Hyun-Yong Lee

Photoinduced transformations in amorphous Se75Ge25 thin film by XeCl excimer-laser exposure

The scalar photoinduced changes of the optical absorption edge and the optical constants in amorphous Se75Ge25 chalcogenide thin film have been studied using XeCl excimer laser light with a wavelength of 306 nm. The glass transition temperature (Tg) of this material is evaluated to be approximately 220 °C, at which the as-deposited film is initially annealed. The optical energy gaps Eop of as-deposited and initially annealed Se75Ge25 thin films are 1.90 and 1.84 eV, respectively. When initially annealed films are exposed to a 4.05 eV excimer laser (≫Eop) with energy densities of 100, 120 and 180 mJ/cm2, a photodarkening effect that exhibits a decrease in the optical transmittance (Top) and Eop and an increase of the refractive index n and the extinction coefficient k in the vicinity of the absorption edge (1.4–3.0 eV) is observed. In particular, in the case of a thin film exposed by 120 mJ/cm2, Eop and n+ik measured at 673.7 nm(1.84 eV), i.e., an absorption edge of initially annealed thin film, are 160 eV...

Photoinduced dichroism and its low-temperature characteristics in obliquely deposited amorphous As–Ge–Se–S thin films

The photoinduced dichroism and its low-temperature characteristics in obliquely deposited amorphous As–Ge–Se–S thin films have been studied using a linearly polarized 632.8 nm He–Ne laser light and a control system capable of increasing the film temperature from 77 K. Our experimental results have been discussed on the basis of native valence-alternation pairs depended on the film fabrication. Although the absorption slopes in the extended region (hν>Eop) decrease with increasing deposition angle, the optical energy gap Eop remains the same as for 0° films, i.e., Eop=2.04 eV. A columnar structure with an inclination angle of approximately 70° is formed in 80° deposited films. While the value of saturated dichroism Dsat itself remains constant, independent of the intensity, it depends strongly on the deposition angle θ and the film temperature T, i.e., Dsat(θ,T). For example, Dsat(80°,77 K) is more than four times Dsat(80°,300 K), and the values of Dsat(0°,300 K) and Dsat(80°,300 K) are about 4.2% and 6.0%...

Sub-0.1 µm Patterning Characteristics of Inorganic Thin Films by Focused-Ion-Beam Lithography

Sub-0.1 µm patterning characteristics of low-pressure chemical-vapor-deposited Si3N4 and normally(0°) and obliquely(60° and 80°) deposited Se75Ge25 inorganic thin films have been investigated using low-energy Ga+ focused-ion-beam (FIB) lithography. These thin films act as a negative type resist for CF4-reactive-ion-etching (RIE) development. In the case of 0°-deposited Se75Ge25 and Si3N4 resists exposed by 30 keV Ga+ FIB and developed by CF4 RIE under a gas pressure of 150–200 mTorr, the image-contrasts (γ) are reasonably high, about 4.4 and 3.5, respectively. Their sensitivities (S), nevertheless, are relatively low in comparison with that of conventional polymer resist. Therefore, this problem should be solved, especially in order to employ these films as resists of ion-projection lithography. In the case of an 80°-deposited Se75Ge25 resist, columnar structures with an a ngle of approximately 65° are formed which disappear after annealing at the glass-transition temperature. The γ of this resist is evaluated to be about 4.0, similar to that of 0°-deposited Se75Ge25, but the S is enhanced to be about 7.0×1014 ions/cm2, which corresponds to below half that of 0°-deposited Se75Ge25. With an exposure of 30 keV FIB with a beam diameter of 0.1 µm and just above the threshold dose, negative-type fine patterns with linewidths of about 0.06–0.09 µm are fabricated successfully.

Three‐dimensional Monte Carlo calculation of Ga+ ion penetration in an a‐Se75Ge25 thin film

Three‐dimensional (3D) Monte Carlo (MC) simulation for Ga+ ion penetration in an amorphous Se75Ge25 thin film which acts as a positive resist in focused ion beam lithography is presented. For 3D MC simulation, both the depth and the lateral distance in the resist are divided into discrete cubic pixels with 25×25×25 A. Scattering and stop positions as well as deposited energy density by ∼104 ion trajectories are summed up in these pixels. Also, these MC data are expanded for a focused ion beam with a proper ion dose. Therefore, the 3D stop‐ion distributions and the 3D deposited energy profiles by ions implanted into the resist are obtained. The peak concentration of MC simulation associated with a dose of 1015/cm2 and an incident energy of 80 keV amounts to 2×1020 ions/cm3 and is located at a distance of about 400 A from the surface which is shifted about 40 A to the surface in comparison with Lindhard, Scharff, and Schiott‐based calculation.

