Combining and Matching Optical, Electron-Beam, and X-Ray Lithographies in theFabrication of Si Complementary Metal-Oxide-Semiconductor Circuits with 0.1 and Sub-0.1 Micrometer Features

摘要

In the fabrication of large-area Si complementary metal-oxide-semiconductorcircuits with 100 and sub-100 nm features, it is inefficient to use direct-write electron-beam (e-beam) lithography for all of the layers, in part because of the exceedingly long writing times. Instead, a strategy of 'mix and match' is preferred, in which coarse features on all layers are defined by optical projection and only the fine features are written by e-beam lithography. We describe a strategy that combines optical, e-beam, and x-ray lithographies, and solves the problem of scale matching and distortion in such a mix-and-match scheme. Layers that include only coarse features are exposed directly on Si wafers using a G-line stepper. This same stepper is also used to expose, on a chromecoated quartz wafer, arrays of e-beam field alignment marks along with any coarse features required in this 'critical layer'. This pattern is then transferred by deep ultraviolet proximity printing onto an x-ray mask and plated up in gold. The e-beam writes the fine features using the e-beam field-alignment marks as reference. Because the arrangement of the e-beam field-alignment marks reflects the distortion and scale of the optical stepper, overlay in the final circuit on the wafer is ensured. Furthermore, considerable e-beam writing time is saved. The final pattern is transferred onto the device wafers using x-ray lithography.