Advanced DRAM manufacturing demands rigorous and tight process control using high measurement precision,
accurate, traceable and high throughput metrology solutions. Scatterometry is one of the advanced metrology techniques
which satisfies all the above mentioned requirements and it has been implemented in semiconductor manufacturing for
some time for monitoring and controlling critical dimensions and other important structural parameters. One of the
major contributions to the optical critical dimensions metrology uncertainty is the variations in optical properties
(n&k's) of film stack materials. And it is well-known that the optical properties of materials depend very much on
process conditions (such as operating conditions of deposition tools). However, in traditional scatterometry approach all
the n&k's have been used as fixed inputs in a scatterometry model which might result in significant metrology error.
This paper shows the use of the integrated scatterometry system in a real production environment. The significant
improvement in accuracy of CD data was achieved following the implementation of new floating n&k's option for the
Optical Digital Profilometry (ODPTM) system. It has been clearly shown that to achieve desired sub-nanometer accuracy
in scatterometry measurements for advanced processes we need to pay scrupulous attention to every detail of the
scatterometry modeling and measurement. Still further work is needed to better understand the impact of n&k's
variations on tool-to-tool matching.
Scatterometry is one of the advanced optical metrology techniques has been implemented in semiconductor
manufacturing for monitoring and controlling critical dimensions, sidewall angle and grating heights as well
as thicknesses of underlying films, due to its non-destructive nature, high measurement precision and speed.
In traditional scatterometry approach, the optical properties (n&k's) of film stack have been used as fixed
inputs in a scatterometry model, therefore, the process engineers have to assume that there is no significant
impact on measurement results by small deviation from pre-extracted n&k's. However, n&k's of actual
production wafers will always vary from the fixed values used in the model. The magnitude of the variations
and its impact on the accuracy of scatterometry measurements has not been well-characterized yet.
In this study, a low-k dielectric stack with noticeable n&k's variations was generated. The low-k dielectric
stack has the refractive index (n) variation around 0.01 @ 633nm within a wafer, and is under two layers of
patterned PR and BARC. Different scatterometry models with fixed and floated n&k's have been analyzed.
Although comparable repeatability was obtained with either fixed or floated n&k's model, the correlation
(R2) to CD-SEM result has been improved by floating n&k in the model in comparison to that of fixed n&k
model. In this paper, we also discuss some differences in applying various optical models (i.e, EMA and
Cauchy) in scatterometry measurements.
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