JPH05109630A - Method for forming semiconductor thin film - Google Patents

Abstract

PURPOSE:To enable an Si-Ge semiconductor thin film where impurity concentration distribution and film thickness are uniform to be formed without any crystalline defect or with less crystalline defect as compared with before on a large- area Si substrate. CONSTITUTION:A silicon substrate 15 is placed in a reaction reactor with a hydrogen gas environment and then infrared rays are irradiated to the substrate 15, thus enabling a natural oxide film 61 to be eliminated. An inside of the reaction reactor is set to a mixture gas environment of SiH4 and GeH4 and then Si1-xGex thin film 63 (0<X<=0.1) is allowed to grow by a film thickness of 50 nm or less on the substrate while heating the substrate with infrared rays. While a concentration of GeH4 is increased as compared with that when forming Si1-xGex thin film 63 and the substrate is heated by infrared rays, an Si1-yGey thin film 65 is formed on the Si1-xGex thin film 63 (X<Y).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a Si-Ge based semiconductor thin film.

[0002]

2. Description of the Related Art In recent years, for the purpose of application to high-speed bipolar devices, microwave devices, or superlattice structure devices,
The Group IV semiconductor thin film growth technology is making rapid progress. And this technique was generally performed by the molecular beam epitaxy (MBE) technique. This is because the film can be formed at a relatively low temperature, so that the advantage that the impurity distribution of the formed thin film is not disturbed can be obtained.

As an example of such a thin film forming technique, for example, Japanese Patent Laid-Open No. 64-90519 discloses that a group IV hydrogen-based gas, which is a source of a group IV semiconductor thin film, is blown from a nozzle of an MBE apparatus to irradiate a substrate. At this time, a method of forming a Group IV semiconductor thin film by irradiating a halogen-based gas is disclosed.

In the MBE technique using a solid source, when forming a thick IV group semiconductor thin film, it was necessary to stop the film formation for supplementing the source due to the limitation of the source house capacity. In, the source gas can be continuously supplied from the outside of the device. Therefore, the group IV semiconductor thin film could be continuously formed in a large thickness. Further, in this method, the halogen gas acts so as to remove the hydrogen gas adsorbed on the dangling bond on the substrate surface, which promotes the dissociation of the source gas on the substrate surface and the adsorption of the group IV element on the substrate. , The growth rate of the semiconductor thin film could be increased.

[0005]

However, it is difficult to grow a single crystal semiconductor thin film having a uniform film thickness and film quality on a large-diameter wafer not only by the above method but also by the MBE technique using a gas source. The current problem is that it is difficult to implant impurities into a semiconductor thin film at a high concentration. The former is considered to be due to the directivity of the gas source blowing nozzle, and the latter is considered to be due to the MBE technique itself, in which a substrate is irradiated with a molecular flow to form a film.

Further, in the MBE technique, since it is necessary to maintain the degree of vacuum in the growth chamber at an ultrahigh vacuum of 10 ^{-10 to} 10 ^-11 Torr, the growth chamber is exposed to the atmosphere once and then brought to the target degree of vacuum again. Therefore, there is a problem in that the growth chamber needs to be baked for about 30 hours while exhausting the growth chamber.

Further, in forming a group IV semiconductor thin film on a silicon substrate, generally, before starting film formation, the substrate is subjected to a reduction treatment in a hydrogen gas atmosphere and a heat treatment in a hydrogen chloride gas atmosphere so that the substrate is naturally treated. Removes oxide film and dirt. However, even if the pretreatment is performed in this way, the effect of the original unevenness of the underlying surface and the effect of a small amount of carbonized material or metal oxide remaining on the underlying surface cannot be neglected. There is a problem that the film does not grow uniformly, and there is a problem that misfit dislocations and defects occur in the film or at the interface between the thin film and the base.

[0008] Each of these problems is a major obstacle to industrial application of a group IV semiconductor thin film to an actual semiconductor device, and therefore improvement is desired.

