Method of forming a germanium film on a semiconductor substrate that includes the formation of a graded silicon-germanium buffer layer prior to the formation of a germanium layer

Abstract

A composite of germanium film for a semiconductor device and methods of making the same. The method comprises growing a graded germanium film on a semiconductor substrate in a deposition chamber while simultaneously decreasing a deposition temperature and decreasing a silicon source gas and increasing a germanium source gas over a predetermined amount of time. The graded germanium film comprises an ultra-thin silicon-germanium buffer layer and a germanium film.

We claim:  
     
         1 . A method of forming a graded germanium film on a semiconductor substrate comprising: 
 placing said semiconductor substrate in a deposition chamber; and    while simultaneously decreasing a silicon source gas and increasing a germanium source gas and decreasing a deposition temperature over a predetermined amount of time, said graded germanium film comprises an ultra-thin Silicon-germanium buffer layer and a germanium layer.    
     
     
         2 . A method as in  claim 1  wherein said simultaneously decreasing a silicon source gas and increasing a germanium source gas and decreasing a deposition temperature over a predetermined amount of time further comprises: 
 decreasing said silicon source gas from a first rate down to second rate;  
 increasing said germanium source gas from third rate up to a fourth rate; and  
 decreasing said deposition temperature from a first temperature down to a second temperature.  
 
     
     
         3 . A method as in  claim 2  further comprising maintaining said deposition temperature at said second temperature for another predetermined amount of time to form a germanium layer.  
     
     
         4 . A method as in  claim 3  further comprising injecting a dopant source gas into said deposition chamber during said another predetermined amount of time to dope said germanium layer.  
     
     
         5 . A method as in  claim 1  wherein said simultaneously decreasing a silicon source gas and increasing a germanium source gas and decreasing a deposition temperature over a predetermined amount of time further comprises: 
 decreasing said silicon source gas at a rate of 1 sccm to 2 sccm per second;  
 increasing said germanium source gas at a rate of 3.8 sccm to 4.5 sccm per second; and  
 decreasing said deposition temperature at a rate of 1° C. to 1.5° C. per second.  
 
     
     
         6 . A method as in  claim 1  wherein said growing a graded germanium film on a substrate further comprising: 
 depositing a mask over said silicon substrate, said mask having a pattern defining areas for growing said graded germanium film on said silicon substrate; and  
 injecting an etchant source gas into said deposition chamber.  
 
     
     
         7 . A method of forming a semiconductor device comprising: 
 introducing a silicon source gas at a first flow rate into a deposition chamber having a substrate whereon a graded germanium film is formed, said deposition chamber set at a first deposition temperature;    for a first predetermined amount of time, simultaneously decreasing said first flow rate to a second flow rate and decreasing said first deposition temperature to a second deposition temperature while introducing a germanium source gas at an increasing flow rate into said deposition chamber, said germanium source gas is increased to a third flow rate; and    for a second predetermined amount of time, introducing an etchant source gas into said deposition chamber while alternating flows of said etchant source gas and said germanium source gas with a flow of said dopant source gas wherein when said germanium source gas and said etchant source gas are present in said deposition chamber, said dopant source gas flow is shut off and wherein when said dopant source gas is present in said deposition chamber, said germanium source gas and said etchant source gas flows are shut off.    
     
     
         8 . A method as in  claim 7  wherein said introducing an etchant source gas into said deposition chamber while alternating flows of said etchant source gas and said germanium source gas with a flow of said dopant source gas alternating further comprising: 
 simultaneously maintaining said flows of said etchant source gas and said germanium source gas while shutting off said dopant source gas for a third predetermined amount of time;  
 simultaneously shutting off said flows of said etchant source gas and said germanium source gas while maintaining said flow said dopant source gas for a fourth predetermined amount of time, wherein said further predetermined amount of time is less than said third predetermined amount of time; and  
 repeating said simultaneously maintaining said flows of said etchant source gas and said germanium source gas while shutting off said dopant source gas and said simultaneously shutting off said flows of said etchant source gas and said germanium source gas while maintaining said flow of dopant source gas for as many times as necessary.  
 
     
     
         9 . A method as in  claim 8  wherein said third predetermined amount of time is about 10 seconds and said fourth predetermined amount of time is about 5 seconds.  
     
