Picture and Location
The tool is located at B7 on the Lab Map.
SAMs are organic molecular chains whose spontaneous self-assembly allows for the formation of a compact single monolayer. Similarly to ALD, SAMs deposition is driven by a self-limited chemisorbed surface reaction. However, while an ALD film is achieved by sequencing a finite number of reactant exposures and purges (referred to as ALD cycles) until a desired film thickness is achieved, SAMs formation is the result of a single cycle under Expo mode conditions. Besides the introduction of the SAMs organic precursor, a catalytic co-reactant such as water can also be introduced. The quality of vapor deposited SAMs is strongly dependent on the precursor dosage and length of the exposure which will affect the level of saturation and ordering on the surface. The ballast kit attached to MVD enables pressure endpoint control of the SAMs dose in order to achieve highly reproducible dosage of the reactants. The operational sequence used during the end point pressure control is shown below (diagram courtesy of Ultratech/Cambridge Nanotech):
Because of the self-limiting nature of the precursors, MVD systems can achieve near monolayer-at-a-time growth conditions with extreme uniformity over large areas. Additionally, the thin organic films have tremendously conformal coatings even under extreme topology. However, the deposition rate is extremely slow (in general on the order of monolayers/hour) and this technique is not ideal for films thicker than a few tens of nanometers.
MVD is a molecular vapor deposition (MVD) system. It is a self assembling monolayers (SAMs)-based configuration of a Savannah S200 from Cambridge Nanotech with 1 SAMs delivery port and 4 standard atomic layer deposition (ALD) lines. The system can accommodate pieces up to an 8" wafer.
The MVD is classified as a Gold contamination level tool.
The following materials are NOT allowed:
- Polymers not specifically approved.
- Wet samples
- Anything with melting points or ignition points below 250C
- Plastic, including Teflon
- Non-encapsulated particles
- Samples small enough to fall into the exhaust line
A Note on III-V MaterialsTraditionally III-V materials in SNF are classified as gold contaminated. However, because the MVD operates at low temperatures III-V materials can be used in the MVD under the following conditions (failure to adhere to these rules will result in removal from use of the tool):
- The III-V materials in question do not violate any of the above restrictions
- Users wishing to use III-V materials must speak directly to the quality circle about their plans before beginning to use these materials in the system.
- III-V materials should never touch the inside of the deposition chamber or the tweezers that are used in the chamber.
How to make a Carrier Wafer for MVD
A clean Si, SiN, or SiO2 substrate must be used as a carrier wafer.
- Grow about 100nm SiO2 on a Si <100> wafer. SiO2 can be deposited, but needs to be on both front and back.
- Pattern SiO2 with resist. The pattern should be a larger area than your piece as this pattern defines your pocket.
- Dry etch SiO2. Note: wet etch does not work because you need to keep the backside oxide.
- Strip the photoresist.
- Etch pockets
- Wet etch Si wafer with SiO2 as a mask in TMAH heated to about 90C for a few hours. This makes a recess with depth dependent on your initial mask because TMAH stops on the Si 111 planes. The chips can sit on the crystal smooth angled sidewalls of the trenches, which are very flat allowing good thermal conduction from the substrate, and hence the substrate heater, to your chip.
- You could also try a DRIE of Si to define your pocket. Here
the etch would be vertical and your pocket would have an approximately
Performance of the Tool
- Deposit high quality organic film
- Tightly controlled thickness through monolayer at a time growth.
- Organic film deposition with angstrom precision.
- Ultra-conformal deposition.
- The MVD process chamber can run with a maximum temperature of 150C.
- The ozone generator can be used to clean the chamber.
- The SAMS expansion chamber can be used to control dosing of one precursor at a time.
- ALD valves can be used to dose SAMS.
- The plasma cleaner can be used to plasma treat substrates prior to deposition.
What the Tool CANNOT do
- Deposit thick films. This is because of both the extremely slow deposition rates and the expense of material precursors.
- Films thicker than 50nm require prior approval from the quality circle.
- Selective MVD is a difficult issue and current research topic. It should not be expected that materials will deposit only on certain materials.
MVD is specifically for organic thin films. Inorganic films are not available and not allowed here.
