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Wet Bench Nitride, wbnitride

The Nitride Wet Bench is used for hot phosphoric acid stripping of nitride films from silicon or quartz substrates. This Wet Bench contains a hot pot, in addition to dump rinse and spin-rinse-dry modules.

Picture and Location

 Wet Bench Nitride

The tool is located at FG56 on the Lab Map.

Process Capabilities

Cleanliness Standard

 The wbnitride wet bench is in the Clean Equipment Group.


How to Become a User

  1. Read all material on the SNF website concerning the wbnitirde.
  2. Contact SNF training contact on the Equipment Summary page.


Operating Procedures

Read the Wet Bench Operating Instructions. Please note these instructions are generic and cover following wet benches: wbnonmetal, wbmetal, and wbnitride.

Potential Hazards

Although the Santa Clara Plastics Nitride Etch Wet Bench can be operated in a safe manner if appropriate procedures and safety precautions are followed, it is important to realize that there are a number of potential hazards associated with the operation and maintenance of this equipment.


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:

85% phosphoric acid - Corrosive


Input power is 208 volts AC, three phase at 30 AMPS. Only qualified personnel should be working on the electrical parts of this system. If any electrical problems are seen with the system -- PUSH THE EMERGENCY POWER OFF BUTTON.


Phosphoric Acid (in the Nitride etch bath). You should read the Material Data Safety Sheets on these chemicals before working at this station.

Emergency Shut-Down Procedures

In the event of an emergency, the Santa Clara Plastics Nitride Etch Wet Bench should be shut down by:



  • Pressing the EMERGENCY POWER OFF button -- on the upper left corner of the control panel. This will shutdown all power to the bench.


  • If the exhaust shuts down while there are chemicals in the benches EVACUATE THE LAB.




 The Nitride Etch wetbench is to be used by people who are etching or stripping nitride from silicon or quartz wafers, performing clean processing on Si or SiO2 substrates which cannot be processed at another wetbench (using personal quartzware).

Do not work at this wetbench unless you are on the qualified users list. To get on the list contact the trainer responsible for the wetbench.

No glass, GaAs, or wafers with metal on them may go into the nitride bath. No metal tweezers may be cleaned at the wetbench; they are cleaned in the litho solvent hood.

General Wet Processing Policies;

  1. You may not work at this station until you have been checked out by the principal technician and added to the qualified users list .
  2. You must be familiar with the Material Safety Data Sheets (MSDS) of the chemicals you will be using.
  3. You must be aware of the locations of the safety shower and eyewash (be able to locate it with your eyes closed).
  4. You will find ARGDRI;s (highly absorbent, chemical resistant pads) located near each wetbench. They are to be used for chemical spills. Know where they are and how to use them (read the Safety Manual).
  5. You must not work at this station unless someone else is in the lab. You will not be able to enable the bench unless another person has been active in the lab in the last 60 minutes.
  6. Wear a faceshield, apron and yellow Nitril gloves when working a the bench.
  7. Be sure the main power to the bench is on.
  8. Verify the exhaust is working by looking at the magnehelic gauge (near the floor on the right hand side). It should read greater than 0.5.
  9. Wear yellow Nitril (chemical resistant) gloves under vinyl 'flexigloves'. The yellow Nitril (chemical resistant) gloves are to protect you from the chemicals and the vinyl gloves are to keep the wetbench free of contamination. If you touch anything besides the cassette you are working with, the gloves should be replaced before you handle the cassette again. Fresh vinyl gloves are especially important when loading and unloading the spin dryer.
  10. Do not leave wipes on the deck of the wetbench; the venting is strong enough that they will be sucked to the back of the bench and quite possibly into a hot pot. This contaminates the hot pot and requires a system shutdown to clean. Call a technician if this occurs.
  11. Do not leave chemicals at the wetbench or in the transfer cart. This is shared equipment, so do not tie the cart up. There are instructions for transferring chemicals in the lab on the door of the pass-through cart and in the Safety Manual.

