Temperature Sensitive Micro-electro-mechanical

Systems

Amy KumpelRichard Lathrop

John SlaninaHaruna Tada

Tufts UniversityTAMPL REU 1999

Overview

• Background information of T-MEMS– current project goals

• Experimental Setup– recent modifications

– how it works

• Experimental Results– imaging

– numerical model

• Conclusion and future work

An Introduction to T-MEMS

• Measurement and characterization– mechanical properties of micro-scale devices– thermal properties of device materials under

high temperatures

• Application to rapid thermal processing (RTP)

Composition of T-MEMS

• Tri-layered cantilever beams• 1.03 m SiO2, 0.54 m poly-Si

• 0.19 m SiO2 (thin, protective coat)

0.19 m SiO2

1.03 m SiO2

0.54m poly-Si

Si substrate

Composition of T-MEMS

• Tri-layered cantilever beams• 1.03 m SiO2, 0.54 m poly-Si

• 0.19 m SiO2 (thin, protective coat)25 m well etched into Silicon substrate

• Beams are processed at 840°C– initial experimental condition is room temperature

• Upward room temperature curvature– due to differences in th of poly-Si and SiO2

(beams bend downward when heated)

• Initial curvatures vary with material and/or deposition rate– typical curvatures range from 5 to10 m for a

100m poly-Si beam

Fabrication Process

SiO2

Poly-Si

Our Goals

• Modify the experimental setup to decrease system error

• Collect curvature data from poly-Si beams• Determine Young’s Modulus, E(T), and the

coefficient of thermal expansion, (T), of thin films (poly-Si, SiNx) at high temperatures

• Improve method for curve fitting and resolution analysis

CCD camera

collimatedlight sourcebeam splitter

Al reflector

quartz plate

W-halogen lamp and housing sample

thermocoupleSi wafer

quartz rod

Experimental Setup

Modifications

• Fixed Mounting– CCD camera, beam splitter, collimated light source

• Leveling– all surfaces with mounting plates or rods– the system is leveled to the Silicon wafer (sample)

• Alignment– collimated light source to beam splitter – CCD camera to beam splitter

• light source centered in the IMAQ image when aligned

Experimental Setup with Modifications

Experimental Procedure

• Center sample to CCD camera• Heat T-MEMS (slowly) to ~800°C using W-

halogen lamp then gradually cool to room temperature

• Save the beam image every ~20-30 seconds during the run

• Set LabVIEW SCXI program to record temperature vs. time data

Imaging Results

0

100

200

300

400

500

600

700

800

900

1000

0 60 120 180 240 300 360

tem

per

atu

re (

°C) 120 sec

180 sec0 sec

210 sec

270 sec

300 sec

60 sec

240 sec

time (seconds)

Imaging Results

Deflection vs. Temperature

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 100 200 300 400 500 600 700 800 900

Temperature (deg C)

Def

lect

ion

(m

icro

ns)

Determining E(T) and (T)

• Two material properties approximate beam

curvature for both Poly-Si and SiO2

– Young’s Modulus (E)

– Coefficient of Thermal Expansion ()

• Estimate E(T) from previous publications

• Find a best fit (T) using a numerical model

of the thin film poly-Si layer

Preliminary Results for (T) of Poly-Si

0.E+00

2.E-06

4.E-06

6.E-06

8.E-06

1.E-05

0 200 400 600 800

Temperature (°C)

Co

eff

icie

nt

of

Th

erm

al

Ex

pa

ns

ion

Conclusion

• Modified setup for increased accuracy

• Acquisition of data with new setup

• Used numerical method for determining the thermal properties

Future Work

• Create x-y-z stage for easy movement of sample

• Take more data with new setup

• Modify numerical method for thermal properties

• Get more values for E(T) and (T)

• Modify LabVIEW programs

• Help Haruna with her thesis

• MACIS or MANTIS?

Any Questions

For Us?