CN115390369A

CN115390369A - Accurate focusing overlay error measurement system and method

Info

Publication number: CN115390369A
Application number: CN202211144462.1A
Authority: CN
Inventors: 李星辉; 邓富元; 李一鸣; 单硕楠; 王晓浩
Original assignee: Shenzhen International Graduate School of Tsinghua University
Current assignee: Shenzhen International Graduate School of Tsinghua University
Priority date: 2022-09-20
Filing date: 2022-09-20
Publication date: 2022-11-25

Abstract

The invention discloses an accurate-focusing overlay error measuring system and method, which are used for measuring overlay errors of a measured object, wherein the overlay error measuring system comprises an optical component and a control component, the control component is connected with the optical component, a light path in the optical component forms an out-of-focus information measuring module and a diffraction spot imaging module, the out-of-focus information measuring module is used for measuring spectral information of the measured object, the control component is used for judging whether the measured object is currently in a focus position according to the spectral information of the measured object, and is used for adjusting the position of the measured object when the measured object is not currently in the focus position so as to enable the measured object to be in the focus position; the diffraction light spot imaging module is used for acquiring diffraction light spots of the measured object, and the control assembly is used for calculating the overlay error of the measured object according to the diffraction light spots of the measured object acquired by the diffraction light spot imaging module. The invention can realize automatic and quick focusing so as to improve the measurement efficiency and precision of overlay errors.

Description

Accurate focusing overlay error measurement system and method

Technical Field

The invention relates to the technical field of photoetching, in particular to an overlay error measuring system and method for accurate focusing.

Background

In recent years, the field of integrated circuit manufacturing has developed rapidly, and double exposure technology has been widely used. With the extension of the lithography technology node, the lithography process puts higher requirements on the alignment precision, and the lithography process enters the sub-nanometer field. Overlay error (overlay error) is one of important performance indexes for describing interlayer overlay accuracy, and the two most mainstream overlay error measurement technologies at present are image-based overlay (IBO) and diffraction-based (DBO) overlay error measurement technologies respectively. However, due to the limitation of imaging resolution, the IBO technique has been gradually unable to meet the requirements of new process nodes for overlay measurement. The DBO detection technique has proven to be an effective overlay error detection technique, and is currently widely applied to the lithography process of advanced nodes.

As shown in fig. 1, the overlay error measurement mark has a double-layer grating structure (a lower-layer grating structure 02 and an upper-layer grating structure 03, respectively), and a silicon substrate 01 is disposed below the double-layer grating. The previous exposure image is subjected to the steps of development, etching, deposition and the like to form a lower grating structure 02; and the photoresist pattern after the exposure and development forms an upper grating structure 03. The position error between two exposures is the overlay error. The measurement principle is as follows: when measuring light enters the double-layer grating sleeve mark, the asymmetry of the mark structure caused by the sleeve mark error enables the light intensity of the high-order light of the diffracted light to generate asymmetry, and the asymmetry approximately presents linear change along with the sleeve mark error in a smaller sleeve mark error measuring range. If the overlay error is recorded as E, the diffraction light intensity of each level of the incident light is respectively I ⁺ And I ^- The asymmetry can be expressed approximately as: a = I ⁺ -I ^- K · E, where k is a factor related to measurement light, process, and the like.

Because the overlay mark is marked on the silicon chip, the structure of the overlay mark often has height difference in different measurement areas, and the object to be measured is possibly not in the depth of field range of the measurement system. In order to improve the measurement efficiency as much as possible and further improve the measurement accuracy, it is important to automatically and quickly focus the overlay error measurement system.

The above background disclosure is only provided to assist understanding of the concept and technical solution of the present invention, which does not necessarily belong to the prior art of the present patent application, and should not be used to evaluate the novelty and inventive step of the present application in the case that there is no clear evidence that the above content is disclosed at the filing date of the present patent application.

