System Description and Operating Instructions for PlasmaTherm CCP PECVD
A PECVD (Plasma Enhanced Chemical Vapor Deposition) system reacts gases in a RF plasma to deposit materials, such as SiO2 and SiXNy. The plasma allows the deposition to occur at a lower temperature than a pure thermal process does. This operates at 13.6MHz, has a load lock and one deposition chamber. The system is configured in what is called a CCP (Capacitive Couple Plasma) configuration, also known as a parallel plate configuration. In this tool the wafers sit on the grounded plate/electrode and RF power is supplied to the top plate/electrode where the gas is introduced through holes in this electrode. This configuration is useful for depositions in low density plasmas where ion bombardment is less damaging. A unique feature of this system is the use of He gas dilution to control stress in the deposited films. While the He dilution system has not been modeled, it is proposed that some of the low mass He ions gain extra energy from oscillating plasma boundary layer, known as the sheath, and these energetic ions are useful for shifting the deposition from tensile toward compressive film stress. This enhance energy mechanism relies on the fact that the light He ions have a sheath transit time, which is shorter than the RF period. This behavior is similar to what occurs with larger ions when low frequency (~ 400 MHz) RF is mixed with the normal 13.6 MHz power.
This system is dedicated for working with 4” wafers in that it has a 4 slot wafer holder, which moves between the load lock and the deposition chamber. To achieve the most uniform films, it is best to always run to a wafer in each slot except when coating or cleaning the holder. Note that after the holder is moved into the deposition position, the electrode move up and holds the wafers above the holder. The electrode fully contacts the back of the wafers so their temperature is uniform and there is no deposition to the wafer backsides.
Another key feature of this tool is the end point detector and software used to monitor when the plasma cleaning process is complete. The detector is a compact visual optical spectrometer, which allows the software to monitor the 704nm F emission line. Free F is the active component is the chamber cleaning processes and searches a maximum at end point when there no deposition material left to etch.
This tool is a Plasma-Therm Shuttlelock model configured for PECVD deposition. The Coral name for the tool is CCP-Dep. At the SNF, this system is used primarily for depositing low-stress silicon nitride, silicon dioxide, amorphous and silicon carbide layers. It can also be used for depositing silicon oxynitride layers, which have not been characterized at this writing. The stress level in the nitride films can be controlled by varying the He:N2 .flow as shown in the appendix.
This system has the following gases available for processing:
1. SiH4 (5% in He) for Si source for all films
2. N2O for oxide
3. NH3 for nitride and oxynitride
4. N2 for nitride stress control
5. He for nitride stress control and for dilution
6. CH4 for carbide
This system uses the following gases for cleaning:
7. SF6 for free F source during cleaning
8. N2O for increasing free F during cleaning
The other controllable parameters are:
1. Temperature (100 – 350C). The initial recipes are all at 300C.
2. Pressure (500 - 2000mT)
3. RF Power (0 to 600W). Nominal power levels are: Nitride (100W), Oxide (200W), a-Si (25W), SiC ( 25W) and plasma clean (500W).
· Load Lock
· Reaction Chamber
· Process Monitor/Control Computer
· Mechanical Pumps – load lock pump located in finger wall and main pump located in basement.
· Heat exchanger – located in basement
· End Point Laptop Computer – on table to right of tool
To operate the tool it is best to first understand the 4 equipment- modes ( On, Standby, Ready and Run) in which the system can be. These modes are selected by the 4 buttons at the bottom right of the process monitor screen.
is the state the tool first goes to after starting the Sysmon software and completing the system
ON button is used to exit the STANDBY or READY modes and
return to the EQUIPMENT-ON mode.
the ON mode the gate valves are closed and the temperature is set at
- You do not want leave the tool in this mode because the chamber will cool down in this mode.
STANDBY –The STANDBY mode serves two purposes;
1) It can be used to leave the system in a temperature-controlled vacuum state. When finished processing leave system in STANDBY.
2) It can perform STANDBY Service menu functions. These functions enable the operator to do such things as venting, pumping and manually controlling loading and unloading.
The system must be in the EQUIPMENT-ON mode before STANDBY can be activated. To activate the STANDBY mode, click the STANDBY button.
- The READY button is used to prepare
the system for wafer processing or to perform READY.
- The READY mode indicates that the system is process-ready.
