SPI Plasma-Prep™ II Plasma Etcher, Cleaner and Asher

Etch-clean-ash using dry plasma chemistry with barrel-reactor isotropic etching in a plasma etcher.

SPI Plasma-Prep II, a compact, "bench-top" sized plasma etcher, which can also serve as a plasma asher or even a plasma cleaner, uses dry plasma chemistry to reveal hidden detail for SEM and TEM analysis. This room-temperature plasma etching process works selectively, gently - and is well-suited for many applications in the EM lab, including work in: life sciences, materials science, electronics, AEM, failure analysis and general electron microscopy, including asbestos sample preparation*. Additionally, it is also widely used for the cleaning before use of microscope slides, both glass and quartz, and it is also used for the cleaning of transmission cells for a variety of different types of spectroscopic instrumentation.

(*Complies with AHERA and Yamate procedures for TEM asbestos sample preparation.)

Definitions:
We want to be sure we are all using the same language, which in microscopy, is not always the case. When one is talking about ashing, they are usually talking about taking the "etching process" to the extreme, that is, the sample is completely etched away so nothing (of what will etch) is left. So a coal sample, for example, that is "ashed" is one where all of the organics have been etched away and all that remains are the inorganics. This is always done at 100 watts with the Plasma Prep II in its standard configuration.

If the sample is just going to be etched, we are usually talking about removing the top surface layers of the sample. We are talking about much more than nanolayers, or sorbed monolayers, we are talking about a reasonable amount of material being removed. For example, if there is extensive organic contamination on a metallurgical fracture surface, and we want it to be cleaned, this is "etching". If we are removing a glass passivation layer on an electronic device, this is etching because a layer of material is indeed being removed. This is not to be confused with plasma cleaning. "Etching" is again normally done with the standard Plasma Prep II configuration operating at 100 watts.

Plasma cleaning involves the removal is just the outer few atomic layers on a samples surface. The amount being removed, even if viewed by the highest resolution FESEM in the world, can not be detected. But it is the removal of this outer contamination present on many samples that contributes to sample contamination and artifacts, such as "raster burns" on a highly polished metallurgical sample. The material we are addressing is not tenaciously held, and in fact is generally thought to be very loosely held, and one does not need the an energetic plasma produced by 100 watts, typically a plasma of 10 watts power is more than enough. And in many instances, if one did use 100 watts, they would run the real possibility of changing their sample, for example, if they were etching with oxygen, they could change their sample (e.g. etching out of carbon precipitates) and if one was using argon to remove metal oxides, one could even get etching of a metal sample itself. But if either oxygen or argon is used in a 10 watt plasma, there is just enough energy to remove (some way "tickle") the surface, and remove these loosely held contaminants but not actually etch the underlying surface.

We know that some of those in our field who should know better seem to use these terms somewhat interchangeably. They are not interchangeable and they all have unique meanings. We don't want to be on a soap box for people to use the right semantics, but at the same time, we want to do all possible to make sure that our customers get the system that is both right for them as well as the integrity of their samples. If you want to have the Plasma Prep II configured for 10 watt operation, the price is the same, just be sure to let us know when you place your order that you want the 10 watt configuration for plasma cleaning. Remember this for the SEM application and is not to be confused with the TEM application for plasma cleaning.

What can be etched?
The chemistry of the plasma is what determines what can be etched. For example, anything carbonaceous, including diamond, and many other polymers such as PTFE can be readily etched with pure oxygen. Most metal oxides can be etched with argon. Passivation layers such as SiO₂ or Si₃N₄ can be removed only with CF₄ or 90% CF₄/10% O₂. Silicon can be etched with SiF₄. Aluminum can be etched with BCl₃. Quite a bit is known about what plasma chemistry is needed to etch different materials:

As indicated above, the SPI Plasma Prep II is also widely used to remove organic residues and/or contaminants from non-flat surfaces that can become trapped in difficult-to-reach areas such as on newly manufactured (non-polymeric) prosthetic devices. A quick treatment with oxygen, for example, will remove such residues or other layers of carbonaceous composition and there will be an immediate improvement in wettability and overall adhesion characteristics.

Eliminates the need for high temperatures and wet chemicals.
Improves surface wettability and "conditions" TEM grids.
Removes photoresist residues.
Removes organic residues and "conditions" surfaces such as on prosthetic devices.
Will not alter or contaminate the sample for Auger or surface analysis.
Will not dissolve away corrosion products as would be the case if HF was being used.
Retains fine structural detail.
Exciting new applications for life science research.