The present invention has been made in view of the above circumstances. Therefore, an object of the present invention is to solve the above-mentioned problems and form a Si-Ge (germanium) -based semiconductor thin film which is superior in film quality to the conventional one. To provide a way to do it.

[0010]

In order to achieve this object, according to the present invention, in a method of forming a Si-Ge based semiconductor thin film on a lower surface of silicon in a reaction furnace, the inside of the reaction furnace is made of silicon. Containing a Group IV hydrogen-based gas containing germanium and a Group IV hydrogen-based gas containing germanium and heat treating the underlayer while Si _1-X Ge _x
The step of forming a thin film and the concentration of the above-mentioned Group IV hydrogen-containing gas containing germanium in the above-mentioned atmosphere are adjusted to the above-mentioned Si
Forming a Si _1-Y Ge _Y thin film on the above _- mentioned Si _1-x Ge _X thin film while making the concentration higher than when forming the _1-x Ge _X thin film and heating the above-mentioned underlayer. (Where Ge composition ratios X and Y are 0 <X <
It is a value that satisfies 1,0 <Y <1 and X <Y. ).

The term "silicon underlayer" as used in the present invention means not only the Si substrate itself, but also a Si substrate on which an Si epitaxial layer is formed, and a substrate other than the silicon substrate. It means various Si underlayers on which a group IV single crystal film is to be grown, such as those having layers formed thereon, and intermediates (so-called wafers) in which elements are formed in these materials.

In implementing the present invention, the above-mentioned S
It is preferable to form the i _{1 -X} Ge _X thin film so that the film thickness t is in the range of 0 <t ≦ 50 nm and the Ge composition ratio X is in the range of 0 <X ≦ 0.1. ..

As the group IV hydrogen-containing gas containing silicon, for example, SiH ₄ (silane), Si ₂ H
₆ (disilane), Si (CH ₃ ) H ₃ (methylsilane), Si ₃ H ₈ (trisilane), Si (CH ₃ ) ₂ H
₂ (dimethylsilane), Si (CH ₃ ) ₃ H (trimethylsilane), Si (CH ₃ ) ₄ (tetramethylsilane), Si ₂ (CH ₃ ) ₆ (hexamethyldisilane),
Si (CH ₃ ) ₃ F (fluorotrimethylsilane) and Si (CH ₃ ) ₂ F ₂ (difluorodimethylsilane)
It is preferable to use one kind or two or more kinds of gas selected from the group of gases.

As group IV hydrogen-containing gas containing germanium, GeH ₄ (germane), GeF ₄ (germanium tetrafluoride), GeF ₂ (germanium difluoride), GeF (germanium fluoride) and GeH ₃ F
It is preferable to use one kind or two or more kinds of gases selected from the group of (fluorogermane) gas. It is good to

Further, in carrying out the present invention, Si _1-X G
It is preferable to heat the silicon underlayer during the formation of each of the e _x thin film and the Si _1-Y Ge _y thin film by irradiating the underlayer with infrared rays. As an infrared light source,
For example, a tungsten-halogen lamp or a xenon-arc lamp can be used.

[0016]

According to the structure of the present invention, the Si _1-X Ge _X thin film and the Si _1-Y Ge _Y thin film are formed by a chemical reaction. For this reason, problems such as nozzle directivity in the MBE method do not occur, and it becomes possible to grow a Si—Ge based semiconductor thin film having a uniform film thickness and film quality on a large diameter wafer. Further, since the hydrogen-based gas is used as the raw material gas, the silicon underlayer undergoes a strong reducing action in forming the Si _1-x Ge _x thin film, so that the carbide and metal oxide on the silicon underlayer surface are removed.

The Si _1-X Ge _X thin film can be used as a buffer layer, and the Si _1-Y Ge _Y thin film can be used as an original growth layer for forming a semiconductor device. At this time, the Si _1-X Ge _X thin film contributes to a reduction in the degree of lattice mismatch between the Si _1-Y Ge _Y thin film and the silicon underlayer, and a reduction in irregularities on the silicon underlayer surface. As a result, Si
The crystallinity of the _1-Y Ge _Y thin film can be improved.

