Ultrafast Optical Measurements of Aluminum Films Deposited by Chemical Vapor Deposition
Anthony L. Bartolotta ’18, Samuel A. Gartenstein ’17, Issai A. Torres ’20, Brian Daly (Physics)
We report ultrafast optical measurements of the thickness of aluminum layers deposited on various sample materials by use of a Denton Vacuum Desk Top Pro™ sputter coater. This machine produces aluminum films by means of a physical vapor deposition sputtering process. In this process argon gas is ionized in a chamber at near vacuum pressure; argon ions collide with an aluminum target, releasing aluminum atoms that coat the sample material. The motivation for coating the surface of a thin film is that it allows us to perform laser ultrasonic measurements of said film. The laser heats the aluminum layer and causes thermal expansion, sending an ultrasound wave through the aluminum and the material behind it. Using this technique we can measure the thickness of the aluminum layer and determine material properties of the underlying film. A major component of this summer’s work was using this laser measurement to calibrate the sputter coater. By taking measurements on aluminum films deposited by the sputter coater, we attempted to determine how varying sputter time and ionization power affects film thickness. By knowing how parameters of the sputter coater will affect film thickness and quality, we will be able to reliably produce coatings that are suitable for any optical measurements we would like to take. Our data shows that we can accurately predict film thickness within 5 to 10 nanometers. Additionally we took scanning electron micrographs of some of the aluminum films to observe how aluminum grain size is affected by parameters of the sputter coater, and how this relates to the thickness and optical properties of the aluminum layers. More research is to be conducted and more SEM photographs should be taken to better establish the relationship between the parameters of the sputtering process and the properties of the aluminum film.