Defects in Silicon Crystals -Volume Defects Agglomeration of point defects Void formed by a collection of vacancies Precipitates of dopants or impurities Precipitate Three-dimensional defects (Volume Defects): 。 Doping concentration exceeds the solubility of the dopant in the crystal> precipitation of dopant atoms in amorphous or crystalline clusters After CZ silicon growth,temperature reduces to normal operation temperature> precipitation or clustering of oxygen atoms Precipitation can be useful to getter/collect unwanted impurities(heavy metals), e.g.,precipitating oxygen in the bulk of the wafer,away from surface region
Defects in Silicon Crystals –Volume Defects Agglomeration of point defects • Void formed b y a collection of vacancies • Precipitates of dopants or impurities Precipitate Three-dimensional defects (Volume Defects): • Doping concentration exceeds the solubility of the dopant in the crystal Æ precipitation of dopant atoms in amorphous or crystalline clusters • After CZ silicon growth, temperature reduces to normal operation temperature Æ precipitation or clustering of oxygen atoms • Precipitation can be useful to getter/collect unwanted impurities (heavy metals), e g precipitating oxygen in the bulk of the wafer away from surface region e.g., precipitating oxygen in the bulk of the wafer, away from surface region
Silicon Wafer Fabrication
Silicon Wafer Fabrication
Raw Material and Purification Process sequence from starting material to polished wafer sp, RAW MATERIAL (QUARTZITE) MCS DISTILLATION AND REDUCTION EGS POLYCRYSTALLINE SILICON CRYSTAL GROWTH SINGLE CRYSTAL SILICON GRIND,SAW,POLISH WAFER
Raw Material and Purification Process sequence from starting material to polished wafer Process sequence from starting material to polished wafer SiO 2 MGS EGS
SiO2→MGS MGS:Metallurgical SUBMERGED ELECTRODE Grade Silicon QUARTZITE,COAL. COKE,WOOD CHIPS 0 0 c0,si0,H20 CONDENSE SiO Sio+CO-Sio2+C 1600C- 一一一 FORM SIC Sio+2C* FROM SiO AND C SiG +CO MELT S102 5i02+c Sio +Co Sic +Sio2=Si+Sio+Co 上U- LIQUID SILICON MGS DISCHARGE SI 7 Si(Al+Fe) Furnace 98%pure Submerged-electrode arc furnace 2C(solid)+SiO,(solid)>Si(liquid)+2CO(gas)
SiO2 Æ MGS MGS: Metallurgical Grade Silicon 98% pure MGS Si(Al+Fe) F 98% pure urnace Submerged-electrode arc furnace 2C(solid)+SiO2(solid)ÆSi(liquid)+2CO(gas)
MGS→EGS FILTER L COOLING Si SLIM ROD Grind to powder H2 QUARTZ BELL JAR Mg-Si ppb purity (1013- 1014cm-3)of EGS N2 for CZ or FZ HCI Liquid at RT FLUIDIZED BED DISTILLATION CVD REACTOR @300C SiHCI3 MGS(s)+HCI(g)>SiHCI(D) separated 2SiHCI3(g)+2H2(g)>2Si(s)+6HCI(g)
MGS Æ EGS Grind to d b it (1013 pow er ppb purity (1013- 1014cm-3) of EGS for CZ or FZ Liquid at RT @ 300oC MGS(s)+HCl(g)ÆSiHCl3(l) SiHCl3 separated 2SiHCl3(g)+2H2(g)Æ2Si(s)+6HCl(g)