Shin-Ichiro Kuroki

Enlargement of Crystal Grains in Thin Silicon Films by Continuous-Wave Laser Irradiation

The cw laser recrystallization of amorphous silicon (a-Si) thin films deposited on SiO2 films with Si(100) substrates was investigated by controlling irradiation conditions. The effects of the laser spot shape and laser-irradiated region overlap were found important resulting in two dimensional crystal growth different from conventional lateral crystallization. A laser beam spot was designed to realize a gradual temperature slope in the laser-irradiated region. The crystal grain growth of the Si thin films was effectively enhanced. Raster scanning was performed to make the crystal growth direction regular and effectively enhanced the crystallization of the recrystallized Si thin films. The laser-irradiated region overlap also effectively enhanced the crystallization of the recrystallized Si thin films. Consequently, (100) well-oriented polycrystalline Si thin films with an average grain size of 1.60 µm, which is about 5 times larger than that obtained by conventional excimer laser recrystallization, were obtained.

Cu Single Damascene Integration of an Organic Nonporous Ultralow-

An integration of an organic nonporous ultralow-k dielectric fluorocarbon (k = 2.2) deposited by microwave-excited plasma-enhanced CVD into Cu single damascene interconnects is developed in this paper. The changing of the chemical structure of the fluorocarbon was found after dry etching, which resulted in the degradation of electrical properties during the postetching cleaning process. A nitrogen plasma treatment was applied as a postetching process to minimize damage introduction to the fluorocarbon in the following damascene fabrication processes, and a line-to-line leakage current was significantly improved without the variance of effective dielectric constant (keff = 2.5) in Cu lines. In a thermal stress test at 350°C after Cu-interconnect fabrication, no degradation of the Cu line resistance and line-to-line capacitance was found, which indicated a sufficient thermal stability of the fluorocarbon film in Cu single damascene interconnects. Therefore, this robust organic nonporous fluorocarbon film is considered as one of the promising candidates of ultralow-k dielectrics for high-performance Cu interconnects in the future.

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The enhancement factors of a new structure called the nanograting metal–oxide–semiconductor field-effect transistor (MOSFET), which was proposed to achieve higher current drivability, were analyzed. From the measurement of the transconductance, the drivability enhancements of both n- and p-type MOSFETs were confirmed. This was mainly ascribed to the increased effective channel width. However, the enhancement ratios in nMOS and pMOS were different. In the nanograting MOSFETs, the existence of the current flowing in the direction on the (110) surface caused the effective electron mobility to be lower and the effective hole mobility to be higher than that in the conventional devices on the (100) surface. The stress from the polycrystalline silicon (poly-Si) gate also resulted in the change of the mobility. Because of the reasons above, the mobility difference between the nanograting nMOSFET and pMOSFET became slighter, thus, the area balance of the nanograting complementary MOS (CMOS) circuit could be improved. Combining this with the increased drivability could give the area advantage of the nanograting CMOSFETs.

Fluorocarbon Dielectric Deposited by Microwave-Excited Plasma-Enhanced CVD

Drivability-improved MOSFETs were successfully fabricated by using nano-grating silicon wafers. There was almost no additional process change in device fabrication when the height of the gratings was less than the conventional macroscopic wafer surface roughness. The MOSFETs with the grating height of 35 nm showed 21% improvement in current drivability compared to the conventional one with the same device occupancy area. And the roll-off characteristic of threshold voltage of nano-grating device held the line of conventional one in despite of the 3-D channel structure. The technology provides great advantages for drivability improvement without paying much tradeoff of process cost. This proposal will be useful to CMOS-LSIs with high performance in general.

Analysis of Drivability Enhancement Factors in Nanograting Metal-Oxide-Semiconductor Field-Effect Transistors

A novel chemically, thermally and electrically robust Cu damascene interconnects with an organic non-porous ultralow-k (ULK) dielectric fluorocarbon (k=2.2), deposited by an advanced microwave excited plasma enhanced CVD, is demonstrated. A practical nitrogen plasma treatment (NPT) was employed to minimize chemically damage introduction to fluorocarbon in post-etching cleaning and CMP processes. Also, a new structure with a delamination-protective-liner (DPL), instead of barrier-metal, between Cu and fluorocarbon is introduced to avoid thermally induced electrical degradation and to reduce the interconnect delay significantly (by >;30% in 32 nm-node). Non-porous ULK fluorocarbon with NPT and DPL technologies is a promising candidate for high performance Cu interconnects.

Characteristics of Nano-Grating N-Channel MOSFETs for Improved Current Drivability

Random crystallographic orientations of polycrystalline silicon (poly-Si) grains in the films grown on a SiO2 substrate by chemical vapor deposition were laterally aligned by maintaining the 110 restricted pillar texture through double Si+ self-ion implantations. The in-plane X-ray diffraction pattern and rocking curve clearly indicate the lateral alignment. The oblique-angle Si+ self-ion implantation was also found to be useful for increasing the amount of the 110 pillar texture. The electron backscatter diffraction (EBSD) pattern supports the increase in the amount of the 110 pillar texture and the lateral crystal orientation alignment. The transmission electron micrography and EBSD results also suggest that grain size is increased by double Si+ self-ion implantations. Although further systematic optimization may be required, the technique will be useful for improving the electrical characteristics of poly-Si devices for future electronic systems on insulators.