Importance

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Abstract

A poly layer on a substrate is covered with nitride. A reverse tone load implant mask and etch opens an area, which is then boron implanted. Controlled oxidation follows to grow oxide on the boron-doped region only, thereby thinning the poly there. Strip the nitride and then dope the poly layer. The oxide shields the boron-doped region from further substantial doping. Next, apply a poly definition photoresist mask. Etch the exposed oxide and poly to define a poly line having a boron-doped resistor therein. The difference in etch rates between heavily doped and lightly doped poly is compensated for by the adjustment of thickness of the boron-doped region. Hence, the etch for both types of poly concludes at about the same time, leaving the underlying layers substantially intact. Sources and drains may be implanted thereafter without an additional load implant mask.

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First Claim