| AVS 64th International Symposium & Exhibition | |
| Plasma Science and Technology Division | Monday Sessions |
| Session PS+AS+SS-MoA |
| Session: | Plasma Surface Interactions |
| Presenter: | Adam Pranda, University of Maryland, College Park |
| Authors: | A. Pranda, University of Maryland, College Park S.A. Gutierrez-Razo, University of Maryland, College Park Z. Tomova, University of Maryland, College Park J.T. Fourkas, University of Maryland, College Park G.S. Oehrlein, University of Maryland, College Park |
| Correspondent: | Click to Email |
Numerous polymer etching models have been previously developed to correlate the structure or composition of the polymer to the plasma etching behavior1. A key assumption in these models is that the polymer structure remains homogenous as it is etched. For applications in photoresist pattern transfer, this assumption is not valid since high-energy ion bombardment results in the formation of a heterogeneous structure consisting of a 2-3 nanometer thick dense amorphous carbon (DAC) layer on the polymer surface which mediates the overall etch rate.
In this work, we experimentally examined several key plasma and sample parameters that impact the etching behavior for a set of model polymers and PR193 and PR248-type photoresist. These parameters include plasma composition, fluxes of incident species in the plasma, intensity of ion bombardment-induced surface modifications that affect the etching behavior, polymer chemical composition and molecular structure, along with UV and VUV sensitivity in a plasma environment. From our experimental work, we have found that the thickness and intensity of the DAC layer is highly dependent on the chosen plasma parameters and the polymer composition/molecular structure.
We compare various models of the etching behavior of a polymer based on parameters such as the polymer chemical composition/structure and the flux of incident species in the plasma relative to experimentally observed relationships. Of key significance is the relationship between reactive plasma species and the state of the DAC layer.
One of the experimental correlations we have identified is that a molecular structure consisting of a greater ratio of carbon carbon-type bonding results in a more optically dense DAC layer, which limits the ion flux that reaches the bulk layer, and thus leads to a lower steady-state etch rate. In the presence of any reactive species in the plasma, such as oxygen or fluorocarbon, there is an additional component to the etch rate due to chemical sputtering which results in an increase in the etch yield of the DAC layer. Once the DAC layer is sufficiently depleted, the ion flux reaching the bulk layer increases and thus the bulk etch rate increases as well. Utilizing the experimental results, we seek to arrive at an etching model that can be applied in the development of new photoresists that attain a target steady-state etch rate.
The authors gratefully acknowledge the financial support of this work by the National Science Foundation (NSF CMMI-1449309) and the US Department of Energy Office of Fusion Energy Sciences (DE-SC0001939).
1. Oehrlein, G. S. et al. J. Vac. Sci. Technol. B Microelectron. Nanom. Struct.29, 10801 (2011).