- For the READY mode to be activated,
the system must be in STANDBY mode and have a valid program/recipe
- To enter the READY mode, click the READY button. To exit the READY mode, click the ON or STANDBY buttons
- The RUN mode is used to begin the process. The system cannot RUN unless it first achieves a READY mode and passes some self-tests. So pay attention to the status windows as you start your run.
- To activate the RUN mode, click the RUN button.
- During the RUN
mode, only the Process buttons (i.e, END
STEP and ABORT) and ALARM button are recognized. The system
will continue processing unless the operator clicks END STEP or
ABORT or there is a system failure or compliance error.
- To stop a process, it is usually better to use the END Step command since it allow the system to go though the post deposition purge steps before stopping.
Located above the mode buttons. You should keep your eye on these messages.
- Info – Describe the current operation being performed
- Warning – Indicates a fault has been found which may stop you from going to your next operation.
- Alarm – A serious fault has been found, which will stop all processes. You can silence the alarm by hitting the Alarm Silence button. Once the fault that caused the alarm has been remove, you need to hit the Hold button to clear the alarm.
“Gas suspected in chamber” means chamber needs to be pumped down before you can proceed. How to do this will be explained further below.
”Temp Channel ½ is off” means that the heat exchanger in the basement needs to be restarted by a staff member.
Consult with the staff if there is a warning, which you do not understand.
Is temperature setting correctly ?
Check the substrate temperature by opening the lower right front cabinet door and looking at the temperature controller display. The bottom number is the set point and the upper number is the temperature. If the set point is not at your deposition temperature (300C is typical), the tool is not in STANDBY mode or the STANDBY temperature setting needs to be changed. It can take 30 min for the chamber to heat up from rm temp, so you will want to immediately change the set point if needed. Checking system before use.
- Activate the tool (CCP-Dep) in Coral
- If need be login on the process monitor display, go to Login under the Utility menu.
- The operator login name is “oper” and the password is “oper”.
Go to STANDBY
Change substrate temperature setting if needed by selecting STANDBY TEMPERATURE under the UTILITY menu. The heater exchanger temperature should be set to 70C for 300C and 80C for 350C. You can load while you wait for the chamber heat up.
If you cannot see of diagrams of both the loadlock and chamber on the display, change the display using the WINDOWS menu and selecting “Overview Diagram”.
- Vent Loadlock: Select the Utilities/Loadlock/Vent. The loadlock diagram on the display will show "atmosphere" when it is vented.
- Open the loadlock (LL) and load
your wafers as shown. If you are running less then 4 wafers, fill the empties
- DO NOT use plastic tweezers to load or unload your wafers. The wafer carrier is at the deposition temperature when it comes out of the chamber.
- You will need prior approval to use any wafer materials besides Si and quartz in this tool.
- Close LL lid completely.
process- Batch or Chamber?
You may choose to use Batch or Chamber to process your samples. When using Batch the system is in a production-like mode; recipe times cannot be changed, but the wafer platen will move automatically in and out of the chamber.
In Chamber mode when the recipe is Run you will be asked for a deposition time, but you will need to manually load/unload the platen into the chamber.
Checking a Recipe using Batch Mode:
Select the Process menu, then select Batch. The Batch Editor window will come up. In this window under the File menu select Load and then select the Batch Process you want to run. Batch processes end in .bch.
Batch Processes combine deposition or clean recipes with the transfer of the wafer carrier in and out of the chamber, so a user can run their process in one automatic step with wafers beginning and ending in the loadlock. More advanced users can use a manual option where transfers and running a recipe are separately steps.
Please Note: recipes run as Batch will not allow users to change deposition times. Dep times can be changed by editing the recipe or running in Chamber Recipe mode (see below)
Running a Process in Batch Mode
- Press the READY button
- Make sure the chamber lid is closed completely, as the system will not run a process if the lid is open.
- Press the RUN button.
- If the chamber is not up to temperature, you be given a status line saying the system is waiting for the chamber to come up to temperature. You may need to set the standby temp to the same as the recipe temp in Utilities/Set Standby Temperature.
- Watch the LL pump down followed by the transfer of carrier into the chamber. When the process sequence begins stay through the thermal soak step, the stabilization step and the first minute of the deposition step. Most problems occur before this point in the process. If you have to stop the process after the gases are flowing, it is best to use the End-Step bottom instead of Abort since this allows the process to go through the N2 flush step. Note: the Hold button does not pause the process. It is use for clearing alarms.