Disclosure of Invention

In order to solve the technical problems, the invention provides an overlay error measuring system and method with accurate focusing, which can realize automatic and rapid focusing so as to improve the measurement efficiency and precision of overlay errors.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention discloses an overlay error measuring system with accurate focusing, which is used for measuring an overlay error of a measured object and comprises an optical assembly and a control assembly, wherein the control assembly is connected with the optical assembly, a light path in the optical assembly forms an out-of-focus information measuring module and a diffraction light spot imaging module, the out-of-focus information measuring module is used for measuring spectral information of the measured object, and the control assembly is used for judging whether the measured object is currently in a focus position according to the spectral information of the measured object and adjusting the position of the measured object when the measured object is not currently in the focus position so as to enable the measured object to be in the focus position; the diffraction light spot imaging module is used for obtaining diffraction light spots of the measured object, and the control assembly is used for calculating the alignment error of the measured object according to the diffraction light spots of the measured object obtained by the diffraction light spot imaging module.

Preferably, the optical assembly includes a light beam incident unit, an out-of-focus information measuring unit and a diffraction spot imaging unit, wherein the light beam incident unit and the out-of-focus information measuring unit together form an out-of-focus information measuring module, and the light beam incident unit and the diffraction spot imaging unit together form a diffraction spot imaging module.

Preferably, the light beam incident unit includes a light source, a dispersive lens group, a negative lens group, a beam splitter and an objective lens, wherein the light source is configured to generate multi-wavelength composite light to sequentially pass through the dispersive lens group, the negative lens group, the beam splitter and the objective lens and then enter the defocus information measuring unit and the diffraction spot imaging unit, the dispersive lens group is configured to split the multi-wavelength composite light generated by the light source, and the negative lens group is configured to collimate a light beam with a target wavelength; the spectroscope is used for coupling a light path entering the defocusing information measuring unit and a light path of the diffraction light spot imaging unit, and the objective lens is used for converging light with different wavelengths and collecting diffraction light on the surface of the measured object.

Preferably, out of focus information measuring unit includes speculum, spatial filter element, lens and spectrum appearance, the speculum is arranged in being coupled out with the 0 th order diffraction light in the beam of light that jets out in the beam incident unit, spatial filter unit is arranged in only making 0 th order diffraction light in focus on the range finding light on measured object surface passes through in order to form the confocal of light path, lens set up in spatial filter element with in order to pass through between the spectrum appearance 0 th order diffraction light coupling entering of spatial filter unit the spectrum appearance, the spectrum appearance is used for gathering the spectral information of the range finding light on measured object surface.

Preferably, the diffraction light spot imaging unit includes a filter and a CCD imaging detector, wherein the filter is used for obtaining the light beam with the target wavelength from the light beam emitted from the light beam incidence unit, and the CCD imaging detector is used for receiving the light beam with the target wavelength to obtain the diffraction light spot of ± 1 st order.

Preferably, the control assembly includes a central processing unit, a digital signal processing module and a module for driving the movement of the object to be measured, the central processing unit is connected to the digital signal processing module and the module for driving the movement of the object to be measured, wherein: the utility model discloses a defocusing information measurement module, including defocusing information measurement module, central processing unit, digital signal processing module, drive measured object moving module, central processing unit is used for receiving defocusing information measurement module measures the spectral information of measured object and sends for digital signal processing module, digital signal processing module is used for the basis whether the spectral information of measured object judges the measured object is currently in the focus position, central processing unit is used for the measured object is not sent when in the focus position and adjusts the signal of measured object's position gives drive measured object moving module, drive measured object moving module is used for the basis signal drive the measured object is along the direction removal that is on a parallel with the focus so that the measured object is in the focus position.

Preferably, the control assembly further comprises an overlay error calculation module, the central processing unit is connected with the overlay error calculation module, wherein: the central processing unit is used for receiving the diffraction light spots of the measured object obtained by the diffraction light spot imaging module and sending the diffraction light spots to the alignment error calculation module, and the alignment error calculation module is used for calculating the alignment error of the measured object according to the diffraction light spots of the measured object.

