Alignment device, photolithography machine and alignment method

Abstract

The present invention provides an alignment device, a photolithography machine and an alignment method. The illumination provided by the illumination unit is diffracted by a grating mark and generates diffracted light, and the diffracted light is divided into a third diffracted light with a second polarization direction and a fourth diffracted light with a first polarization direction by the light splitting unit. After the third diffracted light and the fourth diffracted light are transmitted through the first wave plate, they interfere in both the first polarization direction and the second polarization direction and generate interference light. Then, the light energy of the first polarized light and the second polarized light in the interference light is respectively obtained by a first detector and a second detector. When the grating mark is moved until the light energy respectively obtained by the first detector and the second detector reaches a preset value, the position of the grating mark is the alignment position. Therefore, the present invention can realize the interference of diffraction orders without using a self-reference interference prism, which is not only low in cost and easy to operate, but also has high alignment accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated circuit manufacturing, and in particular to an alignment device, a photolithography machine and an alignment method. Background Art

[0002] In the field of integrated circuit manufacturing technology, a photolithography machine can apply a mask pattern to a photosensitive film layer such as a photoresist on a silicon wafer (also called a substrate) to prepare the desired circuit structure. In order to accurately control the position of each photolithography on the silicon wafer, it is necessary to set photolithography alignment marks (usually grating marks) on the silicon wafer, and determine the position of the corresponding photolithography alignment marks on the silicon wafer by setting one or more corresponding alignment devices, thereby determining the alignment position of the silicon wafer.

[0003] Currently, commonly used alignment devices use self-referencing interference prisms to achieve interference of diffracted light, and then determine the position of grating marks on silicon wafers. However, alignment devices based on self-referencing interference prisms have some unavoidable defects. For example, self-referencing interference prisms use prism components that require special optical design and manufacturing, which have high processing indicators, are difficult to assemble and adjust, and require high costs; and self-referencing interference prisms are usually bulky, which will produce some negative effects such as low-bandwidth vibration modes, which will ultimately affect the alignment accuracy.

[0004] Therefore, a new alignment device and alignment method are needed to avoid the disadvantages of using a self-referencing interference prism, so as to reduce the alignment measurement cost and improve the alignment accuracy. Summary of the invention

[0005] An object of the present invention is to provide an alignment device, a photolithography machine and an alignment method to solve at least one of the problems of high alignment measurement cost and low alignment accuracy.

[0006] In order to solve the above technical problems, the present invention provides an alignment device, which comprises: an illumination unit, a spectroscopic unit and a detection unit; wherein:

[0007] The illumination unit is used to provide illumination;

[0008] The light splitting unit comprises a first polarization beam splitter prism, a first lens group and a second lens group; the light is diffracted by a grating mark to generate diffracted light, and the diffracted light is divided into a first diffracted light having a first polarization direction and a second diffracted light having a second polarization direction by the first polarization beam splitter prism; the first diffracted light is reflected by the first polarization beam splitter prism and then converted into a third diffracted light having a second polarization direction by the first lens group, and the third diffracted light is transmitted to the detection unit by the first polarization beam splitter prism; the second diffracted light is transmitted by the first polarization beam splitter prism and then converted into a fourth diffracted light having a first polarization direction by the second lens group, and the fourth diffracted light is reflected by the first polarization beam splitter prism to the detection unit;

[0009] The detection unit includes a first wave plate, a second polarization beam splitter, a first detector and a second detector; the third diffracted light and the fourth diffracted light change polarization directions after being transmitted through the first wave plate, so as to interfere in the first polarization direction and the second polarization direction respectively and form interference light; the interference light is divided into a first polarization light and a second polarization light through the second polarization beam splitter; the first detector acquires light energy of the first polarization light, and the second detector acquires light energy of the second polarization light;

[0010] When the grating mark is moved until the light energies respectively acquired by the first detector and the second detector reach preset values, the position of the grating mark is the alignment position.

[0011] Optionally, in the alignment device, the first polarization direction and the second polarization direction are perpendicular to each other.

[0012] Optionally, in the alignment device, the first polarized light has a first polarization direction, and the second polarized light has a second polarization direction.

[0013] Optionally, in the alignment device, the first lens group includes a second wave plate and a first isosceles right-angle prism; the second lens group includes a third wave plate and a second isosceles right-angle prism; wherein the two surfaces where the right-angle sides of the first isosceles right-angle prism and the second isosceles right-angle prism are located are coated with a reflective film;

[0014] After passing through the second wave plate, the first diffracted light enters the first isosceles right-angle prism, and is reflected by two surfaces of the right-angle sides of the first isosceles right-angle prism in sequence, and after passing through the second wave plate again, the polarization direction is changed to the second polarization direction to form the third diffracted light;

[0015] After passing through the third wave plate, the second diffracted light enters the second isosceles right-angle prism, and is reflected in turn by the two surfaces where the right-angle sides of the second isosceles right-angle prism are located. After passing through the third wave plate again, the polarization direction is changed to the first polarization direction to form the fourth diffracted light.

