In this paper we propose a “film on grating” (FoG) measurement technique using spectroscopic ellipsometry (SE) that can enable sub-Ångstrom level precision for multi-layer film thickness measurement on topographies that closely approximate the device structure. FoG follows the industry trends to 'measure what matters' and provides thickness measurement data from patterned structures that has much stronger correlation to actual device performance. We also explore the impact of deviations in the film stack that can appreciably alter the device performance. One of the key device performance metrics that we will investigate is the leakage current, which is highly sensitive to process variations or defectivity. Measuring both the thickness and the bandgap of the HK dielectric permits excellent correlation with leakage current as determined by electrical testing of the device. The ability to predict electrical parameters effectively will greatly accelerate learning cycles during process development and can enable real time product control on existing inline metrology tools.
In recent technology nodes, advanced process and novel integration scheme have challenged the precision limits of conventional metrology; with critical dimensions (CD) of device reduce to sub-nanometer region. Optical metrology has proved its capability to precisely detect intricate details on the complex structures, however, conventional RCWA-based (rigorous coupled wave analysis) scatterometry has the limitations of long time-to-results and lack of flexibility to adapt to wide process variations. Signal Response Metrology (SRM) is a new metrology technique targeted to alleviate the consumption of engineering and computation resources by eliminating geometric/dispersion modeling and spectral simulation from the workflow. This is achieved by directly correlating the spectra acquired from a set of wafers with known process variations encoded. In SPIE 2015, we presented the results of SRM application in lithography metrology and control , accomplished the mission of setting up a new measurement recipe of focus/dose monitoring in hours. This work will demonstrate our recent field exploration of SRM implementation in 20nm technology and beyond, including focus metrology for scanner control; post etch geometric profile measurement, and actual device profile metrology.
Controlling thickness and composition of gate stack layers in logic and memory devices is critical to ensure transistor performance meets requirements, especially at 10nm node due to the 3-d geometry of devices and tight process budget. It has become necessary to measure and control each layer in the gate stack before and after dielectric and metal gate deposition sequences. A typical gate stack can have 5-7 layers including the interfacial layer, high-k dielectric, metal gate stack, work function layers, and cap layers. Similarly, PMOS channel strain is controlled using a graded Si<sub>x</sub>Ge1-<sub>x</sub> stack grown epitaxially over fins in the source/drain regions. This graded stack can have 2-4 layers of different thicknesses and Ge concentrations. This paper discusses the benefit of using spectroscopic ellipsometry with multiple angles of incidence to accurately and precisely determine the thickness of individual layers in critical gate layer stacks at various process steps on planar and grating surfaces. We will also show the benefit of using an advanced laser-based ellipsometer, for ultra-precise measurement of the gate interfacial layer oxides.
CD uniformity requirements at 20nm and more advanced nodes have challenged the precision limits of CD-SEM metrology, conventionally used for scanner qualification and in-line focus/dose monitoring on product wafers. Optical CD metrology has consequently gained adoption for these applications because of its superior precision, but has been limited adopted, due to challenges with long time-to-results and robustness to process variation. Both of these challenges are due to the limitations imposed by geometric modeling of the photoresist (PR) profile as required by conventional RCWA-based scatterometry. Signal Response Metrology (SRM) is a new technique that obviates the need for geometric modeling by directly correlating focus, dose, and CD to the spectral response of a scatterometry tool. Consequently, it suggests superior accuracy and robustness to process variation for focus/dose monitoring, as well as reducing the time to set up a new measurement recipe from days to hours. This work describes the fundamental concepts of SRM and the results of its application to lithography metrology and control. These results include time to results and measurement performance data on Focus, Dose and CD measurements performed on real devices and on design rule metrology targets.
We describe a solution for image restoration in a computational
camera known as an extended depth of field
(EDOF) system. The specially-designed optics produce
point spread functions that are roughly invariant with object distance
in a range. However, this invariance involves a trade-off
with the peak sharpness of the lens. The lens blur
is a function of lens field-height, and the imaging sensor introduces signal-dependent noise. In this context, the principal contributions
of this paper are: a) the modeling of the EDOF focus recovery
problem; and b) the adaptive EDOF focus recovery approach, operating in signal-dependent noise.
The focus recovery solution is adaptive to complexities of an EDOF imaging system,
and performs a joint deblurring and noise
suppression. It also adapts to imaging conditions by accounting for the state of the sensor (e.g., low-light conditions).
Precise simulation of digital camera architectures requires an accurate description of how the radiance image is transformed by optics and sampled by the image sensor array. Both for diffraction-limited imaging and for all practical lenses, the width of the optical-point-spread function differs at each wavelength. These differences are relatively small compared to coarse pixel sizes (6μm-8μm). But as pixel size decreases, to say 1.5μm-3μm, wavelength-dependent point-spread functions have a significant impact on the sensor response. We provide a theoretical treatment of how the interaction of spatial and wavelength properties influences the response of high-resolution color imagers. We then describe a model of these factors and an experimental evaluation of the model's computational accuracy.
The new generation of Digital Still Cameras (DSCs) provide a capability of capturing raw data that make it possible to measure the fundamental metrics of the camera. Although CCDs are used in a majority of DSCs, the number of cameras with CMOS-based sensors are increasing. Using first principles, the performance of comparable CCD and CMOS- based DSCs are measured. The performance metrics measured are electronic noise, signal-to-noise ratio, linearity, dynamic range, resolution, and sensitivity. The dark noise and dark current are measured as a function of exposure time and ISO speed. The signal response and signal-to-noise response are measured as a function of intensity and ISO speed. The resolution is measured in terms of the Modulation Transfer Function (MTF) using both raw and rendered data. The spectral sensitivity is measured in terms of camera constants at several wavelengths. Subjective image quality is also measured using scenes that exhibit limiting performance. The ISO speed performance is compared against a film camera.