AVS1997 Session MM-ThA: Processes/Microprobes

Thursday, October 23, 1997 2:00 PM in Room K

Thursday Afternoon

Start	Invited?	Item
2:00 PM		MM-ThA-1 Dry Processing of Polycarbonate G.T. Cibuzar, K.G. Roberts (University of Minnesota) Fabrication of MEMS devices has traditionally been done using inorganic materials such as those used in traditional silicon processing. Plastics represent another class of materials that have broad applicability to MEMS, especially in biotechnology, due to the low cost, surface chemistry properties and ease of manufacture of plastic molded components. For example, recent MEMS research in the area of fluid handling systems could benefit from plastic materials if suitable processing methods are developed. Extending MEMS to biomedical-related applications using plastic components creates a need for processing techniques compatible with traditional silicon processing (or minor variations) and with the temperature and chemical solubility issues of plastics. We have studied the lithographic patterning and dry etching of several plastic materials, focusing on polycarbonate (PC). Standard photoresist processing techniques were modified to allow for the solubility and temperature-related issues of PC. Dry etching in a standard reactive ion etching system was performed using CF₄/O₂, CHF₃/O₂ and SF₆/O₂ at pressures from 31 to 100mtorr and a power of 200W. Masking was done using a wet-etched patterned one micron sputter deposited Al layer. Etch rates and sidewall profile angle were determined as a function of gas ratio, pressure and power for feature sizes ranging from 10 to 100 microns in size. Etch rates of greater than 0.5 microns per minute were obtained with optimized etching parameters. Data on processing of other plastics such as acrylic, nylon, ABS, Delrin, and various forms of polyethylene will also be discussed.
2:20 PM		MM-ThA-2 Deep Silicon RIE with Profile Control J. Chen, J. Chong (Cornell University); M. DeVre (Plasmatherm); P.G. Hartwell, C. Lee, B.W. Reed, R. Webb, N.C. MacDonald (Cornell University) Using a Plasmatherm SLR 770 system and a flourine-based process¹, we have the capability to rapidly etch silicon while controlling the profile of the resultant structure. Through adjustment of the processing parameters feature dimensions can be increased, decreased, or maintained as the etch progresses into the substrate. This results in the ability to fabricate a wide range of complex structures. In addition, etching is both rapid and uniform, allowing both fabrication of very high aspect ratio structures and through-wafer etching. One such structure is a co-axial waveguide spanning the thickness of the wafer. The device is designed to transmit microwave energy through the substrate. The structure consists of a circular pillar of single crystal silicon within a cylindrical cavity etched through the entire wafer. The deep etching yields vertical sidewalls perpendicular to the surface of the wafer, in contrast to the profile given by traditional KOH-etching. Electrical contact is made by the central pillar through the beams supporting the structure. Another device is a released SCREAM² actuator with 60:1 aspect ratio beams. This represents a tripling of the typical 20:1 aspect ratio, and allows a substantial increase in the device's capacitance and the force generated without a corresponding increase in the area taken up by the device. The out-of-plane stiffness is increased by a cubic factor, allowing fabrication of much larger and more planar structures than previously possible. ¹Patent No. 5501893: Method of Anisotropically Etching Silicon. Inventors: Laermer, Franz, and Andrea Schilp. Issued Mar 26, 1996. ²Shaw, Kevin, Lisa Zhang, and N.C. MacDonald. SCREAM I: A Single Mask, Single-Crystal Silicon, Reactive Ion Etching Process for Microelectromechanical Structures. Sensors and Actuators, Vol 40, 1994, pp. 63-70.
2:40 PM		MM-ThA-3 The Design, Fabrication and Characterization of a Thermal Microprobe Yongxia Zhang, Yanwei Zhang (New Jersey Institute of Technology); J. Blaser, T. Sriram, A. Enver (Digital Equipment Corporation); R.B. Marcus (New Jersey Institute of Technology) A thermal microprobe has been designed and built for high resolution temperature temperature sensing. The thermal sensor is a thin-film thermocouple junction at the tip of an Atomic Force Microprobe (AFM) silicon probe needle. Only wafer-stage processing steps are used for the fabrication. For high resolution temperature sensing it is essential that the junction be confined to a short distance at the AFM tip. This confinement is achieved by a controlled photoresist coating process. Experiment prototypes have been made with a Au/Pd junction confined to within 0.3 micron of the tip, with the two metals electrically seperated elsewhere by a thin insulating oxide layer. Cantilevers are 200-450 microns long,1-3 microns thick, and 20-40 microns wide, with resonant frequencies in the range 10-100 kHz. The device is designed for insertion in an AFM instrument so that topographical and thermal images can be made with the same tip. Large contact pads permit mechanical and ohmic contacting with spring clamps. Processing begins with double-polished, n-type, 4-inch-diameter, 300 microns thick silicon wafers. Atomically-sharp probe tips are formed by a combination of dry and wet chemical etching, and oxidation sharpening. The metal layers are sputtering deposited and the cantilevers are released by a combination of KOH and dry etching. The thermal mass is kept low in order to cause minimal disturbance of the component under measurement and maximum temperature sensitivity. A resistively-heated calibration device was made for temperature calibration of the thermal microprobe over the temperature range 25-110 °C. Over this range the thermal microprobe is 4.5-5.6 µV/°C and is linear.
3:00 PM		MM-ThA-4 Microfabrication of 3D-microcoil for Miniature NMR Spectrometer Y. Xu, G. Friedman (University of Illinois, Chicago); P. Neuzil (Stanford University); A. Feinerman (University of Illinois, Chicago) Miniature Nuclear Magnetic Resonance (NMR) Spectrometer has many prospective applications in chemical analysis, materials study and biological study. The micro RF sensing coil is the critical part of the spectrometer. We choose spiral shape coil having flat wire geometry to improve the sensitivity and reduce signal to noise ratio (SNR). The multi-turn microcoils are made on cylindrical fiber by regular UV light lithography using a specially designed mask. The method is novel and simple. The charateristics of the coil are to be measured.