JPH0370123A - Method for forming crystalline semiconductor film - Google Patents

Abstract

PURPOSE:To carry out solid growth from a 'species' which is prepared in advance and to form a crystalline semiconductor film at an arbitrary grain size by forming a crystalline species by a crystal nucleus which is produced at the initial stage of process to form a deposit film by vapor method, or an island-shaped single crystal of a thin film arranged on a substrate by agglomeration reaction. CONSTITUTION:A 'species' 2 of crystal growth is formed to an arbitrary nucleus concentration on an amorphous insulating material or a substrate 1 having it on the surface by solid method using vapor method such as plasma CVD, thermal CVD or agglomeration reaction. An amorphous semiconductor 3 is deposited to cover the 'species' 2 of crystal growth by a method such as plasma CVD, LPCVD, and sputtering. If annealing is carried out in a temperature region which is lower than the starting temperature of crystallization of the deposited amorphous semiconductor material and higher than the starting temperature of growth, growth is carried out from the species 2. However, since new nucleus does not develop from inside the amorphous layer, an initial nucleus concentration is maintained. If further growth is carried out, formed crystalline grains 4 collide one another to form a grain boundary 5, thereby stopping growth.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for forming a crystalline semiconductor film, and particularly to a method for forming a polycrystalline thin film with large grain size on an amorphous insulating substrate or an insulating film at a relatively low temperature. Regarding how to.

The present invention is applied to crystalline semiconductor thin films used in electronic devices such as semiconductor integrated circuits, optical devices, etc., for example.

[Conventional technology] Many methods for forming semiconductor thin films for semiconductor electronic devices on amorphous insulators have been reported, but in recent years, methods for forming large-grain polycrystalline thin films for the purpose of manufacturing high-speed devices have been developed. In particular, there are an increasing number of reports on Among these, a typical method is to melt and solidify an amorphous or polycrystalline semiconductor layer using thermal energy such as a laser or a rod-shaped heater to obtain a polycrystalline film with large grain sizes on the order of millimeters (Si
ngle Crystal 5ilicon on n
on-3ingleCrystal In5ulato
rs, Journal of CrystalGro
wth vol, 63. No, 3.0ctober
1983 edited by G, W, Cu1le
n), etc. In addition, amorphous Sl is heat-treated for a long time (several tens to hundreds of hours) near the critical temperature at which Si crystal nuclei are generated (approximately 600°C) to form a polycrystalline thin film with an average grain size of several μm. (T, Noguchi, H
, Hayashi, H. Ohshima.

Polysilicon and Interface
s, Boston 1987゜Mater, Re
s, Soc, Symp, Proc, v
ol, 106 (Elsevier 5science P
publishing, New York 1988)
P, 293) have been reported.

[Problem that the invention is trying to solve]

However, among the above conventional examples, the melt recrystallization method using a laser or the like has the following problems. That is, a considerably high temperature may be required to melt the semiconductor layer. For example, amorphous or polycrystalline S
Heat of 1,420 to 1,450° C. or higher is required to melt L, and therefore the material constituting the substrate is required to be able to withstand such temperatures. Furthermore, if the semiconductor layer is melted while being scanned with a laser or a rod-shaped heater, protrusions and film breaks are likely to occur, and SOI (Sil
It becomes difficult to make ultra-thin films of iconOn In5ulator).

On the other hand, although the method of annealing an amorphous semiconductor layer at a relatively low temperature is suitable for thinning the film with almost no change in the shape of the film due to the low temperature, it has the following problems. That is, in the above method, the amorphous layer is annealed near the critical temperature for nucleation of the amorphous material (for example, around 600°C in the case of amorphous SL), and the crystal nuclei generated at the initial stage become more solid. This is a phase growth method, but with this method, new nuclei are generated one after another while the initial nuclei are growing in a solid phase, resulting in large variations in the grain size of the produced polycrystalline film. I end up. In other words, it is difficult to control grain size distribution. In addition, with this method, the time from the start of annealing until the first generation of "crystal nuclei" (i
(ncu-bation time) becomes extremely long, ranging from several hours to several tens of hours.

