Aspect ratio (structuring)
As aspect ratio ( engl. Aspect ratio ) is known in the process technology the ratio of the depth or height of a structure to its (smallest) lateral dimension. In general, the larger the aspect ratio and the smaller the absolute size of the structure, the more difficult it is to manufacture. The aspect ratio is of particular relevance in microtechnology .
Examples:
- If a 60 mm deep hole is drilled with a 6 mm drill, this hole has an aspect ratio of 10 (: 1).
- If a 40 µm wide, arbitrarily long and 100 µm deep trench is produced in a silicon wafer in an etching process , this trench has an aspect ratio of 2.5 (: 1). Aspect ratios of this kind greater than 1 require the use of anisotropic structuring methods , for example reactive ion etching (RIE).
- With wet chemical etching , which is used extensively in circuit board production in the electronics industry, isotropic etching can only produce structures with aspect ratios less than 1. Conductor tracks that are to be produced from a 50 µm thick copper layer by photolithography and wet chemical etching must therefore have a distance of more than 50 µm from one another everywhere. In the case of monocrystalline substrates, such as silicon wafers, anisotropic etching, for example with potassium hydroxide , can also be used to produce wet-chemical structures with a high aspect ratio.
Individual evidence
- ↑ Ulrich Mescheder: Microsystem technology. Springer-Verlag, 2013, ISBN 978-3-322-94037-7 , p. 39 ( limited preview in the Google book search).
- ↑ Marc J. Madou: Manufacturing Techniques for Microfabrication and Nanotechnology. CRC Press, 2011, ISBN 978-1-420-05519-1 , p. 217 ( limited preview in Google book search).