Control of boron penetration in surface-channel PMOS devices is critical in order to ensure tight threshold voltage (Vt) distribution. Previous work has focused on studying relatively gross boron-penetration effects, which give rise to large shifts in Vt. In practice, low-voltage CMOS technologies are sensitive to small degradation in PMOS Vt scatter due to the onset of boron penetration. Moreover, the use of rapid thermal annealing can give rise to difficult trade-offs between poly depletion and boron penetration. As both of these effects can influence the PMOS Vt we propose a sensitive, systematic, methodology to distinguish between depletion and penetration effects and illustrate its application in a number of advanced CMOS processes, with oxide thickness ranging from 30-50 angstrom.
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