- After the process is complete, the wafer holder should transfer back to the LL and the LL should vent to atmosphere.
Checking a Recipe in Chamber Mode
1. Selecting Process/Chamber/Open will open a window showing all the recipes. At this point selecting the recipe you want will open the Process Editor. A recipe is composed of 7 or more steps. The initial steps set and stabilize the temperature, pressure and gas flows while the final steps purge and evacuated the chamber. The key step is the deposition step (typically #4). It sets the final flows, pressure, RF power and time.
2. The OPEN command is useful for checking a recipe but be very careful not to make any changes. In this mode it is easy to overwrite standard recipes. In the editing section you will be shown how to create a new recipe to which you can make changes.
3. Closing Recipe without makes any changes -- At this time make no change. At the bottom of the edit window select Exit and do not Save. This should get you back to the chamber window in Standby mode.
Running a Process in Chamber mode
Go to Maintenance/Wafer Handling. A screen with a schematic of the LL and chamber will appear. Click the Load button.
You will be prompted when the load is complete. Exit from the screen.
Click on Ready to load the conditions. You may encounter a warning about the temperature. This is usually because the recipe temp and standby temp are different. Set the standby temp to the same as the recipe temp in Utilities/Set Standby Temperature.
Once Ready is achieved, click Run. This will start the recipe. You will prompted for deposition time.
At the completion of the recipe you will prompted by a message on the screen. Click on it and exit the screen. Click on the STANDBY button. Go to Maintenance/Wafer Handling and click the Unload option.
- Verify the system is in STANDBY mode.
- If the system does not auto-vent, select the Utilities menu and click on the Vent option. Once the chamber is vented, lift the loadlock lid and unload wafers.
- Unload wafers from platen.
- Hint: Let the sample(s) cool before placing them in a container; this is typically done using a metal block. Otherwise, they will melt the plastic of your holder or box, contaminating the sample(s) and making it very difficult to remove them from the container. (The only exception is if the sample holder(s) are fairly thick Teflon, and even then this is NOT recommended.)
- If more wafers are to be processed, repeat.
- Close the LL lid completely.
- Leave the tool in Standby to allow the temperatures to be
maintained. If you raised the temp to higher than 300C set it back to 300C/70C using Utilities/Set Standby Temperature
Chamber Cleaning and Conditioning
Chamber cleaning is accomplished by using SF6 and N2O. Cleaning should be performed when the accumulated deposition layer reaches 4um. It should also be done in conjunction with a nitride coat when changing the chamber status from contaminated to clean. The wafer transfer plate should be loaded into the chamber with no dummy wafers for clean and coat procedures.
Cleaning without using Endpoint
- Recipes used for cleaning and coating without using the endpoint are CLEAN-1 and SNPREDEP.
- For mixed SiO2 and SiN layers the clean recipes etches about 1000A/min. Add an additional 3 mins to the calculated etch time. For example, for 4um layer; 40 mins plus 3 min = 43mins.
- Cleans for silicon carbide should be at least equal to the SiC deposition time.
Cleaning with EndpointEndpoint detection when used to clean the chamber and wafer transfer plate can be a powerful way to insure that the etchback is complete but hasn't over etched. The fluorine spectra (the white line on the graph) is followed via an optical sensor until it saturates out. The EP program then turns off the recipe.
Using the EndPoint Works software- please keep in mind this is a work in progress and subject to change as we make improvements and adjustments to the instructions.
- On the lap top located next to the ccp dep tool click on the EndpointWorks icon labeled V1.4.
- Chose the recipe from the recipe tab. The recipe from April will automatically turn off the recipe (though not as of this writing- you'll need to End Step to stop the cleaning) The recipe No Algorithm Nancy will not.
- Use the CLEAN EP 300 or 350 recipe.
- After the recipe has started, check the EP program on the external PC to make sure it has started. If not click on Strat button to get it going.
- Since you may be stopping the recipe manually here's what you are looking for; the blue line (a derivation of the slope of the Fluorine curve) goes to 0 and the white line (Fluorine spectra) is up at 14000 to 16000.
- Use End Step to stop the recipe if needed.
