A device and method for testing a key dimension of a conical surface diffraction wafer

Abstract

The application discloses a kind of conic surface diffraction wafer critical dimension testing device and method, the device includes wafer pose adjustment module, light scattering detection module, light incidence module and host computer;Wafer pose adjustment module is used to realize the pose adjustment of wafer, light incidence module is incident to the diffraction light of wafer surface with detection light, and light scattering detection module is used to detect diffraction light intensity;Host computer is used to calculate the diffraction polar angle and diffraction azimuth angle of each diffraction order, controls light scattering detection module to move to corresponding position according to the calculation result to carry out the light intensity detection of each diffraction order, and the diffraction efficiency under different laser wavelength, incidence polar angle and incidence azimuth angle is calculated in combination with reference light intensity, and the critical dimension of wafer is obtained according to diffraction efficiency.The application adopts conic surface diffraction mode to combine the mode of multiple wavelengths to measure wafer critical dimension, can obtain more dimensional information, and significantly improve the measurement sensitivity of complex three-dimensional nanostructure.

Description

Technical Field

[0001] This invention belongs to the field of integrated circuit measurement, specifically relating to a device and method for testing critical dimensions of a cone-shaped diffraction wafer. Background Technology

[0002] There are three main methods for measuring critical dimensions: critical dimension measurement equipment based on optical microscopes (MCD), critical dimension scanning electron microscope (CD-SEM), and optical critical dimension measuring instrument (OCD).

[0003] MCDs measure key dimensions such as linewidth based on the imaging principle of optical microscopes. However, their measurement resolution is limited by the wavelength of incident light and the optical resolution of the microscope objective. They are mainly used for chips with process technologies above 100nm and can no longer meet the needs of measuring key dimensions in advanced processes of high-end chips.

[0004] The CD-SEM measurement method mainly uses a high-resolution scanning electron microscope to directly image and observe the wafer surface, and extracts key dimensional parameters such as chip linewidth through image recognition algorithms. CD-SEM has advantages such as high precision in measuring linewidth variations and line edge roughness, but it also has a series of disadvantages: it requires the wafer to be placed in a vacuum, resulting in slow measurement speed and large equipment size, which is not conducive to integration; and the high voltage charge accumulation may be destructive to the sample material.

[0005] OCD measurement methods are mainly based on light scattering measurement technology. By measuring the scattered light spectrum signal on the wafer surface and combining it with a fast calculation algorithm for the scattered photoelectric magnetic field, key dimensional information such as the chip's linewidth can be indirectly calculated. OCD measurement equipment has become a major tool in advanced integrated circuit manufacturing processes. However, in current polarization-reflection spectral OCDs, both the incident light and the diffracted light are perpendicular to the grating lines, resulting in weak acquisition of three-dimensional structural information and low accuracy in inverting complex morphologies. When measuring ultra-large aspect ratio structures or extremely small linewidths, the low energy and low signal-to-noise ratio of higher-order diffraction orders in plane wave diffraction make it difficult for the inversion algorithm to reach convergence during iteration. Summary of the Invention

[0006] The purpose of this invention is to provide a cone diffraction wafer critical dimension testing device and method. By using cone diffraction combined with multi-wavelength methods to measure the critical dimensions of the wafer, more dimensional information can be obtained, significantly improving the measurement sensitivity of complex three-dimensional nanostructures.

[0007] To achieve the above objectives, one aspect of the present invention provides a wafer critical dimension testing device for conical diffraction, comprising a wafer pose adjustment module, a light scattering detection module, a light incident module, and a host computer;

[0008] The wafer pose adjustment module includes a motion controller, a wafer fixing fixture, and a wafer pose five-axis motion actuator. The wafer fixing fixture is fixed on the wafer pose five-axis motion actuator and is used to fix the wafer to be tested. The wafer pose five-axis motion actuator is used to realize the pose adjustment of the wafer. The motion controller is used to drive the wafer pose five-axis motion actuator.

