Sustainable Manufacturing

By Chris Jones, Edwards Vacuum

Regular followers of this blog will notice a shift in focus with this post. For the last year or so we have covered issues related to service and support for vacuum and abatement systems that enable semiconductor processes. With this post we will shift our focus to the more general topic of sustainability in semiconductor manufacturing. In a recent internal review that included 15 fabs and 3 equipment manufacturers from our customer base, sustainability, circular economy, and emissions and waste management were among the highest priorities of manufacturers and stakeholders. Although semiconductor manufacturing is not among the largest contributors to global warming, its contributions are measurable and significant. It is incumbent upon us to do everything we can to limit negative environmental effects of our activities.

IPCC Report

The Intergovernmental Panel on Climate Change (IPCC) recently released its 6^th assessment report (AR6) on the physical science basis of climate change. The report includes detailed predictions that have achieved nearly complete acceptance within the scientific community and paints a dire picture of climate changes that will almost certainly occur if humans do not curtail their climate changing activities. Major conclusions enumerated in the report’s summary for policymakers include

• It is unequivocal that human influence has warmed the atmosphere, ocean and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred.
• The scale of recent changes across the climate system as a whole and the present state of many aspects of the climate system are unprecedented over many centuries to many thousands of years.
• Human-induced climate change is already affecting many weather and climate extremes in every region across the globe. Evidence of observed changes in extremes such as heatwaves, heavy precipitation, droughts, and tropical cyclones, and, in particular, their attribution to human influence, has strengthened since AR5.
• Improved knowledge of climate processes, paleoclimate evidence and the response of the climate system to increasing radiative forcing gives a best estimate of equilibrium climate sensitivity of 3°C with a narrower range compared to AR5.

The report goes on to describe 5 scenarios likely to result from various levels of global warming, demonstrating increasingly severe impact for higher levels of warming.

A framework for mitigation

Most discussion about ways to limit warming focus on reducing and eventually eliminating emissions of greenhouse gases that are the underlying cause of global warming. There is evolving consensus that some form of carbon pricing approach is required, which applies economic pressure to reduce emissions by forcing emitters to pay the cost incurred by all for their emissions into a commonly shared environment. At this point, policy makers are struggling just to establish the basic concepts and definitions needed to make such a program work. Understanding the evolving terminology of these schemes is essential background for any discussion of the topic.

Concepts and Terminology

Greenhouse Gases (GHG)

Light from the sun hits and warms the earth, which re-emits some of that energy as infra-red radiation. Greenhouse gases in the atmosphere absorb the infra-red light and become warmer. The warming atmosphere induces changes throughout the environment – the warmer the temperature, the more severe the changes. CO₂, CH₄, CF₄, SF₆, N₂O, NF₃ are some of the greenhouse gases released by the semiconductor industry. Some gases are long-lived and absorb more infra-red radiation than CO₂. The best solution is to reduce the use of greenhouse gases or substitute gases that are easier to destroy (such as replacing CF₄ with NF₃ where possible).

Global Warming Potential (GWP)

The Global Warming Potential (GWP) was developed to allow comparisons of the global warming impacts of different gases. Specifically, it is a measure of how much energy the emissions of 1 ton of a gas will absorb over a given period, relative to the emissions of 1 ton of carbon dioxide (CO₂). The larger its GWP, the more a gas warms the earth compared to CO₂. The period usually used for GWPs is 100 years. GWPs provide a common unit of measure, which allows analysts to add up emissions estimates of different gases and allows policymakers to compare emissions reduction opportunities across sectors and gases. CO₂ has a GWP of 1 (by definition) but is also the major greenhouse gas in the atmosphere. GWPs for other gases commonly used in the semiconductor industry are much higher: CH₄ – 28, N₂O – 265, CF₄ – 6,630, NF₃ – 16,100, SF₆ – 23,500 (AR5).

Greenhouse Gas Protocol (GHGP)

GHG Protocol (GHGP) establishes comprehensive global standardized frameworks to measure and manage greenhouse gas (GHG) emissions from private and public sector operations, value chains and mitigation actions. The GHG Protocol (GHGP) has defined three scopes of emissions. The scopes correlate to who owns those emissions and the level of control applicable to changing those emission levels at each stage.

• Scope 1 – Direct GHG emissions directly from operations that are owned or controlled by the reporting company (boilers, vehicles, process gases).
• Scope 2 – Indirect GHG emissions by others from the generation of purchased or acquired electricity, steam, heating, or cooling consumed by the reporting company
• Scope 3 – All indirect emissions (not included in scope 2) that occur in the value chain of the reporting company, including both upstream (from suppliers) and downstream emissions (transport, distribution, storage).

