In order to protect some deposited materials from reacting with air or water vapor, they are usually immersed in low-viscosity (hydrocarbon) mineral oil during storage and shipment. Before installing these composition materials shipped in oil into the vacuum system, we must use solvents to remove these oils. The choice of solvents is based on the premise that they do not act as additional contamination sources for the vacuum system or the subsequent thin-film processes.
Choice of the Solvent
Some highly reactive deposition materials may react with certain solvents. Therefore, always choose the solvent that is strictly hydrocarbon in nature.
Here are some solvents that are NOT recommended. You’d better NOT use them to remove the oil:
- Do not use pyridine-like solvents containing nitrogen.
- Do not use sulfur containing solvents, such as carbon disulfide.
- Do not use any of the numerous chlorine-containing solvents, such as trichlorethylene is an example.
- Do not use solvents, such as alcohols, ketones, esters, ethers, furans, or others containing oxygen.
And, here are some recommend some solvents. To minimize the expense associated with high purity, clean (solute-free) hydrocarbon solvents, you can use technical grade solvents, such astechnical grade hexane, heptane, iso-octane, in the initial cleaning steps.
NOTE: High purity grades of hexane, heptane, or iso-octane must be shipped, stored, and used from glass containers. It’s important to note that plastic squash bottles are not a suitable container choices for solvents. Although they are very convenient for storing and handling solvents, the low molecular weight polymers in the plastic are leached out by the solvent and remain as a residue when the solvent evaporates. Again, never use solvents stored in plastic containers.
Precautions for Handling Organic Solvents
Nearly all organic solvents are health hazards, so please make sure:
1) DO NOT breathe in solvent vapors or swallow solvent liquid
2) DO NOT allow skin contact with the solvent or splashing solvent to touch the eyes
3) DO NOT allow exposed flames or heaters near the vapor
And, note that all solvent handling
1) Should be done in an extractive fume hood, or glove box.
2) Should be done only while wearing suitably protective eye shields, aprons, and absorbent respirator masks
3) Should be done only while wearing gloves that have been tested to demonstrate that the solvents in use neither dissolve the gloves nor permeate through them.
In order to delay the interaction between air and the material, it is better to clean the material in a leak-tight glove box under a slight positive pressure of argon. If this is not possible, please ensure that all cleaning steps are completed as quickly as possible in a fume hood or a well-ventilated area. This can minimize the time the material is exposed to the air and also reduce the time the operator is exposed to solvent fumes.
Equipment and Materials Needed
Here are the cleaning materials you need:
- Suitably sized, chemically and physically clean glass receptacles (beakers or petrie dishes)
- Technical purity d (used in the initial cleaning steps)
- Extremely high purity hydrocarbon solvents (used in the following cleaning steps)
- Lint-free tissues
- Chemically and physically clean tongs or tweezers to handle the materials
Detailed Cleaning Procedure
First, you need to prepare no less than three beakers / petri dishes, and ensure that you can fill in enough technical solvent to completely immerse the deposition material. Similarly, prepare a beaker/petri dishes of no less than three, with enough high-purity solvent in it to completely immerse the material.
Second, remove the material from its packaging and quickly wipe off the excess oil with a lint free tissue. After that, immediately immerse the material in beakers or petrie dishes with technical solvent (DTS01), and stir the material or solvent to promote dissolution. (Note: The time between removing the material and putting it in the solvent must be as short as possible, so as to reduce the time that the material is exposed to the air. And, do not attempt to dry completely since this increases air exposure and does little to reduce contamination.)
Third, remove the material from the TSD01 and quickly wipe off excess solvent with a fresh tissue. Then, repeat the 2rd step and immediately immerse the material into TSD02 and stir the solvent.
Repeat the above process until the material go through all the 6 beakers or petrie dishes (3 with technical solvent and 3 with high-purity solvent).
When the material is removed from the last beaker or petrie dish with high-purity solvent (DHS03), immediately transfer the material to the vacuum chamber that should be pre-flushed (and continue to be flushed) with argon. The chamber should be always vented with argon.
When the material is mounted in its source, stop Ar flow, close the chamber flanges, and pump. If the depositionmaterial is a reactive sputter target such as Ca, Ba, Sr that quickly oxidizes, please presputter it for a short time.
For all the time the material is in the chamber, make sure that argon continues flowing at high volumetric speed when the chamber is open, and keep it at high vacuum when the chamber is closed.