JP3494467B2 - Method of forming semiconductor thin film - Google Patents

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 semiconductor thin film, and more particularly to a method for forming a thin film of HBT (hetero bipolar transistor) having a graded SiGe epitaxial base layer.

[0002]

2. Description of the Related Art In recent years, IV for the purpose of application to high-speed heterobipolar, microwave devices, or superlattice structures
Development of devices of group semiconductor (for example, SiGe) thin film heterostructure is progressing. Above all, SiGe on Si substrate
A SiGe strained epitaxial (mixed crystal) thin film obtained by heteroepitaxially growing a thin film has attracted particular attention. Conventionally, various devices have been developed for the SiGe / Si strained superlattice structure by utilizing the electrical and optical properties caused by the lattice strain. Among these devices, as an example of a device having a lattice strain structure, there is a hetero bipolar transistor (HBT) based on SiGe mixed crystal (Document I: “Silicon-based device”, Maruzen Co., Ltd., July 1991). Issued, PP. 219-226).

As a method of forming a hetero-bipolar transistor (hereinafter referred to as SiGe-HBT) based on this type of SiGe mixed crystal, conventionally, a gas source molecular beam (gas source MBE) epitaxial method, an ultra-vacuum chemical vapor phase has been used. There are a growth (UHV-CVD) method and a low pressure chemical vapor deposition (LPCVD) method.

Although a conventional method for forming a SiGe mixed crystal base layer for SiGe-HBT is not disclosed in Document I,
Usually, the base layer is formed by keeping the film formation temperature constant and changing the gas flow rate ratio. The inventors of the present application also conducted a follow-up experiment to form the base layer.

Next, the film forming conditions at the time of conducting the additional test will be described with reference to FIG.

Forming period of SiGe mixed crystal base layer (period I
II) is a SiGe mixed crystal base layer in which the substrate (wafer) temperature in the furnace is kept constant, for example, a constant amount (15 ccm) of SiH ₄ gas is supplied into the furnace and the GeH ₄ gas flow rate is controlled by a mass flow meter. A predetermined Ge composition ratio gradient was formed therein. Si formed in this way
The Ge composition profile of Ge-HBT has a gradient of the Ge composition ratio in the SiGe mixed crystal base layer from the collector junction to the emitter junction, as disclosed in Document I. By forming such a gradient of the Ge composition ratio in the SiGe mixed crystal base layer, the band gap formed at the boundary between the collector layer and the emitter layer and the SiGe mixed crystal base layer is continuously changed to create a drift electric field. be able to. It has been reported that, by providing such a gradient in the SiGe mixed crystal base layer, the SiGe-HBT can reduce the base transit time by almost half as compared with a silicon homobipolar transistor (Si-BT) and the like (P in Document I).
P. 220-221).

[0007]

However, when the mixed crystal base layer for SiGe-HBT is formed by the conventional forming method, good SiG is obtained for the following reason.
e The mixed crystal base layer could not be obtained. The reason is S
The control of the SiH ₄ gas and the GeH ₄ gas when the iGe mixed crystal base layer has a Ge composition ratio gradient is generally performed by C
This is performed by controlling the flow rate ratio of the Ge source gas and the Si source gas from the gas supply unit of the VD thin film device. At this time, the relationship between the GeH ₄ gas flow rate and the SiGe growth rate is
As disclosed in Document II, the SiGe film formation rate increases almost linearly as the GeH ₄ gas flow rate increases (Document II: “Effect of silicon”).
source gas on silicon-ger
umanium chemical vapor de
position kinetics at ato
mospheric pressure ", T.W. I. K
amins at. Appl. Phys. Lett. 6
1 (1), 6, Jul 1992, PP. 90-9
2).

