Effective–CD: a contribution toward the consideration of line edge roughness in the scatterometric critical dimension metrology

Bartosz Bilski,Karsten Frenner,Wolfgang Osten

doi:10.1117/1.jmm.16.2.024002

Bartosz Bilski, Karsten Frenner + Show 1 more

Open Access

https://doi.org/10.1117/1.jmm.16.2.024002

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Abstract

We present an overview of our research on the relation between line edge roughness (LER) and optical critical dimension metrology (OCD). Referring to a known fact that LER does have an impact on OCD, we discuss a novel approach that allows for its better understanding. Namely, we show that, in the presence of LER, one can observe a characteristic scatterometry-measured CD offset, which we call effective–CD. The fact that the effective–CD is characteristic renders it to be a good means of accessing the information about LER present on the CD. To assure the completeness of this overview, we begin by reviewing some previously published results, which have drawn our attention and first led us to observing the characteristic influence of LER on a CD measurement. Next, we extend our model-based simulations to confirm the presence of the effective–CD for complex-roughness models, and finally, we demonstrate an experimental verification of our effective–CD hypothesis. We are convinced that our approach will help to better understand the impact of LER on a CD measurement and will be considered a useful contribution to the development of measurement methods for challenging scenarios, in which realistic CD is affected by the presence of LER.

Highlights

The semiconductor industry continues to drive patterning solutions by reducing device dimensions or, by printing nodes of a continuously shrinking critical dimension (CD)
We present an overview of our research on the relation between line edge roughness (LER) and optical critical dimension metrology (OCD)
We have conclusively demonstrated that LER has an impact on optical CD metrology

Summary

Introduction

The semiconductor industry continues to drive patterning solutions by reducing device dimensions or, by printing nodes of a continuously shrinking critical dimension (CD). As CD values shrink further, the phenomenon of line edge roughness (LER) gains substantial attention.[1] LER is defined as “a deviation of a feature edge (as viewed top-down, e) from a smooth, ideal shape (d),” or as[1]. LER 1⁄4 3 · σ 1⁄4 3 · RMSðe − dÞ. The “gains substantial attention” is expressed by statements like “LER can become the most significant source of linewidth control problems for features ≤ 50 nm.”[1] In the light of such statements, it is clear why optical scientists are striving to provide process engineers with a solution that would contribute to solving the stated linewidth control problem

Line Edge Roughness Indeed has an Impact on a CD Measurement

Concept of the Effective–CD

Experimental Effective–CD Observation

The Results

Conclusions and Outlook

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