Ultra SFP Stress-Free Polishing Tool for Wafers

The Ultra SFP tool for advanced packaging solutions is designed to address yield issues arising from through-silicon via (TSV) processes and fan-out wafer-level packaging (FOWLP), such as copper overburden post-TSV fill and wafer warpage issues that plague FOWLP processes.

The Ultra SFP leverages ACM’s proven stress-free polishing (SFP) technology and integrates it with chemical mechanical planarization (CMP) and wet-etch chambers into a single system. The processed wafer moves through the chambers in a 3-step approach to gently remove copper overburden and relieve wafer warpage before the final planarization and wet-etch steps. Additionally, with its built-in electrolyte recycle and reuse system, the SFP consumes significantly reduced levels of chemicals, making it a more sustainable and environmentally friendly option at a lower cost of ownership.

Similar to ACM’s electro-copper plating technology, but in reverse, the Ultra SFP’s proprietary electrochemical reaction mechanism involves the simultaneous delivery of electrolytes and a power source to the wafer as it rotates on the chuck to electrically remove metal ions from the wafer surface. In both TSV and fan-out applications, Ultra SFP's 3-step approach effectively eliminates any process-induced stress to the wafer. In TSV applications, SFP is used to remove bulk copper overburden (post-TSV fill) down to 0.2 µm. Next, CMP is used to planarize the wafer and remove the remaining copper down to the titanium barrier layer. Finally, a wet-etch step is performed to remove the titanium and expose the oxide layer. In FOWLP, this same sequence of process steps can be used to eliminate wafer warpage, remove copper overburden, and planarize redistribution layers.

Because both the electrolyte and wet-etchant chemistries are recycled and reused in real-time through a built-in electrolyte recycling system, the Ultra SFP can significantly reduce the overall usage of consumables. Furthermore, the system’s ability to reclaim the removed metals, which can then be used for other purposes, adds to its sustainable nature.

The Ultra SFP 335 is configured with two SFP chambers, one CMP station, and two wet-etch/clean chambers. Process chemistries required include electrolytes, copper slurry, copper etchant, and titanium etchant. All three processes achieve a 0.5 µm/min removal rate, less than 3% within-wafer nonuniformity, and less than 1.5% wafer-to-wafer nonuniformity.