WO2019096574A1

WO2019096574A1 - Method and device for mask inspection

Info

Publication number: WO2019096574A1
Application number: PCT/EP2018/079619
Authority: WO
Inventors: Jörg Frederik Blumrich
Original assignee: Carl Zeiss Smt Gmbh
Priority date: 2017-11-17
Filing date: 2018-10-30
Publication date: 2019-05-23
Also published as: DE102017127117A1

Abstract

The invention relates to a method and a device for mask inspection, for inspecting a mask for use in lithography, the method comprising the following steps: identifying at least one region at which the line width of structures present on the mask (110, 210, 310, 410, 510) deviates from a mean line width according to a qualitative estimation; and quantitively determining said deviations by measuring the line width in the at least one identified region; wherein the identification of the at least one region is based on measurements of the intensity of electromagnetic radiation after the diffraction of said radiation on the mask, and the mask (110, 210, 310, 410, 510) is illuminated with illumination light in a collimated beam path during these intensity measurements.

Description

Method and device for mask inspection

The present application claims priority to German Patent Application DE 10 2017 127 117.1, filed on 17 November 2017. The content of this DE application is incorporated by reference into the present application text by "incorporation by reference".

BACKGROUND OF THE INVENTION

Field of the invention

The invention relates to a method and a device for mask inspection.

State of the art

The inspection of masks for use in lithography is of great importance inasmuch as any defects present on the mask can result in possibly greater production of components being unusable. A special challenge here is the mask inspection of masks with comparatively large dimensions, as used, for example, in the manufacture of flat screens or the lithographic production of the printed conductors, controls, etc. required in such flat screens. With regard to the dimensioning of such flat screens and the "copying systems" usually used for lithographic production (with a reproduction scale of 1: 1), the masks in question may have dimensions of the order of magnitude of one or more square meters. In order to identify mask defects in a reasonable time, in particular in the form of deviations of the line width of the structures present on the mask despite these comparatively large dimensions, it is known, taking advantage of the fact that such line width deviations to the human eye practiced on the Mask visible differences in brightness to perform a pre-inspection by a suitably trained person, wherein the identified areas then undergo an in-depth quantitative (eg electron microscopic) measurement of the line width.

In practice, however, the problem arises that the inspections carried out visually by employees are not readily reproducible and, moreover, are not feasible in situations in which suitable personnel trained to carry out such inspections are currently not available.

SUMMARY OF THE INVENTION

Against the above background, it is an object of the present invention to provide a method and apparatus for mask inspection which is also useful with masks of comparatively large dimensions, e.g. Masks for the lithographic production of flat screens, enabling a reliable and reproducible inspection within a reasonable time.

This object is achieved by the method according to the features of independent patent claim 1 and the device according to the features of independent patent claim 9.

An inventive method for mask inspection, for inspection of a mask for use in lithography, comprises the following steps: Identifying at least one region for which, according to a qualitative estimation, deviations of the line width of structures present on the mask from a mean line width exist; and

Quantitatively determining these deviations by measuring the linewidth in the at least one identified region;

wherein the identification of the at least one region is based on measurements of the intensity of electromagnetic radiation after its diffraction on the mask, wherein the mask is illuminated with illumination light in a collimated beam path during these intensity measurements.

In particular, the invention is based on the concept of carrying out a transmission measurement on the respective mask to be inspected with the aim of identifying regions with significant linewidth deviation not only at certain points, but under illumination of the relevant mask with a collimated beam path In this way, for a comparatively large mask area or even for the entire mask, an intensity measurement is simultaneously and simultaneously measured using a surface-measuring intensity sensor and thus a reproducible and large-scale qualitative assessment (with regard to whether and where deviations of the Line width in the structures available on the mask are to be expected) to perform.

By further exploiting the fact that intensity differences occurring in the obtained measurement result are proportional to deviations of the line width, areas of the mask can be identified in this way automatically, reproducibly and without dependence on certain trained operators, for which according to an initially qualitative evaluation. estimate deviations of the line width from a mean line width are to be expected. The areas quickly and reliably identified in this way can then be subjected to a quantitative measurement of the line width in a subsequent second step, which is known per se For example, can be done using electron microscopic or scatterometric method.

According to one embodiment, the measurements of the intensity of electromagnetic radiation are carried out after their diffraction on the mask such that electromagnetic radiation diffracted into higher diffraction orders than the zeroth diffraction order is at least partially, in particular completely, eliminated from the component contributing to the intensity measurement.

In one embodiment, this elimination is done using at least one aperture.

According to one embodiment, the intensity measurements are performed with a flat-measuring intensity sensor.

