EUV scatterometer with a high-harmonic-generation EUV source.

We have developed an extreme ultraviolet (EUV) scatterometer based on the analysis of coherent EUV light diffracted from a periodic array with nano-scale features. We discuss the choice of appropriate orders of the high harmonics generated coaxially along with the intense Ti:sapphire laser pulses for high resolution spatial performance. We describe an inverse-problem methodology for determining the structural parameters, and present preliminary measurement results confirming the functionality of the scatterometer. A rigorous coupled-wave analysis measurement algorithm was developed to extract accurately and quickly the relevant constitutive parameters from a measured diffraction pattern using a library-matching process.

Infrared differential interference contrast microscopy for 3D interconnect overlay metrology.

One of the main challenges for 3D interconnect metrology of bonded wafers is measuring through opaque silicon wafers using conventional optical microscopy. We demonstrate here the use infrared microscopy, enhanced by implementing the differential interference contrast (DIC) technique, to measure the wafer bonding overlay. A pair of two dimensional symmetric overlay marks were processed at both the front and back sides of thinned wafers to evaluate the bonding overlay. A self-developed analysis algorithm and theoretical fitting model was used to map the overlay error between the bonded wafers and the interconnect structures. The measurement accuracy was found to be better than 1.0 micron.

Characterization of high density through silicon vias with spectral reflectometry.

Measurement and control is an important step for production-worthy through silicon vias etch. We demonstrate the use and enhancement of an existing wafer metrology tool, spectral reflectometer by implementing novel theoretical model and measurement algorithm for high density through-silicon via (HDTSV) inspection. It is capable of measuring depth and depth variations of array vias by Discrete Fourier Transform (DFT) analysis in one shot measurement. Surface roughness of via bottom can also be extracted by scattering model fitting. Our non-destructive solution can measure TSV profile diameters as small as 5 µm and aspect ratios greater than 13:1. The measurement precision is in the range of 0.02 µm. Metrology results from actual 3D interconnect processing wafers are presented.

Reflectometer-based metrology for high-aspect ratio via measurement.

We develop a modified thin film model with adjustable ratio of the illuminated surface areas for accurate reflectivity calculation of deep via structures. We also propose a method combining a half oblate spheroid model and a reflectance modulation algorithm for extraction of via bottom profile from the measured reflectance spectrum. We demonstrate the use and enhancement of an existing wafer metrology tool, spectral reflectometer by implementing novel theoretical model and measurement algorithm for through-silicon via (TSV) inspection. Our non-destructive solution can measure TSV profile diameters as small as 5 microm and aspect ratios greater than 13:1. The measurement precision is in the range of 0.02 microm. Metrology results from actual 3D interconnect processing wafers are presented.

Overlay measurement using angular scatterometer for the capability of integrated metrology.

Angular scatterometry, which has the advantage of good measurement precision, is an optical measurement technology based on the analysis of light scattered from periodic features, such as a linear grating, and is proposed as an alternative solution for overlay metrology. We present overlay measurements using an angular scatterometer and a bright-field microscope. A theoretical library based on rigorous coupled wave theory was created, and the reflected signatures measured by angular scatterometer were matched to the library to obtain structure parameters, including overlay, critical dimension (CD), and sidewall angle at the same time. The results reveal that angular scatterometer has a good precision and low tool-induced shift for overlay measurements, and has the potential for integrated metrology.

Scatterometry-based metrology with feature region signatures matching.

Scatterometry takes advantage of the sensitivity exhibited by optical diffraction from periodic structures, and hence is an efficient technique for lithographic process monitoring. A feature region measurement algorithm has been developed to extract accurately and quickly the relevant constitutive parameters from diffraction data. It is a method for efficiently determining grating structure by seeking the reflectance at some angles contains more information about the structure of the surface relief profile than the reflectance at other angles in a library data match process. The number of measurements and size of signature matching library will be reduced in a great percentage by performing the feature region algorithm.

Through-focus technique for nano-scale grating pitch and linewidth analysis.

We report results of experimental investigations into a through-focus method relevant to sub-wavelength feature dimension measurement. The method linearizes the partial derivative values of a focus indicator with respect to minimum intensity order, and hence permits determination of pitch using a classical linear method. By evaluating the variations in focus indicator of the different captured images obtained at various focal positions, the through-focus curves show a response to sub-resolution changes in the grating structure. The results suggest that sub-wavelength feature dimensions can be evaluated using regular optical microscopes by implementing the through focus method.