The Causes of Property Variations of Ibad-Titanium Nitride
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THE CAUSES OF PROPERTY VARIATIONS OF IBAD-TITANIUM NITRIDE R. A. KANT*, S. A. DILLICH**, B. D. SARTWELL*, and J. A. *Naval Research Laboratory, Washington, D.C. 20375 **Worcester Polytechnic Institute, Worcester, MA 01609
SPRAGUE*
ABSTRACT The influence of the growth conditions on the composition, microstructure, and mechanical properties of TiN formed with low energy Ar+ ion bombardment during reactive physical vapor deposition was studied. The ratios of the incident ion and atom fluxes at the growth surface were varied systematically and were found to have a strong influence on both the composition and the microstructure of the films. These changes correlated well with measured changes in mechanical and optical properties. The films were examined using Auger electron spectroscopy, transmission electron microscopy, and their mechanical properties were studied using hardness, friction, and wear testing. INTRODUCTION There are several methods for making thin films of TiN and many employ some form of ion bombardment during deposition to improve film properties. However, there has been only limited understanding of the role of the bombardment and a satisfactory explanation has not been available for many of the observed variations of physical properties. One of the major problems has been that, until recently, the deposition parameters could not be independently controlled nor fully characterized, e. g., ion energy and flux are usually coupled and an unknown fraction of the ions may be multiply charged or neutralized causing difficulties in measuring ion flux. Thus, variations in a single processing parameter could cause other parameters to change in an uncontrollable or unpredictable manner and lead to unpredictable and potentially undesirable property changes. Several years ago Kant et al [1] developed an apparatus which allowed independent control over, and characterization of, each of the deposition parameters. They used that system to ion bombard TiN during reactive deposition at room temperature. The resultant films were consistently and inexplicably different from conventionally prepared TiN. Finding the source of the differences was complicated by the very lack of information about the conventional processes that motivated the work in the first place. In a subsequent study, Kant examined the influence of ion bombardment on surface reactions between Ti and gaseous N [2]. Although that investigation did not involve film deposition, the results indicated that significant quantities of unreacted or excess gas molecules could be present at a growth surface during deposition and that ion bombardment should substantially reduce their levels. The purpose of the work reported here was to investigate the extent to which the presence and incorporation of such excess gases during reactive deposition of TiN affect film properties, and the extent to which ion bombardment induced property changes could be attributed to gas incorporation. TiN films were grown for a matrix of carefully controlled and well characterized ionic
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