Electron Cyclotron Resonance Hydrogen Plasma Research Articles

Amorphous {100} platelet formation in (100) Si induced by hydrogen plasma treatment

The defect formation in (100) Si at low temperatures during electron cyclotron resonance hydrogen plasma treatment has been studied. The temperature effect on crystalline defect morphology is studied by transmission electron microscopy and high resolution transmission electron microscopy. A high density of hydrogen-stabilized {111} platelets is observed at 240 °C, whereas a large number of amorphous {100} platelets is observed at 385 °C. The formation of amorphous {100} platelets without {111} platelets at 385 °C is reported. The amorphous {100} platelet at 385 °C results from the precipitation of oxygen promoted by hydrogen-enhanced oxygen diffusion. The low-temperature photoluminescence study and the spreading resistance profiles for the hydrogenated Si support the proposed mechanism of the amorphous {100} platelet.

Mechanism of Surface Roughness in Hydrogen Plasma‐Cleaned (100) Silicon at Low Temperatures

Surface roughening and defect formation of (100) Si at low temperatures during electron cyclotron resonance hydrogen plasma cleaning are studied in an ultrahigh vacuum environment, and a new model is proposed to explain their mechanisms. The effect of process parameters on surface roughness is quantitatively analyzed by atomic force microscopy and reflection high energy electron diffraction. Crystalline defect morphology is studied by transmission electron microscopy to understand its role in surface roughness. Surface roughness is strongly related to {111} platelet defects at the Si subsurface region and subsequent preferential etching at positions where {111} platelet defects intersect the Si surface. The formation of {111} platelet defects is determined by the subsurface hydrogen concentration, which is determined by incident hydrogen flux and substrate temperature. The preferential nucleation of etching reactions on the {111} platelet may be explained by the classical nucleation theory. Hydrogen ion flux and substrate temperature can be controlled successfully to tailor {111} platelet defect formation and hence, surface roughness.

In-situ low-temperature (600°C) wafer surface cleaning by electron cyclotron resonance hydrogen plasma for silicon homoepitaxial growth

Electron cyclotron resonance (ECR) hydrogen plasma was applied at 600°C to in-situ clean the silicon surface of contaminants, such as oxygen and carbon species for subsequent low-temperature epitaxial growth. The standard condition with in-situ hydrogen plasma cleaning at 600°C has been optimized and process variables such as d.c. bias, cleaning time, microwave power, and cleaning gas pressure were varied with respect to the standard condition. The epitaxial films, which were deposited in our chemical vapor deposition systems, immediately after these in-situ cleaning processes were characterized by cross-sectional transmission electron microscopy, etc. The role of a hydrogen ion in in-situ cleaning was clarified by investigating cleaning efficiencies for a variety of conditions. The hydrogen ion, which was produced by ECR plasma excitement, played a crucial role in removing surface contaminants in low-temperature (600°C) in-situ ECR plasma cleaning processes.

Post-Deposition Annealing and Hydrogenation of Hot-Wire Amorphous and Microcrystalline Silicon Films

AbstractAmorphous and microcrystalline silicon films deposited by hot-wire chemical vapor deposition were submitted to thermal annealing and to RF and electron-cyclotron resonance (ECR) hydrogen plasmas. Although the transport properties of the films did not change after these post-deposition treatments, the power density of a Ar+ laser required to crystallize the amorphous silicon films was significantly lowered by the exposure of the films to a hydrogen plasma. This decrease was dependent on the type of hydrogen plasma used, being the strongest for an ECR plasma with the substrate held at a negative bias, followed by an ECR hydrogen plasma with the substrate electrode grounded, and finally by an RF hydrogen plasma.

Surface roughness and defect morphology in electron cyclotron resonance hydrogen plasma cleaned (100) silicon at low temperatures

Surface roughening of (100) Si at low temperatures during electron cyclotron resonance hydrogen plasma cleaning is studied in an ultrahigh vacuum environment. The effects of process parameters on surface roughness are quantitatively analyzed by atomic force microscopy besides reflection high energy electron diffraction. Crystalline defect morphology is studied by transmission electron microscopy to understand its role in surface roughness. Surface roughness is strongly related to the nucleation and growth of {111} platelet defects at the Si subsurface region and the preferential etching at positions where {111} platelet defects intersect the Si surface. Hydrogen ion flux and substrate temperature can be successfully controlled to tailor the {111} platelet defects, therefore, surface roughness.

