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Wet Bench Metal, wbmetal

The Metal Wet Bench is used for processing of silicon wafers with standard metals. In addition to the standard dump rinse and spin-rinse-dryer modules, this station also has an aluminum etch hot pot, hot pot for stripping resist from metal-coated wafers, hot pot for final cleaning of metal wafers before anneal, two HF tanks, and a room temperature bath for peroxide solutions.

Picture and Location

Wet Bench Metal

 The tool is located at FG45 on the Lab Map.

 

Process Capabilities

Cleanliness Standard

 

The wbmetal wet bench is in the Semiclean Equipment Group.

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

Substrates may contain standard SNF metal films. Photoresist is acceptable only in the Al Etch, PRS-3000 and HF etchant baths, not in the PRS1000 bath.
Consult staff members or the Materials Section of the website for more details about which specific materials are acceptable at this station.

Substrates

Substrates must be 3" or 4" rounds, which can be handled by the dedicated cassettes at this station. Only silicon, silicon germanium, and quartz substrates may be processed at this station, subject to the constraints in the Materials Allowed section (section 1.3). Odd-sized substrates must be processed at wbflexcorr.


 

Performance of the Tool

What the Tool CAN do

  • The wbmetal wet bench is used for photoresist stripping, general cleaning, and etching of Si, SiGe, or quartz wafers which may contain standard metal films (aluminum [Al], tungsten [W], and titanium [Ti], deposited using SNF systems.) This station contains (from left to right, at the back of the bench):

    Three quartz hot pot containing:

      • 50:1 HF (left of the twin tanks)
      • 6:1 BOE or 20:1 BOE (Either may be in the right one of the twin tanks; check station log and label over the tank)

    And a polypro tank for Ti or W etchants containing:

    • Peroxide-based metal etchant, non-fluorine-containing (Either Ti or W etchant may be in the tank; check station log and label over the tank)
    The front of the bench contains an overflow rinse tank [3a], two automatic dump rinsers [3], a glove wash [4], DI hand sprayer, and an N2 gun. There is a dedicated spin-rinse dryer just to the right of the main bench.

 

What the Tool CANNOT do

  • Wafers that at any point have previously been processed on any equipment in the "gold" equipment group cannot be processed here

 

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 Procedures

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

 

Chemical Hazards

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

Aluminum etchant - Corrosive, oxidizer, toxic, air/water reactive
PRS-3000 Photoresist Stripper - Flammable
PRS-1000 Metal Clean - Flammable
50:1 HF, 6:1 BOE and 20:1 BOE
- Corrosive, toxic
5:1:1 H2O:H2O2:NH4OH
- Oxidizer, corrosive
30% Hydrogen Peroxide Solution (used for W etchant) -
Oxidizer, corrosive

Chemical Frequency

  • PRS-3000: once per week or as-needed.
  • Al Etch, PRS-1000, 50:1 HF, and BOEs: once per month.
  • 5:1:1 H2O:H2O2:NH4OH and H2O2 solutions: as needed

How to fill the chemical tanks

  • Al Etch, PRS-3000 (discontinued March 2014), PRS-1000, 50:1 HF, 20:1 BOE, 6:1 BOE, and hydrogen peroxide (30% in
    water) are all pre-mixed chemicals.
    Once the chemical is removed from the hot pot or tank, use the DI sprayer to rinse the hot pot or tank well. Rinse down the sides from top to bottom, but do not splash water outside the hot pot or tank. Be careful not to over-rinse the HF tanks, because the HF waste collection tank has limited capacity.
    If you drain
    PRS-3000 or PRS-1000, don't rinse the tank with water, rinse the tank with fresh chemicals, drain the tank and completely fill it up with fresh chemicals.
  • The 5:1:1 H2O:H2O2:NH4OH must be mixed at the station.

 

Cassettes

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

 

Tweezers

Tweezers used at this station should be Teflon-coated stainless steel. They should be decontaminated according to the standard lab procedures for tweezers cleaning.