According to this document II, G in SiGe mixed crystals when various silicon-containing group IV hydrogen gases are used.
It has been reported that the relationship between the e composition ratio and the growth rate (deposition rate) of SiGe and the relationship between the germane (GeH ₄ ) gas flow rate and the SiGe growth rate when the silicon-containing group IV hydrogen gas is kept constant. According to this, for example, when the GeH ₄ gas flow rate is changed, the SiGe growth rate changes substantially linearly (see P. 91 of Document II, (a) and (b) of FIG. 1). However, when the film forming temperature is lowered (for example, 625 ° C.), the linearity is lost and the bent line has an inclination. Further, the SiGe growth rate also changes depending on the film forming temperature. When the film forming temperature is high (eg 700
It has been found that the growth rate of (° C.) Is higher than that when the film forming temperature is lowered.

Therefore, when the film forming temperature is high, GeH
_{When the 4} gas flow rate is increased, the SiGe growth rate is increased, and it is necessary to control the GeH ₄ gas flow rate in seconds.
In general, a mass flow meter is used for controlling the gas flow rate, and it is the current situation that it is difficult to control the gas in units of seconds using this mass flow meter. Therefore, normal Si
The formation of Ge mixed crystal base layer, in order to facilitate control of the GeH ₄ gas flow rate, may be set relatively low deposition temperature (substrate temperature), it is adopted a method of controlling the GeH ₄ gas flow rate There is. However, as disclosed in Document II, if the film forming temperature is lowered, the SiGe growth rate also decreases, and the film forming time becomes longer accordingly. As described above, when the film forming temperature is lowered and the GeH ₄ gas flow rate is decreased (for example, the Ge composition is 10% or less), the growth rate is further reduced, and it takes time to form the SiGe film. For this reason, impurities (here, the residual impurities in the furnace of the thin film forming apparatus) are often taken into the SiGe mixed crystal base layer, and the quality of the SiGe mixed crystal base layer is deteriorated. is there.

Further, the increase in the film forming time also causes a decrease in throughput (the throughput here means the number of wafers processed per unit time), and there is a problem that the device cannot be mass-produced. .

Therefore, there has been a demand for a method of forming a semiconductor thin film which can easily form a stable GeH ₄ gas flow rate and can form a graded SiGe mixed crystal base layer in a short time.

[0012]

According to the present invention, when a SiGe mixed crystal thin film is formed on a base, the period from the start of film formation to the end of film formation is defined as the SiGe mixed crystal film formation period. The temperature at the start of film formation (referred to as the film formation start temperature) during this period is set to a temperature lower than the temperature at the end of film formation (referred to as the film formation end temperature). Further, a temperature gradient is provided between the film formation start temperature and the film formation end temperature. The temperature gradient at this time is preferably 5 ° C./min to 30 ° C./min. Further, germanium (Ge) -containing I with respect to the flow rate of the Si-containing group IV hydrogen gas at the film formation start temperature
The flow rate of the group V hydrogen gas (referred to as a flow rate ratio) is made larger than the flow rate ratio of the film formation end temperature, and then the flow rate ratio is gradually decreased with the lapse of time from the start of film formation to the end of film formation.

[0013]

According to the present invention described above, the film formation temperature at the start of film formation is set to a temperature lower than that at the end of film formation, and a temperature gradient is provided at the start and end times of film formation. Therefore, at the start of film formation, the growth rate is low because the film formation temperature is low, but since the temperature gradient is provided toward the end of film formation, the film formation temperature rises with respect to the predetermined flow rate ratio. The growth rate increases. Therefore, the film formation time for forming the SiGe mixed crystal base layer is shortened.

At the end of film formation, the growth rate decreases as the flow rate ratio decreases, but since the film formation temperature is high, the decrease in growth rate can be suppressed. Therefore, it is possible to keep the SiGe film formation rate from the start of film formation to the end of film formation substantially constant.

