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STS PECVD, sts

The STS is a plasma-enhanced chemical vapor deposition system which is used for low temperature (350°C) deposition of oxide, nitride, and oxynitride. Features:1) Low temperature PECVD (350°C) of silicon dioxide, silicon nitride, and oxynitride. 2) Large deposition electrode: up to 5 - 3", 4 - 4" wafers or a single 6" wafer can be accomodated. 3) Programmable dual frequency operation for precise stress control.

Picture and Location

 STS PECVD

The tool is located at B5 on the Lab Map.

Background

 

Process Capabilities

Cleanliness Standard

 

The sts deposition system is in the "Gold Equipment Group".

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

For equipment compatibility with specific materials, click <here>.

Performance of the Tool

What the Tool CAN do

  • Item A.

 

What the Tool CANNOT do

  • Item A.

 

Process Monitoring

 

Contact List and How to Become a User

Contact List

The following people make up the Tool Quality Circle:

  • Process Staff: Usha Raghuram
  • Maintenance: Jim Hayden
  • Super-Users:

 

Training to Become a Tool User

 

Operating Procedures

 

Special Notes:

 

This system is Gold contaminated. The PECVD STS deposition tool is mainly used for depositing of silicon nitride film. A mix-frequency program is available for this process. A low frequency program is available for the silicon dioxide process. The system is equipped with 13.56 MHz and 187.5 kHz frequencies. The temperature of the system is always kept at 350 degrees. Therefore, only the materials that are stable at this temperature are allowed in the STS deposition system. Please make sure you wear only latex gloves when you are working with this system. Don’t wear any vinyl gloves. Use only clean metal tweezers. You can process 4 of 4" wafers at a time (in the center of the wafer platen). With prior approval from staff, additional training is required for special processing of wafers coming out of the STS PEVCD with clean (non-contaminated) wafers. Separate tools needed for this procedure. To find out about the status of the system, check the run sheet filled out before you. Please make sure that you fill out a run sheet while you are running a process on the STS.

  1. Stand by mode:
    1. Make sure the Ar to the pump key is open (up). This key is the black toggle key located in the right hand side of the system. If the Ar Purge key is left off for a long time while you are not running any process, the chamber will get oil back fill from the pump. This will contaminate the chamber as well as your wafer. To clean this contamination the O2 descum program should be run prior to any process.
    2. Make sure that lights to the RF power supplies are on (green).

     

  2. Start up, Loading the wafer & deposit:
     
    1. Enable the STS on Coral. The keyboard on the STS will not work if the system is not enabled.
    2. Switch off the Ar purge key (switch down)
    3. Use the keys on the keyboard to select (F3) "vent"   from the menu.
    4. Pause for at least 5second before Selecting  "open valve" (F1). DOS software is old and slow to respond.
    5. This will start venting the chamber. Make sure you hear the sound of valve  opening. A message" venting the chamber, please wait" will appear on the screen. Check the process chamber lid seal. Wait until the seal is opened and there is a gap between the lid and the base of the chamber. This will take 2 -5 minutes.
    6. While pressing the two blue  buttons located under the chamber on the panel to lift the lid all the way up.  This should rise slowly so that you do not release any particles.
    7. Make sure there are no particles on the wafer platen. You can use the N2 gun located next to the system to remove the particles. Please make sure that the N2 gun is aimed downward to avoid any particle trapping in the shower head.
    8. Locate wafers in the center of the platen. Please note that the wafers start to move on the platen, when the pump down starts. So please load your wafers accordingly surrounding your samples with pieces so they don't move to an edge during pump down.
    9. Select  "close valve" (F1) to close the lid
    10. While pushing in  both blue buttons until the lid is completely down, and the computer screen will has changed showing the Mimic or Text page.
    11. Only at this time you may use a slow pump if desired by turning the black knob under the chamber in the direction of the line, waiting approximately five minutes. Close by turning the knob perpendicular to the line.
    12. Using the arrow keys selecting the desired recipe, then press enter . This will start the pump down of the system. This will take about 5 minutes. Wait until the pump down is complete.
    13. Select "Deposit" (F1) to start the process.
  3. Unloading the wafer, shut down:

     

