Jin-Hyo Boo

Growth of TiO2 thin films on Si(100) substrates using single molecular precursors by metal organic chemical vapor deposition

Abstract Growth of titanium dioxide (TiO2) thin films on Si(100) substrates was carried out using a single molecular precursor at deposition temperature in the range of 300–700°C by the metal organic chemical vapor deposition (MOCVD) method. Titanium(IV) isopropoxide, (Ti[OCH(CH3)2]4), was used as a precursor without any carrier gas. Crack-free, anatase type TiO2 polycrystalline thin films with a stoichiometric ratio of Ti and O were successfully deposited on Si(100) at temperature as low as 500°C. XRD and TED data showed the formation of the highly oriented anatase phase with the [211] direction for the TiO2 thin films grown on Si(100) at below 500°C, whereas with increasing the deposition temperature to 700°C, the main film growth direction was changed to be [200], suggesting a possibility of epitaxial thin film growth. Two distinct growth behaviors were observed from the Arrhenius plots. Below 500°C, the growth rate of TiO2 is apparently limited the substrate temperature. The activation energy for TiO2 film deposition calculated in this region is approximately 77.9 kJ/mol, while that for a film grown above 500°C shows a negative value, indicating a predominant diffusion controlled deposition process. Using Al/TiO2/p-Si metal-insulator semiconductor (MIS) diode structure, a dielectric constant was also obtained from a capacitance-voltage (C–V) curve to be 21.

Growth of magnesium oxide thin films using single molecular precursors by metal-organic chemical vapor deposition

Thin films of MgO have been deposited on Si(100) and c-plane sapphire substrates by the metal‐organic chemical vapor deposition (MOCVD) method using Mg(tmhd)2 and Mg(acac)2 as single molecular precursors and oxygen as carrier gas. We have synthesized the metal‐organic precursors used in this study. Strongly [111] oriented polycrystalline MgO films were obtained on both Si(100) and c-plane sapphire substrates using these precursors in the temperature range 500‐6008C. The MgO thin films grown on Si(100) at 6008C and on cplane sapphire at 5008C with Mg(tmhd)2 are highly oriented in the [111] direction, whereas the MgO film grown on Si(100) at 3508C and then annealed at 5208C has no preferred orientation. In the case of using Mg(acac)2 as precursor, however, the MgO film deposited on c-plane sapphire surface at a deposition temperature above 5008C was grown with more [110] and [100] dominant orientation relatively rather than [111]. Furthermore, we have also shown that the synthesized precursors Mg(tmhd)2 and Mg(acac)2 are suitable precursors for obtaining MgO thin films by MOCVD and the substrate or precursor type and the growth temperature will be important factors influencing either the crystal growth direction or the crystallinity of the films. q 1999 Elsevier Science S.A. All rights reserved.

Synthesis and characteristics of NH2-functionalized polymer films to align and immobilize DNA molecules

We developed a method to use NH2-functionalized polymer films to align and immobilize DNA molecules on a Si substrate. The plasma-polymerized cyclohexane film was deposited on the Si substrate according to the radio frequency plasma-enhanced chemical vapor deposition method using a single molecular precursor, and it was then treated by the dielectric barrier discharge method in a nitrogen environment under atmospheric pressure. Changes in the chemistry of the surface functional groups were studied using X-ray photoelectron spectroscopy and Fourier transformed infrared spectroscopy. The wettability of the surfaces was examined using dynamic contact angle measurements, and the surface morphology was evaluated using atomic force microscopy.We utilized a tilting method to align λ-DNA molecules that were immobilized by the electrostatic interaction between the amine groups in NH2-functionalized polymer films and the phosphate groups in the DNA. The DNA was treated with positively charged gold nanoparticles to make a conductive nanowire that uses the DNA as a template. We observed that the NH2-functionalized polymer film was useful for aligning and immobilizing the DNA, and thus the DNA-templated nanowires.

Effect of annealing temperature on dielectric constant and bonding structure of low-k SiCOH thin films deposited by plasma enhanced chemical vapor deposition

