STS PECVD Instructions

Transcription

1 STS PECVD Instructions I. Introduction A PECVD (Plasma Enhanced Chemical Vapor Deposition) reacts gases in a RF- (Radio Frequency) - induced plasma to deposit materials such as SiO 2 and Si X N Y. This PECVD system operates at 13.56MHz and 380kHz. The tool has one chamber that is used for all depositions and utilizes a loadlock. This system is designed to control the stress of deposited films by adjusting the ratio of the high frequency (HF) power supply time, t HF, to the low frequency power supply, t LF. The bottom electrode where the samples are placed is called the platen, and the upper electrode where gases enter the chamber is called the showerhead. The STS PECVD can process a wide range of sample sizes. The number of samples depends on the size of the samples. The system can accommodate from 3" to 6" wafers, but deposition is typically done on 4" substrates. If samples are not wafers, there are two ceramic holder plates that are shaped like wafers that they can be placed on. Deposition will be uniform regardless of any through-wafer or through-sample holes. Typical deposition rates range from 100A/min to 400A/min, depending mainly on power, pressure, and gas flows. This system does have the capability to deposit SiO 2 at rates exceeding 500A/min; however, the quality of that material will not be great. That capability was designed to allow thick sacrificial SiO 2 layers to be deposited quickly. Caution: This system cannot process samples with thickness exceeding 2mm. Those samples should be processed in the PlasmaTherm PECVD. II. Machine Specifications At the MiRC, this system is used primarily for depositing silicon nitride films, silicon dioxide, and silicon oxynitride layers. Specific information on the required HF: LF ratios to generate a specific stress level in a film can be found in the documentation section for silicon nitride. For silicon oxynitride, similar principles apply. See the trainer for information on techniques to do so. This system has the following gases available for processing: SiH 4 (2% in N 2 ) N 2 O NH 3 N 2 This system uses the following gases for cleaning: CF 4 O 2 III. System Components 1. Heat exchanger 2. Mechanical Pump 3. Roots blower 4. Circuit breakers 5. Gas cabinet (chase) with switch 6. Reaction chamber with platen and aux-showerhead-temperatures IV. Deposited Materials and Precursor Gases 1. Silicon dioxide - SiO 2 - SiH 4, N 2 O

2 2. Silicon nitride - Si X N Y - SiH 4, NH 3 3. Silicon oxynitride - SiO X N Y - SiH 4, NH 3, N 2 O V. Operating Instructions 1. Loading a sample 1. Login to the access controller box 2. Press F3 to select the load/unload screen 3. Press V to vent the loadlock. Note that the system will cycle 4 times through the vent process; the process takes a few minutes as a result. The system will be at atmosphere when the loadlock pressure reads ~716 Torr and the seal between the O-ring and the lid will be noticeably weaker. Note: If the system says "Waiting" and no options are enabled, see Troubleshooting section of the instructions to resolve this problem. Note: This PECVD will begin to pump the loadlock back down if it is not opened within 45 seconds of the Vent process finishing. 4. Open the loadlock chamber lid and place the wafer and/or sample holder on the tray with the wafer or holder flat lined up with the open area in the substrate holder. Make sure that the sample / holder is securely in place and not wobbling. Note: If a polymer is processed in the system and it contaminates the chamber, e.g. clogs the showerhead, requires a physical chamber clean, etc., YOU WILL LOSE ACCESS TO THE MACHINE. 5. Close the loadlock Cover 6. Press L to load the sample. The loadlock will pump down and then the wafer will be loaded. Sometimes the change in air pressure will cause the sample to move. If this happens, press F1 immediately to abort the loading process. Please vent the chamber and re-seat your sample. 7. Press F3 to return to the main operating system after your sample has been loaded into the chamber. 8. IMPORTANT: There are two ways of viewing the system. F7 shows the system with gas lines, valves, the roots blower, etc., as a diagram. F8 displays that information in text. F8 will allow you to alter process parameters while your process is running, but F7 - Mimic - is extremely good for getting a systems level perspective on how things work, what valves are open when, and how gas line purges actually work. 2. Running a Process 1. Press F2 and select the desired process 2. After the process has been selected, the system will go through several steps. Don't worry about what they are; each time they come up and a choice is presented, e.g. "F1 - Abort," hit F1 only once (if you hold it down too long the key will stick and bad things will happen), continue doing so until the main menu is back (e.g. options for the F1 - F4 keys are displayed). At this point the process has load successfully. 3. After making sure the sample is indeed loaded, press F1 to start the process.