[0009] The light incident module includes a monochromatic light source with continuously adjustable wavelength and an optical element module. The emitted laser light from the monochromatic light source is divided into a reference light and a probe light by the optical element module. The probe light is incident on the wafer surface to produce conical diffraction.

[0010] The light scattering detection module includes a first photodetector and a detector two-axis motion actuator. The first photodetector is used to detect the intensity of diffracted light and the intensity of detection light, and the detector two-axis motion actuator is used to drive the first photodetector to rotate for detection.

[0011] The host computer is used to control the wafer pose adjustment module to adjust the wafer pose, change the incident polar angle and incident azimuth angle of the laser incident on the wafer surface, control the monochromatic light source to change the laser wavelength, calculate the diffraction polar angle and diffraction azimuth angle of each diffraction order, control the light scattering detection module to move to the corresponding position according to the calculation results to detect the light intensity of each diffraction order, and calculate the diffraction efficiency under different laser wavelengths, incident polar angles and incident azimuth angles in combination with the reference light intensity, and obtain the key dimensions of the wafer based on the diffraction efficiency.

[0012] Another aspect of the present invention provides a method for testing critical dimensions of a wafer using conical diffraction, comprising:

[0013] The light incident module directs probe light onto the wafer surface to produce conical diffraction;

[0014] Calculate the diffraction polar angle θ based on the incident polar angle and the incident azimuth angle. m and diffraction azimuth angle φ m ;

[0015] The light scattering detection module is based on the diffraction polar angle θ m and diffraction azimuth angle φ m Move to the detection point and measure the light intensity l of diffraction order m. m The light incident module measures the intensity of the reference light. ;

[0016] The wafer pose adjustment module adjusts the wafer position to avoid the optical path, and the light scattering detection module moves to detect the laser intensity. t The light incident module measures the intensity of the reference light. ;

[0017] Calculate diffraction efficiency ;

[0018] The wafer pose adjustment module adjusts the wafer pose, changes the incident polar angle and incident azimuth angle, and the monochromatic light source adjusts the light wavelength. The above steps are repeated to calculate the diffraction efficiency, forming a test dataset of diffraction efficiency - incident polar angle - light wavelength.

[0019] The key dimensions of the wafer are determined by comparing the test dataset with the simulation database.

[0020] According to the cone diffraction wafer critical dimension testing apparatus and method of the present invention, the cone diffraction method combined with multi-wavelength method is used to measure the critical dimension of the wafer, which can obtain more dimensional information and significantly improve the measurement sensitivity of low reflectivity material nanostructures. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the present invention, the accompanying drawings used in the description of the embodiments of the present invention 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:

[0022] Figure 1 This is a schematic diagram of the structure of a wafer pose adjustment module according to an embodiment of the present invention;

[0023] Figure 2 This is a schematic diagram of the structure of a detector two-axis motion actuator according to an embodiment of the present invention;

[0024] Figure 3 This is a schematic diagram of the principle of a cone-shaped diffraction wafer critical dimension testing device according to an embodiment of the present invention;

[0025] Figure 4 This is a schematic diagram of the incident polar angle and incident azimuth angle according to an embodiment of the present invention;

[0026] Figure 5 This is a flowchart of a method for testing critical dimensions of a cone-shaped diffraction wafer according to an embodiment of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions 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 are within the scope of protection of this invention.

[0028] One embodiment of the present invention provides a wafer critical dimension testing device based on conical diffraction optical angular spectrum analysis to measure the critical dimensions of the wafer. The device includes a wafer pose adjustment module, a light scattering detection module, a light incident module, and a host computer. The wafer pose adjustment module, light scattering detection module, and light incident module are connected to the host computer via a data bus to achieve coordinated control and data interaction among the modules.

[0029] like Figures 1-3 As shown, the wafer pose adjustment module includes a motion controller, a wafer fixture 6, and a five-axis wafer pose adjustment mechanism, used to achieve precise alignment and pose adjustment of the wafer in three-dimensional space. The wafer fixture is used to fix the wafer, and it is fixed to the five-axis wafer pose adjustment mechanism. The five-axis wafer pose adjustment mechanism is used to adjust the wafer's pose, and the motion controller is used to control the movement of the five-axis wafer pose adjustment mechanism.

