Collection system and overlay error measurement equipment

Abstract

The invention discloses a collection system and overlay error measurement equipment, and the collection system comprises an objective lens which is used for obtaining marking light from an object plane and enabling the marking light to be imaged on an image plane, the object plane is used for placing a to-be-detected object, and the marking light is light diffracted after illumination light enters a mark of the to-be-detected object; the first phase modulation element is arranged on a pupil plane of a collection light path of the collection system and is provided with at least two first modulation pixels, and the first modulation pixels are used for modulating the phase of the marking light passing through the first modulation pixels; the driver is connected with the first phase modulation element and is used for respectively controlling the driving voltages of the at least two first modulation pixels; and the detection element is arranged on the image surface and is used for receiving the marking light. The collection system is applied to the overlay error measurement equipment, and can avoid the situation that the imaging quality is influenced by the wave aberration introduced by the equipment error, so that the influence of the wave aberration introduced by the equipment error on the measurement accuracy can be avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor technology, and in particular to a collection system and an overlay error measuring device. BACKGROUND

[0002] Overlay (OVL) measurement is an important part of the semiconductor production process, which represents the alignment deviation between the current layer pattern and the previous layer pattern of a wafer. In the wafer production process, after the exposure of a layer pattern, a special device is used to measure the overlay error, and the overlay error measurement of the wafer can not only directly detect the precision of the current layer manufacturing process, but also can be used to measure the quality of the entire process flow.

[0003] The existing device for measuring the overlay error obtains the light generated by the mark of the wafer through an objective lens, and then obtains the overlay error between different layer patterns of the wafer according to the light intensity distribution of the mark diffraction light. Among them, by setting a wedge on the pupil surface of the objective lens, the light generated by the mark is deflected into multiple light fields after passing through the wedge, and the images formed by each light field on the image plane are separated, so that the overlay error in different directions can be obtained. However, in actual application, the errors of various components of the device will introduce wave aberration to the imaging of light on the image plane, such as the installation error of the device components or the wave aberration existing in the objective lens itself, which will affect the imaging quality and the measurement accuracy. SUMMARY

[0004] The present application discloses a collection system and an overlay error measuring device, which can avoid the influence of wave aberration on measurement accuracy.

[0005] In a first aspect, the present application provides a collection system, comprising:

[0006] an objective lens, configured to obtain mark light from a to-be-measured object and form an image of the mark light on an image plane;

[0007] a first phase modulation element, disposed on a pupil surface of a collection light path of the collection system, the first phase modulation element being provided with at least two first modulation pixels, the first modulation pixels being configured to modulate the phase of the mark light passing through the first modulation pixels;

[0008] a driver, connected to the first phase modulation element, configured to control the driving voltage of the at least two first modulation pixels respectively;

[0009] a detection element, disposed on the image plane.

[0010] The collection system provided in the application is provided with a first phase modulation element at the pupil of the collection light path, the first phase modulation element is provided with at least two first modulation pixels, the first modulation pixel modulates the phase of the mark light passing through the first modulation pixel, the mark light is modulated in units of modulation pixels by the first phase modulation element, the wave aberration introduced by the equipment error can be compensated, and the imaging quality affected by the wave aberration introduced by the equipment error can be avoided.

[0011] In some embodiments, the first phase modulation element comprises:

[0012] The first sub-phase modulation element is provided with at least two first modulation pixels;

[0013] The second sub-phase modulation element is provided with at least two second modulation pixels;

[0014] The driver is connected to the first sub-phase modulation element and the second sub-phase modulation element respectively, and is further used for controlling the driving voltage of the at least two second modulation pixels respectively.

[0015] In the embodiment, the first sub-phase modulation element and the second sub-phase modulation element independently modulate the phase of the mark light respectively, and the flexibility of modulating the phase of the mark light can be improved.

[0016] In some embodiments, the at least two second modulation pixels of the second sub-phase modulation element are divided into at least two sub-zones, the second modulation pixels in any sub-zone are used for introducing linear phase to the mark light passing through the sub-zone, and the linear phases introduced by the second modulation pixels in the at least two sub-zones are different.

[0017] In the embodiment, the second sub-phase modulation element can modulate the phase of the mark light in sub-zones, so that the mark light is deflected into multiple light fields after passing through the second sub-phase modulation element, the light fields are imaged and separated on the image plane, the phase of the mark light is modulated in units of modulation pixels by the first sub-phase modulation element, the wave aberration introduced by the equipment error can be compensated, and the measurement accuracy affected by the wave aberration introduced by the equipment error can be avoided.

[0018] In a second aspect, the application provides a overlay error measurement device, comprising:

[0019] A light source;

[0020] The collection system according to any one of the above.

[0021] The overlay error measurement device provided in this application has a first phase modulation element disposed on the pupil plane of the light collection path. The first phase modulation element has at least two first modulation pixels. The first modulation pixels modulate the phase of the marker light passing through them. By modulating the phase of the marker light with the first phase modulation element on a pixel-by-pixel basis, wavefront aberrations introduced by equipment errors can be compensated, thus avoiding the impact on image quality caused by wavefront aberrations introduced by equipment errors. Therefore, this overlay error measurement device can avoid the impact on image quality caused by wavefront aberrations introduced by equipment errors, thereby avoiding any impact on measurement accuracy.

[0022] In some embodiments, the overlay error measuring device further includes:

[0023] The second phase modulation element is disposed on the pupil surface of the illumination light path of the collection system, and is provided with at least two third modulation pixels. The third modulation pixels are used to modulate the phase of the illumination light passing through the third modulation pixels.

