Phase shift lithography in the manufacture of sub-120 nm low-voltage DSP circuits

In this paper the successful integration of alternating aperture phase-shift lithography methodology into a 0.12 mum random-logic CMOS process flow is discussed. This methodology enabled the fabrication of a digital signal processor (DSP) operating at 100 MHz with a 1.0 V Supply voltage with a measured stand-by current of less than 100 muA and a dynamic power dissipation of 0.23 mW/MHz. The phase-shifted DSP chip clocks above 170 MHz at 1.5 V, a threefold improvement over the 0.24 mum device, demonstrating an improvement approximately proportional to 1/L-2. A commercially available software tool was used to generate the phase-shift mask patterns to reach this milestone DSP performance. Two million transistors in this DSP integrated circuit with critical dimensions (CD) of 0.24 mum are phase shifted down to gate lengths below 0.12 mum. The CMOS process flow is optimized to achieve a low power-delay product and transistor implants are designed for conventionally designed circuits to be operational at low voltages. The technology features symmetric NMOS/PMOS threshold-voltage, nitrogen incorporated gate oxides, and a novel WSi/WSiN-polycide gate electrode stack to prevent Boron lateral diffusion.