JPH0324719A - Forming method of single crystal film and crystal products - Google Patents

Abstract

PURPOSE:To easily form a single crystal Si film whose orientation is arranged in order, by utilizing selective epitaxial growth of an Si wafer, setting the window size, the mask thickness, and the pitch between windows, etc., at suitable values, eliminating a mask, oxidizing the whole part, and polishing the adequate amount of crystal. CONSTITUTION:Crystal growth processing is performed on a silicon substrate wherein a silicon wafer 1 surface is exposed from a minute aperture part of a mask 2 formed on the silicon wafer 1 surface, and single crystal 3 is grown in the mask 2 surface, from a minute exposed surface. The mask 2 is eliminated, a substratum is subjected to oxidizing process, and polishing is performed from the edge of the grown single crystal side. That is, by a series of the above treatments, the grown part by selective epitaxial growth and lateral direction growth can be electrically isolated from the initial Si wafer 1. Further, by performing polishing from above so as to slightly leave the grown part, an Si single crystal film 3 having the same face orientation as the original Si wafer 1 can be formed. Thereby an Si single crystal film wherein not only the face orientation of each region but also the orientation in a face are arranged in order can be easily obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for forming a single crystal film on an oxide, and specifically relates to a method for forming a single crystal film on an oxide, and more specifically, a single crystal film used in electronic devices such as semiconductor integrated circuits, surface acoustic devices, etc. Regarding membranes.

BACKGROUND OF THE INVENTION Generally, when thin films are deposited on non-quality insulating substrates such as SiOg, the crystal structure of the deposit is amorphous or polycrystalline due to the lack of long-range order in the substrate material. Here, an amorphous film is a film in which short-range order at the level of the nearest neighbor atoms is preserved, but no longer-range order, and a polycrystalline film is a film that has a specific crystal orientation. It is a film made up of single crystal grains that are isolated and aggregated by grain boundaries. For example, when forming St polycrystals on SiOi by the CVD method, if the deposition temperature is below about 580°C, it will result in poor quality silicon, and if the temperature is higher than that, the grain size will be several hundred to
It becomes polycrystalline silicon distributed between several thousand pieces. however,
The grain size and distribution of polycrystalline silicon vary greatly depending on the formation method.

Furthermore, by melting and solidifying non-quality or polycrystalline films using thermal energy such as a laser or a rod-shaped heater,
Polycrystalline thin films with large grain sizes on the order of microns or millimeters have been obtained (Single Crystal Si
licon on non-single-cryst
alInsulators, Journal of C
crystal growth vol. 63. No. 3
, October 1983 edited by G
J. Cullen). A transistor was formed in the thin film of each crystal structure formed in this way, and the electron mobility was measured from its characteristics, and when compared with the electron mobility in single crystal silicon, it was found that the electron mobility due to melting and solidification ranges from several micrometers to several am. For polycrystalline silicon with a grain size distribution of , it is about the same as that for single-crystal silicon, and for polycrystalline silicon with a grain size distribution of several hundred to several thousand, it is about 10-'' of single-crystal silicon, In addition, non-quality silicon is 2x10” of single crystal silicon.
An electron mobility of about ' is obtained. These results show that there is a large difference in electrical properties between devices formed in single crystal regions within crystal grains and devices formed across grain boundaries. In other words, the deposited film of poor quality obtained by the conventional method has an amorphous or polycrystalline structure with a grain size distribution, and the device fabricated there has a
Its performance is significantly inferior to devices fabricated using single crystal layers. Therefore, its applications are limited to simple switching elements, solar cells, photoelectric conversion elements, etc. Therefore, in order to form high-performance electronic devices, semiconductor single-crystal thin films with no grain boundaries or with controlled grain boundary positions are required. As an example of a non-quality SL single crystal thin film without grain boundaries, SO
S (Silicon on Sapphire) and SIMOX (Separation by Impla)
ntation of Oxygen), lamination,
Oxidation separation (USP 4,361,600) has been reported, and JP-A-63-107016 has been reported as a method for forming semiconductor thin films with controlled grain boundary positions. SOS uses sapphire (single crystal AI!) on the substrate. (Os), and SL is heteroebitaxially grown on its surface. This technique has the problems that the sapphire substrate is very expensive and that Al, which is a component of the substrate, diffuses into the Si film. SIMOX implants high-energy O'' (oxygen ions) into a Si wafer and anneales it to reduce the SL on the surface.
While maintaining the single crystal structure of Sin. This is a technology for forming the intermediate layer of This technology uses very high energy and implants highly concentrated oxygen ions, resulting in poor throughput and high temperatures. Because annealing is required, stress on the substrate is a concern. In addition, the bonding technology consists of two sheets of S with oxidized surfaces.
I-wafers, or two Si wafers, one oxidized and the other not, are bonded together and annealed to make them adhere at the atomic level, and polished from one side to form a thin Si layer. This is a method of forming a single-crystal Si thin film in which polishing is stopped when a . This method is expensive because it polishes most of one wafer, and it also requires polishing a wafer that originally has uneven thickness and stopping polishing at a position where only a small amount of the Si layer remains. Therefore, it is extremely difficult to control. Oxidation separation involves forming irregularities on the surface of the St wafer, applying a mask to the top and side surfaces of the convex parts, and then oxidizing the entire wafer. As a result, oxidation progresses from the unmasked portion, and the entire convex portion is insulated from the substrate side by SiO2. However, although this method provides an SOI structure, the St layer is separated into a bulk instead of a thin film. Even if this is polished, an St single crystal thin film cannot be obtained because the interface between SiOi and Si is not flat.

