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An aqueous tetramethylammonium hydroxide (TMAH) solution is widely used for silicon wet anisotropic etching to perform bulk micromachining for the fabrication of microstructures on a silicon wafer. To reduce the etching time to increase the productivity, etchant must provide high etch rate. In the present work, the etching characteristics of Si{110} in low concentration TMAH (5 wt%) with the addition of various concentrations (5–20%) of reducing agent hydroxylamine (NH2OH) have been studied to increase the etch rate of Si{110} to reduce the etch time for the fabrication of microstructures. Moreover, it is aimed to enhance the undercutting at convex corner for the fast release of the structure. The etch rate of Si{110} and the undercutting at convex corners with the addition of NH2OH increases by more than three times that in pure TMAH. In addition to the etch rate and undercutting, the effect of NH2OH on etched surface morphology is investigated systematically. The present study is focused to enhance the application of wet etching in silicon micromachining for the fabrication of various kinds of microstructures for applications in microelectromechanical systems.
References
-
-
1)
-
60. Pal, P., Sato, K., Chandra, S.: ‘Fabrication techniques of convex corners in (100)-silicon wafer using bulk micromachining: a review’, J. Micromech. Microeng., 2007, 17, (10), pp. R111–R133 (doi: 10.1088/0960-1317/17/10/R01).
-
2)
-
33. Pal, P., Singh, S.S.: ‘A new model for the etching characteristics of corners formed by Si{111} planes on Si{110} wafer surface’, Engineering, 2013, 5, (11), pp. 1–8 (doi: 10.4236/eng.2013.511A001).
-
3)
-
32. Singh, S.S., Avvaru, V.N., Veerla, S., et al: ‘A measurement free pre-etched pattern to identify the 〈110〉 directions on Si{110} wafer’, Microsyst. Technol., 2017, 23, (6), pp. 2131–2137 (doi: 10.1007/s00542-016-2984-2).
-
4)
-
54. Gosálvez, M.A., Xing, Y., Hynninen, T., et al: ‘Faster simulations of step bunching during anisotropic etching: formation of zigzag structures on Si (1 1 0)’, J. Micromech. Microeng., 2007, 17, (4), pp. S27–S37 (doi: 10.1088/0960-1317/17/4/S02).
-
5)
-
5. Pal, P., Sato, K.: ‘Complex three dimensional structures in Si{100} using wet bulk micromachining’, J. Micromech. Microeng., 2009, 19, p. 105008, (doi: 10.1088/0960-1317/19/10/105008).
-
6)
-
51. Lunak, S., Veprek Siska, J.: ‘The catalytic effect of cations on the decomposition of alkaline solutions of hydroxylamine’, Collect. Czech. Chem. Commun., 1974, 39, pp. 391–395 (doi: 10.1135/cccc19740391).
-
7)
-
29. Tanaka, H., Yamashita, S., Abe, Y., et al: ‘Fast etching of silicon with a smooth surface in high temperature ranges near the boiling point of KOH solution’, Sens. Actuators A, 2004, 114, (2–3), pp. 516–520 (doi: 10.1016/j.sna.2003.11.036).
-
8)
-
61. Pal, P., Sato, K.: ‘A comprehensive review on convex and concave corners in silicon bulk micromachining based on anisotropic wet chemical etching’, Micro Nano Syst. Lett., 2015, 3, (1), pp. 1–42 (doi: 10.1186/s40486-015-0012-4).
-
9)
-
25. Seidel, H., Csepregi, L., Heuberger, A., et al: ‘Anisotropic etching of crystalline silicon in alkaline solutions I: orientation dependence and behavior of passivation layers’, J. Electrochem. Soc., 1990, 137, pp. 3612–3626 (doi: 10.1149/1.2086277).
-
10)
-
38. Ahn, M., Heilmann, R.K., Schattenburg, M.L.: ‘Fabrication of ultrahigh aspect ratio freestanding gratings on silicon-on-insulator wafers’, J. Vac. Sci. Technol. B., 2007, 25, (6), pp. 2593–2597 (doi: 10.1116/1.2779048).
-
11)
-
45. Michael, A.: ‘The structures and reactions of hydroxylamine and its derivatives’, J. Am. Chem. Soc., 1921, 43, (2), pp. 315–332 (doi: 10.1021/ja01435a009).
-
12)
-
26. Dziuban, J.A.: ‘Microwave enhanced fast anisotropic etching of monocrystalline silicon’, Sens. Actuators A, 2000, 85, (1), pp. 133–138 (doi: 10.1016/S0924-4247(00)00373-3).
