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Wet Bench Clean_res-piranha and -hf, (former wbnonmetal)

This bench (semi-automated) is part of the Clean Equipment Group for 3", 4", and 6" Si, SiGe, and quartz substrates and is primarily used for stripping photoresist, removing scribe dust and wet oxide etching. Wafers may not contain or have ever contained any metals, nor been exposed to equipment which may pose this contamination risk. This station contains two hot pots for 90% sulfuric acid/hydrogen peroxide ("piranha") for stripping resist ,two Teflon tanks containing 50:1 HF, 20:1 BOE, or 6:1 BOE for etching oxide, one hot pot for phosphoric acid, three automatic dump rinsers and two spin/rinse dryers.

Picture and Location



The tool is located at G6 on the Lab Map.

Process Capabilities

Cleanliness Standard

The wbclean_res (piranha, hf, hotphos) is in the Clean Equipment Group.

Only Si, SiGe, or quartz wafers may be processed here.

If wafers have been previously etched in KOH, they must undergo decontamination procedure at wbdecon before processing at this station.

No GaAs is allowed here. Wafers with any metals, even if the metal has been stripped, are not allowed at this station.

Materials control policies are governed by equipment groups; for the description of this policy, click <here>.


Substrates must be 3", 4", or 6" rounds, which can be handled by the dedicated cassettes at this station. Only silicon, silicon germanium, and quartz substrates which do not have (or ever had) any metals on them may be process at this station, subject to the constraints in the Materials Allowed section. Odd-sized substrates must be processed at wbflexcorr.

Performance of the Tool

What the Tool CAN do

  • The wbclean_res-piranha and -hf wet bench contains (from left to right, at the back of the bench):
    Two quartz hot pots containing sulfuric acid/hydrogen peroxide (9:1 "piranha") for wafer cleaning and photoresist stripping of "clean" wafers, at 120C for 20 minutes, two Teflon tanks containing 50:1 HF, 20:1 BOE or 6:1 BOE used for general wet oxide etching, and one hot pot containing phosphoric acid to etch silicon nitride.
    The front of the bench contains four automatic dump rinsers, a glove wash, DI hand sprayer, and a N2 gun.
    There are two dedicated spin-rinse dryers just to the right of the main bench, the bottom dryer is for 3" or 4" wafers and the top dryer is for 6" wafers.
    Wafers containing standard SNF lab photoresist may be processed.


What the Tool CANNOT do

  • Substrates containing any metals or metal films are strictly prohibited from being processed here, even if the metal is covered with photoresist or has been previously removed.
    Wafers that at any point have received processing on any equipment outside of the "clean" equipment group" cannot be processed here. 
    Consult staff members for more details about which specific materials are acceptable at this station.


How to Become a User


  1. Read all material on the SNF website concerning the wet bench, including Process Capabilities, Wet Bench Operating Instructions for WAFAB, and Additional Process Info.
  2.  View the Diffusion Wetbench Training movie (13 min).
  3. View the Delrin Tweezer Cleaning (9 min) and the Metal Tweezer Cleaning (9 min) movies as well.
  4. Print the SNF Shadowing Form and the wet bench checklist on clean room paper and contact a qualified user of the wet bench to arrange to ‘shadow’ them while they use the tool. You are responsible to be with that labmember for the full time they are operating the tool, and it would be intelligent to ask questions and try to become as familiar as possible with the wet bench during this ‘shadowing.’  You may have to shadow the qualified user more than one time. The qualified user and you will have to sign the SNF Shadowing Form.
  5. Contact SNF training contact on the Equipment Summary page. There is a written test for the tool.


Operating Instructions

Read the Wet Bench Operating Instructions for WAFAB benches. Please note these instructions are generic and cover following wet benches: wbclean-1 and 2, wbclean-3, wbdecon, and wbclean_res.


System Overview

This is a WAFAB brand wet bench (installed in 2017).
This bench is equipped with (from the left to right side of the bench):

two quartz-lined, temperature controlled hot pots, bath-1 and bath-2, for sulfuric cleans which aspirate into the acid waste neutralization system:

wbclean_res piranha baths

three Teflon-lined tanks (bath-3 and bath-5 for HF etching, bath-4 for water rinse only) which drain into HF waste collection system:

wbclean_res HF baths

four dump rinsers.

wbclean_res dumprinser

Each of these modules has its own microcontroller unit, mounted in the overhead control panel.