We investigated the effect of annealing temperature on the properties of SiCOH films deposited by plasma-enhanced chemical vapor deposition using or a mixture of Si–O containing and hydrocarbon precursors, decamethyl-cyclopentasiloxane (DMCPSO-C10H30O5Si5) and cyclohexane (CHex-C6H12). These SiCOH films were deposited at pressures of 0.6 and 1.5 Torr and the as-deposited SiCOH films were subjected to annealing temperatures from 25 to 500 °C in a furnace for 1 h in N2 ambient at a pressure of 1 atm. The relative dielectric constants, k, of the SiCOH films deposited at 0.6 and 1.5 Torr were 2.76 and 2.26, respectively, before the annealing process. The subsequent annealing of the SiCOH film at 500 °C further reduced the k values to as low as 2.31 and 1.85, respectively. Decreases in the refractive index, hardness, and modulus were observed as the annealing temperature increased to 450 °C. However, further increasing annealing temperature to 500 °C caused the refractive index, hardness, and modulus to increase again. Trends of decreases in both the hardness and modulus with increasing annealing temperature were found. The refractive index and the film thickness retention also decreased with increasing annealing temperature. The change in the k value as a function of the annealing temperature was correlated with the change in the Fourier transform infrared absorption peaks of C–Hx, Si–CH3, and Si–O related groups. As the annealing temperature increased, the intensity of both the CHx and Si–CH3 peaks decreased, respectively. In particular, the C–H2 (asymmetric and symmetric) peaks provide direct evidence of the presence of ethylene groups in the SiCOH films. Thus the decrease in intensity of the peaks corresponding to the CHx groups and Si–O cage structure in the SiCOH films was considered to be responsible for lowering they dielectric constant, refractive index, hardness and modulus of the films. The leakage current density of the SiCOH films at 1 MV/cm is obtained ~10-8 A/cm2 with the 450 °C annealed films, which can be considered as an acceptable leakage current level for the interconnect application.

Plasma-polymerized thiophene films for corrosion protection in microelectronic devices

The corrosion failure of electronic devices has long been a major reliability concern. This failure is an ongoing concern because of miniaturation of integrated circuits and the increased use of polymers in packaging [1–3]. Recently, copper is replacing aluminum in advanced microelectronic devices as the interconnecting metal due to its lower bulk resistivity. However, copper does not form a self-passivating oxide compared with aluminum and the resistance to corrosion decreases in humid and oxygen-containing environments [4]. On the other hand, in advanced logic devices, the number of interlayer dielectrics has increased to four or five, so that wiring delay is beginning to dominate the total signal delay in ultra-large-scale-integrated circuits (ULSIs). To lower the signal delay, plasma-polymerized thin films with low dielectric constant have been developed by varying the deposition parameters [5–7]. However, these plasma-polymerized thin films as interlayer dielectrics have a high tendency to adsorb water in the presence of moisture and can act as an electrolyte between two dissimilar metals, forming a galvanic cell in the microelectronic devices [8–10]. Therefore, it is necessary to investigate the effect of corrosion induced by interlayer dielectrics in the microelectronic devices. In this paper, thiopene was considered as a possible candidate for the interlayer dielectric for multilevel metallization of semiconductor devices [11]. Generally, the electrical conductivity of thiopene was found to be very low (10−15–10−10 S/cm) [12]. The protective abilities of thiopene in 3.5 wt% NaCl solution were examined by electrochemical measurements and wettability tests. Plasma polymerization was carried out in a vacuum chamber made of stainless steel. Polymer-like thin films were deposited on disk-shaped steel specimens by plasma-enhanced chemical vapor deposition (PECVD). After cleaning the sample using acetone, isopropyl alcohol and distilled water, the substrates were in-situ pre-treated with Ar plasma to give an oxygen-free surface and a buffer layer for enhancing film adhesion. The deposition lasted up to 2 h, depending on the RF power and deposition temperature. The general deposition pressure and temperature were 2–4 × 10−1 Torr and 473 K, respectively. The typical conditions of the PECVD process applied in this study are 30–100 W of RF power, 20 sccm of Ar carrier gas, and 20 sccm of H2 bubbler gas. Thiopene (C4H4S) was used as the organic precursor. For a better understanding of the effect of thiopene films on corrosion behavior, impedance (Z) measurements for the steel electrodes coated and uncoated with the films were performed at Ecorr after immersion for 2 h in 3.5 wt% NaCl solution open to air. A perturbation AC potential of amplitude 10 mV was applied over the frequency range 100 kHz to 10 mHz. Only 5 frequencies per decade were measured. All potentials were referred to the saturated calomel electrode (SCE), and the counter electrode was a highpurity graphite rod. The plot was analyzed with Z-view softwave. Polarization measurements of the electrodes, both bare and covered with thiopene film were carried out potentiodynamically in 3.5 wt% NaCl solution at room temperature. After immersion of the electrode in the solution for 2 h, the potential of the electrode was swept at a rate of 0.166 mV/s from the initial potential of −250 mV vs. Ecorr to the final potential of 1000 mV vs. Ecorr. In order to evaluate the wettability of the surface film, contact angle measurements were carried out on the coated surfaces by the sessile drop method with a microscopic goniometer. The measurement was performed using a drop of 2 μl water at room temperature.

