JPS6352407A - Manufacture of semiconductor substrate - Google Patents

Abstract

PURPOSE:To enable single-crystal silicon of a large area to be formed on an insulating layer without occurrences of condensation, depletion, and cut-out stages, by forming a heat absorptive layer or a high-heated conductivity layer on the upper part of a polycrystal or amorphous semiconductor layer through an insulating layer having a partial opening. CONSTITUTION:A mask resisting an atmosphere of oxide such as silicon nitride is mounted on a partial surface of a silicon substrate 1 and followed by heat oxidation, so that a silicon oxide film 20 is formed on the surface. Successively, the mask of silicon nitride is removed to expose the surface part which is not oxidized and polycrystal silicon 30 is piled on this part by a vapor growth method. This polycrystal silicon 30 is recrystalized to become a single crystal in the later process, however, at that time the part, where the silicon on the substrate is exposed without being oxidized, functions as core crystal 4. After polycrystal silicon 30 is piled, a silicon oxide film 21 is piled by a vapor growth method and then the silicon oxide film, which is formed in the area a little larger than the area of the core crystal 4, is removed and then a polycrystal silicon 31 is piled again. After such composition, the polycrystal silicon 30 is dissolved and recrystalized.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a structure in which a single crystal semiconductor layer is formed on an insulator, so-called S○I (Silicon on In5ul).
ator).

[Conventional technology]

As a method of forming a single crystal semiconductor layer on an insulator, a polycrystalline or amorphous semiconductor layer is deposited on the insulator, and then heated and melted using a laser, electron beam, or infrared rays, and recrystallized. method is known. In this method, in order to obtain a large-area single crystal semiconductor layer, a seed crystal is prepared, the part adjacent to the seed crystal is melted, and the f4 melted part is scanned to promote single crystal growth. It will be done.

When silicon is used as the semiconductor layer, a common method is to form an insulating layer on the surface of a silicon substrate, open a window in a portion of the insulating layer, and use the window portion as a seed crystal. Related structures of this type include, for example, JP-A-56-80125 and JP-A-57-4592.
Examples include No. 0.

[Problem that the invention seeks to solve]

In the above-mentioned conventional technology, an important issue is to reliably propagate the crystal orientation of the seed crystal when molten silicon recrystallizes. Usually, polycrystalline amorphous silicon deposited on an insulating layer with a window formed in a part of the surface of a silicon substrate has a step difference between the window, that is, the single crystal silicon of the silicon substrate and the insulating film. Therefore, it is first necessary to melt and recrystallize polycrystalline silicon on single crystal silicon to form a single crystal, and to propagate this crystal orientation over the step onto the insulating layer. However, thermal conductivity is different between silicon and the absolute amorphous layer (usually a silicon oxide film is used), and because silicon has a high thermal conductivity, heat applied to polycrystalline silicon on single-crystal silicon escapes to the silicon substrate. Therefore, melting the polycrystalline silicon here requires greater energy than melting the polycrystalline silicon on the insulating layer. As a result, excessive heat is applied to the polycrystalline silicon on the insulating layer, causing molten silicon to aggregate on the insulating layer, and as a result of this reaction, depleted areas with no silicon are formed, and steps are cut off. However, there was a problem in that single crystal growth was inhibited.

The purpose of the present invention is to melt and recrystallize polycrystalline or amorphous silicon on a seed crystal and an insulating layer without causing silicon agglomeration or two-step depletion during melt-recrystallization, and to melt and recrystallize a silicon substrate. The objective is to realize single crystal growth with propagated crystal orientation.

[Means for solving problems]

The above purpose is to heat the polycrystalline silicon on the insulating layer as much as necessary to melt it without applying excessive energy; This is achieved by varying the amount of heat given to each part so as to provide enough heat to compensate for this.

Polycrystalline silicon on single-crystal silicon or on an insulating layer is heated from above by laser, electron beam, infrared rays, or the like. Therefore, by providing the polycrystalline silicon with a substructure or a substructure, it is possible to control the thermal energy provided.

