JPH0722330A - Method for forming strain hetero epitaxial layer - Google Patents

Abstract

PURPOSE:To provide the title forming method of strain hetero epitaxial layer capable of easily controlling the critical film thickness in the least ruggedness of thin film yet optimum for the maximum throughput. CONSTITUTION:A natural oxide film 11 adhering to the surface of a silicon substrate 10 in a reaction furnace is removed by the title forming method of strain hetero epitaxial layer. Later, a buffer layer 12 having carbon atoms is formed on the substrate 10 in the reaction furnace using a mixed gas of at least silicon-containing IV group based hydrogen gas, e.g. a mixture gas of SiH4 gas and carbon-containing IV group based hydrogen gas e.g. CH4 gas. Finally, an Si-Ge mixed crystalline thin film 14 is formed on the buffer layer 12 using another mixed gas of SiH4 gas and GeH4 gas.

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 strained heteroepitaxial layer, and more particularly to a film formation method for suitably controlling the critical film thickness of a strained heterostructure and the stress in the strained heteroepitaxial layer. .

[0002]

2. Description of the Related Art In recent years, a group IV group semiconductor thin film device having a heterostructure has been rapidly developed, and such a device is used as a high-speed hetero bipolar device, a microwave device or a superlattice structure device. As a thin film used for these devices, Si having a strained heterostructure is used.
-Ge mixed crystal thin films have received particular attention. This thin film is formed by heteroepitaxially growing a Si-Ge thin film on a silicon substrate.

The Si-Ge mixed crystal thin film is a solid solution at all rates, and a desired thin film can be formed by arbitrarily changing the atomic composition ratio of each. When this Si-Ge mixed crystal thin film is combined with a Si crystal to form a heterostructure and applied to a device, the crystal structure and the electron band structure change from the bulk state. Regarding the change in the crystal structure and the electron band structure, see Reference I (“Silicon-based hetero device”,
Furukawa et al., Maruzen Co., Ltd., issued July 1991).

According to Document I, the Si-Ge mixed crystal thin film is
Si-G made as bulk because it is a solid solution
It is known that the lattice constant of the e mixed crystal is almost proportional to the Ge atomic composition ratio. Therefore, the lattice constant of the Si-Ge mixed crystal thin film increases as the Ge concentration increases. Therefore, when the Si—Ge mixed crystal thin film is formed on the Si crystal, the heterostructure becomes a strained heterostructure and a lattice-relaxed heterostructure (see P. 177 of Document I).

The strained heterostructure formed at this time is Si
Due to the difference in lattice constant between the crystal and the Si-Ge mixed crystal thin film (S
The lattice constant of the Si-Ge mixed crystal thin film is larger than that of the i-crystal because it contains Ge.) A compressive stress is applied to the Si-Ge mixed crystal thin film to form a tetragonal strained heterostructure.

Further, when the tetragonal crystal type grows, lattice relaxation occurs to change to the cubic crystal type. At this time, misfit dislocations are generated at the Si-Ge / Si interface in the lattice-relaxed heterostructure having the cubic type. This misfit dislocation becomes a factor that adversely affects the electrical characteristics and optical characteristics of the device together with crystal defects in the heteroepitaxial layer.

Therefore, in order to advance the physical property research and deviceization of the strained heterostructure, it is important to control the critical film thickness without causing misfit dislocations in the strained heteroepitaxial layer. As the strained heterostructure continues, the film thickness increases, strain energy increases, lattice relaxation occurs, and misfit dislocations occur. The film thickness at which dislocations occur and lattice relaxation occurs is called the critical film thickness.

Conventionally, the study of the critical film thickness regarding the Si-Ge / Si strained heterostructure has been studied mainly from the relationship between the Si concentration and the Ge concentration of Si-Ge, and in particular, it is necessary to control the Ge concentration. Is an important factor for the critical film thickness.

Conventionally, as a method for forming a strained heterostructure of a Si-Ge mixed crystal, a CVD (chemical vapor deposition) method or an MB method is used.
E (Molecular Beam Epitaxial) method and the like have been studied.
However, in this CVD method, the heating temperature must be raised during the film forming process, and misfit dislocations are likely to occur at the Si-Ge / Si interface. Therefore, conventionally, it has been difficult to form a Si-Ge mixed crystal thin film having a strained heterostructure by the CVD method.

On the other hand, the MBE (Molecular Beam Epitaxial) method has been studied as a method for forming a strained heterostructure. In this MEB method, the film formation process is performed at a relatively low heating temperature in order to impart strain stress to the epitaxial layer.

