SESSION 1: RCA Clean and Field Oxide Growth

Substrate Doping: ______

Orientation: ______

  • Preparation
  1. Turn on oxygen tank
  2. Turn on nitrogen on the panel
  3. Turn On the main circuit breakers for furnace.
  4. Disable alarms by pressing “silence” on all 4 furnaces.
  5. Turn on power on furnace (tube1) by holding the power button and flipping the switch
  6. on the front panel ,press enable for the wet oxidation furnace.(this ensures gas flow is ON)
  7. Turn on the Nitrogen supply (check behind for nitrogen flow in flowmeter)
  8. Set the temperature on the master reader to 1100o C.
  9. open bubbler and fill water to 2/3rd of the capacity(ensure that the water level does not obstruct the flow of oxygen into the bubbler)
  10. ON heater and set the ribbon heat element to 25 % (note: if smoking occurs around the ribbon heat element turn knob to less than 25%)

Since the wet oxidation is performed in a water vapor ambient, the bubbler should create as much water vapor as possible. Therefore bring the bubbler up to boiling and maintain the temperature around 100º C. Meanwhile,

  1. Mix a solution of H2O:H2O2:NH4OH (5:1:1) and heat it on a hot plate at setting 3.
  2. Mix a solution of H2O:H2O2:HCl (6:1:1) and heat it on a second hot plate at setting 3.

These solutions are needed for the RCA clean.

  • RCA Clean
  1. Load wafers into wafer rack (holds 8).
  2. 12 minutes heated H2O:H2O2:NH4OH (5:1:1).
  3. Rinse in running DI water 1 minute.
  4. 15 seconds in BOE (10-1). BOE is held in a plastic or teflon beaker.
  5. 12 minutes heated H2O:H2O2:HCl (6:1:1).
  6. Rinse in running DI water 1 minute.
  7. Place wafer on a technicloth and blow dry. Inspect for cleanliness.
  8. When the solutions have cooled, dispose of properly and rinse glassware.

** Note: Waste bottles for solutions containing H2O2 must have vented (white) caps. This is VERY important!

  • Wet oxidation
  1. load the wafers onto the boat.
  2. after the furnace reaches a temperature of 11000 C ,turn the knob on the oxygen cylinder to let oxygen out (pressure should be 15 psi) and in the front panel switch ON oxygen and off nitrogen.
  3. Check in the flowmeter if oxygen is flowing into the furnace.
  4. After 10 min open the glass cover of the furnace
  5. Wait 15 seconds, then slide the boat one-quarter of the way to the center. Repeat until the boat is in the center of the furnace.
  6. close the glass lid.
  7. After 50 min ,pull the wafers out of furnace the same way it was pushed into the furnace.
  • Remove wafers
  1. Place wafers in Petri dishes.
  2. Turn off the breakers of furnace on the wall.
  3. OFF oxygen, ON nitrogen.
  4. Once the furnace cools, turn off the nitrogen flow on the rotameter panel. Turn off the nitrogen supply on the wall. Replace cap.
  5. turn off the main power circuit breaker
  • Measure thickness
  1. Use the Filmetrics system to measure the thickness of the field oxide layer. The target thickness is 5000 Å.
  2. Compare this measurement to what you might expect from the attached chart of oxide colors and graphs of oxide thickness vs. time.

SESSION 2: Base Photolithography and Source/Drain Etch

  • Photoresist spin
  1. Ethanol scrub with a swab, Ethanol, LIMONENE, Methanol spin 5 seconds each.
  2. Dehydration bake at 120º C hot plate for 3 minutes.
  3. Make sure there is liquid in the HMDS beaker. HMDS vapor application 3 minutes.
  4. Make sure that the vent valve on the photoresist spinner is closed (in this position, the "T" on the top of the valve points away from the open nozzle). Spin 5206E photoresist at 6000 rpm for 30 seconds.
  5. Open the vent valve in order to remove the wafer. Close it again for the next user.
  6. Wait between 4 and 10 minutes.
  7. Soft bake 100º C 2 minutes.
  8. Wait for another 2 minutes.

The TA should make sure that the mask aligner is in operating condition before starting. This includes turning on the UV lamp, the vacuum, nitrogen, and air on the wall, the microscope light, the power switch for the mask aligner, and the switch for the compressed air on the flowmeter box. The 2" wafer chuck and mask holder should also be installed.

  • UV Mask aligner exposure
  1. Slide the mask holder into its seat in the mask aligner.
  2. Place the wafer on the wafer chuck and slide the carousel under the mask holder. Raise the wafer using the lever on the left side of the machine. Now use the x- and y-micrometers to position the wafer underneath the hole in the mask holder. Lower the wafer and retract the carousel.
  3. Remove the mask holder and place it upside-down on the table. The mask for the base lithography is marked 1A & 1B. Place the mask on the mask holder with the metal side facing up. (This way, once the mask holder is turned over, the wafer contacts the metal pattern on the mask.) Turn on the "Vacuum Mask" switch on the console. Place the mask holder in the aligner and tighten the screws gently.
  4. Slide the carousel underneath the mask. Raise the wafer with the lever until either a) the lever is in the 11 o'clock position, or b) the wafer makes contact with the mask.