In view of the above-mentioned problems, the present invention forms in advance a "seed" for crystal growth in an amorphous semiconductor layer, and the "seed"
The present invention provides a method of forming a crystalline semiconductor film with an arbitrary grain size using a method of solid phase growth.

[Means for Solving the Problems] According to the present invention, a single crystalline seed is placed on a substrate having a surface formed of an amorphous insulator, and then an amorphous semiconductor is placed on the substrate so as to cover several seeds. A method for forming a crystalline semiconductor film in which crystals are grown in a solid phase by heat treatment after being deposited on a semiconductor film, wherein the single crystalline seed is generated at the beginning of the process of forming a deposited film by a vapor phase method. Provided is a method for forming a crystalline semiconductor film in which the crystalline semiconductor film is a single crystal nucleus, or a thin film disposed on the substrate is formed into an island-like single crystal by an agglomeration reaction.

In the present invention, first, a "single crystal seed" for crystal growth is formed in a gas phase or solid phase on a substrate having a surface made of an amorphous insulator.

At this time, the nuclear density (seed density) of the "single-crystalline seeds" is controlled by a method described later. The "single-crystalline seed" (hereinafter abbreviated as r-seed J) herein refers to a single-crystalline substance from which a single crystal can be grown in a solid phase.

Next, an amorphous semiconductor is deposited so as to cover several species on the substrate surface on which the "seeds" have been formed, and this is deposited at a temperature lower than the nucleation critical temperature (Tc) of the amorphous semiconductor, and the seeds are If present, the temperature is higher than the growth initiation temperature (To) at which the seed can grow, that is, T o < T <
Annealing is performed at a temperature of Tc to induce solid phase growth.

Next, the method of the present invention will be explained using the drawings.

FIGS. 1(a) to 1(e) are process diagrams of the method of the present invention, which will be explained step by step.

(a) *An amorphous insulator or a substrate 1 having the amorphous insulator on its surface is prepared. The substrate is, for example, a quartz substrate, a Si
Examples include wafers whose surfaces are oxidized, Si wafers, alumina wafers on which SiO□, Si3N4, etc. are deposited, and others.

(b) On the substrate, for example, plasma CVD, thermal CVD
A type of crystal growth method 2 is formed to have an arbitrary nucleus density (seed density) using a gas phase method such as the above, or a solid phase method using a coagulation reaction. The method for forming seeds is as follows (i):
(if) is preferred.

(i) Vapor phase method In this method, at the beginning of the process of forming a polycrystalline film by the CVD method, fine crystal grains, that is, crystal nuclei are generated randomly on the substrate, and later growth nuclei that grow from these crystal nuclei. It takes advantage of the phenomenon in which the particles collide with each other and form a film (Figure 2). In other words, this is a method in which CVD is stopped at the point when crystal nuclei are randomly generated, that is, at the point in time shown in FIG. 2(a), and the obtained crystal nuclei are used as "seeds." At this time, the nuclear density can be obtained arbitrarily by changing CVD conditions such as temperature, pressure, type of gas, introduction of etching gas, and its flow rate, and by changing the material of the substrate surface. An example is shown in FIG.

FIG. 3 shows the nucleus density when SL nuclei were formed by CVD on substrate surfaces of 5iOi and 5iJ4, respectively. Examples of CVD conditions are:
The gas system uses SSi32C1 as the S1 source gas, H2 as the atmospheric gas, and HCI gas having an etching effect is introduced therein as an additive gas. The temperature is 9
The temperature was fixed at 50° C., the pressure was 150 Torr, and the deposition time was fixed at 20 minutes. S on the surface of 5LO2, Si3N4 when only the flow rate of HCI gas was changed under these conditions.
It shows the nuclear density of i.

