AVS 50th International Symposium
    Thin Films Monday Sessions
       Session TF-MoA

Paper TF-MoA8
Deposition of Low k OSG Films Exhibiting Enhanced Mechanical Properties by PECVD

Monday, November 3, 2003, 4:20 pm, Room 329

Session: Atomic Layer Deposition and Low-k
Presenter: A.S. Lukas, Air Products and Chemicals, Inc.
Authors: J.L. Vincent, Air Products and Chemicals, Inc.
R.N. Vrtis, Air Products and Chemicals, Inc.
A.S. Lukas, Air Products and Chemicals, Inc.
M.L. O'Neill, Air Products and Chemicals, Inc.
B.K. Peterson, Air Products and Chemicals, Inc.
M.D. Bitner, Air Products and Chemicals, Inc.
G.J. Karwacki, Air Products and Chemicals, Inc.
Correspondent: Click to Email
Silica is the traditional insulating material used in interlayer dielectrics and has a k of 3.9-4.2. To achieve the lower k's required for the next generation of IC's, methyl (Me) groups may be added to the silicate structure by using organosilane precursors. The lower k in the resulting organosilicate glass (OSG) is attributed to the decreased density, increased hydrophobicity, and reduction of the polarizability of the material. We previously demonstrated the use of diethoxymethylsilane (DEMS) to deposit OSG films by PECVD with k's of 2.7-3.3 (dense) and 2.0-2.5 (porous). However, this decrease in k comes at the expense of the mechanical properties due to the disruption of the silicate network by terminal Si-Me. Our modeling studies show that the benefit of adding Me to lower the k diminishes after a Si/Me ratio of about 2/1 in the OSG material, yet the mechanical properties continue to decline as the Si/Me ratio approaches 1/1. Our dense DEMS OSG films (k = 3.0) are deposited at temperatures > 350 C. These films have excellent mechanical strength and a Si/Me ratio of 2/1. However, our process for porous DEMS OSG (k < 2.5) requires a deposition temperature below 280 C, resulting in a Si/Me ratio close to 1/1 and significantly decreased mechanical strength. We found that the Me incorporation can be reduced in by using a precursor mixture of DEMS and a second silica source without Me groups. This allows the control of the terminal Me content in the final film chemically, as opposed to using process conditions such as high temperature or plasma power. We were successful in depositing OSG films with Si/Me ratios of 2/1 from precursor mixtures at deposition temperatures as low as 200 C. For example, a porous OSG with a post-anneal k of 2.2 and a nanoindention hardness of about 0.6 GPa was deposited at 270 C. This is a nearly 2-fold increase in the mechanical strength as compared to films with identical k deposited without the second silica source.