Thụ động hóa bề mặt silicon: Vật lý và hóa học - Luận án tiến sĩ

PHYSICS AND CHEMISTRY OF SILICON SURFACE PASSIVATION Thesis by David J. Michalak In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy CALIFORNIA INSTITUTE OF TECHNOLOGY Pasadena, California 2006 (Defended December 15, 2005) UMI Number: 3235586 INFORMATION TO USERS The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleed-through, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted.

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ProQuest Information and Learning Company 300 North Zeeb Road P. Box 1346 Ann Arbor, MI 48106-1346 © 2006 David Michalak All Rights Reserved Acknowledgements Caltech is truly an amazing place. The source of Caltech’s greatness really stems from the truly diverse and amazingly talented people here. I have had the pleasure to interact with countless colleagues who are not only excellent at science, but in other dimensions as well.

Because so many of these people have been instrumental in my development, both scientifically and personally, I will attempt to mention and thank as many of them as possible in the next few pages. First and foremost is my academic advisor Nate Lewis. Nate is truly an amazing scientist and advisor. He has allowed me the intellectual freedom to pursue those scientific directions that piqued my curiosity.

In lab, I was also allowed the freedom to hypothesize, try, fail, reconsider, and iterate all on my own: a usual sequence of events that practiced my scientific development and developed my confidence. Yet at the same time, Nate could always identify within 5 minutes the source of a problem that had me occupied beyond my means. In addition to being an excellent academic advisor, Nate has been a good friend through many adventures, whether mountain biking, windsurfing, jet skiing, or killing horses. Many of my close friends have been fellow Lewis groupies.

I met Elizabeth “Libby” Mayo as a prospective graduate student at Caltech some weekend in early March 1999. Since then, we have gotten ourselves involved in countless wild ideas, pranks, and ridiculous experiences. Shawn “Sean” Briglin idealizes the perfect friend. Our discovery of mountain boards, master plans, and the San Gabriel Mountains has sent us on numerous, and occasionally near-death, adventures.

Libby, Sean and I were co-founders of the “Skate Squad” TV show, which served as an excellent source of distraction from the intellectual iv stresses of grad school. Florian Gstrein has been an excellent friend and scientific colleague over the past several years. Florian and I collaborated on several projects, and I can fondly remember the countless hours we’d spend together working in the lab or trying to understand the data we had just collected. Lauren Webb and I have braved trips to Brookhaven, Rutgers, Stanford, and probably some other places I’ve since forgotten.

Pat Hurley, David Knapp, and Matt Traub have been great friends and scientific colleagues; I wish we could have spent more time together. During my first couple years at Caltech, Rob Rossi and Will Royea were extremely helpful at introducing me to the field of semiconductor surface science. Bruce Brunschwig, the director of the Molecular Materials Research Center (MMRC), has been a wonderful academic resource, knowledgeable on countless subjects, and he has also been a great friend with an excellent personality. The Lewis group is blessed with an administrative staff that flawlessly runs all behind-the- scenes activities making payment reimbursements, travel arrangements, and grant submissions easy.

Outside her usual duties, Nannette Pettis invited the group to her house for numerous Calzone nights and even let a bunch of us, wielding sledge hammers and axes, bring downa large shed in her back yard. In addition to running everything perfectly, Sherry Feick has increased the morale of the whole group by spoiling us with various baked goods, her caring attitude, and her ceaseless sense of good humor. Sherry has been a great friend and colleague I will miss. From Thai Elvis, to brick oven pizza, to wild parties, all the Lewis group members have made the lab an enjoyable place to be.

I am also grateful for mentorship and friendships outside the Lewis group. Not only have I learned from a wide range of great classes, but the members of my committee have been excellent as well. Rudy Marcus represents an ideal role model on a scientific : and personal level; it has been a joy to learn from him. I have also benefited from both the scientific rigor and friendship of Pat Collier, the latter of which was developed over a margarita (or two) at Amigos and during the re-creation of ZZ Top songs.

Harry Gray, the most recent addition to my committee, has been a great source of guidance and support for academics as well as life. He, Jonas Peters, and David Goodstein took the time to chat with me and my dad about science policy. All of these professors exemplify the caring and interdisciplinary nature that makes Caltech one of a kind. A good friend is one who will selflessly spend many hours helping you overcome your own research problems, and for this reason I am in great debt to Robert Strittmatter, who spent countless hours helping me to understand and repair a broken contactless photoconductivity decay apparatus.

Tom Dunn has also been very helpful whenever I was confronted with equipment no longer working. I am also thankful for the excellent work of Lillian Kremar in the purchase department, who flawlessly sent various chemicals to various cities around the country at short notice. Dian Buchness has beena great co- conspirator in Holiday party planning. And I also have to thank Joe Drew for not getting too upset when Julie and I, caught by security, almost dumped his cart in Millikan pond one fortuitous Holiday-party evening.