Changing Chemicals

  • Check the log before you begin to see when the chemicals were last changed. The frequency of the change on these baths is dependent on the usage. Recommended changes are posted on the log sheet. A decrease in etch rate is a good indicator that the bath needs changing. Fill in any changes of chemicals you make on the log sheet.
  • The hot pot, the dump rinser, the spin/rinse dryer, and the plenum all drain into the general lab acid waste neutralization (AWN) system. These modules may be used only when the AWN is functioning. When there is a problem with the AWN, the yellow light (above wbnonmetal) will flash. When the AWN warning system is flashing, no processing at any of the acid wet benches is allowed; proceed with following instructions:
    Don't aspirate the phosphoric acid!
    If a cassette is already in the hot pot, finish the process and place the cassette in the dump rinser. Don't start the dump rinser!
    If a cassette is already in the dump rinser, stop the dump rinser!
    If a cassette is already in the spin/rinse dryer, continue the process.
    Once the AWN system alarm has been cleared, continue processing.
  • The hot pot must be below 50 °C to be drained. The wetbench controllers have a safety interlock which will prevent draining if the temperature is too high.
  • Rinse the hot pot out well and fill it up once with DI water before adding new chemicals. The hot pot drains to the acid neutralization system.
  • Remember to turn off the 'aspirate' button before adding chemicals to the bath.
  • Always Add Acids to water (AAA), never the other way around.
  • Always open bottles under an exhausted hood and be sure the bottle is far enough back under the hood to take full advantage of the exhausting of fumes and prevent them from escaping into the room.
  • Place the bottle cap upside down on the deck of the bench to prevent contamination from getting around the cap's edge and into the bottle upon replacement.
  • Do not touch the inside of the bottle cap or the area around the mouth of the bottle with your gloves. This will contaminate the chemical.
  • If the cap gets contaminated, rinse it thoroughly and replace it on the bottle.
  • If any chemicals get on the outside if the bottle, be sure to rinse and dry the bottle before returning it to the pass-through carts.
  • It is important to return chemicals to the pass-through ASAP (someone may be waiting to use them), and return them to the proper shelf. The shelves are labeled to prevent non-compatible chemicals from being stored together. Never leave chemicals at the wetbench or on the transfer cart. Even empty bottles should be returned to the pass-through cart.
  • The temperature controlled baths are labeled so be sure to put the correct chemicals in them. At the Nitride Wetbench, the temperature controlled Nitride Strip bath is in the center and the tweezers cleaning area is to the right.

Start-up and Run Procedures


General Information- Nitride Etch System

Before starting you should have verified that the power and exhaust are functioning properly. Before going any further; READ THIS;

  • Do Not operate the system without liquid in the hot pot.
  • Do Not operate the system without first mixing the phosphoric acid with a cassette handle. You must do this while the bath is at room temperature or you risk splashing acid back.
  • Do not operate the system without the cover in place.
  • Do not change flowmeter or settings on the controller.  The exception is the timer on the controller.  If you have a question about the settings or operation of the hot pot contact the technicians in charge of it.
    DI water drip: 4 - 5 (do NOT change it!)
    Coil water flow: 7 (do NOT change it!)
Additional tips for successful nitride etching or stripping
  • Start with an 50:1 (2%) HF dip, dump rinse and spin/dry at wbnonmetal.  This removes any native oxide which will inhibit the nitride etch. Then take the cassette with handle over to the hot phosphoric bath.
  • Be sure to mix the solution before heating it.  This is to make sure that the water is not 'floating' on top of the phosphoric acid.  Not mixing it may cause a splash-back when you immerse your wafers into the hot solution.  Use a clean cassette handle to 'swish' the chemical.
  • The interlock to the nitride etch hot pot is the low liquid sensor.  If it is lit, make sure that you have enabled the bench.
  • The liquid should be filled up to over the red rectangles but under the black printing.  It is about two bottles of phosphoric acid.
  • The bath is set for 155 ± 0.7 °C.  It will take about 45 minutes for the bath to reach temperature.  Plan accordingly.
  • Use the non-metal cassettes and handles (yellow button) for nitride etch.
  • Leave the cassette handle on the cassette when putting your wafers into phosphoric bath.
  • The DI water drip light will turn on automatically based on the temperature of the bath (starting at about 100°C). No need to make any adjustments to it.
  • Be very careful removing the cassette from the hot phosphoric bath.  The high temperature, 155 °C, causes the Teflon to expand, making the cassette and handle feel 'loose'.
  • Wafers go directly from the hot phosphoric bath into the dump rinser.
  • Photoresist should not go into the bath; the chemistry will destroy the resist, causing contamination of the bath.
  • Selectivity of nitride to Silicon and Silicon Dioxide is very good.  The etch rates per min are;
Etch rates for materials based on 10 min etch.  
Nitride (low stress) ~32A /min
SiO2 ~0.8A /min
Si/Poly ~0.8A /min



