Semiconductor film formation device

A semiconductor film formation device has: a reaction vessel that includes a gas flow path to allow source gas to pass through and a substrate mount site provided in the gas flow path to mount a substrate; a temperature control means that is disposed opposite to the substrate mount site and close to the reaction vessel to control the internal temperature of the reaction vessel; and a thermal conductivity adjusting member that is disposed between the reaction vessel and the temperature control means. The thermal conductivity adjusting member has a section with a thermal conductivity different from the other section along the gas flow path.

The present application is based on Japanese patent application No. 2003-072909, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a semiconductor film formation device and, particularly, to a semiconductor film formation device that is provided with a temperature control means to control the internal temperature of reaction vessel to offer a good evenness in film thickness and composition ratio.

2. Description of the Related Art

Conventionally, the CVD (chemical vapor deposition) method is used to grow a semiconductor film on the surface of a wafer. In the CVD method, source gases supplied into a reaction vessel react with each other on the surface of a substrate disposed in the reaction vessel and its reacted product is deposited on the substrate while being grown as a semiconductor film. It is desired that the semiconductor film thus produced has a good evenness in thickness, composition and impurity distribution. Such evenness is influenced by conditions of gas flow and temperature distribution in the reaction vessel. Thus, it is important to finely control these conditions to have a semiconductor film with good evenness.

Japanese patent application laid-open No. 4-132213 discloses a semiconductor film formation device that the internal temperature distribution of reaction vessel is controlled by providing pipes for coolant in the wall of reaction vessel and by separately setting the temperature or flow rate of coolant to be supplied through the pipes.

However, the conventional semiconductor film formation device has problems as below.

The device is complicated in its structure since it needs to provide pipes for coolant in the wall of reaction vessel. Therefore, the manufacturing cost must be increased.

Further, the device is complicated in its operation since it needs to separately set the temperature or flow rate of coolant to be supplied through the pipes. Therefore, the operating or maintenance cost must be increased.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a semiconductor film formation device that the internal temperature distribution of reaction vessel can be suitably conducted while simplifying its structure and operation.

According to a first aspect of the invention, a semiconductor film formation device comprises:

a reaction vessel that includes a gas flow path to allow source gas to pass through and a substrate mount site provided in the gas flow path to mount a substrate;

a temperature control means that is disposed opposite to the substrate mount site and close to the reaction vessel to control the internal temperature of the reaction vessel; and

a thermal conductivity adjusting member that is disposed between the reaction vessel and the temperature control means;

wherein the thermal conductivity adjusting member has a first section with a thermal conductivity different from the other section along the gas flow path.

According to a second aspect of the invention, a semiconductor film formation device comprises:

a reaction vessel that includes a gas flow path to allow source gas to pass through and a substrate mount site provided in the gas flow path to mount a substrate; and

a temperature control means that is disposed opposite to the substrate mount site and close to the reaction vessel to control the internal temperature of the reaction vessel;

wherein the reaction vessel has a section with a wall thickness smaller than the other section to form an interspace between the reaction vessel and the temperature control means.

According to a third aspect of the invention, a semiconductor film formation device comprises:

a reaction vessel that includes a gas flow path to allow source gas to pass through and a substrate mount site provided in the gas flow path to mount a substrate;

a temperature control means that is disposed opposite to the substrate mount site and close to the reaction vessel to control the internal temperature of the reaction vessel;

a plate member that is disposed opposite to the substrate mount site in the gas flow path; and

a thermal conductivity adjusting member that is disposed between the temperature control means and the plate member;

wherein the thermal conductivity adjusting member has a first section with a thermal conductivity different from the other section along the gas flow path.

According to a fourth aspect of the invention, a semiconductor film formation device comprises:

a reaction vessel that includes a gas flow path to allow source gas to pass through and a substrate mount site provided in the gas flow path to mount a substrate;

a temperature control means that is disposed opposite to the substrate mount site and close to the reaction vessel to control the internal temperature of the reaction vessel; and

a plate member that is disposed opposite to the substrate mount site in the gas flow path;

wherein the reaction vessel has a section with a wall thickness smaller than the other section to form an interspace between the reaction vessel and the temperature control means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

FIG. 1is a cross sectional view showing a semiconductor film formation device in the first preferred embodiment of the invention.

