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Wet Bench Clean-1 and 2 (former wbdiff)

The Wet Bench Clean-1 and 2 is used for cleaning 3", 4", and 6" silicon, silicon germanium, or quartz wafers prior to processing in diffusion furnaces, LPCVD furnaces or before metal deposition. The cleans performed here are high quality, final cleans which precede high temperature processing. To be processed at this station, wafers may not contain or have ever contained any metals, nor been exposed to equipment which may pose this contamination risk. This station contains 2 sets of SC1 and SC2 cleans, HF tanks in addition to dump rinse and spin-rinse-dry modules. The available chemical baths are: 5:1:1 H2O:H2O2:NH4OH for removal of trace organics, 5:1:1 H2O:H2O2:HCl for removal of trace metal ions, 50:1 HF, and 6:1 BOE for oxide etching.

Picture and Location

Wbclean-1 and -2 WAFAB  
The tool is located at F7 on the Lab Map.

 

Process Capabilities

Cleanliness Standard

The wet bench clean-1 and 2 is in the Clean Equipment Group.
Materials control policies are governed by equipment groups; for the description of this policy, click <here>.
Wafers that have been processed in equipment outside of this equipment group may not be processed at this bench, with the exceptions as listed below.

Special cases:

This wet bench is used before every critical furnace or deposition process. Therefore, perhaps more than any other station in the lab, it is absolutely imperative that procedures for proper handling and processing of materials be scrupulously observed, in order to minimize risk of contamination and thus minimize the potential for adversely affecting the research of other labmembers who use this equipment.

We ask that users to be very careful about their processing. We also recognize that occasional mistakes can happen, particularly in this dynamic research environment -- we only ask that users quickly report mistakes or accidents, so that staff can respond quickly to minimize any problem.

 

Substrates

Only 3", 4",and 6" silicon, silicon germanium, or quartz rounds or similarly contamination-free substrates may be cleaned here (no GaAs wafers allowed). Wafers must not have (nor ever have had) any metals or silicides on them. Wafers must not have any photoresist or scribe dust on them. Photoresist clean must be done at wbclean_res-piranha prior to cleaning at this bench.

 

Performance of the Tool

What the Tool CAN do

This station contains two hot pots and two Teflon tanks in addition to dump rinse and spin-rinse-dry modules. The available chemical baths are:

  • 5:1:1 H2O:H2O2:NH4OH for removal of trace organics
  • 5:1:1 H2O:H2O2:HCl for removal of trace metal ions
  • 50:1 HF, for oxide etching
  • 6:1 BOE for oxide etching

 Standard Prediffusion Clean consists of the following steps:

  1. 5:1:1 H2O:H2O2:NH4OH (10 minutes, 50°C), followed by dump/rinse
  2. 50:1 HF (30 seconds, RT), followed by dump/rinse
  3. 5:1:1 H2O:H2O2:HCl (10 minutes, 50°C), followed by dump/rinse
  4. Spin dry
Standard Pre-LPCVD or Pre-Metal clean consists of similar steps, but in different order:
  1. 5:1:1 H2O:H2O2:NH4OH (10 minutes, 50°C), followed by dump/rinse
  2. 5:1:1 H2O:H2O2:HCl  (10 minutes, 50°C) followed by dump/rinse
  3. 50:1 HF (30 seconds, RT), followed by dump/rinse
  4. Spin dry

 

What the Tool CANNOT do

Wafers that at any point have received processing on any equipment outside of the "clean" equipment group cannot be processed here. Substrates containing absolutely any metals or metal films are strictly prohibited from being processed here, even if the metal has been previously removed. Wafers must not contain any photoresist (they must be cleaned at wbclean_res-piranha first). If wafers have previously come into contact with KOH, decontamination must be performed. Wafers processed outside SNF may not be processed at this station without first consulting with staff. 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, Operating Procedures, and Additional Processing.
  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 to register for a training session. Training sessions are posted on the Training Calendar  There is also written test for the tool, which should be completed before the training session.

 

Operating Procedures 

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

 

System Overview

This is a WAFAB brand wet bench (installed in 2014). The 8 foot bench contains 2 sets of diffusion cleans separated by a partition (from left to right, at the back of the bench):

1. Set (wbclean1): SC1, 50:1 HF, SC2

2. Set (wbclean2): SC1, 50:1 HF, 6:1 BOE, SC2


All four quartz-lined, temperature controlled hot pots aspirate into the acid waste neutralization system.
The chemicals are:

  • SC1
    5:1:1 H2O:H2O2:NH4OH at 50°C +/- 10; for removal of trace organics
  • SC2
    5:1:1 H2O:H2O2:HCl at 50°C +/- 10. for removal of trace metal ions

 (insert picture)

 

Three Teflon-lined HF tanks which drain into HF waste collection system:

  • Two tanks for 50:1 HF at room temperature for oxide etching
  • One tank for 6:1 BOE at room temperature for oxide etching

 (insert picture)

 

The front of the bench contains four automatic dump rinsers.