[0030] The light scattering detection module includes a first photodetector 9 and a detector biaxial motion actuator 7, used to achieve omnidirectional acquisition of the diffraction angle spectrum, improving the sensitivity and spatial resolution of signal acquisition. The light incident module is used to achieve wavelength selection of broadband light sources and real-time monitoring of laser wavelengths. The host computer integrates a signal acquisition card, data processing unit, and control module, responsible for the synchronous coordination of various parts of the device, raw data acquisition, and reconstruction and analysis of diffraction angle spectrum information.

[0031] The wafer pose five-axis motion actuator includes three linear motion axes and two rotary axes, namely the first linear motion axis 4, the second linear motion axis 5, the third linear motion axis 2, the first rotary axis 3, and the second rotary axis 1. The three linear motion axes are driven by servo motors combined with lead screws, and the two rotary axes are driven by the first rotary motor.

[0032] The second rotary axis 1 is located below the other four motion axes and can drive the remaining motion axes to rotate around the Z-axis. The third linear motion axis 2 is located above the second rotary axis 1 and below the other three motion axes, and achieves precise vertical displacement of the other three motion axes through precision guide rails and lead screw transmission. The first rotary axis 3 is located above the third linear motion axis 2, and its rotational direction is connected to the second linear motion axis 5, enabling the rotation of the first linear motion axis 4 and the second linear motion axis 5. The first linear motion axis 4 and the second linear motion axis 5 are arranged orthogonally to each other and are mounted together on the first rotary axis 3, enabling precise translation in mutually perpendicular directions in the horizontal plane. A wafer jig 6 is fixed to the mover on the second linear motion axis 5.

[0033] The motion controller is responsible for receiving instructions from the host computer, precisely driving the servo motors of each motion axis, and providing real-time position information.

[0034] The detector's two-axis motion actuator 7 has an L-shaped structure. Its vertical arm is a two-section telescopic structure, driven by a motor and a lead screw to achieve length adjustment, enabling vertical movement along the Z-axis. An integrating sphere 8 and a first photodetector 9 are installed at the moving end of the vertical arm to detect the intensity signals of the scattered light and the probe light, respectively. The integrating sphere is used to eliminate intensity errors caused by different incident angles. The horizontal arm is connected to a second rotary motor located below the second rotating shaft 1, driving the entire L-shaped structure to rotate around the Z-axis, enabling the detector to perform a full scan within the curved surface formed by the rotational motion of the vertical arm.

[0035] The first and second rotary motors are hollow rotary motors. The first rotary motor on the second rotating shaft 1 is coaxially integrated with the second rotary motor of the detector's two-axis motion actuator 7. The power supply and signal lines of the wafer pose adjustment module and the light scattering detection module are led out through the hollow shaft and connected to the conductive slip ring of the first rotary motor on the second rotating shaft 1. The conductive slip ring then distributes the lines to the ports of the base, achieving stable power supply and high-speed signal transmission under dynamic rotation. This integrated design effectively avoids the tangling problem of traditional external cables during rotation, significantly improving the stability and reliability of the system operation.

[0036] like Figure 3 As shown, the light incident module includes a monochromatic light source 10 with continuously tunable wavelength and an optical element module. The monochromatic light source 10 has a wavelength range of 250nm-950nm. The optical element module includes an achromatic lens 11, a polarizer 12, a beam splitter 13, and a second photodetector 14.

[0037] The emitted light from the monochromatic light source 10 is finally incident on the surface of the wafer under inspection. Its optical path is as follows: After being coupled out by optical fiber, the emitted light from the monochromatic light source 10 passes through the achromatic lens 11 and the polarizer 12. The beam splitter 13 splits the emitted light into two paths: one is the reference light and the other is the probe light. The probe light shines directly on the wafer surface, and the reference light is incident on the second photodetector 14.

