Eunah Kim

Principle of ferroelectric domain imaging using atomic force microscope

The contrast mechanisms of domain imaging experiments assisted by atomic force microscope (AFM) have been investigated by model experiments on nonpiezoelectric (silicon oxide) and piezoelectric [Pb(Zr,Ti)O3] thin films. The first step was to identify the electrostatic charge effects between the tip, the cantilever, and the sample surface. The second step was to explore the tip–sample piezoelectric force interaction. The static deflection of the cantilever was measured as a function of dc bias voltage (Vdc) applied to the bottom electrode (n-type Si wafers) for noncontact and contact modes. In addition, a small ac voltage (Vac sin ωt) was applied to the tip to measure the amplitude (Aω) and phase (Φω) of the first harmonic (ω) signal as a function of Vdc. By changing from the noncontact to the contact mode, a repulsive contribution to the static deflection was found in addition to the attractive one and a 180° phase shift in Φω was observed. These results imply that in the contact mode the cantilever buckl...

High resolution study of domain nucleation and growth during polarization switching in Pb(Zr,Ti)O3 ferroelectric thin film capacitors

The domain nucleation and growth during polarization switching in Pb(Zr,Ti)O3 (PZT) ferroelectric thin film capacitors with Pt top (TE) and bottom electrodes (BE) were studied by means of atomic force microscopy (AFM). The experimental configuration used in this study differs from that conventionally used (AFM tip/PZT/BE) where the AFM tip acts as a positionable TE. A small ac voltage was applied between the electrodes with a step by step increasing dc bias voltage. The induced piezoelectric vibration was detected by the AFM tip, its amplitude and phase determined with the lock-in amplifier. The phase difference between the applied ac voltage and the piezoelectric signal as a function of the x-y position was nearly locked at 0 or 180, representing film regions with parallel (in-phase) and antiparallel (antiphase) polarization direction, respectively. The polarization reversal was induced by application of a step by step increasing dc bias field opposite to the polarization of the prepoled sample. At each ...

Measurement and calculation of optical band gap of chromium aluminum oxide films

The optical band gap is a basic property of optical materials. The measured band gap depends not only on the material but also on its characteristics such as crystallinity and stoichiometry. The optical band gap of chromium aluminum oxide films was measured and calculated by three different methods. Firstly, we used the conventional experimental-graphical method, which is commonly used. However, this method is applicable only to an all-crystalline phase or an all-amorphous phase. The second one was an experimental-calculation method applicable to films composed of both crystalline and amorphous phases. We calculated the optical band gap between the highest occupied molecular orbital of O2p and the lowest unoccupied molecular orbital of Cr3d in Cr1.71Al0.29O3 films composed of both amorphous and crystalline phases. Also, a band gap for the d–d transition was obtained. Finally, the measured value was compared with the theoretical optical band gap calculated by the discrete variational-Xα (DV-Xα) method.

On measurement of optical band gap of chromium oxide films containing both amorphous and crystalline phases

Abstract A method to calculate the optical band-gap of thin films composed of both crystalline phase and amorphous phase is suggested. Chromium oxide films were taken for the optical band-gap measurement, and the results were compared with those obtained by the conventional method. There is discrepancy between the values calculated by two different methods. The discrepancy decreases as the deposition temperature increases to the point where crystalline peaks occur. It has been speculated that the simple Taucs relation for pure amorphous film would lead to an underestimation of the fundamental band-gap of the film composed of both amorphous and crystalline phases. A modified Taucs equation, δ=f1δc+(1−f1)δa, approach suggested by Krankenhagen et al. [J. Non-Cryst. Solids 198–200 (1996) 923] yields optical band-gap of the Cr2O3 film in the range of 4.7~5 eV when the deposition temperature was varied from room temperature to 300°C.

Attenuated phase-shifting masks of chromium aluminum oxide

Chromium aluminum oxide was chosen as a new candidate for use as an attenuated phase-shifting mask (Att-PSM) material. The compositions of films were correlated with optical properties. With the measured and the fitted data, we simulated the transmittance and the phase shift using the matrix method. Consequently, we acquired optimum parameters for Att-PSMs, such as Al/Cr = 1.9-2.5 and d = 120 nm at a 193-nm wavelength, Al/Cr = 1.0-1.7 and d = 128 nm at a 248-nm wavelength, and Al/Cr = 0-0.1 and d = 170 nm at a 365-nm wavelength. This simulation was verified by transmittance measurement.

