Sub-20nm hybrid lithography using optical, pitch-division, and e-beam

Abstract

A roadmap extending far beyond the current 22nm CMOS node has been presented several times.[1] This roadmap includes the use of a highly regular layout style which can be decomposed into "lines and cuts."[2] The "lines" can be done with existing optical immersion lithography and pitch division with self-aligned spacers.[3] The "cuts" can be done with either multiple exposures using immersion lithography, or a hybrid solution using either EUV or direct-write ebeam.[4] The choice for "cuts" will be driven by the availability of cost-effective, manufacturing-ready equipment and infrastructure.Optical lithography improvements have enabled scaling far beyond what was expected; for example, soft x-rays (aka EUV) were in the semiconductor roadmap as early as 1994 since optical resolution was not expected for sub-100nm features. However, steady improvements and innovations such as Excimer laser sources and immersion photolithography have allowed some manufacturers to build 22nm CMOS SOCs with single-exposure optical lithography.With the transition from random complex 2D shapes to regular 1D-patterns at 28nm, the "lines and cuts" approach can extend CMOS logic to at least the 7nm node. The spacer double patterning for lines and optical cuts patterning is expected to be used down to the 14nm node. In this study, we extend the scaling to 18nm half-pitch which is approximately the 10-11nm node using spacer pitch division and complementary e-beam lithography.For practical reasons, E-Beam lithography is used as well to expose the "mandrel" patterns that support the spacers. However, in a production mode, it might be cost effective to replace this step by a standard 193nm exposure and applying the spacer technique twice to divide the pitch by 3 or 4.The Metal-1 "cut" pattern is designed for a reasonably complex logic function with ~100k gates of combinatorial logic and flip-flops. Since the final conductor is defined by a Damascene process, the "cut" patterns become islands of resist blocking hard-mask trenches. The shapes are often small and positioned on a dense grid making this layer to be the most critical one. This is why direct-write e-beam patterning, possibly using massively parallel beams, is well suited for this task. In this study, we show that a conventional shaped beam system can already pattern the 11nm node Metal-1 layer with reasonable overlay margin.The combination of design style, optical lithography plus pitch-division, and e-beam lithography appears to provide a scaling path far into the future.

Towards a novel positive tone resist mr-PosEBR for high resolution electron-beam lithography

“…For this reason there has been put significant effort into the improvement of the performance of EBL tools in recent years which has led to the development of multi-beam and hybrid technologies. [2][3][4][5] Besides the technical advancements of EBL systems the resist materials used are vital for high quality and high throughput EBL. For an ideal EBL resist material it is desirable to have high sensitivity, high contrast, high resolution, and high plasma etching resistance for pattern transfer to the substrate.…”

Chemically amplified phenolic fullerene electron beam resist

“…7 However, as resolution requirements have increased there has been increasing focus on EBL for volume production, with the development of a number of multi-beam and hybrid technologies. [8][9][10][11] Due to the low-throughput, even for multibeam EBL, the sensitivity of e-beam resists is considered a very important factor. For high voltage e-beam exposure, a 50-60 mC cm À2 resist sensitivity requirement has been set out by ITRS, whilst low voltage systems, such as MAPPER, 11 require sensitivities of 30-60 mC cm À2 .…”

1D design style implications for mask making and CEBL

“…Similar results have been presented for cut patterns written by e-beam. [11] Figure 5. Metal-1 cuts at 12nm node using simple OPC; from [6].…”

“…• Cut/hole masks will eventually be replaced by e-beam direct write using complementary e-beam lithography (CEBL). [7][8][9][10][11] This transition is gated by the availability of multiple column e-beam systems with throughput adequate for highvolume manufacturing. A brief description of 1D and 2D design styles will be presented, followed by examples of 1D layouts.…”