Design, fabrication, and characterization of a compact magnetron sputtering system for micro/nano fabrication

Abstract

A general rule of thumb for new semiconductor fabrication facilities (fabs) is that revenues from the first year of production must match the capital cost of building the fab itself. With modem fabs routinely exceeding $1 billion to build, this rule serves as a significant barrier to entry for groups seeking to commercialize new semiconductor devices aimed at smaller market segments which require a dedicated process. To address this gap in the industry, we are developing a I" Fab line of dedicated tools which processes small 1-2" wafers and feature the same functionality as large-scale commercial micro/nano fabrication tools, but with a significant reduction in cost and footprint. To enable the envisioned 1" Fab a reality, this thesis describes the design, development and testing of a sputtering physical vapor deposition tool, a critical tool in the 1" Fab line of tools.

The tool is designed to be compatible with the 1" Fab's four-module, modular tool infrastructure, and also to allow for sharing of its peripheral equipment with other components of the 1" Fab. The modularity feature allows for multiple tools be created using an interchangeable tool platform while the shared backend equipment feature allows for a sizable cost-saving benefit, as the cost of peripheral equipment for any given tool is up to 70% of the tool's total cost. Our developed sputtering tool features the successful implementation of these two design components with a final build cost of around $25k - roughly one-seventh of the cost of a commercial tool. The sputtering tool's performance was fully characterized for both reactive and nonreactive sputtering processes. The tool's non-reactive metal depositions were examined in detail using a design of experiment response surface model.

Deposition rates of up to 5.5 A/s were observed while maintaining a uniformity of ~3% across the wafer. Utilizing a direct sputter technique, this represents a deposition rate that is 4x faster than state of the practice tools while also attaining the same level of uniformity. Alongside the development of metal depositions processes, the reactive sputtering capabilities of the tool were also demonstrated through successful process development for the deposition of Aluminum Nitride (AlN). Three unique operation regions, for AlN reactive sputtering were discovered with the highest quality AlN depositions observed in transition region. Stable and repeatable depositions were achieved via the development of two control methods - voltage control and flow control. Using this optimized process, highly c-axis aligned films with columnar growth structures were observed indicating the production of high quality AlN films.

This successfully developed tool alongside its optimized processes is well suited for integration into the 1" Fab, further enabling the realization of our envisioned low-cost micro/nano fabrication platform.