By Debra Vogler, SEMI
The introduction of new materials, such as III-Vs, into high-volume manufacturing of semiconductors, likely will occur sometime around the 7nm and/or 5nm nodes. III-V’s introduction, along with the potential transition to 450mm wafers, and the increasing expansion of global regulatory requirements, will heighten environmental, health and safety (EHS) concerns that must be addressed as the industry goes forward. The Sustainable Manufacturing Forum to be held in conjunction with SEMICON West 2014, will feature experts in the manufacture of semiconductors, microelectronics, nanoelectronics, photovoltaics, and other high-tech products.
One of the Sustainable Manufacturing Forum speakers, Richard Hill, Technology Infrastructure manager at SEMATECH, will discuss how the addition of III-V materials into the high-volume manufacture of semiconductors will bring sustainability issues to the forefront, primarily driven by the toxicity of arsenic that is used in much greater quantities in III-V production. Challenges include wastewater treatment, toxic gas detection control and abatement, and the need for robust protocols to ensure operator and maintenance personnel safety. Hill will speak at the Next Generation Eco Fab session on July 9 at SEMICON West.
SEMATECH recently completed a joint study of III-V EHS challenges with the College of Nanoscale Science and Engineering (SUNY CNSE). The assessment consisted of running 300mm wafers through a representative 5nm III-V process flow (Figure 1). (Many semiconductor industry experts agree that III-V materials will enter the process flows in high volumes at 5nm.) Among the processes that will pose the greatest challenges with respect to III-V materials are MOCVD, CMP, wet etch/clean, dry etch, and film deposition. The project was heavily focused on understanding the levels of arsenic that would be present in wastewater, as well as loading of other III-V materials. The impact of III-V outgassing that could occur during processing and the amounts of gases that could be released when a tool is opened for maintenance were of particular interest in the project.
Among the high-level challenges associated with wet etch are the potential for arsine and phosphine outgassing (during processing).
“Wet etch tools are designed to have a controlled environment,” said Hill, “but they are not like high-vacuum systems that are designed to contain toxic gases.” Hill told SEMI that if the exhaust system fails during the processing of a wafer, it is critical to know the risks and ensure mitigation. The SEMATECH/CNSE project looked at a range of different chemistries and identified those that are low risk for arsine and phosphine generation (and therefore, a low risk of outgassing) and those that had a high risk of outgassing. The low risk chemistries are, naturally, the ones that the industry should try to design into a III-V flow.
The joint project also evaluated the III-V loading in wastewater from the wet etch process. “There were measurable quantities of arsenic in the waste stream,” said Hill. Though he added that while the levels weren’t significantly high, some treatment of the waste water would have to be done depending on what’s allowable within local discharge limits and permits. With the industry looking ahead to 5nm and already designing the fabs of the future, Hill believes that these results will be important for specifying wastewater treatment.
The joint SEMATECH/CNSE project also evaluated the wastewater stream from the burn wet scrubber when III-V materials are used in a contact etch (dry) process. The study found measurable arsenic in the wastewater. “Fabs of the future will need wet treatment facilities for arsenic and indium,” Hill told SEMI. “In recent years, concerns about indium have been elevated, and we believe that tighter restrictions on it will be introduced in the future.” Chamber clean is also critical when etching (dry) III-V materials. “If you don’t do the right type of cleaning regimen, you could have next-wafer contamination.” Additionally, without the proper protocol, maintenance personnel could be exposed to arsine or phosphine when the chamber is opened, depending on the process. The cleaning protocol is highly dependent on the type of etch being done, and each type could have different requirements.
For Hill, the key takeaway from the joint evaluation was that, while there are risks when processing III-V materials, there are no showstoppers — solutions can be engineered. “People should take these risks seriously, but they shouldn’t be scared off by them,” said Hill.
Sustainability and the Role of Collaboration and Standards
Steve Moffatt, CTO, Front-end Equipment at Applied Materials (also a speaker at the Next Generation Eco Fab session at the Sustainable Manufacturing Forum at SEMICON West), told SEMI that many established procedures for dealing with arsine and phosphine already exist. He views the efforts by the industry going forward as one of accurately quantifying the size and scope of the problem. “The methods are in place, but the absolute quantities of III-Vs will be substantially higher,” said Moffatt.
Additionally, other emissions (e.g., PFCs) that are well regulated and generally understood, will see an increase in the quantities as a result of more layers being processed for 3D chips. Even the potential transition to 450mm wafers will figure into the industry’s need for a more accurate scope of the EHS challenges involved. The increase in wafer size will naturally lead to larger manufacturing equipment noted Moffatt and that, in turn, will drive increases in energy, water, and process chemical consumption at both the tool and fab levels.
As regulatory pressure increases on a global scale, the situation also becomes more complex. Beyond the use of new materials such as III-Vs and nanomaterials, Moffatt commented that new methods of energetics (i.e., ways of putting energy into a processing system) will require very careful and close assessment of the risk control measures. Another sustainability issue arises from the basic fact that, as opposed to the highly prevalent element of silicon in the earth’s crust, many of the newer materials being used in higher quantities for semiconductor manufacturing (e.g.,Ga, As, etc.) are much less abundant. These exotic materials, of necessity, must be handled in the most efficient of ways.
Going forward, there will be increased regulatory pressure to reduce a fab’s carbon footprint and produce more sustainable products. Moffatt says the industry can expect more pressure to reduce greenhouse gas (GHG) emissions along with adhering to conflict minerals regulations and managing EHS concerns throughout the entire life-cycle of a product (Figure 2). “One company can’t do it on its own, it’s a life-cycle consideration,” said Moffatt. “If we have the right collaboration together, we have a greater probability with the right kinds of standards of bringing good, effective green chemistry solutions to high-value problems.”
Regarding standards activities on energetics, Moffatt pointed to ongoing collaboration and hazard assessment between SEMI, SEMATECH and other industry groups.
“We will need to continually evaluate the need for additional standards activities — both new and updates — in addition to industry collaboration on “Green” chemistry,” said Moffatt. “As a starting point, sustainability concerns could be built into the initial assessment of new chemicals and processes, which will begin the discussion and raise awareness of these issues.”
Hill (SEMATECH) and Moffatt (Applied Materials) will be joined by speakers from IMEC, Intel, Samsung, Air Products, and MW Group at the “Next Generation Eco Fab” session of the Sustainable Manufacturing Forum at SEMICON West 2014, July 7-10 in San Francisco, Calif. For more information, visit: http://www.semiconwest.org.