Clean Build Protocol–Foundation for Cleanliness at World Class Fab
Clean build protocol prevents built-in contamination, facilitates equipment hook-up and readiness for fab production while providing a basis for daily operations cleaning.
By Larry Mainers & Reid Rotatori
New cleanroom facilities and ultraclean production standards demand better, more efficient, and earlier initiation of construction-related and long-term critical cleaning practices. At Digital Equipment Corporation`s (DEC–Hudson, MA) recently completed 450,000 ft.2 Class 1 submicron facility, clean build protocol–rather than blitz cleaning at construction completion–prevented built-in contamination, which could surface and reduce yields, while facilitating equipment hook up, immediate readiness for fab production and the basis for advanced daily operations cleaning.
Contaminants at cleanroom construction projects are myriad. Dust from interstitial spaces, gypsum particles from wallboard and other materials, metal filings, rust particles, concrete dust, human saliva, skin and hair–if not systematically removed during construction–can be entrapped inside walls, at wall panel seams, on tee bars, in air ducts or other areas, and be released over time by building vibration, settling or other means, to undermine production. Though fabs maintain positive air pressure to help ensure cleanliness, contaminants from interstitial or other areas may be drawn or allowed into critical zones through unexpected shifts in air pressure, air balance problems, fan malfunction, airlock breach, or power outages.
Also, where clean-build methods aren`t followed–including ensuring enclosure integrity through testing and balancing–construction particles may be released from gaps in wall seams or other discrete spots, bypass room filtration and affect the process.
Clean Build Required at DEC`s Class 1 Submicron Site
While construction decontamination of Class 10 or higher rooms is often achieved primarily through a “superclean” at building completion, this method was inadequate for DEC`s Class 1 submicron facility. Besides leaving built-in contamination, the heavy-duty methods required by singular blitz cleaning and the abrasive effect of dirt build-up could produce porous surfaces that trap and release contaminate.
Higher class rooms may tolerate small releases of contamination without problems, but even minute amounts of foreign matter released in Class 1 submicron zones may be disastrous. With a mission to create a facility to support fab technologies into the next century, DEC wanted assurance that the building itself wouldn`t be a source of time-released particulate.
Clean build protocol helps ensure that all areas are meticulously cleaned and recleaned with approved techniques during construction to avoid surface damage and to prevent future sources of contamination. Equipment hookup requirements in Class 1 submicron fab zones require early partitioning, effective buffering, and repeated cleaning to create, maintain and protect ultraclean envelopes.
Having the facility “process ready” at construction completion also prevents costly delays. For these reasons, DEC decided to contract a “clean builder” with protocol experience.
Builder as a Guardian of Clean Build Protocol
The builder was responsible for implementing the protocol. In short, this meant appointing a clean zone director who was charged with overseeing the establishment and maintenance of clean zones buffered by adjacent clean areas, monitoring air and surface particle counts intensely during construction, handling logistics with up to 500 workers and tons of materials and supplies on-site, and enlisting/focusing the services of numerous subcontractors.
This included employing a specialty cleaning firm, which used cleanroom-specific procedures and methods to remove construction particulate as it was produced, starting at core clean zones where fab processes were to be initiated. Overall, the decontamination motto for all parties was: “Prioritize, clean, monitor, reclean, protect clean zones and take no chances.”
Tooling-up requirements in the inner sanctums of the DEC facility required delineating and ultracleaning these areas as early as possible, so cleanroom-ready fab equipment could be unwrapped and installed without being contaminated. This involved creation of buffer cells or spheres–conceptual and literal clean zones–surrounding even cleaner inner cells.
The core cells, which were ultimately certified Class 1 submicron, were protected and surrounded by outer buffer cells destined for higher classification, which, in turn, were enclosed by marginally less-clean spheres in widening ripples of descending cleaning and protocol. The cell or sphere boundaries followed actual building partitions or walls where possible, but, given the incomplete and staggered construction, often had to be created through temporary walls and structures. These stepped spheres were set up following a priority from inner to outer zones, starting at fab areas, then to interstitial locations, then to the nonclassified exterior parts of the facility.