In a second aspect, the present invention discloses a method for measuring an overlay error of a measured object by using the overlay error measuring system of the first aspect, comprising the following steps:

s1: measuring the spectral information of the measured object by adopting the defocusing information measuring module;

s2: the control assembly judges whether the object to be measured is in the in-focus position currently according to the spectral information of the object to be measured, if so, the step S4 is executed, and if not, the step S3 is executed;

s3: the control assembly adjusts the position of the measured object to enable the measured object to be in an in-focus position;

s4: acquiring diffraction light spots of the measured object by adopting the diffraction light spot imaging module;

s5: and the control component calculates the overlay error of the measured object according to the diffraction light spots of the measured object acquired by the diffraction light spot imaging module.

Preferably, the control assembly includes a central processing unit, a digital signal processing module and a module for driving the object to be measured to move, the central processing unit is connected to the digital signal processing module and the module for driving the object to be measured to move simultaneously, wherein:

the step S2 specifically includes: the central processing unit receives the spectral information of the measured object measured by the defocusing information measuring module and sends the spectral information to the digital signal processing module, the digital signal processing module judges whether the measured object is in a focus position currently according to the spectral information of the measured object, if so, the step S4 is executed, and if not, the step S3 is executed;

step S3 specifically includes: the central processing unit sends a signal for adjusting the position of the measured object to the measured object driving moving module, and the measured object driving moving module drives the measured object to move along the direction parallel to the focal length according to the signal so that the measured object is in the in-focus position.

Preferably, the control assembly further comprises an overlay error calculation module, the central processing unit is connected with the overlay error calculation module, wherein:

step S5 specifically includes: the central processing unit receives the diffraction light spots of the measured object acquired by the diffraction light spot imaging module and sends the diffraction light spots to the overlay error calculation module, and the overlay error calculation module calculates the overlay error of the measured object according to the diffraction light spots of the measured object.

Further, the method also comprises the step S6: and the module for driving the measured object to move drives the measured object to move in the horizontal direction perpendicular to the focal length so as to measure the next area to be measured of the measured object, and the step S1 is returned.

Compared with the prior art, the invention has the beneficial effects that: according to the accurate-focusing overlay error measuring system and method, the defocusing information measuring module and the diffraction light spot imaging module are formed through the light path in the optical assembly, so that automatic focusing can be performed through the overlay error measuring system, optical energy is effectively utilized, imaging quality and signal-to-noise ratio are improved, measuring accuracy is improved, and the requirement of a higher process node on overlay measurement is met. Moreover, defocusing information can be obtained through analysis of the measured spectrum, and the focusing speed and the focusing precision are effectively improved compared with the traditional automatic focusing technology.

In a further scheme, the defocusing information measuring unit utilizes 0-order diffracted light to perform fixed-focus distance measurement, and the diffracted light spot imaging unit +/-1-order diffracted light is used for measuring overlay error, so that the problems of light intensity crosstalk, pixel saturation and the like caused by simultaneous detection of 0-order and +/-1-order on a detector are avoided, and the measurement precision is further improved.

Drawings

FIG. 1 is a schematic illustration of overlay error measurement marks;

FIG. 2 is a schematic diagram of a precision focus overlay error measurement system according to a preferred embodiment of the present invention;

FIG. 3 is a schematic view of the optical assembly of FIG. 2;

fig. 4 is a flowchart illustrating a method for measuring an overlay error in a precise focus according to a preferred embodiment of the present invention.

Detailed Description

The embodiments of the present invention will be described in detail below. It should be emphasized that the following description is merely exemplary in nature and is in no way intended to limit the scope of the invention or its applications.

It will be understood that when an element is referred to as being "secured to" or "disposed on" another element, it can be directly on the other element or be indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or be indirectly connected to the other element. In addition, the connection may be for either a fixed function or a circuit/signal communication function.

