With the increase of process complexity in advanced nodes, the requirements of process robustness in overlay metrology continues to tighten. Especially with the introduction of newer materials in the film-stack along with typical stack variations (thickness, optical properties, profile asymmetry etc.), the signal formation physics in diffraction-based overlay (DBO) becomes an important aspect to apply in overlay metrology target and recipe selection.
In order to address the signal formation physics, an effort is made towards studying the swing-curve phenomena through wavelength and polarizations on production stacks using simulations as well as experimental technique using DBO. The results provide a wealth of information on target and recipe selection for robustness. Details from simulation and measurements will be reported in this technical publication.
While semiconductor manufacturing is moving towards the 14nm node using immersion lithography, the overlay requirements are tightened to below 5nm. Next to improvements in the immersion scanner platform, enhancements in the overlay optimization and process control are needed to enable these low overlay numbers. Whereas conventional overlay control methods address wafer and lot variation autonomously with wafer pre exposure alignment metrology and post exposure overlay metrology, we see a need to reduce these variations by correlating more of the TWINSCAN system’s sensor data directly to the post exposure YieldStar metrology in time. In this paper we will present the results of a study on applying a real time control algorithm based on machine learning technology. Machine learning methods use context and TWINSCAN system sensor data paired with post exposure YieldStar metrology to recognize generic behavior and train the control system to anticipate on this generic behavior. Specific for this study, the data concerns immersion scanner context, sensor data and on-wafer measured overlay data. By making the link between the scanner data and the wafer data we are able to establish a real time relationship. The result is an inline controller that accounts for small changes in scanner hardware performance in time while picking up subtle lot to lot and wafer to wafer deviations introduced by wafer processing.
Optical lithography, currently being used for 45-nm semiconductor devices, is expected to be extended further towards
the 32-nm and 22-nm node. A further increase of lens NA will not be possible but fortunately the shrink can be enabled
with new resolution enhancement methods like source mask optimization (SMO) and double patterning techniques
(DPT). These new applications lower the k1 dramatically and require very tight overlay control and CD control to be
successful. In addition, overall cost per wafer needs to be lowered to make the production of semiconductor devices
acceptable. For this ultimate era of optical lithography we have developed the next generation dual stage NXT:1950i
immersion platform. This system delivers wafer throughput of 175 wafers per hour together with an overlay of 2.5nm.
Several extensions are offered enabling 200 wafers per hour and improved imaging and on product overlay.
The high productivity is achieved using a dual wafer stage with planar motor that enables a high acceleration and high
scan speed. With the dual stage concept wafer metrology is performed in parallel with the wafer exposure. The free
moving planar stage has reduced overhead during chuck exchange which also improves litho tool productivity.
In general, overlay contributors are coming from the lithography system, the mask and the processing. Main contributors
for the scanner system are thermal wafer and stage control, lens aberration control, stage positioning and alignment. The
back-bone of the NXT:1950i enhanced overlay performance is the novel short beam fixed length encoder grid-plate
positioning system. By eliminating the variable length interferometer system used in the previous generation scanners the
sensitivity to thermal and flow disturbances are largely reduced. The alignment accuracy and the alignment sensitivity
for process layers are improved with the SMASH alignment sensor. A high number of alignment marker pairs can be
used without throughput loss, and furthermore the GridMapper functionality which is using the inter-die and intra-die
scanner capability can reduce overlay errors coming from mask and process without productivity impact.
In this paper we will present the main design features and discuss the system performance of the NXT:1950i system,
focusing on the improvements made in overlay and productivity. We will show data on imaging, overlay, focus and
productivity supporting the 3X-nm node and we will discuss next improvement steps towards the 2X-nm node.
The lithography roadmap demands overlay reduction along with increased productivity. New applications are proposed
as lithography solution for the 32-nm node and possibly beyond. Most of them require very tight overlay and multiple
exposures. Major contributors in the overlay budget are coming from the exposure system, like thermal stability, lens
aberrations stability, stage positioning and alignment. An additional complexity is the interaction with the actual process
and the pattern on the reticle. To keep the lithography roadmap affordable, the cost per wafer needs to be tamed by
boosting the productivity of the exposure tool.
To enable new applications in a production environment a new generation lithographic exposure tools was developed,
with improved overlay and increased productivity. The optical column contains an improved 1.35 NA immersion lens.
Compared to the former generation the combination of overlay and productivity requirements are met by a high
acceleration wafer stage along with a new stage position measurement system, introducing new technologies paving the
way to meet the future roadmap requirements. The increased disturbances caused by the higher accelerations are
countered by a short-beam interferometer system thus ensuring optimal positioning performance. Further productivity
enhancements are reached by reducing non-exposure time.
The latest performance results will be presented; this will include overlay results as well as other critical system
As the semiconductor industry looks into the near future to extend manufacturing beyond 100nm, a new optical lithography system was developed by ASML. To achieve the aggressive industry roadmap and enable high volume manufacturing of sub 100nm resolutions at low k1 requires a number of challenges to be overcome. This paper reviews the design, system performance and measurements of a High NA, Dual stage 193nm TWINSCAN system planned for high volume manufacturing for 80nm applications. The overall system capability to effectively measure and control to a high precision the various attributes upon process control necessary for adequate CD control, in the low k1 regime will be shown. This paper will discuss the needed imaging control and the requirement for an extremely stable and matured platform. The system's dynamic, focus, leveling and dose delivery performance will be shown. Additionally, the automated control features of the optical system will be shown that enable the use of the various resolution enhancement techniques (RET) currently under development. The ability to optimize imaging performance with the control and flexibility in the pupil formation optics will be discussed. Finally, experimental results of an in-situ measurement technique with automated feedback control to optimize projection lens aberrations, which has a direct impact to imaging fidelity, will be shown. In summary, the lithographic system functionality and performance needed to achieve 80nm volume manufacturing will be presented.