(It is possible to see the wafer make contact with the mask by looking at the reflection of the mask in the wafer through open areas of the mask. As the wafer is raised into contact with the mask, the reflection disappears.)

  1. Use the variable thickness adjustment (the dial at the front of the machine which looks like a potentiometer) to either raise or lower the wafer so that it is just barely in contact with the mask with the lever in the 11 o'clock position.
  2. Turn the lever completely so that it sets (at about the 9 o'clock position).
  3. On the console, change the switch from "Standard" to "MJB HP3". Set the exposure time to 10 seconds.
  4. Press the green button to expose. This mask aligner is old and needs a little help retracting at the end of the exposure.
  5. Return the console switch to "Standard".
  6. Lower the wafer, retract the carousel and remove the wafer.

Do not take the wafer out of the photolith room until you are certain that wafer is developed fully!

  • Develop
  1. Develop the wafer in AZ 400K (1:4 diluted) until the wafer "flashes", and then an additional 20 seconds. Agitation is important. The total developing time should be less than or about one minute. (If it is longer than one minute, then the exposure time should have been longer than 10 seconds.)
  2. Rinse the wafer (in the wafer rack) in running DI water for one minute.
  3. Blow-dry completely on a technicloth. Inspect under the microscope.
  • Tencor (profilometer) plot
  1. Make a Tencor plot of one of the transistors on your wafer across the source and drain regions. This measurement reveals the thickness of the photoresist layer.
  • Etch source and drain regions
  1. Fill a teflon beaker with BOE.
  2. Etch the wafer until regions unprotected by photoresist appear to have been etched down to silicon, and then for 1 additional minute. Agitation is important. The etch rate of thermally-grown SiO2 in BOE is approximately 500 Å/min.
  3. Place wafer in rack and rinse in running DI water for 1 minute.
  4. Place on technicloth and blow dry. Inspect visually and under microscope.

At this point, if it seems that the etch is not complete, it is useful to Tencor the sample again to establish how much of the SiO2 layer has been etched away. The wafer may be placed back into the BOE and etched for additional time if necessary.

  • Tencor plot
  1. A profile taken at this point should confirm the Filmtronics measurement.
  • Resist strip
  1. Rinse with acetone for 30 sec.
  2. Rinse the wafers in running DI water for 1 minute.
  3. Blow dry on a technicloth and inspect.
  4. Any resist remaining on the wafers may be removed with either an oxygen plasma, a few minutes more in the stripping solution, or both.
  • Clean mask

SESSION 3: Sacrificial Oxidation (Dry oxidation)

  • Preparation/Turn on the furnace
  1. Mix a solution of H2O:H2O2:NH4OH (5:1:1) and heat it on a hot plate at setting 3.
  2. Mix a solution of H2O:H2O2:HCl (6:1:1) and heat it on a second hot plate at setting 3.
  3. On circuit breakers for furnace on the side wall.
  4. Disable alarms by pressing “silence” on all 4 furnaces.
  5. switch on the dry oxidation furnace (tube 2)
  6. on the front panel ,press enable for the wet oxidation furnace.( this ensures gas flow is ON)
  7. Turn on the Nitrogen supply (check behind for nitrogen flow in flowmeter)
  8. Set the temperature on the master reader to 1050o C.
  • RCA Clean
  1. Ethanol scrub with a swab, Ethanol, LIMONENE, Methanol spin 5 seconds each.
  2. Load wafers into wafer rack (holds 8).
  3. 12 minutes heated H2O:H2O2:NH4OH (5:1:1).
  4. Rinse in running DI water 1 minute.
  5. 15 seconds in BOE (10-1). BOE is held in a plastic or teflon beaker.
  6. 12 minutes heated H2O:H2O2:HCl (6:1:1).
  7. Rinse in running DI water 1 minute.
  8. Place wafer on a technicloth and blow dry. Inspect for cleanliness.
  9. When the solutions have cooled, dispose of properly and rinse glassware.
  • Prepare furnace for operation
  1. After the furnace temperature reaches 1050o C , open oxygen tank regulator. Also open the gas outlet on the regulator.
  2. ON oxygen, OFF Nitrogen.
  3. Run for 10 minutes.
  • Dry oxidation
  1. Load wafers into the 2" wafer boat, all facing into the gas flow. The loop should be at the rear of the boat - it is for pulling the boat out of the furnace.
  2. Place the boat in the carrier. Once the ten minutes have elapsed, carefully place the carrier against the end of the furnace tube and push the boat into the furnace with the quartz rod.
  3. Wait 15 seconds, then push the boat one-quarter of the way to the center. Repeat until the boat is in the center of the furnace.
  4. Place the cap on the end of the furnace (be careful!).
  5. Monitor the oxygen flow. Heat for 1 hour.
  • Remove wafers
  1. Turn off the furnace by flipping the breaker on the front.
  2. Remove the wafer boat by quarters - move the boat, wait 15 seconds, move the boat, etc. Drag the boat onto the carrier to remove from the furnace.
  3. Place wafers in Petri dishes.
  4. Turn off oxygen on the rotameter panel and at the cylinder
  5. Turn on nitrogen flow on the rotameter panel.
  6. Turn off the furnace breakers on the wall.
  7. Once the furnace has cooled, turn off nitrogen flow on the rotameter panel.
  • Tencor
  • Photograph
  • Mount wafers on 4" carriers with black wax
  1. In the black wax hood, place a 4" Si carrier on the hot plate. After a short time (about one minute), melt a small amount of black wax onto the carrier in two places, so that two 2" wafers will fit on the carrier.
  2. Place two wafers on the carrier. Press in place with a toothpick if necessary.
  3. Remove carrier and allow it to cool. Check to insure that the wafers are firmly attached.