[0011]

[Problems to be Solved by the Invention] However, CVD
In the method, the heating temperature must be raised during the film formation process as described above, misfit dislocations are likely to occur at the Si-Ge / Si interface, and a gas containing Si in the reaction furnace. And a gas containing Ge are mixed to form a Si—Ge mixed crystal thin film at a high heating temperature, so that the Ge composition ratio becomes large. Therefore, since the lattice constant in the crystal of the Si—Ge mixed crystal is increased and the strain stress is increased, the critical film thickness cannot be increased. For this reason, there is a problem that it is difficult to control the critical film thickness only by the composition ratio of Ge. Further, there is a problem that the surface morphology is deteriorated due to the segregation effect of Ge even if the film thickness is below the critical film thickness due to the Ge concentration.

Further, in the CVD method, the S
There is a problem that the surface unevenness of the Si—Ge mixed crystal thin film formed on the i substrate becomes large. It is considered that this is due to the phenomenon described below.

When forming a Si-Ge mixed crystal thin film on a Si substrate, a lattice mismatch occurs at the Si-Ge / Si interface in the crystal due to the difference in the lattice constant and the thermal expansion coefficient between Si and Si-Ge. For this reason, it is considered that the surface morphology (morphology) of the Si-Ge mixed crystal thin film changes, and the surface irregularities occur. A Si-Ge mixed crystal thin film having such a surface cannot be applied to a device.

On the other hand, in the MBE method, since the film forming process is performed at a low heating temperature, the film forming rate becomes slow, and it is not possible to dope deeply with impurities, for example, high-concentration impurities of boron (B). , Because it is still in the experimental stage and throughput (wafer throughput / time) cannot be obtained,
There is a problem that it is not suitable for mass production.

The present invention has been made in view of the above-mentioned problems. Therefore, the first object of the present invention is to easily control the film thickness of the critical film thickness and the strain stress, and To provide a method for forming a strained heteroepitaxial layer capable of reducing surface morphology. A second object is to provide a method for forming a strained heteroepitaxial layer suitable for throughput.

[0016]

In order to achieve this object, in the method for forming a strained heteroepitaxial layer of the present invention, a predetermined heating temperature is applied to a substrate by using a raw material gas, so that In forming a strained heteroepitaxial layer having a buffer layer and a Si-Ge mixed crystal thin film, (a) the reaction furnace is evacuated to a vacuum to remove the native oxide film adhering to the base, and then at least silicon is formed. Forming a buffer layer having carbon (C) atoms on a base using a mixed gas of a group IV hydrogen gas containing carbon and a group IV hydrogen gas containing carbon, and (b) thereafter forming Si on the buffer layer. And a step of forming a Ge mixed crystal thin film.

Further, in carrying out the present invention, preferably, the mixed gas used in the step (a) is a group IV hydrogen gas containing silicon, a group IV gas containing germanium, and a group IV hydrogen containing carbon (C). It is recommended to use a mixed gas with gas.

Preferably, the mixed gas used in the step (a) is a mixed gas of a silicon-containing group IV hydrogen gas and a carbon (C) -containing group IV hydrogen gas.

Further, in carrying out the present invention, it is preferable that the buffer layer in the step (a) is a Si-Ge-C based buffer layer.

The buffer layer in step (a) is replaced with S
It is preferable to use an i-C type buffer layer.

In carrying out the present invention, preferably, the silicon-containing Group IV hydrogen gas according to claim 1 is used as SiH ₄ , Si ₂ H ₆ , Si (CH ₃ ) H ₃ and Si ₃ H.
₈ , Si (CH ₃ ) ₂ H ₂ , Si (CH ₃ ) ₃ H, Si
(CH ₃ ) ₄ , Si (CH ₃ ) ₆ and Si (CH ₃ )
_One gas selected from the 3F gas group or a mixed gas of two or more gases. Further, preferably, the carbon-containing Group IV hydrogen gas is replaced with CH ₄ , C ₂ H ₆ , and C ₃ H.
_It is preferable to use one kind of gas selected from the group of ₈ and C ₂ H ₄ gas or a mixed gas of two or more kinds of gas.

In carrying out the present invention, preferably, the pressure of the vacuum exhaust in the step (a) is set to 10 ⁻⁷ Pa.
A high vacuum of (Pascal) or lower is recommended.

