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Lam 590 SiO2/SiN

• Automatic, cassette-to-cassette, single wafer plasma etcher for silicon nitride and silicon dioxide etching
• This document describes the general operation of Lam2
• It also covers the recipe loading/modifying procedures and how to set up the automatic endpoint detection.

1. Definitions & Process Terminology
   1. Plasma Etcher: An etcher that uses the radical gas atoms/molecules, generated by plasma, as the main etchants to remove the thin film material on a substrate or the substrate itself.
   2. Etch Rate (ER): The rate of the thin film being etched away, usually in A/minute.
   3. Etch Non-Uniformity: A measure of the etch uniformity across the wafer. It is defined as (max ER min ER)/(2 X average ER), usually in %.
   4. Isotropic/Anisotropic Etch: An etch process that has the same ER in all directions is isotropic. An etch process that etches in the direction perpendicular to the substrate surface is anisotropic. A plasma etcher, e.g. Lam1 usually etches more anisotropically.
   5. Etch Selectivity: A measure of comparing film loss between the etched thin film and other layers, such as photoresist or underlaying substrate/film. The higher this ratio, the more desirable the process.
   6. Over-Etch: An optional second etch step with etch chemistry that maximizes the etch selectivity. It removes the residual film due to previous etch non-uniformity with minimum damage to the underlying substrate/film. The etch rate is usually lower in this step.
   7. Automatic Endpoint Detector: An optical device that traces the light emitted by the etch byproduct in the plasma. It can be programmed to end the etch process at a specified condition. Lam1 uses Channel A (405 nm) to monitor the amount of SiN species in the plasma (nitride etch) and Channel B (520 nm) to monitor the amount of CO species in the plasma (oxide etch).
   8. Control Panel and CRT
      1. START button: Starts the process.
      2. STOP button: Stops the wafers in the entrance cassette from being sending into the system.
      3. RECIPE button: Displays, on the CRT, the recipe currently loaded in the system.
      4. STATUS button: Displays, on the CRT, the current status of the system. It also includes the current process parameters and wafer location.
      5. PARAMETER button: Displays, on the CRT, the menus of the operating parameters of the system and the automatic endpoint detector.
      6. OPTIONS button: For diagnostic/maintenance purposes only.
      7. Arrow keys: Moves the cursor on the CRT.
      8. FIELD SELECT button: Toggles options available in the highlighted fields where the cursor is pointing out on the CRT.
      9. LOAD/SAVE buttons: Currently not used.
2. Safety
   1. RF Radiation Hazard: Lam2 uses a 13.56 MHz Radio Frequency power supply as a plasma generator. If suspect RF power leakage, stop etch process by pressing the red emergency stop button.
   2. UV/Strong light Hazard: The plasma emits UV/Strong light. Do not look straight into the plasma for a long period of time.
   3. Toxic Gas Hazard: Although Lam2 uses non-toxic gases, however, the etch byproducts may be toxic/reactive. Stop etch process if suspect a vent leakage.
   4. All applicable safety rules should be followed.
3. Statistical/Process Data
4. Available Processes, Gases, and Process Notes
   1. Processes (Refer to Appendix for tables of available processes and their parameter settings.)
      1. Standard Oxide Recipe (SIO2ET): Used for etching silicon oxide.
      2. Process Monitor Recipe (SIO2MON): Same as the SIO2ET recipe without the over-etch step. Used for process monitor test.
      3. Clean Recipe (CLEAN): Used to clean the process chamber. It is performed monthly by the process staff only. The cleaning process erodes the upper graphite electrode. Excessive electrode erosion will have adversely impact on etch rate and uniformity.
   2. Process Gases
      1. Ar:
      2. He: Used to increase the etch uniformity in either process.
      3. O₂: Used in the O2CLEAN recipe to clean organic contamination in the chamber. Also used in the over-etch step in the standard recipes.
      4. CHF₃: Secondary etch gas for oxide, also used to form sidewall polymer.
      5. CF₄: Main etch gas for oxide.
   3. Process Notes
      1. Lam2 uses high RF power (850W). For long etch process, the electrode temperature may increase which may cause photo-resist burning. It is recommended that the user break a long etch step into several 3-5 minute segments and insert a cooling step in between. It is reported that if the electrode temperature exceeds 20C, significant photo-resist burning occurs.
      2. After etching, it is recommended that you dip your wafers in 100:1 HF for 30 seconds to remove residual spattered oxide left behind by the etch process.
      3. Do not use the option button on the control panel. The operation overwrites the safety interlocks built in the system. It is restricted for staff use only.
      4. DO NOT ETCH ANY TYPE OF GLASS SUBSTRATES (PYREX 7740) IN LAM ETCHER
5. Equipment Operation
   1. Downloading a Recipe
      1. Make sure that Lam2 is at IDLE state. No process is running.
      2. On Lam2-PC, press ESC several times until the Control Menu is on the monitor.
      3. Select number 6: Send Rec, then press ENTER. The monitor will show a list of recipes.
      4. Enter the number/alphabet of the recipe of your choice, then press ENTER. The monitor will display: Recipe download successfully. If not, see Troubleshooting. Section 10.1.
