Effects of pressure and substrate bias on the film deposition by DC and RF magnetron sputtering considering charged flux = DC와 RF 마그네트론 스퍼터링 시 하전된 플럭스를 고려한 압력과 기판 바이어스가 박막 증착 거동에 미치는 영향

국문 초록 (Abstract)

최근 DC 및 RF 마그네트론 스퍼터링 공정에서 하전된 플럭스의 생성과 필름 증착에 대한 하전된 플럭스의 영향이 연구되었다. 따라서 하전된 플럭스 생성에 영향을 미치는 증착 파라미터를 DC 및 RF 스퍼터링 시스템에서 연구하였다. 특히, 플라즈마를 생성하기 위해 사용되는 아르곤(Ar) 압력과 기판 바이어스 하에서의 하전 거동을 연구하였다.
먼저, DC 마그네트론 스퍼터링에 의해 증착된 은(Ag) 박막의 성장 속도, 결정도 및 비저항에 대한 스퍼터링 파워, 작동 압력 및 바이어스의 영향을 연구하였다. 박막은 20, 50, 100, 200 W의 스퍼터링 파워, 2.5, 5, 10, 20 mTorr의 공정 압력과 -300, 0, +300 V의 기판 바이어스 공정 조건 하에서 30분 동안 증착되었다. 모든 스퍼터링 파워에서 박막의 성장률은 양의 바이어스에 의해 증가한 반면, 음의 바이어스에 의해 감소하였다. 예를 들어, 스퍼터링 파워 100W와 공정 압력 2.5mTorr에서, 박막의 두께는 각각 -300, 0, +300V에서 346, 378, 416nm였다. 기판 바이어스 효과는 공정 압력이 감소함에 따라 두드러졌다. 바이어스에 따른 박막성장속도의 변화를 고려하면 음으로 하전된 플럭스의 양은 대략 10%로 추정된다. 공정 압력이 감소함에 따라 증착된 막의 결정화도는 양의 바이어스에 의해 증가한 반면, 네거티브 바이어스에 의해 감소하였다. 박막의 저항값도 같은 경향을 보였다. 은 필름의 증착 거동의 이러한 변화는 하전된 플럭스의 효과로 이해할 수 있다.
또한, RF 마그네트론 스퍼터링에 의해 증착된 텅스텐(W) 막에 아르곤 가스 압력과 기판 바이어스가 미치는 영향을 조사하였다. 텅스텐은 일반적으로 반도체용 구리 배선을 대체하는 재료로 사용되고 있다. 실온에서 스퍼터링에 의해 증착된 텅스텐 박막은 상대적으로 저항이 높은 준안정 β상을 갖고, 특정 조건 하에서 상대적으로 저항이 낮은 안정한 α상으로 변환되는 것이 일반적으로 관찰되어 왔다. 20 mTorr 및 -100 V의 기판 바이어스 하에서 1초간의 짧은 증착 초기 단계에서, 투과 전자 현미경(TEM)을 사용하여 β상 텅스텐의 나노 크기의 입자를 관찰하였다. 그러나 동일한 압력 및 바이어스 조건에서 증착 시간이 10분으로 증가함에 따라 텅스텐 필름은 α상과 β상이 공존하였다. α상 텅스텐의 비율은 음의 바이어스가 -100에서 -200V로 증가함에 따라 더 증가하였다. 또한 바이어스가 +100에서 -100V로 변경됨에 따라 필름 밀도가 증가하고 표면 거칠기가 감소했다. 이러한 결과는 음의 바이어스가 β상에서 α상으로 텅스텐의 상을 변화시킨 것을 나타낸다. α상 텅스텐의 형성과 필름의 저항값에 대한 바이어스 효과는 압력이 증가함에 따라 더욱 두드러졌다.
또한, DC 스퍼터링 시 이온화율을 높이기 위해서 DC 마그네트론 스퍼터링 시스템에 유도 결합 플라즈마(ICP)를 설치하였다. 텅스텐 박막은 -200, 0, +200V의 기판 바이어스 조건에서 ICP 파워를 0에서 200W로 증가시키면서 증착되었다. ICP 파워가 증가하고 기판에 음의 바이어스가 가해질 때 α상 텅스텐의 성장이 향상되고 텅스텐 막의 저항이 감소하였다. 그러나 XRD(X-ray diffraction) 데이터와 비저항 측정 결과로부터 α상 텅스텐의 성장을 위한 최적화된 공정 조건이 있음을 알 수 있었다. 이 연구에서 가장 낮은 저항을 가지는 텅스텐 박막은 ICP 파워가 100W이고 기판 바이어스가 -200V일 때 얻어졌다.

