UNIVERSIDAD DE LA REPÚBLICA ORIENTAL DEL URUGUAY UNIVERSITÉ DE LIMOGES (FRANCE) CO-ADVISED THESIS For the degree DOCTOR EN INGENIERÍA QUÍMICA de la Facultad de Ingeniería de MONTEVIDEO DOCTEUR DE L’UNIVERSITÉ DE LIMOGES Spécialité: Matériaux Céramiques et Traitements de Surface Gustavo SÁNCHEZ MATHON February the 12 th 2009, Montevideo, Uruguay PIEZOELECTRIC ALUMINUM NITRIDE THIN FILMS BY PECVD Advisors: Aldo BOLOGNA ALLES / Pascal TRISTANT, Christelle DUBLANCHE-TIXIER Jury : President : Prof. Jean Claude LABBE SPCTS, Limoges (France) Revisors: Prof. Miriam CASTRO UNMDP, Mar del Plata (Argentina) Prof. Abdou DJOUADI IMN, Nantes (France) Members: Prof. Ismael PIEDRA-CUEVA FING, Montevideo (Uruguay) Prof. Enrique DALCHIELE FING, Montevideo (Uruguay) Dr. Christelle DUBLANCHE-TIXIER SPCTS, Limoges (France) Prof. Pascal TRISTANT SPCTS, Limoges (France) Prof. Aldo BOLOGNA ALLES FING, Montevideo (Uruguay) Acknowledgments I want to express my sincere gratitude to my thesis advisors, Dr. Aldo Bologna Alles, Dr. Pascal Tristant and Dr. Christelle Dublanche-Tixier for their friendship and guidance throughout the course of this work. I also gratefully acknowledge Dr. Jean Claude Labbe, Dr. Ismael Piedra-Cueva, Dr. Abdou Djouadi, Dr. Miriam Castro, and Dr. Enrique Dalchiele for serving on my committee. I would also like to thank to several members of the SPCTS laboratory at Limoges for their support: Daniel Tetard, Thérèse Merle, Valérie Coudert, Phillippe Thomas, Alexandre Boulle, René Guinebretiere, Bernard Soulestin, Fabrice Rossignol, Daniel Merle and Cédric Jaoul. I would like to give a special acknowledge in this sense to Hervé Hidalgo. I want to acknowledge to Jaume Esteve and Joseph Montserrat from the Instituto de Microelectrónica de Barcelona for their assistance in the cleanroom fabrication of SAW devices, as well as to Aurelian Crunteanu from X-LIM (Limoges) for his assistance in the cleanroom fabrication of BAW devices as well in the device characterizations. Furthermore, I would like to thank Florent Tetard (Université Paris XIII) as well as Bassam Abdallah, Eric Gautron, Vincent Fernandez and Jonathan Ahmon (Institut des Matériaux de Nantes) by their assistance in other characterizations. I would like to remember the rest of the PhD students at Limoges for their friendship and their hospitality: Salman Asad, Christophe Cibert, Sébastien Menessier, Béatrice Sourd, Hamid Belghazi, Claire Tendero, Aure Arcondeguy, Cécile Marchand, Olivier Tingaud and Fabrice Goutier. - 2 - I want to remember Dr. Jean Desmaison, who was my advisor at the beginning of this work, and acknowledge his wife, Dr. Martine Desmaison-Brut for her friendship during my stages at Limoges. I want to express my gratitude to all the institutions that have support this work in different ways: the University of Limoges, the University of the Republic (Uruguay) and the French Embassy in Uruguay. Particularly, I want to thank some persons of these institutions by their special disposition: Gaëlle Peyrat and Graciela Vigo. Lastly and most importantly, I would like to thank my family. I thank my wife Isabel and my son Daniel for their role in helping me attain this goal. - 3 - Abstract Polycrystalline aluminum nitride thin films were produced with a microwave-plasma enhanced chemical vapor deposition technique. The plasma-injector distance, the substrate temperature and the RF bias were the main variables which allowed achieving this objective. At the time, it was possible to control the preferential orientation as <0001> or <1010>, both interesting for piezoelectric applications. The growth mechanisms that conducted to film microstructure development under different process conditions were explained, enriched by the comparison with a physical vapor deposition sputtering technique. The obtained films were characterized in their piezoelectric performance, including the construction of surface acoustic wave devices and bulk acoustic wave devices. Adequate piezoelectric response and acoustic velocities were obtained for <0001> oriented films, while <1010> oriented films did not show piezoelectric response under the configurations essayed. An extensive analysis was done in order to explain these behaviors. Keywords: aluminum nitride, thin films, PECVD, film microstructure, piezoelectricity, SAW devices, BAW devices. - 4 - Resumen Películas delgadas policristalinas de nitruro de aluminio fueron producidas empleando una técnica de deposición química en fase vapor asistida por plasma de microondas. La distancia plasma - inyector, la temperatura de substrato y la polarización RF del porta-substrato fueron las principales variables que permitieron alcanzar ese objetivo. Al mismo tiempo, fue posible controlar la orientación preferencial como <0001> o <1010>, ambas de interés para