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Plasma-Therm RIE

Table of Contents:
I: Introduction
II: Machine Specifications
III: System Components
IV: Etched Materials and Precursor Gases
V: Operating Instructions
VI: Creating a Recipe
VII: Troubleshooting
VIII: DO's and DON'Ts
IX: Check-off requirements

I. Introduction

A Plasma Thermal RIE (Reactive Ion Etcher) system reacts gases in a RF- (Radio Frequency) - induced plasma to etch materials such as Si, SiO2, SiXNY, metals, and occasionally polyimide. This RIE system operates at 13.56MHz and has two chambers that are used for etching of nonmetallic materials and metals like Al respectively. The bottom electrode where the samples are placed is called the platen, and the upper electrode where the gases enter the chamber is called the showerhead.

The Plasma Thermal RIE can process a wide range of sample sizes. The number of samples depends on the size of the samples. A typical run can process anywhere from one to four 4" wafers. This system was built and optimized for etching Al on the left chamber and SiO2/SiXNY on the right. Best results will be obtained for those materials.

II. Machine Specifications

The right chamber of this system is equipped with the following gases for processing of non-metallic inorganic materials or polymers:

  • Ar
  • O2
  • CHF3
  • SF6

The left chamber of this system is equipped with the following gases for processing of metals suchy as Al:

  • BCl3
  • Cl2
  • CHCl3
  • SiCl4

III. System Components

  1. Heat Exchanger
  2. Mechanical Pump, Turbo Pump
  3. Circuit Breakers
  4. Reaction chambers

IV. Etched Materials and Precursor Gases

  • Right Chamber

    • SiO2 - CHF3
    • SiXNY - CHF3, O2
    • Si - CHF3, SF6, Cl2
    • Polyimide - CHF3, O2, Ar

  • Left Chamber

    • Aluminum, Titanium, Chromium - Cl2,BCl3, CHCl3, SiCl4
    • Silicon - Cl2, CHCl3

V. Operating Instructions

  1. Select active chamber

    1. Login to the access controller box - always perform the steps described in Part A FIRST, before starting to process samples. No exceptions.
    2. Press the ON button in the bottom left of the screen even if it is already highlighted.
    3. Select the Utilities Menu and SELECT ACTIVE CHAMBER - pick desired chamber.

  2. Loading a sample

    1. Press the STANDBY button located in the same location.
    2. Select the Utilities Menu and select VENT
    3. Once the N2 is flowing into the chamber, open the chamber by lifting the lid up.
      1. Select the Utilities Menu and click the CLOSE GATES option.
      2. CAUTION: it normally takes 40 - 60 seconds to vent the chamber
      3. HINT: If you try to vent the system and the display does not show the chamber as vented after 1 minute, try gently pulling on the lid to see if it can be raised; if raised, see step 7.
    4. Take a dry TexWipe and wipe the outer edge of the chamber, taking care not to touch the platen - just the metal areas outside the O-ring on the bottom.
      1. If the chamber appears dirty, RUN A CLEAN PROCESS
      2. DO NOT touch the showerhead or the walls of the reaction chamber with anything, as it will contaminate them and prevent proper gas flow.
    5. Load sample(s) into the chamber.

      Note: If your sample contaminates the chamber, e.g. polymer that decomposes and clogs the showerhead, etc., you will face disciplinary action. Think very carefully before putting anything (e.g. uncured photoresist or SU-8, etc.) that could get all over the chamber walls, platen, etc., into the chamber!

    6. Close the chamber lid completely

  3. Operating

    1. Record the normal operating parameters of your recipe in your notebook. Once a process is loaded, open it to check that the parameters match those that you have written down in your notebook. If recipe information is not recorded, the staff will not provide any assistance in dealing with process-related issues.
    2. If the recipe needs to be modified, choose the EDIT option from the Process menu. Open the recipe in question, make required changes, and save it (see section 6, editing/creating recipes, for details)

      DO NOT overwrite standard processes, e.g. if you choose a recipe that is not yours, DO NOT save it under that filename. Save it under a filename that will allow others to determine what it is, in the same directory you found it. Use only 8-character (e.g. DOS compatible) filenames. If only deposition time needs to be changed, that will be taken care of when the process is run. Try to share processes with other members of your group to avoid excessive numbers of personalized recipes on the system

    3. Select the Process menu and LOAD your recipe

      Note: System must be in STANDBY mode to load a recipe.

    4. Press the READY button
    5. Make sure the chamberlid is closed completely, as the system will not run a process if the lid is open
    6. Press the RUN button
    7. If the selected process has the variable (var)-time option enabled for the RF/process step, enter the desired run time - if not the default one; press Enter or select OK.
    8. Watch the process until it has been depositing for one minute. Most errors, if any, with processes occur during either gas stabilization phase or during the first minute of the process etching. (See section VII, Troubleshooting, for more details on what errors can occur and how to resolve them). Record any unusual results or readings.

  4. Unloading a Sample

    1. Select the STANDBY button.
    2. Select the Utilities menu, click on the VENT option.
    3. Once the chamber is vented, lift the chamber lid.
    4. Unload sample(s) from chamber.

      Hint: if STANDBY and READY buttons cannot be switched after 20 sec, hit ABORT one time. If this does not work, go find the maintenance staff.

    5. If more samples are to be processed, repeat
    6. Close the chamber lid completely
    7. Start a clean process running. Clean processes are found in the process directory, specifically, CLEAN.PRC or, if processing organics, O2CLEAN.PRC.
    8. Log out of the access controller box

VI. Creating a Recipe

Overview

In general, a recipe should have four steps: an initial step, two process steps, and an end step. The initial step evacuates the chamber and removes the air inside. The first process step is a gas purge step, and it also sets the process pressure. It allows the chamber pressure and gas flows time to stabilize. Because the RF power is off, no processing will actually take place during this step. The second process step performs the process. Always record the parameters of the recipe and its name in your notebook

Instructions

From the Process menu choose Build to create a new recipe or Edit to edit an existing one. A list of the recipe steps will be displayed on the right side of the screen. To edit a step, double click on it. To create a new step, select the step that will go after the new step and click the appropriate button for the type of step you want at the bottom of the screen.