      5. Press ENTER, the monitor will display a blank chart for end point tracing when the wafer is being etched.
   2. Modifying or Creating Recipes
      1. Usually the standard recipes are sufficient for silicon nitride etching. If you need a new recipe for your own special application, please consult the process staff first. Recipes can be displayed on the screen, where each column represents one process step. The left most column contains process parameters and applicable units. Other columns show the process parameter values for each etch step.
      2. Press RECIPE button on the control panel. The CRT will display the current recipe stored in the system memory.
      3. Use the arrow keys to move the cursor to the field you want to modify. Use the numeric keys to enter the new value. If you make a mistake, use CE key to erase the entry. Afterwards, You must use an arrow key to move the cursor out of the field for the entry to be stored in the system memory. For example, to change the pressure unit, move the cursor to the pressure unit brackets, then press Field Select button to toggle between MTORR and TORR.
      4. Use the same method to toggle entries in the COMPL field. This field/row specifies how a particular step gets completed. There are five entries you can choose from:
         1. TIME: The step will complete after the time entered in the WAIT field. The process then advances to the next step.
         2. STABILITY OR TIME: The step will complete and the process advances to the next step when all the parameters in the step reach their set points within the time limit entered in the MAX field. Otherwise, an alarm will sound. If the alarm sounds, move the CRT cursor to the MANUAL ENDPT: OFF field, wait till all parameters reach their set points, then press FIELD SELECT button to advance to the next step. If one or more parameter will not reach their set points after a few minutes, see Section 10.0 for troubleshooting. To avoid frequent false alarm, enter reasonable time, at least 30 seconds, in the MAX field.
         3. TIME & ENDPT: The step will prompts the machine to move to the next step when the Automatic Endpoint Detection conditions are met or after the time entered in the WAIT field is elapsed.
         4. OVERETCH: The step will complete after the percentage, entered in the % filed, of time of the previous etch step.
         5. RECIPE: Signifies this is the end of the recipe. All parameters in this step and after are ignored.
      5. Add or delete steps by using copy feature at the bottom of the recipe page. Since there is no delete step feature in the system, you will have to copy the next step to the step you plan to delete. Then, repeat the copy operation until you reach the last step in the recipe. The copy feature is also useful for creating a recipe with several cycles of the same steps.
         1. Move the cursor to the STEP# field and enter the step number to be copied and the step number to copy to.
         2. Move the cursor to the COPY field and press FIELD SELECT button. Both of the step numbers in the STEP# filed will be increased automatically.
         3. Press FIELD SELECT repeatedly as many time as you plan for the recipe.
   3. Setting up Automatic Endpoint Detection (skip this section when using standard recipe):
      1. Press the PARAMETER Button. Then press the FIELD SELECT button a few times until the CRT display the endpoint setup page. There are four endpoint steps you can set up. Unless you plan to etch multi-layers in one recipe, you only need to set up one.
      2. Move the cursor to the SAMPLING INPUT. Press the FIELD SELECT button until A ONLY is selected. Lam1 uses the channel of the automatic endpoint detector.
      3. Move the cursor to the next line. Enter the number of the main etch step. It is the step that has the TIME & ENDPT in the COMPL field.
      4. Move the cursor to the next line. Enter the DELAY time. The automatic endpoint detector disregard any signal in this first period of the etch step because the plasma just starts and is stabilizing. The normal DELAY time is 15 seconds.
      5. Move the cursor to the next line. Enter the NORMALIZE time. The automatic endpoint detector collects and averages the tracer signal from the plasma in this second period of the etch step. The averaged (normalized) signal strength is used as the base for endpoint triggering. Lam1 standard recipes use 5 seconds NORMALIZE time.
      6. Move the cursor to the next line. Enter the TRIGGER AT PERCENTAGE of the normalized value. When the tracer signal reaches the percentage, the end point is triggered and the etch step completes and the process advances to the next step. To prevent under-cutting the substrate, the endpoint is set to trigger at 90%.
   4. Processing Wafers
      1. If Lam2 has been idle for more than 8 hours, you should run 3 dummy wafers to warm up the system.
      2. Download the recipe using Lam2-PC by following instructions above. Press the RECIPE button to check the recipe. Modify the recipe by following Section 9.3 if needed. Press the STATUS button to display the system status.
      3. Load wafers into the blue cassette with flat toward the front. Select the size of the wafer (4 or 6) using the toggle switch next to the entrance indexer. Load the cassette onto the entrance indexer (left side) with the cassettes H bar sitting in the center slot. Load an empty cassette on to the exit indexer (right side). The cassette will be lowered into the exit indexer.