Climate change and neutrality statements – the challenge

A special report issued in 2018 by the IPCC said that countries must bring carbon dioxide emissions to “net zero” by 2050 to keep global warming to within 1.5 °C of pre-industrial levels. Generally, there is less agreement as to which gases must be included in the net-zero definition. Even the 2018 report uses CO_2e, CO_2eq, and CO₂. This has created ambiguity, and countries and organizations have defined net zero according to their own criteria. In Sept 2020, the CDP (formerly the carbon disclosure project) developed methods on behalf of the Science Based Targets Initiative (SBTi) for setting and assessing net-zero targets based on robust climate science.

Other terms are also used to describe GHG emissions, such as “carbon neutral”. Differences among definitions are problematic. For instance, China’s definition of “carbon neutral” only includes CO₂ itself. The EU has adopted “climate neutral”, which includes all GHGs. Other methods for zero and neutral assessments exist, and the ambiguity problem has yet to be resolved.

Carbon Neutral versus Net Zero

Carbon neutral and net-zero – are often used interchangeably but are very different. Carbon neutrality is defined by the PAS 2060 standard as “a condition in which during a specified period there has been no net increase in the global emission of greenhouse gases to the atmosphere as a result of the greenhouse gas emissions associated with the subject during the same period”. The “period” aspect increases ambiguity by failing to declare absolute emissions. Net-zero definitions also vary. The CDP clearly defines net zero targets that include GHGP scope 1, 2 and 3 emissions and must align to a 1.5°C science-based targets. Carbon neutrality for an organization only requires scope 1 and 2. Scope 3 emissions are encouraged but not mandatory and the level of temperature ambition for carbon neutrality is rarely specified.

Carbon Capture

The technologies used to capture and use or permanently store carbon dioxide are known as carbon capture and storage (CCS) or carbon capture, utilization, and storage (CCUS). These technologies separate CO₂ from the exhaust gases of industrial processes by using CO₂-absorbing chemicals, pressure changes or membrane filters. Capturing CO₂ uses energy, but work is ongoing to reduce both the energy use and other costs. One example of CCS is the capture, compression, and transport of CO₂ to a geological formation, where it is injected beneath a non-permeable barrier rock that prevents the CO₂ from migrating upwards. Once injection has finished, the well is plugged. The CO₂ eventually combines chemically with elements found in the surrounding salty water and remains stored between impermeable layers of rock indefinitely. Potentially, CCS can permanently store huge amounts of CO₂. In an alternative to storage, CO₂ can be used as a raw material to make plastics, concrete, chemical reactants, and synthetic fuels.

Carbon Offsets and Credits

Carbon offsets represent emission reductions that are achieved outside a capped sector. In cap-and-trade schemes, companies are assigned emission caps that they must not exceed. If they cannot meet the cap, they may invest in a program that reduces emissions outside their sector, generating a carbon offset, which they can then apply against their own emission to meet the cap. Carbon offset investments may include reforestation, renewable energy, methane capture/combustion, and more.

Decarbonization

Decarbonization is about reducing CO₂ emissions resulting from human activity, with an eventual goal of eliminating them entirely. The 2015 Paris Agreement set an ambition to limit global warming to less than 2°C above pre-industrial levels and pursue efforts to limit it to 1.5°C – in part by pursuing net zero carbon by 2050. In practice, getting to zero net emissions requires a fundamental transformation of our economy, most importantly, shifting from fossil fuels to alternative low-carbon energy sources based on green electricity and green molecules (biofuels and hydrogen). Acceleration of decarbonization is needed to achieve the net zero goals.

Science Based Target Initiatives

An emissions reduction target is defined as ‘science-based’ if it is developed in line with the scale of reductions required to keep global warming below 1.5°C from pre-industrial levels. Currently there are two methods provided by SBTi.

• The Absolute Contraction Approach (ACA) ensures that companies setting targets deliver absolute emissions reductions in line with global decarbonization pathways. Two-thirds of the targets approved by the SBTi in 2020 used the ACA method to limit global warming to 1.5°C.
• The Sectoral Decarbonization Approach (SDA) is an alternative method that allows carbon-intensity metrics and targets to be derived from global mitigation pathways for some of the most carbon-intensive activities, such as road transportation, aviation, the generation of electricity or the production of basic materials. Some activities decarbonize faster than the global average (e.g. power generation), others are slower (e.g. aviation, cement production, etc.). The current version of the SDA supports 1.5°C targets for power generation, while the methods for other sectors rely on well-below 2°C pathways from the IEA.

Coming next

Our understanding of human impacts on the environment has expanded rapidly in recent years, and new knowledge is being added daily. In the next post to this blog, we will look specifically at semiconductor manufacturing – the flow of materials into and out of the system and the management of the waste streams that are released to the environment or transported off-site for treatment and disposal.