STS ICP-RIE. Scott Munro (2-4826,

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1 STS ICP-RIE LOCATION: Plasma Etch Area PRIMARY TRAINER: Scott Munro (2-4826, 1. OVERVIEW The STS ICP-RIE is available to users who require deep anisotropic silicon etching with near vertical sidewalls using Bosch and unswitched RIE processes. The Bosch process is a two step process that alternates between an etching step and a deposition step, and is repeated until the desired depth is achieved. The sidewalls are not perfectly smooth, however, and a noticeable scalloping along the sidewalls is observed. An unswitched recipe introduces the etch and deposition gases simultaneously, giving a scallop free sidewalls, but is limited to relatively shallow etch depths. 1

2 2. SAFETY PRECAUTIONS There is potential for harmful gases to form during the etch process. Both the process chamber and the loadlock are purged with Nitrogen and vented to minimize this hazard. Ensure that the loadlock is fully is fully vented before opening the door. The process chamber is heated to upwards of 150 o C. There is a heat shield covering the bottom, but there are still areas of the chamber that are hot. Avoid touching. Reflected power occurs when power is not fully transferred from the source to the plasma. A set of capacitors automatically adjust to minimize the reflected power. Running the plasma for an extended time with high reflected power may permanently damage the system. If the capacitors fail to minimize the reflected power and remains consistently above 10% the RF power, stop processing immediately, and contact NanoFab staff. The STS uses advanced software, and will stop processing if one or more etch parameters becomes out of tolerance. Users are not allowed to circumvent these set tolerances. If you are bringing any new materials into the NanoFab for use in your process, it is necessary to fill out a chemical import form (available on our website, and supply an MSDS data sheet to Stephanie Bozic. 3. PROCESS COMPONENTS OR FEATURES Wafers should be prepared with an etch mask appropriate to withstand the duration of the etch. For shallow etches, a photoresist mask may be suitable; for deep etches, a hard mask, such as metal or an oxide, may be required. Photoresist etch masks may be difficult to remove after etching. Acetone and IPA rinses may remove the bulk of the resist, but an ashing with an oxygen plasma may be required to completely remove the resist. There may also be residual polymer on the wafer surface, which may also be removed with an oxygen plasma, or, as a last resort, a commercially available polymer removal solution is available. Please contact the appropriate trainers if interested in the above processes. 4. OPERATING INSTRUCTIONS 4.1 It is recommended that the chamber is pre-conditioned prior to processing device wafers. This is done using a clean, bare silicon wafer and processing for 25 cycles on the Bosch etch labeled condition in the software. The conditioning wafer must be a piranha cleaned wafer, and when processed with the above recipe, the wafer should appear similar to what it looked like before processing (ie. shiny and reflective). Do not continue processing if the conditioning wafer appears different, is hazy or has a coloured film on the surface. These may indicate a problem with the process. Contact NanoFab staff for further assistance. 4.2 The operating software should be running and the screen below on display. The system should be in Active mode; ensure this mode is selected before processing. If not, click the Mode button, select Active mode, and press Change. The system will undergo a series of check before active mode is displayed. 2

3 Process control window Loadlock control window System Mode Mode Change Operating Software 4.3 Sample Loading - In the Loadlock Control window, press the Vent button to vent the loadlock. Wait until the chamber is fully vented before opening the loadlock door. The door will open slightly on its own, do not force it open. 4.4 Load the wafers into either slot, and note the position of each wafer (the holders are marked 1 or 2). For wafer to wafer consistency, line up the wafer flats with the notches on the centre of the carousel. Close the chamber and do up the latch. Press the Pump and Map button on the Loadlock Control window. This will evacuate the loadlock chamber and a sensor will detect which position(s) the wafer(s) are in. Active Slot # Vacuum Control Pump/Vent Transfer Window 3

4 4.5 Once base pressure has been reached (<80mT), the first wafer may be loaded. Click the slot # and enter in the position of the wafer which is to be processed. Load the conditioning wafer if performing the chamber clean. When the desired slot # is entered, press the Load button to load the wafer into the process chamber. 4.6 Recipe Selection and Modification Press the Recipe button in the Process Control window to load the recipe edit screen. Exit Open Save Save As # of Cycles Recipe Window 4.7 Press the Recipe Open button to open a list of standard recipes. Select the desired recipe, and click OK. 4.8 Each recipe will have a minimum of two steps; the first is a Standby step, where base conditions and stabilization times are set; and a second step, which is the actual etch step. Select the second step to view etch parameters. 4.9 Refer to the STS ICP-RIE information sheet located by the tool for processing information, including etch rate, selectivity, uniformity of select materials as a starting point for your process. Etch information will vary between different processes and is dependant on a number of parameters, so please use the information as a guideline only. If this is the first etch, it is recommended that the process be ran on a test wafer to determine your own etching parameters In the Cycles cell, enter the desired number of cycles. If using the unswitched recipe, enter the process time. For the condition recipe, ensure the time is set to 25 cycles. Press the Save button and close the Recipe Window by clicking the Exit button. 4

5 Note: Any changes other than process time are only to be performed by staff and advanced users. If you are neither and would like to make further changes to standard recipes, or develop your own, please contact a trainer. The NanoFab does encourage further development of its tools. When making changes other than time or cycles, ensure to save as a unique name Sample Processing At this point, a wafer should be loaded in the process chamber and a recipe edited and saved. To begin the process, press the Select button to load the list of recipes, select the desired recipe, and press Process. The recipe will be loaded (and should be displayed as such on the Process Control window), and the process will begin. It will be a few minutes before the plasma is struck as the system undergoes a series of checks and stabilization time. ICP Power -Forward -Reflected Gas settings RF Power -Forward -Reflected Loaded recipe display Process status Select and Process Process Control Window Blue = setpoint, yellow = actual Process step display 4.12 Record process information in the logbook, including any error messages or processing issues. If the process needs to be stopped during a run, press the Abort button. Any system errors are to be reported to NanoFab staff. 5

6 4.13 Unload and Shutdown When the process is finished, Process Complete will be displayed in the Status window. Press the Unload button the transfer the wafer from the process chamber to the loadlock. Visually inspect the wafer to ensure processing is complete 4.14 If a second wafer is to be processed, refer back to section If processing is complete, remove wafers, close the chamber door, and click the Pump Only button in the Transfer window to put the machine in standby mode. 5. TROUBLESHOOTING A common error is the He leak up rate (He LUR) out of tolerance error. This usually occurs during the initialization step of a process where the wafer is tested to ensure there is good contact between the wafer and the cooled chuck. The wafer is loaded onto and o-ring and held down by eight ceramic fingers, and He is flowed between the wafer and the chuck. If there is a poor seal between the wafer and the o-ring, the LUR will exceed tolerance. Users should ensure that wafers are thoroughly cleaned before processing; both front and back-side; and if using a scribe to mark wafers, mark only in the centre of the wafer. If you encounter an unexpected error or require assistance please contact the primary or secondary trainer listed above. Should they not be available, please contact any staff member for assistance. 6. APPROVAL QUALIFIED TRAINER: Scott Munro TRAINING COORDINATOR: Stephanie Bozic 6