Bringing Existing Tools to a New Level of Performance
Tony Martinez and Wen-Jen Tsai
Enhancing the capabilities and extending the useful life of existing semiconductor production equipment allows manufacturers to extend process capability, increase flexibility and lower wafer cost.
An emerging trend is for manufacturers to upgrade 200mm and 300mm tools to a new, more contemporary level of performance. Many economical, reliable and fully depreciated tools, first commissioned in the early 2000s or before, are still used in a variety of applications where scaling isn’t the main goal. These tools are often candidates for upgrades and performance improvement adjustments that increase uptime and efficiency, and extend their lifetimes.
For example, Applied Materials has done this with our 200mm Centura DPS etch tools. At multiple customer sites we have achieved more than twice—sometimes nearly three times—the mean wafers between cleans (MWBC) RF exposure time, significantly increasing tool productivity.
GREATLY INCREASED TOOL PRODUCTIVITY
A case in point is one customer whose fab output was constrained during a transition to a new process mix. Following the introduction of the customer’s new process, their 200mm Applied Centura DPS Al metal etch system was experiencing particle excursion issues, leading to a low and unpredictable MTBC of 60–90 RF hours. In addition, the customer wanted to switch gases in one process step from a fluorine-based gas (CHF3 with Cl2 and BCl3) to a nitrogen-based chemistry (N2 with Cl2 and BCl3), which required additional process modifications.
Applied Materials suggested an analysis by its FabVantage consulting group to examine the situation and recommend remedial actions. The FabVantage team included individuals with deep process and equipment knowledge who worked with the customer to evaluate the tool’s existing performance baseline and evaluate it against all relevant benchmarks, best known methods (BKMs) and best practices. Quantitative recommendations were then established for a series of process, hardware, and recipe performance improvements and first implemented on a golden tool to validate them.
One recommendation was to use an enhanced dome temperature control unit (E-DTCU) to keep particle formation in the dome to a minimum. Other recommendations included:
- Hardware: To further reduce the need for frequent chamber cleans, the existing polyimide electrostatic chucks (ESC) in the tool’s chambers were replaced by new ceramic ESCs, along with change-outs of the existing process kits to yttria-coated kits. Polyimide ESCs are susceptible to accelerated wear and buildup of organic residues, whereas ceramic ESCs are resistant to buildup and don’t attract as many deleterious chemicals.
- Process: As part of this change, the in-situ cleaning was tuned and optimized for the ceramic ESC. After implementing these changes on the golden tool, it was necessary to demonstrate process transparency. This was done by checking the etch rate and the etch rate within-wafer (WIW) uniformity on an Al etch process and by measuring the oxide loss on patterned wafers.
Ceramic electrostatic chuck.
Figure 1 shows the etch rate and uniformity for an Al etch process. In addition to the etch rate and uniformity being matched to within 1%, the etch rate profile was preserved, as indicated in the wafer maps. Figure 2 shows the etch profile results, indicating amount of oxide removed. Oxide loss, as measured by scanning electron microscopy (SEM), was calculated in both dense and isolated regions of the wafer. Oxide loss matches were identified to within 4% in the dense regions and within 1% in the isolated regions.
Figure 1. Etch contour maps showing the results of process transparency testing. Colors on the map indicte etch rate, angstroms/minute.
Figure 2. Cross-section SEMs of etch profile before and after the changes. The left SEM in each pair shows a dense region on the wafer, and the right SEM shows an isolated region. Numbers in the table denote the amount of oxide removed in angstroms.
Together, these performance improvements have resulted in a more than 60% improvement in MTBC with no degradation in tool performance. They have also increased processing flexibility in the fab, eliminating Al metal etch as a major source of the fab’s bottleneck.
WORKING TOGETHER FOR BEST OUTCOME
This project, the first of multiple, ongoing engagements with this customer, is an example of how the FabVantage team can serve as trusted advisors and problem-solving partners for customers, helping extend tool performance to a new level, reduce fab constraints and lengthen the useful life of an existing manufacturing asset. In addition, it demonstrates how Applied Materials can apply the correct services and hardware solutions at all customer technology nodes and on a wide array of processes to help them find ways to get more good wafers out the door at lower cost.
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