2024 Research Needs Document: Environment Safety and Health
Semiconductor Research Corp. (SRC)
Research Triangle Park, NC 27703

Chapter 2 of the Microelectronics and Advanced Packaging Technologies Roadmap (MAPT) outlines key research priorities in the areas of environmental sustainability and energy efficiency to ensure sustainable growth of microelectronics. The Call-for-Research document issued by the SRC environment, safety, and health (ESH) technical advisory board provides additional specifications to aide in the development of research proposals to address environmental sustainability challenges outlined in Chapter 2 of the MAPT roadmap pertaining to sustainable semiconductor manufacturing.

Research Needs

MAPT Chapter 2: Section 2.3.3. Material selection

To continue to drive innovation and achieve the desired functionality required by today's market, the demand for new and innovative materials and chemistries is increasing. At the same time, there is also a need to develop more efficient, more effective, and safer materials and chemistries. New integrated software tools are needed to bring together leading-edge computational tools (e.g., modeling and simulation from atomistic to mesoscale) and high-throughput experimental tools (e.g., physical chemical characterization and synthesis), while simultaneously allowing for predictions and/ or optimization against key performance metrics. AI for materials discovery and materials understanding has the potential to substantially accelerate the development and application of more environmentally sustainable materials and chemistries (i.e., safer, biodegradable, improved recyclability, etc.). Specific needs in this area include:

Projects that advance and validate structure-function and structure property estimation methods for basic physicochemical data like vapor pressure and aqueous solubility for chemicals like PFAS and oniums are desired.

• Advancements in computational toxicology methods are needed to screen and enable new chemicals and technologies, address concerns with existing chemicals, and inform the selection of viable alternatives.
• Computational tools are needed to simulate and explore new chemistries and chemical synthesis routes and to facilitate wafer device fabrication process invention, development and optimization. Aided by computational methods for chemical property and toxicity evaluation (environmental and human health), these methods would facilitate advanced wafer technology development with effective, optimized, safe, efficient, and benign processes.
• The industry is looking for viable alternatives to PFAS (MAPT Roadmap table 2.3) in the many semiconductor industry specific areas in which they are currently used (photolithography, plasma etch and chamber clean, heat transfer fluids, lubricants and pump oils, fluoropolymer plastics, electronics packaging). The Semiconductor Industry Association (SIA) website (www.semiconductors.org/pfas) contains extensive documentation of the application specific uses in the semiconductor industry and the associated performance requirements.

MAPT Chapter 2: Section 2.3.4. Wafer Fabrication

The manufacturing of microelectronics is resource intensive, and considerations for the potential environmental impact of a new technology node need to be an integral part of all phases of the technology, from research to product design and development to manufacturing at scale. Minimizing the environmental impact of microelectronics and associated products will require continued commitment and collaboration across the entire semiconductor supply chain and ecosystem to:

• Lower greenhouse gas (GHG) emissions (e.g., CO₂, SF₆, CH₄, N₂O, HFCs, PFCs, NF₃, etc.).[1] 
• Develop processes that minimize environmental impact and waste generation, minimizing the use of energy, water, and input materials and other natural resources.
• Identify alternative chemistries and processing methods that are safer, more efficient, and more effective.
• Develop circular economy pathways for process materials and end-of-life finished goods to increase reuse or recycling.

Specific needs in this area include:

• Potential use of digital twins for key manufacturing processes that with the aid of experimental validation might be used to help design and optimize processes for reduced chemical, water, and energy input; and reduced air emissions, wastewater, and waste generation.

Photolithography

• Following the photolithography imaging process, residual photoresist and antireflective coatings are stripped from wafers using photoresist stripping operations. Plasma “ashing”, solvent stripping, and aqueous stripping are the principal photoresist stripping methods. Characterization of the PFAS occurrence and fate in photoresist plasma stripping and photoresist wet chemical stripping operations like the hot sulfuric-peroxide (H2SO4:H2O2) process would be useful.
• Alternatives to the use of NMP as a photoresist solvent and photoresist stripping agents are desired.

