Having consistent high quality photo masks is one of the key factors in lithography in the wafer fab.
Combined with stable exposure- and resist processes, it ensures yield increases in production and fast learning
cycles for technology development and design evaluation.
Preventive controlling of incoming masks and quality monitoring while using the mask in production is
essential for the fab to avoid yield loss or technical problems caused by mask issues, which eventually result
in delivery problems to the customer.
In this paper an overview of the procedures used for mask qualification and production release, for both logic
and DRAM, at Infineon Dresden is presented.
Incoming qualification procedures, such as specification checks, incoming inspection, and inline litho process
window evaluation, are described here. Pinching and electrical tests, including compatibility tests for mask
copies for high volume products on optimized litho processes, are also explained. To avoid mask degradation
over lifetime, re-inspection checks are done for re-qualification while using the mask in production.
The necessity of mask incoming inspection and re-qualification, due to the repeater printing from either the
processing defects of the original mask or degrading defects of being used in the fab (i.e. haze, ESD, and
moving particles, etc.), is demonstrated.
The need and impact of tight mask specifications, such as CD uniformity signatures and corresponding
electrical results, are shown with examples of mask-wafer CD correlation.