It is to be understood that the terms "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like are used in an orientation or positional relationship indicated in the drawings to facilitate the description of the embodiments of the invention and to simplify the description, and are not intended to indicate or imply that the device or element so referred to must have a particular orientation, be constructed in a particular orientation, and be constructed in a particular manner of operation, and are not to be construed as limiting the invention.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the embodiments of the present invention, "a plurality" means two or more unless specifically limited otherwise.

The existing automatic focusing technology mainly comprises an image method, a laser triangulation distance measuring method and the like. The image method mainly utilizes the imaged graph to evaluate the image definition, and utilizes a focusing search algorithm to drive and control a lens according to an imaging result so as to realize accurate focusing; however, this method is generally time-consuming and highly dependent on the performance of the processor. In addition, the method is a laser triangulation ranging method, a laser beam irradiates a target to be measured at a certain incident angle, the laser beam is reflected and scattered on the surface of the target, the reflected laser beam is converged and imaged by a lens at another angle, and light spots are imaged on a CCD sensor; when the measured object moves along the laser direction, the light spot on the position sensor moves, and the displacement of the light spot corresponds to the moving distance of the measured object, so that the distance value between the measured object and the base line can be calculated by the light spot displacement distance through algorithm design; the method has the advantages of simple structure and high reliability, but has the problem of poor precision for smaller objects.

The confocal method is adopted in the invention, the confocal method utilizes the conjugate relation of a confocal system, has unique optical axial characteristics and high flexibility, and is particularly suitable for short-distance precise displacement measurement.

As shown in fig. 2, a preferred embodiment of the present invention discloses an overlay error measuring system with precise focusing, which is used for measuring an overlay error of a measured object, and includes an optical assembly 100 and a control assembly 200, the control assembly 200 is connected to the optical assembly 100, a light path in the optical assembly 100 forms an out-of-focus information measuring module 110 and a diffraction spot imaging module 120, the out-of-focus information measuring module 110 is used for measuring spectral information of the measured object, and the control assembly 200 is used for determining whether the measured object is currently in-focus position according to the spectral information of the measured object, and for adjusting the position of the measured object when the measured object is not currently in-focus position, so that the measured object is in-focus position; the diffraction light spot imaging module 120 is configured to obtain diffraction light spots of the object to be measured, and the control component 200 is configured to calculate an overlay error of the object to be measured according to the diffraction light spots of the object to be measured obtained by the diffraction light spot imaging module.

Specifically, the control assembly 200 includes a central processing unit 210, a digital signal processing module 220, an overlay error calculating module 230, a measured object moving driving module 240 and a light intensity controlling module 250, wherein the central processing unit 210 is connected to the digital signal processing module 220, the overlay error calculating module 230, the measured object moving driving module 240 and the light intensity controlling module 250, and wherein: the central processing unit 210 is configured to receive spectral information of the measured object measured by the defocus information measuring module 110 and send the spectral information to the digital signal processing module 220, the digital signal processing module 220 is configured to determine whether the measured object is currently located at a focal position according to the spectral information of the measured object, the central processing unit 210 is configured to send a signal for adjusting the position of the measured object to the measured object moving driving module 240 when the measured object is not currently located at the focal position, and the measured object moving driving module 240 is configured to drive the measured object to move along a direction parallel to the focal length according to the signal so that the measured object is located at the focal position; the central processing unit 210 is further configured to receive the diffraction light spot of the measured object obtained by the diffraction light spot imaging module 120 and send the diffraction light spot to the overlay error calculation module 230, where the overlay error calculation module 230 is configured to calculate an overlay error of the measured object according to the diffraction light spot of the measured object. The intensity control module 250 adjusts the intensity of the light sources in the optical assembly 100 as needed.

The optical assembly comprises a light beam incidence unit, a defocusing information measuring unit and a diffraction light spot imaging unit, wherein the light beam incidence unit and the defocusing information measuring unit jointly form a defocusing information measuring module, and the light beam incidence unit and the diffraction light spot imaging unit jointly form a diffraction light spot imaging module.

