3차원 박막 두께 측정을 위한 영상타원계측기에 관한 연구

Abstract

As the rapid developments of semiconductor, display, and LED industries, thin film technology which is a key issue in these fields has become increasingly important. Particularly, in the semiconductor and display fields, the thin film in the manufacturing process has various thicknesses from μm to nm and the thickness of the thin film is becoming thinner in order to make the product smaller. Furthermore, the structure of the thin film having nm thickness is made more complicated. And it is being utilized in various forms in accordance with the rapid development of manufacturing technology in today's several fields. It is expected that the utilization will gradually increase. So the technique for precisely measuring and inspecting geometrical dimensions and material properties of these film layers has been attractive in order to manufacture such thin film structures with much more attention. A superior approach of the these is an ellipsometry that obtains the film thickness profiles of the film layers. This technique has been reported to have a repeatability of less than 0.1 nm and widely used to measure film thicknesses. The principle of ellipsometry uses the polarization change between the incident and reflected lights on the specimen. However, the typical ellipsometry focuses on not an area measurement but a point measurement, which is not enough to reconstruct 3D film thickness profiles. In this investigation, I describe the imaging ellipsometric methods to measure the 3D thickness profiles of a multi-layered film. In order to measure 3D profile at once, an imaging technique is combined with the ellipsometry. I adopt a low magnification imaging lens approximately 1x to extend the measuring area. And two kinds of ellipsometry techniques (null imaging ellipsometry and photometric imaging ellipsometry) are implemented and compared in this thesis. The whole system of two type imaging ellipsometry was constructed as the Polarizer - Compensator(quater wave plate) - Specimen - Analyzer (PCSA) type. And the calibration of each imaging ellipsometry is essential for measurement to know incident angle for specimen and the rotation angles of the optical components accurately. It was performed with two steps; One is the hardware calibration by hand. The other is the software calibration which uses the computer program(matlab) to confirm the accurate variables that are an incident angle and rotation angles of the polarizer and the analyzer. In the null imaging ellipsometry, I used a laser diode with a monochromatic wavelength as the source. Then the refractive index of the silicon (Si) wafer was measured and the thickness of the single layer film were measured in 3D. However, this method has the disadvantage that the measurement time is very long. So, to overcome this limitation, a photometric imaging ellipsometry was introduced. In the photometric imaging ellipsometry, I used the monochromatic light transmitted through the optical filter with the broadband light source in order to measure the multi layers of film structure. And I measured the 3D profiles of the single layer and the multi layers of thin films. Thereafter, the certificated reference materials (CRMs) for the single layered film structure provided in KRISS were successfully measured by photometric imaging ellipsometry and the repeatability for 15 consecutive measurements was less than 0.5 nm.