NOVELTY - Plasma is generated and accelerated between cathode and anode of a plasma source (1) in channel(s) of system of conductive cascaded plate(s) between cathode and anode at sub-atmospheric pressure. The plasma is released from plasma source(s) to a treatment chamber (2). The substrate is exposed in the treatment chamber to an etching agent by the plasma, while the treatment chamber is sustained at a reduced, near vacuum pressure and a negative alternating bias voltage is applied between the substrate and plasma during exposure.    USE - Etching of substrates, such as semiconductor substrates, particularly silicon substrates (both claimed), used in manufacture of semiconductor devices and solar cells.    ADVANTAGE - The method enables localized etching of substrates by plasma, which offers an improved precision and controllability together with a significant plasma density, such that aspect ratios and process rates beyond those of existing plasma techniques are attainable.    DETAILED DESCRIPTION - Plasma is generated and accelerated between a cathode and an anode of a plasma source (1) in channel(s) of system of conductive cascaded plate(s) between the cathode and anode at sub-atmospheric pressure. The plasma is released from plasma source(s) to a treatment chamber (2) through a constricted passage opening. The substrate is exposed in the treatment chamber to an etching agent by the plasma, while the treatment chamber is sustained at a reduced, near vacuum pressure and a negative alternating bias voltage is applied between the substrate and plasma during exposure. Sulfur hexafluoride and octafluorocyclobutane are introduced in the plasma, respectively for etching the substrate and for creating a protective layer on the substrate. An INDEPENDENT CLAIM is included for device for etching substrate with plasma.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the device used for etching substrate using plasma.    Plasma source (1)    Treatment chamber (2)    Plasma arc (3)    Plasma jet (4)    Substrate (9)