Etching Techniques: The Basics for Precision Manufacturing

Micronit offers a comprehensive range of etching techniques that can be utilized to meet any requirements in precision manufacturing. With over 25 years of experience, we specialize in guiding our customers through every step of the way, from idea to manufacturing.

Etching and lasering techniques 

Etching is a technique used to remove material from a glass or silicon substrates surface by means of chemical or physical interactions. By making use of lithography technology, parts of the surface can be shielded from the etching, creating specific patterned 3-dimensional surface geometries. And fluidic channels and chambers with pillars can be realized with nanometer accuracy. Micronit has vast experience in etching using glass and silicon, and we also offer possibilities to etch thin films consisting of dielectrics and metals. 

Etching can be performed using wet or dry techniques, depending on the substrate material and the desired geometry of the etched structure. In wet etching, liquid chemicals are used, whereas dry etching makes use of gases or plasmas as etchants. Herein, wet etching is based on chemical removal of substrate surface material, whereas dry etching combines both chemical and physical removal. 

Alternatively, Micronit has in-house laser etching technologies allowing for the realization of vias in glass substrates, which is the primary technique for fast and accurate drilling of complete wafer-through holes for microfluidic in- and outlets.

Wet etching: Uniform and reproducible 

Wet-etching is a precise technique used in microfabrication to create intricate patterns on glass wafers. It begins with photolithography, a process that uses light to transfer geometric shapes onto a light-sensitive material. This material acts as a protective layer for the glass wafer surface. The wafer is then exposed to hydrofluoric acid (HF), which selectively dissolves the unprotected areas. The depth and width of the etched channels increase until the desired dimensions are achieved, at which point the wafer is removed from the HF bath. To finalize the structure, the etched wafer can be fusion bonded with another layer, creating sealed microfluidic chips. This technique allows for the creation of highly detailed and functional microstructures essential for various applications.

Glass is the preferred material for wet-etching due to its exceptional optical properties and chemical resistance. It offers a smooth surface with roughness in the angstrom range, ensuring high precision in microfabrication. Glass is also fully transparent, which is crucial for applications requiring optical clarity. Wet-etching on glass achieves highly accurate structures, with an etch depth accuracy of around 5%, significantly better than the typical 10%. The initial mask openings, defined by photolithography, ensure extreme precision. Additionally, glass's inherent shape stability and flatness make it ideal for producing ultra-flat products. Furthermore, multiple wafers can be processed simultaneously in a single etching step, making the process efficient and scalable for industrial applications.

Micronit applies wet chemical etching techniques to create structures in a desired material, for this you have two techniques - isotropic and anisotropic. 

• Isotropic etching methods (glass)

  Our wet etching of glass is performed using fluorine-based solutions in combination with photolithography. Wet chemical etching results in isotropic characteristics, in effect exposed glass material is removed in all directions. The wet isotropic wet etching of glass is a highly controlled process within Micronit’s many established capabilities. Utilizing spray etch processing technologies, highly precise, uniform, and reproducible geometries over 150- and 200-mm glass substrates are obtained.

• Anisotropic etching methods (silicon)

  For silicon we can offer wet chemical etching based on anisotropy. In this process the etching takes place along the crystal direction of the silicon, and the final etched shape is related to the etching speed of the different crystal planes in the monocrystalline silicon. Using a hard mask (from either silicon dioxide or silicon nitride) atop the silicon, patterned with photolithography, complex and precisely defined structures with predictable etch angles are obtained. For anisotropic wet chemical etching, spray etching is applied, using alkali hydroxides, towards highly unform etching of up to 150- and 200-mm substrates.

Single depth etching vs. double depth etching

When it comes to wet-etching, understanding the difference between single depth etching and double depth etching is essential for achieving the desired microfluidic structures. Single depth etching involves creating channels of a uniform depth across the entire wafer. This method is simpler and faster, as it only requires one etching step, making it ideal for applications where consistent depth is critical. Single depth etching is commonly used for straightforward designs where uniform channel dimensions are sufficient.

In contrast, double depth etching, or multi-level etching, involves multiple etching steps to create channels of varying depths on the same wafer. This technique allows for more complex and functional designs, enabling the integration of different microfluidic components within a single chip. Double depth etching starts with an initial etching step to achieve the first depth, followed by additional photolithographic masking and etching steps to reach the second, deeper level. This approach is beneficial for applications requiring intricate features, such as valves, pumps, or complex fluid routing systems, providing greater design flexibility and functionality. Understanding when to use single versus double depth etching helps optimize the manufacturing process for specific microfluidic applications.

Dry etching: For more complex issues 

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.<

• 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. 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, thgough-wafer etching, multiple depth etching, variable taper angle of the sidewalls, and selectively stopping on silicon oxide or nitride membranes.

Dry & Wet Etching Techniques Overview 

Getting started 

At Micronit, we take pride in our role as your development and manufacturing partner. We understand that developing a high-quality product cannot be done without the knowledge of specialized manufacturing techniques. That is why we can put our extensive expertise to work to bring your ideas to life. From concept to production, we are here to guide you with solutions that exceed your expectations. Want to learn more about our technical capabilities? Download our complete overview of capabilities.

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.