Further, the Si _1-x Ge _x thin film has a thickness t
Is in the range of 0 <t ≦ 50 nm and the Ge composition ratio X is 0 <
In the structure of forming so that X ≦ 0.1, this Si _1-x Ge _x thin film seems to function well as a buffer layer, and as will be apparent from the experimental results described later, This Si _1-X Ge _X
The defect density in the Si _1-Y Ge _Y thin film formed on the thin film is reduced.

Further, in implementing the present invention, Si
_{In the} structure in which the silicon underlayer is heated in forming each of the _1-X Ge _X thin film and the Si _1-Y Ge _Y thin film by irradiating the substrate with infrared rays, the infrared rays are efficiently absorbed by the silicon and the silicon underlayer is formed. After being heated for a short time, and after the irradiation of infrared rays is stopped, the temperature of the silicon base drops in a short time. Therefore, heating and cooling of the base can be performed in a short time. As a result, compared with the case of using other heating means (for example, electric furnace), the Si _1-x Ge _x thin film and the Si
_{It is} possible to control the film thickness of each _1-Y Ge _Y thin film with high accuracy and contribute to the improvement of film quality.

[0020]

Embodiments of the method for forming a semiconductor thin film of the present invention will be described below with reference to the drawings. It should be noted that each of the drawings used for the description only schematically shows the shape, size, and arrangement relationship of each constituent component to the extent that the present invention can be understood. Further, in the following description, specific materials and specific numerical conditions will be described, but these materials and conditions are merely preferable examples, and the present invention is not limited thereto.

1. Description of Thin Film Forming Apparatus First, an example of an apparatus suitable for carrying out the method of the present invention will be described.

FIG. 2 is a diagram schematically showing the overall structure of this apparatus. In this case, FIG. 2 shows a state in which a silicon substrate 15 (hereinafter, also abbreviated as “substrate”) is placed in the reaction furnace 11 as a base of silicon in this case.

As shown in FIG. 2, this apparatus includes a reaction furnace (chamber) 11 made of, for example, quartz. The reaction path 11 has a structure in which the substrate 15 can be freely placed on and taken out from the substrate support 13 inside.

Further, a heating unit 12 is provided outside the reaction furnace 11. The heating unit 12 is composed of an infrared irradiating means of any suitable structure such as an infrared lamp.
As the infrared lamp 12, a tungsten halogen lamp or any other suitable lamp is used. Preferably, a plurality of infrared lamps 12 are arranged so that the inside of the reaction furnace 11 can be heated uniformly. Then, a temperature measuring means 14 for measuring the surface temperature of the substrate 15, for example, a thermocouple is provided in the vicinity of the substrate 15.

Further, this apparatus is provided with exhaust means 21 and 22 for exhausting the inside of the reaction furnace 11. Further, automatic opening / closing valves 24, 25, 26, 27, 28, 29, 30 are provided between the exhaust means 21, 22 and the reaction furnace 11. By appropriately opening and closing these valves, the pressure in the reaction furnace 11 can be controlled to any suitable pressure, and a low vacuum exhaust state and a high vacuum exhaust state can be formed in the reaction furnace 11. This degree of vacuum can be measured by a vacuum gauge 34.

Further, this device is provided with a relief valve 31. The valve 31 is automatically opened when the pressure inside the reaction furnace 11 exceeds atmospheric pressure, for example, 760 Torr. The exhaust means 22 exhausts the gas supplied from the gas supply source (described later) into the reaction furnace 11 by opening the valve 31. In addition, the exhaust means 21 and 22 described above are configured by, for example, the diffusion pump 21 and the rotary pump 22 connected to the pump 21. These exhaust means are connected to and communicate with the reaction furnace 11 via an exhaust pipe 23 arranged as shown in the figure and required valves among the above-mentioned valves. Further, in FIG. 3, reference numerals 32 and 33 are vacuum gauges (or pressure gauges) provided in communication with the exhaust pipe 23. The vacuum gauge 33 is, for example, a Pirani vacuum gauge used for pressure measurement in the range of 1 × 10 ⁻³ Torr, and the vacuum gauge 33 is an ion gauge used for pressure measurement in the range of 10 ⁻³ to 10 ⁻⁸ Torr.

