The deposition rate for the front wafer is 0.02 wafer/s.
The deposition rate for the front wafer can be calculated using the formula:
Deposition Rate = (Flow Rate of Silane) / (Number of Wafers)
Given that the tube diameter is 25 cm and the wafer diameter is 20 cm, the cross-sectional area of the tube is pi*(25/2)^2 = 490.87 cm².
The flow rate of silane can be calculated by dividing the volume of silane gas injected per unit time by the cross-sectional area of the tube.
Assuming a uniform flow rate, the volume injected per unit time is equal to the volume of silane gas required to deposit a layer of silicon with a thickness equal to the wafer thickness.
Thus, the flow rate of silane is equal to (Wafer Thickness) / (Deposition Time).
Given that the distance between wafers is 0.5 cm and the wafer thickness is 0.01 cm, the deposition time can be calculated as the distance between wafers divided by the deposition rate: 0.5 cm / (100 wafers) = 0.005 cm/wafer.
Therefore, the flow rate of silane is 0.01 cm / 0.005 cm/wafer = 2 wafer/s.
Finally, the deposition rate for the front wafer can be calculated as the flow rate of silane divided by the number of wafers: 2 wafer/s / 100 wafers = 0.02 wafer/s.