Optimizing Atomic Layer Etch (ALE) Processes Using Optical Emission Monitoring

To etch thin layers with high precision, low damage, and excellent selectivity, atomic layer etch (ALE) is becoming an increasingly popular option. ALE is especially relevant to the etching of 2D materials.

Atomic Layer Etch (ALE)

An optimized etch tool for well-controlled ALE has been developed by Oxford Instruments Plasma Technology. This involves fast gas dosing to accurately deliver dosing gas and precisely deliver RF power to the substrate to optimally control DC bias[1].

The software controls switching between ALE and conventional etching, allowing ALE and traditional etch modes in the same process recipe.

Here, the use of optical emission spectroscopy (OES) has been reported to highlight the potential issues of employing a traditional plasma etch tool for ALE, and to demonstrate the ability of the new hardware to provide accurate dosing (Figures 1 and 2). Also, the ALE hardware has a much shorter gas decay time of 4 seconds compared to the gas decay time of more than 15 seconds required for a traditional etch tool using a standard MFC (Figure 3).

Variability in Cl OES intensity observed when using 2 sec gas pulses in a conventional etch tool, due to MFC turn on time scatter and control system timing delays.

Figure 1. Variability in Cl OES intensity observed when using 2 sec gas pulses in a conventional etch tool, due to MFC turn on time scatter and control system timing delays.

Improved stability with optimized ALE hardware.

Figure 2. Improved stability with optimized ALE hardware.

Improvements in gas pulse timing and gas decay time when using optimized ALE hardware.

Figure 3. Improvements in gas pulse timing and gas decay time when using optimized ALE hardware.

As OES enables monitoring of etch species, dose pulses, and purging efficiency, it is an ideal tool to optimize the ALE process sequence. Therefore, the number of process runs required for ALE process development can be minimized using OES. Detecting potential sources of contamination and optimizing chamber preparation are also possible using OES due to the ability of monitoring contaminant gases.

This information has been sourced, reviewed and adapted from materials provided by Oxford Instruments Plasma Technology.

For more information on this source, please visit Oxford Instruments Plasma Technology.

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