Nitride Etch Controller


The operator control panel looks like this:

Wbnitride controller

Located under the Temperature and Timer display windows are the Status and Alarm LED's.  In the normal stand by mode, i.e., the wetbench not enabled and the bath not at temp, only the Alarm status indicator should be lit and flashing.  An audible alarm may be functioning as well.  The following Alarm indicators should be lit; L Temp and Liq Level.

When the wetbench is enabled the Liq Level LED will turn off.  Alarm and L Temp will stay on until the bath has reached it proper temp.

The STATUS LED display panel has the following indicators;

Normal- the controller is in normal operating mode.  All parameter conditions have been met.

Hold- the controller is in standby condition.  The TIMER will display HOLD alternating with the current timer count.  Various alarm conditions will put the controller in hold state.  HOLD is exited by pushing the HOLD (on-off) button on the Power panel.  When in the hold state the power to the bath heaters and DI H2O drippers is denied.  If the timer was on at the onset of the hold condition it will continue to count.  It may not be started if controller is on hold state.

Setup- the controller is in setup mode.  This mode allows for selected parameter values and limits to be entered.  Lab users should not have need to change any parameter except time (described later in this document).  If you think you want to change any parameters or that are set incorrectly, please see one of the technicians responsible for the wetbench.

Alarm- indicates the controller or process has gone outside the preset tolerances.  There will be another LED lit to show which parameter has drifted.  Alarm status mode will go off when the tolerance is back to normal.

Heat- shows that power to the heating portion of the bath is on.  As the bath reaches temperature, the LED will be lit only a fraction of the time.  At temp it should light about every 10 seconds.

DI H2O-indicates the dripper is adding DI water to the bath.  You should check to make sure the flowmeter indicates water is flowing at least once during you process.

The ALARM LED display panel has the following indicators;

System- the controller has a problem with the software which has been detected by the diagnostic routines.  The unit may need to be re-powered or commands need re-entering.

Sensor- indicates that the process temp or redundant over-temp sensor is either open, shorted or not connected.  Heater input is stopped and the temperature flashes in the process temperature display alternating with "SN".

Redundant High Temp- indicates that the redundant over-temp thermocouple has sensed the bath temperature to be over 10 degrees above the set point.  When the bath has returned to normal temperature the controller has to be turned back on by pressing the "PWR (on-off)" button and the "HOLD (on-off)" key.  Essentially, the system has shut off and must be re-started.

Hi-Acid Concentration- alarms anytime the concentration of acid raises the boiling point of the solution to other than the process set point.  Two °C above the set temperature of 155 ± 0.7 °C, the system will add DI water. When it alarms several actions are initiated; the dripper adds water to the bath as the controller increases the bath temp seeking the boiling point.  If the boiling point is not attained within five minutes, the controller will place the bath into HOLD status shutting off the dripper and heater.  When this alarm is activated the process display will read "HI" with the sensed bath temp. DI water drip: 4 - 5 (do NOT change it!).

Low-Temperature ("L TEMP")- If the bath temperature drops below the set point once it has risen to it during warm-up the LED will activate.  The bath temp and "LO" will alternately flash in the temperature display.  No other controller functions will be triggered.

