1. Microstructures for Temperature Uniformity Mapping during PECVD
SFR Workshop
May 24, 2001
Dwight Howard, Eunice Lee, Scott Collins and Rosemary Smith
MicroInstruments and Systems Laboratory
Davis, CA
2001 GOAL: to demonstrate a thermal mapping array for PECVD, using thin film microstructures and/or MEMS thermal actuators by 9/30/2001.
5/24/2001

2. Motivation
Small feature reproducibility requires film thickness uniformity
Uniformity of PECVD films depends on spatial control of process parameters:
plasma composition (gas flow rates and pressure)
plasma energy (power)
substrate surface Temperature
Substrate surface temperature relies on thermal conductivity of substrate and contact of substrate to platen, and is not controlled or monitored.
A simple, tool independent, low cost, temperature mapping method for PECVD processes would provide useful data for process and tool development.
5/24/2001

3. Thin Film Temperature Sensor Metal, thin film, bilayer resistors
500Å Cr
SiO2
Silicon
Al/Cr or Al/PolySi Resistor
Effect: permanent change in R with T
Mechanism: interdiffusion, alloying, or annealing
5/24/2001

4. Al/Cr Resistors R/R0 R/R0 Temperature (C) 10 8 6 4 2 1 130 150 170 190
1.3 8
1.25
2nd Phase Formation
1.2 6
1.15 4
1.1 2
1.05
1.0 1
130
150
170
190
210
230
250
270
290
310
330
350
Temperature (C)
5/24/2001

5. Temperature Mapping Demonstration Al/Cr Resistors, 120 nm PECVD Si3N4
platen set T= 330 C
time = 10 min
SiH4 + NH3
Al/Cr
312 < TS < 330
5/24/2001

6. Al/PolySi Resistors
An alternative resistor structure employing VLSI materials
Highly reproducible effect, independent of Al thickness and underlying film, but mechanism is as yet undetermined.
5 min
10 min
20 min
Al, 600 Å
PolySi, 6000 Å
SiO2 Si
5/24/2001

7. Al/PolySi Temp Mapping Demonstration 100 nm PECVD Si3N4
Degrees, C
400
350
300
250
Platen T=300C
300 < T < 380 C
5/24/2001

8. MEMS Thermal Actuator (remaining task for 2001)
Aluminum, 1 mm
Cantilever Beam
Silicon, 2 mm
aAl=23(10-6) C-1 aSi=2.6(10-6) C-1
Silicon
Thermal expansion coefficient mismatch strain displacement
T= T0
T1 >T0
TC>T1
TC depends on geometry of cantilever.
Array of microstructures with varying TC.
Readout can be an optical imager.. in situ or post processing.
5/24/2001

9. Thermal Actuator as Temperature Sensor
Al/polySi Bimetal Actuator T
Bending Cantilever Beam
Buckling Microbridge
5/24/2001