Method for three-dimensionally measuring a 3D aerial image of a lithography mask

• US 10,634,886 B2
• Filed: 07/27/2018
• Issued: 04/28/2020
• Est. Priority Date: 07/22/2014
• Status: Active Grant

• Current Assignee: CARL Zeiss SMT GmbH (Carl-Zeiss-Stiftung)
• Original Assignee: CARL Zeiss SMT GmbH (Carl-Zeiss-Stiftung)
• Inventors: Matejka, Ulrich, Husemann, Christoph, Ruoff, Johannes, Perlitz, Sascha, Mann, Hans-Jurgen
• Primary Examiner(s): Liu, Li
• Application Number:
  US16/047,324
• Publication Number:
  US 20180357758A1
• Time in Patent Office: 641 Days
• CPC Class Codes: G02B 13/08 Anamorphotic objectives
• CPC Class Codes: G02B 17/0647 using more than three curved mirrors G02B17/0668, G02B17/0694 take precedence
• CPC Class Codes: G02B 17/0828 off-axis or unobscured systems in which all of the mirrors share a common axis of rotational symmetry
• CPC Class Codes: G02B 17/0848 off-axis or unobscured systems in which not all of the mirrors share a common axis of rotational symmetry, e.g. at least one of the mirrors is warped, tilted or decentered with respect to the other elements
• CPC Class Codes: G02B 21/04 involving mirrors
• CPC Class Codes: G02B 21/361 Optical details, e.g. image relay to the camera or image sensor G02B21/364 takes precedence; illumination details G02B21/06 and subgroups
• CPC Class Codes: G02B 27/0988 Diaphragms, spatial filters, masks for removing or filtering a part of the beam
• CPC Class Codes: G02B 5/005 Diaphragms for cameras G03B9/02
• CPC Class Codes: G03F 1/84 Inspecting
• CPC Class Codes: G21K 7/00 Gamma- or X-ray microscopes

Abstract

In a method for three-dimensionally measuring a 3D aerial image in the region around an image plane during the imaging of a lithography mask, which is arranged in an object plane, a selectable imaging scale ratio in mutually perpendicular directions (x, y) is taken into account. For this purpose, an electromagnetic wavefront of imaging light is reconstructed after interaction thereof with the lithography mask. An influencing variable that corresponds to the imaging scale ratio is included. Finally, the 3D aerial image measured with the inclusion of the influencing variable is output. This results in a measuring method with which lithography masks that are optimized for being used with an anamorphic projection optical unit during projection exposure can also be measured.

Claims

1. A method for three-dimensionally measuring a 3D aerial image in the region around an image plane during the imaging of a lithography mask, which is arranged in an object plane, while taking into account a selectable imaging scale ratio in mutually perpendicular directions with the following steps:

performing a manipulation of a pupil of an imaging optical unit used for the imagining of the lithography mask,

inclusion of an influencing variable in the imaging of the lithography mask, in which the influencing variable corresponds to the imaging scale ratio,

performing a digital simulation step using information from the pupil manipulation step and from the inclusion step to generate a 3D aerial image, and

output of the 3D aerial image measured with the inclusion of the influencing variable.

2. The method according the claim 1, wherein the measurement is carried out with a measuring optical unit, the imaging scale of which is the same in mutually perpendicular directions, the inclusion of the influencing variable being performed by converting the data of a measured 2D imaging-light intensity distribution in the region of a plane corresponding to the image plane.

3. The method according to claim 1, wherein the inclusion of the influencing variable corresponding to the imaging scale ratio is performed by a digital simulation of the imaging with the imaging scale ratio.

4. A metrology system for three-dimensionally measuring a 3D aerial image in the region around an image plane during the imaging of a lithography mask, which is arranged in an object plane, in which the metrology system is configured to take into account a selectable imaging scale ratio in mutually perpendicular directions with the following steps:

performing a manipulation of a pupil of an imaging optical unit used for the imagining of the lithography mask,

inclusion of an influencing variable in the imaging of the lithography mask, in which the influencing variable corresponds to the imaging scale ratio,

performing a digital simulation step using information from the pupil manipulation step and from the inclusion step to generate a 3D aerial image, and

output of the 3D aerial image measured with the inclusion of the influencing variable;

wherein the metrology system comprises;

an illumination optical unit for illuminating the lithography mask to be examined, and

an imaging optical unit for imaging the object towards a spatially resolving detection device.

5. The metrology system of claim 4, in which the metrology system is configured to carry out the following steps to prepare the output of the 3D aerial image:

measuring a 2D imaging-light intensity distribution in the region of a plane corresponding to the image plane,

displacing the lithography mask perpendicularly to the object plane by a predetermined displacement, and

repeating the “

measuring” and

“

displacing”

steps until a sufficient number of 2D imaging-light intensity distributions to reproduce a 3D aerial image are measured.

6. The metrology system of claim 5, comprising a measuring optical unit configured to carry out the measurement, the imaging scale of which is the same in mutually perpendicular directions, the inclusion of the influencing variable being performed by converting the data of the measured 2D imaging-light intensity distribution.