Next, the gas supply system will be described. In this embodiment, a supply pipe 5 having a gas supply system arranged as shown in the drawing.
8 and an automatic opening / closing valve 5 provided at an appropriate position on the supply pipe 58
1, 52, 53, 54, 56, a valve 57, and flow rate controllers 46, 47, 48, 49, 50.
A raw material gas source (not shown) is connected to the raw material gas source connecting portions (hereinafter, “connecting portion”) 41 to 45 on the side opposite to the reaction furnace 11 of each flow rate controller. And valves 51-5
A desired raw material gas can be supplied to the reaction furnace 11 by opening / closing each 6 arbitrarily suitably. In this embodiment, the connecting portion 41 is hydrogen (H ₂ ) gas, the connecting portion 42 is hydrogen diluted 10% silane (SiH ₄ ) gas, the connecting portion 43 is hydrogen diluted 10% germane (GeH ₄ ) gas, and the connecting portion is An inert gas such as nitrogen (N ₂ ) gas can be supplied to 45. The connecting portion 44 can be used, for example, for connecting a gas source for doping desired impurities into the Si-Ge based semiconductor thin film.

2. Description of Thin Film Forming Method Next, an example of forming a Si—Ge based thin film will be described. In this example, silane (SiH ₄ ) was used as the source gas.
And germane (GeH ₄ ) are used, and a silicon substrate is used as a silicon base. It is preferable to use a silicon substrate whose main surface is (100), whose main surface is (110) or whose main surface is (111). This is because the substrate is widely used at present and is suitable for epitaxial growth of Si-Ge thin films.

FIGS. 1A to 1D are process drawings for explaining the method of forming a semiconductor thin film of this embodiment. In both figures, the silicon substrate 15 is used as the wafer in the main process.
FIG. 4 is a cross-sectional view taken along the thickness direction of FIG. FIG. 3 is an explanatory diagram of a heating cycle performed in the forming method of this embodiment. The heating cycle is shown with temperature on the vertical axis and time on the horizontal axis. The following description will be made with reference to FIGS. 1 to 3 as appropriate.

2-1. Cleaning In this embodiment, the substrate on which the semiconductor thin film is formed is cleaned before the semiconductor thin film is formed. This cleaning may be carried out by performing a cleaning process that is usually performed during epitaxial growth to remove the natural oxide film.
The cleaning method described below is used.

2-1-a. Pretreatment First, the substrate 15 is precleaned using chemicals, pure water, etc., as is conventionally done.

Next, in order to prevent a natural oxide film from being formed on the substrate 15, an inert gas source (not shown) is introduced into the reaction furnace 11 via a gas supply unit, for example, an inert gas as a purging gas. For example, nitrogen gas is introduced in advance. Here, a reducing gas, a silane-based gas, and a germane-based gas, which will be described later, are not introduced yet. Therefore, the valves 56 and 57
Open and close the valves 51, 52, 53, 54, 55.

Next, the substrate 15 is placed in the reaction furnace. The substrate 15 is fixed on the substrate support 13.

Even if such attention is paid, a natural oxide film 61 is formed on the surface (deposition surface) of the substrate 15 (FIG. 1 (A)). Therefore, heat treatment in a reducing gas atmosphere is performed on the substrate that has been pretreated to remove the natural oxide film 61 as follows.

2-1-b. Removal of Natural Oxide Film First, the valve 56 is closed to stop the supply of the inert gas into the reaction furnace 11.

