High quality reticles are critical to the success of the 90 nm wafer node. Even though many wafer fabs are planning to use 193nm exposure tools, the k1 factor (minimum feature size x NA/λ) will be pushed to very low levels. With low k1 lithography, very small mask errors propagate to the wafer. This is especially true for contact and via layers. New generation mask writing tools have been developed to meet these needs. 50 kV electron beam tools can produce high quality masks , but their high costs and low throughputs result in high mask costs. On the other hand, DUV laser writers, with inherently high throughput, can produce high quality masks at a significantly lower cost than e-beam writers.
The fundamental technical distinction between laser and e-beam mask writers is resolution, manifest primarily as a corner rounding difference. While corner rounding has essentially no impact in wafer lithography (low NA at the mask renders wafer lithography a low pass filter), it cannot be ignored in mask pattern inspection, which uses high NA optics. In this study, it is demonstrated that reticles patterned on laser and e-beam tools can be inspected in database mode with full sensitivity at design rules beyond 130 nm. Further, a new energy measurement algorithm is used to evaluate contact patterns on both e-beam and laser-written masks, and it is shown that currently available laser mask writers should be extensible to the 90 nm node, even for these high MEEF features.