Low-temperature Electron Cyclotron Resonance Research Articles

55‐3: Development of Low‐Temperature Metal Dry‐Etching Equipment via ECR Plasma Source

This paper presents the dry etching performance and expectation of highly conductive thin metal films that are hardly etched at low temperature with conventional plasma dry etching equipment. Dry etching is performed using a combination of H2 and HCl gases in a reactive ion etching system with low temperature susceptor and electron cyclotron resonance (ECR) plasma source. We could achieve high electron temperature enough to dissociate and ionize H and Cl radicals from H2 and HCl molecules.

Impact of the Deposition Temperature on the Structural and Electrical Properties of InN Films Grown on Self-Standing Diamond Substrates by Low-Temperature ECR-MOCVD

The progress of InN semiconductors is still in its infancy compared to GaN-based devices and materials. Herein, InN thin films were grown on self-standing diamond substrates using low-temperature electron cyclotron resonance plasma-enhanced metal organic chemical vapor deposition (ECR-PEMOCVD) with inert N2 used as a nitrogen source. The thermal conductivity of diamond substrates makes the as-grown InN films especially attractive for various optoelectronic applications. Structural and electrical properties which depend on deposition temperature were systematically investigated by reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and Hall effect measurement. The results indicated that the quality and properties of InN films were significantly influenced by the deposition temperature, and InN films with highly c-axis preferential orientation and surface morphology were obtained at optimized temperatures of 400 °C. Moreover, their electrical properties with deposition temperature were studied, and their tendency was correlated with the dependence on micro- structure and morphology.

Chemical and electronic passivation of 4H-SiC surface by hydrogen-nitrogen mixed plasma

We propose a low-temperature electron cyclotron resonance microwave hydrogen-nitrogen mixed plasma treatment method for passivating 4H-SiC surface and investigate the effects of treatment on the structural, chemical, and electronic properties of the surface. The results indicate that the method is highly controllable and could result in an atomically ordered, unreconstructed, smooth, and clean SiC surface. The absence of surface band bending is indicative of an electronically passivated SiC surface with a surface state density as low as 5.47 × 1010 cm−2. This effect could be attributed to the simultaneous effects of H and N passivating on SiC surface.

Effect of TMGa flux on GaN films deposited on Ti coated on glass substrates at low temperature

Highly c-axis-oriented GaN films were deposited on Ti coated glass substrates using low temperature electron cyclotron resonance plasma enhanced metal organic chemical vapor deposition system (ECR-PEMOCVD) with trimethyl gallium (TMGa) as gallium source. The influence of TMGa flux on the properties of GaN films were systematically investigated by reflection high energy electron diffraction (RHEED), X-ray diffraction analysis (XRD), atomic force microscopy (AFM) and Raman scattering. The GaN film with small surface roughness and high c-axis preferred orientation was successfully achieved at the optimized TMGa flux of 1.0 sccm. The ohmic contact characteristic between GaN and Ti layer was clearly demonstrated by the near-linear current-voltage (I–V) curve. The GaN/Ti/glass structure has great potential to dramatically improve the scalability and reduce the cost of solid-state lighting light emitting diodes.

Lead phthalocyanine films deposited by ECR plasma-induced sublimation

Lead phthalocyanine (PbPc) thin films deposited by vacuum sublimation with Ar low-temperature electron cyclotron resonance (ECR) plasma treatment are investigated by means of reflection high-energy electron diffraction, atomic force microscopy, infrared spectroscopy, x-ray photoelectron spectroscopy and spectral ellipsometry. The intensity of plasma treatment is varied by the radio-frequency power input and the value of electrical bias applied to the sample. The films grown with and without plasma assistance are compared. The plasma intensity is considered to significantly influence the crystalline structure, surface morphology and film composition. At a low intensity the plasma assistance is analogous to vacuum annealing of films. At a medium intensity, a porous polymer matrix filled with PbPc in crystalline phases (monoclinic and triclinic) is formed in the films. At a high intensity, all the films consist of a compact polymer matrix, similar to a glassy solid, with small inclusions of PbPc molecules. The succession of PbPc molecule destructions in the growing film layer with plasma intensity increase is established by IR spectroscopy. The mechanism of polymer matrix formation is suggested.