The first method is to provide a film that reduces or absorbs heat on the polycrystalline silicon on the insulating layer, and on the polycrystalline silicon on the monocrystalline silicon, no such film is provided or the heat is absorbed first. The structure is such that part of the heat is given to polycrystalline silicon on single-crystal silicon. A second method is to provide a film below the polycrystalline silicon on the insulating layer that directs the thermal energy toward the polycrystalline silicon on the single-crystal silicon.

[Effect]

In the first method, the upper structure is the upper part of the polycrystalline silicon on the insulating layer through a film with low thermal conductivity such as a silicon oxide film; This refers to a directly provided film with good heat absorption or a film with high thermal conductivity. Due to the presence of these films, the heat given to the upper part of the polycrystalline silicon on the insulating layer is reduced and given to the polycrystalline silicon, and part of the reduction is absorbed by a film with good heat absorption or a film with high thermal conductivity. Go through! ■Thermal energy flows into the polycrystalline silicon on the crystalline silicon, and the thermal energy is increased in this area. Since the distribution of thermal energy can be adjusted by adjusting the thickness of the upper structure, sufficient thermal energy can be applied to melt each polycrystalline silicon without being excessive.

The second substructure method involves providing a highly thermally conductive film on top of the insulating layer and extending it to the edge of the exposed window of single crystal silicon to create the same heat flow as above. The same effect occurs.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure shows the cross-sectional structure of a sample before being heat-treated to make polycrystalline silicon into a single crystal by recrystallization.

This structure is fabricated by the following steps. By providing a mask against an oxidizing atmosphere such as silicon nitride on a part of the surface of the silicon substrate 1 and performing thermal oxidation.

A silicon oxide film 2o is formed on the surface. The thickness of the silicon oxide film 20 was 1 μm. Thereafter, the silicon nitride mask is removed to expose the unoxidized portions, and polycrystalline silicon 30 is deposited by vapor phase growth. This polycrystalline silicon 30 is recrystallized in a later step to become a single crystal, but at this time, the exposed silicon portion of the substrate that is not oxidized functions as a seed crystal 4. After depositing the polycrystalline silicon 30, a silicon oxide film 21 is deposited by vapor phase growth, and a seed crystal 4 is deposited.
After removing the silicon oxide film in a slightly wider area, polycrystalline silicon 31 is deposited again. t, yt like this
After forming the polycrystalline silicon 30, the polycrystalline silicon 30 is melted and recrystallized.

Recrystallization is performed by heating with a laser, electron beam, halogen lamp, strip heater, or the like.

In this example, a carbon strip heater was used.

FIG. 2 is a schematic diagram of the paired crystallization treatment. To simplify the explanation of the principle, a single layer of polycrystalline silicon was used. Usually, the polycrystalline silicon 30 is covered with a silicon oxide film 22 to prevent evaporation. After preheating the entire sample substrate, bring the strip heater 5 close to the surface side and turn the heater to 1600℃~20oO
When heated to .degree. C., the polycrystalline silicon 30 is melted by the radiant heat and becomes molten silicon 6. Since the strip heater 5 has an elongated shape in the direction perpendicular to the plane of the paper, the molten silicon 6 also has a strip-like shape. Then, when the strip Peter 5 is scanned in the direction of the arrow 70 (at approximately 1/sec), the iF-shaped molten silicon moves and recrystallized silicon 80 is formed.

In order to control the crystal orientation of recrystallized silicon 33, it is necessary to place seed crystals 4 at various locations as shown in FIG. If this is applied, the silicon will aggregate into a round shape and break off, as shown in Figure 3. This is because the heat given to the polycrystalline silicon on the seed crystal 4 flows in the direction of the arrow 71, that is, toward the silicon substrate 1 side, because the thermal conductivity of silicon is higher than that of the silicon oxide film. In order to melt the crystalline silicon 30, thermal energy must be increased, so excessive heat is applied to the polycrystalline silicon 30 on the silicon oxide film 20, making it easier for the molten silicon to agglomerate due to surface tension. It is from.

