Overlay error measurement device and overlay error measurement method

Abstract

The present invention provides an overlay error measurement device and an overlay error measurement method, which belong to the field of semiconductor detection. The grating interferometry measurement system of the overlay error measurement device uses different wavelengths to illuminate the alignment grating and optimize the overlay error measurement result. The auxiliary measurement system measures the overlay error based on the acoustic field or thermal field excited by the pulse of the alignment grating buried in the wafer; the measurement method includes placing the wafer, pre-positioning the wafer, adjusting the grating interferometry measurement, optical interferometry measurement of the overlay error, and auxiliary measurement of the acoustic field and thermal field. The present application improves the accuracy of overlay error measurement under various deformation conditions by assigning wavelength weights; the alignment grating buried in the wafer is measured with the assistance of the acoustic field or thermal field, so as to realize various deformations of the overlay error and the position determination and overlay error measurement buried in the wafer, thereby improving the scope of application and facilitating promotion and application in the field of semiconductor quantity detection and processing.

Description

Technical Field

[0001] The invention belongs to the field of semiconductor detection and processing and manufacturing, and specifically relates to an overlay error measurement device and an overlay error measurement method. Background Art

[0002] During semiconductor measurement and processing, it is necessary to accurately position the wafer to be measured or processed. Automatic focusing is commonly used, but it needs to be aligned in advance. There are many commonly used alignment methods, such as alignment and measurement methods based on video images, alignment methods based on dual-light path illumination wave plates, alignment methods based on moiré fringes, and alignment and measurement methods based on grating diffraction interference. These methods have their own advantages and disadvantages, but the alignment and measurement method of grating diffraction interference is the most accurate, so it is also the mainstream alignment development direction of high-precision measurement in the future. However, the alignment mark needs to be oxidized, coated with glue, etched, etc. during the manufacturing process, and the alignment mark itself will also undergo morphological changes, such as depressions, slopes, top or bottom collapse, and other deformations, which will affect the final alignment effect.

[0003] Therefore, it is necessary to develop an alignment measurement device and a measurement method that can correct various deformations to solve the error influence caused by the deformation of the grating itself.

[0004] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art or prior art. Summary of the invention

[0005] In order to overcome the deficiencies of the prior art, an object of the present invention is to provide an overlay error measurement device and an overlay error measurement method, which can solve the above-mentioned problems.

[0006] Design principle: Build a multi-band optical overlay measurement system. Based on the influence of different deformations on alignment measurement, correct the alignment deviation caused by the deformation of the alignment grating. By comparing the differences in the sensitivity of multiple wavelengths to the alignment grating deformation, select the appropriate wavelength combination and assign corresponding weights to different wavelengths to optimize the final calculation results. At the same time, measure the alignment grating buried in the wafer with the aid of acoustic field or thermal field imaging.

[0007] An overlay error measurement device includes a grating interferometry measurement system based on multi-band illumination and an auxiliary measurement system which are electrically connected to a measurement and control processor, wherein the grating interferometry measurement system uses different wavelengths to illuminate an alignment grating and optimize the overlay error measurement result; and the auxiliary measurement system performs overlay error measurement on an acoustic field or a thermal field excited by a pulse based on an alignment grating buried in a wafer.

[0008] Optionally, the grating interferometry measurement system includes an illumination optical path and an imaging detection optical path, wherein the illumination optical path includes a multi-band combination light source, an illumination adjustment light group, a first polarization beam splitter and an objective lens, and the multi-band combination light source is used to provide an illumination light beam with multiple optional wavelengths to the alignment grating through the illumination optical path; the imaging detection optical path includes the objective lens, a self-reference interference lens group, an interference adjustment lens group, an imaging adjustment light group and a detector, and the optical information of the detector is transmitted to the measurement and control processor, and the measurement and control processor calculates the corrected overlay error measurement result based on the multi-wavelength optimization method.

[0009] Optionally, the illumination adjustment light group includes a combiner, a collimator group and an aperture, which are used to combine, collimate and adjust the outgoing illumination light.

