In the CMP planarization process, detecting the final polishing point is extremely important for maintaining high yield rates. Therefore, various methods for detecting the final polishing point have been developed.
We consider it vital that the SiO2 film thickness across a representative area be measured extremely precisely at high speed in the final stages to accurately control film polishing. However, up until now there has not been any wholly satisfactory method to achieve this.
In order to measure a fine representative film area (test pattern) both rapidly and accurately, we concluded that the non-contact, non-destructive and highly reliable methods of spectrometric analysis were most promising.
Based on these considerations, we developed a compact spectrometric film thickness measurement system which can accurately inspect test patterns at high speeds and installed it adjacent to the CMP equipment's polishing table. Using this system as a film thickness monitor, we can now measure film thickness while rinsing away slurry contaminants, halt polishing at any stage, and calculate the remaining polishing time from the current and desired thicknesses.
This system's pattern identification function can automatically measure the film thickness with very fine test patterns (as small as 40 square microns). When used with SiO2 single layer films, the experimental prototype's measurements proved reliably reproducible (showing a deviation of less than 4 nm at 3 σ over repeated trials), and required thirty seconds or less per wafer (including time for pre-alignment and five-point measurement). The system's theoretical basis and actual operations are described below.