WEE Processing Of Negative Tone Resists For Protective Seal Rings
Wafer Exposure is a process wherein Photoresist at or near the edge of the wafer is exposed. It is important that the exposure faithfully follow the edge of the wafer, meaning the flats must be provided for and even when necessary and… especially in Wafer Level Chip Scale Processing (WLCSP) wafer warpage must be accommodated. The tool must carry out the necessary metrology to determine with great precision where the edge of the wafer is so that the exposure means can be properly maneuvered to create the desired exposure at the wafers edge.
When positive Photoresist is employed the WEE tool is primarily used to permit an absolute minimum exposure width at the edge to minimize yield losses at the edge and in the case of “notch” exposure…used when the wafer will be immersed in a rack type plating system the WEE will not only improve yield it will minimize precious metal waste at the plating contact regions.
When negative Photoresist is employed the WEE tool is used to provide a means of protecting or sealing the edge of the wafer to prevent contamination reaching the devices within the boundary of the WEE exposure path. A Second exposure can be used to protect wafer ID marks or exclusion zones.
By using precise positioning of the exposure mask and even being able to reconfigure the mask dimensions programmatically a properly configured WEE tool can be a powerful method to increase yields and lower costs and waste, and increasing throughput as one WEE can accommodate multiple steppers.