Investigating metal-plasma interactions in reactive ion etching of novel metal alloys for application in compute & memory technologies

Background

There is always an ever-growing demand for fast and reliable devices in computation and memory technology. This acts as a driving force towards continuous exploration and study of complex materials to achieve good device specifications such as high scalability, low power consumption, non-volatility and high endurance. A good example is the extensive research being carried out now on phase change memories (PCM), resistive random access memories (Re-RAM) and ovonic threshold selectors (OTS) to replace the conventional Static-RAM (SRAM), whose drawbacks include poor scalability from the use of multiple transistors, volatility and high operational power consumption. These advanced memories and selectors employ the use of complex ‘novel metal alloys’ such as chalcogenides (GeSbTe, SiGeAsTe, SiGeAsSe) and metal oxides like InGaZnO. They portray intrinsic electronic properties which make them optimal for advanced class of PCMs, Re-RAMs and OTS.

Current challenges & research description

A key challenge in implementing these aforementioned metal alloys and metal oxides into an actual integration scheme is their patterning at nano-scale level without damaging or interfering with their intrinsic properties. Typically, dry reactive ion/chemical etch techniques are desired to attain high scalability. This means the etch gas (/etchant) will chemically react with the metal system under consideration and generate volatile by-products to leave behind features of different dimensions and shapes (defined by the lithography masks being used). And, herein lies the importance to study and understand the interaction of an ‘etch’ plasma with the metal systems. A chemical reaction between the etchant and the metal system is never a binary process, and is prone to generate some undesirable collateral effects. For instance, the metal system under consideration may get doped with the etchant during the etch process or the metal surface may be chemically modified post the patterning step. There can also be possibilities of void formation and defect generation in the metal films due to the use of a certain type of chemical etch technique and plasma parameters (temperature, precursor of the etchant). It is therefore extremely critical to comprehend and control the interactions between the plasma and the novel metal systems to ensure that their intrinsic properties are not altered adversely for their respective technology applications.

In the framework of this PhD activity, the candidate is needed to carry out the following functions –

1. The candidate is expected to carry out a comprehensive literature study on the different computational and memory technologies, and the complex novel metal systems being used for such applications (as indicated in the introduction).
2. The candidate should also review the different types of chemical etch techniques and applications being used in the technology industry.
3. At IMEC, we have diverse etch tools which possess advanced etching capabilities including atomic layer etching (ALE). These etch capabilities can be applied to design etching experiments on a chosen novel metal system. The effects on the metal alloy/oxide films can be analyzed in-depth by using characterization techniques like transmission electron microscopy (TEMs), X-ray photo electron spectroscopy (XPS), atomic force microscopy (AFM), etc.
4. The candidate should express interest in deep diving into simulating /modelling their experiments (for example, by using ab-initio modelling or molecular dynamics) to investigate the physical origin of the morphological and characterization results attained. This type of modelling-centric approach will help the candidate to harness their analytical skills, as well as enable them to strategize and propose new enhanced etching processes for the technology applications.
5. The problem statement for the candidate will be extended to the integration of the novel metal system with secondary layers acting as top and bottom electrodes in a functional electrical configuration of a chip. Hence, it becomes key to investigate the collateral physical or chemical damage meted out to these metal systems during the etch of the top and bottom electrodes through the similar approach of experimentation and modelling. This way the candidate can build and refine their scientific knowledge as well as be exposed to integration schemes used in the electronic industry.    
6. It is crucial for the candidate to make use of the multi-faceted environment provided by IMEC. They should be willing to work with different individuals in a team comprising many process and device experts (in processing, integration, physical characterization, modeling etc.). It is key that the student is open-minded and is able to absorb any new knowledge and constructive criticism from his/her peers and colleagues. They should display good problem-solving skills, however, communicate immediately and effectively when in need for guidance.