Abstract:
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.

Description:
[0001]    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  
         [0002]    1. Field of the Invention  
           [0003]    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.  
           [0004]    2. Description of the Related Art  
           [0005]    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.  
           [0006]    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.  
           [0007]    However, the conventional semiconductor film formation device has problems as below  
           [0008]    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.  
           [0009]    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  
         [0010]    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.  
           [0011]    According to a first aspect of the invention, a semiconductor film formation device comprises:  
           [0012]    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;  
           [0013]    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  
           [0014]    a thermal conductivity adjusting member that is disposed between the reaction vessel and the temperature control means;  
           [0015]    wherein the thermal conductivity adjusting member has a first section with a thermal conductivity different from the other section along the gas flow path.  
           [0016]    According to a second aspect of the invention, a semiconductor film formation device comprises:  
           [0017]    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  
           [0018]    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;  
           [0019]    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.  
           [0020]    According to a third aspect of the invention, a semiconductor film formation device comprises:  
           [0021]    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;  
           [0022]    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;  
           [0023]    a plate member that is disposed opposite to the substrate mount site in the gas flow path; and  
           [0024]    a thermal conductivity adjusting member that is disposed between the temperature control means and the plate member;  
           [0025]    wherein the thermal conductivity adjusting member has a first section with a thermal conductivity different from the other section along the gas flow path.  
           [0026]    According to a fourth aspect of the invention, a semiconductor film formation device comprises:  
           [0027]    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;  
           [0028]    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  
           [0029]    a plate member that is disposed opposite to the substrate mount site in the gas flow path;  
           [0030]    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. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]    The preferred embodiments according to the invention will be explained below referring to the drawings, wherein:  
         [0032]    [0032]FIG. 1 is a schematic cross sectional view showing a semiconductor film formation device in a first preferred embodiment of the invention;  
         [0033]    [0033]FIG. 2 is a schematic cross sectional view showing a modification of the semiconductor film formation device in the first embodiment;  
         [0034]    [0034]FIG. 3 is a schematic cross sectional view showing another modification of the semiconductor film formation device in the first embodiment;  
         [0035]    [0035]FIGS. 4A and 4B are cross sectional views showing compositional examples of thermal conductivity adjusting member  101  in the first embodiment;  
         [0036]    [0036]FIG. 5 is a schematic cross sectional view showing a semiconductor film formation device in a second preferred embodiment of the invention;  
         [0037]    [0037]FIG. 6 is a schematic cross sectional view showing a modification of the semiconductor film formation device in the second embodiment;  
         [0038]    [0038]FIG. 7 is a schematic cross sectional view showing a semiconductor film formation device in a third preferred embodiment of the invention;  
         [0039]    [0039]FIG. 8 is a schematic cross sectional view showing a semiconductor film formation device in a fourth preferred embodiment of the invention; and  
         [0040]    [0040]FIG. 9 is a schematic cross sectional view showing a modification of the semiconductor film formation device in the fourth embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     First Embodiment  
       [0041]    [0041]FIG. 1 is a cross sectional view showing a semiconductor film formation device in the first preferred embodiment of the invention.  
         [0042]    A reaction vessel  102  of silica glass is provided with a substrate  104  of 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 vessel  102 , passing through the surface of the substrate  104 , discharged from the right opening of the reaction vessel  102 . The source gas is arsine (AsH 3 ) gas as V group source gas and trimethylgallium (TMG) gas as III group source gas, and the carrier gas is hydrogen gas.  
         [0043]    The reaction vessel  102  is also provided with heaters  105  on its one outer surface, and the temperature of substrate  104  is thereby set to be 600° C. The reaction vessel  102  is further provided with a cooling jacket  103  of stainless steel to cool the reaction vessel  102  on the other outer surface. The cooling jacket  103  is connected to the reaction vessel  102  through a thermal conductivity adjusting member  101  of carbon.  
         [0044]    As shown in FIG. 1, the thermal conductivity adjusting member  101  has a difference in thickness between regions. Namely, it has a full thickness in regions  1  and  3  and a reduced thickness in region  2 , whereby, in region  2 , an interspace  106  with a rectangular cross section is formed between the thermal conductivity adjusting member  101  and the outer surface of reaction vessel  102 . Due to the existence of interspace  106 , the thermal conductivity of the thermal conductivity adjusting member  101  in region  2  lowers as compared to that in regions  1  and  3 . As a result, the cooling effect in region  2  lowers as compared to that in regions  1  and  3 .  
