Space-resolved electron density and temperature evaluation by x-ray pinhole camera method in an ECR plasma

The characteristics of the spatial distribution of electron cyclotron resonance (ECR) plasma in an ECR-plasma enhanced metalorganic chemical vapour deposition system with a divergent magnetic field are investigated by a single Langmuir probe. The results show that the spatial distribution in the resonance room has a significant density gradient in both radial and axial directions. The ECR plasma density attains its highest value, about 3.0 × 1011 cm−3, at a position that moves away from the ECR point in the direction of the microwave window for about 2.5 cm. This peak is about ten times higher than the central plasma density in the downstream of the reactor chamber. Analysis of the spatial distribution in the reactor chamber shows that the ECR plasma in the upper region has poor radial and axial uniformity of plasma density and electron temperature under the influence of the magnetic field, whereas the plasma in the downstream region has fine radial uniformity. This excellent uniformity has extensive application in plasma processing. Furthermore, there is a maximum plasma density and a maximum electron temperature corresponding to a proper magnetic current. A change of magnetic current does not distort the characteristics of spatial distribution in the reactor chamber.

This study examines the strong dependence of electron cyclotron resonance (ECR) plasma generation on the microwave conditions and the magnetic field profiles in the ECR plasma. When an introduced microwave frequency oscillates and has a large ripple, the ECR plasma around the ECR region vibrates and regularly turns on and off. The microwave oscillation and the microwave ripple must be eliminated to prevent poor etching anisotropy. Moreover, the nonuniform plasma causes disturbed ion motions due to magnetohydrodynamic (MHD) plasma instability. It is found that uniform and high-density ECR plasma is generated by optimizing the waveguide, the location of the ECR region and the magnetic field profiles for precise ULSI patterning. Based on these results, we determine the essential features for realizing a compact ECR plasma source.

This study examines 10-100 µs modulated electron cyclotron resonance (ECR) plasma discharge for controlling the generation of reactive species in plasmas. The electron temperature, density and reactive species are measured by means of a Langmuir probe and an actinometric optical emission spectroscopy in the pulsed plasma. Good correlation is found between the density ratio of CF2 radicals and F atoms in the CHF3 plasma, and the combination of the pulse duration and intervals. These characteristics are explained in terms of the dependence of the generation of reactive species in the ECR plasma on time (10-100 µs). This method provides for control of the polymerization and achievement of highly selective etching to Si during SiO2 etching.

TiO2 (titania) films on titanium substrates were fabricated by electron cyclotron resonance (ECR) plasma oxidation. A calcification experiment of the Ti substrates treated with the ECR plasma was carried out by immersing in a supersaturated solution with respect to hydroxyapatite (HA) and octacalcium phosphate (OCP), but slightly saturated with respect to dicalcium phosphate, dihydrate (DCPD). After the immersion, OCP precipitated predominantly on TiO2 film, whereas formation of HA, the most stable phase under physiological condition, was inhibited. The calcification ability was affected by the substrate temperature during the ECR plasma oxidation. The surface roughness increased with increasing the oxidation temperature. These results indicate that the surface oxidation by ECR plasma modulates the surface characteristics to enhance OCP precipitation.

Summary form only given, as follows. A basic theory of the plasma electron temperature in ECR plasmas has been reported in recent studies in connection with application to the plasma etching technologies. However, the previous theoretical study of the ECR plasmas is primitive and ad hoc. We therefore develop a theory for plasmas generated by the electron-cyclotron-resonance (ECR) mechanism and an experiment is conducted to compare the theoretical prediction and experimental measurements. Due to a large electron mobility along the magnetic field, electrons move quickly out of the system, leaving ions behind and building a space charge potential, which leads to the ambipolar diffusion of ions. In a steady-state condition, the plasma generation by ionization of neutral molecules is in balance with plasma loss due to the diffusion, leading to the electron temperature equation, which is expressed in terms of the plasma size, chamber pressure, and the ionization energy and cross section of neutrals. The electron temperature decreases as the chamber pressure increases. Based on the ambipolar diffusion of ions, a self-consistent theory of the plasma density profile is developed. The power balance condition leads to the plasma density equation, which is also expressed in terms of the electron temperature, the input microwave power and the chamber pressure.

In a conventional, axial electron cyclotron resonance (ECR) plasma source, the substrate is typically in the diverging magnetic field region immediately downstream from the ECR region. Due to the high electron mobility along magnetic field lines, the substrate potential may influence the properties of the plasma. A substrate electrode consisting of seven, individually biasable, concentric rings was positioned below the ECR source, such that the potential at the termination of the field lines could be controlled. The ECR source used was a commercial, 1.5-kW device operating at 2.45 gHz and utilized two large electromagnets to provide magnetic fields in the range of 200–1000 G. The plasmas were diagnosed by means of a microwave interferometer in the source region, an automated Langmuir probe, and an array of ground potential metal rings in both the source and sample regions of the chamber. The results suggest that ions in this source are poorly confined (by the magnetic field) while electrons are well confined. The electron density could be increased slightly by electron reflection from the substrate region, or could be depleted strongly by substrate potentials exceeding the floating potential. The net efficiency of these sources is low: only about 14% of the ion flux from the plasma is incident on the sample position. The rest of the ions are lost at the source walls.

