JPH04298023A - Manufacture of single crystal silicon thin film - Google Patents

Abstract

PURPOSE:To provide a method for manufacturing a single crystal silicon thin film of good electrical properties by using a plasma CVD device. CONSTITUTION:Reaction gas of SiF4:SiH4:F2 (gas ratio of 2:1:5, F/H ratio of 9:2) is supplied into a reaction chamber of high vacuum and a pressure thereof is regulated to 0.2Torr. The reaction gas is formed to plasma and a 2.0mum-single crystal silicon thin film 2 is formed on a single crystal silicon substrate 1 which is heated to 350 deg.C. In the manufacture method, the number of halogen atoms is regulated to be more than the number of hydrogen atoms; therefore, hydrogen concentration in the reaction gas is lowered, a surface of epitaxial growth is not covered excessively with hydrogen atom, and hydrogen is hard to be left in a formation film of single crystal silicon. Accordingly, it is possible to improve uniformity of crystal and to improve electric properties such as electron mobility.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for producing a single crystal silicon thin film, and in particular, the present invention relates to a method for producing a single crystal silicon thin film using a plasma CVD apparatus, in which a single crystal silicon thin film having excellent electrical properties such as electron mobility is required. It is about the method.

0002

[Prior art] Bipolar transistor, bipolar I
As a semiconductor material for C, MOS, LSI, memory, etc.
In recent years, single-crystal silicon thin films have attracted attention.

Conventionally, this single-crystal silicon thin film has been obtained by epitaxial growth using chemical vapor deposition, and thermal CVD.
D method is generally applied. For example, in the case of epitaxial growth of silicon, a silicon single crystal substrate is used as the substrate, and a single crystal silicon thin film is produced by thermally decomposing silane, chlorosilane, etc. diluted with hydrogen gas at a high temperature of 1000 to 1150 °C. ing.

However, recently, there has been an increasing demand for miniaturization in the production of bipolar ICs, and silicon single crystal substrates with high impurity (dopant) concentrations are used on silicon single crystal substrates of 0.5 to 1.0 mm.
There is a need to form an epitaxial layer as thin as 5 μm and with a low impurity concentration. Nevertheless,
As shown in FIG. 3, a single crystal silicon thin film b formed on a single crystal substrate a containing a dopant by a conventional thermal CVD method is caused by impurities contained in the substrate a being diffused into the single crystal silicon thin film b. There is a drawback that a transition region c with a thickness of 1.5 to 2.5 μm is formed at the critical interface between the epitaxial layer and the substrate a. Here, the region of the epitaxial layer in which the dopant in the single crystal substrate a is diffused by 10 ppm or more is defined as the transition region. For this reason, conventional methods have not been able to adapt to the miniaturization of the IC (see "Nikkei Micro Devices", October issue, 1985, p. 80).

Therefore, in recent years, there has been a strong desire to develop a technique for forming a single crystal silicon thin film without diffusing impurities contained in a single crystal substrate.

As a result of research conducted in line with such demands, it has recently been discovered that such objects can be achieved by plasma CVD. As an example, capacitively coupled R
By performing glow discharge decomposition of a mixed system of SiH4 and SiH2 F2 diluted with a large amount of hydrogen using an F plasma CVD device, it is possible to decompose (100
) It has been reported that single crystal silicon with good surface conditions can be grown on a silicon single crystal substrate (
Japanese Journal of Ablide Physics, Volume 26, L951-953 [1987]).

On the other hand, Japanese Unexamined Patent Publication No. 63-222096 discloses a method for manufacturing a single crystal silicon thin film by discharging and decomposing a mixed gas consisting of silane, fluorosilane, and hydrogen in an amount more than 5 times that of (silane + fluorosilane). is described, and in the example, two silicon single crystal wafers are used as the substrate.
It is stated that when the silicon substrate was heated to 50° C. and used, it was confirmed that a single crystal silicon thin film was epitaxially grown from the silicon substrate.

[0008]

[Problem to be Solved by the Invention] However, in these conventional low temperature plasma CVD methods, in which the impurities contained in the substrate rarely diffuse toward the growth layer, it is difficult to sufficiently diffuse radicals. Some effort is needed.

[0009] That is, S formed by decomposing SiH4
Radicals such as iH3 are thought to contribute to silicon film formation, but when such radicals fly in and the dangling bonds of Si are exposed, they immediately attach to the dangling bonds. As a result, it grows randomly and becomes amorphous or microcrystalline and does not become a single crystal. At this time, if hydrogen is present in excess on the growth surface, radicals can sufficiently diffuse on the growth surface to inactivate the growth surface and reach stable sites, making crystal growth possible. For this reason, it has been thought that in the conventional plasma CVD method, it is necessary to have a large amount of hydrogen gas present in the reaction gas.

