As tolerance requirements for the lithography process continue to shrink, the complexity of the optical proximity
correction is growing. Smaller correction grids, smaller fragment lengths and the introduction of pixel-based simulation
lead to highly fragmented data fueling the trend of larger file sizes as well as increasing the writing times of the vector
shaped beam systems commonly used for making advanced photomasks. This paper will introduce an approach of
layout modifications to simplify the data considering both fracturing and mask writing constraints in order to make it
more suitable for these processes. The trade-offs between these simplifications and OPC accuracy will be investigated.
A data processing methodology that allows preserving the OPC accuracy and modifications all the way to the mask
manufacturing will also be described. This study focuses on 65nm and 45nm designs.
CD control is one of the main parameters for IC product performances and a major contributor to yield performance. Traditional SEM metrology can be a challenge on particular layers due to normal process variation and has not proven to provide sufficient focus monitoring ability. This in turn causes false positives resulting in unnecessary rework, but more importantly missed focus excursions resulting in yield loss.
Alexander Starikov, Intel Corporation, alludes to the fact that focus and exposure "knobs" account for greater than 80% of CD correctible variance1. Spansion F25 is evaluating an alternative technology using an optical method for the indirect monitoring of the CD on the implant layer. The optical method utilizes a dual tone line-end-shortening (LES) target which is measured on a standard optical overlay tool. The dual tone technology enables the ability to separate the contributions of the focus and exposure resulting in a more accurate characterization of the two parameters on standard production wafers. Ultimately by keeping focus and exposure within acceptable limits it can be assumed that the CD will be within acceptable limits as well without the unnecessary rework caused by process variation.
By using designed experiments this paper will provide characterization of the LES technique on the implant layer showing its ability to separate focus-exposure errors vs. the traditional SEM metrology. Actual high volume production data will be used to compare the robustness and sensitivity of the two technologies in a real life production environment. An overall outline of the production implementation will be documented as well.
A method has been developed for calculating the statistical effects of spatial noise on the overlay measurement extracted from a given overlay target. Previously, this metric has been shown to correlate well to the random component of Overlay Mark Fidelity (OMF), and that OMF is a significant contributor to the noise hierarchy. Quantitative diagnostic methods are required in order to assess the capabilities of overlay metrology and provide visibility into root-causes of potential inaccuracies intrinsic in the processing of overlay targets. We explore the use of this target noise metric for improved process control including improved overlay modeling, process fault detection, and process troubleshooting. In this paper we demonstrate the use of this additional metric for multiple layers in a large volume of production data utilizing existing production sampling.