JPH03256333A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To easily perform solid growth from a seed and to reduce a crystal defect due to an increase in a single crystal growing region or a decrease in a stress in a film at the time of single crystal growing by reducing in thickness a densified amorphous silicon film by using etching capable of flattening the surface, and then solid growing it. CONSTITUTION:An amorphous silicon film 6 having about 800nm of thickness is deposited by electron beam depositing in an ultrahigh vacuum. After the film 6 by heat treating is subsequently densified in vacuum, a sample is removed from the vacuum, the surface of the sample is etched by a normal bias sputtering method to form the film 6 on an insulating film about 300nm, and the surface of the film 6 is etched with mixture solution of fluoric acid and nitric acid to remove the damage layer on the film 6 generated by the bias sputtering method. Then, the thinned film 6 is heat-treated in a nitrogen atmosphere to be solid grown to form a single crystallized silicon film 7.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a MOS transistor having good electrical characteristics and having an ultra-thin single-crystal silicon film on an insulating film as an active region.

[Conventional technology]

Conventionally, the method of forming a semiconductor single crystal thin film on an insulating film formed on the surface of a semiconductor substrate is described in F.E.D. 3-Day Workshop Extended Abstracts (19).
1988) pages 113 to 118 (Extended
Abstracts of 5thInternat
ional Workshop on Future
ElectronDevices-THree Di
Mensional Integration-[FE
D3D WORKSHOP], May 30 to
June 1, 1988. Miyagi-Zao.

pp. 1.13-118). The process was as follows. ■A thermal oxide film is formed on the surface of a single-crystal silicon substrate by the usual selective oxidation method. At this time, the area where the oxide film is not formed is as follows.

It becomes a seed for later lateral crystal growth. ■Remove the nitride film used for selective oxidation and the oxide film laid underneath it,
A deposited silicon film (800 nrn) is applied to the sample surface. ■ Crystal-grown protective film (500 nm) on the deposited silicon film
) is deposited, and the deposited silicon film is single crystallized by electron beam irradiation. The deposited silicon film and the seed surface are once melted by this electron beam irradiation, and during the subsequent resolidification process, single crystal growth progresses laterally from the seed surface to the region above the oxide film, and the deposited silicon film on the oxide film is Single crystallized.

(2) The single crystal film formed on the insulating film is etched into an ultra-thin single crystal silicon layer with a desired thickness. (2) Fabricate a device using a normal polycrystalline silicon gate MOS transistor formation process on an ultra-thin single-crystal silicon layer.

Further, a field effect thin film transistor (TPT) whose active layer is a polycrystalline silicon layer formed by solid-phase growth of an amorphous silicon film has been proposed in Japanese Patent Laid-Open No. 39070/1983.

[Problem to be solved by the invention]

The method for forming a single crystal silicon film on an insulating film involves melting and resolidifying the polycrystalline silicon film by irradiating the polycrystalline silicon film deposited as described above with an electron beam to form an S○■ structure. There is a crystal growth method (liquid phase growth method) that does this. Other liquid phase growth methods include methods using a strip heater and laser irradiation, but all of these methods are crystal growth methods that use localized high-temperature heating and have the problem of damage to the base. Furthermore, since the process conditions are influenced by the underlying structure, there are problems in selecting an appropriate area and in reproducibility of the process.

On the other hand, there is a solid-phase growth method that utilizes solid-phase growth of an amorphous silicon film as a method for forming an S○ structure using a low-temperature process. This method uses an amorphous film as the deposited silicon film and heat-treats the sample in a nitrogen atmosphere at about 600° C. to obtain a crystal growth region. Therefore, there is no problem with non-uniformity and reproducibility of crystal growth due to temperature differences.

However, this in-phase growth method has a problem in that when the thickness of the amorphous silicon film is reduced, the lateral crystal growth distance becomes shorter. Therefore, in order to form a single-crystal thin film on an insulating film using solid-phase growth, a thick single-crystalline silicon film is formed in advance, as is used in liquid-phase growth.
After that, a method of forming an ultra-thin single crystal silicon layer by etching may be considered. However, this method cannot be used because a high density of defects exists near the interface between the single crystal film formed by solid-phase growth and the edge film.
Ultra-thin SO film with good crystallinity formed using a low-temperature process
It is difficult to use the I structure for device formation. [Means to solve the problem] Etching (e.g., An ultra-thin SOI layer formed by solid-phase growth after obtaining a desired film thickness using bias sputtering is used for the active region of the MoS transistor.

