Patent ID: 6864490

Claim:
A reflectometer device for determining quality characteristics of a mask blank, comprising: a. a source of electromagnetic radiation in the extreme ultraviolet region; b. a monochrometer, said monochrometer comprising a mirror, a rotatable grating, and an exit slit, electromagnetic radiation from said source of electromagnetic radiation in the extreme ultraviolet region traveling to said mirror for reflection to said rotatable grating and for reflection therefrom through said exit slit, said reflection from said grating creating a narrow beam of electromagnetic radiation in the extreme ultraviolet region, a first portion of said narrow beam of electromagnetic radiation impinging onto the blank mask in a confined area; c. means for rotating said grating of said monochrometer; d. a detector for receiving electromagnetic radiation in the extreme ultraviolet region from said impinging first portion of said narrow beam directly reflected from the mask blank and measuring the intensity of said reflected electromagnetic radiation, and for receiving a second portion of said narrow beam of electromagnetic radiation in the extreme ultraviolet region from said monochrometer and measuring the intensity of said second portion of said narrow beam; and e. a comparator receiving from said detector said measured intensities of said reflected first portion of said narrow beam of electromagnetic radiation and of said second portion said narrow beam of electromagnetic radiation, and determining the reflectivity of said mask blank, therefrom.