Shimpei Iijima

0.1 mu m CMOS devices using low-impurity-channel transistors (LICT)

Summary form only given. It was found that LICTs are very effective for providing low threshold voltages with good turn-offs in 0.1 mu m CMOS devices. Attention is given to device fabrication criteria, key process technologies used, and the features achieved using LICTs.<<ETX>>

Design and performance of 0.1- mu m CMOS devices using low-impurity-channel transistors (LICT's)

0.1- mu m CMOS devices using low-impurity-channel transistors (LICTs) with dual-polysilicon gates have been fabricated by nondoped epitaxial growth technology, high-pressure oxidation of field oxide, and electron-beam lithography. These devices, with gate lengths of 0.135 mu m, achieved normal transistor operation at both 300 and 77 K using 1.5-V supply voltage. Maximum transconductances are 203 mS/mm for nMOS transistors and 124 mS/mm for pMOS transistors at 300 K. Low-impurity channels grown on highly doped wells provide low threshold voltages of about 0.35 V for nMOS transistors and about -0.15 V for pMOS transistors at 77 K, and preserve good turn-offs with subthreshold swings of 25 mV/decade at 77 K. LICTs suppress short-channel effects more effectively, compared with conventional devices with nearly uniform dopings.<<ETX>>

The Study of Ultrathin Tantalum Oxide Films before and after Annealing with X-Ray Photoelectron Spectroscopy

The effects of post-deposition annealing on the microstructure of tantalum oxide ( Ta2O5) deposited on Si are evaluated by means of X-ray photoelectron spectroscopy. With the peak decomposition technique and the angle-resolved X-ray photoelectron spectroscopy (ARXPS) method we found that there is SiO2 layer and Ta suboxide at the interface. By using a simple two-layer model, the thickness of both the Ta2O5 layer and the interfacial SiO2 layer could be evaluated. Investigating Ta2O5 films this way before and after annealing revealed that annealing has the following effects on the interfacial reaction. With post-deposition annealing under O2, Ar, or N2 gas, the Si substrate is oxidized by oxygen from the Ta2O5 layer. The Ta2O5 is partly reduced and N2 gas activates this reaction. The thickness of the interfacial SiO2 layer is reduced by nitridation of the Si substrate.

Reduction of current leakage in chemical-vapor deposited Ta 2 O 5 thin-films by oxygen-radical annealing [DRAM dielectric]

The electrical properties of CVD-Ta/sub 2/O/sub 5/ thin-films are improved by post-deposition oxygen-radical annealing. Since this annealing is carried out at very low pressure (10/sup -6/ torr), the growth of SiO/sub 2/ in Ta/sub 2/O/sub 5//Si interface is small, and the residual carbon in the film is reduced. The damage to the Ta/sub 2/O/sub 5/ film caused by oxygen ion bombardment is negligible, because few charged particles reach the film. A critical voltage V/sub crit/ of 1.45 V for the leakage current less than 10/sup -8/ A/cm/sup 2/ was realized by these Ta/sub 2/O/sub 5/ films with the effective thickness t/sub eff/ of 2.59 nm. The V/sub crit/ value for oxygen-radical annealing is higher than that for oxygen-plasma annealing.

A New Atmospheric Pressure Ionization Mass Spectrometer for the Analysis of Trace Gas Impurities in Silicon Source Gases used for Semiconductor Fabrication

A new atmospheric pressure ionization mass spectrometer (APIMS) was developed for the measurement of trace gas impurities in silicon source gases, such as monosilane and disilane. To prevent ionization instability caused by Si compound formation, the ion source is divided into a discharge chamber and a reaction chamber (bi-compartment). Impurity species are ionized in the reaction chamber by reactant ions which are generated by corona discharge using an inert gas in the discharge chamber. As the deposition was greatly reduced by this method, stable measurement was possible for over 60 h. Ions of SiH3OH+2 and Si2H5OH+2 were found to be produced from trace water in monosilane. The detection limit (S/N) for water in nitrogen was found to be 5 ppt, which is comparable to that obtained with our previous single-compartment ion source.

Ta/sub 2/O/sub 5/ capacitors' dielectric material for giga-bit DRAMs

We fabricated 256-Mbit DRAM cells using a 0.5 /spl mu/m high CROWN capacitor with crystallized Ta/sub 2/O/sub 5/ dielectric film. We confirmed that the crystallized Ta/sub 2/O/sub 5/ (3.3 nm of SiO/sub 2/-equivalent thickness) was very stable in the conventional metallization process. The key issues for manufacturing were to eliminate the hydrocarbon contaminants during high temperature O/sub 2/ annealing. Our preliminary investigation of Ta/sub 2/O/sub 5/ metal-insulator-metal (MIM) capacitors suggested that it is possible to fabricate 1-Gbit DRAM cells using the amorphous Ta/sub 2/O/sub 5/ MIM capacitor with a CROWN structure.

Quantitative Analysis of Trace Water in Monosilane Gas Using Atmospheric-Pressure Ionization Mass Spectrometer with Bicompartment Ion Source

Quantitative analysis of trace amount of water at the ppb level or less in monosilane gas was conducted using an atmospheric-pressure ionization mass spectrometer with a bicompartment ion source which prevents Si compound deposition in the ion source. Water ion which is not detected in the usual form of H2O+ due to the lower ionization potential of SiH3+ than that of H2O+, was detected as cluster ions (SiH3OH2)+, (SiH3OH2H2O)+, (Si2H5OH2)+ and (Si2H5OH2H2O)+. These ions were identified by the collision-induced dissociation method. The intensity of each of these ions changed with monosilane concentration. An independent calibration curve of monosilane concentration was obtained from the total intensity of these ions. In this raw monosilane gas, about 20 ppb of water was detected. This was decreased to 2.5 ppb upon using an adsorption-type purifier. The detection limit (S/N) was estimated to be 5 ppt.