Isamu Kato

Preparation of silicon nitride films at room temperature using double‐tubed coaxial line‐type microwave plasma chemical vapor deposition system

Silicon nitride films were prepared at room temperature using the double‐tubed coaxial line‐type microwave plasma chemical vapor deposition system. The dependence of film composition and properties on the flow rate of SiH4 gas and on the partial pressure of N2 gas in the deposition chamber has been investigated. A new simple method was suggested and employed to determine the film composition from the refractive index and nitrogen concentration. The flow rate of SiH4 gas was varied between 1 and 10 ml/min. The flow rate of N2 gas was at 50 ml/min and the partial pressures of N2 gas in the deposition chamber were set at 0.015 and 0.0036 Torr by changing the size of the substrate table. With an increasing flow rate of SiH4 gas, the following effects upon the films were obtained: proportional increases in the deposition rate, shifts to lower energy of the absorption edge, decreases in the film density, and decreases in the concentration of N and the N–H bond. Increases in the refractive index, the Si/N ratio,...

Microwave Plasma CVD System to Fabricate α-Si Thin Films out of Plasma

This study has been concerned with the development of a system to fabricate thin films by a microwave plasma chemical vapour deposition method while keeping the substrate out of the discharge plasma. Si thin films are fabricated in a deposition region using an improved coaxial line type microwave CW discharge tube without a silicon deposition on the discharge tube wall. A very uniform Si thin film has been fabricated over a circle with a 10 cm diameter and the deposition rates are 50 to 400 A/min. The structure of the fabricated films is amorphous and the optical band gap is 1.8 to 2.0 eV.

MICROWAVE PLASMA CVD SYSTEM FOR THE FABRICATION OF THIN SOLID FILMS.

This study was concerned with the development of a process for the deposition of thin-films from a microwave plasma of semiconductor materials. A coaxial line type microwave CW discharge was used to create uniform plasmas and a-Si films were fabricated from Ar gas containing 10% SiH4. The X-ray diffraction patterns shown that the fabricated films, where the microwave power is large, are crystallized and the structure of the other films is amorphous.

ANALYSIS OF RADIAL DISTRIBUTION OF PLASMA PARAMETERS IN A COAXIAL-LINE MICROWAVE DISCHARGE TUBE.

The discharge mechanism in a coaxial‐line microwave discharge tube that makes uniform plasma along the circumference of the tube has been analyzed. The analysis includes the skin effect of microwave penetration into the plasma and the equilibrium between generation and losses of the charged particles. It is shown that the radial distributions of electron density and electron temperature can calculated from measured values of the radial distribution of light intensity. The electron density is about 1012 cm−3 near the center axis of the plasma column and is close to trapezoidal in shape. The electron temperature is about 4×104 K near the tube wall and decreases monotonically toward the center of the plasma column.

Radial distribution of excited atoms in a new coaxial line type microwave cw discharge tube

A study has been made of a new microwave discharge method to obtain a plasma suitable for a gas laser medium and plasma chemical vapor deposition. When the plasma frequency is higher than that of the microwave power supplied to the plasma in the coaxial line mode, the plasma plays an important role as the inner conductor of the coaxial line. Therefore a cylindrical plasma of the arbitrary size which is uniform along the circumference and in the radial direction can be produced. The radial distribution of the excited atom density of the plasma has been measured using the side‐light method. It is shown that the microwave discharge has the proper distribution. The distribution is not bell‐shaped, but is either trapezoidal in shape or has a central dip.

Oxidation Properties of Silicon Nitride Thin Films Fabricated by Double Tubed Coaxial Line Type Microwave Plasma Chemical Vapor Deposition

Silicon nitride films have been fabricated under different deposition conditions using a double tubed coaxial line type microwave plasma chemical vapor deposition system. The oxidation and annealing properties of the films have been analyzed using infrared absorption spectroscopy. It is shown that oxidation proceeds via (Si-H2)n bonds in the voids. During the process, hydrogen atoms are released. The N-H bonds which form the remainder in the bulk are not affected by oxidation. Based on this finding, films which have a large concentration of N-H bonds and a lower concentration of Si-H bonds show greater resistance to oxidation. Under adequate conditions, the stoichiometric oxidation-resistant silicon nitride films can be fabricated outside the discharge plasma even at room temperature.

Photoluminescence from thermally oxidized hydrogenated amorphous silicon nanoball films fabricated by double-tubed-coaxial-line-type microwave plasma chemical vapor deposition system

Using a double-tubed-coaxial-line-type microwave plasma chemical vapor deposition (MPCVD) system, hydrogenated amorphous silicon (a-Si:H) nanoball films, which include Si nanocrystals, can be fabricated. A high deposition rate of 1600 A/s is achieved at a gas flow rate of 30 ml/min. Photoluminescence (PL) around 780 nm is observed at room temperature after the a-Si:H nanoball film is thermally oxidized in air or in pure oxygen gas. We have fabricated thermally oxidized a-Si:H nanoball films under various fabrication and oxidation conditions. As the substrate temperature during deposition becomes higher, the PL intensity decreases, and PL cannot be observed above 200°C. The PL intensity is the strongest when the substrate is set about 6 cm from the discharge tube end. As the discharge time increases, the film thickness increases and saturates, and consequently the PL intensity increases and also saturates.

Deposition of hydrogenated amorphous silicon films using a microwave plasma chemical vapor deposition method with DC bias

A DC bias is applied to a substrate placed in spatial afterglow plasma created by the double-tubed coaxial line-type microwave plasma chemical vapor deposition system. This DC bias method enables us to control only the ion bombardment energy without changing the ion flux density and the radical density. Hydrogenated amorphous silicon films were deposited, varying only the ion bombardment energy. With increasing ion bombardment energy, the dihydride bonds Si-H2 and the polyhydride bonds (Si-H2)n decrease, and the monohydride bonds Si-H and the film density increase.

Calculations of line absorption for the Voigt profile

Line-absorption calculations of the 388.9 nm triplet and the 501.6 nm singlet lines of helium have been performed for the Voigt profile. These results can be used to measure the absolute concentration of He 2s3S and 2s1S metastable atoms for the various discharge conditions by the reabosorption method.

Effect of Ar+ Ion Bombardment During Hydrogenated Amorphous Silicon Film Growth in Plasma Chemical Vapor Deposition System

We have developed the double tubed coaxial line type microwave plasma chemical vapor deposition (MPCVD) system to fabricate hydrogenated amorphous silicon (a-Si:H) films. We have studied the influence of Ar+ ion bombardment during a-Si:H film growth and clarified that the ion bombardment causes film surface heating effect and ion implanting effect. It is not sufficient to discuss only whether films are of good quality or not, when the ion bombardment energy is increased. In this study, we show that the effect of ion bombardment can be separated into the film surface heating effect and the ion implanting effect and discuss the influence of each effect on the film properties. We also show that the film surface temperature can be expressed as a function of the sheath voltage. It is clarified that a film with low dangling bond density can be fabricated at low temperatures if there is no ion bombardment.