JPH0733319B2 - Manufacturing method of single crystal thin film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a single crystal thin film, and more particularly to low temperature formation of a silicon single crystal thin film having a small amount of impurities.

[Background Art] The low-temperature formation method of a single crystal thin film has attracted attention as a very important elemental technology for achieving high integration of semiconductor devices.
Various approaches have been attempted for this low temperature formation.

However, thermal CVD (Chemical
Vapor Deposition (Chemical Vapor Deposition) method requires high temperature of about 1000-1100 ℃. Also,
Optical CV of fluorosilane or disilane that we proposed
The method D required a temperature of about 600-700 ℃. As described above, in the conventional technique, a fairly high temperature is still required, and a technique for forming a single crystal thin film at a sufficiently low temperature which is not always satisfactory has not been completed.

The present inventor has conducted photodecomposition of silane and fluorosilane (photo CV
Proposed a technology to obtain a single crystal thin film at low temperature by D method) (Japanese Patent Publication No. 05-047518, Japanese Patent Publication No. 05-047519, Japanese Patent Publication No. 05)
No. 049637, Japanese Patent Publication No. 06-050730). However, the photo-CVD method has a practical problem that as the film formation time becomes longer, the light-transmitting window becomes cloudy, though gradually, and the amount of light transmission gradually decreases. As a result of further study to solve this problem, it was found that a single crystal silicon thin film grows by glow discharge decomposition, which has high practicality in a larger area than photo-CVD and high-speed manufacturability. That is, glow discharge decomposition is performed at a substrate temperature of 300 ° C. or lower by using a raw material gas in which hydrogen is added to a mixed gas of fluorosilane and silane in an amount of 5 times or more. Further, after etching the substrate, a vacuum is applied. It is disclosed herein that it has been found that the amount of impurities mixed in can be greatly reduced by performing discharge of a mixed gas of fluorosilane, silane, and hydrogen without burning.

DISCLOSURE OF THE INVENTION The present invention comprises at least a first step of performing plasma etching and a second step of discharging a mixed gas of silane, fluorosilane and hydrogen in a discharge chamber in which a substrate is loaded. It lies in the method for producing the characteristic single crystal thin film.

The first step in the present invention is a step of plasma etching the surface of the substrate to be the main surface on which the single crystal thin film is formed.
As such an etching gas, tetrafluorosilane may be mentioned as an etching gas particularly preferable in the present invention. Note that tetrafluorosilane can be used also in the second step and is preferable in that the problem of incorporation of impurities due to residual etching gas does not occur.

In the second step of the present invention, a mixed gas composed of silane, fluorosilane and hydrogen is discharged and decomposed, and the first step is performed.
This is a step of forming a single crystal thin film on the surface of the substrate etched in the step. The fluorosilane used in the second step may be SiH _4-n F _n (n = 1 to 4) or Si ₂ F
₆ is effectively used. Also, as silane, Si _m H
Monosilane, disilane, trisilane and the like represented by _{2m + 2} (m = 1 to 3) are effectively used.

The present invention basically forms a single crystal thin film on a substrate, but as a particularly preferred embodiment, it is epitaxial growth on a single crystal substrate. A silicon wafer or sapphire is used as the substrate.

High-frequency glow discharge, direct-current glow discharge, microwave discharge, etc. can be effectively used as the discharge in the present invention.

The basic constitution of the present invention is as described above, and particularly preferable embodiments thereof are as follows.

That is, the present invention relates to a first step of discharging tetrafluorosilane to perform plasma etching in a discharge chamber loaded with a substrate, and a mixed gas of fluorosilane, silane, and hydrogen, preferably silane. And a second step of discharging and decomposing a mixed gas containing hydrogen in an amount 5 times or more that of fluorosilane, and is a method for forming a single crystal thin film on a heated crystalline substrate.

In other words, the present invention comprises at least the first step and the second step, and in the second step, it is indispensable to perform discharge decomposition in the state where hydrogen coexists with fluorosilane and silane. It is more preferable to discharge-decompose a gas in which hydrogen is mixed in an amount 5 times or more that of silane and fluorosilane.