[0024] The collector is connected to the driver and the second phase modulation element, and is also used to control the driving voltage of at least two third modulation pixels respectively.

[0025] In this embodiment, a second phase modulation element is disposed on the pupil plane of the illumination optical path. The second phase modulation element is provided with at least two third modulation pixels. The third modulation pixels modulate the phase of the illumination light passing through them. By modulating the phase of the illumination light with the third phase modulation element on a pixel-by-pixel basis, wavefront shaping can be performed, which can improve the light intensity and signal-to-noise ratio of the illumination light illuminating the object under test. By pre-compensating for the scattering or wavefront aberration of the marker light, higher imaging resolution and contrast, more efficient and stable optical control, deeper penetration depth, and lower exposure can be obtained.

[0026] In some embodiments, the overlay error measuring device further includes:

[0027] The first beam-splitting element is positioned between the objective lens and the image plane of the collecting system;

[0028] The light source is positioned on the incident light path of the first beam splitter, the objective lens is positioned on the reflected light path of the first beam splitter, and the second phase modulation element is positioned between the light source and the first beam splitter.

[0029] In this embodiment, the illumination light emitted by the light source is deflected into the objective lens by the first beam splitter, and the number of optical elements used is small.

[0030] In some embodiments, the overlay error measuring device further includes:

[0031] The second beam splitter is positioned between the objective lens and the image plane of the collecting system, with the objective lens located on the reflected light path of the second beam splitter.

[0032] The third beam splitter is disposed on the incident light path of the second beam splitter, and the light source is disposed on the incident light path of the third beam splitter;

[0033] A reflective element is disposed on the reflected light path of the third beam splitter, and a second phase modulation element is disposed between the reflective element and the third beam splitter.

[0034] In this embodiment, by arranging a second beam splitter, a third beam splitter, and a reflector, the illumination light passes back and forth through the second phase modulation element. If the second phase modulation element remains stable during the round trip of the illumination light, the illumination light travels from the third beam splitter through the second phase modulation element to the reflector, following a completely opposite path to the illumination light being reflected by the reflector and then returning to the third beam splitter through the second phase modulation element. After passing through the objective lens, the illumination light is incident on the object surface. The light diffracted by the illumination light onto the marker, i.e., the marker light, is transmitted back through the objective lens to the image plane for imaging. By measuring the wavefront information of the marker light, its perfect wavefront shaping conditions can be calculated. By adjusting the phase of the illumination light through feedback from the second phase modulation element, the wavefront aberration of the marker light can be perfectly compensated.

[0035] In some embodiments, the overlay error measuring device further includes:

[0036] The fourth beam-splitting element is positioned between the objective lens of the collection system and the first phase modulation element;

[0037] The signal detection unit is located on the reflected light path of the fourth beam splitter;

[0038] The signal processing unit is connected to the signal detection unit and the driver of the collection system, respectively.

[0039] In this embodiment, the wavefront information of the marker light from the objective lens is acquired by the signal detection unit, and the first phase modulation element is controlled to modulate the phase of the marker light based on the wavefront information. This achieves adaptive adjustment of the phase modulation of the marker light from the objective lens, avoiding frequent manual adjustments and enabling the collection system to maintain efficient operation in complex and dynamic environments, thus improving system stability and adaptability. Furthermore, the fourth beam splitter separates the marker light from the objective lens into a single beam that is incident on the signal detection unit. This allows the wavefront information of the marker light to be monitored and adaptively adjusted simultaneously with the collection system's measurement of the marker light.

[0040] In some embodiments, the overlay error measuring device further includes:

[0041] The signal detection unit is located at a preset position on the optical path between the objective lens and the image plane of the collection system. The signal detection unit can be moved into and out of the preset position.

[0042] The signal processing unit is connected to the signal detection unit and the driver of the collection system, respectively.

[0043] The wavefront information of the marker light from the objective lens is acquired by the signal detection unit, and the first phase modulation element is controlled to modulate the phase of the marker light based on the wavefront information. This achieves adaptive adjustment of the phase modulation of the marker light from the objective lens, avoiding frequent manual adjustments and enabling the collection system to maintain efficient operation in complex and dynamic environments, thus improving system stability and adaptability. In this embodiment, partial energy loss of the marker light during the collection process for measurement can be avoided, preventing a decrease in optical energy in the main measurement optical path. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 A schematic diagram of a collection system provided in the first embodiment of this application;

[0046] Figure 2 This is a schematic diagram of the first phase modulation element of the collection system according to the second embodiment of this application modulating the phase of the marker light;

[0047] Figure 3 A schematic diagram of the first phase modulation element of the collection system according to the third embodiment of this application;

[0048] Figure 4 A schematic diagram of a collection system provided in the fourth embodiment of this application;

[0049] Figure 5 This is a schematic diagram of an overlay error measuring device provided in the fifth embodiment of this application;

[0050] Figure 6 This is a schematic diagram of an overlay error measuring device provided in the sixth embodiment of this application;

[0051] Figure 7 This is a schematic diagram of an overlay error measuring device provided in the seventh embodiment of this application;

[0052] Figure 8-1A schematic diagram of an overlay error measurement device provided in the eighth embodiment of this application, showing the optical path being moved into the signal detection unit;

[0053] Figure 8-2 This is a schematic diagram of an overlay error measurement device provided in the eighth embodiment of this application, showing the signal detection unit moving out of the optical path.