Deposition and properties of highly c-oriented of InN films on sapphire substrates with ECR-plasma-enhanced MOCVD

InN films with highly c-axis preferred orientation were deposited on sapphire substrate by low-temperature electron cyclotron resonance plasma-enhanced metal organic chemical vapor deposition (ECR-PEMOCVD). Trimethyl indium (TMIn) and N2 were applied as precursors of In and N, respectively. The quality of as-grown InN films were systematically investigated as a function of TMIn fluxes by means of reflection high-energy electron diffraction (RHEED), X-ray diffraction analysis (XRD), and atomic force microscopy (AFM). The results show that the dense and uniform InN films with highly c-axis preferred orientation are successfully achieved on sapphire substrates under optimized TMIn flux of 0.8 ml·min−1. The InN films reported here will provide various opportunities for the development of high efficiency and high-performance semiconductor devices based on InN material.

Highly c-axis oriented GaN films grown on free-standing diamond substrates for high-power devices

GaN films with highly c-axis preferred orientation are deposited on free-standing thick diamond films by low temperature electron cyclotron resonance plasma enhanced metal organic chemical vapor deposition (ECR-PEMOCVD). The TMGa and N 2 are applied as precursors of Ga and N, respectively. The quality of as-grown GaN films are systematically investigated as a function of deposition temperature by means of X-ray diffraction (XRD) analysis, Hall Effect measurement (HL), room temperature photoluminescence (PL) and atomic force microscopy (AFM). The results show that the dense and uniformed GaN films with highly c-axis preferred orientation are successfully achieved on free-standing diamond substrates under optimized deposition temperature of 400 °C, and the room temperature PL spectra of the optimized GaN film show a intense ultraviolet near band edge emission and a weak yellow luminescence. The obtained GaN/diamond structure has great potential for the development of high-power semiconductor devices due to its excellent heat dissipation nature.

Silicon nitride thin films deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition for micromechanical system applications

Thin silicon nitride films have been deposited by a low temperature (20 °C) Electron Cyclotron Resonance (ECR) plasma directly on Si substrates. Varying the process pressure, gas composition and radio frequency bias power, films with different properties were obtained. Characterization by Fourier transform infra-red spectrometry reveals the presence of Si–N, Si–H and N–H bonds in the films. Refractive indexes in the range from 1.77 to 2.9 and deposition rates from 13 to 18 nm/min were determined by ellipsometry. Buffered hydrofluoric acid (BHF) etch rates from 0.7 to 509 nm/min, and KOH etch rates lower than 1 nm/min were obtained. Optical emission spectroscopy showed a strong correlation between the concentration of NH molecules produced in the plasma and porosity of the films. Finally, the films that presented high resistance to etching in KOH and BHF were used to fabricate suspended membranes on Si substrates. With these results, the ECR plasma produced SiN x films that have been used for fabrication of membranes in microelectromechanical systems.

Low temperature plasma etching for Si3N4 waveguide applications

Highly selective and anisotropic low temperature electron cyclotron resonance plasma etching process for silicon nitride optical rib waveguide devices compatible with integrated circuit technology is presented. Etching at low temperatures (−30°C) with SF6∕O2 chemistry in combination with a silicon dioxide hard mask achieved good anisotropy with the vertical sidewalls.

Low-temperature electron cyclotron resonance plasma-enhanced chemical-vapor deposition silicon dioxide as gate insulator for polycrystalline silicon thin-film transistors

Silicon dioxide films have been deposited at temperatures below 270°C in an electron cyclotron resonance (ECR) plasma reactor from O2, SiH4, and He gas mixture. Pinhole density analysis as a function of substrate temperature for different microwave powers was carried out. Films deposited at higher microwave power and at room temperature show defect densities (<7pinhole∕mm2), ensuring low-temperature process integration on large area. From Fourier transform infrared analysis and thermal desorption spectrometry we also evaluated very low hydrogen content if compared to conventional rf-plasma-enhanced chemical-vapor-deposited (PECVD) SiO2 deposited at 350°C. Electrical properties have been measured in metal-oxide-semiconductor (MOS) capacitors, depositing SiO2 at RT as gate dielectric; breakdown electric fields >10MV∕cm and charge trapping at fields >6MV∕cm have been evaluated. From the study of interface quality in MOS capacitors, we found that even for low annealing temperature (200°C), it is possible to considerably reduce the interface state density down to 5×1011cm−2eV−1. To fully validate the ECR-PECVD silicon dioxide we fabricated polycrystalline silicon thin-film transistors using RT-deposited SiO2 as gate insulator. Different postdeposition thermal treatments have been studied and good device characteristics were obtained even for annealing temperature as low as 200°C.

