Youn-Seoung Lee

Adhesion and interface chemical reactions of Cu/polyimide and Cu/TiN by XPS

Abstract The chemical reaction at the interface between Cu and polyimide (PI) and between Cu and TiN at room temperature has been investigated using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). In case of Cu/TiN, there was no interface chemical reaction, but in case of Cu/PI system, there existed marked interface chemical reaction. From XPS core-level spectra, it was found that Cu atoms react mainly to oxygen and nitrogen in the PMDA (pyromellic-dianhybride) part of polyimide. Especially, the initial growth mode of Cu on polyimide was found by Cu LMM Auger spectra as follows; at first CuNO complex is formed, then CuOC complex formation by the weak interaction, and metallic Cu growth occurs simultaneously.

Titanium oxide films on Si(100) deposited by electron-beam evaporation at 250 °C

Titanium oxide films with a thickness of a 400 nm were deposited on p-type Si(100) at 250 °C by electron-beam evaporation where titanium dioxide was evaporated in oxygen environment at a pressure of 2×10−6–4×10−5 Torr. Effects of oxygen flow rate (FO2) between 0 and 40 sccm on properties such as crystallinity, surface roughness, and chemical states of the films have been investigated. Oxygen resonance backscattering spectroscopy shows that all films are oxygen rich, i.e., the ratio of oxygen to titanium of the films ranged from 2.25 to 2.3. X-ray diffraction patterns show that these films grown at 250 °C are polycrystalline of anatase TiO2. Ti K-edge x-ray absorption near-edge spectroscopy (XANES) spectra show that the films have mixed phases of anatase and rutile TiO2. More than 70% of the films is anatase TiO2 and its proportion of the films is decreased with increasing FO2. XANES spectra from the films grown at FO2=0 sccm are very similar to that of the powdered anatase TiO2. X-ray photoelectron spectr...

Characterization of TiN barriers against Cu diffusion by capacitance–voltage measurement

Sputtered TiN was studied as a diffusion barrier in Cu/TiN/Ti/Si and Cu/TiN/Ti/SiO2/Si multilayer structures using various characterization methods, and their sensitivities for detecting breakdown of the barrier were compared. It was confirmed by scanning electron microscopy and Auger electron spectroscopy that breakdown of the TiN barrier occurred through out-diffusion of Si in addition to in-diffusion of Cu. Breakdown temperatures varied by more than 100 °C depending on characterization methods, and capacitance–voltage (C–V) measurement was most sensitive for detecting the failure of the TiN barrier. The effects of rapid thermal annealing (RTA) on barrier properties of TiN were investigated, and it was found by C–V measurement that the TiN(400 nm) RTA treated at 700 °C in a NH3 ambient was stable up to 590 °C for 2 h, while the reference TiN (400 nm) was stable up to 450 °C for 2 h.

Band alignment in ultrathin Hf–Al–O∕Si interfaces

Band alignment in Hf–Al–O thin films, grown on Si(100) by atomic layer deposition, was determined via x-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy. The changes in conduction band offset, valence band offset, and bandgap were obtained as a function of annealing temperature. The bandgap Eg was found to be 5.7±0.05eV for as-deposited Hf–Al–O. After annealing at 600 °C, the increase in Eg was 0.2 eV, and then nearly unchanged up to 850 °C. The conduction band offset ΔEc increased slowly from 0.82±0.05eV at room temperature to 1.28±0.05eV at 850 °C. Even though the band profile of Hf–Al–O is still asymmetric with respect to HfO2, it satisfies the minimum requirement for the determination of the carrier barrier height. The band profiles, obtained via reflection electron energy loss spectroscopy, provided us some insight, which is both convenient and at the same time important, into the way to identify high-k dielectric materials, and we also found that the Hf–Al–O is a promi...

XPS core-level shifts and XANES studies of Cu–Pt and Co–Pt alloys

The K and L 2,3 absorption edges and core-level binding-energy shifts for pure Co, Cu and Pt and Co-Pt and Cu-Pt alloys are measured to investigate changes in electronic structures of these alloys. Enhancements and depletion of the white lines in the alloys as compared to pure elements were correlated with changes in the unoccupied density of states upon alloying. We find that the Pt atoms lost d 3/2 electrons and gained d 5/2 electrons when alloyed with Cu and Co. However, the total 5d occupancy changes of the Pt were very little in Cu-Pt alloys, and this is consistent with the small shifts of Pt 4f core-level binding energy. From the quantitative analysis of Cu and Co K-edge absorption spectra, it is found that Cu and Co have significant valence occupation changes due to dehybridization of p-d states. From these results, we suggest that the core-level shifts are affected mainly by the d-valence electron changes in these alloys.

