Ultrahigh Vacuum Electron Cyclotron Resonance Research Articles

Effects of direct-current bias on the carbonization of Si(100) at low temperatures using electron cyclotron resonance chemical vapor deposition

A thin 3C–SiC layer is formed heteroepitaxially by the carbonization of Si(100) surface at low temperatures by using an ultra-high vacuum electron cyclotron resonance chemical vapor deposition system. Substrate direct-current (DC) bias was an important parameter to affect the crystallinity of the thin films, which could control the flux or total dose of irradiating species, which were involved in the formation of the film. By controlling the substrate bias, the crystallinity changes from amorphous to crystalline. That means the flux or dose of the ions in the plasma affect the crystallinity of growing thin films. In case the substrate was biased positively, Reflection high-energy electron diffraction (RHEED) showed the formation of the heteroepitaxial SiC layer. This implies the importance of the control of total dose of impinging species. Axial plasma potential profiles were measured to investigate the energy of the ions impinging on the surface. RHEED showed the formation of crystalline 3C–SiC when a defect free, clean Si surface was provided by the H 2 plasma cleaning and a positive bias voltage was applied to the substrate during carbonization process. By two-step carbonization using the proper values of bias voltage and CH 4/H 2 flow ratio, crystalline 3C–SiC could be formed at the substrate temperature of 600 °C

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.

Angle-dependent photoluminescence spectra of hydrogenated amorphous silicon thin films

Multiple sharp peaks were observed in the visible photoluminescence spectra of amorphous silicon thin films, prepared by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition on oxidized silicon substrates. The angular dependence of the photoluminescence, measured by a home-built fiber-optics device, revealed that the origin of these sharp features was due to Fabry–Pérot cavity interference effects. The interference is enhanced by deposition on thermally grown oxide layers with relatively smooth surfaces. We also consider how thin-film interference effects can add to the already existing confusion regarding the photoluminescence (PL) mechanism of porous and other luminescent forms of silicon and propose angle-dependent PL spectroscopy as a remedy for identifying spectral features due to interference effects.

Low temperature in situ boron doped Si epitaxial growth by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition

Boron-doped silicon epitaxial layers were grown by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition at 440–510 °C. Reflection high-energy electron diffraction and transmission electron microscopy (TEM) were used to study the effect of boron doping on the crystalline quality of silicon epitaxial layers. At growth conditions where undoped defect-free Si epitaxial layers were successfully obtained at 440 °C, in situ boron-doped epitaxial layers were replete with twins. However, at conditions with increased ion energy flux and at a higher temperature, 470 °C, no twins were observed. TEM analysis revealed the presence of an amorphous phase in the twinned epitaxial layers. It is believed that the amorphous phase formation, presumably from the reaction between B and O during the doping process, appeared to hinder the growth of the epitaxial layer, leading to degradation of the Si crystalline quality. Defect-free boron-doped Si epitaxial layers were able to be obtained by suppressing the amorphous phase formation at conditions with increased growth temperature and higher ion energy flux.

In situ boron doping of Si and Si1−xGex epitaxial layers by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition

We report on the growth of in situ boron doped Si and Si1−xGex epitaxial layers at 510 °C by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition. Boron concentration increases with B2H6 partial pressure. The boron concentration decreases as microwave power increases in Si epilayers and as Ge fraction increases in Si1−xGex epilayers. Enhanced ion bombardment at these conditions promotes the desorption of boron hydride in the growth surface. No growth rate change is observed in the Si epilayer with B2H6 partial pressure. However, a significant growth rate decrease is observed for the Si1−xGex epilayer with B2H6 partial pressure.

Noncontact minority carrier lifetime measurement of Si and SiGe epilayers prepared by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition

A 70 MHz inductively coupled rf bridge probe is used to measure the minority carrier lifetime of the Si and SiGe epilayers grown by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition (UHV-ECRCVD) at temperatures below 560 °C. Proper surface treatments before HF immersion are required for the accurate measurement of the bulk minority carrier lifetime. The effects of the process parameters such as the substrate dc bias, the distance of the ECR layer from the substrate, and the substrate temperature, including in situ surface cleaning, on the minority carrier lifetime of the Si and SiGe epilayers are examined by the rf bridge probe. It is confirmed that the rf bridge probe can monitor the epitaxial quality of low temperature Si and SiGe epilayers, making it an indispensable tool for the high quality device fabrication with Si and SiGe epitaxial layers grown by low temperature UHV-ECRCVD.

Low Temperature SiGe Heteroepitaxy by Ultrahigh Vacuum Electron Cyclotron Resonance Chemical Vapor Deposition

ABSTRACTDislocation-free Si1−xGex epilayers are successfully grown on (100) silicon at 440°C by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition (UHV-ECRCVD). The effects of process parameters on the crystallinity of Si1−xGex epitaxial layers were studied. As the GeH4 flow rate increases and consequently Ge fraction increases above 20%, Si1−xGex epilayers become damaged heavily by ions. When Ge fraction is larger than 20%, process parameters like total pressure need to be adjusted to reduce the ion flux for high quality Sil−xGex. Growth rate of Si1−xGex epitaxial layers increases at 440°C with Ge content in the film. It is presumed that the hydrogen desorption from the surface is the rate-limiting step, however, the enhancement in growth rate is comparatively suppressed and delayed.

