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.