Abstract
Optical scatterometry is the state of art optical inspection technique for quality control in lithographic process. As such, any boost in its performance carries very relevant potential in semiconductor industry. Recently we have shown that coherent Fourier scatterometry (CFS) can lead to a notably improved sensitivity in the reconstruction of the geometry of printed gratings. In this work, we report on implementation of a CFS instrument, which confirms the predicted performances. The system, although currently operating at a relatively low numerical aperture (NA = 0.4) and long wavelength (633 nm) allows already the reconstruction of the grating parameters with nanometer accuracy, which is comparable to that of AFM and SEM measurements on the same sample, used as reference measurements. Additionally, 1 nm accuracy in lateral positioning has been demonstrated, corresponding to 0.08% of the pitch of the grating used in the actual experiment.
Highlights
The demand for faster, smaller, lighter and, at the same time, high-data density electronic devices sets stringent requirements for nanolithography, the science of writing small features into a photo-sensitive resist layer on top of a silicon wafer [1]
Optical scatterometry is the state of art optical inspection technique for quality control in lithographic process
We report on implementation of a coherent Fourier scatterometry (CFS) instrument, which confirms the predicted performances
Summary
The demand for faster, smaller, lighter and, at the same time, high-data density electronic devices sets stringent requirements for nanolithography, the science of writing small features into a photo-sensitive resist layer on top of a silicon wafer [1]. In order to obtain the intended line shapes and sizes, a reliable inline process control has to take place This is achieved by printing special targets on the wafer, typically gratings, which are successively measured in order to adjust dose, exposure time, over-. The metrology task of this process control is achieved by means of Incoherent Optical Scatterometry (IOS) In this technique, which is a very well established method for the inspection of periodic structures like gratings, an incoming beam is shone on the target and the part of the light which is scattered by it in reflection is measured in the far field. But not least, CFS with focused spot is not limited to measuring periodic structures but can be applied to analysis of multilayer structures, material sciences, photonics industry, biosensing, detection of isolated structures and other forms of non-contact metrology
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