According to one embodiment, the electromagnetic radiation is projected onto the surface-measuring intensity sensor via a magnifying optical system.

According to one embodiment, the electromagnetic radiation is projected onto the surface-measuring intensity sensor via a reduction optics.

According to one embodiment, the electromagnetic radiation has a wavelength of at least 13 nm (for example EUV radiation having a wavelength of approximately 13.5 nm), in particular of at least 190 nm (for example DUV radiation of an ArF laser having a wavelength of approximately 193 nm) in particular of at least 360 nm (eg light of the i-line with a wavelength of about 365 nm). In particular, broadband electromagnetic radiation of which the wavelength is e.g. may include the visible spectral range.

In one embodiment, the mask is designed for use in the manufacture of flat panel displays. The invention further relates to a device for mask inspection, for inspection of a mask for use in lithography, the device being designed to perform a method with the features described above. For advantages and preferred embodiments of the device, reference is made to the statements in connection with the inventive method.

Further embodiments of the invention are described in the description and the dependent claims.

The invention will be explained in more detail with reference to embodiments shown in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Show it:

Figure 1-2 are schematic representations for explaining the underlying principle of the present invention; and

3-5 are schematic diagrams for explaining further possible embodiments of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following, the principle underlying the invention is first explained with reference to FIGS. 1 and 2, whereupon further possible embodiments of the invention will be described with reference to FIGS. 3-5. The embodiments of the invention have in common that a mask inspection, in particular for the examination of masks with comparatively large dimensions (such as, for example, for the lithographic production of flat screens), carries out a two-stage inspection insofar as areas are first identified in a first step for which deviations of the line width of structures present on the mask from a mean line width are to be expected. In a subsequent second step, a quantitative determination of the relevant deviations by actual measurement of the line width is then carried out only in the relevant areas identified in the first step.

It is further common to the embodiments of the invention that, for said identification of the regions in the first step, illumination of the mask with illumination light is carried out in a collimated beam path (i.e., with at least one beam of mutually parallel beams). The intensity of the electromagnetic radiation correspondingly diffracted at the mask is then measured by means of a surface-measuring intensity sensor, conclusions being drawn from changes in intensity which are ascertained on line width changes of the structures present on the mask.

1 shows, in a merely schematic representation, a mask 110 to be inspected with structures located on the mask, wherein the electromagnetic radiation generated by a light source 101 is illuminated in a collimated beam path after appropriate shaping by optics symbolized by a lens 105 for illuminating the mask 110 the mask 110 strikes and corresponding directions in the different diffraction orders are diffracted at the structures located on the mask 110.

As also indicated schematically in FIG. 1, aperture 120 arranged in the beam path in the light propagation direction after mask 110 can be achieved by coupling out higher diffraction orders (in the example of the ± 1st order of diffraction) that only electromagnetic radiation the zeroth diffraction order impinges on a surface-measuring intensity sensor 130 (eg in the form of a CCD camera).

FIG. 2 merely schematically indicates a mask 210 which has regions 211, 212 with different values of the line width. Corresponding regions on the mask 210 with a line width deviating from the mean line width can now be identified by the intensity measurements described above in that - as also indicated in FIG. 2 - the respective line width changes are proportional to one the intensity measurements are determined intensity change.

It should be noted that the above-described identification of the areas concerned with deviations of the line width from the mean value is initially qualitative in that the actual value of the line width in this identification is not yet determined. Rather, it is sufficient for the identification of the relevant areas in the first step to determine in which areas deviations from the average line width on the mask and corresponding defects are to be expected. An exact measurement of the actual values of the line width is then required in the subsequent second step only for the relevant areas identified in the first step, so that a more precise and, if necessary, depending on an exact measurement of the line width over the entire mask Mask dimension unreasonable time expenditure is avoided.

Preferably, the pixel size of the areal intensity sensor 130 is selected such that its projection onto the mask 110 is greater than the mean linewidth of the repeating structures on the mask 110 by at least a factor 20, more particularly at least a factor of 100 in that an average intensity value is independent of the relative position between the intensity sensor 130 per pixel or intensity sensor element on the surface-measuring intensity sensor 130 and mask 110. For example, given a typical value of the average linewidth of the repeating structures on the mask 110 in the range of (1 -2) pm, the pixel size of the areal intensity sensor 130 may have a value of at least 100pm, thus achieving a plurality of pixels per pixel Lines contribute to the intensity measurement and thus it has no significant effect on the measurement result, whether the pixel edge concerned coincides with the edge or the center of a line on the mask 110.

FIG. 3 shows a further schematic representation of the structure described above, wherein associated geometric parameters are shown in particular for explaining advantageous embodiments of the diaphragm used for eliminating higher diffraction orders. In this case, components analogous or substantially functionally identical to those of FIG. 1 are designated by reference numerals increased by "200".

