Microdefects And Defect Engineering Of Iso-group Elements Doped Czochralski Silicon Used For Large-scale Integrated Circuits

With the rapid development of ultra large-scale integrated circuits(ICs),the requirements on silicon materials become increasingly stringent.The control and elimination of microdefects in Czochralski(CZ)silicon is the most important issue for the development of silicon materials.For the larger diameter CZ silicon wafers, the oxygen concentration is reduced to a certain extent.Moreover,the thermal budget for the manufacturing of contemporary IC featuring super-shallow junction is significantly lowered.The two regards as mentioned above are not favorable for oxygen precipitation and therefore the internal gettering(IG)capability for CZ silicon wafers so that the traditional IG process is challenged.On the other hand,the gate oxide integrity(GOI)of metal-oxide-semiconductor(MOS)devices and furthermore the yield of IC will be deteriorated by the void defects commonly existing in large diameter silicon wafers.Addressing the control of microdefects and the enhancement of IG capability,the strategy of co-doping in CZ silicon has been developed.In this dissertation,based on the growth of new type CZ silicon crystals doped with iso-group elements(germanium and carbon),the oxygen precipitation behavior and the formation and elimination of void defects in both the lightly germanium doped CZ(GCZ)silicon and high-carbon-content CZ(H[C]CZ)silicon have been intensively investigated.Moreover,the mechanisms for the effect of germanium and carbon on the oxygen precipitation and grown-in defects in CZ silicon have been reasonably exploited.Furthermore,the IG processes appropriate for GCZ and H[C] CZ silicon wafers have been well developed.Listed below are the most important results achieved in this work.(1)The effects of germanium on oxygen precipitation in CZ silicon have been investigated.It is found that the formation of grown-in oxygen precipitates and oxygen precipitation during the post-growth anneals in a wide temperature range of 650-1150℃can be enhanced by the germanium-doping in CZ silicon.It is suggested that the germanium-related complexes generated during the crystal growth,such as Ge-V and Ge-V-O complexes,act as the heterogeneous nucleation centers for oxygen precipitates in GCZ silicon.Moreover,it is found that the thermal stability of oxygen precipitates at high temperature for GCZ silicon is remarkably weakened,which is attributed to the small precipitates and plate-like precipitates formed in GCZ silicon.(2)The IG processes for GCZ silicon wafer based on the conventional furnace anneal(CFA)and rapid thermal anneal(RTA)have been developed.With the three-step of high-low-high anneal,the density of bulk microdefects(BMDs)is increased and the denuded zone(DZ)is narrowed in the GCZ silicon wafer with respect to the conventional CZ silicon wafer,which is ascribed to the enhancement of oxygen precipitation by the germanium doping.It is also found that a high density of BMDs and a DZ with a desirable width can be generated in GCZ silicon wafer subjected to the low-high two step anneal or a single high temperature anneal following a RTA at high temperature,meaning that the RTA-based IG processes feature substantially lower thermal budget.Note that it has been definitely clarified that there are hardly tiny oxygen precipitates existing in the DZ formed by the CFA- and RTA-based IG processes for GCZ silicon wafer and,moreover,the IG capability of GCZ silicon wafer is superior to that of CZ silicon wafer.(3)The effects of high-content carbon on oxygen precipitation in H[C]CZ silicon have been investigated and,furthermore,the IG processes for H[C]CZ silicon wafers have been developed.It is found that oxygen precipitation occurring in the IG processes is enhanced by the high-content carbon,due to the formation of carbon-related complexes,including C(3)center and C-V complexes,in H[C]CZ silicon. On the other hand,both the DZ without tiny oxygen precipitates and a higher density of BMDs with respect to that of CZ wafer can be generated in H[C]CZ silicon wafer through the CFA- and RTA-based IG process,which sheds light on the application of H[C]CZ silicon wafer in the manufacturing of IC.(4)The influences of the light germanium-doping and the heavy carbon-doping on the formation of void defects in CZ silicon have been investigated.It is found that the small-sized voids in a higher density and the large-sized voids in a lower density are generated in GCZ silicon wafer while the large-sized voids in a lower density are formed in H[C]CZ silicon wafer,with respect to those in CZ silicon wafer.It is believed that during the post-cooling of crystal growth the interaction of germanium or carbon and vacancy to form the complexes prior to the formation of voids consumes a number of vacancies,therefore,the formation of voids in GCZ and H[C]CZ silicon shifts to a lower temperature,thus leading to generating smaller but denser voids. Moreover,the voids in GCZ and H[C]CZ silicon wafers can be annihilated at lower temperatures with respect to those in CZ silicon wafer,which facilitates to increase the GOI of MOS devices.(5)The effect of light germanium-doping on the mechanical properties of CZ silicon wafer has been tentatively investigated.Due to the high density of small-sized oxygen precipitates preformed in GCZ silicon,the climbing of dislocations can be suppressed by the pinning effect of small-sized oxygen precipitates on the dislocations.As a result,the warp and bow of CZ silicon wafer doped with the germanium can be significantly reduced during the thermal cycles of device fabrication, which is beneficial for the elimination of voids within the near-surface region of silicon wafer.(6)According to the computation based on first principle,it is theoretically pointed out that the interaction among the germanium/carbon,oxygen and vacancy and therefore the formation of complexes in specific structures are thermodynamically favorable.Based on the experimental evidences,it is believed that such complexes can be formed in silicon during the post-crystal-growth cooling process.On one hand,the complexes consumes a part of vacancies in silicon involved during the crystal growth,thus leading to smaller voids in higher density;on the other hand, they can act as the heterogeneous nucleation centers for the enhanced oxygen precipitation. Likewise,the germanium and carbon related complexes can be also formed during the RTA process,which also promote oxygen precipitation during the subsequent anneals.With the theoretical and experimental works,a qualitative model for elucidating the mechanism for the effects of germanium and carbon on the behaviors of microdefects(oxygen precipitate and void)in CZ silicon has been tentatively developed.