Method for patterning poly(acrylic acid) sacrificial layers for use in solder-based self-assembly

Abstract

Solder-based self-assembly is a method for micromachining three-dimensional structures on silicon. This process has been used for educational purposes due to the significant experience gained by students interested in semiconductor processing. However, patterning the silicon dioxide sacrificial layer, involves handling hazardous materials such as buffered hydrofluoric acid. To provide a safer alternative to this dangerous etchant, we describe a method for using poly(acrylic acid), a water soluble polymer, as a patternable sacrificial layer in the solder-based self-assembly process. Key to this method, in order of steps; is the use of thermal crosslinking, a partial development technique; oxygen plasma ashing; and a strong alkaline solution to etch the sacrificial layer and reflow the solder. Plasma ashing is important to keep water and alkaline developers from etching the vulnerable poly(acrylic acid) layer too early in the process. This method is able to achieve the goal of promoting the self-assembly of three-dimensional structures on silicon. Beyond its use in our solder-based self-assembly process, this method may also prove useful in any application requiring the use of a patternable sacrificial layer made from poly(acrylic acid), as well as other polymers of a similar nature. One such application is explored, in which the technique for patterning poly(acrylic acid) is used as a potential way to pattern crystal colloidal masks of nanospheres for use in nanosphere lithography. This technique allows for spin-coating, an inexpensive deposition technique, to be used to both form and pattern these nanosphere masks with micro-scale features. iii DEDICATION This thesis is dedicated to those professors, colleagues, fellow students, family members, and friends who helped to support and guide me on this, the start of my journey, into the world of academia. I hope that I have made, and will continue to make, all of these people proud as I move forward with my life and career. I would also like to thank all of my committee members, Dr. Dawen Li, Dr. Sushma Kotru, and Dr. Tonya Klein for their support as well. Each of them acted as professors and mentors to me in critical classes during both my undergraduate and graduate years, and they only helped to further my love for the area of research I have decided to pursue. Naturally, I would also like to thank Dr. Anthony Arduengo and Dr. Jason Runyon, both of whom acted as mentors for me in my earliest days at the university. I know that had these two chemists not entered into my life, my love for chemistry would never had blossomed and led into the work I do today. Finally, I would also like to thank everyone who has been a part of my journey these last few years of my life. Without these friends and family, I would not have made it this far. Thank