To produce a device isolation trench you first use CVD to deposit an oxide of 50nm on Si(100). You follow that by a dry thermal oxidation at 1000C for 30 min. At last you fill the rest of the trenches with a CVD Si3N4 layer.
a) Explain what is the final thickness of the dry thermal oxide layer you grew?
b) Define what benefit might the thermal oxide layer provide?
c) Depict the layer structure that results, labeling separately the Si substrate, CVD oxide, thermal oxide, and nitride layers. Use just a simple planar portion of the layer structure.