[0016] Optionally, in the alignment device, the second wave plate and the third wave plate are both half wave plates.

[0017] Optionally, in the alignment device, the light field of the third diffracted light is symmetrical about a first plane, and the light field of the fourth diffracted light is symmetrical about a second plane; wherein the first plane is the symmetry plane of the first isosceles right prism and is perpendicular to the plane where the corresponding hypotenuse is located; and the second plane is the symmetry plane of the second isosceles right prism and is perpendicular to the plane where the corresponding hypotenuse is located.

[0018] Optionally, in the alignment device, the second wave plate and the first isosceles right-angle prism can rotate synchronously along a first clockwise direction, and the third wave plate and the second isosceles right-angle prism can rotate synchronously along a second clockwise direction.

[0019] Optionally, in the alignment device, when the first clockwise direction is a clockwise direction, the second clockwise direction is a counterclockwise direction; or, when the first clockwise direction is a counterclockwise direction, the second clockwise direction is a clockwise direction.

[0020] Optionally, in the alignment device, when the first isosceles right-angle prism rotates by an angle θ along a first clockwise direction, the second wave plate synchronously rotates by an angle θ / 2, the second isosceles right-angle prism rotates by an angle θ along a second clockwise direction, and the third wave plate synchronously rotates by an angle θ / 2. At this time, the angle β between the fast axis directions of the second wave plate and / or the third wave plate relative to the first polarization direction and the rotation angle θ satisfy the following formula:

[0021] 4β+2θ=90°×(2k+1);

[0022] Wherein, k is an integer.

[0023] Optionally, in the alignment device, the first mirror group includes a fourth wave plate, a first plano-convex cylindrical mirror and a first reflector; the second mirror group includes a fifth wave plate, a second plano-convex cylindrical mirror and a second reflector; wherein,

[0024] The first diffracted light is first transmitted through the fourth wave plate, then sequentially transmitted through the first plano-convex cylindrical mirror and reflected by the first reflector, and then transmitted through the fourth wave plate again, and the polarization direction is changed to the second polarization direction, so as to form a third diffracted light;

[0025] The second diffracted light is first transmitted through the fifth wave plate, then transmitted through the second plano-convex cylindrical mirror and reflected by the second reflector in sequence, and then transmitted through the fifth wave plate again to change the polarization direction to the first polarization direction to form a fourth diffracted light.

[0026] Optionally, in the alignment device, the fourth wave plate and the fifth wave plate are both quarter wave plates.

[0027] Optionally, in the alignment device, the light field of the third diffracted light is symmetrical about a third plane, and the light field of the fourth diffracted light is symmetrical about a fourth plane; wherein the third plane is the symmetry plane of the first plano-convex cylindrical mirror and is perpendicular to the corresponding plane; and the fourth plane is the symmetry plane of the second plano-convex cylindrical mirror and is perpendicular to the corresponding plane.

[0028] Optionally, in the alignment device, the alignment device also includes a third reflector, a sixth wave plate and an objective lens; the light is reflected by the third reflector, vertically irradiated on the grating mark to diffract and generate diffracted light, and the diffracted light is converged by the objective lens and transmitted through the sixth wave plate so that the diffracted light enters the spectroscopic unit as 45-degree linear polarized light.

[0029] Optionally, in the alignment device, the sixth wave plate is a half wave plate.

[0030] Optionally, in the alignment device, the first wave plate is a half wave plate.

[0031] Based on the same inventive concept, the present invention also provides a lithography machine, which includes the alignment device.

[0032] Based on the same inventive concept, the present invention also provides an alignment method, comprising:

[0033] The illumination unit provides illumination;

[0034] The light is diffracted by the grating mark and generates diffracted light, and the diffracted light is divided into a first diffracted light with a first polarization direction and a second diffracted light with a second polarization direction by the first polarization beam splitter prism of the beam splitting unit; the first diffracted light is reflected by the first polarization beam splitter prism, and then converted into a third diffracted light with a second polarization direction by the first lens group, and the third diffracted light is transmitted to the detection unit by the first polarization beam splitter prism; the second diffracted light is transmitted by the first polarization beam splitter prism, and then converted into a fourth diffracted light with a first polarization direction by the second lens group, and the fourth diffracted light is reflected by the first polarization beam splitter prism to the detection unit;

[0035] The third diffracted light and the fourth diffracted light change polarization directions after being transmitted through the first wave plate in the detection unit, so as to interfere in the first polarization direction and the second polarization direction respectively and form interference light; the interference light is divided into the first polarization light and the second polarization light by the second polarization beam splitter prism; the first detector acquires light energy of the first polarization light, and the second detector acquires light energy of the second polarization light;

[0036] The workpiece stage is moved to drive the grating mark to move. When the light energies respectively acquired by the first detector and the second detector reach preset values, the position of the grating mark is the alignment position.

