| Summary: | 碩士 === 國立中興大學 === 精密工程研究所 === 90 === The P- epitaxy on heavy boron doped wafer has been well employed in power MOS device for reducing vertical on-resistance and also provide effective latch-up hardening for advanced CMOS technology. However, the micro-defect generated from the substrate greatly affects the quality of epitaxial layer. To control the density of bulk micro-defect as well as to create a comfortable denuded zone is an important research subject of applying heavy boron doped substrate for IC manufacture. In this resear- ch, a systematical two-step (low — high) and three-step (high-low- high) anneals was carried out to investigate the bulk-micro -defect (BMD) for B+ Cz silicon. Some important information described as follows were obtained.
The increase of boron concentration enhanced the oxygen precipitation. The high density of stacking faults was observed with much short nucleation annealing. The feature of etched stacking faults in heavy boron doped silicon is much plump (more less like elliptic shape) than that in light boron doped silicon. The feature of the bulk defects in the heavy doped silicon is different from that of the light doped silicon, in upon with the annealing time and annealing temperature.
The denuded zone generated after two-step anneal is not easy to be observed, A long high temperature annealing prior to the two-step anneal is needed. 1150 ℃ annealing up to 4 hours can generate a denuded zone size of about 20 um. The wet ambient can provide a much wide denuded zone than dry N2 anneal.
The poly-silicon film deposition process reduce the denuded zone size drastically for the medium to high oxygen concentration silicon used in this research. Therefore, it is not appropriated to use the poly film as back side gettering for high oxygen concentration wafers.
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