Initial Step

All recipes start with an initial step. This step will evacuate the chamber and bring the chamber to the desired operating temperature. Set the pressure to 0mTorr and set the time to 30 seconds. This will cause the system to evacuate as much air from the chamber as possible before starting the process. The chamber will be evacuated as much as possible; it may not reach 0. Don't worry about it, if the machine proceeds then it's fine. The user should describe the recipe in the Description box. The first few words will be displayed by the file name when the recipe is loaded.

Process Steps

Most processes usually have two process steps. They should be identical with a few exceptions. The process step dialog box has five major areas: time, pressure, gas flow, and power.

Time

The first process step's "Terminate by" time should be set to "Fixed Time" This step will be used to stabilize the chamber conditions. The time for this step is not critical, but 30--60 seconds is good. The second step will actually perform the etch. If the process' "Terminate by" time is set to "Variable Time," upon running the recipe the user will be prompted for the process time before each time the recipe is run. This is usually more convenient than editing the recipe each time. However, the process time can be selected as "Fixed Time" and set manually in the recipe.

Pressure

Set the pressure to the desired process pressure for both process steps. The process pressure is measured in mTorr.

Gas Flow

Set the flow rate for each gas here. The flow rates are given in sccm (standard cm3/min). The maximum flow rates are shown on the gas bottles displayed on the screen as well as the same line as the gas flow. The flow rates should be the same for both process steps; DO NOT exceed 90% of the rated maximum MFC flow rate.

Power

Leave the power set to zero in the first step. Set it to the desired process power for the second step. DO NOT exceed 400W.

End Step

All recipes have an end step that evacuates the chamber. Make sure it is present. Once complete, you will vent the chamber using the Utilities, Vent option.

Note: when a process is modified, only the copy on the disk is changed. If the process is already loaded, it will need to be reloaded for the changes to be reflected.

VII. Troubleshooting

Q:The system is alarming. How do I silence the alarm?

A: Select the SILENCE button in the lower right corner of the screen.

Q:How do I stop a process that has a problem?

A: Use the END STEP button on the bottom to skip the other step(s) and end the process. Do not use the ABORT button.

Q:The process went into HOLD during the gas stabilization phase and began alarming. What do I do?

A: The process pressure may not have been in compliance. If this caused the error, press the HOLD button in the middle of the bottom of the screen and let the gases back to the desired pressure. Sometimes the system does not increase gas flow fast enough and can cause this error. The process should continue without problems. If this happens more than twice, cease processing and go find the maintenance staff and/or the trainer.

Q:The system went into hold because of high levels of reflected RF power. What do I do?

A: If you know that the power and pressure you are using has worked before, try pressing HOLD one time only to make the system try again. If it still doesn't work, contact a MiRC staff member. DO NOT PRESS HOLD MORE THAN ONCE. If you keep pressing hold, you will cause serious and expensive damage to the power supply If the reflected power is too high, the process will stop and the alarm will sound. Usually, if you still have reflected power (in the range of 5 - 20W), the chamber needs to be cleaned. You can do this by running the batch named CLEAN using the instructions above. You will want to remove your sample from the system before you do this. If this happens even for a known-good clean process, contact the maintenance staff, place a 'machine down' sign on the system, and submit a Pettit service request. Mark the machine down, vent the chamber, remove your sample(s), and pump the chamber back down.

Q:The system's reflected power is more than 1W but it is not alarming. What do I do?

A: This indicates the chamber is still dirty. The chamber will probably back- or re-deposit material on your substrate and create micro-masking and thus grass. Therefore, you need to run a clean process.

Q:The system is stuck in a mode e.g. when the process is complete, it will not switch from READY to STANDBY. No process is running, and at least 30 seconds have elapsed. What do I do?

A: This is the ONLY case where pressing the ABORT button is acceptable. If pressing this button only once does not solve the problem, stop processing and go find the maintenance staff.

Q:How do I get approval to process a material on the system that is not listed under allowed materials?

A: Go to the Material Exception - Approval page and fill it out. Incomplete information will result in an automatic rejection of your request.

VIII. DO's and DON'Ts

DO NOT

  • attempt to open the chamber while a process is running
  • touch the showerhead or chamber walls at all
  • proceed with processing in the face of an unknown error. Contact the maintenance staff first.
  • use the machine if another use has placed a 'machine down' sign on the system; ask the technical staff to verify that it is working.

DO

  • ask the trainer, cleanroom / technical staff, and other users questions about anything that is not clear or that you do not understand.

IX. Check-off requirements

To be checked off, you must be able to do, to demonstrate, and to know the following items if asked:

  • Locate the relevant components of the system (heat exchanger, etc.)
  • Know the materials that can be deposited and know what each gas is used for (e.g. clean, precursors for what materials, etc.)
  • Know the specific materials and processes you will be using the system for
  • Be familiar with the other materials that can be deposited in the system.
  • Vent the chamber
  • Load a sample
  • Load a process
  • Edit a process and save it as yours.
  • Run a sample
  • Unload a sample
  • Run a clean process
  • Demonstrate how to handle the following errors:
    • Pressure will not go into equilibrium during the gas stabilization phase of a process
    • Levels of reflected RF power exceeding 1W
    • Levels of reflected RF power exceeding 5W
    • Process that has a general error and must be terminated