JPS61264716A - Recrystallizing method of polycrystalline silicon on insulating substrate - Google Patents

Abstract

PURPOSE:To enhance the reliability by placing an insulating substrate on a susceptor formed with recesses on a special part, melting a polycrystalline Si by the heat of the susceptor due to the high frequency heat, and solidifying the Si layer part above the recesses from the center. CONSTITUTION:A plurality of recesses 24 are formed on a susceptor 21. The recesses 24 correspond to the prescribed region for a semiconductor element formed in the following steps. An insulating substrate 23 attached with a polycrystalline Si film 22 is placed at the set position on the susceptor 21. The susceptor 21 is heated by the high frequency heat 12 in an inert atmosphere to melt the film 22. Then, when the heated state is altered to a cooled state, the melted part above the recesses starts solidifying from the center. When the cooling is further advanced, the melted Si part of a semiconductor element forming region is solidified from the center to start crystal growth, thereby forming the special part in one crystal grain range. Since the Si film part above the contacting position is melted and recrystallized, the film part becomes to contain slightly larger grain diameter than that at the initial time.

Description

[Detailed Description of the Invention] [Summary] In order to recrystallize a polycrystalline silicon film on an insulating substrate to form a region without grain boundaries, a susceptor having a recess corresponding to this region is heated with high frequency. The polycrystalline silicon film on the insulating substrate placed thereon is melted and solidified from the center of the polycrystalline silicon film portion above the recess.

[Industrial application field]

The present invention relates to an SOI substrate (Si
licon On Insulating 5ubst
More specifically, it relates to a method of recrystallizing a polycrystalline silicon film on an insulating substrate to form a region for forming a semiconductor element.

[Conventional technology]

The insulating substrate is fused silica (i.e. quartz glass, Si
A polycrystalline silicon film is formed by chemical vapor deposition (CVD) on a substrate of O Melting and recrystallizing crystalline silicon films has been performed in the following manner. As shown in FIG. 5, a carbon susceptor 2 having an elongated protrusion 1 is prepared, and quartz plates 3 having a thickness equal to the height of the protrusion are placed on both sides of the protrusion 1. The dimensions of the protrusion 1 are, for example, approximately 500 μm in lfi width and height. A fused silica insulating substrate 5 having a polycrystalline silicon film 4 is mounted on the susceptor 72 (that is, on the protrusion 1 and the quartz plate 3), and is slid from one end of the insulating substrate 5 to the other end. The projections 1 are brought into contact with each other in sequence.

The susceptor 2 is heated with high frequency to melt only the portion of the polycrystalline silicon film 4 above the protrusion 1 of the susceptor 2, and the quartz plate 3 is melted.
The temperature of the upper polycrystalline silicon film portion can be a little lower than the melting point of silicon. Therefore, the polycrystalline silicon film on the insulating substrate 5 can be recrystallized by the zone melting method, and as a result, the silicon grain size (g
rain 5ize). This means that SO
Various methods of forming a silicon single crystal film on an insulating film (or substrate) as I technology (for example, Kazuo Maeda, latest L
Although it is not possible to achieve single crystallization as in SI Process Technology, (1983), p. 632 (see Kogyo Kenkyukai), the aim was to make the semiconductor element formation region free of grain boundaries.

[Problem that the invention seeks to solve]

Although the above-mentioned recrystallization of a polycrystalline silicon film can considerably increase the size of each silicon grain, it is not possible to intentionally make a specific region where a semiconductor element is formed without grain boundaries.

[Means to solve the problem]

In the present invention, a specific portion of a polycrystalline silicon film on an insulating substrate (
In order to make the susceptor (region) a silicon crystal without grain boundaries, a recess is formed in the susceptor to be radio-frequency heated at a location corresponding to this specific part, an insulating substrate is placed on the susceptor, and the susceptor is heated by radio-frequency heating. The polycrystalline silicon film is melted by heat and solidified from the center of the polycrystalline silicon layer above the recess to recrystallize the entire polycrystalline silicon film.

[For production]

In order to solidify from the center of a specific polycrystalline silicon layer, when heating and melting the polycrystalline silicon film,
The partially melted polycrystalline silicon film on the part of the insulating substrate that is in contact with the susceptor is melted by heating it to a higher temperature than the partially melted polycrystalline silicon film on the part of the insulating substrate that is not in contact with the susceptor (on the recess). Body temperature is not equalized. When the temperature of the molten material is lowered while there is a temperature difference, the center of the silicon molten material above the recess, where the temperature is the lowest, first becomes below the melting point, and solidification begins from there until at least upper part of the recess)
can be a part without grain boundaries.

〔Example〕

Hereinafter, the present invention will be described by way of preferred embodiments thereof with reference to the accompanying drawings.

As shown in FIGS. 1 and 2, a susceptor 21 to be subjected to high-frequency heating and an insulating substrate 23 with a polycrystalline silicon film 22 placed on the susceptor are prepared.

The insulating substrate 23 is made of fused silica and has a thickness of 400-500μ.
It is preferable that the plate has a thickness of m, and if it becomes thick, a sufficient temperature difference in the polycrystalline silicon film cannot be formed in heat transfer from the susceptor to the polycrystalline silicon film.

