The low cost of production of microelectronic components means that mobile phones and other electronic devices are an inextricable part of life. Key to such devices are semiconductor wafers, which must be clean and free from contamination; however, the need for such cleaning and the fast expansion of the industry could have devastating effect on the environment.
Removal of Contaminants from Semiconductor Components
Industry demands an effective and efficient process to remove contaminants and impurities – alkali, metals, heavy metals, organic contaminants, dopants - from semiconductor components without damaging the wafer. Without their removal, the wafer’s performance and functionality could be affected.
Cleaning of semiconductor wafers is therefore a vital stage in electronics production, one that is expected to grow to $6.8bn by 2024. There are various means of cleaning semiconductor wafers using wet chemistry-based cleaning technology and etch cleaning technology, and steps might include pre-diffusion cleaning, particulate removal, metallic ion removal, film removal and a post etch clean.
Effects of Cleaning Semiconductor Wafers on the Environment
A popular wet-chemistry based technology is rotary wafer etch cleaning which uses a chemical process to remove contamination. Processing wafers one at a time is becoming increasingly common and requires each be treated with hydrofluoric acid and ozonized water. Hydrofluoric acid is highly corrosive and dissolves many materials – including glass. It’s also an acute poison which instantly and irreversibly damages the lungs and corneas, and can interfere with body calcium metabolism leading to systematic toxicity, cardiac arrest and death. Ozonized water acts as a sanitizer, and is a strong disinfectant with may uses.
The use of such chemicals can be incredible dangerous – if used manually to clean wafer, there would need to be two people present at all times; thankfully though, such processes are automated and performed by machines.
But if these chemicals present a danger to human health, what impact do they have on the environment and our desire for clean technology?
Clean technology is any process, products or service that reduces the negative environmental impact through significant energy efficiency improvements, sustainable use of resources or environmental protection activities. This can cover quite a broad range, from recycling, to renewable energy to electric motors!
Semiconductor wafer cleaning systems, unfortunately, don’t appear to be incredibly clean, or environmentally friendly. During the cleaning process, huge amounts of ultrapure water is used, which causes water stress, and the resulting run-off can cause water acidification and toxicity. The level of severity of both acidification and toxicity depends on the sensitivity of the local ecosystem and efficiency of waste water treatment plants, but could present a danger to human health and the surrounding ecosystems
Eutrophication is also possible: as a result of cleaning processes, excessive amounts of nutrients and minerals could end up in a body of water and result in dense plant and algae growth, and oxygen depletion of the water. Again, the severity depends on the local ecosystem and treatments plants.
Building semiconductor wafers requires intensive use of raw materials, which can lead to resource depletion. And after use, if not disposed of properly, devices containing such wafers can contaminate soil, water and air due to the presence of metals and other compounds. On a positive note, consumers are now much more aware of the need to recycle their electronic goods not only to protect and prevent contamination of the environment, but also to recover the precious raw materials inside them.
The process is also incredibly energy intensive, and emissions during the cleaning process and those from general plant functioning can lead to global warming and summer smogs. The severity of such smogs depend on the sensitivity of the local ecosystem and the efficiency of volatile organic compound (VOC) treatment units within the plant.
While consumer demand drives the desire for small electronic devices containing several microelectronic chips, all of which need to be cleaned to ensure proper functionality and performance, the processes required to clean such semiconductor wafers could be detrimental to clean technology and the environment at large.
References and Further Reading