Kee-Soo Nam

Behavior of the molybdenum silicide thin film by 193nm exposure

In order to embody high resolution at 32 nm and below, molybdenum silicide (MoSi) phase shift mask (PSM) is essential material in the ArF lithography process, generally. But some problems reported from for the variation of PSM characteristics like transmittance variation and chemical durability. This change in characteristics is an issue for the yield drop in the semiconductor device manufacturing. So we study the behavior of MoSi PSM thin film in the view point of the ArF laser exposure in this paper. Firstly, the problems of MoSi thin film by the 193 nm exposure are observed. From the result, 0.36 % of the transmittance was changed by 193 nm irradiation with 10 kJ of energy. Accordingly, MoSi thin film characteristics were degraded by the ArF laser irradiation. The reason for the transmittance degradation by irradiation for MoSi thin film was analyzed. Also, we found that the oxygen was activated by the ArF laser and this activated oxygen penetrated to MoSi thin film. Consequently, the transmittance increased by the penetrated oxygen. Then we investigated the improvement scheme for MoSi thin films irradiation characteristic. First, the transmittance of the thin film was changed by the reactive gas ratio change. Also, the Si ratio in the MoSi thin film was changed. Lastly, densification process was applied. Consequently, the densification process for the MoSi thin film improved the irradiation characteristics.

Development and characterization of advanced phase-shift mask blanks for 14nm node and beyond

Recently, the development of semiconductor process for 14nm node and beyond is in progress. The mask-making process demands higher resolution and CD accuracy to meet requirements. Current conventional ArF PSM has several problems such as higher 3D effect and higher loading effect due to the thicker film. These problems cause the CD performance degradation. This study is about the manufacturing of advance ArF PSM, which has thinner phase shift layer and higher etch rate Cr absorber film. The thickness of phase shift film is less than 60nm and the total etch-time for the Cr absorber film is reduced more than 30%. The mask CD performance of this new blank was evaluated in terms of CD uniformity, CD linearity, pattern resolution, and loading effect and so on. Adapting to this new blank, we can achieve better CD performance by reducing the loading effect. In addition, the chemical durability and ArF exposure durability were also improved. In conclusion, the mask-making process margin was extended by using this new blank, and it is expected that we can achieve the required specifications for 14nm node and beyond.

Development of advanced multi-tone mask by using two different transmittance modulation materials

Multi-tone mask (MTM) consists of more than two layers having different transmittance modulation layers. A novel method is proposed to manufacture a MTM based on two kinds of transmittance modulation materials such as chromium and molybdenum. Different modulation materials cannot be only act as etch-stopper to each other, but also they play a role as a separator between the layers consisted of MTM. Furthermore, clearly classified modulation layers contribute to define one of the targeted transmittance according to different etching process. Especially, a conventional MTM requires three mask writing processes to form three patterns whereas the proposed MTM structure makes it possible to form three patterns by using only two mask writing processes. It is found that the turnaround time of proposed MTM is remarkably decreased as value of 30% compared to that of conventional MTM. MoSi-/Cr-based tri-tone mask configuration having 37, 15, and 0% of transmittance had been demonstrated based on the optimized thin-film conditions. Optical uniformity characteristics were also carried out to evaluate the photomask performance. Consequently, the proposed MTM is not only expected to extend the variation of objective transmittance, but also it is a very promise method for achieving a high performance photo-mask by reducing its fabrication cost.

The study of the birefringence as MoSi based materials for immersion lithography

According to the semiconductor technology roadmap, immersion lithography is emerging for 32 nm and below technology. Therefore, immersion lithography requires new process parameters such as high refractive index fluid, stepper, resist, and birefringence. A lot of research for those items has been done, and the components and materials of thin film used blankmask have become more important. The birefringence of thin film is an especially essential issue for the development of advanced technology. Accordingly, we studied birefringence with thin film characteristics. Having a transmittance of 6% at 193 nm, six different kinds of molybdenum silicon-based thin films were prepared by DC magnetron sputter. The thin films were deposited on 6.3 mm thick quartz using O2, N2, CH4 and CO2 reactive gasses. We studied the effects of thin film composition, substrate, heat treatment, and dopant in this paper. First, we measured the birefringence as thin film composition and substrate by the 250AT Exicor system. We studied the effect of reactive gas flow rate and types on birefringence, and we selected thin film material adaptable to reduce the birefringence from the above results. Next, we doped the transition metal to the selected materials to decrease the birefringence. Then we did heat treatment to the thin films by using rapid thermal process (RTP) to further reduce the birefringence. According to the results, we confirmed that the birefringence was influenced by thin film composition and it was controlled by the tuning of thin film composition, dopants, and heat treatment. Next, we analyzed the intensity of crystal state and density of thin films by using x-ray diffractometer (XRD) and x-ray refractometer (XRR). Finally, we analyzed the thin film characteristics by using various analytic tools.

