Processing of Thick Dielectric Films for Power MEMS: Stress and Fracture
- PDF / 100,067 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 14 Downloads / 147 Views
Processing of Thick Dielectric Films for Power MEMS: Stress and Fracture Kuo-Shen Chen1, Xin Zhang2, and S. Mark Spearing3 1 Department of Mechanical Engineering, National Cheng-Kung University, Tainan, Taiwan, 701 2 Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02139, U.S.A. 3 Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, MA 02139, U.S.A. ABSTRACT This paper presents residual stress characterization and fracture analysis of thick silane based PECVD oxide films. The motivation for this work is to elucidate the factors contributing to residual stress, deformation and fracture of oxide films so as to refine the fabrication process for power MEMS. It is shown that residual stress in oxide films strongly depended on thermal processing history. Dissolved gases were found to play an important role in governing intrinsic stress. The tendency to form cracks is a strong function of film thickness and annealing temperature. Mixed mode fracture mechanics was applied to predict critical cracking temperature, and there is a fairly good match between theoretical predictions and experimental observations. INTRODUCTION Chemical vapor deposition (CVD) is an important deposition process for the fabrication of microelectronic devices and microelectromechanical systems (MEMS). CVD films are used to create both electrical and mechanical elements. For power MEMS [1], target applications are often desirable to push electrical and mechanical power requirements to higher levels. This presents a direct impact of demanding thicker films in order to provide functions such as electrical insulation for dielectrics or sufficient stiffness for mechanical flexure [2-3]. However, the ability to deposit film with thickness significantly greater than the current capability of a few micrometers is limited by the stress level present in the film [4-5]. The deleterious effect of residual stress tends to increase with film thickness. In particular, excessive wafer bow and cracking prohibit integration within a device. Since both issues are related to the residual stress exhibited in the oxide films during deposition and subsequent thermal processing, it is important to provide a fundamental understanding on the residual stress and fracture of the films. EXPERIMENTAL STUDIES All PECVD oxide films were deposited using a five-station continuous plasma processing EE8.4.1
system (Concept OneTM, NovellusTM Inc.) [6]. The nominal gas flow rates were 300 standard cubic centimeters per minute of SiH4, 9500 sccm of N2O and 1500 sccm of N2. Deposition was carried out at 400°C with deposition rates on the order of 1 µm/min. The film thickness varied from a few micrometers to a few ten micrometers. The substrate materials used were four inch, orientation boron doped silicon wafers approximately 500 µm thick. PECVD typically utilizes plasma to dissociate reactant gas molecules into atoms, ions and radicals in order to enhance chemical reaction, and increa
Data Loading...