Further, when controlling the flow rate ratio, the flow rate ratio at the start of film formation is set to be larger than that at the end of film formation, and the flow rate is controlled by decreasing the flow ratio as time passes to the end of film formation. Therefore, since the film formation temperature at the start of film formation is initially low, the control of the flow rate ratio becomes easier because the growth rate of SiGe decreases. Therefore, the flow rate ratio can be controlled using the mass flow meter. In the SiGe mixed crystal base layer thus formed, the Ge composition ratio on the boundary side with the collector layer is large, while the Ge composition ratio on the boundary side with the emitter layer is small, and the Ge composition ratio slopes. Can have

Further, since the film formation time is shortened, SiGe
Residual impurities mixed in the mixed crystal base layer are reduced. Moreover, the throughput at the time of forming a thin film is improved.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for forming a semiconductor thin film according to the present invention will be described below with reference to the drawings. In addition, FIG.
The shape, size, and arrangement of each component are only schematically shown to the extent that the present invention can be understood. In the embodiment of the present invention, SiGe epitaxial (mixed crystal) for SiGe-HBT (hetero bipolar transistor) is used.
The method of forming the base layer will be described as an example.

1A and 1B are S of the present invention.
FIG. 2 is an explanatory diagram for explaining film forming conditions for explaining a method of forming iGe-HBT, and FIG. 2 is a configuration diagram of an apparatus used for forming this thin film. FIG. 3 is a sectional view of the SiGe-HBT structure formed in the embodiment of the present invention. However, in FIG. 3, some hatching is omitted for the sake of clarity.

First, an apparatus used for forming a semiconductor thin film will be described with reference to FIG.

This apparatus is roughly composed of a reaction furnace section 11, a vacuum exhaust system 23 and a gas supply system 49.
The reaction furnace portion 11 is a metal reaction furnace (chamber) 1
0, water is circulated to cool the chamber wall so that the chamber wall does not reach a high temperature. In addition, a substrate support 14 is provided in the reaction furnace 10, a substrate 18 is arranged downward on the substrate support 14, and the substrate 1
It is structured so that 8 can be placed freely in and out.

In addition, the substrate heating mechanism 1 is provided in the reaction furnace 10.
2 is provided, and therefore, the substrate heating mechanism 12 enables any suitable temperature setting. As the heating mechanism 12, it is suitable to use, for example, an infrared lamp. A temperature measuring means 16 is provided to measure the surface temperature of the substrate 18, and the temperature of the substrate heating mechanism can be controlled. As the temperature measuring means 16, for example, a thermocouple is used. Further, the reaction furnace 10 is divided into an upper part and a lower part with the substrate support 14 as the center. The upper part is called the substrate heating mechanism side 12 and the lower part is called the gas head side 20.
Further, exhaust ports 22 and 24 for vacuum exhaust are provided. Further, vacuum gauges 38 and 40 for measuring the degree of vacuum in the reaction furnace 10 are provided. Further, the reaction furnace 10 is provided with a gas head 20 corresponding to the substrate. The gas head 20 has a gas introduction passage and a cooling water introduction passage that penetrate the outer wall of the reaction furnace.

Next, the vacuum exhaust system of this apparatus will be described.

The vacuum exhaust system 23 is provided with exhaust means 26, 28 and 30 for exhausting the inside of the furnace 10 to vacuum, and an automatic opening / closing valve 34 is connected to the exhaust means 28 side, and the exhaust means 30 side. An automatic opening / closing valve 36 is connected to. The automatic opening / closing valve 34 and the exhaust port 22 are connected, and the valve 36 and the exhaust port 24 are connected. Therefore, the pressure inside the reaction furnace 10 is controlled by opening and closing the valves 34 and 36 arbitrarily and appropriately. Further, the upper part and the lower part in the reaction furnace 10 are configured so that the pressure can be controlled independently.

Next, the gas supply system of this apparatus will be described.