[0010] However, when hydrogen is present in excess, hydrogen tends to be left behind in the epitaxially grown film, and as a result, the uniformity of the crystal deteriorates, and as a result, the determined electron mobility of the single crystal silicon thin film becomes a small value. There was a drawback that it became. For example, it is known that a single-crystal silicon thin film produced by conventional methods contains approximately 1 atomic percent hydrogen (Japanese Journal of Abrid Physics, Vol. 26, No. 6, No. 951). Page [198
7]).

[0011] As described above, the conventional method has the problem that it is not possible to obtain a high-quality single-crystal silicon thin film having large electron mobility.

[0012] Therefore, the present inventors conducted further research in order to obtain a high-quality single-crystal silicon thin film with large electron mobility using the plasma CVD method, which has the advantage of being able to lower the substrate temperature. This has led to the completion of the present invention.

[0013]

[Means for Solving the Problem] That is, the invention according to claim 1 is a method for turning a reactive gas containing silicon atoms, halogen atoms, and hydrogen atoms into plasma using a plasma CVD apparatus, and depositing a single crystal on a heated single crystal substrate. Assuming a method for manufacturing a single crystal silicon thin film to form a crystalline silicon thin film,
The method is characterized in that the number of halogen atoms in the reaction gas is adjusted to be greater than the number of hydrogen atoms,
On the other hand, the invention according to claim 2 is the invention according to claim 1, in which the supply gas of silicon atoms is SiF4, Si
It is characterized in that it is composed of a silicon halide gas selected from Cl4 and Si2 F6, and the supply gas of hydrogen atoms is hydrogen gas.

[0014] Furthermore, the invention according to claim 3 is based on claims 1 to 3.
In the invention according to Item 2, the thickness of the impurity diffusion transition region from the single crystal substrate of the single crystal silicon thin film is 500 angstroms or less, and the hydrogen concentration in the thin film is 500 angstroms or less.
It is characterized by being 0 ppm or less.

In such technical means, SiH4, Si
Silicon hydride such as 2 H6, Si3 H8, SiHm
X4-m (where m is 1 to 4, preferably 2 to 4,
X is Cl or F atom, preferably F atom), and SiF4, SiCl4
, and Si2 F6 can be used.

[0016] Furthermore, SiF4, SiCl4, Si2
Silicon halides such as F6 were conventionally considered to be etching gases in silicon crystal thin film production technology, but in the present invention, by containing hydrogen gas in the reaction gas, these silicon halides have film-forming properties. We succeeded in making this gas function as a silicon atom supply gas.

[0017] Also, SiF4, SiCl4, Si2
Silicon halide such as F6 is Si having a hydrogen atom.
It is easy to handle because it has lower flammability than silicon hydrides such as H4, Si2 H6, Si3 H8, and halogenated silanes such as SiHmX4-m. The invention according to claim 2 was made by focusing on the characteristics of silicon halide, and S is used as a supply gas for silicon atoms.
The danger is reduced by applying a silicon halide gas selected from iF4, SiCl4, and Si2F6.

On the other hand, as the gas for supplying halogen atoms having etching properties, the above-mentioned SiF4, SiCl4,
Silicon halides such as Si2 F6 and SiHm
halogenated silane represented by m and F2 or C
Halogen gas such as 12 can be applied. These gases release halogen atoms that can etch silicon surfaces under plasma conditions. That is, halogen atoms in the plasma always expose a clean silicon growth surface, remove impurities from the growing silicon film,
It is thought to have functions such as preventing polymerization of silane in the gas phase.

In addition, as a supply gas for the hydrogen atoms required for the crystal growth of the single crystal silicon thin film, hydrogen gas and supply gases other than this gas may be selected from the viewpoint of not introducing unnecessary impurities into the reaction system. SiH4, Si2H6, S
Silicon hydrides such as i3 H8 and halogenated silanes represented by SiHm X4-m can be applied.

Next, in the invention according to claims 1 to 3, unlike the conventional method related to plasma CVD, the number of hydrogen atoms in the reaction gas is etchable halogen atoms such as fluorine atoms and/or chlorine atoms. The biggest feature is that it is smaller than the number. Such conditions can be easily achieved by making the total amount of halogen atoms contained in the reaction gas larger than the total amount of hydrogen atoms contained in the reaction gas. The total amount of the halogen atoms contained in the reaction gas is about 2 to 1 of the total amount of hydrogen atoms contained in the reaction gas.
000 times, particularly preferably 5 to 400 times.

