Junsi Gao

Plasma breaking of thin films into nano-sized catalysts for carbon nanotube synthesis

Abstract Iron thin films deposited by pulse laser deposition (PLD) were broken into uniform nano-sized catalysts by plasma bombardment for carbon nanotube (CNT) synthesis. Size distributions of broken catalysts were obtained in terms of plasma discharge conditions. Vertically arranged high-density (10 13 per m 2 ) CNTs were synthesized using microwave plasma chemical vapor deposition (MP-CVD) system and the gas mixture of N 2 and CH 4 on optimally broken catalysts with few carbonaceous particles on a large area Si substrate. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy (RS) were used to evaluate the obtained CNTs.

Electrical characteristics of p–n junction diodes fabricated by Si epitaxy at low temperature using sputtering-type electron cyclotron resonance plasma

This article reports the electrical characteristics of p–n junction diodes that were formed by directly depositing a Sb-doped n-type epilayer on a p-type substrate by using a dc-bias electron cyclotron resonance plasma sputtering system at a low temperature of 400 °C and a conventional vacuum of 5×10−7 Torr. The reverse current density of the n+–p junctions diodes depends on deposition gas pressures and substrate biases. The n+–p junction diodes exhibit, under optimum conditions, a reverse current density as low as 9.5×10−9 A/cm2 at a reverse bias voltage of 5 V and an ideality factor of 1.05. The excellent characteristics of the n+–p junction diode are due to the integrity of interface between n+ epilayer and p-type Si substrate.

Optimum discharge condition of DC bias electron cyclotron resonance plasma sputtering for high quality Si epitaxial growth

An electron cyclotron resonance (ECR) plasma sputtering method, combined with DC substrate bias, has been developed to deposit single crystal thin films at the low substrate temperature of 400°C and a conventional base pressure of 5×10-7 Torr. At the optimum discharge condition of deposition pressure of 2.2 mTorr and substrate bias of +10 V, with both the ECR power and the rf power for sputtering of 500 W, crystallographically perfect single crystal deposition was found to be possible. These results have been interpreted as supplying a sufficient ion flux to adatoms while maintaining a sufficiently low ion energy to avoid substrate and film damage during deposition.

Room Temperature Deposition of Silicon Nitride Films for Passivation of Organic Electroluminescence Device Using a Sputtering-Type Electron Cyclotron Resonance Plasma

Dense silicon nitride (SiN) films were deposited at room temperature by a sputtering technique using an electron cyclotron resonance (ECR) plasma. Film properties were studied using ellipsometry, chemical etching, Fourier transform infrared spectroscopy, and thermal desorption spectroscopy. A SiN film deposited under the optimum condition of nitrogen gas flow rate had a refractive index of 2.03 and showed a large Si–N bond number. The SiN film had a high barrier against moisture penetration relative to SiN films prepared by chemical vapor deposition at 900°C. This indicates that the film deposited using a sputtering-type ECR plasma has the potential to be utilized as a passivation layer of devices such as organic electroluminescence, which require low temperature processing.

Growth of Epitaxial Silicon Film at Low Temperature by Using Sputtering-Type Electron Cyclotron Resonance Plasma

A novel method for growth of epitaxial silicon films on Si substrates at a low temperature of 400°C has been developed using a sputtering-type electron cyclotron resonance plasma. The chamber has a base pressure of 5×10-7 Torr, and the growth method includes in situ cleaning of Si substrates using suitable plasma bombardment and subsequent deposition at a high sputter rate to prevent impurity monolayer formation at the beginning of the deposition. The epitaxial growth conditions were investigated using spectroscopic ellipsometry and electron backscattering diffraction, and the effect of the Ar gas flow rate, for both the in situ cleaning and the deposition conditions, was studied. At the optimum growth conditions, Si thin films having characteristics close to crystal Si substrates were obtained. The deposition rate was as high as 6 nm/min.

Study of the effects of discharge conditions and substrate temperature on Si epitaxial deposition using sputtering-type electron cyclotron resonance plasma

It was found that epitaxial Si films could be deposited on Si substrates by using a sputtering-type electron cyclotron resonance plasma that had a conventional base pressure of 5×10−7 Torr. The effects of discharge conditions and substrate temperature were studied systematically in order to understand the necessary conditions for epitaxial growth. It was found that discharge gas pressure, target power for sputtering, and substrate temperature play crucial roles in the epitaxial deposition. The implications of the changes of the three parameters are discussed in detail.

Effect of Substrate Bias on Si Epitaxial Growth Using Sputtering-Type Electron Cyclotron Resonance (ECR) Plasma

Control of the energy of ions hitting the substrate during in situ cleaning and deposition was found to be very important for deposition of epitaxial Si thin film. This was studied by applying a substrate bias in the range of -30 to +30 V in a sputtering-type electron cyclotron resonance (ECR) plasma system. During in situ cleaning, positive bias voltage reduced the ion bombardment energy, and resulted in epitaxial deposition of Si crystal film even at a low gas pressure of 0.8 mTorr, at which epitaxial deposition was not possible previously. During deposition, obvious improvements in the crystallinity of the epitaxial Si film were achieved when the ion energy was reduced by applying a positive bias. On the other hand, application of a negative bias for the deposition process resulted in amorphous film even when deposition was performed at the high gas pressure of 1.7 mTorr, at which epitaxial deposition was possible previously.

Electrical properties of low-temperature epitaxial doped Si thin films fabricated by using a sputtering-type electron cyclotron resonance plasma

The electrical properties of Sb-doped n+ epitaxial Si films have been investigated. These films were fabricated at low temperatures of below 515 °C and at a conventional base pressure of 5×10-7 Torr using a sputtering-type electron cyclotron resonance plasma. It was found that the Sb dopants in the target were almost wholly incorporated into lattice sites of epilayers and the Hall mobility of the epilayers grown at 515 °C was comparable to that of the bulk Si. A reverse current density as low as 1×10-8 A cm-2 was obtained by a direct deposition of an n+ epilayer on a p-type substrate, which suggests the formation of a high-quality interface between the epilayer and the substrate. The precise control of the deposition gas pressure, substrate potential and substrate temperature was found to be very important for the fabrication of high-quality epilayers. Heavily B-doped p+ epilayers were also fabricated at a substrate temperature of 515 °C. The B dopant was wholly incorporated into the epitaxial layers, but annealing at temperatures of more than 700 °C was required to electrically activate the B dopant. The electrical activation mechanism has been discussed and it has been inferred that the B dopant occupied interstitial sites in the as-grown epilayers.