High resolution monitoring of CD variations
An optical metrology method is disclosed for evaluating the uniformity of characteristics within a semiconductor region having repeating features such a memory die. The method includes obtaining measurements with a probe laser beam having a spot size on the order of micron. These measurements are compared to calibration information obtained from calibration measurements. The calibration information is derived by measuring calibration samples with the probe laser beam and at least one other technology having added information content. In the preferred embodiment, the other technology includes at least one of spectroscopic reflectometry or spectroscopic ellipsometry.
1. A method of generating a map of a test wafer illustrating the uniformity of a process comprising the steps of:
scanning the surface of a test wafer with a first laser probe beam, with the spot size of the first laser probe beam on the test wafer being on the order of one micron;
detecting the reflected first laser probe beam and generating first output signals;
comparing the first output signals to stored calibration information, said calibration information being generated by scanning a region on the surface of a calibration wafer with a second laser probe beam, with the spot size of the second laser probe beam on the calibration wafer being on the order of one micron and detecting the reflected second laser probe beam and generating second output signals and by directing a broadband probe beam to said region on the calibration wafer, with the spot size of the broadband probe beam on the wafer being larger than the spot size of the laser probe beam and detecting the reflected broadband probe beam and generating third output signals as a function of wavelength and analyzing the characteristics of the calibration wafer based on the third output signals and correlating the results of the analysis with the second output signals; and
generating a two dimensional map of variations in the characteristics of the test wafer based on the comparison of the first output signals to the calibration information.
2. A method as recited in claim 1 , wherein the spot size of the broadband probe beam on the calibration wafer is on the order of 15 microns.
3. A method as recited in claim 1 , wherein the first and second output signals contain information corresponding to multiple angles of incidence.
4. A method as recited in claim 1 , wherein said broadband probe beam is directed to the calibration wafer at normal incidence and the third output signals correspond to normal incidence spectroscopic measurements.
5. A method as recited in claim 1 , wherein said broadband probe beam is directed to the calibration wafer at a non-normal angle of incidence and the third output signals correspond to off-axis spectroscopic ellipsometry measurements.
6. A method as recited in claim 1 , wherein the calibration information is generated using a neural network.
7. A method as recited in claim 1 , wherein the first and second laser probe beams are generated by the same laser.