Richard L. Lozes

Contrast limitations in electron-beam lithography

State-of-the-art proximity effect correction (PEC) schemes show a degradation in contrast when they are applied to small features. It seems impossible to achieve a contrast better than that of the uncorrected pattern. In this article we provide mathematical proof that it is impossible to improve the contrast for the class of linear PEC kernels. For this class, higher resolution can only be achieved at the expense of contrast. This fundamental limitation implies a trade-off between the desired minimum feature size (related to critical dimension linearity) and contrast (related to critical dimension uniformity).

Phase-shift mask technology: requirements for e-beam mask lithography

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.

Proximity effect correction at 10 keV using ghost and sizing for 0.4 μm mask lithography

An investigation of proximity effect correction at 10 keV using ghost and sizing indicates 0.4 μm design targets can be achieved on a raster scan lithography system. It is shown through simulation and experiment that the proximity effect can be effectively eliminated by use of ghost. Sizing provides an additional degree of freedom to control process latitude and wall angle.

Raster Shaped Beam Pattern Generation for 70 nm Photomask Production

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.