Soft X-ray dosimetry and its application on the lithography beamline at SSRL

We describe simple methods of soft X-ray dosimetry (1000–3000 eV) for synchrotron based X-ray lithography. These methods are generally applicable to other synchrotron installations and possibly to so-called “stand alone” X-ray sources. A double crystal monochromator of synthetic multilayer crystals was used to obtain narrow band X-rays for energy-dependent measurements. The quantum efficiency of a stainless steel vacuum photocathode is shown to be well modeled by a simple power law, and its use in measuring the quantum efficiency of semiconductor diodes is described. The photocathode modeling is used in conjunction with the monochromator to demonstrate that resist sensitivity depends uniquely on absorbed dose density. The validity of the modeling is discussed, and the limitations of each type of detector are outlined. Suggestions are made for the application of these inexpensive detectors to real time source calibration in practical X-ray lithography equipment.