Extended defects in Si films epitaxially grown by low-temperature ECRCVD

Si films grown epitaxially by low-temperature electron–cyclotron resonance chemical-vapor deposition (ECRCVD) were investigated by analyzing extended defects in these films. Extended defects were made visible by Secco etching and scanning (SEM) and transmission (TEM) electron microscopy were used to analyze them in detail. Films grown on Si(1 0 0) wafers show different kinds of etch pits with characteristic shapes, sizes and crystallographic alignments. Their correlation to crystallographic defects is discussed. The typical total etch pit density for boron-doped samples grown at 580 °C on Si wafers is in the range of 10 8 cm −2. Films grown on poly-Si seed layers on glass are strongly affected by Secco etch due to growth regions of different structural qualities and a high density of extended defects. Solar cell test structures were prepared from both types of samples and their results discussed in view to the density of extended defects.

Structural defects and photoluminescence of epitaxial Si films grown at low temperatures

Silicon layers grown by low-temperature Electron Cyclotron Resonance Chemical Vapour Deposition (ECR-CVD) were investigated using photoluminescence (PL) and defect etching. Different forms of etch pits could be observed using Scanning Electron Microscopy. The densities of the etch pits and the intensities of defect-related PL bands are compared. A correlation between two kinds of elliptical etch pits, two PL peaks and the impurity content was found. One of these PL peaks has an energy of 903 meV, usually attributed to the so-called rod-like defects. The orientation of the related etch pits is, however, not consistent with the orientation of rod-like defects. Possible explanations for this behaviour are discussed.

Numerical investigation of the production mechanism of a low-temperature electron cyclotron resonance plasma

The mechanism to decrease the electron temperature in an electron cyclotron resonance (ECR) plasma was numerically investigated using a fluid model. A mixture of argon and nitrogen was used as the working gas under the assumption of plasma nitriding by reactive sputtering. It was found that the power loss due to the vibrational excitation of nitrogen molecules by electron impact contributed to the decrease of electron temperature and the effect was promoted by the application of a mirror-type magnetic field configuration.

Characteristics of Tunneling Nitride Grown by Electron Cyclotron Resonance Nitrogen-Plasma Nitridation and Its Application to Low-Voltage Electrical Erasable-Programmable Read-Only Memory

Characteristics of a tunneling-nitride insulator grown by low-temperature electron cyclotron resonance (ECR) nitrogen-plasma nitridation are presented. The ECR nitridation shows a very high growth rate at lower temperatures and the thickness is proportional to the growth time. For example, we obtain a thickness of 16 [nm] and a refractive index of 1.75 after the nitridation time of 80 [min] at 400°C. The barrier heights measured from the Fowler-Nordheim (F-N) tunneling current are 2.3 [eV] and 1.4 [eV] in the inversion and the accumulation modes, respectively. These lower heights allow us much faster programming and erasing times of an electrical erasable-programmable read-only memory (EEPROM) with the ECR nitride than those of the conventional EEPROM with the thermal oxide. A double-gate EEPROM with an ECR-nitride tunneling insulator was fabricated. Surprisingly, it does not show any threshold voltage (VTH) degradation even after 100,000 cycles of programming and erasing.

Low-temperature Si epitaxial growth on oxide patterned wafers by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition

Low-temperature electron cyclotron resonance hydrogen plasma cleaning was developed for low-temperature epitaxial growth of Si by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition on oxide-patterned wafers. Defect-free undoped Si epitaxial layers could be obtained by optimizing the hydrogen ion flux and cleaning time, however, in the case of boron-doped Si epitaxial growth, Si epilayers had defect zones away from the bird’s beak along the window edges and a defect-free zone at the center of the window. Cross section transmission electron microscopy and energy dispersive spectroscopy results suggest that the defect zone formation is closely related with local oxygen contamination. Possible origins of the local oxygen contamination are discussed.

Low temperature Electron Cyclotron Resonance plasma technique for low loss integrated optics

Electron Cyclotron Resonance (ECR) plasma deposition process implies low temperatures at high deposition rates producing uniform and mechanically stable thin films. For these reasons ECR became an attractive tool for integrated optics technology. In this work we have combined ECR with other techniques as Reactive lon Etching (RIE) and Pulsed Laser Deposition (PLD), in order to develop a new fabrication method of channel waveguides. We report here results on alumina-based strip-loaded waveguides. Amorphous Al 2O 3 core of 0.7 μm were deposited over Si/SiO 2 substrate by PLD technique and overcladded with a 0.5 μm SiO 2-ECR film. Standard UV-photolitographic techniques and RIE were used to define a set of strips on the SiO 2. These strips give the additional confinement of the light in the Al 2O 3 core. The optical losses at 633 nm were measured using an imaging technique. The relative scattered light power as function of the propagation along the channels shows a maximum optical loss of 4.5 dB/cm.