[0010] Optionally, the self-referencing interferometer group includes a second polarization beam splitter, a reflection receiving right-angle prism and a transmission receiving right-angle prism, and the right-angle prism is used to flip the wavefront of the measurement beam by 180°.

[0011] Optionally, the interference adjustment lens group includes a first 1 / 4 wave plate, a second 1 / 4 wave plate and a third 1 / 4 wave plate; the first 1 / 4 wave plate is arranged between the first polarization beam splitter and the objective lens, and is used to adjust the illumination light beam into circularly polarized light; the second 1 / 4 wave plate and the third 1 / 4 wave plate are arranged between the corresponding right-angle prism and the second polarization beam splitter, and are used to convert the light beam into S-polarized light or P-polarized light; the measurement light beam output by the self-reference interference lens group combined with the second 1 / 4 wave plate and the third 1 / 4 wave plate of the interference adjustment lens group is a superimposed light beam with orthogonal polarization states and wavefronts that are 180° mirror-symmetrical to each other.

[0012] Optionally, the imaging adjustment light group includes an eliminator mirror group, a half-wave plate and a third polarization beam splitter; the eliminator mirror group includes a compensation mirror, multiple lenses and a measuring aperture, which are used to eliminate noise from the outgoing measuring light beam, the half-wave plate is used to rotate the polarization direction of the passing measuring light beam by 45°, and the third polarization beam splitter is used to split the measuring light beam into S-polarized light and P-polarized light that interfere destructively and constructively in two directions.

[0013] Optionally, the detector includes a plurality of detection units for receiving a multi-level mixed measurement light beam of a plurality of wavelengths after being adjusted and split by the imaging adjustment light group.

[0014] Optionally, the auxiliary measurement system includes a pulse exciter and a field probe, wherein the pulse exciter emits pulses obliquely toward the alignment grating, and the alignment grating generates acoustic field radiation or thermal radiation due to material effects, and the field probe receives the diffraction image formed by the acoustic field radiation or the thermal electron temperature gradient map formed by the thermal radiation.

[0015] Optionally, the alignment grating uses a reflective rectangular phase grating with an aluminum film coated on the surface.

[0016] The present invention also provides an overlay error measurement method based on the above-mentioned overlay error measurement device. The overlay error measurement method includes the following steps.

[0017] Place the wafer, and place the wafer with the alignment grating on the motion adjustment stage. The grating period of the alignment grating is , the initial position is , the reflection coefficient is r, f is the duty cycle of the grating, is the raster shape.

[0018] Wafer pre-positioning, preliminary adjustment of the wafer, so that the wafer notch is aligned with the initial position on the motion adjustment stage.

[0019] Grating interferometry adjustment, multi-band selection and weighting of the grating interferometry system, thereby obtaining optimized optical measurement conditions.

[0020] The overlay error is measured by optical interferometry. The selected multi-band combined light source is used to illuminate the alignment grating and the overlay error is calculated based on the assigned weights.

[0021] Optionally, the overlay error measurement method also includes: turning on the auxiliary measurement system, emitting pulses to the alignment grating buried in the wafer, obtaining a diffraction image formed by the pulsed acoustic field radiation or a thermal electron temperature gradient map formed by thermal radiation, thereby achieving the position determination of the alignment grating and the overlay error measurement.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: the device and method of the present application improve the accuracy of overlay error measurement under different deformation conditions by assigning wavelength weights; and assist in measuring the alignment grating buried in the wafer with the aid of an acoustic field or a thermal field, thereby realizing various deformations of the overlay error and the position determination and overlay error measurement buried in the wafer, thereby improving the adaptability range, providing a basic guarantee for ultra-precision overlay error measurement, and facilitating promotion and application in the field of semiconductor quantity detection and processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a schematic diagram of an overlay error measurement device of the present invention;

[0024] Figure 2 Schematic diagram of the overlay error measurement method of the present invention.

