a semiconductor device have the following drawbacks. First, in the method of thermally oxidizing the silicon substrate surface to form a silicon oxide film, which is a gate oxide film, as shown in FIG. 4(b).
As shown in FIG. 2, there is a problem in that the film thickness of the portion A near the boundary with the field oxide film 2 for element isolation becomes thinner. This is because during thermal oxidation to form gate oxide film 4B after field oxide film 2 is formed, the oxide film is directly exposed to the silicon substrate in areas where the silicon substrate is exposed at a sufficient distance from the edge of the field oxide film. This is because, in contrast, in the vicinity of the field oxide film, there is a time delay in which the oxidizing species reacts with the silicon substrate only after it has diffused through the field oxide film.

The thinning rate, which is the ratio of the film thickness near the boundary with the field oxide film to the film thickness at a sufficient distance from the field oxide film, is slightly influenced by the shape of the edge of the field oxide film. According to experiments conducted by the inventor of the present application, it was approximately 80%. That is, 20n
In the case of forming a gate oxide film of m, the thickness of the silicon oxide film at part A near the boundary with the field oxide film is only 16 nm. Then, the dielectric strength voltage of the gate oxide film is determined by the thin part, and even for a silicon oxide film without any defects, it would be about 16V in the above example, and 2
The inherent breakdown voltage of 20 V for a 0 nm silicon oxide film cannot be obtained.

Further, sacrificial oxidation is performed prior to the formation of the gate oxide film, and although the influence of the quality of the crystal surface of the silicon substrate can be removed to some extent, the above-mentioned problems are not solved. The thickness of the gate oxide film that satisfies the characteristics of the semiconductor device is determined by the thickness of the film at a sufficient distance from the field oxide film, so if the silicon oxide film described above is used as the gate oxide film, This causes a decrease in manufacturing yield.

[0008] Furthermore, in terms of the amount of charge that can be poured into the silicon oxide film, which is one indicator of the quality of the silicon oxide film,
The amount of charge depends on the thickness of the film, and it has been found through experiments that the amount of charge decreases exponentially as the film thickness becomes thinner.For example, the amount of charge that can be poured into a silicon oxide film with a thickness of 15 nm has been found to be Comparing the amount of charge with a 12 nm thick silicon oxide film, only about 70% of the amount of charge that can be poured into a 15 nm silicon oxide film can be poured into a 12 nm silicon oxide film. Therefore, there is a problem in that the reliability of the semiconductor device having the above-mentioned gate oxide film is lowered.

In addition, as a method for simultaneously solving the problem of thinning near the boundary with the field oxide film and the problem caused by oxygen on the crystal surface of the silicon substrate, a silicon oxide film is deposited by CVD or sputtering. There is a way to wear it. However, silicon oxide films formed by this method are generally inferior in film quality to silicon oxide films obtained by thermally oxidizing silicon, and when compared with dielectric strength, the electric field strength deteriorates by more than 1 MV/cm. The reality is that there are. Therefore, there is a problem that manufacturing yield and reliability cannot be ensured even with a film thickness that satisfies the performance of the semiconductor device.

The present invention has been made in view of these problems, and it prevents thinning of the gate oxide film in the vicinity of the field oxide film, and provides a MOS type in which a silicon oxide film with excellent film quality is used as the gate oxide film. An object of the present invention is to provide a method for manufacturing a semiconductor device having a semiconductor element.

[0011]

Means for Solving the Problems A method for manufacturing a semiconductor device of the present invention includes the steps of forming a field oxide film on a silicon substrate to separate element formation regions, and forming a silicon layer on the surface of the silicon substrate in the element formation regions. a step of forming;
The method includes a step of oxidizing the silicon layer to form a gate oxide film.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained in detail with reference to the drawings. FIGS. 1A to 1C are cross-sectional views of a semiconductor chip for explaining a first embodiment of the present invention, particularly showing the case where the semiconductor chip is applied to a transfer gate of a memory cell in a dynamic RAM.

First, as shown in FIG. 1(a), a field oxide film 2 for insulation isolation is formed on a silicon substrate 1 by a known method.
selectively formed on top. Next, as shown in Figure 1(b),
On the surface of this silicon substrate 1, a single crystal silicon layer 3 having a thickness of about half of the desired silicon oxide film, for example, 8 nm, is formed.
is deposited by a known method, for example, epitaxial growth using silane gas. At this time, a single crystal silicon film is formed on the surface of the silicon substrate 1, and a field oxide film 2 is formed on the surface of the silicon substrate 1.
A polycrystalline silicon film is formed thereon.

