You perform LPCVD of polysilicon using SiH4 at 610 C with a pressure of 300 mtorr and a gas flow rate of 90 sccm. The resulting highly conformal deposition has a rate of 6.4 nm/min. 4-1. What is the impingement rate of SiH4 molecules on the surface of the wafer? 4-2. What fraction of the impinging molecules get incorporated into the film? 4-3. Assuming the surface of the furnace has an inner diameter of 0.25 m, a length of 2 m, and you are depositing on 50 wafers that have a diameter of 200 mm, what fraction of SiH4 gas gets pumped out of the furnace unused? Hints: At standard temperature and pressure (STP) the molar gas volume is 22.7 L. Also note that the atomic density of silicon is 5×1022 atoms/cm3. 4-4. If you did not wait for the temperature to become uniform in the tube (i.e., the front was 590C .