The MVD consists of the following components:
- An Ultratech/Cambridge Nanotech Savannah system: The Savannah
system is similar to the ALD Savannah system in the SNF. Enhanced
capabilities for SAMS depositions include an expansion chamber which is
used to control the amount and repeatability of the SAMS dose and an
ozone generator which can be used to clean the chamber between runs. (Diagram courtesy of Ultratech/Cambridge Nanotech)
- O2 plasma cleaner: The plasma cleaner can be used to clean substrates prior to deposition.
- MBraun Glovebox: The N2 atmosphere in the glovebox is controlled for humidity, oxygen, and temperature. This can be beneficial to reduce surface reactions and contaminants following surface preparation steps such as plasma clean.
The MVD is still in the process of inital characterization so no monitors are being performed.
The films available on the MVD at any specific time are determined by the precursors installed in the system. The list of available precursors is maintained on this page, while the list of installed precursors is maintained on Badger and the MVD control software. The file on the computer is the final word on what precursors are installed on the system currently. In the event that Badger and the file on the computer disagree - follow the document on the control computer.
Current films available (in stock precursors):
- DETA (diethylenetriamine)
- APTES ((3-Aminopropyl)triethoxysilane)
- ODS (octadecyltrimethoxy silane)
For the list of currently installed precursors consult the document on the MVD and Badger for the most recent changes.
*Other organic thin film depositions are welcome to be characterized. Please contact the quality circle to explore more options. New materials and special runs can be possible as needed and with appropriate planning.
Contact List and How to Become a User
The following people make up the Tool Quality Circle:
Process Staff: Michelle Rincon (mmrincon at snf dot stanford dot edu)
Maintenance: Mike Dickey (mdickey at stanford dot edu) and Jim Haydon (jhaydon at stanford dot edu)
- Super Users: J Provine (jprovine at stanford dot edu)
Training to Become a Tool User
- Shadowing. Contact a current user of the MVD and request that they introduce you to the system and demonstrate the use of the system for you. If you do not know an MVD user, contact the user list (mvd at snf dot stanford dot edu) or check badger for upcoming user reservations. It is up to the user if they are willing to have you shadow them. If you have trouble finding someone to shadow, please feel free to contact the quality circle for help. (Helpful hint: ask lots of questions.)
- Written Quiz. After shadowing a user, contact the Michelle Rincon or J Provine to take the short written quiz for the MVD. The quiz is closed book and all the information should be known to someone who has studied the online documentation and has gone through a shadowing.
- Oral Qualification Exam. After the written quiz has been passed, you may schedule a final oral qualification exam with a superuser or staff. At this exam you are expected to demonstrate your ability to run the tool safely and appropriately without any input. Once this final stage is satisfactorily passed, you will be given full access and utilization for the MVD.
- Make reservation in Badger
- At least 24 hours prior to reservation time, make a comment in the maintenance section to request the specific precursors you would like to use for your run. The precursors are swapped frequently so do not assume that a precursor that is on the tool when you make your reservation will still be there when you are going to be running. If your reservation is for the weekend, please make the comment by the end of the day Thursdays.
- The MVD system includes an N2 glovebox that is controlled for humidity, oxygen, and temperature. The system must be enabled in Badger to use the glovebox or any of the equipment inside the glovebox. DO NOT OPERATE THE SYSTEM WITHOUT BEING ENABLED ON BADGER.
- Check that the system is in working condition: all the heaters enabled and within range, the precursor gas lines are open, and the reaction chamber is pumping to below 250mTorr with a carrier flow of 5sccm. If any of these features are not found to be in range, report the situation on Badger. The base pressure creeps over time as the capacitive pressure sensor drifts with deposited film and over time. The key is that the pressure is low, stable, and similar to the previous reported value. Note the base pressure at 5sccm to check with your process is done to ensure nothing has changed during deposition.
Check the status of the system on the control computer. This is the final note about what precursors are loaded on the tool will be here.
- Load your desired recipe: right click on the recipe in the control software and select from the Windows file list.
Edit your recipe as needed: During an expo mode, the carrier flow rate is typically reduced to 5 sscm. See the More on Recipes subsection for more information about writing and editing recipes.
Vent the ALD chamber: press the “Vent Chamber” button
Load your wafers and clean nitrile gloves into the loadlock of the glovebox and pump/purge 10 times. The wafer carrier should be unsealed to prevent explosion during pumping. SEE GLOVEBOX section for details of glovebox operation.