[0038] The cone diffraction wafer critical dimension testing device of this invention utilizes cone diffraction optical angle spectral analysis technology to test wafer critical dimensions. The principle is as follows:

[0039] A monochromatic light source 10 generates laser light of a specific wavelength. After being conditioned by an achromatic lens 11 and a polarizer 12, the laser light is split into a reference beam and a probe beam by a beam splitter 13. The reference beam is used to monitor changes in laser intensity, and the probe beam is used to generate a diffraction signal incident on the wafer surface. When the probe beam is incident on the wafer surface, the incident wave vector k can be decomposed into the incident polar angle. and incident azimuth ,like Figure 4 As shown. Incident azimuth angle If the diffraction value is not equal to 0, then conical diffraction will occur. In this case, there must be two corresponding diffraction angles, one of which is the diffraction polar angle. The other is the diffraction azimuth angle. Both are related to the incident azimuth angle The relationship is shown in equations (1) and (2):

[0040] (1)

[0041] (2)

[0042] In the formula, The incident polar angle, Let m be the incident azimuth angle, and m be the diffraction order. The diffraction polar angle, The diffraction azimuth angle. λ is the wavelength of light, and d is the grating period of the wafer microstructure.

[0043] For critical dimensions of a wafer, such as common asymmetric trapezoidal gate structures, the diffraction efficiency of light is related to its structural parameters. By changing the laser wavelength, incident polar angle, and incident azimuth angle, multidimensional test data can be obtained. During the test, the wafer orientation adjustment module adjusts the wafer orientation to change the laser incident polar angle and incident azimuth angle, and the monochromatic light source adjusts the wavelength to change the wavelength. The diffraction polar angle and diffraction azimuth angle of each diffraction order can be calculated using equations (1) and (2). The light scattering detection module moves to the corresponding position to detect the light intensity based on the calculation results, and combined with the reference light intensity, the dataset under different laser wavelengths, incident polar angles, and incident azimuth angles can be calculated. By comparing the test dataset with the simulation database, the critical dimensions of the wafer can be obtained.

[0044] Embodiments of the present invention also provide a method for testing critical dimensions of a cone-shaped diffraction wafer, utilizing the testing apparatus described in the above embodiments of the present invention to perform critical dimension testing of the wafer. Figure 5 As shown, the critical dimension testing method for cone-shaped diffraction wafers according to an embodiment of the present invention includes the following steps:

[0045] Step S1: The wafer pose adjustment module adjusts the wafer to be measured to the origin of the coordinate system so that the normal of the wafer surface is perpendicular to the incident beam.

[0046] Step S2: Set initial variables i=1 (wavelength number) and j=1 (incident angle number);

[0047] Step S3: Input the coordinates of the test point of the wafer under test, the incident azimuth angle φ, the initial wavelength λ of the monochromatic light source when j is 0, the wavelength step size Δλ of the monochromatic light source, the incident angle step size Δθ, the grating period d of the wafer microstructure, and the diffraction order m into the host computer.

[0048] Step S4: The wafer pose adjustment module adjusts the wafer under test to the measurement point;

[0049] Step S5: Adjust the wafer orientation so that the initial incident polar angle θ i =90°;

[0050] Step S6, calculate the diffraction polar angle θ m and diffraction azimuth angle φ m ;

[0051] Step S7, set the monochromator laser wavelength λ i =λ （i-1） +Δλ;

[0052] Step S8, the light scattering detection module determines the diffraction polar angle θ. m and diffraction azimuth angle φ m Move to the detection point and test the light intensity of diffraction order m. l m ;

[0053] Step S9: The second photodetector of the light incident module measures the intensity of the reference light. ;

[0054] Step S10: The wafer pose adjustment module adjusts the wafer position to avoid the optical path, preventing the laser from incident on the wafer, and the moving light scattering detection module detects the laser intensity. l t ;

[0055] Step S11: The second photodetector of the light incident module measures the intensity of the reference light. ;

[0056] Step S12, calculate diffraction efficiency ;

[0057] Step S13: Record the diffraction efficiency , λ j Polar angle of incidence θ i Change the variable j = j + 1;

[0058] Step S14: Determine whether the monochromator laser wavelength is greater than 950nm. If not, return to step S7 to continue execution. If it is satisfied, proceed to the next step and variables i=i+1 and j=1.