The gas supply system 49 includes gas introduction paths 42a and 42b and automatic opening / closing valves 50, 51, 52, 53, 8
0, 81 and 82, automatic flow rate controllers (also called mass flow meters) 60, 61, 62 and 63, and gas supply units 70, 71, 72 and 73.
Further, exhaust means 32 is provided so that the gas supply system 49 can be exhausted without passing through the reaction furnace 10. The gas introduction passage 42a is connected to the automatic opening / closing valves 50 to 52, and the valves 50, 51, 52 are connected to the automatic flow controllers 60, 61, 62, respectively. Then, the automatic flow rate controllers 60, 61, 62
Are connected to gas supply units 70, 72 and 72, respectively. Further, exhaust pipes 73, 74 and 75 are provided between the valves 50, 51 and 52 and the automatic flow controllers 60, 61 and 62.
Are connected, and the exhaust pipes 73 to 75 are connected to the exhaust pipe 76 via the automatic flow controllers 80 to 82. Further, the exhaust pipe 76 is connected to the exhaust means 32.

Next, with reference to FIGS. 1A, 1B, 2 and 3, a method of forming SiGe-HBT, particularly SiG.
A method of forming the mixed crystal base layer will be described.

FIGS. 1A to 1B are graphs showing the temperature characteristic of the heating cycle of the substrate temperature of the present invention, and the silicon-containing I
IV containing germanium with respect to the flow rate of group V hydrogen gas
The relationship of the flow rate of the group hydrogen gas (referred to as flow rate) is shown.
In FIG. 1A, the horizontal axis represents time (arbitrary), the vertical axis represents substrate temperature (° C.), and in FIG. 1B, the horizontal axis represents time (minutes). The vertical axis shows the flow rate ratio.

First, prior to forming the SiGe mixed crystal base layer 91, a cleaning process is performed to remove the oxide film of the underlayer 90. At this time, for example, a Si substrate (hereinafter referred to as a substrate) is used as the base 90.

The substrate 90 is dipped in a solution of sulfuric acid-hydrogen peroxide solution heated to 120 ° C. to form an oxide film on the substrate 90. At this time, the thickness of the oxide film is set to about 10Å. Immediately thereafter, the substrate 90 is immersed in a 1 wt% HF solution for about 3 minutes to completely remove the oxide film.

Next, the substrate 90 from which the cleaning and the oxide film are removed is immediately carried into a CVD thin film forming apparatus (hereinafter referred to as a reaction furnace). At this time, the heating temperature of the reaction furnace 10 is preferably set to 300 ° C to 450 ° C.

Next, the valves 34 and 36 are opened, and the inside of the reaction furnace 10 is, for example, 1 × using the exhaust means 26, 28 and 30.
The substrate 90 is cleaned by evacuation to 10 ⁻⁸ Pa. Then, while measuring the temperature of the substrate 90 by the measuring means 16, the inside of the reaction furnace 10 is heated by radiant heating by the infrared lamp 12. The substrate temperature at this time is, for example, 800 ° C.
The substrate 90 is cleaned by performing a heat treatment at 850 ° C. for about 2 to 5 minutes (period I in FIG. 1A).

Next, the substrate temperature is once lowered to about 625 ° C. and the heating temperature is kept constant, and then the SiGe mixed crystal base layer 91 is formed on the substrate 90. At this time, when the film formation is started T ₁
The period from the completion of the film formation to T ₂ is called a SiGe mixed crystal thin film formation period (period II). The temperature at time T ₁ is called the film formation start temperature, and the temperature at time T ₂ is called the film formation end temperature. Keep it at 625 ° C for cleaning period I,
The temperature is raised at a predetermined temperature rising rate from time T _1, and at time T ₂ , the film formation end temperature is kept constant for a certain period of time. In this way, defects or strains in the crystal are adjusted by keeping the film formation end temperature constant. At this time, it is preferable that the temperature increase rate from the film formation start temperature of 625 ° C. to the film formation end temperature of 700 ° C. be an appropriate temperature increase rate of 5 to 30 ° C./min. Further, the rate of temperature increase of 20 ° C./minute is optimal because the growth rate can be made almost constant.