SESSION 4: Ion Implantation

This step is performed outside of UVA. No lab this week.

Dose: ______

Energy: ______

Species: ______

SESSION 5: Etch Gate Region

  • Remove wafers from carriers
  1. Place the carrier on the hot plate in the black wax hood.
  2. Once the wax is hot, it is possible to slide the wafers off of the carrier with a toothpick.
  3. Rinse the wafers in 3 beakers of LIMONENE for 20 seconds each, then a beaker of Methanol for 20 seconds. Blow dry on a technicloth wipe and inspect.

Note: if G-wax (which is clear) was used in place of black wax, it is necessary to use acetone as the solvent in place of LIMONENE.

  • Photolithography
  1. Follow the instructions from SESSION 2, Base Photolithography, from their beginning through "Develop". The only change is that now mask #6A & 6B should be used.

A complication which arises in this step and all subsequent steps is that it becomes necessary to align the features on the wafer to the mask. Be very careful that the orientation of the wafer on the carousel matches the orientation of the mask!

  • Etch gate region
  1. Fill a teflon beaker with BOE.
  2. Etch the wafer until regions unprotected by photoresist appear to have been etched down to silicon, and then for 1 additional minute. Agitation is important. The etch rate of thermally-grown SiO2 in BOE is approximately 500 Å/min.
  3. Place wafer in rack and rinse in running DI water for 1 minute.
  4. Place on technicloth and blow dry. Inspect visually and under microscope. The wafer may be placed back into the BOE and etched for more time if necessary.

It is possible to monitor the progress of the BOE etch by repetitively etching for short periods of time and measuring with the Tencor. If open regions become deeper with continued exposure, then the BOE is removing material and the etch is incomplete. Conversely, if open regions are not etched deeper with continued exposure to BOE, then the etch is finished. This technique is useful, but may not be found to be necessary here.

  • Resist strip
  1. Put all the wafers in the wafer rack, and place the rack in acetone for at least 2 minutes. Stir.
  2. Rinse the wafers in running DI water for 1 minute.
  3. Blow dry on a technicloth and inspect.
  4. Any resist remaining on the wafers may be removed with either an oxygen plasma, a few minutes more in the stripping solution, or both.
  • Clean mask

SESSION 6: Gate Oxide Growth

This process is identical to SESSION 3, Sacrificial Oxidation, with the exceptions that

  1. The oxidation should last 2 hours.
  2. There is no need to mount the wafers on carriers at the end.
  • Tencor

SESSION 7: Etch Source/Drain Contacts

This process is identical to SESSION 5, Etch Gate Region, with the exceptions that

  1. There is no need to remove the wafers from carriers at the start of the session.
  2. Mask #5A & 5B should be used.
  3. In this session it is the source and drain contacts, rather than the gate, which are etched. It is here that the method of monitoring the BOE etch with the Tencor is most likely to be useful.
  • Tencor
  • Clean mask

SESSION 8: Evaporate Aluminum

  • RCA clean
  1. Mix the solutions and follow the directions for RCA clean as under SESSION 3, Sacrificial Oxidation.
  • Mount wafers on evaporator carousel and load into evaporator
  1. Close and pump down evaporator.
  • Deposit 2000 Å of aluminum.
  • Remove wafers

SESSION 9: Aluminum Contact Lithography

  • Photolithography
  1. Follow the instructions from SESSION 2, Base Photolithography, from their beginning through "Develop". Use mask #3A & 3B.
  • Etch contacts
  1. Heat a beaker of Transene Type D Aluminum Etchant to 50º C.
  2. Etch wafer until it flashes, then 20 seconds extra. The etch rate is approximately 100 Å/sec.
  3. Rinse in the wafer rack, 1 minute in flowing DI water.
  4. Blow dry on a technicloth.
  5. Inspect, especially for undercutting. Etch more if necessary.
  • Resist strip
  1. 30 seconds rinse in Acetone
  2. Blow dry.
  • Clean mask

SESSION 10: DC Testing

Use the Semiconductor Parameter Analyzer in the probe room.

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