[0023]

According to the above-described method of forming a strained heteroepitaxial layer of the present invention, first, the reaction furnace is evacuated to a vacuum, and then the natural oxide film formed on the base is heat-treated and removed in the reaction furnace. Thus, after removing the natural oxide film by vacuum evacuation, no oxide remains on the surface of the underlayer. Then, a buffer layer having carbon atoms is formed on the underlayer in the reaction furnace by using a mixed gas of at least a silicon-containing group IV hydrogen gas and a carbon (C) -containing hydrogen gas. The addition of this carbon atom reduces the lattice constant of silicon. For the detailed reason for this,
It will be described later. Then, a Si—Ge mixed crystal thin film is formed on this buffer layer. Si-Ge formed in this way
The heterostructure of the mixed crystal thin film extends in the vertical direction reflecting the single crystal structure of the buffer layer having a small lattice constant, and the strain stress in the Si—Ge mixed crystal thin film determined by the Ge composition can be increased.

Using the above-mentioned buffer layer formation as a mixed gas, a silicon-containing Group IV hydrogen gas and a germanium-containing I
It is performed using a mixed gas of a V group-based gas and a carbon (C) -containing hydrogen-based gas or a mixed gas of a silicon-containing Group IV-based hydrogen gas and a carbon (C) -containing hydrogen-based gas. Therefore, a Si-Ge-C-based or Si-C-based buffer layer is formed. Such a Si-Ge-C system or Si-
By forming the C-based buffer layer, the hetero interface between the underlayer (for example, a silicon substrate) and the Si-Ge-C-based or Si-C-based buffer layer becomes a heterostructure having carbon. Further, the buffer layer becomes a crystal layer having a short lattice constant close to that of the underlying silicon crystal. Therefore, in the Si-Ge mixed crystal thin film formed on the Si-Ge-C-based buffer layer, the strain stress is controlled only by the conventional Ge concentration. Stress is obtained. As a result, the deterioration of the surface morphology caused by the increase of Ge concentration can be suppressed and the critical film thickness can be increased.

Further, since the group IV hydrogen gas containing silicon is used, a silicon single crystal can be formed on the base.

Further, since the carbon-containing IV gas is used, carbon atoms bond with silicon atoms or silicon-germanium atoms to reduce the lattice constant of the buffer layer.

[0027]

Embodiments of the present invention will be described below with reference to the drawings. It should be noted that each drawing merely schematically shows the shapes, arrangements and dimensions of the respective constituents to the extent that the present invention can be understood. Further, it should be understood that the embodiments described below are merely preferred examples and are not limited to the embodiments of the present invention.

Prior to explaining the method for forming a strained heteroepitaxial layer of the present invention, a thin film forming apparatus used in the present invention will be described with reference to FIG.

This apparatus comprises a heating furnace body 101, an exhaust system 102, and a gas supply system 104.

The heating furnace body 101 comprises a reaction furnace (chamber) 30, a substrate heating mechanism 32, a substrate support 34, a temperature measuring means 36, a gas head 40, exhaust ports 42 and 44, and vacuum gauges 58 and 60. There is. A water cooling tube is provided on the outer wall of the reaction furnace 30, and the water cooling tube serves to prevent the temperature of the wall of the chamber from becoming high during thin film formation. A substrate support 34 for supporting a substrate 38 is provided in the chamber 30, and the substrate 38 is installed downward using the support 34.
The heating furnace body 101 has a structure in which the substrate 38 can be freely taken in and out of the furnace or placed on the support 34.

In the chamber 30, a heating mechanism 32 is provided.
It is equipped with The heating mechanism 32 uses, for example, a resistance heating body. In addition, a measuring means 36 for measuring the surface temperature of the substrate 38 is provided near the substrate 38. The temperature measuring means 38 is, for example, a thermocouple.

In the chamber 30, a substrate support 34 is provided.
It is divided into the upper part and the lower part via.

The upper part is the heating mechanism 32 part, and the lower part is the gas head 40 part. The gas head 40 is provided with gas introduction pipes 62, 6 that penetrate the outer wall of the chamber 30.
4 and the cooling water introducing pipe 66.

Further, exhaust ports 42 and 44 are independently provided in the upper part and the lower part.

Next, an exhaust system 102 for exhausting this device will be described. The exhaust system 102 is the exhaust means 4
6, 48 and 50, and automatic opening / closing valves 54 and 56. A turbo molecular pump, for example, is used as the exhaust means 46, 48, and 50 for evacuating the inside of the chamber 30. Further, the automatic opening / closing valves 54 and 56 and the exhaust means 46, 48 and 50 are connected by an exhaust pipe.

Next, the gas supply system 104 for the source gas will be described.