Etching Gases/ Chamber Cleans/ Chemical Deposition

• During certain plasma etching operations that utilize a PFC gas, a polymer deposit is formed on the sidewall of the etched feature to facilitate preferential removal of wafer substrate from the bottom of the feature, and achieve high aspect ratio structures. Characterization of the side wall polymer composition and fate would advance the release modeling.
• PFC/HFC alternatives and/or optimized processes that use smaller quantities and produce smaller waste streams with lower GWP are desired. Areas of interest include process and recipe optimization, and improved end point detection, among others.
• Develop alternatives to N2O for use in deposition processes. N2O is used extensively in deposition processes and is difficult to abate. As such, it represents one of the largest unabated GWG emissions in the industry. 
• Develop and validate improved air emission measurement and control methods. In addition to point of use (POU) abatement systems that are conventionally used for PFC and other gases, fabs also employ "house" level wet type scrubbers and thermal abatement processes.  Thermal abatement has conventionally been employed to mitigate stack emissions of organic solvents, but there is increasing interest in the potential use of “house” level systems for the abatement of PFC gases and potential PFAS emissions.
• Develop PFC and HFC abatement systems that can achieve higher DREs (99.99%) without generating hazardous air pollutants, NOx, CO, and other GHGs. CF₄, for instance, is particularly difficult to destroy and can be created in some processes. Similarly, NOx/N2O can be created during thermal oxidation of PFCs, as well as in process gas and boiler use. Improved abatement and fundamental learning on abatement process chemistry and design are desired.
• Develop and demonstrate N₂O reduction systems that do not produce large amounts of NOx.

Chemical mechanical planarization (CMP) & Wet Chemistries

• Develop and demonstrate more efficient and benign wet etchant and CMP (chemical mechanical planarization) processes and process formulations.  CMP is one of the largest consumptions of ultrapure water and producers of wastewater. 

• Wet chemical etchants and wafer cleaning formulations are used in large quantities and generate significant quantities of aqueous effluents. Alternative and/or optimized wet etching and cleaning formulations and processes with reduced chemical usage and minimal waste generation, and benign chemistries are a key goals.

Heat Transfer Fluids

• Lower GWP heat transfer fluids that are effective in semiconductor manufacturing heat transfer applications and which do not have increased flammability or other safety concerns are of great interest.

MAPT Chapter 2: Section 2.3.5 Backend Assembly, Test, and Packaging Operations

Packages need to be designed for recycling and recovery in mind. Projects in this area could include efforts to:

• Understand if packages can be designed to be more easily disassembled for recycling or repair of a defective chiplets. 
• Develop alternatives for PFAS used in substrate materials, underfills, adhesives and other packaging materials which do not have increased flammability or other safety concerns are also of great interest.
• Develop a multi-chiplet package such that defective or malfunctioning components can be isolated and removed enabling more efficient repairs, upgrades, or modifications without replacing the entire system.

MAPT Chapter 2: Section 2.3.6. Chemical Waste and Aqueous Effluent

For the continued growth of the industry, it is imperative to develop recycling, treatment, and abatement technologies to ensure that the release of chemicals and GHG is minimal. In addition, process effluent should be characterized during the development phase to ensure an understanding of process byproducts so that leading-edge semiconductor devices can be manufactured in the safest possible manner and environmental issues can be addressed proactively.

Chemical waste

The generation, recycling, and disposal of chemical wastes is an important aspect of the industry's intersects with the environment, and efforts need to continue to identify opportunities to increase chemical recycling and make semiconductor manufacturing processes more circular by decreasing the use of raw materials and minimizing waste generation. Specific research needs in this area include:

• Develop and demonstrate efficient recovery and purification processes for chemicals, gases, and other raw materials, including water.
• Where possible, utilize circular pathways. Important areas of interest include:
  • Improved characterization and control methods, including sensors and smart systems. For example, studies looking at the design and demonstration of more intelligent tools and environmental control processes that utilize sensors to monitor and optimize and reduce  chemical, water and energy use with reduced process emissions are of interest.

  • Recovery of solvents, CMP particles, TMAH, acids, bases, ammonia, hydrogen peroxide, etc.