Liquid-level ("LIQ LEVEL")- both high and low liquid conditions are monitor and if sensed heater and dripper activity are suspended until the condition is rectified.  The process display will flash the "LL" symbol alternating with the bath temp.

POWER KEYS segment contains the following membrane keys and their functions;

PWR (on-off) and HOLD (on-off) keys- in the case of a power outage or emergency power off at the wetbench, the controller will remain off (all display black) until the PWR key is pressed.  Once pressed the system goes into HOLD status, i.e., power is denied to the heaters and the DI dripper.  Pushing the HOLD key will activate full controller functions.  A second pressing of the HOLD key will but the system back into HOLD status.  Pressing the PWR key a second time will return the system to a dormant condition.

The usual stand-by mode of the wetbench is HOLD status (because the interlock is on the liquid level sensor), hence HOLD must be pressed in order to activate the heaters and dripper.

ADJ DRIP key- will only work for the period of time it is depressed.  It adds DI water to the bth via the dripper.  Generally, labusers will not need to use it unless to verify that the dripper system works when there is doubt about it.  Adjustments to the DI water flow are made by SNF staff.

ALARM SILEN key- turns off audible alarms (du...) and will stop any alarm prompts which are flashing in the temperature window.  Any  alarm LED's which are lit will remain lit.  The audible alarms will not turn back on to signal any conditions which have already been announced.

SETUP keys are used for programming the controller (so the average user should not have to adjust them) and have the following functions;

POLL PARAM key enters the controller into program mode.  It steps through the various parameters and displays their values in the temp and time alpha-numeric windows.  Below is the key to the parameter code.  All changes, except for time, are made by staff only.  Users may be locked out of the program capability by an access code.

Code Description Range and Units

CS Timing Period, 0 to 99:59 mm:ss (you may change time)
PA Timing Pre-alert 0 to :59 sec
BR Boil Rate, 0 to 10 % power/10 7.5 %
SP Process Temperature Set Point, 0 to 250.0°C 155 °C
LO Low Temperature Alarm, -0 to -50.0 °C -15 °C
AC1 Access Code, Security Level 1, 2 digits, 01-99 ------
CA RTD Calibration, +/- 9.9 °C 0
Cd Timer Count Direction, Down or Up Down
LS Liquid Level Sensor Alarm, N/O or N/C 00
AS Aux. (optional) Alarm, N/O or N/C 01

ARROW keys are used to change the value of the displayed parameter.  They may be temporary or saved to the EPROM as permanent values.  See SAVE.

SAVE key, when pressed in the set-up mode will save the parameter values to memory.  To temporarily change values, do not use the save key.  Use EXIT.

EXIT key returns the controller to normal operating mode from the setup mode.  Any parameter values which were changed, but not saved will be lost.

VIEW SET PT key displays the desired boiling point temperature and the length of the timing cycle.

TIMER KEYS segment ;

STOP/RESET key brings up the value of the timing period  in the TIME display window.  Once started, the timing period may be temporarily halt the timer by pressing STOP/RESET once.  Pressing START will resume the count.  Pressing STOP/RESET twice will set the timer back to the original value.

START key initiates the timing cycle.

STOP/RESET key- once the timing cycle period is entered using the 'CS' parameter, press STOP/RESET to bring the new value up into the TIME display window.  The count down (or up) can be temporarily halted by pressing STOP/RESET once.  Pressing it again resumes the count at the point it was interrupted.  Pressing the key twice quickly will reset the timer to the original time.  STOP/RESET also stop the pulsing count which started at the end of the timing period.  ALARM SILEN will stop a audible alarm.

One added feature is to see the original time period entered while in timing mode, press VIEW SET PT.  The value will appear in the TIME display window momentarily.   



Spin-Rinse Dryer (SRD)




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
1 0 20
 2 400 180
x   x
 3 2000 10
 4 2000 120 0   x   x    
 5 1000 120
  x   x    x
 6 600 60 0   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. The 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.