In the invention according to claims 1 to 3, an inert gas such as a rare gas, preferably helium, neon, argon, etc., may be added as a diluent gas to the reaction gas. The diluent gas is 1 to 1 for the above halogen atom.
It is preferable to use an amount of 1,000 times, particularly 1 to 100 times. In this case, the number of halogen atoms is calculated by the total amount of halogen atoms, which are fluorine atoms and/or chlorine atoms, contained in the reaction gas.

Furthermore, regarding the relationship between the film-forming silicon atoms and the etching halogen atoms, it is preferable that the number of halogen atoms be approximately 1 to 500 times, particularly 3 to 300 times as large as that of silicon atoms. A halogen atom is a silicon atom.
If the etching rate is less than 500 times, the etching rate will be too low and it will not be possible to keep the substrate surface in the best condition to facilitate the growth of single crystal silicon, whereas if the etching rate is more than 500 times, the etching rate will be too high and the silicon crystal will grow. This is because the growth rate decreases.

[0023] As an example of the combination of the above reaction gases, SiH4 and Si2 H6 are used as film-forming gases.
It is preferable to apply SiF4 and F2 individually or in a mixture as etching gases. However, this technical means is not limited to such applications.

[0024] In this technical means, a reaction gas satisfying the above conditions is heated at a power density of 0.01 to 10 W/cm.
2, preferably 0.05 to 5 W/cm2 to turn the reaction gas into plasma, about 100°C to 700°C, preferably about 200°C to 600°C, more preferably about 300°C.
A single crystal silicon thin film is formed on a single crystal substrate maintained at a constant temperature between .degree. C. and 500.degree.

[0025] Here, if the substrate temperature is lower than 100°C, the crystal structure is disturbed and becomes a polycrystalline structure, resulting in poor quality. If the substrate temperature is made higher than 700° C., the performance cannot be further improved, and the advantages of the plasma CVD method as a low-temperature method cannot be utilized.

[0026]Although the power density varies depending on the type of reaction gas and the pressure inside the chamber, the power density is 0.01.
If it is smaller than 10 W/cm2, the pressure of the reaction gas must be sufficiently lowered, resulting in a slow film formation rate.
If it exceeds 2, it is not preferable because the quality of the thin film cannot be maintained at a high level.

[0027] Furthermore, since the pressure inside the chamber for generating the plasma is related to the amount of energy possessed by atoms etc. that reach the substrate, the pressure is between 0.01 Torr and more.
It is necessary to set the pressure to 15 Torr, especially 0.05 Torr.
It is preferable to set it as Torr - 5 Torr.

Here, the epitaxial growth of silicon by the plasma CVD method is achieved by, for example, an apparatus as shown in FIG.

That is, in FIG. 2, a silicon atom supply gas such as SiH4 or SiF4, a hydrogen atom supply gas, and a halogen atom supply gas are supplied to the vacuum reaction chamber 11 from gas supply sources 17 and 18, and the high frequency power supply 16 supplies them in parallel. A high frequency discharge is caused between the flat plate electrodes 12 and 13, and the pump 19
The structure is such that the reaction gas is exhausted. Then, the single crystal substrate 14 is placed on the electrode 13 and heated by the heater 15, and crystal growth is performed on the single crystal substrate 14. Note that the above-mentioned discharge is other than high-frequency discharge, for example, direct current discharge,
Any method such as microwave discharge may be used.

[0030] This technical means not only makes it possible to produce an intrinsic single crystal silicon thin film, but also allows the formation The monocrystalline silicon thin film to be used can be p-type or n-type. Examples of the dopant gas in this case include hydrides such as diborane, phosphine, and arsine.

[0031] Furthermore, the single-crystal substrate that can be applied to this technical means must be a single-crystal substrate whose lattice constant is the same or almost the same as that of silicon because of the epitaxial growth of silicon; for example, a silicon single-crystal substrate, aluminum oxide (Al2O3: sapphire) single crystal substrate, and calcium fluoride (CaF2)
: Fluorite) single crystal substrate, etc.

As described above, the invention according to claims 1 to 3 can be applied to all fields where epitaxial growth has conventionally been performed.
For example, bipolar transistor, bipolar IC, M
It can be applied to semiconductors such as OS, LSI, and memory, as well as to the production of solar cells.