    1. When the process step is completed, the program will go to the next step, which is "16 hours Warm down". This step is the last step of all processes, which will perform a N2 purge to the chamber for 16 hours to protect the chamber from any pump oil back fill. You should abort this step to end the program. To abort this step select "Abort " ( F1)
    2. Wait until the purging of the gas lines is complete and system is in the standby mode (this usually takes about  5 minutes for the silicon nitride process)
    3. Then select "vent" (F3)
    4. Select "Open the vent valve" (F1)
    5. Using the two blue buttons in front of the hardware, pressing both buttons until the Lid is completely up before releasing.
    6. Unload your wafer
    7. Select "Close Lid" (F1)
    8. Using the two blue buttons in front of the hardware,  wait until the Lid is completely down before releasing.
    9. If no wafers are loaded in the chamber, it is not necessary to use the slow pump knob at this time. Select desired recipe using the arrow keys and then enter.
    10. This will start to pump down the chamber. Wait until the pump down is complete (takes about 2-5 minutes). Once you see the four F1, F2, F3, F4 on the screen.
    11. Turn on the Ar Purge key (key up)
    12. Disable the system on Coral.
  1. Modifying a program:
    1. Select "Main Menu" (F6). This only work if the F1, F2, F3, F4 on the bottom of the screen.
    2. Change the level from operator to service level by:
      1. In front of the command, type in" level", then enter
      2. Will ask for a password, leave blank and press enter
    3. Type in "setup"
    4. Using the arrow keys select load/save and then enter

    5. Select "load process" then enter
    6. Select  the desired program, then enter
    7. Select  Dep. Def’N, then enter, you'll have five options.
    8. Select  "modify step" then enter. This will show three steps of the process which are: 15 min. warm up, Mix Freq. Nit., and 16 h warm down.
    9. Using arrow keys, highlight the 2nd step "Mix Freq. Nit.", then enter
    10. Highlight "R.F. info.", then enter
    11. Select  "Low RF setting", enter
    12. Select  "Process Time", enter
    13. Enter the desired process time as: hh:mm:ss, enter
    14. Push "Esc" key 3 times.
    15. Highlight " Load/Save"
    16. Select  "Save", enter
    17. Enter the file name. Please note that each user will have only one program. It will warn you about over writting your file. Answer yes.
    18. Push any key first then "Esc" key 2 times.
    19. Then there will be a message "Do you want to quit now?"
    20. Answer: yes "Y" then enter. This will take you to the main menu screen
    21. Select  "Text page" (F8). This will take you to the text page.
    22. Select  "new process" (F2)
    23. Select  the desired program from the list
    24. Choose "deposit" (F1)
  1. Loading a new program:

The procedure for loading a new program without opening the chamber to air is as follows:

    1. Select  "new process" (F2)
    2. Select  the desired program from the list. This will load the program to the system
    3. Select  "deposit" (F1)
  1. Cleaning the Chamber:

The total thickness of the film deposited in the chamber including predep. steps should not exceed 4.5 micron. A seven steps cleaning procedure is required for cleaning of the STS chamber as follows:

    1. Run program "Etchbak3". This program which takes about 2 1/2 hours, cleans the walls and the platen of the chamber using CF4 gas and O2.
    2. Vent the system and lift the lid. Then use folded clean wipe soaked with IPA to wipe the upper part of the wall then lower part of the wall and quartz window. Then clean the o-ring. Use the N2 gun to remove all the particle from the platen and under the platen. The last part that you need to wipe is under the hot platen. Please make sure that during the wipe don’t touch the shower head or the hot platen. Also don’t squeeze any IPA on the hot platen.
    3. Run the o2descum  recipe. This recipe is set for 15 minutes.
    4. Run oxpredep recipe. This will coat the chamber with 1 micron of silicon dioxide. This recipe is set for 30 minutes
    5. Repeat step 2 of the cleaning procedure, exactly the same way with soaked clean wipes.
    6. Run the o2descum recipe, time is set for 15 minutes.
    7. Run the silicon nitride recipe for the thickness of 0.25 micron only if the next user is going to deposit nitride. This will take about 26 minutes. The purpose of this step is seasoning the chamber with the process that you are interested to run after cleaning procedure.

