Patterning of narrow porous SiOCH trenches using a TiN hard mask

Abstract

For the next technological generations of integrated circuits, the traditional challenges faced by etch plasmas (profile control, selectivity, critical dimensions, uniformity, defects, ...) become more and more difficult, intensified by the use of new materials, the limitations of lithography, and the recent introduction of new device structures and integration schemes. Particularly in the field of the interconnect fabrication, where dual-damascene patterning is performed by etching trenches and vias in porous low-k dielectrics, the main challenges are in controlling the profile of the etched structures, minimizing plasma-induced damage, and controlling the impact of various types of etch stops and hard mask materials. Metallic hard masks can help thanks to their high selectivity toward low-k materials, and by avoiding low-k exposure to potentially degrading ashing plasmas. In this paper, we will present some key issues related to the patterning of narrow porous SiOCH trenches with a metallic (TiN) hard mask. Narrow trenches (down to 40 nm width) can be opened into TiN with a critical dimensions bias (around 10 nm) attributed to carbon and silicon containing deposits on the photoresist and TiN sidewalls during the etching. Porous SiOCH etching using a TiN hard mask instead of the conventional SiO 2 hard mask may lead to severe profile distortions, attributed to TiF x compounds which settle on the trenches sidewalls. A chuck temperature of 60°C and fluorine-rich plasmas are required to minimize those distortions. An etching process leading to almost straight porous SiOCH profiles presenting a slight bow has been developed. However a wiggling phenomenon has been evidenced for the etching of narrow and deep trenches. This phenomenon is attributed to the highly compressive residual stress in the TiN hard mask, which is released when the dielectric is not mechanically strong enough to withstand it.

Residue growth on metallic-hard mask after dielectric etching in fluorocarbon-based plasmas. I. Mechanisms

“…4 From the 45 nm interconnect-technology node, the introduction of porous ultralow-k ͑ULK͒ materials is mandatory in order to compensate for the increase in metal resistance. An important problem of current technologies is that electric signal propagation through metal interconnects is delayed by the resistance ͑R͒ of the metal lines and the capacitance ͑C͒ between adjacent metal lines.…”

Selective dry etching of TiN nanostructures over SiO2 nanotrenches using a Cl2/Ar/N2 inductively coupled plasma

“…10 They also provide a better selectivity with SiO 2 than F-based plasmas. 12 In addition, TiF x species formed during F-based etching processes may form residues when they react with water in clean room atmosphere. 13 It is also reported that BCl 3 plasmas can form nonvolatile BN x compounds on surface.…”

Study of Ti etching and selectivity mechanism in fluorocarbon plasmas for dielectric etch

“…1 However, low etching selectivity (ES), severe faceting, and low-k damage are common problems for pattern transfer processes using SiC and SiO 2 masks. [1][2][3] In this study we investigated basic con-siderations, etching mechanisms, and erosion properties of Ti metal hardmasks for pattern transfer into low-k materials using fluorocarbon (FC)/Ar plasmas. The most promising hard mask candidates are metallic masks such as Ti, TiN, Ta, and TaN.…”