The gas supply system 104 includes an automatic opening / closing valve 6
8, 70, 72, 73, 88, 90 and 92, automatic flow controllers 74, 76, 78 and 79, and gas sources 80, 82, 84 and 86. Further, an exhaust means 52 is provided so that the gas introduction pipe can be exhausted independently. Here, the gas introduction pipe 62 is connected to the automatic opening / closing valve 6
8, 70, 72, and the gas introduction pipe 6
Reference numeral 4 is connected to the automatic opening / closing valve 73. Further, the automatic opening / closing valves 68, 70 and 72 are connected to the raw material gas supply unit 8 via the automatic flow rate controllers 74, 76 and 78.
0, 82 and 84 are connected. At this time, the source gas is, for example, silane (SiH ₄ ) gas or germane (Ge).
H ₄ ) gas and methane (CH ₄ ) gas.

On the other hand, automatic opening / closing valves 88, 90 and 9
2 is connected to the exhaust means 52 by a gas introduction pipe. Therefore, the automatic opening / closing valves 68, 70, 72, 8
By opening and closing 8, 90 and 92 arbitrarily,
The inside of the gas introduction pipe of the reaction gas supply system can be independently evacuated without going through the chamber-30.

The gas introduction pipe 64 is connected to an automatic flow rate controller 79 via an automatic opening / closing valve 73, and further connected to a carrier gas supply unit 86, for example, a hydrogen (H ₂ ) gas supply unit. .

Further, a T-shaped gas supply pipe branches from a gas introduction pipe provided between the automatic opening / closing valve 68 and the automatic flow controller 74, and the gas introduction pipe on one side has an automatic opening / closing valve 88. It is connected to the. Similarly, a T-shaped gas supply pipe branches from the gas inlet pipes of the automatic opening / closing valve 70 and the automatic flow rate controller 76, and the valves 72 and 78, respectively.
It is connected to 2.

Next, the method of forming the strained heteroepitaxial layer of the first embodiment of the present invention will be described with reference to FIGS. 1, 2 and 3.

FIG. 1 shows the heating cycle and gas flow curve of the first embodiment. In the figure, the horizontal axis represents time and the vertical axis represents heating temperature. Also, FIG.
(D) is a process drawing of the strained heteroepitaxial layer formed in the first embodiment.

First, a silicon substrate (hereinafter referred to as a substrate) is used as the base 10. Substrate 10 used at this time
Has a crystal plane because it has a Si single crystal structure. In the first embodiment of the present invention, as an example, (100)
A Si single crystal having a plane is used.

Before the substrate 10 (or 38) is carried into the chamber 30, the substrate 10 is previously cleaned to remove the oxide film and contaminants adhering to the surface thereof.

The cleaning liquid used at this time is, for example, a mixed liquid in which sulfuric acid (H ₂ SO ₄ ) and hydrogen peroxide (H ₂ O ₄ ) are arbitrarily and suitably mixed. Then, the cleaning liquid is added to 120
After heating to about C, the substrate 28 is immersed in the cleaning liquid for about 10 minutes. By such treatment, about 10 A is applied to the surface of the substrate 28.
An oxide film (not shown) of about ° (the symbol of A ° represents angstrom) is formed. Then, the substrate 28
The oxide film formed on the surface of the substrate 10 is completely removed by immersing in a cleaning solution of a% volume HF solution for about 3 minutes. Immediately thereafter, the cleaned substrate 10 is loaded into the chamber 30.

Immediately after the substrate 10 is loaded into the chamber 30, the automatic opening / closing valves 54 and 56 are opened. Subsequently, the inside of the chamber 30 is evacuated to an ultrahigh vacuum of, for example, 1 × 10 ⁻⁸ Pa (Pascal) by using evacuation means (for example, turbo molecules) 46, 48, and 50 and cleaned (T _{1 in} FIG. period).

Next, the automatic opening / closing valve 73 is opened and the carrier gas 86, while adjusting the automatic flow rate controller 79,
For example, hydrogen gas is supplied into the chamber 30. continue,
The chamber 30 is heated to, for example, 900 ° C. to 1000 ° C.
The temperature is maintained at about C for a predetermined period (T ₂ period in FIG. 1). At this time, the natural oxide film ((A) in FIG. 2) attached to the surface of the substrate 10 is removed by evaporation or hydrogen reduction action. The structure at this time is shown in FIG.

Next, the heating temperature in the furnace is lowered while observing the heating measuring means 36 by using the heating mechanism 32, and the substrate temperature is set to about 750 ° C., for example. However, a suitable temperature may be in the range of 600 ° C to 900 ° C.

