With the development of semiconductor technology, the critical dimensions of advanced chips are constantly shrinking, even requiring complex three-dimensional structures. The development of these technologies has put forward extremely high requirements for etching processes, especially in terms of selectivity and accuracy. Traditional plasma etching technology is difficult to meet this high-precision requirement. Atomic Layer Etching (ALE) is a high-precision etching technique that can be regarded as the reverse process of Atomic Layer Deposition (ALD). ALE has the self limiting property of thin film etching, which can remove only one atomic layer in each cycle period, thereby achieving size and precision control at the atomic layer level. Although early ALE technology was considered unsuitable for practical production due to its low efficiency in removing materials, with the continuous reduction of critical device dimensions (many functional layers have thicknesses less than 2-3nm), ALE technology has ushered in new development opportunities.
ALE technology can be mainly divided into two types: plasma enhanced ALE and thermal ALE. Both of these technologies involve two and a half reaction processes, operating according to the principle of self limitation.
1. Plasma enhanced ALE
The first half reaction: Introduce reaction gas 1 into the reaction chamber, undergo a chemical reaction with the material surface, and form a self limiting layer. Stop introducing reaction gas 1 and discharge excess reaction gas 1 and by-products from the reaction chamber.
The second half reaction: introducing ions with a certain energy (usually argon ions Ar ⁺) to bombard the surface, or introducing a second gas 2 to remove the self confinement layer through physical or chemical reactions. Stop introducing high-energy particles or reactive gas 2, and remove the by-products and excess particles or gas 2 generated during the etching process to complete one ALE cycle.

2. Hot ALE
The first half reaction: Introduce reaction gas 1 into the reaction chamber, undergo a chemical reaction with the material surface, and form a self limiting layer. Stop introducing reaction gas 1 and discharge excess reaction gas 1 and by-products from the reaction chamber.
The second half reaction: In the absence of plasma, the reaction gas 2 is activated by thermal energy to remove the self confinement layer through chemical reaction. Stop introducing reaction gas 2 and remove the by-products and excess gas 2 generated during the etching process to complete one ALE cycle.

3. Advantages of ALE process
High precision: The ALE process can remove only one atomic layer per cycle, ensuring extremely high dimensional accuracy.
Self limiting: The etching process within each cycle has self limiting properties, avoiding excessive etching and improving the controllability and repeatability of the process.
Selectivity: The ALE process can selectively etch specific materials without affecting other materials, which is particularly important for devices with multi-layer structures.
ALE technology, with its high precision, self limitation, and selectivity, has become an indispensable part of advanced chip manufacturing. With the continuous reduction of critical device dimensions, the application prospects of ALE technology are becoming increasingly broad, providing strong technical support for the future microelectronics industry. With the continuous advancement and improvement of technology, ALE is expected to play an important role in more fields and promote the sustainable development of the semiconductor industry.

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