11/8/ Microplasma Optical Emission Spectrometer (MOES) on a chip SFR Workshop November 8, 2000 Michiel Krüger, David Hsu, Scott Eitapence, K. Poolla, C. Spanos, D. Graves, O. Solgaard Berkeley, CA 2001 GOAL: to build a microplasma generating system and test it with bulk optical components by 9/30/2001.

11/8/ Motivation and background Motivation –Precise detection of compounds near substrate required during semiconductor manufacturing –Organic compounds, emitted during DUV, can coat optics of stepper Background –Small atmospheric pressure glow discharges can be used for species excitation. –Glow discharge optical emission spectroscopy has long history in analytical chemistry

11/8/ Microplasma Optical Emission Spectrometer Basic idea: –OES from plasma reveals info about gas composition in chamber Interdisciplinary: –plasma physics and chemistry –MEMS processing –optics and metrology Inter-departmental: –chemical engineering –electrical engineering –mechanical engineering

11/8/ MOES (cont.) Generation of plasma with hollow cathode Generation of plasma possible if: 0.05<p. D<10Torr. cm Smaller diameter (  75  m) allows plasma generation at atmospheric pressure! This results in smaller sensor Many applications in (and outside!) IC processing industry (for example in lithography) D cathode dielectric anode plasma  mm

11/8/ Schematic of initial MOES experimental configuration detector array grating lens Combination of –Bulk optical optical components –Microplasma chamber, fabricated in Si substrate Light emitted from discharge is captured by lens and collimated onto grating Diffracted light from grating is focused on detector array to record spectrum

11/8/ Mica dielectric (drilled hole) Silicon chip with 200  m hole and aluminum cathode Molybdenum anode First experiments: plasma in 200  m hole, 100Torr N 2 ambient vacuum chamber chip mica dielectric molybdenum

11/8/  200  m  0.7  m  1  m substrate poly-Si SiO  m Currently fabricated in UCB Microlab Relatively simple to make XeF 2 etch to achieve required depth and undercut Very small diameters, i.e. high pressure, possible cathode anode plasma

11/8/ Fabrication process and challenges Fabrication –OES cavity defined by deep reactive ion etching/XeF 2 isotropic etch –anode/cathode defined on front and backside of wafer (metal or doped Silicon) Challenges –Microplasma stability and contamination –Device sensitivity –Packaging of device –Exploration of pulsed operation to make autonomous power supply possible –Integration of micro discharges onto chips for other applications

11/8/ and 2003 Goals Build micro-optics for spectral analysis. Complete the preliminary designs for integrated MOES, by 9/30/2002. Design and test integrated MOES. Calibration studies, sensor characterization, by 9/30/2003.