Simulation and fabrication of attenuated phase-shifting masks: CrF x

To acquire the required resolution for 248- and 193-nm lithography, a study of attenuated phase-shifting mask (Att-PSM) technology is in progress. We performed a simulation study using a matrix method to calculate relative transmittance and the amount of phase shift of light through the PSM. However, we found that the average film composition changed with deposition time. Accordingly, optical constants were found to be a strong function of film thickness. Therefore we rearranged the relationship between deposition parameters (e.g., deposition time or gas flow rate ratio) and optical constants (e.g., refractive index and extinction coefficient) to extract the empirical formula for the optical constants with respect to film composition. To verify our simulation study, we fabricated a phase shifter based on our simulation result, which was found to have a transmittance of 8.3% and a phase shift of 179.5 degrees . Consequently, we obtained a reliable optimum condition for the deep-ultraviolet Att-PSM.

Electronic Structure Simulation of Chromium Aluminum Oxynitride by Discrete Variational-Xα Method and X-Ray Photoelectron Spectroscopy

We use a first-principles discrete variational (DV)-Xα method to investigate the electronic structure of chromium aluminum oxynitride. When nitrogen is substituted for oxygen in the Cr–Al–O system, the N2p level appears in the energy range between O2p and Cr3d levels. Consequently, the valence band of chromium aluminum oxynitride becomes broader and the band gap becomes smaller than that of chromium aluminum oxide, which is consistent with the photoelectron spectra for the valence band using X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). We expect that this valence band structure of chromium aluminum oxynitride will modify the transmittance slope which is a requirement for photomask application.

Simulation of optical constants range of high-transmittance attenuated phase-shifting masks used in KrF laser and ArF laser

Phase-shifting masks (PSMs) have provided us a breakthrough in the future semiconductor industry by extending lithography further to the submicrometer order. PSMs have been used over the past several years, and their requirements have changed due to the development of semiconductor technology. We investigated high-transmittance attenuated PSMs (HT-Att-PSMs) that satisfy the requirements of 20§ 5% transmittance and 180 ‐ phase shift at the exposure wavelength and less than 40% transmittance at the inspection wavelength. Regarding the wavelength, we targeted the inspection wavelength of 248 nm for ArF laser (exposure wavelength of 193 nm) HT-Att-PSM, and 365 nm for KrF laser (exposure wavelength of 248 nm) HT-AttPSM. In this study, we developed refractive index-extinction coefficient-thickness (n-k-d) charts showing optimum optical constant ranges for HT-Att-PSM using the matrix method. The simulation was verified by comparing calculated transmittance data with measured ones.

Water-induced degradation of chromium fluoride films

Abstract As an optical film, chromium fluoride is an important material because it has good transparency in short wavelength region. However, it was found that chromium fluoride film degrades at humid condition. Therefore, we investigated the degradation phenomena of chromium fluoride films under 100% humid condition. The degraded samples were analyzed by several thin film analyzing techniques. With these results, we proposed a possible degradation mechanism consisting of multi-step reactions. First, H 2 O molecules are permitted to the porous structure in the films to percolate through numerous microchannels and microvoids. Then, the water molecules react with the chromium fluoride film to make hydroxide bonding producing HF gas. HF gas evolves and gathers at some spots, and dome structure was developed. Chromium oxide precipitates around HF gas gathered dome. After time passes, HF gas evolution occurs followed by explosion of the dome structure, and crater-like feature remains as a result around the dome. It was found that the chromium oxide ring is left around the feature. In the whole process, cracking also occurred due to the molecular volume difference between CrF x and degraded part.

A simulation model for thickness profile of the film deposited using planar circular type magnetron sputtering sources

The thickness profile of the film deposited by planar circular‐type magnetron is simulated considering the relationship between magnetic field profile and target erosion rate. The model is confirmed by the measurement of the film thickness profiles of the Cr films deposited in this study. It is found that the model is applicable to the magnetron sputtering process at low gas pressure. Furthermore, it can be used to predict the thickness profile of the films deposited by magnetron sputtering with various shapes of magnets.