Tsutomu Tsukada

New Ultra-High-Frequency Plasma Source for Large-Scale Etching Processes.

A low temperature, uniform, high-density plasma is produced by an ultra-high-frequency (UHF) discharge using a new spokewise antenna. The plasma is uniform within ±5% over a diameter of 30 cm. The plasma density, 1×1011 cm-3, for low electron temperatures of 1.5-2.0 eV, is almost proportional to the UHF power even at a low UHF power. No magnetic field is needed to maintain a high-density plasma. Consequently, the plasma source is fairly simple and lightweight. The plasma source can accomplish a notch-free poly-Si etching profile with a high etching rate at a narrow space pattern of less than 0.3 µ m.

Low‐temperature, uniform, and high‐density plasma produced by a new ultra‐high‐frequency discharge with a spokewise antenna

A low‐temperature, uniform, high‐density plasma is produced by an ultra‐high‐frequency (UHF) discharge with a new spokewise antenna. The plasma is uniform within ±5% over a diameter of 20 cm. The plasma density, 5×1010 cm−3 for low‐electron temperatures of 1.5–2.0 eV, is almost proportional to the UHF power even at a low‐UHF power of 100 W. No magnetic field is needed to maintain a high‐density plasma. Consequently, the plasma source is fairly simple and lightweight. The plasma source should ease serious problems in etching processes that use conventional high‐density plasmas.

Adhesion of copper films on ABS polymers deposited in an internal magnet magnetron sputtering system

In order to metallize ABS polymer surfaces without electroless plating, thin copper films were deposited by an internal magnet, coaxial cylindrical magnetron sputtering system. The adhesion of the metallized layers was evaluated by measuring peel strength. Average strength higher than 1 kg/cm was obtained with an appropriate process of metallizing. Several factors, which might influence the adhesion, such as conditions of sputtering, pretreatment of the polymer before sputtering, and the constitution of the polymer were studied. Oxygen plasma treatment before the metallization was found to improve the adhesion. Topographical change of the polymer surface was observed with SEM for the oxygen‐plasma‐treated substrate. Also, surface change in atomic constitution and chemical bonding energies were detected by ESCA and ir spectroscopy. It was found that the peel strength was higher for substrates of smaller butadiene content, which implied that tensile strength of polymer affected the peel strength of the meta...

Plasma diagnostics and low-temperature deposition of microcrystalline silicon films in ultrahigh-frequency silane plasma

Microcrystalline silicon thin films were formed on quartz substrates by ultrahigh-frequency (UHF) plasma enhanced chemical vapor deposition from a mixture of silane (SiH4) and hydrogen (H2) gases at low substrate temperatures (Ts). The UHF plasma was excited at a frequency of 500 MHz. The deposition rate and the crystallinity of the films were investigated as a function of H2 dilution, total pressure, mixture ratio of SiH4 to H2 and Ts. A crystalline fraction of 63% with a high deposition rate of 7.7 A/s was obtained even at a Ts of 100 °C. At a temperature of 300 °C, a crystalline fraction of approximately 86% was achieved at a deposition rate of 1.4 A/s. Diagnostics of the UHF plasma have been carried out using a Langmuir probe, ultraviolet absorption spectroscopy, and optical emission spectroscopy. Good crystallinity was explained by the balance of the sheath voltage and atomic hydrogen densities in the UHF plasma. Namely, the UHF plasma source achieving a high density plasma with a low electron temper...

Etching Characteristics by M=0 Helicon Wave Plasma.

The each characteristics of SiO2 and Al?Si?0.5%Cu were studied using the M=0 helicon wave plasma etching apparatus. A high concentration of F radicals was observed during SiO2 etching using fluorocarbon gases. The etch rate of SiO2 was strongly dependent on the concentration of F radicals in the plasma. A method of increasing the selectivity of SiO2 to poly-Si was discussed. The Al?Si?0.5%Cu film deposited on the wafer of 200 mm diameter was anisotropically etched with high selectivity to photoresist using Cl2 and BCl3 gases. The etch rate uniformity across a wafer was also discussed.

