Effluent Slurry Extraction Systems®

The ability to safely extract spent slurry from the polishing process has become mission-critical. In today’s CMP processes, the mean residence time of the slurry on the pad can exceed 30 seconds. As such, the slurry has plenty of time to accumulate unwanted reaction by-products (from the film being polished) as well as pad shavings (from conditioning and the contacting retaining ring). These can contribute significantly to wafer-level defects as they continue to enter and re-enter the pad-wafer interface dozens of times (depending on the platen RPM) before eventually leaving the system. Furthermore, some odd-shaped nano-particles may get chipped off when pressured by the retaining ring and the wafer during billions of stick-slip events that take place in a 1-minute polish. Knowing the extent of debris uptake by the spent slurry during polishing and whether or not nano-particles can maintain their overall morphology during polishing is critical in ensuring efficient, high-quality, and high-yielding planarization processes.

Traditional ways to sample spent slurry during polishing have been either through the slurry waste line or from inside the capture tub that surrounds the platen. These methods are far from ideal. First and foremost, they cannot be done safely and without having a technician defeat the safety interlocks of the cabinetry that surrounds the polisher to get close to moving parts of the polisher. Second, the capture tub can be quite dirty and contaminated with myriad dried-out and co-mingled slurries and debris from runs performed over months of operation. Lastly, the waste line may be contaminated as well; it will surely contain residual water from rinsing steps.

On the other hand, our latest product offering, the Effluent Slurry Extraction (ESE®) system, can safely draw working slurry from the surface of the pad during polishing. This is done by modifying the design of the Injector Bottom Unit (IBU) of the SIS® (see figure below).

For the ESE® to work, the SIS® PEEK IBU has to be re-machined to allow for the captured slurry to enter the slurry track that runs across the length of the part. These machined tracks act as gutters or “aquifers”. Only then, the ESE®, which operates in reverse mode (as opposed to the SIS® which injects the slurry), can accumulate and pump out the spent slurry. The figure below shows the modification that we do on the IBU. Here, for the ESE® to work, the SIS PEEK IBU has to be re-machined to allow for the captured slurry to enter the slurry track that runs across the length of the part. These machined tracks act as gutters or “aquifers”. Only then can the slurry be vacuumed off the surface of the pad.

The schematic below shows how the ESE® gets installed on a typical polisher.

A video showing the efficient and stable operation of the ESE® on a 300-mm wafer polishing process can be seen here. For enhanced visual contrast, we have dyed the slurry red. One can see that a bow wave is formed in the back of the injector’s leading edge, which contains used slurry and pad conditioning debris that can cause polishing defects. The spent slurry captured by this method can be easily pumped out and analyzed in-line for pH, refractive index, zeta-potential, particle size distribution, and large particle counts. Samples can also be sent out for SEM, EDX, and other types of analyses.

The SEM and EDX results below clearly show how contaminated, and debris-filled, the working slurry can be during typical copper (top figure with a Dupont IC1010 pad) and barrier (bottom figure with a Fujibo H800 pad) polishing processes with in-situ conditioning.

There appears to be a huge difference in the morphology of the debris depending on the pad and the process.

It is important to note that ESE®, just like the SIS®, is completely passive and does not require power or any specialized software to be integrated with commercial polishers. Simple kits are available for all AMAT and Ebara polishers, as well as all Accretech, Fujikoshi, SpeedFam-IPEC, and Revasum polishers.

ESE® is sold to customers as a kit that can be installed, used, and removed in less than 30 minutes with maximum ease and efficiency. Each Kit is comprised of a mount and an injector unit. Since ESE® is used only when spent slurry capture is needed, the entire system (including the IBU) will not wear appreciably during years of use. So, unlike the SIS®, no replacement or consumable parts are involved.

The ESE® Kit for the AMAT RLK Prime® is shown below:

As other examples, ESE® Kits for the AMAT RLK® and Mirra®, as well as the SpeedFam-IPEC 472 are shown below:

Please contact us if you need more information.