| Copper(Cu),as one of the transitional metals,is a common contaminant during the fabrication of silicon wafers and devices.Due to the properties of high diffusion coefficient and sharp solubility dependence on temperature in silicon,Cu precipitation easily occurs during the cooling process of annealing.This brings about detrimental effects on the yield and even the reliability of devices.In the past decades,Cu precipitation in silicon has been extensively and intensively investigated.The effects of annealing conditions,conduction type,and existing defects such as dislocation, stacking fault on Cu precipitation have been well elucidated.While,we are still lacking in the knowledge about the effects of point defects,impurities[e.g.nitrogen (N),phosphorous(P),arsenic(As),antimony(Sb),and boron(B)],and oxygen precipitates on Cu precipitation.In this dissertation,the effects of point defects including silicon interstitial(Sii) and vacancy(V),oxygen precipitates,nitrogen-doping,and heavily doped impurities including P,As,Sb and B on Cu precipitation and its related recombination activity in Czochralski(CZ) silicon have been intensively investigated.The most important results achieved in this dissertation are listed below.(1) The effect of Sii on Cu precipitation behavior in n-type CZ silicon has been investigated.The Cu-contaminated silicon wafers were cooled down from 1000℃with a rate of 30℃/s to enable Cu precipitation.In the sample without delieberately induced Sii atoms,Cu precipitates exhibit as spheres with a diameter of～100nm; while,in the sample with an amount of Sii atoms induced by a prior thermal oxidation, a number of sphere-like Cu precipitates sized in 10-20nm assemble on and around the dislocations,forming so-called Cu precipitate colonies.It is well known that the concentration of Sii atoms induced by the thermal oxidation decreases from the surface to the bulk of the silicon wafer.Moreover,most of the Cu atoms diffused into silicon locate at the interstitial sites.Due to the repelling interaction between the Sii and interstitial Cu(Cui) atoms,the concentration of Cui atoms is much higher in the bulk of the silicon wafer with a prior thermal oxidation.In this context,during the cooling process,a part of supersaturated Cui atoms preferentially precipitate in the bulk of silicon wafer,emitting an amount of Sii atoms.Such Sii atoms will aggregate into dislocations in certain regions.Afterwards,the remnant Cui atoms preferentially precipitate on the existing dislocations,leading to the formation of Cu precipitate colonies.By comparison,for the sample without the prior thermal oxidation,the concentration of Cui atoms is nearly uniform across the silicon wafer.In this case,Cu precipitation proceeds via a homogeneous nucleation mechanism,forming sphere-like precipitates with the minimum surface energies.(2) The effect of vacancy on Cu precipitation in n-type CZ silicon has been investigated.The Cu-contaminated silicon wafers were cooled down from 1000℃with a rate of 30℃/s to enable Cu precipitation.In the sample without deliberately induced vacancies,Cu precipitates exhibit as spheres with a diameter of～100nm; while,in the sample injected with an amount of vacancies by the prior rapid thermal processing(RTP) at high temperature,a number of sphere-like Cu precipitates sized in 10-20nm assemble on and around the dislocations,forming Cu precipitate colonies. The concentration of vacancies induced by the RTP decreases from the bulk to the surface of the silicon wafer.Because the vacancies can significantly enhance Cu precipitation,a part of supersaturated Cui atoms preferentially proceeds in the bulk of silicon wafer.Afterwards,the Cu precipitate colonies further form via the mechanism as described in the above paragraph.(3) The effect of point defects on the recombination activities of Cu precipitates and the formation of Cu-related deep level centers in p-type CZ silicon have been investigated.It is revealed that the vacancies increase the minority carrier capture cross section,resulting in the enhanced recombination activity of Cu precipitates; while,the Sii atoms decrease the Cu precipitate density,leading to the weakened recombination activity of Cu precipitates.Additionally,it is believed that the complex of Cui and vacancies and that of Cui and Sii lead to the deep levels of Ev+0.35eV and Ev+0.32eV,respectively.The electronic states of these two deep levels are proved to be localized.(4) The Cu precipitation behaviors in p-type CZ and nitrogen-doped CZ(NCZ) silicon have been comparatively investigated.In the case of cooling from 1000℃with a rate of 30℃/s in Ar,in CZ silicon the Cu precipitates exhibit as spheres with a diameter of～100nm;while,in NCZ silicon a number of sphere-like Cu precipitates with diameters of 10-30nm assemble on and around the dislocations,forming Cu precipitate colonies.Furthermore,it is revealed that for the Cu precipitates formed in the cooling process from 800-1100℃with a rate of 30℃/s under the atmosphere of Ar,N2,or O2,their recombination activities in NCZ silicon are weaker than those in CZ silicon.The above results are originated from the effect of relatively larger grown-in oxygen precipitates in NCZ silicon on Cu precipitation behavior.(5) The Cu precipitation behaviors in heavily P-,As- and Sb-doped CZ silicon have been comparatively investigated.All of the Cu-contaminated silicon wafers were cooled down from 1000℃with a rate of 30℃/s to enable Cu precipitation.In heavily P-doped silicon the Cu precipitates are revealed as spheres with a diameter of～80nm; while,in heavily As/Sb-doped silicon,Cu precipitate colonies,in which a number of sphere-like Cu precipitates with a diameter of～20nm assemble on and around the dislocations,are generated.Furthermore,the annealing temperature(700-1000℃) or cooling rate(30℃/s-10℃/min) exerts different effects on Cu precipitation in heavily P-doped and As-doped silicon.Because the covalent radii of P atom and As/Sb atom are,respectively,smaller and larger than that of Si atom,the tensile and compressive lattice stresses are,respectively,induced in heavily P-and As/Sb-doped silicon.It is believed that the difference in the natures of lattice stresses in heavily P-and As/Sb-doped silicon brings about the different Cu precipitation behaviors,as described above.(6) The Cu precipitation behaviors in n/n+(P-,As-or Sb-doped) epitaxial silicon wafers under different annealing conditions have been comparatively investigated.It is shown that all the heavily doped silicon substrates have strong capabilities of gettering Cu contaminated on the epitaxial layer.Moreover,it is found that the gettering capability increases in turn from heavily Sb-,As-to P-doped silicon substrates.(7) The Cu precipitation behavior in heavily B-doped CZ silicon has been investigated in comparison with that in control lightly B-doped CZ silicon.The Cu-contaminated silicon wafers were cooled down from 1000℃with a rate of 30℃/s to enable Cu precipitation.In heavily B-doped silicon,a number of sphere-like Cu precipitates with a diameter of～10um assemble on and around the dislocations, forming Cu precipitate colonies,which is quite different from the spherical Cu precipitates with a diameter of～100nm formed in lightly B-doped silicon.The formation of Cu precipitate colonies in heavily B-doped silicon is ascribed to the fact that the relatively larger grown-in oxygen precipitates can serve as the heterogeneous nucleation sites for Cu precipitation.Furthermore,it is revealed that the Cu precipitate colonies induced in the cooling process of 1000℃annealing can be transformed into spherical Cu precipitates by the annealing at temperatures of 1000℃and above; however,they can not be completely dissolved.It is supposed that the thermal stability of Cu precipitates is related to lattice tensile stress and grown-in oxygen precipitates.
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