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Contamination Groups for Controlling Process Flow Materials

This page describes the general classifications by which materials and equipment are grouped into at SNF which help minimize cross-contamination. There are many exceptions, depending on the tool, material, and process flow. For any questions about contamination concerns, contact an SNF staff member.

Overview:

Equipment in SNF is classified in one (or more) of three contamination group levels, described below. When defining the process flow, the choice of processing tools which are acceptable will depend on the previous tool and materials used. In general, wafers can be processed in only equipment within the same contamination group or in groups representing higher contamination risk , the progression of "Clean" -> "Semi-Clean" -> "Gold-Contaminated" is acceptable, but the reverse is not.
Certain equipment, some in the lithography area,  characterization area, general purpose wet benches, and a few other exceptions, appear in more than one group or "All" groups, either because of low risk of cross-contamination, or because intervening cleaning procedures reduce contamination risk, or because special precautions may be taken to prevent contamination. The Materials/Equipment Group column on the Equipment Summary page tells you in which equipment group each tool is. Equipment groupings are a very general planning tool -- as you refine your process flow, make sure to check it against the Materials requirements for each individual piece of equipment. There are a few exceptions in which non-standard equipment sequence may be acceptable -- these are explained in the "Process Capabilities" section for each piece of equipment. If you have non-standard process flow requirements (or any other questions about Materials policy), please discuss your project with a member of the PROM committee, who should be able to help you design a process flow to accommodate your needs.

Clean:

Equipment with the lowest tolerance for contamination fall into this group. Other than for photolithography and some approved analytical tools, wafers containing any metals or metal films are strictly prohibited from being processed in this equipment. Wafers that at any point have received processing on any equipment outside of this group cannot be processed on anything listed in this group. Wafers previously undergoing lithography are acceptable for processing (following appropriate photoresist restrictions or resist stripping procedures). Processing in any of the general-purpose wet benches must be done with appropriately dedicated labware to prevent cross-contamination. Given the appropriate materials considerations wafers processed in Clean equipment may subsequently be processed in any Clean, Semi-Clean or Gold-Contaminated tool.

Semi-Clean:

Semi-Clean "A":  Wafers containing standard metals (Aluminum, Tungsten, Titanium) may be processed in Semi-Clean equipment.   Moreover, any wafers processed in semi-clean equipment are considered to be Semi-Clean (excepting lithography or some approved analytical tools).  Processing in any of the general-purpose wet benches must be done with appropriately dedicated labware to prevent cross-contamination. Given the appropriate materials considerations, wafers processed in Semi-Clean equipment may subsequently be processed in any Semi-Clean or Gold-Contaminated tool.

Semi-Clean "B":  This sub-class covers other metals previously approved for use in Semi-Clean equipment, except where otherwise noted.  These materials are deposited in equipment used for CMOS compatible films.  At SNF, only the SCT sputter deposition system qualifies, although other sources of these films may be permitted on a case-by-case basis.  The Semi-Clean "B" materials are:  Ni, Co, Pt, Al, Hf, Ta, Mo, W, Ti, Cr, Zr, Pd.

Semi-Clean B wafers may be processed in all Semi-Clean equipment EXCEPT FOR the following restrictions:

  1. Semi-Clean B wafers must be cleaned or wet-etched using dedicated Semi-Clean labware at the wbflexcorr-3and-4 or wbflexcorr-1and-2 benches (i.e., do not use wbmetal baths.)
  2. Semi-Clean B wafers may be etched in Semi-Clean plasma etch tools provided the Semi-Clean B film is not being etched.  Etching other films and stopping on Semi-Clean B films is OK.  However, dry etching of Semi-Clean B films is permitted only on a case-by-case basis.

Gold-Contaminated:

Wafers containing non-standard metals, including gold, may be processed in this equipment. Except for lithography or some approved analytical tools, wafers processed in this equipment are considered gold-contaminated. There are no restrictions as to which equipment groups previous processing has taken place; however, subsequent processing may take place only in tools in this equipment group.

Litho/Analytical Tools:

Because of their general necessity throughout a process flow, all lithography and some analytical tools (and also some wet benches, see below) appear in all three equipment groups. Standard resist stripping and equipment-specific, pre-clean procedures designed into the particularly sensitive process modules minimize any potential contamination risk from shared lithography (and other select) tools. Some analytical tools present low risk of cross-contamination; other analytical tools are particularly sensitive to contamination issues or run high risk of transferring contaminants. Consult the materials guidelines for each of these tools, before processing. As always, when in doubt about contamination risks in any step in your process flow, don't hesitate to contact the PROM committee.

General Purpose Wet Benches:

Certain wet benches have few restrictions on materials, but appear in all equipment groups. The use of designated and/or personal glassware/labware insures that cross-contamination risks are minimized. Consult the Materials use guidelines for each wet bench.

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