Abstract:
A manufacturing method for semiconductor device includes: loading a wafer to a reaction chamber and placing the wafer on a support member; supplying process gas including source gas to a surface of the wafer, controlling a heater output and heating the wafer to a predetermined temperature while rotating the wafer at a first rotational speed, and thereby forming a film on a surface of the wafer; stopping supplying the source gas; decreasing a rotational speed of the wafer to a second rotational speed which enables an offset balance of the wafer to be maintained and stopping the heater output; and decreasing a temperature of the wafer while rotating the wafer at the second rotational speed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2010-194323 filed on Aug. 31, 2010, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     The present invention relates to a manufacturing method and a manufacturing apparatus for semiconductor device for forming a film by, for example, supplying reaction gas to a surface of a semiconductor wafer while heating a back surface. 
     In recent years, following requirements for reduced cost and higher functions of semiconductor devices, higher productivity and quality are also required in film forming process. 
     In the film forming process, for example, Japanese Patent Application Laid-Open No. 11-67675 discloses conveying a wafer in a manufacturing apparatus, supplying process gas from above, and rotating the wafer at a high speed of about 900 rpm while heating the wafer by means of a heater to cause epitaxial growth. 
     Further, after an epitaxial film is formed on the wafer in this way, the rotation speed of the wafer is decreased and a heater output is stopped to decrease the temperature of the wafer to convey the wafer out of the manufacturing apparatus. 
     SUMMARY 
     A manufacturing method for semiconductor device according to the present invention includes: loading a wafer to a reaction chamber and placing the wafer on a support member; supplying process gas including source gas to a surface of the wafer, controlling a heater output and heating the wafer to a predetermined temperature while rotating the wafer at a first rotational speed, and thereby forming a film on a surface of the wafer; stopping supplying the source gas; decreasing a rotational speed of the wafer to a second rotational speed which enables an offset balance of the wafer to be maintained and stopping the heater output; and decreasing a temperature of the wafer while rotating the wafer at the second rotational speed. 
     A manufacturing apparatus for semiconductor device according to the present invention includes: a reaction chamber configured to load a wafer therein; a support member provided in the reaction chamber and configured to place the wafer thereon; a process gas supply mechanism configured to supply process gas to a surface of the wafer; a gas discharge mechanism configured to discharge gas and to control a pressure in the reaction chamber; a rotation driving control mechanism configured to control a rotational speed of the wafer to a first rotational speed when a film is formed, and to a second rotational speed when a temperature of the wafer is decreased; a heater configured to heat the wafer to a predetermined temperature; and a temperature control mechanism configured to control the heater to a predetermined temperature when the process gas including source gas is supplied, to stop a output when stopping supplying the source gas and the rotational speed of the wafer is decreased to the second rotational speed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view of an epitaxial growing device used in one embodiment of the present invention; 
         FIG. 2  is a flowchart of a manufacturing method for a semiconductor device according to one embodiment of the present invention; 
         FIG. 3  is a view illustrating temporal changes of a wafer temperature (In) in the center of the wafer, the rotational speed and offset temperature (Out-In) in the outer periphery of the wafer on the basis of the wafer temperature (In) according to one embodiment of the present invention; 
         FIG. 4  is a view illustrating temporal changes of a wafer temperature (In) in the center of the wafer, the rotational speed and offset temperature (Out-In) in the outer periphery of the wafer on the basis of the wafer temperature (In) according to a comparison example; 
         FIG. 5  is a schematic view illustrating a gas flow upon high speed rotation; and 
         FIG. 6  is a schematic view illustrating a gas flow upon low speed rotation. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the present embodiment of the invention, an example of which is illustrated in the accompanying drawings. 
     There is a concern that a wafer is misaligned when the temperature of the wafer is decreased upon high speed rotation, and therefore the rotational speed is generally decreased to about 600 rpm, gas is vented, H 2  gas is purged and then the rotational speed is decreased to about 100 rpm to turn off the heater. 