다국어 초록 (Multilingual Abstract)

In recent years, the generation of charged flux during direct current (DC) and radio frequency (RF) magnetron sputtering and its effects on film deposition were studied. Thus, the deposition parameter that affects the generation of charged flux was examined in both DC and RF sputtering system. In particular, the charging behavior under the argon (Ar) pressure which is utilizing to generate plasma and the substrate bias were studied.
First of all, effects of sputtering power, working pressure, and bias on the growth rate, crystallinity, and resistivity of Ag thin films deposited by DC magnetron sputtering were investigated. Thin films were deposited on the substrate under the electric biases of − 300, 0, and + 300 V for 30 minutes with sputtering powers of 20, 50, 100, and 200 W and working pressures of 2.5, 5, 10, and 20 mTorr. Under all sputtering powers, the growth rate of the thin film was increased by the positive bias, whereas it was decreased by the negative bias. For example, the film thicknesses were 345.7, 377.9, and 416.0 nm at − 300, 0, and + 300 V, respectively, at a sputtering power of 100 W and a working pressure of 2.5 mTorr. The bias effect was enhanced as the working pressure decreased. Considering the change of the film growth rate according to the bias, the amount of negatively charged flux was estimated to be roughly 10 %. As the working pressure decreased, the crystallinity of the deposited films increased by the positive bias whereas it decreased by the negative bias, which is indicated by the full width at half maximum (FWHM) determined by X-ray diffraction of the Ag (111) peak. The film resistivity had the same tendency. This change in the deposition behavior of the Ag film can be understood as the effect of the charged flux.
In addition, effects of Ar pressure and substrate bias on tungsten (W) films deposited by RF magnetron sputtering were investigated. W is generally used as a material to replace copper interconnects for semiconductors. It is commonly observed that tungsten thin films deposited by sputtering at room temperature have a metastable β-phase with relatively high resistivity and transform into a stable α-phase with relatively low resistivity under certain conditions. In this study, to obtain W films with low resistivity suitable for interconnect materials for semiconductors, we tried to identify deposition parameters for the formation of α-phase W by varying the substrate bias and argon (Ar) pressure in an RF magnetron sputtering system. In the initial stage for 1 s of deposition under 20 mTorr and a substrate bias of –100 V, β-phase W nanoparticles were observed using transmission electron microscopy (TEM). However, as the deposition time increased to 10 min under the same pressure and bias condition, the W film became a mixture of α- and β-phases. The fraction of α-phase W increased further as the negative bias increased from –100 to –200 V. In addition, the film density increased and the surface roughness decreased as the bias changed from +100 to –100 V. These results indicate that the negative bias triggered the phase transformation of W from β to α. The bias effect on the formation of α-phase W and film resistivity became more pronounced as pressure increased.
Furthermore, inductively coupled plasma (ICP) was installed in the DC magnetron sputtering system to increase the ionization rate during DC sputtering. W thin films were deposited at substrate biases of -200, 0, and +200 V with increasing the ICP power from 0 to 200 W. The growth of α-phase W was enhanced and the resistivity of W film decreased when the ICP power was increased and a negative bias was applied to the substrate. However, from the X-ray diffraction (XRD) data and resistivity measurement results, it is shown that there are optimized process conditions for growing α-phase W. The W thin film with the lowest resistivity in this study was obtained when the ICP power was 100 W and the substrate bias was -200 V.

