Control of exposure in charged-particle-beam microlithography based on beam-transmissivity of the reticle

An electron-beam microlithographic exposure method performed using an electron-beam microlithographic exposure device comprising an illumination-beam source, an illumination-optical system through which the illumination beam passes, a reticle stage, a projection-optical system through which a patterned beam passes, and a substrate stage including a beam-current sensor, the method comprising:

• mounting a reticle on the reticle stage relative to the illumination beam, the reticle defining electron-transmitting (and non-forward-scattering) regions and electron-forward-scattering regions that collectively define a pattern on the reticle, and a transmitted-current-detection window that is as transmissive and non-forward scattering to the illumination beam as any of the electron-transmitting regions of the reticle;
• moving the substrate stage to place the beam-current sensor in a beam-current-sensing position;
• moving the reticle stage to place the transmitted-current-detection window at an illumination-beam-irradiation position;
• irradiating the transmitted-current-detection window with the illumination beam, while measuring a beam current of the resulting patterned beam with the beam-current sensor;
• determining whether the measured beam current is outside a predetermined beam-current range defined between lower and upper thresholds;
• if the measured beam current is outside the predetermined range, then changing at least one parametric setting of at least one of the illumination-beam source and illumination-optical system so as to bring the measured beam current within the predetermined range;
• and
• from the measured beam current within the predetermined range, calculating a beam-current density at the substrate stage and an exposure time for exposing the substrate with a specified dose using the reticle.

A charged-particle-beam (CPB) microlithographic exposure apparatus, comprising:

• a CPB source that emits an illumination beam toward a reticle defining a pattern to be transferred to a sensitive substrate;
• a reticle stage on which the reticle is mounted;
• an illumination-optical system situated between the CPB source and the reticle stage and configured to irradiate a region of the reticle with the illumination beam;
• a projection-optical system situated downstream of the reticle stage and configured to project and image a patterned beam, propagating downstream of the reticle and comprising scattered and non-scattered charged particles of the illumination beam passing through the illuminated region of the reticle, onto the sensitive substrate;
• a substrate stage, situated downstream of the projection-optical system, on which the sensitive substrate is placed for exposure, the substrate stage comprising a beam-current sensor;
• and
• a controller connected to and configured to control respective operations of the CPB source, the illumination-optical system, the reticle stage, the projection-optical system, the substrate stage, and the beam-current sensor;
• wherein a beam current of the patterned beam reaching a position on the sensitive substrate is measured by the beam-current sensor, and the controller is configured to calculate exposure conditions for the sensitive substrate based on which of a plurality of types of reticles is mounted to the reticle stage and based on the beam current sensed by the beam-current sensor.