The structure shown in Figure 1 above shows this type of agglomeration.

This prevents breakage. FIG. 4 shows the heat distribution during recrystallization with the structure shown in FIG. 1. Although recrystallization in this case also uses a covering silicon oxide film, it is omitted in the figure. In (a), the thermal radiation 9 of the strip heater is located in front of the seed crystal 4, and this radiant energy melts the upper layer polycrystalline silicon 31, and the heat spreads to the silicon oxide film 21 as indicated by the arrow 7.
1 to melt the underlying polycrystalline silicon 20, and simultaneously flow in the direction of arrow 73, that is, in the direction of the seed crystal 4, preheating the polycrystalline silicon 30 on the seed crystal 4. Next, when the radiant energy reaches the seed crystal, as shown in (b), the seed crystal 4 has not yet been sufficiently heated and has not melted, while the silicon oxide film 2o has not yet solidified and melted. The condition is maintained. Even in this state, a heat flux as indicated by the arrow 74 occurs. Next, when the thermal radiation 9 neglects the seed crystal part and melts the polycrystalline silicon 31 on the upper silicon oxide film 21 as shown in (c), the heat flux from here in the direction of the arrow 75 increases in the step (b). In addition to the heating, the polycrystalline silicon 3o on the seed crystal 4 is melted.

Then, as the radiant energy moves further away, it solidifies even on the seed crystal as shown in (d), recrystallization further extends onto the silicon oxide film 20, and the crystal orientation of the seed crystal is propagated.

The effects of this embodiment are as follows when compared with FIG. 2, which does not have two layers of polycrystalline silicon. In this embodiment, in order to melt the lower layer polycrystalline silicon 3o, the upper layer polycrystalline silicon 3o is melted.
This is done by indirectly giving the heat absorbed by 1. Therefore, excess thermal energy can be applied to the upper layer of polycrystalline silicon 31, and as a result, the heat flux in the direction of the seed crystal 4 can be made larger than in the case of a single layer in FIG. Polycrystalline silicon 30 can be easily melted. At this time, excessive thermal energy is applied to the upper layer polycrystalline silicon 31, and eventually two stages of agglomeration and breakage occur in the upper layer recrystallized silicon 81 as shown in FIG. 4(e), but this is not a problem. Further, the film thickness of the polycrystalline silicon on the seed crystal 4 is thicker for the upper layer and the lower layer, so that no break occurs in the recrystallized silicon 80 in the lower layer as shown in FIG. 4(e).

In addition, the polycrystalline silicon 3o in the lower layer is indirectly heated to the polycrystalline silicon 31 in the upper layer and is given appropriate thermal energy, so that agglomeration and depletion of the molten silicon are avoided, and as a result, the crystal orientation of the seed crystal is changed. single crystal growth with propagation is possible.

Next, another embodiment of the present invention will be described. Figure 5 shows a cross-sectional view of the sample structure before the recrystallization process.
Upper layer silicon oxide film 2 with a slightly wider window in the upper part
In this embodiment, a film with good thermal conductivity is formed on the carbon film 100. The action of this carbon film 100 is similar to that of the upper layer polycrystalline silicon 31 in the first embodiment, which weakens the thermal energy applied to the polycrystalline silicon on the lower layer silicon oxide film 20 than the radiant energy itself.
The amount of heat is required to melt the polycrystalline silicon on the silicon oxide film 20, and on the other hand, since the carbon film 100 itself is directly adhered to the polycrystalline silicon 30 on the seed crystal 4, a heat flux is generated in the direction of the seed crystal 4. Polycrystalline silicon 3 on seed crystal 4
It acts to give extra heat to 0. the result,
As in the first embodiment, polycrystalline silicon 3 on seed crystal 4
0 can be melted to prevent agglomeration and depletion of recrystallized silicon on the silicon oxide film 2o. In addition, is the surface covered with Z? In addition to carbon, high-melting point metals such as tungsten and tantalum can also be used for the film.