Next, the automatic opening / closing valve 88 is opened, and a silane-containing group IV hydrogen gas, for example, a silane (SiH ₄ ) gas diluted with 10% hydrogen (hereinafter referred to as SiH ₄ gas) is exhausted by the exhaust means 52. Shed. At this time, the automatic opening / closing valve 68 is closed. Subsequently, with the SiH ₄ gas still flowing to the exhaust means 52 side, the valve 90 is opened and a germanium-containing group IV system, for example, hydrogen diluted 1% volume germane (GeH ₄ ) gas (hereinafter referred to as GeH ₄ gas). ) Is made to flow to the exhaust means 52 side. At this time, the automatic flow controllers 74 and 76 are adjusted in advance so that the mixing ratio of the hydrogen diluted 1% volume silane (SiH ₄ ) gas and the hydrogen diluted 1% volume germane (GeH ₄ ) gas becomes a predetermined mixing ratio. deep.

Further, the valve 92 is opened, and a carbon-containing Group IV hydrogen gas, for example, hydrogen diluted 1% volume methane (CH ₄ ).
A gas (hereinafter referred to as CH ₄ gas) is flowed to the exhaust means 52 side. At this time, 1% volume methane (CH ₄ ) diluted with hydrogen
Automatic flow controller 7 so that the mixed gas of gas and hydrogen diluted 1% volume silane (SiH ₄ ) gas and hydrogen diluted 1% volume Germane (GeH ₄ ) gas has a predetermined mixed gas ratio.
Adjust 8 beforehand. Then, after closing the valves 88, 90 and 92, the valves 68, 70 and 72 are opened and S
A mixed gas of iH ₄ gas, GeH ₄ gas and CH ₄ gas is supplied into the chamber 30 (period T _{3 in} FIG. 1). At this time, the Si—Ge—C based buffer layer 12 is formed on the substrate 10.
Are formed ((C) of FIG. 2). The film thickness of the buffer layer 12 formed at this time is about 10 A ° to 100 A °. The crystal orientation of the buffer layer 12 is the same (100) plane as the silicon substrate 10.

Next, the valves 68, 70 and 72 are closed so that SiH ₄ gas, GeH ₄ gas and CH ₄ gas are not supplied into the chamber 30. Then, the valve 92
Is closed and the valves 88 and 90 are opened to allow SiH ₄ gas and GeH ₄ gas to flow to the exhaust means 52 side. afterwards,
Immediately, open the valves 68 and 70, and add SiH ₄ gas and G
A mixed gas of eH ₄ gas is supplied into the chamber 30 and kept for a predetermined period (T ₄ period in FIG. 1). At this time, the respective gas flow rates are adjusted by the automatic flow rate controllers 74 and 76 in advance so that the mixing ratio of the SiH ₄ gas and the GeH ₄ gas becomes a predetermined gas flow rate in the chamber 30. The heating temperature at this time is about 750 ° C., which is the same as in the previous step.
However, a suitable temperature may be in the range of 600 ° C to 900 ° C.

Thus, the Si-Ge mixed crystal thin film 14 having a strained heterostructure is formed on the Si-Ge-C based buffer layer 12 ((D) of FIG. 2).

Next, after closing the valves 68 and 70,
The valves 88 and 90 are opened, and the exhaust means 52 is used to exhaust the inside of the gas introduction pipe. At this time, SiH ₄ gas and Ge
The H ₄ gas is not supplied into the chamber 30. Subsequently, the valve 73 is opened and hydrogen gas is supplied to the chamber 30 while adjusting the gas flow rate of the automatic flow controller 79.
And heat the substrate 10 at room temperature (about 20 ° C.).
℃ until) cooling (T ₅ period in FIG. 1). afterwards,
The substrate 10 is taken out of the chamber 30.

By the steps described above, the buffer layer 12 and the Si-Ge mixed crystal thin film 14 are sequentially formed on the Si substrate 10. The buffer layer 12 and Si-Ge formed at this time
The mixed crystal thin film 14 is generically called a strained heteroepitaxial layer 17.

Next, the change in the Si lattice constant when carbon (C) is introduced into the Si-Ge mixed crystal will be described with reference to FIG. In the figure, the horizontal axis represents the angle (second) and the vertical axis represents the X-ray diffraction intensity. Further, FIG. 4 shows a typical peak value of the X-ray diffraction curve actually obtained by copying.