[0054] The reference numerals in the accompanying drawings include:

[0055] 10-Surface;

[0056] 20 - First phase modulation element; 21 - First sub-phase modulation element; 22 - Second sub-phase modulation element; 23 - Second phase modulation element; 201 - First quadrant partition; 202 - Second quadrant partition; 203 - Third quadrant partition; 204 - Fourth quadrant partition; 205 - Local region;

[0057] 30 - Objective lens; 40 - Detector element; 60 - Driver; 70 - Signal detection unit; 80 - Signal processing unit; 90 - Light source;

[0058] 51-First beam splitter; 52-Second beam splitter; 53-Third beam splitter; 54-Fourth beam splitter; 55-Reflecting element. Detailed Implementation

[0059] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0060] Overlay (OVL) measurement is a crucial step in semiconductor manufacturing, characterizing the alignment deviation between the current layer pattern and the previous layer pattern on a wafer. During wafer fabrication, after the exposure of a pattern layer, specialized equipment is used to measure overlay error. Measuring wafer overlay error not only directly verifies the precision of the current layer's manufacturing process but also serves to assess the quality of the entire process flow.

[0061] Existing equipment for measuring overlay errors acquires diffracted light from markings on a wafer using an objective lens, and then obtains the overlay error between different layers of the wafer based on the intensity distribution of the diffracted light. In diffraction-based overlay error measurement, the markings are arranged with periodically arranged structural units. When illumination light shines on the markings, diffraction occurs. By acquiring the diffracted light and obtaining its intensity distribution, the overlay error is calculated. However, in practical applications, errors in various components of the overlay error measurement equipment can introduce wavefront aberrations into the imaging of the diffracted light on the image plane. For example, installation errors of equipment components or wavefront aberrations inherent in the objective lens itself can affect image quality and thus measurement accuracy. To address this, this application provides a collection system and an overlay error measurement device that can avoid the impact of wavefront aberrations on measurement accuracy.

[0062] For reference Figure 1 , Figure 1 This is a schematic diagram of a collection system provided for a first embodiment. (See diagram below.) Figure 1 As shown, the collection system includes an objective lens 30, a first phase modulation element 20, a driver 60, and a detector element 40. The objective lens 30 is used to acquire the marking light from the object plane 10 and image the marking light onto the image plane. The object plane 10 is used to place the object to be tested, which may be a wafer. The marking light is the light diffracted after the illumination light is incident on the mark of the object to be tested. The first phase modulation element 20 is disposed on the pupil plane of the collection optical path of the collection system. The first phase modulation element 20 is provided with at least two first modulation pixels. The first modulation pixels are used to modulate the phase of the marking light passing through the first modulation pixel. The driver 60 is connected to the first phase modulation element 20 and is used to control the driving voltage of at least two first modulation pixels respectively. The detector element 40 is disposed on the image plane and is used to receive the marking light.

[0063] Light rays from object plane 10 enter objective lens 30 and are imaged after passing through objective lens 30. The object to be tested is placed on object plane 10. Light rays from object plane 10 enter objective lens 30 and are focused onto image plane after passing through objective lens 30, forming an image on image plane. The object to be tested has a mark on it, and the light rays diffracted from the mark on the object to be tested (i.e., the mark light) enter objective lens 30 and are imaged on image plane after passing through objective lens 30. Both object plane 10 and image plane are virtual planes in the optical path of objective lens 30.

[0064] The light path from the objective lens 30 to the image plane passes through the first phase modulation element 20. The first modulation pixel is an optical medium; applying a driving voltage to the first modulation pixel can adjust its optical properties, including but not limited to refractive index and transmittance. The driver 60 controls the driving voltage of any first modulation pixel, thereby adjusting the optical properties of that first modulation pixel.

[0065] The driver 60 controls the driving voltage of any first modulation pixel, thereby adjusting the refractive index of any first modulation pixel to modulate the phase of the marker light after it passes through the pixel. By introducing a phase to the marker light passing through the first modulation pixel to compensate for wavefront aberration, the wavefront aberration present after the marker light from the objective lens 30 passes through the first phase modulation element 20 is compensated, allowing the marker light from the objective lens 30 to be imaged on the image plane, thus reducing or even eliminating wavefront aberration. The driver 60 can control the driving voltage of any first modulation pixel to control the phase introduced by each pixel to compensate for wavefront aberration, enabling flexible compensation of wavefront aberration.

[0066] In this embodiment's collection system, a first phase modulation element 20 is disposed on the pupil plane of the collection optical path. The first phase modulation element 20 is provided with at least two first modulation pixels. The first modulation pixels modulate the phase of the marker light passing through them. By modulating the phase of the marker light with the first phase modulation element 20 on a pixel-by-pixel basis, wavefront aberrations introduced by equipment errors can be compensated, thus avoiding the impact of wavefront aberrations on image quality. Therefore, this collection system, when applied to an overlay error measurement device, can avoid the impact of wavefront aberrations introduced by equipment errors on image quality and measurement accuracy. Furthermore, by providing the first phase modulation element 20 in the collection optical path to introduce a phase into the marker light for wavefront aberration compensation and wavefront shaping, light from different points within the entire field of view can be simultaneously corrected to obtain better image quality. Simultaneously, since high-intensity focusing of the illumination light is not required, optical or thermal damage to the object under test caused by high-power illumination light can be avoided, thus protecting the object under test.

