<title>Use of scanning thickness mapping technique to perform precision measurements of thin film thickness</title>

Abstract

By means of electron-beam induced x-rays, the thickness of films used in fabrication of integrated circuits can be measured with high precision. The thickness modulated intensity of the x-rays generated from the sub-layer material due to penetration of the electron beam is correlated to the thickness of the surface film and displayed as a 3-D thickness map of the film material)'2 Scanning thickness mapping is a technique for measuring and plotting film thickness over the surface of the devices with high spatial resolution in the X-Y plane, using the modulation effect on electron beam induced x-rays. This technique has been implemented at this laboratory using a scanning electron microscope (SEM) in conjunction with an energy dispersive x-ray analyzer (EDXA). Since the electrons must interact with the material below the film that is being measured, they must be of sufficient energy to penetrate the film and produce enough x-rays in the sub-layer to be detectable in a reasonable time frame. To accomplish this, the analyst is required to initially determine the optimum beam energy for the sample to be measured. Typically, the optimum beam energy is several kilovolts above the onset of beam penetration through the film. This report will present data obtained for a dielectric film over aluminum metal and aluminum on silicon. A simulated 3-D scanning thickness mapping display of dielectric thickness was obtained by converting raw x-ray intensity data received from the energy dispersive x-ray analyzer. The raw x-ray intensity data was corrected for x-ray absorption effects and translated into film thickness values. These calculated values were then compared to SEM visual measurements of a cross-sectioned sample. Correlation between the scanning thickness mapping measurements and the SEM visual measurements will be discussed. The benefits of this technique are the high degree of characterization of the film thickness in the X-Y plane, and the detection of hole defects in film and thickness non-uniformities at contact areas or at steps.© (1990) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.