Error component analysis in the metrology of x-ray masks

Abstract

Understanding and minimizing error sources in the fabrication and metrology of sub-half micron lithographic masks will be the challenge of the 1990’s. X-ray masks, with their relatively thick absorber on thin membrane structures, pose the greater challenge in both fabrication and metrology. Registration data for x-ray masks of different formats have been acquired and analyzed for various error components. Measurement error components are machine measurement accuracy, cassette reloading error, and system temperature stability. Fabrication error components are e-beam placement errors, stress related distortion, and e-beam heating of the membrane during writing. This paper will consider primarily the error components related to e-beam writing and metrology. The primary metrology system used was the MEBES III. Machine measurement error has been determined to be relatively independent of format or substrate evaluated. Cassette reloading has been shown to have a significant impact on measurement error and is dependant on format and/or cassette design. Errors due to e-beam heating during pattern writing have been measured and will be discussed. The errors attributed to these components are not limiting to 0.5-μm mask technology, but must be reduced to address 0.25-μm x-ray masks.