[0067] Each first modulation pixel includes an incident surface and an exit surface. Marking light is incident on the incident surface of the first modulation pixel, passes through the first modulation pixel, and exits from its exit surface. The first modulation pixels of the first phase modulation element 20 are arranged in an array. The number, shape, and size of the first modulation pixels included in the first phase modulation element 20 can be set according to the precision requirements of the marking light modulation phase. The more first modulation pixels included in the first phase modulation element 20 and the smaller the size of each individual first modulation pixel, the higher the precision of the marking light modulation phase of the first phase modulation element 20, but the difficulty of controlling the first phase modulation element 20 by the driver 60 will increase. The fewer first modulation pixels included in the first phase modulation element 20 and the larger the size of each individual first modulation pixel, the lower the precision of the marking light modulation phase of the first phase modulation element 20. In practical applications, the number and size of the first modulation pixels can be determined by balancing the precision requirements of the marking light modulation phase of the first phase modulation element 20 and the situation of the driver 60.

[0068] The first phase modulation element 20 can be a liquid crystal spatial light modulator. In this embodiment, the first phase modulation element 20 includes a first substrate, a second substrate, an alignment film, and liquid crystal. The alignment film is located between the first substrate and the second substrate, and the liquid crystal is located between the first substrate and the alignment film or between the second substrate and the alignment film. The alignment film has fine trenches, and electrodes are respectively disposed on the surfaces of the first substrate and the second substrate. A driving voltage is applied to the liquid crystal through the electrodes. When no driving voltage is applied to the liquid crystal, the liquid crystal molecules are sequentially aligned according to the direction of the fine trenches of the alignment film. The marking light passes through the first substrate, the liquid crystal, and the second substrate in sequence and is emitted. The phase delay of the marking light is related to the thickness and refractive index of the liquid crystal. When a driving voltage is applied to the liquid crystal, an electric field is formed between the first substrate and the second substrate, causing the liquid crystal molecules to tilt and the refractive index of the liquid crystal to change. The phase delay of the marking light changes after passing through the first substrate, the liquid crystal, and the second substrate in sequence, and the phase of the marking light is modulated. The phase delay of the marking light after passing through the liquid crystal is related to the thickness and refractive index of the liquid crystal, and the refractive index of the liquid crystal is related to the driving voltage. Therefore, by adjusting the driving voltage applied to the liquid crystal, the phase delay of the marking light after passing through the liquid crystal can be adjusted accordingly.

[0069] The first phase modulation element 20 can be an electro-optic crystal array modulator. An electro-optic crystal is a medium exhibiting an electro-optic effect. Under the influence of an applied electric field, the refractive index of this medium changes, altering the phase delay of the marking light after it passes through the electro-optic crystal, thus modulating the phase of the marking light. The phase delay of the marking light after passing through the electro-optic crystal is related to the refractive index of the electro-optic crystal, and the change in the refractive index of the electro-optic crystal is related to the electric field strength of the applied electric field. Therefore, by adjusting the driving voltage applied to the electro-optic crystal, the phase delay of the marking light after passing through the electro-optic crystal can be adjusted accordingly. For example, for an electro-optic crystal exhibiting a linear electro-optic effect, its refractive index change is linearly related to the electric field strength of the applied electric field, and the phase delay of the marking light after passing through the electro-optic crystal is also linearly related to the electric field strength of the applied electric field. The electro-optic crystal can be lithium niobate (LiNbO3) crystal, gallium arsenide (GaAs) crystal, or lithium tantalate (LiTaO3) crystal.

[0070] In some embodiments, during overlay error measurement, the system needs to be able to deflect the diffracted light from the marker on the object under test into multiple light fields, separating the images formed by each light field on the image plane to obtain overlay errors in different directions. To address this, in this embodiment, at least two first modulation pixels of the first phase modulation element 20 are divided into at least two partitions. The first modulation pixel of any partition is also used to introduce a linear phase into the marker light passing through that partition. The linear phases introduced by the first modulation pixels of the at least two partitions are different. The marker light from the objective lens 30 passes through each partition, and the different linear phases introduced by the first modulation pixels of each partition cause the marker light to be deflected in different directions after passing through each partition. This results in the marker light being deflected into multiple light fields after passing through the first phase modulation element 20, allowing the images formed by each light field on the image plane to be separated, thus meeting the measurement requirements. For example, refer to... Figure 2 , Figure 2 This is a schematic diagram of the first phase modulation element of the collection system in the second embodiment modulating the phase of the marker light, as shown. Figure 2 As shown, the wavefront of the marker light after passing through the first phase modulation element 20 is the result of the superposition of two parts: the linear phase modulation introduced by the partition of the first phase modulation element 20 on the marker light and the local phase modulation performed by each first modulation pixel of the first phase modulation element 20 on the marker light. In this embodiment, the first phase modulation element 20 is used to partition and deflect the marker light into multiple light fields and to compensate for the wavefront difference of the marker light.

[0071] For example, in overlay error measurement, the markings on the object under test include four sub-markers arranged in a four-quadrant configuration. These four sub-markers are two grating marks in the X direction and two grating marks in the Y direction. By obtaining the diffraction energy distribution of the two grating marks in the X direction, the overlay error in the X direction can be calculated. Similarly, by obtaining the diffraction energy distribution of the two grating marks in the Y direction, the overlay error in the Y direction can be calculated. To meet the requirements for measurement using four-quadrant markings, refer to... Figure 3 , Figure 3 This is a schematic diagram of the first phase modulation element of the collection system in the third embodiment. At least two first modulation pixels of the first phase modulation element 20 are divided into four partitions arranged in a four-quadrant configuration. The marker light from the objective lens 30 is deflected into four light fields by these partitions after passing through the first phase modulation element 20, and these four light fields are imaged and separated on the image plane. The first phase modulation element 20 is divided into four partitions, including a first quadrant partition 201, a second quadrant partition 202, a third quadrant partition 203, and a fourth quadrant partition 204, which deflects the marker light into four light fields deflected at the four corners respectively. Corresponding to the local wavefront aberration of the marker light, the first modulation pixels in a local region 205 of the first phase modulation element 20 can introduce a phase to the marker light to compensate for the local wavefront aberration.

