Probing into the kerf
"The first system was built and tested in close co-operation with a leading German semiconductor manufacturer who has since bought their third system," reports Dr Claus Dietrich, SUSS test systems international sales and marketing manager.
Successfully contacting such small pads during automated wafer characterisation is impossible when using a normal cantilever probecard as the scrub of the needles is too long. Vertical probecards are usually employed instead. FormFactor’s MicroSpring technology uses such a vertical design. However, with this type of probecard there are alignment problems. Alignment systems for such probing of 300mm wafers can require a large footprint.
SUSS uses three additional cameras to determine the position of the probecard pins in relation to the pads in its MicroAlign system. This enables a smaller footprint for the prober system. A horizontal camera is used to control the contact height which optimises overtravel margins and scrub parameters. A software algorithm using high-level pattern recognition techniques is the basis for position alignment. A profile of the wafer is created with the use of live video cameras in order to compensate for potential differences in wafer thickness and the probecard is then automatically aligned to ensure that the scrub lengths are varied accordingly.