In addition, for the method limited by the board as described above,
There is also a method of obtaining a semiconductor single crystal thin film with controlled grain boundary positions, which is not limited by the substrate, as disclosed in JP-A-63-107016. This method uses two types of non-quality materials with different nucleation densities to form semiconductor single crystal nuclei at arbitrary points, performs selective growth, causes the grown crystals to collide with each other at arbitrary positions, and forms grain boundaries. can be formed.

[Problems to be Solved by the Invention] As described above, while each of the above conventional examples has excellent features, they also have many problems. Therefore, the purpose of the present invention is to (1) use relatively inexpensive S1 wafers, (2) use common equipment and common processes, and
(2) To provide a Si single-crystal film that is insulated and isolated at any in-plane area, and in which not only the plane orientation but also the in-plane orientation of each region is aligned. [Means and effects for solving the problem] According to the present invention, a substrate in which the surface of a silicon wafer as a base material is exposed through a minute opening of a mask formed on the surface of a silicon wafer is subjected to crystallization or lengthening treatment, and A single crystal is grown on the mask surface from a minute exposed surface, the mask is removed, the substrate is subjected to oxidation treatment, and the substrate subjected to the oxidation treatment is polished from the side of the grown single crystal. A method for forming a single crystal film, a crystalline article obtained by the method, and a substrate having a mask having minute openings and a base material made of a single crystalline material subjected to a crystal growth treatment. , growing a single crystal through the opening, removing the mask from the base, subjecting the base to oxidation treatment, and polishing from the side of the grown single crystal opposite to the base material side. A method for forming a crystalline film is provided. The present invention is directed to selective epitaxial growth (SEG) of, for example, an SL single crystal from an opening with a minute area using, for example, silicon oxide as a mask.
xialGrowth) and lateral growth (E L O
:EpitaxialLateral Overg
After growth, the mask is removed and the entire surface is oxidized to electrically separate the SEG-ELO grown portion from the original St wafer, and the top surface is polished to leave a small portion of the grown portion. By doing this, an SL single crystal film having the same plane orientation as the original Si wafer is formed on the silicon oxide. [Embodiment Example] Next, an embodiment example of the present invention will be explained using FIG. In FIG. 1(a), for example, the surface of a Si wafer 1 as a base material is thermally oxidized and silicon oxide (SiO*) is applied to a mask 2.
Suppose that As will be described later in FIG. 1(b), the thickness of the mask is determined by the fact that etchant may enter the gap between the growing crystal and the St wafer surface even when the crystal is ELOLed. thickness, i.e. 0.1 u
The thickness is preferably 0.5μ or more, more preferably 0.5μ or more. In addition, when the mask material is obtained by thermal oxidation of St wafer, the upper limit of the mask thickness is 2 μm considering productivity.
A value of about m is appropriate. However, this is not the case if the mask material is formed not by thermal oxidation of St but by deposition by CVD or the like. However, if we consider filling the gap between the elongated crystal and the Si wafer by oxidizing it later, the upper limit is about 4μ.

