Damage Analysis of Reactive Ion and Atomic Layer Etched Silicon

Abstract: Dry etching is one of the most important methods of pattern transfer in nanofabrication. There are many dry etching methods, the most commonly used is reactive ion etching (RIE), that is based on a continuous supply of reactive ions and radicals generated in a radio-frequency (RF) plasma discharge. The RIE approach can be very accurate and may provide high resolution etching, below 10 nm in lateral direction. However, as the patterning resolution in lateral and vertical directions increases, the continuous etching approach may not satisfy the new requirements for dry etching. Atomic Layer Etching (ALE) is one of the most advanced etching techniques due to its layer-by-layer control over the etched materials. The etching in ALE regime can be characterised as a self-limiting. ALE process based on four steps where the surface modification is separated from the etching process. Those ALE steps form the etch process cycles, which are repeated to remove the necessary amount of material. Dry etching techniques, including RIE and ALE, use energetic ions to remove the etched atoms from the surface. Typically, their energy greatly exceeds binding energy of atoms in crystalline lattice (few eVs) that may result in implantation of impinging ions and/or displacement of the substrate atoms that results in radiation damage. The ion energy in RIE can be in the 100-300 eV range, while ALE requires much lower energy of 20-50 eV. Therefore, one can expect that ALE is a low damage etching technique. In the current MSc-thesis a comparative study of the radiation damage in Si (100) etched using a conventional RIE with Cl2/Ar+ process and a newly developed ALE with the same etch chemistry. Then the surface damage analysed by measuring the contact potential difference (CPD) by Kelvin Force Probe Microscopy (KFPM). The results of these experiments indicate that the damage caused by RIE process was high as the values of CPD and the work function of the etched surface was much lower than the values of ALE samples. While ALE process showed almost minimum damage formation on the etched Si sample according to the CPD values that were close to pristine Si (100). Finally, this project opens the door for further studies of ALE damage in different conditions than it used in this study because of its importance for nanofabrication and semiconductor industry.