Shuichi Saito

Suppression of Titanium Disilicide Formation on Heavily Arsenic-Doped Silicon Substrate

Titanium disilicide formation on heavily arsenic-doped silicon substrate was investigated. The suppression of disilicide formation was due to the existence of an incubation time, but not to the reduction of the disilicide formation rate. The incubation time for disilicide formation was induced when the amount of arsenic was above a critical concentration (5×1020 atoms/cm3) at the silicon surface. Arsenic concentration higher than the critical value induced the retardation of transformation from the titanium-rich silicides to the disilicide. When the arsenic concentration was lower than the critical value, the disilicide formation occurred without an incubation time.

Silicon Surface Imperfection Probed with a Novel X-Ray Diffraction Technique and Its Influence on the Reliability of Thermally Grown Silicon Oxide

Silicon surface imperfection was investigated by an X-ray diffraction technique under the condition of simultaneous specular and Bragg reflections, using the tunability of synchrotron radiation in conjunction with an asymmetric reflection. The surface roughness was the main imperfection on the conventional mechanochemical polished silicon wafer, and this surface imperfection was reduced by a series of sacrificial oxidation procedures. The time-dependent dielectric breakdown (TDDB) characteristics were also improved by these procedures. In this way, the reliability of the metal oxide semiconductor capacitor was dependent on the surface imperfection of the silicon substrate.

Effect of CHF3 Addition on Reactive Ion Etching of Aluminum Using Inductively Coupled Plasma

The role of CHF3 gas addition in reactive ion etching (RIE) processes using inductively coupled plasma for aluminum wirings were investigated. With increasing of the amount of CHF3 gas addition to the etching gas, the pattern profile changed from reverse to ordinary taper and the pattern width increased. It was considered that by adding CHF3 to the main etching gas, a larger amount of passivation layer deposited on the sidewall of the resist and Al pattern, which suppressed side etching of the pattern. To clarify the role of CHF3 addition, XPS, FT-IR and TDS analyses were carried out to study the structure of the passivation layer. Consequently, it is considered that the pattern sidewall is composed of AlF3, an organic polymerized film and a passivation layer including ammonium salt and B oxide. Due to the addition of CHF3 gas into the etching gas, AlF3 is additionally formed, which is deposited on the pattern sidewall, resulting in the change of the etched pattern profile and width.

Formation of Ammonium Salts and Their Effects on Controlling Pattern Geometry in the Reactive Ion Etching Process for Fabricating Aluminum Wiring and Polysilicon Gate

The role of N2 gas addition in the reactive ion etching (RIE) processes for aluminum wiring and polysilicon gate fabrication was investigated. With an increase in the amount of N2 gas added to the etching gas, the pattern profile changed from a reverse to an ordinary taper and the pattern width increased. By AES analysis, nitrogen was detected in the pattern sidewall passivation layer when N2 gas was added. Optical emission spectroscopy of the plasma revealed that hydrogen was supplied from the decomposition product of the photoresist in RIE of aluminum with BCl3/Cl2. XPS, FT-IR and TDS analyses were carried out to study the structure of the passivation layer. Consequently, it was confirmed that nitrogen combined with hydrogen to form N–H bonds in NH4+, and that NH4+ coupled with Cl-, AlCl4- and SiF62- during aluminum and polysilicon RIE, respectively. It was also found that ammonium salts were deposited on the pattern sidewall, and played a major role in controlling the etching profile and pattern width.