Diffraction based overlay metrology for α-carbon applications
2008
Applications that require overlay measurement between layers separated by absorbing interlayer films (such as α-
carbon) pose significant challenges for sub-50nm processes. In this paper scatterometry methods are investigated as an
alternative to meet these stringent overlay metrology requirements. In this article, a spectroscopic Diffraction Based
Overlay (DBO) measurement technique is used where registration errors are extracted from specially designed
diffraction targets. DBO measurements are performed on detailed set of wafers with varying α-carbon (ACL)
thicknesses. The correlation in overlay values between wafers with varying ACL thicknesses will be discussed. The total
measurement uncertainty (TMU) requirements for these layers are discussed and the DBO TMU results from sub-50nm
samples are reviewed.
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