Sematech team makes 100-nm features

06/01/1998

SEMATECH team makes 100-nm features

New results from a SEMATECH lithography research program suggest that current-generation 248-nm deep ultraviolet wavelengths can generate well-controlled 100-nm (0.1-?m) features on the wafer, using a combination of optical proximity correction (OPC) design features and 4? alternating phase-shift photomasks (PSM). The ability to image features of less than half a wavelength with excellent CD control would give a substantial boost to optical lithography, and push the need for post-optical tools ever further into the future.

John S. Petersen, SEMATECH fellow and leader of the DELPHI project, said, "We are extremely pleased with results on the printed layers. The data clearly indicate that OPC combined with alternating phase-shift can overcome proximity related CD error, while taking full advantage of the resolution improvement of the PSM technique. Ultimately, demonstrating the feasibility of OPC to correct for these effects may be considered one of the milestones on the road to implementation of alternating PSM into subwavelength production."

The conclusion is that this work presents the first clear picture of how to solve the proximity problems encountered with deep subwavelength phase-shift processing. It is also significant that production worthy PSM were produced, and that the design process worked around coherence-enhanced PSM-OPC problems. Robert Socha, National Semiconductor senior engineer assigned to DELPHI, says, "Now, we are optimistic that our 248-nm DUV capital infrastructure can survive a few more generations."

The team engineers designed test reticles containing a myriad of 180? phase-shifted structures combined with MicroUnity`s subresolution OPC "scattering bar" features and fine selective biasing, the latter done with MicroUnity`s MaskRigger software. They simulated the entire imaging process with PROLITH 3D from FINLE Technologies; this program incorporates the latest resist models used at SEMATECH. These simulations fine-tuned the placement and size of the OPC structures needed to obtain the desired image. TEMPEST, a simulation program from the University of California at Berkeley that simulates the electromagnetic field at the mask, was used to minimize diffraction related feature placement problems and to further improve process latitude. TEMPEST provided the best mask topography for shaping the projected image. The final development step validated the alternating PSM and topographical design with non-OPC test masks designed by Benchmark Technologies.

Maskmaker Photronics fabricated the OPC reticles using its UltraRes process and phase-shift fabrication techniques, which achieve resolution of reticle features down to 250 nm. SEMATECH used these highly complex reticles to print wafers using a 0.53-NA 248-nm exposure tool from Integrated Solutions Inc. Cross-section scanning electron microscopy provided by Charles Evans & Associates was used to make thousands of measurements of the tiny resist features. The measurements were then compiled and analyzed by MicroUnity and SEMATECH to determine optimal process conditions. - P.B.