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Drytek4 Model 100 (modified), drytek4

The Drytek plasma etchers at SNF all use chlorine and fluorine-based chemistries for etching various Si, polysilicon, nitride, tungsten, tungsten silicide films. Drytek4 is a contaminated etcher. It has been modified to use a single electrode. Drytek4 (contaminated) also has additional capabilities for oxide etching and argon sputter etching.

Picture and Location

 Drytek4

Background

Drytek 4 is a Plasma Etcher used primarily for etching oxide and nitride films on Ga As and silicon substrates. Poly, Si, Ti, and Resist may also be etched in Drytek 4. Non-standard metals, such as gold may be put in Drytek 4, but these metals may not be etched.  See the Materials section of our web site for details.

Drytek 4 has one etch electrode and differs from other Dryteks (RIE) and uses SF6, CHF3, F318, C2F6, Ar, N2, O2. Contact Jim McVittie to approve any process not indicated.

 

 

Process Capabilities

Cleanliness Standard

 Drytek4 is considered contaminated.

 

Performance of the Tool

What the Tool CAN do

  • Standard recipes for etching oxide and nitride films on Ga As and silicon substrates.

What the Tool CANNOT do

  • Non-standard metals, such as gold may be put in Drytek 4, but these metals may not be etched. 
 

Special Notes or Restrictions:

This system is gold contaminated. Check the Materials section for Material and Equipment Compatibility.

 

Contact List and How to Become a User

Contact List

The following people make up the Tool Quality Circle:

  • Process Staff: Usha Raghuram
  • Maintenance: Elmer Enriquez
  • Super-Users:  Jim Kruger (jimkruger@yahoo.com)

 

Training to Become a Tool User

We do not have a staff member assigned to training on it at this time.  What we suggest is that labmembers wanting training on the tool contact a trained research group co-worker or other trained labmember for training and/or shadowing.  Once the 'trainee' is comfortable in the use of the tool they contact the responsible Process Staff member for badger qualification.  This is done with the understanding that the newly trained labmember may be approached for training eventually.

If you cannot find someone to train you after looking at history in badger please contact the responsible Process Staff member and a trainer will be identified.

The labmember is responsible for having read and understood any and all documentation related to the tool. A Training Check List is included in these Operating Instructions. It can be a good tool to make sure everything has been covered in the shadowing session.

Please print and fill out this Shadowing Form. After the session give the form to the responsible staff member for qualification.

 

 

Operating Procedures

General Operating Information

  • The Main system electronics are ON at all times.
  • The Vacuum pumps are located in the basement and are ON.
  • No pre treatment is required
  • No post treatment is required.

 

Gas Information:

GAS SWITCH #

Chemical Symbol

Chemical Name

Maximum flow

1

C4F8 or C2F6

F318 or 116

   1 slpm

2

Ar

Argon

200 sccm

3

SF6 or CHF3

Sulfur Hexafluoride or Freon 23

100 sccm

4

O2 or N2

Oxygen / Nitrogen

20 sccm

 

Button Information

MICRO RESET

  • Resets the Microprocessor memory and starts 2 pump/purge cycles. Push (the blue light comes on) and release the button. MICRO RESET does not work unless the button pops back out (the blue light goes out).
 

CYCLE START

  • Starts the microprocessor program.
 

CYCLE HOLD

  • Holds the microprocessor at the current step in the program. If the program is running, the timer continues timing, the plasma continues etching. Press a second time to end the CYCLE HOLD (if the time is up the etch ends).


CLEAR WAFER

  • Press to end a process before the timer has timed out. The gases will be pumped out of the chamber. The chamber will be vented.
  • CLEAR WAFER also allows you to end one process before the time is up and will advance to the next selected process.

 

Operating Procedure

Check Standby Conditions

  • Check the Reservation page and the machine status (problems, shutdowns) on the computer lab management system.
  • Check the front top panel.
  • White PROCESS select buttons (1,2,3) OFF
  • Pressure ~ 200 – 400 mTorr
  • CYCLE START, CYCLE HOLD and CLEAR WAFER buttons OFF.
  • Green Standby light is ON (Low N2 is flowing).
  • Should be pumped down (momentarily put the chamber toggle down to the OPEN CHAMBER position, the lid should not raise).

 

Check the lower left panel:

  • The VENT toggle switch should be down, at the VENT position.
  • Machine button – ON.
  • System button – ON.
  • Mechanical Pump button – ON.
  • Blower button – ON.
  • If any of these 4 buttons are not on, DO NOT proceed. Notify maintenance or technician.
  • RF Power Supply (white) breaker in down position – OFF.
  • Cooling water flow meters (3) should be at their mark or above.

