Nobuyuki Kosaka

Surface defect inspection system with an optical spatial frequency filter for semiconductor patterned wafers

We previously developed a surface defect inspection system for semiconductor patterned wafers. The system utilizes spatial frequency technology, where regular periodic patterns were eliminated, and only defects are imaged at the image plane by using a spatial frequency filter. The system had a detection sensitivity of 0.8 micrometers and an inspection speed of 30 minutes for the 6 inch wafer. With the advent of 16 MDRAMs having a design rule of 0.5 micrometers , however, higher detection sensitivity of about 0.3 micrometers is required. Thus, we have been developing an advanced inspection system based on the previous achievement to meet the emerging needs. The problem to tackle is the signal-to-noise-ratio (SNR) improvement. To achieve higher SNR on the filtered image, we introduced the following two ideas: (1) angled incidence of the laser on the wafer surface and the avoidance of regular reflection light entering the optical system, and (2) a spatial filter which is composed of two photo-plates facing each other. We have developed an optical imaging system and have experimentally shown that the system images defects down to 0.2 micrometers with adequate SNR with a view field of 1000 X 1000 micrometers .

Inspection Of Patterned Wafer Surface Using Electrooptic Spatial Light Modulator

An electrooptic spatial light modulator, used as an intensity spatial filter, makes real-time inspection of periodic patterns possible by making the adjustment of object attitude unnecessary. The ways for preparing the filter and detecting defects in periodic pattern in real time are described. Results of detection of defects are presented.