-
13)
-
9. Tabata, O., Asahi, R., Funabashi, H., Shimaoka, K., Sugiyama, S.: ‘Etch rate and selectivity of TMAH vs EDP anisotropic etching’, Sens. Actuators A, 1992, 34, pp. 51–57 (doi: 10.1016/0924-4247(92)80139-T).
-
14)
-
41. Gosálvez, M.A., Zubel, I., Viinikka, E.: ‘Wet etching of silicon’, in Markku, T., Motooka, T., Airaksinen, V.M., et al (Eds.): ‘Handbook of silicon based MEMS materials and technologies’ (William Andrew, Norwich, NY, USA, 2015), , pp. 477–502.
-
15)
-
7. Tang, B., Sato, K., Zhang, D., et al: ‘Fast Si (100) etching with a smooth surface near the boiling temperature in surfactant-modified tetramethylammonium hydroxide solutions’, Micro Nano Lett., 2014, 9, pp. 582–584 (doi: 10.1049/mnl.2014.0214).
-
16)
-
46. Cisneros, L.O., Rogers, W.J., Mannan, M.S.: ‘Comparison of the thermal decomposition behaviour for members of the hydroxylamine family’, Thermochim. Acta, 2004, 414, (2), pp. 177–183 (doi: 10.1016/j.tca.2003.09.023).
-
17)
-
4. Ashok, A., Pal, P.: ‘Silicon micromachining in 25 wt% TMAH without and with surfactant concentrations ranging from ppb to ppm’, Microsyst. Technol., 2017, 23, (1), pp. 47–54 (doi: 10.1007/s00542-015-2699-9).
-
18)
-
35. Tolmachev, V.A., Granitsyna, L.S., Vlasova, E.N., et al: ‘One-dimensional photonic crystal obtained using vertical anisotropic etching of silicon’, Semiconductors, 2002, 36, pp. 932–935 (doi: 10.1134/1.1500475).
-
19)
-
34. Holke, A., Henderson, H.T.: ‘Ultra-deep anisotropic etching of (110) silicon’, J. Micromech. Microeng., 1999, 9, pp. 51–57 (doi: 10.1088/0960-1317/9/1/306).
-
20)
-
44. Schnakenberg, U., Benecke, W., Löchel, B., et al: ‘NH4OH-based etchants for silicon micromachining: influence of additives and stability of passivation layers’, Sens. Actuators A, 1990, 25, (1–3), pp. 1–7 (doi: 10.1016/0924-4247(90)87001-Y).
-
21)
-
9. Zubel, I., Kramkowaka, M.: ‘The effect of isopropyl alcohol on etching rate and roughness of (100) Si surface etched in KOH and TMAH solutions’, Sens. Actuators A, 2001, 93, pp. 138–147 (doi: 10.1016/S0924-4247(01)00648-3).
-
22)
-
58. Pal, P., Singh, S.S.: ‘A simple and robust model to explain convex corner undercutting in wet bulk micromachining’, Micro Nano Syst. Lett., 2013, 1, (1), pp. 1–6 (doi: 10.1186/2213-9621-1-1).
-
23)
-
55. Van Veenendaal, E., Sato, K., Shikida, M., et al: ‘Micromorphology of single crystalline silicon surfaces during anisotropic wet chemical etching in KOH and TMAH’, Sens. Actuators A, 2001, 93, (3), pp. 219–231 (doi: 10.1016/S0924-4247(01)00655-0).
-
24)
-
14. Yang, C.R., Chen, P.Y., Yang, C.H., et al: ‘Effects of various ion-typed surfactants on silicon anisotropic etching properties in KOH and TMAH solutions’, Sens. Actuators A, Phys., 2005, 119, pp. 271–281 (doi: 10.1016/j.sna.2004.09.017).
-
25)
-
37. Lee, D., Yu, K., Krishnamoorthy, U., et al: ‘Vertical mirror fabrication combining KOH etch and DRIE of (110) silicon’, J. Microelectromech. Syst., 2009, 18, pp. 217–227 (doi: 10.1109/JMEMS.2008.2009840).
-
26)
-
1. Elwenspoek, M., Jansen, H.V: ‘Silicon micromachining’ (Cambridge University Press, UK, 1998).
-
27)
-
25. Chen, J., Liu, L., Li, Z., et al: ‘Study of anisotropic etching of (100) Si with ultrasonic agitation’, Sens. Actuators A, 2002, 96, (2), pp. 152–156 (doi: 10.1016/S0924-4247(01)00786-5).
-
28)
-
14. Pal, P., Sato, K., Gosalvez, M.A., et al: ‘Fabrication of novel microstructures based on orientation dependent adsorption of surfactant molecules in TMAH solution’, J. Micromech. Microeng., 2010, 21, (1), p. 015008, (doi: 10.1088/0960-1317/21/1/015008).