     However, if the film thickness increases when a pressure resistance of semiconductor elements becomes higher, the wafer is more susceptible to the influence of an offset balance when the temperature is decreased, and there is a problem that slip is generated on the wafer. 
     The embodiment of the present invention is made in response to this problem. 
     Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 
       FIG. 1  is a sectional view of an epitaxial growing device used in the present embodiment. As illustrated in  FIG. 1 , a reaction chamber  11  in which, for example, a Si wafer w of φ 200 mm is formed has a quartz cover  11   a  covering an inner wall where necessary. 
     In the upper part of the reaction chamber  11 , gas supply ports  12   a  are provided which are connected with process gas supply mechanisms  12  which supply process gas including source gas and dilution gas. Further, in the lower part of the reaction chamber  11 , gas outlets  13   a  which are connected with gas discharge mechanisms  13  which discharge gas and control the pressure in the reaction chamber  11  at a constant pressure (normal pressure) are provided at, for example, two portions. 
     A distribution plate  14  which has fine penetration holes for rectifying and supplying supplied process gas is provided below the gas supply ports  12   a.    
     Further, a susceptor  15  which is made of, for example, SiC and is a support member on which a wafer w is placed is provided below the distribution plate  14 . The susceptor  15  is disposed on a ring  16  which is a rotation member. The ring  16  is connected with a rotation driving control mechanism  17  which has, for example, a motor through a rotation axis which rotates the wafer w at a predetermined rotation speed. 
     Heaters which heat the wafer w and which are composed of an in-heater  18   a  and an out-heater  18   b  which are made of, for example, SiC are disposed inside the ring  16 , and are respectively connected with a temperature control mechanism  19 . Further, a disk-shaped reflector  20  which efficiently heats the wafer w is disposed below these in-heater  18   a  and out-heater  18   b.    
     Furthermore, a push-up pin  21  is disposed which supports the wafer w from the back surface penetrating the susceptor  15 , in-heater  18   a  and reflector  20 , and has, for example, three pins. The push-up pin  21  can place the wafer w on the susceptor  15  by placing the conveyed wafer w above the susceptor  15  and lowering the wafer w. 
     Using this epitaxial growing device, a Si epitaxial film is formed on the wafer w. 
     As illustrated in  FIG. 2 , the wafer w is first conveyed in the reaction chamber  11  by means of a conveying arm (not illustrated). The wafer w is placed on the susceptor  15  by placing the wafer w on the push-up pin  21  and lowering the wafer w (Step  1 ). 
     The temperature control mechanism  19  heats the in-heater  18   a  and out-heater  18   b  to predetermined temperatures, respectively to heat the wafer w to, for example, 1140° C., and the rotation driving control mechanism  17  rotates the wafer w at, for example, 900 rpm. 
     Process gas for which the process gas supply mechanism  12  controls the flow rate and which is mixed is supplied onto the surface of the wafer w in the rectified state through the distribution plate  14 . The process gas uses, for example, trichlorosilane as source gas, is diluted to 2.5% by H 2  of dilution gas to adjust the concentration, and is supplied at, for example, 50 SLM. 
     By contrast with this, discharge gas containing extra surplus process gas and HCl including a reaction byproduct is discharged below from the surrounding of the susceptor  15 , and is discharged from the gas discharge mechanisms  13  through the gas outlets  13   a.    
     Thus, a Si epitaxial film is grown on the wafer w until the film thickness becomes, for example, 80 pm (Step  2 ). 
     The process gas supply mechanisms  12  stop supplying source gas, and source gas in the reaction chamber is discharged (vented) (Step  3 ). The rotation driving control mechanism  17  decreases the rotational speed at, for example, 20 rpm/sec while supplying H 2  as purge gas, and the temperature control mechanism  19  stops outputs of the in-heater  18   a  and out-heater  18   b  (Step  4 ). 
     Thus, while the rotational speed is decreased to 600 rpm and is maintained, and the temperature of the wafer w is decreased (Step  5 ). Further, after the temperature of the wafer is decreased to about 800° C., rotation is stopped and the wafer is unloaded (Step  6 ). 
