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Study of low temperature poly silicon for solar cells

Study of low temperature poly silicon for solar cells. Advisor: Dr. Hon Kuan Student: Tsung-Yu Li Date ： 98/04/22. Outline. Introduction Experimental Results and discussion Conclusions References. Introduction. 這兩篇報告是 利用多晶矽薄膜作為晶種並以兩階段退火，製備低溫多晶矽薄膜於太陽能電池，討論其微結構與電性之研究。

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Study of low temperature poly silicon for solar cells

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  1. Study of low temperature poly silicon for solar cells Advisor: Dr.Hon Kuan Student: Tsung-Yu Li Date：98/04/22

  2. Outline • Introduction • Experimental • Results and discussion • Conclusions • References

  3. Introduction • 這兩篇報告是利用多晶矽薄膜作為晶種並以兩階段退火，製備低溫多晶矽薄膜於太陽能電池，討論其微結構與電性之研究。 • 此技術的特點在於所成長的多晶矽晶粒的橫向長度大於縱向的寬度。第一階段以500°C 持溫1 小時，探討鋁金屬誘發再結晶。 • 第二階段以不同退火溫度與時間分析鋁金屬誘發多晶矽之影響，完成之試片以X 光繞射分析儀（XRD）進行結晶性分析，確認Si 的結晶面存在與否，並以拉曼光譜分析相互印證，以場發射式電子顯微鏡（FE-SEM）觀察其表面結構與截面結構。 • 以霍爾量測分析載子移動率，載子濃度，電阻率。最後並測試電流-電壓的特性已確定其暗電流的機制。實驗結果證實，經由兩階段退火的製程確實能有效降低多晶矽膜之製程溫度並獲得較佳的微結構組織。

  4. Experimental • 實驗流程 • PART I 先蝕刻Al • PART II 沉積完非晶矽再蝕刻Al

  5. Results and discussion (a) SiO2 film (200nm) (b) Al film(250nm) (c) a-Si film(250nm) 未退火表面的SEM圖

  6. Results and discussion 未退火側面SEM截圖

  7. Results and discussion 未退火XRD分析圖 未退火Raman分析圖

  8. Results and discussion first step annealing process at 500°C for 1 hour，without Al etching off

  9. Results and discussion first step annealing process at 500°C for 1 hour ，and Al etching off

  10. Results and discussion XRD spectra of poly-Si thin film annealed at 500°C for 1 hour and Al etched off

  11. Results and discussion XRD spectra of Part I specimens annealed at (a) 450 °C, and (b)500 °C and 5 different durations and Al etched off

  12. Results and discussion XRD peak intensity plot versus different annealing duration of Part I specimens annealed at 450 °C, and 500 °C

  13. Results and discussion XRD FWHM plot versus different annealing duration of Part I specimens annealed at 450 °C, and 500 °C

  14. Results and discussion Crystal size of polycrystalline silicon thin film versus different annealing duration of Part I specimens annealed at 450 °C, and 500 °C D：晶粒大小 K=1 常數 λ：X 光波長 △（2θ）：半高峰寬 θ：繞射角

  15. Results and discussion XRD spectra of Part II specimens annealed at (a) 450 °C, and (b)500 °C and 5 different durations and Al etched off

  16. Results and discussion XRD peak intensity plot versus different annealing duration of Part II specimens annealed at 450 °C, and 500 °C

  17. Results and discussion XRD FWHM plot versus different annealing duration of Part II specimens annealed at 450 °C, and 500 °C

  18. Results and discussion Crystal size of polycrystalline silicon thin film versus different annealing duration of Part II specimens annealed at 450 °C, and 500 °C

  19. Results and discussion Raman spectra of single crystalline silicon 鋁誘發多晶矽主要的結晶強度在結晶面（111）方向， 由Widenborg[37]的研究中指出的單晶矽之Raman 波數是在520 cm-1。 另且由JIN [38]等人研究中指 出Si-Si 鍵結在Raman 波數中499 cm-1時即會產生峰值，且知是屬於多 晶矽。

  20. Results and discussion Raman spectra of part I specimens under 5 different annealing durations and annealing duration of (a) 450°C, and (b) 500 °C, and Al etched off

  21. Results and discussion Raman spectra of part II specimens under 5 different annealing durations and annealing duration of (a) 450°C, and (b) 500 °C, and Al etched off

  22. Results and discussion SEM photos of part I specimens with the second step annealing process at 450°C for (a)15 ,(b)30, (c)60, (d)120, and (e)240 minutes.

  23. Results and discussion SEM photos of part I specimens with the second step annealing process at 500°C for (a)15 ,(b)30, (c)60, (d)120, and (e)240 minutes.

  24. Results and discussion part I specimens with the second step annealing process at 450°C for (a)15, (b)30, (c)60, (d)120, and (e)240 minutes.

  25. Results and discussion part I specimens with the Second step annealing process at 500°C for (a)15, (b)30, (c)60, (d)120, and (e)240 minutes.

  26. Results and discussion SEM photos of part II specimens with the second step annealing process at 450°C for (a)15 ,(b)30, (c)60, (d)120, and (e)240 minutes.

  27. Results and discussion SEM photos of part II specimens with the second step annealing process at 500°C for (a)15 ,(b)30, (c)60, (d)120, and (e)240 minutes.

  28. Results and discussion part II specimens with the second step annealing process at 450°C for (a)15, (b)30, (c)60, (d)120, and (e)240 minutes.

  29. Results and discussion part II specimens with the second step annealing process at 500°C for (a)15, (b)30, (c)60, (d)120, and (e)240 minutes.

  30. Results and discussion Leakage current variation of part I specimens versus bias voltage under 5 different annealing durations and annealing temperature of (a) 450 °C and (b) 500°C

  31. Results and discussion Leakage current variation of part II specimens versus bias voltage under 5 different annealing durations and annealing temperature of (a) 450 °C and (b) 500°C

  32. Results and discussion Resistivity variations of part I and part II specimens versus bias voltage under 5 different annealing durations and annealing temperature of (a) 450 °C and (b) 500°C

  33. Results and discussion Mobility of poly-silicon thin film of part I and part II specimens as a function of annealing duration

  34. Results and discussion Carrier concentration of poly-silicon thin film of part I and part II specimens as a function of annealing duration

  35. Conclusions • 以退火溫度450 °C 持溫15 分鐘進行第二階段退火，成功研製膜厚1μm 的多晶矽薄膜且橫向晶粒大小約為3~5 μm。 • 在第二階段退火時間15 分鐘以上時，皆能誘發出多晶矽結晶，且退火時間60分鐘後峰值強度達穩定，研判其晶粒誘發完全。 • 第一階段退火後未經鋁蝕刻且馬上沉積a-Si（1μm）做第二次退火再蝕刻鋁時，會有殘留的鋁在晶界上無法徹底清除。 • 第一階段退火後經鋁蝕刻之多晶矽試片的漏電流集中在10-7 A/cm2處，電阻率落在103~106 Ω-cm 之間，其中500 °C 持溫30 分退火之試件具有最高的載子移動率，其值為23.4 cm2/V.s；第一階段退火後未經鋁蝕刻之試片之多晶矽之漏電流集中在10-9 A/cm2 處，電阻率落在108 Ω-cm之間。

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