The measurement conditions at this time are as follows. The diffractometer uses a high resolution X-ray diffractometer (manufactured by Philip Co., di-crystal directivity). The film thickness of the buffer layer used for the measurement sample is 2000 A ° to 2500 A ° which is ten times thicker than the film thickness of the buffer layer of the first embodiment of the present invention. Also, the composition concentration ratio of carbon is 0.9% and 2%,
The Ge concentration ratio is 25% (constant).

The peak value a in FIG. 4A is Si _1-xy
It represents the X-ray diffraction intensity when the concentration ratio of carbon atoms in Ge _x C _y (where x and y represent the composition ratio of Ge and C) is 0.9%. The peak value b is (4
The diffraction intensity of the (00) plane is shown. In addition, FIG.
_Shows the X-ray diffraction intensity when the concentration ratio of carbon atoms of Si _1-xy Ge _x C _y is set to 2%. The peak value d represents the X-ray diffraction intensity of the (400) plane of the Si crystal.

As can be understood from FIGS. 4A and 4B, when the carbon composition concentration ratio increases, Si
The peak value a of the diffraction intensity of _1-xy Ge _x C _y shifts to the plus angle side and becomes the peak value c of FIG. 4B. This means that the lattice constant of Si _1-xy Ge _x C _y can be reduced by adding carbon atoms to Si-Ge.

Next, FIGS. 3, 5 and 7 (A)-
A method for forming a strained heteroepitaxial layer according to the second embodiment of the present invention will be described with reference to FIG. Note that FIG.
[FIG. 7] is a diagram for explaining a heating cycle and a gas flow of the second embodiment. Further, FIG. 6 shows a process chart of forming the strained heteroepitaxial layer of the second embodiment. Here, the description of the same steps as those in the first embodiment will be partially omitted.

First, a silicon substrate is used as the base 20. The substrate 20 is made of Si single crystal, and the crystal plane is, for example, the (100) plane.

Since the method of cleaning the substrate 20 before loading the substrate 20 into the chamber 30 is the same as that of the first embodiment, its explanation is omitted. Further, the steps until the inside of the chamber 30 is evacuated to a vacuum and the natural oxide film 21 adhered on the substrate 20 is removed by the same method as in the first embodiment. Therefore, the T ₁₁ period and the T ₁₂ period of FIG. 5 are the same as the T ₁ period and the T ₂ period of FIG.

Therefore, in the second embodiment, the natural oxide film 21 is used.
The process after removing (FIG. 6C) will be described.

First, the heating means 32 is adjusted to lower the substrate temperature while watching the measuring means 36. At this time, the substrate temperature is set to about 750 ° C. However, the heating temperature may be, for example, in the range of 650 ° C to 850 ° C. First, the valve 88 is opened, and the hydrogen-diluted 10% volume SiH ₄ gas 80 is flown to the exhaust means 52 side. At this time, when the SiH ₄ gas is supplied to the chamber 30, the pressure in the furnace is, for example, 1 × 10 ⁻³ T
The automatic flow controller 74 is adjusted in advance so that the pressure is reduced to about orr. Then, the valve 92 is opened and, for example, hydrogen diluted 1% volume methane (CH ₄ ) gas is flowed to the exhaust means 52 side. At this time, SiH ₄ gas and CH ₄
The CH ₄ gas automatic flow rate controller 78 is adjusted in advance so that the gas mixture ratio of the gases becomes a predetermined value.

Next, the valves 88 and 92 are closed and the valves 68 and 72 are opened, and the mixed gas of SiH ₄ gas and CH ₄ gas is introduced into the chamber 30 for a predetermined period (T ₁₃ period in FIG. 4).
Supply. At this time, the Si—C based buffer layer 22 having carbon atoms is formed on the Si substrate 20 ((C) of FIG. 6).

Next, S is formed on the Si--C based buffer layer 22.
An i-Ge mixed crystal thin film 24 is formed. This forming method is the same as in the first embodiment. The structure thus formed is shown in FIG. Here, the Si—C based buffer layer 22 and the Si—Ge mixed crystal thin film 24 are collectively referred to as a strained epitaxial layer 27.

Next, the change in the lattice constant of Si _1-x C _x will be described with reference to FIGS. 7 (A), 7 (B) and 7 (C). The film thickness of the buffer layer of the experimental sample used at this time is made ten times thicker than the film thickness of the buffer layer of the second embodiment, as in the case described with reference to FIG. here,
It is set to about 1000 A ° to 2000 A °. In addition, the peak values a, b, and c have a carbon composition ratio of 0.08%, 0.
It is the value of the X-ray diffraction intensity when it was set to 19% and 0.76%.

