Yongbeom Kim

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.

Fluorinated silicon nitride film for the bottom antireflective layer in quarter micron optical lithography

Fluorinated silicon nitride thin film as a bottom antireflective layer (BARL) material, being suitable for line-patterning in KrF excimer laser (248 nm) lithography, has been studied by film fabrication/characterization and computer simulation. Three-dimensional reflectance simulation process suggests that the 0% reflectance between photoresist (PR) and BARL can be achieved by selecting proper combinations of film optical properties such as refractive index (n), extinction coefficient (k) and thickness (d). For the PR/300 A BARL/c-Si or PR/300 A BARL/W-Si structure at a wavelength of 248 nm, the simulation process reveals that nearly 0% reflectance could be obtained when the n and k values of the film are 2.109 and 0.68 or 2.052 and 0.592 respectively. The fluorinated silicon nitride films prepared by ICP enhanced CVD have been evaluated with the variations of flow rates under the two conditions of and 3:20 (sccm). The film n and k values at 248 nm vary in the ranges of 1.665 - 2.352 and 0.007 - 0.695 respectively, depending on gas flow ratio. As it is very sensitive to the film thickness, the reflectance could be reduced, using compoter simulation, to almost 0% by changing the film thickness. Furthermore, the ARL performance for line/space processed by the KrF excimer laser stepper and the stripping ability/selectivity show this material to be a superior candidate for deep-UV microlithography applications.

Optical proximity correction using a transmittance-controlled mask (TCM)

When small feature delineation is considered using existing exposure tools, special techniques might be needed such as phase shift mask, oblique illumination, top surface imaging, etc. When different types of patterns exist simultaneously or island patterns exist predominantly, optical proximity effect will become more important to be controlled. In this study, six different mask types were prepared and evaluated in view of a pattern fidelity and process latitude for 256 mega bit DRAMs storage node patterns. The masks used for this experiment were conventional transmission mask, serif patterned mask, square patterned Transmittance Controlled Mask (TCM), horizontally rectangular TCM, vertically rectangular TCM, and cross patterned TCM. The cross patterned TCM had three different transmittance on it and was evaluated also. In view of both pattern fidelity and process latitude, cross-TCM showed the best result. The vert-TCM also showed fairly good result. But the worst results always came from the conventional mask. From plane surface area point of view, once serif mask or TCMs are used, the areas always improved ranging from 120% to 145% at the best focus condition compared to the convention mask. There was not so much difference among three different transmittance in view of pattern fidelity and process latitude. As one of candidates for optical proximity correction, since small serif delineation on mask level is not easy for devices with small features such as 1 giga bit DRAM or beyond, TCM is more promising which has much bigger and easily writable gray area.

Carbon antireflective coating (ARC) technology for both KrF and ArF lithography

In device integration smaller than 0.18 micrometer design rule, application of the ARC (antireflective coating) technology is unavoidable and SiON ARC and organic ARC are well-known materials up to now. In this paper, as an alternative way, new carbon ARC (CARC) material with the properties of easy stripping and good step coverage is presented. The details of its characteristics related to photo, etch and cleaning process and electrical properties after application to the real devices is investigated. The feasibility of the new CARC for both KrF and ArF lithography was confirmed.

Feasibility of new ARC using PECVD for both KrF and ArF lithography

We developed and confirmed the feasibility of a new carbon ARC (CARC) for both KrF and ArF lithography. CARC has high conformability on topography and is easily removable during the resist stripping process. Also good ARC performance and etch characteristics of CARC with sublayers are obtained. Thus, CARC is a promising alternative to SiON ARC and organic ARC.

Characteristics of Ge-based ARL for DUV lithography

Germanium based ARL (Anti Reflective Layer) having high conformality over topography and removable during resist strip process was developed. Its various characteristics were investigated. The ARLs were composed with GeN, and (Ge,Si)Nx and fabricated by reactive RF sputtering. The optical constants of Ge based materials were measured and the ARL performance for DUV lithography was obtained. Since the GENx is dissolved in water during resist develop process, it can not be used. Therefore, silicon was added to solve this problem. Thin film characteristics of (Ge,Si)Nx compound were analyzed using XRD, XPS, AES, SEM. The ARL performance was confirmed by resist patterning. Because the (Ge,Si)Nx material is removable by H2SO4 strip, yet most of current inorganic ARL is not, it has advantages for process simplicity.

Optical proximity correction of bit line pattern in DRAM devices

In the bit line patterns of high density DRAM, there has not been enough to process latitude because of the optical proximity effect. To correct this problem, we suggest TCM (transmittance controlled mask) as a sort of optical proximity correction which has the same pattern of mask with the controlled transmittance. The parameters of established mask including transmittance and bulge size were decided by simulation. After evaluating the aerial image measurement system, wafer was evaluated to exposure tool with i-line exposure source. As a result, application of TCM can improve the overlay margin more than normal mask and DOF with 0.4micrometers as compared with normal mask.