Optical Repair Template for Phase-Shift Photomasks
Original Publication Date: 2000-Mar-01
Included in the Prior Art Database: 2003-Jun-18
Optical Repair Template for Attenuating Photomasks Large opaque defects are frequently the cause of yield loss for photomask fabrication. Small opaque extensions, or bridges can often be repaired. Large opaques can lead to non-repairable masks because usually an entire image is lost. Current repair technology is not designed to recreate an entire image on a mask. Attenuating photomasks, unlike binary masks, consist of a multilayer stack. The potential for non-repairables increases because each layer is susceptible to opaque defects. A typical process flow for attenuating masks goes as follows: An image is patterned onto the plate in photoresist. Following develop, the top layer (chrome) is dry etched. The photoresist is then stripped off the plate. The bottom layer (attenuator) is now ready for dry etching. Here the chrome acts as a hard mask. Second level processing consists of lithography, and then the chrome is wet stripped off to form a frame around the mask. Two types of non-repairable defects can form during this process. The first is called a chrome non-repairable. This occurs when something prevents the chrome from being patterned. The second is called a MoSi residual (MoSi is the attenuator). In this case, the chrome is successfully patterned, but something prevents the attenuator from being etched. Below are examples of the two defects.