Akihiko Isao

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

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.

Advanced process with magnetically enhanced RIE for phase-shifting mask fabrication

Phase-shifting needs the critical dimension (CD) accuracy to be less than 0.05 micrometers for the metal and shifter pattern on a phase-shifting mask. Thus we have investigated a new etching process using magnetically enhanced reactive ion etching (MERIE). A magnetic field was provided by two pairs of solenoid coils outside the chamber. By using this MERIE system, the etching characteristics of chromium (Cr) and spin on glass (SOG) were evaluated. A Cl2 and O2 gas mixture was used for Cr etching. The etching selectivity had a maximum when the concentration of O2 was 20%. The etching selectivity increased with an increase in the magnetic field and gas pressure as well as with a decrease in the rf power. High etching selectivity and anisotropic etching features were obtained when the magnetic field was 100 G, the gas pressure 10 - 30 Pa, and the rf power density 0.18 - 0.22 W/cm2. Phase-shifting masks fabricated with this system show a CD accuracy of better than 0.05 micrometers , so 64 MB DRAM phase-shifting masks can be successfully fabricated with this MERIE system.