[0025] In the figure,

[0026] 100. Grating interferometry system; 1. Multi-band combined light source; 2. Combiner; 3. Collimator group; 4. Aperture; 5. First polarization beam splitter; 6. First 1 / 4 wave plate; 7. Objective lens; 8. Second polarization beam splitter; 9. Reflection receiving right angle prism; 10. Transmission receiving right angle prism; 11. Second 1 / 4 wave plate; 12. Third 1 / 4 wave plate; 13. Eliminator group; 14. Half wave plate; 15. Third polarization beam splitter; 16. Detector;

[0027] 200, auxiliary measurement system; 17, pulse exciter; 18, field probe;

[0028] 300, measurement and control processor;

[0029] 400. Motion adjustment of the stage. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Overlay error measurement device

[0032] An overlay error measurement device, see Figure 1 The overlay error measurement device includes a grating interferometry measurement system 100 based on multi-band illumination and an auxiliary measurement system 200 which are electrically connected to a measurement and control processor 300, wherein the grating interferometry measurement system 100 uses different wavelengths to illuminate the alignment grating and optimize the overlay error measurement result; the auxiliary measurement system 200 performs overlay error measurement on the acoustic field or thermal field excited by a pulse based on the alignment grating buried in the wafer.

[0033] The alignment grating adopts a reflective rectangular phase grating with an aluminum film coated on the surface.

[0034] The period of the alignment grating is , T can be selected as 8, 10, 16, 18, 20, etc. The machining error of the period of the alignment grating needs to be controlled within ±1 The coating thickness of the alignment grating is 45nm-55nm, preferably 50nm. The alignment grating is a rectangular phase grating, and therefore is 180° mirror-symmetrical.

[0035] The alignment grating is set within the slide line between each lithography area on the wafer surface, mainly used for optical overlay error measurement; or the alignment grating is buried below the wafer surface, mainly used for overlay error measurement in acoustic field or thermal field.

[0036] The grating interferometry system 100 includes an illumination optical path and an imaging detection optical path. The illumination optical path is used to project a plurality of illumination light beams of selected wavelengths onto an alignment grating of known parameters. The imaging detection optical path is used to receive a measurement light beam reflected from the alignment grating and process the measurement light beam into multiple beams that have been accepted to achieve overlay error measurement.

[0037] The illumination optical path includes a multi-band combination light source 1, an illumination adjustment light group, a first polarization beam splitter 5 and an objective lens 7. The multi-band combination light source 1 is used to provide illumination light beams with optional multiple wavelengths to the alignment grating through the illumination optical path.

[0038] Furthermore, the illumination adjustment light group includes a combiner 2, a collimator group 3 and an aperture 4, which are used for combining, collimating and regulating the outgoing illumination light.

[0039] Among them, the imaging detection optical path includes the objective lens 7, the self-reference interference lens group, the interference adjustment lens group, the imaging adjustment light group and the detector 16. The optical information of the detector 16 is transmitted to the measurement and control processor 300, and the measurement and control processor 300 calculates the corrected overlay error measurement result based on the multi-wavelength optimization method.

[0040] Furthermore, the self-reference interferometer group includes a second polarization beam splitter 8, a reflection receiving right-angle prism 9 and a transmission receiving right-angle prism 10, and the right-angle prism is used to flip the wavefront of the measurement beam by 180°.

[0041] Furthermore, the interference adjustment lens group includes a first 1 / 4 wave plate 6, a second 1 / 4 wave plate 11 and a third 1 / 4 wave plate 12. The first 1 / 4 wave plate 6 is arranged between the first polarization beam splitter 5 and the objective lens 7, and is used to adjust the illumination light beam into circularly polarized light; the second 1 / 4 wave plate 11 and the third 1 / 4 wave plate 12 are arranged between the corresponding right-angle prism and the second polarization beam splitter 8, and are used to convert the light beam into S-polarized light or P-polarized light.

