Plasma treatments to improve line-width roughness during gate patterning

Abstract

The major issue related to line width roughness (LWR) is the significant LWR of the photoresist patterns printed by 193-nm lithography that is partially transferred into the gate stack during the subsequent plasma etching steps. The strategy used today to overcome this issue is to apply postlithography treatments to reduce photoresist pattern LWR before transfer. In this article, we investigate the impact of various plasma treatments (HBr, H 2 , He, Ar) on the minimization of the LWR of dense and isolated photoresist patterns and its transfer during gate patterning. To do so, we use critical dimension scanning electron microscopy measurements combined with power spectrum density fitting method to extract unbiased LWR values and provide a spectral analysis of the LWR. We show that plasma treatments that lead to carbon redeposition from the gas phase on the resist pattern sidewalls are less efficient to reduce LWR than plasma treatments where the redeposition is limited. Among all plasma chemistries, H 2 plasmas seem very promising to decrease resist LWR in the whole spectral range, while maintaining square resist profiles. In addition, we show that all frequency roughness components are not equally transferred during gate patterning, and more particularly that the high frequency roughness components are lost.

Understanding the efficacy of linewidth roughness postprocessing

“…19 As the aforementioned derivations show, withinfeature variation, σ LWR ðLÞ, is affected by both the increase in correlation length and the increase in roughness exponent. For example, Azarnouche has shown that a combination of a VUV cure followed by etching steps increased the roughness exponent of a very long 80-nm wide feature from 0.57 to 0.9, and increased the correlation length of that feature from 16 to 41 nm.…”

“…A plot of the square-root of Eq (19). for the short-length linewidth roughness (LWR) at constant PSD(0) as a function of the line length L, in multiples of the correlation length ξ.…”

The Influence of H2Plasma Treatment on LWR Mitigation: The Importance of EUV Photoresist Composition

“…Besides the LWR improvement, maintaining the integrity of the resist profile after plasma treatment is also a major challenge, which needs to be addressed . Plasma exposure induces profile and line width loss by resist shrinking, due to depletion and outgassing of organic material, or flowing mechanisms …”

“…It can be seen from Figure , that PR 8 has the highest roughness improvement. However, hydrogen plasma treatment is only able to reduce the mid and high frequency roughness …”

“…The impact of a hydrogen based plasma treatment can provoke large resist modifications which in turn improve the LWR . Recent literature shows the importance of hydrogen vacuum‐UV (VUV) radiation on the LWR improvement process .…”