Wisconsin Center for Applied Microelectronics

1550 Engineering DrivePhone: 608/262-6877

Madison, WI 53706Fax: 608/265-2614

STS Multiplex ICP System

Operating Procedure

Rev. 5/6/14

Material Restrictions:

All materials allowed for use in this equipment are listed in PDF form on the WCAM My Web Space. To view the listing following these steps:

  1. Open the UW website for My WebSpace.
  2. Log on using your UW NetID and password.
  3. Click on the star in the upper left corner.
  4. Under Bookmarks click on Group Directories.
  5. Scroll down the list of organizations to WCAM.
  6. Click on WCAM.
  7. Double click on the first file folder to open “Approved Materials.”
  8. Double click on the WebsiteRpt to view the approved materials for equipment.
  9. Within the PDF you can perform a search.

System Requirements

  1. The materials allowed in the STS are very limited. Mainly only silicon and photoresist is allowed in the STS. Absolutely no exposed metals allowed on your sample!
  1. The system requires 100mm (4in) wafers. If you have smaller wafers or pieces, you will need to use the STS Carrier Mounting Procedure to secure them to a 100mm carrier wafer.
  1. If you intend to etch deeper than 200 microns, you must mount your sample to a 100mm carrier wafer using the STS Carrier Mounting Procedure. It is the responsibility of the user to make sure they do not etch thru their carrier wafer.

i)If a silicon wafer is used for a carrier wafer for deep etches it must be considerably thicker than the samples.

ii)A thick dielectric layer of SiO2 or SiN can be put on the carrier wafer to reduce the etch rate of the carrier wafer in relation to the silicon samples, but the carrier wafer can still be etched thru so care still needs to be taken.

iii)A good carrier wafer for deep etches is a quartz wafer. The middle portion of a quartz carrier wafer must be covered with the silicon substrate samples so the STS detection system recognizes that there is a 100mm wafer in the loadlock.

  1. The outer 10mm of the top of the wafer and the complete backside of the wafer should be a completely clean bare silicon wafer surface.

STS Carrier Mounting Procedure

  1. On a 4-inch carrier wafer drop a small amount of PR 1827 onto the wafer. DO NOT SPIN. No samples or photoresist should be within 10 mm of the wafer edge.
  2. Put silicon wafer sample on photoresist. Bake 10 minutes in 90C oven.

Log Into CRESS

Interacting with the control computer

Locate the system control computer on the table next to the system.

You should see several system windows on the screen. The windows are titled:

A) Process Control - ICP

B) ICP View

C) Sequencer

D) Plan View

E) Transfer

These windows will control the system and inform you about the operating status.

In the red banner across the top of the screen you should see the termMonitor Mode.

System Pre-Check

  1. On the controller rack check the following:
  2. Conductivity meter – should read < 1.8
  • Turbo mag drive 1000 – should read “R” for remote, “NORMAL”, and 600Hz
  • Temperature of the chamber lid – should read 45
  1. At the computer monitor check:
  • On the Process Control ICP Window – should be in ACTIVE MODE.
  1. Make sure the water recirculator temperature is at 5C.

*See staff if these conditions are not met

Vacuum Pump– Getting started

You will need to turn on the nitrogen to ONE of the vacuum pumps for the system. The control box is located near the computer monitor.

  1. Press the SETUP button and the SETUP indicator should light.
  2. The display will ask for a password — 202.
  3. Use the UP Arrow to enter a 2 as the first digit.
  4. Press ENTER.
  5. 0 is the second digit so just press ENTER.
  6. Use the UP arrow to enter a 2 as the third digit
  7. Press ENTER.
  8. Now the display should read
    “SETUP MENU, Inlet Purge”
  9. Press the DOWN arrow once
  10. Now the display should read
    “SETUP MENU, Gas Ballast”
  11. Press ENTER
  12. Now the display should read
    “GAS BALLAST, OFF”
  13. Press the UP arrow to turn on the gas ballast.
  14. Press ENTER.
  15. Press NORMALbutton.

