Oxide Thickness Profile Measurement by Dispersive White-Light Interferometry in CMP Process

Thickness profiles of CMPed oxide thin films are precisely measured by means of spectrally-resolved analysis based on dispersive white-light interferometry. This method allows not only the top surface profile but also the film thickness of an oxide film layer to be measured simultaneously with fine lateral and depth resolutions, leading to a complete 3-D tomographical reconstruction of the measured thin film. Besides, very thin films of less than 0.1 micrometer thickness can be accurately measured with precision in the nanometer range. No mechanical depth scanning is required during measurement, thus the proposed method is fast enough for the non- contact in-line inspection required for effective quality assurance of CMPed wafers. The measurement of the thickness of oxide thin films is essential in the fabrication of semiconductor integrated circuits. The International Technology Roadmap for Semiconductor (ITRS) (1) projects that the feature size will continue to shrink below 45 nm, whereas the wafer size will increase from the current standards of 200 and 300 mm up to 450 mm. In line with the global trend, many novel materials are required to be deposited in the form of thin films, whose thickness should be precisely controlled with high precision. For the purpose, suitable means of film thickness metrology is demanded which should be able to provide feedback necessary for effective control of the manufacturing process of semiconductor devices (2). Recently, much attention is being paid to the development of in-line measurement tools for the sake of advanced process control (APC), especially for the CMP (chemical mechanical polishing) process. Information on the film thickness is important not only for assessing the polishing performance real time, but also for appropriate detection of the end point of the polishing process (3). The chip makers have generally utilized various measurement methods, such as scanning electron microscope (SEM), transmission electron microscope (TEM), atomic force microscope (AFM), stylus, X-ray fluorescence (XRF), reflectometer, ellipsometer, and sheet resistance measurement for the CMP process. Although the wafer under inspection should be destroyed, the instruments such as SEM, TEM, AFM, and XRF can be used effectively for the process development in the initial stage and/or for the precise analysis of any problem encountered in the later stage of process control. It is because these methods are available for