EUV produces 22 nm cells

IMEC has produced what it claims are the world’s first functional 22 nm CMOS SRAM cells made using extreme ultraviolet (EUV) lithography.

The 0.099 µm² SRAM cells are made with FinFETs and have both the contact and metal1 layer printed using Dutch company ASML’s full field EUV alpha demo tool (ADT).

The ultra-small circuit structures were made using US company Applied Material’s advanced deposition systems.

The results were presented during IMEC’s core partner review week, which was attended by 250 experts representing IMEC’s industrial partners in its CMOS scaling program.

The density of the new cells is 0.099 µm², representing a 47% area scaling compared to the 0.186 µm² of IMEC’s 32 nm cell reported last year. For the front-end-of-line process, IMEC used its high-k/metal-gate FinFET platform.

The FinFETs consist of H_fO₂ as dielectric and TiN as metal gate and NiPt silicide for the source/drain. The minimum active FIN pitch is 90 nm. The FinFET layers were printed using 1900i immersion lithography tools.

The metallisation of the contact holes was realised using Applied Materials contact processing modules for inter-layer barrier Ti and TiN before tungsten fill and chemical mechanical polishing.

Compared with the 32 nm cell, where only the contact holes were printed with the EUV tool, IMEC now used ASML’s ADT to pattern both the contact with a size of ~45 nm and metal1 layers (60 width and 46 nm spaces). The results show a good overlay performance.

The single patterning approach further strengthens the case for EUV as a cost-effective solution.

Luc Van den hove, chief operating officer at IMEC, said:

"Our successful fabrication of 22 nm SRAM cells with EUV is an important milestone, both for the development of 22 nm processes and for the roadmap of EUV lithography.

“This SRAM cell integration shows that EUV photo process technology is making excellent progress as a cost-effective single patterning approach. We believe that EUV remains a candidate for use in the later stages of 22 nm technology.