         [0045]    Semiconductor films are grown by using the semiconductor film formation device of this embodiment, which is provided with the thermal conductivity adjusting member  101 , and by using a semiconductor film formation device without the thermal conductivity adjusting member  101 . 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 member  101 , while it is 10 nanometers/sec. in case of without the thermal conductivity adjusting member  101 . The in-plane thickness distribution is ±1.0 percent in case of with the thermal conductivity adjusting member  101 , while it is ±2 percents in case of without the thermal conductivity adjusting member  101 . Thus, the evenness of film thickness is improved in this embodiment.  
         [0046]    The reasons why the above results are obtained will be described below.  
         [0047]    In region  1  where the source gas and carrier gas are firstly introduced in the reaction vessel  102 , the cooling effect at the lower inside of reaction vessel  102  is predominant Therefore, a large temperature gradient is formed in the reaction vessel  102 . When the mixed gases are introduced into region  1 , 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 vessel  102 . As a result, the concentration of source gas on the upper side of reaction vessel  102  lowers and the deposition of semiconductor film on the wall surface is reduced. Thus, the wasting of source gas can be prevented.  
         [0048]    Subsequently, in region  2  near the substrate  104 , the cooling effect at the lower inside of reaction vessel  102  lowers. Therefore, the temperature gradient formed in the reaction vessel  102  reduces and the thermal diffusion effect lovers. Thereby, the source gas flown concentrating the lower inside of reaction vessel  102  in region  1  is diffused to the upper inside of reaction vessel  102  according 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 substrate  104 . Also, it is assumed that the evenness of in-plane thickness distribution is improved since the wasting of source gas in region  1  is suppressed and, therefore, the source gas near the substrate  104  does not get low rapidly.  
         [0049]    Then, in region  3  on the downstream side of substrate  104 , the cooling effect by the cooling jacket  103  increases again, the source gas concentrates to the lower inside of reaction vessel  102 , and the deposition of semiconductor film on the wall surface is reduced.  
         [0050]    Although in this embodiment the thermal conductivity adjusting member  101  has two-stage thickness portions, i.e., thick portion and thin portion, it may have a curved cross section as shown in FIG. 2 or a stepwise cross section as shown in FIG. 3. In other words, due to the curved cross section or stepwise cross section, there is formed an interspace  106  having a variable height along the direction of gas flow between the thermal conductivity adjusting member  101  and the outer surface of reaction vessel  102 . According as the height of interspace  106  increases, the thermal conductivity of the thermal conductivity adjusting member  101  lowers. Namely, the cooling effect is minimized at the maximum height of interspace  106 . In this way, temperature distribution in each region can be further finely controlled.  
         [0051]    The method of providing the stepwise cross section with the thermal conductivity adjusting member  101  may be such that a plurality of thermal conductivity adjusting member members are stacked as shown in FIG. 4A or such that a plurality of thermal conductivity adjusting member members with different thicknesses are crosswise arranged as shown in FIG. 4A.  
         [0052]    Although in this embodiment the thermal conductivity adjusting member  101  directly contacts the reaction vessel  102 , these may be disposed through a gap without being directly contacted each other.  
         [0053]    Although in this embodiment the thermal conductivity adjusting member  101  is of carbon, it may be of metal or ceramics.  
         [0054]    As described above, a difference in temperature between regions of reaction vessel  102  is made by varying the height of interspace  106  formed between the thermal conductivity adjusting member  101  and the outer surface of reaction vessel  102 . Therefore, the semiconductor film formation device of this embodiment can control the temperature distribution and gas concentration distribution in the reaction vessel  102  without complicating the device structure.  
       Second Embodiment  
       [0055]    [0055]FIG. 5 is a cross sectional view showing a semiconductor film formation device in the second preferred embodiment of the invention.  
         [0056]    Different from the first embodiment, the cooling jacket  103  of stainless steel is connected to the reaction vessel  102  of silica glass through a thermal conductivity adjusting member  107  that is composed of members  108  and  110  which are of stainless steel and a member  109  of carbon. In this structure, since the thermal conductivity of stainless steel members  108  and  110  is greater than that of carbon member  109 , a portion of reaction vessel  102  to contact the stainless steel members  108  and  110  is cooled more rapidly than that to contact the carbon member  109 . 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 vessel  102  is made.  
         [0057]    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 member  101 , and by using a semiconductor film formation device without the thermal conductivity adjusting member  101 . 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 member  101 , while it is 10 nanometers/sec. in case of without the thermal conductivity adjusting member  101 . The in-plane thickness distribution is ±0.9 percents in case of with the thermal conductivity adjusting member  101 , while it is ±2 percents in case of without the thermal conductivity adjusting member  101 . Thus, the evenness of film thickness is improved in this embodiment.  
