Knowledge Center
Knowledge Center

Atomic Layer Etch (ALE)

ALE is a next-generation etch technology to selectively and precisely remove targeted materials at the atomic scale.


ALE is a promising next-generation etch technology that has been in R&D for the last several years, but until now there has been little or no need to use it. Unlike conventional etch tools, which remove materials on a continuous basis, ALE promises to selectively and precisely remove targeted materials at the atomic scale.

As the industry migrates from 10nm to 7nm finFETs, the trenches or gaps between the fins will shrink to between 10 to 15 angstroms or 5 atoms across. Typically, chipmakers use an etch tool to remove materials within these tiny trenches during the fabrication flow. But there are signs that conventional etch tools are struggling to do this job at these advanced nodes. So to perform this difficult task, the industry may require a new class of etch tools like ALE that can selectively remove ultra-thin materials or mere atoms without damaging the structure around it.

ALE is mono-layer etching with etch-cycle dynamics from etchant adsorption to etching product desorption. Not all ALE tools are the same, however. Tool vendors that are fielding or developing ALE appear to be taking different approaches.

Lam Research has been talking about ALE. Basically, the company is implementing more of a traditional and sequential ALE process. For this, the desired chemistry is first pumped into a chamber and dispersed on the surface. This step, called “reaction A,” forms a reactive layer on the surface. Then, there is a removal step, called “reaction B.” In this step, ions or other chemistries remove the undesired parts of the structure. The steps are then repeated.

Generally, chlorine is one of the more common reactants (reaction A) used for silicon, germanium and III-V materials, according to Lam Research. Argon can be used for the removal step. In total, the industry has evaluated some 20 materials for ALE, according to Lam.

There are other approaches as well. Applied Materials uses a plasma to generate etching chemistry inside a chamber with two different areas, mixing ions, radicals and neutrals. The system also includes hardware that blocks the undesired ions, allowing the desired chemistry to disperse on the surface. What’s more, it’s a non-line-of-sight technology.

Hitachi High-Technologies has two ALE offerings. One utilizes our ECR technology with several hardware modifications for high-throughput capability. The other chamber provides reverse ALD process capability without surface damage to the non-etched layers.

TEL sells traditional etch products as well as a gas chemical etch system (Certas) for ALE.

The industry is developing thermal ALE, which removes materials in an isotropic or unidirectional basis. For isotropic applications, the ALE tool injects gas molecules that can travel anywhere, allowing it to potentially do things plasma ALE can’t. Both thermal and plasma ALE can be used to accomplish different tasks.

Development is also ongoing for hybrid plasma-thermal ALE.

Selective ALE is another technology in R&D. With today’s ALE, the tool removes a targeted structure. Selective ALE takes this one step further, allowing etch of a particular material on a surface.