利用常壓噴射式電漿沉積氧化物薄膜及其性質研究

Characterization of Oxide Thin Films Deposited by an Atmospheric Pressure Plasma Jet

許峻銘(Chun-Ming 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(2014年)

https://doi.org/10.6342/NTU.2014.03088

摘要

本研究為利用常壓噴射式電漿系統(atmospheric pressure plasma jet)沉積氧化矽與氧化鋅薄膜，其中研究先探討此電漿的性質與應用方向，藉由改變不同電漿氣體來源、施加電壓或氣體流量探討其噴流下游放射光光譜圖與溫度，研究發現隨著施加電壓增加及氣體流量減少，噴流下游氣體溫度皆會下降，而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。根據下游氮氣激發態放射光強度變化、溫度變化趨勢與一氧化氮的濃度變化，可藉由模擬得此電漿下游流場屬於紊流，說明了外界氣體來源的不可忽略性。最後經由分子光譜模擬可得其電漿氣體溫度，此電漿氣體溫度約為950~1200 K，為具有高溫且高反應性的電漿系統，本研究另探討了電漿造成的基板加熱溫度，這對後續薄膜製程的晶向與晶格大小有很大的關係。
本研究在沉積氧化鋅透明導電薄膜的部分利用噴霧熱解法處理先驅物水溶液之方法，利用1.7 MHz超音波霧化器(nebulizer)將鋅化物水溶液霧化後，再通入載流氣體將此先驅物通入電漿下游反應，本製程結合噴霧熱解法設備便宜與常壓電漿具有高反應性的優點，提供高沉積薄膜速率且可大面積製備氧化鋅薄膜的製程方法。首先先從不同先驅物下探討其沉積結構，發現以氯化鋅當作先驅物下其沉積有最平整、粗糙度最小且結晶性最好的氧化鋅薄膜。對此本研究探討以氯化鋅當作先驅物的最佳化條件，發現在氣體流量增加或電漿施加電壓下降時其結構皆出現片狀結構，我們發現此片狀結構即為氯化鋅反應成氧化鋅的中間產物，鹼式氧化鋅(Zinc hydroxide chloride monohydrate)，在反應中若系統提供的能量不足或滯留時間不夠其沉積皆會出現此中間產物，代表了反應的不完全。而在最佳化條件下:施加電壓275Volt、氣體流量30slm其氯化鋅可完全轉化成氧化鋅且有最好的導電性平均值約1.4 Ohm-cm、穿透率可達接近90 %的透明導電薄膜。
本研究另探討了氧化矽薄膜的沉積，利用起泡法(bubbler method)將先驅物的蒸氣壓送進電漿系統後反應，本研究分別使用三種先驅物:矽酸乙酯(TEOS)、六甲基二矽氧烷(HMDSO)和六甲基二矽氮烷(HMDSN)。其沉積有不同的最適化條件且經分析後皆為類無機之氧化矽。本研究發現在相同的分壓下，TEOS先驅物的沉積速率非常慢，但其結構皆為平整的薄膜，而HMDSN雖然沉積快速，但其漏電電流密度值非常大，應與其結構的不緻密或鍵結混亂有關，而相對於三者，HMDSO當作先驅物的沉積有沉積速率快、薄膜平整且漏電電流密度值小等的優點，研究發現在400 nm下其漏電電流密度即大約10-7 A/cm.^2，為漏電非常小的沉積。故本研究以此先驅物的沉積當作介電層應用於薄膜電晶體中，其可運作說明了此常壓下沉積的氧化矽薄膜當做介電層應用於原件中的可能性。

關鍵字

常壓噴射式電漿 ； 氧化鋅 ； 氧化矽 ； 薄膜電晶體

並列摘要

Deposition zinc oxide and silica-like thin films by the atmospheric pressure plasma jet were studied. To understand the plasma system property and application fields, we first investigate into the plasma optical emission spectra and gas temperature by changing the manipulate variable such as applied voltage, gas type and flowrate. Our research has demonstrated that higher applied voltage and lower gas flowrate will decrease the plasma gas temperature because of the different energy density. But the higher flowrate cause the plasma gas have more excited molecules. By the simulation of the plasma downstream intensity distribution, temperature trend and NO concentration, we found that the turbulence type matchs the downstream flowfield well and it illustrates the non-negligible of outside ambient gas. Futher, our study shows the plasma gas temperature and substrate temperature by the method of simulation molecules emission and thermalcouple measurement. The downstream gas temperature are between 950 K to 1200 K, which makes the plasma system belonging to high temperature plasma type.
To deposit zinc oxide thin films, we use the 1.7 MHz nebulizer and nitrogen carrier gas to spray the precursor solution into the plasma system. The different precursor effect, applied voltage and gas flowrate effect were studied in this research. First, we found the only one precursor, zinc chloride, can deposit the less roughness, smooth and high crystalline thin films. Otherwise the particle-like structure appears. Next, to find the optimized condition of zinc chloride as precursor deposits zinc oxide thin films, the gas flowrate and applied voltage were setting as manipulate variable. In our study, we found that under the applied voltage 275 V and gas flow rate 30 slm, the deposition has best film property with resistivity of 1.4 ohm-cm and transimmion near 90 %. Otherwise the deposition will appear the sheet-like structure and has poor optical and electric property. By the XRD identified, we found the sheet-like structure is the ZHC (Zn5(OH)8Cl2•H2O), which is the intermedia of the reaction. The appearance of ZHC can be explained by the non-enough power and shorter residence times in those condition.
In next research topic, the silica-like thin films deposited by the APPJ were studied. In this system, we use the bubbler method with nitrogen as the carrier gas to send the saturated vapor pressure to the plasma system. Three different precursors were tested, which are tetraethylorthosilicate (TEOS), Hexamethyldisiloxane (HMDSO) and hexamethyldisilazane (HMDSN). Each precursor has their optimized deposited condition and all deposition show the inorganic-like silica structure. In the TEOS system, we found the deposition rate was much lower than the others but the film has the advantage of smoothness and well-coverage. In the HMDSN system, the deposition rate were rapid but the films have worst leakage current density. It is in regard to its complicated bonding and structure. On the contrary, the HMDSO system has advantage of higher deposition rate, less-roughness and lower leakage current. In this research, we use films deposited from HMDSO as the dielectric layer in the thin films transistor (TFT) and it can work quite well. This TFT result shows the potential and capable of this atmospheric pressure deposited films as the device’s dielectric layer.

並列關鍵字

atmospheric pressure plasma jet ； ZnO ； SiO2 ； TFT

參考文獻

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