[0072] In some embodiments, the transmittance of the first modulation pixel is adjustable. The driver 60 controls the driving voltage of any first modulation pixel, thereby adjusting the transmittance of any first modulation pixel and enabling any first modulation pixel to modulate the intensity of the marker light after passing through it. By modulating the intensity of the marker light with the first phase modulation element 20 on a unit basis, the imaging quality of the marker light by the collection system is improved, which helps to improve the measurement accuracy when applied to overlay error measurement.

[0073] For reference Figure 4 , Figure 4 A schematic diagram of a collection system provided for the fourth embodiment, as shown below. Figure 4 As shown, in some embodiments, the first phase modulation element 20 includes: a first sub-phase modulation element 21, which is provided with at least two first modulation pixels; a second sub-phase modulation element 22, which is stacked with the first sub-phase modulation element 21 and is provided with at least two second modulation pixels; and a driver 60 is connected to the first sub-phase modulation element 21 and the second sub-phase modulation element 22 respectively, and is also used to control the driving voltage of at least two first modulation pixels and at least two second modulation pixels respectively.

[0074] The second modulation pixel is an optical medium. Applying a driving voltage to the second modulation pixel can adjust its optical properties, including but not limited to refractive index and transmittance. The driver 60 controls the driving voltage of any second modulation pixel, thereby adjusting its optical properties. The driver 60 also controls the refractive index of any second modulation pixel, causing each second modulation pixel to modulate the phase of the marker light after passing through it. The first sub-phase modulation element 21 and the second sub-phase modulation element 22 independently modulate the phase of the marker light, improving the flexibility of phase modulation of the marker light.

[0075] In some embodiments, at least two second modulation pixels of the second sub-phase modulation element 22 are divided into at least two partitions. The second modulation pixel in any partition is used to introduce a linear phase into the marker light passing through that partition. The linear phases introduced by the second modulation pixels in the at least two partitions are different. In this embodiment, the marker light from the objective lens 30 passes sequentially through the second sub-phase modulation element 22 and the first sub-phase modulation element 21. The marker light passes through each partition of the second sub-phase modulation element 22, and the linear phase introduced into the marker light by the second modulation pixels in each partition is different. This causes the marker light to be deflected in different directions after passing through each partition, resulting in multiple light fields after deflection. The images formed by these light fields on the image plane can be separated to meet measurement requirements. A phase for compensating wavefront aberration is introduced into the marker light passing through the first modulation pixel of the first sub-phase modulation element 21, thus compensating for the wavefront aberration present after the marker light from the objective lens 30 passes through the first phase modulation element 20. By setting the first sub-phase modulation element 21 and the second sub-phase modulation element 22, the flexibility of phase modulation for marking light partitioning and phase modulation for compensating wave aberrations can be improved, and the difficulty of controlling a single phase modulation element can be reduced.

[0076] This application also provides an overlay error measurement device, including: a light source 90 for emitting illumination light; and a collection system as described in any of the preceding embodiments. In this embodiment, the overlay error measurement device has a first phase modulation element 20 disposed on the pupil plane of the collection light path. The first phase modulation element 20 has at least two first modulation pixels. The first modulation pixels modulate the phase of the marker light passing through them. By modulating the phase of the marker light with the first phase modulation element 20 at the modulation pixel level, wavefront aberrations introduced by device errors can be compensated, thus avoiding the impact of wavefront aberrations on image quality. Therefore, this embodiment of the overlay error measurement device can avoid the impact of wavefront aberrations introduced by device errors on image quality, thereby avoiding the influence of wavefront aberrations on measurement accuracy.

[0077] Existing overlay error measurement equipment requires strict assembly and adjustment of each component to reduce the impact of equipment errors on measurement accuracy, such as installation errors of equipment parts. However, this makes assembly and adjustment very difficult. For objectives, strict control of wavelet aberration is required throughout the entire process from design to manufacturing, which increases the design and manufacturing costs of objectives. In contrast, the overlay error measurement equipment of this embodiment can compensate for wavelet aberrations introduced by equipment errors by modulating the phase of the marker light. This avoids increasing the assembly and adjustment difficulty of the overlay error measurement equipment and avoids increasing the design and manufacturing costs of objectives.

[0078] For reference Figure 5 , Figure 5 A schematic diagram of an overlay error measuring device provided in the fifth embodiment is shown below. Figure 5As shown, in some embodiments, the overlay error measurement device further includes: a second phase modulation element 23 disposed on the pupil plane of the illumination optical path of the collection system, having at least two third modulation pixels, the third modulation pixels being used to modulate the phase of the illumination light passing through the third modulation pixels; a driver 60 of the collection system connected to the second phase modulation element 23, also used to control the driving voltage of at least two third modulation pixels respectively. The illumination light path from the light source 90 to the object plane 10 passes through the second phase modulation element 23. The third modulation pixels are optical media; applying a driving voltage to the third modulation pixels can adjust the optical properties of the third modulation pixels, including but not limited to refractive index and transmittance. The driver 60 controls the driving voltage of any third modulation pixel, thereby adjusting the optical properties of any third modulation pixel.