The effect of annealing on the 0.5% Ce-doped Ba(ZrxTi1 x)O3 (BZT) thin films deposited by RF magnetron sputtering system

Structure and electrical properties of Ce-doped Ba(ZrxTi1� x)O3(BCZT) thin films with the mole fraction of x ¼ 0:2 and the thickness of about 100 nm have been investigated. Ce-doped BZT films were prepared on Pt/Ti/SiO2/Si substrates by a RF magnetron sputtering system. X-ray diffraction patterns were recorded for the samples deposited with four different substrate temperatures. The thickness and the surface roughness of the films deposited with different Ar/O2 ratios were measured. The oxygen gas, which was introduced during the film deposition, had an influence on the growth rate and the roughness of the film. The roughness of the sample, which was deposited with the Ar to O2 ratio of 1:1 at the substrate temperature of 5001Cand annealed at 600 1C, was from 2.33 to 2.02 nm. The surface roughness of samples, deposited at different Ar to O2 ratios, was increased after annealing. It was found that the dissipation factor was reduced when the top electrode was deposited before annealing of the samples. r 2002 Elsevier Science Ltd. All rights reserved.

METAL-DOPED ZnO THIN FILMS: SYNTHESIS, ETCHING CHARACTERISTIC, AND APPLICATION TEST FOR ORGANIC LIGHT EMITTING DIODE (OLED) DEVICES

Metal-doped ZnO films with various metal contents (Al, Ag and Li of 0–10 wt.%) were prepared by RF magnetron sputtering system with specially designed ZnO targets. The structural, optical and electrical properties of MZO films depended on the type and content of doping in target. Electrical resistivity of LZO thin films increased with increasing Li doping amounts between 0 and 4 wt.%, suggesting that an epitaxial LZO film has high resistivity. We observed morphology in pure ZnO films by using different etchant. In addition, etching rate were contrasted with the etchant concentration and pH. The etching rate is proportional exponentially to pH value. These data will be the technical basis for TCO application. Also, the dry etching rate decreased with increasing the Cl2 concentration in CH4/H2/Ar + additive Cl2 gas mixture but metal dopants were etched effectively.

Growth behavior of titanium dioxide thin films at different precursor temperatures

The hydrophilic TiO2 films were successfully deposited on slide glass substrates using titanium tetraisopropoxide as a single precursor without carriers or bubbling gases by a metal-organic chemical vapor deposition method. The TiO2 films were employed by scanning electron microscopy, Fourier transform infrared spectrometry, UV-Visible [UV-Vis] spectroscopy, X-ray diffraction, contact angle measurement, and atomic force microscopy. The temperature of the substrate was 500°C, and the temperatures of the precursor were kept at 75°C (sample A) and 60°C (sample B) during the TiO2 film growth. The TiO2 films were characterized by contact angle measurement and UV-Vis spectroscopy. Sample B has a very low contact angle of almost zero due to a superhydrophilic TiO2 surface, and transmittance is 76.85% at the range of 400 to 700 nm, so this condition is very optimal for hydrophilic TiO2 film deposition. However, when the temperature of the precursor is lower than 50°C or higher than 75°C, TiO2 could not be deposited on the substrate and a cloudy TiO2 film was formed due to the increase of surface roughness, respectively.

Etching Characteristics of ZnO and Al-Doped ZnO in Inductively Coupled Cl2/CH4/H2/Ar and BCl3/CH4/H2/Ar Plasmas

ZnO and Al-doped ZnO (AZO) were etched in Cl2/CH4/H2/Ar (Cl2-based) and BCl3/CH4/H2/Ar (BCl3-based), inductively coupled plasmas (ICPs) and their etching characteristics were compared by varying the Cl2/(Cl2+CH4) and BCl3/(BCl3+CH4) flow ratios, top electrode power and dc self-bias voltage (Vdc). The etch rates of both ZnO and AZO layers were higher in the Cl2-based chemistry than in the BCl3-based chemistry. The AZO and ZnO etch rates were increased and decreased, respectively, with increasing Cl2 or BCl3 flow ratio. Optical emission measurements of the radical species in the plasma and surface binding states by optical emission spectroscopy (OES) and X-ray photoelectron spectroscopy (XPS), respectively, indicated that, with increasing Cl2 or BCl3 flow ratio; the effective removal of Al in the AZO enhanced the AZO etch rate, whereas the reduced removal of Zn by the Zn(CHx)y products reduced the ZnO etch rate.

Selective growth of TiO2 thin films on Si(100) surfaces by combination of metalorganic chemical vapor deposition and microcontact printing methods

We successfully patterned TiO2 thin films by metalorganic chemical vapor deposition (MOCVD) on Si(100) substrates where the surface was first modified by an organic thin film. The organic thin film [octadecyltrichlorosilane (OTS)] of self-assembled monolayers (SAMs) was deposited by microcontact printing. Selective deposition of a 130 nm thick TiO2 film was done on a 300–500 °C surface prepared by MOCVD without any carrier or bubbler gas. Auger electron spectroscopy and x-ray diffraction analyses showed that the deposited TiO2 material was stoichiometric, polycrystalline, and consisted of anatase phase. Alpha-step profile and optical-microscopic images also showed that the boundaries between the OTS SAMs and selectively deposited TiO2 thin film areas are definite and sharp. Capacitance–voltage measurement of a TiO2 thin film yielded a dielectric constant of 29, suggesting possible application to electronic materials.