     
         10 . A method of forming a graded germanium film having a silicon-germanium buffer layer and a germanium layer on a semiconductor substrate: 
 obtaining a deposition temperature and a deposition pressure in a deposition chamber used for said forming of said graded germanium film;    placing said semiconductor substrate in said deposition chamber;    introducing a silicon source gas flow into said deposition chamber;    while ramping down said deposition temperature, simultaneously decreasing said silicon source gas flow and increasing a germanium source gas flow for a first predetermined amount of time; and    maintaining said germanium source gas flow for a second predetermine amount of time.    
     
     
         11 . A method as in  claim 10  wherein said simultaneously decreasing of said silicon source gas flow and increasing said germanium source gas flow for said first predetermined amount of time further comprises: 
 decreasing said silicon source gas from a first flow rate down to second flow rate;  
 increasing said germanium source gas from third flow rate up to a fourth flow rate; and  
 decreasing said deposition temperature from a first temperature down to a second temperature.  
 
     
     
         12 . A method as in  claim 10  further comprising injecting a dopant source gas into said deposition chamber during said second predetermined amount of time to dope said germanium layer.  
     
     
         13 . A method as in  claim 10  said simultaneously decreasing of said silicon source gas flow and increasing said germanium source gas flow for said first predetermined amount of time further comprises: 
 decreasing said silicon source gas at a rate of 1 sccm to 2 sccm per second;  
 increasing said germanium source gas at a rate of 3.8 sccm to 4.5 sccm per second; and  
 decreasing said deposition temperature at a rate of 1° C. to 1.5° C. per second.  
 
     
     
         14 . A method of selectively forming a graded germanium film having a silicon-germanium buffer layer and a germanium layer on a semiconductor substrate comprising: 
 obtaining a deposition temperature and a deposition pressure in a deposition chamber used for said forming of said graded germanium film;    placing said semiconductor substrate in said deposition chamber, said semiconductor substrate comprising a dielectric mask;    introducing a silicon source gas flow into said deposition chamber;    while ramping down said deposition temperature, simultaneously decreasing said silicon source gas flow and increasing a germanium source gas flow for a first predetermined amount of time; and    maintaining said germanium source gas flow for a second predetermine amount of time.    
     
     
         15 . A method as in  claim 14  further comprising: 
 introducing an etchant source gas into said deposition chamber.  
 
     
     
         16 . A method as in  claim 14  further comprising: 
 for a third predetermined amount of time, introducing an etchant source gas into said deposition chamber while alternating flows of said etchant source gas and said germanium source gas with a flow of said dopant source gas wherein when said germanium source gas and said etchant source gas are present in said deposition chamber, said dopant source gas flow is shut off and wherein when said dopant source gas is present in said deposition chamber, said germanium source gas and said etchant source gas flows are shut off.  
 
     
     
         17 . A method as in  claim 16  said introducing an etchant source gas into said deposition chamber while alternating flows of said etchant source gas and said germanium source gas with a flow of said dopant source gas is repeated as many times as necessary.  
     
     
         18 . A composite of germanium film comprising: 
 a graded germanium film grown on a silicon substrate wherein said graded germanium film comprises a silicon-germanium buffer layer and a germanium layer, and wherein said graded germanium film is formed from simultaneously decreasing a deposition temperature while decreasing a silicon source gas and increasing a germanium source gas in a deposition chamber for a predetermined amount of time.    
     
     
         19 . A composite of germanium film as in  claim 18  wherein said silicon substrate is monocrystalline silicon.  
     
     
         20 . A composite of germanium film as in  claim 18  wherein said graded germanium film has a first thickness and wherein silicon-germanium buffer layer has a second thickness that is 15% to 30% of said first thickness and said germanium layer has a third thickness that is 70% to 85% of said first thickness.  
     
     
         21 . A composite of germanium film as in  claim 18  wherein said silicon-germanium buffer layer is an ultra-thin layer.  
     
     
         22 . A composite of germanium film as in  claim 18  wherein said germanium layer has a dislocation density less than 10 9  per cm 2 .  
     
     
         23 . A composite of germanium film as in  claim 21  wherein said silicon-germanium buffer layer has a thickness less than 0.5 μm.  
     
     
         24 . A composite of germanium film as in  claim 18  wherein said graded germanium film is used to form a semiconductor selected from the group consisting of a transistor and a detector.  
     
     
         25 . A composite of germanium film as in  claim 18  wherein said graded germanium film is selectively grown on said silicon substrate.  
     
     
         26 . A composite of germanium film as in  claim 18  wherein said graded germanium film is selectively grown said silicon substrate and is further doped with a dopant for said semiconductor.  
     
     
         27 . A composite of germanium film as in  claim 15  wherein said dopant is one of boron, phosphorous, and arsenic.