Friday, July 23, 2021

Green CVD—Toward a sustainable philosophy for thin film deposition by chemical vapor deposition

Thin films of materials are critical components for most areas of sustainable technologies, making thin film techniques, such as chemical vapor deposition (CVD), instrumental for a sustainable future. It is, therefore, of great importance to critically consider the sustainability aspects of CVD processes themselves used to make thin films for sustainable technologies. Here, we point to several common practices in CVD that are not sustainable. From these, we offer a perspective on several principles for a sustainable, “Green CVD” philosophy, which we hope will spur research on how to make CVD more sustainable without affecting the properties of the deposited film. We hope that these principles can be developed by the research community over time and be used to establish research on how to make CVD more sustainable and that a Green CVD philosophy can develop new research directions for both precursor and reactor design to reduce the precursor and energy consumption in CVD processes.




Electrical energy consumption and greenhouse gas emission in 300 mm logic wafer production for relevant technology nodes in production in 2021 and to be ramped up in the next five years.

We foresee a new research field focused on developing more sustainable CVD processes without impacting the performance of the deposited film negatively. To develop this, we suggest an adaption of a philosophy similar to Green Chemistry,8 a philosophy for all areas of chemistry and chemical engineering to make more sustainable processes and products. Green chemistry focuses on reducing the amount of hazardous materials used and generated, the amount of energy consumed, and designing less harmful molecules. Here, we outline suggestions for such a Green CVD philosophy

A Green CVD philosophy needs to focus on reducing the total energy consumption, reducing molecular consumption by increasing the efficiency in atom usage, and reducing the use of and formation of hazardous molecules. This should be done for the whole process chain of a CVD process—from precursor synthesis to waste gas abatement. A sustainable CVD process must also take an active stand against human rights abuse throughout the whole materials chain, use renewable energy for CVD equipment, and make use of the excess heat produced by CVD equipment. 

Summary of a suggested Green CVD philosophy

From this breakdown of the CVD process, we suggest the following principles to summarize a sustainable Green CVD philosophy:
(1) Use precursors that can be supplied to the process in close to the stoichiometric ratios in the target film to reduce molecular waste.
(2) Use precursors that undergo reactions with lower activation energies to reduce energy consumption and molecular waste.
(3) Use less hazardous precursor molecules to make the CVD process safer.
(4) Use precursors that produce less harmful by-products that are easier to handle.
(5) Minimize waste and energy consumption in the precursor supply chain.
(6) Minimize the thermal budget and vacuum volume of the CVD reactors.
(7) Use the most energy-efficient way to activate the deposition chemistry, including plasma methods.
(8) Recycle unconsumed CVD gases and precursors.
(9) Identify, prevent, address, and account for human rights abuses in the CVD supply chain.
(10) Use renewable energy for the CVD process and harvest excess heat.

Finally, we appreciate that industry is reluctant to change precursors and CVD processes that have been successfully brought into high volume production. As we have already pointed out, the research area of Green CVD should strive to make a given CVD process more sustainable without causing negative effects on the performance of the deposited film. Ideally, Green CVD should not affect the price of the CVD processing step either. It is very reasonable to expect that the demands for more sustainable production will increase and with that a need for more sustainable CVD. As in other research, a strong collaboration between industry and academia will strengthen the Green CVD development effort.
Full article in JVSTA: 

Green CVD—Toward a sustainable philosophy for thin film deposition by chemical vapor deposition
Journal of Vacuum Science & Technology A 39, 051001, (2021); https://doi.org/10.1116/6.0001125  Henrik Pedersen, Seán T. Barry, and Jonas Sundqvist


 

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