[Effect]

The densification of an amorphous silicon film deposited in an ultra-high vacuum and subsequently heat-treated in a vacuum changes the film quality of the amorphous silicon film, and this change in film quality is the result of lateral solid-phase growth. Determine the distance. Therefore, even if solid-phase growth is performed after thinning a densified amorphous silicon film, a lateral in-phase growth distance corresponding to the thickness of the deposited film can be obtained.

Furthermore, the high density of crystal defects that occur in the SOI structure obtained by in-phase growth occurs during in-phase growth, and is caused by stress within the film during crystal growth. In order to reduce these crystal defects, it is necessary to thin the amorphous silicon film and then perform solid phase growth.

Furthermore, regarding the thinning of a dense amorphous silicon film, single crystal growth on the insulating film by solid phase growth of the amorphous silicon film starts from the contact area between the amorphous silicon film and the substrate. First proceed toward the surface.

Next, after getting over the insulating film step part, it moves laterally, so
By using a thinning method in which the surface of the amorphous silicon film becomes flat so that it can easily climb over the stepped portion, crystal growth at the stepped portion is facilitated.

By using the method for forming an ultra-thin film S○ structure as described above, a wide single-crystal silicon thin film can be formed even in an ultra-thin silicon layer, and furthermore, since the single-crystal growth progresses in a thin film, it is possible to form an insulating/insulating film. Since the number of defects occurring in the single crystal film near the interface with the SOI layer can also be reduced, the electrical characteristics of a MOS transistor using this ultra-thin SOI layer as an active region can be improved.

〔Example〕

The present invention will be explained in detail below.

<Example 1> Example 1 will be described with reference to FIG. A p-type crystal silicon substrate 1 was heat treated in an oxygen atmosphere at 1000° C. for 18 minutes to form an oxide film 2 of about 20 nm. Next, a nitride film 3 of about 120 nm was deposited by CVD. Thereafter, the nitride film 3 was selectively removed by a normal photo-etching process. The pattern portion at this time serves as a seed for the single crystal growth that will be performed later, and is
The stripes were shaped perpendicular to the 00> direction. This sample was heat-treated for 24 minutes in a wet oxygen atmosphere at 1000° C. to form an oxide film 4 of about 200 nm (a).

Next, the nitride film 3 and oxide film 2 were removed to form a substrate exposed portion 5 (seed). After that, low energy Ar (argon) ion beam sputtering and 68%
After cleaning the surface of the sample through a heat treatment process at 0°C for 60 minutes to form a clean sample surface, amorphous silicon with a thickness of approximately 800 nm was deposited by electron beam evaporation in an ultra-high vacuum (less than IXlo-'Pa). Film 6 was deposited (b)
. Subsequently, the amorphous silicon film 6 was densified by heat treatment in vacuum at 450° C. for 1 hour. Thereafter, the sample was taken out of the vacuum, and the surface of the sample was etched by the usual bias sputtering method, so that the thickness of the amorphous silicon film 6 on the insulating film was about 300 nm. Furthermore, in order to remove the damaged layer on the surface of the amorphous silicon film 6 caused by the bias sputtering method, the surface of the amorphous silicon film 6 was etched by approximately 50 nm using a mixed solution of hydrofluoric acid and nitric acid (c
).

Next, the thinned amorphous silicon film 6 was heat treated in a nitrogen atmosphere at 600° C. to perform in-phase growth to form single crystal silicon i@7 (d). As a result of this heat treatment, crystal growth first started in the vertical direction from the seed 5 of the sample, and then, after passing over the pattern edge of the oxide film 4, crystal growth progressed in the horizontal direction from there. In this horizontal single crystal silicon film 7, polycrystalline nuclei are generated in the amorphous silicon film 6 on the oxide film 4, and the amorphous silicon film 6 grows to become a polycrystalline silicon film 8. Seed 5 by
This is the area where single crystal growth has progressed from the beginning.