[0037] In summary, the present invention provides an alignment device, a photolithography machine and an alignment method. The alignment device includes: an illumination unit, a spectrometer unit and a detection unit. The illumination provided by the illumination unit is diffracted by a grating mark and generates diffracted light, and the diffracted light is divided into a first diffracted light with a first polarization direction and a second diffracted light with a second polarization direction by the first polarization splitter prism. After the first diffracted light is reflected by the first polarization splitter prism, it is converted into a third diffracted light with a second polarization direction by the first lens group, and the third diffracted light is transmitted to the detection unit by the first polarization splitter prism; after the second diffracted light is transmitted by the first polarization splitter prism, it is converted into a fourth diffracted light with a first polarization direction by the second lens group, and the fourth diffracted light is reflected to the detection unit by the first polarization splitter prism.

[0038] The third diffracted light and the fourth diffracted light change their polarization directions after being transmitted through the first wave plate, so as to interfere in the first polarization direction and the second polarization direction respectively and form interference light. The interference light is divided into the first polarization light and the second polarization light by the second polarization beam splitter prism. The first detector obtains the light energy of the first polarization light, and the second detector obtains the light energy of the second polarization light. When the grating mark is moved until the light energy obtained by the first detector and the second detector respectively reaches the preset value, the position of the grating mark is the alignment position. Therefore, the present invention uses a beam splitting unit to divide the diffracted light into the third diffracted light and the fourth diffracted light, and uses the first wave plate to achieve the interference of the two in the first polarization direction and the second polarization direction and generate interference light, and the first detector and the second detector respectively obtain the light energy of the first polarization light and the second polarization light in the interference light, without using a self-reference interference prism, to achieve interference of diffraction orders, and at the same time, it is also compatible with diffracted light with multiple arrangement directions. Not only is the cost low, the operation is simple, but also the alignment accuracy is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a schematic structural diagram of an alignment device in Embodiment 1 of the present invention;

[0040] Figure 2 is a schematic structural diagram of a light splitting unit in Embodiment 1 of the present invention;

[0041] Figure 3 is a schematic diagram of the optical path of the second diffracted light in the first embodiment of the present invention;

[0042] Figure 4 is a schematic structural diagram of a light splitting unit in Embodiment 1 of the present invention;

[0043] Figure 5 is a schematic diagram of the change of polarization direction in the first embodiment of the present invention;

[0044] Figure 6 It is a structural schematic diagram of the light splitting unit in the second embodiment of the present invention. DETAILED DESCRIPTION

[0045] The following is a further detailed description of an alignment device, a lithography machine and an alignment method proposed in the present invention in combination with the accompanying drawings and specific embodiments. According to the following description, the advantages and features of the present invention will become clearer. It should be noted that the accompanying drawings are all in a very simplified form and use non-precise proportions, which are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention. In addition, the structure shown in the accompanying drawings is often a part of the actual structure. In particular, the emphasis that each drawing needs to show is different, and sometimes different proportions are used.

[0046] <Example 1>

[0047] In order to solve the above technical problems, this embodiment provides an alignment device, see Figure 1-2 The alignment device comprises: an illumination unit 10, a light splitting unit 20 and a detection unit 30. The illumination unit 10 is used to provide illumination. The illumination unit 10 is a light emitter, which provides linearly polarized light.

[0048] The light splitting unit 20 includes a first polarization beam splitter prism PBS1, a first lens group 201 and a second lens group 202. The polarization beam splitter prism has the following characteristics: it reflects light in a first polarization direction and transmits light in a second polarization direction. The first polarization direction and the second polarization direction are perpendicular to each other. The light is diffracted by a grating mark M and generates diffracted light. Figure 2Wherein, abcd is the light field distribution of the diffracted light, and the ac direction is perpendicular to the bd direction. The diffracted light is divided into a first diffracted light having a first polarization direction and a second diffracted light having a second polarization direction by the first polarization beam splitter prism PBS1. After the first diffracted light is reflected by the first polarization beam splitter prism PBS1, it is converted into a third diffracted light having a second polarization direction by the first lens group 201, and the third diffracted light is transmitted to the detection unit 30 by the first polarization beam splitter prism PBS1. After the second diffracted light is transmitted by the first polarization beam splitter prism PBS1, it is converted into a fourth diffracted light having a first polarization direction by the second lens group 202, and the fourth diffracted light is reflected by the first polarization beam splitter prism PBS1 to the detection unit 30.