Outside of lab, I have been extremely lucky to live in the same city as my best friend from home (the Lancaster, PA, ‘hood). As my closest and oldest friend, Jay Olin has always been there to provide the necessary mix of keeping it real, experiencing new things, and mixing with the Caltech crowd. From music, to games, to filming, to mountain boarding, to just chilling, Jay has been a great part of my life and social group at Caltech. Thanks buddy! Vi I have enjoyed a closer relationship with my sister, Sarah, over the past several years; her visits over holidays and other breaks have always been fun.

My mom has been a great support over the past several years, and it’s been wonderful to share beach holidays with her in California. I have also really enjoyed playing jazz with my dad when he and Bev come for visits. I look forward to seeing more of my parents while I’m on the East Coast for the next couple months. Lastly, and most importantly, is Juliane Fry.

She has been a never-ending, and much-needed, source of optimism, hope, and love. It has been truly wonderful to spend the last several years with her talking science, relaxing with friends, and escaping on diverse mini-breaks. We have battled several moves, day-to-day grad school life, and most recently the thesis process together. She has provided an endless source of support and also the necessary dose of distraction.

I look forward to experiencing the next stages in life together. I love you, Jules! This acknowledgement would be incomplete without a listing of the many other people who have meant more to me than such a simple list can justify. I have been really lucky to live, as roommates, with so many easy-going yet vivacious people such as Theofilos Strinopoulos, Jamie Lindfors, Brett Maune, and, more recently and for a longer time, Juliane Fry, Wendy Belliston Bittner, Garrett Bittner, Christine Ueda, and fellow honorary housie Robert Dirks. Other honorary housemates that have provided much joy and entertainment are Maria Campa, David Knapp, and Donna, Oded, and Charlie Aharonson.

It has been great sharing life with all of these creative and fun individuals. Music is a great hobby of mine and it has been a joy to play with such talented musicians as long-time friend and excellent musician, Jay Olin, with whom we wrote the vũ “Skate Squad” soundtrack and formed the death metal band, “Toxic Waste.” With fellow Toxic Waste-er and Donkey Show-er Colin Cameron, I discovered the joys of weird time signatures. Andrew Spakowitz and I have been playing music together since I first arrived at Caltech, and we’ve shared a fun evolution of various types of music (on various instruments) over the years: Andrew Spakowitz, Colin Cameron, Nicholas Wisniewski, and I as “The Donkey Show”; Andrew Spakowitz, Brendan Kayes, Francis, Lady Lo, and I as the unnamed Hip-Hop, Reggae fusion band; and many other bands with too many guitarists. In this last hour, I’m sure I’ve missed many people very important and dear to me.

While my foggy head missed thanking you on paper, know that, at moments of higher clarity, I have not forgotten your help, support, and love. Lastly, I want to thank all of the people who have spent several hours with a nut who thinks making a TV show about cops on skateboards is a good idea. While the premise for “Skate Squad” is quite abstract, all of the dedicated help from numerous friends has made it something far better than I could have ever hoped for. Thanks! vi Abstract Low interfacial electron-hole recombination rates are essential for low-noise electronic devices and high-efficiency solar energy converters.

This recombination rate is dependent on both the surface electrical trap state density, Nr„, and the surface concentrations of electrons, ø;, and holes, ø;. A reduction in Nr, is often accomplished through surface chemistry, and lower recombination rates, through lower Nr, values, have been demonstrated in this work for surfaces chemically treated to produce methoxylated, Si-O—CHs, overlayers. The H—Si(111) surfaces can react with methanol quickly in the presence of an oxidant or slowly in neat anhydrous methanol. Mechanisms have been proposed for both reactions.

Low recombination rates can also be achieved through control of the surface physics; a large ø; or ps can lower recombination rates. To date, low recombination rates have often been attributed only to a reduction in Nz, without a direct measurement of n, and ps, partly because the importance of v, and p; has not been fully recognized and partly because an accurate evaluation oŸz; and ø; can be very difficult. Surface recombination rates of silicon immersed in liquids containing various redox species (e., Fe” ° Ib, MetgFe”°, or CoCp2””) were studied using an rf photoconductivity decay apparatus and compared with n, and p, values obtained from Mott-Schottky and other analysis techniques. The results demonstrate that the observed recombination rates can only be correlated with Nr.

values when n, ~ ps. In all other cases, the recombination rate was low due to a large mở; or p; even for surfaces with large Nr. 1X The full impact of this work was further realized through a study of the recombination rates of H—-Si immersed in solutions of 48% HF, 40% NH4gF, and buffered HF (BHF), because such measurements are often performed for in situ monitoring of the surface quality during wafer processing steps. Our results demonstrate that only HF contacts can be used for in situ monitoring because n; ~ p;.

For NH4F or BHF contacts, low recombination rates were observed only because ø; >> ?;, and Nr, cannot be inferred from these measurements. Table of Contents Acknowledgements .cccccccssessecsstsessesseceesseesseceeseseceeeeseeeeseneesneeeesesesneeeesneseaesnesates iii ÂU -ö:ỞÖ O. Vili Table of COn€TIẲS. LH HT HH ng TH ng TK HH kh HH ni X List Of Figures 1n .