SUB-QUARTER MICRON LOGIC-GATE-PATTERN FABRICATION USING HALF-TONE PHASE-SHIFTING MASKS

A new technique for enhancing the resolution of isolated line patterns is proposed. It is based on the balance in the intensity and the phas e between the 0th-order rays and the rays diffracted from a line patte rn. We deduce this technique from a condition of a high-contrast image by using the complex amplitude. We show that this technique can bk ac hieved with an optimized halftone phase-shifting mask and optimized of f-axis illumination. The optimum transmittance of the mask is 30% for a 0.4-lambda/NA line pattern and the optimum illumination for isolated lines in the x and y direction is quadrupole-shaped illumination whos e centers are (+/-0.4, +/-0.4). We tested this method in KrF lithograp hy with an 8% halftone phase-shifting mask and found that a complex 0. 20-mu m gate pattern can be fabricated with a large depth of focus of 1.2 mu m.