All About Recipes
In general, a recipe should have five steps: an initial step, a thermal soak, three process steps, an evacuation step and an end step. The initial step evacuates the chamber, and sets the process temperature. The second step brings the chamber up to temperature at the process pressure. The first of the process steps introduces the process gases and allows the gas flows and pressure to stabilize. Because the RF power is off, no processing will actually take place during this step. The second process step adds the RF power and performs the actual deposition. The last process step purges the chamber with N2 to remove all the process gases except N2. The evacuation step turns off the N2 and pumps the chamber to it base pressure. The end step continues to pump the chamber and terminates the process sequence.
It is best to start with an existing recipe. From the Process menu choose Chamber/Open 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 10mTorr and set the time to 10 seconds. This will cause the system to evacuate as much air from the chamber as possible before starting the process. 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 have at least 4 process steps; Thermal Soak, Gas Stabilization, Deposition and N2 Flush.
The process step dialog box has five major areas: time, temperature, pressure,
gas flow, and power. Here is more information on those parameters;
A process step can be terminate by Fixed time, by Variable (Var) time, by Endpoint and Deposition Thickness. Most process steps are fixed time. Deposition steps are often variable time although they can be Fixed time or terminated by a thickness in A if a deposition rate has been saved for the particular recipe. Finally, cleaning processes can be terminated by a signal from the optical emission endpoint system.
Set the temperature to the desired process temperature in the Initial step.
Set the pressure to the desired process pressure for each process step. The process pressure is measured in mTorr.
- Gas Flow
Set the desired flow rate for each gas in each process step. The flow rates are given in sccm. Typically, gas flows are the same in the gas stabilaiztion step and in the following deposition/etch step.
- RF Power
Leave the power set to zero in all steps except the deposition/etch step. . Set it to the desired process for the second process step. Typically, the power is below 100 w for deposition steps.
Examples of each of the Process Steps are:
Typical Thermal Soak Step
Typical Gas Stabilization Step
- N2 Purge/Flush
All recipes have a N2 purge after the last deposition or etch step. Since the system has a load lock, the purge step can be as short as 30s.
All recipes have an evacuation step before the End step.
Typical Evacuation Step
- End Step
All recipes have an end step that evacuates the chamber. Set the pressure to 30mTorr and set the time to 60 seconds. If auto-vent is desired, make sure to change that setting to YES.
Typical End Step
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.
Q:The system is alarming. How do I silence the alarm?
Note the cause of the alarm in the Info window. Click on the ALARM button to silence the alarm. Next click on the HOLD button to return to STANDBY or RUN mode. If the cause of the alarm has not be fixed the alarm will sound again.
Q: The computer has locked up and I cannot perform any operations on the machine.
You will need to reboot the computer by doing the following steps;
- Push 'RESET' on the PlasmaTherm computer found by opening the cabinet doors under the tool. It will be roughly in the center.
- Wait for the virus scan to complete.
- Windows log on will show on the screen. The login is '3333' and the password is '3333'. Hit ok after keying in the login and password.
- Operator log on will appear. The login is '3333' and the password is '3333'. Log in.
- Put the tool into 'STANDBY'.
- You will notice an Alert that says 'Gas suspected in chamber'. This is a default message and there may not really be gas in the chamber. However, you will need to pump out the chamber in order to proceed.
- Go to SERVICE/MAINTENANCE/PUMP/SYSTEM (lo Vac). This will initiate the chamber pump out. When the Alert has gone away you may proceed to unloading wafer, venting the loadlock or running a recipe.
- To finish, go to UTILITIES/STANDBY TEMPS and verify the temps you want are showing. You will need to change the heat exchanger from 65C to 60C.
- If this procedure does not work, put the tool in Shutdown on the lab computer system and contact a responsible staff member.
DO's and DON'Ts
Never push the Abort Button!
What the qual is:
The qual is a quick check of the status of the tool.
The qual is a 6 minute deposition of the recipe SiN350-1 (100W, 950mT, 200sccm 5%SiH4 in He, 6sccm NH3, 400sccm N2, 1000 He, 65C/350C) after the standard etch back and coat.
Recorded results may contain;
- 9-pt thickness measurements
- average thickness
- min/max thickness
- % uniformity
- refractive index
Other characteristics that may be checked on a less frequent basis are;
- Pin hole density
- Film stress
- Wet etch rate
Frequency of the qual:
It will be run when an equipment problem is flagged on Badger, when the tool is in engineering observation (say, when there is one of those pesky intermittent problems) or when the tool has undergone major repair.
Depending on the nature of the equipment problem a more in depth study may be run.
Results of the qual:
Are posted here.