EFFECTS OF ELECTRON TEMPERATURE IN HIGH-DENSITY CL2 PLASMA FOR PRECISE ETCHING PROCESSES

Silicon etching characteristics are investigated by using radio‐frequency (rf) biased ultrahigh frequency (UHF) and other conventional plasmas (electron cycotron resonance plasma, inductive coupled plasma, surface wave plasma) determined by using a Cl2 etchant. The silicon etching rate and its pattern dependence are significantly improved by decreasing the electron temperature when supplying a 600‐kHz rf bias. In particular, use of the UHF plasma allows high‐rate and microloading‐free silicon trench etching. It is suggested that a larger number of negative ions are generated in the UHF plasma because of the extremely low electron temperature. The low‐frequency bias accelerates the negative and positive ions alternately to the substrate surface. As a result, the low‐frequency biased UHF plasma reduces the charge accumulation on the substrate.

Probe diagnostics of supermagnetron plasma with applications of continuous and pulse-modulated rf electric fields

Parameters of supermagnetron plasma produced by rf (radio frequency) pulse, with 49.6 ms on and 0.4 ms off, were investigated by probe characteristics measured at 10–100 μs after the rf pulse in order to avoid disturbance in the measurement. The plasma parameters obtained by a continuous rf electric field and the phase differences of the rf electric field to both parallel electrodes were compared with those of rf pulse plasma. A double probe was mainly used in Ar as a standard gas, and a single probe was used in He gas for rf electric field free measurements using pulse-modulated rf plasma. He gas was used for extended time measurements because of a low probe contamination as a result of sputtering from two electrodes. A high electron density of an order of 1011 cm−3 was observed at low gas pressure (20 mTorr) for Ar plasma, and a low electron temperature of 1.1–1.2 eV was observed for He rf plasma. As for an rf phase difference dependence between two rf powers supplied to two parallel electrodes, maximum...

Essential points for precise etching processes in pulse-time-modulated ultrahigh-frequency plasma

Since ultrahigh-frequency (UHF) plasma has a low electron temperature (less than 2 eV) and uniform density, the effects of electron confinement due to the sheath potential barrier or plasma potential distributions are less prominent than with electron cyclotron resonance plasma or inductive coupled plasma. Consequently, multiple cusp magnetic fields are needed to maintain pulsed UHF plasma even at pulse intervals of a few tens of μs and they can significantly improve the etching rate and etching selectivity. Moreover, the characteristics of pulse-time-modulated plasma strongly depend on the substrate position from the generation region to the downstream region. Near the plasma generation region, pulsed plasma can be used to produce a higher rate and higher selectivity for polycrystalline silicon etching, compared with a continuous discharge. By transporting the plasma from the generation region to the downstream region, however, improvements in the etching characteristics of the pulsed plasma are graduall...

Dependence of Electron Energy Distributions on Discharge Pressure in Ultrahigh-Frequency and Inductive-Coupled Cl2 Plasmas

In the ultrahigh frequency (UHF) plasma, a high ion density and a high energy tail in the electron energy distributions can be maintained in a wide pressure range from 3 to 20 mTorr, whereas in the inductively coupled plasma (ICP) these characteristics are drastically reduced when the gas pressure is increased. This indicates that the ionization in the UHF plasma does not depend significantly on the gas pressure from 3 to 20 mTorr because the discharge frequency is higher than the electron collision frequency in the UHF plasma. As a result, the UHF plasma possesses a wider process window for highly-selective polycrystalline silicon etching than the ICP.

Growth of Preferentially Oriented Microcrystalline Silicon Film Using Pulse-Modulated Ultrahigh-Frequency Plasma

Microcrystalline silicon films were formed on glass substrate at 300°C using pulse-modulated ultrahigh-frequency plasma, with variation of the pulse duty ratio (10–100%) and the pulse frequency (2–50 kHz). We found that the ratio of (111) to (220) crystalline orientation of films can be precisely controlled by changing the duty ratio or frequency. Variation in crystalline orientation closely correlated with the ratio of silicon atom density to hydrogen atom density in the plasma. Strongly preferential (111) growth was achieved, and we propose that the mechanism for this involves the ratio between silicon species and hydrogen atoms in the pulse-modulated plasma.