Identifier

etd-05182005-120737

Degree

Doctor of Philosophy (PhD)

Department

Electrical and Computer Engineering

Document Type

Dissertation

Abstract

Use of low relative dielectric constant (low-k) material as an interlayer dielectric is among important approaches to reduce the RC time delay in high performance ultra-large-scale integrated circuits. Copper metallization is another approach besides the use of low-k material, in reducing the RC delay time, because of its well-known characteristics of low resistivity and high electromigration resistance. Fluorocarbon films containing silicon (SiCF) have been developed in this work for low-k interlayer dielectric applications below 50 nm linewidth technology. The films were prepared by plasma enhanced chemical vapor deposition (PECVD) using gas precursors of tetrafluoromethane as the source of active species and disilane (5 % by volume in helium) as both an active species source and a reducing agent to control the ratio of fluorine to carbon in the films. The basic properties for these low-k interlayer dielectric films were studied along with characterization of their fabrication process. Electrical, mechanical, chemical and thermal properties were evaluated including dielectric constant, electrical field strength, surface planarity, residual stress, hardness, chemical bond structure, and shrinkage upon heat treatment. Deposition process conditions were optimized for film thermal stability while maintaining a relative dielectric constant value as low as 2.0. The average breakdown field strength of the SiCF films was 4.74 MV/cm and its optical energy gap was in the range of 2.2 to 2.4 eV. The hardness and residual stress in the SiCF films deposited under the optimized conditions were respectively measured to be in the range of 1.4 to 1.78 GPa and in the range of 11.6 to 23.2 MPa of compressive stress. For integrated microsystems as well as for ULSI circuits, surface modification of SiCF films by wet chemical treatment and by X-ray irradiation were examined to facilitate copper metallization. Feasibility of copper deposition by recently developed electroless techniques is discussed in conjunction with the studies utilizing wet chemical modification of the film surface. The effect of X-ray irradiation on the chemical structure of the films is also discussed. Additionally, means for selective surface modification of the films are introduced by exposing the films through an X-ray mask.

Date

2005

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Pratul K. Ajmera

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