3 4. If the chamber is not at the correct temperature, the process will move to that step and adjust itself to the correct temperature, whether higher or lower. Please be patient as the system takes a while to adjust process temperature. If the system displays "Cannot reach setpoint" or similar message when doing this, ignore the message and do not press F1. Please allow the system to come to the correct temperature automatically. 5. After this, the system will pump the chamber and attempt to match the tuning capacitors for the power supplies. The system will then enter the "Gas Stabilization" phase where it begins to flow the precursor gases so that when the process initiates, the chamber will be at ideal process conditions. If the system alarms because of the pressure at this point, please hit whichever key "F1 or F2" is listed on the screen as Resume and let the system try again. If that fails, see Troubleshooting. 6. The system will then match the tuning capacitors again and attempt to strike the plasma. The capacitors will auto-tune at this point to the necessary settings to minimize the reflected power. Please keep in mind that this will take several seconds. After this finishes, the reflected power should be less than The system may alarm at this point. Even though the reflected power is at 0, that does not mean that the forward power is within the tolerance limit (usually 10%) of the setpoint (ex. 20W). E.g. if the system's reflected power is 0 but the power level is staying at 17W or 18W, the system will go into Hold with a "Power out of compliance" error. If this happens, hit whichever key - F1 or F2 - is Resume. If this happens more than once, see Troubleshooting. 8. Stay and watch your process for the first two minutes of deposition. Thereafter, come check on it every 15 minutes to make sure it is working. 3. Unloading a Sample 1. Once the process is complete, the main menu that shows values for the F1 - F4 keys will come up. 2. Press F3 to select the load/unload. Note: If the screen says "Waiting" for 30 or more seconds and no options are enabled, see the Troubleshooting section. 3. Press U to unload the sample. 4. When the loadlock is vented, the chamber pressure will be approximately 716 Torr and the seal between the O-ring and the lid will be noticeably weaker. The loadlock may be opened and the sample removed at this point. If other samples are to be run, repeat this process. 5. Close the loadlock; run a clean process - see section 4, "Cleaning". 4. Cleaning 1. Make sure the main menu is selected (F1 - F4 values showing) 2. Press F2 and select the CLEAN.SET recipe. 3. Follow the procedure used in "Loading a Process" - step 2 - to avoid waiting.

4 4. Press F1 to initiate the run. Please make sure it starts successfully and the plasma lights before you leave. 5. Log out of the system at the access controller. VI. Creating a Recipe 1. Press F6 to enter the main system's text-based menu. Type "SETUP" and press enter. If "SETUP" is not a valid command, type "LEVEL" and enter "MIRC". Now try "SETUP" again. 2. A new menu bar on a black screen will come up. It will have three options: Load/Save, Dep/Def'n, and Standby/Purge. Select File then Load Process to load the desired recipe. Always use another recipe as a template. 3. Select Dep / Def'n. You will have several options such as add step, remove step, and modify step. To add a step, choose add step. To remove a step, choose remove step. To modify a step, choose modify step. Then select the step to modify. The parameters for the step will be displayed. You can change one of the parameters by selecting it from the menu at the top and entering a new value. 4. Press Esc to return to the menu bar. Choose File, Save to save your recipe. Remember to choose a name that you will remember, that will allow others to determine what you are depositing, and that does not overwrite another recipe, unless it is yours. 5. To exit the recipe editor, press Esc to display the menu bar, then press Esc again. When asked if you want to quit, answer Y. 6. Time - Time is set under the "13.56MHz" or "380kHz" RF options. Two things can be set: if both power supplies are to be used - alternated between to control stress - make sure that the ratio of t HF :t LF has been calculated and that proper values are chosen for those numbers. Then set them as times for each power supply. Set the overall process time - in that case only - as the process time. Otherwise, the process time is set as the Low or High RF time if only one power supply is being used. 7. Pressure - Set the base chamber pressure to 0mTorr [this pressure is what the system will pump the chamber down to during purge cycles], set the process pressure to your desired value [pressure your process will run at], and set the Trip pressure to 1700mTorr [upper pressure bound that, if exceeded, will cause process to go into hold]. 8. Pumpout times - leave it set at 30 seconds. 9. Gas Flows: DO NOT EXCEED 90% of rated capacity on the MFCs. If the capacity is not shown on the screen, that number is the maximum allowed flow for that gas. 10. Power: DO NOT EXCEED 250W on either power supply. Although higher powers are used during clean processes, powers in that range can damage the system in normal processing mode and will hurt your substrate. 11. Temperature: Set the temperatures to the desired process temperature. Remember, the Aux temperature is the temperature of the showerhead; the main / platen temperature is the process temperature for your wafer. DO NOT EXCEED 300C on platen temperature or 250C on the AUX - showerhead. 12. Endpoint detection / End detection - leave this option disabled.