[0049] Wherein, the detection unit 30 includes a first wave plate 301, a second polarization beam splitter prism PBS2, a first detector PD1 and a second detector PD2. The first wave plate 301 is a half wave plate. After the third diffracted light and the fourth diffracted light are transmitted through the first wave plate 301, the polarization direction is changed to +45 degree polarization and\or -45 degree polarization, so that the two can interfere in the first polarization direction and the second polarization direction respectively, and form interference light. The interference light is divided into a first polarized light and a second polarized light by the second polarization beam splitter prism PBS2. The first polarized light has a first polarization direction, and the second polarized light has a second polarization direction. The first detector PD1 obtains the light energy of the first polarized light, and the second detector PD2 obtains the light energy of the second polarized light. When the grating mark M is moved to the point where the light energy obtained by the first detector PD1 and the second detector PD2 respectively reaches a preset value, the position of the grating mark M is the alignment position. Optionally, the first detector PD1 and the second detector PD2 are point energy detectors.

[0050] In addition, the alignment device further includes a third reflector 40, a sixth wave plate 60 and an objective lens 50. The light is reflected by the third reflector 40, irradiated vertically on the grating mark M to diffract, and generates diffracted light, and the diffracted light is converged by the objective lens 50, transmitted by the sixth wave plate 60, changes polarization direction, and then enters the light splitting unit 20. The sixth wave plate 60 is a half wave plate, so that the diffracted light enters the light splitting unit as 45-degree linear polarized light, and the light energies of the first diffracted light and the second diffracted light separated by the first polarization beam splitting prism PBS1 are equal, so as to reduce errors.

[0051] Therefore, the alignment device provided in this embodiment can achieve interference of diffraction orders without using a self-reference interference prism, which is not only low-cost and easy to operate, but also has high alignment accuracy.

[0052] For further information, see Figure 2 , the first lens group 201 includes a second wave plate 2011 and a first isosceles right angle prism 2012. The second lens group 202 includes a third wave plate 2021 and a second isosceles right angle prism 2022. Wherein, the two surfaces where the right angle sides of the first isosceles right angle prism 2012 and the second isosceles right angle prism 2022 are both coated with a reflective film. The second wave plate 2011 and the third wave plate 2021 are both half wave plates. Therefore, after the first diffracted light passes through the second wave plate 2011, it enters the first isosceles right angle prism 2012, and is reflected by the two surfaces where the right angle sides of the first isosceles right angle prism are located in sequence, and after passing through the second wave plate 2011 again, the polarization direction is changed to the second polarization direction to form the third diffracted light. After passing through the third wave plate 2021, the second diffracted light enters the second isosceles right-angle prism 2022, and is reflected in turn by the two surfaces where the right-angle sides of the second isosceles right-angle prism 2022 are located. After passing through the third wave plate 2021 again, the polarization direction is changed to the first polarization direction to form the fourth diffracted light.

[0053] Wherein, due to the reflection effect of the first isosceles right-angle prism 2012 and the second isosceles right-angle prism 2022, the light field of the third diffracted light is symmetrical about the first plane, and the light field of the fourth diffracted light is symmetrical about the second plane, so as to realize the positive and negative order interference of the third diffracted light and the fourth diffracted light in the subsequent light propagation. Wherein, the first plane is the symmetry plane of the first isosceles right-angle prism 2012, and is perpendicular to the plane where the corresponding hypotenuse is located. That is, the first isosceles right-angle prism 2012 can be divided into two equal planes of sub-isosceles right-angle prisms. The second plane is the symmetry plane of the second isosceles right-angle prism 2022, and is perpendicular to the plane where the corresponding hypotenuse is located. That is, the second isosceles right-angle prism 2022 can be divided into two equal planes of sub-isosceles right-angle prisms.

[0054] For details, please refer to Figure 3 , the light beam B1 and the light beam D1 in the second diffracted light are two light beams incident on the planes where the two right-angled sides of the second isosceles right-angle prism 2022 are located. The light beam B2 and the light beam D2 are the corresponding light beams B1 and D1 that are reflected by the planes where the two right-angled sides of the second isosceles right-angle prism 2022 are located. It can be seen that the light field formed by the emitted light beams is symmetrical to the plane where the axis ac is located. Figure 3is a top view of the optical path, so the plane where the axis ac is located is perpendicular to the plane of the second isosceles right-angle prism 2022, and passes through the intersection of the corresponding two right-angle sides. After the outgoing light beam is transmitted through the third wave plate 2021, the fourth diffracted light is formed. Then the light field of the fourth diffracted light is mirror-symmetrical. Similarly, the light field of the third diffracted light is also mirror-symmetrical. Therefore, after passing through the first wave plate 301, the positive and negative orders of the diffracted light can be sequentially coherent to obtain the corresponding interference light.

