Optical emission represents the bulk property of plasma, which in turn can be correlated to the
chamber surface condition and can be exploited for monitoring and characterizing chamber
condition. This presentation demonstrates the approach of utilizing plasma optical emission spectra
(OES) for the application on Applied Materials' Tetra<sup>TM</sup> etcher chamber condition monitor. Time-resolved
plasma optical emission spectra are collected with a spectrometry unit built in to the
TetraTM photomask etch module. Studies on OES analysis show that information related to chamber
surface condition can be correlated to the changes in emission spectrum of plasma. The effectiveness
of this methodology can be verified by Cr etch rates. Results can lead to procedure development for
chamber monitoring, chamber recovery and chamber seasoning applications.
As technology advances with feature size shrinking for the
state-of-the-art integrated circuit (IC) fabrication, the degree
of reduction in critical dimension (CD) features on a photomask shrinks at a faster pace, thanks to the ever aggressive
optical proximity correction (OPC) design. In addition to stringent CD requirement, defect control has also become one
of the most difficult challenges for advanced photomask manufacturing as a result of reduction in printable defect size.
Therefore, keeping a photomask etching chamber at an optimal condition becomes very critical for controlling in both
defectivity and CD fidelity.
In the present study, analyses on optical emission spectrum (OES) collected in an Applied Materials' Tetra<sup>TM</sup> chrome
etch module have been performed to understand (1) the impact of Cr etching on the chamber condition, and (2) the
effectiveness of in-situ chamber dry clean for chamber condition control and potential particle reduction. Results showed
that, with the right selection of chamber materials (to be compatible with process chemistry and etching condition), the
main impact of Cr etching on chamber condition and particle performance is from resist etch-by-products. Various
plasma dry clean chemistries have been explored to address the effectiveness for the removal of such etch-by-products.
As a result, an in-situ chamber clean (ICC) procedure is developed and has been validated to be production-worthy for
desired particle control and chamber stability control.