The foundations of leading edge DRAM manufacturing are built on accurate EUV lithography exposures in close synergy with cutting-edge immersion layers as well as advanced patterning schemes (e.g. self-aligned multiple patterning). Final device yield critically depends on the subsequent and accurate stacking of multiple layers with device features of precise width and edge placement. To support the ever-decreasing requirements for both the EUV as well as the DUV, (edge) placement accuracy, scanner enhancements are required on both platforms. In this paper we report on the improvements of the NXT:2100i immersion scanner to further reduce the (edge) placement errors within the die (intra-field) and across the full wafer (inter-field). The NXT:2100i incorporates a new projection optics with built-in distortion manipulator that extends the intra-field correction capability for both X and Y directions. The external overlay interface is extended with the distortion manipulator degrees of freedom to handle high spatial frequent distortion data of a to-be-matched scanner or high spatial frequent overlay fingerprints measured by after develop or after etch metrology. Thermal conditioning of the reticle is improved with a fast conditioned internal reticle library resulting in lower reticle-to-reticle temperature variation. Improved lens metrology (aberrations) and reticle align accuracy (alignment/overlay) is achieved with a better integrated image sensor. Improved alignment accuracy and reduced alignment process dependencies for wafer alignment are realized with 12-colors parallel measurements and by adding more alignment marks measurements at the wafer measure side without throughput impact. In concert with the hardware components, various software algorithms are updated, yielding improved inter- and intra-field overlay setup and improved reticle heating induced overlay. We will detail the specific module performance items as well as the system performance of the NXT:2100i scanner, both in reference (DRAM relevant overlay) to DUV as well as to EUV scanners.
As overlay tolerances tighten node-over-node, the measurement and control of overlay has progressed from the low (spatial) frequent domain toward higher spatial frequencies. At present up to 3rd order in the (non-scanning) slit direction can be addressed on high end systems. With the introduction of an advanced distortion-manipulator on an ArFi immersion scanners a significant improvement in the spatial frequency of overlay control can be achieved. This actuator will now enable at least up to 9th order lens distortion manipulation and control in the (non-scanning) slit direction, with future extendibility to on-the-fly adjustments while scanning. The manipulator setup and distortion control is fully incorporated in the scanner software and allows for lens fingerprint optimization, better dynamic lens heating control, and scanner stability control to maintain overlay performance over time. Also an external scanner overlay optimization interface is made available that enables machine-to-machine matching within the immersion platform as well as for cross-matching to the EUV platform. Via this interface also high spatial-frequent process corrections can be send to the scanner. In this paper, we will show the capability of the scanner-integrated distortion manipulator on abovementioned aspects using on-scanner aberration metrology, and in-resist distortion and overlay metrology.
Even with the large-scale adaption of EUV Lithography to High Volume Manufacturing, numerous device-critical product layers will still be exposed with Immersion Lithography Technology and therefore ZEISS and ASML keep investing in the next generation immersion extensions. The overlay accuracy has to be controlled over the exposure field more accurately and also on a higher spatial frequency grid. To support this functionality, a novel manipulator will be incorporated into the next generation of immersion optics, which is especially well-suited for high frequent distortion tuning. Furthermore, lens distortion measurements and adjustments will be done based on more field points. In this paper, we will show the unique correction functionality of this manipulator and show its various application fields for improving the performance of ASML scanners.
Modern mirror optics often consists of a limited number of elements, in which many aberrations may be attacked by adjusting only one element in five degrees of freedom, i.e. all degrees of freedom except the rotation around the optical axis. When the adjustment has to be reusable and mass and stiffness are of importance, a hexapod mechanism is 'the mechanism of choice' for this function. This choice holds even though the hexapod controls six degrees of freedom, while control of only five degrees of freedom is required, simply because there was no known configuration that does only control the required five degrees of freedom while maintaining the superior mass and stiffness properties of the hexapod.
In this paper a mechanical configuration is presented that offers a worthwhile alternative for the simultaneous adjustment of five degrees of freedom (one rotation constrained), in the sense that:
1. The rotation around one axis is constrained by the mechanical configuration, meaning that only the required five degrees of freedom have to be controlled. This means only five instead of six actuators are needed, which results in an increase in reliability.
2. The mass and stiffness of the mechanism are comparable with the hexapod.
3. From a mechanical and control point of view the configuration is less complex than the hexapod.
Although the possibility of a 6 degrees of freedom adjustment based on a single body pulled onto on six adjustable supports follows directly from the kinematic theory, such mechanisms are seldom used in actual products. Two major drawbacks for the use of this solution are:
1. Due to the sliding contact between the body and the supports, friction will occur and may inhibit movement.
2. Coupling between the adjusted axes cannot be avoided, this may interfere with the necessity of an adjustment procedure with a limited number of iterations
This paper presents a matrix calculation method that offers a prediction whether the body will move as required, depending on the position of the supports and on the magnitude of the friction. This method enables to check the functionality of a design. This method has been used in the design of several adjustment mechanisms consisting of a body pulled onto six supports.
The matrix calculation method also allows predicting the movement of the adjusted body due to adjustment of the separate supports. Using this it is relatively simple to simulate the movements that an operator will observe, and in this way check whether an operator is capable to handle the couplings present in the adjustment. Using the simulation the adjustment procedure can be optimized.
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