Simulation of three-dimensional stop-ion and deposited energy distributions in amorphous chalcogenide resist film by Ga ion exposure

The Monte-Carlo (MC) simulation of three-dimensional (3D) stop-ion and deposited energy distributions in amorphous chalcogenide resist film by Ga/sup +/ ion beam exposure are presented. This paper is a part of the development of 3D MC Code suited for focused ion beam (FIB) lithography. For 3D MC simulations which are based on the simulation of individual energetic ions through their successive collisions with resist constituents, both the target depth (z-direction) and the lateral distance (x- and y-direction) are divided into discrete cubic pixels with 25/spl times/25/spl times/25 /spl Aring/, nuclear scattering and stop-ion positions and ion-loss energies are summed up in these 3D pixels by /spl sim/10/sup 4/ Ga/sup +/ ion trajectories, and then 3D ion concentration and deposited energy distribution profiles are obtained by an Ga/sup +/ ion beam exposure with proper shape and dose.

Monte carlo simulation of focused ion beam lithography in inorganic resists

Summary form only given. The bilayer film of Ag/a-Se/sub 75/Ge/sub 25/ and the monolayer film of a-Se/sub 75/Ge/sub 25/ act as a negative and a positive resist in ion beam lithography, respectively. We have discussed the numerically calculated values such as ion range, ion concentration and ion transmission coefficient, and the defocused Ga/sup +/ ion-induced characteristics in inorganic resists. Monte-Carlo method is based on the simulation of individual particles through their successive collisions with resist atoms. By the summation of the scattering events occurring in a large number N(N/spl Gt/1000) of simulated trajectories within the resist, the distribution for the range parameters of primary and recoiled ions and the energy dissipation profiles for various ion beam energies are evaluated. Also this text contains the exposure and development results.

Improvement of holographic grating efficiency in Ag/AsGeSeS double layer

We have investigated the effect of Ag doping and the polarization dependence in Ag/As/sub 40/Ge/sub 10/Se/sub 15/S/sub 35/, and As/sub 40/Ge/sub 10/Se/sub 15/S/sub 35//Ag double layers, with respect to the holographic grating formation.

Photodarkening and photoinduced anisotropy in amorphous chalcogenide thin films induced with He-Ne laser

Photoinduced dichroism in As/sub 40/Ge/sub 10/Se/sub 15/S/sub 35/ thin films induced with illumination of 1.96 eV light has been studied. Photodarkening has been also investigated. The photoinduced anisotropy sustains a metastable state after cessation of illumination, while it can be erased with illumination of unpolarized light or annealing at 62/spl deg/C. The kinetics of saturated dichroism (D/sub sat/) was satisfied with Gaussian approximation according to the temperature changes.

CF/sub 4/-RIE development characteristics of columnar-SeGe ion resists with focused-ion-beam lithography

In the very near future, focused-ion-beam lithography (FIBL) may play an important role for the microelectronic device fabrication. In particular, FIBL is evaluated as a novel vacuum technique available to generate original pattern (or masks), with the sub-0.1 /spl mu/m linewidth for X-ray lithography (or ion-projection lithography). In order to delineate a fine pattern, it is essential to develop a lithographic tool with high resolution and a resist with high sensitivity. In this work, the sub-0.1 /spl mu/m patterning characteristics of the columnar structural Se-Ge resists have been studied using low-energy Ga/sup +/-FIB exposure and CF/sub 4/ reactive-ion-etching (RIE) development. The Se-Ge ion resists were normally (0/spl deg/) and obliquely (60/spl deg/ and 80/spl deg/) deposited on Si substrate and parts of resists were annealed for several minutes at glass transition temperature (T/sub g//spl sim/220/spl deg/C). After annealing, FIB exposure and CF/sub 4/-RIE development were performed. For 80/spl deg/-obliquely deposited and T/sub g/-annealed resist, the threshold dose (D/sub 1/) is evaluated to be approximately 7/spl times/10/sup 14/ [ions/cm/sup 2/], which corresponds to half of that for non-annealed 0/spl deg/-resist. The fine patterns with about 0.06/spl sim/0.09 /spl mu/m linewidths were obtained successfully for an exposure just above D/sub 1/.

The temperature and energy dependence of photoinduced scalar phenomena in chalcogenide thin films

Temperature and energy dependence of thermal bleaching (TB) effect and photorefraction (PR) change, in chalcogenide As/sub 40/Ge/sub 10/Se/sub 50-x/S/sub x/ (x=0, 25, 35 at.%) thin films have been investigated. When these films were exposed for 15 min using the blue-pass filtered Hg lamp (/spl sim/4300 /spl Aring/) after annealing for 30 min around the glass transition temperature Tg (200/spl deg/C), the stable characteristics of scalar effect were shown in As/sub 40/Ge/sub 10/Se/sub 15/S/sub 35/ composition, and in that composition the refractive index change /spl Delta/ n was varied up to 0.02-0.46 according to each thickness conditions and the optical energy gap was shifted to a longer wavelength of approximately 0.67 eV, especially for 1000 /spl Aring/-thickness. Also, in the case that light source was He-Ne laser, we could observe refractive index change /spl Delta/ n and red-shift of absorption edge.