Scanner matching based on CD or patterning contours has been demonstrated in past works. All of these published works require extensive wafer metrology. In contrast, this work extends a previously proposed optical pattern matching method that requires little metrology by adding the component requirements and the procedure for creating an automation flow. In a test case, we matched an ASML XT:1900i using a DOE to an ASML NXT:1950i scanner using FlexRay. The matching was conducted on a 4x nm process test layer as a development vehicle for the 2x nm product nodes. The paper summarizes the before and after matching data and analysis, with future opportunities for improvements suggested.
Source Mask Optimization (SMO) technique is an advanced RET with the goal of extending optical lithography lifetime by enabling low k1 imaging [1,2]. Most of the literature concerning SMO has so far focused on PV (process variation) band, MEEF and PW (process window) aspects to judge the performance of the optimization as in traditional OPC . In analogy to MEEF impact for low k1 imaging we investigate the source error impact as SMO sources can have rather complicated forms depending on the degree of freedom allowed during optimization.
For this study we use Tachyon SMO tool on a 22nm metal design test case. A free form and parametric source solutions are obtained using MEEF and PW requirements as main criteria. For each type of source, a source perturbation is introduced to study the impact on lithography performance. Based on the findings we conclude on the choice of freeform or parametric as a source and the importance of source error in the optimization process.
In a semiconductor factory, each lithographic scanner is combined with a laser source and a track to form a lithocell. Quite frequently, lithographers have to deal with running the same lithographic process on multiple lithocells. Usually a new process is developed for one cell, and then transferred to other cells. However, small but non-negligible differences between lithocells, may result in yield losses. Nevertheless, several scanner's parameters (called proximity manipulators) can be used to compensate for these differences and match the secondary lithocells to the reference one.
Recently a new advanced process matching methodology called Pattern Matcher has been developed. Using this method, we performed successful proximity matching of several ArF scanners in the production environment. In this paper, we discuss the principles of Pattern Matcher approach as well as methodology for data acquisition and present results of our matching.
There are many IC-manufacturers over the world that use various exposure systems and
work with very high requirements in order to establish and maintain stable lithographic
processes of 65 nm, 45 nm and below. Once the process is established, manufacturer
desires to be able to run it on different tools that are available. This is why the proximity
matching plays a key role to maximize tools utilization in terms of productivity for
different types of exposure tools.
In this paper, we investigate the source of errors that cause optical proximity mismatch
and evaluate several approaches for proximity matching of different types of 193 nm
and 248 nm scanner systems such as set-get sigma calibration, contrast adjustment, and,
finally, tuning imaging parameters by optimization with Manual Scanner Matcher.
First, to monitor the proximity mismatch, we collect CD measurement data for the
reference tool and for the tool-to-be-matched. Normally, the measurement is performed
for a set of line or space through pitch structures.
Secondly, by simulation or experiment, we determine the sensitivity of the critical
structures with respect to small adjustment of exposure settings such as NA, sigma
inner, sigma outer, dose, focus scan range etc. that are called 'proximity tuning knobs'.
Then, with the help of special optimization software, we compute the proximity knob
adjustment that has to be applied to the tool-to-be-matched to match the reference tool.
Finally, we verify successful matching by exposing on the tool-to-be-matched with
tuned exposure settings.
This procedure is applicable for inter- and intra scanner type matching, but possibly
also for process transfers to the design targets.
In order to illustrate the approach we show experimental data as well as results of
imaging simulations. The set demonstrate successful matching of critical structures for
ArF scanners of different tool generations.
The TWINSCAN XT:1000H extends KrF lithography to expose layers that previously required more costly ArF
lithography. These layers, including implants and metal interconnects, contain multiple, through pitch or random, 2-
dimensional (2D) features.
In this paper, we show process windows for 115 nm random via holes using conventional illumination, 110 nm dense &
isolated via holes using a soft quasar illumination shape, 95 nm trenches through pitch with an annular illumination
mode as well as the process windows for a combination of patterns representative for implant structures using a soft
annular illumination mode.
We also prove that the XT:1000H can be integrated in an existing high volume manufacturing environment: transfer of a
65 nm logic metal-1 layer from a high NA XT:1400 dry ArF scanner to the XT:1000H has been evaluated by optimizing
the illumination settings and applying advanced mask design approaches to meet requirements for exposure latitude,
depth of focus and MEEF. In addition, we show that the CD proximity matching performance between the XT:1000H
and NA 0.8 XT:850 KrF scanners can be maximized using illumination setting optimization and EFESE focus scan.
