METHOD FOR DETERMINING A REGISTRATION ERROR

Abstract

The invention relates to a method for determining a registration error of a structure on a mask for semiconductor lithography, comprising the following method steps: generating an image of at least one region of the mask, determining at least one measuring contour in the image, and matching the forms of a design contour and a measuring contour to one another while at the same time matching the registration of the two contours.

Claims

1. A method for determining a registration error of a structure on a mask for semiconductor lithography, comprising the following method steps: generating an image of at least one region of the mask, determining at least one measuring contour in the image, and matching the forms of a design contour and a measuring contour to one another while at the same time matching the registration of the two contours.

2. The method of claim 1, wherein the registration is matched by minimizing the mean lateral distances of the two contours in the image plane.

3. The method of claim 1, wherein the matching of the forms and registration of the contours is brought about by a modification of the design contour.

4. The method of claim 1, wherein the matching of the forms and registration of the contours is brought about by a modification of the measuring contour.

5. The method of claim 1, wherein lateral distances between the measuring contour and the design contour are used as a measure of the quality of the matching.

6. The method of claim 5, wherein a method of optimization, in particular a multidimensional Newton method, is used for minimizing the lateral distances.

7. The method of claim 5, wherein the mean value of all the lateral distances is used as a measure of the progress made in the optimization.

8. The method of claim 1, wherein the matching is performed separately for individual subregions of the image.

9. The method of claim 1, wherein certain regions of the image are not used for the matching.

10. The method of claim 9, wherein the regions that are not used for the matching are regions in which defects have been detected.

11. The method of claim 1, wherein an alternating modification of the forms and the mean lateral distances is performed.

12. The method of claim 2, wherein the matching of the forms and registration of the contours is brought about by a modification of the design contour.

13. The method of claim 2, wherein the matching of the forms and registration of the contours is brought about by a modification of the measuring contour.

14. The method of claim 2, wherein lateral distances between the measuring contour and the design contour are used as a measure of the quality of the matching.

15. The method of claim 2, wherein the matching is performed separately for individual subregions of the image.

16. The method of claim 2, wherein certain regions of the image are not used for the matching.

17. The method of claim 2, wherein an alternating modification of the forms and the mean lateral distances is performed.

18. The method of claim 3, wherein the matching of the forms and registration of the contours is brought about by a modification of the measuring contour.

19. The method of claim 3, wherein lateral distances between the measuring contour and the design contour are used as a measure of the quality of the matching.

20. The method of claim 3, wherein the matching is performed separately for individual subregions of the image.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0025] Exemplary embodiments and variants of the invention are explained in more detail below on the basis of the drawing, in which:

[0026] FIG. 1 shows an exemplary representation of the initial situation,

[0027] FIG. 2 shows the exemplary development of parameters used for the matching,

[0028] FIG. 3 shows the result of the matching, and

[0029] FIG. 4 shows the result of the matching with a defective structure.

DETAILED DESCRIPTION

[0030] FIG. 1 shows an exemplary representation of the initial situation. The design contours are presented here by solid lines. The measuring contours are represented in FIG. 1 by dotted lines. The imaging used as a basis can be in particular an electron micrograph. The slight offset between the contours and a considerable deviation in the form of the contours themselves from one another can be seen well in FIG. 1. The aim in the evaluation of the example shown in FIG. 1 is therefore essentially that of determining the registration error, that is to say the offset of the measured contours with respect to the mask design. As already mentioned, one of the factors on which the accuracy in the determination of the registration error depends is the extent to which the measuring contour and the design contour deviate from one another. It is therefore important in the determination of the registration error to achieve matching between the design contour and the measuring contour that is as good as possible.

[0031] FIG. 2 shows the exemplary development of the parameters used for the matching of the forms and the mean lateral distances over 8 iteration steps. In this case, the upper 4 graphs represent parameters for the registration, known as registration parameters, whereas the graphs of the lower row, with the exception of the graph on the right, represent what are known as form parameters.

[0032] Specifically:

[0033] Registration Parameters:

[0034] 1. TranslationX: Displacement of the contours in the x direction (0th order)

[0035] 2. TranslationY: Displacement of the contours in the y direction (0th order)

[0036] 3. Scale: How the contour extends to scale about an origin (1st order)

[0037] 4. Rotation: Rotation of the contour about an origin (1st order) Other conceivable parameters for the optimization of the matching are the asymmetric scale and the asymmetric rotation, which are not used however in the example shown. Furthermore, the parameters of the first order can also be converted into ScaleX, ScaleY, Rotation X and Rotation Y.

[0038] In the example shown, the registration parameters mentioned were applied to the measuring contour. It is also conceivable to apply the registration parameters to the design contour; furthermore, combined application to the measuring contour and the design contour is also conceivable, but in the case of this variant it should be ensured that there are no undesired redundancies, and consequently an unwanted dependence of the parameters.

