David Wei

Sub-90nm pitch Cu low-k interconnect etch solution using RF pulsing technology

Self-aligned via (SAV) schemes are commonly used for back-end-of-line (BEOL) interconnect structures that have scaled to <; 90nm BEOL pitch [1]. In one implementation of this scheme, a TiN metal hard mask (MHM) is used for trench pattern definition, while the interconnect vias are patterned using a tri-layer resist mask such that the vias are self-aligned to the underlayer trench lines [2]. In this work, we describe a SAV etch process using RF pulsing in a capacitively coupled etch reactor that provides a solution to both via distortion / striation and critical dimension (CD) bias loading. Electrical results will be discussed.

Understanding the dishing difference between a line and a bond pad in Cu CMP

In Cu chemical mechanical polishing (CMP), dishing for a line differs from that of a bond pad. Even if the linewidth and the side length of a square pad are the same, dishing in a line is much more severe than dishing in a pad. In this paper, we show that pad deformation may be the reason. Pad deformation over a line is primarily restricted by two sides of its surrounding areas, while pad deformation over a pad is restricted by all four sides of its surrounding areas. Therefore, it is easier for the polishing pad to touch the Cu in a line than in a bond pad, which increases dishing. The result is also verified against experimental data.

Flexible polishing surface (FPS) vs rigid polishing surface (RPS) in CMP: pros and cons

Two major conceptual CMP approaches, namely flexible polishing surface (utilized in linear belt CMP) and rigid polishing surface (hard platen rotary and orbital CMP) concepts are compared with regard to process stability, uniformity, planarization efficiency and other performance features. A new CMP characteristic, Normalized Removal Work, the amount of wafer layer material removed by a unit of active pad area (NRW=(Thickness removed)/(Active pad area), [A/sq. inch]), is used to analyze and compare the concepts. The NRW shows how much of the removed material is transferred and redeposited over a unit of pad area. It influences all aspects of the CMP process. Low NRW is good for CMP, high NRW is bad for CMP.