200 mm SCALPEL mask development

SCattering with Angular Limitation Projection Electron beam Lithography (SCALPEL) is a true 4X reduction technology that capitalizes on high resolution capabilities (50 nm) from electron beam exposure and high throughput capabilities (approximately 30 wafers/hour) from projection printing. Current mask blank fabrication for SCALPEL technology uses widely available 100 mm, [100] crystalline silicon wafers. The use of 100 mm crystalline [100] wafers and a wet, through wafer etch process causes the patterned strut width to increase as the wafer is etched and must be accounted for in the mask blank fabrication process. In the wet etch process, a 100 μm wide strut grows to 800 μm at the strut-membrane interface. As a consequence, the maximum printable die size due to the wafer size and the decreased amount of open area between each strut is 8×8 mm. Additionally, crystal defects in the silicon wafer affect the wet etch process and contribute to mask blank failures. A partial solution for an increased die size is to increase the wafer size used to make the SCALPEL mask blank. A 200 mm wafer is capable of producing larger die sizes. This can be further improved by dry etching of the grill structure to form struts with vertical sidewalls. As a result, die sizes of 25×25 mm or 16×32.5 mm can be produced depending on the grill pattern used. However, use of large wafers and dry etching for mask blank formation has significant issues that must be addressed. Among the issues to be addressed are etch chemistries, etch mask materials, and wafer handling.