Copper-related light-induced degradation in crystalline silicon

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School of Electrical Engineering | Doctoral thesis (article-based) | Defence date: 2015-04-24
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Date
2015
Major/Subject
Mcode
Degree programme
Language
en
Pages
80 + app. 44
Series
Aalto University publication series DOCTORAL DISSERTATIONS, 37/2015
Abstract
Unintentional copper and nickel impurities are common in silicon-based devices due to the abundance of contamination sources in industrial silicon crystallization and wafer processing lines. High solubility and diffusivity result readily in significant impurity concentrations, which cause charge-carrier recombination and reduce the device response. This work confirms that nickel diffuses as fast as copper in silicon, emphasizing the importance of contamination control in silicon-based devices. Copper contamination is known to form recombination-active defects in silicon during illumination, which is observed as copper-related light-induced degradation (Cu-LID). In order to identify the  extent of degradation in silicon-based devices, this work focuses on determining the properties of Cu-LID in gallium-doped Czochralski (Cz) silicon, boron-doped Cz-Si, and boron-doped multicrystalline silicon. Cu-LID is determined to be predominantly a bulk recombination effect, and the formed defects are found to be stable at 200°C. Slower Cu-LID is observed in Ga-Si compared to B-Si, suggesting that Cu-LID formation is limited by the effective copper diffusivity. Cu-LID is shown to completely disappear after negative sample surface charging and illumination. The negative surface charge is achieved by corona charging or aluminum oxide deposition. Cu-LID removal is observed to have no impact on classical boron-oxygen-related light-induced degradation (BO-LID), which has previously been shown to recover at 200°C. Unlike BO-LID, the activation energy of Cu-LID is found to depend on the silicon doping concentration. Hence, Cu-LID and BO-LID are concluded to be two different degradation effects, which can occur simultaneously in silicon-based devices.

Kiselbaserade elektroniska komponenter är ofta oavsiktligt förorenade av koppar och nickel från otaliga kontaminationskällor i industriella komponentframställningsprocesser. Metallernas höga diffusivitet samt löslighet leder fort till markanta orenhetskoncentrationer, vilka förorsakar rekombination av laddningsbärare och nedsatt komponentrespons. Denna avhandling bekräftar att nickel diffuserar lika fort som koppar i kristallint kisel, vilket betonar vikten av metallorenhetskontroll i kiselbaserade komponenter. Kopparorenheter förorsakar fotodegradadering (Cu-LID) i kisel via formationen av rekombinationsaktiva koppardefekter under illuminering. För att fastställa omfattningen av fotodegradadering i kiselbaserade komponenter, fokuserar denna avhandling på att identifiera egenskaper för Cu-LID i gallium-dopat Czochralski (Cz) kisel, boron-dopat Cz-Si och boron-dopat mångkristallint kisel. Cu-LID finnes orsaka främst bulkrekombination och de formade koppardefekterna är stabila i 200°C. Cu-LID sker långsammare i Ga-Si jämfört med B-Si, vilket antyder att fotodegraderingsprocessen begränsas av den effektiva koppardiffusiviteten. I avhandlingen förhindras kopparrelaterad fotodegradadering fullständigt genom att kombinera negativ kiselytladdning med illuminering. Den negativa ytladdningen skapas via deposition av koronaladdning eller aluminiumoxidtunnfilm. Avlägsning av Cu-LID inverkar inte på klassisk bor-syre-relaterad fotodegraderingen (BO-LID), som förekommer i kisel utan kopparföroreningar och försvinner i 200°C. I motsats till BO-LID beror aktiveringsenergin för Cu-LID på dopingkoncentrationen i kiselmaterialet. Följaktligen fastställs Cu-LID och BO-LID vara två skilda former av fotodegradering, vilka kan förkomma samtidigt i kiselbaserade elektroniska komponenter.
Description
Supervising professor
Savin, Hele, Assistant Prof., Aalto University, Department of Micro and Nanosciences, Finland
Keywords
copper, degradation, lifetime, nickel, silicon, degradering, kisel, koppar, livstid, nickel
Other note
Parts
  • [Publication 1]: J. Lindroos, M. Yli-Koski, A. Haarahiltunen, M. C. Schubert, and H. Savin, Light-induced degradation in copper-contaminated gallium-doped silicon, Physica Status Solidi - Rapid Research Letters 7, No. 4, p. 262-264 (2013). http://dx.doi.org/10.1002/pssr.201307011.
  • [Publication 2]: J. Lindroos, M. Yli-Koski, A. Haarahiltunen, and H. Savin, Room-temperature method for minimizing light-induced degradation in crystalline silicon, Applied Physics Letters 101, 232108 (2012). http://dx.doi.org/10.1063/1.4769809.
  • [Publication 3]: Y. Boulfrad, J. Lindroos, Mt. Wagner, F. Wolny, M. Yli-Koski, and H. Savin, Experimental evidence on removing copper and light-induced degradation from silicon by negative charge, Applied Physics Letters 105, 182108 (2014). http://dx.doi.org/10.1063/1.4901533.
  • [Publication 4]: J. Lindroos and H. Savin, Formation kinetics of copper-related light-induced degradation in crystalline silicon, Journal of Applied Physics 116, 234901 (2014). http://dx.doi.org/10.1063/1.4904197.
  • [Publication 5]: J. Lindroos, Y. Boulfrad, M. Yli-Koski, and H. Savin, Preventing light-induced degradation in multicrystalline silicon, Journal of Applied Physics 115, 154902 (2014). http://dx.doi.org/10.1063/1.4871404.
  • [Publication 6]: J. Lindroos, D. P. Fenning, D. J. Backlund, E. Verlage, A. Gorgulla, S. K. Estreicher, H. Savin, and T. Buonassisi, Nickel: A very fast diffuser in silicon, Journal of Applied Physics 113, 204906 (2013). http://dx.doi.org/10.1063/1.4807799.
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