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Modular or Custom Cleanroom? It Depends

Weigh the pros and cons of standardized versus custom facilities

Don Yeaman

Don Yeaman is principal planner, advanced technologies, with HDR.

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This photo of the University of Washington Nanofabrication Facility lithography prep bay highlights the extensive environmental controls possible in a custom cleanroom.

When investing in a cleanroom, one of the first things many people ask is whether a pre-manufactured solution could work. After all, a pre-fab cleanroom often is available with many different options (e.g., various cleanliness classes and several room widths and heights), and it can be significantly less expensive than a custom solution.

But the best answer to that question is the infamous, “maybe.” Or better yet, “it depends.”

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It can be a critical mistake to believe that just because a modular cleanroom works for one application means that it’s the best solution for all. The decision about whether to invest in a “standard” or “custom” solution should ultimately be informed by a comprehensive understanding of the type of work that the cleanroom will support. This knowledge, along with insight into how this work may change over time as technology evolves, is critical to weigh the pros and cons of a standardized versus custom cleanroom. It could very well be that a prefabricated solution makes the most sense, but requirements should be fully vetted first.

The (relatively) easy part: making a room “clean”

Almost all cleanrooms share a common requirement to provide a safe environment and be adaptable/flexible to accommodate changing programs and technology. Checking off the requirements that make a room “clean” is a relatively straightforward process:

  • Does it provide a clear emergency exit path?
  • Does it have dedicated hazardous chemical and gas delivery paths?
  • Does it meet the codes required for safety fixtures, signage, and a monitoring and control system?

Meeting requirements put forward by ISO is typically the easiest part of the decision matrix. And most, if not all, modular solutions can provide an as-built/at-rest cleanliness level to meet any ISO class specification. For a cleanroom to be adaptable, however, it should provide at a minimum extra space that can accommodate the following types of changes:

  • Space in the utility generation rooms so systems can be upsized or additional modules can be added to increase utility system quality. This is typically low-cost space.
  • Space in the utility routing zone so new system mains or laterals can be added. Again, this type of space is usually pretty inexpensive.

Another consideration is to determine a growth path so that if the program requires cleanroom expansion, space exists to do so. The cleanroom also must be designed in such a way that the cleanroom doesn’t need to be shut down when expansion construction occurs.

Beyond meeting ISO requirements and including space for future adaptability, the ideal cleanroom design solution requires close scrutiny of all technical requirements of the processes and a comprehensive understanding of the process tools that support them. Furthermore, it requires a close look at what future processes and process tools might be required to account for sufficient adaptability.

The hard part: making a cleanroom work

This view of the etch bay in the NIST Precision Measurement Lab nanofabrication cleanroom highlights the diverse process equipment to be accommodated in a typical fab, best suited to a custom cleanroom solution.

The complete list of cleanroom requirements can only be understood after clearly defining the near-term and long-term mission and goals of the facility. These principles determine the processes that will be performed in the cleanroom, which in turn define the types of process tools to be installed, which also drives the environmental requirements (vibration, temperature, humidity, EMI, and AMC control). Process tools and their expected utilization rates also drive the sizes and quality levels of all house utility systems, plus the amounts of hazardous chemicals and gases that will be used and stored.

Environmental control (cleanliness class, T&H control)

When considering pre-fabbed cleanroom solutions, it’s imperative to know if temperature and humidity control are included as a part of the system. Often, packaged cleanrooms rely on the house HVAC system to provide air at the right temperature and humidity set point. In effect, the modular cleanroom takes on the environmental characteristics of the parent space it sits within. If your cleanroom will be a retrofit into an existing building, it’s very unlikely that the existing HVAC system would have the capability to provide the humidity control required for micro or nanoscale processes.

Packaged cleanroom systems also don’t provide EMI or vibration control and can actually negatively affect those requirements. For example, a university in Texas bought a modular cleanroom system and installed it in one of their existing buildings. This cleanroom consisted of a large, six-sided metal room with an enclosed filter plenum above, an integrated raised floor system, and integrated air return shafts on the sides. When the cleanroom was turned on, the vibration of the fan filter units was transmitted to the unit’s raised floor and subfloor structure, preventing some of their process equipment from working properly and halting research until the modular cleanroom could be modified and some of its components reworked or replaced.

Utility demands (more exhaust, more power, more cooling water)

The University of Washington Nanofabrication Facility renovation incorporated pre-fabricated components such as pressurized plenums in a custom cleanroom. This photo shows the extensive process support systems required in most microelectronics fabrication cleanrooms.

Modular cleanrooms can be great solutions that save significant time and money when cleanroom processes can be performed using standard hoods, sinks, and tabletop equipment. They aren’t the best solutions in processes that need specialized equipment, high utility loads, and support equipment such as pumps, power supplies, and chillers. However, it’s also important to consider that cleanroom processes change over time, and the design for the room should accommodate those changes. Two important questions to ask:

  • Will the product substrate material or size change over time? For example, will you switch from silicon or ceramic substrates to compound semiconductors or from three-inch substrates to six-inch?
  • Will the process equipment set change significantly over time? For example, possibly adding multi-chamber dep or etch equipment or switching from single substrate processing to batch.

If specialized demands exist or if there is a fairly good chance they will in the near future, a custom solution that can deliver the required adaptability might be the better option.

Investigating a solution

The considerations outlined in this article are critical to good decision-making when it comes to cleanroom investments. If all that is required is a “clean” room, then a modular pre-fabricated solution will make sense—for example, in an aerospace integration and test facility, or a medical device assembly. A closer look at the functions to be performed in the cleanroom and their associated environmental and process support systems may indicate another direction.

Good decision-making about those investments is critical to productive and successful research activities. While it can be tempting to skip the step of investigating current and future processes and process tools, try to resist it. The small amount of extra time spent truly understanding requirements will pay dividends in the long run.