Paper PS+SS+TF-FrM3
High Performance Self Align Contact Etching with Newly developed Quasi-ALE

Friday, October 23, 2015, 9:00 am, Room 210B

The Self-Aligned Contact (SAC) process has been widely adopted to achieve aligned narrow contacts between electrodes as the pitch shrinkage has progressed with the miniaturization of devices in high-scale integration. In SAC fabrication, it is important to achieve high selectivity of the interlayer insulator (SiO₂) over an etch stop film (SiN) to improve insulation tolerance between the contact plug and the wiring. Such high-selective etch processes have been realized by depositing fluorocarbon (FC) film selectively on the SiN film by using the composition difference between SiO₂ and SiN with fluorocarbon plasma, which protects SiN surface during SiO₂ etch. In order to minimize SiN loss, a balance of FC film thickness and the penetration depth of the ion energy on SiN become significant [1,2]. When trying to achieve improved SiN loss reduction, reducing ion energy is one effective solution, but a balance of ion energy flux and FC radical flux (E_i Γ _i / Γ _CF) breaks down, resulting in an excess amount of deposition, causing etch stop to occur. This is caused by the limited control margin of the ion energy flux over the FC radical flux ratio using conventional processes.

Atomic Layer Etching (ALE) concept has attracted great attention in recent years for its precise fabrication potential at the atomic level and its ability to solve this issue [3,4]. ALE method enables clear separation of ion energy flux and FC radical flux supply by controlling E_i Γ _i / Γ _CF dynamically using a new parameter of flux ratio respective to step time. Furthermore, specific control of the surface condition at each cycle is expected to be effective for precise fabrication. This report discusses the application of the ALE concept in the SAC process as a Quasi-ALE scheme with consideration for implementation to volume production. This scheme realized a dramatic improvement of SiO₂ etch performance with substantial reduction of SiN loss. Further analysis of the surface condition by XPS, SIMS, HR-RBS helped determine the mechanism of selectivity enhancement. Quasi-ALE technology is a promising weapon, corresponding to leading-edge processes of various fabrication requirements along with the miniaturization of devices, towards 10nm and beyond.

Reference

[1] T.Tatsumi, M.Sekine et al. JVST B 18(4), 2000

[2] M.Matsui, M.Sekine et al. JVST A 19(4), 2001

[3] D.Metzler, G.S.Oehrlein et al. JVST A 32(2), 2014

[4] M. Honda, AVS 61th Int. Symp. & Exhibit. (2014)