IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Thin Films Tuesday Sessions
       Session TF-TuM

Paper TF-TuM11
Multi-layer Chromium-based Optical Coatings for 157nm Lithography

Tuesday, October 30, 2001, 11:40 am, Room 123

Session: Optical Thin Films
Presenter: P.D. Rack, Rochester Institute of Technology
Authors: P.D. Rack, Rochester Institute of Technology
B.W. Smith, Rochester Institute of Technology
A. Bourov, Rochester Institute of Technology
D. Baiko, Rochester Institute of Technology
M.G. Lassiter, Photronics Corp.
Correspondent: Click to Email
Chromium based multi-layer films have been the dominant masking material for optical microlithography. The next generation optical lithography exposure wavelength is expected to be 157nm from an F2 laser source. Of critical interest for this exposure wavelength is the optical properties of the chromium multi-layer mask. Traditionally the masking film has been ~100-120 nm thick, however for accurate critical dimension control for off-axis illumination sources, it is desirable to thin the masking film thickness. To design a process to deposit a thinned masking material, the composition of the standard masking material was initially confirmed via x-ray photoelectron spectroscopy depth profiling. The composition of the film was determined to be a CrxNy film with a graded CrxOyNz anti-reflecting top layer. To evaluate the thinned materials, a design of experiments was performed to reactively sputter a metallic chromium target in an Ar-N2 and an Ar-N2-O2 ambient, respectively. After successfully reproducing the ~120nm thick multi-layer film, a series of scaled films with a total thickness of 50 and 80 nm were deposited. Vacuum ultra violet (VUV) transmission, reflection, and spectroscopic ellipsometry measurements were performed on each film and the optical constants (n and k) of the individual layers were determined. Finally, the entire multi-layer film stack was modeled with an effective medium approximation and found to correlate well with the experimental reflection and transmission data. In this presentation, we will discuss reactive sputter deposition metallic chromium to form the CrxNy/CrxOyNz multi-layer thin films. The optical characterization results will be presented and discussed in regard to the reflection and optical density requirements necessary for a masking material. Finally the modeling of the spectroscopic ellipsometry will be presented and the effective media approximation of the film stacks will be discussed.