¾ 實驗發現，隨著BST薄膜沉積瓦數越高，BST薄膜較為緻密，
且表面粗糙度越低。經過退火處理後，表面粗糙度皆呈增加的趨勢；
但經過電漿處理後，發現對低沉積瓦數所沉積的BST薄膜，較高的電 漿功率下，O2-離子填補養空孔的效應大於離子轟擊效應，所以表面 粗糙度會降低，但對高沉積瓦數而言，離子轟擊效應則大於O2-離子 填補養空孔的效應。
¾ 從漏電流密度-電場強度圖來看，漏電流隨沉積瓦數增加而下 降，而1000 W所沉積的BST薄膜在 1 MV/cm的電場下更可達到 1×10-8 A/cm2。此外，漏電流的對稱性也隨著沉積瓦數增加而更好，顯示沉 積瓦數愈高，較不受到Ta底電極與BST薄膜界面粗糙度的影響。在電 漿表面處理，發現僅電漿功率的影響較大，但對1000 W所沉積的薄 膜而言，並沒有達到改善效果，原因在於N2O電漿表面處理後，由於 離子轟擊效應大於O2-離子填補養空孔的效應，所以表面粗糙度比未 經電漿處理的BST薄膜要高，故結果與 500 W所沉積的BST薄膜相反。
¾ 退火 500℃後，氧的擴散造成Ta底電極與BST薄膜間形成一層 相 當 厚 的Ta2O5， 導 致Ta/BST/Ta 結 構 的 漏 電 流 機 制 由 dielectric relaxation current主導。經退火 400℃處理後，在低電場強度時為S-E 主導，高電場強度時是由P-F所主導，因此退火後所形成的Ta2O5並未
改變其漏電流機制。從電容密度的結果，亦可發現BST薄膜經退火 400℃處理的電容值主要是受到表面粗糙度的影響而增加，但退火 500℃處理後受Ta2O5影響而下降。
¾ Cu 金屬化製程上，在退火 400℃後，Cu 離子會沿著氧擴散的 途徑而向表面擴散出去，導致BST 薄膜表面形成 hillocks，導致表面 粗糙度變化較大；當Ta 以阻障層的形式應用在銅電極上，退火 400℃
後Cu 並未擴散至表面，顯示 Ta 有效阻礙氧擴散並抵擋銅擴散，避免 形成氧化銅，造成Cu 擴散到表面去。
¾ Cu 底電極的表面粗糙度比 Ta/Cu 底電極結構要大，且影響到 BST 薄 膜 表 面 粗 糙 度 ， 因 此 Cu/BST/Cu 結 構 的 漏 電 流 較 Cu/Ta/BST/Ta/Cu 結構的漏電流大。在漏電流機制上，Cu/BST/Cu 與 Cu/Ta/BST/Ta/Cu 結構在低電場下為 Schottky emission，高電場下則為 Poole-Frenkel effect 主導，顯示 Ta 阻障層未改變漏電流機制。
第六章 未來工作
由以上的實驗結果，在介電常數的表現上並不佳，除了BST薄膜 為非晶質狀態外，BST薄膜應用在Ta金屬上的結晶性並不佳，而在銅 製程整合，雖然Ta可以有效減少表面粗糙度，且退火400℃下可以有 效阻擋氧的擴散，避免退火後產生hillocks，但是在整合上仍須改進，
因此未來針對要改進的方向，如下所列：
(1). 採用不同退火方式：
若要整合銅金屬化製程，則後段處理溫度不能太高，因此採取如 ELA(Excimer Laser annealing)處理，藉由高能量的雷射束，瞬間提供 高能量，由聲子傳遞熱能，使BST薄膜能夠產生結晶，此方法的好處 是因為聲子傳遞的範圍不大，因此產生結晶的範圍不大，但對薄膜電 容來說，可以藉由控制雷射的能量密度，使薄膜全部結晶，而不會影 響到底電極。
(2). 在電極上生成陣列式的奈米點或量子點：
由材料觀點看，相較於平坦的電極表面，奈米點或量子點將成為 成核成長(nucleation and growth)處，藉此降低BST薄膜結晶的活化 能，輔以適當的沉積溫度，將有助BST薄膜的結晶，且在電性方面亦 值得探討。
(3). 阻障層：
雖然Ta可以緩和Cu的表面粗糙度，但BST薄膜沉積在Ta上的結晶 性不佳，且電性的表現仍有待改善，因此尋找更合適的阻障層，亦是 未來一重要課題。
參考文獻
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1 S. Ezhilvalavan, T. Y. Tseng, “Progress in the developments of (Ba,Sr)TiO3 (BST) thin films for Gigabit era DRAMs”, Materials Chemistry and Physics, 65 227 (2000).
2 A. I. Kingon, J. P. Maria, and S. K. Streiffer, “Alternative dielectrics to silicon dioxide for memory and logic devices”, Nature, 406 1032 (2000).
3 王念民, “動態隨機存取記憶體製程技術趨勢＂, 電腦與通訊, 第
8 C. S. Hwang, “(Ba,Sr)TiO3 thin films for ultra large scale dynamic random access memory. A review on the process integration”, Materials Science and Engineering, B56 178 (1998).
