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Stresses in Thin Films Final Presentation. Cynthia Macht, Nick Svencer, Heather Stern Tufts University, TAMPL July 31, 1998. Overview. Initial Goals Setup Modifications Samples Data Conclusions. Initial Goals. Design and Construct Apparatus Fabricate Samples

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Stresses in thin films final presentation

Stresses in Thin FilmsFinal Presentation

Cynthia Macht, Nick Svencer, Heather Stern

Tufts University, TAMPL

July 31, 1998

TAMPL


Overview
Overview

  • Initial Goals

  • Setup Modifications

  • Samples

  • Data

  • Conclusions

TAMPL


Initial goals
Initial Goals

  • Design and Construct Apparatus

  • Fabricate Samples

  • Test Thin Film Samples for Stress and Relaxation at High Temperatures

    • Polymers

    • Silicon Wafers

  • Analyze Data

TAMPL


Final apparatus
Final Apparatus

  • Split-Beam Laser Technique

  • Heater Raised Around Sample

  • Stainless Steel Sample Holder

  • Quartz Plate

  • Two Fans

  • Thermocouples

TAMPL


Quartz

Plate

TAMPL


Final apparatus continued
Final Apparatus Continued

New Sample Holder

-Stainless Steel

Higher Temperatures

-58% Open Space

Fans in Place on Heater

-Reduces Convection

Currents Above

Quartz Plate

TAMPL


Laser Schematic

Large Mirror

Wall

x

laser

Beam

Splitter

Mirror

S

Sample

R

TAMPL


Obstacles to dot measurement
Obstacles to Dot Measurement

  • Extremely Slight Bending of Silicon Wafers

    • Difficult to Detect Change in Dot Distance

  • Dots Change Shape During Experiment

    • Loss of Reference Point

Human Error

CCD Camera

TAMPL


Polystyrene samples
Polystyrene Samples

  • Brass Substrate

    • Thickness .010-.031”

  • Polystyrene Film

    • Thickness .006-.007” +/- .001”

    • Polymer Sold by Polaroid

TAMPL


Formulas to Determine Stress of Thin Films

Curvature

Where, K=curvature, R=radius of curvature,

x=distance between laser dots on wall,

S=distance between dots on sample

L=total length traveled by laser beam

Stoney Formula

Where =stress of the film,

=Young’s modulus of the substrate

=thickness of substrate

=Poisson’s Ratio of the substrate

=thickness of the film

TAMPL


Polystyrene Relaxation curve, average temp = 344.45°K,

time constant = 1/.013244=75.51s

Time vs. Change in Curvature of .010”Brass/.006±.001”Polystyrene

Change in Curvature (1/m)

Time (s)

TAMPL


Polystyrene Relaxation Curve, average temperature = 330.75°K

time constant =1/.03199=31.26s

Time vs. Change in Curvature of .010”Brass/.007±.001”Polystyrene

Change in Curvature (1/m)

Time (s)

TAMPL


Polystyrene Relaxation Curve, average temperature = 351.19°K

time constant =1/.01739=57.50s

Time vs. Change in Curvature of .031”Brass/.006±.001”Polystyrene

Change in Curvature (1/m)

Time (s)

TAMPL


Polystyrene conclusions
Polystyrene Conclusions 351.19°K

  • Relaxation time constant range of polystyrene 31-76 s

TAMPL


Silicon wafers fabricated by northeastern university
Silicon Wafers 351.19°KFabricated by Northeastern University

  • Silicon Nitride on Silicon Wafer (SiNx)

    • Silicon Nitride Thickness 840 Å

    • Silicon Substrate Thickness .37 mm

  • Silicon Dioxide on Silicon Wafer (SiO2)

    • Silicon Dioxide Thickness 1970 Å

    • Silicon Substrate Thickness .37 mm

TAMPL


TAMPL 351.19°K


Formulas for Thin Film Curvature 351.19°K1

1Townsend, Barnett, & Brunner, 1987.

TAMPL


Silicon: Coefficient of Thermal Expansion = ~3.58E-6/ºC 351.19°K

Young’s Modulus = 1.30E11 Pa

TAMPL


Silicon oxide conclusions
Silicon Oxide Conclusions 351.19°K

  • Coefficient of thermal expansion of Silicon Oxide is slightly smaller than that of Silicon which is ~3.58E-6

TAMPL


TAMPL 351.19°K


Silicon: Coefficient of Thermal Expansion = ~3.58E-6/ºC 351.19°K

Young’s Modulus = 1.30E11 Pa

TAMPL



TAMPL 351.19°K


Silicon nitride conclusions
Silicon Nitride Conclusions 351.19°K

  • Coefficient of thermal expansion of SiNx is slightly smaller than that of Silicon which is ~3.58E-6

  • SiNx relaxes at 773ºK

TAMPL


Final conclusions
Final Conclusions 351.19°K

  • Developed an instrument to measure curvature in a variety of thin film materials, from polymers to semiconductors

TAMPL


Visit Our Web Site At: 351.19°K

http://www.tufts.edu/~nsvencer/stressmain.html

TAMPL


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