A reaction vessel102of silica glass is provided with a substrate104of single-crystal gallium arsenide disposed on its inner surface. Source gas to form semiconductor film and carrier gas to carry the source gas are supplied into the left opening of the reaction vessel102, passing through the surface of the substrate104, discharged from the right opening of the reaction vessel102. The source gas is arsine (AsH3) gas as V group source gas and trimethylgallium (TMG) gas as III group source gas, and the carrier gas is hydrogen gas.

The reaction vessel102is also provided with heaters105on its one outer surface, and the temperature of substrate104is thereby set to be 600° C. The reaction vessel102is further provided with a cooling jacket103of stainless steel to cool the reaction vessel102on the other outer surface. The cooling jacket103is connected to the reaction vessel102through a thermal conductivity adjusting member101of carbon.

As shown inFIG. 1, the thermal conductivity adjusting member101has a difference in thickness between regions. Namely, it has a full thickness in regions1and3and a reduced thickness in region2, whereby, in region2, an interspace106with a rectangular cross section is formed between the thermal conductivity adjusting member101and the outer surface of reaction vessel102. Due to the existence of interspace106, the thermal conductivity of the thermal conductivity adjusting member101in region2lowers as compared to that in regions1and3. As a result, the cooling effect in region2lowers as compared to that in regions1and3.

Semiconductor films are grown by using the semiconductor film formation device of this embodiment, which is provided with the thermal conductivity adjusting member101, and by using a semiconductor film formation device without the thermal conductivity adjusting member101. Then, between the semiconductor films thus grown, its average growth rate and in-plane thickness distribution are evaluated. The average growth rate is increased to 12 nanometers/sec, in case of with the thermal conductivity adjusting member101, while it is 10 nanometers/sec. in case of without the thermal conductivity adjusting member101. The in-plane thickness distribution is ±1.0 percent in case of with the thermal conductivity adjusting member101, while it is ±2 percents in case of without the thermal conductivity adjusting member101. Thus, the evenness of film thickness is improved in this embodiment.

The reasons why the above results are obtained will be described below.

In region1where the source gas and carrier gas are firstly introduced in the reaction vessel102, the cooling effect at the lower inside of reaction vessel102is predominant. Therefore, a large temperature gradient is formed in the reaction vessel102. When the mixed gases are introduced into region1, there occurs a thermal diffusion phenomenon that relatively heavy molecules are diffused to a low-temperature region. So, the source gas concentrates to the low-temperature region on the lower side of reaction vessel102. As a result, the concentration of source gas on the upper side of reaction vessel102lowers and the deposition of semiconductor film on the wall surface is reduced. Thus, the wasting of source gas can be prevented.

Subsequently, in region2near the substrate104, the cooling effect at the lower inside of reaction vessel102lowers. Therefore, the temperature gradient formed in the reaction vessel102reduces and the thermal diffusion effect lovers. Thereby, the source gas flown concentrating the lower inside of reaction vessel102in region1is diffused to the upper inside of reaction vessel102according as the thermal diffusion effect lowers. Thus, it is assumed that the growth rate is enhanced since the concentration of source gas rises near the surface of substrate104. Also, it is assumed that the evenness of in-plane thickness distribution is improved since the wasting of source gas in region1is suppressed and, therefore, the source gas near the substrate104does not get low rapidly.

Then, in region3on the downstream side of substrate104, the cooling effect by the cooling jacket103increases again, the source gas concentrates to the lower inside of reaction vessel102, and the deposition of semiconductor film on the wall surface is reduced.