Concerning the composition ratio of this mixed gas used in the second step, it is convenient to express it as the feed gas supply flow rate (volume) ratio to the thin plate forming apparatus for forming a single crystal thin film, and the preferable flow rate range is as follows. is there. That is, fluorosilane / silane = 0.5 to 50, particularly preferably 1 to 20,
Hydrogen / (fluorosilane + silane) is 5 or more. The single crystal thin film tends to be formed in a region with a large amount of hydrogen added, but if the amount of hydrogen added is too large,
This is not preferable because the growth rate of the single crystal thin film decreases. In the present invention, the hydrogen / (fluorosilane + silane) mixing ratio is preferably 5 to 70, preferably 10 to 50, and particularly preferably 12 to 30.

In the present invention, the method of forming the mixed gas to be used is not a critical factor and is not particularly limited. For example, by introducing a gas mixed in advance outside the forming apparatus or in the forming apparatus, It is useful to mix hydrogen so as to satisfy the dilution degree. of course,
There is no problem in using hydrogen-diluted fluorosilane or silane.

In addition, according to the present invention, not only an intrinsic single crystal thin film can be formed, but also a single crystal thin film formed by mixing a group III and V group dopant gas such as diborane and phosphine into a source gas. Valence electron control can be performed on p-type and n-type, respectively.

In the present invention, the power source for generating electric power used for plasma etching and glow discharge is of course not critical and is not particularly limited. As a concrete example, a high frequency power supply, a direct current high voltage power supply, a microwave power supply, etc. are useful.

In the present invention, there is no particular critical limitation on the pressure of the tetrafluorosilane and the mixed gas and the discharge power during plasma etching and glow discharge decomposition.

Of course, the conditions at the time of glow discharge decomposition affect the growth rate of the single crystal thin film, and the substrate temperature is appropriately changed according to the desired growth rate to effectively grow the single crystal thin film epitaxially. it can.

As shown in Examples described later, one of the excellent features of the present invention is that the temperature for forming a single crystal thin film is extremely low as compared with the conventional method.

[Preferred Embodiments for Carrying Out the Invention] Next, embodiments of the present invention will be described. Discharge means,
A single crystal material substrate is placed in a thin film forming apparatus having at least a substrate introducing means, a substrate holding means, a substrate heating means, a gas introducing means, and a vacuum evacuation means, and the substrate under vacuum evacuation is 100 to 400.
Heat to ℃. Tetrafluorosilane is introduced under vacuum evacuation, and high-frequency power is applied so as to be 10 Torr or less to cause glow discharge.

Since an etching rate of 10 A / min or more is achieved by the main discharge, 10 minutes is sufficient as the etching time for cleaning the substrate surface.

After etching, a method of continuously adding a raw material gas for forming an epitaxial film and proceeding to the next step, or evacuating once and then introducing the raw material gas can be used. The first step and the second step can be performed in different discharge chambers. The source gas is supplied to the apparatus with a flow ratio of fluorosilane to silane of 1 to 10 and a flow ratio of hydrogen to (fluorosilane + silane) of 10 times or more. The pressure inside the device is reduced to 10 Torr or less by the vacuum exhaust means, and the discharge is started at 1 to 100 W.
A thin film is formed in the process. Since the thin film starts to be formed when the discharge starts, the discharge is stopped at the time when the surface film thickness is reached, taking the film formation rate into consideration. Further, the film formation time can be determined while the film thickness is being measured by the film thickness monitor.

[Effects of the Invention] The single crystal thin film obtained in the present invention is basically formed even at a low substrate temperature of 300 ° C or lower, and even at an extremely low temperature of 200 ° C or lower. Further, by performing the plasma etching of the first step before the second step, the impurities in the obtained single crystal thin film can be extremely reduced.

Further, the present invention is an excellent technique from the viewpoint of pollution prevention because it does not require harmful mercury unlike the photo CVD method. Furthermore, it is a technology that is superior from the practical point of view because it achieves higher speed film formation than the photo CVD method.