         [0058]    Although in this embodiment the members  108 ,  109  and  110  composing the thermal conductivity adjusting member  101  each have a single structure, they may be structured such that, for example, the member  109  is formed by vertically stacking members  111 ,  112  with different thermal conductivities as shown in FIG. 6. In this way, the temperature distribution in reaction vessel  102  can be controlled.  
         [0059]    Although the members  108 ,  109  and  110  of this embodiment are of carbon or stainless steel, they may be of metal such as copper and aluminum or ceramics.  
         [0060]    As described above, a difference in temperature between regions of reaction vessel  102  is made by varying the thermal conductivity of thermal conductivity adjusting member  107 . Therefore, the semiconductor film formation device of this embodiment can control the temperature distribution and gas concentration distribution in the reaction vessel  102  without complicating the device structure.  
       Third Embodiment  
       [0061]    [0061]FIG. 7 is a cross sectional view showing a semiconductor film formation device in the third preferred embodiment of the invention.  
         [0062]    Different from the preceding embodiments, the thickness of reaction vessel  102  wall where the reaction vessel  102  of silica glass is next to the cooling jacket  103  of stainless steel is changed between regions thereof as shown in FIG. 7.  
         [0063]    In this structure, the cooling effect is relatively large in regions  1  and  3  where the reaction vessel  102  has a thick wall to contact the cooling jacket  103  and is relatively small in region  2  where the reaction vessel  102  has a thin wall to neighbor the cooling jacket  103  through the interspace  106 . 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 vessel  102  is made.  
         [0064]    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 vessel  102  with a changed wall thickness between regions and by using a semiconductor film formation device which has the reaction vessel  102  without 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 vessel  102  with changed wall thickness, while it is 10 nanometers/sec. in case of the reaction vessel  102  without changed wall thickness. The in-plane thickness distribution is ±1.1 percents in case of the reaction vessel  102  with changed wall thickness, while it is ±2 percents in case of the reaction vessel  102  without changed wall thickness. Thus, the evenness of film thickness is improved in this embodiment.  
       Fourth Embodiment  
       [0065]    Although in the preceding embodiments the horizontal type semiconductor film formation devices are explained that gas flows in one direction in the reaction vessel  102 , the invention can be also applied to a semiconductor film formation device with multiple gas flow directions.  
         [0066]    [0066]FIG. 8 is a cross sectional view showing a semiconductor film formation device in the fourth preferred embodiment of the invention.  
         [0067]    A reaction vessel  208  is provided with a susceptor  209  of carbon disposed on its upper inner surface and a water-cooling jacket  203  of stainless steel on its lower inner surface. A silica plate  202  is disposed on the water-cooling jacket  203  through a thermal conductivity adjusting member  201  of stainless steel. A gas nozzle  207  is disposed connected to the center position of reaction vessel  208 . Two substrates  204  of single-crystal gallium arsenide are disposed on the lower surface of susceptor  209  such that they are positioned at an equal distance from the gas nozzle  207 . The substrates  204  and the susceptor  209  are heated to an average temperature of 600° C. by a heater  205  disposed on the reaction vessel  208 .  
         [0068]    The thermal conductivity adjusting member  201  is structured such that there is formed an interspace  206  having a variable height along the direction of gas flow between the thermal conductivity adjusting member  201  and the lower surface of silica plate  202 .  
         [0069]    In this device, source gases of arsine, trimethylgallium and carrier gas of hydrogen to be introduced into the reaction vessel  208  through the gas nozzle  207  move through a space surrounded by the susceptor  209  and the silica plate  202  in the radial direction, passing through the surface of the substrate  204 , discharged from the circumferential edge of the reaction vessel  208 . 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 vessel  208  by providing the thermal conductivity adjusting member  201  of this embodiment.  
         [0070]    Semiconductor films are grown by using the semiconductor film formation device of this embodiment, which is provided with the thermal conductivity adjusting member  201 , and by using a semiconductor film formation device without the thermal conductivity adjusting member  201 . 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 member  201 , while it is 12 nanometers/sec. in case of without the thermal conductivity adjusting member  201 . The in-plane thickness distribution is ±0.6 percents in case of with the thermal conductivity adjusting member  201 , while it is ±1.8 percents in case of without the thermal conductivity adjusting member  201 . Thus, the evenness of film thickness is improved in this embodiment.  
         [0071]    Although in this embodiment the thermal conductivity adjusting member  201  is 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 in FIG. 9, a silica plate  202  with different thicknesses between regions may be used.  
         [0072]    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.  
         [0073]    Although the invention has been described with respect to the specific embodiments for complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.