OTS (February 2009) -- At FSI’s recent FSI Knowledge Services™ Seminar held in Asia, representatives of MagnaChip described their experience with the ZETA^® System ViPR™ photoresist stripping process in a 200mm production fab, attributing it to reductions in cycle time by as much as 11x over the ash and clean process of record.

Their analysis demonstrated a cumulative time savings over many layers in one product amounting to 10% of total processing time. In addition to dramatically reducing the number of cleaning systems required, the ZETA^® System ViPR™ process eliminates the added capital/operating cost and process complexity of dry ash systems in most stripping applications.

The ZETA^® System ViPR™ process was initially introduced for 300mm applications creating 65nm and smaller devices. The all-wet process was quickly and broadly accepted for its ability to strip heavily implanted photoresist without the material losses caused by ash and clean methods. Material loss is less concerning at the larger device geometries typical of 200mm processes, but the lower margins associated with their more mature products and markets bring increased pressure to reduce manufacturing costs at every opportunity. The MagnaChip presentation clearly demonstrates the value returned by the ZETA^® System ViPR™ process in 200mm applications.

Photoresist stripping has always been difficult as manufacturers apply high energies and doses to create deep ion implants. The ion bombardment forms a tough skin on the surface of the photoresist that resists attack by conventional sulfuric acid/peroxide (SPM) wet cleaning chemistries. Ashing provided a viable means to breakdown this surface layer for the geometries in production when it first became apparent. The ViPR™ process’ success derives from its ability to generate significantly higher chemical activity at the wafer surface than competing SPM technologies by maximizing temperature and reactivity.

MagnaChip evaluated stripping capability over a wide range of implant levels. As shown in Table 1 below, the ViPR™ process efficiently strips resist in all but the highest energy/dose processes. Note that since Magnachip completed its evaluation of ViPR™ stripping, FSI has further increased its high dose implant strip capability up to 5e15 40keV implants by introducing the latest ViPR™ hardware and processes.

Table 1: Ashing Performance of ZETA^® System.

The presentation also includes the results of their evaluation of other critical process performance criteria, including film loss, defectivity and particle generation, oxide etch uniformity, wafer backside cleaning, and electrical characteristics. In all cases the ZETA^® System ViPR™ process met process requirements and equaled or exceeded the performance of the ash/clean process of record. Certainly the most significant finding was the 75% decrease in stripping process cycle time from 145 minutes to 35 minutes per cycle. This improvement in cycle time was projected to achieve a 10% reduction in total processing time for one product considered. Faster cycles ultimately contribute to faster product development and lower manufacturing costs, an effect that is further enhanced in most cases by eliminating the cost of ashing. The ZETA^® System ViPR™ process offers manufacturers the somewhat unusual opportunity to improve both time to market and profitability.

Table 2: Time for 1 Step Photoresist Removal and Post Cleaning.

FSI customers may order the MagnaChip presentation and other presentations from the FSI 2008 Asia Knowledge Seminar Series on the FSI Website.