[0079] The driver 60 controls the driving voltage of any third modulation pixel, and can adjust the refractive index of any third modulation pixel, so that any third modulation pixel modulates the phase of the illumination light after passing through the third modulation pixel. A phase for compensating wavefront aberration is introduced into the illumination light passing through the third modulation pixel by any third modulation pixel, so that the illumination light is incident on the mark of the object under test. The mark light generated by the mark is transmitted to the image plane after passing through the objective lens 30. The wavefront aberration of the mark light can be compensated, so that the mark light from the objective lens 30 is imaged on the image plane, and its wavefront aberration is reduced or even eliminated. Therefore, the overlay error measurement device of this embodiment can avoid the influence of wavefront aberration on imaging quality due to equipment errors, and can avoid the influence of wavefront aberration on measurement accuracy. In this embodiment, a second phase modulation element 23 is provided in the illumination optical path. The phase of the illumination light is modulated by the second phase modulation element 23 in units of modulation pixels to perform wavefront shaping, which can improve the light intensity and signal-to-noise ratio of the illumination light illuminating the object under test. By pre-compensating for the scattering or wavefront aberration of the marker light, higher imaging resolution and contrast, more efficient and stable optical control, deeper penetration depth, and lower exposure can be obtained.

[0080] Each third modulation pixel includes an incident surface and an exit surface. Illumination light is incident on the incident surface of the third modulation pixel, passes through the third modulation pixel, and exits from its exit surface. The third modulation pixels of the second phase modulation element 23 are arranged in an array. The number, shape, and size of the third modulation pixels included in the second phase modulation element 23 can be set according to the precision requirements of the illumination light modulation phase. The more third modulation pixels included in the second phase modulation element 23 and the smaller the size of each individual third modulation pixel, the higher the precision of the illumination light modulation phase of the second phase modulation element 23, but the difficulty of controlling the second phase modulation element 23 by the driver 60 will increase. The fewer third modulation pixels included in the second phase modulation element 23 and the larger the size of each individual third modulation pixel, the lower the precision of the illumination light modulation phase of the second phase modulation element 23. In practical applications, the number and size of the third modulation pixels can be determined by balancing the precision requirements of the illumination light modulation phase of the second phase modulation element 23 and the situation of the driver 60.

[0081] The second phase modulation element 23 can be a liquid crystal spatial light modulator. In this embodiment, the second phase modulation element 23 includes a first substrate, a second substrate, an alignment film, and liquid crystal. The alignment film is located between the first substrate and the second substrate, and the liquid crystal is located between the first substrate and the alignment film or between the second substrate and the alignment film. The alignment film has fine trenches, and electrodes are respectively disposed on the surfaces of the first substrate and the second substrate. A driving voltage is applied to the liquid crystal through the electrodes. When no driving voltage is applied to the liquid crystal, the liquid crystal molecules are sequentially aligned according to the direction of the fine trenches of the alignment film. When a driving voltage is applied to the liquid crystal, an electric field is formed between the first substrate and the second substrate, causing the liquid crystal molecules to tilt. The refractive index of the liquid crystal changes, and the phase delay of the illumination light changes after it passes through the first substrate, the liquid crystal, and the second substrate in sequence. The phase delay of the illumination light after passing through the liquid crystal is related to the thickness and refractive index of the liquid crystal, while the refractive index of the liquid crystal is related to the driving voltage.

[0082] The second phase modulation element 23 can be an electro-optic crystal array modulator. An electro-optic crystal is a medium exhibiting an electro-optic effect. Under the influence of an applied electric field, the refractive index of this medium changes, altering the phase delay of the illumination light after it passes through the electro-optic crystal, thus modulating the phase of the illumination light. The phase delay of the illumination light after passing through the electro-optic crystal is related to the refractive index of the electro-optic crystal, and the change in the refractive index of the electro-optic crystal is related to the electric field strength of the applied electric field. Therefore, by adjusting the driving voltage applied to the electro-optic crystal, the phase delay of the illumination light after passing through the electro-optic crystal can be adjusted accordingly. The electro-optic crystal can be a lithium niobate (LiNbO3) crystal, a gallium arsenide (GaAs) crystal, or a lithium tantalate (LiTaO3) crystal.

[0083] In real-world scenarios, the illumination light emitted by the light source 90 may exhibit uneven intensity distribution, affecting the intensity distribution of diffracted light generated by the markings on the object under test, thereby impacting measurement accuracy. To address this, in some implementations, the transmittance of the third modulation pixel is adjustable. The driver 60 controls the driving voltage of any third modulation pixel, thereby adjusting the transmittance of any third modulation pixel and enabling each third modulation pixel to modulate the intensity of the illumination light after passing through it. The second phase modulation element 23 modulates the intensity of the illumination light at the modulation pixel level to improve the light intensity and signal-to-noise ratio of the object under test illuminating the surface 10.

[0084] In some embodiments, the objective lens 30 is also used to transmit and direct illumination light onto the object surface 10, as can be seen from [reference needed]. Figure 5 As shown, a first beam splitter 51 is disposed between the objective lens 30 and the image plane of the collecting system. A light source 90 is positioned in the incident light path of the first beam splitter 51, and the objective lens 30 is located in the reflected light path of the first beam splitter 51. A second phase modulation element 23 is disposed between the light source 90 and the first beam splitter 51. The illumination light emitted by the light source 90 passes through the second phase modulation element 23 and then enters the first beam splitter 51, where it is reflected back to the objective lens 30. In this embodiment, the first beam splitter 51 is used to redirect the illumination light emitted by the light source 90 into the objective lens 30, resulting in a smaller number of optical elements. For an exemplary embodiment, please refer to... Figure 5 As shown, the first beam splitter 51 can be formed by two triangular prisms. The inclined surfaces of the two triangular prisms are attached and a first film is provided. When the illumination light is incident on the first film of the first beam splitter 51 from the incident light path, the illumination light is reflected. When the marking light from the objective lens 30 is incident on the first film of the first beam splitter 51 from the reflected light path, the marking light is transmitted and further incident on the detector element 40.

