Haruhiko Kusunose

True CW 193.4-nm light generation based on frequency conversion of fiber amplifiers

We present a source of line-narrowed continuous-wave (CW) radiation at 193.4 nm with over 10 mW of output power for the first time, to our knowledge. The system configures four successive frequency conversions of outputs from three single-frequency fiber amplifiers at 1064, 1107, and 1963 nm. The 266-nm beam produced by frequency quadrupling of 1064-nm light is sum-frequency mixed with the 1963-nm light to generate 234.3-nm radiation, which is consequently mixed with the 1107-nm light to generate 193.4-nm radiation. Both mixings are achieved in temperature-tuned non-critically phase-matched (NCPM) crystals.

Attenuated phase-shifting mask with a single-layer absorptive shifter of CrO, CrON, MoSiO, and MoSiON film

Attenuated phase-shifting mask with a single-layer absorptive shifter of CrO, CrON, MoSiO or MoSiON films has been developed. The optical parameter of these films can be controlled by the condition of sputtering deposition. These films satisfy the shifter requirements, both the 180-degrees phase shift and the transmittance between 5 and 20% for i-line. MoSiO and MoSiON films also satisfy the requirement for KrF excimer laser light. Conventional mask processes, such as etching, cleaning, defect inspection and defect repair, can be used for the mask fabrication. Defect-free masks for hole layers of 64 M-bit DRAM are obtained. Using this mask, the focus depth of 0.35-micrometers hole is improved from 0.6 micrometers to 1.5 micrometers for i-line lithography. The printing of 0.2-micrometers hole patterns is achieved by the combination of this mask and KrF excimer laser lithography.

Phase measurement system with transmitted UV light for phase-shifting mask inspection

This paper describes a direct phase measurement system with transmitted UV-light for phase shifting mask (PSM) inspection using a shearing interferometer microscope. Measurements were made with 365 nm monochromatic light of mercury arc lamp. The accuracy of this system is sufficient for the application for phase shifting mask inspection. The measurement results are in good agreement with the calculation based on quartz step height measurement and refractive index. Wafer exposure results of attenuating-type PSM also agree with the phase measurement results.

Novel Technique for Phase-Shifting-Mask Repair Using Focused-Ion-Beam Etch-Back Process

For the repair of phase-shifter (PS) defects with good topology and without optical deterioration, a new repair technique has been developed by using focused-ion-beam (FIB) etch-back and laser-explosion processes. This technique mainly consists of three steps: (1) leveling of defects by FIB-assisted chemical vapor deposition (CVD) or filling with spin-coated SOG film, (2) etch-back or/and exposure by Ga-FIB scanning with the detection of total secondary ions which inform the end point of etch-back, and (3) elimination of Ga-implanted shifter (or quartz) layer by a Nd:YAG laser shot. The excess shifter (bump defect) was rubbed out by adjusting the milling rate of the FIB-CVD film and its confined defects. For the missing shifter (divot defect), the filling SOG was screened off within the defect by use of Ga-FIB milling (exposure) and development. The Ga-implanted layer was eliminated by the laser explosion and so the repaired area was recovered in transmittance from less than 50% up to 98%.

Effect of Phase Error on Lithographic Characteristics Using Attenuated Phase-Shifting Mask

An attenuated phase-shifting mask is one of the most useful technologies for sub-half-micron lithography. However, it is necessary to control new parameters such as phase or transmittance when a phase-shifting mask is applied to practical use. We investigated the effect of phase error on lithographic characteristics for a hole pattern using an attenuated phase shifting mask. It is found that a phase error causes a decrease of depth of focus (DOF) and shift of best focus position. It is indicated that this effect depends on several optical parameters such as hole size and wavelength. In the case of the 0.4 µ m hole pattern with i-line stepper, the phase tolerance must be less than 2.7° to control loss of DOF within 0.1 µ m. It is also found that the edge slope effect of the shifter is rather small and the side wall angle of 70° is acceptable.

