3.155J/6.152J Lecture 12,
MEMS Lab Testing
Prof,Martin A,Schmidt
Massachusetts Institute of Technology
10/20/2003
Information on Quiz
Wednesday,Oct,22,in-class
Closed Book
Covers lecture materials covered in problem
sets through lithography
Five questions,20 pts,each
A formula sheet will be provided
Sample quizzes from previous terms and the
formula sheet are on the course web site
Spring 2003 – Prepared by C,Ross
Fall 2002 – Prepared by R,O’Handley
Content somewhat different from this term
Fall 2003 – M.A,Schmidt 3.155J/6.152J – Lecture 12 – Slide 2
Outline
Review of the Process and Testing
Mechanics
Cantilever
Fixed-Fixed Beam
Second-order effects
Residual stress
Support compliance
References
Senturia,Microsystems Design,Kluwer
Fall 2003 – M.A,Schmidt 3.155J/6.152J – Lecture 12 – Slide 3
The Process – Lab 1
Grow 1.0Pm of Si-Rich Silicon Nitride (SiN
x
)
LPCVD Process (details to follow)
Characterize (UV1280)
Thickness
Refractive index
Fall 2003 – M.A,Schmidt 3.155J/6.152J – Lecture 12 – Slide 4
The Process – Lab 1
Pattern Transfer
Deposit photoresist
Expose on contact aligner
Plasma etch using SF
6
chemistry
Strip resist
Fall 2003 – M.A,Schmidt 3.155J/6.152J – Lecture 12 – Slide 5
The Process – Lab 2
KOH Undercut Etch
20%,80C
Fall 2003 – M.A,Schmidt 3.155J/6.152J – Lecture 12 – Slide 6
The Process – Lab 3
Break the wafer into die
Mount the die on a metal plate
Test using the Hysitron Nanoindenter
F
w
Fall 2003 – M.A,Schmidt 3.155J/6.152J – Lecture 12 – Slide 7
Testing
Cantilever
Young’s Modulus
Fixed-Fixed Beams
Young’s Modulus
Residual Stress
Fall 2003 – M.A,Schmidt 3.155J/6.152J – Lecture 12 – Slide 8
The Mask
Fall 2003 – M.A,Schmidt 3.155J/6.152J – Lecture 12 – Slide 9
The Mask - Cantilevers
Fall 2003 – M.A,Schmidt 3.155J/6.152J – Lecture 12 – Slide 10
The Mask – Fixed-Fixed Beams
Fall 2003 – M.A,Schmidt 3.155J/6.152J – Lecture 12 – Slide 11
Fall 2003 – M.A,Schmidt 3.155J/6.152J – Lecture 12 – Slide 12
Cantilever Data
0
2
4
6
8
10
12
0 100 200 300 400 500 600
Displacement (nanometers)
For
c
e
(
m
i
c
r
o
N
e
w
t
ons
)
F = k x
Material Properties,Elastic/Plastic
Fall 2003 – M.A,Schmidt 3.155J/6.152J – Lecture 12 – Slide 15
Material Properties,Brittle
Fall 2003 – M.A,Schmidt 3.155J/6.152J – Lecture 12 – Slide 16
Fall 2003 – M.A,Schmidt 3.155J/6.152J – Lecture 12 – Slide 23
Fixed-Fixed Beam
0
200
400
600
800
1000
1200
1400
1600
1800
0 500 1000 1500 2000 2500 3000 3500
Displacement (nanometers)
Loa
d (m
i
c
r
o
N
e
w
t
ons
)
Fixed-Fixed Beam,Large Displacement
Beam stretches under large displacement
Becomes ‘stiffer’
Solved by Energy Methods
c = w
Ref,Senturia (Kluwer)
Fall 2003 – M.A,Schmidt 3.155J/6.152J – Lecture 12 – Slide 24
Effect of Residual Stress
Not an issue in cantilevers
For a point load,F,in the center of a bridge
Important when
Ref,Senturia (Kluwer)
Fall 2003 – M.A,Schmidt 3.155J/6.152J – Lecture 12 – Slide 27
MEMS Lab Report
Report Young’s Modulus extracted from
Cantilevers
Fixed-Fixed Beams
Explain differences from ideal theory
Compare to literature values for mechanical
properties
Assess the effects of,
Residual stress
Estimate from measurements
Experimental error
Compliant supports
Beam versus Plate
Others….
Fall 2003 – M.A,Schmidt 3.155J/6.152J – Lecture 12 – Slide 29