Recent years have seen a fast technical development within the display area. Displays get ever higher pixel density and
the pixels get smaller. Current displays have over 800 PPI and market forces will eventually drive for densities of 2000
PPI or higher. The transistor backplanes also get more complex. OLED displays require 4-7 transistors per pixel instead
of the typical 1-2 transistors used for LCDs, and they are significantly more sensitive to errors.
New large-area maskwriters have been developed for masks used in high volume production of screens for state-of-theart
smartphones. Redesigned laser optics with higher NA and lower aberrations improve resolution and CD uniformity
and reduce mura effects. The number of beams has been increased to maintain the throughput despite the higher writing
resolution. OLED displays are highly sensitive to placement errors and registration in the writers has been improved. To
verify the registration of produced masks a separate metrology system has been developed. The metrology system is self-calibrated
to high accuracy. The calibration is repeatable across machines and sites using Z-correction. The repeatability
of the coordinate system makes it possible to standardize the coordinate system across an entire supply chain or indeed
across the entire industry. In-house metrology is a commercial necessity for high-end mask shop, but also the users of the
masks, the panel makers, would benefit from having in-house metrology. It would act as the reference for their mask
suppliers, give better predictive and post mortem diagnostic power for the panel process, and the metrology could be
used to characterize and improve the entire production loop from data to panel.