When the amorphous silicon film 6 was grown in a solid phase, single crystal growth from the seed end was carried out within 7 hours when the crystal growth was completed, and the distance traveled during that time was about 5 μm. At this time, Table 1 shows the single crystal growth distances of samples conducted for comparison.

Table 1 Umbrella: Samples in which the amorphous silicon film was thinned by isotropic etching Note that these results are the distances after the crystal growth of each sample was completed. From the table, we can see the following:

■If the thickness of the deposited film is thin, no lateral crystal growth will occur even if densification is performed (Sample 1). ■ Even if the thickness of the deposited film is thick, if densification is not performed, the distance of lateral crystal growth will be short (sample 2), and if the sample without densification is made thinner, lateral crystal growth will not occur at all ( Sample 3). ■In the samples in which the deposited film was thick and densified, the distance of lateral crystal growth was the longest regardless of whether or not there was subsequent thinning (Sample 4, Sample 5 [Sample 5 is the method of the present invention] sample formed by the manufacturing method]). ■In the sample in which the amorphous silicon film was thinned using isotropic etching, the lateral in-phase growth distance was short due to the influence of the one-step difference (sample 6). Regarding samples 5 and 6, the cross-sectional structure diagrams are shown in the second
As shown in the figure.

As shown above, when forming a single crystal silicon thin film on an insulating film using solid phase growth, it depends on the thickness of the amorphous silicon film when it is deposited, and the influence of the film thickness during solid phase growth. It turns out that it is difficult to receive. In addition, when examining the crystallinity within the single crystal growth up to 200 nm from the interface with the insulating film of Sample 5, which had a thinned densified amorphous silicon film, and Sample 4, which did not have a thinner densified amorphous silicon film, it was found that Sample 5, which had a thinner densified amorphous silicon film, was better than the other sample. There were fewer defects compared to 4.

Next, in order to separate the elements to be formed in the single crystal silicon film 7 formed as described above, the single crystal silicon film outside the element formation region was selectively removed by a normal photo-etching process. Thereafter, boron (B) ions are implanted (4
0 keV, I x 10”c “2) was performed (e).

The subsequent steps are a normal polycrystalline silicon gate MO8)-
A transistor formation process was used. The gate oxide film of the device is 35 nm thick, and the train and source are formed by arsenic (As) ion implantation (80 keV, 5 x 1
0"cm-2).

The n-channel MOS transistor (
The field effect mobility of a device (gate length: 2 μm, gate width: 2 μm) is approximately 720 cm+”/V−s, which is similar to the field effect mobility (
A value 1.2 times that of approximately 600 cm"/V-s) was obtained. The thickness of the single crystal silicon film of the formed device was approximately 90 nm.
It was m.

Further, in this embodiment, etching of the single crystal silicon layer was used to separate the elements, but the same effect can be obtained by using selective oxidation.

The above is an example of a MOS transistor manufactured in a lateral single crystal growth region formed by solid phase growth of a dense amorphous silicon film.

Next, an example of an element in a polycrystalline silicon region formed by in-phase growth of a dense amorphous silicon film will be described.

<Example 2> After forming a densified amorphous silicon film 6 by the same procedure as in Example 1 (see FIG. 2C), solid phase growth was performed by heat treatment in a nitrogen atmosphere at 600°C. A polycrystalline silicon film 8 was used (see FIG. 2). With this heat treatment,
In a region 10 μrn or more away from the seed, polycrystalline nuclei were generated in the amorphous silicon film 6 on the oxide film 4, and the amorphous silicon film 6 grew to become the polycrystalline silicon film 8.

Next, in order to separate the elements to be formed in the polycrystalline silicon film 8, the polycrystalline silicon film outside the element forming region was selectively removed by a normal photo-etching process. Thereafter, boron (B) ions were implanted to make the element formation region of the polycrystalline silicon film 8 p-type (see FIG. 2C). What are the subsequent steps?

A conventional polycrystalline silicon gate MO8)-transistor formation process was used. Note that the gate oxide film of the device is 35
Arsenic (As) ion implantation was used to form trains and sources.