[0039] The form parameters (first 3 graphs of the lower row) serve for changing the form of the contours in order to match the appearance of the measuring contour and the design contour. For the variant shown, the form parameters described below were used (other form parameters are also conceivable):

[0040] 1. Sigma is the width of a Gaussian filter by means of which an object created from the design contour is filtered.

[0041] 2. Thresh is the function value of the Gaussian filtered object from which a new design contour is calculated.

[0042] 3. Bias is the value by which the design contour newly calculated in 2. is displaced in the normal direction.

[0043] The form parameters can also be applied either to the measuring contour or to the design contour (as in the example shown), or else in a combined or divided manner.

[0044] The 4th graph of the lower row shows the optimization criterion already mentioned above, MeanResid. It can be seen well in the figure that, as from the 3rd iteration, the value for MeanResid begins to stagnate; in this case, the matching can be ended.

[0045] In principle, it should be ensured that the optimization parameters are chosen linearly independently of one another and produce an effect on the signal. For example, there is no sense in wanting to determine a translation in the X direction if the image only contains lines running in the X direction.

[0046] FIG. 3 shows the result of the matching. The much improved superposing of the measuring contour and the design contour when using the optimized form and registration parameters can be seen well.

[0047] FIG. 4 shows the result of the matching with a defective structure; the area of the defect is represented in FIG. 4 by a dotted line. The considerable lateral deviation of the measured structure from the target structures can be seen well in FIG. 4. Such a defect would lead to considerable errors in the determination of the registration errors. It is therefore recommendable not to take regions with greatly deviating errors, as represented in the figure, into consideration in the matching.

[0048] In some examples, the determination of a registration error of a structure on a mask, the determination of at least one measuring contour in an image of at least one region of the mask, and the matching of the forms of a design contour and a measuring contour to one another while at the same time matching the registration of the two contours, and various computations and/or processing of data (e.g., image data and/or mask design data) described above can be implemented by one or more computers according to the principles described above. In some examples, the processing of data can be performed by one or more cloud computer servers. The one or more computers can include one or more data processors for processing data, one or more storage devices for storing data, such as one or more databases, and/or one or more computer programs including instructions that when executed by the one or more computers cause the one or more computers to carry out the processes. The computer can include one or more input devices, such as a keyboard, a mouse, a touchpad, and/or a voice command input module, and one or more output devices, such as a display, and/or an audio speaker. The computer can show graphical user interfaces on the display to assist the user.

[0049] In some implementations, the computer can include digital electronic circuitry, computer hardware, firmware, software, or any combination of the above. The features related to processing of data can be implemented in a computer program product tangibly embodied in an information carrier, e.g., in a machine-readable storage device, for execution by a programmable processor; and method steps can be performed by a programmable processor executing a program of instructions to perform functions of the described implementations by operating on input data and generating output. Alternatively or in addition, the program instructions can be encoded on a propagated signal that is an artificially generated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal, that is generated to encode information for transmission to suitable receiver apparatus for execution by a programmable processor.

[0050] The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit).

[0051] In some implementations, the operations associated with processing of data described in this document can be performed by one or more programmable processors executing one or more computer programs to perform the functions described in this document. A computer program can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment.

[0052] For example, the computer can be configured to be suitable for the execution of a computer program and can include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only storage area or a random access storage area or both. Elements of a computer include one or more processors for executing instructions and one or more storage area devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from, or transfer data to, or both, one or more machine-readable storage media, such as hard drives, magnetic disks, magneto-optical disks, or optical disks. Machine-readable storage media suitable for embodying computer program instructions and data include various forms of non-volatile storage area, including by way of example, semiconductor storage devices, e.g., EPROM, EEPROM, and flash storage devices; magnetic disks, e.g., internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM discs.

[0053] In some implementations, the processing of data described above can be implemented using software for execution on one or more mobile computing devices, one or more local computing devices, and/or one or more remote computing devices. For instance, the software forms procedures in one or more computer programs that execute on one or more programmed or programmable computer systems, either in the mobile computing devices, local computing devices, or remote computing systems (which may be of various architectures such as distributed, client/server, or grid), each including at least one processor, at least one data storage system (including volatile and non-volatile memory and/or storage elements), at least one wired or wireless input device or port, and at least one wired or wireless output device or port.

[0054] In some implementations, the software may be provided on a medium, such as a CD-ROM, DVD-ROM, or Blu-ray disc, readable by a general or special purpose programmable computer or delivered (encoded in a propagated signal) over a network to the computer where it is executed. The functions may be performed on a special purpose computer, or using special-purpose hardware, such as coprocessors. The software may be implemented in a distributed manner in which different parts of the computation specified by the software are performed by different computers. Each such computer program is preferably stored on or downloaded to a storage media or device (e.g., solid state memory or media, or magnetic or optical media) readable by a general or special purpose programmable computer, for configuring and operating the computer when the storage media or device is read by the computer system to perform the procedures described herein. The inventive system may also be considered to be implemented as a computer-readable storage medium, configured with a computer program, where the storage medium so configured causes a computer system to operate in a specific and predefined manner to perform the functions described herein.

[0055] Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable sub combination. The separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments.