Monitoring temperature and sample characteristics using a rotating compensator ellipsometer

#The subject invention relates to evaluating samples using a rotating compensator ellipsometer. More specifically, the rotating compensator ellipsometer is utilized to monitor simultaneously and independently sample characteristics, in particular temperature and oxide thickness.

#There is considerable interest in the semiconductor industry in optically monitoring wafers during the fabrication process. Various metrology tools have been developed to characterize thin film layers formed on silicon substrates. Parameters of particular interest include thin film thickness, index of refraction and extinction coefficient.

#Recently, a need has developed for measuring very thin gate dielectrics. These gate dielectric layers are typically only about 20 angstroms thick. In order to measure these layers accurately, very stable and repeatable systems are necessary.

#FIG. 1 is a schematic diagram of a rotating compensator ellipsometer.

#FIGS. 2a and 2b are graphs illustrating the variation of the sine and cosine 4ω signals with temperature.

#FIG. 3a is a graph illustrating the variation of the sin 2ω signal with temperature.

#Referring to FIG. 1, there is illustrated a rotating compensator ellipsometer 10 shown in position to measure characteristics of a sample 12. The sample 12 consists of a substrate 14 such as silicon. One or more thin films 16 are formed on the upper surface of the substrate.

#The ellipsometer 10 includes a light source 20 for emitting a probe beam of radiation 22. In one preferred embodiment, light source 20 is a helium neon laser emitting a monochromatic beam at 633 nm. The advantage to a helium neon laser is that it generates a collimated beam of light of a known fixed wavelength which, in an ellipsometer configuration, substantially minimizes alignment, calibration, and measurement problems. It should be noted, however, the subject invention can be implemented with other light sources, including solid state lasers or laser diodes. It should also be noted that one advantage of this approach is that light in the visible region (greater than about 450 nm) can be used successfully to perform the measurements.

#In addition, a polychromatic light source could be used with a monochrometer for scanning the wavelength. Alternatively, all wavelengths from the broadband source could be detected simultaneously as disclosed in U.S. Pat. No. 5,877,859, assigned to the same assignee herein and incorporated by reference.