Agenda: EEL6935 Advanced MEMS (Spring 2005) Instructor: Dr. Huikai Xie Lecture 6 Through-wafer Interconnect EEL6935 Advanced MEMS 2005 H. Xie 1/21/2005 1 Motivations: Wafer-level packaging CMOS 3D Integration Chemical Sensors Proximity sensors Fabrication Processes: Through-hole contacts DRIE or Wet etching or Porous silicon Conduction provided by Diffusion Metal deposition/plating Polysilicon Thermomigration, or temperature gradient zone melting Silicon plug Through-Wafer Interconnect EEL6935 Advanced MEMS 2005 H. Xie 2 Through-Wafer Interconnect -1 DRIE Through-Hole plus Cu Electroplating Through-Wafer Interconnect -2 DRIE Through-Hole plus Doped Poly-Si (1) E.M. Chow et al, U. Florida/Stanford, JMEMS, vol.11 (2002) Frontside DRIE Si Backside DRIE Si J. H. Wu et al, MIT, IEEE Transactions on electron devices, 51(11), November 2004 EEL6935 Advanced MEMS 2005 H. Xie 3 Thermal oxide Doping BHF glass removal EEL6935 Advanced MEMS 2005 H. Xie 4
Through-Wafer Interconnect -2 DRIE Through-Hole plus Doped Poly-Si (2) Oxide Doping Through-Wafer Interconnect -2 DRIE Through-Hole plus Doped Poly-Si (3) Oxide passivation to fill vias Metallization Pattern signal poly-si N+ poly Signal N+ poly Shield Bulk Silicon Pattern shield poly-si Oxide E.M. Chow et al, U. Florida/Stanford, JMEMS, vol.11 (2002) EEL6935 Advanced MEMS 2005 H. Xie 5 EEL6935 Advanced MEMS 2005 H. Xie 6 Through-Wafer Interconnect -3 Isolated Silicon Plug (1) Through-Wafer Interconnect -3 Isolated Silicon Plug (2) Six-wafer combustion chamber for a microengine (MIT) A. Mehra et al, MIT, J. Vac. Sci. Technol. B 18(5), Sep-Oct 2000 EEL6935 Advanced MEMS 2005 H. Xie 7 A. Mehra et al, MIT, J. Vac. Sci. Technol. B 18(5), Sep-Oct 2000 EEL6935 Advanced MEMS 2005 H. Xie 8
Polymer: SU-8 Polymer Materials: SU-8, PMMA, BCB, PDMS, Parylene, Liquid crystal polymer, Applications: Properties: Transparent Optical MEMS High aspect ratio Biocompatible BioMEMS Flexible Low processing CMOS Integration temperature Easy spin-on deposition Packaging Planarization Microfluidics: microchannels, lab-on-a-chip, utas Wafer Bonding Packaging: epoxy, BCB Biocompatible coating RF applications: Antennas, varactors, etc. Fuel Cells Data Storage EEL6935 Advanced MEMS 2005 H. Xie 9 SU-8 is a negative, epoxy-type, near-uv photoresist (365 nm). Can be as thick as 2 mm Aspect ratios up to 25 have been demonstrated with a standard UV-lithography. Originally developed, and patented by IBM-Watson Rechearch Center (Yorktown Height-USA). In 1996 the material has been adapted for MEMS applications during a collaboration between EPFL-Institute of Microsystems and IBM-Zurich. The main part is the EPON SU8 epoxy from Shell Chemicals. It is a highly functionalized molecule with 8 epoxy groups. The polymerization is done by a cationic photopolymerization mechanism http://www.geocities.com/guerinlj/ EEL6935 Advanced MEMS 2005 H. Xie 10 SU-8: Processing SU-8 Microstructures Spin-coating: over 1mm thickness achievable Soft bake: 95 C; 25 minutes for 100µm thick layers, 180 minutes for 200 µm Exposure: near-uv (365nm); continuous long-time high-dose exposure causes hard-skin on the SU8 surface; Stepwise exposures (expose, then cool down, then expose, cool down again, ) Post exposure bake: 95 C for 15 minutes, or 50 C for 1 hour; lower temperature baking yields lower residual stress. Development: room temperature; development time depends on thickness Hard bake (not required): 200 C; increase internal stresses or even results in cracks. SU-8 Stripping High-pressure water jets High temperature ashing: in an inert gas Chemical etching: e.g. fuming nitric acid Plasma etching http://www.geocities.com/guerinlj/ SF6/O2 plasma, nickel as mask (Hong et al, DTIP 03) EEL6935 Advanced MEMS 2005 H. Xie 11 Star structure with aspect ratio of 14.5 EPEL/IBM (1997) EEL6935 Advanced MEMS 2005 H. Xie 12
SU-8 Example Devices All-photoplastic, Soft Cantilever Cassette Probe for Scanning Force Microscopy (SFM) SU-8 Example Devices Single-lever Scanning Force Microscopy (SFM) Probe IBM Zurich/U. Neuchâtel EEL6935 Advanced MEMS 2005 H. Xie 13 IBM Zurich EEL6935 Advanced MEMS 2005 H. Xie 14 SU-8 Example Devices Polymer RF MEMS Scanning Near-field Optical Microscopy (SNOM) Probe Micromachined Inductor With SU-8 With SU-8 stripped 50µm-thick SU-8 e.g., Q~20.5 at 4.45GHz, 2.6nH IBM Zurich in collaboration with Profs. N.F. de Rooij and F. Marquis-Weible EEL6935 Advanced MEMS 2005 H. Xie 15 Prof. M. Allen s group at Georgia Tech EEL6935 Advanced MEMS 2005 H. Xie 16
Polymer for High-Density Data Storage Millipede MEMS-based High-density Scanningprobe Data Storage Gray-tone lithography A method for fabricating structures in SU-8 photoresist having smoothly varying elevations has been developed at U. of Washington by M. Afromowitz team. Gray-scale structures up to 1 mm in height may be fabricated with one exposure step. 0.5Tb/in 2 1Tb/in 2 Writing: Thermal softening; tip pressing Indentation 1 Reading: thermal conductance Indentations: 25nm apart 1Tb/in 2 Erasing: nearby pressing Polymer bits Parallel Processing Vettiger,Despont, Eleftheriou et al of IBM Zurich EEL6935 Advanced MEMS 2005 H. Xie 17 These exceedingly linear SU-8 ramps (transparent in visible light, but opaque in this SEM) have lengths of 2.6 mm and maximum elevations of 0.5 mm EEL6935 Advanced MEMS 2005 H. Xie 18 Term Project The objective of this project is to find MEMS solutions for some practical problems and/or develop new MEMS designs. 1.Form teams (Jan. 28) Up to three students per team 2. Project proposal (Feb. 18) - Problem statement (motivation) - Your proposed solution(s) - To be accomplished tasks - Project schedule 3. Proposal presentation (Feb. 18) 8 minutes presentation + 2 minutes questions 4. Progress presentation (Mar. 18) 8 minutes presentation + 2 minutes questions 5. Final presentation (Apr. 18&20) 15 minutes presentation + 3 minutes questions 6. Final report (due Apr. 26) EEL6935 Advanced MEMS 2005 H. Xie 19 Project#1 Presentation Time: 1/26, 12:50pm Place: PSY 287 Adrian Steve Yawei Jessica Maojiao He Julio Shane Hongwei Deyou Eric Bryan Ankur Project #1 Poly-SiC MELO EFAB SOI Gray-scale lithography Black silicon Dissolved wafer process Porous silicon molding? Sol gel 5 minutes presentation + 2 minutes questions EEL6935 Advanced MEMS 2005 H. Xie 20