Maskless lithography (ML) systems have been researched as an alternative technologies of the conventional
photolithography systems. Digital micromirror devices (DMD) can be used in ML systems as a role of photomask in the
conventional photolithography systems. For high-throughput manufacturing processes DMDs in ML systems must be
driven to their operational limits, often in harsh conditions. We propose an optical system and detection methodologies
to detect DMD malfunctions to ensure perfect mask image transfer to the photoresist in ML systems. We categorize
DMD malfunctions into two types. One is bad DMD pixel caused from mechanical defect and the other is data transfer
error. We detect bad DMD pixels with 20×20 pixels using white and black image tests. We confirm data transfer errors
at high frame rate operation of DMD by monitoring changes in the frame rate of a target DMD pixel driven by the input
data with a set frame rate of up to 28,000 frames per second (fps).
We study the distributions of line/space (L/S) patterns based on exposure dose variation using point array techniques (a type of digital maskless lithography). The intensity distributions of L/S patterns were simulated using the point array technique, and the pattern profiles were obtained by applying the effect of the photoresist contrast to the intensity distribution. As the dose increased, line width also increased. An experiment was performed to verify the simulation results. The minimum line widths of the L/S patterns were about 3.44 and 3.89 μm at laser power levels of 100% and 60%, respectively. The standard deviations of the line widths were 0.28 and 0.03 μm at the 4 and 13 μm L/S patterns, respectively.
In this study, we analyze the uncertainty in an optical testing system using a Shack-Hartmann sensor for a wavefront
measurement device. The main uncertainty sources of the optical testing system are the Shack-Hartmann sensor, the
image relay optics, and the pinhole source. Using a homemade high-precision plane-wave source as a reference, we
develop a simple method to calibrate the optics of the system and the Shack-Hartmann sensor itself. It is found that the
wavefront error of a pinhole source is negligible, and that the error due to the image relay optics installed between the
test lens and the Shack-Hartmann sensor is 0.030 λ (RMS). By warming up the Shack-Hartmann sensor for about 1 hour,
the measurement values are stabilized to within 0.001 λ (RMS). After calibrating the optical testing system with the
reference source, overall uncertainty in the optical testing system is reduced to 0.009 λ (RMS). Performance of the
optical testing system is evaluated by measuring the wavefront errors of various optical components, such as a numerical
aperture (NA) 0.25 aspheric lens and a digital video disc (DVD) pick up lens.