Dynamics of GaAs surfaces exposed to argon and hydrogen electron-cyclotron-resonance plasmas observed by real-time optical reflection spectroscopy

The dynamics of the interaction of electron-cyclotron-resonance (ECR) plasmas with the surface of GaAs substrates are studied by real-time optical reflection spectroscopy. Analysis with a three-phase ambient/overlayer/substrate model yields information on the time-dependent composition of the near-surface region, such as the thickness, degree of amorphization, and oxide and void fraction in the overlayer. Using this technique, it is observed that the thickness of the damaged layer formed by the impact of energetic ions increases linearly with the ion energy during argon ECR sputter etching. Furthermore, the dynamics of a cleaning process with a hydrogen ECR plasma have been studied. At temperatures between 300 and 500 °C this cleaning can be characterized by a two-step process. During the first few seconds of exposure, the oxide layer is removed; in the second step, the GaAs is etched gently, which leads to a surface region with little damage to the crystal. At lower temperatures, cleaning is not successful and a thick damaged overlayer is formed.

Temperature-dependent dry cleaning characteristics of GaAs (111)B surfaces with a hydrogen electron cyclotron resonance plasma

The cleaning of the GaAs (111)B surface with a hydrogen electron cyclotron resonance discharge plasma is investigated at temperatures between 200 and 500 °C and compared with the GaAs (100) surface. It is found that during the exposure the GaAs (111)B is etched in a non-Arrhenius way with a higher etch rate at low temperatures. For temperatures 300–500 °C, the surface is severely roughened after exposure, while the (100) surface remains smooth in all cases. The near-surface crystalline quality of GaAs (111)B remains higher than that of (100).

Low-temperature in situ cleaning of silicon (100) surface by electron cyclotron resonance hydrogen plasma

Low-temperature, defect-free, in situ cleaning of silicon prior to homoepitaxy is successfully developed by an electron cyclotron resonance hydrogen plasma treatment in an ultrahigh vacuum chamber. The plasma potential distribution was measured by a Langmuir probe method to understand the effect of the substrate dc bias during hydrogen plasma cleaning. It changes from downhill to uphill distribution as the dc bias changes from a negative to a positive value, which leads to a decrease in the ion number density arriving at the substrate and results in the complete suppression of the defect formation in the Si substrate. In situ hydrogen plasma cleaned Si wafer always resulted in higher quality epilayers than ones cleaned only by so-called hydrogen passivation after the HF dip. We found that there is a critical dose of the hydrogen ions during in situ plasma cleaning beyond which crystalline defects are observed in the Si substrate, subsequently leading to the poor crystallinity of the epilayers. The dose of the hydrogen ions during plasma cleaning can be effectively controlled by the substrate dc bias, the microwave power, the magnet current, and the cleaning time.

On the Influence of Illumination During Ion Damage Defect Anneal of Silicon

AbstractAn exploratory deep level transient spectroscopy (DLTS) study on the possible role of illumination during thermal annealing has been carried out on Si with extended defects generated by Ar implantation and electron cyclotron resonance (ECR) hydrogen plasma. Experiments with rapid thermal anneal (RTA) using quartz-halogen lamps show only a minor role for illumination on anneal of defects generated by Ar ion damage as well as thermal generation of defects under post-hydrogenation anneal. However, significant differences are evident relative to conventional furnace anneal and it appears likely that recombination-assisted defect reactions may be quite significant in Si processing when high intensity sources such as arc lamps are adapted in RTA systems.

Real-time investigations of GaAs surface cleaning with a hydrogen electron cyclotron resonance plasma by optical reflection spectroscopy

The composition changes during GaAs oxide removal and the subsequent cleaning with a hydrogen electron cyclotron resonance plasma have been investigated with real-time optical reflection spectroscopy. It is found that the oxide is not completely removed at low temperatures, resulting in a thick damaged surface region. At moderate temperatures (300–500 °C) the plasma exposure is characterized by a two-step process: a removal of the native oxide in a few seconds followed by a gentle etch of the GaAs. In the latter step the plasma exposure leads to a surface region with little damage to the crystal.

