In this work, we report metrology solutions using scatterometry Optical Critical Dimension (OCD)
characterization on two advanced CMOS devices: novel n-channel gate-last In0.53Ga0.47As FinFET with
self-aligned Molybdenum (Mo) contacts and p-channel Ge FinFET formed on Germanium-on-Insulator
(GOI) substrate. Key critical process steps during the fabrication of these advanced transistors were
identified for process monitor using scatterometry OCD measurement to improve final yield. Excellent
correlation with reference metrology and high measurement precision were achieved by using OCD
characterization, confirming scatterometry OCD as a promising metrology technique for next generation
device applications. In addition, we also further explore OCD characterization using normal incidence
spectroscopic reflectometry (SR), oblique incidence spectroscopic ellipsometry (SE), and combined SR+SE
technologies. The combined SR+SE approach was found to provide better precision.
KEYWORDS: Germanium, Scatterometry, Transmission electron microscopy, Scanning electron microscopy, Transistors, Metrology, Etching, Front end of line, 3D modeling
In this work, we report the first demonstration of scatterometry Optical Critical Dimension (OCD) characterization on advanced Ge Multi-Gate Field-Effect Transistor (MuGFET) or FinFET formed on a Germanium-on-Insulator (GeOI) substrate. Two critical process steps in the Ge MuGFET process flow were investigated, i.e. after Ge Fin formation, and after TaN gate stack etching process. All key process variations in the test structures were successfully monitored by the floating or fitting parameters in the OCD models. In addition, excellent static repeatability, with 3σ lower than 0.12 nm, was also achieved. The measurement results from OCD were also compared with both Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) measurements. Excellent correlation with both SEM and TEM was achieved by employing OCD characterization, confirming scatterometry OCD as a promising metrology technique for next generation multi-gate transistor with an advanced channel material.
A novel concept of contact holes patterning for 193 nm immersion lithography is demonstrated in this study.
Conventional contact holes patterning involve targeting a square printed feature on the wafer and applying optical
proximity correction (OPC) such as corner serifs addition and dimensional biasing. As dimension of contact holes
reduces, the resolution enhancement provided by conventional OPC methods has become limited. This is because at
smaller dimension, more light is diffracted towards higher order and is not captured in the pupil plane. As a result, the
corners of the printed features are rounded and features appear circular as dimension reduces. Hence, the efforts made to
generate OPC assist features using a square target are inefficient. In this paper, the patterning of contact hole using
circular target is demonstrated. The imaging performance of isolated and regular contact holes array is reported.
Comparison with conventional approach is made. The effects of the proposed method on critical dimension (CD), depth
of focus (DOF), and image contrast is investigated.
In this paper, a novel optical proximity correction (OPC) method for contact hole patterning is demonstrated.
Conventional OPC for contact hole patterning involves dimensional biasing, addition of serifs, and sub resolution assist
features (SRAF). A square shape is targeted in the process of applying conventional OPC. As dimension of contact hole
reduces, features on mask appear to be circular due to strong diffraction effect. The process window enhancement of
conventional OPC approach is limited. Moreover, increased encounters of side lobes printing and missing contact holes
are affecting the process robustness. A new approach of changing the target pattern from square to circular is proposed in
this study. The approach involves a change in shape of mask openings and a radial segmentation method for proximity
correction. The contact holes patterns studied include regular contact holes array and staggered contact holes. Process
windows, critical dimension (CD) and aerial image contrast is compared to investigate the effectiveness of the proposed
contact holes patterning approach relative to conventional practice.
Previous study has shown that off-axis illumination (OAI) which employs duplicate conventional source shape such as
double dipole, double annular or double quadrupole can reduce the effect of line width fluctuation and process window
degradation at the forbidden pitch. In this paper, influence of the new OAI source shape on line end shortening and
corner rounding effect is studied. Despite the advantage of reduced line width fluctuation, the proximity effect at line
ends and corners for new source shapes need to be examined because both lateral and longitudinal pattern fidelity is
important in actual implementation. Simulation study will be used for the study of line end shortening and corner
rounding effect using new source shapes and the results will be compared with those resulted from annular illumination.
Line end structures such as end to end, staggered, and T-shaped patterns are used for line end shortening study. For
corner rounding, L-shaped and U-shaped structure are used. The pattern density and line end separation of feature will be
varied to determine the important factors that cause image distortion. Results has shown that new source shapes have
similar line end shortening and corner rounding characteristic with the conventional one. Besides, the variation of new
source shapes for different pattern density and line end separation is relatively smaller compared with conventional OAI
source shapes.
In this paper, a study on customized illumination shape configurations as resolution enhancement for 45nm technology
node will be presented. Several new source shape configurations will be explored through simulation based on 193nm
immersion lithography on 6% Attenuated Phase Shift Mask. Forbidden pitch effect is commonly encountered in the
application of off axis illumination (OAI). The illumination settings are often optimized to allow maximum process
window for a pitch. This is done by creating symmetrical distribution of diffraction order on the pupil plane. However, at
other pitch, the distribution of diffraction order on the pupil plane results in severe degradation in image contrast and
results in significant critical dimension (CD) fluctuation. The problematic pitch is often known as forbidden pitch. It has
to be avoided in the design and thus limited the pitch range to be imaged for particular illumination. An approach to
modify off axis illumination to minimize the effect of forbidden pitch is explored in this study. The new customized
shape for one dimensional line and space pattern is modified from current off axis illumination. Simulation study is done
to evaluate the performance some customized shapes. The extent of CD fluctuation and CD through pitch uniformity is
analyzed to determine the performance enhancement of the new illumination shapes. From simulation result, the
proposed modification have significantly improved the through pitch performance and minimized the effect of forbidden
pitch.
193nm immersion lithography has successfully enabled numerical aperture (NA) greater than 1.0 which allows rooms for
improvement in resolution as well as depth of focus. In this study, critical dimension (CD) and depth of focus (DOF)
performance for the 45nm technology node for dry and immersion lithography is compared using commercial available
simulation tool. The study is based on one dimensional line and space pattern with pitch vary from 150 to 500nm. The
effects of mask transmission and phase angle change on CD through pitch performance and DOF are also presented in
this paper. Increase in mask transmission will result in increase of CD through pitch and reduction of DOF. When phase
angle for the phase shift mask is less than 180 degree, CD through pitch and DOF drop. Finally, mask defects caused by
haze on several locations which include MoSi lines, line edges, and space between line ends are simulated. The influence
of these defects on CD and the potential line end bridging problem is presented.
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