APPLICATIONS

Wafer Geometry Inspector

Basics

Rounding the edges of 300 mm wafers made of ultra-pure silicon primarily serves to reduce the susceptibility of this brittle material to breakage. Depending on the further processing steps to be carried out, such as coating procedures, the wafer edges are specially ground to produce the specific contour required by the customer. Contour deviations must be kept to an absolute minimum.

For this reason it is essential that edge contours are measured as precisely as possible for the purpose of quality assurance.  Geometrical parameters such as blunt and facet lengths, half angles and radii can be determined from the measured contour for pass/fail assessments.  Specific standards and specifications for these parameters have been developed by SEMI technical committees.

Up until now, determining edge geometry parameters in accordance with these guidelines was very equipment and personnel-intensive. The time-consuming measurements were based on a combination of various different optical and mechanical examination methods and were consequently not free from subjective influences. Moreover, the measurement principle behind the profile projection techniques employed does not allow the contours of the edge to be measured in the notch.

The development of integrated measuring systems based on light-sectioning technology has made it possible to bring about a significant increase in measurement precision while at the same time considerably reducing the time involved. In addition, these systems are capable of measuring the edge contour in the notch area within a single measurement procedure.