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Optical Repair Template for Phase-Shift Photomasks

IP.com Disclosure Number: IPCOM000013233D
Original Publication Date: 2000-Mar-01
Included in the Prior Art Database: 2003-Jun-18
Document File: 4 page(s) / 106K

Publishing Venue

IBM

Abstract

Optical Repair Template for Attenuating Photomasks

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Optical Repair Template for Phase-Shift Photomasks

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.

Chrome Non-repairable MoSi Residual

    The optical repair template takes advantage of the multilayer structure, and attempts to repair what would otherwise be a

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non-repairable in a single layer mask. Two procedures currently exist that attempt to repair the MoSi residual defect.

    For the first method, the chrome is stripped and the operator attempts to 'redraw' structures using the surrounding images as guidelines. The defect would look similar to a chrome non-repairable. This method is highly dependent on the skill and patience of the operator, and is simply impossible with current repair tools, especially with irregular shape images.

    The next method is similar to the optical repair template, but not nearly as efficient. The chrome layer acts as a drawing template, and the operator attempts to repair inside the template with several small laser ablations. Again the skill and patience of the operator becomes extremely important. Also, the potential to damage the underlying attenuator is large. The optics used on repair tools is not the greatest. It is difficult to determine the exact edge of the template. Since several small laser ablations are used, some overlapping occurs. This da...