Micromechanical Characterization of Dielectric Thin Films
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MICROMECHANICAL CHARACTERIZATION OF DIELECTRIC THIN FILMS
James M. Grow New Jersey Institute of Technology, Newark, NJ 07102. ABSTRACT
A nanoindenter has been used to obtain Young's modulus and hardness data for a variety of dielectric thin films including silicon carbide, boron nitride, silicon carbonitride, and silicon oxide. These films, were synthesized by low pressure and plasma enhanced chemical vapor deposition, and had a thickness from 0.25 to a few microns. For the BN films, the modulus and hardness of the films decreased significantly as the deposition temperature increased while the reverse was true for the SiC films. In both cases, these changes were related to variations in the compositions of the deposits due to the onset of different reactions as the temperature is increased. Silicon carbonitride films oxidized slowly when synthesized at temperatures below 2000 C and the Young's modulus of these films increased at higher deposition temperatures. For silicon dioxide, there was little change in the composition of the films over the deposition temperature range investigated (375-4750 C), thus correspondingly, small variations in the micromechanical properties of the material. However, moisture and hydrogen removal caused by an anneal at 8000 C resulted in an significant increase in the modulus and hardness of these films. INTRODUCTION
The recent development of a depth-sensing indentation tester (Nanoindenter) for determining the micromechanical properties of thin films has provided a powerful tool which yields valuable information for evaluating film properties. Hardness can be determines from the plastic behavior during the initial indent and Young's modulus can be calculated from the elastic behavior during subsequent unloading segments 1 ,2. This study will focus on the Young's modulus data because the hardness data was, in general, very similar but not as reproducible. Any surface defects will greatly affect the hardness of the film because of its dependence on the penetration of the surface by the indenter. Since these plastic type behaviors are typically removed in the initial indent, defects become compressed before the Young's modulus is determined. This paper will demonstrate the type of information available when using a nanoindenter to characterize the mechanical properties of dielectric films. EXPERIMENTAL PROCEDURE
The Young's modulus and hardness data were determined using a Nano Instruments indenter. The system consists of a diamond tip, with the same area to depth ratio as the traditional Vickers pyramid, mounted on a loading column that is suspended on thin leaf springs. At the top of the loading column is a coil and magnet assembly that provides a controlled loading force with a resolution of about 0.5 jtN. The position of the indenter is determined by a capacitance displacement gauge which allows one to detect displacement changes of 0.2-0.3 nm. In this work, the maximum drift rate prior to testing was 0.1 nmn/s, the loading rate was 200 VN/sec to a maximum load of 4.5 inN, the ho
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