[0055] However, due to the design characteristics of the isosceles right-angle prism, diffracted light is irradiated on the edges of the isosceles right-angle prism. The diffracted light passing through the edges may have reflectivity error, reflection angle error, phase error and other problems, and its intensity, phase and propagation direction will be affected.

[0056] Therefore, in order to prevent the diffracted light from irradiating the edge of the isosceles right-angle prism, the second wave plate 2011 and the first isosceles right-angle prism 2012 can be synchronously rotated along the first clockwise direction, and the third wave plate 2021 and the second isosceles right-angle prism 2022 can be synchronously rotated along the second clockwise direction. Further, when the first clockwise direction is the clockwise direction, the second clockwise direction is the counterclockwise direction; or, when the first clockwise direction is the counterclockwise direction, the second clockwise direction is the clockwise direction.

[0057] See also Figure 4 When the first isosceles right-angle prism 2012 rotates by an angle θ along the first clockwise direction, the second wave plate 2011 rotates by an angle θ / 2 synchronously, the second isosceles right-angle prism 2022 rotates by an angle θ along the second clockwise direction, and the third wave plate 2021 rotates by an angle θ / 2 synchronously. The corresponding symmetry planes of the light fields of the third diffracted light and the fourth diffracted light also rotate accordingly. Figure 4 In the figure, br-dr indicates the symmetry plane of the third diffraction light field, and ar-cr indicates the symmetry plane of the fourth diffraction light field.

[0058] See also Figure 5, taking the second diffracted light as an example, where s is the first polarization direction, p is the second polarization direction, and f is the fast axis direction of the second wave plate or the third wave plate (i.e., half wave plate). The angle between the f and s directions is β, and ar-cr is a schematic diagram of the symmetry plane of the fourth diffracted light field. The second diffracted light with the second polarization direction p is changed to direction 1 by the third wave plate 2021, and then passes through the second isosceles right-angle prism 2022, and the polarization direction is changed to direction 2. At this time, it passes through the third wave plate 2021 again, and the polarization direction is changed to s. Taking θ=22.5° as an example, β=11.25°, the angle between direction 1 and direction s is β-(90°-β)=-67.5°, and the angle between direction 2 and direction s is (90+67.5°-θ)+(90-θ)=202.5°. After direction 2 passes through the third wave plate 2021, the polarization direction changes to β-(202.5°-β)=-180°, which is the s direction. Therefore, the value of β and the rotation angle θ satisfy the following formula:

[0059] 4β+2θ=90°×(2k+1);

[0060] Wherein, β is the angle β between the fast axis directions of the second wave plate 2011 and / or the third wave plate 2021 and the first polarization direction, and k is an arbitrary integer, which can be 1, 2, 3 or 4, etc.

[0061] Furthermore, when the rotation angle θ is 0 degrees, β takes the value of ±22.5° / ±67.5°, and it can be obtained that the rotation angle of the second wave plate 2011 and / or the third wave plate 2021 is half of the rotation angle θ, and the rotation direction is the same as the rotation direction of the first isosceles right-angle prism 2012 and / or the second isosceles right-angle prism 2022.

[0062] Therefore, after rotating a certain angle, the diffracted light can be prevented from irradiating the edges of the isosceles right-angle prism, thereby reducing the error and improving the accuracy.

[0063] Based on the same inventive concept, this embodiment also provides a lithography machine, which includes the alignment device.

[0064] Based on the same inventive concept, this embodiment also provides an alignment method, including:

[0065] Step 1: The lighting unit 10 provides lighting.

[0066] Step 2: The light is diffracted by the grating mark M and generates diffracted light, and the diffracted light is divided into a first diffracted light having a first polarization direction and a second diffracted light having a second polarization direction by the first polarization beam splitter prism PBS1 of the beam splitter unit 20. After the first diffracted light is reflected by the first polarization beam splitter prism PBS1, it is converted into a third diffracted light having a second polarization direction by the first lens group 201, and the third diffracted light is transmitted to the detection unit 30 by the first polarization beam splitter prism PBS1. After the second diffracted light is transmitted by the first polarization beam splitter prism PBS1, it is converted into a fourth diffracted light having a first polarization direction by the second lens group 202, and the fourth diffracted light is reflected by the first polarization beam splitter prism PBS1 to the detection unit 30.

[0067] Step 3: After the third diffracted light and the fourth diffracted light are transmitted through the first wave plate 301 in the detection unit 30, the polarization direction is changed to +45 degree polarization and\or -45 degree polarization, so that the two can interfere in the first polarization direction and the second polarization direction respectively and form interference light. The interference light is divided into the first polarization light and the second polarization light by the second polarization beam splitter prism PBS2. The first detector PD1 obtains the light energy of the first polarization light, and the second detector PD2 obtains the light energy of the second polarization light.