     When a slip state of the wafer on which the Si epitaxial film is formed in this way is evaluated by X-Ray Topography (XRT), the maximum slip length is equal to or less than 5 mm, and cumulative slip length is equal to or less than 20 mm. This slip state is substantially improved compared to the maximum slip length 50 mm and cumulative slip length 650 mm in a wafer formed according to a conventional method. 
     Meanwhile,  FIG. 3  illustrates temporal changes of a wafer temperature (In) in the center of the wafer, the rotational speed and an offset temperature (Out-In) in the outer periphery of the wafer on the basis of the wafer temperature (In). Although the offset temperature maintains +4° C. which is an optimal value when a film is formed, the offset temperature increased upon vent, decreases when rotation starts decreasing and the heater is turned off, and then increases. Herein, the offset balance means the balance of the offset temperature. 
     By contrast with this,  FIG. 4  illustrates as a comparison example, temporal changes of a wafer temperature (In), the rotational speed and an offset temperature (Out-In) in conventional process in which rotation is decreased, gas is purged, rotation is set to a low speed and the heaters are turned off. Compared to the present embodiment illustrated in  FIG. 3 , while the change of the temperature in the center of the wafer is the same, the temperature in the outer periphery immediately after the heaters are turned off decreases significantly, and the offset balance is significantly collapsed. 
     This is for the following reason. In case of high speed rotation (for example, 600 rpm), as illustrated as a schematic view in  FIG. 5 , purge gas  51  is attracted to the wafer w, is placed in the laminar flow state on the wafer w and is discharged from a peripheral part, so that a temperature distribution becomes uniform and, consequently, the offset balance is maintained. However, in case of low speed rotation (for example, 100 rpm), as illustrated as a schematic view in  FIG. 6 , purge gas  61  is discharged below from a peripheral part without being attracted to the wafer w, and therefore the temperature in the peripheral part decreases (the offset temperature decreases). 
     In addition, although the rotational speed which enables the offset balance to be maintained in this way fluctuates depending on, for example, the diameter of the wafer and film forming temperature, the rotational speed may be roughly 50% or more of the rotations upon film formation. 
     By contrast with this, upon high speed rotation, the change of the temperature significantly influences the offset balance, and the wafer is more likely to be misaligned. Hence, by decreasing the rotational speed in a range which enables the offset balance to be maintained and turning off the heaters, it is possible to suppress the influence on the offset balance. In this case, the rotational speed decreases to some degree until the temperature actually decreases after the heaters are turned off, so that the heaters may be turned off at the same timing when the rotational speed starts decreasing. 
     Further, by maintaining the rotational speed (for example, 600 rpm) which enables the offset balance to be maintained until at least 100° C. decreases (to, for example, 800° C.), and decreasing the temperature, it is possible to decrease the temperature of the wafer without collapsing the offset balance. 
     According to the present embodiment, it is possible to decrease the temperature of the wafer without collapsing the offset balance and, consequently, prevent the wafer from slip generation and stably form, for example, a quality epitaxial film on a wafer productively. 
     Further, it is possible to improve the yield rate of wafers, improve the yield rate of semiconductor devices formed through element forming process and element separating process and improve reliability such as stability of element characteristics. By applying the present embodiment to epitaxial forming process of power semiconductor devices such as power MOSFET and IGBT in which films having the thickness equal to or more than 40 μm need to be grown in an N-type base area, P-type base area and insulation separation area in particular, it is possible to provide good element characteristics. 
     Further, although a case has been described with the present embodiment where a Si single crystal layer (epitaxial film) is formed, the present embodiment is applicable to form a poly Si layer and SiC single crystal layer. Further, the present embodiment is also applicable to form, for example, films other than SiO 2  film, Si 3 N 4  film, and Si film, or is applicable to a GaAs layer or compound semiconductors such as GaAlAs and InGaAs. The present embodiment can be variously modified and implemented in a range which does not deviate from the scope of the invention. 
     Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.