9 C. Feldman, “Formation of thin films of BaTiO3 by Evaporation”, View of Science Instrument, 26 463 (1954).
10 A. J. Moulson and J. M. Herbert, “Electroceramics” Materials, Properties, Applications, p52 (1990).
11 林振華, “電子材料”, 全華科技圖書股份有限公司, 90 年 12 月 12 B. Jaffe, W. R. Cook, Jr., and H. Jaffe, “Piezoelectric ceramics”, Academic Press, India, 1971.
13 陳皇鈞, “陶瓷材料概論”, 曉園出版社, 1988 年 4 月 14 吳朗, “電子陶瓷-介電陶瓷”, 全欣資訊圖書
15 C. C. Hwang, M. H. Juang, M. J. Lai, C. C. Jaing, J. S. Chen, S.
Huang, and H. C. Cheng, “Effect of rapid-thermal-annealed TiN barrier layer on the Pt/BST/Pt capacitors prepared by RF magnetron co-sputter technique at low substrate temperature”, Solid-State Electronics, 45 121 (2001).
16 S. I. Ohfuji, M. Itsumi, and H. Akiya, “Dielectric Properties of Electron-Cyclotron-Resonance-Sputtered (Ba,Sr)TiO3 Films”, Jpn.
Journal Applied Physics Letters, 36 5854 (1997).
17 T. Matsumoto, A. Niino, S. Baba, K. Numata, and S. Miyakea, “Low temperature preparation of perovskite oxide films by ECR sputtering assisted with microwave treatment”, Surface and Coatings Technology, 174-175 611 (2003).
18 Y. Ding, J. Wu, Z. Meng, H. L. Chan, and Z. L. Choy, “Oxygen pressure dependence of structural and tunable properties of PLD-deposited Ba0.5Sr0.5TiO3 thin film on LaAlO3-substrate”, Materials Chemistry and Physics, 75 220 (2002).
19 Y. C. Choi, J. Lee, and B. S. Lee, “Improvements of the Properties of Chemical-Vapor-Deposited (Ba,Sr)TiO3 Films through Use of a Seed Layer”, Jpn. Journal Applied Physics Letters, 36 6824 (1997).
20 E. Ngo, P. C. Joshi, M. W. Cole, and C. W. Hubbard, “Electrophoretic deposition of pure and MgO-modified Ba0.6Sr0.4TiO3 thick films for tunable microwave devices”, Applied Physics Letters, 79 248 (2001).
21 T. J. Zhang, H. Ni, and W. Wang, “Preparation and Characterization of Epitaxial-Grown Ba0.65Sr0.35TiO3 Thin Films by the Sol-Gel Process on Pt/MgO Substrates”, Journal of Materials Synthesis and Processing, 10 17 (2002)
22 J. H. Won, S. H. Paek, Y. S. Hwang, and K. K. Kim, “Phase formation and characteristics of r.f.-sputtered barium-strontium titanate thin films on various bottom layers,” Journal of Materials Science, 6 161 (1995).
23 J. Im, O. Auciello, P. K. Baumann, S. K. Streiffer, D. Y. Kaufman, and A. R. Krauss, “Composition-control of magnetron-sputter-deposited (BaxSr1-x)Ti1+yO3+z thin films for voltage tunable devices”, Applied Physics Letters, 76 625 (2000).
24 S. K. Streiffer, C. Basceri, C. B. Parker, S. E. Lash, and A. I. Kingon,
“Ferroelectricity in thin films: The dielectric response of fiber-textured (BaxSr1-x)Ti1+yO3+z thin films grown by chemical vapor deposition”, Journal Applied Physics Letters, 86 4565 (1999).
25 C. Kugeler, R. Liedtke, and R. Waser, “Leakage current properties of Ba0.7Sr0.3TiO3 thin films depending on the film thickness”, Applications of Ferroelectrics, 2002. ISAF 2002. Proceedings of the 13th IEEE International Symposium.
26 Y. Fukuda, H. Haneda, I. Sakaguchi, K. Numata, K. Aoki, and A.
Nishimura, “Dielectric Properties of (Ba, Sr)TiO3 Thin Films and their Correlation with Oxygen Vacancy Density”, Jpn. Journal Applied Physics Letters, 36 L1514 (1997).
27 C. S. Hwang, and S. H. Joo, “Variations of the leakage current density and the dielectric constant of Pt/(Ba,Sr)TiO3/Pt capacitors by annealing under a N2 atmosphere”, Journal of Applied Physics, 85 2431 (1999).
28 H. J. Cho, S. Oh, and C. S. Kang, “Improvement of leakage current characteristics of Ba0.5Sr0.5TiO3 films by N2O plasma surface treatment”, Applied Physics Letters, 71 3221 (1997).