As shown in fig. 3, the light beam incident unit includes a light source 11, a dispersive lens group 12, a negative lens group 13, a beam splitter 14 and an objective lens 15, the defocus information measuring unit includes a mirror 21, a spatial filter element 22, a lens 23 and a spectrometer 24, and the diffraction spot imaging unit includes a narrow band filter 31 and a CCD imaging detector 32. The object to be measured comprises an overlay measuring mark 310 and a silicon chip 320; the module 240 for moving the object to be measured includes a motor driving device 241, a focusing movement device 242, a scanning movement device 243, and a silicon stage or holding device 244.

The function of the individual components of the optical component is as follows:

light source 11: generating multi-wavelength composite light by a polychromatic light source or a broadband light source;

the dispersive lens group 12: a dispersion lens group for splitting the light beam;

negative lens group 13: the light rays are collimated, so that the light beams with the target wavelength are collimated in parallel;

beam splitter 14: coupling of the light path of the ranging light and the imaging light is achieved;

objective lens 15: converging light with different wavelengths, forming focuses at different positions on the main optical axis along the Z-axis forward direction, and collecting diffracted light on the surface of the measured object;

the reflection mirror 21: coupling out the 0 th order diffraction light for ranging;

spatial filter element 22: the spatial filtering structure with a small hole or slit structure filters the returned distance measuring light and only enables the distance measuring light focused on the surface of the object to be measured to pass through, so as to realize light path confocal, wherein the small hole or slit structure is generally within the magnitude of hundreds of micrometers, such as 100-900 micrometers, and in other embodiments, an optical fiber can be adopted to replace a light inlet;

lens 23: the distance measuring light ray passing through the spatial filter element 22 is coupled into the spectrometer 24;

the spectrometer 24: collecting spectral information of ranging light focused on the surface of a measured object to enable the surface of the measured object to be positioned on a focal plane of a target wavelength light beam, and realizing focusing;

narrow band filter 31: to obtain light of a single wavelength, light of a target wavelength;

CCD imaging detector 32: and receiving the +1 order and-1 order of the obtained diffracted light for overlay error calculation.

In addition, the object to be measured is composed of two parts:

overlay measurement mark 310: the double-layer grating structure has a certain grating period;

silicon wafer 320: carries the overlay measurement mark, and forms the measured object with the overlay measurement mark 310.

The module 240 for moving the object to be measured includes the following components (the motor driving device 241 is not shown in the figure):

focus movement device 242: the device is used for driving the silicon chip to move along the Z axis so as to change the distance between the silicon chip and the objective lens;

the scanning movement device 243: the automatic focusing device is used for driving the silicon chip to move in an X-Y plane so as to realize automatic focusing at different positions;

silicon wafer stage or clamping device 244: ensuring that the silicon chip does not generate any offset when doing displacement motion;

light starts from a light source 11, is split into ranging light containing a plurality of wavelength information after passing through a dispersion lens group 12, and is collimated through a negative lens group 13; after reaching the beam splitter 14, the light beams with different wavelengths can be focused at different positions on the optical axis through the objective lens 15; when focused on the object to be measured, i.e. the overlay measurement mark 310 with the double-layer grating, multi-wavelength diffraction occurs, and diffracted light containing orders 0, ± 1, is collected via the objective lens 15 and passed through the beam splitter 14. The 0 th order diffracted light is coupled out by the reflector 21, and passes through the spatial filter element 22, so that the ranging light of the 0 th order diffracted light, which has only the wavelength focused on the surface of the object to be measured, passes through the small hole or slit structure of the spatial filter element 22 (wherein, the 0 th order diffracted light includes light of various wavelengths, and then passes through the spatial filter element 22, it can be ensured that only the light of the specific wavelength just focused on the surface of the object to be measured forms a spectrum confocal condition, while the light of other wavelengths can be filtered out), thereby forming a light path confocal condition, and then the light path confocal condition is coupled into the spectrometer 24 through the lens 23.

