In this work, the authors will review the laser operation and imaging fundamentals behind a new method of alternating wavelengths in a single exposure and the application to Customer use cases. Two focal positions are created that are averaged over the exposure field, which can be turned on and off, thus eliminating any potential scanner calibration issues. The main focus of this work is the application of this imaging method (single exposure with two focus positions) to significantly improve the sidewall angle linearity of features in extremely thick photoresist applications. This novel technique, called MFI (multi-focal imaging), can be tuned specifically to provide the required amount of focus offset for a specific thick photoresist application. There are several Customer use cases that have been evaluated in simulation and demonstrated on wafer.
One of the most critical challenges in the lithography process is to effectively control all critical patterns over the full exposure field, across wafer, and from lot to lot consistently. ASML’s advanced dose-control solutions have been widely adopted to control CDU of critical patterns. A new high-order dose-control capability is introduced with extended controllability over a larger number of patterns to mitigate the stochastic effect and optimize dies-in-spec performance. Traditionally, designed marks or patterns are placed in the die for dense metrology sampling required for the advanced high-order dose-control applications. However, this method has a few disadvantages especially for logic foundry use cases. For example, the designed marks are often not identical to random logic critical patterns, thus leading to a situation in which marks are controlled well while device patterns are not. In-die placement of the designed marks normally imposes constrains in device layout, which is not acceptable in some cases such as large-die layouts. A preferred approach would be to measure directly on device-critical and/or weak-point (WP) patterns. But this brings up another challenge in metrology of device WP patterns. With conventional CDSEM the amount of data points is limited by the tool throughput. WP patterns are typically 2D patterns, with normally a high noise contribution from local variations (due to resist stochastics) and metrology. Thus to suppress the local variations, averaging of many local measurements of 2D WP patterns is preferred. This requires a high throughput e-beam metrology tool capable of making massive amount of inline measurements within a given cycle time. To address these challenges, we have developed a method of using yield-limiting device patterns to directly control dose and thus improve CDU. Close to 100 WPs per in-die location have been selected with a dense die coverage to minimize the contribution to global CDU from the local variations and metrology noise. A high-speed e-beam metrology tool is used to measure all the selected WP patterns. A CDU budget breakdown (BB) has been analyzed to identify and quantify CDU contributors, such as reticle fingerprint, OPC error, local CDU, metrology noise, etc. Different in-die WP sampling and dose-control methods are studied in this work to achieve optimal CDU correction while keeping the metrology cycle time under control for HVM implementation.
All chipmakers understand that variability is the adversary of any process and reduction is essential to improving yield which translates to profit. Aggressive process window and yield specifications necessitate tight inline variation requirements on the DUV light source which impact scanner imaging performance. Improvements in reducing bandwidth variation have been realized with DynaPulse™ bandwidth control technology as significant reduction in bandwidth variation translates to a reduction in CD variation for critical device structures.
Previous work on a NAND Via layer has demonstrated an improvement in process capability through improve source and mask optimization with greater ILS and reduced MEEF that improved CDU by 25%. Using this Via layer, we have developed a methodology to quantify the contribution in an overall CDU budget breakdown. Data from the light source is collected using SmartPulse™ allowing for the development of additional methodologies using predictive models to quantify CD variation from Cymer’s legacy, DynaPulse 1 and DynaPulse 2 bandwidth control technologies. CD non-uniformities due to laser bandwidth variation for lot to lot, wafer to wafer, field to field and within field is now available based on known sensitivities and modeled. This data can assist in understanding the contribution from laser bandwidth variation in global and local CDU budgets.
As EUV approaches high volume manufacturing, reticle defectivity becomes an even more relevant topic for further investigation. Current baseline strategy for EUV defectivity management is to design, build and maintain a clean system without pellicle. In order to secure reticle front side particle adders to an acceptable level for high volume manufacturing, EUV pellicle is being actively investigated. Last year ASML reported on our initial EUV pellicle feasibility. In this paper, we will update on our progress since then. We will also provide an update to pellicle requirements published last year. Further, we present experimental results showing the viability and challenges of potential EUV pellicle materials, including, material properties, imaging capability, scalability and manufacturability.
C. van den Berg, G. de Boer, S. Boschker, E. Hakkennes, G. Holgate, M. Hoving, R. Jager, J. Koning, V. Kuiper, Yue Ma, I. van Mil, H. W. Mook, T. Ooms, T. van de Peut, S. Postma, M. Sanderse, P. Scheffers, E. Slot, A. Tudorie, A. M. Valkering, N. Venema, N. Vergeer, A. Weirsma, S. Woutersen, M. Wieland, B. Kampherbeek
Currently, three MAPPER multi-electron beam lithography tools are operational. Two are located at customers, TSMC
and LETI, and one is located at MAPPER. The tools at TSMC and LETI are used for process development. These tools
each have 110 parallel electron beams and have demonstrated sub-30 nm half pitch resolution in chemically amplified
resists.
One important step towards the high volume tool is the capability to stitch the exposure of one electron beam to the next.
The pre-alpha tool at MAPPER has been upgraded with an interferometer to enable exposures with a scanning stage and
demonstrate first beam-to-beam stitching. A scan of 200 micrometers has been used to create a stitch area of 50 x 3
microns. The stitch error over all stitches was found to be below 25 nm.
The electron beam position stability during the 10 seconds required for beam-to-beam stitching showed a contribution to
the stitch error of 2.3 nm. The beam separation measurement, used to correct the static error, adds about 2.2 nm and the
stage stability and linearity adds another 5 nm in the scan (interferometer) direction. In the perpendicular direction the
stage instability gives the largest contribution to the stitch error (15 nm) due to the use of capacitive sensors.
Overall, the electron beam stability and the beam position correction method work correctly and with sufficient accuracy
for the high volume tool, 'Matrix'. The wafer stage for the Matrix system will incorporate full interferometer control to
attain the needed positioning accuracy and stability.
An endoscope test bench is presented to test the optical quality of endoscopes on a regular basis to assure optimal image quality during surgery. A power LED and a photo diode are used to measure the transmission of the illumination fibers. Captures of target images displayed on a LCD screen as seen through the endoscope with a high resolution camera are analyzed to determine the contrast for different spatial line pairs. Transmission and contrast plots are compared to reference data to determine whether an endoscope is still acceptable for clinical application. Results show that endoscopes degrade gradually but steadily over time. In time a large database of various types of endoscope will be built to fine-tune the criteria for approval or rejection of the endoscopes.
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