 

Control Panel

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

  1. 3130 EPO. 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.
  2. Plenum Flush. This is for flushing the plenum. To be used for maintenance purposes by staff.
  3. Enable/Disable LED. This shows the Coral enable/disable status of the station.
  4. 3150 Process Controller. This controls heating, the aspirator, and the timer for the left hot pot (Al Etch II).
  5. Stirrer/N2 Bubbler/DI Fill. The "Stirrer" button controls the stirrer on the Al Etch bath. The "N2 Bubbler" is disconnected. The "DI Fill" button controls the water valve in the overflow rinse bath.
  6. 3150 Process Controller. This controls heating, the aspirator, and the timer for the middle hot pot (PRS-3000).
  7. 1100A Quick Dump Rinser. This controls the left dump rinser.
  8. 3150 Process Controller. This controls heating, the aspirator, and the timer for the right hot pot (PRS-1000).
  9. 3170A Process Timer. This is the timer for the left tank (50:1 HF, the left one of the twin tanks).
  10. Left Drain Switch. This controls the drain valve for the far left tank (50:1 HF, the left one of the twin tanks).
  11. 1100A Quick Dump Rinser. This controls the right dump rinser.
  12. 3170A Process Timer. This is the timer for the center tank (6:1 BOE/20:1 BOE, the right one of the twin tanks).
  13. Center Drain Switch. This controls the drain valve for the center tank (6:1 BOE/20:1 BOE, the right one of the twin tanks).
  14. 3170A Process Timer. This is the timer for the far right tank (peroxide-based etchants).
  15. Right Drain Switch. This controls the drain valve for the far right tank (peroxide-based etchants).

 

Lower Front Panel Controls

To allow the user to avoid reaching over wafers and acid, many of the module functions can be actuated from the lower front panel. The front panel functions available are as follows (from left to right):
      1. Process timer for the far left hot pot (Al Etchant).
      2. Left quick dump/rinser, process timer for the right hot pot (PRS-1000).
      3. Process timer for the left tank (left one of the twin tanks).
      4. Right quick dump/rinser, process timer for center tank (right one of the twin tanks: 6;1 BOE/20:1 BOE).
      5. Process timer for the far right tank (peroxide etchants).

Spin-Rinse Dryer (SRD)

 

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
 0     x
     
 2 400 180
15
x   x
     
 3 1800 10
0
  x
    x
 
 4 1800 120 0   x   x    
 5 1800 120
0
  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" flashes on the display, press the STOP button until "Idle" stops flashing.

 

 

Additional Process Info

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, wbnonmetal, wbdecon, wbclean-3, and wbmetal.

Photoresist Strip

Only the PRS-3000 (in use since April 2014) bath is to be used for photoresist stripping from metal-containing wafers. PRS-1000 is also used in the industry as a resist stripper, its use here is limited to the final clean before a furnace or deposition step. Because of the small amount of caustic base in both PRS-3000 and PRS-1000, wafers must be very dry before going into these baths, otherwise the exposed metal may be etched. If you drain PRS-3000 or PRS-1000, don't rinse the tank with water, rinse the tank with fresh chemicals, drain the tank and completely fill it up with fresh chemicals.

The PRS-3000 resist strip is effective when resist has been used for masking wet aluminum etching. However, resist which has been used to mask implant, AMT oxide etch, or P5000 aluminum etch , or plasma etch is hardened by these processes and will require a special plasma etch prior to PRS-3000 to be completely removed. Check the Process Info links for wbmetal for more details.

PRS-3000 contains:
1-Methyl-2 pyrrolidinone, 40-60%
Thiophene, Tetrahydro-, 1,1-dioxide, 30-50%
2-Propanol, 1-amino-, 5-15%

It has a flash point of 93 degrees C. Do not mix with strong oxidizing agents (strong acids or strong reducers).

PRS-1000 contains:
2-(2-Ethoxy-ethoxy)ethanol (10-30%),
sulfolone (25-45%), 1-Methyl-2-Pyrrolidinone (35-55%),
Tetraethylene Glycol (1-10%), monomethanolamine (<0.1%) .
PRS-1000 should not be mixed with strong oxidizers (i.e., strong acids or reducing agents.)

Aluminum Etch

The aluminum etchant used here is ( under evaluation which consists of 74% Phosphoric Acid, 10% Acetic Acid, 2% Nitric Acid, 22% water, and Surfactant). Wafers need to be completely wet (hence, the cascade rinser in front of this bath) before being placed in the Al etch solution. One micron of Al or Al/Si will etch in about one minute. However, the Al etch solution will not etch the silicon in AlSi, so an additional Si freckle-etch in drytek2 is required.

Al Etch II is a strong acid and oxidizing chemical mix. It should not be mixed or come in contact with PRS-3000 or PRS-1000.

(Cyantek's AL-11 Aluminum Etchant which consists of 72% Phosphoric Acid, 3% Acetic Acid, 3% Nitric Acid, and 22% water, production has been discontinued as of Feb 2014).

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