Reduction of carrier depletion in p+ polysilicon gates using laser thermal processing

Abstract

A novel laser thermal processing (LTP) technique was used to fabricate p+-gated MOS capacitors with ultrathin gate oxides. It is found that the introduction of LTP prior to the gate activation anneal increases the carrier concentration at the poly-Si gate/gate oxide interface substantially, as compared to rapid thermal anneal (RTA) alone. Thus, LTP readily reduces the poly-depletion effect in p+-poly-Si gates. This is achieved without observable gate oxide degradation or boron penetration. Secondary ion mass spectrometry analyzes show that the boron concentration near the gate/gate oxide interface increases significantly after the post-LTP anneal. A possible mechanism for this increase in carrier concentration is the diffusion of boron atoms toward the gate oxide by a complex process known as explosive crystallization.