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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.

 

Contact List and How to Become a User

Contact List

The following people make up the Team Matrix:

  • Process Staff: Usha 
  • Maintenance: Elmer
  • Super-Users: Jim Kruger

 

Training

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


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;

 

Recent Etch Rates

15 June 2015

STRIP recipe: 30 sec strip at 185C, 1.6 3612 resist

Etch Rate = 9040A/min (Average 4520A/min, Uniformity = 3.92%

 

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 Matrix qual is to monitor the efficiency at which PR is stripped from wafers. 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 Matrix qual runs one wafer patterned with 1.6um of 2612 PR through the standard Strip.rcp process. Nanospec measurements are taken before and after the process to calculate the PR strip rate.

 

Procedure

Wafers for Processing

SUMO Wafer #
(all Si 4" wafers)
Coating Pattern
(using SUMO mask)
83  - 1.6um 3612 PR pattern, 1 min bake @ 110C

 

Pre-Process Wafer Measurements

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

For Wafer 83, 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. 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 average.
  4. Record results on the SUMO Qualification Log Sheet. 

 

Strip Process

Follow the standard operating procedure for Matrix. Remember to:

  • Season the chamber using the desired qual process at least once + running the strip.rcp process.
  • Load wafers from the bottom of the cassette (Slot 1).
  1.  Choose Directory 03112015.
  2. Select the standard QUAL_ST.RCP process for 2 minutes (120 sec).
  3. Recipe parameters should be as such:
  • FROMLOT = 01
  • LOTSIZE = 01
  • LOT ID: NANCY1
  • StepID: (varies)
  • TIME: 2 minutes
  • 450 W
  • 40% O2
  • 185 C
  • 3.75 T Ash Rate 6020 A/min
  • Pins Down

 

Post-Process Wafer Measurements

After processing, examine the wafer 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. Then:

  1. Measure post-process 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 strip-rate for PR by subtracting the post-process thickness from the pre-process thickness and dividing by process time.

 

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.

 

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 Information 

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

 

How to Create a Pocket Wafer

From the ALD section of the wiki:

  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.
  5. 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.
  6. 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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