 

Check the lower right panel:

  • Cap and Coil toggle – MANUAL.
  • The BIRD Meter’s arrow pointed to the right (FWD) to read power (wattage).

 

Check behind the machine:

  • Gas Whitey valves – OFF, except for the gases used by the previous user.
  • Gas supply valves (round) are ALL CLOSED at this time.

 

Setup and system check:

  • Enable “Drytek 4” and turn EMPTY sign over to “IN USE”.
  • Press “stand-by” to end the pump program. It will automatically vent the chamber, once vented the red LED light is on, wait an additional ~3 minutes, as it cycles through several times.
  • Press the chamber lift toggle switch down to open the chamber.
  • Inspect for cleanliness or any other problem.
  • Push the chamber lift toggle switch up to close the chamber.
  • Pump all gases out of the shared gas lines that you intend to use by,
  1. Select the appropriate white Process button(s) 1, 2, 3 (should light up).
  2. Select the gases to be purged from each process button(s) 1, 2, 3, by pushing the Dip rocker switches for each gas needing to be purged.
  3. The gas Whitey valve should be pointed to the ON position in the back, leaving the round valve close for purging.
  4. Make sure, CYCLE HOLD, CLEAR WAFER and STANDBY buttons are off (no lights on).
  5. Press CYCLE START to pump out the gases from the gas lines.
  6. Run with NO wafer loaded and NO RF for about 10 minutes, Pressure will drop below 70 mTorr when gas lines are completely empty
  7. Once time has elapse, process ends.

 

Running DRY RUN Setup:

  • Turn the desired gasses ON at the wall behind Drytek 4 and undesired off by rotating the gas Whitey valve.
  • Open the desired gas with the round valve.
  • RF time toggle switch(s) should always be in the UP position (laser isn’t an option).
  • Set the process time(s) using the thumbwheel; Left two digits are minutes and right two digits are seconds. Give yourself enough time to adjust setting (20 minutes).
  • Turn on the RF power supply below (white breaker), the red light will come on.
  • Press the CYCLE START button.
  • Allow for gascvstabilization and adjust as necessary.
  • With the plasma running, adjust the RF power to the desired wattage. DO NOT operate Drytek4 above 150 watts.
  • Use the Bird Meter for accurate measurement of the forward and reflected power. Read the top scale, the range is 0 – 250 watts.
  • If the reflected power is >5 W, set the Machine’s analog meter (turning the knob) so the arrow is pointing towards “REV PWR”.
  • Adjust the cap and coil pots (for each process) in manual mode to get the reflected power down to less than 5 watts.
  1. There is one pot each for adjusting cap and coil to lower reflected power on each process 1, 2, 3.
  2. Start by using the pot settings last used
  3. Adjust (tune) the cap and coil pots while watching the analog meter on the RF power supply. You’ll Need to do this for each Process (1, 2, 3) you intend to use.
  4. It may be necessary to push “Cycle Hold” once the process is running so that you will have time to make all the necessary adjustments. After the adjustments are made you can push “CYCLE HOLD” again to end the process (if the time is up) or to continue the process on the clock (if the time is not up).

 

Etch Procedure:

  • After the system is vented, push the chamber lift toggle switch down to open the chamber and place the sample(s) on the chuck.                   
  • Close the chamber door, pushing the chamber toggle up.
  • Make sure CYCLE HOLD, CLEAR WAFER, and STANDBY buttons are off
  • Set the process time(s) using the thumbwheel.
  • Press CYCLE START
  • Monitor the gas flows, pressure and RF power during the etching process
  • When the process is complete, the system will evacuate the gases and vent the chamber (~3 minutes). Open chamber by pressing toggle down and remove the sample.
  • Repeat the etch procedure until all samples are etched.
  • Close the chamber door, pushing the chamber toggle up.

 

Shutdown Procedures:

  • Turn off the white process selection buttons 1,2,3.
  • Toggle the RF power OFF (white breaker, red light goes out), left bottom panel.
  • Press “STANDBY” button (green light goes on).
  • Press “CYCLE START”, after pumping the chamber pressure should read in the range of 200 – 400 mTorr.
  • Turn off the round valves in the back of the system, leaving the black Whitey valves on so that the next user will know which gasses were last used for purging.
  • This leaves the system in the standby condition.
  • Make sure Log book is filled out and noting any problems.
  • Disable “Drytek 4 and turn the IN USE sign over to EMPTY.