[0068] Step 4: Move the workpiece stage to drive the grating mark M to move. When the light energies respectively acquired by the first detector PD1 and the second detector PD2 reach preset values, the position of the grating mark M is the alignment position.

[0069] The relationship between the displacement x of the grating mark and the light energy I1 acquired by the first detector and the light energy I2 acquired by the second detector is as follows:

[0070]

[0071] Wherein, x is the displacement of the grating mark, and t is the period of the grating mark.

[0072] The following is a detailed description of the calculation process for obtaining the above formula:

[0073] See also Figure 1-2 , the diffraction order light field of the grating mark M is:

[0074]

[0075] Where n is the diffraction order, t is the period of the grating mark M, and x is the displacement of the grating mark M. Here we first assume that the amplitude is 1, the angle between the fast axis of the half-wave plate and the first polarization direction is 22.5 degrees, and take the +1 and -1 order diffracted light as examples.

[0076] The optical path of the diffracted light entering the detection unit 30 through the first lens group 201 is as follows:

[0077] The diffracted light passes through the objective lens 50, the sixth wave plate 60, the first polarization beam splitter prism PBS1, the second wave plate 2011, the first isosceles right angle prism 2012, the second wave plate 2011, the first polarization beam splitter prism PBS1, the first wave plate 301 and the second polarization beam splitter prism PBS2 in sequence.

[0078] Therefore, the light field of the first polarized light obtained by the first detector PD1 after passing through the first lens group 201 is:

[0079]

[0080] The light field of the second polarized light obtained by the second detector PD2 after passing through the first lens group 201 is:

[0081]

[0082] The optical path of the diffracted light entering the detection unit 30 through the second lens group 202 is as follows:

[0083] The diffracted light passes through the objective lens 50, the sixth wave plate 60, the first polarization beam splitter prism PBS1, the third wave plate 2021, the second isosceles right-angle prism 2022, the third wave plate 2021, the first polarization beam splitter prism PBS1, the first wave plate 301 and the second polarization beam splitter prism PBS2 in sequence.

[0084] Therefore, the light field of the first polarized light obtained by the first detector PD1 after passing through the second mirror group 202 is:

[0085]

[0086] The light field of the second polarized light obtained by the second detector PD2 after passing through the second mirror group 202 is:

[0087]

[0088] Where J is the Jones matrix of each optical device, E in is the incident light field (1, 0) of the diffracted light. (E +1 +E -1) represents the +1 and -1 order diffraction light fields along the diffraction distribution direction. Since the optical paths of the +1 and -1 order diffraction lights are equal, no additional optical path difference is generated. The subscripts 1 and 2 in the formula respectively represent the corresponding light beams in the first polarization direction and the second polarization direction.

[0089] Therefore, the light energy I1 of the first polarized light detected by the first detector PD1 and the light energy I2 of the second polarized light detected by the second detector PD2 are:

[0090]

[0091] Wherein, x is the displacement of the grating mark, and t is the period of the grating mark.

[0092] It can be seen that as the displacement of the grating mark M changes, the light energy also changes accordingly. When it reaches the peak, it is the desired alignment position.

[0093] <Example 2>

[0094] Since the first lens group and the second lens group are rotated in the first embodiment, the difficulty of the alignment operation is increased and errors are easily generated, so this embodiment provides an alignment device to avoid the disadvantages of the isosceles right-angle prism. This embodiment only introduces the light splitting unit, and please refer to the description of the first embodiment for other components, which will not be described here.

[0095] See also Figure 6 , the first mirror group 201 includes a fourth wave plate 2013, a first plano-convex cylindrical mirror 2014 and a first reflector 2015. The second mirror group 202 includes a fifth wave plate 2023, a second plano-convex cylindrical mirror 2024 and a second reflector 2025. In this embodiment, the first plano-convex cylindrical mirror 2014 and the first reflector 2015 are used to replace the first isosceles right-angle prism 2012 to achieve the same effect. The second plano-convex cylindrical mirror 2024 and the second reflector 2025 are used to replace the second isosceles right-angle prism 2022 to achieve the same effect. And by using the first plano-convex cylindrical mirror 2014 and the second plano-convex cylindrical mirror 2024, there will be no diffracted light distribution and edges, and the diffracted light arranged in various directions can be compatible, thereby improving the alignment accuracy.

[0096] Other optical paths can refer to the description in the first embodiment. The specific optical path in the light splitting unit is as follows: the diffracted light is divided into the first diffracted light and the second diffracted light after passing through the first polarization beam splitter prism PBS1. The first diffracted light is first transmitted through the fourth wave plate 2013, then sequentially transmitted through the first plano-convex cylindrical mirror 2014 and reflected by the first reflector 2015, and then transmitted through the fourth wave plate 2013 again, and the polarization direction is changed to the second polarization direction to form the third diffracted light.

