Paper predicts the use of regular 1D patterns can help extend CMOS logic to 7nm node
At the 2012 SPIE Conference a paper was jointly presented by Tela and engineers from Leti, the French applied research center, that showed the benefits of a highly regular layout style comprised of “lines” and “cuts”. Entitled “Sub-20nm Hybrid Lithography using Optical + Pitch-Division and e-Beam”, the paper concluded that by utilizing regular 1D patterns instead of random 2D shapes – as well as a variety of other techniques – CMOS logic can be extended to the 7nm node using existing immersion lithography.
In the paper, the presenters showed how the “lines” can be done with existing optical immersion lithography and pitch division with self-aligned spacers. The “cuts” can be done with either multiple exposures using immersion lithography, or a hybrid solution using either EUV or direct-write ebeam.
The backdrop to the presentation was the state of optical lithography. 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 the paper, the team demonstrated scaling to 18nm half-pitch which is approximately the 10-11nm node using spacer pitch division and complementary e-beam lithography.
The paper provides an excellent overview of how a combination of design styles, optical lithography plus pitch-division, and e-beam lithography appear to provide a scaling path far into the future.
To download this paper in its entirety, click here.