Although in this embodiment the thermal conductivity adjusting member101has two-stage thickness portions, i.e., thick portion and thin portion, it may have a curved cross section as shown inFIG. 2or a stepwise cross section as shown inFIG. 3. In other words, due to the curved cross section or stepwise cross section, there is formed an interspace106having a variable height along the direction of gas flow between the thermal conductivity adjusting member101and the outer surface of reaction vessel102. According as the height of interspace106increases, the thermal conductivity of the thermal conductivity adjusting member101lowers. Namely, the cooling effect is minimized at the maximum height of interspace106. In this way, temperature distribution in each region can be further finely controlled.

The method of providing the stepwise cross section with the thermal conductivity adjusting member101may be such that a plurality of thermal conductivity adjusting member members are stacked as shown inFIG. 4Aor such that a plurality of thermal conductivity adjusting member members with different thicknesses are crosswise arranged as shown inFIG. 4A.

Although in this embodiment the thermal conductivity adjusting member101directly contacts the reaction vessel102, these may be disposed through a gap without being directly contacted each other.

Although in this embodiment the thermal conductivity adjusting member101is of carbon, it may be of metal or ceramics.

As described above, a difference in temperature between regions of reaction vessel102is made by varying the height of interspace106formed between the thermal conductivity adjusting member101and the outer surface of reaction vessel102. Therefore, the semiconductor film formation device of this embodiment can control the temperature distribution and gas concentration distribution in the reaction vessel102without complicating the device structure.

Second Embodiment

FIG. 5is a cross sectional view showing a semiconductor film formation device in the second preferred embodiment of the invention.

Different from the first embodiment, the cooling jacket103of stainless steel is connected to the reaction vessel102of silica glass through a thermal conductivity adjusting member107that is composed of members108and110which are of stainless steel and a member109of carbon. In this structure, since the thermal conductivity of stainless steel members108and110is greater than that of carbon member109, a portion of reaction vessel102to contact the stainless steel members108and110is cooled more rapidly than that to contact the carbon member109. Therefore, the semiconductor film formation device of this embodiment can have the same effect as the first embodiment such that a difference in temperature between regions of reaction vessel102is made.

Under the same conditions as the first embodiment, semiconductor films are grown by using the semiconductor film formation device of this embodiment, which is provided with the thermal conductivity adjusting member101, and by using a semiconductor film formation device without the thermal conductivity adjusting member101. Then, between the semiconductor films thus grown, its average growth rate and in-plane thickness distribution are evaluated. The average growth rate is increased to 12 nanometers/sec. in case of with the thermal conductivity adjusting member101, while it is 10 nanometers/sec. in case of without the thermal conductivity adjusting member101. The in-plane thickness distribution is ±0.9 percents in case of with the thermal conductivity adjusting member101, while it is ±2 percents in case of without the thermal conductivity adjusting member101. Thus, the evenness of film thickness is improved in this embodiment.

Although in this embodiment the members108,109and110composing the thermal conductivity adjusting member101each have a single structure, they may be structured such that, for example, the member109is formed by vertically stacking members111,112with different thermal conductivities as shown inFIG. 6. In this way, the temperature distribution in reaction vessel102can be controlled.

Although the members108,109and110of this embodiment are of carbon or stainless steel, they may be of metal such as copper and aluminum or ceramics.

As described above, a difference in temperature between regions of reaction vessel102is made by varying the thermal conductivity of thermal conductivity adjusting member107. Therefore, the semiconductor film formation device of this embodiment can control the temperature distribution and gas concentration distribution in the reaction vessel102without complicating the device structure.

Third Embodiment

FIG. 7is a cross sectional view showing a semiconductor film formation device in the third preferred embodiment of the invention.

Different from the preceding embodiments, the thickness of reaction vessel102wall where the reaction vessel102of silica glass is next to the cooling jacket103of stainless steel is changed between regions thereof as shown inFIG. 7.

In this structure, the cooling effect is relatively large in regions1and3where the reaction vessel102has a thick wall to contact the cooling jacket103and is relatively small in region2where the reaction vessel102has a thin wall to neighbor the cooling jacket103through the interspace106. Therefore, the semiconductor film formation device of this embodiment can have the same effect as the preceding embodiments with the thermal conductivity adjusting member such that a difference in temperature between regions of reaction vessel102is made.