      4. Press START button. The entrance indexer will send one wafer (start from the lowest one in the cassette) into the system. The wafer will first go into the entrance load lock, then the main etch chamber. You can watch the wafer movement and the system status from the CRT. (Press STATUS button if needed.)
      5. Once the wafer is in the main etch chamber, the recipe starts. Once it reaches the etch step, Lam2-PC monitor will show the endpoint trace signal from automatic endpoint detector. (If not, press enter or space bar on the Lam2-PC keyboard.)
      6. If you want to stop the current recipe step manually, move the cursor to the MAN EP field, then press the FIELD SELECT button. The recipe will advance to the next step.
      7. Once the recipe completes, the wafer will move to the exit load lock, then the exit indexer. The whole process will repeat itself automatically until the last wafer on the entrance indexer is processed. After the last wafer goes into the exit indexer, tilt the indexer toward you to about 45 degrees then release it to vertical. The exit indexer will rise. When it stops, you can remove the cassette to get your wafers. If you try to remove the cassette when it is still at down in the indexer, you may damage the sensor that monitors the position of the cassette.
      8. If you decide to stop processing some wafers still in the entrance indexer, press the stop button. The entrance indexer will stop sending wafer into the system. However, the wafer(s) already in the system will finish the recipe and return to the exit indexer.
6. Troubleshooting
   1. Lam2-PC Problems
      1. If you or someone hit option 7 on the control menu by mistake, the PC monitor will switch to the WINDOW 3.1 interface. Use CTL+TAB keys to highlight the Lam2 icon, then press enter. The PC monitor will switch back to the control menu.
      2. You can reboot the Lam2-PC by holding ALT+CTL+DEL keys together. After reboot, it will prompt you for some setup value. Enter q for the prompt. It will ask you for the password. Enter lam2-pc. Wait till the control menu shows up on the monitor.
      3. If Lam1-PC displays Unable to send recipe message, press the PARAMETERS button on the Lam1 control panel. Use the FIELD SELECT button to toggle the PARAMETERS field to the LAM LINK. Make sure that the Lam link field is ACTIVE and the baud rate is 9600. Try down load the recipe again using Lam2-PC.
   2. Process Problems
      1. The entrance indexer does not send wafer into the system after the START button is pressed. You need to check the STATUS page on the CRT by pressing the STATUS button on the control panel.
         1. If the recipe has already started running, move the cursor to the MAN EP field, then press FIELD SELECT button repeatedly till the system returns to the IDLE state.
         2. Press PARAMETERS button. Move the cursor to the PARAMETERS field. Press FIELD SELECT button repeatedly to toggle the field to MACHINE. Move the cursor to the START BUTTON field. Press FIELD SELECT button repeatedly to toggle the field to LOAD & PROCESS. Move the cursor out of the field.
         3. If the system alarms for WAFERS IN SYSTEM, move the cursor to WAFERS IN SYSTEM ALARM RESET field, then press FIELD SELECT button to clear the alarm.
         4. If the recipe has not started, check that the cassette sit properly on the entrance indexer.
      2. The system fails to stabilize at the STABILITY OR TIME step.
         1. Wait for a minute. If all process parameters have stabilized, move the cursor to the MAN EP Field on the STATUS page, press FIELD SELECT button to advance the recipe to the next step. If the problem appears often, increase the time in the MAX field of the step in the recipe.
         2. If some of the process parameters do not stabilize after 2 minutes, move the cursor to the MAN EP Field on the STATUS page, press FIELD SELECT button repeatedly till the recipe ends.
      3. The system displays RF alarms.
         1. Press PARAMETER button. Move the cursor to the PARAMETERS field. Press FIELD SELECT button repeatedly to toggle the field to MACHINE. Move the cursor to the RF ALARM RESET field, then press FIELD SELECT button.
         2. Press STATUS button. Move the cursor to the MAN EP field, then press FIELD SELECT button repeatedly till the recipe ends.
         3. Load a dummy wafer to the entrance cassette and start a standard recipe. If the RF alarm occurs again, repeat steps 10.2.3.1-2, then report problem on WAND. If the dummy wafer goes through without problem, it is your wafer or recipe that causes the problem.
      4. The recipe has finished but the wafer does not come out of the system.
         1. Press STOP button. Remove all wafers from both cassettes.
         2. Report the problem. Do not try to find the lost wafer yourself. You may create more damage.
         3. Leave a wafer holder or a box with a note on the top of the system if you want the staff to save your wafer (or pieces of your wafer).
      5. The endpoint trace signal on the Lam2-PC monitor is too small or just a flat line.
         1. Make sure that your wafer has large enough etch area that generates trace signal for the detector. If you can change the graph setting using Lam1-PC control menu.
         2. If the situation does not improve, try using a dummy wafer. If the dummy wafer behaves the same, the window of the detector may need cleaning. Report the problem.
7. Figures And Schematics
8. Appendices

• Lam Control Panel

• Available Processes on LAM2 (Process Settings)
  • Standard Oxide Recipe (SIO2ET)

• Process Monitor Recipe (SIO2MON)

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