The correct answer is B. Silane gas (SiH4).
Silane gas is a chemical compound with the formula SiH4. It is a colorless, flammable gas that is used in the semiconductor industry to deposit polysilicon layers on silicon wafers. Polysilicon is a type of silicon that is used to make the gates of transistors.
Silicon nitride (Si3N4) is a ceramic material that is used in the semiconductor industry as a passivation layer and as a diffusion barrier. It is a white, non-flammable solid that is not soluble in water.
Silicon oxide (SiO2) is a glassy material that is used in the semiconductor industry as an insulator and as a diffusion barrier. It is a white, non-flammable solid that is soluble in water.
None of the mentioned is not the correct answer because silane gas (SiH4) is the chemical that is used for chemical vapor deposition to grow the polysilicon gate layer.