Next, the inside of the reaction furnace 11 is, for example, 1 × 10 ⁻⁶ (10 ⁻⁶ ) T by the exhaust means 21 and 22.
The inside of the reaction furnace 11 is cleaned by exhausting to a vacuum degree of orr. The valves 30 and 24 are used for this vacuum exhaust.
Is closed and the valve 27 is opened, and the valve 25 is operated so that the rotary pump 22 and the reaction furnace 11 are connected. Then, operate the rotary pump 22,
The inside of the reaction furnace 11 is evacuated while monitoring the pressure inside the reaction furnace 11 with a vacuum gauge 34. Further, after the pressure inside the reaction furnace 11 becomes, for example, 1 × 10 ⁻³ Torr, the valve 25 is operated so that the rotary pump 22 is connected to the diffusion pump 21 side, and the valve 24 is further opened.

Next, a reducing gas such as hydrogen gas is introduced into the reactor main body 11 (H ₂ flow indicated by I in FIG. 3). This can be done by opening the flow controllers 51 and 55. The pressure in the reaction furnace 11 is, for example, 10
Adjust the flow controller to be in the range of 0 to 1 × 10 ^-2 Torr.

Next, the natural oxide film 61 is heated by the heating unit 12.
A heat treatment for removing H1 (H1 in step I of FIG. 3).
period). By this heat treatment, the substrate 15 is heated in a reducing gas atmosphere to reduce the natural oxide film 61 of the substrate 15,
The substrate 15 from which the natural oxide film 61 is removed is obtained (FIG. 1).
(B)).

Here, this heat treatment is performed by an infrared lamp which constitutes the heating unit 12. In detail, substrate 1
While measuring the surface temperature of No. 5 by the temperature measuring means 14, the surface temperature of the substrate 15 is, for example, 50 ° C. by an infrared lamp.
/ Sec to 200 ° C / sec at an appropriate rate, preferably about 100 ° C / sec to increase the substrate surface temperature to about 1 ° C, for example.
When the temperature reaches 000 ° C., the heating of the substrate 15 is controlled so that the temperature of 1000 ° C. is maintained for about 10 to 30 seconds.

In this embodiment, since the heat treatment is carried out while the inside of the reaction furnace 11 is maintained in the depressurized state as described above, the reaction product due to the reduction of the natural oxide film is outside the reaction furnace main body 11. It is possible to reduce the degree to which the substrate 15 and the inside of the reaction furnace 11 are contaminated by the reaction products.

Next, the heating of the substrate 15 by the heating unit 12 is stopped, and the valve 51 is closed to stop the supply of the reducing gas. Then, it waits for the substrate 15 to cool until the surface temperature of the substrate 15 reaches room temperature, for example, about 25 ° C. For this cooling, the substrate 15 may be naturally cooled,
You may make it cool forcibly. For the forced cooling, for example, the valves 56 and 57 are opened and the inert gas is supplied to the reactor main body 1
It can be done by introducing a large amount in 5.

Next, the valves 55, 51 and 28 are closed and the valve 27 is opened to open the inside of the reaction furnace 11 at, for example, 1 × 10 ^-6 To.
The inside of the reaction furnace main body 11 is cleaned by evacuating to a high vacuum of rr.

2-2. Formation of Si _1-x Ge _x Thin Film Next, a group IV hydrogen gas containing Si and an IV containing Ge
The silicon substrate 15 is heat-treated in a group-based hydrogen gas atmosphere to form a Si _1-x Ge _x single crystal thin film on the silicon substrate 15 as follows.

First, the valve 27 is closed, and the valves 28 and 5 are
5, 52 are opened, first, hydrogen-diluted 10% silane (SiH ₄ ) as a Group IV hydrogen gas containing Si is fed into the reaction furnace 11, and then the valve 53 is opened to open the Group IV hydrogen containing Ge. In this case, hydrogen diluted 1% germane (GeH ₄ ) is supplied into the reaction furnace 11 as a gas. At this time, the flow rates of both gases are adjusted in advance so that the flow ratio of the hydrogen-diluted silane and the hydrogen-diluted germane is 10: 1 and the inside of the reaction furnace 11 is in a depressurized state of, for example, about 10 Torr.
SiH ₄ + GeH ₄ flow indicated by I).