aplicaciones piezoeléctricas. Los mecanismos de crecimiento que condujeron al desarrollo de la microestructura en las diferentes condiciones fueron explicados. Esta explicación fue enriquecida por la comparación con una técnica de deposición física en fase vapor por pulverización catódica. Las películas obtenidas fueron caracterizadas en su desempeño piezoeléctrico, incluyendo la construcción de dispositivos electroacústicos de onda de superficie y de onda de volumen. Las películas orientadas <0001> mostraron respuesta piezoeléctrica y velocidad de onda acústica adecuadas. Por otro lado, las películas orientadas <1010> no mostraron respuesta piezoeléctrica para las configuraciones ensayadas. Un análisis extenso fue efectuado para explicar las posibles razones de estos comportamientos. Palabras clave: nitruro de aluminio, películas delgadas, PECVD, microestructura de películas delgadas, piezoelectricidad, dispositivos SAW, dispositivos BAW. - 5 - Résumé Des couches minces polycristallines de nitrure d’aluminium ont été produites en utilisant une technique de dépôt chimique en phase vapeur assisté par plasma micro-onde. La distance plasma - injecteur, la température du substrat et la polarisation RF du porte - substrat ont été les principales variables pour arriver à ce but. Dans un même temps, il a été possible de contrôler l’orientation préférentielle comme <0001> ou <1010>, intéressantes pour des applications piézoélectriques. Les mécanismes de croissance qui ont conduit au développement des microstructures dans les différentes conditions ont été expliqués, la comparaison avec une technique de dépôt physique en phase vapeur par pulvérisation cathodique a permis d’enricher la discussion. Les performances piézoélectriques des couches obtenues ont été caractérisées par construction des dispositifs électroacoustiques d’onde de surface et d’onde de volume. Les couches orientées <0001> ont montré une réponse piézoélectrique et une vitesse acoustique adéquates. Par contre, les couches orientées <1010> n’ont pas montré de réponse piézoélectrique dans les configurations testées. Une analyse exhaustive a été conduite pour expliquer les possibles raisons de ces comportements. Mots-clés : nitrure d’aluminium, couches minces, PECVD, microstructure, piézoélectricité, dispositifs SAW, dispositifs BAW. - 6 - Contents INTRODUCTION ...................................................................................................... 14 Chapter 1.................................................................................................................. 16 PIEZOELECTRIC ALUMINUM NITRIDE THIN FILMS: FUNDAMENTALS AND STATE OF THE ART ............................................................................................ 16 1.1 Piezoelectricity ............................................................................................ 16 1.1.1 Applications of the piezoelectric effect.................................................. 19 1.1.2 Bulk acoustic wave devices .................................................................. 21 1.1.3 Surface acoustic wave devices............................................................. 23 1.1.4 Characteristics of piezoelectric film for electro-acoustic devices........... 24 1.1.5 Piezoelectric materials .......................................................................... 27 1.2 Aluminum Nitride ......................................................................................... 29 1.2.1 AlN films for BAW and SAW electro-acoustic devices .......................... 34 1.3 Thin Film Manufacturing Techniques........................................................... 37 1.3.1 Plasma assisted techniques for thin films deposition............................ 38 1.3.2 Plasma assisted techniques for polycrystalline AlN films...................... 41 1.4 Thin Film Growth Mechanisms .................................................................... 44 1.4.1 Development of preferential orientation in AlN thin films....................... 46 1.4.2 Residual stress in thin films .................................................................. 50 1.5 Objectives.................................................................................................... 52 Chapter 2.................................................................................................................. 53 EXPERIMENTAL PROCEDURE .......................................................................... 53 2.1 The MWPECVD technique......................................................................... 53 2.1.1 The reactor ........................................................................................... 53 2.1.2 The process .........................................................................................