Undergraduate Research in Engineering at Rice
Christoph Winkler, Junior Materials Science and Engineering student
Constructing a Physical Vapor Deposition System
with Dr. Suzanne Stemmer Working for Dr. Stemmer this summer (2001), I was given the task of constructing a physical vapor deposition system, which produces thin films and coatings. When I first started working for Dr. Stemmer, her research lab consisted of nothing but an old lab filled with sundry crates and boxes. Now, a fully working PVD system resides in the lab, as shown in the picture below.
Completed Physical Vapor Deposition System.
Layout: The vacuum chamber is in the center of the picture. Bolted to the chamber from the bottom is the ultra high vacuum heater. The cryopump is bolted to the chamber and is on the right. The load lock is also bolted to the chamber and occupies the foreground. Two sputter guns are installed in the chamber and they are located at the top of the picture. The electronic enclosures on the left hold the controllers for the sputter guns, gas lines and heater.Construction of the system was a long and involved process that began with the building of an eighty-one cubic foot softwall clean room, of which one support pillar can be seen in the left corner. Next, of course, all the vacuum hardware had to be mounted and bolted together. One can see that there were over a hundred bolts of various sizes that needed to be tightened and torqued to specification. Since all of the hardware was designed for ultra high vacuum service, everything had to be extremely clean. The oils in one fingerprint could easily prevent the system from reaching a good base pressure. So, while bolting together flanges does not sound difficult, the process of cleaning each piece with three solvents, blow drying with high purity nitrogen, and inspecting the equipment for microscopic pieces of dirt and fiber was definitely an involved task.
Once the hardware was properly installed, it was all tested to ensure proper, leak-free operation. To ensure a good base pressure, the chamber and components were baked at 150oC - 200oC for several hours a day, for five days. Unfortunately, the base pressure attained at that time was only 10-6 Torr, or at least two orders of magnitude higher than what we needed. I spent almost two weeks tearing my hair out trying to locate the leak. By sheer luck, I discovered that a valve and a sputtering gun were leaking severely. Once I removed these components, a base pressure of 10-9 Torr was reached, which is a better, lower pressure than we expected!
Finishing the system was all in the details. No in-house cooling water meant that a chiller would have to be used, so I was in charge of constructing custom water manifolds and lines. I was also in charge of machining shutters for the sputter guns and for the substrate holder. This was actually a large project, since the sputter guns did not come with a feed-through on the flange. We had to have the flanged drilled and professionally welded to ensure leak-free operation in an ultra high vacuum. The 'stock' sample transfer mechanism left much to be desired, so I machined a new, much easier to use and more reliable holder. This was not simple machine work, since each piece must be able to operate in ultra high vacuum, be easy to use, and easy to install. The sample holder had the additional requirement that it had to be extremely thermally conductive, so as to properly heat the substrate.
At this point, the system was mechanically complete. However, the vacuum heater need to be calibrated, meaning the temperature of the substrate - the actual temperature - needed to be correlated with the heater set point temperature. For instance, if I set the heater to 1000oC, the actual temperature of the substrate might be only 850oC due to radiant heating and other heat loss. Measuring the temperature of the substrate in high vacuum at temperatures ranging from room temperature to 1000oC was an arduous task, which required special hardware.
Finally, after most of the summer had passed, we were ready to begin experimenting! Dr. Natelson in the physics department needed me to deposit several thousand angstroms of alumina (Al2O3) onto silicon wafers. The end goal was to produce organic based semiconductors on the alumina. Thus, both the composition and quality of the alumina film I produced would determine the quality of the semiconductor. Each film I produced had to quantitatively analyzed for chemical composition, surface cleanliness, and film thickness. In this process, I was able to learn how to use two scanning electron microscopes, an energy dispersive
X-ray spectrometer system, an atomic force microscope, and several electrometers and other electronic property characterization devices. By using and becoming proficient in these pieces of equipment, I can better analyze the physical properties of the films I'll be sputtering for Dr. Stemmer.
Department of Mechanical Engineering and Materials Science
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