Contamination categorization of Equipments @ IITBNF


Contamination Groups for Controlling Process Flow Materials

This document describes the general classifications by which equipment are grouped at IITBNF to help minimize cross-contamination. There are many exceptions, depending on the tool, material, and process flow. For any questions about contamination concerns, contact System owner/ Faculty incharge for the particular tool. In accordance with Equipment Usage & Training Policy, sample history has to comply with contamination control rules before it can be processed further.


Overview :

Equipment in IITBNF is classified into one of three primary contamination group levels - Clean, Semi-clean and Gold-contaminated. They are described in detail below. When defining the process flow, choice of processing tools which are acceptable will depend on the previous tool and materials used (i.e. sample history). In general, wafers can be processed in only equipment within the same contamination group or in groups which can take higher contamination risk:



The Allowed materials in tools page tells you:
To which equipment group each tool belongs
All substrates, materials, chemicals, gases and targets that are allowed in each tool.

Equipment groupings are for general tool usage. As you refine your process flow, make sure to check it against the materials requirements for every individual tool.


There are a few exceptions in which non-standard equipment sequence may be acceptable. If you have a non-standard process flow requirement, please discuss your project with a member of the Process committee, who should be able to help you design a process flow to accommodate your needs.


Clean :
Equipment with the lowest tolerance for contamination falls into this group. Other than 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 lab-ware to prevent cross-contamination. Given the appropriate materials consideration as given in Allowed materials in tools,wafers processed in Clean equipment may subsequently be processed further in any Clean, Semi-Clean or Gold-Contaminated tool.


Clean PV :

Same definition as "Clean" except the samples will be sodium or potassium contaminated.


Semi clean PV:

Wafers processed in "clean" and "clean PV" equipment can be processed in "semi clean PV" equipment.
The materials allowed in "semi clean PV" equipment are: Ag, Al, Ti, Pd, Pt.
The materials which are not allowed in "semi clean PV" equipment are: Ni, Hf, W, Ta, Cr, Zr, Mo, Au.
Other materials may be allowed after appropriate contamination reviews.
The samples processed in "semi clean PV" equipment are Na and K contaminated.

Semi-Clean
Semi-Clean "A":Wafers containing standard metals (Aluminum, Tungsten, Titanium) may be processed in Semi-Clean A equipment. Moreover, any wafers processed in Semi-Clean A equipment are considered to be Semi-Clean A (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 Allowed materials in tools, wafers processed in Semi-Clean equipment may subsequently be processed in any Semi-Clean or Gold-Contaminated tool.

Semi-Clean "B":This subclass 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. 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 wbgeneral or wbgaas 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 (contact Process committee)


Gold-Contaminated:
Wafers containing non-standard metals, including gold, may be processed in this equipment. 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 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 given in the Allowed materials in tools. As always, when in doubt about contamination risks in any step in your process flow, don't hesitate to contact the Process committee.


Reference:-
Online resources on classification of contamination categories and materials as shared by Stanford Nano Shared Facilities (SNSF), Stanford University, U.S.A.


Last updated on: 20-Jul-2022