| AVS 65th International Symposium & Exhibition | |
| Plasma Science and Technology Division | Thursday Sessions |
| Session PS-ThM |
| Session: | Plasma Sources |
| Presenter: | Shahid Rauf, Applied Materials |
| Authors: | S. Rauf, Applied Materials L. Dorf, Applied Materials K.S. Collins, Applied Materials |
| Correspondent: | Click to Email |
The time-averaged plasma potential in a partially ionized plasma is directly linked to the electron temperature (Te). Plasmas with low Te or plasma potential are attractive for applications that require low ion energy at surfaces. One of the most promising such applications is atomic layer etching. Reactive ion etching relies on reaction of energetic ions and chemically reactive radicals on surfaces for material removal. Ion energy in radio-frequency (RF) plasmas is typically 10s of eV or higher. Since such energetic ions can damage and modify the near-surface material, film etching with atomic precision becomes impractical using low pressure RF plasmas. On the other hand, if the plasma potential is low and capability exists to control the ion energy at the substrate using RF or DC biasing, one can etch material with Å-scale fidelity [1]. Even conventional plasma processes can benefit from low Te as plasma potential determines the energy of ions bombarding the chamber surfaces.
This paper describes a radio frequency (RF) driven low Te plasma source. This source utilizes two RF supplies, a higher frequency source (60 MHz) for plasma production and a lower frequency source (2 MHz) for controlling the ion energy. The plasma source is divided into two regions separated by a perforated plate. A high density (> 1017 m-3) plasma is generated in the primary region next to the RF powered electrode. The DC bias on the powered electrode is high (~ 2000 V) leading to energetic ion bombardment on it. These ions produce secondary electrons that, under the low-pressure condition under consideration, enter the plasma as a beam of energetic electrons and many of them reach the perforated plate. It is demonstrated that the slits in the perforated plate can be designed to prevent the RF primary plasma from leaking into the secondary region while still allowing the beam electrons to pass through. The plasma produced by the beam electrons has moderate density (~ 1016 m-3) and Te < 0.5 eV. The influence of slit dimensions on the characteristics of the plasma in the secondary discharge region is examined in the paper.
[1] L. Dorf, J. C. Wang, S. Rauf, G. A. Monroy, Y. Zhang, A. Agarwal, J. Kenney, K. Ramaswamy and K. Collins, J. Phys. D 50, 274003 (2017).