 

Process Monitoring and Machine Qualification

Each month, tool qualification runs are performed on most tools in the SNF to monitor variations in each tool’s performance. The purpose of the Drytek4 qual is to monitor etch rates. The qual is performed by SUMO members, but users may perform the specified qual process before tool use if more recent qual data is desired for reference.

For more information on the SNF tool performance monitoring system and SUMO, please see the Monthly Tool Monitoring page under the Equipment tab on the SNF wiki.

 

Qual Process Overview

The Drytek4 qual runs two wafers through the SF6/F116 PECVD SiO2 etch process. One wafer with a 1.6um 3612 Photoresist pattern and one wafer with a 10,000A SiO2 coating are etched separately for two minutes. Nanospec measurements are taken before and after etching to calculate the PR and SiO2 etch rate respectively. To calculate the PR:Si selectivity, the two wafers coated in photoresist are then stripped of resist so that the Silicon step height may be measured via Alphastep.

 

Procedure

Wafers for Processing

SUMO Wafer #
(all Si 4" wafers)
Coating Pattern
(using SUMO mask)
Electrode to be Tested
46  10,000A SiO2 - gold
 88  -  1.6um 3612 PR pattern, 1min bake @ 110C  gold

 


Pre-Etch Wafer Measurements

All pre-etch measurements are taken on Nanospec. Reference the SUMO Characterization How-To's for Nanospec operating procedure.

For Wafer 46, use the Oxide on Silicon Recipe (#1). For Wafer 88, use the Positive Resist on Silicon Recipe (#10). Use 10x magnification for all measurements (Objective 1 on Nanospec).

  1.  Use the reference wafer to calibrate before measuring.
  2. Take readings for the Center, Top, Flat, Right and Left positions of the wafer. Readings should be taken about 15mm from the wafer edge.
        a.  For Wafer 88, measure the PR thickness, which is darker in color than the Si. Accidentally measuring the Si will result in a <100A reading.
  3. Calculate the averages.
  4. Record results on the SUMO Qualification Log Sheet. 

  

Etch Process

Before loading the wafers,  season the chamber so that the chamber surface chemistry is brought to equilibrium with the process being run. This enables the actual process to stabilize quickly after the plasma is turned on. This seasoning also leads to more repeatable etching result.

  1. Season the chamber for 10 minutes using the SF6/F116 SiO2 etch. Follow the standard operating procedure as outlined above, or on the procedure print-out at the tool. Be sure to check the program parameters while seasoning and adjust the resistor/capacitor settings as necessary.
  2. Run a separate etch for each of the two wafers. Each etch is 2 minutes.
             a.  Remember to bake Wafer 88 (PR coated) at 110C for 1 min before the etch.
             b.  Monitor gas flow rate, RF power, and reverse power. 
             c.   Keep the reverse power below 5W.
 

   3.    Record process settings on the Drytek4 process log.

 

 

Post-Etch Wafer Measurements

  1. Measure post-etch thickness for all wafers using the same Nanospec as before and the same respective Nanospec analysis recipes.
  2. Take readings for the Center, Top, Flat, Right and Left positions of the wafer. Readings should be taken about 15mm from the wafer edge.
  3. Calculate the etch-rate for PR and SiO2 by subtracting the post-etch thickness from the pre-etch thickness and then dividing by etch time.
  4. To calculate selectivity, measure the Silicon step height of Wafer 88.
  5.              a.   Strip the wafers of PR using the Strip.rcp recipe on Matrix.
                 b.   Measure the step height at each of the 5 points via Alphastep. Readings should be taken about 15mm from the wafer edge.
                 c.   Calculate the average step height.
                 d.   Calculate the amount of Si lost and divide by etch time to determine the Si etch rate.
  6.  Calculate the selectivity by dividing the PR etch rate by the Si etch rate.

 

Reported Data

Qual data may also be found on the Badger comment log. The following data is reported for the Drytek4 qual:

  • PR Etch Rate (3612)
  • Si Etch Rate
  • PR:Si Selectivity
  • SiO2 Etch Rate
  • SiO2:PR Selectivity

 

Qualification Results 

Machine Status States

  • Red: A major sub-system of the tool (RF power supply, mass flow controller, vacuum pump, etc.) is not functioning up to standard.
  • Yellow: A sub-system of the tool not common to all recipes is not up to standard. For example, RF tuning for Process 2 is down, or a specific gas is being replaced.
  • Green: System is up to standard.

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