The mask material does not need to be SiO2 as long as it can be easily etched with a liquid etchant such as a hydrofluoric acid (HF) solution or an etching gas such as a hydrofluoric acid gas. However, when growing, selective growth must be possible. For example, a silicon nitride film has a problem with respect to etching and selective growth. The fine surface of the wafer 1 is exposed by opening a part of the mask 2, which is disadvantageous compared to a mask but can be used, but the size of the opening is 1 μm or more and 4 μm in diameter.
m or less is preferable. This is because if the opening is less than lumφ, many crystals will be broken during the growth process,
Otherwise, there is a tendency for there to be points where it does not grow, and 4μ
This is because if mφ is exceeded, complete separation may not be possible when the mask is removed and the entire wafer is oxidized to insulate and separate the original wafer portion from the newly grown wafer portion. Therefore, it is more preferable that the smoke diameter is about 2μ±0.5μm.
The spacing (pitch) between the openings can be determined freely depending on the application. That is, it can be determined according to the element size when forming an element on the obtained single crystal film. Normally, the crystal size is between 20 μm and 100 μm, and if it exceeds 200 μm, it takes a long time for crystal growth. St wafers are (100), (110), (11
1), etc., should be determined according to the purpose. Since the crystal grows epitaxially, it has the same orientation as the wafer. FIG. 1(b) A crystal growth process is performed by a vapor phase method such as CVD or PVD to obtain an SL crystal 3. in general,? A gas system that allows selective growth is S using H2 as a carrier gas.
There are chlorosilanes such as iC14, SiHClx, and SiH*Clz, and silanes such as SiH4 and SitHa, to which an etching gas such as HCI may be added. For example, in the case of a thermal CVD method, the pressure is preferably several Torr.
From 250 Torr. It is often carried out under reduced pressure, more preferably from 50 Torr to 170 Torr, optimally about 100 Torr, and at a temperature preferably in the range of 850 to 1200°C, more preferably in the range of 900 to 1050°C (the optimum temperature depends on the temperature used). (Varies greatly depending on the type of gas used.) Figure 1 (C) The mask material is etched using the wet method.
For example, if the mask material is SiO2, the etchant can be easily removed using a hydrofluoric acid (HF) solution. Figure 1 (
In the base body 4 obtained by removing the mask in c), the original wafer itself is referred to as a wafer portion 5, and the portion formed further above the upper surface of the wafer portion is referred to as a growth portion 6.

FIG. 1(d) The substrate 4 is thermally oxidized to obtain an S1 oxide 7. It is desirable that this oxidation treatment be carried out until all portions of the growth portion 6 corresponding to the original mask openings are oxidized and the wafer portion and the growth portion are completely insulated and isolated. FIG. 1(e) Polishing is performed from the upper side of the growth portion 6. This polishing may be performed in the same manner as a normal wafer polishing process. Polishing is carried out after the layer of SL crystal 3 in the long part is exposed.
It is only necessary to leave a desired Si film thickness until the L layer disappears.

[Example] Hereinafter, the present invention will be explained by examples using the drawings.

Example 1 In this embodiment, FIGS. 1 to 3 are used.

1. First, a 4-inch Si wafer with a (100) orientation was prepared. The surface of this Si wafer was oxidized to a thickness of 1.2 μm in an OS+OA atmosphere.

Next, as shown in Figure 2, tiny square areas (hereinafter referred to as ``windows'') as openings were patterned on the lattice points. At this time, the size of one side of the square (the value of a in Figure 2) is 2.0 μm, and the space between the windows? (The value of b) was set to 50 μm in both the vertical and horizontal directions. Then, the SiO■ in this window area was etched with a dilute hydrofluoric acid solution, as shown in Figure 1(a).
A Si wafer with a mask was formed as shown in the figure. 2. Next, the masked Si wafer was subjected to selective epitaxial growth (SEG) treatment. The conditions at this time are as follows. Gas type SiHa (: 1g/HCI/H. Gas flow rate
0.53/1.9/100 (J2/min) temperature
Temperature: 1030° C. Pressure: 100 Torr Growth time: 80 minutes As a result, crystals as shown in FIG. 1(b) were grown. When viewed from above the wafer, it looks like FIG. 3. In FIG. 3, the size of b is 50 μm, which is the same as the interval between windows, and a characteristic square pyramid structure surrounded by (311) planes was observed at the top. Furthermore, when growing under the above conditions, adjacent growing crystals collide with each other at the bottom, but there are "voids" in the four corners of the crystals with a diagonal length of approximately 20 L.
LLIl's? A square-shaped void remained. That is, there is no grown Si crystal in this part, and the surface of the SiO2 mask is exposed.

3. Next, the wafer subjected to the crystal growth process was immersed in a concentrated hydrofluoric acid solution for 20 hours to etch the mask.
) was obtained.

4. This substrate was placed in an H2+0■ atmosphere and oxidized under the same conditions as when the mask was first formed.
As shown in figure (d), the SL of the growth part is the SL of the wafer part.
An S1 island completely separated by SiO■ was formed. Incidentally, adjacent crystals collided with each other at their bases, but because the contact area was small and the contact surface was oxidized more (faster) than the others, the crystals were oxidized as shown in Figure 1 (d). , the grown crystals were completely isolated from each other. 5. Next, the substrate subjected to the oxidation treatment is polished from the top surface of the grown crystal using a normal wafer polishing process, that is, mechanical boring (lapping) using abrasive grains, and then mirror-finished using chemical boring. A single crystal S with a length and width of about 50×50μ1 and a thickness of 0.5μm as shown in Figure 1(e)
An L thin film was obtained.

