热退火对多晶硅特性的影响

第26卷　第12期2005年12月

半　导　体　学　报

CHIN ESE J OURNAL OF SEMICONDUCTORS

Vol.26　No.12

Dec.,2005

Received 10J une 2005

Ζ2005Chinese Institute of Electronics

E ffect of Therm al Annealing on Characteristics

of Polycrystalline Silicon

Ren Bingyan 1,Gou Xianfang 1,2,Ma Lifen 1,2,Li Xudong 2,Xu Ying 2,and Wang Wenjing 2

(1Semiconductor Research I nstit ute ,Hebei Uni versit y of Technolog y ,Tianj in 300130,China )

(2B ei j ing S olar Energ y Research I nstit ute ,Bei j i ng 100083,China )

Abstract :Oxygen and carbon behaviors and minority 2carrier lifetimes in multi 2crystalline silicon (mc 2Si )used for solar cells are investigated by FTIR and QSSPCD before and after annealing at 750～1150℃in N 2and O 2ambient.For comparison ,the annealing of CZ silicon with nearly the same oxygen and carbon concentrations is also carried out under the same conditions.The results reveal that the oxygen and carbon concentrations of mc 2Si and CZ 2Si have a lesser decrease ,which means oxygen precipitates are not generated ,and grain boundaries in mc 2Si do not affect car 2bon behavior.Bulk lifetime of mc 2Si increases in N 2and O 2ambient at 850,950,and 1150℃,and the lifetime of mc 2Si wafers annealed in O 2are higher than those annealed in N 2,which shows that a lot of impurities in mc 2Si at high temperature annealing diff use to grain boundaries ,greatly reducing recombination centers.Interstitial Si atoms filling vacancies or recombination centers increases lifetime.K ey w ords :polycrystalline silicon ;oxygen ;lifetime EEACC :2520C

C LC number :TN30411+2 Document code :A Article I

D :025324177(2005)1222294204

1　Introduction

Polycrystalline Si wafers have become preva 2lent in t he recent p hotovoltaic market.However ,t hey need f urt her quality imp rovement for highly efficient ,low 2co st solar cells.First we must under 2stand t he behaviors of imp urities and defect s in t he polycrystalline Si wafers in more detail.Because t here are grain boundaries and more imp urities and defect s ,mc 2Si material has more complicated p hysi 2cal behavior in high temperat ure annealing t han mono 2crystalline silicon.Oxygen in mc 2Si is a very important imp urity t hat affect s t he elect rical and mechanical properties of silicon material during heat t reat ment s [1].However ,t he formation of oxy 2gen precipitates ,t he variety of minor carrier life 2times ,and t he influence of t he annealing ambient are less investigated for polycrystalline silico n solar

cells.In t his paper ,t he effect s of t hermal annealing

on oxygen behavior and carrier lifetimes for poly 2crystalline Si wafers are investigated.

2　Experiment

The polycrystalline Si wafers provided by Ba 2yer Solar Corporation in t his experiment were p 2

type ,019Ω・cm ,and 285

μm t hick.The interstitial oxygen and substit ute carbon concent rations of t he samples were 813×1017and 2×1017cm -3,respec 2tively.For comparison ,p 2type CZ 2Si samples wit h

〈100〉orientation ,1～3Ω・cm ,a t hickness of

330

μm ,and almost t he same oxygen concent ration were also st udied.The samples were cleaned wit h chemical solution ,and Si oxide was removed in an HF (10%)solution.Then t hey were subjected to heat t reat ment at 1260℃for 1h in N 2ambient so as to eliminate t he influence of t hermal history before