Operator Mode – Activating the system

  1. Using the mouse, click on EDIT in the tool bar on the top of the screen
  2. Click on the Operator Mode.
  3. Chose the Standard Mode and click on CHANGE.
  4. Type in the password wafer and hit enter.
  5. Click on Change.
  6. In the red banner across the top of the screen you should see the termStandard Mode.

Sequencer Window – Choosing your process sequence

  1. Using the mouse, click on Select in the sequencer window.
  2. A pop-up window will arise; there are several sequences in the window to choose from.
  3. Using the mouse click on the sequence you desire. Example: WIETCH.
  4. Click on Select.
  5. Using the mouse, click on BATCH in the sequencer window.
  6. A pop-up window will arise; using the keyboard type in the number (1, 2, 3, etc.) of wafers you intend to etch in this session.
  7. Click on OK.
  8. Confirm Naming Mode window is MANUAL.
  9. Click on Next Carousel window.
  10. Type in the name of your wafer and press ENTER.

System Load Lock – Loading your wafer

  1. You may now unlatch and lift the lid (It should open very easily – very little effort is required).
  2. Place your wafer onto the carousel with the wafer flat in line with the white lines on the wafer holder.
  3. Close the lid and latch it using the handle.

Sequencer Window – Starting the sequence

  1. Click on RUN.
  2. The load lock will now pump down. The Transfer status display will indicate “Acquiring [your wafer name].”
  3. The wafer will automatically be placed in the chamber.

Plan View Window – Wafer Transfer

You can watch the wafer transfer from the load lock to the chamber by watching the screen in the Plan View window.

Process Control – ICP Window

Helium leak up check

Once the wafer transfer is complete, the system will automatically begin your etch process.

  1. The display will first tell you that it is “Running process [SEQUENCE] on [your wafer name]”
  2. The system will first perform a Helium leak up check. The display will indicate “[SEQUENCE]: XXXXX: Checking Helium Leak Up Rate.”
  3. Observe the display directly above the Process Status display; it will indicate the helium leak up rate (HeLUR) in mT/min.
  4. The Helium leak up rate must be 8.0 mT/min or the system will alarm and wait for the user to run the abort procedure.
  5. When the Helium leak up check is complete record the rate in the run log.

Process Control –ICP Window

Setting etch time

  1. DURING HELIUM LEAK UP CHECK, you can change your etch time and this will be the only chance.
    Locate the display with HH:MM:SS displayed — above and left of the Process Status display.
    The icon for the etch time looks like:
  1. Click on the display and change the time to your etch time. The data is in the form: HH:MM:SS
  2. The etch will automatically begin once the gas stabilization is complete.

Process Control – ICP Window

Etch

TheHOLDbutton during an etch can be used to pause the etch so the user can leave the tool temporarily. Hitting the HOLDbutton during an etch will turn off the RF power and plasma, but keep the gas flows and chamber pressure stable. A window will pop-up notifying that a user induced hold has been placed. When ready to resume the etch click CLOSE on the pop-up window, and then click RESUME in the Process Control-ICP window.

Process Control –ICP Window

Etch Complete

At the end of the etch process, the Process Status display will indicate “Standby Step: pumping out”

The system will automatically remove the wafer from the chamber and place it in the load lock.

The load lock will vent.

System Loadlock – Unloading your wafer

  1. A Red Alarm Screen will pop-up to indicate that you need to be ready to unload your wafer. Click CLOSEin the pop-up to acknowledge the alarm.
    During the venting, the ICP process will be running DEFAULT.
  2. Once the load lock has vented, the lid will be slightly open.
  3. Lift lid and remove your wafer from the carousel.
  4. Close the lid and latch it using the handle.
  5. Before proceeding to the next step, ensure TRANSFER window status reads: Release of [your wafer name] complete. Ready.

