Plasma etching technologies such as reactive ion etching (RIE), isotropic etching, and ashing/plasma cleaning are the currently used booster technologies for manufacturing all silicon devices based on the scaling law. The needs-driven conversion from the wet etching process to the plasma/dry etching process is reviewed. The progress made in plasma etching technologies is described from the viewpoint of requirements for the manufacturing of devices. The critical applications of RIE, isotropic etching, and plasma ashing/cleaning to form precisely controlled profiles of high-aspect-ratio contacts (HARC), gate stacks, and shallow trench isolation (STI) in the front end of line (FEOL), and also to form precise via holes and trenches used in reliable Cu/low-k (low-dielectric-constant material) interconnects in the back end of line (BEOL) are described in detail. Some critical issues inherent to RIE processing, such as the RIE-lag effect, the notch phenomenon, and plasma-induced damage including charge-up damage are described. The basic reaction mechanisms of RIE and isotropic etching are discussed. Also, a procedure for designing the etching process, which is strongly dependent on the plasma reactor configuration, is proposed. For the more precise critical dimension (CD) control of the gate pattern for leading-edge devices, the advanced process control (APC) system is shown to be effective.

The degradation of porous methyl silsesquioxane (MSQ) films (k=2.2) by plasma irradiation has been investigated using several kinds of gas chemistries, which are used for photoresist strip. The porous MSQ is easily degraded by O2 plasma ash process and the dielectric constant increases largely, even by using the condition that minimizes the damage to nonporous SiOCH films. As the results of several kinds of plasma irradiation, it is clarified that N2 plasma minimizes the degradation of porous MSQ. O2 and H2 plasmas extract methyl (CH3) groups from the porous MSQ films and degrade even the deep part from the film surface. On the other hand, N2 plasma changes the quality of only the film surface and suppresses the degradation of the inside of the film. Furthermore, the small amount of H2 addition to N2 plasma is effective in the increase of the ash rate and the removal of the deposition on the sidewall without the remarkable increase of the dielectric constant. Finally, the optimized N2/H2 ash process minimizes the damaged layer thickness of the sidewall with single damascene structures.

Ensuring gate oxide reliability and low switching loss is required for a trench gate SiC-MOSFET. We developed a trench gate SiC-MOSFET with a p-type region, named Bottom P-Well (BPW), formed at the bottom of the trench gate for bottom oxide protection. We can see an effective reduction in the maximum bottom oxide electric field (Eox) and a significant improvement in dynamic characteristics with a grounded BPW, whose dV/dt is 76 % larger than that with a floating BPW due to reduction in gate-drain capacitance (Cgd). The grounded BPW is found to be an effective means of both suppressing Eox and reducing switching loss.

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To reveal the effects of artificial alteration of water level regime on the regeneration of lakeshore plants from seeds, we examined the factors causing regeneration failure in Lake Kasumigaura, Japan. A survey of microtopography within and around a remnant fragment of lakeshore vegetation revealed that, over a large range, the habitat is frequently inundated in spring under the current water regime, although it was rarely inundated under past water regimes. Analysis of the patterns of seedling emergence and establishment at microsites at various elevations revealed a significant negative correlation between number of inundation days and abundance or species-richness of seedlings that emerged in the spring. Most seedling deaths occurred when the study site was inundated. We suggest that regeneration failure caused by the artificial raising of the lake's water level is one of the principal mechanisms of the recent vegetational decline in the lake.