Equipment
Lab and Coral NameICL / nitrEtch-HotPhos
ModelSemifab WPS-400
SpecialistPaul Tierney    (Robert Bicchieri)
Physical Location2F 3-South Photo
Classification
Process CategoryWet
SubcategoryAcids
Material KeywordsSiNx, Acids
Sample Size6" Wafers, 4" Wafers
AlternativeICL / AME5000, ICL / LAM590-ICL
Keywordsmulti wafer, manual load, both sides of sample, isotropic etch, temperature, manual operation
Description
The nitrEtch-hotPhos is an acid wet station dedicated for chemical etching of silicon nitride films. Hot phosphoric acid etches silicon nitride with excellent selectivity to silicon and SiO2. This chemical bath is intended for stripping silicon nitride films, it is not suitable for patterned etching. The heater is off when the tool is not engaged, make sure to turn on the heater 30 minutes prior to starting etch.

Best forStripping nitride films from wafer.
LimitationsDo not use resist as a mask. Patterning of silicon nitride should be done in a plasma etcher.
Characteristics/FOMThis process etches stoichiometric silicon nitride at a rate of ~ 65A/min.
Caution withThe phosphoric acid is VERY hot (~165C). Review safety regulations and wear personal protective equipment.
Machine Charges (academic rate)25pu/tank
Documents

SOP
Nitride EtchSOP for the ICL hot phosphoric nitride bath
Wet ProcessingRules and guidelines for wet processing

Documents
Etch rates part 2Berkeley etch rate paper
Process Matrix Details

Permitted
Germanium on surfaceSamples with germanium on the surface (typically grown films)
(With Appropriate Chuck),
Germanium buriedSamples with germanium buried below a different film
,
Been in the STS DRIEThe DRIE etch leaves behind polymer residues on the sidewall ripples, which can be a contamination concern for some tools.
,
Been in the SEMA sample viewed in the SEM must have used the appropriate chuck to avoid cross-contamination
,
Been in the Concept1The Concep1 deposits dielectrics on GREEN wafers, however it also accepts metal and there can be cross-contamination for diffusion area
,
Has PhotoresistSamples with photoresist cannot be exposed to high temperatures, which is typical in deposition tools. Outgassing can be a concern.
,
Has PolyimidePolyimide is a very chemically resistant polymer, and can tolerate higher temperatures but cannot be exposed to typical PECVD deposition temperatures or diffusion furnaces. Outgassing can be a concern.
,
Coming from KOHAfter a KOH etch, the samples must receive a special clean because the K ions are highly contaminating to CMOS frontend tools
,
Coming from CMPAfter a CMP, the samples must receive a special clean, because the slurry residues otherwise introduce contamination and particles.


Not Allowed
Ever been in EMLSamples from EML are never permitted to return to ICL or TRL
,
Been in the ALDSamples that have been in any of the ALD systems
,
Pyrex SubstratesPyrex substrates can be a concern due to high sodium content, which contaminates CMOS frontend tools
,
III-V SubstratesAny III-V substrates, e.g. GaAs, GaN, InP, and so on. Note though that many common III-V substrates will also carry the Au flag, but there are some GREEN III-V substrates.
,
PiecesWafer pieces may not be handled by the equipment, and are harder to thoroughly clean - preventing them from running in certain tools.
,
Gold or RED color codeRED color code substrates. These are gold-contaminated or have been processed in gold contaminated tools. Gold and other metals can contaminate silicon devices (GREEN color code) and have to be separated.
,
Any exposure to CMOS metalIf the sample had ever seen a CMOS metal (or a tool that accepts CMOS metal), then some frontend tools could be contaminated by this.
,
CMOS metal on surfaceCMOS compatible metals exposed on the surface. These are Al,Ni,Pt,Ti,TiN. Other metals such as Au are *NOT* part of this.
,
CMOS metal buriedCMOS compatible metals covered entirely by a different material. These are Al,Ni,Pt,Ti,TiN. Other metals such as Au are *NOT* part of this.
,
Has Cured SU8Not fully cured SU8 residues can heavily contaminated plasma chambers or destroy other user's samples, but fully cured SU8 is permitted in certain tools.


For more details or help, please consult PTC matrix, email ptc@mtl.mit.edu, or ask the research specialist (Paul Tierney)