Search

In the stacked structure of PbZr1-xTixO3(PZT)/Pt/TiN/poly-Si for a ferroelectric random access memory (RAM), the mechanism of TiN barrier-metal oxidation was investigated by transmission electron microscopy (TEM). In the cross-sectional TEM images of PZTyPtyTiNySi, titanium oxide was observed beneath the Pt grain boundary. The oxygen was diffused through the Pt grain boundary during the heat treatment in an oxygen atmosphere for crystallization of PZT films. The annealing of the TiN film in ammonia resulted in the suppression of the oxidation during the crystallization annealing of PZT. The minimum required Pt film thickness to protect TiN from oxidation can be reduced from 200 nm to 100 nm.

The effect of surface Fermi level position on dc-characteristics of InP-based heterostructure bipolar transistors (HBT) is reported. The Fermi level of an InP surface covered with silicon oxide was located at an energy position close to the conduction band minimum of InP. This implies that an electron accumulation layer forms at the interface, which acts as a surface leakage path. The HBT passivated with silicon oxide films showed large excess base current and poor current gain. In contrast, the Fermi level position at the silicon nitride/InP interface was found to be near the midgap, and no electron accumulation layer was formed at the interface. The HBT passivated with silicon nitride film showed excellent dc characteristics with very small, excess base current.

A GaAs surface-cleaning method using UVO3treatment was developed. The UVO3treatment involves two processes: GaAs surface oxidation and oxide removal. Surface oxidation is performed by using a mercury lamp at high temperature, such as 180°C. GaAs oxide is removed by NH4OH solution dipping. Spectroscopic ellipsometry and X-ray photoelectron spectroscopy (XPS) study showed that thermally unstable As oxides exist on a non-treated surface; however, surface GaAs oxides are almost completely removed by this treatment. This cleaning method was applied in the field effect transistor (FET)-gate-formation process and, consequently, Schottky leakage current was significantly reduced.

Highly selective etching of InAlAs over InGaAs was observed by irradiation with a 193-nm ArF excimer laser in a Cl2atmosphere. The etching rate of InAlAs relative to that of InGaAs increased as the laser fluence decreased and the Cl2pressure increased, and the highest observed etching rate ratio exceeded 70. The result was compared with the case of etching with HBr gas, where no enhancement of InAlAs etching was observed. It is speculated that the very fast InAlAs etching rate is due to the fast Al reaction and desorption, which introduces new reactive sites on the surface.

Highly selective etching of InGaAs/InAlAs was achieved by irradiation with a 193-nm ArF excimer laser in a HBr and F2atmosphere. Adding F2gas to the HBr gas enhanced the InGaAs etching rate while reducing the InAlAs etching rate, resulting in an etching rate ratio of over 450. The etching mechanism is discussed in terms of pressure dependence and laser fluence dependence data. Our findings suggest that ArF-excimer-laser-assisted etching is feasible for gate-recess etching of InGaAs/InAlAs field effect transistors.

A process technology for a pseudomorphic high electron mobility transistor (P-HEMT) with an offset-gate structure has been developed for millimeter-wave monolithic microwave ICs (MMICs). A HEMT with the offset-gate structure showed both reduced gate-to-drain capacitance and drain conductance compared with a device with a non-offset-gate structure. The device showed a maximum available gain (MAG) of 9 dB at 77 GHz. The device was applied to a 77 GHz three-stage power amplifier, which showed a small-signal gain of 16.5 dB. Under preliminary life testing, this amplifier showed a stable small-signal gain for over 160 hours of testing at 175°C.

Interface properties of an amorphous (a-)Se/GaAs(001) heterostructure made on a Se-stabilized (2×1) GaAs surface are investigated. Photoemission spectroscopy analysis shows that the band alignment is staggered with the valence band discontinuity of -0.27±0.05 eV. Amorphous-Se/GaAs diode current-voltage characteristics also support the staggered alignment. This is suitable for applications to photoelectric devices in which photogenerated holes in GaAs are injected into a-Se for low-noise avalanche multiplication. Capacitance-voltage characteristics of the diode show the presence of interface states near the conduction band edge of GaAs, in agreement with the Fermi-level position measured from photoemission spectroscopy. These pinning states are introduced through the deposition of a-Se, and may be attributed to outdiffused Ga atoms in a-Se.

It was found that lanthanum hexaboride (LaB6) forms a thermally stable Schottky contact with a high barrier height of about 0.9 V on a chemically-etched n-type GaAs(100) substrate. GaAs metal-semiconductor field effect transistors (MESFET's) having excellent DC characteristics were obtained using LaB6as a self-aligned gate. The high barrier height enabled normally-off MESFFT's to have a large operation margin.

A Se-stabilized GaAs(001) surface is examined by extended X-ray absorption fine structure (EXAFS) analysis. The Se K-edge EXAFS shows components due not only to the first but also the second nearest neighbors, indicating that the Se atoms are incorporated into ordered atomic arrangements. Comparing the interatomic distances to those measured for Ga2Se3and GaSe, it is concluded that the nature of the surface compound on the Se-stabilized GaAs surface is close to that of Ga2Se3.

Highly selective etching of InGaAs/InAlAs assisted by a 193 nm ArF excimer laser in HBr and F2atmosphere is used as a gate-recess technique to fabricate InAlAs/InGaAs high-electron-mobility transistors (HEMTs). The HEMT with an Al/Ti gate shows a gate ideality factor of 1.2 and an effective Schottky barrier height of 0.55 eV. For a 0.7 µ m×18 µ m device, a maximum extrinsic transconductance of 610 mS/mm is obtained. The extrinsic transconductance of the HEMT is stable for more than 6 weeks, whereas degradation of the extrinsic transconductance is observed in a device fabricated by etching using citric acid. Enhancement of InGaAs/InAlAs selectivity is caused by formation of a nonvolatile AlFxthin layer on the InAlAs surface, as shown by the X-ray photoemission spectroscopy (XPS) measurements. The good gate electrical characteristics and long-term transconductance stability are attributed to the Al deficiency of the etched surface after the postetching wash. These results demonstrate that this excimer-laser-assisted selective-etching technique is useful for fabricating damage-free, high-performance InAlAs/InGaAs HEMTs.

The chemical reaction and the change in the Schottky barrier height at the Pt/PbZrxTi1-xO3(PZT) interface as a result of annealing was studied by in-vacuoX-ray photoelectron spectroscopy. Annealing at 320° C produced metallic Pb atoms which migrated on the Pt surface. There were more of these atoms when the annealing was done in H2than in a vacuum. After H2annealing, the core level peaks for the elements in the PZT showed a band bending shift of ?0.4 V toward higher binding energy, indicating that the n-type Schottky barrier height at the Pt/PZT interface was lowered by the H2annealing.