Titanium oxide films on Si(100) deposited by e-beam evaporation

Titanium oxide films with a thickness of a 400 nm were deposited on p-type Si(100) at room temperature by e-beam evaporation, and titanium dioxide was evaporated in oxygen environment at a pressure of 2×10−6–4×10−5 Torr. Effects of oxygen flow rate (FO2) on the properties of the films, such as surface roughness, composition, and chemical states, have been investigated. The root-mean-square surface roughness of the films increased with increasing FO2 up to 20 sccm, and then decreased over 20 sccm. X-ray diffraction patterns show that the titanium oxide films are amorphous. Oxygen resonance backscattering spectroscopy shows that all films are oxygen rich, i.e., relative atomic ratio (CO/CTi) of the films ranged from 2.05 to 2.25. But the x-ray photoelectron spectroscopy (XPS) analysis shows that the titanium oxide films were oxygen deficient. The ratio of oxygen to titanium (CO2/CTi) of the films calculated by XPS ranged from 1.82 to 1.93. XPS shows that there exist only Ti3+ and Ti4+ charge states in the f...

Cl2-based dry etching of GaN films under inductively coupled plasma conditions

Dry etching of undoped, n- and p-type GaN films was carried out in Cl2-based inductively coupled plasmas (ICPs) using different rf excitation frequencies of 100 kHz and 13.56 MHz, in which the rf chuck power source operates. The etch rates with lower frequency of 100 kHz are somewhat greater than those with a higher frequency of 13.56 MHz due to higher ion bombarding energy with lower frequency. The highest etch rates with the 100 kHz frequency were obtained at moderately high ICP power of 700 W: ∼9300 A/min of n-GaN, ∼5300 A/min of p-GaN, and ∼7100 A/min of undoped GaN. The 13.56 MHz frequency of rf chuck power source produced maximum etch rates of ∼7900 A/min of n-GaN, ∼5800 A/min of p-GaN, and 6100 A/min of undoped GaN at 20 mTorr, 700 W ICP, and 150 W rf power. The surface roughness was relatively independent of the chuck power up to 150 W in 13.56 MHz and showed fairly smooth morphology (rms 1.1–1.3 nm), while etching at higher rf power (>200 W) produced rougher surface.

Characteristics of perylene-based organic thin-film transistor with octadecyltrichlorosilane monolayer

We fabricated perylene-based organic thin-film transistor (OTFT) with an octadecyltrichlorosilane (OTS) monolayer in an ultrahigh vacuum condition. By current–voltage characteristics, the saturation current and the field effect mobility of OTS–OTFT (gold∕perylene∕OTS∕SiO2∕p+-Si) increased over ∼100 times in comparison with normal-OTFT (gold∕perylene∕SiO2∕p+-Si), and on/off ratio increased over ∼100 times. The saturation current, field effect mobility, and on/off ratio were >1μA, 0.042cm2∕Vs, and >106, respectively. The uniformity of the OTS layer was confirmed by x-ray reflectivity. Perylene thin films on SiO2 and OTS∕SiO2 were compared by atomic force microscopy, scanning electron microscopy, x-ray diffraction, and x-ray photoscopy.

Effect of dry etching conditions on surface morphology and optical properties of GaN films in chlorine-based inductively coupled plasmas

Dry etching of undoped, n- and p-type GaN films has been carried out in a planar type inductively coupled plasma (ICP) system. The effect of etching conditions on surface morphology and optical properties of GaN films etched in Cl2/Ar discharges was studied. All the GaN films showed overall similar etching behavior at 700 W ICP, 150 W rf, 40 mTorr, and 25% Cl2. The surface roughness was relatively independent of the rf power up to 150 W, resulting in quite smooth morphology (root-mean-square roughness 1.1–1.3 nm), while etching at higher chuck powers (>200 W) produced rougher surfaces due to increased ion bombardment. The lattice disorder and point defect density were lower during the ICP etching compared with reactive ion etching. The intensity of the band edge peak of as-grown n-GaN was decreased after the ICP etching, and the extent of intensity decrease was inversely proportional to the applied chuck power. By contrast, the as-grown p-GaN showed a weak intensity of band edge emission, but the peak shi...

Electrical Properties of Electroplated Cu Thin Film by Electrolyte Composite

The electrolyte effects of the electroplating solution in Cu films grown by ElectroPlating Deposition(EPD) were investigated. The electroplated Cu films were deposited on the Cu(20 nm)/Ti (20 nm)/p- type Si(100) substrate. Potentiostatic electrodeposition was carried out using three terminal methods: 1) an Ag/AgCl reference electrode, 2) a platinum plate as a counter electrode, and 3) a seed layer as a working electrode. In this study, we changed the concentration of a plating electrolyte that was composed of CuSO , H SO and HCl. The resistivity was measured with a four-point probe and the material properties were investigated by using XRD(X-ray Diffraction), an AFM(Atomic Force Microscope), a FE-SEM(Field Emission Scanning Electron Microscope) and an XPS(X-ray Photoelectron Spectroscopy).From the results, we concluded that the increase of the concentration of electrolytes led to the increase of the film density and the decrease of the electrical resistivity of the electroplated Cu film.