Compact smartphones and many other modern electronic devices could not exist without plasma etching. In this blog post, we look at the fundamentals of plasma etching and how tools from Hiden Analytical enable accurate analysis of plasma streams in etching applications.
What is Plasma Etching?
Plasma etching is an incredibly precise subtractive manufacturing technique that uses a high-speed stream of ionized gas (plasma) to effectively “carve” very small features into materials.
The process relies on physicochemical interactions between chemical species in the plasma stream and the surface being etched: these react to form volatile products that evaporate from the surface.
First developed for use in integrated circuit manufacturing in the 1960s, plasma etching was a revolutionary technology. It was born out of a need to find an alternative to wet chemical etching techniques, which suffered from several limitations at small scales and produced a large amount of liquid waste.1 Crucially, wet chemical etching is an isotropic technique (literally meaning “the same in all directions”): this results in undercutting when etching channels into a material.
Plasma etching, on the other hand, is an anisotropic technique, meaning it can be used to produce channels that are deeper than they are wide (or vice versa). Plasma etching also enabled greater selectivity and smaller feature sizes than wet chemical etching.
By enabling precise anisotropic etching of silicon, aluminum and silicon dioxide; plasma etching became the key technology that has allowed the critical dimensions of semiconductor devices to steadily shrink over the last half century.2
Applications of Plasma Etching
Without plasma etching, it’s likely that silicon-based electronics would still resemble their bulky 1970’s counterparts, rendering today’s smartphones and laptops non-existent.
Integrated circuit manufacturing is still the primary application of plasma etching today. By producing features varying in size from nanometers to hundreds of microns, plasma etching is used to manufacture a wide variety of semiconductor devices from various materials.
Plasma etching is also used for a number of other applications outside the semiconductor industry. Researchers are using plasma etching to produce micro- or nano-scale texturing of surfaces to produce exotic material properties. For example, etching a micro-cubic structure into silicon can impart anti-icing properties.3
Nanotexturing using plasma etching can also affect the wettability of material surfaces, resulting in either superhydrophobic or superhydrophilic surfaces which repel or attract water, respectively.4,5 Similar ‘functionalization’ of surfaces can also be achieved by using plasma chemistries that generate functional chemical groups that bind to surfaces. Many of these functionalization techniques have applications in medical devices where surface properties play a vital role in biocompatibility, cell interactions and wettability.6
Plasma Etching with Hiden
In any plasma etching process, the chemistry of the plasma stream is fundamental, since gas species produced during plasma etching can react with the material being processed. Developing an effective plasma etching technique for a given process largely depends on finding a plasma chemistry that can react with the material in question to form volatile products, without compromising the surrounding material.7 For these reasons, accurately analyzing the composition of the plasma is absolutely critical.
Hiden Analytical produces a complete range of equipment designed for reliable and precise analysis of plasmas. From plasma probes to quadrupole mass spectrometers (QMS), researchers rely on Hiden Analytical plasma equipment for accurate, reliable analysis in plasma etching applications.8–10 Read more about how researchers are using Hiden Analytical tools in plasma etching applications, or get in touch with us today to learn more about our plasma analysis solutions.
References and Further Reading
1. Sugawara, M. Plasma Etching: Fundamentals and Applications. (OUP Oxford, 1998).
2. Donnelly, V. M. & Kornblit, A. Plasma etching: Yesterday, today, and tomorrow. Journal of Vacuum Science & Technology A 31, 050825 (2013).
3. Hou, W. et al. Anti-icing performance of the superhydrophobic surface with micro-cubic array structures fabricated by plasma etching. Colloids and Surfaces A: Physicochemical and Engineering Aspects 586, 124180 (2020).
4. Dimitrakellis, P. & Gogolides, E. Atmospheric plasma etching of polymers: A palette of applications in cleaning/ashing, pattern formation, nanotexturing and superhydrophobic surface fabrication. Microelectronic Engineering 194, 109–115 (2018).
5. Skarmoutsou, A., Charitidis, C. A., Gnanappa, A. K., Tserepi, A. & Gogolides, E. Nanomechanical and nanotribological properties of plasma nanotextured superhydrophilic and superhydrophobic polymeric surfaces. Nanotechnology 23, 505711 (2012).
6. Wang, J. H. Surface preparation techniques for biomedical applications. in Coatings for Biomedical Applications 143–175 (Elsevier, 2012). doi:10.1533/9780857093677.1.143.
7. Pearton, S. J., Douglas, E. A., Shul, R. J. & Ren, F. Plasma etching of wide bandgap and ultrawide bandgap semiconductors. Journal of Vacuum Science & Technology A 38, 020802 (2020).
8. Hiden. Plasma Etching Selectivity of ZrO2 to Si in BCl3/Cl2 Plasmas. Hiden Analytical Germany.
9. Sha, L. & Chang, J. P. Plasma etching of high dielectric constant materials on silicon in halogen chemistries. Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films 22, 88–95 (2004).
10. Tatsumi, T. et al. Quantitative control of etching reactions on various SiOCH materials. Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films 23, 938–946 (2005).