Proximity Effects in electron beam lithography impact feature dimensions, pattern fidelity and uniformity. These effects
are addressed using a mathematical model representing the radial exposure intensity distribution induced by a point
electron source, commonly named as the Point Spread Function (PSF). PSF models are usually employed for predicting
and compensating for effects up to 15μm. It is well known that there are also some process related phenomena that
impact pattern uniformity that have a longer range, namely CMP effects, fogging, etc.
Performing proximity effects corrections can result in lengthy run times as file size and pattern densities continue to
increase exponentially per technology node. Running corrections for extreme long range phenomena becomes
computational and file size prohibitive. Nevertheless, since extreme long range may reach up several millimeters, and
new technology nodes require a high level of precision, a strategy for predicting and compensating these phenomena is
In this paper a set of test patterns are presented in order to verify and calibrate the so called extreme long range effects in
the electron beam lithography. Moreover, a strategy to compensate for extreme long range effects based on the pattern
density is presented. Since the evaluation is based on a density map instead of the actual patterns, the computational
effort is feasible.
The proposed method may be performed off-line (in contrast to machine standard in-line correction). The advantage of
employing off-line compensation relies on enhancing the employ of dose and/or geometry modulation. This strategy also
has the advantage of being completely decoupled from other e-beam writer’s internal corrections (like Fogging Effect
Correction - FEC).
In electron proximity effects correction (PEC), the quality of a correction is highly dependent on the quality of the model
used to compute the effects. Therefore it is of primary importance to have a reliable methodology to extract the
parameters and assess the quality of a model. Usually, model calibration procedures consist of one or more cycles of
exposure and measurements on the calibration stage. The process and metrology variability may play a key role in the
quality of the final model and, hence, of the PEC result. Therefore, it is important to determine at which level these
variations may impact a calibration procedure and how a calibration design may be implemented in order to enable more
robustness to the resulting model.
In this work, metrology variability was evaluated by measuring the same wafer using two different CD-SEM tools. The
information coming from these analyses was used as reference to a variation induced calibration test using synthetic
data. By inserting variability in synthetic data it was possible to evaluate its impact on the resulting parameter values and
in the final model error evaluation.
The use of optical metrology techniques for process control is now widespread. These techniques are fast and nondestructive,
allowing higher throughputs than non-optical techniques like electron microscopies or AFM. We present
here new developments using complete Mueller polarimetry in the back focal plane of a microscope objective to
characterize overlay for microelectronic industry. Based on fundamental symmetries in the physics of periodic structures
and polarized light and redundancies in the angle-resolved Mueller images we define estimators which vary linearly with
the overlay. As a result, overlay measurement is sensitive to both the direction and sign of the overlay, and it does not
require any detailed modeling of the target structures, provided two independent targets with known overlay values are
available in close locations on the wafer. Realistic simulations on optimized structures suggest that accuracies in the
order of 1 or 2 nm or better should be achievable. Moreover, with high NA objectives the proposed technique can be
implemented with targets with lateral sizes as small as a few μm. Experimental results of both grating line profiles and
overlay determinations will be presented. The samples, elaborated at LETI, have been accurately characterized by optical
imaging AIM techniques and state-of-the-art AFM. The latest developments on the device itself as well as the
advantages, possibilities and limitations of this new metrology technique will be discussed.
Angle resolved Mueller polarimetry implemented as polarimetric imaging of a back focal plane of a high NA microscope objective has already demonstrated a good potential for CD metrology. Here we present the experimental and numerical results indicating that this technique may also be competitive for the measurements of overlay error δ. A series of samples of superimposed gratings with well controlled overlay errors have been manufactured and measured with the angle resolved Mueller polarimeter. The overlay targets were 20-μm wide. When the overlay error is δ is equal to 0, absolute values of elements of real 4×4 Mueller matrix M are invariant by matrix transposition. Otherwise this symmetry breaks down. Consequently, we define the following overlay estimator matrix as E = |M| − |M|t. The simulations show that matrix element E14 is the most sensitive to the overlay error. The scalar estimator of E14 was calculated by averaging the pixel values over a specifically chosen mask. This estimator is found to vary linearly with δ for overlay values up to 50 nm. Our technique allows entering small overlay marks (down to 5-μm wide). Only one target measurement is needed for each overlay direction. The actual overlay value can be determined without detailed simulation of the structure provided two calibrated overlay structures are available for each direction.
Angle resolved Mueller polarimetry implemented as polarimetric imaging of the back focal plane of a high NA
microscope objective has already demonstrated a good potential for CD metrology<sup>1</sup>. In this paper we present the
experimental and numerical results which indicate that this technique may also be competitive for measurements of the
overlay error δ between two gratings at different levels. Series of samples of superimposed gratings with well controlled
overlay errors have been manufactured and measured with the angle resolved Mueller polarimeter. The overlay targets
were 20 μm wide. When overlay error δ = 0 the absolute value of Mueller matrix elements is invariant by matrix
transposition. This symmetry breaks down when δ ≠ 0. As a result, we can define the following overlay estimator matrix:
Ε = |Μ | - |Μ |<sup>t</sup>. The simulations show that matrix element E<sub>14</sub> is the most sensitive to the overlay error. In the
experiments the scalar estimator of E<sub>14</sub> was defined by averaging the pixel values over specifically chosen mask. The
scalar estimator is found to vary essentially linearly with δ for the overlay values up to 50 nm. Our technique allows
entering quite small overlay marks (down to 5 μm wide). The only one target measurement is needed for each overlay
direction. The actual overlay value can be determined without detailed simulation of the structure provided the two
calibrated overlay structures are available for each direction.
Molecular resist have potential interest for low CDs and LERs required in future lithography
technology. The lithographic ability of one of them is exposed in this study, by e-beam and by EUV-IL. Work
on process condition is described and leads to dense-lines resolution down to 32.5nm for.
In this study we investigate the pattern collapse mechanism of dense patterns with resolution under 60nm printed in Extreme Ultra Violet (EUV-IL) and Electron Beam Lithographies (EBL). Pattern collapse occurs when physical properties of the material can't imbalanced the capillary force exerted on the pattern during the drying of the rinse liquid. In former simulation models, the height of the pattern at which collapse occurs (critical height, H<sub>c</sub>) was predicted using either elastic deformation properties, or plasticizing limit value of the resist. Experimental observations of unstuck patterns, lead us to develop 2 new models considering the adhesion properties of the resist film on the substrate. By comparing simulated to experimental results for varying pattern pitchs printed in 2 Chemically Amplified Resists (CARS), we show that pattern collapse behaviour of EUV-IL and EBL patterns is not only ruled by rigidity or strength of the resist but can be perfectly described with equation defining the unsticking of a non bending pattern. Finally by using surfactinated solution on sub-60nm dense patterns, great improvements in H<sub>c</sub> values and increase of process window latitude are shown. However, due to larger capillary force, this efficiency decreases with pattern pitch and appears limited on patterns width smaller than 40 nm.