1. Analytical parameters and optimization in RF-GD-OES
Title ..
Kayvon Savadkouei
GD application lab New Jersey

2. Analytical optimization
Preparation of the sample (sample, bulk or surface)
Carrier gas choice (F exploration, polymer)
Anode diameter selection (sample, sensitivity)
Accessory use (sample)
RF generator power (sample, bulk or surface, sensitivity)
Pressure (sample, bulk or surface)
Flushing time (sample)
Matching box (sample, depth resolution)

3. Sample introduction Easy sample mounting
Let us remind what the lamp does look for: the sample is placed against the lamp in order to cover the o-ring, then the power supply is placed at the back of the sample and the guide comes to them and press the sample against the o-ring to make the air tightness.
Easy sample mounting

4. Sample preparation Sample requirement (SOLID material)
No air entrance through the surface of the sample
Min size: 5mm (to cover the smallest ceramic hole)
Rigid enough to support the low pressure in the source (mounting strategy)
Rigid enough to not be crashed by the pressure applied at the back
Back of the sample flat enough to optimized contact with the power holder (mounting strategy)
Bulk measurement:
Polishing to minimize air entrance
Depth profile
Surface observation: surface contamination issue by packaging and handling
Surface contamination care:
From process
From packaging
SOLUTIONS to improve depth resolution:
Surface cleaning (acetone, ethanol, dry tissue, compressed nitrogen spray)
Decontamination of the lamp: sacrificial sample measurement
Plasma cleaning: Quantum function to decontaminate the surface

5. Sample preparation: plasma cleaning interest
Before plasma cleaning
After plasma cleaning (3 minutes)
At the beginning of sputtering: High carbon; Unstable plasma (Fi, Ar); Distorted profiles (signal spikes) of some elements (Cu, Cr, etc.)
This example from Igor Molchan work illustrates the benefits of the plasma cleaning.
The sample is an Al sample with a thin oxide layer. No special care was taken for sample handling and lamp was exposed to air. The measurement on the left without plasma cleaning (but with a 60s Ar flush) shows surface C contamination and other artefacts.
On the right side an other zone of the sample sample was placed and a plasma established at low power (<5W) and low pressure (<400Pa). Of course these conditions can be adated to the sample: it is possible to start and get a stable rf plasma even at 1W, 200 Pa or in pulsed conditions !
After 3 minutes of plasma cleaning the analysis could start in normal conditions without having to remove the sample. Surface is clean, plasma starts immediately and is stable.
At the beginning of sputtering: Low carbon; Stable plasma (Fi, Ar); Eliminates signal spikes from some elements (Cu, Cr, etc.)
« The concept of plasma cleaning in glow discharge spectrometry» published in JASS
I.S. Molchan, G.E. Thompson, P. Skeldon, N. Trigoulet, P. Chapon, A. Tempez, J. Malherbe, L. Lobo Revilla, N. Bordel, Ph. Belenguer, T. Nellis, A. Zahri, L. Therese, Ph. Guillot, M. Ganciu, J. Michler and Hohl

6. Choice of carrier gas Typical carrier gas: Ar If Fluorine required:
Use of Ne: Ar ionisation potential is smaller than the excitation potential which is required to excite F atoms
UFS (Ar or Ne mixed with O2) - patented
Material: all types of polymers
Interest: improve sputtering rate and depth resolution

7. Anode selection or accessory
7mm
4mm
2mm
1mm

8. Use of accessories Sample shape Sample size Analysis surface size
Surface or substrate porosity
Summary

9. RF power (Excel file operating conditions)
Material nature
Sample thickness
Purpose: bulk or depth profile
Increase of sputtering rate
Optimization:
Bulk:
*adjust to avoid burning, breaking and heating too much => good compromise between sensitivity and precision
*Power range (depends on generator generation and anode used): 5 to 150W max (with generator Cubo)
Surface:
* lower compared to bulk for the same material => good compromise between sensitivity and depth resolution
* adjustment should be made with the most fragile material when multi layered samples are measured
Pulsed function:
* Adjustment of frequency: 2000 to 5000Hz
* Adjustment of duty cycle (period – pulse width ratio): to 0.5

10. Pressure Function: Pressure optimization: Determination of Ar density
Increase of intensity with increase of pressure
Control of the crater shape (essential for depth profiling) to get high depth resolution
Measurement by Pg
Pressure optimization:
Range: Pa
No connection with the anode used
Optimization procedure:
Select the pressure
Run the sample in surface analysis
Check the crater shape with profilemeter (if available) or check the sharpness of interfaces

11. Flush time Pre-flush of Ar before the plasma start
Flush the air from the lamp
Flush the air molecules trapped on surface sample
Quantum function:
Pumping cycle
High pressure
Operating pressure

12. Matching box Minimization of reflected power
Adaptation to the impedance of the sample (material nature, geometry, thickness, depth)
Essential to observe the first ms (first nm)
Parameters check: module and phase and Pr (reflected power)

13. Matching box II

14. Matching box optimization
Run the sample in surface analysis
Zoom the beginning
Note the starting values of mod and pha after the beginning of the analysis
Report these values in the method (measurement part)
Run the sample again to check.