Correct Answer - Option 4 : 4
Explanation:
-
CVD stands for chemical vapor deposition. It is a process used to produce thin films of semiconductor materials.
- The CVD or vacuum deposition process produces high-quality, high-performance solid materials.
- The deposition of required materials is obtained by exposing the substrate to the volatile precursors which decompose on the surface of the substrate to produce the deposit.
- Common materials prepared by CVD are silicon oxide, silicon oxide is deposited by CVD by several processes.
- The sources of gases used in the deposition process are silane and oxygen, dichlorosilane, and nitrous oxide.
- The reaction is:
SiH4 + O2 → The oxides preparedSiO2 + 2H2.
- Now, to improve the efficiency of semiconductor doping can be performed.
- The oxides prepared may be doped with impurities such as Phosphorus to form a P-type semiconductor.
- So, silicon dioxide is alloyed with phosphorus pentoxide.
- The process requires a minimum concentration of phosphorus to be 6%.
- The gas used for depositing Phosphorus is Phosphine and oxygen. The reaction is
PH3 + 5O2 → P2O5 + 6H2
- Now, pyrophoric substances are the gases that ignite spontaneously when exposed to oxygen, and both Phosphine and silane are pyrophoric, flammable, and toxic in nature.
- Hence, Silane and Phosphine are the gases commonly used in CVD that are pyrophoric, toxic, and flammable.
The correct option is 4 i.e., '(A) and (D) only'.
- Nitrogen and argon are unreactive gases.