AVS 51st International Symposium
    Thin Films Monday Sessions
       Session TF-MoA

Paper TF-MoA10
Effect of Trimethylsilylation on the Film Stress of Nanoporous Silica Ultralow-k Film Stacks

Monday, November 15, 2004, 5:00 pm, Room 303C

Session: Mechanical Properties of Thin Films
Presenter: F.M. Pan, National Chiao Tung University, Taiwan
Authors: F.M. Pan, National Chiao Tung University, Taiwan
A.T. Cho, National Nano Devices Laboratories, Taiwan
J.Y. Chen, National Chiao Tung University, Taiwan
L. Chang, National Chiao Tung University, Taiwan
K.J. Chao, National Tsing Hua Univerisity, Taiwan
Correspondent: Click to Email
In advanced dual damascene interconnect structures, ultralow-k dielectrics must be integrated with etch stop and barrier layers, and, therefore, interfacial properties of the film stacks are critical to process yield and reliability of interconnects. In this work, the film stress and effective dielectric property of self-assembled nanoporous silica overcoated by various dielectric thin layers were studied. The nanoporous silica was prepared by spin-coating the sol-gel precursor on the silicon wafer, followed by baking and calcination. Due to the film shrinkage during thermal treatments, the as-prepared nanoporous silica films have a tensile film stress. In order to improve the dielectric property, the nanoporous silica thin film was exposed to hexamethyldisilazane (HMDS) vapor for trimethylsilylation, and a dielectric constant lower than 1.95 could be obtained. The film stress became less tensile after the HMDS treatment. The decrease of the tensile stress can be ascribed to the spring-back effect resulting from the introduction of bulky trimethylsilyl groups in the nanoporous silica layer. Three different capping layer, Si@sub 3@N@sub 4@, SiO@sub 2@ and @alpha@-SiC:H films were separately deposited on the nanoporous film at 300@sup o@C. When directly deposited on the Si wafer, all the three capping materials show compressive stress. While the capping layers were deposited on the as-calcined nanoporous silica, the film stress of the SiO@sub 2@ and Si@sub 3@N@sub 4@ layers was so large that the capping layers cracked. On the other hand, when the capping layers were deposited on the HMDS treated nanoporous silica, the film stacks showed no mechanical failure and the effective dielectric constant could be lower than 2.2. This study suggests that trimethylsilylation of the nanoporous silica low-k dielectric can effectively improve the integrity of the three film stacks in terms of mechanical strength and dielectric property.