  • Recovery of gases including PFCs and HFCs, ammonia, etc.

  • Recovery of metals from wastewaters and sludges.

  • Wet chemical technology advancements, such as concentrating techniques for separation of water/solvent and other mixtures, for improved handling, treatment, and recycling of mixed waste streams, which in turn can reduce hazardous waste generation.

Aqueous effluent

• Semiconductor fabs utilize thousands of meters of polymer plastic piping and tubing consisting of materials like PTFE and HDPE. Likewise manufacturing tools and infrastructure employ thousands of square meters of polymer plastics that are in contact with fluids, some of which are discharged in aqueous effluents. Projects that quantify the extent to which the PFAS in the fluorinated polymer or coatings in these application materials may leach into process fluids and appear in fab effluents as PFAS would be useful. 
• Develop and validate advanced characterization methods, including potential sensors, for measuring and managing chemicals of interest in aqueous effluent streams.
• The current general state of knowledge regarding the factors that control the biodegradation of organic chemicals is poorly developed. Desirable projects include those that characterize the biodegradability of organic chemicals in biological wastewater treatment processes and that elucidate factors like biomass diversity and the POTW design and operational variables that may influence the rate and extent of biodegradation. Chemicals of interest include TMAH, azoles, diaryliodoniums and triarylsulfoniums, isopropyl and other alcohols, photoresist polymers, surfactants, and complexing agents, among others. Advancements in the state of knowledge regarding biodegradation mechanism, pathways, and dependencies may lead to new opportunities for employing resource efficient biotreatment processes.
• Certain azoles and isothiazolinones, and related chemicals serve essential roles as wafer passivating agents and also as corrosion inhibitors in cooling water systems. However, some of these chemicals are known to be potent nitrification inhibitors that can impact biological wastewater treatment systems. The current general state of knowledge regarding the factors that cause a chemical to inhibit biological nitrification is poorly developed. Desired projects include those that:
  • characterize the influence of molecular structure, biomass acclimatization, and other factors on biological nitrification;
  • develop improved test methods for quantifying nitrification inhibition and for tracing the sources of nitrification inhibition within complex waste water systems; and
  • develop alternative formulations that can be demonstrated to be effective alternatives and that do not have inhibitory or other toxicity impacts are needed.
• Develop and demonstrate technology for the separation of PFAS chemicals from semiconductor wastewater effluents. Characterize the factors like molecular structure and wastewater matrix composition that influence separation efficiency and cost. PFAS destruction methods should utilize a fluorine balance to demonstrate the extent of mineralization.
• Develop and demonstrate water re-use technology and management methods. Pre-treatment requirements and efficient methods for handling RO reject, are also if interest, as are total cost of operation and performance metrics.
• Develop fab water and waste management models that tie the flow and composition of wastewater effluents to chemical usage records and key wastewater generating processes, and which can be employed to guide fab wastewater system designs and optimize treatment processes for minimal chemical and energy usage and maximized removal.

Proposals: A number of factors are considered during proposal evaluations. A few factors that bear consideration submitting a proposal include:

• PI should summarize their relevant laboratory and experimental capabilities, including the availability of analytical instrumentation.
• Novel metrology methods including sensors should be validated using established analytical methods.
• Models and computations should be validated with real measurements, or at least employ measurements that have been reported in the literature.
• Proposed treatment and recycling methodologies should employ performance metrics that benchmark a new process against competing technologies and identify the total cost of operation including energy costs and consumables.
• Whereas chemical formulation and fundamental process development are often best initiated at the laboratory scale, the results of a project are more likely to be impactful if they can be demonstrated at the production scale on semiconductor manufacturing tools. This may require partnering with device makers and/or equipment suppliers, or by participating in collaborative research facilities where production scale semiconductor manufacturing tools are available.

Direct link to Chapter 2: srcmapt.org/chapter2/

[1] CO₂: carbon dioxide, SF₆: sulfur hexafluoride, CH₄: methane, N₂O: nitrous oxide, HFCs: hydrofluorocarbons, PFCs: perfluorocarbons, NF₃: nitrogen trifluoride