"Method of Calibrating a Lithographic Apparatus, Device Manufacturing Method and Associated Data Processing Apparatus and Computer Program Product" in Patent Application Approval Process
This patent application is assigned to Asml Netherlands B.v.
The following quote was obtained by the news editors from the background information supplied by the inventors: "A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., comprising part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the 'scanning'-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction.
"In order to monitor the lithographic process, one or more parameters of the patterned substrate, for example the overlay error between successive layers formed in or on it and/or critical line width in a developed metrology target, are typically measured. There are various techniques for making measurements of the microscopic structures formed in lithographic processes, including the use of a scanning electron microscope and/or other various specialized tools. A fast and non-invasive form of specialized inspection tool is a scatterometer in which a beam of radiation is directed onto a target on the surface of the substrate and a property of the scattered or reflected beam is measured. Providing a scatterometer or other metrology tool separate from the lithographic apparatus allows detailed measurements to be made in parallel with production."
In addition to the background information obtained for this patent application, VerticalNews journalists also obtained the inventors' summary information for this patent application: "In order to better control scanner functionality, a module can be used which automatically drives the system towards a pre-defined baseline each day. This scanner stability module retrieves standard measurements taken from a stability monitor substrate using a metrology tool. The monitor substrate had been previously exposed using a special patterning device containing one or more special scatterometry marks (or one or more other marks suitable for whatever other metrology tool is to be used). Using the monitor substrate and that day's measurements (and possibly the historical measurement data from one or more previous days), the scanner stability module determines how far the system has drifted from its baseline, and then calculates substrate-level overlay and focus correction sets. The lithography system then converts these correction sets into specific corrections for each exposure on subsequent production substrates.
"While the scanner stability module attends to stability of performance of a lithography tool over time, there remains generally a need to perform initial calibration of the tool when it is installed, and after any major interruption in operation. This calibration may reveal and correct many more detailed machine--specific characteristics of the apparatus and its various subsystems, which may also vary with different modes of operation. This more detailed calibration may be done by a conventional process using one or more specially manufactured reference substrates and associated exposure and measurement processes. After an interruption in operation, the calibration may need to be performed again. Interruption of production using these tools can be very costly.
"One example of such a stability monitoring process and various calibration methods are described in U.S. patent application publication no. US 2012/0008127. These methods go some way to reducing the throughput penalty of a calibration procedure and/or stability monitoring, and/or to reduce the cost of calibration materials used in such procedures. Some embodiments of the present invention integrate a stability monitoring process and a calibration process in such a manner that productivity is less disrupted.
"Calibration and monitoring methods of the type mentioned become ever more important, as product features reduce in size and further reduction of overlay error becomes ever more critical to maintaining productivity and quality in the manufactured devices. Each further reduction in overlay may involve new sources of error to be identified, measured and corrected, which implies ever more detailed measurement of the performance of a lithography tool in more and more different modes of operation. Even with the methods described in U.S. patent application publication no. US 2012/0008127, the desire for more detailed measurements and corrections may conflict with the desire to keep machines operating productively for the highest possible proportion of their working life.
"Accordingly, it is desirable, for example, to enable calibration of a lithographic apparatus with reduced loss of productivity. Embodiments of the present invention aim to enable more detailed calibration of lithographic apparatus, while maintaining productivity.
"In an aspect, there is provided a method of calibrating a lithographic apparatus, the method comprising:
"(a) supporting a calibration substrate in the lithographic apparatus using a substrate support, the calibration substrate carrying a set of first marks;
"(b) operating a patterning system to apply a pattern comprising a set of second marks onto the calibration substrate, each second mark overlying a first mark;
"© obtaining an overlay measurement on the basis of the overlying first and second marks; and
"(d) using the overlay measurement to calculate calibration data to correct an apparatus-specific deviation of the lithographic apparatus,
"wherein step (b) is repeated while the substrate remains supported by the substrate support so as to apply different sets of second marks while varying one or more operating parameters of the lithographic apparatus between applying the sets of second marks and including a shift between the different sets of second marks such that an overlay measurement of each set can be distinguished.