Further, another embodiment of the present invention is shown in FIG. This cross-sectional view of the sample also shows the structure before the recrystallization process.

This is a film with high thermal conductivity, in this case a tungsten film 200, placed near the window of the seed crystal 4 before depositing the polycrystalline silicon 30.
It has been established. The action of this tungsten film also generates a large heat flux in the direction of the seed crystal 4. In this case, the heat applied to the polycrystalline silicon 30 on the tungsten film is reduced by the generation of heat flux, but it is not reduced on the silicon oxide film, so that the molten silicon coagulates.

Dissipation requires control such as minimizing temperature. Note that tantalum or the like can also be used as the film with good thermal conductivity near the seed crystal 4.

In the above embodiments, a strip heater was used as the heat source for the recrystallization treatment method, but infrared heating using a laser, an electron beam, a lamp, etc. may also be used. With lasers, care must be taken because the absorption rate changes depending on the film thickness and film type. In addition, selective oxidation was used to open the window in seed crystal 4 to alleviate the step difference.
The silicon oxide film may be removed by etching. Furthermore, the layer to be recrystallized may be amorphous silicon as well as polycrystalline silicon. In addition to silicon, it can also be applied to other semiconductors, such as germanium and compound semiconductors.

〔Effect of the invention〕

According to the present invention, due to the action of heat flux by the upper or lower structure of the polycrystalline silicon to be recrystallized, the polycrystalline silicon on the monocrystalline silicon that is the seed crystal has an excess of Because the amount of heat is given, the crystal orientation of the seed crystal can be propagated by melting and recrystallizing, and since the polycrystalline silicon on the union edge layer is not heated excessively, Agglomeration of silicon, depletion due to its reaction, and especially step-cutting in the seed crystal area do not occur, and single crystal growth is achieved in the same direction as the crystal axis of the seed crystal due to the relative scanning of the heating source, resulting in a wide area. An area of single crystal silicon can be formed on the insulating layer.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing the substrate structure before recrystallization processing, which is the main structure of an embodiment of the present invention, Fig. 2 is an explanatory diagram of recrystallization processing, and Fig. 3 shows problems in the conventional technology. Schematic diagram shown, No. 4
The figure is a sectional view illustrating the recrystallization process which is the main process in one embodiment of the present invention, FIG. 5 is a sectional view showing the substrate structure in the middle of the main process in another embodiment of the present invention, and The figure is a sectional view showing a substrate structure in the middle of the main process of still another embodiment of the present invention. 1...Silicon substrate, 20.21...Silicon oxide film, 30.31...Polycrystalline silicon, 4...Seed crystal, 6...7 Molten silicon, 80.81...Recycle Crystalline silicon, 9...thermal radiation.

Claims (1)

[Claims] 1. In a method for manufacturing a semiconductor substrate in which a polycrystalline or amorphous semiconductor layer on an insulator is recrystallized, an insulator having a partially opened upper part of the polycrystalline or amorphous semiconductor layer is provided. A method for manufacturing a semiconductor substrate, characterized in that a heat absorption layer or a high thermal conductivity layer is provided between layers. 2. The method of manufacturing a semiconductor substrate according to claim 1, wherein the heat absorption layer is polycrystalline or amorphous silicon. 3. The method of manufacturing a semiconductor substrate according to claim 1, wherein the high thermal conductivity layer is made of carbon. 4. A method for manufacturing a semiconductor substrate in which a polycrystalline or amorphous semiconductor layer on an insulator is recrystallized, characterized in that a high thermal conductivity layer is provided in a part of the lower part of the polycrystalline or amorphous semiconductor layer. A method for manufacturing a semiconductor substrate. 5. The method of manufacturing a semiconductor substrate according to claim 4, wherein the high thermal conductivity layer is made of tungsten.