High-performance p-channel poly-Si TFT's using electron cyclotron resonance hydrogen plasma passivation

This letter presents a summary of the first detailed investigation of electron cyclotron resonance (ECR) hydrogen plasma exposure treatments of p-channel poly-Si thin film transistors (TFT's). It is shown that ECR hydrogenation can be much more efficient than RF hydrogenation. Poly-Si p-channel TFT's fabricated at low temperatures (/spl les/625/spl deg/C) and passivated with the ECR hydrogenation treatment are shown to exhibit ON/OFF current ratios of 7.6/spl times/10/sup 7/, subthreshold swings of 0.62 V/decade, threshold voltages of -4.6 V, and hole mobilities over 18 cm/sup 2//V.s. >

Silicon surface electrical properties after low-temperature in situ cleaning using an electron cyclotron resonance plasma

Electron cyclotron resonance hydrogen plasma and argon plasma was used to clean Si surface without additional heating within 4 min and 30 s, respectively. Changes in the electrical properties after plasma treatment with different exposure times have been studied and compared using a Schottky diode structure. The reverse saturation current of the Schottky diodes changes less in the case of the hydrogen plasma cleaned samples than the argon plasma cleaned samples. After hydrogen plasma exposure, residual hydrogen introduced into the Si was found to enhance greatly the formation of thermal donors which induces considerable changes in the defect states after annealing. After annealing at ∼450 °C in N2, new defects, caused by thermal donors, appear and these defects decrease significantly at 750 °C. Defects in the argon plasma treated samples annihilate after annealing at 1000 °C for 1 h.

Fabrication of stable hydrogenated amorphous silicon from SiH2Cl2 by ECR-hydrogen-plasma

Abstract Relatively stable high bandgap hydrogenated amorphous silicon (a-Si:H) films were prepared by the microwave electron cyclotron resonance (ECR) hydrogen plasma CVD method using SiH 2 Cl 2 source gas. The substrate position relative to the position of the generation of reactive species affects the structure of these films. The films prepared under optimized condition showed rather high bandgap, 1.83 eV. However, the defect density was low, 3 × 10 15 cm −3 , and the photosensitivity was greater than 7 orders of magnitudes. The defect density was found to saturate at relatively low values (∼ 3 × 10 16 cm −3 ) independent of the illumination intensity.

Effects of substrate temperature and bias potential on hydrogen plasma etching of silicon

Si masked by patterned SiO2 was etched using an electron cyclotron resonance hydrogen plasma. The dependence of the etch rate and the etched profile on substrate temperature and dc bias potential has been investigated, and an etch mechanism has been considered. The substrate temperature was varied between room temperature and 400 °C, and a bias potential between −100 and +100 V was applied. The etch rate of Si had the highest value at the lowest substrate temperature and decreased with increasing temperature. For the bias potential, the etch rate of Si had its peak value at 0 V. It decreased with increase of the potential which was either positive or negative. Si was also etched laterally when the substrate temperature was low. For the negative bias potential, the etched Si had a terrace on the border of a SiO2 mask. It is considered that the temperature dependence of the etch rate and the etched profile is caused by the action of hydrogen atoms, and the bias potential dependence is caused by the action of hydrogen ions. Thus, we conclude that both hydrogen ions with moderate energy and hydrogen atoms play an important role in Si surface etching.

Time-of-Flight Scattering and Recoiling Spectrometry Study of Plasma-Cleaned Silicon Surface

The cleaning process of a Si(100) surface using electron cyclotron resonance hydrogen plasmas was observed by time-of-flight scattering and recoiling spectrometry (TOF-SARS). The effects of substrate temperature and plasma density on the cleanliness and the damage including roughness of the surface were clarified by the observation, because both impurities and damage of the surface were detected by TOF-SARS. The substrate temperature had effects on reduction of the damage and the exposure time to obtain a clean surface. The hydrogen-terminated clean surface with nominal damage was obtained by exposure to the plasma with the electron density on the order of 109 cm-3 at 300° C for 1–5 min.

