Protocol for Cleaning Deposition Materials Shipped in Oil
Deposition materials that react with air or water vapor are protected during storage and shipment by immersion in a low viscosity (hydrocarbon) mineral oil. Before the material can be installed in a vacuum system, this oil must be completely removed using solvents that do not act as additional contamination sources for the vacuum system or the subsequent thin-film processes.
Plastic squash bottles, while very convenient for storing and handling solvents, are particularly poor container choices. Low molecular weight polymers in the plastic are leached by the solvent and are left as residues when the solvent evaporates. Never use solvents that are stored in plastic containers.
It is possible for some, highly reactive, materials to react with certain solvents. Always select solvents that are strictly hydrocarbon in nature (i.e. the solvent molecule contains nothing but carbon and hydrogen).
- Do not use solvents such as alcohols, ketones, esters, ethers, furans, or others containing oxygen.
- 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 of which trichlorethylene is an example.
To minimize the expense associated with high purity, clean (solute-free) hydrocarbon solvents, the initial cleaning steps can use technical grade solvents. Technical grade hexane, heptane, iso-octane are preferred but possible choices include more commercially-named materials such as 'white spirits' or 'laquer thinners' as long as they are certified as strictly hydrocarbon in nature.
High purity grades of hexane, heptane, or iso-octane must be shipped, stored, and used from glass containers.
Handling Organic Solvents
Most (perhaps all) organic solvents are health hazards:
- Do not breath in solvent vapors
- Do not accidentally swallow solvent liquid
- Do not allow skin contact with the solvent
- Do not allow splashing solvent to touch the eyes
- Do not allow exposed flames or heaters near the vapor All solvent handling
- Should be done in an extractive fume hood (or glove box as noted in 1 below)
- Should be done only while wearing suitably protective eye shields, aprons, and absorbent respirator masks
- 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.
- If possible, clean the material in a leak-tight glove box under a slight positive pressure of argon to delay interaction between air and the material. If this is not possible, all cleaning steps must be completed as quickly as possible in a fume hood or very well ventilated area to minimize the material's exposure time to air and the operators exposure to solvent fumes.
Assemble a supply of
- Suitably sized, chemically and physically clean glass receptacles (beakers or petrie dishes)
- Technical purity hydrocarbon solvents
- Extremely high purity hydrocarbon solvents
- Lint-free tissues
- Chemically and physically clean tongs or tweezers to handle the materials
- Arrange a number, not less than three, beakers/petrie dishes with sufficient technical solvent in them to completely immerse the material.
- Similarly, arrange a number, again not less than three, beakers/petrie dishes with sufficient high purity solvent in them to completely immerse the material.
- Remove the material from its packaging and quickly wipe off the excess oil with a lint free tissue.
- Immediately immerse the material in the technical solvent bath #1 (TSB#1). Agitate material or solvent to encourage dissolution. (Note: while the material is immersed in the solvent, it is as protected from reaction as in the original packaging. It is the time spent exposed to air that is important)
- Remove the material from the TSB#1 and quickly wipe off excess solvent. Do not attempt to dry completely since this increases air exposure and does little to reduce contamination.
- Immediately immerse the material in TSB#2. Agitate, remove, dab dry with a fresh tissue.
- Immediately immerse the material in TSB#3. Agitate, remove, dab dry with a fresh tissue.
- Immediately immerse the material in high purity solvent bath #1 (HPSB#1). Agitate, remove, dab dry with a fresh tissue.
- Immediately immerse the material in HPSB#2. Agitate, remove, dab dry with a fresh tissue.
- Immediately immerse the material in HPSB#3. Agitate, remove, and dab dry as completely as possible with a fresh tissue.
- Immediately transfer the material to the vacuum chamber that should be pre-flushed (and continue to be flushed) with argon to reduce the concentration of air components.
- When the material is mounted in its source, stop Ar flow, close the chamber flanges, and pump. If the material is a reactive sputter target such as Ca, Ba, Sr that quickly oxidizes, a short presputter period is recommended before sputtering to produce thin films.
For all the time the material is in the chamber, make sure that:
- The chamber is always vented with argon
- When the chamber is open argon continues flowing at high volumetric speed
- When the chamber is closed, keep it at high vacuum