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February 23, 1995
Mr. John E. Watson
Dear Mr. Watson:
This is in follow-up to our telephone conversation on February 10, 1995, regarding the applicability of the pretreatment categorical standards for electrical and electronic components at 40 CFR Part 469. You asked whether sputtering, vapor deposition, and electroplating occurring in semiconductor manufacturing operations are covered under 40 CFR Part 469 or the metal finishing requirements at 40 CFR Part 433. After reviewing the regulations and supporting documents, we conclude that these operations are covered under both Parts 469 and 433.
Your question is prompted by the applicability statement at 40 CFR 469.10 which explains the coverage of the semiconductor discharge requirements by stating:
The provisions of this subpart are applicable to discharges resulting from all process operations associated with the manufacture of semiconductors, except sputtering, vapor deposition, and electroplating (emphasis added).
The preamble to the final rule (48 FR 15382) explains that these process operations are subject to the electroplating and metal finishing requirements at Parts 413 and 433 respectively. The technical support document, however, contains a more detailed description of the applicability of these discharge requirements. The following discussion is based on the document titled Development Document for Effluent Limitations Guidelines and Standards for the Electrical and Electronic Components Point Source Category (Phase I) (EPA 440/1-83/075).
During the manufacture of semiconductors, material is selectively added and etched on a silicon wafer. Page 4-4 of the Development Document explains that:
The etchant produces depressions, called holes or windows, where the diffusion of dopants later occurs. Dopants are impurities such as boron, phosphorus and other specific metals. ... Diffusion of dopants is generally a vapor phase process in which the dopant, in the form of a gas, is injected into a furnace containing the wafers.
In our view, this discussion indicates that sputtering, vacuum deposition, and electroplating are regulated under 40 CFR Part 469 when those process operations are associated with the photolithographic-etching-diffusion-oxide process sequence in the manufacture of semiconductors.
Page 4-5 of the Development Document explains that the electroplating and metal finishing requirements apply to those process operations that prepare the wafer for final assembly. The requirements under 40 CFR Part 413 have limited applicability. Consequently, we believe that the metal finishing requirements at 40 CFR Part 433 will most likely apply to semiconductor manufacturers. Page 4-5 of the Development Document explains that:
After the diffusion processes are completed, a layer of metal is deposited onto the surface of the wafer to provide contact points for final assembly. The metals used for this purpose include aluminum, copper, chromium, gold, nickel, platinum, and silver. The processes associated with the application of the metal layer are covered by the electroplating or metal finishing effluent limitations and standards.
The metal finishing requirements only cover the process used to deposit a layer of metal onto the surface of the wafer to provide contact points for final assembly. Any wastewater from subsequent operations including wafer passivation, wafer back-lapping and dicing, and assembly in lead frames is covered under 40 CFR Part 469.
The semiconductor manufacturing process is illustrated in Figure 4-1 on page 4-3 of the Development Document. A copy is enclosed for your reference. The operation covered under the metal finishing requirements is labeled "Metal Deposition." Please note, however, that under 40 CFR 433.10(a) one of six primary metal finishing operations must be performed at a facility to bring the 40 other processes, including sputtering, under the metal finishing discharge requirements. Consequently, if a semiconductor manufacturing facility does not perform one of the six primary metal finishing processes, the metal deposition process used to provide contact points is not covered under the metal finishing requirements at 40 CFR Part 433.
You also asked whether wastewater from the cleaning of sputtering equipment would be regulated under Parts 433 or 469. You noted that sputtering is often a "dry" process with the only wastewater associated with this operation occurring when the sputtering equipment is cleaned. Wastewater that results from the cleaning of sputtering equipment is a regulated wastestream under both Parts 433 and 469. We would consider all wastewater generated as a result of sputtering, including cleaning wastewater, to be subject to the categorical discharge limitations. In addition, page 5-4 of the semiconductor manufacturing Development Document identifies waste water from equipment cleaning as a source of process wastewater. Cleaning wastewater that results from sputtering in the photolithographic-etching-diffusion-oxide process sequence is covered under 40 CFR Part 469. Cleaning wastewater that results from sputtering for depositing metal for contact points is covered under 40 CFR Part 433.
Finally, you mentioned that at the semiconductor facility in question, the metal finishing wastewater flow will be relatively low and combining this wastestream with the semiconductor manufacturing wastestreams will likely dilute the concentrations of some regulated pollutants to levels below analytical detection. As we discussed, in such cases the discharger may not use the combined wastestream formula under 40 CFR 403.6(e). Consequently, the discharger would need to establish a separate sampling point for the metal finishing wastewater or perhaps store it temporarily and discharge it with other metal finishing wastewater.
Thank you for your inquiry. I hope this is responsive to your concerns. If you have any questions regarding this matter, please call me at 415.744.1907.
Very truly yours,
L. Keith Silva
cc: Ms. Elaine Brenner, Chief