Before some materials and components–manufactured and packaged in cleanroom conditions–could even be unwrapped, clean stripping, dewrap and wipedown areas were created where those items could be prepared for assembly. Final destination areas for the equipment and components in the cleanroom had to be clean just as the building materials or components did, so as not to contaminate those items, and vice versa. Contractors also had to pre-clean, assemble and set up equipment and products in a designated pre-clean area.
During the building process, every exposed area of raw-edge or freshly cut material–such as openings made for sprinkler systems–was cleaned and sealed with epoxy paint to prevent release of contaminant. Sawing and drilling were only done in protected enclosures or outside the clean space. Welding equipment used in critical areas had to be specially designed, equipped with “smoke-eaters” and isolated from inner clean zones.
The builder was responsible for overseeing the entire clean build program and supervising all contractors to ensure compliance with protocol until the facility was handed over to the owner. Due to its scope and design, the open-ballroom style Hudson DEC facility exemplified and magnified clean build practices and advantages. Protocol was established after preliminary construction began.
How Clean Build Protocol was Developed at DEC
The operational class “boundaries” of DEC`s cleanroom were established by the owner. This was to be a 64,000 ft.2 Class 1 submicron facility, with a total square footage of 300,000 ft.2 of Class 100 or better cleanroom area. Greatly abbreviated, the engineer and builder wrote the “general” specs to meet this goal and construction began.
The first construction steps involved building the physical shell of the cleanroom, especially to enclose the most contaminate-sensitive areas. Air handlers were installed at early stages to produce the positive pressure needed to create clean cells.
Because the term “clean build” means different things to different people, the owner, engineer and builder were careful to define protocol parameters in detail at the DEC project once preliminary work at the site had begun and the work had evolved enough to allow for a clear picture to be formed of how protocol should be defined. Once the building shell was formed, the technical and scheduling requirements were woven into a tapestry of projected, cooperative and systematic action to both create the primary clean zones and surrounding zones, then to gradually purify, tighten and solidify the envelope in harmony with each area`s final classification.
Establishing three broad categories of increasing cleanliness–gross, intermediate and precision clean–which, in turn, were divided into six graduated parts (levels zero through six, with six being cleanest) provided the benchmarks to ensure that areas were being progressively brought up to cleanliness specs and on schedule.
To streamline achieving the cleaning objectives, the builder decided to outsource the cleaning and bid packages were sent out to qualified specialty cleaning firms outlining requirements. Selection criteria included: experience, with sufficient management and staff to handle the scope of the cleaning and equipment inventory such as HEPA vacuums and to accomplish tasks in required time frames; management and staff understanding of cleanroom dynamics, safety procedures and effective cleaning methods, which provided the base knowledge for the additional protocol training that would equip the cleaning technicians to meet the site-specific needs outlined by owner, engineer and builder to bring the project to its goal/classification on time and without mishap.
Protocol classes for all workers–with resource material and lecture time provided by both owner and builder–were conducted to provide: an overview of the project and description of the end product to be manufactured in the cleanroom; instruction on proper behavior, safety and other procedures within each level of protocol; building layout information including fab areas, ante rooms for entry and exit, equipment prep rooms, etc.; gowning, entry and exit procedures; equipment cleaning and inspection methods; a basis for “buy-in” and intelligent involvement by all workers and technicians. Slides, printed handouts, hands-on training, lectures, question and answer sessions, and input sessions were included.
After attending protocol classes, all employees wore badges certifying level clearance. A worker who had attended protocol classes through level two, for instance, wore a badge that indicated such and had clearance to enter clean zones or cells that were up to level two cleanliness standards. Cell borders followed the class boundaries that would exist at construction completion.