The spectrum information obtained by the spectrometer 24 can be used to calculate the spatial position information, i.e. the focusing power, of the object to be measured according to the spectrum confocal principle. Subsequently, the focus moving device 242 is driven by the motor driving device 241 to reposition the silicon wafer 320 in the focal plane, and the imaging system is in focus. At this time, the diffracted ± 1-level light passes through the spectroscope 14 and the narrow band filter 31, and the narrow band filter 31 reaches the CCD imaging detector 32 only through the imaging light focused on the target wavelength of the object to be measured, so that the CCD imaging detector 32 receives the ± 1-level two diffraction spots, thereby performing measurement calculation of overlay error. The target wavelength is a preset specific wavelength, and determines a focal plane of the imaging system with a fixed position. Specifically, the ± 1 st order diffracted light including a plurality of wavelengths passes through the filter 31 to obtain the diffracted light of the target wavelength for imaging.

In the overlay error measurement system, the central processing unit 210 in the control assembly 200 is the core of the whole measurement system, and directly controls the digital signal processing module 220, the overlay error calculation module 230, the measured object driving module 240 and the light intensity control module 250.

As shown in fig. 4, another preferred embodiment of the present invention discloses a method for measuring overlay error with accurate focusing, which is characterized in that the overlay error measuring system is used for measuring overlay error of a measured object, and the method comprises the following steps:

s1: measuring the spectral information of the measured object by using a defocusing information measuring module;

s2: the control assembly judges whether the measured object is in the in-focus position currently according to the spectral information of the measured object, if so, the step S4 is executed, and if not, the step S3 is executed;

further, step S2 specifically includes: the central processing unit receives the spectral information of the measured object measured by the defocusing information measuring module and sends the spectral information to the digital signal processing module, the digital signal processing module judges whether the measured object is in the in-focus position currently according to the spectral information of the measured object, if so, the step S4 is executed, and if not, the step S3 is executed;

s3: the control assembly adjusts the position of the measured object so that the measured object is in the in-focus position;

further, step S3 specifically includes: the central processing unit sends a signal for adjusting the position of the measured object to the measured object moving driving module, and the measured object moving driving module drives the measured object to move along the direction parallel to the focal length according to the signal so that the measured object is located at the in-focus position.

S4: acquiring diffraction light spots of a measured object by adopting a diffraction light spot imaging module;

s5: the control component calculates the overlay error of the measured object according to the diffraction light spot of the measured object obtained by the diffraction light spot imaging module;

further, step S5 specifically includes: the central processing unit receives the diffraction light spots of the measured object obtained by the diffraction light spot imaging module and sends the diffraction light spots to the alignment error calculation module, and the alignment error calculation module calculates the alignment error of the measured object according to the diffraction light spots of the measured object;

s6: and driving the measured object moving module to drive the measured object to move in the horizontal direction perpendicular to the focal length so as to measure the next area to be measured of the measured object, and returning to the step S1 until all the areas to be measured of the measured object are completely measured.

As can be seen from the above embodiments, in a complete work flow, firstly, the defocusing information measuring module 110 measures to obtain the measured object currently located at a certain position, that is, the spectrum information of the double-layer grating overlay measuring mark 310; the digital signal processing module 220 can perform a displacement calculation on the signal to obtain defocus information, which includes a filtering operation on the spectrum. Then, the central processing unit 210 feeds back the calculated displacement value to the motor driving device 241 in the module 240 for driving the object to be measured, and further drives the focusing movement device 242 to move up and down along the optical axis of the imaging system (the optical axis when the optical assembly 100 enters the object to be measured) to carry the object to be measured, i.e., the silicon wafer 320, so as to achieve precise focusing. After focusing is completed, the diffraction spot imaging module 120 starts to operate. The filter can pass through the set imaging target wavelength and filter out light of other wavelength bands, so that +/-1-level light spots of single-wavelength diffracted light are imaged on the CCD imaging detector 32. Then, the overlay error can be measured by the overlay error calculation module 230. Finally, after the measurement of the current region is completed, the central processing unit 210 controls the motor driving device 241 again to drive the scanning movement device 243 to perform the overlay error measurement of the next region to be measured. In addition, the light intensity control module 250 in the system can also adjust the light intensity of the light source 11 according to factors such as objective environment.

