Shinichi Satoh

Resonant frequency and radiation efficiency of meander line antennas

One of the approaches to reducing the size of half-wavelength linear dipole antennas is the meander dipole antenna, where the elements form a meander line. This paper presents a formula for the relationship between the geometrical size and the resonant frequency of the meander line dipole antenna, and a calculation formula for the radiative efficiency is derived from the result. It is shown that the geometrical parameters of the meander line dipole antenna can be determined from the specified radiative efficiency.

Simulation study on comparison between metal gate and polysilicon gate for sub-quarter-micron MOSFETs

Two-dimensional (2-D) process and device simulation is used to investigate the effectiveness of the depletion-free metal gate for a sub-quarter-micron MOSFET as compared with surface channel polysilicon gate MOSFETs which suffer greatly from the gate depletion effect. The results reveal that the subthreshold characteristic for the metal gate NMOSFET is considerably degraded since the depletion-free merit is covered up by an undesirable influence of the buried channel structure, which is indispensable to obtain an appropriate threshold voltage for the midgap gate. Consequently, the drivability of the metal gate MOSFET is comparable to that of the heavily doped polysilicon gate MOSFET under commonly used conditions, and further, the metal gate structure is disadvantaged against the reduction of the supply voltage.

Charge Collection Control Using Retrograde Well Tested by Proton Microprobe Irradiation

Soft error reduction by high-energy ion-implanted layers has been investigated by novel evaluation techniques using high-energy proton microprobes. A retrograde well formed by 160 and 700 keV boron ion implantation could completely suppress soft errors induced by the proton microprobes at 400 keV. The proton-induced current revealed the charge collection efficiency for the retrograde well structure. The collected charge for the retrograde well in the soft-error mapping was proved to be lower than the critical charge of the measured DRAMs (dynamic random-access memories). Complementary use of soft-etror mapping and ion-induced-current measurement could clarify well structures immune against soft errors.

New Method for Soft-Error Mapping in Dynamic Random Access Memory Using Nuclear Microprobe

Locally sensitive positions against soft error in a dynamic random access memory (DRAM) have, for the first time, been investigated using a proton microprobe. Both soft-error (bit-state) mapping and secondary electron mapping images of the investigated area could locally identify sensitive positions against soft error. Two kinds of error modes in a DRAM (i.e., cell mode and bit-line mode) could be directly monitored.

Low thermal budget surface cleaning after dry etching for selective silicon epitaxial growth

We studied the influence of plasma etching damage on epitaxial Si growth using ultrahigh vacuum chemical vapor deposition. The damaged layer induced on substrate surface had an amorphous structure that had some carbon, oxygen, and fluorine in its composition. The damaged layer was removed by in situ preheating above 850°C, before the growth, or by chemical dry etching (CDE). We found that CDE has the effect of decreasing the preheating temperature by 200°C as compared to the case without CDE. Furthermore, the dependence of the surface roughness of grown films on post-etching treatments is also discussed.

Soft error immunity in a DRAM investigated by nuclear microprobes

Abstract A nuclear microprobe has, for the first time, been used to investigate local sensitivity of structures in the 16 Mbit dynamic random access memory (DRAM) against incident particles. Both bit state mapping and secondary electron images of investigated areas were obtained in situ for identification of radiation sensitive areas. Both cell mode and bit line mode soft errors caused by ions incident in a DRAM could be directly monitored.

Charge collection and soft error in DRAMs investigated using 400 keV proton microprobe

Abstract The charge collection efficiency of diodes with various well profiles has been measured for optimization of the carrier profile for buried layers, formed by high-energy ion-implantation, against soft errors. The charge collection efficiency was calculated using the current induced by incident protons when proton microprobes at 220–400 keV were precisely positioned on the junction of an n+ p diode. The proton-induced current is reduced by a retrograde well structure. The charge collection efficiency is 20–35% lower than that of a conventional well. However, carriers created by incident protons would be easily collected by a buried layer deeper than the created carriers. The results are also supported by charge collection simulation.

Soft error susceptibility mapping of DRAMs using a high-energy nuclear microprobe

Abstract Soft errors in 16 Mbit dynamic random access memories (DRAMs) have been investigated using proton microprobes at 400 keV with a spot size of 1 × 1 μm 2 . The newly developed susceptibility mapping can reveal the correlation between the particle hit-position position and the susceptibility to soft errors in a DRAM. The cell-mode soft-errors were found to take place by the incidence of ions within 6 μm around a monitored cell. These errors would be induced by minority carrier diffusion in a lateral direction. This result manifests the possibility of multiple-bit errors by the incidence of an energetic particle.

Improvement of alignment tolerance against contact hole etching by growing of underlying silicon-selective epitaxial layer

Abstract We demonstrated that the influences of a contact hole overlapping a local oxidation of silicon (LOCOS) isolation can be reduced by using selective epitaxial growth, which is improved the alignment margin of the contact hole in the LOCOS region. The experimental results indicated that the epitaxial layer underlying the contact bottoms prevented the TiSi2 layer from penetrating into the Si substrate. Therefore, the leakage current at the overlapping region was drastically suppressed for a configuration where the contact hole and the LOCOS region overlapped. The breakdown voltage was improved compared with a case without an epitaxial layer.

Soft-error study of DRAMs using nuclear microprobe

A method for evaluation of soft errors in DRAMs using a nuclear microprobe developed in order to investigate the local sensitive structure is discussed. The susceptibility in the mapping image of a soft error caused by an ion incident onto or near a storage cell in a DRAM can be directly monitored by this method. Soft errors are induced within 4 mu m of the monitored memory cell. The retrograde well formed by MeV ion implantation has experimentally shown a reduction in soft errors. The charge collection into n/sup +/ layers with a retrograde well and a conventional well was estimated through the device simulation. These simulations agreed with the experimental results.<<ETX>>