Sequencer Window – Chamber clean

  1. Locate the STS CLEAN WAFER and load it into the loadlock.
  2. Go to Page 6 and begin at “SEQUENCER WINDOW: Choosing Your Process Sequence.”
  3. Select the O2CLEAN sequence and follow the etch procedures.
  4. Input the lesser of these 2 process times:
  5. Clean time equal to your etch time if etch was less than 30 minutes; or
  6. 30 minutes.
  7. After cleaning time, unload and return the STS CLEAN WAFER to its storage container.
  8. Proceed to deactivating the system.

Process Control –ICP Window

De-activating the system

In the red banner across the top of the screen you should see the termStandard Mode.

  1. Using the mouse, click on EDIT in the tool bar on the top of the screen
  2. Click on the Operator Mode.
  3. Chose the Monitor Mode and click on Change.
  4. In the red banner across the top of the screen you should see the termMonitor Mode.
  5. You will need to turn off the nitrogen to one of the vacuum pumps for the system. The control box is located near the computer monitor.
  1. Press the SETUP button and the SETUP indicator should light.
  2. The display will ask for a password — 202.
  3. Use the UP Arrow to enter a 2 as the first digit.
  4. Press ENTER.
  5. 0 is the second digit so just press ENTER.
  6. Use the UP arrow to enter a 2 as the third digit
  7. Press ENTER.
  8. Now the display should read
    “SETUP MENU, Inlet Purge”
  9. Press the DOWN arrow once
  10. Now the display should read
    “SETUP MENU, Gas Ballast”
  11. Press ENTER
  12. Now the display should read
    “GAS BALLAST, ON”
  13. Press the DOWN arrow to turn off the gas ballast.
  14. Press ENTER.
  15. Press NORMALbutton.
  1. Complete the run log entry.
  2. Log out of CRESS.

STS Operating Procedure - 1 -

STS Operating Procedure - 1 -

Trouble Shooting—Situation #1

Problem: Wafer did not pass helium leak up test.

Causes: Backside of wafer not clean or the stage o-ring is not clean. The helium leak up rate of the STS Etcher must be less than 8.0 mT/min. or the system will alarm.

Solution:

Abort sequence and remove wafer. Clean the backside of the wafer and attempt sequence again.

The following procedure will stop the process and unload the wafer:

ALARM WINDOW:

  1. Alarms and Requests window will pop up.
  2. Click on CLOSE.

PROCESS CONTROL WINDOW:

  1. Click on ABORT.
  2. The PROCESS STATUS line will read “ICP process . . . aborting”
  3. Wait until the PROCESS STATUS line reads “ICP process . . . aborted”

SEQUENCER WINDOW:

  1. Click on STOP.

TRANSFER WINDOW:

  1. Click on UNLOAD.
  2. When theVENTbutton becomes available, click on it.
  3. The Alarms and Requestswindow will pop up to indicate that you need to be ready to load your wafer. Click CLOSEto acknowledge.
  4. Once the load lock has vented the lid will automatically open.
  5. Lift lid gently and remove your wafer from the carousel.
  6. Close the transfer station lid and latch.

Trouble Shooting—Situation #2

Problem: Wafer in load lock and the chamber not vented. “Excessive Vent Time”

Cause: User not present during load lock vent sequence.

Solution:

  • Try clicking FINISH in the Sequencer Window; or
  • Notify staff to manually vent the load lock.
  • Log in as Staff
  • Click ABORT
  • Click STOP

Trouble Shooting—Situation #3

Problem: Optimizing STS etch profiles

Cause: Etch parameters

Definitions:

Negative profile Positive profile

Solution: Control of profile is best done by controlling the ratio of the etch time to deposition time.

An increase in the C4F8 deposition time will result in a more positive profile.

An increase in the SF6 etch time will result in a more negative profile.

STS Operating Procedure - 1 -