Dry etching of monocrystalline silicon using a laser-induced reactive micro plasma

• Main Authors: Robert Heinke, Martin Ehrhardt, Pierre Lorenz, Klaus Zimmer
• Format: Article
• Language: English
• Published: Elsevier 2021-12-01
• Series: Applied Surface Science Advances
• Subjects: Plasma formation; Laser; Reactive etching; Si; CF4
• Online Access: http://www.sciencedirect.com/science/article/pii/S266652392100115X

Dry etching is a prevalent technique for pattern transfer and material removal in microelectronics, optics and photonics due to its high precision material removal with low surface and subsurface damage. These processes, including reactive ion etching (RIE) and plasma etching (PE), are performed at vacuum conditions and provide high selectivity and vertical side wall etched patterns but create high costs and efforts in maintenance due to the required machinery.In contrast to electrically generated plasmas, laser-induced micro plasmas are controllable sources of reactive species in gases at atmospheric pressure that can be used for dry etching of materials.In the present study, we have demonstrated the laser-induced plasma etching of monocrystalline silicon. A Ti:Sapphire laser has been used for igniting an optically pumped plasma in a CF4/O2 gas mixture near atmospheric pressure. The influence of process parameters, like substrate temperature, O2 concentration, plasma-surface distance, etching duration, pulse energy and crystal orientation on etching rate and surface morphology has been investigated.Typical etching rates of 2–12 µm x min−1 can be achieved by varying mentioned parameters with a decreasing etching rate during the process. Different morphologies can be observed due to the parameters set, smooth as well as rough surfaces or even inverted pyramids.The presented etching method provides an approach for precise machining of silicon surfaces with good surface qualities near atmospheric pressure and sufficiently high material removal rates for ultraprecise surface machining.