A Study on the Defect Measurement of Thin FilmUsing Digital Holography
Hyun-Il Jung
Advisor : Prof. Kyeong-Suk Kim, Ph.D.
Dept. Advanced Parts & Materials Engineering.
Graduate School of CHOSUN University

Holography is a technique devised by Dennis Gabor in 1948 and which enables amplitude and phase information to be recorded on a film by radiating objects with a light source. The recordings are called holograms which mean ‘recording all’. Holography was invented and has been developed to obtain and reconstruct 3-dimensional information of an object. Holography contributes to saving holograms in a computer through an imaging device, for example, CCD cameras. Digital holography is a technique which enables holograms to be recorded and reconstructed as a shape of an object by using computers. It is used in a lot of fields including 3D display, measurement of minute objects, and recording fluid flow because post processing of the data can be achieved.
The thin film used in integrated circuits, thin film memories, and electronic parts is made through vacuum deposition of material, for example, metals, semiconductors, or insulators on a substrate, for example, insulated glass or ceramics, electro plating, laser beam deposition and the like to make a thin film not thicker than 1㎛ . Vacuum deposition is generally used, which is a method of depositing an object for deposition on a substrate in a vacuum chamber. Particles in the chamber, the substrate or the object for deposition lower cohesion efficiency of the object for deposition to result in pin holes, cracks or peeling-off. Accordingly, interruption of element formation, poor conductivity or transmittance, disconnection, deformation of micro structure can occur to lower the performance of thin films, reduce the span of service life and lower the level of safety. To avoid the aforementioned problems to occur, defect inspection is very important to prevent defective thin films from being manufactured.
To facilitate the inspection, this study suggests measurement of a roughness standard specimen and the resolution target by using digital holography to ensure reliability and verify resolution. Sputter deposition is employed to deposit molybdenum on a glass substrate to make a thin molybdenum films. In this case, two types of a clean substrate and a dirty substrate with particles are produced. A reflective digital holography interferometer is built for measurement in order to evaluate defects in a thin film. This study aims to reduce defective products for which semiconductors are used, improve safety and stability, prolong the span of service life and implement energy saving through evaluation of defects.