C and B ion implantations into TiN films were carried out. The implantation energy was 100 keV, and the ion dose was 1 x 10(18) ions/cm(2). Investigations of the implanted layer were carried out by x-ray diffraction analysis and cross-sectional transmission electron microscopy (TEM). Knoop hardness measurements were also made to evaluate the hardness of the modified layer. By x-ray diffraction analysis, TiC was identified in a C ion implanted specimen, and TiB2 was identified in a B ion implanted specimen. From cross-sectional TEM observations of the implanted specimens, it was found that the surface region of the TiN films was not damaged substantially (this was also identified by electron diffraction patterns), and that there was a mixed-textured region with crystalline and amorphous structures in the region with the highest density of implanted elements. However, differences between C and B implantations were also identified in the morphology of the crystalline region and amorphous region. In the C ion implantation, the amorphous region was formed with the lamella structure perpendicular to the ion irradiation direction (parallel to the surface of the film). In the B implantation, the amorphous region was spherically formed. According to the Knoop hardness measurement, the hardness of the TiN film after B implantation increased more than that of the nonimplanted TIN film. On the other hand, the hardness of the TIN films after the C ion implantation tended to decrease compared to the nonimplanted TIN film. The mechanism for improved hardness is presumed to be the result of the formation of a harder compound by reaction between the implanted element and the film element.