Yang Liu


The Semiconductor Industry Association Roadmap 2003 has put 157 nm optical lithography as the next generation lithography wavelength for the node of 70 nm integrated circuits and below. The small departure from 193 nm puts more challenge on imaging tools and processes. One of the crucial areas is the exploration of thin film optical materials for mask coatings at vacuum ultraviolet (VUV) wavelength. Attenuated Phase Shift Mask (APSM) is one of the optical enhancement technologies pushing critical dimension of lithography to diffraction limits. As no existing single material satisfies those demanding requirements of APSM, non-stoichiometric composite materials will be explored to keep optical lithography from demise. In this case, the individual dielectric response of those constituents must be combined in an effective model to reproduce composite film dielectric response. The relationships between thin film microstructure and optical properties are extremely useful for the development and characterization of thin films. Effective Media Approximation (EMA) theory will bridge thin film composition and/or microstructure to optical properties. APSM can improve both resolution and depth of focus with complexity in fabrication. It has become an attractive candidate to replace those of multilevel mask processes such as aligning, rim, or sub-resolution schemes. The APSM should have transmission between 4% and 15% with a π phase shift [1]. Also the thin film must be feasible to pattern. This thesis worked on several potential AI2O3 hosted composite materials. By carefully combining the absorbing and non-absorbing components based on the database of RIT lithography research group for optical properties of various materials, the optical properties of the composite thin film can be tailored to achieve the desired requirements by adjusting the deposition conditions, which include reactive gas partial pressure, power and time. Four promising AI2O3 hosted composite materials were proposed and two of them were fabricated and tested with satisfactory results. An image reversal lift-off process was adapted and modified for patterning of the APSM film. The lift-off process was able to pattern the APSM film with 2 microns critical dimension. AI2O3 hosted oxide non-stoichiometric composite materials satisfy all the APSM film requirements and can be patterned by lift-off process with reasonable critical dimension. Table: Left Column: Criteria, Right Column: Target Range. Left Column: Transmission at 157 nm, Right Column: 4-15%. Left Column: Transmission at 193 nm, Right Column: below 50%. Left Column: Reflectance at 157nm, Right Column: Below 15%. Left Column: Phase Shift at 157 nm, Right Column: 180 degree. Left Column: Critical dimension of patterned film, Right Column: 2 micons. Table 0.1 APSM film requirements.

Library of Congress Subject Headings

Integrated circuits--Masks; Microlithography; Thin films--Optical properties; Thin films--Mechanical properties; Photolithography; Aluminum oxide

Publication Date


Document Type


Student Type


Degree Name

Materials Science and Engineering (MS)

Department, Program, or Center

Center for Materials Science and Engineering


Bruce Smith


Physical copy available from RIT's Wallace Library at TK7874 .L48 2004


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