Fabrication technologies for advanced 5X reticles for 16M‐bit dynamic random access memory

Fabrication technologies for advanced photomasks with a molybdenum silicide (MoSi) film have been developed by using a variable‐shaped electron‐beam (e‐beam) system. These technologies were applied to the fabrication of 5X reticles for 16M‐bit DRAMs. The variable‐shaped e‐beam system is very effective in increasing the throughput for writing reticles which have a great number of figures, such as 16M‐bit DRAMs. The average writing time was 100 min, which was ∼ (1)/(3) of the time when using a conventional raster‐scan e‐beam system. Photomasks with the MoSi film have advantages in comparison with those with conventional chromium (Cr) film. Pattern defects did not appear during the photomask cleaning because of strong adhesion of the MoSi film to the quartz substrate. Moreover, an accurate feature size on the photomasks was obtained, because the MoSi film was easily dry etched. The feature size accuracy obtained was 0.03 μm in 3σ all over the 5 in. blanks.

Continuous-wave 193.4 nm laser with 120 mW output power

This Letter describes an all-solid-state continuous-wave, deep-ultraviolet coherent source that generates more than 100 mW of output power at 193.4 nm. The source is based on nonlinear frequency conversion of three single-frequency infrared fiber laser master-oscillator power-amplifier (MOPA) light sources.

Shape effects of edge-line phase shifter on light intensity contrast

By using two-dimensional simulation, dependence of light intensity contrast on numerical aperture (NA), coherence factor (a) of i-line stepper, shifter-width, phase error and slope angle of phase shifter edges have been investigated. For the slope angle of 90° and the shifter phase of 180°, the highest contrast is obtained for NA=0.65 and a=0.3. As the slope angle becomes to be small, contrast degrades remarkably for high NA(=0.65). On these simulation, 0.18pm resolution limit of isolated space pattern is successfully realized using an image reversal resist process.

Novel process for phase-shifting mask fabrication

In this new process for phase-shifting mask fabrication, molybdenum silicide (MoSi) is used as an optical shield layer and spin-on glass (SOG) as a phase-shifter layer. Chromium is employed as an etch-stopper during SOG etching. Cr etch-stopper will be removed at the end of tiie process, therefore all optical problems related to an etch-stopper are avoided. This Cr etch-stopper is also useful in inspection and repair of shifter remaining defects. At first, we will describe the fabrication process including the shifter-defect inspection and repair. Secondary, we will discuss the phase-shifting mask accuracy and its influence to the printed resist pattern when using the alternating type phase-shifting mask. Lastly,we will mention the application result of development of lithography for 64Mbit DRAM using this process.

Development of high sensitivity and high speed large size blank inspection system LBIS

The production of high-resolution flat panel displays (FPDs) for mobile phones today requires the use of high-quality large-size photomasks (LSPMs). Organic light emitting diode (OLED) displays use several transistors on each pixel for precise current control and, as such, the mask patterns for OLED displays are denser and finer than the patterns for the previous generation displays throughout the entire mask surface. It is therefore strongly demanded that mask patterns be produced with high fidelity and free of defect. To enable the production of a high quality LSPM in a short lead time, the manufacturers need a high-sensitivity high-speed mask blank inspection system that meets the requirement of advanced LSPMs. Lasertec has developed a large-size blank inspection system called LBIS, which achieves high sensitivity based on a laser-scattering technique. LBIS employs a high power laser as its inspection light source. LBIS’s delivery optics, including a scanner and F-Theta scan lens, focus the light from the source linearly on the surface of the blank. Its specially-designed optics collect the light scattered by particles and defects generated during the manufacturing process, such as scratches, on the surface and guide it to photo multiplier tubes (PMTs) with high efficiency. Multiple PMTs are used on LBIS for the stable detection of scattered light, which may be distributed at various angles due to irregular shapes of defects. LBIS captures 0.3mμ PSL at a detection rate of over 99.5% with uniform sensitivity. Its inspection time is 20 minutes for a G8 blank and 35 minutes for G10. The differential interference contrast (DIC) microscope on the inspection head of LBIS captures high-contrast review images after inspection. The images are classified automatically.