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Matthew Walker

University: The University of Tulsa
Major: Electrical Engineering & Computer Science
Gradation Date:    May 2011
Hometown: Anchorage, AK

My project dealt with the optimization and process improvement of the next generation of NIST line width standard reference materials (SRM). The production of SRM calibrated width features on the nanometer scale is useful in both research and industry for the calibration of instruments such as atomic force microscope tips, drives and other nanoscale metrology instruments. Currently NIST is attempting to reduce the uncertainty on the width of these reference materials to less than 1nm. This is a large undertaking which poses significant challenges.

On the cutting edge of research we currently employ single crystal silicon with a nitride mask patterned with focused electron beam technology followed by a anisotropic wet etching process. We then image and post process the chips in a variety of ways. Over the past summer months I have looked principally at modeling the wet etching process with an atomistic kinetic Monte Carlo simulator using a second order approximation of the system. Variables looked at in simulation include temperature, etch time, and reference feature geometry. Results from these simulations were then taken to the lab bench for further physical study and for validation / calibration of the model. This has involved me using and writing simulation and data analysis software, performing actual chemical etching of silicon, and learning how to use an atomic force microscope, a scanning electron microscope, and various other tools.

Primarily the work indicates that etching at lower temperatures (going from 90°C to the 60/40°C range) will improve roughness, however other factors do play in as well. For example, ‘notching’ the hard mask pattern works to overcome the stepflow process and promotes a smoother surface at the cost of smaller reference area. Additionally, simulation work has shown that although a smaller notch produces a worse result mathematically, it may be easier to use in calibration work. Additionally, due to the technical constraints of focused electron beam mask formation simulation work was done on possible geometry biasing.  The simulation results indicating that bowing the notch inwards (much like is done naturally in the current process) will converge on a smooth surface faster than if one bowed the notch outward.

About me:
  This is I, I am me. I was born in Alaska, moved to the UK when I was ten living in both Aberdeen and London, finishing high school in Moscow, Russia and at the time of SURF 2009 claim my home such as it is in Baku, Azerbaijan. I attend The University of Tulsa in Oklahoma with the intent of graduating with a double major in Computer Science and Electrical Engineering. This is a path I can attribute to my dad, for as the son of a petroleum engineer I suppose I have to attribute my fascination with figuring out how things work to him. It was his erector set that I first played with, and as well his collection of Legos. He always told me to never accept things at face value, to always strive to understand the whole system.

I applied to the SURF program mostly because I wanted to see what formal research was like. Overall it has been an amazing experience, you are constantly surrounded by highly intelligent people encouraging you to do your best and more to the point, allow you a tremendous flexibility in how you pursue your work. I started off this summer simply researching etching simulators and then moved into actually etching the silicon and suggesting new experiments and future work based on those results.

On the topic of futures; my own future is murky, just the way I like it. At some point in the future I would like to do two things, attend graduate school (probably in the field of electrical engineering), and work in Antarctica. Beyond that all I know is that the experiences and friends I have gained here at NIST this summer will serve me well no matter what I do, and asides; the memories of working in a bunny suit and going to concerts in the pouring rain will stick with me for life.


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Mathew Walker