Polishing and CMP Tool Requirements

Depending on the ability of slurry suppliers to develop slurries capable of removing both copper and barrier layers without excessive dishing, it may be necessary to use multiple slurries, and possibly to polish wafers on more than one head. The point here is that flexibility is key. It is important that customers have the capability of delivering different slurries to a given head within a polish cycle and to different heads within a tool if desired. 

In addition to controlling the standard process parameters such as down force and the relative velocity, it is also important to have random access capability to route wafers through a CMP tool to optimize both performance and throughput. Low-down-force processes and special CMP pads are likely to be necessary to reduce copper dishing just as they improve oxide planarization. Furthermore, a balance between high relative velocity to reduce copper dishing and moderate relative velocity to minimize the sheering of small oxide feature may be necessary. 

With the growing level of control of copper CMP process comes the requirement for temperature control. Copper CMP is highly temperature sensitive, so hot slurry will enhance the removal of bulk copper. However, barrier metals are significantly less reactive (with the slurries currently available), so there is a significantly greater mechanical contribution to the removal of the barrier layer(s). Consequently, hot slurry is of little benefit for barrier layer removal and may soften the pad and aggravate metal dishing and dielectric erosion. 

In the future, pH control will also be a desirable capability. This capability already exists with tools on which slurries can be changed quickly and may be particularly useful with secondary slurries designed for specific barrier layers or for buffing. 

1 Stap CuTTa Pollat) 2 Stap Cu/Ta Polah 10%Ovarpoliah 10%OvarpoUah 

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