Annealing effects on silicon-rich oxide films studied by spectroscopic ellipsometry S. Spiga a, *, G. Tallarida a , A. Borghesi a,b , A. Sassella b,c , G. De Santi d a Laboratorio MDM, Istituto Nazionale per la Fisica della Materia, via C. Olivetti 2, I-20041 Agrate Brianza (MI), Italy b Dipartimento di Scienza dei Materiali, Universita ` di Milano via Emanueli 15, I-20126 Milano, Italy c Istituto Nazionale per la Fisica della Materia, Universita ` di Milano, via Emanueli 15, I-20126 Milano, Italy d SGS-Thomson Microelectronics, via C. Olivetti 2, I-20041 Agrate Brianza (MI), Italy Received 24 March 1997; accepted 2 January 1998 Abstract Annealing effects on silicon-rich oxide films deposited by plasma enhanced chemical vapor deposition are studied by spectroscopic ellipsometry. From the variations of the film thickness and optical functions caused by thermal treatments at two different temperatures the properties of the different films are derived. Hydrogen and OH release and structural reordering are recognized to be responsible both for thickness decrease and Si–Si bond formation. In samples far from stoichiometric SiO 2 , the presence of Si–Si bonds after high temperature annealing accounts for both refractive index and extinction coefficient increase. Such effects are found to be directly linked to the silicon content in the films.  1998 Elsevier Science S.A. All rights reserved Keywords: Silicon-rich oxide films; Annealing; Plasma enhanced chemical vapor deposition 1. Introduction Recently, silicon-rich (Si-rich) oxide films have been widely studied and characterized in view of the important role they cover in device manufacturing technology. In par- ticular, these films are employed in memory cells, e.g. dynamic and static random access memories, erasable pro- grammable read only memory (EPROM) etc., both as pas- sivation layers and intermetal level dielectrics [1,2]; the determination of their structural, electrical, and optical properties is therefore of crucial importance. Indeed, these oxides are usually deposited by plasma enhanced chemical vapor deposition (PECVD) and several impurities, such as hydrogen and nitrogen, may be included in the film, depend- ing on deposition conditions [3]. It is important to distin- guish these Si-rich oxides from silicon oxynitrides [4], which can be considered true SiO x N y alloys, and whose applications are in fact very different; Si-rich oxides are actually substoichiometric silicon oxides with N and H impurities. To study Si-rich oxide films optical techniques are parti- cularly suitable, being highly sensitive to impurity concen- tration and to the film microscopic structure, rather easy to use, and non-destructive. Moreover, the knowledge of the optical functions of these materials is very useful for micro- electronics applications. For example, EPROM cells are erased by ultraviolet (UV) light exposure; furthermore, dur- ing device fabrication, photolithography steps involve UV light, hence the knowledge of the optical functions of the different materials is important for a sharp definition of the structures. In a recent paper [5] we already reported details about the composition of these films, measured by various ion beam techniques. Rutherford backscattering spectrometry (RBS) was adopted to measure silicon content, nuclear reaction analysis (NRA) for the determination of oxygen and nitro- gen contents, and elastic recoil detection analysis (ERDA) to evaluate the hydrogen content. In the same paper the characterization of these films by means of Fourier trans- form infrared spectroscopy (FTIR) was also reported. A Thin Solid Films 325 (1998) 36–41 0040-6090/98/$19.00  1998 Elsevier Science S.A. All rights reserved PII S0040-6090(98)00423-4 * Corresponding author. +39 39603 5143; fax: +39 39688 1175; e-mail: mdmlab@progetto3000.it