ALE

As chip node dimensions are continuously shrinking, conventional plasma etch processes have reached their limits. Etching ultra-thin, tall and narrow layer at the nanoscale requires Atomic Layer Etching (ALE) technology, which allows to remove material one atomic layer at a time.

This technology is used to selectively etch a variety of oxides or Poly-Silicon, enabling manufacturing of the most advanced devices where high selectivity, high uniformity and low damage are crucial, as a counterpart of the ALD technology.

How does it work?

As for ALD, ALE process cycle consists of sequential injections of reactive gases and ionized noble gas in the reactor, commonly energized by plasma.

In between each pulse, N2 purge is injected to evacuate reactant and by-products formed by precursor adsorption on the surface. As the reaction is self-limited by nature, etch thickness is only dependent on the number of cycles performed, allowing a control of the etched layer at the atomic scale. ALE process is generally performed on single wafer equipment.

Vacuum requirements

As for conventional plasma etch process, Chlorine and Fluorine based chemistries are used, depending on the material to be etched. New emerging ALE processes can also include some deposition steps for improved control of etch profile. This new trend involves the use of silicon precursors typically present on ALD or CVD applications. ALE processes operate at low pressure, in the range of 10-2 to 10-3 mbar. In order to maintain a low vacuum, turbopumps are mounted directly on the chamber reactor, backed by primary dry pumps installed in the basement. As gas flows are continuously increasing, required turbopumps pumping capacity vary from 1,600 to 4,000 l/sec on the newest generation reactors. Dry pumps typically require pumping speeds from 600 to 1,200 m3/h.

By-products to be evacuated are condensable and highly corrosive. This represents a great challenge for vacuum pumps, which should be able to operate at high temperature under a very corrosive environment.