Gas Abatement in the Semiconductor and Solar Manufacturing Industries: Abatement of Perfluorinated Compounds (PFCs) and Other High Global Warming Potential F-Gases, VOCs, and NOx

 

     Semiconductor manufacturing and solar manufacturing release powerful greenhouse gases including perfluorinated compounds (PFCs), sodium hexafluoride (SF6), and nitrogen trifluoride (NF3). PFCs, SF6, and NF3 are types of fluorinated gases, or F-gases.

     According to Wikipedia:

Fluorinated gases (F-gases) are a group of gases containing fluorine. They are divided into several types, the main of those are hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulphur hexafluoride (SF6). They are used in refrigeration, air conditioning, heat pumps, fire suppression, electronics, aerospace, magnesium industry, foam and high voltage switchgear. As they are greenhouse gases with a strong global warming potential, their use is regulated.

     Some F-gases with lower global warming potential (GWP) are being used to replace hydrofluorocarbons (HFCs) of higher GWP in refrigeration. HFCs largely replaced chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) that have even higher GWPs.

     Abatement technologies for these emissions are being improved and deployed as more semiconductor and solar panel manufacturers make emissions reductions commitments. McKinsey & Company reported in May 2022 that among semiconductor manufacturers, there were mixed levels of commitments.

 

 

In the Semiconductor Manufacturing Industry

 

     Most semiconductor manufacturing emissions are Scope 2 emissions generated by the energy that powers the facilities and runs the tools used in them. In several places around the world, this is mainly coal and other fossil fuels. Thus, recommendations for improving emissions profiles include obtaining supplies of cleaner energy.

     The breakdown of emissions by Scope is shown below. Process gas emissions are mainly gases with high GWPs, and most are far above CO2. It is also important to consider their time in the atmosphere.

      McKinsey & Company offers four levers for reducing process gas emissions in semiconductor manufacturing:

1)        Process improvements. This mainly involves incorporating emissions reduction into the engineering designs and operational parameters to optimize emissions reduction alongside cost-savings.

2)        Use of alternative chemistries. This can be effective but also can be wrought with problems as new processes and suppliers are integrated. It is also costly and time-consuming: “While fabs have already implemented some major improvements, such as increased use of NF3, many other shifts, including the replacement of NF3 with F2 or ozone, are still nascent”

3)        Gas abatement. This is currently the best means to reduce emissions in the industry and is expected to remain so in the near term. There are multiple designs for gas abatement including “point-of-use (POU) systems for individual production tools, point-of-area (POA) systems, and central abatement systems.” Costs, effects on other operations, and new metrics like ‘gas destruction and removal efficiency (DRE) are being compared for different designs. Other challenges include space constraints, limiting byproduct gases like Nox and carbon monoxide, and limiting downtime from installation and maintenance of the abatement systems.

4)        Gas recycling. This final lever could largely replace gas abatement: “Fabs can capture unutilized process gases and by-products through various means, such as membrane separation, cryogenic recovery, adsorption, and desorption. They can then refine them into pure process gases that can be used again, potentially reducing process-gas emissions. For this lever to become economically viable, researchers will need to address major challenges related to the separation of process-gas outflows and purification.”

     McKinsey & Company recommends that manufacturers develop an abatement cost curve that incorporates near-term and long-term plans. They recommend that the least expensive measures be implemented first. See below.

     In a November 2022 report McKinsey & Company gives some emissions reductions pathway scenarios for the industry. Some are shown below. They also divide Scope 1 emissions into process gases, heat transfer fluid, and fuel consumption.

     They recommend the following near-term actions:

1)        Process gas. Semiconductor fabs could feasibly install gas-abatement systems that cover 90 percent of tools on average. Processing gas chemistry would have to be optimized to lower GHG usage, such as by replacing nitrogen trifluoride (NF3) and tetraflouromethane (CF4) with fluorine (F2) gas, which has zero global warming potential.

2)        Heat transfer fluid (HTF). At least 70 percent of HTF would need to be replaced with low GWP options. Semiconductor fabs would also need to reduce chiller leakage.

3)        Fuel consumption. Semiconductor companies would need to replace the current fuel supply with clean options, such as hydrogen/biomass.