As can be understood from FIGS. 7A to 7C, Si _1-x increases as the composition concentration ratio of carbon increases.
The peak intensity of C _x gradually shifts in the positive angular direction in the order of peak value a, peak value b, and peak value c. The peak values p ₁ , p ₂ and p ₃ represent the X-ray diffraction intensity generated on the Si single crystal (400) plane. Figure 7
The results of (A) to (C) are that the buffer layer 22 is obtained by adding carbon having a lattice constant smaller than that of Si atoms.
It means that the lattice constant of Si _1-x C _x is reduced. At this time, the Si—Ge mixed crystal thin film formed on the buffer layer receives a compressive stress in the lateral direction and functions to vertically extend the epitaxial layer having the hetero structure.

Further, the unevenness of the surface of the Si-Ge mixed crystal thin film to which carbon is added is smaller than that of the Si-Ge mixed crystal thin film to which carbon is not added. The reason for this is considered to be that the buffer layer containing carbon is present, so that the coefficient of thermal expansion of the Si-Ge / Si hetero interface becomes small and stress relaxation occurs.

Further, as described in the first and second embodiments of the present invention, the strained hetero-epitaxial layer can be formed by the CVD method which has been conventionally considered difficult, so that the throughput can be improved.

In the above-described first and second embodiments of the present invention, the silane gas is used as the silicon-containing group IV hydrogen gas, but the present invention is not limited to this gas. For example, disilane (Si ₂ H ₆ ) , Methylsilane (Si (CH
₃ ) H ₃ ), trisilane (Si ₃ H ₈ ), dimethylsilane (Si (CH ₃ ) ₂ H ₂ ), trimethylsilane (Si
(CH ₃ ) ₃ H), tetramethylsilane (Si (C
H _{3) 4),} hexamethyl silane (Si (CH _{3) 6)}
And fluorotrimethylsilane (Si (CH ₃ ))
_You may use the 1 type (s) or 2 or more types of gas selected from the gas group of 3F).

Further, in the first and second embodiments of the present invention, germanium-containing group IV-based gas is mixed with germane (GeH).
₄ ) Gas was used. For example, germanium tetrafluoride (G
eF ₄ ), germanium difluoride (GeF ₂ ), germanium fluoride (GeF) and fluorogermane (Ge
It may be one kind of gas selected from the gas group of H ₃ F) or a mixed gas of two or more kinds of gases.

In the embodiment of the present invention, methane gas was used as the carbon-containing group IV hydrogen gas. However, for example, ethane (C ₂
H _6), propane (C ₃ H _8), and ethylene (C ₂ H
It may be one type of gas selected from the gas group of ₄ ) or a mixed gas of two or more types of gas.

Further, in the embodiment of the present invention, the crystal plane (100) plane oriented substrate is used as the substrate of the Si substrate, but any other suitable crystal plane may be used.

[0074]

As is apparent from the above description, according to the method for forming a strained heteroepitaxial layer of the present invention, the inside of the reaction furnace is evacuated to a vacuum to first remove the natural oxide film on the underlayer. . Then at least silicon containing IV
A buffer layer having carbon atoms is formed on the underlayer using a mixed gas of a group hydrogen gas and a carbon-containing group IV hydrogen gas. Then, a Si-Ge mixed crystal thin film is formed on the buffer layer. The Si-Ge-C or Si-C lattice constant in the buffer layer formed by such a method is smaller than the lattice constant of silicon alone because it has carbon atoms. Therefore, when a Si-Ge mixed crystal thin film is formed on this buffer layer, the heterostructure of the Si-Ge mixed crystal thin film is
It receives compressive stress and extends vertically. Therefore, the Si-Ge mixed crystal thin film formed on the buffer layer has a conventional G
The desired strain stress can be obtained by introducing a small amount of Ge atoms as compared with the case where the strain stress is controlled only by the e concentration. As a result, the deterioration of the surface morphology caused by the increase of Ge concentration can be suppressed and the critical film thickness can be increased.

Further, by adding carbon atoms into the buffer layer, Si--Ge--C / Si or Si--C /
Since the lattice mismatch of Si can also be reduced, the unevenness on the surface of the strained heteroepitaxial layer is reduced.

In forming the buffer layer, the Si—C based buffer layer may be formed using a mixed gas of silicon-containing group IV hydrogen gas and carbon-containing group IV hydrogen gas. Even with such a Si-C based buffer layer, the lattice constant of the buffer layer can be made smaller than the lattice constant of silicon alone.

Further, since the strained epitaxial layer can be formed by the CVD method, which has been conventionally considered difficult, the throughput (the amount of processing per unit time) is improved and the mass production can be achieved.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a heating curve and a gas flow for use in explaining a first embodiment of the present invention.