목차 (Table of Contents)

• Chapter 1. Introduction 1
• 1.1. Non-classical crystallization 1
• 1.1.1. Theory of charged nanoparticles 2
• 1.1.2. Charge enhanced kinetics 3
• 1.2. Physical vapor deposition (PVD) 11
• 1.2.1. Sputter deposition 11
• 1.2.2. Direct current (DC) sputtering 14
• 1.2.3. Radio frequency (RF) sputtering 15
• 1.3. Purpose of this study 18
• Chapter 2. Effects of Sputtering Power, Working Pressure, and Electric Bias on the Deposition Behavior of Ag Films during DC Magnetron Sputtering Considering the Generation of Charged Flux 19
• 2.1. Introduction 19
• 2.2. Experimental 22
• 2.3. Result and Discussion 25
• 2.4. Conclusion 33
• Chapter 3. Effects of substrate bias and Ar pressure on growth of α-phase in W thin films deposited by RF magnetron sputtering 44
• 3.1. Introduction 44
• 3.2. Experimental 46
• 3.3. Results 48
• 3.4. Discussion 56
• 3.5. Conclusion 62
• Chapter 4. Effects of ICP power on growth of low-resistivity W thin films deposited by DC magnetron sputtering assisted by ICP 75
• 4.1. Introduction 75
• 4.2. Experimental 76
• 4.3. Result and Discussion 78
• 4.4. Conclusion 81
• Bibliography 88
• Abstract in Korean 102

참고문헌 (Reference)

1. New Horizons of Nonclassical Crystallization,, A. Rao, M. Jehannin, H. Cölfen, vol. 141, no. 26, pp. 10120-10136, 2019/07/03 2019, doi: 10.1021/jacs.9b01883, , 2019

2. Stable Prenucleation Calcium Carbonate Clusters,, H. Cölfen, D. Gebauer, A. Völkel, vol. 322, no. 5909, p. 1819, 2008, doi: 10.1126/science.1164271, , 2008

3. Stable prenucleation calcium carbonate clusters,, D. Gebauer, H. Colfen, A. Volkel, vol. 322, no. 5909, pp. 1819-1822, , 2008

4. Electromigration path in Cu thin-film lines,in English, R. Rosenberg, C. K. Hu, K. Y. Lee, vol. 74, no. 20, pp. 2945-2947, doi: https://doi. org/10.1063/1.123974, , 1999

5. Real-time imaging of Pt3Fe nanorod growth in solution,, H.-G. Liao, H. Zheng, L. Cui, S. Whitelam, vol. 336, no. 6084, pp. 1011-1014, , 2012

6. Glow discharge processes: sputtering and plasma etching,, B. Chapman, J. Vossen, vol. 34, no. 7, p. 62, , 1981

7. Structural instability of ultrafine particles of metals,, T. Ichihashi, S. Iijima, vol. 56, no. 6, p. 616, , 1986

8. Recent experimental explorations of non-classical nucleation,, R. Tang, B. Jin, Z. Liu, 10.1039/D0CE00480D vol. 22, no. 24, pp. 4057-4073, 2020, doi: 10.1039/D0CE00480D, , 2020

9. Charged cluster model in the low pressure synthesis of diamond,, J. H. Hahn, D. Y. Yoon, N. M. Hwang, vol. 162, no. 1-2, pp. 55-68, , 1996

10. Prussian Blue mesocrystals prepared by a facile hydrothermal method, R.-P. Ji, J.-S. Jiang, Y. Zeng, M. Hu, 10.1039/B911613N vol. 11, no. 11, pp. 2257-2259, 2009, doi: 10.1039/B911613N, , 2009

