The Semiconductor Industry:

Fluoride is a fairly common element that does not occur in the elemental state in nature because of its high reactivity, but it accounts for about 0. 3 g/kg of the earth’s crust. Fluorides can be found in the waste streams of a number of industries to include “glass manufacturers, electroplating operations, steel and aluminum, pesticides and fertilizer, groundwater and the semiconductor industry” (Pham, 2010). Effluent levels, after treatment, can vary greatly so careful consideration needs to be given to its disposal for the fear that it may seep into our ground water or municipal water supplies.

Fluoridation in the municipal water supplies is a controversial topic, specifically in water supplies. “Most of the modern industrial world has already tried and rejected fluoridation. Rationale for adding it to tap water has been a claimed but never really proven protection against dental caries” (Pham, 2010). In fact, Fluoride is considered to be a poison in most European countries. Industry, at large, creates waste streams, but I will discuss the fluoride waste streams generated from a Semiconductor Manufacturing plant.

What is a Semiconductor? According to the Merriam Webster Dictionary, a semiconductor is any of a class of solids whose electrical conductivity is between that of a conductor and that of an insulator in being nearly as great as that of a metal at high temperatures and nearly absent at low temperatures. Products in a typical semiconductor plant can include IC, VLSI, diode and transistors.

The process for making these objects consist of a repetetive 200 plus step process which can be summarized by the diagram below, Figure 1 (.Figure 1 There has been an increase in the use of semiconductors, which is due to higher demand for high-speed ASICs, solar cells, light-emitting diodes, and laser diodes. Global consumption almost doubled from $3. 55 billion in 2000 to $7. 7 billion in 2005. Ten years ago, the industry accounted for 6% of the U. S. National Gross Product . The demand in semiconductor wafer manufacturing demands an increase in water consumption thus an increase in Hazardous Waste in those waste streams.

“Unit processes of a semiconductor fabrication facility include photolithography, oxidation, etching, dopping, and planarization” . The entire process requires high ultra clean water/ hydrofluoric acid to cleanse silicon wafers during the fabrication process. However, a dilemma lies in the size and the increase in demand of the wafer; the larger in size, the more high ultra clean water/ hydrofluoric acid is required to rinse/cleanse it. Inevitably, the increased water consumption results in a larger quantity of fluoride contained waste water.

Hydrofluoric acid is also used in the wafer etching and chamber cleaning gas in the semiconductor process. Fluoride discharge in these industries is estimated at more than 2,000 tons annually. A typical semiconductor manufacturer could produce an average of 10,000 gallons per day of mixed acidic fluoride waste . In all, it is difficult for “manufacturers to recycle fluoride after this process has been used, because caked calcium fluoride also contains high amounts of silicon as silica, which is difficult to separate from fluoride.

As silica has adverse effects on many semiconductor manufacturing processes, its presence in the caked calcium fluoride negates its value as a raw material” . Therefore, the fluoride from conventional fluoride caking systems is unusable by semiconductor manufacturers, because it is unavailable for recycle or recovery. This is definitely one drawback of using the Conventional method of fluoride removal. The Environmental Management Plan end state is to reduce the fluoride content of waste solutions before introduced in the municipal water disposal system.

There are a few methods and technologies available, but the proposed method is the Fluidized Bed Crystallizer (FBC) Treatment Technology. We will discuss two processes: 1) Conventional Coagulation/ Sedimentation Process and the Fluidized Bed Crystallizer (FBC) Treatment Technology. The Conventional Coagualtion/ Sedimentation Method is the most widely used method of treating wastewater; however, there are more disadvantages than benefits in using this method, particularly in the Semicondcutor Industry. First of all, the coagulation/sedimentation process generates wet sludge.

Disposal of this wet sludge has become increasingly difficult to dispose. Lack of landfill space can also present a problem. Episil Technologies, Inc. , for example,built an FBC, which is 20% smaller than the conventional waste water treatment plant, in Taiwan to address this very concern. Figure 2 illustrates the Conventional Coagulating sedimentation method (treatment flow) using calcium hydroxide as the treatment agent. In the reaction tank, calcium hydroxide is first added to the fluorine-containing waste sludge water and the pH is controlled.

Fluorine ions that dissolve in the waste water then combine with calcium ions and are deposited as calcium fluoride. Under certain conditions, aluminum exhibits a higher bonding strength with fluorine compared with calcium. Secondly, in the first coagulating sedimentation, the solid and liquid separates easily by using the coagulating sedimentation method. A benefit is that it can be accelerated by adding macromolecular flocculant. “Supernatant liquid after solid-liquid separation is discharged as treated water and the sedimentated portion is recovered as sludge” .

Finally, recovered sludge is decreased in volume by a dehydrator and is disposed of as industrial waste. Figure 2 Some issues presented in the Conventional Method is the “Calcium hydroxide, which is frequently sold as slaked lime and is generally inexpensive. But the solubility of calcium hydroxide is low, so the quantity of calcium hydroxide that dissolves in water as calcium ions is very little” . As a result, a large amount of the treatment agent must be added to treat the concentration of the treatment target fluorine.

