Hiroyuki Aoe

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.

Dielectric properties of silicone thin films cross-linked by an electron beam☆

Three kinds of silicone films—dimethylpolysiloxane, methylvinylpolysiloxane and methylphenylpolysiloxane—were cross-linked by electron beam irradiation, and their dielectric properties were examined. The silicones, spun on to conducting substrate, were irradiated by the 10 keV electrons with charge density of 10−4–10−3 coulombs/cm2. The dielectric constant, loss, resistivity and dielectric strength of these films were evaluated with a parallel-plate capacitor configuration. The dielectric constant and loss were less than 3·1 and 0·8 per cent respectively. The resistivity and dielectric strength were higher than 1 × 1015 Ω-cm and 3 × 106 V/cm respectively. All constants of these silicone films were unchanged after 2 months storage in dry air except that the dielectric loss at high frequency was nearly doubled. The insulation between the parallel-plate electrodes was maintained even after heating up to 300°C.

Improvement of the spin-on-glass process by ion implantation for highly reliable MOS devices

We have developed a novel process for intermetal dielectrics (IMD) using ion-implanted organic spin-on glass (SOG). Ion implantation into the SOG films improves the hot carrier (HC) reliability, which deteriorates from the use of organic SOG films. The content of mobile water-related species in the organic SOG films, which was examined by thermal desorption spectrometry (TDS), is reduced by Art-ion implantation under the conditions of 140 keV, 1 x 10 15 ions/cm 2 ; while on the contrary, the content of mobile hydrogen in SOG is increased by ion implantation. The change in the mechanical stress due to ion implantation is small, because ion implantation shrinks SOG only in the direction vertical to the wafer surface. Thus the change in stress due to ion implantation scarcely affect the electrical characteristics of the underlying MOS-FET. Therefore the deterioration of HC reliability for the MOS devices with SOG as IMD is well explained by a water diffusion model rather than by a hydrogen diffusion and mechanical stress model.