[0059] Step S15: Adjust the wafer orientation and change the incident polar angle θ i =θ （i-1） +Δθ;

[0060] Step S16, determine the incident polar angle θ iIf the angle is greater than 180°, return to step S6 and continue running; if the angle is satisfied, proceed to the next step.

[0061] Step S17: Generate a test dataset of "diffraction efficiency - incident polar angle - light wavelength";

[0062] Step S18: The test dataset and simulation database are compared to determine the critical dimensions of the wafer. Electromagnetic field calculation algorithms (rigorous coupled-wave analysis, finite-time difference, etc.) are used to simulate and analyze the optical scattering of micro- and nano-structures on the wafer surface, forming an optical scattering simulation database with different critical dimensions. A database search algorithm based on nonlinear numerical optimization algorithms (Levenberg-Marquardt algorithm, etc.) is constructed to achieve rapid comparison between the wafer light scattering test dataset and the simulation database, thus solving for the measured values ​​of the critical wafer dimensions.

[0063] In summary, this invention presents a cone-face diffraction wafer critical dimension testing device and method. Unlike traditional OCDs that use plane waves incident in a single direction, this invention employs cone-face diffraction combined with multi-wavelength methods to measure wafer critical dimensions. By adjusting the wafer pose, incident light is directed onto the wafer surface at different wavelengths, incident polar angles, and incident azimuth angles to obtain cone-face diffraction. Then, by adjusting the position of the light scattering detection module to detect the intensity of the scattered light, a test dataset of "diffraction efficiency - incident polar angle - light wavelength" is obtained. This dataset is then compared with a database to obtain wafer critical dimension parameter information. Compared to existing technologies, this invention can obtain more dimensional information by adjusting more variables, significantly improving the measurement capabilities for high aspect ratio and complex three-dimensional nanostructures of low-reflectivity materials.

[0064] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A device for testing critical dimensions of a cone-shaped diffraction wafer, characterized in that, The device for measuring critical dimensions of a wafer based on cone diffraction spectral analysis includes a wafer pose adjustment module, a light scattering detection module, a light incident module, and a host computer. The wafer pose adjustment module includes a motion controller, a wafer fixing fixture, and a wafer pose five-axis motion actuator. The wafer fixing fixture is fixed on the wafer pose five-axis motion actuator and is used to fix the wafer to be tested. The wafer pose five-axis motion actuator is used to realize the pose adjustment of the wafer. The motion controller is used to drive the wafer pose five-axis motion actuator. The light incident module includes a monochromatic light source with continuously adjustable wavelength and an optical element module. The emitted laser light from the monochromatic light source is divided into a reference light and a probe light by the optical element module. The probe light is incident on the wafer surface to produce conical diffraction. The light scattering detection module includes a first photodetector and a detector two-axis motion actuator, which is used to realize omnidirectional acquisition of the diffraction light angle spectrum. The first photodetector is used to detect the intensity of the diffraction light and the intensity of the detection light. The detector two-axis motion actuator is used to drive the first photodetector to rotate for detection. The host computer is used to control the wafer pose adjustment module to adjust the wafer pose, change the incident polar angle and incident azimuth angle of the laser incident on the wafer surface, control the monochromatic light source to change the laser wavelength, calculate the diffraction polar angle and diffraction azimuth angle of each diffraction order, control the light scattering detection module to move to the corresponding position according to the calculation results to detect the light intensity of each diffraction order, and calculate the diffraction efficiency under different laser wavelengths, incident polar angles and incident azimuth angles in combination with the reference light intensity, and obtain the key dimensions of the wafer based on the diffraction efficiency; The detector's two-axis motion actuator is an L-shaped structure. Its vertical arm can move vertically along the Z-axis. The first photodetector is installed at the end of the vertical arm's moving end. The horizontal arm is connected to the second rotary motor, which drives the entire L-shaped structure to rotate around the Z-axis, thereby enabling the first photodetector to scan within the rotation plane. The optical element module includes an achromatic lens, a polarizer, a beam splitter, and a second photodetector. The outgoing light from the monochromatic light source passes through the achromatic lens and the polarizer, and is split into two paths by the beam splitter: one path is a reference light, and the other is a probe light. The probe light shines directly onto the wafer surface, while the reference light is incident on the second photodetector, which is used to measure the intensity of the reference light.

