11/8/2000

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Microplasma Optical Emission Spectrometer (MOES) on a chip

SFR WorkshopNovember 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.

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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

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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

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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

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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

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Mica dielectric(drilled hole)

Silicon chip with 200m hole and aluminum cathode

Molybdenum anode

First experiments: plasma in 200m hole, 100Torr N2 ambient

vacuum chamber

chip

mica dielectric

molybdenum

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200m

0.7m 1m

substrate

poly-SiSiO2

50-200m

Currently fabricated in UCB Microlab

• Relatively simple to make

• XeF2 etch to achieve required depth and undercut

• Very small diameters, i.e. high pressure, possible

cathode

anode

plasma

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Fabrication process and challenges

• Fabrication– OES cavity defined by deep reactive ion etching/XeF2 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

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2002 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.