At no time in the last 25 years have semiconductors been more valuable than now. The global pandemic dramatically constrained supply, making it impossible for car manufacturers to build new cars. Every part of those silicon wafers in the lab is worth far more than three years ago. Valuable wafers must be disposed of for one reason more than any other - contaminants. Imagine having to dispose of a 300mm wafer worth $10,000 or more because some sub-micron particles are bridging circuits. If you’ve ever seen the inspection pictures from your lab’s scanning electron microscope or defect analysis group, you’ve seen what one tiny particle can do.
Cleanrooms have a more significant impact on the productivity and profitability of the semiconductor industry than any other. The need for keeping contaminants out of the air and off surfaces is constant and critical. Here is a little background and the most effective ways to keep those tiny particles off your chips.
Semiconductors need to be made in cleanrooms because microscopic circuits at the sub-nanoscale are smaller than many particles floating in the air. Those particles can destroy a semiconductor just by hitting the silicon wafer. Estimates show that yields are as low as 55% per 300mm wafer in many semiconductor labs.
The entire manufacturing process, from etching to photoresist and lithography, has to happen in a cleanroom to protect chips throughout the process.
Cleanroom Requirements
Semiconductor cleanrooms usually have to comply with ISO 14644-1 Class 5. Lower is even better, of course, but ISO5 stipulates a maximum particle count per foot area of 3,520 ≤0.5 um. They must also have a strict quality control system to monitor and maintain classification standards. Anomalies in cleanroom compliance can cost semiconductor manufacturers millions of dollars.
Keeping Your Chips Clean
Keeping semiconductors clean is a function of keeping particles out of the air, and keeping particles out of the atmosphere requires equipment, procedures, people, and lots of cleaning. Let’s get into each one:
Equipment
Essential in maintaining labs and semiconductors cleaning is equipment cycling and filtering the air. HEPA filters and ionizers need to be adequately maintained, which means cleaning filters and checking and adjusting ionizers. Air circulation systems also should be checked regularly.
Procedures and People
Procedures and people are intertwined as processes must be taught to every lab employee and reaffirmed daily. They already know that the wafer box they carry can be worth $100,000 but might not know that every step they take puts particles in the air. It can be hard to comprehend that there are millions of particles per foot area in the cafeteria versus less than 3,750 in the lab.
Everything from wiping down workstations to what water to use is crucial. Most likely, your semiconductor cleanroom is a 24-hour operation, so employees are always present and part of the cleaning. Their training and continual awareness are some of the most important things to maintaining ISO classification. Something as simple as signage and reminders in team meetings can make all of the difference. Make sure they know the procedures and their roles in them.
Cleaning
There is nothing more important for keeping those semiconductors clean than cleaning—chips like ISO standards and the clean air they represent. An impeccable cleanroom cleaning classification means daily, weekly, quarterly, and as-needed cleaning regimens.
Daily Cleaning
Daily cleaning is the most essential of all procedures. In a 24-7 lab, there is no way to pre-clean before the staff comes into work, making cleaning an ongoing task that might have several employees solely dedicated to its execution. Some of the essential components of daily cleaning are:
- Cleaning multiple times daily in a semiconductor cleanroom, including mopping and vacuuming to dry.
- Use a HEPA filter vacuum to vacuum walls.
- All windows and pass-throughs need to be washed and wiped dry.
- Employees must wipe down all work areas at shift end and maybe even more frequently.
- Supplies and products always need to be appropriately stored to prevent pollution.
Weekly Cleaning
Weekly Cleanroom Cleaning might even be twice weekly in continually staffed cleanrooms. The more often, the better. It includes:
- A specific cleaning solution and distilled water are used to mop floors with a HEPA filter vacuum used for drying.
- Walls receive the same treatment.
Quarterly Cleaning
Quarterly cleaning often includes only quarterly action items and things other cleanrooms might do every six months. Semiconductors cleanrooms are busy places, and meeting and exceeding ISO standards requires more work and greater vigilance. These quarterly activities should include complete checks on filters and ionization systems.
As-Needed Cleaning
As-Needed Cleaning will be in your procedures as an activity performed based on awareness. As things show signs of wear or indicate contamination, as-needed cleaning comes into play and can be:
- Wash ceilings regularly to remove deposits and residue.
- Wipe down light lenses.
- Sticky mats need to be changed the minute they show wear.
Antibacterial Fogging
Antibacterial fogging deserves special mention as an occasional cleaning practice, and biological contaminants can be especially problematic for cleanrooms. Hydrogen peroxide fogging uses aerosolized hydrogen peroxide to destroy bacteria, mold, and microbes. It is a safe and effective cleaning method that leaves no residue behind. Employees can return to the cleanroom 24 hours after cleaning, which means this will be one of those rarer events due to monetary loss but still necessary to prevent more significant financial loss caused by not doing it.
Those tiny chips are more valuable than since the early and mid-’90s, and they thrive in lab cleanrooms that get lots of attention paid to them. Experts in Cleanroom Cleaning are among the best investments a facilities manager can make when even a 2% increase in yield can mean millions more in revenue. In semiconductor labs, cleanrooms are constantly in use and need incredible attention to detail in their cleaning. It needs to be as often as possible when one contamination incident might be incredibly costly. Reach out to Pegasus today for expert semiconductor cleaning.
