Gas cushion susceptor system

Abstract

An apparatus and method to position a wafer onto a wafer holder and to maintain a uniform wafer temperature is disclosed. The wafer holder or susceptor comprises a recess or pocket whose surface includes a grid containing a plurality of grid grooves that separate protrusions. A plurality of gas passages is provided in the susceptor to enable an upward flow of gas toward the bottom surface of the substrate. During drop-off of the substrate, a cushion gas flow is provided to substantially slow the rate of descent of the substrate onto the susceptor and to gradually heat the substrate before it makes contact with the susceptor. Optionally, a trickle gas flow may be provided through the aforementioned passages during processing of the substrate to prevent deposition of reactant gases onto the bottom surface of the substrate. A liftoff gas flow may then be provided through the passages to help lift the substrate off of the susceptor after processing is completed and thus aid in removing the substrate from the process chamber. These features help to achieve temperature uniformity and thus quality of deposited films onto the substrate.

What is claimed is:  
     
         1 . A susceptor for supporting a wafer within a reaction chamber, comprising: 
 an upper support surface configured to support a wafer;    a plurality of gas passages within the susceptor, the gas passages having inlet ends configured to receive a gas flow from a source of gas, and having outlet ends opening at said upper support surface;    a gas supply system configured to supply a generally upward flow of gas through said gas passages, said passages configured so that such a gas flow would apply an upwardly directed force to a wafer above said upper support surface, said gas supply system configured to supply a flow rate of gas sufficient to slow the rate of descent of a falling wafer above said upper support surface to a rate of descent no greater than one half of the rate at which the wafer would descend under gravity alone.    
     
     
         2 . The susceptor of  claim 1 , wherein said gas supply system is configured to supply a flow rate of gas sufficient to slow the rate of descent of a falling wafer above said upper support surface to a rate of descent no greater than one quarter of the rate at which the wafer would descend under gravity alone.  
     
     
         3 . The susceptor of  claim 1 , wherein said gas supply system is configured to supply a flow rate of gas sufficient to slow the rate of descent of a falling wafer above said upper support surface to a rate of descent no greater than one quarter of the rate at which the wafer would descend under gravity alone.  
     
     
         4 . The susceptor of  claim 1 , wherein said gas supply system is configured to supply a flow rate of gas sufficient to lift a wafer resting upon said upper support surface.  
     
     
         5 . The susceptor of  claim 1 , said support surface including a plurality of grooves and protrusions, wherein tops of said protrusions are configured to support a wafer, said grooves configured to permit a degree of gas flow underneath the wafer and upward around a peripheral edge of the wafer when the wafer is supported upon said tops of said protrusions.  
     
     
         6 . A substrate holder comprising: 
 a susceptor including a plurality of gas passages and a support surface; and    a gas supply system configured to supply an upwardly directed flow of gas through said gas passages, said gas supply system configured to supply a flow rate of gas sufficient to slow the rate of descent of a 100 mm substrate that is above and falling toward said support surface to a rate of descent no greater than one half of the rate at which the 100 mm substrate would descend under gravity alone.    
     
     
         7 . The substrate holder of  claim 6 , wherein said gas supply system is configured to supply a flow rate of gas sufficient to slow the rate of descent of a 300 mm substrate that is above and falling toward said support surface to a rate of descent no greater than one half of the rate at which the 300 mm substrate would descend under gravity alone.  
     
     
         8 . The substrate holder of  claim 6 , wherein said support surface is defined by tops of a plurality of protrusions, the protrusions being separated by a plurality of crossing grid grooves.  
     
     
         9 . The substrate holder of  claim 6 , wherein said susceptor is formed of at least two independent sections.  
     
     
         10 . The substrate holder of  claim 6 , further comprising a spider assembly configured to support said susceptor, said spider assembly including a central hub and a plurality of spider arms extending radially outward and upward from said central hub, said central hub and said spider arms being hollow to permit said gas to flow upward through said spider assembly into said susceptor.  
     
     
         11 . The substrate holder of  claim 10 , wherein said spider assembly is configured to rotate about a vertical axis and to thereby rotate said susceptor.  
     
     
         12 . The substrate holder of  claim 10 , wherein said susceptor comprises: 
 a lower section having a bottom surface and a top surface, said bottom surface of said lower section having a plurality of spider arm recesses adapted to receive upper ends of said spider arms of said spider assembly, said top surface of said lower section having a set of interconnected grooves, said lower section having internal passages extending from said spider arm recesses to said grooves to permit gas flowing upward through said spider arms to flow through said internal passages into said grooves of said lower section; and    an upper section having a lower recess configured to receive said lower section, said upper section having a lower surface and a top surface, said plurality of gas passages being within said upper section, each of said gas passages having a lower end positioned above one of said grooves in said top surface of said lower section so that gas in said grooves of said lower section can flow into said gas passages in said upper section, each of said gas passages having an upper end opening at said top surface of said upper section so that gas within said gas passages can flow upward into the space above said susceptor.    
     
     
         13 . The substrate holder of  claim 6 , wherein at least some of said gas passages are oriented substantially diagonally such that gas flowing upward through said at least some gas passages exits said at least some gas passages by flowing upward and radially outward.  
     
     
         14 . The substrate holder of  claim 6 , wherein said susceptor is designed to hold a substrate having a predetermined size, some of said gas passages being substantially vertically oriented and positioned so as to be just radially outward of a peripheral edge of a substrate of said predetermined size and centered on said susceptor.  
     
