Advanced Fabrication Technology for MEMs Devices and Applications

   Bulk Micromachining:

• Thru wafer technology
• Wet anisotropic etchants for silicon (100) and silicon (110)-KOH based.
• Deep reactive ion etching (DRIE): two Unaxis 770 systems with up to 6 inch capability,
  etch rates up to 3 µm/min, and aspect ratios of 20-30:1.
• Polysilicon, silicon, and SOI substrates.
• Precise backside wafer alignment-EV620.

   Fabrication of LPCVD and PECVD Based Films (6-inch capability):

• LPCVD Polysilicon: ultra-thin (< 100 nm) to thick 1 µm films with controlled low to stress free films.
• LPCVD N⁺/P⁺ Polysilicon (> 5e19 cm^-3).
• Multilayer structures such as undoped polysilicon/low-temperature oxide (LTO)/doped polysilicon.
• LPCVD silicon nitride: stoichiometric (1100 MPa) and low stress (110-160 MPa) with thicknesses up to 2.5 µm.
• Low temperature oxide (LTO) at 425°C.
• LPCVD TEOS and oxynitride.
• PECVD: TEOS, SiO₂, Si₃N₄, oxynitride, PSG (8at.%), BPSG, a-Si(N⁺/P⁺) with tunable stress and high conformality.
• RTA/RTP in N2/O₂ to 1200°C.
• Ion implantation of B, P, As, and H to medium currents and 200 keV.
• Structural release: wet (CO₂ supercritical drying), dry (SF₆ and XeF₂).
• Anisotropic RIE including ICP based etching of thick (10 µm) oxides and glasses.

• Aligned direct fusion bonding with high temperature annealing (1100°C)-EV501/620.
• Anodic bonding of silicon, and silicon with intermediate layers-EV501.
• In-situ thermo-compression bonding at lower temperatures ~400°C.
• Low temperature (< 400°C) bonding via plasma surface activation.
• Wafer scale packaging with hermetic sealing
• Unconventional bonding materials such as Si₃N₄, SiC, and GaAs.
• Use of PECVD and spin-on based intermediate films.

   High Aspect Ratio MEMs:

• UV LIGA using SU8 with thicknesses up to 1 mm with aspect ratios up to 15:1 and electroplated structures.
• Hot Embossing: silicon and SU8 masters into substrates such as polycarbonate, PMMA, polystyrene, and PETG with feature sizes of 5-50 µm and aspect ratios up to 5:1 with incorporated anti-stiction layers.
• High resolution master template fabrication for molecular transfer lithography and imprint lithography.

• Thermal budget considerations for metallization, film deposition, and annealing.
• Film stress and adhesion issues.
• Film conformality and step coverage for high topology features.
• Stiction issues during release and device operation addressed with critical point drying and SAMs (OTC, FDTS, and vapor deposited).
• Process and device simulation: finite element analysis software.

• All major fabrication areas listed.
• Well characterized and controlled discrete processes.
• Process modules for integrated processing-device targeted.
• Process sequence assembly for documented run sheets.

