AVS 47th International Symposium
    MEMS Wednesday Sessions
       Session MM-WeA

Paper MM-WeA10
Micro- and Nanotube Fabrication using Deposited Porous Silicon

Wednesday, October 4, 2000, 5:00 pm, Room 309

Session: MEMS Processing
Presenter: W.J. Nam, The Pennsylvania State University
Authors: W.J. Nam, The Pennsylvania State University
S. Bae, The Pennsylvania State University
A.K. Kalkan, The Pennsylvania State University
S.J. Fonash, The Pennsylvania State University
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There is a great deal of interest in micro- and nano- scale tube and channel structures. Conventional polycrystalline silicon (poly Si) material has been commonly used in such structures as a sacrificial layer. However, the etch rate of conventional poly Si sacrificial layers decreases rapidly in the case of the small etch access windows needed in etching small dimension structures due to reactant and reaction product transport limitations. Porous Si produced by electrochemical etching can eliminate these problems to some degree due to the multiplicity of transport paths to the access window but its formation requires wet processing. We solve this problem by introducing a new material, porous Si deposited using a high density plasma. Our deposited porous Si, produced using low temperature electron cyclotron resonance (ECR) deposition, can be made polycrystalline or amorphous and has a porosity that is controllable (up to ~90% porosity) without the need for any post-deposition etching. Used as a sacrificial layer, the material exhibits a high etch rate (1.5µm/min) since its connected-void morphology provides excellent transport pathways for the reactants and reaction products even when etched through a small access/exit window. The fast etch rate of this deposited porous Si prevents thinning or damaging of the other structural materials. We report specifically on structures using 500 Å of silicon dioxide as the substrate coating and etch stop layer during the sacrificial (porous Si) layer removal. In these structures, silicon nitride was used for a capping layer. The sacrificial porous Si material was etched out by using 5% tetramethyl ammonium hydroxide (TMAH), at either 30°C or 75°C. All layers (etch stop, sacrificial porous Si, and nitride) were produced in the same ECR tool.