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Dopant concentration at/cm3
Poly-Si
Silicate
Si
Depth
Figure 6.17. Schematic representation of the model used to extract the dopant
diffusivities in silicate films. By fitting the dopant profile in the Si substrate, the dopant
diffusivities in the silicate ans Si substrate can be calculated. See chapter 3. After
reference [6]
penetration profile into the Si substrate by employing the steady-state diffusion model in
a two-boundary system, first developed by Sah et al,6 and applied to thin film SiO 2 and
SiO x Ny systems by other authors. 13,14 This model is described in detail in chapter 3. Due
to the enhanced diffusivity expected in ultra-thin SiO x layers,16 (such as the ~ 10 Å
interfacial layer observed in the HfSix Oy ) the HfSix Oy films were considered the limiting
layer for dopant penetration into the Si substrate in these calculations.
In this model, the polysilicon gate is treated as the constant dopant source on top
of a thin barrier (HfSix Oy ). The concentration of dopant in polysilicon is treated as
constant because the dopant diffusion in polysilicon is rapid, assuring a flat profile after a
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