[0085] In some embodiments, the objective lens 30 is also used to transmit and direct illumination light onto the object surface 10, as can be seen from [reference needed]. Figure 6 , Figure 6 A schematic diagram of an overlay error measuring device provided in the sixth embodiment is shown below. Figure 6As shown, the overlay error measurement device further includes: a second beam splitter 52, disposed between the objective lens 30 and the image plane of the collecting system, with the objective lens 30 located in the reflected light path of the second beam splitter 52; a third beam splitter 53, disposed in the incident light path of the second beam splitter 52, with the light source 90 disposed in the incident light path of the third beam splitter 53; a reflector 55, disposed in the reflected light path of the third beam splitter 53; and a second phase modulation element 23 disposed between the reflector 55 and the third beam splitter 53. Illumination light emitted from the light source 90 is incident on the third beam splitter 53, reflected by the third beam splitter 53 to the second phase modulation element 23, and after passing through the second phase modulation element 23, the illumination light is incident on the reflector 55, reflected back, and passes through the second phase modulation element 23 again. After passing through the second phase modulation element 23, the illumination light is incident on the second beam splitter 52 and reflected by the second beam splitter 52 to the objective lens 30. In this embodiment, by arranging a third beam splitter 53 and a reflector 55, the illumination light passes back and forth through the second phase modulation element 23. If the second phase modulation element 23 remains stable during the round trip of the illumination light, the illumination light travels from the third beam splitter 53 through the second phase modulation element 23 to the reflector 55, and then returns to the third beam splitter 23 after being reflected by the reflector 55. The illumination light passes through the objective lens 30 and is incident on the object plane 10. The illumination light that illuminates the marker diffracted light (i.e., the marker light) is transmitted back through the objective lens 30 to the image plane for imaging. By measuring the wavefront information of the marker light, its perfect wavefront shaping conditions can be calculated. By adjusting the phase of the illumination light through the feedback of the second phase modulation element 23, the wavefront aberration of the marker light can be perfectly compensated.

[0086] The reflecting element 55 may be a mirror. See, for example, [reference needed]. Figure 6 As shown, the third beam splitter 53 can be formed by two triangular prisms. The inclined surfaces of the two triangular prisms are attached together and a third film is provided. When illumination light enters the third film of the third beam splitter 53 from the incident light path, the illumination light is reflected. The illumination light reflected by the reflecting element 55 enters the third film of the third beam splitter 53 from the reflected light path and passes through, and is correspondingly incident on the second beam splitter 52. The second beam splitter 52 can be formed by two triangular prisms. The inclined surfaces of the two triangular prisms are attached together and a second film is provided. When illumination light enters the second film of the second beam splitter 52 from the incident light path, the illumination light is reflected. When the marking light from the objective lens 30 enters the second film of the second beam splitter 52 from the reflected light path, the marking light passes through.

[0087] For reference Figure 7 , Figure 7 A schematic diagram of an overlay error measuring device provided in the seventh embodiment is shown below. Figure 7As shown, in some embodiments, the overlay error measurement device further includes: a fourth beam splitter 54, disposed between the objective lens 30 and the first phase modulation element 20 of the collection system; a signal detection unit 70, disposed in the reflected light path of the fourth beam splitter 54, for receiving the reflected light formed by the marker light through the fourth beam splitter 54 to obtain the wavefront information of the marker light; and a signal processing unit 80, connected to the signal detection unit 70 and the driver 60 of the collection system respectively, for generating a control signal based on the wavefront information and transmitting it to the driver 60. The marker light from the objective lens 30 is incident on the fourth beam splitter 54, and the fourth beam splitter 54 partially reflects the marker light to the signal detection unit 70. The signal detection unit 70 obtains the wavefront information of the marker light based on the received marker light. The wavefront information of the marker light from the objective lens 30 is acquired by the signal detection unit 70, and the first phase modulation element 20 is controlled to modulate the phase of the marker light according to the wavefront information. This achieves adaptive adjustment of the phase modulation of the marker light from the objective lens 30, avoiding frequent manual adjustments and enabling the collection system to maintain efficient operation in complex and dynamic environments, thus improving system stability and adaptability. Furthermore, in this embodiment, the fourth beam splitter 54 separates a beam of the marker light from the objective lens 30 and directs it to the signal detection unit 70. This allows the collection system to monitor the wavefront information of the marker light and make adaptive adjustments while collecting the marker light for measurement. The fourth beam splitter 54 can be, but is not limited to, a semi-transparent mirror; exemplarily, refer to... Figure 7 As shown, the fourth beam splitter 54 can be formed by two triangular prisms. The inclined surfaces of the two triangular prisms are attached and a fourth film is provided. The marker light from the objective lens 30 is incident on the fourth film of the fourth beam splitter 54. Part of the marker light is reflected and reflected to the signal detection unit 70, while part of the marker light is transmitted and further incident on the detection element 40.

