Dry Etching's Role in the Fight Against COVID-19

As the novel coronavirus SARS-CoV-2 (i.e., COVID-19) continues to wreak havoc across the globe, industries across the world have dropped their daily workflows and hyper-focused on tackling the pandemic. Fanatics — a sportswear brand — has revamped its facilities to produce masks and gowns for hospitals. Ford, GM, and Tesla have all been producing ventilators for hospitals. Thousands of other companies (e.g., Amazon, Apple, Google, etc.) have donated to coronavirus relief funds.

Dry etching technology and dry etching equipment manufacturers are also playing a role in the COVID-19 crisis — especially relating to the development of SARS-CoV-2 testing capabilities. Many companies involved in dry or plasma etching are redirecting efforts to help combat the growing pandemic. Scientists, companies, and government laboratories are utilizing the advantages of plasma etching to develop solutions that will assist in the pandemic battle, particularly in the area of more accurate, simpler, and faster testing.

Creating Rapid Testing Capabilities for SARS-CoV-2

Biomedical companies have all been racing to produce a swift, accurate coronavirus test that could expedite the testing and tracing process for countries across the globe. One significant approach involves a combination of electronics, microfluidics, and biosensors that is a subset of sensors known as microelectromechanical systems or MEMS. MEMS-based systems (like lab-on-a-chip) are currently being utilized to perform accurate, rapid testing for SARS-CoV-2 in a variety of ways. Key to the fabrication of MEMS devices is a type of dry-etching plasma technology referred to as reactive ion etching (RIE).

SARS-CoV-2 Testing and Detection: The Story of Cepheid

In MEMS, the integration of electronics and microsensors produces chips that sense and interact with the environment. It is this characteristic that has promoted widespread adoption of MEMS to power a set of applications referred to as the Internet-of-Things (IOT). A specific and powerful use of MEMs is for the detection of DNA segments unique to SARS-CoV-2. Microfluidic MEMs chips using polymerase chain reaction (PCR) biochemistry can detect and amplify patient DNA samples. The chips, more specifically MEMS-PCR chips, are looking for SARS-CoV-2 DNA segments or viral genomes belonging to the novel coronavirus.

One of the leaders in the MEMS space — Cepheid — has recently been granted emergency authorization from the FDA to create and sell a new SARS-CoV-2 rapid test kit. Cepheid’s approach is using a microfluidic MEMS chip to divide or partition a patient’s DNA across multiple channels. The droplet in each channel then undergoes digital PCR which enhances the number of DNA segments available for sensing. The micro-scale parallel processing afforded by MEMS allows for rapid testing with smaller detection limits than traditional PCR testing — affording quicker results at lower detection levels. The report results are impressive. According to EETimes and a recent study published in Emerging Microbes & Infections, MEMS-enabled dPCR is more sensitive (up to 500x the sensitivity of traditional PCR processes) and more accurate than conventional PCR processes that are currently being leveraged to detect SARS-CoV-2.,

As mentioned above, MEMS devices rely on the plasma etching technique known as RIE. RIE is an important manufacturing process for MEMS. Because the device feature depths dimensions are significantly more than in traditional electronics and the aspect ratios are large (aspect ratio – feature depth/ feature width), there are specific RIE processes to address this device characteristic. 

The most well-known RIE variation for silicon structures is commonly referred to as DRIE (Deep RIE because of the depth being etched) and is also commonly called the Bosch process (after the Bosch company who received the patent). Particular to Si-DRIE is the capability to have etching rates commensurate with the typically deep MEMS feature depths while maintaining vertical profiles.

Depending on the aspect ratio of the structure, etching rates may range from a few micron/min to 10s of microns/min. The nature of the Si-DRIE process, relying on a chemical mechanism for etching, can produce selectivities to a mask that range from >30:1 to >500:1 depending on the details. Other MEMS structures in materials such as glass or quartz typically have etch rates in the 0.4 to 0.8um/min and significantly lower selectivities due to the more physical nature of the etching process.

Lab-on-a-chip-based Systems: The Story of DNANudge

Lab-on-a-chip-based systems are miniaturized systems that allow entire laboratory tests to be carried out on a single chip at the nano-scale level. Created via MEMS, Lab-on-a-chip solutions are poised to impact the rapid SARS-CoV-2 testing and tracing market. DNANudge — a brand that uses labs-on-a-chip to carry out DNA testing to help guide you towards smarter nutrition options — has recently transitioned to creating lab-on-a-chip testing for SARS-CoV-2.

DNANudge's NudgeBox and cartridge allow swabs to be placed directly into the box, which then carries out rapid, real-time PCR testing for the novel coronavirus. Like with Cepheid's solution, this testing happens across multiple (72 in this case) wells in the box. The lab-on-a-chip is capable of testing across these 72 independent DNA amplification wells.

Lab-on-a-chips are microfluid devices created using either more traditional RIE or the more complex DRIE technique which provides the technology required for precise, controllable, deep etching. Efficiently manufacturing the volumes needed for testing large populations requires processes to be done on wafer-scale formats. One approach to achieve cost targets is to use the RIE and DRIE to generate molds for polymeric substrates. One example being done at the research level is shown in the figure above from Technion – Israel Institute of Technology (R. Fishler, O. Ternyak and J. Sznitman).

Dry Etching is Leading the Way in SARS-CoV-2 Testing

Research and development in BioMEMS and nanotechnology are making advances a very accelerated pace in critical coronavirus testing capability. Plasma etching processes are contributing to the ability to generate and host unique and complex structures such as microfluidic channels, valves, filters, and tailored surfaces at both micro and nanoscales. Other plasma processes are able to deposit materials that provide critical device functionality. MEMS devices such as lab-on-a-chip are delivering solutions created using RIE equipment, and the solutions are helping the globe tackle the ever-complex problem of testing and tracing during the midst of an ongoing pandemic.

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