The power packet dispatching system, in which electric power is transferred in a pulse-shaped form with information, is expected to realize dynamical management of multiple power sources in independent systems such as robots. In this letter, close-loop control of a stepper motor by power packets is discussed. The precise angle control is achieved by the combined transfer of power and control information in experiments.

Optical parameters of KrF excimer laser stepper are optimized for 0.25 µm level patterning by means of a light intensity simulation method. The light intensity simulation method is applied conventional and two modified illuminations (annular and 4-point) to improve the depth of focus (DOF) at 0.25 µm periodic lines and spaces pattern (L&S). Simulation results obtained are; (1) the DOF of conventional illumination is not sufficient even in the optimum condition (NA=0.5, σ=0.8), (2) more than 1.5 µm DOF could be achieved with an annular illumination, if present resist performance is improved slightly, and (3) wider DOF is obtained in the case of with 4-point illumination. However, the DOF is rather degraded in the specific sized (near double/triple sized) region and oblique pattern, therefore the application of this illumination is restricted into some specific mask layout pattern.

Reduction in the illumination wavelength for exposure leads to higher resolution while keeping the depth of focus. Thus, KrF excimer laser lithography has been positioned as the next generation lithography tool behind g/i-line optical lithography, and many studies have been investigated. In the early days, the excimer laser lithography had many inherent problems, such as inadequate reliability, difficult maintainability, high operating cost, and low resolution and sensitivity of resist materials. However, the performance of the excimer laser stepper has been improved and chemical amplification resists have been developed for the past decade. At present, KrF excimer lithography has reached the level of trial manufacturing of lower submicron ULSI devices beyond 64 Mbit DRAMs.

Fabrication of 0.2 to 0.3 µm features is vital for future ultralarge scale integration devices. An area of particular concern is whether optical lithography can delineate such feature sizes, i.e., less than the exposure wavelength. The use of a phase shift mask is one of the most effective means of improving resolution in optical lithography. This technology basically makes use of the interference between light transmitting through adjacent apertures of the mask. Various types of phase shift masks and their imaging characteristics are discussed and compared with conventional normal transmission masks. To apply these masks effectively to practical patterns, a phase shifter pattern design tool and mask repair method must be established. The phase shifting technology offers a potential to fabricate 0.3 µm features by using the current i-line stepper, and 0.2 µm features by using excimer laser stepper.