Diamond and Three Dimensional Nanoimprint Lithography pp.245-271
Authors: (Jun Taniguchi, Department of Applied Electronics, Tokyo University of Science, Noda, Chiba, Japan)
Abstract: As silicon ULSI devices continue to be scaled down, resist patterning on Si wafers becomes increasingly critical. For Si ULSI, reliable lithographic technology must define features with dimensions below 0.1 μm, and many promising techniques have been developed that transfer features of less than a quarter micron[1-3]. Next-generation lithographic techniques must, however, in addition to high resolution, provide high throughput and large processing latitude at low cost. NIL lithography provides a major breakthrough in nanopatterning because it produced nanometer features over a large area with high throughput and low cost [4-6]. NIL fabricates a resist pattern by deforming the resist layer on the substrate using compression by a nanoscale delineated mold. Because this involves physical contact between the mold and the resist layer on the substrate surface, breakage and distortion of mold patterns during contact or peeling in NIL become serious problems in pattern transfer and productivity. To obtain the high productivity required for mass production, the mold must be durable in repeated NIL processes and strong in contact with the substrate. Diamond is a promising candidate for high productivity because of its many excellent properties, such as large Knoop hardness, large compressive strength, large tensile strength, high thermal conductivity, and a low thermal expansion coefficient. Table 1.1 shows the mechanical and thermal properties of diamond, sapphire, and quartz. The high Knoop hardness, compressive strength, and tensile strength prevent breakage and distortion of the mold. The large thermal conductivity ensures that heat spreads uniformly. The low thermal expansion coefficient ensures that the mold shape changes little due to heating. While these properties are suited to thermal cycle nanoimprint lithography, repeated NIL processes make the mold dirty, however, making it necessary to clean the mold using strong acid and organic solvent. This may chemically change the mold surface or compromise it. The diamond mold does not change or break in cleaning because diamond is hard and chemically inert. Clarification of diamond mold fabrication and imprint properties using the diamond mold is important for high productivity.