鈦酸鉛鋯鐵電薄膜乾式蝕刻製程與其性質的研究

Abstract

本論文以兩種電漿組合(Ar/CF4 and Cl2/BCl3)進行溶膠法製備之鈦酸鉛鋯鐵電薄膜的高密度電漿乾式蝕刻研究，並觀察在兩種不同電漿組合及蝕刻參數下對於PZT薄膜之蝕刻率、蝕刻輪廓、微結構、及電性的影響。 使用Ar/CF4電漿組合在Ar/CF4=1時有最佳的蝕刻率。蝕刻後的遲滯曲線所產生極化值的偏移可用600℃持溫30分鐘熱處理消除，但是蝕刻後所產生的內部電場卻無法消除。由XPS表面成份分析發現Ar/ CF4電漿蝕刻後在表面有Pb與Zr的氟化物殘留，推測是影響電性的原因。 使用Cl2/BCl3電漿組合在純Cl2氣體蝕刻下有最佳的蝕刻效率。蝕刻後並沒有發現遲滯曲線偏移的現象，但是有震盪的現象，可用200℃的熱處理消除，推測是大氣中的濕氣所造成。以掃描式電子顯微鏡觀察蝕刻後的表面輪廓可達75度。 使用Cl2電漿及一般光阻為蝕刻阻擋層，用單一步驟蝕刻W/PZT/Pt堆疊結構，可得到良好的極化特性及低漏電流:在100kV/cm下為1.175E-8 A/cm2 。

High-density plasma dry etching process was used to etch sol-gel derived PZT ferroelectric thin films. Two different kinds of gas mixtures (Ar/CF4 and Cl2/BCl3) were used in this work. Etch properties such as etch rate, profile, microstructure and electrical properties were measured for different gas mixing ratios and plasma conditions. The maximum etch rate of PZT thin films appears under Ar/CF4 of 1. The voltage shift in the hysteresis loop after etching process was observed and could be recovered by thermal treatment at 600oC for 30 min. However, the internal electrical field caused by etching damage cannot be recovered even by thermal treatment. According to XPS analysis, it is suggested that the Pb and Zr atoms of PZT films react with fluorine to form Pb-F and Zr-F that is the cause of the degradation of electrical properties. On the other hand, etching with different mixing ratios of Cl2/BCl3 shows the maximum etch rate can be reached with pure Cl2 plasma. Even though the degradation was not detected, the vibration phenomenon in the hysteresis loop was observed. The vibration is probably related to environmental humidity because it can be recovered by 200oC thermal treatment. Scanning electron microscopy was used to examine etched profiles of PZT thin films. The wall angle of approximately 75 degrees was obtained. In addition, W/PZT/Pt stacked structure by Cl2 plasma was fabricated. PZT films with excellent polarization properties and very low leakage current density of 1.2E-8 A/cm2 at 100kV/cm was derived.