-
29)
-
56. Palik, E.D., Glembocki, O.J., Heard, I.Jr., et al: ‘Etching roughness for (100) silicon surfaces in aqueous KOH’, J. Appl. Phys., 1991, 70, (6), pp. 3291–3300 (doi: 10.1063/1.349263).
-
30)
-
14. Shikida, M., Sato, K., Tokoro, K., Uchikawa, D.: ‘Differences in anisotropic etching properties of KOH and TMAH solutions’, Sens. Actuators A, 2000, 80, pp. 179–188 (doi: 10.1016/S0924-4247(99)00264-2).
-
31)
-
23. Chen, P.H., Peng, H.Y., Hsieh, C.M., et al: ‘The characteristic behavior of TMAH water solution for anisotropic etching on both silicon substrate and SiO2 layer’, Sens. Actuators A, 2001, 93, (2), pp. 132–137 (doi: 10.1016/S0924-4247(01)00639-2).
-
32)
-
42. Narasimha Rao, A.V., Swarnalatha, V., Pal, P.: ‘Etching characteristics of Si {110} in 20 wt% KOH with addition of hydroxylamine for the fabrication of bulk micromachined MEMS’, Micro Nano Syst. Lett., 2017, 5, (1), p. 23 (doi: 10.1186/s40486-017-0057-7).
-
33)
-
48. Wei, C., Saraf, S.R., Rogers, W.J., et al: ‘Thermal runaway reaction hazards and mechanisms of hydroxylamine with acid/base contaminants’, Thermochim. Acta, 2004, 421, (1), pp. 1–9 (doi: 10.1016/j.tca.2004.02.012).
-
34)
-
5. Pal, P., Sato, K.: ‘Various shapes of silicon freestanding microfluidic channels and microstructures in one step lithography’, J. Micromech. Microeng., 2009, 19, pp. 55003 (doi: 10.1088/0960-1317/19/5/055003).
-
35)
-
57. Dong, W., Zhang, X., Liu, C., et al: ‘Mechanism for convex corner undercutting of (110) silicon in KOH’, Microelectron. J., 2004, 35, (5), pp. 417–419 (doi: 10.1016/j.mejo.2004.01.005).
-
36)
-
7. Yang, E.H., Yang, S.S., Han, S.W., et al: ‘Fabrication and dynamic testing of electrostatic actuators with p+ silicon diaphragms’, Sens. Actuators A, 1995, 50, pp. 151–156 (doi: 10.1016/0924-4247(96)80100-2).
-
37)
-
16. Pal, P., Sato, K.: ‘Fabrication methods based on wet etching process for the realization of silicon MEMS structures with new shapes’, Microsyst. Technol., 2010, 16, (7), pp. 1165–1174 (doi: 10.1007/s00542-009-0956-5).
-
38)
-
4. Merlos, A., Acero, M., Bao, M.H., et al: ‘TMAH/IPA anisotropic etching characteristics’, Sens. Actuators A, 1993, 37–38, pp. 737–743 (doi: 10.1016/0924-4247(93)80125-Z).
-
39)
-
27. Sotoaka, R.: ‘New etchants for high speed anisotropic etching of silicon’, J. Surf. Finish. Soc. Jpn., 2008, 59, (2), pp. 104–106 (doi: 10.4139/sfj.59.104).
-
40)
-
10. Shikida, M., Masuda, T., Uchikawa, D.: ‘Surface roughness of single-crystal silicon etched by TMAH solution’, Sens. Actuators A, Phys., 2001, 90, pp. 223–231 (doi: 10.1016/S0924-4247(01)00531-3).
-
41)
-
31. Pal, P., Gosalvez, M.A., Sato, K., et al: ‘Anisotropic etching on Si {110}: experiment and simulation for the formation of microstructures with convex corners’, J. Micromech. Microeng., 2014, 24, (12), p. 125001 (doi: 10.1088/0960-1317/24/12/125001).
-
42)
-
15. Pal, P., Ashok, A., Haldar, S., et al: ‘Anisotropic etching in low concentration KOH: effects of surfactant concentration’, Micro Nano Lett., 2015, 10, pp. 224–228 (doi: 10.1049/mnl.2014.0685).
-
43)
-
39. Kendall, D.L.: ‘Vertical etching of silicon at very high aspect ratios’, Annu. Rev. Mater. Sci., 1979, 9, (1), pp. 373–403 (doi: 10.1146/annurev.ms.09.080179.002105).