     They recommend better industry-wide collaboration on emissions reduction along the semiconductor value chain, including with tool suppliers. They also recommend more research into gas reuse and recycling and alternative chemistries.

     According to a November 2023 report by Boston Consulting Group (BCG) semiconductor emissions make up about 0.3% of global emissions. Chips with higher processing power have higher emissions. Demand for chips continues to increase. The graph below shows BCG’s three pathway scenarios to reduce emissions.

     The table below by gas abatement service provider BAZM shows GWPs of the different process gases along with decomposition temperatures which affect emissions. They note that energy use in semiconductor manufacturing ops declined by 34% from 2001 to 2015. They note:

“Combustion and Plasma destruction has primarily been responsible for impressive levels of PFC emission reductions while the performance and quantity of semiconductors are increasing. The main techniques for gas abatement include the following, either individually or in combination:” Combustion, Thermal, Chemical conversion, Plasma, Catalytic, and Water reaction.

     Gas abatement system downtown, reliability, and maintenance have been problematic in the past. Gas abatement provider consolidation has led to BAZM standardizing the gas abatement sector. Their offerings for the semiconductor and solar manufacturing industries include the following

·        The GST Suite of technologies

                      GAIA - Combustion for high flows

                      Gallant - Combustion for large substrates, e.g., solar

                      Durian - Plasma

                      Dragon - Combustion

                      SWS & Aqua – Water

·        SDS – Chemical

·        Used & Refurbished

                      Delatech CDO - Thermal

                      Vector - Water

                      Guardian – Combustion

                      Edwards, Techarmonic, etc.

 

“These systems can convert the target gases, including PFC's, from the manufacturing process waste into less-harmful by-products.”

     An Atlas gas abatement system brochure-style is shown below.

     Orla McCoy, writing in Ultra Facility notes gives three environmental drivers that constrain gas abatement. In the first case, the constraint is pushing semiconductor manufacturers to further reduce emissions with new air emissions limits. Germany has implemented nee rules on NOx emissions. NOx, or nitrogen oxides, are emitted in the wafer deposition process as the processes use nitrous oxide, ammonia and process nitrogen sources (like NF3). These NOx byproducts are notoriously difficult to abate. They also occur in the solar manufacturing industry. The second environmental constraint is that gas abatement systems currently have high water usage and high energy usage rates. The sustained high temperatures required for gas destruction, where the gases are “cracked” into less harmful gases, is the main factor in high energy use. Burn/wet point-of-use gas abatement is very common in the industry. It generates significant amounts of wastewater, up to half of the total plant wastewater. This comes from the wet scrubbers used to entrap particulate matter in the systems. Water is also used to flush the systems and to increase acidic gas pH to prevent corrosion in abatement system. The third constraint is “The ever-increasing complexity of the semiconductor manufacturing process affects gas abatement systems.” The management of gas byproducts. The use of acid gases leads to higher rates of corrosion in system components, requiring more water. One remedy is “dosing acidic waste gas inside the abatement system with alkaline chemicals – such as sodium fluoride or potassium fluoride – is a standard practice in Europe, but slowly emerging in the US.” Local or regional factors like water abundance and costs and wastewater disposal costs are factors in system adoption. Thus, water recycling and reduction of wastewater volumes are ongoing efforts. An emerging method involves “digitally connecting the process tool using the gas with the abatement technology. By doing so, the gas treatment technology can be run at idle modes or different burner intensities according to the gas and type produced.”

 

 

In the Solar Panel Manufacturing Industry

 

     As U.S. solar manufacturing continues to increase as part of the goal of onshoring some of this manufacturing aided by the Inflation Reduction Act, there is increased scrutiny on gas abatement in the industry.

     A common gas abatement technique for solar manufacturing is regenerative thermal oxidizers (RTOs). This type of gas abatement system abates volatile organic compounds, or VOCs, which include alcohols, silicones, acetates, hydrochloric acid, and other compounds. Coatings applied to panel cells or wafers to enhance strength and conductivity are what lead to the emissions. Some plants utilize multiple layers of coatings which can complicate gas abatement as different chemicals are combusted. The gas abatement systems must also be leak proof as some of these compounds in high concentrations can be deadly.