Example 2 In this embodiment, FIGS. 1 to 5 are used.

1. First, a 5-inch wafer with the (ill) orientation was prepared, and its surface was oxidized to a thickness of 1.5 μm. As shown in FIG. 2, the oxide film is patterned to form a window.

However, the shape of the window was circular, and its diameter was 2 μm. In addition, the interval between windows was set to 30ufl+. After patterning, the window portion was etched with dilute hydrofluoric acid in the same manner as in Example 1 to obtain a wafer with a mask as shown in Figure 1(a). 2. Next, the wafer was subjected to selective epitaxial growth treatment. The conditions are as follows. Gas type SiH*(:
lx/HCI/Ha gas flow rate 0.53/2.5/1
00 (I2/min) Temperature: 990°C Pressure: 100 Torr Growth time: 90 minutes Observing the initial stage of this growth, the SE of the (111) wafer
G grew a hexagonal crystal with a flat surface as shown in Figure 4. In the figure, 21 is a Si wafer, 22 is a mask (S
ins). As the growth continued, the crystals collided with each other while the surface remained flat, as shown in Figure 5. At this time, when I observed it from the top, I found that a diamond-shaped void similar to that shown in Figure 3 had also been formed. The size of this void was about 10 μm in diagonal length.

3. Next, the wafer subjected to the crystal growth process was immersed in concentrated hydrofluoric acid for 20 hours to completely remove the oxide film mask.

4. Next, this substrate was :0. It was placed in an oxidizing atmosphere of 3:2 and oxidized at 1000° C. for 8 hours to oxidize the (111) plane by 1.2 μm.

5. Next, the substrate subjected to the oxidation treatment was polished from the top surface of the grown crystal to obtain a single crystal Si thin film with a thickness of 0.5 μm and aligned with the (Ill) plane.

[Effects of the invention] As explained above, by using SEG of Si wafer, it is possible to set the window size, mask thickness, pitch between windows, etc. to appropriate values, and to completely remove the mask. By performing a series of steps including oxidizing the whole by an appropriate amount, and polishing the crystal by an appropriate amount, a single crystal Si film separated into a relatively large area and with perfectly aligned orientations can be created. Now you can get it. Moreover, if the method of the present invention is used, a single crystal SL film can be obtained easily and at a much lower cost than SOS or SIMOX, which similarly form a single crystal SL film on Stow or other non-quality insulators. Since element isolation, which is always necessary during element formation, is automatically performed in the process of the present invention, and the element isolation width can be small,
It has many advantages, including the ability to increase the degree of integration of electronic devices. In addition, the crystallinity of the film is extremely good, and SOS%SIM
OX, it is equivalent or better than laser melted crystal.

[Brief explanation of drawings]

Fig. 1 is a process diagram showing the method of forming a single crystal film of the present invention, Fig. 2 is an example of a pattern of a mask opening, and Fig. 3 is a (10
0) A diagram showing a grown crystal when performing SEG of a crystal. Figures 4 and 5 are diagrams showing crystal growth when performing SEG of a (111) crystal. Figure 4 shows an initial crystal. FIG. 5 shows a grown crystal.

Claims (1)

[Claims] 1. A crystal growth process is performed on a substrate in which the surface of the silicon wafer as a base material is exposed through a minute opening of a mask formed on the surface of the silicon wafer, and the mask surface is grown from the minute exposed surface. A method for forming a single crystal film, which comprises growing a single crystal thereon, removing the mask, subjecting the substrate to oxidation treatment, and polishing the oxidized substrate from the side of the grown single crystal. . 2. A crystal article obtained by the method of claim 1. 3. Performing crystal growth treatment on a substrate having a mask having minute openings and a base material made of a single crystalline material,
A single crystal characterized in that: a single crystal is grown through the opening, the mask is removed from the base, oxidation treatment is performed on the base, and the grown single crystal is polished from the side opposite to the base material side. How to form a film. 4. The method for forming a single crystal film according to claims 1 and 3, wherein the crystal growth treatment is a vapor phase method. 5. The method of forming a single crystal film according to claims 1 and 3, wherein the mask is a silicon oxide film. 6. The method of forming a single crystal film according to claims 1 and 3, wherein the thickness of the mask is 0.1 μm or more and 4 μm or less.