In particular, in the invention according to claim 3, the thickness of the impurity diffusion transition region from the single crystal substrate of the single crystal silicon thin film is 500 angstroms or less, preferably 400 angstroms or less.
00 angstroms or less, more preferably 350 angstroms or less, and the hydrogen concentration in the single crystal silicon thin film is 50 ppm or less, preferably 10 ppm or less, so the film thickness of the epitaxial layer can be set thin. Not only can the parasitic capacitance of a device to which a single crystal silicon thin film is applied be reduced, but also miniaturization of an IC corresponding to higher density and higher performance can be achieved.

[0034]

[Operation] According to the invention according to claim 1, since the number of etching halogen atoms is adjusted to be greater than the number of hydrogen atoms, the epitaxial growth surface of silicon is covered with hydrogen atoms as the hydrogen concentration decreases. Excessive coverage is eliminated, and as a result, hydrogen is less likely to be left behind in the grown single-crystal silicon film, making it possible to improve the uniformity of the crystal.

On the other hand, according to the invention according to claim 2, in addition to requiring a single-crystal silicon thin film with improved crystal uniformity, there is no need to use flammable silane as a supply gas for silicon atoms, so there is no risk of using ignitable silane. Further, according to the invention according to claim 3, the thickness of the impurity diffusion transition region from the single crystal substrate of the manufactured single crystal silicon thin film is 5.
00 angstroms or less, and the hydrogen concentration in the thin film is 50 ppm or less, it is possible to obtain a single crystal silicon film with a thinner film thickness than in the past, and to improve the electron mobility, etc. of this single crystal silicon thin film. It becomes possible to improve electrical characteristics.

Here, in the invention according to claims 1 to 3, although a large amount of hydrogen, which is conventionally required for crystal growth of a single crystal silicon thin film, is not applied, the single crystal has excellent electrical characteristics. The present inventors speculate as follows about the reason why a silicon thin film is required.

That is, in this technical means, although there is less hydrogen in the reaction chamber, there are relatively more halogen atoms, which have a strong etching effect, than in the prior art. For this reason, the epitaxial growth surface is constantly subjected to etching action. For example, when amorphous growth or the growth of a distorted silicon film that forms grain boundaries occurs, these are constantly subjected to etching action due to their weak bonding strength. While a clean surface is exposed, when silicon enters a predetermined site, its bonding force is stronger than in the above-mentioned growth, so that less etching action occurs and its crystallization is promoted.

Therefore, because epitaxial growth progresses while always exposing a clean surface and cutting weak bonds, a single-crystal silicon thin film with excellent electrical properties can be produced even though a large amount of hydrogen is not applied, contrary to conventional methods. It is assumed that this is what is required.

[0039]

EXAMPLES Examples of the present invention will be described in detail below, but the present invention is not limited to these examples.

[Example 1] In advance, 1×10 −9 Torr
SiF4:SiH4:
H2 (gas ratio is 5:1:3 in volume ratio, and F/H
The ratio is 2:1) as the reaction gas.
The reaction gas was supplied using SCCM, and the pressure of the reaction gas was adjusted to 0.3 Torr.

Next, this reaction gas was heated to 13.56MHZ.
A high frequency power supply was used to generate plasma at a power density of 0.1 W/cm2, and a silicon crystal thin film was formed to a thickness of 2.0 μm on a silicon single crystal substrate heated to 200°C.

When the silicon crystal thin film thus obtained was evaluated by reflection high-speed electron diffraction (RHEED), streak patterns and Kikuchi lines were observed, indicating that it was a good single crystal. found. The specific resistance of this thin film was 15 Ω·cm, and the electron mobility was determined to be 700 cm 2 /V·S using a Hall effect measuring device applying the Petritz method. Moreover, the hydrogen content concentration in the thin film was 10 ppm or less.

[Examples 2 to 10] Example 1 under the conditions shown in Table 1.
A silicon thin film was formed in the same manner as above, and the same evaluation was performed, and the results shown in Table 2 were obtained. The conditions and effects of Example 1 are also listed in Tables 1 and 2.

[0044]

[Table 1]

[0045]

[Table 2]

[Example 11] Hereinafter, this example to Example 18 relate to a manufacturing method to which the invention according to claim 3 is applied.

That is, SiF4 :SiH4 :F
2 (gas ratio is 2:1:5 by volume, and F/H ratio is 9:2) as a reaction gas at 80S.
CCM was supplied, and the pressure of the reaction gas was adjusted to 0.2 Torr.

