Application of x -ray diffraction to microstructure assessment for microelectronic interconnect materials

Rachel Elizabeth Cefalu, Purdue University

Abstract

Polycrystalline copper thin films used in semiconductor applications have been shown to have longer lifetimes and greater resistance to electromigration when the {111} copper texture is maximized. A Bruker AXS Area Detector Diffractometer (2DXRD) was used to characterize copper thin film on tantalum metal based underlayers on silicon wafers. Amorphous, discontinuous, and crystalline continuous samples were examined. The 2DXRD proved to be a useful tool for measuring texture in thin films. It allows for the fast collection of a large amount of data. 2DXRD also is capable of collecting x-ray diffraction data for multiple thin film layers, even those which are buried. Grain size and stress measurements were attempted. Grain size measurements done similarly to texture measurements proved to measure the film thickness rather than the average grain diameter in the plane of the film. When used under similar conditions as texture measurements, the system does not have the precision to accurately measure thin film stresses. Use of the same data as used in measuring textures, therefore, cannot be realized to measure grain size or stress. While many have assumed that in order to enhance the {111} copper texture, the {110} texture of the tantalum underlayer should be maximized. This research shows that maximizing the {110} tantalum underlayer texture is detrimental to the {111} copper texture. The strength of the {111} copper texture was found to vary inversely with the strength of the {110} tantalum texture, and the strongest {111} copper texture of all was found in a sample with an amorphous underlayer.

Degree

Ph.D.

Advisors

King, Purdue University.

Subject Area

Materials science

COinS