Finally, matched machine overlay performance between the XT:1000H and an XT:1900Gi ArF immersion scanner has
In order to minimize manufacturing costs, lithographers have to extend the capabilities of KrF and i-line tools working
with low k1 factor. In this paper we present results of a successful transfer of several lithographic processes from KrF to
During the process transfer, the optimal conditions for 365-nm technology were first determined by simulation and then
verified by exposure of real production layers on a 0.65 NA i-line tool. The goal of the process optimization was to find
settings for 365-nm process, which can match the performance of the 248-nm process. Proximity matching, CD
uniformity, tool throughput and process costs were chosen as the main criteria for successful transfer.
Encountered challenges, the applied methodology and the experimental results have been discussed. Based on the
results, we conclude that low k1 i-line lithography is feasible for mass production with CD as small as 210 nm. The
process does not require additional preparation for 248-nm masks.
A strategy to escape from poor local minima by switching merit functions during local optimization is discussed. As a switching partner, we define a new auxiliary merit function, which also tends to zero for ideal systems, but differs significantly from traditional merit functions. The examples include high-dimensional optimization problems.
The merit function landscape of systems of thin lenses in contact, which are perhaps the simplest possible types of optical systems, shows remarkable regularities. It is easier to understand how the optimization parameter space of these simple systems is divided into basins of attraction for the various local minima if one focuses on the (Morse index 1) saddle points in the landscape rather than on the local minima themselves. The existence and the basic properties of these saddle points can be predicted by thin-lens theory, which is applied on a simplified model of the merit function containing only third-order spherical aberration. The predictions of this simplified model are confirmed by numerical results obtained with a typical merit function based on ray tracing.
In the year 2001 it was reported that the birefringence induced by spatial dispersion (BISD), sometimes also called intrinsic birefringence, had been measured and calculated for fluorides CaF2 and BaF2 in the deep UV range. It was also shown that the magnitude of the BISD in these cubic crystals is sufficiently large to cause serious problems when using CaF2 for lithographic objectives at 157 nm and possibly also in the case of high numerical aperture immersion objectives at 193 nm. Nevertheless the single-crystal fluorides such as CaF2 are the only materials found with sufficient transmissivity at 157 nm and they are widely used at 193 nm for chromatic correction. The BISD-caused effects lead to the loss of the image contrast. In this work we discuss issues related to the design of optical systems considering the BISD effect. We focus on several approaches to the compensation of the BISD-related phase retardation and give examples of lithographic objectives with the compensated phase retardation.
We have shown recently that, when certain quite general conditions are satisfied, the set of local minima in the optical merit function space forms a network where they are all connected through optimization paths generated from saddle points having a Morse index of 1. A new global optimization method, that makes use of this linking network to systematically detect all minima, is presented. The central component of this new method, the algorithm for saddle point detection, is described in detail and we show that the initialization of this algorithm has a significant impact on the performance. For a simple global optimization search (Cooke triplet) several representation forms of the network of the corresponding set of local minima are presented. These representations, which can be visualized in two dimensions, are independent of the dimensionality of the design space so that they can provide insight into the topography of merit function landscapes of arbitrary dimensionality.
The subject of birefringence induced by spatial dispersion (BISD), also called intrinsic birefringence, recently became an important issue for 157-nm lithography. For the deep UV range, because of intrinsic absorption, only crystalline materials can be used as optical materials for lens manufacturing. The physical properties of crystals are basically affected by spatial dispersion, especially at very short wavelengths. The resulting BISD leads to a serious deterioration of optical image quality. Recently the mathematical formalism for analyzing those aspects of the BISD effect that are relevant for optical design has been published. In this work we give an equivalent but simplified derivation of these results. This mathematical formalism is then applied to optical system design and the correction methodology is discussed. An example of optical system is given that has been corrected for the BISD effect.
We discuss a surprising new feature of the merit function landscape in optical system design. When certain conditions are satisfied, the set of local minima forms a network in which all nodes are connected. Each link between two neighboring minima contains a special type of saddle point (more precisely, a saddle point having a Morse index. On this basis, a new global optimization method that takes advantage of this feature is proposed. The central component of the new method, the algorithm for saddle point detection, works in a parameter space of arbitrary dimensionality, and uses only the local optimization engine of the optical design program. For a simple global optimization search (the symmetric Cooke triplet) the network of the corresponding set of local minima is presented.
Three local optimization strategies to escape from a local minimum are discussed. The first strategy is to radically modify the error function. The old and new error function should both tend to zero for ideal systems but must differ sufficiently from another. The second strategy is to temporarily over-design the system, i.e. to make available for optimization more system parameters than a designer would normally use for the given aperture and field specifications. Finally, it is shown that, with a small enhancement of the local optimization algorithm, it is possible to move from one local minimum into a neighboring one by locating a saddle point between them.
The possibility of increasing quanta flux intensity is considered. It was shown, that use of a single capillary glass channel permitse to change the total amount of the photons inciding per second onto the sample surface. Microcapillary devices for the study of macro-molecular structure were made.