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Matrix Plasma Asher, matrix

The Matrix plasma asher is used to strip photoresist from contaminated wafers using a combination of oxygen plasma, high power, higher pressure and a heated chuck (platen).

Picture and Location

Matrix 

Background

 

The Matrix is a resist asher that uses both an Oxygen plasma and heated chuck to strip hard to remove photoresist. Although it is particularly good for getting implanted or plasma damaged resist off samples, a combination of ashing and wet chemical stripping (sulfuric/peroxide or PRS3000) may have to be employed to remove stubborn resist.

In general the tool uses high chamber pressure (3-4Torr) and RF power about 400-500Watts.  A heated chuck, 180-190C degrees also aids in the ashing of resist.

The tool is contaminated and receives 4 inch wafers only.  Labmembers wanting to ash pieces will want to use a pocket wafer.  A pocket wafer has cavities etched deeply into the Si (100um or more) that the samples will fit into.  See the Additional Process Information section for  a description of how to create pocket wafers;

 

 

Process Capabilities

Cleanliness Standard

 The Matrix is a contaminated piece of equipment.

Performance of the Tool

What the Tool CAN do

The Matrix is a good tool for the removal of photoresist on contaminated wafers.  One should keep in mind, however, that when ashing PR off layers of some metals oxidation may occur.  To achieve good contact to those metals the oxide must be removed.

 

Descums have been performed in the tool.  Be advised that the chuck temp

must be lowered.

 

What the Tool CANNOT do

Etching of materials other than photoresist is not recommended.

 

Process Monitoring

 Monitoring is performed by the SUMO group. Results will be posted on Badger.

Contact List and How to Become a User

Contact List

 

The following people make up the Team Matrix:

  • Process and Training Staff: Nancy 
  • Maintenance: Elmer
  • Super-Users: Jim Kruger

 

Training to Become a Tool User

 

The Matrix Plasma Asher is an easy to use machine.

Please follow the following procedure to become a qualified user of the Matrix plasma photoresist ashing system.

Read all material on the SNF website concerning the matrix, including Background, Process Capabilities, Operating Procedures and Process Monitoring.

Shadow a qualified user on the tool.  This is a good time to ask any questions you may have about the operation of the tool.

Contact the responsible staff member for qualification once you feel confident that you can safely and correctly run the system.

Understand that you may be asked to allow another labmember to shadow you.  This is part of your responsibility as a qualified user of the tool.

Operating Procedures

 

 

Standby Check List

  • Check Badger for any reports or comments about the tool.
  • Use the EXIT button to get to the Allwin screen.

NOTE: The door is interlocked, make sure the door is completely closed or the Matrix will not run.

Start-Up Procedures

 

From the Allwin screen chose Process for Production.

 

Load the Recipe

 

Select a recipe from the Recipe File, a column located on the right hand side of the screen.

 

Select Where the Process Data Will Be Stored

 

The process data will be stored on the hard drive after the run is completed.  Specifying where the data will reside will make it easier to retrieve later.

  1. First select a Directory from the Directory List. It is the column in the top middle of the screen. For now we are using the directory named 03112015 (the date the tool was first used).
  2. Next select a Lot ID from the column of Lot ID, left hand side of the screen. For now we are using NANCY1.
  3. Finally, select a Step ID from the Step ID column.
  4. During the run the data will be displayed.
  5. You may want to note these choices to reference later.
  6. You may also create your own directory, lot and step ID's.  Most users do not care to view data later.

 

Load the Cassette

  1. Place your wafer in the designated cassette starting at the first slot.  That is the one closest to the H-bar, facing away from the H-bar.
  2. Place the cassette on the cassette station.
  3. Make sure the Wafer No. box indicates 1. This is the slot number the wafer will be taken from for processing.

 

Run the Lot

  1. Click on the AUTO RUN button. A new screen will appear.
  2. Verify that the From Slot window says 1.
  3. Lot Size should indicate how many wafers you want to process.
  4. Lot and Step IDs should be displayed.
  5. The current tool conditions should be displayed; Temp set point and actual, and pressure.
  6. Click on AUTO RUN to start the wafers processing.  The Process Monitor Screen should be shown.

 Monitor the Process

From the Process Monitor Screen you may

perform the following operations;

Process Monitoring and Machine Qualification

Purpose

The monitoring processing is carried out to ensure the machine is operating with high efficiency in removing the photoresist present on inputted wafers.

 

Frequency

Monitoring will occur on a monthly basis and information regarding the results of such shall be posted for the public to review if desired. Monitoring may also occur as needed/requested by user reports and concerns or after major repairs.

 

Procedure

Wafers for Processing

  • One 4” Si wafer coated with 1.0 um of 3612 photoresist

  • One 4” Si wafer coated with 7.0 um of 220-7 photoresist.

Etch Process

  1. Each wafer is run through the process using the standard O2 Strip program for duration of 2 minutes.

Examining the Wafer

       After a wafer has been run through the 2-minute process, it is removed from the chamber and examined closely to check for stripping efficiency. Careful observation much be taken of the etch parameters, power, pressure, and gas flow.  The photoresist should have cleared from the desired surface of the inputted wafer. The test is binary, was the resist completely removed from the wafer or not.

       If this is not the case, the machine must be experiencing systemic problems and it is the responsibility of the monitor/lab members to contact the responsible maintenance staff members if such problems occur. Reference the Contact List section on the Matrix equipment page (SNF Labmembers wiki).

 

Recycling Wafers

        After both wafers have been examined and the results recorded, they are available to be recycled for future qualification runs. They will only need to be repatterned (if ensured they are fully stripped) in Litho with the same photoresist requirements that were noted in the beginning of this process. This recycling helps save from the need to buy new wafers.

 

Responsibility

This monitoring will be handled by the students of SUMO, but users are encouraged to run a qualification process if they feel the tool is not in good running order. The staff should be informed of the results retrieved from such a run so as to add to the previously collected data


Machine Status States

Red: Shutdown- not available for use.

Yellow: Has an intermittent or 'work around' problem.

Green: The tool is functioning properly.

ADDITIONAL PROCESS INFO

 

Standard Recipe, STRIP is the same as the old O2strip recipe;

  • 3.75 Torr
  • 450 Watts
  • 40% O2 Flow
  • 185 Centigrade
  • Pins Down

 

From labmember aintekofer:

lower chuck temperature (100C)
etch rate for 3612 photoresist ~70nm/min

 

 From the ALD section of the wiki;

How to create a Pocket Wafer

1. Grow about 100nm SiO2 on a Si <100> wafer.  SiO2 can be deposited, but needs to be on both front and back.
2. Pattern SiO2 with resist.  The pattern should be a larger area than your piece as this pattern defines your pocket.
3. Dry etch SiO2. Note: wet etch does not work because you need to keep the backside oxide.
4. Strip the photoresist.
5a. Wet etch Si wafer with SiO2 as a mask in TMAH heated to about 90C for a few hours.  This makes a recess with depth dependent on your initial mask because TMAH stops on the Si 111 planes.  The chips can sit on the crystal smooth angled sidewalls of the trenches, which are very flat allowing good thermal conduction from the substrate, and hence the substrate heater, to your chip.
5b. You could also try a DRIE of Si to define your pocket.  Here the etch would be vertical and your pocket would have an approximately horizontal floor.

 

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