Fujio Terai

Xenon Flash Lamp Annealing of Poly-Si Thin Films

We have investigated xenon (Xe) flash lamp annealing for the crystallization of amorphous silicon (a-Si) films for polycrystalline silicon (poly-Si) thin film transistors on glass substrates. The Xe flash lamp emits white light with a wavelength range of 400-800 nm for 40 μs, thereby instantaneously supplying the energy necessary to crystallize a-Si films to poly-Si films. The distance between electrodes in the lamp is 1000 mm, the bore diameter is 10 mm, and the peak voltage is up to 20 kV. The sample structure is a-Si (50 nm)/SiOx (100 nm) deposited on a glass substrate by plasma-enhanced chemical vapor deposition using SiH 4 gas. An average grain size of 500 nm is obtained without substrate heating during Xe flash lamp annealing when the light energy density is 1.82 J/cm 2 . The grain size is less than 50 nm at 1.55-1.78 J/cm 2 , and a significant grain growth occurs at 1.82 J/cm 2 . The light energy is absorbed by the whole a-Si film, because the Xe flash lamp emits light with a wide wavelength range of 400-800 nm. Therefore, when the light energy exceeds its threshold at which the a-Si film melting point is observed, a-Si films can be partially melted and subsequently crystallized at the top and bottom surfaces, thereby forming large-grain poly-Si.

Newly Developed High-Speed Rotating Disk Chemical Vapor Deposition Equipment for Poly-Si Films

We have developed high-speed rotating disk chemical vapor deposition (CVD) equipment. A high deposition rate, good thickness uniformity and few particles were achieved for polycrystalline silicon (poly-Si) film deposition on a 200-mm-diameter silicon (Si) wafer, by optimizing the structure of the rotating disk CVD equipment. A magnetic bearing motor was used for rotating and controlling the 200-mm-diameter wafer at 3000 rpm, and the substrate temperature was controlled to be 600–900°C. Gas flow was also controlled to avoid the re-adsorption of reaction by-products onto the wafer surface. A deposition rate of 316 nm/min, a film thickness nonuniformity ±3%, and less than 20 particles (over 200 nm in diameter) were achieved at a deposition temperature of 680°C for poly-Si deposition on the 200-mm-diameter wafer. These results show that the number of particles can be reduced even at a high deposition rate. The mechanisms of the high performance for poly-Si deposition are considered to be the reduction in the thickness of the boundary layer of temperature above the wafer surface and the suppression of the vapor-phase reaction.

High-Speed Rotating-Disk Chemical Vapor Deposition Process for In-Situ Arsenic-Doped Polycrystalline Silicon Films

We have developed high-speed rotating-disk chemical vapor deposition (CVD) equipment for polycrystalline silicon (poly-Si) films. This CVD equipment has an enhanced ability to reduce the boundary layer thickness at a given temperature above a wafer surface, and to suppress vapor-phase reactions. We investigated in-situ arsenic-doped poly-Si film deposition using silane (SiH4), arsine (AsH3) and nitrogen (N2) in a high-speed rotating-disk CVD as functions of AsH3 flow rate and deposition temperature. Both the deposition rate and resistivity decreased with increasing AsH3 flow rate. A deposition rate of 120 nm/min, a resistivity of 16 mΩcm, a film thickness nonuniformity of ±5%, and a number of particles of less than 20 (over 200 nm in diameter) were achieved at a deposition temperature of 680°C for in-situ arsenic-doped poly-Si deposition on a 200-mm-diameter silicon (Si) wafer. Moreover, it was confirmed that the concentration of As in the poly-Si film was low at the initial stage of deposition, and that this process has a high gap filling capability in a hole of 0.18 µm width and 7 µm depth. It was also confirmed that there were conditions for a high step coverage of more than 1. These properties are inferred to be due to the adsorbed AsH3 preventing the adsorption of SiH4.

