利用常壓噴射式電漿沉積氧化鋅薄膜及其特性之研究

Study of an Atmospheric Pressure, Pulsed Arc Plasma Jet: Downstream Characterization and its Application to ZnO Thin Film Deposition

許耀文(Yao-Wen Hsu)

指導教授 ： 徐振哲

國立臺灣大學/工學院/化學工程學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.00448

摘要

本研究包含在常壓下運用直流脈衝式電源產生的電弧噴射式電漿之噴流下游區域檢測及其運用至氧化鋅薄膜之沉積與薄膜特性探討。噴流下游區域檢測包含電漿熱性質及光學性質。氧化鋅薄膜之沉積包含製程建立與參數探討，藉由此研究了解此系統應用於薄膜沉積製程之反應機制進而探討各項參數的改變對薄膜品質的影響。
噴流下游之熱性質及光學性質分析發現，隨著施加電壓降低及氣體流量增加，噴流下游氣體溫度下降；噴流下游激發態分子密度受到放電區域的起始密度及衰退影響，在高流量時衰退的密度較少，因此噴流下游的激發態分子密度均隨著施加電壓及氣體流量增加而增加。本系統可藉由改變施加電壓或氣體流量，獨立調整噴流氣體溫度及噴流下游激發態分子的密度。在製程中，前述兩種性質影響了製程的效能，此系統可藉由改變操作變因，調整電漿噴流性質以達特定製程所需之效能。
在氧化鋅薄膜製程方面則利用電漿產生具高反應性的分子在高溫下，以含有鋅之鹽類水溶液作為反應先驅物，藉由超音波霧化裝置將反應先驅物送入電漿反應器中產生反應，並在基材上沉積薄膜。經由X光繞射儀證明此常壓脈衝電弧噴射式電漿系統有能力在極短的時間內將含有鋅的鹽類水溶液反應生成氧化鋅薄膜，且薄膜沉積速率可達1.3 nm/s，顯示電漿反應性之重要性。實驗發現鋁摻雜氧化鋅薄膜之電阻值高，經由導電性原子力顯微鏡分析薄膜後發現不導電之原因可能因為晶粒中心與晶界的不連續以及薄膜部分上面覆蓋太多大顆粒成為電流傳遞的阻障層導致。
藉由電漿操作條件對薄膜之實驗了解電漿對薄膜之影響，經由控制基材與電漿噴嘴間距離，當距離過小時滯留時間不足，反應不完全；當氣體流量增加時，薄膜結構呈現由球形轉為片狀的變化，且薄膜結晶性下降，此時雖然反應性增加但溫度下降，這顯示了溫度與滯留時間為主要的控制變因。當施加電壓越高與氣體流量降低，氣相溫度越高越有助於晶粒的成長。由實驗推論，在本製程中溫度與滯留時間對薄膜之影響較電漿反應性更為重要。此二變因可由電漿施加電壓與氣體流量控制以達到理想的薄膜沉積條件。

關鍵字

常壓噴射式電漿 ； 下游特性檢測 ； 氧化鋅薄膜 ； 超音波噴霧 ； 大面積沉積

並列摘要

An atmospheric pressure nitrogen plasma jet sustained by a repetitive pulsed DC power source is studied. The afterglow characteristics of this plasma jet are studied by an optical emission spectrometer and thermocouples. The effects of the process parameters, namely the applied voltage and the gas flow rate, on the plasma characteristics are investigated. It is shown that the plasma reactivity is controlled by the power deposition to the plasma as well as the decay process of the reactive species upon formation. The reactivity increases with the increase in the applied voltage and with the decrease in the gas flow rate. The jet temperature is primarily controlled by the power density, and it increases with the increase in the applied voltage and with the decrease in the gas flow rate. These observations suggest that the plasma reactivity and the jet temperature of this plasma jet can be nearly independently controlled.
The ZnO thin film deposition process by using an AP plasma jet is studied. In this process, nebulized solution is sprayed into the downstream of the nitrogen plasma jet to perform thin film deposition. XRD analysis confirms that this AP jet has the capability to convert zinc-salt containing solution to well-crystallized ZnO thin films with a hexagonal wurtzite structure in a short time. A 1.3 nm/s deposition rate is obtained using this process. Given the fast deposition rate of this process, we believe that both the temperature and the reactivity of the plasma play important roles. Conductive AFM reveals that there are clear grain boundaries, which leads high resisitivity of the films.
The effects of the plasma operating parameters, namely applied volitage and the gas flow rate, on the film quality are investigated. It is shown that the film quality is controlled by the gas temperature, the reactivity, and the resident time of precursor in the downstream. The film shows a better quality with a moderate distance between the jet nozzle and the substrate. Better quality films can be obtained with low gas flow rate. It is shown that the resident time appears to be the major factor that controls the film quality in this process. The grain size increases with an increase of gas temperature, which means high temperature is helpful for grain growth. By properly adjusting the operating parameters, the optimal deposition condition can be achieved.

並列關鍵字

atmospheric pressure plasma jets ； large-area deposition ； thin films ； ultrasonic spray ； zinc oxide

參考文獻

120. 吳丞以," 常壓脈衝電弧噴射式電漿的診斷" 碩士論文, 國立臺灣大學, 2009.

1. J. H. Lim, C. K. Kang, K. K. Kim, I. K. Park, D. K. Hwang and S. J. Park," UV electroluminescence emission from ZnO light-emitting diodes grown by high-temperature radiofrequency sputtering" Adv. Mater. 18 (20), 2720-2724 (2006).

2. J. Aranovich, A. Ortiz and R. H. Bube," Optical and electrical-properties of ZnO films prepared by spray pyrolysis for solar-cell applications" Journal of Vacuum Science & Technology 16 (4), 994-1003 (1979).

3. Y. Nakanishi, A. Miyake, H. Kominami, T. Aoki, Y. Hatanaka and G. Shimaoka," Preparation of ZnO thin films for high-resolution field emission display by electron beam evaporation" Appl. Surf. Sci. 142 (1-4), 233-236 (1999).

4. P. Mitra, A. P. Chatterjee and H. S. Maiti," ZnO thin film sensor" Mater. Lett. 35 (1-2), 33-38 (1998).