11. Effect of charge on bond strength in hydrogenated amorphous silicon,, G. T. Hefter, P. J. Jennings, B. W. Clare, J. C. L. Cornish, G. Talukder, Journal of computational vol. 15, no. 6, pp. 644-652, , 1994

12. Low emissivity Ag/Ta/glass multilayer thin films deposited by sputtering,, K. S. Lee, S. H. Park, A. Sivasankar Reddy, vol. 110, no. 6, p. 063508, , 2011

13. On the potential of tungsten as nextgeneration semiconductor interconnects, K. Barmak, D. Choi, vol. 13, pp. 449-456, , 2017

14. Thin film deposition with physical vapor deposition and related technologies,, S. M. Rossnagel, vol. 21, no. 5, pp. S74-S87, 2003, doi: 10.1116/1.1600450, , 2003

15. High-resolution EM of colloidal nanocrystal growth using graphene liquid cells,, J. M. Yuk., vol. 336, no. 6077, pp. 61-64, , 2012

16. Macro-effects of resputtering due to negative ion bombardment of growing thin films,, D. J. Kester, R. Messier, vol. 8, no. 8, pp. 1928-1937, 1993/08/01 1993, doi: 10.1557/JMR.1993.1928, , 1928

17. Non-classical crystal growth on a hydrophobic substrate: learning from bivalve nacre,, R. Gao, G. Zhang, X. Feng, R. Wang, 10.1039/D0CE00076K vol. 22, no. 18, pp. 3100-3105, 2020, doi: 10.1039/D0CE00076K, , 2020

18. The effect of surface roughness on the resistivity increase in nanometric dimensions,, H. Marom, M. Eizenberg, vol. 99, no. 12, p. 123705, doi: https://doi. org/10.1063/1.2204349, , 2006

19. Beta (β) tungsten thin films: Structure, electron transport, and giant spin Hall effect,, W. Chen, G. Xiao, Q. Hao, vol. 106, no. 18, p. 182403, doi: https://doi. org/10.1063/1.4919867, , 2015

20. Spontaneous generation of charged atoms or clusters during thermal evaporation of silver,, D.-Y. Kim, N.-M. Hwang, I.-D. Jeon, vol. 96, no. 2, pp. 186-190,, doi: 10.3139/146.101018, , 2005

21. Charged nanoparticles in thin film and nanostructure growth by chemical vapour deposition,, N.-M. Hwang, D.-K. Lee, vol. 43, no. 48, p. 483001, , 2010

22. Crystal growth in colloidal tin oxide nanocrystals induced by coalescence at room temperature,, E. Longo, J. Andres, F. Pontes, T. Giraldi, E. Leite, A. Beltran, vol. 83, no. 8, pp. 1566-1568, , 2003

23. Oriented attachment of particles: 100 years of investigations of non-classical crystal growth,, P. P. Fedorov, V. K. Ivanov, A. Y. Baranchikov, V. V. Osiko, vol. 83, no. 12, pp. 1204-1222, 2014/12 2014, doi: 10.1070/rcr4453, , 2014

24. Stresses, microstructure and resistivity of thin tungsten films deposited by RF magnetron sputtering,, C. Arena, M. Hugon, J. Bessot, F. Varniere, B. Agius, M. Froment, vol. 38, no. 1-4, pp. 269-285, 1989, doi: https://doi. org/10.1016/0169-4332(89)90548-5., , 1989

25. Influences of working pressure on properties for TiO2 films deposited by DC pulse magnetron sputtering,, H. Wang, D. Ju, C. Zhang, W. Chai, W. Ding, vol. 21, no. 6, pp. 741-744, 2009/01/01/ 2009, doi: https://doi. org/10.1016/S1001-0742(08)62334-7., , 2009

26. Residual stress, microstructure, and structure of tungsten thin films deposited by magnetron sputtering,, Q. Zhang, Y. Shen, W. McBride, D. McKenzie, W. McFall, Y. Mai, vol. 87, no. 1, pp. 177-187, , 2000