The wet bench also contains a glove wash, an N2 gun, and a DI water hand sprayer.

wbclean_res glove wash, N2 gun, DI water gun

The wet bench plenum, over which all the modules sit, collects runoff and overflow, and drains into the acid waste neutralization system.

There are two dedicated spin-rinse dryers just to the right of the main bench, which drain into the acid waste neutralization system; the bottom one is for 3" or 4" wafer and the top one is for 6" wafers.

 SRD 4 inch open



Chemical Hazards

Sulfuric acid, hydrogen peroxide, and hydrofluoric acid are used at this wet bench. You must read the Material Safety Data Sheets for these chemicals and understand safe chemical handling procedures before working at this station.

The primary hazard classifications for the chemical mixtures used at this bench are:

For 90% sulfuric/peroxide - Corrosive, oxidizer, air/water reactive
For 50:1 HF, 20:1 BOE and 6:1 BOE - Corrosive, toxic



Chemical Frequency:

    • The 9:1 sulfuric/peroxide clean should be changed once every five days.
    • The 50:1 HF and 6:1 BOE or 20:1 BOE tanks are changed once per month or on an as-needed basis.


How to fill the chemical tanks:

To fill the 9:1 piranha hot pot:

The piranha bath consists of 9 parts of concentrated sulfuric acid and 1 part hydrogen peroxide. Pour about 1 1/2 gallons of sulfuric acid to the bottom of the Teflon dip-stick and then add hydrogen peroxide to the mark on the dip stick. Be very careful: sulfuric acid and hydrogen peroxide give off heat when mixed. Because sulfuric is heavy and viscous while peroxide is thin, they do not always mix well. To help in mixing, place an empty cassette (use station-dedicated handles and cassettes!) into the acid mixture and lift it out. This should be done with the heat off. Rinse the cassette/handle in the dump rinser and dry in the spin/rinse dryer.

To fill the HF tanks:
The 50:1 HF, 20:1 BOE or 6:1 BOE tanks are filled with pre-mixed chemicals. The HF tanks have no level indicator. One and 1/2 bottles of HF should be enough to cover a 4 inch cassette.

How to etch oxide using 50:1 HF, 20:1 BOE or 6:1 BOE


Enable wbclean_res-HF

If you would like to use one of the the two HF baths (bath-3 or bath-5), enable wbclean_res-HF.
Bath-3 contains 50:1 HF.
Bath-5 contains 6:1 or 20:1 BOE, check out the logsheet.
NEW: Bath-4,  located between the HF tanks, is for water rinse only and drains into the HF waste collection in the basement.

The first water rinse after an HF etch is now collected in the HF drain, bath-4.
- BATH-4 DI FILL: press the green START button to fill up the bath-4 with DI water.
- Etch your wafer in one of the two HF tanks, bath-3 or bath-5.
- Dip cassette into the DI water tank bath-4 and place it immediately after the water dip into the dump rinser and start the dump rinser.
- Empty bath-4 and rinse: press the green button at the BATH-4 DRAIN and wait until the bath is empty and then rinse tank carefully using the DI water gun. Once this tank is empty, press the red button at the BATH-4 DRAIN.
This bath stays empty when not in use.



There are dedicated cassettes and handles for all wet benches. This bench has Teflon cassettes and handles with a light-yellow colored button. Use only these designated cassettes and handles!
There are separate, dedicated cassettes and handles for 3", 4", and 6" wafers. A special stainless steel adapter is required to run 3" cassettes in the spin/rinse dryer.



Tweezers used at this station should be Teflon-coated stainless steel. They should be decontaminated according to the standard lab procedures for tweezers cleaning and their dedicated use should be for "dirty non-metal" applications.

Additional Process Information

For the procedures of the specific processes which are normally performed at this station, check the Additional Process Info link:
Additional Process Info. Please note these process info are generic and cover following wet benches:wbclean_res-piranha and -hf, wbmetal, and wbgen2.

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