Next, the heating portion 12 heats the silicon substrate 15 in such a gas atmosphere (H2 period of step II in FIG. 3).

Here, this heat treatment is performed by an infrared lamp which constitutes the heating unit 12. In detail, substrate 1
While measuring the surface temperature of No. 5 by the temperature measuring means 14, the surface temperature of the substrate 15 is, for example, 50 ° C. by an infrared lamp.
/ Sec to 200 ° C / sec at an appropriate rate, preferably about 100 ° C / sec to increase the substrate surface temperature to about 1 ° C, for example.
When the temperature reaches 000 ° C., the heating of the substrate 15 is controlled so as to maintain the state of 1000 ° C. for about 10 to 20 seconds.

In the process of this step II, Si _1-X Ge _x having the same plane orientation as that of the substrate 15 is formed on the substrate 15.
Single crystal film (Ge composition ratio X = 0.1 in this case) 63 is 30
It grows to a film thickness of ˜40 nm (FIG. 1 (C)).

2-3. Formation of Si _1-Y Ge _Y Thin Film Next, heating of the substrate 15 by the heating unit 12 is stopped, and the flow rate ratio of the above-mentioned hydrogen-diluted SiH ₄ and hydrogen-diluted GeH ₄ is 4: 1 and the inside of the reaction furnace 11 is The flow rates of these gases are adjusted so that the pressure is reduced to about 10 Torr (process III SiH ₄ + GeH ₄ flow − in FIG. 3).

When the atmosphere in the reaction furnace is adjusted in this way, the substrate 15 on which the Si _1-x Ge thin film 63 is formed is heated by the heating device 12 while the surface temperature of the substrate 15 is measured again by the temperature measuring device 14. This heating e.g. raises the surface temperature of the substrate 15 at a suitable rate between 50 [deg.] C./sec and 200 [deg.] C./sec, preferably about 100 [deg.] C./sec. When it becomes about 60-12
The substrate 15 is heated so that the state of 1000 ° C. is maintained for 0 seconds (H3 period of step III in FIG. 3).

In this process III, Si _1-X G
On the e _x single crystal film 63, a Si _1-Y Ge _y single crystal film having the same plane orientation as that of the substrate 15 (in this case, the Ge composition ratio Y =
0.2) 65 grows to a film thickness of about 250 nm (FIG. 1).
(D)).

If this Si _1-Y Ge _Y single crystal film 6 is used,
When it is desired to dope impurities for controlling the conductivity type of this film, the following process may be performed, for example. Explaining this thin film 65 as a P-type Si-Ge epitaxial thin film, for example, first, a P-type impurity-containing gas, for example, 100 ppm hydrogen-diluted diborane (B ₂ H ₆ ) gas is used as a doping gas in the reaction furnace 11. Introduce. This can be done, for example, by connecting a cylinder filled with this gas to the connection portion 44 of FIG. 2 and opening the valves 54 and 55. Next, the infrared rays from the heating unit 12 are irradiated with Si _1-X G
The boron (B) decomposed and adsorbed on the surface of the single crystal thin film 65 by irradiating the single crystal thin film 65 on _x is thermally irradiated with the single crystal thin film 65.
Spread inside. As a result, a structure including the P-type Si _1-Y Ge _Y epitaxial thin film 65 is obtained. The heating temperature and heating time of the single crystal thin film 65 for diffusing boron may be, for example, 800 ° C. and about 20 seconds.

Next, the heating of the substrate 15 by the heating unit 12 is stopped, and the valves 52 and 53 are closed to stop the supply of hydrogen diluted SiH ₄ and hydrogen diluted GeH ₄ . Then, the surface temperature of the substrate 15 is room temperature, for example, about 25 ° C.
Wait until substrate 15 cools until For this cooling, the substrate 15 may be naturally cooled or may be forcibly cooled. Forced cooling is for example valve 5
This can be done by opening 6, 57 and introducing a large amount of inert gas into the reaction furnace.

After that, the pressure in the reaction furnace 11 was changed to 1 atm (7
The substrate on which crystal growth has been performed is taken out from the reaction furnace 11 at 60 Torr).

