The continuous development of three-dimensional chip/wafer stacking technology has created the metrology
requirements for in-line 3D manufacturing processes. This paper summarizes the developing metrology that has been
used during via-middle & via-last TSV process development at ITRI (Industrial Technology Research Institute). An IR
metrology tool including broadband infrared microscopic imaging module and a specific infrared laser confocal module
is developed for the thinned wafers thickness measurement with spatial resolution of 0.5 μm. An existing spectral
reflectometer is used and enhanced by implementing novel theoretical model and measurement algorithm for HDTSV
inspection. It is capable of measuring via depth/bottom roughness/bottom profile in one shot measurement. A metrology
module based on two sets of dual-channel capacitive sensors for metallization film thickness measurement is applied to
make critical process control in the fab. We will share real metrology results and discuss possible solutions for 3D
TSV (Through Silicon Via) is a vertical via that passes through a silicon wafer or chip. This technology is a major
enabler for three-dimensional integrated circuits (3D ICs) of stacking different functional chips. Vertical stacking chips
of 3D ICs allows gates to be placed closer and thereby provides more computing process in a compact space. As TSV
technique with unique processing steps that are not used in standard 2D ICs, a number of new parameters need to be
measured and controlled. TSV etching depth is a critical parameter for ensuring the performance of 3D ICs, thus
metrology and inspection of the TSV etching depth are very profitability of the overall manufacturing process.
Spectroscopic reflectometry (SR) is currently being used in industry to measure the internal reflectance of thin films,
from which the thickness and other properties can be obtained. It is a non-contact and non-destructive in-line metrology
tool. In this study, we demonstrate the use of SR by employing the fast Fourier transform (FFT) algorithm for measuring
the etching via depth and the thickness of oxide layer in one shot measurement. First, the specifications of reflectometer
system, such as spectral range and resolution of spectrometer for depth analysis are discussed. The depth resolution is
better in the longer measuring spectral range, thus small difference of TSVs' depth can be well distinguished. The
spectrometer with high resolution is used to collect the authentic spectrum from etching depth with high aspect ratio. We
verified our system through a mutual measurement comparison with the national standard traceable step height system.
Our system is capable of measuring step height up to 100 um and measurement precision is in the range of 0.6 um. In
this report, TSV arrays with nominal CD 5~25 um, and aspect ratio up to 10 are measured. Metrology results from actual
3D interconnect processing wafers indicate our system provides excellent correlation to cross-section scanning electron
microscope (SEM) measurement results. The maximum discrepancy between each other is smaller than 1 um.
Semiconductor device packaging technology is rapidly advancing, in response to the demand for thinner and smaller
electronic devices. Three-dimensional chip/wafer stacking that uses through-silicon vias (TSV) is a key technical focus
area, and the continuous development of this novel technology has created a need for non-contact characterization. Many
of these challenges are novel to the industry due to the relatively large variety of via sizes and density, and new processes
such as wafer thinning and stacked wafer bonding. This paper summarizes the developing metrology that has been used
during via-middle & via-last TSV process development at EOL/ITRI. While there is a variety of metrology and
inspection applications for 3D interconnect processing, the main topics covered here are via CD/depth measurement,
thinned wafer inspection and wafer warpage measurement.
We focus on the capability and theoretical limits of a model-based scatterometry method to determine overlay using a single two-dimensional array target. We use our modeling capability to design an optimized test target for scatterometer-based overlay measurements in a range of semiconductor films. We propose a methodology to measure the overlay using a single two-dimensional array target designed with intentional offsets, x and y, between the top and bottom grid arrays along the X and Y directions. This method allows extraction of the two-dimensional overlays from first diffraction order measurements through bi-azimuth angle analysis (0 and 90 deg with respect to the incidence plane), and includes a simple linear response algorithm. Two critical issues are taken into account: correlation of x and y and lithography process errors. We have simulated the diffraction signatures of a two-dimensional target with a pitch of 400 nm and linewidth of 100 nm, and optimized the overlay target design to maximize the measurement sensitivity and minimize the correlation of two axial measurements. We also investigate the influence of parameter variations on overlay measurement error
The potential of scatterometry has been developed for many years, but it is challenging to accurately and quickly obtain
the overlay error from diffraction data. We presented a method to measure the overlay error by choosing an optimal
measurement target design for scatterometry. All of the simulations in this study were calculated by rigorous coupled
wave analysis. A set of two layer grating model were developed for evaluation of overlay measurement sensitivity at
different incident angle, such as theta (0° to 90°) and phi (0° to 180°). We also compared the optical response of zero
order and first order diffraction signature. We can use appropriate target design and measured condition to maximize the
overlay measurement sensitivity and reduce the noise from lithography printing error. In addition, the diffractive
signature imaging microscope (DSIM) is introduced to measure the diffraction signature. This instrument is a full-optical
operation system without any mechanical movement, so it has good stabilization.
