Shin-ichi Motoyama

Deposition of Cathode Coupled Plasma Enhanced Chemical Vapor Deposition SiN Films Using Liquid Source Material

Silicon nitride (SiN) films were prepared using 1,1,1,3,3,3-Hexamethyldisilazane (HMDS) instead of monosilane (SiH4) by the cathode coupled plasma enhanced chemical vapor deposition (PE-CVD). As HMDS and NH3 were used, SiN film prepared at RF power of 300 W shows high insulation performance, breakdown voltage of which is 7 MV/cm. This value is same as Si3N4 films deposited by thermal CVD. These films can be used for insulating films in various semiconductor devices. In addition, because it has higher optical transparency than SiN films deposited using SiH4, it can be used for optical coating films.

Improvement in Homogeneity and Ferroelectric Property of Mist Deposition Derived Pb(Zr,Ti)O3 Thin Films by Substrate Surface Treatment

Pt/TiO2/SiO2/Si substrate UV surface treatment was carried out with O3 or N2/O2 atmosphere before film deposition to improve the homogeneity of mist deposition (MD)-derived Pb(Zr, Ti)O3 (PZT) films. The effect of the surface treatment was determined by measuring the contact angle of the distilled water on Pt substrates. The largest improvement in wettability was achieved in the N2/O2 atmosphere at the O2 partial pressure of approximately 10%. The macroscopic homogeneity of PZT films deposited onto the surface-treated Pt substrates was dramatically improved with a decrease in the contact angle. Although the contact angle of 0° was achieved by over 5 min UV treatment in any atmosphere, the P–E hysteresis properties and J–E characteristics were further improved with treatment time, even after the contact angle of 0° was reached. The improvement in electrical properties corresponded closely to the improvement in microscopic surface roughness. The PZT film deposited onto UV/N2-treated Pt substrates for 30 min showed the two fold remanent polarization (2Pr) of 52 µC/cm2, while the PZT film on the 5-min-treated substrate showed 44 µC/cm2.

Influence of Dry Recess Process on Enhancement-Mode GaN Metal-Oxide-Semiconductor Field-Effect Transistors

To gain a flat recess profile with uniform etching depth, dry recess experiment with different inductively coupled plasma (ICP) etching conditions was done on an AlGaN/GaN heterostructure. Trenching effect at the bottom near the sidewall was observed when positive photoresist was utilized and the ICP power was low. The recess profile was improved by adopting SiO2 as the etching mask and increasing the ICP power. GaN metal–oxide–semiconductor field-effect transistors (MOSFETs) on AlGaN/GaN heterostructure with different gate recess conditions were fabricated and characterized. The maximum field-effect mobility of 152.8 cm-2 V-1 s-1 and the minimum interface state density of 1.39×1011 cm-2 eV-1 were obtained from the optimized gate recess condition with ICP power of 100 W, bias power of 20 W and etching mask of SiO2.

GaN MOSFET with Boron Trichloride-Based Dry Recess Process

The dry recessed-gate GaN metal-oxide-semiconductor field-effect transistors (MOSFETs) on AlGaN/GaN heterostructure using boron trichloride (BCl3) as etching gas were fabricated and characterized. Etching with different etching power was conducted. Devices with silicon tetrachloride (SiCl4) etching gas were also prepared for comparison. Field-effect mobility and interface state density were extracted from current-voltage (I-V) characteristics. GaN MOSFETs on AlGaN/GaN heterostructure with BCl3 based dry recess achieved a high maximum electron mobility of 141.5 cm2V−1s−1 and a low interface state density.

Fabrication of Pb(Zr, Ti)O3 Thin Films by Liquid Source Misted Chemical Deposition Method Equipped with a Mist-Droplet Size Controller

The liquid source misted chemical deposition (LSMCD) method has attracted much attention for fabricating integrated ferroelectric random access memories (FeRAMs). We have developed a new atomizer and an advanced refiner with ultrasonic vibration which made possible the efficient generation of mist droplets with a diameter of 0.2 μm. In a conventional system, the droplet-size distributions measured by a particle counter were significantly changed by changing the carrier gas flow rate. However, by applying vibration to the refiner, the range of the carrier gas flow rate in which the droplets with sizes of less than 0.2 μm were the primary components has been expanded. The PZT thin films were fabricated using this refined mist. The films fabricated with vibration showed well saturated hysteresis loops and higher 2P r than that fabricated without vibration. The 2P r and 2E c of the films were 62 μC/cm2 and 120 kV/cm, respectively. Moreover, we fabricated a PZT film as thin as 55 nm that exhibited ferroelectric properties by LSMCD with vibration.

Field isolation for GaN MOSFETs on AlGaN/GaN heterostructure with boron ion implantation

We report the investigation of boron ion implantation as a device field isolation process for GaN metal-oxide-semiconductor field-effect transistors (MOSFETs) on AlGaN/GaN heterostructure. In the mesa isolation region of a bar-type MOSFET, a parasitic MOS-channel existed and widened the designed channel width, which would result in an overestimated mobility compared with a ring-type MOSFET. After boron ions implantation in the isolation region, the overestimation of field-effect mobility of bar-type MOSFETs was eliminated. The sub-threshold characteristics and on-state drain current of the bar-type MOSFETs coincide with the ring-type devices. Long-channel ring-type MOSFETs, with and without ion implantation, were fabricated on the recess region to evaluate the sub-threshold characteristics. The MOSFETs with boron ions implanted into the recess region showed a low drain current up to the gate bias of 10V. The result indicated that boron ion implantation prevented the formation of parasitic MOS-channel in the isolation region and achieved field isolation. The current–voltage characteristics of MOSFETs with the normal recess condition demonstrated no degradation of device performance after boron ions implanted into the isolation region. Boron ion implantation by further optimization can be a field isolation method for GaN MOSFETs.

InGaN-Based Light-Emitting Diodes Fabricated on Nano Patterned Sapphire Substrates with Pillar Height of More than 600 nm by Nanoimprint Lithography

GaN-based light-emitting diodes (LEDs) were fabricated on nano patterned sapphire substrates (nano-PSSs) by nanoimprint (NIP) lithography. A nano-PSS with a pillar height of more than 600 nm was achieved. The surface emission of the LEDs was strongly affected by pillar height, and the surface emission intensity was highest at a pillar height of 250 nm. In contrast, the external quantum efficiency of the LEDs on the nano-PSSs with diameters of 100 and 450 nm was approximately 30% higher than that on a flat sapphire substrate, which is similar to that on a conventional PSS.

Reactive Ion Etching of NiFe Film with Organic Resist Mask and Metal Mask by Inductively Coupled Plasma

Etching of NiFe films covered with an organic photo-resist or Ti was successfully performed by an inductively coupled plasma-reactive ion etching (ICP-RIE) system using CHF₃/O₂/NH₃ discharges exchanging CHF3 for CH₄ gas gradually. Experimental results showed that the organic photo-resist mask can be applied to the NiFe etching. In the case of the Ti metal mask, it was found that the etching-selectivity Ti against NiFe was significantly varied from 7.3 to ~0 by changing CHF₃/CH₄/O₂/NH₃ to CH₄/O₂/NH₃ discharges used in the ICP-RIE system. These results show that the present RIE of NiFe was dominated by a chemical reaction rather than a physical sputtering.