MEMS Switches for Binary Logic and Nonvolatile Memory under Hostile Environment CNF Project # 752-98 Principal Investigator: Edwin C. Kan User: Nick Y. Shen Affiliation: School of Electrical and Computer Engineering, Cornell University Contact Info: ys69@cornell.edu, kan@ece.cornell.edu Figure: SEM picture of a sandwich tether-shape device. The large Poly2 anchor is made to ensure that Poly1 is the only moving layer under actuation.	CNF Project # 752-98
Hinged Atomic Force Microscopy Cantilevers CNF Project # 883-00 Principal Investigator: Frederick Sachs, PhD Users: Arthur Beyder, David Yang Affiliation: Physiology and Biophysics, State University of New York at Buffalo Contact Info: beyder@buffalo.edu, yxy@buffalo.edu, sachs@buffalo.edu Figure: [A] Dies and thin silicon membranes are fabricated by backside KOH. We use compensation structures for convex corners. [B] Membranes are patterned on topside levers. [C] Hinges are released by Bosch etch. LPCVD Si3N4 hinges are protected by SiO2 during all processing. [D] Dual-hinge & torsion levers can be fabricated using this process with modification only at the CAD level.	CNF Project # 883-00
The Dynamical Properties of Micromechanical Resonators CNF Project # 891-00 Principal Investigator: Melissa A. Hines Users: Yu Wang, Joshua A. Henry Affiliation: Department of Chemistry, Cornell University Contact Info: yw55@cornell.edu, jah76@cornell.edu, Melissa.Hines@cornell.edu Nanomechanical resonators with Si(111) faces fabricated. Process uses standard Si(111) wafers (not SOI). Q of resonators affected by surface termination. Oxide-terminated resonators up to twice as lossy as H-terminated resonators. Figure: 7 µm wide, 250 nm thick hexagonal paddle oscillator fabricated from Si(111) wafer and suspended by 450 nm wide silicon wires.	CNF Project # 891-00
Undercut Control for Surface Micromachined Oscillators CNF Project # 599-96 Principal Investigator: Harold G. Craighead Users: Rustom Bhiladvala, Rob Reichenbach Affiliation: Applied & Engineering Physics, Cornell University Contact Info: rbb32@cornell.edu, rbr9@cornell.edu, hgc1@cornell.edu Circular arcs (Figure 1) mark remnants of the first, long, sacrificial layer etch done before device patterning. Figure 1: A surface micromachined paddle, 20 µm on a side, with 2 µm beams and support undercut limited to 2 µm has been created using the technique described.	CNF Project # 599-96
A Surface Micromachined 3-Axis Accelerometer CNF Project # 963-01 Principal Investigator: William N. Carr User: Lijun Jiang Affiliation: New Jersey Institute of Technology Contact Info: LJ2@njit.edu, carr@adm.njit.edu A three-axis accelerometer by surface micromachining. Fully differential capacitive readout with highly sensitive, low-noise circuit board. Demonstration of the feasibility for fabrication 3-axis accelerometer in surface micromachining. ANSYS 6.1 simulation for design improvement. Figure (top): SEM image of a lateral-axis accelerometer. Figure (bottom): Close-up view of the spring beams for lateral accelerometer.	CNF Project # 963-01
Microfabricated Model Silicon Probes with Microfluidic Channels for Drug Delivery CNF Project # 319-87 Principal Investigator: Michael S. Isaacson Users: Scott Retterer, Keith Neeves Affiliation: Applied and Engineering Physics, Biomedical Engineering, Chemical Engineering, Cornell University Contact Info: str8@cornell.edu, kbn4@cornell.edu, msi4@cornell.edu Model silicon probes, fabricated using bulk subtractive etching techniques, have been used to stimulate a neural tissue response to chronically implanted prosthetic devices in vivo. Various histological techniques were used to characterize the immune response. Microfluidic channels to be used for local drug delivery have been incorporated into the probe design. Figure: Model neural probe tip with a surface micromachined fluidic channel.	CNF Project # 319-87
A Microfabricated PCR-Based Biosensor CNF Project # 884-00 Principal Investigator: Dr. Carl A. Batt User: Nathaniel C. Cady Affiliation: Dept. of Microbiology, Cornell University Contact Info: ncc4@cornell.edu, cab10@cornell.edu An integrated DNA purification / PCR amplification device has been fabricated in a microfluidic format. The device is capable of purifying DNA from bacterial cells and performing PCR amplification via a miniaturized thermocycler. Figure: Integrated DNA purification / amplification microchip consisting of RIE-etched silicon and PECVD oxide. Inset shows the 10 µm square pillars in the purification portion of the device.	CNF Project # 884-00
Photonic Bandgap Materials CNF Project # 694-98 Principal Investigator: Yuri Suzuki User: Lu Chen Affiliation: Materials Science & Engineering, Cornell University Contact Info: LC60@cornell.edu, Suzuki@ccmr.cornell.edu Figure: 2-D honeycomb PBC structure is etched to 8 µm deep by Cl plasma etching.	CNF Project # 694-98
MEMS Device Development CNF Project # 639-97 Principal Investigator: Joel Kubby Users: Pinyen Lin, Jingkuang Chen Affiliation: Xerox Wilson Center for Research & Technology Contact Info: plin@crt.xerox.com, pgulvin@crt.xerox.com, jkubby@crt.xerox.com SOI-MEMS process for integrating MEMS optical switches with silicon waveguides and Arrayed Waveguide Gratings (AWG) to form Photonic Light Circuits (PLC's). Use of silicon platform enables integration of functions in a compact system to lower cost of components. Reconfigurable Optical Add/Drop Multiplexers (ROADM) and Wavelength Routers have been prototyped. Figure: Chip-scale Reconfigurable Optical Add/Drop Multiplexer ROADM fabricated in an SOI-MEMS technology. Use of high index contrast silicon waveguides enables the ROADM chip to have centimeter scale dimensions.	CNF Project # 639-97