A method for inspecting a lens deformation defect of a lithography machine by using a test reticle

Abstract

The application discloses a method for checking lens deformation defects of a photoetching machine by using a test mask, and relates to the technical field of photoetching machine maintenance and calibration. The test mask is additionally provided with six groups of alignment marks, and a total of eight groups of alignment marks can be used to realize 90 degrees and 180 degrees rotation of the test mask. The test mask is used to expose a wafer twice at 0 degrees and 90 degrees, and the positions of the two times of exposure are analyzed. If the positions are relatively same, the test mask itself has defects, and the lens defects are excluded. If the positions of the two times of exposure are different, the lens deformation is considered.

Description

Technical Field

[0001] This invention relates to the field of lithography machine technology, specifically to a lithography machine maintenance and calibration technology. Background Technology

[0002] A lithography machine is a key piece of equipment used to manufacture integrated circuits and other micro- and nano-sized devices. It uses optical technology to transfer chip design patterns onto photoresist or a photolithographic film, and then uses chemical or physical methods to transfer the patterns onto the chip surface to form a fine circuit structure.

[0003] The lens system is a crucial component of a photolithography machine. Its primary function is to focus the light beam generated by the light source onto the photoresist surface to form the desired pattern. After a period of use, the lens may become distorted, leading to image distortion and requiring inspection and calibration. Current calibration methods utilize a test mask to expose the wafer. The test mask, for example... Figure 1 As shown, the installation of the mask onto the stage is achieved through alignment marks. Abnormal data from the exposed pattern is then analyzed to determine if the lens is distorted. However, if the test mask itself has a problem, it may cause pattern distortion, affecting the analysis results. Furthermore, there is only one set of alignment marks; if the mask is rotated, alignment cannot be performed. Summary of the Invention

[0004] The purpose of this invention is to provide a method for overhauling and calibrating a lithography machine lens system, eliminating the influence of defects in the test mask itself.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for inspecting lens deformation defects in a lithography machine using a test mask.

[0007] The test mask includes a border, within which a graphic area is provided. At least four alignment mark sets are provided on the border. The alignment mark sets are used to test the alignment between the test mask and the mask support platform. The alignment marks in each alignment mark set have a mirror-symmetric structure, with the axis of symmetry passing through the center of the test mask. Adjacent alignment mark sets can overlap after rotating 90° or 270° around the center of the mask.

[0008] The inspection method is as follows:

[0009] Step 1: Install the test mask on the mask-bearing stage and use the alignment mark set to align and position the two.

[0010] Step 2: After alignment, the wafer to be inspected is exposed using the lens to be inspected and the test mask, and the position of the distortion and deformation of the pattern on the wafer is recorded.

[0011] Step 3: Rotate the test mask by 90° or 270° and align and position the two again using the alignment mark set;

[0012] Step 4: After alignment, expose again and record the location of the distortion and deformation of the pattern on the wafer.

[0013] Step 5: Analyze the distortion positions of the two exposures. If the positions are relatively the same, it indicates a defect in the test mask itself, ruling out a lens defect. If the distortion positions are different, consider the lens deformation problem.

[0014] Furthermore, there are four alignment mark sets, each set including two alignment marks. The two alignment marks within each set are mirror-symmetric, with the axis of symmetry passing through the center of the test mask. Each set of alignment marks matches the alignment marks on the mask stage.

[0015] Furthermore, after the first exposure is completed, the wafer stage moves the wafer to bring the next area into the exposure field for a second exposure.

[0016] Furthermore, a scanning electron microscope is used to measure the shape and actual size of the exposed pattern and compare it with the design pattern; if the measurement results deviate significantly from the design requirements, it is determined that the pattern is distorted. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of a test mask for existing technology;

[0018] Figure 2 This is a schematic diagram of the structure of the test mask of the present invention;

[0019] Figure 3 This is a comparison image of the pattern shape from two separate exposures;

[0020] Figure 4 This is a comparison image of the pattern shape from two separate exposures. Detailed Implementation

[0021] The test mask used in this invention is as follows: Figure 2 As shown, the image includes a border, which primarily serves a fixing function. A graphic area is set within the border to generate the pattern after exposure. Four sets of alignment marks are located on the border or the outer edge of the graphic area. These alignment marks are used to test the alignment between the photomask and the photomask stage. The alignment marks on a lithography machine photomask typically use combinations of the following shapes:

[0022] Cross-shaped alignment mark: The cross-shaped alignment mark is the most common shape, consisting of two perpendicularly intersecting lines.

