Laboratory of Physics of Interfaces and Thin Films

The application of plasma enhanced chemical vapour deposition (PECVD) to the challenge of growing high quality thin films over large areas has been a great success story, leading to the widespread availability of flat-screen televisions, and a great reduction in the cost of solar energy. However, challenges to improve the quality and speed of the deposition process by modifying the plasma source remain a rich source of research opportunities.

 

At the LPICM, in addition to research on plasma deposition using conventional, capacitively coupled Radio Frequency (RF) sources, we are investigating the use of alternative methods of generating plasmas.  We are focusing on the use of microwave sources and Tailored Voltage Waveforms (VWT).

For information on internships, doctoral studies, post-doctoral positions, or collaborations, please contact Dr. Pavel Bulkin

For information on internships, doctoral studies, post-doctoral positions, or collaborations, please contact Dr. Tatiana Novikova

Low-temperature, gas discharge plasma is widely used to grow nanoparticles for various purposes. Typical examples are nanocrystalline films for solar cells and semiconductor nanocrystals for nanoelectronics and luminescence applications [link] which usually involve particles as small as 2-4 nm. Nevertheless, detection of particles with sizes below 20 nm is not a simple task. In our laboratory we try to address the problem with a new approach based on the use of corona discharge. Unlike other detection techniques, this method is sensitive to the charge polarity of nanoparticles. The main idea here is to observe the corona discharge response in the postplasma regime when the rf power is switched off caused by nanoparticles initially created in an rf plasma. An emissive probe biased to a sufficient negative potential is used to create a negative corona in the postplasma regime. Preliminary results have revealed that the corona discharge is sensitive to the presence of positively charged nanoparticles.

Negative corona in the postplasma regime in SiH4-Ar-H2 mixture

For information on internships, doctoral studies, post-doctoral positions, or collaborations, please contact Dr. Sergey Abolmasov

In close collaboration with the Physics of Plasmas Laboratory (LPP) at the Ecole Polytechnique, we are investigating the use of Voltage Waveform Tailoring for plasma processing. 

 

By changing the shape of the excitation voltage waveform from sinusoidal to a peak or trough -like shape, one can arbitrarily change the ion bombardment energy observed by the electrodes.  This allows us to decouple the power injected into the plasma from the average ion-bombardment energy - a powerful tool for plasma-processing.

We have demonstrated this concept through the deposition of hydrogenated silicon thin films, and have shown that the morphology of the deposited film can be changed from amorphous to nanocrystalline, simply by changing the shape of the waveform.  This is observed through in-situ spectroscopic-ellipsometry [link], and is shown in the figure below.

 This technique holds immense promise for a number of plasma processing applications, as one can independently control RF power and ion bombardment energy, and potentially on a standard RF large area PECVD reactor.

For information on internships, doctoral studies, post-doctoral positions, or collaborations, please contact Dr. Erik Johnson