Clean Room vs the SubFab: The key reasons to align
The cleanroom cannot function without the vacuum and abatement system. Without its essential services, operations in the cleanroom come to a sudden and costly halt.
The differences between SubFab and the Cleanroom are many, but in some of those differences lie opportunities to improve yields, reduce downtime, avoid scrapped wafers, decrease maintenance costs, increase productivity and profitability, and more.
Below is a summary of the similarities & differences that lie in the equipment, maintenance techniques, measuring practices and the people across the Fab.
Equipment
The cleanroom is typically filled with a wide variety of process tools from many different manufacturers. The range of on-tool vacuum pumps is vast, the variety and complexity of process tools and operating interfaces in the cleanroom makes providing vacuum and support complicated. Fleet management and optimisation is more complex, as tools are grouped and isolated by process.
However, not all cleanroom tools require on-tool vacuum pumps, but almost all tools require vacuum and abatement services down in the SubFab. In contrast to the cleanroom, the SubFab, is usually a large open space packed with vacuum pumps, abatement systems, in many cases, from a single manufacturer. Yes, this lends itself well to fleet management. But significant variations within the equipment fleet reflect the complexity found in the cleanroom. Vacuum and abatement equipment behave differently from process to process, depending on the type of process (deposition, etching, or cleaning). Making poor maintenance decisions can create inefficiency, downtime and critical safety hazards. Fleet management must have the attention to detail and expert support, that is just as important as in the cleanroom.
Maintenance
In the cleanroom, the physical constraints of the large integrated process tools means maintenance is almost always performed on-site. Process tool maintenance is typically managed on a time or count basis interval, although more recently there is a rise of predictive or condition-based analytics driving maintenance decisions.
In the SubFab technology advancements have allowed the meantime between service for vacuum and abatement equipment to become much longer than those for process tools. Some critical pumps and abatement systems are maintained on a regular schedule, but maintenance tends to be reactive – sometimes even run-to-fail, with back-up pumps at the ready. This dilutes the benefit of the longer service intervals and can cause unplanned tool downtime.
Measuring
Differences in the way vacuum equipment is monitored and measured in cleanroom and SubFab reflect of the different aspects of the process they address. In the chamber, process vacuum is critical and process engineers constantly monitor vacuum levels, check for leaks, and detect process endpoints. Most of these vacuum sensors are add-ons, typically not natively integrated with the process tools. Frequent measurements and inspections are used to confirm process performance. The cleanroom operational paradigm is inherently data intensive.
Sensors for SubFab vacuum equipment are typically integrated, with many hundreds of relevant vacuum and abatement parameters monitored and available through equipment controllers. This can go up to thousands of parameters for the most complicated equipment, such as those supporting EUV lithography tools. This represents a significant data set that needs to be integrated with fab process data. But in the SubFab, we have yet to take full advantage of the insights we might derive from this data. Smart Manufacturing initiatives are now making inroads into this potential, and we expect to reap the benefits in the years ahead.
People
Creating integrated circuits requires many people with a wide range of skills and both theoretical and hands-on knowledge. These skills range across physics and chemistry, materials science, electrical engineering and electronics, mechanical engineering, control systems and more. The skill sets and people needed again reflect the different aspects of the process carried out in the cleanroom vs the SubFab. In the cleanroom, operators, technicians, and engineers are highly skilled – PhD’s are not uncommon.
On-site SubFab personnel are also highly skilled, particularly in view of the risks posed by hazardous materials, but because much of the maintenance is performed off-site, there is also an army of highly skilled technicians and PhD engineers working behind the scenes at the service and manufacturing facilities. This PhD level knowledge of process chemistries and vacuum physics is crucial in designing both equipment and maintenance procedures, and, when needed, in solving problems on site. As a significant amount of the SubFab’s domain expertise is based off-site, maintenance complexity is hidden and opportunities to optimize its effectiveness are often overlooked.
There are many differences between the clean room and the SubFab, but in these differences lie opportunities to improve yields, reduce downtime, avoid scrapped wafers, decrease maintenance costs and more.