(ii) Solid-phase method As shown in FIG. 4, in this method, a non-single-crystal thin film 12 is formed on a substrate 11, and then annealed at a temperature lower than the melting point of the material constituting the thin film 12. This is a method of causing an agglomeration phenomenon to occur and using the obtained island-shaped single crystals as "seeds" 13. According to experiments conducted by the present inventors, it was found that this agglomeration phenomenon occurs extremely easily in an H2 atmosphere, but does not occur at all or is extremely unlikely to occur in other atmospheric gases such as N*, Ar, He, O*, etc. Ta. In addition, P, As, B are added to the non-single crystal thin film to be aggregated.
, It was also found that doping with impurities such as Sn accelerates the aggregation reaction.

When seeds 13 are formed using an aggregation reaction, the seed nucleus density is controlled by changing the thickness of the thin film before aggregation. In other words, as shown in FIG. 5(a), if the thickness of the thin film 12 before treatment is small, seeds 13 that are finely divided and aggregated after heat treatment are obtained, resulting in a high nuclear density.

On the other hand, if a thick film is used, the seeds 13 will aggregate into a large volume per seed 13 as shown in FIG. 5(b), resulting in a decrease in the density of nuclei.

An example of controlling the nuclear density of species 13 is shown in FIG.

Figure 6 shows the relationship between the thickness of the original polycrystalline SL thin film and the average internuclear distance of the seeds obtained after agglomeration, after depositing polycrystalline Si on 5ins and coagulating it. It is something that The nuclear density at this time is equal to the reciprocal of the square of the average internuclear distance. Note that when impurities are doped into a polycrystalline Si film, a relatively thick film of 4000 particles becomes about 1000 particles in an H2 atmosphere.
It has been confirmed through experiments by the present inventors that agglomeration occurs when annealing at a temperature of 400 Å or less, and that thin films of 400 Å or less can be agglomerated by annealing at a relatively low temperature of about 850 ℃ (the melting point of Si is about 1450 Å). ℃). Further, when the film thickness of polycrystalline SL exceeds 0.5 μm (5000 people), it becomes difficult to aggregate, and when it exceeds about 1 μm, aggregation tends to no longer occur.

Substances that cause aggregation include, in addition to Si, semiconductor elements such as Ge and Sn, compound semiconductors such as GaAs, and even 5i.
-Ge, mixture of 5i-3n etc., Au, Ag, C
u, Pt, metals such as Pd, Pt-3L, In-3
There are alloys such as n, etc., and any other substance that easily aggregates may be used.

The "agglomeration" phenomenon in the present invention refers to a phenomenon in which atoms move in a solid phase in order to minimize the surface energy of a substance or to relieve internal stress.

(c) Returning to the process diagram in Figure 1 again, step (c)
Explain. In (c), an amorphous semiconductor 3 is deposited to cover one type of crystal growth 2 obtained in step (b). This is plasma CVD.

This is realized by methods such as LPGVD and sputtering.

(d) Next, this is annealed in a temperature range lower than the crystallization start temperature of the amorphous semiconductor material deposited in (c) and higher than the growth start temperature. Then, growth occurs from the seed 2 placed in advance, but no new nuclei are generated from within the amorphous layer, so the initial density of nuclei is maintained.

(e) As the growth continues, the grown single crystal grains 4 collide with each other, forming a Grain Boundary.
y (grain boundary) 5 is formed and growth is stopped. At this time, the average particle size G, S is the nucleus density of the seed initially formed in step (b), N, D, and when closed, G, S, = 1
/ N, D.

It becomes a relationship.

A crystalline semiconductor film can be formed as described above.

〔Example〕

The present invention will be explained below using examples.

Example 1 This will be explained using FIG.

(a) A quartz substrate was used as the base.

(b) Deposition was performed using a CVD apparatus under the following conditions.

・Gas components SiH, C12/HCI/H.

・Flow rate 0.53 / 0.80 /100 (
fl/m1n) Temperature: 950° C. Pressure: 150 Torr Deposition time: 120 seconds As a result, a substrate containing Si species with a nucleus density of lXl0'/am'' was obtained.

