Spectroscopic Ellipsometer for Solar Thin Film Analysis

I would like to share the training of Ellipsometer for Solar Thin Film analysis on 13th to 14th October 2010 in Hong Kong Science and Technology Park (HKSTP).


The trainer was Mr. Charles Lin (Application Engineer, Radiation Technology Co., Ltd.) and his training topic entitled “Spectroscopic Ellipsometers and their extension by SOPRA” and the training included theoretical and practical session.

Firstly, Mr. Lin introduced the instrumentation of Ellipsometer. The detector range of the Ellipsometer which employed in HKSTP was from 170nm to 2000nm (From deep UV to NIR). Mr. Lin also briefed some optional sources below:
· GXR Option (X-ray Reflectometry) – Lithography, advanced semiconductor films (high absorption – k)
· IRSE Option – dielectric films & materials characterization doped semiconductors epi layers
· EPA Option – fundamental research on porous thin films
· Cryostat Option – fundamental research superconductive materials

Then the optical schema was showed. Xe Lamp was used as source and installed shutter to reduce the background signal. The attenuators in front of Xe Lamp used to reduce the intensity. The diaphragm worked like Iris. The microspot was employed which is 200μm (diameter) for focus (a series of lens). After reflected on the sample surface, the signal received from detector. The optional compensator was specific for small absorption (k) but it was not installed in HKSTP’s ellipsometer.

The following diagrams showed the overlapping of parallel beams from back side reflection. That was why microspots should be used to avoid the overlapping effect. (The substrate thickness of sample should be larger than 0.7mm.)

Then he mentioned different analysis methodology. However, we need to understand the sample characteristic such as approximate thickness, reflective index (n) and absorption (k) before analysis.

The Bulk substrate model was used for non-transparent material or metal substrate.

Dispersion law was commonly used in the analysis but it was found difficult to analyze too thick sample.

Lastly, he concluded the precise and reproducible optical set up plus advanced modeling software could come out the good result of analysis.

The practical part was demonstrated the operation of Ellipsometer. The trainer set up the ellipsometer.

He showed us the sample which was Silicon Nitride (Si3N4).

The properties of SiO2 and Si3N4 were showed in the Table 1.

Then engineer turned the distance of stage to optimize the signal.

Close shot of Si3N4 sample

Find the maximum intensity when turn the equipment.

The lower diagram of the following photo showed three peaks and each peak represented about 1000Å thickness.

Engineer prepared the other sample which was SiO2.

Close shot of SiO2 sample

The lower diagram of the following photo showed many peaks indicating that SiO2 sample was much thicker than Si3N4 sample.

And then using modeling simulation calculated the actual thickness of that sample.

I took a photo with the Ellipsometer.

For more information:
PV Testing Laboratory Service in HKSTP: http://lab.hkstp.org/e/default_home.asp?url=/e/customize/analysis_solar.asp
Radiation Technology Co., Ltd.: www.raditech.com.tw