Next, after opening the valve 80 of the thin film forming apparatus, the valve of the gas supply unit 70 is opened, and a silicon-containing group IV hydrogen gas (eg, SiH ₄ gas) is flowed to the exhaust means 32 side. At this time, when the SiH ₄ gas is supplied to the reaction furnace 10, the Si flow rate controller 60 is used in advance so that the pressure inside the furnace is reduced to about 1 Pa.
It is recommended to adjust the H ₄ gas flow rate. Then, the valve 80 is closed and the valve 50 is opened to supply SiH ₄ gas into the reaction furnace 10. At this time, preferably SiH
_It is good to set the flow rate of ₄ gases to 15 sccm.

Next, by opening the valve 52 and the gas supply unit 72 by using the same method as for the SiH ₄ gas, SiH ₄
In addition to the gas, a group IV group hydrogen gas containing germanium (for example, germane (GeH ₄ gas)) is flowed to the exhaust means 23 side. Then, the valve 52 is opened and GeH ₄ is fed to the reactor 10.
Supply gas. At this time, it is preferable that the film formation start time T
The GeH ₄ gas flow rate of ₁ is preferably set to ₄ sccm, for example. At this time, the flow rate ratio is 0.27. Here, the flow rate ratio is represented by GeH ₄ gas flow rate / SiH ₄ gas flow rate. The SiH ₄ gas flow rate is kept constant during the SiGe mixed crystal thin film formation period (period II). The flow rate ratio is increased at the start of film formation T _{1, and} is gradually decreased with the lapse of time to T ₂ at the end of film formation. At this time,
At the end of film formation, the flow rate of GeH ₄ gas at T ₂ is set to 1 sccm.
It is good to At this time, the flow rate ratio is 0.13.
The control of the GeH ₄ gas flow rate at this time was performed at a set flow rate of the mass flow controller of 1 sccm / min. At this time, the film thickness of the SiGe mixed crystal base layer 91 is, for example, 200
Å ~ 400Å.

In addition, the growth rate of this embodiment is as follows.
It is preferable to set as follows according to the residual impurities in 0 and the amounts of oxygen (O ₂ ) and water (H ₂ O) in various gases. That is, when the amount of impurities is 1 ppm, the growth rate is 1
More than 00Å / min, and the amount of impurities is 10ppb-1pp
In the case of m, it is preferable to set it to 25 Å / min or more. Further, when the growth rate is 100 Å / min, preferably,
It is preferable to set the film forming temperature in the range of 625 to 725 ° C.

Thereafter, a doped polysilicon layer 92 is formed and used as an emitter layer. After that, the electrode 96 is formed on the emitter layer 92. In this way
The SiGe-HBT having the collector layer 90, the base layer 91 and the emitter layer 92 of SiGe-HBT is completed (see FIG. 3). In the description of this embodiment, the method of forming the polysilicon layer 93, the p ⁺ polysilicon layer 94 and the silicon oxide film 95 is omitted.

FIG. 4 shows experimental data used for explaining the relationship between the GeH ₄ gas flow rate and the Ge composition ratio. At this time, SiH ₄ gas is used as a gas mixed with the GeH ₄ gas, and the film formation temperature is 675 ° C. GeH on the horizontal axis in the figure
₄ Gas flow rate (sccm) is taken and the vertical axis is Ge composition / Si
The Ge mixed crystal, that is, the relationship of the Ge composition ratio (%) is plotted and shown. As can be understood from FIG. 4, when the GeH ₄ gas flow rate is 1 ccm or more, the Ge composition ratio increases almost linearly. That is, the GeH ₄ gas flow rate is 1, 2,
Ge composition ratio is 1 at 3, 4 and 5 sccm, respectively.
5%, 20%, 30%, 35%, and 40%.

