Two-phase high-density charge coupled devices fabricated by electron-beam lithography

Abstract

One hundred and twenty-eight-bit, two-phase, high-density CCD linear shift registers with double-level polysilicon overlapping gate electrodes have been fabricated using electron-beam lithography for all levels of pattern delineation. The polysilicon gate electrodes are 0.15 mil long and the channel widths on two shift registers are 0.25 and 0.06 mil. The critical registration accuracy is ±1500 Å. These represent cell sizes of 0.1 mil2 corresponding to packing densities of 10–20 million bits/in. Charge transfer efficiency with VΦ=10 V and without fat zero is at least 0.9997 for 0.05 mil2 shift register. The low, uniform leakage current (1.5–4 nA/cm2) observed in CCD’s fabricated by electron-beam lithography compares favorably with those fabricated using optical lithography and larger geometry sizes. This indicates that no significant electron beam induced residual damage is present in these CCD structures.