A typical set of sheet resistivity versus deposition time curves for temperatures ranging from 850oC to 1150oC are plotted in Figure 6. Each user should determine similar sets of curves that are characteristic of their diffusion process, since these will depend somewhat on such parameters as the type of BoronPlus source being used, furnace recovery and heating/cooling rates, gas flow rates, etc.
When the various processing conditions are optimized, uniformities of 2% across the silicon, 3% across the boat, and 4% run-to-run should be attainable. Although these uniformities are generally considered to be typical of the planar diffusion system, most processors have been able to significantly improve over them.
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Certain types of silicon surface damage have been reduced when BoronPlus sources are used in place of other types of dopant materials. Typical "necklace damage" shown in Figure 7(A) was eliminated as shown in Figure 7(B) when BoronPlus sources were used in a similar 1100oC isolation predeposition cycle.
BoronPlus® is a registered trademark of Techneglas Inc.
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