Due to the scope of the undertaking–many stages of construction were going on at the same time–some areas were under roof and “tight,” while in other places, only steel framework was complete. As a result, the clean zone cells, beginning with fab areas, had to be artificially created with temporary walls, anterooms and gowning areas to create the protective barriers where cleaning and tooling-up could be carried out without wholesale recontamination from other less-clean areas. A cell was always only one protocol level lower than the one it surrounded, so contamination potential would be minimized.
This created the buffering necessary to maintain the envelope, and gradually tighten it by incrementally and respectively raising the protocol levels of interconnected cells or spheres through cleaning, re-cleaning and other measures.
The Hi-Tech Cleaning Process
The cleaning firm`s 32 technicians used 14 HEPA-filtered vacuums and other equipment to begin systematic decontamination at fab areas as directed by the builder`s clean zone director. Preliminary particle counts were at 1,000,000 per ft.3 concentration.
At the gross cleaning (Level 1) stage–which started after the building shell was formed and critical areas were enclosed–a thorough vacuuming was followed by tack wipedown of ceilings, walls, and floors under construction, as well as pipes, duct work, light fixtures, etc. Particle counts were at 30,000 0.5- micron particles per ft.3 of air after gross cleaning.
At the intermediate cleaning (Levels 2-3)–which started after ceiling, wall and floor assembly were complete–a total ceiling-to-floor vacuuming was performed, followed by wipedown with certified wipes and daily floor wet cleaning using lint-free mopping equipment. Gowning was required and restricted entry/exit requirements had to be met. Particle counts were at Class 10,000 levels after intermediate cleaning.
Precision cleaning (Levels 4-6) started after ceiling ULPA filters were installed to prepare the room for certification testing. The actual cleaning process never changed; only the phase and intensity, with the latter increasing at higher levels of protocol. Particle counts were at Class 1 submicron levels at the end of precision cleaning.
Cleaning in Unison
A wall-to-wall cleaning method was employed to ensure no areas were missed and to reduce worker fatigue. A team of technicians formed a line from one perimeter wall to the other. The group was evenly divided so that all workers had equal area to clean. The group worked across the room until the other end was reached, starting at the ceiling and continuing to the subfloor. The system ensured that no area was omitted and thorough coverage was obtained. Cleaning technicians used 15-gallon 150 cfm (ft.3 per minute) HEPA vacs, rated at 99.97 percent efficiency. Cleanroom wipes were used to hand-clean every surface after vacuuming. Special wiping and folding procedures, and overlapping strokes guaranteed cleanliness and eliminated omissions. DI (deionized water) and semiconductor-grade isopropyl alcohol were used in wipedowns, depending on the application.
Using 14 HEPA vacs in unison resulted in excellent filtration of the ambient air. Approximately 2,100 ft.3 of air was cleaned per minute, totaling 126,000 ft.3 per hour. Lower-than-expected particle accounts were consistently achieved by using this equipment and method.
Thousands of particle counts were taken by owner, engineer and builder to ensure protocol standards were being met. Areas were carefully monitored by both airborne and surface particle counts. Air sampling devices provided print-outs to document counts during various stages of progressive cleaning, and highlighted the areas that needed re-cleaning to maintain the integrity of the cell`s environment. Air sampling also provided a general indication of how well air handling systems equipped with temporary filters were functioning as air movers to remove particulate. Black-light testing and oblique white-light tests helped show surface particle counts, and where re-cleaning was required. Constant monitoring, recleaning and sign-off documentation provided reassurance that the building envelope was being progressively tightened, and construction contamination was being removed and controlled in greater and greater measure.
Cleaning was applied in a cascading, stepped manner, going from clean to less-clean, and followed fab process and tooling-up priorities until the entire complex reached its final states of classification. Fab areas were certified at Class 1 submicron levels, support areas and labs at Class 10 to 100, and periphery support zones at Class 1,000. Fan decks concluded at Class 10,000, and sub-fab areas at 10,000. It`s also noteworthy that 300,000 ft.2 of DEC`s facility existed at better than Class 100 by facility completion.
DEC`S contamination control in construction of its 450,000 ft.2 cleanroom in Hudson, MA was intensive, ongoing and followed each phase of construction rather than a one-step final cleanup at facility completion.
