Scanning interference evanescent wave lithography for sub-22 nm generations

Abstract

In this paper, we report progress in developing a scanning evanescent wave lithography (EWL) imaging head with a twostage gap control system including a DC noise canceling carrying air bearing that floats at a constant air gap with regulated air pressure, and an AC noise canceling piezoelectric transducer with real-time closed-loop feedback from gap detection. Various design aspects of the system including gap detection, prism design and alignment, software integration, feedback actuation and scanning scheme have been carefully considered to ensure sub-100 nm gapping. To validate the design concepts, a prototyped scanning EWL imaging head is integrated into a two-beam interferometer platform for gapping tests and imaging evaluation. Experimental results show successful gap gauging at sub-100 nm with gap noise root-mean-square around 1.38 nm in static gapping and 4.64 nm in linear scanning gapping. We also demonstrate scanning imaging results with NA comparable to previously reported static imaging using both fused silica prism and sapphire prism. Our gapping and imaging results confirmed the promise of scanning EWL to extend optical lithography to sub-22 nm generations.

Novel prism designs for solid immersion optical lithography in the ultra high-NA regime

“…The prism angles that allow an NA of ~1.751 are given in Figure 2(a) and the fabricated prism is shown in Figure 2(c). This IL system shares similarities with the amplitude splitting Smith-Talbot interferometer (STI) [11] in that both operate in the UHNA regime, and use a solid-immersion medium with greater RI than the resist RI. The STI system however separates the exposure beam using a phase mask where each beam interacts with separate tunable mirrors before prism entry [11].…”

“…This IL system shares similarities with the amplitude splitting Smith-Talbot interferometer (STI) [11] in that both operate in the UHNA regime, and use a solid-immersion medium with greater RI than the resist RI. The STI system however separates the exposure beam using a phase mask where each beam interacts with separate tunable mirrors before prism entry [11]. Our wavefront-splitting interferometer reduces the number of beam processing steps where a mask splits the beam which then refracts at prism entry sending the two beams towards the prism's internal mirrors (see ray-tracing in Figure 2(b)).…”

“…Our wavefront-splitting interferometer reduces the number of beam processing steps where a mask splits the beam which then refracts at prism entry sending the two beams towards the prism's internal mirrors (see ray-tracing in Figure 2(b)). The fixed refraction and mirror reflection angles however restrict the system to a single NA whereas the tuning mirrors of the STI offer a range of working NAs [11].…”

Scanning interference evanescent wave lithography for sub-22-nm generations

“…1,2 Other non-optical approaches, such as extreme ultraviolet (EUV) lithography, maskless lithography (ML2), nanoimprint lithography (NIL), and directed selfassembly (DSA) lithography, can offer advantages in terms of mask cost or resolution; but the paths forward for integration are difficult. 6 The associated challenge in maintaining a sub-100-nm air gap is addressed through prototyping a scanning EWL (s-EWL) head with two-stage gap actuation and feedback system. 4,5 The physical limitations of imaging imposed by the refractive indices of the materials were surpassed through the interference of evanescent waves at near fields.…”