[0097] The second diffracted light is first transmitted through the fifth wave plate 2023, then sequentially transmitted through the second plano-convex cylindrical mirror 2024 and reflected through the second reflector 2025, and then transmitted through the fifth wave plate 2023 again, and the polarization direction is changed to the first polarization direction to form the fourth diffracted light. The fourth wave plate 2013 and the fifth wave plate 2023 are both quarter wave plates.

[0098] Similarly, the light field of the third diffracted light is symmetrical about the third plane, and the light field of the fourth diffracted light is symmetrical about the fourth plane. The third plane is the symmetry plane of the first plano-convex cylindrical mirror 2014 and is perpendicular to the corresponding plane. The fourth plane is the symmetry plane of the second plano-convex cylindrical mirror 2024 and is perpendicular to the corresponding plane.

[0099] Therefore, the light splitting unit 20 provided in this embodiment can avoid the disadvantages brought by the isosceles right-angle prism, reduce the difficulty of operation, and improve the alignment accuracy.

[0100] In summary, in the alignment device, lithography machine and alignment method provided in each embodiment, the diffracted light is divided into the third diffracted light and the fourth diffracted light by using a spectroscopic unit, and the third diffracted light and the fourth diffracted light are mirror-symmetrical, so that the positive and negative diffraction orders do not overlap. Then, the polarization direction is changed to +45 degree polarization and\or -45 degree polarization through the first wave plate 301, so that the two can interfere in the first polarization direction and the second polarization direction respectively, and form interference light. The first detector PD1 and the second detector PD2 respectively obtain the light energy of the first polarized light and the second polarized light in the interference light, and the interference of the diffraction orders can be achieved without using a self-reference interference prism, which is not only low in cost and easy to operate, but also has high alignment accuracy.

[0101] The above description is only a description of the preferred embodiments of the present invention, and is not intended to limit the scope of the present invention. Any changes or modifications made by a person skilled in the art in the field of the present invention based on the above disclosure shall fall within the scope of protection of the claims.

Claims

1. An alignment device, characterized in that: The alignment device comprises: an illumination unit, a light splitting unit and a detection unit; wherein, The illumination unit is used to provide illumination; The light splitting unit comprises a first polarization beam splitter prism, a first lens group and a second lens group; the light is diffracted by a grating mark to generate diffracted light, and the diffracted light is divided into a first diffracted light having a first polarization direction and a second diffracted light having a second polarization direction by the first polarization beam splitter prism; the first diffracted light is reflected by the first polarization beam splitter prism and then converted into a third diffracted light having a second polarization direction by the first lens group, and the third diffracted light is transmitted to the detection unit by the first polarization beam splitter prism; the second diffracted light is transmitted by the first polarization beam splitter prism and then converted into a fourth diffracted light having a first polarization direction by the second lens group, and the fourth diffracted light is reflected by the first polarization beam splitter prism to the detection unit; The detection unit includes a first wave plate, a second polarization beam splitter, a first detector and a second detector; the third diffracted light and the fourth diffracted light change polarization directions after being transmitted through the first wave plate, so as to interfere in the first polarization direction and the second polarization direction respectively and form interference light; the interference light is divided into a first polarization light and a second polarization light through the second polarization beam splitter; the first detector acquires light energy of the first polarization light, and the second detector acquires light energy of the second polarization light; When the grating mark is moved until the light energies respectively acquired by the first detector and the second detector reach preset values, the position of the grating mark is the alignment position.

2. The alignment device according to claim 1, characterized in that The first polarization direction and the second polarization direction are perpendicular to each other.

3. The alignment device according to claim 1, characterized in that The first polarized light has a first polarization direction, and the second polarized light has a second polarization direction.

4. The alignment device according to claim 1, characterized in that The first lens group includes a second wave plate and a first isosceles right-angle prism; the second lens group includes a third wave plate and a second isosceles right-angle prism; wherein the two surfaces where the right-angle sides of the first isosceles right-angle prism and the second isosceles right-angle prism are located are coated with a reflective film; After passing through the second wave plate, the first diffracted light enters the first isosceles right-angle prism, and is reflected by two surfaces of the right-angle sides of the first isosceles right-angle prism in sequence, and after passing through the second wave plate again, the polarization direction is changed to the second polarization direction to form the third diffracted light; After passing through the third wave plate, the second diffracted light enters the second isosceles right-angle prism, and is reflected in turn by the two surfaces where the right-angle sides of the second isosceles right-angle prism are located. After passing through the third wave plate again, the polarization direction is changed to the first polarization direction to form the fourth diffracted light.

5. The alignment device according to claim 4, characterized in that The second wave plate and the third wave plate are both half wave plates.

