The feasibility of alternative blank substrate materials for large-scale FPD mask process and manufacturing

Photomask technology has contributed to the capability and productivity of integrated circuit (IC) and flat panel display (FPD) manufacturing with the implementation of masks that have improved process capability, margins and yield including but not limited to advanced binary or multi-tone masks and phase shifting masks. These masks are mainly composed of various chrome and phase shift materials deposited onto very high quality and stable substrates made out of fine grade fused silica materials. However, for large-scale masks like those used in manufacturing masks for FPD lithography, the cost and availability of such high quality substrates can be a prohibitive factor for cost effective production. Moreover, it is possible for some layers of these non-IC, large format applications, such very high performance fused silica substrates may not be necessary to meet the lithographic imaging requirements. Therefore, it seems desirable to understand the properties of alternate substrate materials to see if they might be suitable for improving the cost and availability factors in the large format applications. In this paper, we evaluate the optical and physical properties of various non-standard materials including thermal expansion, transmission, flatness and defectivity to better understand how these parameters might impact the imaging of certain layers. We compare major parameters in the lithography process such as CD, registration, displacement, defect printability and chemical durability related to process performance and variation. Moreover, we characterize defects and their impact on process using a general inspection tool and AIMS to assess the importance of certain defect modes especially of the embedded or inclusion type. Bubbles that occur in glass manufacturing process are analyzed and we attempt to classify the patterning impact using simulation and matching with AIMS. Finally, we draw conclusions on the suitability of these alternate materials to deliver a much lower cost mask solution for use in certain large format imaging applications by considering specifically the flat panel process and performance predictions.