Abstract:
A method of forming a film on a wafer by decomposing a material gas includes placing the wafer on a top surface of a susceptor, heating the susceptor, measuring the temperature of the top surface of the susceptor. supplying a flow of the material gas to a location above the top surface the susceptor, and thermally decomposing the material gas to deposit a film on the wafer. The quantity of the material gas supplied to the location above the top surface of the susceptor is adjusted and the density of the material gas at the location above the top surface of the susceptor is kept constant by controlling the flow of the material gas to the location above the top surface of the susceptor, including by increasing the flow of the material gas as the temperature of the top surface of the susceptor decreases.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a film forming apparatus and method used for manufacturing a semiconductor device or the like. 
         [0003]    2. Background Art 
         [0004]    Japanese Patent Laid-Open No. 2004-165454 discloses a film forming apparatus for forming a film on a wafer (processing object) by introducing a material gas into a reaction furnace. This film forming apparatus is intended to measure a wafer temperature and reflect the measurement result in a film formation condition to obtain a desired film thickness. 
         [0005]    When a film is formed on a wafer in a reaction furnace, a grown product is deposited also on a susceptor. A deposit deposited on the susceptor causes an amount of heat transmitting from the susceptor toward above the susceptor to decrease. This causes the temperature above the susceptor to decrease. For that reason, the density of the thermally decomposed material gas (hereinafter referred to as “decomposed gas”) decreases, resulting in a problem that quality of the growth film changes over the time. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention has been implemented to solve the above-described problem and it is an object of the present invention to provide a film forming apparatus capable of maintaining a density of a thermally decomposed material gas. 
         [0007]    The features and advantages of the present invention may be summarized as follows. 
         [0008]    According to one aspect of the present invention, a film forming apparatus includes a susceptor having a first portion that holds a wafer on a top surface thereof and a second portion connected to the first portion, a gas supply section that supplies a material gas to above the susceptor, a first heater that heats the first portion, a second heater that heats the second portion, and a temperature control apparatus that controls temperatures of the first heater and the second heater, wherein the temperature control apparatus keeps the temperature above the susceptor constant by increasing the temperature of the second heater while maintaining the temperature of the first heater during film formation onto the wafer. 
         [0009]    According to another aspect of the present invention, a film forming apparatus includes a susceptor having a first portion that holds a wafer on a top surface thereof and a second portion connected to the first portion, a gas supply section that supplies a material gas to above the susceptor, a first heater that heats the first portion, a second heater that heats the second portion, a temperature control apparatus that controls temperatures of the first heater and the second heater, and a thermometer that measures a temperature of a top surface of the susceptor, wherein the temperature control apparatus keeps the temperature of the top surface of the susceptor constant by increasing the temperature of the second heater every time the measured temperature of the thermometer decreases while maintaining the temperature of the first heater during film formation onto the wafer. 
         [0010]    According to another aspect of the present invention, a film forming apparatus includes a susceptor that holds a wafer on a top surface, a heater that heats the susceptor, a thermometer that measures a temperature of a top surface of the susceptor, a gas supply section that supplies a material gas to above the susceptor, a mass flow controller that adjusts the amount of gas supplied to the gas supply section, and a gas flow rate setting section that controls the mass flow controller, wherein the gas flow rate setting section keeps constant the density of the material gas thermally decomposed above the susceptor by controlling the mass flow controller so as to increase the amount of gas supplied to the gas supply section as the temperature of the thermometer decreases. 
         [0011]    Other and further objects, features and advantages of the invention will appear more fully from the following description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a cross-sectional view of a film forming apparatus according to a first embodiment; 
           [0013]      FIG. 2  is a cross-sectional view of the film forming apparatus with a deposit deposited on the susceptor; 
           [0014]      FIG. 3  shows temperatures of the first heater and the second heater; 
           [0015]      FIG. 4  is a cross-sectional view of a film forming apparatus according to a second embodiment; 
           [0016]      FIG. 5  is a diagram illustrating a temperature change of the thermometer and a temperature change of the second heater or the like; and 
           [0017]      FIG. 6  is a cross-sectional view of a film forming apparatus according to a third embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0018]    A film forming apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings. The same or corresponding components will be assigned the same reference numerals and duplicate description may be omitted. 
       First Embodiment 
       [0019]      FIG. 1  is a cross-sectional view of a film forming apparatus  10  according to a first embodiment of the present invention. The film forming apparatus  10  is provided with a reaction furnace  12 . An internal configuration of the reaction furnace  12  will be described. A susceptor  16  supported by a support stand  14  is provided in the reaction furnace  12 . The susceptor  16  includes a first portion  16   a  that holds a wafer on a top surface thereof and a second portion  16   b  connected to the first portion  16   a.  The first portion  16   a  is a peripheral portion of the susceptor  16  and the second portion  16   b  is a central portion of the susceptor  16 . 
