Advanced Plasma Cleaning System

By Richard Mitro, Gatan, Inc.

The origin of sample contamination can be attributed to one or a combination of sources. The most common form of contamination results from sample preparation and normal handling. Examples include: embedding and mounting polymers (G-1, G-2, etc.), the polishing media and lubricants, the residue remaining after solvent rinsing, and finally normal handling.

Plasma cleaning itself originated within the semiconductor industry many years ago and became the industry standard for wafer cleaning. More recently, it was adapted for plasma cleaning TEM and SEM samples. The primary purpose of plasma cleaning is to remove carbonaceous materials on the sample in order to improve sample imaging quality. The key here is to clean samples without changing elemental composition, structural characteristics or creating surface damage.

Plasma Cleaning Benefits
- Enhanced imaging capability
- Improved accuracy when performing composition microanalysis
- Longer viewing & acquisition times for EDX and EBSD in a SEM
- Use of smaller probe size; a “must” for STEM and EELS analysis in a TEM

Advanced Features
The goal in designing SOLARUS was to deliver value to our customers. We wanted a plasma system offering flexibility, ease of use, superior repeatability and high throughput. Our unique design exceeds these goals. We started with a real-time RF auto-match and variable RF power supply (10W – 65W) to ensure optimum plasma power and low loss under any cleaning condition. We then incorporated the H2/O2 gas recipe (Patent Pending). This unique chemistry provides superior cleaning with less sputter damage to all samples including holey carbon films and allows samples to remain significantly cooler during cleaning than with the traditional Ar/O2 gas recipe. The additional mass flow controllers (MFC) support three independent process gases such as H2, O2 and Ar for accurate gas control and long term plasma stability. Finally, the interactive touch screen interface offers seven pre-programmed recipes with optimized process parameters for greater consistency and repeatability.

Easy Operation
Our Advanced Plasma Cleaning Systemis designed to provide consistent results quickly and easily for any user regardless of skills or experience. The interactive touch screen interface makes managing the cleaning process simple by offering continuous feedback including full-time diagnostics. The Advanced Plasma Cleaning Systemis also multi-lingual offering a choice of six operating languages: English, French, German, Chinese, Japanese and Korean.

Simple Four-Step Operation
1. Load the sample
2. Select a recipe.
3. Touch START to begin the cleaning cycle.
4. Touch VENT to remove the sample.

Sample Loading
Loading and cleaning samples in the Advanced Plasma Cleaning System is simple and fast. The front loading chamber ports accept either one or two side entry TEM sample holders; adapters accept any manufacturers TEM holder. The chamber also has easy access through the top loading lid for cleaning multiple TEM grids (> 50 individual grids) or multiple SEM samples.

Process
The full-time turbo drag pumping system speeds up the entire cleaning cycle. Typical run rates are less than 2 minutes for two TEM samples in TEM holders, versus up to 20 minutes for other plasma cleaners in the market.
• Pump down - 50 seconds vs. 3 minutes.
• Cleaning rates 30sec – 120sec vs. 2min – 10min.
• Venting - 5 seconds vs. 6 minutes.

Data Points
1. TEM silicon sample showing cleaning efficiency
2. TEM Holey carbon film
3. TEM Lacey carbon “hole”
4. SEM semiconductor sample

For complete product and ordering information on our Advanced Plasma Cleaning System, please contact your local Gatan Sales office.

Holey Carbon Film Sample contaminated with 1 drop of oil in 50 ml acetone

Lacey Carbon Hole (6 months old off the shelf)

Contaminated semiconductor sample showing scan window

After 10min H2/O2 cleaning all contamination removed with no apparent Si damage