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Research

Archived Projects

Research projects that are a bit older have been moved to this page. We're not saying you're old — just kind of marinated.


Comparison of Techniques for Polysilicon Residual \ Stress Measurements

Experimental work comparing wafer curvature measurements, micro-rotating structures, buckling microstructures, and vibrating microstructures for the measurement of residual stresses in thin polysilicon films.

Student: Andrew Mueller, ME Masters of Science student.
Advisor: Prof. White, ME

     
SEM images of surface-micromachined polysilicon structures developed at Tufts by Andrew Mueller and Robert White. Fabrication was conducted partly at the Tufts Microfab, partly at the MIT Microsystems Technology Laboratory and partly at the University of Michigan Nanofabrication Facility.


Calibration Targets for Dual Emission Laser Induced Fluorescence (DELIF)

Calibration wafers have been fabricated to calibrate an optical measurement technique called Dual Emission Laser Induced Fluorescence (DELIF), which is used to determine fluid film thickness between a glass wafer and a polishing pad during Chemical Mechanical Polishing (CMP). Sqaure wells measuring 1mm2 and 0.25mm2 are etched into these glass wafers to known depths (up to 130um). The necessary well etch depth depends on the surface roughness of the polishing pad. In order for fluid layer thickness difference under the wells to be detectable, the well depth should be at least 3 times the surface roughness of the pad.

Student: Caprice Gray, ME PhD student.
Advisors: Prof. Rogers, Prof. nno, Prof. White, ME

  
(Left) Photograph of etched glass calibration wafers used to determine thin fluid film thickness during DELIF.
(Right) A light microscope picture of a single 1mm2 calibration well 23 microns deep.


Micromachined Shear Stress Sensors for in-situ Monitoring of Surface Forces in ChemiMechanical Planarization

A PDMS microstructure is being developed to measured the interaction forces that occur between a wafer and a polishing pad during CMP. The PDMS structures deflect in response to fluid forces and solid-solid contact forces. An optical method is used to monitor structure deflection in-situ.

Student: Minchul Shin, ME PhD student, Doug Gauthier and Andrew Mueller, ME Masters of Science students.
Advisor: Prof. White, ME

  
(Left) SEM image 30 micron diameter, 100 micron tall PDMS post-in-well developed for the CMP shear stress sensor project.
(Right) Angled light microscope picture showing a portion of the array with different sized PDMS posts-in-wells.


Thermal Design and Fabrication of Microscale Heaters

Microscale heaters with integrated thermistors were fabricated as an undergraduate research project. The devices use thin sputtered nickel films for both heating and sensing elements. The processes involved were standard photolithography, sputtering, and liftoff. Some of the heaters were functional, and some failed. Residual stresses, particles, and/or human error in processing appear to have caused the observed defect in some of the heater lines.

Student: Michael Rizzolo, ME undergraduate.
Advisor: Prof Wong, ME