FIG. 5 shows experimental data used for explaining the relationship between the Ge composition ratio and the growth rate of the SiGe mixed crystal. The horizontal axis represents the Ge composition ratio (%), and the vertical axis represents the growth rate (Å / min).

As can be understood from FIG. 5, the film forming temperature is 6
10%, 20%, 30% and 40% G at 25 ° C
The growth rate with respect to the e composition ratio is 50, 70, 120, 1
It becomes 50Å / min, and if plotted, it will be a straight line connected by black circles. On the other hand, when the film forming temperature is 700 ° C., 10
The growth rates are 120, 140, and 170 Å / min for Ge composition ratios of%, 20%, and 30%, which are plotted as straight lines connected by white circles. Therefore, when forming a conventional SiGe mixed crystal base layer while keeping the film formation temperature constant (for example, 675 ° C.) and changing the Ge composition ratio, especially in a region where the Ge composition ratio is large, the growth rate is high. Also grows. Therefore, the mass flow meter could not follow, and the gas flow rate could not be precisely controlled. On the other hand, in the embodiment of the present invention, a temperature gradient is provided between the film formation start temperature at the time of film formation start (T ₁ ) and the film formation end temperature at the time of film formation end (T ₂ ). Therefore, at time T ₁ , even if the film formation start temperature is low, the temperature is increased linearly or stepwise, so that the growth rate of SiGe increases. On the other hand, at the end of film formation (T ₂ ), the GeH ₄ gas flow rate (Ge
Since the composition ratio) is small, the growth rate is low, but the growth rate is not lowered because the film formation temperature is high. Therefore, the growth rate from the start of film formation to the end of film formation can be made substantially constant. Therefore, since the film forming temperature is lowered as in the conventional case, the growth rate does not decrease and the film forming time is shortened.
The probability of impurities being mixed into the iGe mixed crystal base layer is reduced, and therefore, the film quality of the SiGe mixed crystal base layer becomes uniform. Also, because the film formation time is shortened,
Since the throughput is improved, the SiGe-HBT can be mass-produced.

FIG. 6 is a distribution diagram schematically showing the Ge composition when the cross section of the collector layer (base), the base layer and the emitter layer of FIG. 3 is measured by X-ray diffraction and converted into Ge composition. Is. The vertical axis represents the Ge composition ratio (%) and the horizontal axis represents the film thickness (Å). At this time,
The boundary between the collector layer and the base layer is the starting point (0Å), and the minus sign is added to the direction of the film thickness on the emitter layer side.

As can be understood from FIG. 6, the starting point (0Å)
Then, the Ge composition ratio becomes 25%, and then Ge
The composition ratio decreases linearly, and the thickness of the base layer is 300Å
Then, the value of the Ge composition ratio becomes 10%, and then the Ge composition ratio rapidly becomes 0%. Here, the rising and falling values of the Ge composition ratio are shown by straight lines, but in reality, they are expressed by curves. When the Ge composition profile of FIG. 6 is compared with the conventional reference I, in the reference I, the inclination of the Ge composition ratio of the base layer is inclined in a triangular shape from the emitter side to the collector side (reference I, Figure 8.
44), this embodiment has a trapezoidal inclination.
Therefore, in the embodiment of the present invention, in terms of energy band, the height of the barrier for holes injected from the base layer to the emitter layer is made higher than the height of the barrier for electrons injected from the emitter layer to the base layer. Can be large. Therefore, lower the carrier concentration of the emitter layer,
There is also an advantage that the injection efficiency on the emitter side does not decrease even if the carrier concentration of the base layer is increased.

Further, in the embodiment of the present invention, SiGe-
Although the example of the HBT has been described, the present invention is not limited to this HBT, and may be applied to, for example, SiGe-MOS.

Further, according to the present invention, the temperature gradient during the SiGe mixed crystal thin film formation period is set to 5 to 30 ° C./min.
Since the film formation start temperature can be lowered, the control of the GeH ₄ gas mass flow meter becomes easy.

