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Nickel Plating Into Porous Silicon
1. Nickel Displacement Deposition into Porous Silicon with Ultrahigh Aspect Ratio Chengkun Xu, Xi Zhang, King-Ning Tu, and Ya-hong Xie* Department of Materials Science and Engineering University of California, Los Angeles, CA 90095, USA
2. 01/14/11 Aspect ratio: 100~200 Cross-talk issue in integration of the digital and RF analog circuits The noise from digital circuits can be transmitted through the conducting Si substrate and degrade the performance of analog circuit elements. Strategy: fabricate ground structure via metal deposited porous region on Si substrate. Analog circuits Noisy digital circuits Si Plated PS region 1~2 μ m 200 μ m
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5. (a) before deposition, (b) after 8 h deposition. Displacing nature of the deposition process 2Ni 2+ + 4e = 2Ni Nickel deposit grows into the pore wall rather than on top of it, leading the pore mouth to stay open. Nickel deposit thickness is about 300 nm. Ni Si
6. 01/14/11 Increasing nickel ion concentration from 0.1M to 1.0M Lowering solution pH from 8 to 7 Enhancement of Ni 2+ mass transport Nickel deposition uniformity was improved. 0.1M 1.0M pH=8 pH=7
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8. After 4h deposition Nickel deposition profile under optimal conditions Nickel was deposited all the way down to the bottom and the deposition becomes uniform along the pore depth in 4h.
10. 01/14/11 Summary With the improvement of nickel ion transport and the use of additive coumarin, the nickel deposition process shifts from mass transfer limitations to interfacial kinetics control and becomes uniform along the pore depth. Eventually, we achieved nickel deposition all the way down to the pore bottom. The deposition time is substantially shortened to 4 h.