When the cleaning procedure is completed the chamber will be coated with a total thickness of 1.25 micron. So please add this thickness to the film thickness that you get on the first run after cleaning and record it in the run sheet. If nitride wasn't needed or deposited the total thickness will be recorded on the log sheet as

1.0 um.

last updated 9/20/11 JP

Process Monitoring and Machine Qualification

Tool Qualification Run:

 

Procedure:

Test standard oxide recipes (high frequency and low frequency) 1 time each per month (or after significant maintenance work) with 1 run of 4 wafer each. Test standard nitride recipe 1 time per month (or after significant maintenance work) with 1 run of 4 wafer each.

Std_hfox and std_lfox for oxide. Std_1knit for nitride.


Preparation:

1. Clean 12 L test wafers using standard semi-conductor clean in wb-clean1 or wb-clean2


High Frequency Oxide

1. Check that the chamber deposition thickness is less than 4 microns. If it is greater than 4 microns, run etchback recipe.

2. Run std_hfox for 1 minute to deposit an initial layer of oxide onto the chamber. (This step is not necessary if the last deposition material was oxide).

3.  Vent the chamber and load 4 wafers onto the platter. Placing them as close to centered as possible.

4. Run std_hfox for 3 minutes.

Recipe Parameters:

  • N2O: 1400 sccm

  • 2% SiH4: 400 sccm

  • Pressure: 650 mTorr

  • Temperature: 350 C

  • Low-Frequency Power (Forward/Reverse): 41 W/ 1 W

Results:

  • Deposition rate: ~340 A/min

Stress @ 950 A thickness: ~105-140 mPa


Low Frequency Oxide

1. Check that the chamber deposition thickness is less than 4 microns. If it is greater than 4 microns, run etchback recipe.

2. Run std_lfox for 1 minute to deposit an initial layer of oxide onto the chamber. (This step is not necessary if the last deposition material was oxide).

3.  Vent the chamber and load 4 wafers onto the platter. Placing them as close to centered as possible.

4. Run std_lfox for 3 minutes.

Recipe Parameters:

  • N2O: 1400 sccm

  • 2% SiH4: 400 sccm

  • Pressure: 650 mTorr

  • Temperature: 350 C

  • Low-Frequency Power (Forward/Reverse): 70 W/ 0 W

Results:

  • Deposition rate: ~354 A/min


Nitride Deposition Using Dual Frequency

1. Check that the chamber deposition thickness is less than 4 microns. If it is greater than 4 microns, run etchback recipe.

2. Run std_1knit for 3 minutes to deposit an initial layer of oxide onto the chamber. (This step is not necessary if the last deposition material was oxide).

3.  Vent the chamber and load 4 wafers onto the platter.

4. Run std_lfox for 10 minutes.

Recipe Parameters:

  • N2O: 33.5 sccm

  • 2% SiH4: 2000 sccm

  • Pressure: 650 mTorr

  • Temperature: 350 C

  • Low-Frequency Power (Forward/Reverse): 25 W/ 0 W, 2 sec

  • High-Frequency Power (Forward/Reverse): 25 W/ 0 W, 5 sec

Results:

  • Deposition rate: ~340 A/min

Stress @ 950 A thickness: ~105-140 mPa


Measure:

1. Measure the thickness and index of refraction at 9 points across the wafer using woollam using STS PECVD Nitride and Silicon Oxide (100 - 10,000 Ang) respectively

2.  Report the average thickness, standard deviation, and n at 633nm for the wafer. Note the platter position of each wafer.

Record:

1. Record the average thickness, standard deviation, and n at 633nm for the wafer.

____________________________________________________________________________________________________________________________ 

Process Qualification Results

Machine Status States

Red: Unable to use

Yellow: Some restrictions or problem.

Green: Able to use equipment under normal conditions.

 

Process Monitoring Results: Ran four wafers ran through Low Frequency and four through High Frequency oxide. Average results for each wafer listed below.

Low Frequency    test wafers                               High Frequency   test wafers   

B 357 A /min      *6:1 BOE 1566 A/min                 394 A/min         *6:1 BOE 2269 A/min

R 362 A/min         6:1 BOE 1327 A/min                 405 A/min           6:1 BOE  2643 A/min

F 364 A/min       *20:1 BOE 379 A/min                 415 A/min          *20:1 BOE  596 A/min

L 368 A/min          20:1 BOE 454 A/min                397 A/min            20:1 BOE 593 A/min   


Etche Rates with an Asterisk indicate that the etch test was repeated.


 

 

 

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