The mechanism of chemically amplified resist plays a critical role in the modeling of the latent image. To achieve a
practical model which can fit into the time frame of OPC, some simplifications and assumptions have to be made. We
introduced regression kernels that take into account best exposure focus difference between isotropic pitch, dense, and
line end features for the evaluation of image intensity. It compares the image intensity (signal) over small changes
above and/or below the regressed "nominal" image position, which in principle corresponds to evaluating the intensity
signal at various depths of a fixed resist profile thus can also be regressed for optimization during model development.
Our calibration has shown that the model brought a great improvement in prediction for difficult structures such as dense
features at or near the optical resolution limit and 2-dimensional features, which are the limiter of the overall model
fitting accuracy for 45nm node and below. By replacing other existing techniques, total number of output kernels used
for OPC operation is actually reduced with improvement of model accuracy. This model is proven to be a very effective
yet accurate addition to the current OPC technology.
Acceptance of Sub Resolution Assist Feature (SRAF) has been widely recognized in lithography patterning. In general,
with the insertion of SRAF in optically adjacent space area of design main feature, the aerial image intensity profiles of
the corresponding main features are apparently being either constructively or destructively alternated at imaging plane
[Figure 1]. From lithography patterning perspective, the optimized or better pattern imaging process requires
constructive SRAF. Such SRAF is inserted into available space for main feature to obtain optimal or better image
contrast, better imaging resolution and depth of focus (DOF) which is similar or close to optimal focus latitude.
However, the complementary destructive SRAF insertion can adversely occur in certain circumstances. In this paper, we
study the theoretical understanding of the constructive and destructive effects against design main features imaging
associated with the efforts to include SRAF (it's either driven by rule, model or mishap). In addition, an evaluation
scheme is developed and being explored in many aspects in order to describe the constructive and destructive response of
inserted SRAF. Such evaluation scheme has derived an application to detect the degree of SRAF insertion coverage
accuracy, impact on manufacturing, and most usefully, to access potential layout required optimization in design space
based on these complementary effects mechanism throughout several off-axis illumination conditions.
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