Aiming at the problem of overlay error scattering imaging, the invention improves an automatic focusing method suitable for overlay error measurement, and provides a new focusing method; the traditional method combining eccentric laser triangulation ranging and image processing has many disadvantages, such as a visual field blind area caused by oblique incidence of an optical path, limited measurement precision, long time consumption in the measurement process and the like. In the invention, the used automatic focusing method has higher measurement precision for the characteristics of ultra-short working distance and ultra-small depth of field with high numerical aperture, and can realize accurate positioning. In the scheme, particularly, aiming at the diffraction characteristic of the measured object (namely, the double-layer grating overlay measurement mark), the 0-order diffraction light is innovatively utilized for fixed-focus distance measurement, and the +/-1-order diffraction light is used for overlay error measurement; focusing and measuring are carried out firstly, and a complete overlay error measuring system is formed. The whole optical system is compact and has high utilization rate of light energy.

The system and the method for measuring the overlay error with accurate focusing disclosed by the preferred embodiment of the invention have the advantages that: automatic focusing is performed before overlay error measurement, so that light energy is effectively utilized, imaging quality and signal-to-noise ratio are improved, measurement accuracy is improved, and the requirement of a higher process node on overlay measurement is met. The automatic focusing method is different from the traditional image processing automatic focusing method, avoids a large amount of image processing and searching processes, can obtain out-of-focus information through analysis of a measured spectrum, and effectively improves focusing speed and focusing precision compared with the traditional automatic focusing technology. When measuring light is incident to the double-layer grating overlay measuring mark, the asymmetry of the mark structure caused by the overlay error enables the light intensity of diffracted light to generate asymmetry, and the asymmetry approximately presents linear change along with the overlay error in a smaller overlay error measuring range; and coupling out 0-order diffraction light, thereby avoiding the problems of light intensity crosstalk, pixel saturation and the like caused by simultaneous detection of 0-order and +/-1-order on a detector, and further improving the measurement precision.

The background of the invention may contain background information related to the problem or environment of the present invention rather than the prior art described by others. Accordingly, the inclusion in this background section is not an admission by the applicant that prior art is available.

The foregoing is a further detailed description of the invention in connection with specific/preferred embodiments and it is not intended to limit the invention to the specific embodiments described. It will be apparent to those skilled in the art that various substitutions and modifications can be made to the described embodiments without departing from the spirit of the invention, and these substitutions and modifications should be considered to fall within the scope of the invention. In the description herein, references to the description of the term "one embodiment," "some embodiments," "preferred embodiments," "an example," "a specific example," or "some examples" or the like are intended to mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction. Although embodiments of the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the scope of the invention as defined by the appended claims.

Claims

1. An accurate-focusing overlay error measuring system is characterized by being used for measuring overlay errors of a measured object and comprising an optical assembly and a control assembly, wherein the control assembly is connected with the optical assembly, a light path in the optical assembly forms an out-of-focus information measuring module and a diffraction light spot imaging module, the out-of-focus information measuring module is used for measuring spectral information of the measured object, and the control assembly is used for judging whether the measured object is currently in a focus position according to the spectral information of the measured object and adjusting the position of the measured object to enable the measured object to be in the focus position when the measured object is not currently in the focus position; the diffraction light spot imaging module is used for obtaining diffraction light spots of the measured object, and the control assembly is used for calculating the alignment error of the measured object according to the diffraction light spots of the measured object obtained by the diffraction light spot imaging module.

2. The overlay error measurement system of claim 1 wherein the optical assembly comprises a beam incident unit, a defocus information measurement unit, and a diffraction spot imaging unit, wherein the beam incident unit and the defocus information measurement unit together form a defocus information measurement module, and the beam incident unit and the diffraction spot imaging unit together form a diffraction spot imaging module.

