OTS (July 2006) -- The first ZETA® G3 spray cleaning systems, shipped March 2006, have been accepted and are in the process of production qualification. The ZETA G3 is the third generation on the ZETA platform.
Enhancements to the platform’s robotics and cassette handling capabilities have yielded a 30 percent increase in post-ash clean throughput compared to the previous-generation platform. The ViPR™ all wet strip process for highly implanted photoresist, first introduced with the ZETA platform, has passed initial production testing at several implant levels. The ViPR process yields more than 50 percent reduction in cycle time compared to combined ash and clean processes for the same step. Continuing qualification of the ViPR process on additional implant levels will provide integrated process yield improvement data over the next few months.
ZETA G3 System
Providing both faster edge contact wafer handling as well as mini-environment performance improvements, the ZETA G3’s feature set builds on the experience accumulated through the previous two generations—FSI has shipped over 1,000 spray cleaning systems. The system’s flexible chemistries allow a single system to run multiple recipes, effectively substituting one system for several. In-line blending with inputs for up to eight fresh chemicals and two re-circulated chemicals deliver fresh mixtures directly to the wafer and save on the cost of specialty chemicals by permitting multiple custom blends. Closed-loop process controls ensure repeatable performance. Wafers enter and leave the controlled environment of the nitrogen-purged process chamber dry. The ZETA system’s centrifugal technology enhances mass transfer at the wafer surface to remove heavy contaminants.
ViPR Process
The ViPR all-wet photoresist stripping process provides a much-need alternative to ash and clean processes required for highly implanted resists. When subjected to high dose or high energy ion implantation, photoresist forms a tough skin of cross-linked amorphous carbon that cannot be stripped with traditional wet chemistries like the widely used “piranha process.” They can be removed with aggressive ashing and wet post-ash clean (PAC), but these processes can damage the delicate structures of a semiconductor device. In particular, they are associated with significant loss of silicon and oxide, a loss that is made more critical by the continuing reduction in device size and layer thickness. One study showed a significant improvement in drive current for 65nm logic devices associated with a reduction of silicon loss.
The ViPR process is an all-wet variant of standard piranha. The primary difference is the higher on wafer temperature of 200°C. At this temperature, the formation of radicals that can attack the cross-linked carbon is enhanced by a factor of 500 when compared to the standard process temperature of 150°C. However, immersion-type cleaning systems cannot sustain the higher temperature, as the chemicals will decompose and evaporate. The ViPR process takes advantage of the ZETA G3 system’s sophisticated chemical sequencing and liquid dispensing capabilities, to raise the process temperature at the wafer surface. ViPR process can eliminate the need for ashing in all but the highest dose/energy implants (see figure 1).
Figure 1: Using the ViPR process, ashing can be eliminated for all but the highest dose/energy implants.
In addition to eliminating the material loss and surface damage associated with ashing, ViPR process offers a significantly shorter cycle time. A typical ash and clean process takes 80 minutes compared to 25 minutes for ViPR process. Assuming a cycle time of 1.2 days between photolithography processes, the difference of 55 minutes constitutes a 3 percent reduction in total overall cycle time.
Summary
ZETA G3 platforms have been accepted and are in production qualification at major semiconductor fabs. The ZETA system offers a 30 percent improvement over its predecessor in post-ash clean cycle time. The sophisticated chemical handling capabilities of the system enable the new ViPR all wet stripping process for highly implanted photoresist. The ViPR process uses standard piranha chemicals to raise wafer surface temperature to 200°C. Eliminating the ashing process reduces surface damage and loss of material, resulting ultimately in improved electrical performance. It can also provide a 3 percent reduction in overall mask layer cycle time.