Ultrahigh-Vacuum Electron Cyclotron Resonance-Plasma Chemical-Vapor-Deposited SiNx Films for X-Ray Lithography Mask Membrane: As-Deposited Properties and Radiation Stability

In this paper, a new approach to improve the radiation stability of silicon nitride film is presented using an ultrahigh-vacuum electron cyclotron resonance plasma chemical vapor deposition system. A membrane with a high optical transmittance (∼99% at 633 nm) can be obtained with a lower SiH4/NH3 flow ratio. The X-ray radiation immunity, however, can be improved with a higher SiH4/NH3 flow ratio at the sacrifice of optical transmittance. Shrinkage of the band gap and the generation of energy states in the band gap with increasing Si/N ratio of the film are speculated to be primary parameters for improving the radiation stability of silicon nitride film. Hydrogen content in the low 1021 atom/cm3 range, however, does not seem to have a critical effect on the radiation immunity, even though the Si-H bonds may act as the source for the radiation-induced damage.

Stress-controlled silicon nitride film with high optical transmittance prepared by an ultrahigh-vacuum electron cyclotron resonance plasma chemical-vapor deposition system

An ultrahigh-vaccuum electron cyclotron resonance plasma chemical-vapor deposition system with a substrate heating component has been applied to deposit silicon nitride film. Low background pressure (∼5×10−9 Torr) and efficient plasma excitation at a low deposition pressure (<10−3 Torr) result in a low oxygen impurity content in the silicon nitride film. Process flexibility of this system, i.e., control of the SiH4 to NH3 flow ratio, deposition pressure, and substrate temperature, allows the deposition of near-stoichiometry silicon nitride film with a high optical transmittance as well as a suppressed amount of hydrogen impurity and a low film stress.

Heteroepitaxial growth of InN on AlN-nucleated (00.1) sapphire by ultrahigh vacuum electron cyclotron resonance-assisted reactive magnetron sputtering

A novel deposition technique, ultrahigh vacuum electron cyclotron resonance (ECR)-assisted reactive magnetron sputtering, has been developed for the preparation of group IIIA nitride thin films. In initial experiments, thin films of the semiconductor InN have been deposited on AlN-seeded (00.1) sapphire substrates, and the properties of these films studied as a function of growth temperature. Comparison to InN thin films grown by conventional reactive magnetron sputtering shows enhanced Hall mobilities (from about 50 to over 80 cm2/V s), a decreased carrier concentration (by about a factor of 2), an increased optical band gap, and an apparent reduction in homogeneous strain that is in part due to film relaxation induced by the ECR beam and in part to enhanced nitrogen content and more nearly stoichiometric films.

Low-temperature silicon homoepitaxy by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition

High quality silicon homoepitaxial layers are successfully grown at 560 °C by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition (UHV-ECRCVD) using a SiH4/H2 plasma. The effects of substrate dc bias on the in situ hydrogen plasma clean and the subsequent silicon epitaxial growth are examined by the reflection high-energy electron diffraction (RHEED), secondary ion mass spectroscopy (SIMS), and cross-section transmission electron microscopy (XTEM). It is observed that the substrate dc bias plays a significant role in obtaining a damage-free, clean Si substrate prior to epitaxial growth. Severe damage in the Si surface is observed by XTEM, though RHEED shows a streaky pattern, when the substrate is electrically floating, but the damage can be suppressed with +10 V dc bias to the substrate. Substrate dc bias during plasma deposition drastically changes the crystal structure from polycrystalline at −50 V to high quality epitaxial silicon at substrate biases greater than +50 V. Precise control of the ion energy during in situ cleaning and plasma deposition is very important in low-temperature Si epitaxy by UHV-ECRCVD and it is possible by proper control of the substrate dc bias.

Dielectric thin film deposition by electron cyclotron resonance plasma chemical vapor deposition for optoelectronics

An ultrahigh vacuum electron cyclotron resonance (ECR) plasma source has been used to deposit a:Si, Si3N4, SiNx, SiOxNy, and SiO2 dielectric thin films on InP and related compound semiconductors for optoelectronic applications. Films are deposited without substrate heating using mixtures of SiH4, N2, O2, and Ar. Following deposition, thermomechanical properties have been studied by annealing to 450 °C in N2. High temperature film stability is strongly influenced by the addition of Ar to the gas mixture, indicating an important role of ion bombardment during film growth by ECR plasma chemical vapor deposition. In addition, for applications as optical coatings for photonic devices, film refractive index can be accurately controlled by the N2/O2/Ar flow rate ratios.

Epitaxial growth of silicon at low temperature by ultrahigh vacuum electron cyclotron resonance plasma chemical vapor deposition

Epitaxial growth of a silicon thin film has been accomplished at a temperature lower than 650 °C by electron cyclotron resonance plasma chemical vapor deposition using an ultrahigh vacuum chamber. Ar plasma from the same electron cyclotron plasma ion source is also used for surface cleaning of the substrate. The relationship between the cleaning condition of a substrate and the quality of an epitaxially grown silicon film is examined in detail. The energy of Ar plasma in the cleaning process should be kept lower than 100 eV in order to obtain films of good crystal quality. Otherwise, damage by Ar ion bombardment cannot be restored by annealing at lower than 700 °C. The epitaxial growth also should be carried out without the accelerating bias voltage to avoid residual compressive stress in the film. An epitaxial film with perfect crystal structure (indicating only a Kikuchi pattern of reflection of high-energy electron diffraction) is obtained at the substrate temperature of 710 °C.