Method for CVD process control for enhancing device performance

Abstract

A method and system for controlling the introduction of a species according to a determined concentration profile of a film comprising the species introduced on a substrate. In one aspect, the method comprises controlling the flow rate of a species according to a determined concentration profile of a film introduced on a substrate, and introducing a film on a substrate, the film comprising the species at a first concentration at a first point in the film and a second concentration different than the first concentration at a second point in the film. Also, a bipolar transistor including a collector layer of a first conductivity type, a base layer of a second conductivity type forming a first junction with the collector layer, and an emitter layer of the first conductivity type forming a second junction with the base layer. An electrode configured to direct carriers through the emitter layer to the base layer and into the collector layer is also included. In one embodiment, at least one of the first junction and the second junction is between different semiconductor materials to form at least one heterojunction. The heterojunction has a concentration profile of a semiconductor material such that an electric field changes in an opposite way to that of a mobility change.

What is claimed is:  
     
         1 . A method comprising: 
 controlling the flow rate of a species according to a determined concentration profile of a film comprising the species introduced on a substrate; and    introducing a film on a substrate, the film comprising the species at a first concentration at a first point in the film and a second concentration different than the first concentration at a second point in the film.    
     
     
         2 . The method of  claim 1 , wherein determining the concentration profile comprises: 
 determining a concentration of the species introduced on a substrate for a first plurality of flow rates;    determining a growth rate of the species grown on a substrate for a second plurality of flow rates; and    determining a concentration profile of the species for a unit of time.    
     
     
         3 . The method of  claim 1 , wherein the introduced film comprises a thickness, the method further comprising: 
 controlling the flow rate to introduce the film at a graded concentration of the species throughout the thickness of the film.    
     
     
         4 . The method of  claim 3 , wherein the flow rate is controlled so that the graded concentration of the species comprises a linear gradient.  
     
     
         5 . The method of  claim 1 , wherein controlling the flow rate comprises controlling the mass flow rate of the species.  
     
     
         6 . The method of  claim 1 , wherein the introduction of the film on a substrate comprises introducing the species and growing the film on the substrate.  
     
     
         7 . A machine readable medium comprising executable program instructions that when executed cause a digital processing system to perform a method comprising: 
 controlling the flow rate of a species according to a determined concentration profile of a film comprising the species introduced on a substrate, the film comprising the species at a first concentration at a first point in the film and a second concentration different than the first concentration at a second point in the film.    
     
     
         8 . The medium of  claim 7 , wherein determining the concentration profile comprises: 
 determining the concentration profile of the species for a unit of time according to data stored in a memory comprising:    determining a concentration of the species introduced on a substrate for a first plurality of flow rates;    determining a growth rate of the species grown on a substrate for a second plurality of flow rates.    
     
     
         9 . The medium of  claim 7 , wherein the instructions of the medium further comprise: 
 controlling the flow rate to introduce a film at a graded concentration of the species throughout a thickness of the film.    
     
     
         10 . The medium of  claim 9 , wherein the flow rate is controlled so that the graded concentration of the species comprises a linear gradient.  
     
     
         11 . The medium of  claim 7 , wherein controlling the flow rate comprises controlling the mass flow rate of the species.  
     
     
         12 . The medium of  claim 7 , wherein the introduction of the film on a substrate comprises introducing the species and growing the film on the substrate.  
     
     
         13 . A system for growing a film on a substrate comprising: 
 a chamber;    a species source comprising a species, the species source coupled to the chamber to introduce the species into the chamber;    a mass flow meter coupled to the species source; and    a processor coupled to the species source comprising a machine readable medium comprising executable program instructions that when executed cause the processor to perform a method comprising: 
 controlling the introduction of the species into the chamber according to a determined concentration gradient of a film comprising the species introduced on a substrate to introduce a film on a substrate, the film comprising the species at a first concentration at a first point in the film and a second concentration different than the first concentration at a second point in the film.  
   
     
     
         14 . The system of  claim 13 , wherein the medium further comprises instructions that when executed cause the processor to perform a method comprising: 
 determining the concentration profile of the species for a unit of time according to data comprising:    determining a concentration of the species introduced on a substrate for a first plurality of flow rates;    determining a growth rate of the species grown on a substrate for a second plurality of flow rates.    
     
     
         15 . The system of  claim 14 , wherein the data relating to the concentration of the species and the growth rate are stored in the processor.  
     
     
         16 . The medium of  claim 14 , wherein the introduced film comprises a thickness, the instructions of the medium further comprise: 
 controlling the flow rate to introduce a film at a graded concentration of the species throughout a thickness of the film.    
     
     
         17 . The medium of  claim 16 , wherein the flow rate is controlled so that the graded concentration of the species comprises a linear gradient.  
     
     
         18 . A bipolar transistor comprising: 
 a collector layer of a first conductivity type; a base layer of a second conductivity type forming a first junction with said collector layer; and    an emitter layer of the first conductivity type forming a second junction with said base layer;    an electrode configured to direct carriers through the emitter layer to the base layer and into the collector layer,    wherein at least one of the first junction and the seconds junction is between different semiconductor materials to form at least one heterojunction,    wherein the heterojunction has a concentration profile of a semiconductor material such that an electric field changes in an opposite way to that of a mobility.    
     
     
         19 . The bipolar transistor of  claim 18 , wherein the base layer comprises Si 1-x Ge x , where x is less than or equal to 1.  
     
     
         20 . The bipolar transistor of  claim 19 , wherein the conductivity type of the base layer is defined by a first dopant concentration and wherein the base layer comprises a first spacer region between the emitter layer and the base layer and a second spacer region between the base layer and the collector layer, each spacer defined by a dopant concentration less than the first dopant concentration.  
     
     
         21 . The bipolar transistor of  claim 20 , wherein the concentration profile of the semiconductor material of the heterojunction comprises the concentration profile of at least one of the first spacer region and the second spacer region.  
     
     
         22 . The bipolar transistor of  claim 21 , wherein the conductivity type of the collector layer is N-type, the conductivity type of the base layer is P-type and the conductivity type of the emitter type is N-type.