Special Features of the SPI Plasma Prep II Plasma Etcher:

Air Vent Bleed Control Valve - Allows operator to precisely control the rate or air flow when venting the chamber; prevents a sudden rush of air that would disturb sample fibers and possibly cross-contaminate multiple samples in the chamber. Valve is inside the cabinet to discourage unauthorized tampering of the bleed rate.
Low Temperature Operation - Ideal for bulk samples; ashes organics without destroying delicate specimen structure.
Rugged Circuitry/Sturdy Chassis - Performs consistently at high voltage/high output for long periods. In our own EM laboratories, we run our Plasma-Preps constantly!
Compact, Efficient Design - Small footprint, with room inside to process samples in batch quantities. 10-1/2" (26.7cm)H x 14-3/4" (37.5cm) L x 12" (30.5cm)W; chamber is 4" (10.15cm) internal diameter, 6" (15.25cm) deep. Weight: 32 lbs (14.5kg).
RF Monitor/Safety Signal - Audible signal lets you know when RF amplifier impedance is not matched to the reactor. If the match is not improved, the generator automatically switches to pulse mode to prevent overheating of the RF tubes.
Safety Switch - Automatically cuts the RF field for safe sample viewing.
Plasma Cleaning at very low power
Quartz chamber available as optional item for use with reactive fluorine (e.g. CF₄) gasses which would "etch" ordinary glass and cause it to become frosted.

Comparisons among units:
Many global organizations need to standardize testing in laboratories in different countries so that results from one country can be reliably compared with any other country. Also, laboratories with a very high sample throughput may need more than one plasma asher/etcher to keep up with their workload. In such situations, the PlasmaPrep II has been found capable to meet the challenge.

Special note:
Note that the SPI Plasma Prep II has been manufactured with materials that are fully compatible for use with CF₄. This is not the case for many of the other units on the market that are compatible only with oxygen, nitrogen and argon. This is an extremely important advantage should one be using the system in a failure analysis laboratory environment. Life science users at times wish to literally etch the surface of a glass microscope slide and without a CF₄ compatible system, this could not be done.

Options for the vacuum system:
The recommend strongly that consideration be given for the purchase of two what are really optional items. First there is the oil mist filter that should go onto every vacuum pump. This is more of a safety issue and we recommend the installation of an oil mist filter on the pump. And we would also recommend the installation of a foreline trap between the pump and the instrument itself in order to virtually eliminate the possibility of any backstreaming vapors from the pump to the Plasma Prep II chamber.

Applications for SEM:


A)Glass passivated circuit before;	B)after CF₄ 1hr.	C)Statocyst organ etched 3 min. using O₂.

Applications for TEM:

Low temperature oxygen plasma etched thin section of bacterium embedded in SPI Chem Low Acid GMA for TEM. Higher magnification view and additional information available.

Operation is Simple...
Insert a specimen into the reaction chamber via the sample carrier. Introduce the reactive gas, reduce the pressure to 200µm and apply RF power (13.56MHz) to the atmosphere in the chamber. This excites the gas molecules to a highly reactive plasma state. Gentle, low-temperature reactions, like oxidation of organics using oxygen, or removal of glass by carbon tetrafluoride, occur without damage to the rest of the specimen. We are often times asked about the specifications on the purity of the gases being used for the etching. For most users, the lesser expensive "technical" grade of gases is sufficient, both for oxygen as well as the reactive fluorine compounds, but when absolutely no (or minimal) residues are wanted on the final substrate, "research" grade gases, which are much more expensive, should be considered. For the normal user, however, they are not likely to see much difference between technical vs. research grade gas purities.

Other applications:
Many important applications for the SPI Plasma Prep II are found outside the microscope laboratory and often times the role of the Plasma Prep II is to activate a surface for either adhesion promotion or other purposes. One novel example is the use of the Plasma Prep II Simulated Conditions in Space and to simulate how materials might behave in space.

Although the unit arrives essentially ready to set up and operate, there are still a few items that one must procure separately.

	SPI #	Each	In Stock
Plasma-Prep II (110 V)	11005-AB	$5500.00	No
Plasma-Prep II (220 V)	11005-AX	8500.00	No

PPII with quartz chamber (110 V)	11005Q-AB	11215.48	No
PPII with quartz chamber (220 V)	11005Q-AX	11417.98	No

Optional Items
Vacuum Gauge: Allows accurate prediction of etching time!
110v	11019-AB	978.73	Yes
220v	11019-AX	1034.65	Yes

Leybold Vacuum Pump	10405-AB	4325.00	Yes
Oil Mist Filter	10410LK-AB	399.67	Yes
Foreline trap
Leybold Model RST25KNF Refillable Foreline Trap	10407FK-AB	705.53	Yes

Special Safety Message: We recommend the Leybold Model D4B 2.8 cubic feet/min. pump charged with Fomblin pump fluid, SPI # 10405-AB. The Leybold Model D2.5E 2.1 cubic feet/min pump, SPI # 10404-AB, has adequate pumping capacity, but it is not available charged with Fomblin fluid.

Check out our list of Spare Parts for the SPI Plasma Prep II and Plasma Prep III.

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