[0023] T-shaped alignment mark: The T-shaped alignment mark is also a common shape, consisting of a vertical line and a horizontal line.

[0024] Circular alignment mark: A circular alignment mark is a circular shape.

[0025] Each alignment mark set includes two sets of alignment marks, which are mirror-symmetric with their axis of symmetry passing through the center of the test mask. Each set of alignment marks matches the alignment marks on the mask support platform. Adjacent alignment mark sets coincide after rotating 90° or 270° around the center of the mask. The test mask of this invention has a total of 8 alignment marks, enabling 90° and 180° rotation of the mask.

[0026] The method for determining the distortion of a lens system is as follows:

[0027] Step 1: Install the test mask onto the mask stage and use the alignment mark set to align and position the two. After the test mask is installed, it needs to be aligned with the wafer again.

[0028] Step two: After alignment, the wafer is exposed using the lens to be inspected and the test mask, and the location of any distortion or deformation of the pattern on the wafer is recorded. After exposure, the wafer stage can move one step to allow the next area of ​​the wafer to enter the exposure field for a second exposure. Two exposures can also be performed between adjacent layers of the wafer.

[0029] Step 3: Rotate the test mask by 90° or 270° and align and position the two again using the alignment mark set;

[0030] Step 4: After alignment, expose again and record the location of the distortion and deformation of the pattern on the wafer.

[0031] Step 5: Analyze the distortion positions on the pattern after the two exposures. If the positions are relatively the same, the distortion positions will rotate accordingly with the pattern. Figure 3 The image shows a test of the mask itself to rule out lens defects; if the distortion location is different, the distortion location does not rotate with the mask.

[0032] As Figure 4 As shown, we need to consider the lens distortion problem.

[0033] To address distortion in the lens system, a scanning electron microscope can be used to measure the shape and actual size of the exposed pattern and compare it with the design pattern. If the measurement results deviate significantly from the design requirements, it is determined that the pattern is distorted.

[0034] This invention enables the test mask to be rotated and aligned by adding alignment marks to the test mask. By comparing and analyzing two measurements at 0° and 90°, the influence of the mask itself can be eliminated, thus accurately determining the defects of the lens system.

Claims

1. A method for inspecting lens deformation defects in a lithography machine using a test mask. The test mask includes a border, within which a graphic area is provided. At least four alignment mark sets are provided on the border. The alignment mark sets are used to test the alignment between the test mask and the mask support platform. The alignment marks in each alignment mark set have a mirror symmetric structure, with the axis of symmetry passing through the center of the test mask. Adjacent alignment mark sets can coincide after rotating 90° or 270° around the center of the mask. The inspection method is as follows: Step 1: Install the test mask on the mask support stage and use the alignment mark set to align and position the two. Step 2: After alignment, the wafer to be inspected is exposed using the lens to be inspected and the test mask, and the position of the distortion and deformation of the pattern on the wafer is recorded. Step 3: Rotate the test mask by 90° or 270° and align and position the two again using the alignment mark set; Step 4: After alignment, expose again and record the location of the distortion and deformation of the pattern on the wafer. Step 5: Analyze the distortion positions of the two exposures. If the positions are relatively the same, it indicates a defect in the test mask itself, thus ruling out a lens defect. If the location of the distortion is different, then lens deformation should be considered.

2. The method for inspecting lens deformation defects in a lithography machine using a test mask according to claim 1, characterized in that: There are four alignment mark sets. Each alignment mark set includes two sets of alignment marks. The two sets of alignment marks in the alignment mark set are mirror symmetric, and the axis of symmetry passes through the center of the test mask. Each set of alignment marks matches the alignment marks on the mask stage.

3. The method for inspecting lens deformation defects in a lithography machine using a test mask according to claim 1 or 2, characterized in that: After the first exposure, the wafer stage moves the wafer to bring the next area into the exposure field for a second exposure.

4. The method for inspecting lens deformation defects in a lithography machine using a test mask according to claim 1, characterized in that: A scanning electron microscope is used to measure the shape and actual size of the exposed pattern and compare it with the design pattern; if the measurement results deviate significantly from the design requirements, it is determined that the pattern is distorted.

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