Interfacial characteristics of AlGaAs after in situ electron cyclotron resonance plasma etching and molecular beam epitaxial regrowth

Regrown/processed AlGaAs interfaces using secondary ion mass spectrometry, cross section transmission electron microscopy (TEM), and reflection high energy electron diffraction have been characterized. Two sets of samples, GaAs/Al0.4Ga0.6As (with GaAs on top) and Al0.4Ga0.6As/GaAs (with Al0.4Ga0.6As on top), are used as starting materials. For the GaAs/Al0.4Ga0.6As samples that are first exposed to atmosphere, the experiment is performed in an integrated processing system where etching and regrowth chambers are linked together by ultrahigh vacuum transfer modules. The etching process includes electron cyclotron resonance (ECR) hydrogen plasma cleaning of GaAs native oxides, ECR SiCl4 plasma anisotropic deep etching into Al0.4Ga0.6As, and an optional, brief Cl2 chemical etching. Regrowth is carried out using solid-source molecular beam epitaxy (MBE). Despite the in situ processing, significant amounts of C, Si, and O impurities at the 10, 5, and 50×1012 cm−2 levels exist at the interfaces. However, the impurity level is one order of magnitude smaller than that in air-exposed, ECR plasma etched and MBE regrown Al0.4Ga0.6As/GaAs of the set 2 samples. As revealed using TEM, isolated small particles (presumably correlated to aluminium oxides) exist at the regrown/processed interface of the set 1 samples, but no other defects such as dislocation are seen. Impurities and defects are mainly caused by the high reactivity of AlGaAs during ECR plasma etching.

Surface cleaning of C-doped p+ GaAs with hydrogen electron cyclotron resonance plasma

We report surface cleaning of C-doped p+-GaAs epilayers with hydrogen electron cyclotron resonance plasma. Native oxides on the surface of the p+-GaAs layer can be removed at a very low substrate temperature of 150 °C. In addition, carrier concentrations decrease after cleaning at about 300 °C, which is attributed to the hydrogenation of carbon acceptors caused by hydrogen plasma exposure. A cleaning temperature of about 400 °C, a cleaning time of about 5 min, and microwave power of about 30 W appear to be optimum for the regrowth process.

Hydrogen Passivation of Polysilicon Thin-Film Transistors by Electron Cyclotron Resonance Plasma

We have investigated the method of hydrogenation of polysilicon thin-film transistors (TFT) by electron cyclotron resonance (ECR) plasma. It is found that with decreasing pressure (1.5 to 0.35 mTorr) of the hydrogen plasma, the substrate temperature rises due to bombardment of hydrogen ions. At the same time, the amount of hydrogen supplied by the ECR plasma increases. Due to these two effects, the passivation proceeds more quickly under low pressure. The amount of hydrogen supplied by a low-pressure ECR hydrogen plasma is higher than that supplied by other means such as Al sintering or rf hydrogen plasma. When polysilicon TFTs are exposed to the ECR hydrogen plasma, the hydrogenation reduces 75% of the electrically active defect states in 15 min. Polysilicon TFTs with an offset-drain structure reached an on/off current ratio of 8 decades after such ECR hydrogen passivation.

Removal of GaAs surface contaminants using H2 electron cyclotron resonance plasma treatment followed by Cl2 chemical etching

We report a novel dry process to remove the surface contaminants C, Si, and O from GaAs substrates. This method utilizes an electron cyclotron resonance hydrogen plasma to remove the native oxides, followed by a very brief Cl2 chemical etching of GaAs to further reduce C and Si residues, and a final vacuum anneal. Characterization by secondary ion-mass spectrometry (SIMS) typically reveals the removal of C, Si, and O at the overgrown/processed interface to the levels below the SIMS detection limit. The as-processed GaAs surface, a Ga-stabilized reconstructed (4×6), is atomically smooth, and is as clean as a surface of freshly grown GaAs epilayers.

Polycrystalline silicon thin film transistors on Corning 7059 glass substrates using short time, low-temperature processing

A new fabrication process for polycrystalline silicon thin film transistors on 7059 glass substrates is reported. This unique fabrication process has the advantages of short processing time and low processing temperature (≤600 °C). The processing is based on the key step of using an ultrathin Pd layer, introduced to the surface of the glass prior to the deposition of an a-Si:H film, to reduce the crystallization time and temperature. It is also based on using an electron cyclotron resonance hydrogen plasma to reduced the passivation time. The n-channel TFTs produced by this new fabrication process have mobilities of 20 cm2/V s, and off-currents of 0.5 pA/μm.