Atsuhiro Nishida

The influence of SiN films on negative bias temperature instability and characteristics in MOSFET's

We investigated a method of suppressing both negative bias temperature instability (NBTI) in PMOSFETs and initial characteristic degradation in NMOSFETs, using test structures constructed using several SiN films. It was found that the thickness and area of the SiN films play a crucial role in order to suppress both of these effects. In this work, two experiments, in which SiN films were deposited all over the wafer and the films were patterned, were carried out. In the former, the thickness of SiN films is strictly limited to a range from 6 nm to 7 nm in order to suppress both NBTI in PMOSFETs and initial characteristic degradation in NMOSFETs. In the latter, the thickness is not strictly limited. NBTI in PMOSFETs and initial characteristic degradation can be suppressed by constructing the SiN film area so that hydrogen reaches the gate oxide but water does not reach the gate oxide. The area of the SiN films can be easily determined by taking water diffusion into account.

Evaluation of the gate oxide transformed by ion implantation

Abstract Ion implantation-induced damage to the gate oxide of antenna MOS capacitors has been investigated. It is confirmed that ion implantation into the MOS capacitors causes charge-induced damage and ion bombardment-induced damage. The degradation of the gate oxide due to ion implantation varies according to the relation between the projected range and the thickness of the polysilicon electrode. The mechanism of the oxide damage is discussed based on the results of current-voltage measurements and structural analyses by ESR and FTIR-ATR.

Development of a laser processing technology for high thermal radiation multilayer module

We developed a laser drilling technique using UV laser (lambda=355nm) for epoxy resin that includes aluminum oxide filler at high density to realize a high thermal radiation multilayer module. By studying the laser condition to see what conditions enable the via hole to make good contact with the metal layer, it was found that both laser fluence and a beam diameter had threshold. Here threshold fluence was lower than threshold diameter, so when the diameter was smaller than the threshold, unprocessed aluminum oxide filler remained in the via hole. Hence, when the resin with high density filler was irradiated with a UV laser, while the resin evaporated the aluminum filler with high melting point was hardly processed but rather discharged from the via hole with the gaseous resin. It follows from this that high speed drilling by low laser fluence is possible when the filler size is smaller than the via hole diameter, and we realized a high thermal radiation multilayer substrate at low cost. Applying the developed laser drilling technique, we made inverter modules. Measuring the temperature distribution using IR camera, heat from the power device was diffused to the metal substrate through thermal via holes

The effect of surface electric and magnetic fields on negative charge-up during high-current ion implantation

The breakdown characteristics of a thin gate oxide during high-current ion implantation with an electron shower have been investigated by controlling the energy distribution of the electrons. Deterioration of the oxide has also been discussed with regard to the total charge during ion implantation in comparison with that of the TDDB (time dependent dielectric breakdown). Experimental results show that the high-energy and high-density electrons which concentrated in the circumference of the ion beam due to the space charge effect cause the degradation of the thin oxide. It is confirmed that eliminating the high-energy electrons by applying magnetic and electric fields lowers the electron energy at the water surface, thereby effectively suppressing the negative charge-up.<<ETX>>

Development of Material and Processing Technology for High Thermal Conductive Multilayer Module

We have developed a multilayer substrate that is formed from a high thermal conductive resin including ceramic fillers at high density in order to realize a module that is more miniaturized and has lower thermal resistance. First, we realized a resin with a very high filler filling rate of 75% by mixing two kinds of spherical fillers different in particle size. The thermal conductivity of the insulation resin films we developed is 4.4 W/mK. And we were able to make resin films with a thickness from 35 mum-120 mum. Additionally, with the improvement of adhesion between Cu and resin affected by control of the resin fluidity and filler diameter, a high thermal conductive multilayer substrate could be realized. The reliability of the high thermal conductive multilayer substrate formed from the developed resin was then investigated. Even after 1000 cycles of HC test (heat cycle test: 233 K-398 K, 30 minutes at each temperature), the resistance of the daisy chain pattern did not change. The THB test results (temperature, humidity, and bias test: 358 K, 85% RH, 50 V), showed that an insulation layer of more than 60 mum thickness gives enough dielectric reliability. Finally, we made a high voltage (350 V) drive inverter power supply circuit module for automobile applications including the high thermal conductive multilayer substrate we developed. Applying a multilayer substrate enabled the inverter module to be downsized to 85% of the one with a conventional monolayer substrate. Further, the thermal resistance of the miniaturized module was the same as the conventional module. In addition, the results of HC test and THB test indicated that the reliability of the developed module is sufficient for automobile applications.