Investigation of airborne molecular contamination adsorption rate as storage materials in mask

The haze issue has gradually increased in the 65 nm node technology and beyond. This issue has been reporting that it is caused by chemical reaction among ions like SO42-, NH4+ and aromatic hydrocarbon compounds (AHCs) such as butylated hydroxy toluene (BHT), toluene and etc. on mask by 193 nm laser in general. This haze growth causes defects with accumulation of exposure energy. Finally, it decreases the lifetime of photomask with an increase in defects. The source of this haze is generated from storage materials as well as chemical residue in the photomask process. Therefore, we investigated the adsorption rate of airborne molecular contamination (AMC) on each layer with storage materials which were assumed to be the source of the haze. We analyzed adsorbed ions and volatile organic compounds (VOCs) on each layer to verify the effects of storage materials for some storage periods by automatic thermal desorption gas chromatography/mass spectrometer (ATD GC/MS) and ion chromatography (IC). Also, we investigated the contact angle of each layer as AMC concentration of storage materials. From the experimental results, we confirmed that the adsorption rate of AMC was different on each layer as storage materials.

The behavior of substrate dependency as surface treatment in the positive chemically amplified resist

Positive chemically amplified resist (CAR) is widely used because of its benefit to high resolution in the semiconductor industry. Recent numerous studies have reported that resist pattern error such as resist scum and adhesion fail at the interface between substrate and positive CAR is caused by substrate dependency. Hence resist pattern error must be minimized. In this study we have observed the phenomena at the positive CAR coated mask blanks. And then we applied various surface treatments to the Cr film to minimize resist pattern error. Firstly, resist pattern error was occurred by the substrate dependency in the positive CAR coated mask blanks. We have investigated the root causes of this pattern error, we found that nitrogen radical and OH radical in the Cr film could combine with proton in the positive CAR easily. So various surface treatments were applied to minimize detrimental effects of substrate dependency to the positive CAR. And the behavior of substrate dependency was observed by various analyses to verify the effect of surface treatment method. The results showed that substrate dependency could be controlled by surface treatment in the positive CAR coated mask blanks.

A Study of Haze Generation as Thin Film Materials

For high quality products in the semiconductor and photomask industries, exposure wavelength has been shortening from i-line to ArF to embody the high resolution as critical dimension (CD) shrinkage and the specifications have been restricted. However, a new defect issue called haze has appeared that is shortening the wavelength. This defect is caused by the photoreaction of chemical residues exposed to SO4 2-, NH4 + and other chemicals. Accordingly, in this paper we investigated the generation of haze in thin film materials. For fabrication of various thin films, the materials which were metal, compound material without nitrogen, and compound material with nitrogen, were deposited on a quartz substrate using sputtering. Then, we chemically treated the thin film materials using various conditions including sulfuric peroxide mixture (SPM) and standard cleaning (SC-1). First, the concentration of ions on the thin film materials was measured using ion chromatography (IC) analysis. Second, haze defects were inspected after exposure in order to evaluate the difference in haze generation on the thin film materials. Also, we investigated the numbers and shape of the occurrences of haze.

A study of storage life extension for high performance chemically amplified resist coated blanks

The importance of advanced e-beam writing system and chemically amplified resist (CAR) coated blank is increasing gradually in high-end grade photomask manufacture according to CD embodiment of 90 nm and beyond technology node requiring because of the shrinkage of design rule in the semiconductor industry. However, many studies have been reported that CAR has several troubles and especially, CAR sensitivity change is occurred by airborne molecular contamination (AMC). So, the storage life of CAR coated blank is shortened. This problem may cause the difficulty of high-end grade photomask manufacture because it is hard to secure stable mean to target (MTT) and CD uniformity by sensitivity change, T-top profile and footing profile. Therefore, the purpose of this paper is to investigate the storage life extension for high performance CAR coated blank through improvement of the packing materials. Firstly, a variety of packing materials were collected and the selected packing materials were analyzed by Automatic Thermal Desorption Gas Chromatograph/Mass Spectrometer (ATD GC/MS) and Ion Chromatograph (IC) to examine AMC generated from the packing materials. As a result, molecular condensables such as alcohols, hydrocarbons and fatty acids were detected and molecular acids and molecular bases those are NH4+, Cl-, NOx- and SOx- were also detected from the packing materials, respectively. From the above results, we selected the best packing materials which generated the least AMC and the worst packing materials which generated the most AMC. Additionally, we verified photomask process with CAR coated blanks which were packed with those packing materials with post coating delay (PCD) by 50 kV e-beam writing system. In consequence, dose to clear (DTC) showed 4.6 μC/cm2 at 0 day PCD for both of the best and the worst packing materials of CAR coated blank. After 90 days PCD, DTC variation was only 0.4 μC/cm2 for the best packing materials, but DTC variation of 4.0 μC/cm2 showed in the worst packing materials. There was 10 times difference in DTC variation between the best and the worst packing materials. As well as, the CD variation at 0.5 μm dense line presented less than 5 nm movement for 90 days PCD.