3. Experimental Results Under the above-mentioned thin film forming conditions, the cleaning condition, S
i _1-Y Ge _X formation conditions of the single crystal film 65 was a Ge composition ratio Y = 0.2 and a film thickness 250nm approximately for each constant i.e. Si _1-Y Ge _X single crystal film 65, Si _1-X G
By changing the Ge composition ratio X and the film thickness of the e single crystal film variously, S
Various structures including an i substrate / Si _1-X Ge single crystal film / Si _{1- Y} Ge _X single crystal film are formed. Then, the defect density in the Si _{1 -Y} Ge _x single crystal film for each of these structures was measured. 4, the vertical axis represents Si _1-X Ge _X Ge composition ratio X of the single crystal film having a film thickness of the film on the horizontal axis, and with these thicknesses and composition ratios, Si _1-Y Ge _Y single Defect density in crystal film (piece /
is a diagram showing the relationship between cm ^2).

As is clear from FIG. 4, the composition ratio X is 0.
It can be seen that under the conditions of 1 or less and the film thickness of 50 nm or less (all do not include 0), the defect density is less than 10 defects / cm ^2, which is extremely small as compared with the case other than this condition. In addition, the Si _1-X Ge _X thin film 63 is formed on the silicon substrate 15.
An experiment was also conducted in which the Si _0.8 Ge _0.2 thin film 65 was directly grown without forming a film. However, in this case, as shown in the cross-sectional view of FIG. 5, misfit dislocations 71 and defects 73 were generated in the film or at the interface between the thin film and the base, and the practicality was not recognized.

Although the embodiment of the method for forming a semiconductor thin film of the present invention has been described above, the present invention is not limited to the above embodiment.

For example, in the above embodiment, hydrogen diluted with SiH ₄ and hydrogen diluted with GeH ₄ are used as the semiconductor thin film forming gas.
It was gas. However, the gases that can be used are not limited to these. Instead of SiH ₄ gas, for example, Si ₂ H ₆ , Si
_{(CH 3) H 3, Si} 3 H 8, Si (CH 3) 2 H 2,
Si (CH ₃ ) ₃ H, Si (CH ₃ ) ₄ , Si ₂ (CH
₃ ) ₆ , Si (CH ₃ ) ₃ F and Si (CH ₃ ) ₂ F
_{Even if} one or more gases selected from the gas group of ₂ or a mixed gas of SiH ₄ and these gases is used, the same effect as that of the embodiment can be expected. Further, instead of GeH ₄ , for example, GeF ₄ , GeF ₂ , GeF and Ge.
Even if one or more gases selected from the H ₃ F gas group or a mixed gas of GeH ₄ and these gases is used, the same effect as that of the embodiment can be expected.

Further, in the above-mentioned embodiment, the substrate is heated by using the tungsten-halogen lamp, but instead of using this, a xenon arc lamp, a laser beam or a heater may be used.

Further, in the above-mentioned embodiment, the silicon base is cleaned before the thin film is formed, but it should be understood that this is not essential.

[0060]

As is apparent from the above description, according to the method for forming a semiconductor thin film of the present invention, Si _1-X Ge is formed.
_{The X} thin film and the Si _1-Y Ge _Y thin film can be formed by a chemical reaction. For this reason, problems such as nozzle directivity in the MBE method do not occur, so that a Si-Ge based semiconductor thin film having a uniform film thickness and film quality can be grown on a large diameter wafer. Further, since the hydrogen-based gas is used as the source gas, the silicon underlayer undergoes a strong reducing action when the Si _1-x Ge _x thin film is formed, so that the carbide and metal oxide on the silicon underlayer surface can be removed.

The Si _1-X Ge _X thin film can be used as a buffer layer, and the Si _1-Y Ge _Y thin film can be used as an original growth layer for forming a semiconductor device. At this time, the Si _1-X Ge _X thin film contributes to a reduction in the degree of lattice mismatch between the Si _1-Y Ge _Y thin film and the silicon underlayer, and a reduction in irregularities on the silicon underlayer surface. As a result, Si
The crystallinity of the _1-Y Ge _Y thin film can be improved. Further, the critical film thickness (film thickness capable of maintaining a single crystal state) can be increased.