Excess calcium hydroxide added in the waste water is recovered with calcium fluoride as waste sludge. To further decrease fluorine levels, a secondary treatment (second coagulating sedimentation tank) using an aluminum treatment agent is used to lower the concentration. The problems of aluminum are that aluminum is much more expensive than the calcium treatment agent, and sludge generated after treatment has a poor dehydrating capability. So, the conventional method is adequate for low fluorine concentration treatment of waste water.

FBC Technology is highly efficient in which the overall reaction is generated. There is also a slow sludge production directly resulting in a crystal purity higher than 90% and “usually worthy of being reused”. The benefits of the FCB is also a low investment due to the reduced amount of space needed and there is a low operating cost, because the process runs automatically and requires low maintenance. The FBC technology is summarized on Table 1. How does the FBC wastewater treatment technology work?

FBC uses silicate sands as carriers to recover metal salts or inorganic ions from wastewater in crystal forms. Properly controlled recycle flow provides mixing to maintain sand fluidization. Control of chemical reagent addition provides supersaturation to form crystals. Crystals are then discharged when they grow to be 1 to 2 inches in diameter. The process is illustrated below (Figure 3). (Figure 3) www. itri. org. tw/eng/lib/DownloadFile. ashx? AttNBR=715 Fabs are held accountable and must be in compliance with federal and state statutes.

Ensuring compliance brings many benefits to the company, including “increasing investments in more efficient, less polluting production techniques and technologies” (PPRC Web site). Applicable federal statutes to the Semiconductor Industry include the following: 1) Emergency Community Right-to-Know Act (EPCRA) and Toxic Release Inventory (TRI) reporting requirements 2) Clean Air Act (CAA) and National Emission Standards for Hazardous Air Pollutants (NESHAP) 3) Resource Conservation and Recovery Act (RCRA)

4) Clean Water Act (CWA) and National Discharge Pollutant Elimination System (NDPES) 5) Occupational Safety and Health Administration (OSHA) and National Institute for Occupational Safety and Health (NIOSH) The Semiconductor industry leads the way in finding innovating ways to increase Pollution Prevention (P2) opportunities and source reduction. Given the industry’s waste streams, “there is potential for cost savings, reduction in emissions and greenhouse gases, improved efficiencies and worker safety, reduced waste, and possible expanded markets” .

The International Sematech Manufacturing Initiative (ISMI) concluded that the global semiconductor industry could save almost $500 million per year in energy costs. More water-efficient equipment and processes, along with recycling and reclamation, reduce cost and environmental impact” Water is becoming scarcer in many areas where semiconductor fab plants are located; therefore, reducing water consumption makes the facility more welcome among the community. Water recycling systems are initially capital-intensive, but offer great cost savings many times over depending on how many times the water can be recycled.

Typically 60-70% of the UPW used in fabs can be recycled cost-effectively. Other benefits of reducing water use are the conservation of water for flora and fauna in the region, as well as subsequent reduction of effluents and groundwater contamination . The industry uses many chemicals to produce semiconductors, including hazardous materials. “Hazardous wastes generated costs more than $2 per pound to manage,” according to the PPRC Measurement Project. Minimizing use of chemicals reduces purchase, management and disposal costs.

It also reduces worker exposure to hazardous and toxic materials. It also reduces liability and the cost of treatment and pollution abatement. Greenhouse gas emissions contribute to global warming and climate change, but the semiconductor industry has successfully and significantly reduced emissions of perfluorocarbons (PFCs), potent greenhouse gases, since 1997(PPRC Web site). In conclusion, using the FBC technology will aid in Pollution Prevention (P2), minimize waste, and allow the plant to use reclaimed water.

Applying this technology will also reduce water and energy consumption while lessening future liabilities. Most importantly, employing the best environmental practices will allow the company to maintain a good image with employees, customers, stakeholders, and the public. Taiwan has led the way on many of these studies. In one study, when the FBC system was installed, it cost an average of $7,300 a month, while the operation of a new system cost $1,450 per month.

“The investment return was about two years” ( .Clearly, FBC is the better technique to meet the semiconductor manufacturers and environmentally conscience citizens expectations. References (n. d. ). Retrieved 04 26, 2011, from PPRC Web site: http://www. pprc. org/hubs/subsection. cfm? hub=1004&subsec=11&nav=11&CFID=3236048&CFTOKEN=29782418 Bue, L. S. (2005). Reduction of PFC Emissions: State-of-Technology Report 2005. Austin, TX: ISMI. Chion, C. F. , Lee, M. S. , Liao, C. C. , Shao, H. , & You, H. S. (1997). The Reclamation by Crystallization Technology for Semiconductor Fluoride-Containing Wastewater Treatment.

Asian Pacific Regional Conference, 573-579. Chuang, T. C. , Huang, C. J. , & Liu, J. C. (2002). Treatment of Semiconductor Wastewater by Dissolved Air Flotation. Journal of Environmental Engineering, Vol. 128, No. 10, 974-980. Jangbarwala, J. , & Krulik, G. A. (2006). USA Patent No. WO/2005/065265. Kurosaki, H. (2008). Reduction of Fluorine-Containing Industrial Waste. Oki Technical Review, 53-56. Pham, T. (2010, January 14). Retrieved April 30, 2011, from Article Alley Website: http://www. articlealley. com/article_1345156_27. html? ktrack=kcplink