Short Sheet for wbnitride


  1. Enable wbnitride.
  2. Use a cassette handle to careful swish the acid in the etch bath.
  3. Turn coil water flow on to 7.
  4. Press the PWR and then HOLD (on-off) buttons to start heating the bath.  The Liq Low alarm should light should go off, but the L Temp light will turn on. Heating the bath to 155 °C should take about 45 minutes or less.
  5. Press ALARM SILEN to stop the audible alarm.
  6. Monitor the heating of the bath by periodically looking at the controller for alarms.
  7. Change the etch time if desired by toggling to the CS parameter.  The up and down arrows will change the value.
  8. Carefully lift the top of the bath and place an etch Teflon cassette (yellow button) with your wafers in it into the bath.  Be careful, as the bath is tall.  Leave the handle on the cassette.  The bath is hot enough that the Teflon expands and will make it impossible to insert the handle once at temperature.
  9. Very cautiously remove your cassette when the timer alarms.  It will be 'loose' because the temperature of the bath.
  10. Rinse and dry.
  11. Press PWR to turn off the bath.
  12. Turn coil water flow back to 0.
  13. Disable wbnitride.


Interlocks and Safety Features

The Santa Clara Plastics Nitride Etch Wet Bench is equipped with Several interlocks and safety features to protect personnel from the hazards described in above. It is important to bear in mind, however, that no system is entirely fool-proof -- there is no substitute for a thorough understanding of the operating procedures, maintenance procedures, potential hazards, and safety procedures associated with this piece of equipment.





  1. There is an interlock that prevents the hot pots from being aspirated at too high a temperature (must be below 50 degrees C). An alarm will sound when you attempt to drain a solution that is too hot.


  2. When the DRAIN/ASP light is on there is an interlock to disable the HEATER ON/OFF button.


  3. The drain/aspirators will automatically time out after 10 minutes, unless you press the button again to reset before the 10 minutes are up.


  4. There is an overtemp interlock that will shut off the power to the heater. A reset button will allow the heater to turn on, but if the temperature is still indicated as being to high the heater will again turn off.






  1. If there is a low liquid level in the recirculation loop, RUN will default to the STANDBY condition. In this condition the heater will not operate and the recirculation will discontinue.


  2. If the system overtemps the heater will shut down, the pump will stop and the low level light will go on. When the temp drops the low level light will go off, but the heater will not go back on until it is reset.


  3. HEAT light indicates that the system is heating the closed recirculating loop to bring up the temp of the bath.


  4. RECIR light indicates that the system is recirculating solution that is within .25 degrees of the setpoint.





  1. There is a continuous purge of the dump rinsers and a dump cycle automatically every 90 minutes. The DUMP DOOR must be closed.


  2. The temperature set point, undertemp limit, overtemp limit, process time, and prewarn time are all programed into the controller. Only the principal operator of the benches will have access to modify these setpoints.


  3. If the power is turned off to the station, the memory will remain stored for ~10,000 hours.


  4. The timer has a four second prewarn alarm that beeps for ~4 seconds just prior to the end of the clean cycle (this gives the operator time to get ready to remove the wafers).


  5. Pressing the stop button during the cycle will freeze the display (wafers may be lifted for inspection). Pressing start again will continue the timing.

Routine Maintenance and Calibration Procedures



  1. Keep the bench top clean. Rinse off any drips of acid with the DI gun and dry using N2 gun.


  2. Do not leave cleanroom wipes on the bench, as they will be sucked to the back of the bench and into the chemical baths contaminating them and causing a potential fire hazard.


  3. Once each morning a clean cassette should be run through the spin dryer to rinse it out. This will also let you know if the water resistivity is OK. When the spin dryer is on Auto, it will not spin dry until a high enough resistivity is obtained.


  4. Check over the bench for damage to hot pots, temperature sensors or other obvious problems. Notify the technician in charge if any problems are observed.


The facilities requirement of the Santa Clara Plastics Nitride Etch Wet Bench are as follows:


Required facilities:



Acid Waste (HF)


Acid Waste (Neutralization)


Deionized Water


Exhaust Scrubbed


House Nitrogen


Industrial Water




Facilities not required unless used:



Oil Free Compressed Air

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