Also, Si _1-X Ge _X thin film and Si _1-Y G thin film
In the case where the silicon underlayer is heated by infrared irradiation when forming each e _Y thin film, the underlayer can be heated and cooled in a short time, so that another heating means (for example, an electric furnace) is used.
Compared with the case of using Si _1-X Ge _X thin film and Si _1-Y
The thickness of each Ge _Y thin film can be precisely controlled, and the quality of the film can be improved.

[Brief description of drawings]

FIG. 1 is a process chart for explaining a method for forming a semiconductor thin film of an example.

FIG. 2 is a diagram for explaining thin film forming conditions of an example, showing gas supply conditions and substrate heating conditions.

FIG. 3 is an explanatory view schematically showing the entire system of a film forming apparatus used for carrying out the present invention.

FIG. 4 is a diagram showing the relationship between the condition of the Si _1-X Ge _X film and the defect density in the Si _1-Y Ge _Y film formed on this film.

FIG. 5 is a diagram for explaining a comparative example (in the case where no Si _1-x Ge _x film is provided).

[Explanation of symbols]

15: Silicon substrate 61: Natural oxide film 63: Si _1-X Ge _x single crystal film 65: Si _1-Y Ge _Y single crystal film

Claims (6)

[Claims] 1. A method for forming a Si—Ge (germanium) -based semiconductor thin film on a lower surface of silicon (Si) in a reaction furnace, wherein the reaction furnace contains a group IV hydrogen-based gas containing silicon and germanium. Of the group IV hydrogen-based gas, and while heat treating the underlayer, the Si _1-X Ge
A step of forming an _X thin film, and making the concentration of the group IV hydrogen-containing gas containing germanium in the atmosphere higher than the concentration when the Si _1-x Ge _x thin film was formed and heat-treating the underlayer. And a step of forming a Si _1-Y Ge _Y thin film on the Si _1-x Ge _x thin film, wherein the Ge composition ratios X and Y are 0 <X < 1,0 <Y <
It is a value that satisfies 1, X <Y. ). 2. The method for forming a semiconductor thin film according to claim 1, wherein the Si _1-x Ge _x thin film has a thickness t of 0 <t ≦ 50.
A method of forming a semiconductor thin film, which is characterized in that the composition ratio X of Ge is in the range of 0 nm and the composition ratio X of Ge is in the range of 0 <X ≦ 0.1. 3. The method for forming a semiconductor thin film according to claim 1, wherein the main surface of the silicon base is (100),
A method of forming a semiconductor thin film, characterized in that a main surface having a (110) surface or a main surface having a (111) surface is used. 4. The method of forming a semiconductor thin film according to claim 1, wherein the Group IV hydrogen-based gas containing silicon is Si
_{H 4, Si 2 H 6,} Si (CH 3) H 3, Si 3 H 8,
Si (CH ₃ ) ₂ H ₂ , Si (CH ₃ ) ₃ H, Si (C
H ₃ ) ₄ , Si ₂ (CH ₃ ) ₆ , Si (CH ₃ ) ₃ F, and Si (CH ₃ ) ₂ F ₂ are selected from the gas group, and one or more kinds of gases are used. Method for forming a semiconductor thin film. 5. The method for forming a semiconductor thin film according to claim 1, wherein the group IV hydrogen-based gas containing germanium is Ge.
A method of forming a semiconductor thin film, wherein one or more gases selected from a gas group of H ₄ , GeF ₄ , GeF ₂ , GeF and GeH ₃ F are used. 6. The method for forming a semiconductor thin film according to claim 1, wherein the heat treatment of the underlayer at the time of forming the Si _1-X Ge _X thin film and the Si _1-Y Ge _Y thin film is irradiated with infrared rays. A method for forming a semiconductor thin film, which is performed by