The Integration of Interlayer Dielectric Deposition and Chemical Mechanical Polishing
- PDF / 1,203,661 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 8 Downloads / 185 Views
into the process flow. The integrity of the ILD layers was not directly affected by CMP process, but the problem became dramatically evident after the integration of CMP into the process flow. The effect existed before the introduction of CMP but was not detected due to the sequence of process steps. In the present case, the back-end-of-line (BEOL) processing consists of metal deposition followed by a TEOS based ILD deposition. Gap fill between metal lines is accomplished by using a dep-etch-dep process. The etch process serves to facet the comers of the initial ILD layer above the metal edge and promotes filling between the metal lines of the subsequent deposition process. The etching is done in a magnetically enhanced reactive ion etcher (MERLE) using Argon (Ar) and CF4. The ILD layer is planarized using CMP and vias are etched through to the underlying metal. The vias are filled with a blanket tungsten film using chemical vapor deposition (WCVD). CMP is then used to remove the tungsten film from the field areas and form the tungsten plugs. In the older generation technology, planarization and tungsten plug formation were accomplished by photoresist planarization and tungsten etchback using a reactive ion etch (RIE) process. The WCVD and tungsten RIE were performed in a multi-chamber tool using sequential processing. Following the introduction of CMP into the process flow, intermittent flaking or peeling of the tungsten film from the wafer was observed after tungsten deposition and before CMP. The magnitude of the problem varied by time, lot to lot, and within a lot. The delamination of the tungsten film from the wafer was indicative of an adhesion related issue induced by the compressive stress in the deposited tungsten film. Optical microscopy revealed the delaminating front to originate from a large open field area or die edge and terminate in areas where tungsten
109 Mat. Res. Soc. Symp. Proc. Vol. 477 0 1997 Materials Research Society
plugs were present in some density. It was concluded from these observations that the tungsten plugs that form the contacts and vias were 'pinning' the delaminating film in place, suggesting that the mechanism for delamination was not poor adhesion of the tungsten film to the TEOS layers. Photoreflectance measurements of ILD thickness remaining after the film had peeled away, indicated there was a substantial amount of ILD, c. 2-3kA, remaining on the wafer. This data was supported by profilometry measurements of step heights from areas where the film had peeled adjacent to areas where the film stack was still intact, (see Figure 1). It should be noted this adhesion issue went unnoticed in the previous BEOL process flow because the tungsten film was etched back immediately following the WCVD and before the wafer was exposed to atmosphere or available for inspection.
.Tilm fracture observed along this line Delaminating Film
Data Loading...
