With the replacement of SiO2 by high-k Hf-based dielectrics in complementary metal–oxide–semiconductor technology, the measurement of the high-k oxide bandgap is a high priority. Spectroscopic ellipsometry (SE) is one of the methods to measure the bandgap, but it is prone to ambiguity because there are several methods that can be used to extract a bandgap value. This paper describes seven methods of determining the bandgap of HfO2 using SE. Five of these methods are based on direct data inversion (point-by-point fitting) combined with a linear extrapolation, while two of the methods involve a dispersion model-based bandgap extraction. The authors performed all of these methods on a single set of data from a 40 Å HfO2 film, as well as on data from 20 and 30 Å HfO2 films. It was observed that the bandgap values for the 40 Å film vary by 0.69 eV. In comparing these methods, the reasons for this variation are discussed. The authors also observed that, for each of these methods, there was a trend of increasing bandgap with decreasing film thickness, which is attributed to quantum confinement. Finally, the authors observed a greater variation in bandgap values among the methods for the 40 Å films than among the methods for the 30 and 20 Å films. This is attributed to the larger tail in the extinction coefficient k curve for the 40 Å film.
The design of the world's first production worthy broadband ultra-violet and visible small spot spectroscopic ellipsometer is described. The instrument, called the Prometrix® UV-125OSE, was developed by the Prometrix division of Tencor Instruments in cooperation with SOPRA S.A., a pioneer in the field of spectroscopic ellipsometry. It has the ability to measure both the thickness and refractive index of different layers on a wide variety of materials in multiple layer film stacks. In this paper the optical system will be reviewed and spot size data presented. We will further discuss some of the design considerations such as the angle of incidence and allowed spread of the collection beam. Data characterizing the precision and stability of the instrument is presented for a variety of films including SiO on silicon, and Si3N4 on silicon, and a multiple layer stack of SiO I poly-Si I SiO on silicon.
A method of imaging sub-0.5-µm-dense photoresist lines with the real-time scanning optical microscope by the use of elliptically polarized light is developed. The imaging method takes advantage of the fact that polarized light undergoes a change in polarization when reflected from a grating structure. A confocal scanning optical microscope is modified to image this light. The resulting images show an increase in the detected intensity of the light reflected from the substrate region of the grating. Increasing this signal level improves the ability of the microscope to make linewidth measurements on photoresist structures as small as 0.3 µm. Results from several different semiconductor substrates are presented. A brief review of the grating theory is presented to suggest possible origins for the increase in light intensity.
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