Investigation On Oxygen Precipitation In Heavily Boron Doped Czochralski Silicon

Nowadays, COMS technology has been extensively applied for ULSI (ultra-large-scale integrated) circuits industry. The N/N+ and P/P+ epitaxial structures, which become popular with the development of COMS technology, because they can avoid the Latch-up and a Softerror of ULSI while they combined with the intrinsic gettering (IG) technique. For the substrate of heavily boron doped wafer, it has been proved that oxygen concentration is increased and oxygen precipitation is enhanced by HB (heavily boron-doping) during crystal growth, which is beneficial for IG and therefore improve the yield of ULSI. Thus it is very important to investigate the behavior of oxygen and oxygen precipitation in heavily boron-doping Czochralski silicon (CZSi). However, there are few papers about it, especially the effect of RTP. In this research, oxygen precipitation in heavily boron-doping CZSi in different conditions have been systematically investigated.In this paper, firstly, the effect of heavy boron-doping on oxygen precipitation was investigated. After annealed at different conditions, it is found that oxygen precipitation is enhanced by heavily boron doping, especially at high temperature. We consider that the complexes of BmOn (m,n > 1) or the point defects induced by heavily boron doping may be involved in the nucleation of oxygen precipitates at high temperature range of crystal cooling. Therefore it is reasonably deduced that the density of voids in HB CZ silicon increases and the size of voids decreases due to the reduction of vacancy concentration as a result of heavy boron-doping enhanced oxygen precipitation prior to the void formation.Then, the effect of heavily doped boron on IG of Czochralski silicon was also investigated. It is found that no DZ (denuded zones) were observed in the HB samples subjected to high one-step temperature, ramping annealing respectively. For conventional high-low-high three-step IG annealing, the DZ becomes narrower and BMD density is higher in HB samples than that in LB samples, as a result of HB enhancing oxygen precipitation.Finally, the effect of rapid thermal process (RTP) on oxygen precipitation in HB is investigated in this paper. On contrary to LB wafer, the DZ cannot form in the HB silicon subjected to RTP pre-annealing. Thus it is considered that the technique of DZ formation by means of RTP may not be suitable for heavily boron-doping CZ silicon. Since the higher concentration vacancy could decrease the stress inducing by oxygen precipitates, the size of the oxygen precipitation with higher density was smaller in the HB Si samples in comparison with the samples without RTP pre-annealing. Moreover, as for the technique to generate DZ by RTP in lightly boron-doping samples, it was found that the behavior of oxygen precipitation and DZ was determined by the annealed temperature, followed annealing and ambient of RTF as well.