1. In this problem, we will consider a simplified Si APCVD reactor. It has a rectangular section, 30 cm wide and 15 cm high. Its length is 120 cm. The input gas stream consists of SiH4 diluted with H2. According to the flow metering instruments located in the 30 °C lab, the pressure in the input gas line is 1 atm, the H? flow rate is 1000 cm³/s and the SiH4 flow rate is 1 cm³/s. The reactor temperature is 1000 °C but we assume there is no deposition on the walls.
(a) What are the partial pressure of H2 and SiH4 in the chamber?
(b) What are the bulk gas velocities of H2 and SiH4?
(c) What is the residence time of each gas species in the reactor?
(d) A tilted susceptor is now inserted into the chamber. Its tilt is calculated so that the boundary layer thickness is constant all along its length. The susceptor is a triangular wedge 30 cm wide, 60 cm long and 3 cm high at its downstream end. What are the gas velocities at this end?
(e) The susceptor holds 4 wafers in a line parallel to its longitudinal axis, each 10 cm in diameter. There is no deposition on the walls or susceptor and the growth rate on the wafers is 0.05 µm/min. What percentage of the SiH4 is being consumed?
(f) Assume that the growth rate measured on the first wafer is 0.2 µm/min. If the growth rate is totally dominated by mass transport and is proportional to the SiH4 partial pressure at the upstream edge of the wafer, what growth rate do you expect to measure on the second wafer? Assume that the deposition reaction can be completely expressed by
SiH4 ? Si + 2H2
