1. Automatic Pinhole-filter Alignment of a Diffraction Phase Microscope for Wafer Defect Inspection
Melissa Crawford, Renjie Zhou, and Prof. Lynford Goddard
Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign
My experiment
Introduction
Results
Replicated part of a defect inspection setup for automatic pinhole alignment experiment
Created code using Labview to align the system for “first light” from the pinhole
Organized and put together parts for creating interchangeable pinhole holders
Aligning the system as new parts are added
Semiconductor manufacturers want to be able to detect defects
Main methods of defect inspection:
Scanning electron microscopy
Optical microscopy- favored for inline inspection given it is nondestructive
The alignment system works most of the time, but there are still some runs that have to be repeated
We are still working on figuring out the best scanning protocol to use
Motivation 1 2 3 7 6 5 4
First order
The DPM system has to be very precisely aligned:
Manual alignment can take from hours to days
An automatic system could shorten the time to minutes and allow anyone to align the system
Zero order
Diffraction Phase Microscopy (DPM)
Preliminary results for a one axis test +1
The plot above was generated from a one axis scan. The initial peak is where the zero order beam goes through the filter. The secondary smaller peak only occurs when the first order beam passes through the pinhole. -1
My setup in the lab
Diffraction Orders
This half of the setup I replicated!
Future Work
Integrating this alignment system with the entire microscope inspection setup is the next step
Ongoing modifications in order to achieve higher success rates in less time
Pinhole filter
+1 order
0 order 1
Collimator 2
Collimation lens
635 nm laser incident on the wafer surface
Reflected beam goes through a diffraction grating, creating multiple beam orders
The first order beam is filtered through a 10 µm pinhole, while the zero order passes through unchanged
Interferogram is formed on the camera for retrieving the phase and amplitude information from the wafer.
Acknowledgments 3
Diffraction grating 4
Fourier lens
Thanks go to Renjie Zhou and Prof. Lynford Goddard for their support and guidance throughout this project and also to the Semiconductor Research Corporation (SRC), the PURE committee, and to Rockwell Collins for giving me the chance to work on this project. 5
Pinhole filter 6
Image lens 7
detector