AVS 56th International Symposium & Exhibition
    Plasma Science and Technology Tuesday Sessions
       Session PS1-TuM

Paper PS1-TuM11
Control of TiN Sheet Resistance in Downstream Plasma PR Strip

Tuesday, November 10, 2009, 11:20 am, Room A1

Session: Advanced FEOL and BEOL Etch
Presenter: L. Diao, Mattson Technology, Inc.
Authors: V. Vaniapura, Mattson Technology, Inc.
L. Diao, Mattson Technology, Inc.
S. Xu, Mattson Technology, Inc.
Correspondent: Click to Email
Semiconductor integrated circuit density has increased continuously by shrinking the device size. Interconnects between multiple stacked metal layers need to be moved closer together hence thinner and narrower. However, the reduction of the interconnect dimensions increases electrical resistance and a subsequent loss of device performance. This leads to an ongoing effort to search for materials with lower electrical resistance suitable for interconnects to integrate into IC production. Metals like tungsten, titanium are good choices but require the use of conductive diffusion barriers. Titanium nitride (TiN) is widely employed as diffusion barrier layer and/or adhesion layer due to its low sheet resistance (Rs). Integration challenges occur with TiN during high temperature photoresist (PR) strip. The commonly used PR removal process, down stream oxygen plasma, can increase sheet resistance of TiN significantly. In order to understand how to reduce this adverse effect on the TiN layers, extensive studies of sheet resistance change (ΔRs) were conducted. TiN samples were treated with plasma exposure of different chemistries in an inductively coupled plasma reactor. Optical emission spectroscopy (OES) was used to observe the presence of reactive species in the plasma of different chemistries. The experimental results show that pure reducing chemistries were effective in maintaining the Rs, and the addition of these reducing chemistries to oxygen plasmas can significantly reduce ΔRs. OES analyses indicate that ΔRs is mainly caused by the oxidation of TiN with the present of reactive oxygen species in the plasma. Reactive oxygen content is controlled by the percentage of reducing chemistry in total flow. The dependences of ΔRs of TiN to various process parameters were investigated in detail. A majority of the Rs shift happens in the first tens of seconds of plasma exposure, which indicates that it is caused by modification of top surface. Based on this work, an optimized chemistry and process regime have been identified to greatly reduce or even suppress sheet resistance increase without compromising PR removal productivity.