Advanced processing methods like multiple patterning necessitate improved intra-layer uniformity and balancing monitoring for overlay and CD. To achieve those requirements without major throughout impact, a new advanced mark for measurement is introduced. Based on an optical measurement, this mark delivers CD and overlay results for a specified layer at once. During the conducted experiments at front-end-of-line (FEOL) process area, a mark selection is done and the measurement capability of this mark design is verified. Gathered results are used to determine lithography to etch biases and intra-wafer signatures for CD and overlay. Furthermore, possible use cases like dose correction recipe creation and process signature monitoring were discussed.
Before each wafer exposure, the photo lithography scanner’s alignment system measures alignment marks to correct for placement errors and wafer deformation. To minimize throughput impact, the number of alignment measurements is limited. Usually, the wafer alignment does not correct for intrafield effects. However, after calibration of lens and reticle heating, residual heating effects remain. A set of wafers is exposed with special reticles containing many alignment marks, enabling intra-field alignment. Reticles with a dense alignment layout have been used, with different defined intra-field bias. In addition, overlay simulations are performed with dedicated higher order intra-field overlay models to compensate for wafer-to-wafer and across-wafer heating.
Monitoring long-term performance of projection optics in lithographic exposure systems will become more and more important, especially for 193nm wavelength. Various effects influence the quality and long-term stability of a lens projection system. Using the well known and established blazed phasegrating method, it is possible to identify lens degradation before it becomes a significant detractor in a manufacturing process. A two beam interferometer formed by a blazed grating reticle is used to measure the aberration values. This works for all DUV tools, and therefore it allows a comparison of tools from different suppliers. The test can be run after regular preventive maintenance or as daily monitor checks, in order to evaluate lens aberration over time. By storing the results, it is easy to generate a tool individual database. With this paper, we will show aberration data over time and the possibility to increase tool performance and stability.