New Inductively Coupled Plasma System Using Divided Antenna for Photoresist Ashing

We have developed an inductively coupled plasma (ICP) system with a small chamber for 300-mm-diameter-wafer processes, and a good uniformity of ashing, and both low substrate temperature and low pressure were achieved. The features of this ICP system are substrate temperatures lower than 60°C in order to suppress chemical reactions, and low pressures of 3–5 Pa to suppress the both oxidation of Cu wiring and the degradation of low-k films. Furthermore, the antenna is divided plurally and capacitively coupled. This new antenna can achieve good uniformity in a small chamber because the capacitive coupling to the chamber through a quartz glass window can be easily controlled by reducing series impedance, even when the radio frequency (rf) power is very high. Moreover, the damage to the quartz glass window can be decreased by controlling the series impedance of the antenna, resulting in a long-lasting quartz window. The chamber structure was also optimized by performing an original plasma simulation to improve the uniformity of ashing rate. As results for 300-mm-diameter wafers in the 460-mm-diameter chamber, an average ashing rate of 848 nm/min with a uniformity of ±5.5% was obtained for photoresist films under the following conditions: an O2 gas flow rate of 200 sccm, a substrate temperature of 60°C, a gas pressure of 3 Pa and an rf power of 4 kW.

A design method of a robust controller for hydraulic actuation with disturbance observers

In this paper, a design method of a robust controller for hydraulic actuators is proposed. Generally speaking, the hydraulic actuator generates hydraulic force, and a load is driven by the hydraulic force. In order to control the hydraulic actuators, non-linearity caused by chamber pressures and natural feedback meaning the effect by the load velocity on the hydraulic pressure dynamics should be considered. A controller with feedback linearization is one of the methods to compensate the effects of the non-linearity and the natural feedback. However, since the method is based on the model parameters of the hydraulic actuator, the control performance is affected by modeling errors and modeling uncertainties. Therefore, a robust controller for the hydraulic actuator is proposed to complement the disadvantage of the conventional method. To design the proposed controller, a part of the feedback linearization, that is, pressure (nonlinearity) compensation is used to linearize the hydraulic pressure dynamics virtually. By using the virtually linearized hydraulic dynamics and the nominal mass, the nominal model of the hydraulic pressure and that of the load motion dynamics model are designed. Then, the effects which prevent each dynamics from behaving as the nominal models are defined as disturbances. In the proposed controller, two types of the observers are designed to compensate the disturbances. In this paper, the design details are shown and the validity of the proposed method is shown by simulation and experiments.

A Remote Operated Quadruped Robot System for Investigation of Reactor Building

A remote operated quadruped robot has been developed for disaster site which can move on stairs, slopes, and uneven floor under the radiation-polluted environment, such as TEPCO Fukushima Daiichi nuclear power plants [1][2].In particular, the control method for stable walking and the remote operation system have been developed to move on stairs in the reactor building.We applied this robot to investigation of suspicious water leakage points in reactor building at Fukushima Daiichi nuclear power plants unit2[3]. In this investigation, a small vehicle equipped with camera and a manipulator which is connected the vehicle with cable were mounted on the robot and were carried to near the target by the quadruped robot and the investigation was carried out with the small vehicle.© 2014 ASME

Plasma ashing using microwaves via slot antenna for 300-mm wafers

We developed a downflow asher which incorporates a large-sized microwave excited plasma source with a slot antennas, for 300 mm wafers. An ashing rate of 4.5 micrometer/min and uniformity of plus or minus 5.1% were obtained at a wafer temperature of 250 degrees Celsius. The ashing rate was approximately fourfold and the uniformity level was similar to those obtained with conventional downflow asher. The newly developed asher incorporates: (1) a high-density plasma source with slot antennas, (2) a processing chamber the shape of which is optimized by gas flow simulations and (3) a compact, high- speed wafer transportation system with an originally developed vacuum robot which is primarily responsible for the high ashing rate. The maximum overall throughput, including that of the transportation system, is 160 wafers/h. Application of this system to the ashing of 300 mm wafers is expected.