Although SiH ₄ gas is used in the embodiment of the present invention, disilane may be used. In this case, when disilane is used, the growth rate can be increased with respect to the film forming temperature, so that the film forming time can be further shortened.

Further, in this embodiment, the infrared lamp is used as the heating means, but the heater may be set outside the reaction furnace and heated by utilizing radiant heat.

[0046]

As is clear from the above description, in the method for forming a semiconductor thin film of the present invention, a temperature gradient is provided between the film formation start temperature and the film formation end temperature. At this time, the film formation start temperature is lower than the film formation end temperature. Then, the flow rate ratio at the start of film formation is set to be larger than that at the end of film formation, and the flow rate ratio is gradually decreased as time goes to the end of film formation. For this reason, the growth rate during the SiGe mixed crystal thin film formation period can be kept substantially constant, and G
It is possible to form a SiGe mixed crystal base layer having a gradient of e composition ratio. Therefore, the impurities such as residual impurities in the reaction furnace are suppressed from being mixed into the base layer, so that the film quality of the SiGe mixed crystal base layer becomes uniform. Further, since the film forming time is shortened, the throughput is reduced, so that when manufacturing a semiconductor thin film element, the element can be mass-produced.

[Brief description of drawings]

1 (A) to 1 (B) are a heating cycle diagram and a flow rate characteristic diagram provided for explaining film forming conditions of a SiGe mixed crystal base layer of the present invention.

FIG. 2 is a schematic configuration diagram of a CVD thin film forming apparatus used in the present invention.

FIG. 3 is a cross-sectional view for explaining the structure of the graded SiGe-HBT of the present invention.

FIG. 4 is an explanatory diagram for explaining a relationship between a GeH ₄ gas flow rate and a Ge composition ratio.

FIG. 5 is an explanatory diagram for explaining a relationship between a Ge composition ratio and a growth rate.

FIG. 6 is an explanatory diagram provided for explaining a Ge composition profile of SiGe-HBT of the present invention.

7 (A) to (B) are a heating cycle diagram and a flow rate characteristic diagram for explaining film forming conditions of a conventional SiGe mixed crystal base layer.

[Explanation of symbols]

90: Underlayer (collector layer) 91: SiGe mixed crystal base layer (base layer) 92: n ⁺ polysilicon layer (emitter layer) 93: Polysilicon layer 94: p ⁺ polysilicon layer 95: Silicon oxide film 96: Electrode

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 21/205 H01L 21/331

Claims (3)

(57) [Claims] 1. When forming a SiGe mixed crystal thin film on a base using a CVD method, the period from the start of film formation to the end of film formation is SiG.
The mixed crystal thin film formation period is set, and the temperature at the start of film formation (referred to as the film formation start temperature) during the period is set lower than the temperature at the end of film formation (referred to as the film formation end temperature), and A temperature gradient is provided between the film formation start temperature and the film formation end temperature, and germanium (Ge) -containing IV with respect to the flow rate of the group IV hydrogen gas containing silicon (Si) at the film formation start temperature.
The flow rate of the group-based hydrogen gas (referred to as a flow rate ratio) is set to be larger than the flow rate ratio of the film formation end temperature, and the flow rate ratio is changed as time elapses from the start of the film formation formation to the end of the film formation formation. A method for forming a semiconductor thin film, which is characterized in that the size is successively reduced. 2. The method for forming a semiconductor thin film according to claim 1, wherein the temperature gradient between the film formation start temperature and the film formation end temperature is in the range of 5 ° C./min to 30 ° C./min. A method for forming a semiconductor thin film, comprising: 3. The method for forming a semiconductor thin film according to claim 1, wherein the group IV hydrogen gas containing germanium is silane (SiH ₄ ) or disilane (Si ₂ H ₆ ). Method for forming semiconductor thin film.