27. Inductivelycoupled- plasma-assisted planar magnetron discharge for enhanced ionization of sputtered atoms,, M. Kamai, Y. Setsuhara, S. M. Musil, vol. 36, no. 7S, p. 4568, , 1997

28. Microstructure, Growth, Resistivity, and Stresses in Thin Tungsten Films Deposited by Rf Sputtering,in English, G. A. Rozgonyi, T. T. Sheng, F. B. Alexander, P. Petroff, A. K. Sinha, vol. 44, no. 6, pp. 2545- 2554,, , 1973

29. Oriented attachment and mesocrystals: Non-classical crystallization mechanisms based on nanoparticle assembly,, M. Niederberger, H. Cölfen, 10.1039/B604589H vol. 8, no. 28, pp. 3271-3287, 2006, doi: 10.1039/B604589H, , 2006

30. Microstructure of thin tantalum films sputtered onto inclined substrates: Experiments and atomistic simulations,, J. Dalla Torre., vol. 94, no. 1, pp. 263-271, 2003, doi: https://doi. org/10.1063/1.1579112, , 2003

31. Visible and near infrared light absorbance of Ag thin films deposited on ZnO under layers by magnetron sputtering,, T. Tomioka, H. Omoto, K. Kato, A. Takamatsu, vol. 95, no. 8, pp. 2352-2356, , 2011

32. Effects of Substrate Bias and Ar Pressure on Growth of α-phase in W Thin Films Deposited by RF Magnetron Sputtering,, G. S. Jang, S. M. Ahn, N.-M. Hwang, D. Y. Kim, 2022/12/29 2022, doi: 10.1007/s13391-022-00399-9, , 2022

33. Aggregation-based crystal growth and microstructure development in natural iron oxyhydroxide biomineralization products,, J. F. Banfield, H. Zhang, S. A. Welch, T. T. Ebert, R. L. Penn, vol. 289, no. 5480, pp. 751-754, , 2000

34. Nonclassical crystallisation pathway directly observed for a pharmaceutical crystal via liquid phase electron microscopy,, J. Cookman, V. Hamilton, U. Bangert, S. R. Hall, vol. 10, no. 1, p. 19156, 2020/11/05 2020, doi: 10.1038/s41598-020-75937-2, , 1915

35. Comparison of the Deposition Behavior of Charged Silicon Nanoparticles between Floating and Grounded Substrates,in English, C. S. Kim, W. K. Youn, N. M. Hwang, J. Y. Lee, S. Iijima, S. S. Lee, Article vol. 118, no. 22, pp. 11946-11953, Jun 2014, doi: 10.1021/jp5001144., , 1946

36. Ionization energy and electron affinity of a metal cluster in the stabilized jellium model: Size effect and charging limit,, C. Fiolhais, J. P. Perdew, M. Brajczewska, M. Seidl, vol. 108, no. 19, pp. 8182- 8189, , 1998

37. Li-doped ZnO nanorods with single-crystal quality – non-classical crystallization and self-assembly into mesoporous materials, S. Polarz, S. Dilger, C. Lizandara-Pueyo, M. Gerigk, A. Hoffmann, M. R. Wagner, 10.1039/C3CE41670D vol. 16, no. 8, pp. 1525-1531, 2014, doi: 10.1039/C3CE41670D., , 2014

38. Alpha- vs. beta-W nanocrystalline thin films: A comprehensive study of sputter parameters and resulting materials' properties,in English, R. Spolenak, F. T. N. Vullers, vol. 577, pp. 26-34, doi: https://doi. org/10.1016/j. tsf.2015.01.030., , 2015

39. Effect of inductively coupled plasma and plasma parameters on magnetron sputtered Al-Doped ZnO highly conductive thin films at low-temperature,, P. J. Xiang, S. B. Jin, B. B. Sahu, J. B. Kim, J. G. Han, vol. 123, no. 20, p. 205107, , 2018