This study reveals the strong dependence of electron cyclotron resonance (ECR) plasma generation on the microwave conditions in the ECR plasma. When the introduced microwave frequency oscillates and has a large ripple, the ECR plasma around the ECR position vibrates. As a result, the half-value width of ion energy distributions around the ECR position is extended. Therefore, the microwave conditions cause plasma instability and disturb the ion flight paths to the substrate. The etching characteristics thus are degraded because of the low anisotropy and the deposition. In order to establish a stable discharge around the ECR position, the oscillation and ripple of this introduced microwave frequency must be accurately controlled.

There are several applications which require plasma to be produced over large volumes (~few cubic meters) and where it is desirable to have high radial/axial uniformity and high plasma density. Although electron cyclotron resonance (ECR) plasma sources are efficient and yield high plasma densities, these do not scale well with the volume. This paper presents a scheme for large volume plasma production that retains the advantages of ECR plasma sources without sacrificing on uniformity or high plasma density. It uses multiple, compact ECR plasma sources (CEPS) that are highly portable and easily mountable on any chamber. The large volume plasma system (LVPS) described in the paper is a scalable, circular cylindrical vessel of diameter ≈ 1m, consisting of source sections (SS) and spacer sections (SPS). The CEPS were mounted in azimuthally symmetric manner on matching ports along the periphery of the source sections, and the system was configured for 4/6 CEPS (one SS, two SPS, height ≈ 1.1 m) and 12 CEPS (two SS and three SPS, height ≈ 1.55 m). Since plasma filling in this scheme is radially inwards, the decrease in the volume to be filled as the plasma flows inwards, partially offsets the depletion of plasma as it flows away from the sources. This results in a more uniform plasma density over the system volume. The scheme also takes advantage of the magnetic field of the CEPS (produced by ring magnets) to produce a cusp magnetic field inside the chamber aiding confinement and uniformity. The paper discusses the development of the LVPS and presents plasma production results for two different configurations of the LVPS. The mechanism of plasma production is discussed in the light of results obtained for single CEPS.

More and more importance has been attached to inductively coupled plasma (ICP) in semiconductor manufacture. For a deep understanding of the plasma discharge process in the etching reactor, this study made a three-dimensional simulation on the Ar plasma discharge process with the commercial software CFD-ACE, which is according to the real experiment conditions and data supplied by North Microelectronic Corporation. The error of the simulation results is in the range of ±20% with credibility. The numerical results show that the three-dimentional spatial distribution of electron density is reduced from the chamber center to the wall. The distribution of electron density, electron temperature and power deposition is related to the shape and placement of the coil.

ABSTRACTA new electron cyclotron resonance (ECR) plasma etching technology has been developed to realize simultaneously high selectivity, high rate and anisotropic etching for phosphorus doped poly-Si and WSix/poly-Si at a low ion energy. In this technology, a substrate is located around the ECR position (875 gauss position) in an ECR plasma. As a result of ECR position etching, under the low pressure of 5 × 10−4 Torr, a high etching rate and an infinite selectivity to SiO2 etching are realized by using C12/O2 and Cl2/O2/SF6 etching gas.

This paper contains results of numerical and experimental investigation of glow discharge plasma created in a chamber of a new-type large-volume coaxial gridded hollow cathode. The discharge is created in argon at 25 Pa by applying time-varying power with frequency 20 kHz on electrodes. A 2-D model of the discharge was built using COMSOL Multiphysics. Self-consistent description of the discharge was obtained using the extended fluid approach, which couples continuity equations for charged particles and electron energy balance with Poisson's equation for electric potential. Electron transport coefficients and rates of electron-impact reactions were calculated using the electron energy distribution function. The spatial and radial distributions of plasma potential (V p ), electron density (n e ), and electron temperature (T e ) were obtained. It is shown that the plasma inside the chamber is similar to the negative glow of a dc glow discharge. Comparison of numerical results with the Langmuir probe measurements of electron density and electron temperature is presented and showed a good agreement.

Production of low-electron-temperature electron cyclotron resonance plasma with large area using 915 MHz microwave

An inner coating system has been developed with the use of scanning coaxial electron cyclotron resonance (ECR) plasma. In this system, plasma was generated by the ECR method inside a coaxial metallic or insulated tubes under low pressure and narrow gap conditions. ECR plasma was transported along the tube axis by controlling the position of ECR points. By inserting the insulated tube into the metallic tube, discharge at low pressure was realized. We succeeded in coating titanium onto the inner surface of an insulated tube of 27 mm inner diameter and 480 mm length. Using this coating system, titanium nitride (TiN) films were deposited in the metallic tube at an Ar flow rate of 0.1 sccm, an N2 flow rate of 0.1 sccm and a total pressure of 0.14 mTorr.

Electron cyclotron resonance (ECR) plasma thermal oxide has been investigated as a gate insulator of poly-Si TFT's. The ECR plasma thermal oxide grown on poly-Si film shows good electrical characteristics and renders a smooth interface with the poly-Si film. The fabricated poly-Si TFTs, even without plasma hydrogenation, show high performance characteristics. Both as-fabricated and plasma hydrogenated TFT's exhibit only a small threshold voltage shift (/spl Delta/V/sub th/ >

We have developed an apparatus that can measure the three-dimensional distribution of microwave electric field intensity in electron cyclotron resonance (ECR) plasmas. The reflection edge of the incident microwaves depends on the plasma density in the etching chamber: it is the ECR zone when the electron density (n e) is above 1×1011 cm-3 and the electrode when n e is below 1×1011 cm-3. The spatial distribution of the ion saturation current density at the electrode is the same as that of the microwave electric field intensity at the ECR zone. Therefore, in order to obtain uniform ion saturation current density, the intensity of the microwave electric field at the ECR zone must be kept uniform.