Tracking carbon to silicon ratio

1. A method comprising:

supplying sources of carbon and silicon at a carbon:silicon ratio into a chemical vapor deposition chamber containing a substrate under conditions effective to cause growth by hot wall chemical vapor deposition of silicon carbide on the substrate;

collecting exhaust gases from the chamber;

performing mass spectrometry on the exhaust gases to determine the partial pressure of a carbon or silicon species in the exhaust gases;

measuring the carrier concentration in the silicon carbide by capacitance-voltage profiling;

repeating the supplying of sources of carbon and silicon, the collecting of exhaust gases, the performing of mass spectrometry, and the measuring of the carrier concentration one or more times at different carbon:silicon ratios;

creating a correlation curve to correlate the carrier concentration to the partial pressure of the carbon or silicon species;

supplying the sources of carbon and silicon into the chemical vapor deposition chamber containing a second substrate under the conditions effective to cause growth by hot wall chemical vapor deposition of silicon carbide on the second substrate;

collecting exhaust gases from the chamber;

performing mass spectrometry on the exhaust gases to determine the partial pressure of the carbon or silicon species in the exhaust gases;

adjusting the amount of the sources of carbon and silicon entering the chamber in response to the partial pressure of the carbon or silicon species according to the correlation curve to maintain a maximum carrier concentration of 10 16 /cm 3 throughout the depth of the silicon carbide;

wherein the exhaust gases are collected at a point having a direct line of sight to the location of silicon carbide growth.

2. The method of claim 1 , wherein the carbon source is propane and the silicon source is silane.

3. The method of claim 1 , wherein the carbon species is an acetylene species having a mass of 26 amu.

4. The method of claim 1 , wherein the adjusting is performed continuously during the silicon carbide growth process.

5. The method of claim 1 , wherein the silicon species is a silane species having a mass of 28-31 amu.

6. The method of claim 1 , wherein the exhaust gases are collected by a tube that is not degraded during a silicon carbide growth process.

7. The method of claim 1 , wherein the substrate is a 4H—SiC substrate, a 6H—SiC substrate, a 3C—SiC substrate, or a polytype SiC substrate.

8. The method of claim 1 ; wherein the exhaust gases are collected by a tube so that laminar flow of the exhaust gases reaches the collection point of the tube.