The Double-Sided Rugged poly Si (DSR) technology has been developed for high density DRAMs. The DSR technology was achieved using transformation of rugged poly Si caused by ion implantation. The DSR can increase the surface area of the storage electrode, because it has rugged surfaces on both upper and lower sides. The 2-FINs STC (STacked Capacitor cell) with DSR was fabricated in the cell size of 0.72 µm2, and it is confirmed that the DSR can increase the surface area 1.8 times larger than that of smooth poly Si. It is expected that 25 fF/bit is obtained with a 300 nm-thick storage electrode. These effects show that sufficient capacitance for 256 Mb DRAMs is obtained with a low storage electrode. It is confirmed that there is no degradation in C-V and I-V characteristics. Moreover, the DSR needs neither complicated process steps nor special technologies. Therefore, the DSR technology is one of the most suitable methods for 256 Mb DRAMs and beyond.

Water desorption from interlayer dielectric, spin-on-glass and SiO2 film deposited with tetraethylorthosilicate and O3, was controlled in order to reduce MOSFET hot-carrier degradation by using plasma SiO2 film as a water blocking layer. Two kinds of plasma SiO2 film were used in this study: SiH4 plasma SiO2 film deposited with SiH4 and N2O, and TEOS plasma SiO2 film deposited with TEOS and O2. Thermal desorption spectroscopy was used to study water desorption. Reduction of water desorption was obtained using plasma SiO2 film with water blocking ability; this reduction of water desorption resulted in suppression of the MOSFET hot-carrier degradation. The water blocking ability was obtained by low pressure deposition for SiH4 plasma SiO2 and low flow rate ratio of TEOS to O2 deposition for TEOS plasma SiO2. Water absorption studies of plasma SiO2 film using Fourier transform infrared spectroscopy revealed that water blocking ability is associated with small amount of water absorption both in SiH4 plasma SiO2 film and in TEOS plasma SiO2 film. Consequently, it is considered that the water blocking ability, as well as water absorption, of plasma SiO2 film depends on porosity.