“Structured”, “Textured” or “Engineered” Surfaces

In this article we describe the design of a universal ultra-precision positioning platform to be used in the development of many different nano-manufacturing processes. The system incorporates the concept of employing different interchangeable manufacturing and characterization tools with one ultra-precision positioning system. A multi-linear-motor-driven XY planar stage floating on a thin film of air is used to traverse a substrate through a 10 mm × 10 mm travel range with an XY linear position resolution of less than 1 nm and an angular resolution about the Z axis of 0.05 μrad over a range of about a degree (determined by plane mirror interferometer optics). A piezoelectric transducer (PZT) driven tripod positioning system is used to align each manufacturing and characterization tool with the substrate through a travel range of 40 μm along the Z axis and 245 μrad of rotation about the X and Y axes. The mechanical design, an overview of the system error analysis, preliminary component performance results, and the results of the first micro-imprint fabricated with the machine are presented.

Multi-scale Alignment and Positioning System – MAPS

Optical overlay measurement methods are very effective since they are rapid and non-destructive. Imaging techniques need sophisticated image processing and suffer from the wave-optical resolution drawback. Presently, leading edge devices are offered with 5 through 10 nm measuring accuracy. In this paper a method is proposed that relies on the diffraction of a probing laser beam at a periodic reference pattern. This special pattern is implemented in the circuit layout. After the resist patterning of the second of two consecutive layers, the diffraction at the resulting net grating is measured. If an appropriate grating design is chosen, the misalignment error can be directly extracted from the diffraction efficiency. In order to obtain a strong diffraction signal and thus a sufficient signal-to-noise ratio optimum grating designs have been computed by means of rigorous diffraction modeling. Experimental results supported by rigorous modeling suggest that this technique could have the potential to meet next generation overlay accuracy requirements.

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Light diffraction based overlay measurement

This paper discusses the past, present, and future of length and dimensional measurements at NIST. It covers the evolution of the SI unit of length through its three definitions and the evolution of NBS-NIST dimensional measurement from early linescales and gage blocks to a future of atom-based dimensional standards. Current capabilities include dimensional measurements over a range of fourteen orders of magnitude. Uncertainties of measurements on different types of material artifacts range down to 710 –8

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Length and Dimensional Measurements at NIST.

Recent advances in optical imaging techniques have unveiled new possibilities for optical metrology and optical-based process control measurements of features in the 65 nm node and beyond. In this paper we discuss methods and applications that combine illumination engineering and structured targets which enable sensitivity to nanometer scale changes using optical imaging methods. These methods have been investigated using simulation tools and experimental laboratory apparatus. The simulation results have demonstrated substantial sensitivity to nanometer changes in feature geometry. Similar results have now been observed in the laboratory. In this paper we will show simulation data to motivate the use of low numerical aperture and structured illumination optical configurations. We will also present the basic elements and methods which we are now using in the design of an optical tool specifically designed for these types of measurements. Target configurations which enhance the scattered electromagnetic fields will be shown along with experimental verification of the methodology. The simulation and experimental apparatus is used to explore and optimize target geometry, optical configurations, and illumination structure for applications in both critical dimension and overlay metrology.

High-resolution optical metrology

We present results of investigations into optical focus and edge detection algorithms relevant to overlay metrology. We compare gradient energy, standard deviation, contrast and summed intensity of acquired images as focus metrics for bright-field, scanning confocal, and confocal microscopy. For our purposes, gradient energy calculated via Sobel filtering was found to be the best criterion for an autofocus algorithm. We predict, based on theoretical results, that all of the focus algorithm we considered will focus in different heights relative to the object depending on the material properties of the object. Edge detection is accomplished via a window and spline technique for whole image data, and by application of a multiple line regression algorithm for single scan data. Measurements accomplished through these techniques are compared to state of the art scattering and analysis models.

Focus and edge detection algorithms and their relevance to the development of an optical overlay calibration standard

Overlay Metrology: Recent Advances and Future Solutions | NIST

In this paper we describe our design and the manufacturing of a 2D grid artifact of chrome on quartz on a 150 mm X 150 mm X 6.35 mm plate. The design has been agreed upon by a number of Semiconductor Equipment Manufacturers International participants working on a 2D grids calibration task force within the microlithography committee of SEMI. We present the measurement procedures and describe the algorithms used in the measurement process. We have procured a prototype artifact which is expected to be developed into a National Institute of Standards and Technology (NIST) distributed standard reference material once the final design has been agree upon. We will present measurements made at leading industrial sites and develop a traceability chain based on these measurements in combination with NIST based measurements. The artifact has been measured on the NIST linescale interferometer as well as other NIST metrology tools. We will also present the status of the comparisons between these measurements and those performed by the industrial collaborators.

Two-dimensional calibration artifact and measurement methodology

Accurate overlay measurements rely on robust, repeatable, and accurate feature position determination. In our effort to develop traceable overlay standards we have examined a number of edge detection methods and the parameters which affect those measurements. The samples used in this study are a comprehensive set of prototype overlay wafer standards. The methods for determining the position of a feature generally rely on some determination of edges, and the resulting feature centerline can be significantly affected by the method of choice. We have compared cross- correlation, centroid, and edge-threshold methods as well as an integrated least squares method. This paper is focused on empirical results obtained through the measurement of relevant overlay targets and pitch specimens. The data presented in this paper was acquired using charge coupled device (CCD)-based arrays.

Comparison of Edge Detection Methods Using a Prototype Overlay Calibration Artifact

A new optical alignment artifact under development at NIST is described. This artifact, referred to as a stepped microcone, is designed to assist users and manufacturers of overlay metrology tools in the reduction of tool-induced measurement errors. We outline the design criteria and diamond turning lathe techniques used for manufacturing this structure. The alignment methods using this artifact allow the separation of error components associated with the optical system or the mechanical positioning systems as encountered when performing measurements in different focal planes.Although some difficulties have been encountered when performing measurements in different focal planes. Although some difficulties have been encountered in the actual diamond turning process,the data presented show some improvements with the more recent prototypes which indicate that this method of fabrication will be useful. Photometer scan data and CCD image acquisition hardware show a significant optical response at the step edges from these structures. Initial analysis of the optical response of these edges shows sensitivity to the material used and the details of the manufacturing processes.

Edward Kornegay

Papers

Focus and edge detection algorithms and their relevance to the development of an optical overlay calibration standard

Overlay Metrology: Recent Advances and Future Solutions | NIST

Two-dimensional calibration artifact and measurement methodology

Comparison of Edge Detection Methods Using a Prototype Overlay Calibration Artifact

Method to characterize overlay tool misalignments and distortions