Technology challenges for integration near and below 0.1 μm

Technology challenges for silicon integrated circuits with a design rule of 0.1 μm and below are addressed. We begin by reviewing the state-of-the-art CMOS technology at 0.25 μm currently in development, covering a logic-oriented processes and dynamic random access memory (DRAM) processes. CMOS transistor structures are compared by introducing a figure of merit. We then examine scaling guidelines for 0.1 μm which has started to deviate for optimized performance from the classical theory of constant-field scaling. This highlights the problem of nontrivial subthreshold current associated with the scaled-down CMOS with low threshold voltages. Interconnect issues are then considered to assess the performance of microprocessors in 0.1 μm technology. 0.1 μm technology will enable a microprocessor which runs at 1000 MHz with 500 million transistors. Challenges below 0.1 μm are then addressed. New transistor and circuit possibilities such as silicon on insulator (SOI), dynamic-threshold (DT) MOSFET, and back-gate input MOS (BMOS) are discussed. Two problems below 0.1 μm are highlighted. They are threshold voltage control and pattern printing. It is pointed out that the threshold voltage variations due to doping fluctuations is a limiting factor for scaling CMOS transistors for high performance. The problem with lithography below 0.1 μm is the low throughput for a single probe. The use of massively parallel scanning probe assemblies working over the entire wafer is suggested to overcome the problem of low throughput