New critical dimension optical metrology for submicron high-aspect-ratio structures using spectral reflectometry with supercontinuum laser illumination

As the semiconductor industry moves forward towards advanced packaging, through silicon vias (TSVs) with a top Critical Dimension (CD) down to 1 µm and aspect ratio 1:15 or higher are being projected. This poses a major challenge to optical metrology as the dimensions of the lattice get close to the wavelength of the visible light. White-light interferometry is commonly used to measure the depth of the vias, but suffers from decreasing signal-to-noise ratio depending on aspect ratio and diameter. To understand the limitations and develop new approaches for sensing these structures, modelling has proved to be a valuable tool. In this paper, we present results from electromagnetic wave propagation analysis compared to experimental interferometry data from high aspect ratio samples. Effects of via shape, spacing and dimension as well as simulation parameters on the resulting spectra are shown. Simulation can thus be used to predict for which type of vias a successful measurement can be expected.

Section: Methodsmentioning

confidence: 99%

Experimental study and modelling of high aspect ratio through silicon vias (TSVs)

Schöttler,

Meyer,

Avellan

2023

“…Founded on the concept of the conservation of Etendue, the maximization of the light efficiency for the measurement of a single HAR structure with a small opening size (i.e., small Etendue) is achieved by applying a spatially coherent supercontinuum laser with a small source size and a small divergence angle [16,17]. The system design concept is shown in Fig.…”

Section: System Design Concept and The Na-controlled Beam Shaping Met...mentioning

confidence: 99%

Non-integral model-based scatterometry for single-structure OCD metrology

Chein,

Yang,

et al. 2023

A new non-integral optical scatterometry technique has been introduced to circumvent issues with traditional methods in the critical dimension (CD) characterization of micro and nano-structures in semiconductor inspections. This method uses the high spatial coherence of the laser source, and an adjustable numerical aperture (NA) for effective beam shaping, enabling precise measurement of high-aspect-ratio structures. It incorporates a model-based approach with a virtual optical system and the Finite-Difference Time-Domain (FDTD) method for multiple CD characterizations, improving measurement precision. Early tests indicate a minimal average bias of 1.74% from calibrated references and standard deviations within 7 nm.

“…High-aspect-ratio through silicon via (TSV) plays an important role in 3D integration process, and spectral reflectometry can be used to measure TSV structures [1,2]. As size of critical dimensions gets smaller, it is more difficult to use traditional fast Fourier transform method [3] to retract TSV geometry parameters, since TSV with small top critical dimension allows less light past through and the diffraction effect is profound as via diameter is close to wavelength, therefore the reflectivity model cannot be simply explained by calculating the path difference between the wave front reflected by the top surface regions and the wave front reflected by the etched via bottom as estimated in [1]. Therefore, a big database of reflectivity spectrum for TSV structures, either from simulations or experiments, is needed for data analysis algorithm to perform the inverse problem.…”

Section: Introductionmentioning

confidence: 99%

Using singular value decomposition to study near electromagnetic field of the 3D through silicon via array with high aspect ratio

Chen,

Wang,

2023

Inspecting the structure of the through silicon via (TSV) with high aspect ratio is important because they are used for 3D IC stacking. In reflectometry, simulation of near field data for TSV hole arrays is used to investigate reflection spectrum for TSV with different geometry parameters such as depth and top critical dimension. We investigate simulation results of electromagnetic field data for different TSV array using the finite-difference time-domain (FDTD) method. Near field simulation data are stored as n by n complex matrices, where n represent the number of simulation region grid points. The matrices are large in dimension, and it is necessary to compress a huge data set by looking for the dominant singular value terms to keep the information as much as possible. We find that the singular value terms shrink fast in the first few terms. It is shown that after using singular value decomposition to compress near field data, the far field reflectivity spectrum is still close to the accurate results. We propose to use data after singular value decomposition for data analysis to investigate the TSV parameters mapping to the near field data.