Three-dimensional deep sub-wavelength defect detection using λ = 193 nm optical microscopy

Abstract

Optical microscopy is sensitive both to arrays of nanoscale features and to their imperfections. Optimizing scattered electromagnetic field intensities from deep sub-wavelength nanometer scale structures represents an important element of optical metrology. Current, well-established optical methods used to identify defects in semiconductor patterning are in jeopardy by upcoming sub-20 nm device dimensions. A novel volumetric analysis for processing focus-resolved images of defects is presented using simulated and experimental examples. This new method allows defects as narrow as (16 ± 2) nm (k = 1) to be revealed using 193 nm light with focus and illumination conditions optimized for three-dimensional data analysis. Quantitative metrics to compare two-dimensional and three-dimensional imaging indicate possible fourfold improvements in sensitivity using these methods.

Effects of wafer noise on the detection of 20-nm defects using optical volumetric inspection

“…Processing Although optical focus-resolved 3-D volumetric defect detection has been described in depth elsewhere, 3,4 it is important to reiterate the required steps to better explain the results presented. A schematic of the process is shown as Fig.…”

“…Due to wafer shifting to obtain the "reference" volume, there are two copies of the defect visible in each panel of the figure. 4, there are a greater number of nondefect subvolumes. 2(a) are due to the presence of a defect, with the remaining subvolumes attributable to noise.…”

“…3,4 Volumetric processing of the full 3-D scattered field is not restricted to focusresolved imaging as is shown here; angle-resolved sampling of the 3-D scattered field can be similarly processed. 3,4 Volumetric processing of the full 3-D scattered field is not restricted to focusresolved imaging as is shown here; angle-resolved sampling of the 3-D scattered field can be similarly processed.…”

Application of measurement configuration optimization for accurate metrology of sub-wavelength dimensions in multilayer gratings using optical scatterometry

“…We should also mention that the proposed method is not only useful in optical scatterometry, but would also be applicable in the closely related field of optical wafer defect detection. Two of its primary implementation methods, namely, interferometric [21][22][23] and through-focus microscopy [24][25][26], also rely on generating overdetermined measurement data using multiple measurement configurations.…”

Optical volumetric inspection of sub-20nm patterned defects with wafer noise

“…We have recently developed a new, three-dimensional volumetric defect inspection method for mitigating the effects of random noise while using the continuity of the defect to bolster defect detection [3,4]. Initially, we are utilizing the full three-dimensional scattered field using focus-resolved imaging; though not performed here, angle-resolved sampling of the three-dimensional scattered field can also be processed volumetrically.…”