We report results of theoretical modeling into a scatterometry-based method relevant to overlay measurement. A set of
two array targets were designed with intentional offsets difference, d and d+20 nm, between the top and bottom grid
arrays along the X and Y directions. The correlation of bi-azimuth measurements is the first critical issue been taken into
account. The method linearizes the differential values of scatterometry signatures at the first diffraction order with
respect to designed offsets, and hence permits determination of overlay using a classical linear method. By evaluating the
process variations (eg. CD, roundness and thickness) on overlay measurement error, a set of two overlay target design
were optimized to minimize the correlation of bi-azimuth measurements and maximize the measurement sensitivity.
Angle-resolved scatterfield microscope (ARSM) is developed for several years. It combines the optical microscope
and angle-resolved scatterometer with a relay lens and an aperture. In our research, the spatial light modulator (SLM)
is used to instead of the relay lens and the aperture. In the SLM, the phase modulation is used to simulate the Fresnel
lens, and then an incident plane wave is modulated and focused on the back focal plane of the objective lens. A plane
wave with an angle which is according to the position of focused point on the back focal plane is emitted from the
entrance pupil of the objective lens. By modulating the SLM, the angle of plane wave from the objective lens can be
changed. In our system, an objective lens with NA 0.95 and the magnification of 50 is used for wide angle scan.
A bare silicon wafer and a grating with the pitch of 417nm are measured with full-angle scan. By using the SLM, the
advantage is full-optical modulation, that is, the mechanical motion is not needed in the ARSM. Thus, the system
will have higher throughput and stabilization.
We propose a method to measure the overlay by choosing an optimal measurement design with a modified scatterometer
system. This method is capable of measuring zero and non-zero diffraction orders at theta (zenith) and phi (azimuth)
angles of incidence by carefully modulating the optical system. Thus a large quantity of angular scatterometry data can
be measured in a short period of time with no mechanical or vibrational movement. We used a rigorous diffraction
theory to model the measurement sensitivity using an overlay with two layer gratings at a fixed wavelength in the range
of the theta (zenith, 0° to 90°) and phi (azimuth, 0° to 180°) incident angles. We compared the measurement sensitivities
at theta and phi dependence. In addition, we compared the optical responses of zero order and first order diffractive
overlays. We propose a methodology to measure the overlay using overlay targets with two gratings, designed with an
intentional offset difference between the top and bottom gratings to maximize the measurement sensitivity and minimize
the response to the process noise.
Scatterometry takes advantage of the sensitivity exhibited by optical diffraction from periodic structures, and hence is an efficient technique for lithographic process monitoring. Even though the potential of this technique has been known for many years, it is challenging to accurately and quickly extract the multilayer grating overlay from diffraction data. We propose a method to measure the overlay by selecting an optimal measurement design based on the theoretical modeling of differential signal scatterometry overlays. A set of two grating overlay targets are designed with an intentional offset difference between the top and bottom gratings, to maximize the differential signal measurement sensitivity and to minimize the response to the process noise. We model the measurement sensitivity to overlays of two layer gratings, at a fixed wavelength and with a range of azimuth incidence angles from 0 to 180 deg, by means of rigorous diffraction theory. We compare the optical response of the zero- and first-order diffractive overlays. We show that with the appropriate target design and algorithms, scatterometry overlay achieves improved accuracy for future technology nodes.