Hints, Tips and Solutions

Q. When I simulate my process flow the simulated profile is always lower than the SRP measurements. What could be causing this ?

A. In many simulated process flows the surface oxide is etched completely off after which there may be some diffusion cycles. When ATHENA performs a diffusion step it will model the diffusion of dopants not only into the silicon but also across region boundaries for instance from silicon to the gas above the silicon surface. So if no oxide is present on the surface of the silicon, dopant loss may occur into the gas. To illustrate a 1e14 Boron implant @ 50 KeV is performed into silicon and is annealed at 1150C for 60 minutes. Figure 1 shows the resulting Boron profile when an oxide layer is deposited just before the diffusion and when the silicon surface is exposed. Clearly significant dopant may be lost if no oxide is present. It is important therefore to check in each input deck that a surface oxide is present before any diffusion step is performed.