6. The alignment device according to claim 4, characterized in that The light field of the third diffracted light is symmetrical about the first plane, and the light field of the fourth diffracted light is symmetrical about the second plane; wherein the first plane is the symmetry plane of the first isosceles right prism and is perpendicular to the plane where the corresponding hypotenuse is located; the second plane is the symmetry plane of the second isosceles right prism and is perpendicular to the plane where the corresponding hypotenuse is located.

7. The alignment device according to claim 4, characterized in that The second wave plate and the first isosceles right-angle prism can be synchronously rotated along a first clockwise direction, and the third wave plate and the second isosceles right-angle prism can be synchronously rotated along a second clockwise direction.

8. The alignment device according to claim 7, characterized in that When the first clockwise direction is a clockwise direction, the second clockwise direction is a counterclockwise direction; or, when the first clockwise direction is a counterclockwise direction, the second clockwise direction is a clockwise direction.

9. The alignment device according to claim 7, characterized in that When the first isosceles right-angle prism rotates at an angle θ along a first clockwise direction, the second wave plate rotates synchronously at an angle θ / 2, the second isosceles right-angle prism rotates at an angle θ along a second clockwise direction, and the third wave plate rotates synchronously at an angle θ / 2. At this time, the angle β between the fast axis directions of the second wave plate and / or the third wave plate relative to the first polarization direction and the rotation angle θ satisfy the following formula: 4β+2θ=90°×(2k+1); Wherein, k is an integer.

10. The alignment device according to claim 1, characterized in that The first mirror group includes a fourth wave plate, a first plano-convex cylindrical mirror and a first reflector; the second mirror group includes a fifth wave plate, a second plano-convex cylindrical mirror and a second reflector; wherein, The first diffracted light is first transmitted through the fourth wave plate, then sequentially transmitted through the first plano-convex cylindrical mirror and reflected by the first reflector, and then transmitted through the fourth wave plate again, and the polarization direction is changed to the second polarization direction, so as to form a third diffracted light; The second diffracted light is first transmitted through the fifth wave plate, then transmitted through the second plano-convex cylindrical mirror and reflected by the second reflector in sequence, and then transmitted through the fifth wave plate again to change the polarization direction to the first polarization direction to form a fourth diffracted light.

11. The alignment device according to claim 10, characterized in that The fourth wave plate and the fifth wave plate are both quarter wave plates.

12. The alignment device according to claim 10, characterized in that The light field of the third diffracted light is symmetrical about the third plane, and the light field of the fourth diffracted light is symmetrical about the fourth plane; wherein the third plane is the symmetry plane of the first plano-convex cylindrical mirror and is perpendicular to the corresponding plane; the fourth plane is the symmetry plane of the second plano-convex cylindrical mirror and is perpendicular to the corresponding plane.

13. The alignment device according to claim 1, characterized in that The alignment device also includes a third reflector, a sixth wave plate and an objective lens; the light is reflected by the third reflector, vertically irradiated on the grating mark to diffract and generate diffracted light, and the diffracted light is converged by the objective lens and transmitted through the sixth wave plate so that the diffracted light enters the spectroscopic unit as 45-degree linear polarized light.

14. The alignment device according to claim 13, characterized in that The sixth wave plate is a half wave plate.

15. The alignment device according to claim 1, characterized in that The first wave plate is a half wave plate.

16. A photolithography machine, characterized in that: The lithography machine comprises an alignment device as claimed in any one of claims 1-15.

17. An alignment method, characterized in that: Using the alignment device as described in any one of claims 1 to 15, the alignment method comprises: The illumination unit provides illumination; The light is diffracted by the grating mark and generates diffracted light, and the diffracted light is divided into a first diffracted light with a first polarization direction and a second diffracted light with a second polarization direction by the first polarization beam splitter prism of the beam splitting unit; the first diffracted light is reflected by the first polarization beam splitter prism, and then converted into a third diffracted light with a second polarization direction by the first lens group, and the third diffracted light is transmitted to the detection unit by the first polarization beam splitter prism; the second diffracted light is transmitted by the first polarization beam splitter prism, and then converted into a fourth diffracted light with a first polarization direction by the second lens group, and the fourth diffracted light is reflected by the first polarization beam splitter prism to the detection unit; The third diffracted light and the fourth diffracted light change polarization directions after being transmitted through the first wave plate in the detection unit, so as to interfere in the first polarization direction and the second polarization direction respectively and form interference light; the interference light is divided into the first polarization light and the second polarization light by the second polarization beam splitter prism; the first detector acquires light energy of the first polarization light, and the second detector acquires light energy of the second polarization light; The workpiece stage is moved to drive the grating mark to move. When the light energies respectively acquired by the first detector and the second detector reach preset values, the position of the grating mark is the alignment position.

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