2. The apparatus as claimed in claim 1, characterized in that, The wafer pose five-axis motion actuator includes five motion axes, namely a first linear motion axis, a second linear motion axis, a third linear motion axis, a first rotation axis, and a second rotation axis; The second rotation axis is located below the other four motion axes and can drive the four motion axes to rotate around the Z-axis; The third linear motion axis is located above the second rotation axis and below the other three motion axes, enabling the vertical displacement of these three motion axes; The first rotation axis is located above the third linear motion axis and can drive the first and second linear motion axes to rotate. The first linear motion axis and the second linear motion axis are arranged orthogonally to each other and are both mounted on the first rotation axis, enabling them to translate in mutually perpendicular directions in the horizontal plane. A wafer fixture is fixed on the second linear motion axis.

3. The apparatus as described in claim 2, characterized in that, The first, second, and third linear motion axes are driven by servo motors combined with lead screws, while the first and second rotary axes are driven by a first rotary motor.

4. The apparatus as described in claim 3, characterized in that, The light scattering detection module also includes an integrating sphere, which is installed at the end of the moving end of the vertical arm to eliminate light intensity errors caused by different incident angles.

5. The apparatus as described in claim 4, characterized in that, The first and second rotary motors are hollow rotary motors, which are coaxially integrated. The power supply lines and signal lines of the wafer pose adjustment module and the light scattering detection module are led out through the hollow shaft and connected and fixed to the conductive slip ring of the first rotary motor.

6. A method for testing critical dimensions of a cone-shaped diffraction wafer, characterized in that, Performing wafer critical dimension testing using the apparatus of any one of claims 1-5, comprising: Step 1: The light incident module incident the probe light onto the wafer surface to generate conical diffraction; Step 2: Calculate the diffraction polar angle θ based on the incident polar angle and the incident azimuth angle. m and diffraction azimuth angle φ m ; Step 3, the light scattering detection module determines the diffraction polar angle θ. m and diffraction azimuth angle φ m Move to the detection point and measure the light intensity l of diffraction order m. m The light incident module measures the intensity of the reference light. ; Step 4: The wafer pose adjustment module adjusts the wafer position to prevent the laser from hitting the wafer, and the moving light scattering detection module detects the laser intensity. t The light incident module measures the intensity of the reference light. ; Step 5, calculate diffraction efficiency ; Step 6: The wafer pose adjustment module adjusts the wafer pose, changes the incident polar angle and incident azimuth angle, and the monochromatic light source adjusts the light wavelength. Steps 1-5 are repeated to form a test dataset of diffraction efficiency-incident polar angle-light wavelength. Step 7: Compare the test dataset with the simulation database to determine the critical dimensions of the wafer.

7. The method as described in claim 6, characterized in that, Calculate the diffraction polar angle θ based on the incident polar angle and the incident azimuth angle. m and diffraction azimuth angle φ m : ， ， in, The incident polar angle, Let m be the incident azimuth angle, and m be the diffraction order. λ is the wavelength of light, and d is the grating period of the wafer microstructure.

8. The method as described in claim 6 or 7, characterized in that, The step of comparing the test dataset with the simulation database to determine the wafer critical dimensions includes: performing simulation analysis on the optical scattering of the micro-nano structures on the wafer surface to form an optical scattering simulation database with different critical dimensions; and using a database search algorithm to compare the test dataset with the simulation database to solve for the measured values ​​of the wafer critical dimensions.

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