Disclosed is a grinding-and-etching system using a dry-etching for removing strains from plate-like objects such as semiconductor wafers, which are caused in grinding such objects. The co-displacing member can herein be releasably connected to the tube or the flexible element, and the connection can be broken when the co-displacing member is forced into the tube. The spatial intensity distribution of the emission from the VCSEL is used for the generation of error signals in an optical pick-up unit. This process varies the power consumption of the component in a manner that is proportional to a value of the input signal. Light is directed incident to the surface of film in contact with the substrate.