The construction contractor implemented guidelines to achieve the desired level of protocol at construction completion and immediate readiness for fab production. A clean zone director helped ensure protocol was met during construction. Ongoing construction cleaning was outsourced to a dedicated cleanroom cleaning company adhering to three levels of protocol–gross, intermediate and precision cleaning.
Progressively finer levels of cleanliness were achieved to meet Class 100 or better status at construction completion.
Advantages to Owner
Clean build construction, though initially more expensive than traditional methods, prevents the building itself from being a source of contamination, and produces a facility that`s immediately “process ready.”
When fab processes begin, fewer defects result, increasing profits and shortening return on investment time. Employing a specialty cleaning firm reduces management levels and increases cleanliness levels during construction.
After construction, certified cleaning technicians that are already familiar with the site and its requirements may be contracted to perform daily maintenance, eliminating downtime and learning curve delays, while ensuring cleanliness and long-term profitability. n
Larry Mainers is president and chairman of TEC International, a precision cleaning firm with offices located throughout the United States and internationally. He has extensive experience in cleanroom-critical applications, including pre- and post-construction work, return air duct, interstitial, and subfloor cleaning, airborne and surface particle monitoring techniques, wet bench and laminar flow testing, and regular maintenance of cleanroom environments. Specializing in Class 10,000 to Class 1 submicron facilities, he serves as a cleanroom consultant to hi-tech construction firms, semiconductor, pharmaceutical and fiberoptic manufacturers in the United States and abroad.
Reid Rotatori is contracts manager for the Advance Technology Group of Marshall Contractors (Rumford, RI), a division specializing in cleanroom and critical construction for hi-tech process industries such as pharmaceuticals, biotechnology, R&D, food processing, and microelectronics. He has 21 years of industry experience, with the last 11 years spent developing customized “build clean” programs for state-of-the-art microelectronics fab facilities throughout the United States.
TEC International cleaning technicians used 15-gallon 150 cfm HEPA vacs, rated at 99.97
percent efficiency, to clean the Class 10,0000 fan deck area.
Criteria for Selecting a Cleanroom Cleaning Firm
Evaluate training practices and methods by examining the company`s standards and operating policy manual. Note the firm`s mission statement, orientation methods, code of ethics, safety practices, as well as information provided to employees on cleanroom contamination sources, cleaning equipment, chemicals and procedures, service schedules to be adhered to, etc. Principles–in addition to procedures–should be conveyed that permit an understanding of individual cleanroom dynamics, situations and processes. Discern how employees are trained and groomed to work on-site in your facility.
Obtain a client list and contacts to confirm the quality of services and support structure provided. Seek experienced cleaning firms with a broad cleanroom customer base.
Review an equipment inventory list showing the type and quantity of equipment available. For example, sufficient HEPA vacuum cleaners should be on hand and deployed to provide efficient cleaning of surfaces, as well as filtration of ambient air. Wipes and cleaning items should be cleanroom certified. Gowns, hoods, hairnets, booties, overboots, gloves, etc. should be inventoried and available in sufficient quantities.
Evaluate the firm`s contamination monitoring policies. Effective cleanroom cleaning can only be ensured through intensive environmental monitoring, carried out by rigorous air sampling as well as surface checks using black and oblique white lights. Documentation of results should be handled by the cleaning firm`s management, and submitted to you for periodic review to ensure that cleaning methods meet room specifications.
Select a company with a sufficiently large, skilled, low-turnover workforce. A highly trained staff equals better, more professional service and lower turnover. Lower turnover means trained “regulars” in the cleanroom, rather than temporary workers.
Verify that management and supervisory staff are committed to understanding the fab process at your cleanroom, your expectations, special site procedures for cleanroom entry, gowning policies and any particular areas of concern. Be sure their knowledge and expertise is sufficient to handle the unexpected, such as power outages, accidents, unusual contamination situations, chemical spills, etc., so that staff and process are protected and liability is minimized.n