Reactive Gas Enhancement (CAIBE/RIBE)

Adding Reactive Gases to Ion Beam Etching

The performance of the common inert (Argon) ion beam nanofabrication equipment can be enhanced when chemically reactive gases are added to the process. By the inclusion of chemical reactants to the ion beam etch variables, the process can be designed to optimize the physical and chemical etch components. With the ability to uniquely set, control and know the physical/chemical etch parameters, the process engineer can increase etch rates, achieve high aspect ratios, and improve mask to substrate selectivity. Applications where reactive gas enhancement  has been successful include the use of CI-based reactive gases to etch laser facets in III-V materials; the use of fluorinated reactive gases to etch slanted diffractive gratings in fused silica; the use of O2 to etch nanostructures in diamond for high power spectral applications; and the use of CH3OH to etch multilayer magnetic tunnel junction cells.

Nanoquest I

Nanoquest I

Nanoquest II

Nanoquest II

Nanoquest III/IV

Nanoquest III/IV

Chemically Assisted Ion Beam Etching (CAIBE)

chemically assisted ion beam etchingIf the beam ions are generated from an inert gas and the chemically active species are directed at the substrate separately and independent of the ion beam, then this process method is called "chemically assisted ion-beam etching," or "CAIBE". The chemical reactive gas is introduced to the substrate through either a multi-orifice gas ring or injection nozzle. Either gas device promotes a local pressure region which drives adsorption of the reactive gas to the substrate surface. As the incoming inert ions (Ar+) bombard the surface, they transfer energy to enhance or "assist" any one of a possible chemical reaction mechanisms to create volatile products. In chemically assisted ion-beam etching (CAIBE), the reactive material removal is only one component of the overall etch, the inert ion beam contributes a physical component to the etch as it bombards the substrate with determinants such as it's kinetic energy and current density.

Reactive Ion Beam Etching (RIBE)

reactive ion beam etching (RIBE)The performance of the Argon/CAIBE ion beam process method can be further developed when chemically reactive gases are fed into the ion source. The reactive gas becomes part of the plasma charge. By inclusion of chemical reactants into the discharge, the ion beam is composed of reactive ions which possess both physical and chemical energy to enhance the ion beam etching metrics. With the proper chemistry, this technique typically improves etch rate and material selectivity. If the beam ions are generated from a reactive gas and directed at the substrate, the process is called "reactive ion-beam etching", or "RIBE". Reactive ion-beam etching (RIBE) intentionally introduces reactive gas into the ion source plasma discharge. These ions from the discharge are accelerated to form a directed beam with physical and reactive properties. These ions are directed at the substrate, imparting kinetic energy and chemical activity to the sputtering process on the surface. Due to the confined structure of the ion beam and our substrate stage which is capable of angle tilt,  the ions can strike the substrate at a prescribed angle of incidence (AOI). The combination of RIBE/CAIBE and the AOI process operation enables simple fabrication of slanted or angled etch features in a variety of material systems.

Gas Injection for CAIBE

Typical reactive gas introduction techniques
gas injection for CAIBE1. Injected into the vacuum chamber
     1. From gas kinetics, can determine the arrival (impingement) rate for the molecules or atoms of the reactive gas
          1. With a known background pressure, the arrival rate of molecules at the surface can be       calculated and correlated to the process rate.
     2. Suited to uniform distribution over substrate and independent of stage tilt angle
     3. Less prone to process scale limitations and maintenance tasks
     4. Requires higher gas flow and pressure than local stage gas manifolds

2. Injected through a manifold close to the substrate stage
     1. Can reduce comparable flow rate for the reactive gas, thereby decreasing pressure, throughput or pumping speed considerations
     2. Can locally concentrate gas to stage region when high reactivity or etch rates are desired
     3. Complicates gas arrival rate determination and uniform distribution over substrate
     

Typical gas injection manifold hardware:
1. Gas ring surrounds substrate stage and introduces gas through distributed orifices at a distance to promote a local high pressure and uniform adsorption of reactive gas across the substrate.
2. Gas injection nozzle is near and pointed at substrate stage. It is located at an orientation to promote a local high pressure and even distribution of reactive gas across the substrate.
3. Whether gas ring or nozzle, the gas injection is upstream and remote from the stage, pointing at the stage but its distance creates a uniformly diffuse distribution of arriving reactive gas across the substrate based on chamber pressure.

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