Hiroaki Nakaoka

Plasma doping for silicon

Very shallow and dense doping was realized by using the plasma doping method. This method was applied to fabricate diodes and MOS transistors with photo-resist as a mask material. This method is likely to be an alternative to ion implantation due to its properties of low energy and high throughput. The brief history of plasma doping is also reviewed.

Quarter-micrometer SPI (Self-aligned Pocket Implantation) MOSFET's and its application for low supply voltage operation

A novel SPI (Self-aligned Pocket Implantation) technology has been presented, which improves short channel characteristics without increasing junction capacitance. This technology features a localized pocket implantation using gate electrode and TiSi/sub 2/ film as self-aligned masks. An epi substrate is used to decrease the surface impurity concentration in the well while maintaining high latch-up immunity. The SPI and the gate to drain overlapped structure such as LATID (Large-Angle-Tilt Implanted Drain) technology allow use of the ultra low impurity concentration in the channel region, resulting in higher saturation drain current at the same gate over-drive compared to conventional device. The carrier velocity reaches 8/spl times/10/sup 6/ cm/sec and subthreshold slope is less than 75 mV/dec, which can be explained by low impurity concentration in the channel and in the substrate. The small gate depletion layer capacitance of SPI MOSFET was estimated by C-V measurement, and it can explain high performance such as small subthreshold slope. On the other hand, the problem and the possibility of low supply voltage operation have been discussed, and it has been proposed that small subthreshold slope is prerequisite for low power device operated at low supply voltage. In addition, the drain junction capacitance of SPI is decreased by 65% for N-MOSFETs, and 69% for P-MOSFETs both compared with conventional devices. This technology yields an unloaded CMOS inverter of 48 psec delay time at the supply voltage of 1.5 V. >

New Methods for ultra-Shallow Boron Doping by Using Plasma, Plasma-Less and Sputtering

1. lntroduction The ultra shallow doping for sub-tenth micron CMOS has been proposed by low energy ion implantationl ) and solid phase diffusion2). We have been further developing a practical method for obtaining ultra shallow doping profiles at near room temperature. This technology was named plasma doping3). The shallow doping methods must satisfy the following key items. 1) low energy for shallow junctions 2) high through-put for productivity and fabrication of densely concentraled layers 3) low temperature lo avoid photoresist damage and undesired boron diffusion 4) safety; if possible, un use of no toxic gas (for example BzHo)