1. Microsensors for Monitoring Wafer Uniformity of Plasma Processes
SFR Workshop
November 8, 1999 Ribi Leung, Dwight Howard, Scott D. Collins, and Rosemary L. Smith
MicroInstruments and Systems Laboratory
UCDavis
This work describes in-situ sensors
for peak temperature and undercut mapping of RIE processes.
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2. Abstract
The goal of this project is to realize specific microsensors for in situ plasma process monitoring.
Thin, multilayer, metal film resistors are being evaluated as surface peak temperature recording devices.
Au/Cr resistors, which are effective for 150 <T < 250 C, have been fabricated and tested in an ECR plasma tool.
Au/Al and Au/Cr/Al resistors are being evaluated for detection of T≤150C.
An RIE undercut sensor has been designed and is in the testing phase.
Temperature and undercut sensors will be integrated for combined measurements later this year.
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3. Temperature Dependence of Au/Cr Resistance
Inter-diffusion of Au/Cr is an irreversible process that produces
a permanent increase in resistivity as a function of time • Temp.
TIME FUNCTIONS (3, 6, and 10 min.)
0.9 1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
150
170
190
210
230
250
Temperature (C)
Au/Cr Interdiffusion
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4. Thin Film Resistor Pattern
4 pt probe measurement
Resistor Array
500 µm
Ri≈ 700 Ω R i
= 670 Ω
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5. Wafer Surface Resistance Map
Peak T varied from C, across 4 in. wafer
Au/Cr : Initial R variation
Au/Cr: R after ECR (6 min, 1200W, Ar) 1 2 3 4 5 6 7 8 9 10 S1 S2 S3 S4 S5 S6 S7 S8 S9 1 2 3 4 5 6 7 8 9 10 S1 S2 S3 S4 S5 S6 S7 S8 S9
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6. Au / Al Resistors Resistance Change at Lower Temperatures A u / C r l2 . 5 3 4 6 7 9 1 D E G R S N T I l
OHMS
color change
Au/Al Resistors also exhibit a visible color change at T≈ 120 C which can be a useful tool. However, these structures may be too unstable at room T to be reliable.
Interposition of a Cr layer, i.e. Au/Cr/Al, to limit inter-diffusion at Room T is under investigation.
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7. RIE Undercut Variation Sensor
Resistance determined by lateral diffusion (≈1µm) of ion
implanted dopant redistribution after drive-in.
Resistance increases with undercut
Submicron undercut yields 10-15% ∆R
Oxide mask
Polysilicon
Ion Implantation i I V
RIE
undercut
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8. Progress vs Milestones
June 1999
Determine wafer surface temperature range during RIE processing. (Preliminary Results)
Map surface temperature variation in specific RIE tools. (Done)
June 2000
Optimize materials for temperature sensitivity and range.
Test undercut sensors in RIE (in progress).
Test integrated Temperature and undercut sensors in RIE.
Determine undercut variation in specific RIE tools.
2/22/2019

9. Future Directions: A MEMS Device for T Mapping versus Time
Thermal micro-actuator positions shadow mask over etch/deposition window, creating steps in film height.
Location of step edge corresponds to
Temperature, height indicates time. T1 T2
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