During the fabrication process for an MOS device it is observed that the threshold voltage in the gate region is different at the end of the process compared with its value immediately after the polysilicon gate electrode is deposited. This results from the various high temperature steps which follow the polysilicon deposition. What is the main reason for this change? A. The high temperature steps cause a small change in the thickness of the gate oxide. B. The high temperature steps result in a redistribution of the dopant in the region below the gate oxide. C. During these high temperature steps, the high concentration of dopant in the heavily-doped source and drain continues to diffuse. As the diffusion is isotropic, some moves sideways into the channel region. [3]