         [0020]    A dent is formed in the first portion  16   a.  A wafer  22  is mounted in this dent via a satellite disk  20 . Therefore, the first portion  16   a  supports the wafer  22  via the satellite disk  20 . Note that the satellite disk  20  is provided to achieve uniform film formation by rotating the satellite disk  20  itself, but may be omissible in the film forming apparatus of the present invention. 
         [0021]    A first heater  30  to heat the first portion  16   a  is provided right below the first portion  16   a.  The first heater  30  is integrally formed, for example, in a concentric or spiral shape in a plan view. A second heater  32  to heat the second portion  16   b  is provided right below the second portion  16   b.  The second heater  32  is integrally formed, for example, in a concentric or spiral shape in a plan view. 
         [0022]    A temperature control apparatus  34  is connected to the first heater  30  and the second heater  32 . The temperature control apparatus  34  is intended to individually control temperatures of the first heater  30  and the second heater  32 . The temperature control apparatus  34  may also be provided in the reaction furnace  12 . 
         [0023]    A gas supply section  40  is provided on a top surface of the reaction furnace  12 . The gas supply section  40  is a section that supplies a material gas from outside the reaction furnace  12  to above the susceptor  16 . The supplied material gas flows toward an peripheral direction of the susceptor  16  and is exhausted from an exhaust port  42 . 
         [0024]    A film formation method using the film forming apparatus  10  will be described. Here, as an example, a GaAsP film is formed using Ga which is a Group 3 element, and As and P which are Group 5 elements. While heating by the first heater  30  and the second heater  32  is in progress, the material gas of Ga, AsH 3  which is the material gas of As and PH 3  which is the material gas of P are supplied from the gas supply section  40  into the reaction furnace  12 . These material gases are decomposed by heat from the susceptor  16  above the susceptor  16  and a decomposed gas allows GaAs(y)P(1−y) to epitaxially grow on the wafer  22 . Here, y takes a value greater than 0 and smaller than 1. 
         [0025]      FIG. 2  is a cross-sectional view of the film forming apparatus  10  with a deposit  50  deposited on the susceptor  16 . With the generation of the deposit  50 , there is a concern about a decrease in the density of the decomposed gas. Therefore, in the first embodiment of the present invention, temperatures of the first heater  30  and the second heater  32  are controlled as shown in  FIG. 3 . That is, the temperature control apparatus  34  causes the temperature of the second heater  32  to increase while maintaining the temperature of the first heater  30  during film formation onto the wafer  22 . The temperature increasing speed of the second heater  32  is determined in such a way as to be able to keep the temperature above the susceptor  16  constant. More specifically, influences of the deposit  50  on the temperature above the susceptor  16  is estimated from experiment data or a simulation or the like and the temperature increasing speed of the second heater  32  is thereby determined. 
         [0026]    During film formation onto the wafer  22 , the amount of deposit in the susceptor  16  increases, but it is possible to keep the temperature above the susceptor  16  constant by increasing the temperature of the second heater  32  while keeping the temperature of the first heater  30  constant. It is thereby possible to prevent changes over the times in the density of the decomposed gas and stabilize the quality of the growth film 
         [0027]    Moreover, by maintaining the temperature of the first heater  30  which has great contribution to the temperature of the wafer  22 , it is possible to keep the temperature of the wafer  22  substantially constant. By increasing the temperature of the second heater  32  which has small contribution to the temperature of the wafer  22 , it is possible to increase the temperature of the second portion  16   b  while maintaining the temperature of the wafer  22 . 
         [0028]    As described above, the film formation method using the film forming apparatus  10  is intended to maintain the density of the decomposed gas on the premise of increasing deposits onto the susceptor  16 , and it is therefore not necessary to replace the susceptor or remove the deposit deposited on the susceptor every time film formation processing is performed. It is thereby possible to solve the problems of a decrease of productivity and cost increase accompanying replacement of the susceptor or removal of the deposit. 
         [0029]    The type of the material gas supplied into the reaction furnace  12  from the gas supply section  40  is not particularly limited if the material gas is thermally decomposed. The first heater  30  may be embedded in the first portion  16   a  and the second heater  32  may be embedded in the second portion  16   b.  Moreover, various modifications can be made within a range in which the features of the present invention will not be lost. These modifications are applicable to the film forming apparatus according to the following embodiments. 