Under the same conditions as the first embodiment, semiconductor films are grown by using the semiconductor film formation device of this embodiment which has the reaction vessel102with a changed wall thickness between regions and by using a semiconductor film formation device which has the reaction vessel102without such a changed wall thickness. Then, between the semiconductor films thus grown, its average growth rate and in-plane thickness distribution are evaluated. The average growth rate is increased to 11.8 nanometers/sec. in case of the reaction vessel102with changed wall thickness, while it is 10 nanometers/sec. in case of the reaction vessel102without changed wall thickness. The in-plane thickness distribution is ±1.1 percents in case of the reaction vessel102with changed wall thickness, while it is ±2 percents in case of the reaction vessel102without changed wall thickness. Thus, the evenness of film thickness is improved in this embodiment.

Fourth Embodiment

Although in the preceding embodiments the horizontal type semiconductor film formation devices are explained that gas flows in one direction in the reaction vessel102, the invention can be also applied to a semiconductor film formation device with multiple gas flow directions.

FIG. 8is a cross sectional view showing a semiconductor film formation device in the fourth preferred embodiment of the invention.

A reaction vessel208is provided with a susceptor209of carbon disposed on its upper inner surface and a water-cooling jacket203of stainless steel on its lower inner surface. A silica plate202is disposed on the water-cooling jacket203through a thermal conductivity adjusting member201of stainless steel. A gas nozzle207is disposed connected to the center position of reaction vessel208. Two substrates204of single-crystal gallium arsenide are disposed on the lower surface of susceptor209such that they are positioned at an equal distance from the gas nozzle207. The substrates204and the susceptor209are heated to an average temperature of 600° C. by a heater205disposed on the reaction vessel208.

The thermal conductivity adjusting member201is structured such that there is formed an interspace206having a variable height along the direction of gas flow between the thermal conductivity adjusting member201and the lower surface of silica plate202.

In this device, source gases of arsine, trimethylgallium and carrier gas of hydrogen to be introduced into the reaction vessel208through the gas nozzle207move through a space surrounded by the susceptor209and the silica plate202in the radial direction, passing through the surface of the substrate204, discharged from the circumferential edge of the reaction vessel208. In this structure, since the cross-section area of gas flow region increases according as being close to the circumference of device, the gas flow rate lowers rapidly. Due to the lowering of gas flow rate, the influence of thermal diffusion to the concentration distribution of source gas increases. Therefore, in order to form a semiconductor film with even thickness, it is highly effective to control the internal temperature distribution of reaction vessel208by providing the thermal conductivity adjusting member201of this embodiment.

Semiconductor films are grown by using the semiconductor film formation device of this embodiment, which is provided with the thermal conductivity adjusting member201, and by using a semiconductor film formation device without the thermal conductivity adjusting member201. Then, between the semiconductor films thus grown, its average growth rate and in-plane thickness distribution are evaluated. The average growth rate is increased to 15 nanometers/sec. in case of with the thermal conductivity adjusting member201, while it is 12 nanometers/sec. in case of without the thermal conductivity adjusting member201. The in-plane thickness distribution is ±0.6 percents in case of with the thermal conductivity adjusting member201, while it is ±1.8 percents in case of without the thermal conductivity adjusting member201. Thus, the evenness of film thickness is improved in this embodiment.

Although in this embodiment the thermal conductivity adjusting member201is formed having different thicknesses between regions, it may be of materials with different thermal conductivities between regions as in the second embodiment. Alternatively, as shown inFIG. 9, a silica plate202with different thicknesses between regions may be used.

Although, in the above embodiments, the thermal conductivity is controlled in the direction parallel to gas flow, the invention can be applied to the other control direction of thermal conductivity. For example, by controlling the thermal conductivity in the direction vertical to gas flow, the effect of controlling the internal temperature distribution of reaction vessel can be obtained. As a result, a semiconductor film that has an excellent evenness in thickness and composition ratio can be obtained.