Yukio Iimura

Low‐stress tantalum absorbers deposited by sputtering for x‐ray masks

A method for fabricating stable and low‐stress tantalum films, suitable for absorbers of x‐ray masks, by dc‐bias, rf magnetron sputtering is presented. The superiority of Xe over Ar as a working gas is demonstrated. The stress‐vs‐bias‐voltage curve has a plateau, where the film stresses are low and constant over the bias voltage ranging from −15 to 20 V. The plateau stresses vary linearly with both the working Xe pressure and the substrate temperature with slopes of 1.2×1010 dyn/cm2 Pa and 8.6×106 dyn/cm2 deg, respectively. By control of the pressure and the temperature, stresses of (3±2)×108 dyn/cm2 are achieved. The Ta film which is stable under a heat treatment up to 300 °C is obtainable when it is deposited at 220 °C and then annealed at 220 °C for 1 h. The density of the films is (15.0±0.5) g/cm3. By x‐ray diffraction the films are found to be in a mixture of the α‐Ta phase and the β‐Ta phase. Ta patterns of 0.15 μm in width were fabricated.

Manufacturing of half-tone phase-shift masks I: blank

Half-tone phase shift mask (HT-PSM) blanks for i-line (365 nm) and g-line (436 nm) lithography, using chromium composites as a half-tone shifter, are brought into production. A bilayer structure of a 10 - 20 nm thick opaque, conductive chrome layer and a phase-shifting CrON layer is proposed, which can be formed by continuous deposition of the two layers and etched continuously by the process similar to that of the conventional chrome photomask. It shows low visible light transmission of less than 30% so that it can be inspected, and also shows enough conductivity to decay the excess charge during electron beam writing. HT- PSMs made of these blanks can be cleaned by sulfuric acid at 100 degree(s)C and can be used at least up to an irradiation of 1 MJ/cm2, when used for i-line exposure. The specification for the transmission is (target +/- 1)% for any point on any plate, and 0.7% range for any point on one plate, where the target ranges from 6% to 10%. The specification for the phase shift is currently (180+/- 10) degree(s).

Development of LEEPL 6025 format mask blanks

Low energy electron proximity projection lithography (LEEPL) has three types of mask formats. One of them, LEEPL 6025 square format, is so designed that electron-beam writers for photomasks can accommodate it. LEEPL 6025 square format blanks manufactured by three methods were evaluated in laying stress on cutting and bonding. The starting substrate was a 200-mm silicon-on-insulator wafer composed of a 2-μm-thick silicon layer, a 1-μm-thick SiO2 layer, and a 725-μm-thick base silicon. Membrane wafers were made after dry etching of the backsides of the starting substrates. They were cut and bonded to frames. Ceramic SiC and a Si-base material were used for the frame. Soldering and other thermal methods were employed for bonding. The findings are: 1) No membranes were broken in cutting and bonding, 2) Chipping was observed after cutting, which requires some edge treatment like edge beveling, and 3) The flatness of the membrane wafer was reduced from 87 to 13 μm by bonding. In conclusion the 6025 square format blanks were successfully manufactured by three methods and evaluated in the first time.