Dong S. Kim

Room-temperature deposition of a-SiC:H thin films by ion-assisted plasma-enhanced CVD

Abstract Tetramethylsilane (TMS) diluted highly with hydrogen is used for depositing a-SiC:H thin films at room temperature under varying degrees of ion bombardment in a 13.56 MHz r.f.-powered, asymmetrical plasma reactor. An impedance analysis is used to estimate apparent ion energy and other plasma parameters such as electron density and the degree of ionization. The a-SiC:H films obtained under high ion bombardment show densities comparable to those deposited at high temperatures; are transparent in most of the visible and IR regions; are resistant to etching in buffered HF solution; and exhibit excellent adhesion to various substrates including silicon wafer, quartz, aluminum, and polymers such as polycarbonate and polyimide. FTIR studies of the films show varying bond structures depending on the level of ion bombardment. When the apparent ion energy flux is increased, the hydrogen content in the film decreases and the level of crosslinking appears to increase.

Annealing effects on a-SiC:H and a-SiC:H(F) thin films deposited by PECVD at room temperature

Abstract Thin films of a-SiC:H and a-SiC:H(F) deposited under high ion bombardment at room temperature by plasma-enhanced chemical vapor deposition were annealed at temperatures ranging from 300 to 600 °C. The effects of the annealing on stress, bonding structures, hydrogen content and optical properties were studied. Both films tend to become more cross-linked as the annealing temperature is increased, but beyond 500 °C the film appears to become oxidized. The hydrogen content of a-SiC:H film starts to decrease when the annealing temperature exceeds 400 °C. Upon annealing, the optical transparency in the visible region improved slightly upon annealing with a-SiC:H film, whereas the opposite behavior is observed with a-SiC:H(F) film. Strikingly different behaviors were observed in the film stress. For a-SiC:H film, the stress decreases progressively as the annealing temperature is increased and becomes zero at 600 °C. For a-SiC:H(F) film, the stress becomes zero at a relatively low annealing temperature of 200 °C, beyond which the stress changes from compressive to tensile.

Deposition of thermally stable, low dielectric constant fluorocarbon/SiO2 composite thin film

Low dielectric fluorocarbon/SiO2 composite films are developed that exhibit good thermal stability and low dielectric constant by using hexamethyldisiloxane (HMDSO) and prefluorobenzene (C6F6) as the monomer source gases, and argon and oxygen as the carrier gases in a dual frequency, inductively‐coupled high‐density plasma reactor. Fourier transform infrared measurements of the films show that they consisted of both SiO2 and amorphous perfluoro tetra fluoroethylene, and the amount of each can be controlled by changing the feed monomer gas ratio. The dielectric constant of the film ranges between 2 and 4 depending on the feed monomer gas ratio. For example, when the monomer gas ratio [HMDSO/(HMDSO+C6F6)] is 0.2, the dielectric constant of the film is ∼2.5. Such a composite film shows good thermal stability and good adhesion on a silicon substrate.

Room Temperature Deposition of Silicon Dioxide Films by Ion‐Assisted Plasma Enhanced Chemical Vapor Deposition

Silicon dioxide (SiO 2 ) thin films were deposited on silicon wafers at 25°C using varying degrees of ion energy flux (IEF) in a 13.56 MHz, RF driven asymmetric plasma reactor from a gas mixture of tetraethoxysilane (TEOS), Ar, and O 2 . On-line mass spectrometer (MS) and optical emission spectroscopy (OES) were used to analyze the plasma chemistry while the films were analyzed by Fourier transform infrared (FTIR) and Rutherford backscattering spectroscopy (RBS). The MS and OES results showed that the decomposition of TEOS was enhanced as the power input was increased and that the role of O 2 was to oxidize the hydrocarbon molecules to carbon oxides (CO and CO 2 ) and water, which lead to fewer hydrocarbon impurities in the film. The refractive index and the density of the film increased while the etching rate of the film decreased with increasing IEF. The low p-etch rates of the films prepared at high IEF (>17 mW/cm 2 ) suggested that the films have quality close to that of thermal oxide. From the FTIR spectra, the observed reduction in film porosity at high IEF coincides with the decreases in SiO-H and C=O peak intensities, and the decreasing shoulder of Si-O-Si antistretching mode in the range of 1260∼1100 cm -1 . Also, the downward shift of the maximum peak of the Si-O-Si stretching suggested that the intrinsic stress of the films increased with increasing IEF. The surface topology measured by an atomic force microscopy was very flat even at a high degree of IEF (average roughness of less than 10 A).

Mechanical properties of a-C:H and a-C:H/SiOx nanocomposite thin films prepared by ion-assisted plasma-enhanced chemical vapor deposition

a-C:H and a-C:H/SiOx nanocomposite thin films were deposited on silicon, aluminum and polyimide substrates at 25 °C in an asymmetric 13.56 MHz r.f.-driven plasma reactor under heavy ion bombardment. Fourier transform infrared spectra of the films indicate that the nanocomposite filmsappears to consist of an atomic scale random network of a-C:H and SiOx. Raman spectroscopy revealed that the sp2 carbon fraction in the nanocomposite film was reduced compared with the a-C:H film. The intrinsic stress of both films increased with increasing negative bias voltage (−Vdc) at the substrate. However, the nanocomposite films exhibited lower intrinsic stress compared w with a-C:H-only films. Especially, a thin SiOx-rich interlayer was very effective in reducing the film stress and enhancing the bonding strength at the interface. The interlayer allowed deposition of thick films of up to 5 μm. Also, the nanocomposite films were stable in 0.1 M NaOH solution and showed good microhardness.

