Angstrom How-To | Tooling Factor
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Today we will be discussing a common thin film deposition parameter known as Tooling Factor. I will do this in two parts. First I will describe theoretically what Tooling Factor is, how it relates to system geometry, different materials, deposition rate, and crystal lifetime. Second, I will provide a practical demonstration on how to determine tooling factor on this Angstrom Engineering Nexdep sputter tool.
Given the cosine-law distribution, and since our sensor is not in the same place as our substrate, there will be a discrepancy between what is measured on the sensor and what is deposited on the substrate. When designing a film deposition tool, the sensor location is a balance between ensuring it intercepts enough deposition flux to be accurate, but also limiting the flux as much as possible to prolong the lifetime of the sensor.
To account for these factors, the Tooling Factor is introduced so users can enter a target thickness and the deposition software will adjust accordingly. To calculate Tooling Factor, we first must perform a deposition with a target thickness and estimated tooling factor. This estimated factor is an educated guess based on experience, or perhaps an in-depth knowledge of the geometry of your chamber. Once the deposition is complete we simply measure the thickness of the film and plug the values into this formula.
Now that the tooling factor is calculated, we can enter this into the deposition software and can begin depositing films.
OK so here we are at our deposition tool where I will show how to determine Tooling Factor. This is an Angstrom Engineering NEXDEP sputter tool with Aeres control software. For more information on this tool and others we offer, go to www.angstromengineering.com.
We are going to sputter an aluminum film on a glass slide but first, we must discuss sample preparation.
To measure the thickness of our film, we are going to use a stylus profilometer. So, we must create area on our substrate where no film is deposited. There are several ways to do this, I will demonstrate two.
The first method is to use an etch resist pen like this one from MG Chemicals to draw a line on the substrate. After the film is deposited, if we dip the substrate in a solvent such as methanol, the etch resist will dissolve and lift off the aluminum deposited on top of it, leaving the bare substrate.
The second method is to simply use some kapton tape, and tape off an area on the substrate. After the deposition is complete, the tape is carefully removed to expose the substrate beneath.
Here we are back at the tool. I have secured the samples on the stage and loaded the stage in the tool. Now we are ready to pump the chamber down.
Ok so our chamber is pumped down and we are ready to begin our deposition. I’ve set up a sputter process in which we will aim to deposit 200 nm or 2000 Angstroms of aluminum.
We are at the profilometer where first I am going to show you how to expose the substrate in both of our samples. For the kapton tape sample we simply remove the tape to expose the substrate. For the sample with the etch resist, we could dip the substrate in the solvent right away but we like to attempt to remove the material on top of the etch resist first. To do this we place a strip of kapton tape over the etch resist and peel it off. As you can see most of the material adheres to the tape. Now we can use solvent to remove the etch resist to expose the substrate.
Now I have loaded a sample onto the profilometer stage and we are ready to measure our step.
OK, so we have deposited at film of 120 nm. This means our tooling factor guess was slightly off. No problem, that is why we are performing this process! Plugging our target thickness, estimated tooling factor, and measured thickness into our formula we get a new tooling factor of 45%. We can now enter this new tooling factor in our deposition software and proceed with our depositions.
Conclusion
In this video, we have discussed and demonstrated the concept of Tooling Factor as it relates to physical vapor deposition processes. We hope you enjoyed the video and found it informative. Stay tuned to our YouTube channel for more videos on thin film deposition concepts. If you have any comments or questions, please comment below or contact us at www.angstromengineering.com
I’m Dr. Chris Haapamaki, Happy Depositing.
References:
M. Ohring, “Materials Science of Thin Films – Deposition and Structure”, 2nd Edition, Academic Press 2002
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