Identifying ALE window in plasma etching of SiO2 and Si3N4 with Impedans Octiv VI probe.


Impedans serves the semiconductor manufacturing industry by providing Octiv VI Probes. Whether it’s an ALD, ALE, RIE or ICP plasma tool, Octiv VI probes provide live and cost-effective solutions to RF measurements including current, voltage, phase and Impedance in CW and pulsed RF/DC environments. These measurements provide crucial insights into the tool performance enabling correlation of electrical variables with process parameters like ion flux, etch and deposition rates etc.

A recent publication in Plasma Processes and Polymers highlights the effectiveness of Impedans Octiv Poly VI probe system in atomic layer etching of SiO2 and Si3N4. Octiv measurements played a key role in elucidating the relationship between the etch rate and the bias voltage across various precursors.

Experimental setup 

Plasma etching of SiO2 and Si3N4 samples were studied in an inductively coupled plasma reactor equipped with a source of 13.56 MHz on top and bias power of 12.56 MHz applied through the bottom electrostatic chuck as shown in Figure 1a. Throughout the process, the bias voltage was monitored using a voltage‐current (VI) probe (Octiv Poly; Impedans). Experiments employed C4F8 alongside the low global warming potential gases, especially of perfluoroisopropyl vinyl ether (PIPVE) and perfluoropropyl vinyl ether (PPVE) precursors to assess the etch rate of SiO2 and Si3N4 in relation to the bias voltages.

Inductively coupled plasma reactor and diagnostic tools

Figure 1 Schematic of the inductively coupled plasma reactor and diagnostic tools.



The ion energy is the most important parameter in the anisotropic ALE process, with three different regions— incomplete etch, ALE window, and physical sputtering—identified based on the ion energy in the etching step. The Etch Per Cycle (EPC) of SiO2 investigated by controlling the bias voltage in Ar plasma is shown in Figure 2. The ALE window region with a constant EPC of SiO2 was confirmed at bias voltages between 50.0 and 57.5 V for all precursor plasmas.

Figure 2 Etch per cycle of SiO2 using C4F8, PIPVE and PPVE plasmas in the fluorination step in ALE process as a function of bias voltage  

The EPC of Si3N4 was also investigated with respect to the bias voltage, as shown in Figure 3. The ALE window region of Si3N4 was observed at bias voltages between 50.0 and 57.5V, the same as that of SiO2 while the EPC of Si3N4 was approximately two times higher than that of SiO2.

Figure 3 Etch per cycle of Si3N4 using C4F8, PIPVE and PPVE plasmas in the fluorination step in ALE process as a function of bias voltage.


Octiv measurements helped the researchers to identify the ALE window for both SiO2 and Si3N4 substrates. These measurements revealed the significant influence of bias voltage in regulating ion energies crucial for the etching process. Further, it was found that the bias voltage for ALE window is same for both SiO2 and Si3N4 samples under similar conditions while the etch per cycle is double for the later as compared to the former.

Utilizing Impedans’ Octiv VI probe to measure bias voltage offers direct insights into the etching process, enabling precise identification of the ALE window. Consequently, control over the etching profile can be achieved through manipulation of bias voltages.Top of Form

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Jihye Kim et al. et al, Plasma Process Polym. 2024;e2300216