[0088] For reference Figure 8-1 and Figure 8-2 , Figure 8-1 This is a schematic diagram of an overlay error measurement device provided in the eighth embodiment, showing the signal detection unit moving into the optical path. Figure 8-2 A schematic diagram of an overlay error measurement device provided in the eighth embodiment, showing the signal detection unit moving out of the optical path, as shown. Figure 8-1 and Figure 8-2As shown, in some embodiments, the overlay error measurement device further includes: a signal detection unit 70, wherein a preset position is provided on the optical path between the objective lens 30 of the collection system and the image plane; the signal detection unit 70 can move into and out of the preset position; when the signal detection unit 70 moves into the preset position, it is used to receive the marker light to obtain the wavefront information of the marker light; and a signal processing unit 80, which is connected to the signal detection unit 70 and the driver 60 of the collection system respectively, and is used to generate a control signal based on the wavefront information and transmit it to the driver 60. During the process of the collection system collecting the marker light for measurement, the signal detection unit 70 can be moved out of the preset position; when it is necessary to monitor the wavefront information of the marker light and for adaptive adjustment, the signal detection unit 70 can be moved into the preset position. The overlay error measurement device may also include: a movable motion motor, wherein the signal detection unit 70 is disposed on the motion motor and can move with the motion motor; the motion motor drives the signal detection unit 70 to move into or out of the preset position. The motion motor does not require a high speed, but it needs high positioning accuracy to ensure that the positioning error of the control signal detection unit 70 when moving into or out of the preset position is within an acceptable range. In this embodiment, the wavefront information of the marker light from the objective lens 30 is acquired by the signal detection unit 70, and the first phase modulation element 20 is controlled to perform phase modulation on the marker light based on the wavefront information. This achieves adaptive adjustment of the phase modulation of the marker light from the objective lens 30, avoiding frequent manual adjustments and enabling the collection system to maintain efficient operation in complex and dynamic environments, thus improving system stability and adaptability. Furthermore, this embodiment can avoid partial energy loss of the marker light during the measurement process, preventing a decrease in the light energy in the main measurement optical path.

[0089] The signal detection unit 70 may employ, but is not limited to, a Shack-Hartmann wavefront sensor, a shear interferometer, or a curvature sensor.

[0090] The foregoing preferred embodiments have further illustrated the objectives, technical solutions, and advantages of the present invention. It should be understood that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A collection system characterized by, The collection system comprises: an objective lens for collecting a mark light from an object to be measured and imaging the mark light on an image plane; a first phase modulation element arranged at a pupil plane of a collection light path of the collection system, the first phase modulation element being provided with at least two first modulation pixels for modulating a phase of the mark light passing through the first modulation pixels; a driver connected to the first phase modulation element for controlling driving voltages of the at least two first modulation pixels respectively; a detection element arranged at the image plane.

2. The collection system of claim 1, wherein, The at least two first modulation pixels are divided into at least two sub-zones, and the first modulation pixels in any of the sub-zones are further used for introducing a linear phase to the mark light passing through the sub-zone, and the linear phases introduced by the first modulation pixels in the at least two sub-zones are different.

3. The collection system of claim 1, wherein, The first phase modulation element comprises: a first sub-phase modulation element provided with the at least two first modulation pixels; a second sub-phase modulation element arranged in a stack with the first sub-phase modulation element and provided with at least two second modulation pixels; the driver is connected to the first sub-phase modulation element and the second sub-phase modulation element respectively, and is further used for controlling driving voltages of the at least two second modulation pixels respectively.

4. The collection system of claim 3, wherein, The at least two second modulation pixels of the second sub-phase modulation element are divided into at least two sub-zones, and the second modulation pixels in any of the sub-zones are used for introducing a linear phase to the mark light passing through the sub-zone, and the linear phases introduced by the second modulation pixels in the at least two sub-zones are different.

5. A lithography apparatus comprising: a metrology device according to any one of claims 1 to 4. The collection system comprises: a light source; the collection system according to any one of claims 1 to 4.

6. The overlay metrology apparatus of claim 5, wherein, Further comprising: a second phase modulation element arranged at a pupil plane of an illumination light path of the collection system, the second phase modulation element being provided with at least two third modulation pixels for modulating a phase of the illumination light passing through the third modulation pixels; the driver of the collection system is connected to the second phase modulation element, and is further used for controlling driving voltages of the at least two third modulation pixels respectively.

7. The overlay metrology apparatus of claim 6, wherein, Further comprising: a first light splitting element arranged between the objective lens and the image plane of the collection system; the light source is arranged on an incident light path of the first light splitting element, the objective lens is arranged on a reflection light path of the first light splitting element, and the second phase modulation element is arranged between the light source and the first light splitting element.

8. The overlay metrology apparatus of claim 6, wherein, Further comprising: a second light splitting element arranged between the objective lens and the image plane of the collection system, and the objective lens is arranged on a reflection light path of the second light splitting element; a third light splitting element arranged on an incident light path of the second light splitting element, and the light source is arranged on an incident light path of the third light splitting element; a reflecting element arranged on a reflection light path of the third light splitting element, and the second phase modulation element is arranged between the reflecting element and the third light splitting element.

9. The overlay metrology apparatus of claim 5, wherein, Further comprising: a fourth light splitting element arranged between the objective lens and the first phase modulation element of the collection system; a signal detection unit arranged on a reflection light path of the fourth light splitting element; a signal processing unit connected to the signal detection unit and the driver of the collection system respectively.

10. The overlay metrology apparatus of claim 5, wherein, Further comprising: A signal detecting unit is arranged at a preset position on the light path between the objective lens and the image plane of the collection system, and can be moved into and out of the preset position. A signal processing unit is connected with the signal detecting unit and the driver of the collection system, respectively.

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