- Double Check that glovebox environment is nominal and was not disturbed by introduction of any material you will use for your experiment.
- Pressure : < 5 – 6 mBar
- H2O : < 0.1ppm
- O2 : < 0.1 ppm
- If items b and c are not within the range stated, please report this in Badger so that the staff can evaluate the problem and determine the source of this issue.
- With the gloves double gloved with the latex gloves you brought into the chamber, remove the insulating shield from on top of the Savannah ALD chamber and place on the left.
- Load your wafers into the reaction chamber (Be Careful It is HOT). Do not use plastic tweezers or wear clear vinyl gloves when working in the reaction chamber because of the possibility of melting these elements and contaminating the chamber. Teflon coated metal tweezers are allowed. All tweezers and substrates should be clean as described above.
Close the lid snd replace the insulating shield on top of the Savannah chamber.
Take off the gloves and pump the chamber by pushing the "PUMP" button in the control software.
- When the system has reached base pressure (check that it is similar to what base pressure you found the system in - different by not more than a few mTorr), run your recipe by pushing the "START" button.
- Check to make sure the pressure pulses of your recipe are in the correct range by monitoring the pressure readout in the control software. The reactor pressure should remain under the maximum interlock pressure (it is set to lower than atmospheric pressure as lid opens at ~760 Torr). The SAMs pulse command can be aborted at any time by pressing the Abort command or by clicking “Next Recipe Step” button.
- If you need to stop your deposition at any time during the process, press the "STOP" button which will leave the heaters and the pump on but stop the recipe. Do NOT close the control program overall.
- When the process finishes, check that the base pressure has returned to the initial value. This checks that the system is not leaking and has returned to its original state.
- Vent the chamber and remove your wafers and close the lid. Transfer your
wafers to glovebox loadlock. The wafer carrier should be unsealed to prevent
explosion during pumping. Also transfer your used gloves and any other materials you brought in with you to the glovebox loadlock.
- Pump down the Savannah chamber.
- Loadthe standby recipe STANDBY and run it (please see A Note on Shutdown subsection)
- Unload your wafers and used gloves and any other waste from the loadlock chamber.
- Pump/purge the loadlock three times after removing your items to remove any air from the load lock. Leave the lever in the "CLOSED" position.
- Lock the computer monitor screen ("window"-Lock). NOTE: do not log off the computer as this will disconnect the control software from the e-box.
- Disable the system on Badger.
Operating the Loadlock
Generally, only the smaller loadlock should be used since it takes much less time to pump down. Both loadlocks should be pumped down when not in use. Use of the larger loadlock requires prior approval from Michelle Rincon.
- Check that glovebox environment is nominal.
- Pressure : < 5 – 6 mBar
- H2O : < 0.1ppm
- O2 : < 0.1 ppm
- If items b and c are not within the range stated, please
report this in Badger so that the staff can evaluate the problem and determine
the source of this issue.
- Push lever to “refill” position to vent the loadlock.
- Push the lever to “closed”. Otherwise, the loadlock door will not open. This is a safety feature to ensure that the door does not fly open and injure the user since gas is being pumped into the loadlock chamber.
- Open the loadlock door, load sample into the boat (using clean gloves), and close the door.
- It is hard to reach inside the LL once you have the gloves on, so place objects at the far end of the boat.
- Everything you place in the loadlock must be capable of surviving a vacuum, and cannot contain any air pockets as they will contaminate the glove box. Any plastic bags should be left open. Any bottles or chemicals should have their caps loosened. If this presents a chemical hazard for any reason, consult with Michelle Rincon on best practices.
- Pump/purge the loadlock a total of 10 times (to prevent contamination of glovebox)
- Push lever to “evacuate” to evacuate the loadlock.
- Wait until the pressure drops to <-25 inHg
- Push lever to "refill"
- Repeat steps a-c 10 times.
- Push lever to "evacuate", let the chamber pump all the way down to -30 inHg (full vacuum) and then push the lever to "refill" to bring the chamber back up to atmospheric pressure.