     
         15 . The substrate holder of  claim 6 , wherein said plurality of gas passages comprises at least twenty passages.  
     
     
         16 . The substrate holder of  claim 6 , wherein said gas passages are positionally balanced with respect to said support surface of said susceptor, such that an upward flow of said gas through said passages causes substantially balanced application of force onto a substrate above said support surface.  
     
     
         17 . A method of supporting a substrate, comprising: 
 releasing a substrate above a support surface of a susceptor, such that said substrate is permitted to descend toward said support surface by gravitational force;    providing a cushioning flow of gas upwardly through a plurality of gas passages provided in said susceptor, said cushioning gas flow providing an upwardly directed force onto said substrate, the flow rate of said cushioning gas flow being sufficient to slow the rate of descent of said substrate to a rate no greater than one half of the rate at which said substrate would descend under gravity alone; and    permitting said substrate to come into contact with said support surface.    
     
     
         18 . The method of  claim 17 , wherein said susceptor includes a plurality of outer gas passages positioned just radially outward of a peripheral edge of said substrate when said substrate is centered upon said support surface of said susceptor, said outer gas passages being substantially vertical so that upward gas flow through said outer gas passages flows substantially vertically upward above said susceptor, said method further comprising providing gas flow through said outer gas passages to counteract sideward sliding of said substrate.  
     
     
         19 . The method of  claim 18 , wherein said gas flow is provided through said outer gas passages while said substrate descends toward said support surface of said susceptor.  
     
     
         20 . The method of  claim 18 , wherein said gas flow is provided through said outer gas passages while said substrate is in contact with said support surface of said susceptor.  
     
     
         21 . The method of  claim 17 , wherein said cushioning flow of gas exits each of said gas passages at said support surface by flowing upward and radially outward.  
     
     
         22 . The method of  claim 17 , said support surface having a plurality of grooves extending radially outward beyond the peripheral edge of said substrate, said method further comprising: 
 providing a trickle flow of gas through said plurality of gas passages after said substrate comes into contact with said support surface and while processing said substrate, the flow rate of said trickle gas flow being sufficient to cause said gas to flow under said substrate through said grooves and upward around a peripheral edge of said substrate without disrupting contact between said substrate and said support surface.    
     
     
         23 . The method of  claim 17 , further comprising: 
 after said substrate is in contact with said support surface, providing a liftoff flow of gas through said plurality of gas passages, said liftoff gas flow being sufficient to lift said substrate off of said support surface; and    removing said substrate from above said support surface.    
     
     
         24 . The method of  claim 23 , wherein said susceptor includes a plurality of outer gas passages positioned just radially outward of a peripheral edge of said substrate when said substrate is centered upon said support surface of said susceptor, said outer gas passages being substantially vertical so that upward gas flow through said outer gas passages flows substantially vertically upward above said susceptor, said method further comprising providing gas flow through said outer gas passages to counteract sideward sliding of said substrate after said liftoff gas flow is provided.  
     
     
         25 . The method of  claim 17 , wherein said susceptor is configured with a pocket to support a 300 mm semiconductor substrate.  
     
     
         26 . The method of  claim 17 , wherein said susceptor is configured with a pocket to support a 200 mm semiconductor wafer.  
     
     
         27 . The method of  claim 17 , wherein said susceptor is configured with a pocket to support a 150 mm semiconductor wafer.  
     
     
         28 . The method of  claim 17 , wherein said rate of descent of said substrate is no greater than one third of the rate at which said substrate would descend under gravity alone.  
     
     
         29 . The method of  claim 17 , wherein said rate of descent of said substrate is no greater than one quarter of the rate at which said substrate would descend under gravity alone.  
     
     
         30 . The method of  claim 17 , wherein at the moment that said substrate comes into contact with said support surface, the temperature difference between said substrate and said support surface is no greater than 100° C.  
     
     
         31 . The method of  claim 17 , wherein said contact between said substrate and said support surface produces a curl of said substrate of no greater than 0.200 inches.  
     
     
         32 . The method of  claim 17 , wherein said contact between said substrate and said support surface produces a curl of said substrate of no greater than 0.100 inches.  
     
     
         33 . The method of  claim 17 , wherein said contact between said substrate and said support surface produces a curl of said substrate of no greater than 0.050 inches.  
     
     
         34 . The method of  claim 17 , wherein said susceptor has a temperature within the range of 200-1000° C., and said substrate has a temperature within the range of 0-100° C. at the time of said releasing of said substrate.  
     
     
         35 . A method of loading a substrate onto a susceptor, comprising: 
 releasing a substrate above a support surface of a susceptor, such that said substrate is permitted to descend toward said support surface by gravitational force;    providing a cushioning flow of gas that imparts an upwardly directed force onto said substrate, the flow rate of said cushioning gas flow being sufficient to slow the rate of descent of said substrate to a rate no greater than one half of the rate at which said substrate would descend under gravity alone; and    permitting said substrate to come into contact with said support surface.    
     
     
         36 . A method of loading a wafer onto a susceptor, comprising: 
 releasing a wafer above a susceptor, said wafer having a peripheral edge; and    providing a plurality of substantially vertical upwardly directed gas jets radially exterior of said peripheral edge of said wafer, said jets substantially inhibiting sideward motion of said wafer as said wafer descends toward said susceptor.