"By using this method, it is possible to calculate parameter-specific, apparatus-specific calibration data based on knowledge of the parameter variation used to form different measured marks. The parameter-specific calibration data can be used to enhance the correction of specific errors during patterning operations on product substrates. The shifting of the applied pattern in exemplary embodiments is sufficient so that the second marks of the pattern applied at different times from overlying one another. In general, the only requirement is to ensure that overlay measurements can be obtained that somehow distinguish the effects of the changed operating parameters.
"In some embodiments of the invention, the patterning and measuring for stability monitoring, of the type described in the introduction, can be performed as part of the repetitions in step (b). If desired, some or all of the measurements in step © can be performed on an apparatus separate from the lithographic apparatus being calibrated. Thus embodiments of the invention can be designed so as to implement both initial set-up and stability monitoring, with reduced interruption in processing throughput.
"An embodiment of the invention may be applied in different types of lithographic apparatus, whether optical or imprint, for example. In the example of an optical, scanning type apparatus, examples of parameters that may be varied between times include field size, field center, illumination mode, scan direction, step direction and/or alignment model. The parameter-specific, apparatus-specific calibration data may include interfield calibration data that defines one or more parameter-specific corrections to be applied across the substrate as a whole, and/or one or more parameter-specific intrafield corrections defining corrections to be applied within each field.
"In an aspect, there is provided a method of manufacturing a device wherein a lithographic apparatus is used to apply a device pattern to a device substrate, and wherein as a preliminary step the lithographic apparatus is calibrated by a method as described herein. In an embodiment of such a method, the lithographic apparatus may continue to operate to apply one or more device patterns to one or more device substrates, concurrently with performance of step © and/or (d) of the method described above, and after completion of step © and/or (d), one or more device patterns is applied to one or more further device substrates using the obtained calibration data.
"An embodiment of the invention may be implemented by suitable programming of an existing control system of a lithographic apparatus and/or associated equipment, and/or using a separate data processing apparatus.
"In an aspect, there is provided a data processing apparatus programmed to calculating parameter-specific, apparatus-specific calibration data for a lithographic apparatus in accordance with a method described herein, based on a set of overlay measurements and on knowledge of parameter variations used to form different measured marks. Such a data processing apparatus may be further programmed to cause the lithographic apparatus to perform step (b) of the method described above in accordance with a stored recipe that defines a sequence of repetitions of step (b) and associated parameter variations.
"In an aspect, there is provided a computer program product comprising instructions to causing a programmable data processing apparatus to perform a method as described herein or as a data processing apparatus as described herein.
"These and other features and advantages of embodiment of the present invention will be understood by the skilled reader from a consideration of the exemplary embodiments discussed below. Further features and advantages of embodiments of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. It is noted that the invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein.
BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES
"Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:
"FIG. 1 depicts a lithographic apparatus, according to an embodiment of the present invention;
"FIG. 2 depicts a lithographic cell or cluster including the apparatus of FIG. 1;
"FIG. 3 is a schematic diagram of a control mechanism in a lithographic process utilizing a scanner stability module;
"FIG. 4 illustrates a first set of calibration and stability monitoring processes using the scanner stability module of FIG. 3;
"FIG. 5 illustrates a second set of calibration and stability monitoring processes using the scanner stability module adapted and operated, in accordance with an embodiment of the present invention;
"FIG. 6 illustrates a reference substrate set being used in the method of FIG. 4;
"FIG. 7 illustrates a calibration substrate set being created and used in a modified calibration method according to an embodiment of the present invention;
"FIG. 8 illustrates multiple exposures and calculation of corrections in an example of the method of FIG. 7;
"FIG. 9 illustrates multiple exposures and calculation of corrections in a further example of the method of FIG. 7; and
"FIG. 10 is a view of a lithographic apparatus control unit controlling the apparatus and method, according to an embodiment of the present invention."
URL and more information on this patent application, see: SCHMITT-WEAVER,
Keywords for this news article include: Asml Netherlands B.v., Information Technology, Information and Data Processing.
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