Eiji Nagasawa

Process of forming electrodes and interconnections on silicon semiconductor devices

A process of forming electrodes and interconnections in a silicon semiconductor device comprises the steps of forming an insulating film on a silicon substrate, defining an opening in the insulating film, depositing a layer of metal having a high melting point on the insulating film, implanting ions to mix an interface between the metal layer and the silicon substrate, heating the construction in a temperature in the range of from 400 to 650 degrees Celsius to form a silicide of the metal layer in the opening, and selectively etching away an unreacted metal layer so as to self-align the silicide metal layer with the opening. The silicide metal layer is then annealed in a non-reducing gas atmosphere at a temperature ranging from 800 to 1,100 degrees Celsius.

Mo- and Ti-silicided low-resistance shallow junctions formed using the ion implantation through metal technique

Mo-and Ti-silicided junctions were formed using the ITM technique, which consists of ion implantation through metal (ITM) to induce metal-Si interface mixing and subsequent thermal annealing. Double ion implantation, using nondopant ions (Si or Ar) implantation for the metal-Si interface mixing and dopant ion (As or B) implantation for doping, has resulted in ultrashallow ( ≤ 0.1-µm) p⁺-n or n⁺-p junctions with ∼30-Ω sheet resistance for Mo-silicided junctions and ∼5.5-Ω sheet resistance for Ti-silicided junctions. The leakage current levels for the Mo-silicided n⁺-p junctions (0.1-µm junction depth) and the Mo-silicided p⁺-n junction (0.16-µm junction depth) are comparable to that for unsilicided n⁺-p junction with greater junction depth ( ∼0.25 µm).

Low-resistance MOS technology using self-aligned refractory silicidation

A new low-resistance MOS technology has been developed for use in VLSIs with scaled MOSFETs. A new MOSFET is featured by gate and source-drain being refractory silicided in self-alignment and isolated from one another, even without any insulating spacers on gate sides. An essential part of the MOSFET fabrication process is the ion implantation through metal (ITM) silicidation technique, which consists of ion-beam-induced metal-silicon interface mixing and appropriate annealings to form high-quality refractory metal silicides in self-alignment with silicon patterns and with good reproducibility.

A Self-Aligned Mo-Silicide Formation

Mo-silicides, formed by a new technique combining ion implantation through metal film (ITM) to induce metal/Si interface mixing and also to form doped layers with appropriate subsequent annealings, were found to have excellent properties in film uniformity and self-aligned formation for exposed Si areas (contact holes). These excellent silicidation properties in the ITM technique were also confirmed for patterned poly-Si silicidation. Lateral silicide growth out of contact holes, usually observed in silicidation using mere thermal reaction of refractory-metal/Si structures, was markedly suppressed in the ITM silicidation.

Efficient infrared‐to‐visible conversion in BaY2F8 : Yb,Er crystal by confinement of excitation energy

Efficient up‐conversion of near‐infrared energy was realized by confinement of infrared energy in an optical cavity containing a BaY2F8 : Yb,Er single crystal. The lifetime of the ytterbium excited state showed a marked increase and, in a typical instance, became as long as 3.6 msec. Combined with 8% efficiency GaAs : Si diode, an over‐all conversion efficiency of nearly 0.04% was obtained for a 50‐mA diode‐exciting current.

Quantitative Elucidation of the Infrared-to-Visible Conversion Processes in YF3: Yb, Er Phosphors

A method of systematic evaluation and determination of host parameters is developed for infrared-to-visible conversion phosphors based on a simple rate equation model. Calculated rise characteristics of the visible emissions are in satisfactory agreement with the experimental results obtained for YF3: Yb, Er phosphors. Several host parameters, such as nonradiative decay rate and energy transfer coefficient, were obtained systematically by fitting the calculated curves with expermental data. It was shown that the conversion efficiency of the infrared light into the green emission is dependent on nonradiative decay rate as well as sensitizer excited state lifetime, both of which are sensitive to preparation procedures. Discussions are presented on the applicability limit of the rate equation model.

A highly stable Al−Si contact to Mo-silicided shallow junctions

Highly stable (up to 550°C) contacts have been realized in an Al–2%Si contact to n+–p and p+–n shallow junctions (Xj~0.16 µm) covered by a 0.1 µm thick uniform MoSi2 layer, which was formed by the ion implantation through metal ITM technique. Low contact resistance was maintained, at submicron (0.5 µm square) Al–Si/MoSi2 contacts, after 550°C sintering for 30 minutes.

Via-hole filling by simultaneous deposition and ion etching

Abstract The calculated maximum aspect ratio (depth-to-diameter ratio) for via-hole filling without cavity creation by bias-sputtering, considering the shadowing effect, was found to be in good agreement with the experimental value, which was practically less than 1. The results indicated that reducing the shadowing effect is essential to enable the filling of via-holes with high aspect ratios by a simultaneous deposition and ion etching technique. Partially ionized evaporation was chosen as a technique with little shadowing effect. Experimental results by arc-discharge partially ionized evaporation showed that via-holes with an aspect ratio ∼1 were filled with Mo.

An image method application to multilayer spreading resistance analysis

Abstract A numerical program to obtain the impurity profile within a semiconductor material from the measured spreading resistance data was developed. In the program, an image method was applied to calculate the spreading resistance of the multilayered structure, which consisted of a stack of layers, each of homogeneous resistivity, with thicknesses equal to the spacing of the spreading resistance data. The solution adopted in the present program is described in this paper. Converting results from the spreading resistance data to the impurity profile of an implanted and diffused sample and buried channel are also shown.