Question

Which of the following gases commonly used in CVD are pyrophoric, toxic, and flammable?

(A) Phosphine

(B) Argon

(C) Nitrogen Oxide

(D) Silane

(E) Nitrogen

Choose the most appropriate answer from the options given below:

(1) (B) and (C) only

(2) (C) and (E) only

(3) (B) and (E) only

(4) (A) and (D) only

1. 1
2. 2
3. 3
4. 4

Answer 1

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.