Radiant energy – Calibration or standardization methods
Reexamination Certificate
1999-09-09
2001-09-18
Nguyen, Kiet T. (Department: 2881)
Radiant energy
Calibration or standardization methods
C250S491100, C250S492200
Reexamination Certificate
active
06291819
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of calibrating an electron beam system for lithography in making patterns on a semiconductor wafer or in making a mask therefor. More specifically, the invention relates to a method of calibrating the electron beam system by using a standard grid and thereby improving the accuracy of XY placement on a stage of the electron beam system.
Electron beam systems, or electron beam tools, are used in lithographic processes called electron beam lithography, or e-beam lithography, to make masks for producing patterns on semiconductor wafers or to produce patterns directly on semiconductor wafers. The electron beam of an electron beam system is electrically and magnetically deflected by a computer-controlled deflection system in a known manner whereby the electron beam writes a desired pattern on a substrate to produce the mask or writes a desired pattern directly on a semiconductor wafer. All electron beam systems have inherent errors. As a result, distortions are present in the pattern written by the electron beam unless the electron beam system is calibrated to correct for such errors.
A known method of calibrating an electron beam system uses a two-dimensional standard grid and an algorithm for adjusting the computer-controlled deflection system for deviations of the electron beam from the standard grid due to the errors inherent in the electron beam system. This known method is a self-calibration method, which involves the use of an imperfectly constructed measurement gauge, or standard, and an imperfectly calibrated measuring or manufacturing machine to calibrate each other. A number of algorithms exist for self-calibration of electron beam systems through the use of metrology standards, such as standard grids, in two dimensions. Such algorithms are described in, for example,
Statistical Perspectives of Self
-
Calibration,
Raugh, M. R. et al., Proceedings of SPIE, Vol. 2725, pp. 114-121, April 1996;
Error Estimation for Lattice Methods of Stage Self
-
Calibration,
Raugh, M. R., Proceedings of SPIE, Vol. 3050, pp. 614-625, 1997;
Overlay Can Be Improved by Self
-
Calibrated XY Measuring Instrument: A Lattice Perspective,
Raugh, M. R., Proceedings of SPIE, Vol. 2884, pp. 379-391, July 1996; and
Obtaining a Physical Two
-
Dimensional Cartesian Reference,
Takac, M. T. et al., Journal of Vacuum Science Technology, B 15(6), pp. 2173-2176, November/December 1997.
All metrology or calibration standards have their own built-in errors. These errors must be characterized so that their effects can be compensated in calibration methods. Typically, a two-dimensional grid is physically rotated so that errors due to its orthogonality and symmetry can be nulled. Thus, one requirement of all of the methods using metrology standards is that the standard to be calibrated, such as a standard grid, must be able to undergo both translation and rotation during the calibration process. However, standard grids for an electron beam system must be fixed inside the system, and the freedom to both translate and rotate the standard grid is not usually available due to, for example, mounting requirements. Furthermore, even when the freedom is available, a very precise mechanical function is required.
SUMMARY OF THE INVENTION
By the present invention, a method of calibrating an electron beam system is provided which does not require physical rotation or translation of a standard grid to various presentations in the system. Instead, the method of the present invention uses multiple copies of the same standard grid in the various presentations. The method of the present invention characterizes errors that are common to all copies of the standard grid, such as those induced by equipment, for example, an electron beam system, in making a standard grid mask and those induced from the subsequent manufacturing steps for making the copies of the standard grid. The method of the present invention does not characterize errors that are not common to the copies of the standard grids, such as those caused by variations in the manufacturing process from one standard copy grid to the next. It assumes those errors are small compared to the errors that are common to all copies of the standard grid, which is typically true.
The method of the present invention makes use of a standard grid mask fabricated on an electron beam lithography system or tool to make a set of standard grids, standard grid copies that all share the same errors to a high degree of accuracy. The steps of the method include fabricating the standard grid mask using the electron beam lithography system, and then using the standard grid mask in a conventional manner, such as in a conventional stepper, to make standard grids. The same stepper and the same subset of stepper optics are used for making each standard grid, so that a set of standard grids is obtained in which each standard grid contains identical mask and stepper errors. In order to calibrate an electron beam system, several of the identical standard grids are installed in the electron beam system in different presentations and are treated as different presentations of the same grid for the purposes of applying known algorithms, such as those described in the publications mentioned earlier herein.
REFERENCES:
patent: 3644700 (1972-02-01), Kruppa et al.
patent: 3874916 (1975-04-01), Livesay et al.
patent: 4390788 (1983-06-01), Hayashi et al.
patent: 4467211 (1984-08-01), Smith et al.
patent: 4728799 (1988-03-01), Gordon et al.
patent: 4737646 (1988-04-01), King et al.
patent: 5043586 (1991-08-01), Giuffre et al.
patent: 5301124 (1994-04-01), Chan et al.
patent: 5315123 (1994-05-01), Itoh et al.
Raugh, “Error estimation for lattice methods of stage self-calibration,” Mar. 1997, Proceedings of SPIE, vol. 3050, pp. 614-625.
Raugh, “Overlay Can Be Improved By Self-Calibrated XY Measuring Instrument: A Lattice Perspective,” Sep. 1996, Proceedings of SPIE, vol. 2884, pp. 379-391.
Takac et al., “Obtaining a Physical Two-Dimensional Cartesian Reference,” Nov./Dec. 1997, J. Vac. Sci. Technol., pp. 2173-2176.
Raugh et al., “Statistical Perspectives of Self-Calibration,” Proceedings of SPIE, vol. 2725, pp. 114-121.
International Business Machines - Corporation
Nguyen Kiet T.
Petraske Eric W.
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