Etched bonded silicon wafers as test objects for the resolution power of subsurface voids

Bonding of silicon wafers is a method that is widely used in microsystem technology. To quantify the quality of the bond only IR interference techniques which are restricted to vertical sizes of voids 2 size were sawed out of the wafer pair followed by grinding and polishing these structures under small angles of 34 feet to 3 degrees. With working frequencies of 200 MHz and 400 MHz we obtained good results with structures that have a height of 50 nm and a horizontal size of some micrometers. It was possible to show structures that were covered with a silicon layer that is 70 micrometers thick. Additionally wafer pairs with metallic interlayers were investigated. The results are compared with images taken with an IR transmission optical microscope.