Abstract
In this paper, we detect and characterize the carbon contamination layers that are formed during the illumination of extreme ultraviolet (EUV) multilayer mirrors. The EUV induced carbon layers were characterized ex situ using spectroscopic ellipsometry (SE) and laser generated surface acoustic waves (LG-SAW). We show that both LG-SAW and SE are very sensitive for measuring carbon layers, even in the presence of the highly heterogeneous structure of the multilayer. SE has better overall sensitivity, with a detection limit of 0.2 nm, while LG-SAW has an estimated detection limit of 2 nm. In addition, SE reveals that the optical properties of the EUV induced carbon contamination layer are consistent with the presence of a hydrogenated, polymeric like carbon. On the other hand, LG-SAW reveals that the EUV induced carbon contamination layer has a low Young's modulus (<100 GPa), which means that the layer is mechanically soft. We compare the limits of detection and quantification of the two techniques and discuss their prospective for monitoring carbon contamination build up on EUV optics.
Highlights
The semiconductor industry’s desire to create smaller integrated circuit features on semiconductors has been a major driver for the development of lithographic techniques and quality optics for short wavelengths
We investigated the sensitivity of both spectroscopic ellipsometry (SE) and laser generated surface acoustic waves (LG-Surface acoustic waves (SAW)) for two carbon layer morphologies
SE has a lower limit of detection, we find that LG-SAW is able to distinguish different phases of carbon more accurately
Summary
The semiconductor industry’s desire to create smaller integrated circuit features on semiconductors has been a major driver for the development of lithographic techniques and quality optics for short wavelengths. I.e. multilayer mirrors (MLMs) must be used because materials are highly absorbing at short wavelengths. There are about ten such optics in the light collection and imaging train, meaning that the throughput of the system is just a few percent. Under these circumstances it is very important to maximize throughput by eliminating or removing surface contaminants that are deposited within the wafer scanner itself
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