5 VII. Troubleshooting Q: What if no options in the load / unload menu are enabled and the system read "Waiting"? A: Consult the technical staff. Q: What if the system will not reach equilibrium during gas stabilization (e.g. pressure out of compliance)? A: Hit F1 for RESUME or ABORT, whichever option is enabled. If RESUME is selected, then please be patient while the system attempts to reach equilibrium. If this is required more than once, please notify the technical staff. Q: What if the system skips the deposition step and goes right through the gas line purge and then completes the process? A:There is something wrong with your recipe or the system. 1. Check that all the values are in compliance (e.g. chamber/aux temperature). 2. Then check your recipe to see if the parameters have changed. Q: What if the RF power is showing reflected power but the levels are low (<2W); however, my process is stopping because the forward power is not in range? A: The start positions for the capcitors are probably not set correctly. It takes the system some time to set those to optimal settings. Hit F1 to resume and once your recipe is running fine, record these numbers (Tune and Load) for each power supply. When your process is done, go change those parameters in your recipe. Q: What if the process temperatures are not in range? A: Give the system time to reach the desired temperature. Generally it takes the system 1 minute to raise its temperature by degrees C. Q: How do I get approval to process a material on the system that is not listed under allowed materials? A: Go to the Exceptions web page. Please explain in detail why you need to process this material (is it a polymer, what is the melting point, etc.) and answer the questions about whether it could contaminate or harm the system or other users's samples. Include a link to the relevan paper if it is online; do not attach a.pdf copy except where it says to upload. Incomplete information will result in automatic rejection of your request for an exception for that material. VIII. DO's and DON'Ts DO NOT TURN THE SYSTEM OFF!! hit F4 and exit the software press OFF on the front of the machine abort an unload process, as it will leave your sample in the machine. If your sample becomes stuck in the machine, you will cause significant machine downtime and will face disciplinary action. DO make sure your sample only has approved materials on it make sure you load your sample properly run a clean process.

6 IX. Check-off requirements 1. Locate the relevant components of the system (heat exchanger, etc.) 2. Know the specific materials that can be deposited and know what each gas is used for (e.g. clean, precursors for what materials, etc.) 3. Know the specific materials and processes you will be using the for 4. Be familiar with the other materials that can be deposited in the system 5. Vent the chamber 6. Load a sample 7. Load a process 8. Edit a process and save it as yours 9. Run a process 10. Unload a sample 11. Run a clean process 12. Demonstrate how to handle the following errors: o Pressure will not go into equilibrium during the gas stabilization phase of a process o Levels of reflected RF power exceeding 1W o Forward RF power is not in range during a recipe o Levels of reflected RF power exceeding 5W o Process that has a general error and must be terminated X. Personal Safety To prevent risk of personnel injury, all maintenance and repair procedures must be undertaken by technically qualified person(s) who are fully aware of all relevant safety precaution associated with processing, operating and maintaining the equipment. If you detect any chemical fume from the process chamber, please STOP your process and contact a staff member immediately. Potentially lethal voltages (in excess of 30 volts AC and 50 volts DC) are present on the equipment. If you see any open and broken wire or exposure electrical parts, DO NOT try to fix it. You have to contact a staff member right away. To prevent an uncontrolled hazardous gas flow to the process chamber, which could result in personal injury, DO NOT open the by-pass valve in the gas box when flowing a process gas.