     According to Anoosheh Oskouian, CEO of Ship & Shore Environmental in a July 2023 article in Solar Builder magazine, the gas abatement systems “capture all of that from a direct source inside. On the outside, we build enclosures around the area to collect VOCs that are in the air.” “The VOCs are sucked through ducts and piping and then destructed in a process of combustion with heat.” Ship & Shore’s VOC abatement process yields water and CO2 while reducing VOC emissions from all VOCs they collect by 98-99%. It is unclear how much VOC emissions they don’t collect. 

     How much VOCs can be emitted varies by state and country:

“California, which has the most stringent air pollution rules in the country, is referred to as 10-ton area — 10 tons is the maximum a facility can send out. So, thinking back to the 98 to 99% VOC destruction — “basically, that 2% of the overall emissions can go out and they will stay below the allowable levels,” Oskouian explains. Texas is a surprisingly close second with between 10-25 tons/year.”

     U.S. EPA guidance allows variable levels of VOC emissions based on population levels relative to emission locations. The maximum allowed in rural unpopulated areas is 100 tons of VOC emissions per year. There are IRA incentives for solar manufacturing in general and also for gas abatement, including VOC abatement. To get incentives emissions must be reduced by at least 20%. Gas abatement can also lead to less toxic panels at the end of their lives. Future solar panel recycling facilities will also have to consider their emissions as heat and chemistry are often used to recover materials. Oskouian also notes:

“The panels we’ve evaluated in the U.S. have a lot more alcohol of different types instead of more harmful materials like cyanide or hydrochloric acid,” she notes. “But if we are also recycling panels that were made outside the U.S. without our domestic manufacturing regulations in mind, they may have larger amounts of the more toxic, harmful chemicals.”

     This suggests that U.S. solar panels will have better emissions and overall environmental mitigation than panels in other areas and imported panels.

     A 2010 paper in Photovoltaics International explored methods, configurations, treatment combinations of gas abatement, and environmental impacts of VOCs and NOx. Some figures from the paper are shown below. They note that:

“Such treatments usually comprise central acid scrubbing, NOx scrubbing, Volatile Organic Compound (VOC) removal and several local treatments for dust, silane, and VOCs, while caustic scrubbing is an option for monocrystalline PV cell production.”

     The oxidation systems in use are similar to those used for coal-fired power plants. Among the graphs below are system layouts, costs comparisons, treatment combinations, system schematics, and estimation of environmental impacts.  

 

 

 

 

References:

 

Sustainability in semiconductor operations: Toward net-zero production. McKinsey & Company. May 17, 2022. Sustainability at semiconductor fabs | McKinsey

Keeping the semiconductor industry on the path to net zero. McKInsey & Company. November 4, 2022. The path to net zero: Semiconductor sustainability | McKinsey

A Net Zero Plan for the Semiconductor Industry. Gaurav Tembey, Trey Sexton, Christopher Richard, Ramiro Palma, and Jan-Hinnerk Mohr. Boston Consulting Group (BCG). November 7, 2023. A Plan to Reduce Semiconductor Emissions | BCG

Greenhouse Abatement in the Semiconductor Industry. BAZM Solutions. Greenhouse Abatement in the Semiconductor Industry (bazmsolutions.com)

Gas abatement: environmental drivers and constraints. Adam Stover and Josh McCrory. Orla McCoy. Ultrafacility.  Gas abatement: environmental drivers and constraints | Insights | UltraFacility (ultrafacilityportal.io)

Gas abatement for crystalline silicon solar cell production. Martin Schottler & Susanne Rue & Mariska de Wild-Scholten. Photovoltaics International. August 1, 2010. w10020.pdf (tno.nl)

Atlas Gas Abatement Systems. Atlas? Gas Abatement Systems - EDWARDS - PDF Catalogs | Technical Documentation | Brochure (directindustry.com)

New pollution: The importance of producing PV with minimal VOCs. Chris Crowell. Solar Builder Magazine. July 25, 2023. New pollution: The importance of producing PV with minimal VOCs (solarbuildermag.com)

Fluorinated gases. Wikipedia. Fluorinated gases - Wikipedia