Next, this reaction gas was heated to 13.56MHZ.
A high-frequency power supply was used to generate plasma at a power density of 0.1 W/cm2, and silicon was heated to 350°C on a silicon single crystal substrate (concentration of P as an impurity of 1 x 1018 cm-3) until it reached a thickness of 2.0 μm. A crystal thin film 2 was formed (see FIG. 1).

When the silicon crystal thin film thus obtained was evaluated by reflection high-speed electron diffraction (RHEED), streak patterns and Kikuchi lines were observed, indicating that it was a good single crystal. found.

[0050] Also, from secondary ion mass spectrometry, the thickness of the transition region 3 is 250 angstroms, and the hydrogen concentration is 10
It was found that it was less than ppm. The half width at 520 cm-1 according to Raman spectroscopy of this thin film is 3.5c.
m-1, the specific resistance was 50 Ω·cm, and the electron mobility was determined to be 1300 cm 2 /V·S using a Hall effect measurement device applying the Petritz method. Moreover, the hydrogen content concentration in the thin film was 10 ppm or less.

[Examples 12 to 18] A silicon thin film was formed in the same manner as in Example 11 under the conditions shown in Table 3, and the same evaluation was performed, and the results shown in Table 4 were obtained.

[0052]

[Table 3]

[0053]

[Table 4]

Comparative Example 1 A single crystal silicon thin film was formed on the same silicon single crystal substrate as in Example 1 by thermal CVD.

[0055] Reaction temperature: 1100°C, pressure: 200 Torr
The conditions were as follows, and 100% SiH4 was used as the reaction gas.

[0056] The thin film is 8.0 μm, and the hydrogen concentration is 10 pp.
m or less, and the Raman half-width was 3.5 cm -1 , but the transition region was as wide as 18,000 angstroms.

"Comparative Example 2" SiH4 :SiH2 F2 :H2 as reaction gas
= 1:10:100 mixed gas was used, this reaction gas was supplied at 111SCCM, and the pressure of the reaction gas was 2.0T.
A silicon crystal thin film was formed on the same silicon single crystal substrate as in Example 1 under the conditions that the power density was maintained at 0rr, the power density was 0.8 W/cm2, and the substrate temperature was 250°C.

The resulting thin film had a specific resistance of 30 Ω·cm and an electron mobility of 270 cm 2 /V·S. Further, although the transition region was 500 angstroms, the hydrogen content was 1.2 atomic % (12000 ppm) and the Raman half-width was 7 cm.

[0059]

According to the invention according to claim 1, since hydrogen is less likely to be left behind in a grown single crystal silicon film, it is possible to improve the uniformity of the crystal.

Therefore, it is possible to obtain a single-crystal silicon thin film with improved electrical properties such as electron mobility due to improved crystal uniformity.

Further, according to the invention according to claim 2, a single crystal silicon thin film with improved electrical properties such as electron mobility can be obtained, and there is also an effect of reducing risks and handling management during manufacturing. are doing.

Furthermore, according to the invention according to claim 3, it is possible to produce a single crystal silicon thin film with a thinner film thickness than in the past, and the electrical properties of the single crystal silicon thin film are excellent. This has the effect of enabling application to bipolar ICs, etc., which require miniaturization and high performance.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a single crystal silicon thin film and its substrate according to an example.

FIG. 2 is a configuration explanatory diagram of a plasma CVD apparatus applied to the present invention.

FIG. 3 is a cross-sectional view of a single crystal silicon thin film and its substrate according to a conventional method.

[Explanation of symbols]

1 Silicon single crystal substrate 2 Thin film 3. Transition area

Claims (3)

[Claims] 1. Production of a single-crystal silicon thin film by converting a reactive gas containing silicon atoms, halogen atoms, and hydrogen atoms into plasma using a plasma CVD apparatus to form a single-crystal silicon thin film on a heated single-crystal substrate. A method for producing a single crystal silicon thin film, characterized in that the number of halogen atoms in the reaction gas is adjusted to be greater than the number of hydrogen atoms. 2. The supply gas of silicon atoms is
2. The method for producing a single crystal silicon thin film according to claim 1, wherein the method is composed of a silicon halide gas selected from F4, SiCl4, and Si2 F6, and the supply gas of hydrogen atoms is hydrogen gas. 3. The thickness of the impurity diffusion transition region from the single crystal substrate of the single crystal silicon thin film is 500 angstroms or less, and the hydrogen concentration in the thin film is 50p.
Claim 1 or Claim 2 characterized in that it is pm or less.
The method for producing the single-crystal silicon thin film described above.