NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Gleason, et al. 1 PFC Use & Reduction in the Semiconductor Industry Prof. Karen K. Gleason, Department of Chemical Engineering, MIT Source materials contributed by : Mr. Simon Karecki & Prof. Rafael Reif Department of Electrical Engineering & Computer Science, MIT Dr. Michael T. Mocella Dupont Fluoroproducts © 1999 Massachusetts Institute of Technology. All rights reserved

NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Gleason, et al. 2 Outline l PFC usage l PFC reduction strategies

NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Gleason, et al. 3 Perfluorocompound (PFC) Nomenclature l C 2 F 6 –Perfluoroethane –Hexafluoroethane –Freon-116 –Dupont l CF 4 –Perfluoromethane –Freon-14 l CHF 3 –not truly a PFC (a HFC-hydrofluorocompound) –“PFC-like”: long atmospheric lifetime & high GWP –Fluoroform –Trifluoromethane –HFC-23 –Freon-23

NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Gleason, et al. 4 PFCs - Generally Unreactive => STABLE l Pros –low toxicity, –low explosive hazard l Cons –long lifetimes in the atmosphere (high GWP) –unaffected by current water scrubbers –difficult to abate by subsequent chemical reactions

NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Gleason, et al. 5 U.S. Semiconductor Industry PFC Purchase (1993 )

NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Gleason, et al. 6 PFCs Emitted by Other Industries l Aluminum production –Single largest source (30,000 metric tons world-wide) – CF 4 & C 2 F 6 emitted when aluminum smelting is disrupted (“anode effect”) l Electrical power distribution –Leakage of SF 6 gas electrical insulation from circuit breakers, substations, and transmission lines

NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Gleason, et al. 7 Increase of PFC use in Semiconductor Industry l Increased number of wafers per year l Increased wafer size (more material to etch per step) l Larger number of processing steps per wafer l Shift from wet to dry (gas-phase) processing l New applications (e.g. in-situ diffusion furnace cleaning)

NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Gleason, et al. 8 Commitment to PFC Reductions l PFCs have a very high global warming impact. For all practical purpose, the effects of PFCs are permanent. l The semiconductor industry (through the SIA) has agreed to a Memorandum of Understanding (MOU) with the EPA, which, though voluntary, commits the signatories to attempt to reduce and, if possible, eliminate their PFC emissions. l Semiconductor industry accounts for a small percentage of total greenhouse gas emission. However, IC industry usage is growing while emissions by other industries are decreasing. Also, many small sources contribute to the whole. All industries must contribute to reduction strategies. l PFC are specifically produced for the semiconductor industry, while in other industries they are often an undesired by-product. l Whether or not the contribution of PFC emissions to any actual or perceived global warming effect is significant, the semiconductor industry is committed to reduce and, if possible, eliminate PFC emissions.

NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Gleason, et al. 9 PFCs in Dielectric Film Processes l Dielectric film processes account for the majority of PFC use. l Dielectric film processes presently rely exclusively on PFCs. l PECVD chamber cleaning presently uses more PFCs than wafer patterning (etching) and is the faster growing application, but wafer patterning usage is still significant. l Chemistry for patterning & chamber cleaning may require the same initial qualification work.

NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Gleason, et al. 10 Specific Applications for PFCs l Silicon Dioxide Etching –mostly CF 4 /CHF 3 mixes –also SF 6 and NF 3 l Silicon Nitride Etching –SF 6, NF 3, CF 4 and CHF 3 all used l Chamber Cleaning of CVD oxide & nitrides –mostly C 2 F 6 –new NF 3 processes –also SF 6 and CF 4

NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Gleason, et al. 11 Distribution of PFC Use l 1993 SEMITECH Report –Etch- 36% –Chamber Clean - 64 % l “low hanging fruit” l less stringent requirements for replacement l Largest fraction used by chamber cleaning –long processes times –high flow rates l Volumes used for chamber cleaning are growing l Other etch processes use is smaller (polysilicon, refractory metal like W)

NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Gleason, et al. 12 C 2 F 6 Usage by IC Industry l Typical fab uses 50,000 lbs per year l Typical conversion efficiency is 30 to 40% l 95% of C 2 F 6 is used in chamber cleans l Typical flow rates (sccm) –chamber cleaning –etching from R.G. Ridgeway et. al, Air Products in “Perfluorocompound (PFC) Technical Update (7/13/95) SEMICON/WEST 95

NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Gleason, et al. 13 % Conversion Efficiency l % of inlet gas passing through process unreacted & emitted in the exhaust l Typical values –80-90% for NF 3 –10-15% for CF 4 –30-40% for C 2 F 6 –50-60% for C 3 F 8 l Roughly two-thirds of the most commonly used PFC in the semiconductor industry, C 2 F 6, is vented to the atmosphere.

NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Gleason, et al. 14 Strategies for Reducing PFC Emissions  “Decrease the use and reduce the emissions of potential global warming semiconductor processing materials; specifically the perfluorocompounds (PFCs), such as CF 4, C 2 F 6, NF 3, and SF 6.”  National Technology Roadmap for Semiconductors (SIA): non-PFCs to be available by 2007.

NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Gleason, et al. 15 Ranking of Emission Control Strategies l Cost of ownership (COO)(difficult to access) l Commercial availability l “Greenness” l Destructive/nondestructive Replacement Recovery Plasma Chemical-Thermal Combustion “greenness”commercial availability

NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Gleason, et al. 16 Abatement (Destruction/Decomposition) l Destruction of compounds in the effluent –combustion –plasma –chemical conversion l Short-term solution l Potential high cost of ownership (COO) l Caution: by-products of abatement may themselves be undesirable (NO x, CF 4, HF, COF, HF) or have effects which are yet to be known.

NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Gleason, et al. 17 Combustion-Based Abatement l High degree of PFC decomposition commercially demonstrated l Several manufacturers (Centrotherm, DAS, Delatech, EcoSys, Edwards/Alzeta, Toyo, Sanso.....) l Currently used by fabs to destroy other toxic and/or reactive effluents (silane or TEOS units for CVD can be switched over to operate for PFC abatement during chamber clean) l By-products, such as HF and NOx, require disposal l Nitrogen pump purge effects (larger volume of air to treat and to heat) l COO could be high –hardware –facilitization –consumables (fuel: hydrogen, oxygen/methane/air) –energy (heating of gas) l Safety of operation (~ °C) l Tends to be run continuously

NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Gleason, et al. 18 Chemical-Thermal Abatement (Reactive Adsorption) l Several developmental systems (CS Systems, Edwards, Kanto Denka,...), more commercial demonstrations needed for PFCs l Some fab uses for other applications (ie Cl from metal etch), potential for switching (i.e. dual use). l Nitrogen pump purge effects l No external chemicals/fuels (direct pyrolysis) l Metal consumable [Iron supported on high surface area alumina (Al2O3) pellets is converted to metal ~400°C. In some cases this could be used as ore for metal refining.] l Uses packed bed reactor –solids replacement? (will influence COO) –thermal management (heat needs to be removed from bed) –plugging & breakthrough l Small units, easy on/off use

NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Gleason, et al. 19 Plasma-Based Abatement l Developmental systems (ETC, Texas A&M, MIT, Motorola, Los Alamos, NRL......), commercial demonstration needed l Based on existing plasma technology l Uses undiluted process stream (no nitrogen purge effect) l By-product disposal (HF) l Potential for backstreaming to process reactor l Needs to be controlled based on operation of process reactor l Fast switching l Small l Can be incorporated into CVD tool (sometimes called chamber satellites or processing aides)

NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Gleason, et al. 20 Recycle l Desirable for processes with low conversion efficiencies (10-30%) l Overall efficiency can be 100% with recycle l Pretreatment, such as condensation to remove etch products (acids, pyrophorics, particulates) l Recovered purity must be very high to allow for direct reuse pure PFC reactorseparator etch products unreacted PFC & etch products

NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Gleason, et al. 21 Recovery (+ Recycle/Reclaim) l Developmental activities (Air Liquide, Air Products/Radian BOC, Praxair/EcoSys, Showa Denko....). Commercial demonstration needed. l nitrogen pump purge effects l By-product management (safety issues for concentrated materials) l Favorable COO for direct recycle