Dry Etching: Techniques and Applications

For projects requiring maximum precision, and more control of the shape of the etched geometry, the solution is using a dry etching method. 

With dry etching, a substrate is loaded in a sealed process chamber to produce a plasma under a vacuum of special process gases. From this plasma, reactive species are created allowing for chemical or physical interactions with the substrate.  

These obtained species either interact in a chemical manner (reaction with a surface atom) or physical manner (collision with a surface atom) to remove material from the substrate surface. Herein, atom layer by atom layer is removed to ensure a highly controlled etch process. For an even more selective removal of material, dry etching is traditionally combined with photolithography processing. 

The complex combination of variables in the process chamber allows for steering to process to maximum precision. Which allows us to successfully realize the most challenging projects. 

Types of Dry Etching 

There are two main, distinct types of dry etching. Namely, Reactive ion etching (RIE) and Deep Reactive Ion Etching (DRIE). Both techniques use vacuum chambers and process gasses, but the difference is found in the positioning of the electrodes, the directionality of the plasma species and thus the result of the etch and application. 

At Micronit we offer both RIE and DRIE with for a wide variety of applications. 

RIE of Silicon and Thin films 

RIE allows for isotropic plasma etching in a gaseous environment (which is very similar to the wet etching of glass). During this process exposed substrate is etched in all directions on an atomic level. Hence, an undercut under the masking material is observed, proving rounded, smooth sidewalls.  

Isotropic etching of substrate material (glass or silicon) by RIE can be advantage for some applications. However, this technology is mainly dedicated to the selective etching of thin films, and especially masking layers consisting of dielectrics (silicon dioxide and silicon nitride).  

Micronit offers Reactive Ion Etching for up to 300 mm substrates. 

DRIE of Silicon  

In DRIE, the physical interaction with the substrate surface is available and is mainly used to control the etching geometry. This is made possible by the angle of the sidewall relative to the substrate surface, which minimizes undercutting under the masking material. This allows for the realization of high aspect ratio structures in glass and silicon substrates.  

During the DRIE, traditionally, a cycle of steps is performed. These steps consist of chemical etching, surface coating and selective physical removal of coating and substrate. With each step, tens of nanometres from the exposed substrate surface are removed in depth. During removal there is the option to steer it in the direction of the sidewall, in a straight downward manner, or even by introducing a positive or even negative taper. 

Cycle-based etching in silicon using a Deep Reactive Ion Etch system. 

Micronit offers fluorine gas-based silicon Deep Reactive Ion Etching for up to 200 mm silicon wafers with the following characteristics:  

• Aspect ratio up to 1:50.  
• Through-wafer etching.  
• Multiple depth etching.  
• Variable taper angle of the sidewalls.  

• Selectively stopping on silicon oxide or nitride membranes.  
• Aligned front and backside etching.  

Silicon pillars etched into the substrate surface using DRIE and photolithography.  

Getting started 

At Micronit, we specialize in assisting our customers from concept to manufacturing. Do you have a project that would benefit from our etching solutions? Our experts are ready to work with you and turn your ideas into reality. Contact us and find out how Micronit can support your projects with our advanced etching techniques!