As described above, the method for producing a single crystal of the present invention provides an extremely useful technique for the field of semiconductor device manufacturing, in which a low temperature forming technique of a semiconductor thin film or a semiconductor device is eagerly desired for high integration. There is no choice but to say something.

[Embodiment] The present invention is carried out by using a thin film forming apparatus equipped with a high frequency power introducing means, a discharge electrode, a substrate introducing / extracting means, a substrate holding means, a substrate heating means, a gas introducing means, a vacuum exhausting means and a substrate introducing / extracting chamber. Carried out. Using the substrate loading / unloading means, the cleaned p of the substrate for film deposition
The mold type silicon wafer (100) was introduced from the substrate introducing / extracting chamber by using the substrate introducing / extracting means, and set in the substrate holding means. The substrate was heated to 250 ° C. by the substrate heating means while being evacuated by the vacuum evacuation means. By introducing tetrafluorosilane, the pressure inside the thin film forming apparatus was adjusted and maintained at 0.3 Torr by the pressure adjusting mechanism installed in the vacuum exhaust means. High-frequency power of 20 W was applied and discharged for 3 minutes to perform plasma etching in the first step.

After stopping the introduction of tetrafluorosilane and evacuating,
Monosilane (SiH ₄ ) / difluorosilane SiH ₂ F ₂ / hydrogen
It was introduced at a flow rate ratio of 1/5/100, and the pressure was adjusted and maintained at 1 Torr. When the temperature of the substrate and the pressure inside the thin film forming apparatus became constant, high frequency power of 20 W was applied to the discharge electrode by the high frequency power introducing means to start glow discharge, and the second step was performed. The discharge was stopped when the film thickness reached about 6000A. The average film formation rate was 0.3 A / s. After cooling, the substrate was taken out and observed. As a result, the substrate surface was a mirror surface with no fog. Observe the surface by reflection electron diffraction (RHEED),
The same streak-like Laue spots as the substrate were obtained, and it was confirmed that the single crystal thin film was epitaxially grown from the substrate surface. The resistivity was 100 Ω · cm or more. The impurity distribution in the epitaxial film is shown in FIG. It is clear that the impurity concentration in the film is low, and in particular, the impurity concentration at the interface between the substrate and the epitaxial film is low.

Comparative Example 1 An epitaxial film was formed under exactly the same conditions as in Example 1, except that the plasma etching in the first step was not performed. RHEED pattern and single crystal resistivity is 100 Ω ・ cm
Although the above is indistinguishable from Example 1, as shown in FIG. 1, it is clear that impurities in the epitaxial film, especially impurities at the interface between the substrate and the epitaxial film are large in this comparative example.

[Brief description of drawings]

FIG. 1 is a graph showing the impurity distribution in the epitaxial film formed in this example (solid line) and the comparative example (broken line). In the figure, 0 and N represent the concentration distribution of oxygen atoms and nitrogen atoms, respectively.

Claims (8)

[Claims] 1. A first step of performing plasma etching and silane in at least a discharge chamber loaded with a substrate,
Process for producing single crystal thin film comprising second step of discharging mixed gas consisting of fluorosilane and hydrogen 2. The manufacturing method according to claim 1, wherein tetrafluorosilane is used as an etching gas in the first step. 3. The method according to claim 1, wherein the composition ratio of the mixed gas discharged in the second step is such that hydrogen is 5 times or more that of silane and fluorosilane. 4. The fluorosilane used in the second step is SiH _4-n F _n (n = 1 to an integer of 4) or Si ₂ F _{6 wherein the} fluorosilane is used. Manufacturing method. 5. The method according to claim 1, wherein the silane is represented by Si _m H _{2m + 2} (m = 1 to 3 is an integer). 6. A first claim in which a crystalline substrate is used.
The manufacturing method described in paragraph. 7. The method according to claim 6, wherein the single crystal thin film is epitaxially formed on the crystalline substrate. 8. A crystalline substrate loaded in a discharge chamber and heated in a vacuum is subjected to steps of discharge of tetrafluorosilane and then glow discharge of a mixed gas of silane, fluorosilane and hydrogen. The method according to item 1 of the above.