29 S. J. Chang, J. S. Lee, J. F. Chen, S. C. Sun, C. H. Liu, U. H. Liaw, and B. R. Huang, “Improvement of Electrical and Reliability Properties of Tantalum Pentoxide by High-Density Plasma (HDP) Annealing in N O”,
IEEE Electron Device Letters, 23 643 (2002)
30 M. C. Wang, C. C. Tsai, N. C. Wu, and K. M. Hung, “Structural and dielectric characterization of the (Ba1-xSrx)(Ti0.9Sn0.1)O3 thin films deposited on Pt/Ti/SiO2/Si substrate by radio frequency magnetron sputtering”, Journal of Applied Physics, 92 2100 (2002).
31 M. Yamato, H. Yamada, and T. Kikkawa, “Influence of Bottom Electrodes and Interface Layers on (Ba,Sr)TiO3 Thin Film Leakage Current”, Jpn. Journal Applied Physics Letters, 43 5221 (2004).
32 B. H. Tsao, S. Heidger, and J. A. Weimer, “Sputtered barium titanate and barium strontium titanate films for capacitor applications”, Applications of Ferroelectrics, 2000. ISAF 2000. Proceedings of the 2000 12th IEEE International Symposium.
33汪建和, “材料分析”, 中國材料科學學會, (1998)
34 K. C. Tsai, W. F. Wu, C. G. Chao, C. P. Kuan, and C. C. Wu,
“Enhanced Performance of Ta/Ta2O5/Ta MIM Capacitor by Plasma Oxidation Method”, Proc. of 2004 International Electrics Devices and Materials Symposium, IEDMS (2004).
35 M. S. Tsai, and T. Y. Tseng, “Effect of Bottom Electrode Materials on the Electrical and Reliability Characteristics of (Ba,Sr)TiO3 Capacitors”, IEEE Transactions on Electron Devices, 46 829 (1999).
36D. C. Shye, C. C. Hwang, M. J. Lai, C. C. Jaing, J. S. Chen, S. Huang, M. H. Juang, B. S. Chiou, and H. C. Cheng, “Effects of Post-Oxygen Plasma Treatment on Pt/(Ba,Sr)TiO3/Pt Capacitors at Low Substrate Temperatures”, Jpn. Journal Applied Physics Letters, 42 549 (2003).
37 M. S. Tsai, S. C. Sun, and T. Y. Tseng, “Effect of Bottom Electrode Materials and Annealing Treatments on the Electrical Characteristics of Ba0.47Sr0.53TiO3”, Journal of the American Ceramic Society, 82 351 (1999).
38 W. Y. Hsu, J. D. Luttmer, R. Tsu, S. Summerfelt, M. Bedekar, T.
Tokumoto, and J. Nulman, “Direct current conduction properties of sputtered Pt/(Ba0.7Sr0.3)TiO3/Pt thin films capacitors”, Applied Physics Letters, 66 2975 (1995).
39 M. S. Tsai, and T. Y. Tseng, “Conduction Mechanism and Temperature-Dependent Current-Voltage in (Ba,Sr)TiO3 Thin Films”, Journal of The Electrochemical Society, 145 2853 (1998).
40 S. Maruno, T. Kuroiwa, N. Mikami, K. Sato, S. Ohmura, M. Kaida, T.
Yasue, and T. Koshikawa, “Model of leakage characteristics of (Ba,Sr)TiO3 thin films”, Applied Physics Letters, 73 954 (1998).
41 T. S. Chen, V. Balu, S. Katakam, J. H. Lee, and J. C. Lee, “Effects of Ir electrodes on barium strontium titanate thin-film capacitors for high-density memory application”, IEEE Transactions on Electron
42 Y. Fukuda, K. Numata, K. Aoki, A. Nishimura, G. Fujihashi, S.
Okamura, S. Ando, and T. Tsukamoto, “Effects of Postannealing in Oxygen Ambient on Leakage Properties of (Ba, Sr)TiO3 Thin-Film Capacitors”, Jpn. Journal Applied Physics Letters, 37 L453 (1998).
43 T. Horikawa, T. Makita, T. Kuroiwa, and N. Mikami, “Dielectric Relaxation of (Ba,Sr)TiO3 Thin Films”, Jpn. Journal Applied Physics Letters, 34 5478 (1998).
44 C. Chaneliere, J. L. Autran, R. A. B. Devine, and B. Balland,
“Tantalum pentoxide (Ta2O5) thin films for advanced dielectric applications”, Materials Science and Engineering, R22 269 (1998)
45 W. Luo, Y, Kuo, and W. Kuo, “Dielectric relaxation and breakdown detection of doped tantalum oxide high-k thin films”, IEEE Transactions on Device and Materials Reliability, 4 488 (2004).
46 D. A. Neamen, “Semiconductor Physics & Devices”, (2000)
47 X. F. Chen, W. G. Zhu, and O. K. Tan, “Microstructure, dielectric properties and hydrogen gas sensitivity of sputtered amorphous Ba0.67Sr0.33TiO3 thin films”,Materials Science and Engineering,B77 177
47 X. F. Chen, W. G. Zhu, and O. K. Tan, “Microstructure, dielectric properties and hydrogen gas sensitivity of sputtered amorphous Ba0.67Sr0.33TiO3 thin films”,Materials Science and Engineering,B77 177