Study of the manufacturing feasibility of 1.5-nm direct-tunneling gate oxide MOSFETs: uniformity, reliability, and dopant penetration of the gate oxide

Although direct tunneling gate oxide MOSFETs are expected to be useful in high-performance applications of future large-scale integrated circuits (LSIs), there are many concerns related to their manufacture. The uniformity, reliability, and dopant penetration of 1.5-nm direct-tunneling gate oxide MOSFETs were investigated for the first time. The variation of oxide thickness in an entire 150-mm wafer was evaluated by TEM and electrical measurements. Satisfactory values of standard deviations in the TEM measurements and threshold voltage measurements for MOSFETs with a gate area of 5 μm×0.75 μm, were obtained. These values improved significantly in the case of MOS capacitors with larger gate areas. The oxide breakdown field and the reliability with respect to charge injection were evaluated for the 1.5-nm gate oxides and found to be better than those of thicker gate oxides. Dopant penetration was not observed in n⁺ polysilicon gates subjected to RTA at 1050°C for 20 s and furnace annealing at 850°C for 30 min. Although much more data will be required to judge the manufacturing feasibility, these results suggest that 1.5-nm direct-tunneling oxide MOSFETs are likely to have many practical applications