Thereafter, as shown in FIG. 1(c), the silicon substrate 1 is placed in a normal hydrogen and oxygen gas atmosphere, and the deposited silicon layer 3 is converted into a 20 nm thick silicon oxide film by thermal oxidation. A gate oxide film 4 is then formed. Thereafter, a gate electrode made of polycrystalline silicon and the like are formed on the gate oxide film 4 by a conventional method to form a transfer gate transistor.

As described above, since the gate oxide film 4 is a silicon oxide film obtained by thermally oxidizing the uniformly deposited silicon layer 3, the same film is formed both near the field oxide film and at a sufficiently distant location. A gate oxide film that is thick and has the same quality as a silicon oxide film obtained by thermally oxidizing the silicon surface can be obtained.

FIGS. 2A and 2B are diagrams showing gate dielectric breakdown voltage distributions of transfer gate transistors produced according to this embodiment and the conventional example. Here, the gate dielectric breakdown voltage distribution is shown, which was formed by thermally oxidizing the silicon surface to have a thickness of 20 nm at a sufficient distance from the field oxide film. As is clear from FIGS. 2A and 2B, in the method of this embodiment, the distribution is concentrated around 20V, which is the original withstand voltage of a 20 nm thick silicon oxide film. In contrast, in the conventional method, the voltage is concentrated around 16 V, and it can be seen that in the conventional method, a thin portion is formed in the gate oxide film.

Furthermore, when the dynamic RAM obtained in this example was subjected to a screening test using a power supply voltage 1.5 times the rated voltage, a yield of more than 98% was obtained, whereas the conventional 69 products manufactured by the method
% yield was obtained. This matches the amount of charge that can be injected into the silicon oxide film.

As described above, according to the first embodiment,
The dielectric breakdown voltage of the gate oxide film is improved, and high performance and high quality semiconductor devices can be obtained at a high yield.

In the above embodiment, single crystal silicon was used as the silicon layer 3, but the same effect can be obtained with a polycrystalline silicon layer or an amorphous silicon layer. Further, although polycrystalline silicon is used as the gate electrode, it is clear that other materials may be used without sacrificing the effects of the present invention.

FIGS. 3A and 3B are cross-sectional views of a semiconductor chip for explaining a second embodiment of the present invention.

First, as shown in FIG. 3(a), a field oxide film 2 for insulation isolation is formed on a silicon substrate 1 by a known method.
selectively formed on the silicon substrate to expose the surface of the silicon substrate in the gate region. Next, a single crystal silicon layer 5 having a thickness of about 1/2 of the desired silicon oxide film, for example 8 nm, is deposited only on the exposed silicon surface area of the silicon substrate 1. . This deposition method can be achieved by selective epitaxial growth using dichlorosilane (SiH2 Cl2) and hydrochloric acid (HCl) gas.

Thereafter, as shown in FIG. 3(b), the deposited single crystal silicon layer 5 is converted into a 20 nm thick silicon oxide film by a thermal oxidation method in an ordinary hydrogen and oxygen gas atmosphere, and gate oxidation is performed. A film 4A is formed. Thereafter, a MOS type semiconductor device using polycrystalline silicon as a gate electrode is manufactured by a conventional method.

The second embodiment provides the same effects as the first embodiment, and has the additional advantage that the gate oxide film can be formed only on the necessary gate portions.

[0024]

As explained above, the method of the present invention deposits a new silicon layer on the silicon surface and then converts this silicon layer into a silicon oxide film using a thermal oxidation method to form a gate oxide film. In order to form a gate oxide film, it is possible to obtain a gate oxide film that has the same thickness both near the field oxide film and at a sufficiently distant location, and has the same quality as a silicon oxide film obtained by thermally oxidizing the silicon surface. Furthermore, since the deposited silicon layer does not contain oxygen, there is no need to consider the oxygen concentration on the surface of the silicon substrate, which is a problem when directly thermally oxidizing the silicon substrate. As described above, according to the method of the present invention, high-performance, high-quality semiconductor devices can be obtained at a high yield.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a semiconductor chip for explaining a first embodiment of the present invention.

FIG. 2 is a diagram showing gate dielectric breakdown voltage distribution when using an example and a conventional example.

FIG. 3 is a cross-sectional view of a semiconductor chip for explaining a second embodiment of the present invention.

FIG. 4 is a cross-sectional view of a semiconductor chip for explaining a conventional method of manufacturing a semiconductor device.

[Explanation of symbols]

1 Silicon substrate 2 Field oxide film 3 Silicon layer 4, 4A, 4B Gate oxide film 5 Single crystal silicon layer

Claims (1)

[Claims] 1. A step of forming a field oxide film on a silicon substrate to separate an element formation region, a step of forming a silicon layer on the surface of the silicon substrate in the element formation region, and a step of oxidizing the silicon layer and gate oxidation. 1. A method for manufacturing a semiconductor device, comprising the step of forming a film.