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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 and three Teflon tanks, in addition to two automatic dump rinsers and two spin/rinse dryers. The available chemical baths are: 90% sulfuric acid/hydrogen peroxide ("piranha"), for stripping resist and removing scribe dust (two hot pots), 50:1 HF, 20:1 BOE, and 6:1 BOE for etching oxide.

Picture and Location



The tool is located at G6 on the Lab Map.

Process Capabilities

Cleanliness Standard

The wbclean_res-piranha and -hf b is in the Clean Equipment Group.

Only Si, SiGe, quartz, and similar contamination-free substrates 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,
    and three Teflon tanks containing 50:1 HF, 20:1 BOE, and 6:1 BOE used for general wet oxide etching.
    The front of the bench contains three automatic dump rinsers, a glove wash, DI hand sprayer, and an 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.


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. Wafers containing standard SNF lab photoresist may be processed. 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 Background, Process Capabilities, Operating Procedures and Process Monitoring.
  2.  View the Diffusion Wetbench Training movie (13 minutes, 106 Mbytes).
  3. View the Delrin Tweezer Cleaning (9 minutes, 37 Mbytes) and the Metal Tweezer Cleaning (9 minutes, 64 Mbytes) 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. Please note these instructions are generic and cover following wet benches: wbclean_res-piranha and -hf, wbmetal, and wbgen2.


System Overview

This bench is equipped with:

two quartz-lined, temperature controlled hot pots (for sulfuric cleans) which aspirate into the acid waste neutralization system;

Wbnonmetal hot baths

three Teflon-lined tanks (for HF etching) which drain into HF waste collection system;

HF tank

three dump rinsers.

Dump Rinser

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. 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 tank, 6:1 BOE, or 20:1 BOE 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 and 6:1 BOE tanks are filled with pre-mixed chemicals. The HF tanks have no level indicator. One bottle of HF should be enough to cover a 4 inch cassette.


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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