2A to 2D are process drawings provided for explaining a method for forming a strained heteroepitaxial layer according to a first embodiment of the present invention.

FIG. 3 is a thin film forming apparatus used to explain the formation of a strained heteroepitaxial layer of the present invention.

4 (A)-(B) are S of the first embodiment of the present invention.
It is an X-ray diffraction intensity curve of the buffer layer area | region of i-Ge-C type | system | group.

FIG. 5 is a diagram showing a relationship between a heating curve and a gas flow for explaining the second embodiment of the present invention.

6 (A) to 6 (D) are process charts provided for explaining a method for forming a strained heteroepitaxial layer of a second embodiment of the present invention.

7 (A) to 7 (C) are S of the second embodiment of the present invention.
6 is an X-ray diffraction intensity curve of an i-C system buffer layer region.

[Explanation of symbols]

10, 20: Silicon substrate 11, 21: Natural oxide film 12: Si-Ge-C based buffer layer 14, 24: Si-Ge mixed crystal thin film 17, 27: Strained heteroepitaxial layer 22: Si-C based buffer Layer 30: Reactor (chamber) 32: Heating mechanism 34: Substrate support 36: Temperature measuring means 38: Substrate 40: Gas head 42, 44: Exhaust port 46, 48, 52, 52: Exhaust means 54, 56: Automatic Open / close valve 58, 60: Vacuum gauge 62, 64: Gas introduction pipe 66: Cooling water introduction pipe 68, 70, 72, 73, 88, 90, 92: Automatic opening / closing valve 74, 76, 78, 79: Automatic flow controller 80 : hydrogen diluted 10% by volume silane (SiH ₄₎ gas 82: hydrogen dilution 1% volume germane (GeH ₄₎ gas 84: hydrogen dilution 1% volume methane (CH ₄₎ gas 86: hydrogen H ₂₎ gas

Claims (8)

[Claims] 1. A buffer layer and a Si layer are formed on a substrate by applying a predetermined heating temperature using a source gas in a reaction furnace.
In forming a strained heteroepitaxial layer having a Ge mixed crystal thin film, (a) the inside of the reaction furnace is evacuated to a vacuum to remove the natural oxide film formed on the underlayer, and at least silicon-containing group IV hydrogen Forming a buffer layer having carbon (C) atoms on a base using a mixed gas of a gas and a carbon-containing group IV hydrogen gas; and (b) thereafter, a Si-Ge mixed crystal thin film on the buffer layer. And a step of forming a strained heteroepitaxial layer. 2. The strained heteroepitaxial layer according to claim 1, wherein the mixed gas used in the step (a) is silicon-containing I
A method for forming a strained heteroepitaxial layer, which comprises using a mixed gas of a group V hydrogen gas, a germanium-containing group IV gas, and a carbon (C) -containing group IV hydrogen gas. 3. The strained heteroepitaxial layer according to claim 1, wherein the mixed gas used in the step (a) is silicon-containing I
A method of forming a strained heteroepitaxial layer, which comprises using a mixed gas of a group V hydrogen gas and a carbon (C) -containing group IV hydrogen gas. 4. The strained heteroepitaxial layer according to claim 1, wherein the buffer layer in the step (a) is a Si—Ge—C based buffer layer. Forming method. 5. The method for forming a strained heteroepitaxial layer according to claim 1, wherein the buffer layer in the step (a) is a Si—C based buffer layer. . 6. The silicon-containing group IV hydrogen gas according to claim 1 is used as SiH ₄ , Si ₂ H ₆ , and Si (CH ₃ ).
_{H 3, Si 3 H 8,} Si (CH 3) 2 H 2, Si (CH
₃ ) One gas selected from the gas group of ₃ H, Si (CH ₃ ) ₄ , Si (CH ₃ ) ₆ and Si (CH ₃ ) ₃ F, or a mixed gas of two or more gases. A method for forming a strained heteroepitaxial layer, which comprises: 7. The carbon-containing group IV hydrogen gas according to claim 1, which is one kind of gas selected from a gas group of CH ₄ , C ₂ H ₆ , C ₃ H ₈ and C ₂ H _4. Alternatively, a method of forming a strained heteroepitaxial layer is characterized in that a mixed gas of two or more kinds of gases is used. 8. The strained heteroepitaxial layer according to claim 1, wherein the vacuum exhaust pressure in the step (a) is set to a high vacuum of 10 ⁻⁷ Pa (Pascal) or less. Method of forming heteroepitaxial layer.