12.9 Simulation of Deposition after Transport in the Diffusion Regime

Figure 12.8: The figures show the surface evolution of typical trench structure during a deposition processes. The concentration of the diffusing particles above the wafer is scaled to the interval $[0,1]$ and it is constantly $1$ at the top of the simulation domain.

Step 1. Step 31. Step 61. Step 91. Step 121. Step 151.

Finally we show an example of a simulation of deposition from TEOS where transport takes places in the diffusion regime. In today's manufacturing the majority of processes is best described in radiosity simulations, but in some cases the length of the mean free path of the particles is so small that the process must be modeled by the diffusion equation.

Figure 12.8 shows how a simulation in the diffusion regime proceeds. The concentration of the active species containing silicon was assumed to be constant in the beginning. As the simulation proceeds, the depletion of species near the wafer surface and in the lower part of the channel can be seen.

It is known that the step coverage assumes a characteristic shape resembling two hunches at the trench opening in the case of small mean free paths and small mobility of the reacting molecules at the surface [111]. This case is the one simulated in Figure 12.8 and the formation of the characteristic hunches is observed in the simulations.