(C) 15% of amorphous Si is deposited on the above substrate by LPCVD.
00 people deposited. The conditions at this time were: - Gas component: SiH4 - Flow rate: 50 SCCM - Temperature: 560°C - Pressure: 0.3 Torr.

(d) Next, in the above-mentioned base N2 atmosphere, at 590 °C
After annealing for a period of time, a crystalline SL thin film as shown in (e) was obtained. The average particle size at this time was 3.3 Bm, and the variation in particle size was extremely small.

Example 2 Similarly, explanation will be given with reference to FIG.

(a) The surface of a 4-inch wafer is used as a base at a depth of 2000
The material oxidized to Å was used.

(b) 30% polycrystalline SL was deposited on the above substrate by LPGVD.
0 Å deposited, and then heat-treated at 1000°C for 60 seconds in a N2 atmosphere, it became a single crystal in the form of islands due to an agglomeration reaction, forming crystal grains (seeds) with an average internuclear distance of 0.4 μm.
was gotten. In addition, the nuclear density at this time is 6.3X10'
pcs/am”.

(c), (d), (e) Crystalline SL thin films were obtained in the same manner as in Example 1 below. The average grain size of the obtained thin film was 0.4 μm, which is equal to the average internuclear distance.

Example 3 Similarly, as explained in FIG.
I used something that had been oxidized to humans.

(b) 50% polycrystalline Ge is applied onto the above substrate by sputtering.
0 Å deposited, which was then heated at 820°C for 6 hours in a N2 atmosphere.
When heat treated for 0 seconds, it was single-crystalized into islands due to an aggregation reaction, and crystal grains (seeds) with an average internuclear distance of 0.8 μm were obtained. In addition, the nuclear density at this time is 16 XLO'
The number/C was .

(c), (d), (e) Crystalline Si thin films were obtained in the same manner as in Example 1, that is, by a heteroepitaxial solid-phase growth method in which SL crystals were grown from Ge nuclei. The average grain size of the obtained thin film was 0.8 μm, which is equal to the average internuclear distance.

[Effects of the Invention] According to the present invention, "seeds" for solid phase growth on an amorphous insulator can be formed.
By arranging a material (growth starting point) at an arbitrary nucleus density and growing semiconductor crystals in a solid phase only from that seed, i) controlling the grain size and its distribution in the crystalline semiconductor film with good controllability; Now I can do it.

ii) Since "R type" can be formed in an extremely short time using a general semiconductor device, production efficiency is improved compared to a formation method that requires an incubation time of several hours to several tens of hours. It has also become possible to achieve reproducibility in production.

[Brief explanation of drawings]

Figure 1 is a schematic process diagram showing the formation method of the present invention, Figure 2 is a diagram showing the process of forming a polycrystalline film, and Figure 3 is the HC1 flow rate and SL nuclei on 5i02 or 5t3N4 by CVD method. Figure 4 is a diagram showing the agglomeration process of a thin film. Figure 5 is a diagram showing changes in the average internuclear distance when agglomerated as the thickness of the thin film is changed. FIG. 6 is a correlation diagram showing the relationship between the thickness of a polycrystalline SL thin film and the average internuclear distance of aggregated seeds (nuclei). 1... Substrate 2... Species

Claims (1)

[Claims] 1. After placing a single crystal seed on a substrate having a surface made of an amorphous insulator, and then depositing an amorphous semiconductor on the substrate so as to cover the seed. , a method for forming a crystalline semiconductor film in which crystals are grown in a solid phase by heat treatment, wherein the single crystalline seed is a crystal nucleus generated at the initial stage of the process of forming a deposited film by a vapor phase method. Alternatively, a method for forming a crystalline semiconductor film in which a thin film disposed on the substrate is single-crystalized into an island shape by an aggregation reaction. 2. The method for forming a crystalline semiconductor film according to claim 1, wherein the temperature of the heat treatment is a temperature that allows crystal growth from a single crystalline seed as a starting point, but does not generate crystal nuclei in the amorphous semiconductor. .