Comparative measurement of electron density and temperature profiles in low-temperature ECR discharges by a lithium atom beam and Thomson scattering

In this paper a method to determine spatially-resolved profiles of the electron temperature Te and density ne in an electron-cyclotron-resonance (ECR) discharge is presented. This technique is based on the observation of line emission from a neutral Li atom beam, which is injected into the plasma and excited by electron collisions. A collisional-radiative model valid for the injected Li atoms is used to predict the emission intensities as function of ne and Te for several lines theoretically. In contrast to the electron temperature regime representative for the edge of tokamak discharges (Te>5 eV), the ECR discharge offers a Te range where selected line intensity ratios strongly depend on the electron temperature. Therefore, a comparison of the measured ratios with the calculated ones yields Te profiles for the first time. The ne measurement is performed as in tokamaks by observing the attenuation of the beam due to ionization in the plasma. We present radial profiles of Te and ne for discharges in argon and xenon under different operating conditions. These results are compared with results obtained by Thomson scattering. Our measurements give evidence for a satisfying agreement between the two methods.

Characterization of Microcrystalline Si Films by MeV Ion Scattering Techniques

AbstractRutherford Backscattering Spectroscopy (RBS) and channeling studies with 1.4 MeV−4He ions as well as Heavy-Ion Elastic Recoil Detection Analysis (HI-ERDA) with 230 MeV 129Xe ions have been applied to characterize structural properties and the impurity content of thin Si films. The analytical potential of these ion-beam techniques is demonstrated for two types of samples: (1) μc-Si films prepared by dc magnetron sputtering in a pure Ar plasma and (2) homoepitaxial Si films deposited by low-temperature electron-cyclotron resonance PECVD at the transition from oriented to disordered growth. For μc-Si the atomic area density N.d obtained by RBS was compared with the optical thickness n.d (n=refractive index) derived from the interference structure of IR reflection spectra. It is shown that the ratio R=n.d/N.d of these quantities can serve as a figure of merit for the degree of crystalline order. An apparent similarity was found in the case of the epitaxially grown films between the Si disorder profiles evaluated from the RBS channeling spectra and the hydrogen and oxygen profiles determined by HI-ERDA. This suggests that hydrogen and oxygen are preferentially incorporated in the disordered parts of the films.

Formation of ultrathin oxynitride layers on Si(100) by low-temperature electron cyclotron resonance N2O plasma oxynitridation process

We have undertaken the characterization of the low-temperature direct electron cyclotron resonance (ECR) N2O plasma process on the technically important Si(100) surface by the combined use of the newly developed ultrahigh vacuum (UHV)-based contactless capacitance–voltage (C–V) and x-ray photoelectron spectroscopy (XPS) techniques. An UHV-based contactless C–V measurement system allowed for the first time a direct in situ assessment of electronic properties of “free” Si surfaces and the surfaces covered with an ultrathin insulator layer. The UHV contactless C–V analysis indicated that a oxynitride/Si interface with a minimum interface state density of 1×1011 eV−1 cm−2 could be realized by the ECR N2O oxynitridation process at 400 °C. The angle-resolved XPS study showed that the formation of a phase-separated Si3N4/SiO2 structure is important to realize such a interface at low temperatures. The electronic and the chemical properties of the interfaces were found to be strongly correlated.

Characterization of an n-GaAs layer grown on a GaAs substrate cleaned by an electron cyclotron resonance hydrogen plasma

Two kinds of n-GaAs layers doped with Si to a level of 1017 cm−3 are grown by molecular beam epitaxy on GaAs substrates: those grown on substrates cleaned using low temperature electron cyclotron resonance (ECR) hydrogen plasma and those grown on substrates cleaned by conventional thermal treatment. Comparisons between the electrical properties of both layers are made by capacitance–voltage (C–V) measurement; optical deep-level transient spectroscopy (ODLTS); Van der Pauw and Hall effect measurements; and secondary ion mass spectroscopy (SIMS). It is found from SIMS analysis that for thermally cleaned wafers, C, O, and Si accumulate in the vicinity of the interface between the epilayer and the substrate, whereas only oxygen accumulates at the same interface in ECR-cleaned wafers. The C–V and Hall measurements reveal that the carrier concentration, n, as well as the electron mobility, μ, decrease in the vicinity of the interface for thermally cleaned wafers. These results can be explained theoretically by using a physical model in which Si donors are compensated by unintentionally doped C acceptors. On the contrary, no degradation of n or μ is observed for ECR-cleaned wafers. In addition, ODLTS measurement reveals the presence of deep hole traps due to the transition metals Fe and Cu, and a continuously distributed interface defect state for thermally cleaned wafers, whereas such defects are not observed for ECR-cleaned wafers.