Writing next-generation display photomasks

Tor Sandstrom; Mikael Wahlsten; Youngjin Park

doi:10.1117/12.2241850

25 October 2016 Writing next-generation display photomasks

Tor Sandstrom, Mikael Wahlsten, Youngjin Park

Proceedings Volume 9985, Photomask Technology 2016; 99851D (2016) https://doi.org/10.1117/12.2241850
Event: SPIE Photomask Technology, 2016, San Jose, California, United States

Abstract

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.

Citation Download Citation

Tor Sandstrom, Mikael Wahlsten, and Youngjin Park "Writing next-generation display photomasks", Proc. SPIE 9985, Photomask Technology 2016, 99851D (25 October 2016); https://doi.org/10.1117/12.2241850

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KEYWORDS

Photomasks

Metrology

Calibration

Transistors

Organic light emitting diodes

LCDs

Overlay metrology

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