利用熱脫附法分析氧化鋅摻鋁薄膜的熱穩定性

Thermal Stability of Aluminum Doped Zinc Oxide Thin Films Analyzed by Thermal Desorption Method

吳昇樺(Sheng-Hua Wu)

指導教授 ： 張慎周

崑山科技大學/工程學院/電機工程研究所/碩士(2009年)

摘要

為了探討氧化鋅摻鋁(AZO)薄膜在後續加熱製程中可能產生的變化，其薄膜的熱穩定性是相當重要。薄膜經受熱後結構所產生的改變與光電性質的變化，後續運用到太陽能電池上可能導致光電轉換效率有所變化。本研究使用熱脫附分析法，針對不同製程條件的AZO薄膜與經過氫氣熱處理後的AZO薄膜作熱脫附頻譜分析，觀察薄膜是否有脫附的現象，且脫附量何者最大、有無物種脫附，並找出相對熱脫附量少、光電材料特性穩定之條件。
本研究結果顯示，不同基板溫度製程的AZO薄膜作熱脫附分析，由熱脫附頻譜得知的確有物種從試片中脫附出來，以物種鋁脫附量為最高，其最大脫附速率的溫度點落在100℃及200℃附近，並隨溫度增加至200℃脫附強度隨之減少，結果顯示鋁熱穩定性較差於AZO薄膜中扮演外質角色與報導提出外質半導體穩定性較高其結果是相反。由物種鋁的脫附訊號圖得知，最低脫附強度來判斷其最佳熱穩定性條件，以製程基板溫度200℃下為最佳之熱穩定條件。
由於本實驗過程是在高真空環境下，加熱速率為10℃/Min緩慢加熱，探討經過熱脫附與未經熱脫附分析的AZO薄膜，後續特性分析，成份分析由能量散佈光譜儀得知鋁在薄膜中的含量經過熱脫附後明顯減少許多，證實鋁大量離開AZO薄膜；化學分析由化學分析電子光譜儀可發現，脫附後氧空缺比例有增加且吸附的氧有減少，使導電率提升，並由光電與結構分析經熱脫附後都明顯改善，且經過脫附後平均光穿透率高達92.38%，也是光電性質變化最少之製程參數符合薄膜太陽能電池產業之條件。
最後針對後續氫氣熱處理的AZO薄膜，由熱脫附頻譜得知氧的脫附量有降低，且經氫退火300℃處理後再經熱脫附得到電阻值8.32×10-4 (Ω-cm) ，比脫附前降低了28％左右，且放置1個月後電性沒太大的變化，以製程基板溫度未加熱為氫氣熱處理最佳之熱穩定條件。此研究結果可提供薄膜太陽能電池產業透明電極製程開發對熱穩定性的參考依據。

關鍵字

熱脫附 ； 氧化鋅摻鋁

並列摘要

For evaluating thermal stability of aluminum doped zinc oxide(AZO)thin films, a series of AZO films with different processing recipe were measured with thermal desorption tool. Relative low thermal desorption and stable electrical, optical and materials properties of AZO films process recipe will be found after analyzing these measured results.
The sample holder of thermal desorption tool was linearly heated from room temperature to 500℃ with constant heating rate 10℃per minute. All desorption species show similar desorption peak temperature position around 100℃and 200℃ nearby corresponding to relative maximum desorption rate. The desorption intensity shows increase with temperature up to 200℃. The aluminum species shows maximum thermal desorption amount among all desorption species of AZO thin films, One report describes thermal stability of extrinsic semiconductor is higher than that of intrinsic semiconductor our result is different with that scenario. There are several desorbed species observed from thermal desorption spectroscopy (TDS) by the species to know that The lowest intensity corresponds to best thermal stability condition is the substrate temperature kept at 200℃ under as best thermal stability condition.
Because this experiment process is under high vacuum environment, the heating rate for 10℃/Min slow heating rate: For checking the (TDS) measured result accuracy, some of AZO thin films before and after TDS were with energy dispersive spectroscopy (EDS) measurement. The EDS results indicate for AZO films prepared under the same recipe, the aluminum content decrease most among all species for AZO thin films after TDS measurement. This data supports TDS measurement results. The chemical analysis is measured by X-ray photoelectron spectroscopy (XPS). It was found that after thermal desorption, the oxygen vacancy proportion increases, the adsorbed the oxygen in AZO films has the reduction, causes the conductivity promotion, and by electrical, optical and structure analysis after thermal desorption obviously improves. And that after TDS measurement the average optical transmittance reaches 92.38% of AZO thin films, meets condition of the thin film solar cell industry.
The AZO thin film with the following hydrogen heat treatment checked by the TDS, The oxygen thermal desorption quantity has reduces. And obtains the electrical resistivity after the hydrogen annealing 300℃ condition 8.32×10-4 (ohm-cm), reduced about 28% compared to before TDS measurement, The electrical resistivity of the AZO films samples that after one month storage does not change for the substrate temperature non-heated. This result contributes thermal stability guide for thin films solar cells industry in producing transparent electrodes.

並列關鍵字

Thermal Desorption ； Aluminum Doped Zinc Oxide

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