(insert picture)

Each of these modules has its own micro-controller 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.

 

Spin-Rinse Dryer (SRD)

There are two dedicated spin-rinse dryers just to the right of the main bench, which drain into the acid waste neutralization system.

How to use the SRDs find here: Wet Bench Operating Instructions for WAFAB.

 

Chemical Hazards

You must read the Material Safety Data Sheets for these chemicals and understand safe chemical handling procedures.

The primary hazard classifications for the chemical mixtures used are:

  • 5:1:1 H2O:H2O2:NH4OH - Corrosive, oxidizer
  • 50:1 HF and 6:1 BOE - Corrosive, toxic
  • 5:1:1 H2O:H2O2:HCl - Corrosive, oxidizer
 

Chemical Frequency

    • The 5:1:1 H2O:H2O2:NH4OH clean should be changed once every four hours.
    • The 5:1:1 H2O:H2O2:HCl hot pot should be changed every four hours.
    • The 50:1 HF tank should be changed once/day.
    • The 6:1 BOE is changed once per month or on an as-needed basis.

 

How to fill the chemical tanks

  • To fill the NH4OH hot pot:
    Fill DI water to the bottom of the Teflon dip-stick. Then add hydrogen peroxide to the mark on the dip-stick and then add the NH4OH to the last mark on the dip-stick.

  • To fill the HCL hot pot:
    Fill DI water to the bottom of the Teflon dip-stick. Then add hydrogen peroxide to the mark on the dip-stick and then add the HCl to the last mark on the dip-stick.

NOTE: the H2O2 in both the NH4OH and HCl hot pots will 'boil' off in time and need to be replenished.  This maintains the correct concentration of the mixture.  Simply add H2O2 back to the correct level on the dip-stick.

 

  • To fill the HF tanks:
    The 50:1 HF 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.

Cassettes

This bench has Teflon cassettes and handles with a clear button, no 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

Tweezers used for loading wafers into wbclean cassettes should be Teflon-coated stainless steel. They should be decontaminated according to the standard lab procedures for tweezer cleaning and their dedicated use should be for "dirty non-metal" applications. Wafers should then be unloaded directly from the station-dedicated cassettes into the furnace boats using dedicated vacuum wands at the furnace station or "clean non-metal" tweezers.

Control Panel

The control panel modules are, from left to right are:

  1. Quick Dump Rinse QDR MPC-301, this controls the left dump rinser.
  2. Process Controller DT-V130-33-TA24. This controls heating, the aspirator, and the timer for left hot pot (5:1:1 H2O:H2O2:NH4OH).
  3. Process Timer for the left HF tank (50:1 HF), 30 seconds.
  4. Drain on/off for the left HF tank (50:1 HF).
  5. Quick Dump Rinse QDR MPC-301, this controls the second to the left dump rinser.
  6. Process Controller DT-V130-33-TA24. This controls heating, the aspirator, and the timer for second to left hot pot (5:1:1 H2O:H2O2:HCl).
  7. Photohelic
  8. MPC-901 EMO controller. This controls power to the control panel. It contains the Emergency Off button (top) and the main power On/Off switch. When in use or under standby conditions, the main power should always be left on.
  9. Quick Dump Rinse QDR MPC-301, this controls the second to the right dump rinser.
  10. Process Controller DT-V130-33-TA24. This controls heating, the aspirator, and the timer for the second to the right hot pot (5:1:1 H2O:H2O2:NH4OH).
  11. Process Timer for the second to the right HF tank (50:1 HF), 30 seconds.
  12. Drain on/off for the second to the right HF tank (50:1 HF).
  13. Process Timer for the right HF tank (6:1 BOE).
  14. Drain on/off for the right HF tank (6:1 BOE).
  15. Quick Dump Rinse QDR MPC-301, this controls the right dump rinser.
  16. Process Controller DT-V130-33-TA24. This controls heating, the aspirator, and the timer for right hot pot (5:1:1 H2O:H2O2:HCl).

 

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-1 and-2, wbclean_res-piranha, wbclean-3, wbdecon, and wbmetal.

 

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