Briefly describe why thermal oxidation of silicon has both

Question

1. Holes are etched in 1 µm thick thermal oxide. The wafer is then given one hour wet oxidation at 1000^oC. All oxide is then etched away. What is the resulting step height in silicon (assume <100>?

2. Oxide is often used as a diffusion mask during a fabrication process. Using the figure below, how much oxide is needed to mask a 4 hr boron diffusion at 1150 ^oC@ A 1 hr phosphorous diffusion at 1050 ^oC?

Thickness of SiO₂ needed to mask boron and phosphorous diffusions as a function of time and temperature

3. You want to deposit a Si (atomic weight 28 AMU) film by thermal evaporation of Si at a total pressure of 2 x 10^-7 nitrogen (mass of N₂ Torr at 293K. Residual gas analysis shows that most of the gas content is is 2 x 14 = 28 AMU).

a. Calculate the flux of N₂ on the substrate during RT evaporation.

b. Calculate the flux of Si from the crucible held at 1500 K.

4. Calculate the impingement rate and mean free path for oxygen molecules (M = 32) at 300 K and a pressure of 10^-4 Pa. What is the pressure in Torr?

5. Briefly describe why thermal oxidation of silicon has both linear and parabolic components to the growth rate.