Tsutomu Wada

A pattern edge profile simulation for oblique ion milling

An oblique ion milling simulation method is proposed in which etching and redeposition at the pattern side wall are taken into account. The effective etching rate at the pattern side wall is determined as the difference between the etching rate given by the angular dependency and the redeposition rate. The redeposition rate is assumed to be proportional to the etching rate of the material to be etched at the flat surface. A pattern edge profile simulation is carried out for an oblique ion milling of silicon. The simulation results agreed well with the experimental results with a relatively large ion beam incident angle.

Observation of ferroelectricity in very thin vinylidene fluoride trifluoroethylene copolymer[P(VDF-TrFE)] films by high frequency C-V measurements of Al-SiO2-P(VDF•TrFE)-SiO2-Si capacitors

MIS capacitors with Al–SiO2–P(VDFTrFE)–SiO2–Si structure were fabricated depositing P(VDFTrFE) film by a spin coating method to investigate properties of very thin ferroelectric polymer films. By sandwiching the polymer film with SiO2 films, application of an electrical field high enough for ferroelectricity measurement in several tens nm thick P(VDFTrFE) films became possible. It is revealed that P(VDFTrFE) film as thin as 32nm shows ferroelectricity by high frequency C-V measurements of the capacitors.

Effect of Pre-Annealing in Preventing Gate Oxide Breakdown Voltage Degradation Induced by Polysilicon Gate Delineation Using Ion Milling

Polysilicon gate MUS capacitors were fabricated using Kaufmann-type ion milling apparatus in gate electrode delineation. The breakdown voltage of the MOS capacitors was degraded when the polysilicon sheet resistance at the start of ion milling was higher than 20 kΩ/. The degradation was prevented when the polysilicon sheet resistance was lowered by annealing to less than 2 kΩ/ before ion milling.

Improvement of Schottky MOSFET Characteristics by B+ Implantation in Active Region

Schottky MOSFETs is effective to prevent latch-up in bulk CMOS due to a low minority carrier injection efficiency. However, the Schottky MOSFETs have a disadvantage of low gm, which is due to the offset caused by gaps between the S/D and the inversion layer under the gate electrode. This paper shows that B+ implantation of ~1011/cm2 in active regions for threshold voltage control in conventional CMOS process improves the gm of Schottky p channel MOSFETs. This effect is due to the doped B+ which forms p type layer in the gap regions between the S/D and the inversion layer and eliminates the offset electrically.

DRY LIFTOFF METHOD BY SUBLIMATION OF MOLYBDENUM OXIDE.

A new liftoff method is proposed in which the film to be lifted-off is deposited on a molybdenum pattern. After the deposition, liftoff is done by thermally oxidizing the molybdenum and sublimating the molybdenum oxide. One micro meter thick sputter-deposited silicon dioxide was successfully delineated by this dry liftoff method. Dry liftoff is possible in an oxigen ambient at a temperature of 700°C or higher. The rate at which the molybdenum underneath the silicon dioxide is removed increases with the oxidation temperature and is typically 30 µm/min at 900°C.

Optimum B+ Dose in S/D Regions to Improve Schottky p-Channel MOSFET Characteristics

A major disadvantage of Schottky MOSFETs is that gm is very low in comparison with conventional MOSFETs. Forming the p layer in S/D regions by B+ implantation increases the value of gm in a Schottky p-channel MOSFET. However, too great a B+ dose cannot maintain the Schottky MOSFETs advantages of latch-up prevention and restriction of the short-channel effect, because it changes the S/D into a pn junction from the Schottky junction. Also, too small a B+ dose does not give the maximum possible improvement in gm. This paper presents the optimum B+ dose in the S/D regions for giving the maximum improvement in gm without sacrificing the advantages of the Schottky MOSFET. Experiments on the dependence of gm the short-channel effect, and the latch-up characteristics on the B+ dose in the S/D regions show that the optimum B+ dose is near 1012 cm-2.