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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 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 diffusion 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.
  6. For training please see the Training Calendar for scheduled trainings.

 

Operating Procedures 

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 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: SC1, 50:1 HF, SC2

2. Set: 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.

SRD 4 inch open

 

WARNING: WAFERS MIGHT BREAK DUE TO... 

  • High RPM
  • Thin wafers, chipped wafers, wafers that are scribed deeply
  • Stressed wafers, etched through wafers, wafers with jagged edges
  • Make sure wafers are not “cross slotted” in the cassette!

 

Wafers might stick to the Teflon rod after the spin-dry!

Use extreme caution when removing the cassette!

 

Do not run the spin/rinse dryer without a cassette!

Recipe # 1:

Step RPM Time sec
 Resistivity
 Rinse
 Dry
 PurgeBowl
 Heat
 PurgeManifold
 AntiStat
1 0 20
       x
     
 2 400 180
 15
x   x
      
 3 2000 10
 0
   x
    x
 
 4 2000 120 0   x   x    
 5 2000 120
0
  x   x    x
 6 600 60 0   x  

x

 

  • Open the door to the spin-rinse dryer if you use a 4" cassette and carefully load the cassette.
    If you have a 3" cassette, you must insert the special stainless steel adapter into the spinner assembly first, then load your cassette. Use clean gloves to handle the adapter.
    If the cassette is not full, the wafers should be evenly spaced throughout the boat.
  • Close the door.
  • Select recipe #1.
    If recipe #1 is not selected, press + or - until recipe #1 is on the display.
  • Press the green START button to start the cycle. If the resistivity does not reach the set point within 180 seconds this module will continue in the slow spin/rinse step of the cycle until the resistivity reaches the set point in M/ohms. This ensures that there is no residual acid left on the wafers. When resistivity is reached, the fast spin/dry step will start. When the cycle is done, the rotor will stop spinning and the door interlock will be released. Open the door and make sure that the cassette is upright. Wafers might stick to the Teflon rod after the spin-dry! Use extreme caution when removing the cassette (remember, clean gloves!)
  • Place the cassette into the station dedicated box and transfer the cassette box to the next furnace or deposition step.
  • Return the station dedicated cassette and box to the diffusion wet bench after loading the wafers into the next tool. Do not store your wafers in the station dedicated Teflon cassette!

 

If the SRD has not been run for one hour, an Auto Cycle (A on display) will start, it will rinse and dry the bowl at a low RPM, there should be no cassette inside of the tool. The Auto Cycle does not close the door. The machine will not start an Auto Cycle if the door is open or the controller is interlocked. If the programmed time interval has expired, the tool will continue to attempt starting the Auto Cycle, so as soon as the door is closed, the Auto Cycle will start.

If the Auto Cycle (A) is running, wait until it finishes and then load your cassette, try not to open the door while a program runs.  

If "Idle" or "resistivity" flashes on the display, press the STOP button. 

 

 

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 wbdiff 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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