Yukito Nakagawa

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.

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.

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...

Ion Current Density and Ion Energy Distributions at the Electron Cyclotron Resonance Position in the Electron Cyclotron Resonance Plasma

Extremely highly selective phosphorus-doped polycrystalline silicon etching is achieved at the electron cyclotron resonance (ECR) position in a newly developed ECR plasma etching system. To characterize these etching results, the ion current density and the ion energy distribution in a ECR plasma are measured. Microwave power is absorbed completely at the ECR position. Therefore, the ECR position has maximum ion current density in an ECR plasma. Moreover, the mean ion energy and the width of ion energy distribution has minimum values at the ECR position. The ECR position in the ECR plasma can satisfy a high ion current density and a low ion energy at the same time. These characteristics correspond to the etching results.

Optimization of plasma density and radial uniformity of a point-cusp magnetic field applied capacitive plasma

A feasibility study in the development of a large area high-density plasma source with a higher radial plasma uniformity for large area wafer processing was carried out. Experiments were performed for 200 mm diameter wafers using parallel plate capacitively coupled plasma excited by 60 MHz radio frequency current. Point-cusp magnetic fields that can be easily expanded for 300 mm diameter wafer processing reactors without any technical difficulties are applied to the upper electrode. The point-cusp magnetic fields are generated by arranging 115 permanent magnets on a 266 mm diameter upper electrode with alternate polarity and equal distance. This arrangement of magnets produces a strong magnetic field at the surface of upper electrode and almost a magnetic field-free environment at around 40 mm below the upper electrode. This magnetic field also causes no polarization of the plasma due to the E×B drift of electrons where E and B are the direct current electric and magnetic field strengths, respectively. Ap...

Magnetically Enhanced Dual Frequency Capacitively Coupled Plasma Source for Large-area Wafer Processing

A magnetron-type plasma source of parallel plate configuration has been developed for large-area wafer processing in the semiconductor industry. In this plasma source there are 80 equally separated magnets arranged with alternative polarities on a 40-cm-diameter top rf electrode. These magnets generate magnetic field cusps below the top rf electrode. Since electrons that lie in the magnetic field cusps are confined, a lower self-bias voltage of the top rf electrode results. With this magnet arrangement, the E×B drifts of charged particles are limited to smaller localized areas and canceled out in macro-scale. Therefore, the radial uniformity of the plasma does not differ much from that of a nonmagnetic parallel plate capacitively coupled plasma source. The plasma density of this magnetron-type plasma source monitored at 1.3 Pa is above 1011 cm-3 for rf powers over 1000 W. The plasma nonuniformity over 300 mm area is <±5% at the pressures below 4 Pa. Further, this magnet arrangement yields a magnetic-field-free environment for wafer processing in the close vicinity of the top rf electrode–a feature that cannot be seen in most of the magnetron-type plasma sources.

etching by M = 0 helicon plasma

Etching characteristics in three different modes employing an M = 0 helicon plasma were compared. It was concluded that high selectivity could not be realized in the high source power operation mode in principle. The comparison between the time-modulated discharge mode and the low source power operation mode in the continuous discharge revealed that almost identical etching characteristics could be obtained if, and only if, the imposed source power in the continuous discharge was equal to the net source power in the time-modulated discharge. It was also confirmed that the degree of dissociation of process gases could be controlled by adjusting the source power in a continuous discharge by an M = 0 helicon plasma.

Influence of magnetic field on the self‐bias potential on a radio frequency‐powered electrode in radio frequency plasma

Electric self‐bias potential and its distribution on the radio frequency (rf) electrode in an rf plasma have been measured using probes buried in the electrode. The potential increases almost proportionally with the net rf power (Wrf) ranging from 5 to 80 W. When the magnetic field parallel to the electrode (Wrf=26 W) is applied, the potential is reduced from −150 V (0 T) to −50 V (0.04 T) at the center of the electrode and the gradient in the potential distribution occurs along the E×B direction. This mechanism, the role of the external magnetic field, and the industrial applicability are discussed.

SiO2 Etching Using M= 0 Helicon Wave Plasma

When applying high-density plasma to SiO 2 etching, the ability to control the degree of dissociation is critical. In this study, two methods for controlling the degree of dissociation were evaluated using M = 0 helicon wave plasma. One method was time-modulated discharge and the other adjusting the source power in the conventional continuous discharge. It was concluded that almost identical etching characteristics could be obtained, at least in M = 0 helicon wave plasma, if and only if the applied source power in the continuous discharge was equal to the net source power in the time-modulated discharge. The probe measurement revealed that the electron temperature did not change with increasing source power ; however, the emission spectroscopic study indicated that the high-energy tail of the electron-energy distribution function grew with increasing source power. This is considered to be the cause of the high degree of dissociation.