3. The overlay error measurement system of claim 2, wherein the light beam incident unit comprises a light source, a dispersive lens group, a negative lens group, a beam splitter and an objective lens, wherein the light source is configured to generate multi-wavelength composite light to sequentially pass through the dispersive lens group, the negative lens group, the beam splitter and the objective lens and then enter the defocus information measurement unit and the diffraction spot imaging unit, respectively, the dispersive lens group is configured to split the multi-wavelength composite light generated by the light source, and the negative lens group is configured to collimate a light beam at a target wavelength; the spectroscope is used for coupling a light path entering the defocusing information measuring unit and a light path of the diffraction light spot imaging unit, and the objective lens is used for converging light with different wavelengths and collecting diffraction light on the surface of the measured object.

4. The overlay error measurement system according to claim 2, wherein the defocus information measurement unit includes a mirror for coupling out 0 th order diffracted light in the light beam emitted from the light beam incident unit, a spatial filter unit for passing only ranging light focused on the surface of the object to be measured among the 0 th order diffracted light to form a light path confocal, a lens disposed between the spatial filter unit and the spectrometer for coupling the 0 th order diffracted light passing through the spatial filter unit into the spectrometer, and a spectrometer for collecting spectral information of the ranging light on the surface of the object to be measured.

5. The overlay error measurement system of claim 2, wherein the diffraction spot imaging unit comprises a filter and a CCD imaging detector, wherein the filter is configured to obtain the light beam with the target wavelength from the light beam emitted from the light beam incident unit, and the CCD imaging detector is configured to receive the light beam with the target wavelength to obtain the diffraction spot of ± 1 st order.

6. The overlay error measurement system of any one of claims 1-5, wherein the control assembly comprises a central processing unit, a digital signal processing module, and a module for driving movement of the object to be measured, the central processing unit being connected to both the digital signal processing module and the module for driving movement of the object to be measured, wherein: the central processing unit is used for receiving the spectral information of the measured object measured by the defocusing information measuring module and sending the spectral information to the digital signal processing module, the digital signal processing module is used for judging whether the measured object is at the in-focus position or not according to the spectral information of the measured object, the central processing unit is used for sending a signal for adjusting the position of the measured object to the driving measured object moving module when the measured object is not at the in-focus position, and the driving measured object moving module is used for driving the measured object to move along the direction parallel to the focal length according to the signal so that the measured object is at the in-focus position.

7. The overlay error measurement system of claim 6 wherein the control assembly further comprises an overlay error calculation module, the central processing unit being connected to the overlay error calculation module, wherein: the central processing unit is used for receiving the diffraction light spots of the measured object obtained by the diffraction light spot imaging module and sending the diffraction light spots to the alignment error calculation module, and the alignment error calculation module is used for calculating the alignment error of the measured object according to the diffraction light spots of the measured object.

8. An overlay error measuring method for precise focusing is characterized in that an overlay error measuring system of any one of claims 1 to 5 is adopted to measure the overlay error of a measured object, and the method comprises the following steps:

9. The overlay error measuring method according to claim 8, wherein the control assembly comprises a central processing unit, a digital signal processing module, and a module for driving the object to be measured to move, the central processing unit is connected to the digital signal processing module and the module for driving the object to be measured to move simultaneously, wherein:

the step S2 specifically includes: the central processing unit receives the spectral information of the measured object measured by the defocusing information measuring module and sends the spectral information to the digital signal processing module, the digital signal processing module judges whether the measured object is at a focal position currently according to the spectral information of the measured object, if so, the step S4 is executed, and if not, the step S3 is executed;

10. The overlay error measurement method of claim 9 wherein the control assembly further comprises an overlay error calculation module, the central processing unit being connected to the overlay error calculation module, wherein:

step S5 specifically includes: the central processing unit receives the diffraction light spot of the measured object obtained by the diffraction light spot imaging module and sends the diffraction light spot to the overlay error calculation module, and the overlay error calculation module calculates the overlay error of the measured object according to the diffraction light spot of the measured object;