The field effect mobility of the n-channel MOS transistor formed as described above is approximately 15001/v-5, and the field effect mobility of the device formed by a similar process on a polycrystalline silicon film deposited by conventional CVD ( <10cm
2/V-s) was obtained. In this embodiment, etching of the polycrystalline silicon layer was used to separate the elements, but the same effect can be obtained by using selective oxidation.

<Example 3> Amorphous silicon film 6 densified in the same process as Example 1
After solid-phase growth was performed by heat-treating in a nitrogen atmosphere at 600° C. to form a polycrystalline silicon film 8, heat treatment was further performed at a high temperature (1000° C., 4 hours). after that,
An n-channel MOS transistor was manufactured using the same process as in Example 1, and the field effect mobility of the device was measured to be approximately 160.
cm2/V・S. Note that even when a polycrystalline silicon film deposited by conventional CVD was subjected to high temperature heat treatment, no change was observed in the field effect mobility of the formed n-channel MOS transistor.

<Example 4> Example 4 will be explained with reference to FIG. An amorphous silicon film 6 densified in the same process as in Example 1 (see FIG. 3C)
After etching the silicon to a thickness of approximately 250 nm (see Figure 3), solid phase growth is performed by heat treatment in a nitrogen atmosphere at 600°C to form a polycrystalline silicon film 8.
(See Figure 3C). Thereafter, an n-channel MOS transistor was manufactured using the same steps as in Example 1 (see FIG. 3C). When measuring the field effect mobility of the element, it is approximately 180
c1/V-s, and the characteristics of the device were improved. Note that the field effect mobility of a device fabricated using a polycrystalline silicon film obtained by heat-treating the densified amorphous silicon film 6 in a nitrogen atmosphere at 600° C. and then etching the film to approximately 1100 nm is as follows. It did not increase.

〔Effect of the invention〕

According to the present invention, in a MOS transistor whose active region is a single crystal thin film formed on an insulating film, a densified amorphous silicon film is thinned using etching that can flatten the surface, and then in-phase growth is performed. This facilitates solid-phase growth from seeds, expands the single crystal growth region, and reduces crystal defects by reducing stress within the film during single crystal growth. Therefore, a MOS transistor having good electrical characteristics can be obtained from an element formed in this region. Furthermore, the effects of the present invention are applicable not only to the manufacture of n-channel MOS transistors, but also to the manufacture of P-channel MOS transistors, CMO5 structures, and even to the manufacture of integrated circuits in which these elements are assembled.

[Brief explanation of drawings]

Figures 1 to 3 are cross-sectional views showing the manufacturing process of the present invention.
The table shows the lateral single crystal growth distance formed in each single crystal growth manufacturing process.

Claims (1)

[Claims] 1. In the production of an ultra-thin film MOS transistor whose active region is a single-crystal silicon thin film on an insulating film, the steps include: (1) forming an insulating film on at least a portion of a single-crystal semiconductor substrate;
(2) Depositing an amorphous silicon film that continuously covers the single crystal semiconductor substrate and the insulating film in an ultra-high vacuum; (3) After depositing the amorphous silicon film, continue in a vacuum at temperatures below 500°C. (4) a step of etching the densified amorphous silicon film to a desired thickness by performing an etching process that can flatten the surface; 5) A step of converting the amorphous silicon film into a single crystal by performing heat treatment in a nitrogen gas or inert gas atmosphere at 1200° C. or lower; and (6) converting the thin silicon layer formed on the insulating film into an active region. 1. A method of manufacturing a semiconductor device, comprising a step of forming an element. 2. As the insulating film layer according to claim 1 above,
1. A method of manufacturing a semiconductor device, characterized in that it is constructed of an oxide film, a nitride film, or a laminated structure of both. 3. The heat treatment for single-crystallizing the amorphous silicon film according to claims 1 and 2 above is characterized by using a nitrogen gas or inert gas atmosphere at 550° C. or higher and 800° C. or lower. A method for manufacturing a semiconductor device. 4. A method for manufacturing a semiconductor device, characterized in that nitrogen gas is used as a heat treatment atmosphere for monocrystallizing the amorphous silicon film according to claims 1 to 3 above. 5. A method for manufacturing a semiconductor device, which comprises monocrystallizing the amorphous silicon film according to claim 3, and then further performing high temperature heat treatment at 1000° C. or higher for 1 hour or longer.