EM - Sputter Targets Materials and Mounting

ProSciTech is one of the best suppliers of targets ‐ anywhere. We supply high purity sputtering targets, and these are well produced and modestly priced. Available are a wide range of unmounted disks or washer (annular) type sputtering targets, as well as targets mounted on backing plates, replacing the original target holders.

Often targets are mounted to a backing plate using a conductive glue. Alternatively, if the target is over‐sized, the edge may be formed around the edge of the backing plate ‐ if the target material is soft. If that is your preferred method, please order the target with at least 2mm greater diameter than the backing plate is.

Additionally we can source many other sputtering targets in a variety of materials including ceramics, rare earth elements and metal oxides.

Here are some examples of sputter target materials that we have supplied:
W, Ag, Ti, Ce, ZnS, Au/Pd 60:40, Au/Pd 80:20, Zirconium oxide with 10‐15%wt Y2O3, Cr, Au, Al, Pt, Ir, Cu, Ag/Cu 90:10, Fe, Si micro‐crystalline, Si polycrystalline, Si n‐type, Si p‐type, Si undoped.

Metal targets unless otherwise stated are 4N pure ‐ which is 99.99%.

Note: All listed targets made from Au/Pd are in the ratio 60:40.

Choosing your target material

Your choice of target material depends on the application. For headlight housings and CDs, aluminium is preferred for high optical reflection. Most of our SEM using customers require (a)  good electrical conductivity using a very thin coating, (b) the coating material should not tarnish and (c) possess a very fine grain structure. Greater resolution is possible with higher atomic number metals.

1. Many metals are good electrical conductors (including Cu, Ag, Al), but they may not have other suitable properties. A thick specimen coating would hide small structures in the same way an increasingly thick layer of snow will hide landscape features.
2. Very thin layers of sputtered (or evaporated) metals form islets which eventually merge. These islets are the graininess that may be seen at very high magnifications. Most oxidising metals are not well regarded for SEM coatings; the exception is Cr, which gives possibly the finest deposit of any metal. The target and coated specimens should be kept in a non‐oxidising atmosphere for long term storage. This could be under vacuum or, more cost efficiently for large specimen collections, in a dry nitrogen gas desiccator. (See our page E12).
3. Ultimate spatial resolution attainable in an SEM depends on several factors, and especially the average atomic number of the specimen. As a guide, the atomic number of the coating element is averaged with those of the specimen. So carbon (evaporated) onto a biological sample may at best reach the average atomic number eight. A biological specimen coated with gold (79) could, somewhat arbitrarily, rate an average atomic number of 43. It is not practical to evaporate uranium which is toxic and would oxidise. The most popular target metals for SEM are from the platinum group of elements (Pd, Ir, Pt).

The finest coatings are achieved by the simultaneous evaporation of carbon platinum; or tungsten (requires an electron gun). The finest coating using a sputterer is with Cr, followed by Ir, Pt, Au/Pd amalgam and Au. Carbon is very fine, but too 'soft' (low atomic number) for high resolution. Gold is most used for conventional SEM and is perfectly satisfactory. Finer deposits are only required when using magnifications over ~40k; for that usually a FESEM or a TEM is required. Gold and gold/palladium sputter well using base model sputter coaters running on a rotary vane pump only. Some other metals can also be sputtered from these simple instruments. However, oxidising metals (Cr especially) require a high vacuum pumped system and several of the heavier metals are much better sputtered by a larger instrument with a more generous power‐supply. Iridium is a very brittle metal and we can only produce these targets at least 0.3mm thick ‐ which makes them expensive.

Amalgams are more expensive to produce. So if an amalgam is sought to attain a finer coating, then it may be better to purchase Pt in lieu of Au/Pd, or Ir in lieu of Pt/Pd.

Most used for metal coatings in electron microscopy is gold. Evaporated or sputtered gold until it's a fairly thick coating forms islets and these give gold coating at high powers (> x30k) a granular appearance.

Comparative sputter data for Iridium and other materials on K575X sputter coater

Samples were coated using an Emitech K575X Sputter Coater and were examined using a Hitachi S-5200 Field Emission SEM. Pictures are courtesy of Linda Dailey, Emitech Products Inc.

Gold
Magnification	15,000X	100,000X	300,000X
Coating Time:	10 seconds	10 seconds	10 seconds
Current Used:	20 mA	20 mA	20 mA

Gold/Palladium
Magnification	15,000X	100,000X	300,000X
Coating Time:	10 seconds	10 seconds	10 seconds
Current Used:	20 mA	20 mA	20 mA
Chromium
Magnification	15,000X	100,000X	300,000X
Coating Time:	30 seconds	30 seconds	30 seconds
Current Used:	100 mA	100 mA	100 mA
Iridium
Magnification	15,000X	100,000X	300,000X
Coating Time:	10 seconds	10 seconds	10 seconds
Current Used:	20 mA	20 mA	20 mA
No Coating
Magnification	15,000X	100,000X	300,000X
Coating Time:	N/A	N/A	N/A
Current Used:	N/A	N/A	N/A
Platinum
Magnification	15,000X	100,000X	300,000X
Coating Time:	N/A	N/A	N/A
Current Used:	N/A	N/A	N/A

Magnifications provided are indicative and will vary with reproduction and monitor size used.

Comparative sputtered films using the Q150T Turbo-Pumped Sputter Coater/Carbon Coater (Au, Pt, Ir and Cr)

Mounting:

Most targets are held by a cover or are crimped around the edge ‐ if yours is not that type it must be glued.

The 'glue' used must be electrically conducting.

For 'professional' mounting use a few slivers of indium wire on the support plate, cover with the target and then either place in an oven with a flat weight on top of the target, or use a smoothing iron to heat the gold and hence melt the indium. Placing something like a piece of lens tissue onto the target would protect it.

A temperature a little higher than melting point of indium is required (m.p. 156.6°C) for a short time.

Alternatively use a bit of silver conducting paint, preferably a few small drops of paste at the bottom of the jar.

You could also make a paste using our silver powder and a little commercial epoxy glue ‐ the method can be here. Only spot gluing is required, but keep a weight on the target while drying/ curing.