- Push the lever to "closed"
- Adjust the glovebox pressure using the foot pedals. The nominal operating pressure is 5 mBar, but you will want to use a slightly lower pressure when pushing your hands into the glovebox gloves. Be attentive: the glovebox pressure will change as you push the gloves into the glovebox!
- Put your hands in the glovebox gloves, and add secondary latex gloves.
- It is very important that you always have secondary latex gloves on when working in the glovebox. While the glovebox gloves provide protection, damaging those would result in a lengthy shutdown of the tool and high repair costs. Thus it is best to put on secondary latex gloves.
- Open the door from inside the glovebox, retrieve your items from the boat, and close the loadlock door.
- Pump down the loadlock by pushing the lever to "evacuate".
- Leave the lever in the "closed" position while processing.
Processing Small Pieces in MVD
Small pieces that are larger than 1cm x 1cm can be processed in the MVD without a carrier wafer, but care must be taken to prevent the pieces from being blown around by the strong gas currents in the chamber. An easy method to corral your pieces is with silicon half-wafers:
The recipes are all maintained in the folder C://Cambridge Nanotech/Recipes. Standard recipes listed in this document are kept in that folder. USERS MAY ONLY CHANGE THE NUMBER OF CYCLES FOR STANDARD RECIPES AND WHICH PRECURSOR VALVE IS APPROPRIATE. If you wish to write your own recipe, please contact Michelle to get approval for the recipes BEFORE making any recipe edits.
The parameters controlled in a recipe are listed below with comments about each:
|Heater||Each heater has a unique item number and a value given in degrees Celsius. Do not overheat precursors. The reaction chamber should be operated below 150C. The manifold and exhaust lines should be maintained at elevated temperatures to avoid condensation.
|Flow||This controls the flow of carrier gas flowing through the system. It is defined in sccm (standard cubic centimeters per minute). The standby condition is set to 5sccm to reduce N2 usage. The source is the house nitrogen line.
|Pulse||This command is for pulsing a precursor line. It requires an ALD valve number and the amount of time you want the valve open in seconds. The fastest these valves can fire is 0.015 seconds, so note that even if you define a shorter time that is likely the valve open time you will get. (NOTE: the time needs to be written with a digit to the left of the decimal place i.e. "0.015" vs. "0.15")
|goto||Used to define loops in the recipes. This command takes as an input the step to which the recipe should return. The value for this command defines how many times the loop will run.
|stabilize||This command is used to hold a recipe until a heater has reached the desired value. It takes as input a heater ID number and will wait until that heater demonstrates the set temperature over a few seconds.
|wait||This command takes as inputs a value in seconds that you would like the system to wait before proceeding to the next command. (NOTE: the time needs to be written with a digit to the left of the decimal place i.e. "0.015" vs. "0.15")|
|| This command will close or open the output valve for the reaction chamber depending on a Boolean input. This command is used only in Expo mode.
| SAMS Fill
|| This command enables the actuation of a pneumatic valve in order to fill up the ballast volume. The valve remains open until the ballast pressure reaches the pressure setpoint defined in the recipe (0 to 10 Torr).
A Note on Shutdown
The STANDBY recipe is used to set all the heaters at nominal values and adjust the flow of the N2 carrier gas to a less consumptive value. All of the heaters are maintained at nominal values to avoid condensation or other history related problems in the system. The manual valves for all the precursors can be left open with the ALD valve providing sufficient gating on the precursor. There is no need to adjust anything inside the cabinet with the machine is under normal, "green light" status. Any issues that may require attention need to be documented in Badger in the maintenance tab to alert staff to the issue. Only staff is allowed to open the cabinet.
The following restrictions are in place for reservations on MVD:
- The maximum reservation window is 7 days.
- The maximum primetime reservation any day is 4 hours.
- The maximum reservation time per week is 24 hours.
- Please make a comment in BADGER stating which precursors you will be using at least 24 hours before your run.
Process Monitoring and Machine Qualification
Tool Qualification Run
Recommendation to users with critical processes
Machine Status States
Red: The tool is not capable of depositing any films and needs maintenance or verification of proper working conditions.
Yellow: The tool is capable of depositing some films or films of non-standard quality. Reasons could include the lack of necessary precursor, issues with the machine (pump, heaters, etc), or contamination that needs to be cleaned.
Green: The tool is in working condition for all available films, and those films were found to be within specifications.