-
44)
-
47. Hughes, M.N., Nicklin, H.G.: ‘Autoxidation of hydroxylamine in alkaline solutions’, J. Chem. Soc. A, Inorg. Phys. Theor., 1971, pp. 164–168 (doi: 10.1039/j19710000164).
-
45)
-
49. Cisneros, L.O., Wu, X., Rogers, W.J., et al: ‘Decomposition products of 50 mass% hydroxylamine/water under runaway reaction conditions’, Process Saf. Environ. Prot., 2003, 81, (2), pp. 121–124 (doi: 10.1205/095758203321832598).
-
46)
-
19. Resnik, D., Vrtacnik, D., Aljancic, U., et al: ‘The role of Triton surfactant in anisotropic etching of {110} reflective planes on (100) silicon’, J. Micromech. Microeng., 2005, 15, pp. 1174–1183 (doi: 10.1088/0960-1317/15/6/007).
-
47)
-
52. Nguyen, Q.D.: ‘Electrochemistry in anisotropic etching of silicon in alkaline solutions’. , University of Twente, 2007.
-
48)
-
8. Lee, S., Park, S., Cho, D.: ‘The surface/bulk micromachining (SBM) process: a new method for fabricating released microelectromechanical systems in single crystal silicon’, J. Microelectromech. Syst., 1999, 8, pp. 409–416 (doi: 10.1109/84.809055).
-
49)
-
20. Xu, Y.W., Michael, A., Kwok, C.Y.: ‘Formation of ultra-smooth 45° micromirror on (100) silicon with low concentration TMAH and surfactant: techniques for enlarging the truly 45° portion’, Sens. Actuators A, 2011, 166, pp. 164–171 (doi: 10.1016/j.sna.2010.12.018).
-
50)
-
6. Zubel, I., Kramkowska, M.: ‘Possibilities of extension of 3D shapes by bulk micromachining of different Si (hkl) substrates’, J. Micromech. Microeng., 2004, 15, (3), pp. 485–493 (doi: 10.1088/0960-1317/15/3/008).
-
51)
-
40. Kim, S.H., Lee, S.H., Lim, H.T., et al: ‘Anisotropic bulk etching of (110) Silicon with high aspect ratio’, IEEJ Trans. Sens. Micromach., 1997, 118, pp. 32–36 (doi: 10.1541/ieejsmas.118.32).
-
52)
-
24. Cheng, D., Gosalvez, M.A., Hori, T., et al: ‘Improvement in smoothness of anisotropically etched silicon surfaces: effects of surfactant and TMAH concentrations’, Sens. Actuators A, 2006, 125, pp. 415–421 (doi: 10.1016/j.sna.2005.08.022).
-
53)
-
2. Pal, P., Sato, K.: ‘Silicon wet bulk micromachining for MEMS’ (Pan Stanford Publishing, Singapore, 2017).
-
54)
-
43. Van Den Meerakker, J.E.A.M.: ‘The reduction of hydrogen peroxide at silicon in weak alkaline solutions’, Electrochim. Acta, 1990, 35, (8), pp. 1267–1272 (doi: 10.1016/0013-4686(90)90060-D).
-
55)
-
21. Pal, P., Sato, K., Gosalvez, M.A., et al: ‘Study of rounded concave and sharp edge convex corners undercutting in CMOS compatible anisotropic etchants’, J. Micromech. Microeng., 2007, 17, (11), pp. 2299–2307 (doi: 10.1088/0960-1317/17/11/017).
-
56)
-
22. Zhang, J., Hon, W.C., Leung, L.L.W., et al: ‘CMOS-compatible micromachining techniques for fabricating high-performance edge-suspended RF/microwave passive components on silicon substrates’, J. Micromech. Microeng., 2005, 15, pp. 328–335 (doi: 10.1088/0960-1317/15/2/012).
-
57)
-
59. Kim, B., Cho, D.D.: ‘Aqueous KOH etching of silicon (110) etch characteristics and compensation methods for convex corners’, J. Electrochem. Soc., 1998, 145, pp. 2499–2508 (doi: 10.1149/1.1838668).
-
58)
-
50. Chunyang, W.: ‘Thermal runaway reaction hazard and decomposition mechanism of the hydroxylamine system’. , Texas A&M University, 2005.
-
59)
-
11. Kovacs, G.T.A., Maluf, N.I., Petersen, K.E.: ‘Bulk micromachining of silicon’, Proc. IEEE, 1998, 86, (8) (doi: 10.1109/5.704259).
-
60)
-
17. Tang, B., Yao, M.Q., Tan, G., et al: ‘Smoothness control of wet etched Si{100} surfaces in TMAH + Triton’, Key Eng. Mater., 2014, 609, pp. 536–541.
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