The Waffle Substrate: A Novel Approach to Reducing Substrate Resistance in SiC Power Devices

Abstract:

Silicon carbide (SiC) is enabling the next generation of semiconductor power devices, with performance orders-of-magnitude beyond silicon. The most important power switching device is the SiC power MOSFET, whose performance is limited by three main resistance elements: the channel, drift layer, and substrate. For blocking voltages in the range of 400-900V, substrate resistance is a major limitation. Wafer thinning is currently used to reduce the substrate resistance, but this also reduces the strength of the wafers. We report on a waffle substrate technique that relies on wafer thinning and inductively coupled plasma (ICP) etching to reduce the substrate resistance below levels achievable by thinning alone, while retaining the mechanical stability of a moderately-thinned substrate. This technique can be applied to any SiC device for which substrate resistance is a limitation.

• Periodical: Materials Science Forum (Volume 1004)
• Pages: 738-746
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.1004.738
• Online since: July 2020
• Authors: Noah Opondo*, James A. Cooper, Hang Jie Liao, Wei Nong Chen, Dallas Morisette
• Keywords: Power MOSFET, Specific On-Resistance, Substrate Resistance

References

[1] T. Kimoto, and J. A. Cooper, Fundamentals of Silicon Carbide Technology: Growth, Character­ ization, Devices and Applications, John Wiley & Sons, (2014).

[2] R. Rupp, R. Kern, and R. Gerlach, Laser backside contact annealing of SiC power devices: A prerequisite for SiC thin wafer technology, Power Semiconductor Devices and ICs (ISPSD). 25th International Symposium (2013) 51-54.

DOI: 10.1109/ispsd.2013.6694396

[3] J.D. Wu, C.Y. Huang, and C.C. Liao, Fracture strength characterization and failure analysis of silicon dies, Microelectronics Reliability, vol. 43, no. 2 (2003) 269-277.

DOI: 10.1016/s0026-2714(02)00314-1

[4] J.A. Cooper Jr, US Patent 9,780,206. (2017)[5] R.S. Okojie, C.W. Chang, L.J. Evans, Reducing DRIE­induced trench effects in SiC pressure sensors using FEA prediction, IEEE Journal of Microelectromechanical Systems, Vo. 20, no. 5, (2011) 1174 -1183.

DOI: 10.1109/jmems.2011.2163298

[6] J.­H. Zhao, J. Tellkamp, V. Gupta, and D.R. Edwards, Experimental evaluations of the strength of silicon die by 3­point­bend versus ball­on­ring tests, IEEE Transactions on Electronics Packaging Manufacturing. vol. 32 no. 4 (2009) 248-255.

DOI: 10.1109/tepm.2009.2028329

[7] L.E. Luna, M.J. Tadjer, T.J. Anderson, E.A. Imhoff, K.D. Hobart, and F.J. Kub, Dry Etching of High Aspect Ratio 4H­SiC Microstructures, ECS Journal of Solid State Science and Technology, vol. 6 no. 4 (2017) P207-P210.

DOI: 10.1149/2.0031705jss

[8] S. Tanaka, K. Rajanna, T. Abe, and M. Esashi, Deep reactive ion etching of silicon carbide, Jour­ nal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena vol. 19 no. 4 (2001) 2173-2176.

DOI: 10.1116/1.1418401

[9] N. Okamoto, Elimination of pillar associated with micropipe of SiC in high­rate inductively cou­ pled plasma etching, Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films vol. 27 no. 2 (2009) 295-300.

DOI: 10.1116/1.3077297

[10] M.S. So, S.­G. Lim, and T.N. Jackson, Fast, smooth, and anisotropic etching of SiC using SF6/Ar, Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Pro­ cessing, Measurement, and Phenomena vo. 17 no. 2 (1999) 2055-2057.

DOI: 10.1116/1.590871

[11] J. Biscarrat, J.F. Michaud, E. Collard, and D. Alquier, ICP etching of 4H­SiC substrates, Materials Science Forum, Trans Tech Publ, vol. 740 (2013) 825-828.

DOI: 10.4028/www.scientific.net/msf.740-742.825

[12] G.M. Beheim, and L.J. Evans, Control of trenching and surface roughness in deep reactive ion etched 4H and 6H SiC, MRS Online Proceedings Library Archive, Cambridge University Press vol. 911 (2006).

DOI: 10.1557/proc-0911-b10-15

[13] L. Voss, K. Ip, S.J. Pearton, R.J. Shul, M.E. Overberg, A.G. Baca, C. Sanchez, J. Stevens, M. Martinez, M.G. Armendariz, and others, SiC via fabrication for wide­band­gap high electron mo­ bility transistor/microwave monolithic integrated circuit devices, Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phe­ nomena, vol. 26 no. 2 (2008) 487-494.

DOI: 10.1116/1.2837849

[14] C. Zweben, W. Smith, and M. Wardle, Test methods for fiber tensile strength, composite flexural modulus, and properties of fabric­reinforced laminates, Composite Materials: Testing and Design (Fifth Conference), ASTM International (1979).

DOI: 10.1520/stp36912s

[15] G. With, and H.H. Wagemans, Ball­on­Ring Test Revisited, Journal of the American Ceramic Society vol. 72 no. 8 (1989) 1538-1541.

[16] A. Wereszczak, T. Kirkland, K. Breder, H. Lin, and M. Andrews, Biaxial strength, strength­size­ scaling, and fatigue resistance of alumina and aluminum nitride substrates, International Journal of Microcircuits and Electronic Packaging vol. 22 no. 4 (1999) 446-458.

[17] S. Yoshida, and G. Harris, Properties of silicon carbide, INSPEC, London, UK, p.74 (1995).

[18] S. Adachi, Properties of semiconductor alloys: group­IV, III­V and II­VI semiconductors, John Wiley & Sons vol. 28 (2009).

[19] Opondo, N et al, manuscript in preparation.