Effects of RF Power on Plasma Phase Reactions and Film Structure in Deposition of a‐C:H by Styrene/Argon Discharge

In ion-assisted plasma enhanced chemical vapor depositions (PECVD), the applied RF power affects both plasma phase reactions and deposited film structure. These dual effects are investigated in PECVD of a-C:H films by using styrene and Ar mixture. The films are deposited in a 13.56 MHz, RF driven asymmetric plasma reactor at 25 C. In situ impedance analysis is used to estimate the ion energy and flux at the substrate, while an on-line mass spectrometer (MS) is used to analyze the plasma chemistry, and film structure is characterized by Fourier transform infrared (FTIR) spectroscopy and ellipsometry. The impedance analysis shows that both ion energy and ion flux increase with increasing RF power. The MS data show that the RF power has the major effect on the degree of dissociation of styrene. The FTIR spectra of the deposited films indicate that CH{sub 3} is likely to be the precursor for the diamond-like carbon deposition. The ion energy flux (IEF) is shown to have a significant effect on the film structure. With increasing IEF, films show decreases in hydrogen concentration, increases in sp{sup 2} carbon fraction, and increases in refractive indexes.

Deposition of Fluorinated a ‐ SiC : H Films at Room Temperature

A mixture of tetramethylsilane/CF 4 /H 2 is used for depositing fluorinated amorphous silicon carbide thin films at room temperature under heavy ion bombardment in a 13.56 MHz RF powered, asymmetric plasma reactor. An optical emission spectrometer and a quadrupole mass spectrometer are used to measure the concentrations of chemical species in the plasma phase while the bonding structure of the deposited films is analyzed by Fourier transform infrared spectroscopy (FTIR). The results indicate that the density and the optical properties of the films obtained at room temperature are as good as those deposited at much higher temperatures

Growth Mechanism of Room‐Temperature Deposited a ‐ SiC : H Films by Ion‐Assisted RF Glow Discharge

Tetramethylsilane (TMS) diluted highly with hydrogen is used for depositing a-SiC:H thin films at room temperature under varying degrees of ion bombardment in a 13.56 MHz RF powered, asymmetrical plasma reactor. An impedance analysis is used to estimate the ion energy and flux at the substrate while an optical emission spectrometer (OES) and a quadrupole mass spectrometer (MS) are used to estimate the concentrations of the chemical species in the plasma phase. The measured physicochemical reactor parameters are related to the growth rate using Langmuir-Hinshelwood and Eley-Rideal models. Based on Fourier transform infrared spectroscopy data of the deposited films, the impedance analysis of the reactor, and the on-line measurement data obtained with OES and MS, the growth mechanisms of the film under energetic ion bombardment conditions (low chamber pressure and high power) are suggested.

Effect of Ion Bombardment on the Structure and Properties of PECVD SiO 2

SiO{sub 2} films were deposited on silicon wafers at 25 C by plasma enhanced decomposition of tetraethoxysilane (TEOS) in a mixture of argon and oxygen. The deposition was performed in a rf-powered (13.56 MHz) asymmetric plasma reactor. The effect of ion bombardment was evaluated by varying the ion energy flux (IEF) at the substrate surface from 0.93 to 9.94 W/cm{sup 2}. On-line optical emission spectra (OES) revealed CO, CH, and H peaks whose absorption intensities increased with increasing applied power. On-line mass spectrometer data showed that the peak intensities of OC{sub 2}H{sub 5}, SiOH (m/e = 45), and HSiOH (m/e = 46) fragments decreased with increasing applied power indicating the decomposition of these species. FTIR spectra of the deposited films showed that the concentrations of Si-OH and trapped CO gases in the film decreased with increasing IEF. Also, the FTIR results and the refractive index measurements indicated that the film density increased as a function of IEF. The stoichiometry of the film did not change when IEF was below 2, but for IEF greater than 4.91 W/cm{sup 2}, the film became Si-rich.

Effects of oxidation on optical properties of polymer-like and diamond- like amorphous hydrogenated carbon films

Diamond-like carbon (DLC) film has attracted considerable attention because of its extreme properties such as hardness, thermal conductivity, optical transparency and chemical resistance. Applications include scratch-resistant coating, microelectronics packaging, optical coating and coating on plastics [1-3]. DLC film belongs to the amorphous hydrogenated carbon (a-C:H) family whose properties depend strongly on the method and conditions used for the deposition. Methods such as plasma:enhanced chemical vapour deposition (PECVD), ion beam deposition and sputtering have been used for the deposition. Ion-assisted PECVD is advantageous for depositing a-C:H films because ion bombardment can be used for modifying film properties [4-6]. The degree of the ion bombardment on the substrate can be adjusted by changing the r.f. power, reactor geometry and gas pressure. Depending on the magnitude of the ion energy, the deposited films are classified as polymer-like, diamond-like or graphite-like. At low ion energy, soft, polymer-like carbon (PLC) films are formed, while at moderately high ion energy the hydrogen content in the film decreases and a dense and hard film [1] called diamond-like carbon (DLC) is formed. Because of the ion bombardment used, a-C:H films generally have high residual stress. Heat treatment is often used to relieve this stress. It is thus of interest how the properties of these films change upon oxidation. In this letter, we compare the oxidation behaviours of PLC and DLC films.