Specimen distance measuring system

An electron beam exposure system having a substrate holder for holding a substrate, an electron beam source for projecting an electron beam onto the substrate, and further comprising:

• a shadow plate to intercept electrons backscattered from the substrate and to cast a shadow in the backscattered electrons;
• an electron detector having a width, and positioned such that the shadow is cast intermediate across the detector width and so that the shadow moves across the width of the detector as the distance between the electron source and the substrate changes, the detector operating to produce a detector output signal corresponding to the flux of backscattered electrons impinging on the detector;
• electronic circuitry coupled to the electron detector, and responsive to the detector output signal to produce an indication of the distance between the substrate and the electron beam source.

An electron beam exposure system having a substrate holder for holding a substrate thereon, a focusable electron beam source for projecting an electron beam onto the substrate with the focus of the beam being responsive to a beam focusing electronic signal, and further comprising;

• a shadow plate to intercept electrons backscattered from the substrate and to cast a shadow in the backscattered electrons;
• an electron detector having a width, and positioned so that the shadow is cast intermediate across the detector width and so that the shadow moves across the width of the detector as the distance between the electron source and the substrate changes, the detector operating to produce a detector output signal corresponding to the flux of backscattered electrons impinging on the detector;
• electronic circuitry coupled to the detector, to produce the beam focusing electronic signal responsive to the detector output signal in order to produce a focus for the beam appropriate to the distance between the substrate and the beam source.