LPCVD of doped polysilicon

In Section 17.3.2(i) we have indicated a range of uses for polysilicon. For all of these applications there is a need to control layer structure. In addition, careful control of doping levels is also necessary. This can be done with post-deposition doping but this requires a high temperature (typically 900°C) in order to move the dopant atoms from the surface and to drive them into the layer. This high temperature diffusion step can cause thermal damage. One solution is to use in situ doping at the normal temperature of polysilicon deposition i.e., ca. 600°C. 

The procedure is the same as for depositing polysilicon except that there is an additional flow of the dopant gas. For example, for the incorporation of phosphorous, which of various possible impurity dopants has been the most extensively studied to date, phosphine diluted in an inert gas, such as nitrogen, is introduced into the reactor. The overall process can be represented by 

Deposition temperatures of typically 550-650°C and reactor pressures in the range 15-130 Pa (0.1-1 Torr) are comparable to those used for undoped polysilicon deposition. Flow rate ratios (-y) of PHySil from 10-5 to 10-1 have been reported, but the most commonly used range is 10-3-10-2. 

Some kinetic considerations of chemical vaponr deposition processes Ch. 17 

Overall, then, a reaction scheme of the form shown in the equations in 

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