There are essentially two kinds of imprint masks/templates:
Imprint Masks - Made of rigid fused silica blanks, similar to photomask blanks, 6.35mm thick, for applications where the substrate nanotopography is relatively smooth and require tight overlay such as silicon ICs and thin film heads
Imprint Templates - Made of thinner substrates that are < 1mm thick for applications that do not require nano-resolution overlay. These thin templates allow a single imprint to encompass the entire substrate pattern as in the case of hard disks or III-V substrates.
Imprint masks can be made with commercial photomask materials and processes. In principle, the 1-1 pattern size requirements between the mask and the wafer patterns (known as 1X masks), tests the resolution capability of traditional mask processes. While traditional optical photomasks are 4X, the advent of optical proximity correction (OPC) sub-resolution features, which approach 1.3X the minimum feature size on the wafer are accelerating the resolution of commercial electron beam mask writers. In addition for imprint masks, since the chrome film is only being used as an etch mask (no optical opacity requirements), thinner chrome and electron beam resists are used. Resolution of 24nm half-pitch using standard variable shape beam e-beam tools is available from commercial mask suppliers.
Pattern placement is a challenge in overlay sensitive applications such as silicon ICs and thin film heads. Double patterning for 193nm-i is forcing the photomask industry to meet very tight image placement specifications. This has facilitated the progress of pattern placement to sub-3nm, 3s, over a 26 by 32mm field for 1X imprint masks The use of high-resolution, slower Gaussian beam tools enables even sub-20nm patterning of imprint masks today, and mask replication can be used to offset the cost of producing such masks.
In 1X imprint masks, the mask pattern is identical to the wafer patterns. Therefore, for high volume applications, a small area e-beam generated master mask can be used to create a larger area replica using the J-FIL process. This allows for significant reduction in the cost of the working mask. The mask replication process can also be used to create multiple copies of a mask which this is valuable in high-volume applications such as patterned magnetic media where tens of imprint tools may be needed to operate in parallel.
