Photomask complexity is rapidly increasing as feature sizes are scaled down and as optical proximity correction (OPC) methods become widespread. The growing data content of critical mask levels requires that pattern generator solutions be adapted to maintain productivity. Raster shaped beam (RSB) technology has been developed to enable the production of 70 nm photomasks and the development of 50 nm masks. RSB is built on and extends the capability of the 50 kV MEBES platform. The beam is shaped as it is scanned, printing the mask pattern on a calibrated flash grid. Complex OPC patterns are efficiently tiled by combining a relatively small maximum shape size with a high flash rate of 100 MHz. The maximum shape size and the current density can be adjusted to match a wide set of mask applications. Proximity effects are corrected with dose modulation using a real-time computation.
Phase-shifted patterns (alternating, 90-degree, and chromeless) have been incorporated into a reticle layout, fabricated with a MEBESR III system, and evaluated experimentally at 365 nm using steppers with numerical aperture (NA) ranging from 0.4 to 0.48 and partial coherence ranging from 0.38 to 0.62. Test circuit layouts simulate actual circuit designs with critical dimensions ranging from 0.2 micrometers to 1.2 micrometers . These results, combined with experimental measurement of layer to layer registration and aerial image simulations, provide a first-order assessment of e-beam lithography requirements to support phase-shift mask technology.