Han-Sun Cha

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.

Etching selectivity and surface profile of attenuated phase shifting mask using CF4/O2/He inductively coupled plasma (ICP)

The selectivity and etched profile of MoSiON in high-density CF4/O2/He inductively coupled plasma (ICP) have been studied. The etched profiles of MoSiON along with the quartz surface morphologies were investigated as a function of etching parameters by scanning electron microscopy (SEM). We varied pressure from 5 mtorr to 20 mtorr and CF4 flow rate from 15 sccm to 40 sccm. A smooth quartz surface and a vertical MoSiON slope were observed under 10 sccm CF4, 15 sccm of O2 flow rate, -240 V of DC bias and 5 mtorr pressure. And the other conditions showed rough quartz surface and bad MoSiON slope. Only at the appropriate CF4/O2 Flow rate, high vapor pressure compounds inhibits nonuniform quartz etching.

Dry-Etching Characteristics of Attenuated Phase-Shifting Masks using Cl2/CF4/O2/He Plasmas

The attenuated phase-shifting mask (Att. PSM) is one of the most useful technologies for deep sub-micron lithography. However, several critical mask parameters including critical dimension (CD), sidewall slope and morphology affect the phase-shift layer (MoSiON). In this work, the effects of added Cl2 gas and dc bias voltage in inductively coupled CF4-based plasma were studied. As results of our experiment, the most vertical profile and smoothest surface were obtained at 10 sccm Cl2 and -200 V dc bias. By increasing the dc bias voltage, the undercut of the MoSiON layer decreased. As Cl2 gas increased in the CF4/O2/He plasma, surface roughness decreased but the edge of the Cr slope was damaged at 15 sccm Cl2. It is suggested that the pattern profile and surface roughness of the MoSiON layer can be controlled by both the quantity of Cl2 gas and the dc self-bias voltage.

Evaluation of various alternating phase shifting mask processes for KrF lithography

It is reported that Alternating Phase Shifting Mask (Alt. PSM) enhances the resolution and depth of focus and reduces the mask error enhancement factor efficiently. In spite of above-mentioned advantages, Alt. PSM is rarely used for some problems. One of the problems is the image imbalance between the transmittance of the shift and the nonshift area on Alt. PSM. To minimize the image imbalance, various manufacturing processes are introduced for both single and dual trench structures. In this paper, the image balance was simulated with AIMS and the Solid-CM program. The pattern profile, CD, depth and a phase uniformity of Alt. PSM were investigated experimentally. We carried out 3 types of processes (a) single trench (wet etch process), (b) single trench (dry etch process with undercuts), (c) dual trench (dry etch process with undercuts). The type (a) showed 12 nm of CD uniformity, 1.56 degrees of phase shift uniformity and 63 Angstrom of the shift depth. And its transmittance of the shift region was 99.85 percent. For the type (b), its CD uniformity, phase shift uniformity, depth uniformity and the transmittance of the shift region were 15 nm, 11.56 degrees, 208 Angstrom and 99.76 percent, respectively. And the experiments of the type (c) are now under way.

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.

Highly anisotropic etching of phase-shift masks using ICP of CF4-SF6-CHF3 gas mixtures

There is considerable interest in phase shift masks as a route to extending the resolution, contrast, and depth of focus of lithographic tools beyond what is achievable with the normal chrome mask technology. A problem that has so far hindered the introduction of phase shift masks has been the difficulty of phase and transmittance control when a phase shift mask is applied to practical use. Also, to apply phase shift layer (MoSiON), it remains that effects several critical mask parameters including sidewall slope, surface roughness, and critical dimension. For these reasons, this process requires a high degree of control of the etch process of shift layer. So in this paper, we described a technique for the fabrication of phase shift masks by etch rate of a MoSiON layer. Etching experiments of MoSiON were performed using different fluorinated gas mixtures. Four of them, CF4/O2/He, SF6/O2/He, CHF3/O2/He and Cl2/CF4/O2/He were chosen for high etch rate, sidewall slope, and surface morphology. Each added gases had a unique property on the etch rate, anisotropy, surface roughness and sidewall morphology. Result indicates that vertical slope and smooth surface are obtained using the Cl2/ CF4/O2/He and SF6/O2/He mixture. With increasing O2 flow rate to the SF6/O2/He Plasma and added Cl2 gas to the CF4/O2/He Plasma, the MoSiON etching profile becomes anisotropic without undercutting and trench profile. It is probably due to both increasing etch rate and sidewall passivation of Cl2 ion flux. When Cl2 gas was added to the CF4/O2/He Plasma, the small addition of chlorine was enough to protect the exposed sidewall of the undercutting, therefore, higher flow rate of chlorine had to be added to protect the sidewall of the undercutting by forming a sidewall passivation layer. These results show that both increasing O2 flow rate to the SF6/O2/He Plasma and the addition of Cl2 to the CF4/O2/He plasma are necessary in order to achieve a vertical profile and a smooth surface morphology.