Susumu Kawada

248-nm DUV MoSiON embedded phase-shifting mask for 0.25 micrometer lithography

Over the past five years worldwide efforts have been made to develop new techniques for optical lithography enhancement. These techniques include optical proximity correction, off-axis illumination, pupil filtering and phase-shifting mask (PSM). Among many phase-shifting mask approaches, embedded PSM (EPSM) method has drawn significant interest due to its relatively simple reticle fabrication process and excellent lithographic performance, in particular, for dark field mask layers such as contact and via holes. Perhaps, the most difficult task in materializing the EPSM technology is the creation of a thin film structure that controls both phase and transmission. In addition, this film structure must withstand severe environment of mask making process and yet can be inspected and repaired successfully using currently available tool sets. The newly developed MoSiON material meets these requirements and has demonstrated a feasibility for DUV EPSM pilot production. In this paper, characteristics of the DUV lifetime test results. Details of reticle fabrication process including e-beam writing, dry etching, inspection and repair will be presented along with chemical durability data and process capability. Finally, wafer level lithographic performance for contact holes printed on a step-and-scan and a projection aligner will be shown to demonstrate lithographic performance of 248 nm DUV EPSM for 0.25 micrometer lithography.

Development of a MoSi-based bilayer HT-PSM blank for ArF lithography

HT-PSM has been adopted for semiconductor industry since i-line lithography. We introduced MoSi-based HT-PSM blanks for i-line and KrF lithography. Today they have become popular material and been established mask process widely. Thus it will be convenience for many mask users that MoSi-based HT-PSM could expand to ArF lithography. We have been developing double-layer MoSi HT-PSM blanks, as same structure of KrF. We developed new sputtering method for this expansion to get smaller extinction coefficient with comparatively large refractive index at 193nm. We got following data for T6% MoSi ArF HT-PSM blanks. (1) Table 1 shows typical optical properties of T6% MoSi HT-PSM blanks for ArF. (2) Fig.1 shows a spectroscopic transmittance and reflectance properties of a sample with T=6%(at 193nm: air ref.). In this case, its transmittance of 365nm(that is a wavelength of pattern inspection) is under 40%. It shows that mask users do not need any special inspection systems. In fact, we confirmed our HT-PSM with 40% (at 365nm) was able to be inspected by a KLA-300 series UV. (3) Fig.2 shows chemical durability data. Basically MoSi film has good durability for acid (SPM: 80C H2SO4+H2O2 4:1), and slightly poor durability for alkaline (SC-1: RT. NH4OH+H2O2+H2O 1:1:4). However this 6% film has good enough durability for alkaline, as seen in Fig.2, it changed less than +/- 0.05% of transmittance (at 193nm) and -0.5 degree of phase value (at 365nm). It is evaluated same durability as our HT-PSM for KrF. (4) Table 2 shows ArF laser irradiation durability. In the air, after 10 kjoule/cm2 irradiation (estimated for one year exposure in an ArF stepper), transmittance changed less than -0.3% and phase value less than -2 degree. It seems good enough irradiation durability. (5) Fig.3 shows a typical pattern profile of the T6% MoSi ArF HT-PSM. It was processed by MERIE system (ULCOAT Dry Etcher: MEPS-6025) with CF4+O2 at 6.8Pa, 100W(0.11W/cm2), 80Gauss rotating magnetic field. The profile has more than 85 degree without

Fabrication of MoSiON halftone masks using ZEP7000 for MEBES 4500

Halftone (HT) masks are a well-accepted method of manufacturing Phase Shift Masks (PSM). Recently, investigations of the suitability of HT masks for manufacturing have shifted from contact layers to gate devices. A regular supply of MoSiON-shifter HT mask blanks was obtained for this study. The MEBES 4500 pattern generator has been used for the electron beam writing of 250 nm design rule masks. However, this writing tool has sufficient performance to use in the next generation of masks. We have investigated the fabrication of MoSiON-HT mask using MEBES 4500. In general, because MoSiON is a very low conducting material, there are issues with pattern placement errors caused by charging. This charging effect can be reduced by utilizing an electrical conducting polymer (aquaSAVE) coated on the ZEP resist surface. The resulting registration error is corrected to the same level as that of conventional chrome blanks. Moreover we manufactured KrF-HT masks with contact-type patterns using HT blanks which were coated with electrical conducing polymer on the resist surface. From the results, we determined that we could manufacture production masks without any serious issues.

Attenuated phase-shifting mask blanks for the deep ultraviolet

ULCOAT has developed an attenuated phase shifting mask blank which has entered the production level for i-line blanks, with 180 degree(s) shifting angle and 5% to 20% transmittance. A single layer of MoSiON is employed as the phase shifter. Its simple structure enables good repeatability and stability in the mask making process. This single layer has 5% to 8% transmittance, with 180 degree(s) shifting angle at the deep ultra violet level (KrF Laser). However, it cannot be inspected at 488 nm (the wavelength of a popular pattern checker), due to more than 40% transmittance at that wavelength. Therefore, for deep ultra violet level work, a multi-layer type of MoSiON has been developed by ULCOAT, which achieves less than 40% transmittance at 488 nm.