Effects Of Group-? Elemental Impurities In Czochralski Silicon

Czochralski(Cz)silicon is the base material for manufacturing integrated circuits(ICs).The defects and mechanical strength associated with Cz silicon exert significant impacts on the yield and performance of ICs.Therefore,manipulating defects and improving mechanical strength are important subject matters in silicon materials research.Certain electrically inactive impurities in Cz silicon are supposed to remarkably affect the formation of defects and mechanical strength.In this dissertation,the effects of group-IV elemental impurities(carbon,germanium and tin)on the formation of point defects and oxygen precipitates in Cz silicon has been investigated.Moreover,the carbon effects on the mechanical strength of Cz silicon has been specifically addressed.The primary achievements in this dissertation are listed as follows.(1)Au in-diffusion and deep level transient spectroscopy(DLTS)characterization has been employed to investigate the impact of carbon co-doing on the survival of vacancies from RTP in Cz silicon.It is revealed that the existence of?1017 cm-3 carbon atoms significantly increases the amount of survival vacancies in the form of vacancy-oxygen(VOm,m?2)complexes in CZ silicon when subjected to the 1250 ?/60 s rapid thermal processing(RTP).Moreover,such increase of vacancies becomes more significant with the increase of cooling rate during RTP.First principle calculations suggest that substitutional carbon atom is to somehow tend to trap silicon intersitials and form CI complexes.Under this circumstance,the vacancy-interstitial(V-I)recombination is suppressed to some extent and the survival vacancy concentration is distinctly increased.As a result,the concentration of VOm complexes in carbon doped silicon is increased,resulting in more significant oxide precipitate nucleation in the wafer subject to 1250 ?/60 s RTP.Consequently,when subjected to the same OP anneal consisting of the nucleation anneal at 650 or 800 ? for 4 h and the subsequent growth anneal at 1000 ? for 16 h,carbon co-doped silicon possesses a higher density of bulk microdefects(BMDs)and therefore acquires stronger internal gettering capability.However,the nucleation temperature for OP should be carefully selected as 650 ? in order to form oxide precipitate-free denuded zone.(2)Carbon effects on the mechanical strength of Cz silicon have been investigated using nano-indentation,micro-indentation and dislocation-gliding characterization.The carbon doping is found to reduce the hardness,Young's modulus and indentation fracture toughness to some extent.In the temperature range 550-700 ?,the carbon doping reduces the activation energy of dislocation gliding and therefore increases the dislocation gliding velocity.However,in terms of the gliding of indentation-induced dislocations,it is found that the carbon doping reduces the dislocation gliding velocity,namely,suppresses the motion of dislocation.(3)The impact of?1019 cm-3 germanium(Ge)co-doping on oxygen precipitation(OP)in heavily boron(B)-doped(?1018 cm-3)Cz silicofn subjected to low-high two-step anneal without or with the prior high temperature RTP has been investigated.It is found that the Ge co-doping exhibits the effect of suppression or enhancement on OP in the heavily B-doped Cz silicon without or with the prior RTP.In the case without the prior RTP,the compressive stress introduced by the Ge co-doping compensates the tensile stress arising from the B-doping,which is not beneficial for the growth of oxide precipitates.However,in the case with the prior RTP,the Ge co-doping increases the amount of vacancies introduced by the RTP and,moreover,may enable to generate more heterogeneous nucleation centers of oxide precipitates,thus leading to the enhanced OP in the heavily B-doped Cz silicon.(4)The impact of tin(Sn)co-doing on the vacancy concentration in Cz silicon has been investigated by means of Au in-diffusion in combination with DLTS characterization.It is revealed that the?1017 cm-3 Sn co-doping slightly increases the vacancy concentration in Cz silicon.However,the increase becomes more significant with the prior high-temperature RTP.The effects of Sn co-doping on the oxygen precipitation(OP)behaviors in Cz silicon subjected to the low(650 or 800 ?)-high(1000 ?)two-step anneal have been investigated.In the case without the prior high temperature RTP,the Sn co-doping suppresses OP in Cz silicon.Whereas,in the case with the prior high temperature RTP,the Sn co-doping significantly enhances OP due to the existence of more vacancies that facilitate oxygen precipitate nucleation.Such enhanced OP is beneficial for internal gettering capability of Cz silicon wafers.Moreover,Sn co-doping is found to hardly affect the formation of denuded zone in Cz silicon wafers.