         [0030]    The film forming apparatuses according to the following embodiments will be described focusing on differences from the film forming apparatus  10  according to the first embodiment. 
       Second Embodiment 
       [0031]      FIG. 4  is a cross-sectional view of a film forming apparatus  100  according to a second embodiment of the present invention. An opening  12   a  is provided on the top surface of the reaction furnace  12 . The opening  12   a  is closed with a transparent material  102  such as glass which is transparent to light. A thermometer  104  is provided outside the reaction furnace  12  to measure a temperature of a top surface of the susceptor  16  via the transparent material  102 . The thermometer  104  is a radiation thermometer that measures the temperature of the top surface of the second portion  16   b.    
         [0032]    The temperature control apparatus  106  is connected to the thermometer  104 . The temperature control apparatus  106  causes the temperature of the second heater  32  to increase every time the measured temperature of the thermometer  104  decreases while keeping the temperature of the first heater  30  during film formation onto the wafer  22 .  FIG. 5  is a diagram illustrating a temperature change of the thermometer  104  and a temperature change of the second heater  32  or the like. As shown in  FIG. 5 , when the temperature of the thermometer  104  decreases as the amount of deposit on the susceptor increases, the temperature control apparatus  106  causes the temperature of the second heater  32  to increase. The temperature control apparatus  106  thereby keeps the temperature of the top surface of the susceptor  16  constant. This control is preferably performed automatically and in real time. 
         [0033]    Since the present invention is intended to keep the temperature above the susceptor  16  constant, a place, a temperature of which is to be measured using the thermometer  104  is preferably a portion of the susceptor  16  that contributes most to the temperature above the susceptor  16 . Since the portion of the film forming apparatus  100  that contributes most to the temperature above the susceptor  16  is the second portion  16   b,  the temperature of the second portion  16   b  was measured using the thermometer  104 . However, if it is possible to keep the temperature above the susceptor  16  constant, the temperature of the first portion  16   a  may be measured. 
       Third Embodiment 
       [0034]      FIG. 6  is a cross-sectional view of a film forming apparatus  150  according to a third embodiment of the present invention. The film forming apparatuses according to the first and second embodiments are intended to keep the density of a decomposed gas constant by maintaining the temperature above the susceptor, whereas the film forming apparatus  150  is intended to keep the density constant by increasing the amount of gas supplied. 
         [0035]    The film forming apparatus  150  is provided with the susceptor  16  that holds the wafer  22  on the top surface thereof. A heater  151  is provided right below the susceptor  16  to heat the susceptor  16 . A gas flow rate setting section  152  is connected to the thermometer  104 . The gas flow rate setting section  152  is connected to mass flow controllers  160  and  162  that adjust the amount of gas supplied to a gas supply section  40 . The gas flow rate setting section  152  controls the mass flow controllers  160  and  162 . 
         [0036]    The gas flow rate setting section  152  is provided with a temperature display section  154  that displays a temperature measured using the thermometer  104 . The gas flow rate setting section  152  is provided with a commanding section  156  that commands the amount of each material gas supplied so as to realize a preset film formation process. The temperature display section  154  and the commanding section  156  are connected to an adjustment section  158 . The adjustment section  158  has data of a thermal decomposing rate of each material gas above the susceptor when the susceptor temperature is a reference temperature (predetermined temperature). The adjustment section  158  calculates a difference between this data and the thermal decomposing rate of each material gas above the susceptor at a temperature measured using the thermometer  104 . Based on this difference in thermal decomposing rate, the adjustment section  158  outputs signals to the mass flow controllers  160  and  162  so that the density of the decomposed gas becomes a reference value (predetermined value). 
         [0037]    Since the temperature of the thermometer  104  decreases as the amount of deposit onto the susceptor  16  increases, the gas flow rate setting section  152  controls the mass flow controllers  160  and  162  so as to increase the amount of gas supplied to the gas supply section  40  as the temperature of the thermometer  104  decreases. An increment in the amount of gas supplied is determined so as to be able to keep constant the density of the material gas thermally decomposed above the susceptor  16 . Therefore, according to the film forming apparatus  150 , even when deposit onto the susceptor  16  causes the temperature above the susceptor  16  to decrease, it is possible to maintain the density of the decomposed gas. 
         [0038]    Another configuration may be adopted for the gas flow rate setting section  152  if it can increase the amount of the material gas supplied so as to maintain the density of the decomposed gas. The features of the film forming apparatuses of the respective embodiments described so far may be used in combination as appropriate. 
         [0039]    According to the present invention, it is possible to maintain the temperature above the susceptor and increase the amount of the material gas supplied to thereby maintain the density of the thermally decomposed material gas. 
         [0040]    Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.