We have developed the new technology to measure focus variations in a field or over the wafer quickly for exposure tool
management. With the new technology, 2-dimensional image(s) of the whole wafer are captured with diffraction optics,
and by analyzing the image signal(s), we are able to get a focus map in an exposure field or over the entire wafer.
Diffraction-focus curve is used instead of a CD-focus curve to get the focus value from the image signal(s). The
measurements on the production patterns with the production illumination conditions are available. We can measure the
field inclination and curvature from the focus map. The performance of the new method was confirmed with a test
pattern and production patterns.
As well as measuring CD, monitoring pattern profile is becoming important for semiconductor metrology. Illuminating
the wafer and detecting the reflective light, reflective light intensity in the Fourier space includes the information of CD
and pattern profile variation by form birefringence effect. CD change and profile variation could be detected separately
for the actual wafer. Mathematical simulation is presented the background of our unique approach. The detail results of
CD and pattern profile monitor is shown in this paper.
Considerable effort is directed towards the development of next-generation lithography processes, addressing the need
for transistor densification to meet Moore's Law. The aggressive design rule shrinkage requires very tight process
windows and induces various types of pattern failure with lithography process variations. Since the lithography process
is critical in the wafer fabrication process, the requirements for high sensitivity defect detection in the lithography
process becomes tighter as design rules shrink. Analysis of the root cause of the defects and of their interaction with
various light sources and optics systems configurations for wafer inspection is essential for understanding the detection
limits and requirements from advanced inspection systems targeting future lithography inspection applications.
In this work, we present an analysis of wafer defects light scattering and detection for a variety of 3xnm design rule resist
structures with various polarizations and optics configurations, at the visible, at UV and at DUV wavelengths. The
analysis indicates on the defect scattering and inspection performance trends for a variety of resist structures and defect
types, and shows that control of the polarization of the optical inspection system is critical for enhanced scattering and
detection sensitivity. The analysis is performed also for the 2xnm and 1xnm design rules showing the advantages of
polarized DUV illumination over unpolarized and visible illumination.
Much effort has been done to detect the defects of interest (DOI) by optical inspection systems because the size of the
DOI shrinks according to the design rule of a semiconductor device. Performance of the inspection system is dependent
on complicated optical conditions on illumination and collection systems including wavelength and polarization filter.
Magnitude of defect signal for a given optical condition was estimated using a simulation tool to find a suitable optical
condition and technologies required in the future. This tool, consisting of a near-field calculation using Finite Difference
Time Domain (FDTD) methods and an image formation calculation based on Fourier optics, is applicable not only to
Köhler illumination system but also to confocal system and dark field system. We investigated defect inspection methods
for the 45 nm and the next technology nodes. For inspection of various defects, the system using several wavelengths is
suitable. For inspection of a specific defect, the system with polarization control is suitable. Our calculation suggests that
the defect detection sensitivity for the 1X nm technology node should be increased by more than 10 times compared to
the 45 nm technology node.
There are two kinds of critical dimension (CD) management tools; CD-SEM and Optical CD (OCD). OCD is
preferable to other existing measurement tools, because of its higher throughput and lower photoresist damage. We have
developed an Automated Pattern profile Management (APM) systems based on the OCD concept. For the monitoring
thin line, APM detects light intensity from an optical system consisting of a polarizer and an analyzer set in a cross-
Nicol configuration as a polarization fluctuation. This paper reports our development of monitoring technology for hole.
In the case of hole management, APM detects light intensity from diffraction intensity fluctuation. First of all, the best
conditions for hole management were designed from simulations. The best conditions were off-axis aperture and S
polarizer. In our evaluation of wafers without underlayer, we obtained a good correlation with CD-SEM value. From the
simulation, we consider the APM system to be very effective for shrinking hole process management of the next
generation from the simulation.
We tried to detect the CD variation of the 4x generation hole pattern using the diffraction light on Fourier space with the
polarized light and the modified illumination.
The new technology named DD (Dual Diffraction) method has been developed based on the optical simulation and the
experimental approaches. We introduce the case of detection for the diameter variation on a multi-layered hole pattern
with new method.
As design rule of semiconductor device is shrinking, pattern profile management is becoming more critical, then high
accuracy and high frequency is required for CD (Critical Dimension) and LER (Line Edge Roughness) measurements.
We already presented the technology to inspect the pattern profile variations of entire wafer with high throughput  .
Using the technology, we can inspect CD&LER variations over the entire wafer quickly, but we could not separate the
signal into CD and LER variations. This time, we measured the Stokes parameters, i.e., polarization status, in the
reflected light from defected patterns. As the result, we could know the behavior of the polarization status changes by
dose & focus defects, and we found the way to separate the signal into CD&LER variations, i.e. dose errors and focus
errors, from S2 & S3 of Stokes parameters. We verified that we were able to calculate the values of CD&LER variations
from S2 & S3 by the experiments. Furthermore, in order to solve the issue that many images are needed to calculate S2
& S3 values, we developed the new method to get CD&LER variations accurately in short time.
A new technology was developed to detect Critical Dimension (CD) variations in a Fourier space. The detection
principle is a form birefringence of the wafer. Utilizing this principle, CD and Pattern Edge Roughness (PER) variations
are detected as a polarization fluctuation and converted into light intensity. We have achieved high resolution and high
sensitivity by combining a form birefringence with a novel optical system. This system detects the light intensity in a
Fourier space with a high NA objective, enabling the detection of various lights with different incident angles and
polarization states at a time. We have confirmed through simulations that this system has high sensitivity toward CD
variations. Furthermore, in partnership with Toshiba Corporation, and through the evaluation of wafers fabricated at
Toshiba, we conclude that the light intensity detected by the new system strongly correlates with CD values, and that the
new system is capable of detecting CD variations in sufficient sensitivity.
As the semiconductor design rules shrink down, process margins are getting narrower, and thus, it is getting more
important than ever to monitor pattern profile and detect minor structure variation. A breakthrough technology has been
introduced as a solution to this concern. The new technology converts the fluctuation of polarization ingredient, which is
caused by form birefringence, into light intensity variations as an optical image. This technology, which is called Pattern
Edge Roughness (PER) inspection mode, is proved to be effective for 55nm production process. We also studied the
possibility of the macro inspection method for half pitch 32nm technology node through FDTD method.
In the automatic macro inspection, a diffraction light method is very effective. However, this method needs a shorter wavelength illumination for finer wafer patterns. A wavelength of 193 nm will be needed for half pitch 55 nm. Light source and optics for such shorter wavelength is large and expensive, and chemical clean environment is needed. Therefore, the equipment size and costs will increase dramatically. In order to solve this problem and to comply with the process of half pitch 55 nm and below, we have developed the breakthrough technology. The key is the image of polarization fluctuation caused by a wafer pattern structure. The polarized light is affected by the variation of the wafer pattern structure due to a dose or focus shift. The new technology converts the polarization fluctuation into the gray level of the image. At a result, the sensitivity for the dose or focus shift was enough to detect process errors.