Process optimizations have enabled the patterning of dense 28nm pitch line/spaces with an Inpria metal-oxide resist in one single exposure, relevant for high-volume manufacturing. For the first time, optical and e-beam inspections were correlated with electrical data to gain further insights in improving stochastic defectivity – i.e., both breaks and bridges.
In addition, source optimizations have led to printing the smallest pitch possible with the current NXE:3400 scanner (i.e., 24nm pitch line/spaces and 28nm pitch contact holes), allowing for early material development required for high-NA EUV lithography scanners.
To increase learnings on stochastic patterning failures, defectivity inspection data obtained with scanning electron microscopy, broadband plasma and e-beam technologies were successfully correlated with data obtained from electrical measurements.
The electrical tests were carried out on large-area ruthenium-metallized serpentine structures that allowed to measure electrical opens (and hence bridges in the resist), as well as on metallized fork-fork and tip-to-tip structures that allowed to measure electrical shorts (and hence critical breaks in the resist).
Besides showing a good correlation, the complementary electrical measurements allow to capture important trends across multiple process changes that can help mitigating stochastic printing failures (papers n° 11609-26; 11611-21).
The extendibility of 0.33NA EUV lithography to pitch 28nm resulted from co-optimizing the various contributors to the patterning process, including mask templates, illumination settings, metal-oxide resist and etch processes.
For example, the benefits of using bright field mask tonality and controlled lens aberrations were shown to largely improve the printability at small pitch and critical dimensions (papers n° 11609-27; 11609-29).
Besides pushing the boundaries of single-exposure EUVL for high-volume manufacturing, imec and ASML have brought the 0.33NA NXE:3400 to its extreme resolution with the aim to use it as a platform for early material development for the high-NA EUVL tools.
Steven Scheer, VP advanced patterning process and materials at imec: “Imec and ASML recently also showed the tool’s capability of printing 24nm pitch line/spaces and 28nm pitch contact holes – the latter by optimizing pupil and imaging conditions and by using double line/space exposures at a combined dose of 45mJ/cm2”.
“Pattern transfer could be successfully demonstrated on very thin resists that are relevant for high-NA EUV”, says Andrew Grenville, CEO of Inpria. “This will provide the imec patterning ecosystem with the opportunity to develop resist, metrology and etch processes to accelerate the introduction of the next-generation EUVL system, i.e., the high-NA EXE:5000.”
Scheer added, “These developments will complement the learnings that are currently being obtained from imec’s attosecond analytical and interference lithography lab (the AttoLab), expected to offer a high-NA resist imaging capability to print features down to pitches as small as 8nm.”