Quartz or glass can also be used as the material for the insulating substrate. Polycrystalline silicon film 22 is applied onto this insulating substrate 23.
is formed by a known method (CVD method, etc.), and the formed thickness is, for example, 0.4 μm.

The susceptor 21 is made of carbon, which is a material that can be heated by high-frequency heating and has a melting point higher than that of silicon (1420° C.), and is easily available and easy to process.

A plurality of recesses 24 are provided in this carbon susceptor 21, and these recesses 24 correspond to predetermined areas for semiconductor devices (MOS transistors, etc.) to be formed in a later process, and their depths are The depth is not particularly limited as long as the insulating substrate 22 does not come into contact with it, but it is a depth that is easy to process.

Recrystallization of polycrystalline silicon on an insulating substrate is performed as follows.

An insulating substrate 23 with a polycrystalline silicon film 22 is mounted on the susceptor 21 at a set position. The susceptor 21 is placed in an inert atmosphere, and the susceptor 21 is heated by applying power to a high frequency heating device (dielectric heating device). Heat from the susceptor 21 is transmitted to the insulating substrate 23 through contact points other than the recesses, and further to the polycrystalline silicon film 22. For this reason, heat transfer is slower in the polycrystalline silicon film 22 above the recess 24 than in the contact area, and the temperature is a little lower.

Therefore, as a preheating step, the entire polycrystalline silicon film is
It is preferable to maintain the temperature at 0°C. Furthermore, the polycrystalline silicon film 22 is melted by heating to a temperature higher than the melting point of silicon. The temperature profile of the polycrystalline silicon film, that is, the melt 1 at this time, is as shown in FIG. 3(B). When heating, a rapid temperature rise can cause the insulating substrate to warp or the polycrystalline silicon film to peel off depending on the thermal expansion coefficient of the material, which disturbs the prescribed heating of the polycrystalline silicon film. Heating is performed by gradually increasing the power as shown in FIGS. 4(A) and 4(B).

Next, when the high-frequency power is lowered or cut off to transition from the heating state to the cooling state, the cooling rate of the molten material above the contact point with the susceptor 21 is faster than that of the molten material above the recess 24. No, a temperature profile as shown in FIG. 3(C) will be obtained. This means that solidification begins from the center of the molten part above the recess, and even though the temperature above the recess and the contact point is decreasing, the temperature above the contact point is still low. It is a molten body. As the cooling progresses further, the temperature profile of the silicon film recrystallized from the molten state as shown in FIGS. 3(D) and 3(E) is obtained. In such recrystallization, the silicon melt in the upper part of the recess, that is, in the semiconductor element formation area, solidifies from the center and crystal growth begins, and this specific part (region) is divided into one crystal grain range. It can be within. Since the polycrystalline silicon film portion at the position above the contact undergoes a melting and recrystallization process, the polycrystalline silicon film portion becomes a polycrystalline silicon film portion whose grain size is somewhat larger than the initial one. In this way, the polycrystalline silicon film on the insulating substrate is melted and recrystallized.
An OI substrate is obtained.

〔Effect of the invention〕

When a polycrystalline silicon film on an insulating substrate is recrystallized by controlling the temperature distribution of the film to be recrystallized as described above according to the method of the present invention, a specific portion to be a semiconductor element formation region is There can be no crystalline parts. Therefore, a Sol substrate on which highly reliable semiconductor elements can be formed can be obtained.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a schematic cross-sectional view of a susceptor and an insulating substrate with a polycrystalline silicon film mounted thereon for explaining the recrystallization method according to the present invention, and FIG. 3(A) is an enlarged sectional view of portion 1[rA of FIG. 1; FIG. 3(B) to FIG. 3(E) 4(A) and 4(B) show the temperature distribution (profile) of the polycrystalline silicon film over time in FIG. 3(A), and FIG. 4(A) and FIG. FIG. 5 is a schematic cross-sectional view of a susceptor and a mounted substrate for explaining conventional recrystallization of a polycrystalline silicon film on an insulating substrate. 21... Susceptor, 22... Polycrystalline silicon film, 23... Insulating substrate, 24... Recess, M, P,... Melting point of silicon. Fig. 1 A diagram explaining the recrystallization method according to the present invention Fig. 2 A plan view taken along line nn in Fig. 1 21-m-susceptor 24-one recess

Claims (1)

[Claims] 1. Steps (a) to (e): (a) Step of forming a polycrystalline silicon layer on an insulating substrate; (b) A susceptor having a recess in a portion corresponding to a semiconductor element formation region (c) heating the susceptor by high-frequency heating and melting the polycrystalline silicon layer with the heat; (d) the polycrystalline silicon above the recess; a step of recrystallizing the entire polycrystalline silicon layer without forming crystal grain boundaries in the region by solidifying it from the center in a region where a semiconductor element is formed in the layer; Method of recrystallizing silicon. 2. The method according to claim 1, wherein the heating is performed by gradually increasing the electric power of the high-frequency heating.