Microplasma Optical Emission Spectrometer (MOES) on a chip

1
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.
2
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

3
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

4
MOES (cont.)

• Generation of plasma with hollow cathode
• Generation of plasma possible if
  0.05ltp.Dlt10Torr.cm
• Smaller diameter (?75 mm) allows plasma
  generation at atmospheric pressure!
• This results in smaller sensor
• Many applications in (and outside!) IC processing
  industry (for example in lithography)

D
5
Schematic of initial MOES experimental
configuration

• 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

6
First experiments plasma in 200mm hole, 100Torr
N2 ambient
molybdenum
chip
mica dielectric
vacuum chamber
7
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

plasma
cathode
anode
8
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

9
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.