If, in accordance with FIG. 3, the wavelength of the electromagnetic radiation generated by the light source is denoted by l and the width of the scattering structure on the mask 310 is denoted by "d", then the scattering angle f is between 0. diffraction angle

Order and 1st diffraction order Syrup = - To reduce or minimize

tion of the diaphragm spacing b between the diaphragm 320 and the mask 310 or, for the realization of the largest possible angle of diffusion f, the wavelength l thus preferably has large values. For a width of the scattering structure on the mask 310 of 2 pm and a wavelength λ of 500 nm (corresponding to green light in the visible spectral range), a scattering angle f of approximately 14.5 ° results. For broadband light, the minimum aperture distance is determined by the smallest available wavelength.

In embodiments of the invention, as shown schematically in FIG. 4 or FIG. 5, a reduction optics or magnifying optics for the projection of the electromagnetic radiation diffracted on the mask onto the area-measuring intensity sensor can be used. In FIG. 4 or FIG. 5, analogous or essentially functionally identical to FIG. 1 again Components with reference numbers increased by "300" or "400". FIG. 4 shows the embodiment with a reduction optics (formed by lenses 440, 450). FIG. 5 shows the use of a magnifying optical system (formed by lenses 540, 550). By using such a reduction optics or magnifying optics, the simultaneously detectable measuring range can be made flexible, wherein in an extreme case with the aid of magnifying optics, the entire mask can be detected in a single measuring step. With the help of a reduction optics, however, the lateral resolution can be increased.

When using an enlargement or reduction optics according to FIG. 4 or FIG. 5, an aperture used between the mask and the first lens of the enlargement or reduction optics in the light propagation direction is arranged analogously to the previously described embodiments for the purpose of eliminating higher diffraction orders. In this way it can be avoided that higher diffraction orders are mapped onto the area-measuring intensity sensor 330. In order to ensure that only electromagnetic radiation of the zeroth (0th) order of diffraction impinges on the intensity sensor, the dimensions of the relevant diaphragm are to be selected such that on one side of the diaphragm just the zeroth (0th order of diffraction of a scattering structure of the Mask is transmitted while blocking the aperture on the opposite side already, the +1 -th (or -1 -th) diffraction order or eliminated. For the ratio of

S

Aperture s to the aperture distance b applies tan <p

Although the invention has also been described with reference to specific embodiments, numerous variations and alternative embodiments will be apparent to those skilled in the art, eg, by combining and / or replacing features of individual embodiments. Accordingly, it will be understood by those skilled in the art that such variations and alternative embodiments are encompassed by the present invention and scope the invention is limited only in the sense of the appended claims and their equivalents.

Claims

claims

1. A method for mask inspection, for the inspection of a mask for use in lithography, the method comprising the following steps: a) identifying at least one region for which, according to qualitative estimation, deviations of the line width from on the mask (110, 210 , 310, 410, 510) existing structures of a mean line width; and

b) quantifying said deviations by measuring the linewidth in said at least one identified region; wherein in step a) the at least one region is identified on the basis of measurements of the intensity of electromagnetic radiation after its diffraction at the mask, wherein the mask (110, 210, 310, 410, 510) in these intensity measurements with illumination light in a collimated beam path is illuminated.

2. Method according to claim 1, characterized in that the measurements of the intensity of electromagnetic radiation after its diffraction at the mask are carried out in such a way that electromagnetic radiation diffracted into higher diffraction orders than the zeroth diffraction order is at least partly, in particular completely, is eliminated from the contribution to the intensity measurement.

3. The method according to claim 2, characterized in that this Elimi- renieren using at least one aperture (120, 320) takes place.

4. The method according to any one of claims 1 to 3, characterized in that the intensity measurements with a surface-measuring intensity sensor (130, 330, 430, 530) are performed.

5. The method according to claim 4, characterized in that the electromagnetic radiation on the surface-measuring intensity sensor (530) is projected via a magnifying optics.

6. The method according to claim 4, characterized in that the electromagnetic radiation is projected onto the surface-measuring intensity sensor (430) via a reduction optics.

7. The method according to any one of the preceding claims, characterized in that the electromagnetic radiation has a wavelength of at least 13 nm, in particular of at least 190 nm, in particular of at least 360 nm.

8. The method according to any one of the preceding claims, characterized in that the mask (110, 210, 310, 410, 510) is designed for use in the manufacture of flat panel displays.

9. A device for mask inspection, for inspection of a mask for use in lithography, characterized in that the device is designed to perform a method according to any one of the preceding claims.