[0042] The measuring beam output by the second 1 / 4 wave plate 11 and the third 1 / 4 wave plate 12 of the self-reference interference mirror group combined with the interference adjustment mirror group is a superimposed beam with orthogonal polarization states and wavefronts that are 180° mirror-symmetrical to each other.

[0043] Furthermore, the imaging adjustment light group includes an eliminator mirror group 13, a half-wave plate 14 and a third polarization beam splitter 15; the eliminator mirror group 13 includes a compensation mirror, multiple lenses and a measuring aperture, which is used to eliminate noise from the outgoing measuring light beam, the half-wave plate 14 is used to rotate the polarization direction of the passing measuring light beam by 45°, and the third polarization beam splitter 15 is used to split the measuring light beam into S-polarized light and P-polarized light that interfere destructively and constructively in two directions.

[0044] The detector 16 includes a plurality of detection units, which are used to receive the multi-level mixed measuring light beams of a plurality of wavelengths after being adjusted and split by the imaging adjustment light group.

[0045] In a specific example, the detection unit includes a plurality of photodiodes and a plurality of spectroscopic elements, and the photodiodes receive the measuring light beams from the corresponding spectroscopic elements.

[0046] Among them, the auxiliary measurement system 200 includes a pulse exciter 17 and a field probe 18. The pulse exciter 17 emits pulses obliquely to the alignment grating, and the alignment grating generates acoustic field radiation or thermal radiation due to material effects. The field probe 18 receives the diffraction image formed by the acoustic field radiation or the thermal electron temperature gradient map formed by the thermal radiation.

[0047] Overlay Error Measurement Method

[0048] A method for measuring overlay error based on the above-mentioned overlay error measuring device, see Figure 2 , the overlay error measurement method includes the following steps.

[0049] Place the wafer, and place the wafer with the alignment grating on the motion adjustment stage 400. The grating period of the alignment grating is , the initial position is , the reflection coefficient is r, f is the duty cycle of the grating, is the raster shape.

[0050] The wafer is pre-positioned and preliminarily adjusted so that the wafer notch is aligned with the initial position on the motion adjustment stage 400 .

[0051] Grating interferometry adjustment, multi-band selection and weighting of the grating interferometry system 100, thereby obtaining optimized optical measurement conditions.

[0052] The overlay error is measured by optical interference, using a selected multi-band combination light source 1 to illuminate the alignment grating, and the overlay error is calculated based on the assigned weight.

[0053] The overlay error measurement method also includes acoustic field or thermal field auxiliary measurement: turning on the auxiliary measurement system 200, emitting pulses to the alignment grating buried in the wafer, obtaining a diffraction image formed by the pulsed acoustic field radiation or a thermal electron temperature gradient map formed by thermal radiation, thereby achieving the position determination of the alignment grating and the overlay error measurement.

[0054] The grating interferometry measurement adjustment steps specifically include: first, optically irradiate the alignment grating with multiple different deformation amounts with different wavelengths in the range of 300nm-1000nm, and select multiple wavelengths based on the three dimensions of measurement error size, high signal contrast, and the degree of proximity of the measurement signal peak to the ideal. Specifically, the measurement error size dimension is selected, and the selected wavelength needs to have a low sensitivity to the deformation of the alignment grating, that is, the point with the smallest error; for high signal contrast, the selected wavelength needs to maintain a good measurement signal contrast under various deformations, so that the measurement result has good stability; for the consideration of the degree of proximity of the measurement signal peak to the ideal, the change of the measurement signal peak relative to the ideal state when deformation occurs can reflect the sensitivity of the wavelength to the mark deformation to a certain extent. The smaller the difference between the two, the less sensitive the selected wavelength is to the deformation of the alignment grating.

[0055] Secondly, weights are assigned to the selected wavelengths. , thereby correcting the overlay position measurement error introduced by the alignment grating deformation. Although different types of deformation (such as depression, facade collapse, top or bottom collapse, bulge) will bring different measurement errors to the same wavelength, the error caused by the top and bottom collapse will be larger than the error caused by the facade, so this is also a factor to be considered when assigning comprehensive weights. In a specific example, the alignment position measurement results obtained based on multiple wavelengths can be expressed as: ,in, To align the initial position of the grating, is the current wavelength, The wavelength is The actual position of the illumination beam. Assume that the weights of different wavelengths are , then the overlay error measurement results after different wavelength combinations are expressed as:

[0056] .

[0057] This formula is transformed into an overdetermined equation and solved using the SVD decomposition method to finally obtain the weights corresponding to each wavelength. .

[0058] Of course, the selection of wavelength and the measurement results after weighting can be simulated according to the alignment grating parameters of actual needs during device design to reduce the workload.

[0059] The device and method improve the accuracy of overlay error measurement by assigning weights to wavelengths. The alignment grating buried in the wafer is measured with the aid of an acoustic field or a thermal field, thereby realizing multiple deformations of the overlay error and determining the position buried in the wafer and measuring the overlay error, thereby improving the adaptability range.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An overlay error measurement device, characterized in that: The overlay error measurement device comprises a grating interferometry system (100) based on multi-band illumination and an auxiliary measurement system (200) which are electrically connected to a measurement and control processor (300), wherein the grating interferometry system (100) uses different wavelengths to illuminate an alignment grating and optimizes an overlay error measurement result; and the auxiliary measurement system (200) performs overlay error measurement on an acoustic field or a thermal field excited by a pulse based on an alignment grating buried in a wafer; The grating interferometry system (100) comprises an illumination optical path and an imaging detection optical path for providing illumination light beams with optional multiple wavelengths; the auxiliary measurement system (200) comprises a pulse exciter (17) and a field probe (18); the pulse exciter (17) emits pulses obliquely toward the alignment grating, the alignment grating generates acoustic field radiation or thermal radiation due to material effects, and the field probe (18) receives a diffraction image formed by the acoustic field radiation or a thermal electron temperature gradient image formed by the thermal radiation; The measurement and control processor (300) assigns weights to the selected multiple wavelengths , thereby correcting the overlay position measurement error introduced by the alignment grating deformation; where the weight The solution is: The alignment position measurement results obtained based on multiple wavelengths can be expressed as: ,in, To align the initial position of the grating, is the current wavelength, The wavelength is The actual position of the illumination beam; let the weights of different wavelengths be , then the overlay error measurement results after different wavelength combinations are expressed as: ； This formula is transformed into an overdetermined equation and solved using the SVD decomposition method to obtain the weights corresponding to each wavelength. .

2. The overlay error measurement device according to claim 1, characterized in that: The illumination light path of the grating interferometry system (100) comprises a multi-band combination light source (1), an illumination adjustment light group, a first polarization beam splitter (5) and an objective lens (7), wherein the multi-band combination light source (1) is used to provide illumination light beams with selectable wavelengths to the alignment grating through the illumination light path; The imaging detection optical path of the grating interferometric measurement system (100) comprises the objective lens (7), a self-reference interferometric lens group, an interferometric adjustment lens group, an imaging adjustment optical group and a detector (16); optical information of the detector (16) is transmitted to a measurement and control processor (300), and the measurement and control processor (300) calculates and obtains a corrected overlay error measurement result based on a multi-wavelength optimization method.

3. The overlay error measurement device according to claim 2, characterized in that: The illumination adjustment light group comprises a combiner (2), a collimator group (3) and an aperture (4), and is used for combining, collimating and regulating the outgoing illumination light.

4. The overlay error measurement device according to claim 2, characterized in that: The self-reference interferometer group comprises a second polarization beam splitter (8), a reflection receiving right-angle prism (9) and a transmission receiving right-angle prism (10), wherein the right-angle prism is used to flip the wavefront of the measurement light beam by 180 degrees.

5. The overlay error measurement device according to claim 4, characterized in that: The interference adjustment lens group comprises a first quarter wave plate (6), a second quarter wave plate (11) and a third quarter wave plate (12); the first quarter wave plate (6) is arranged between the first polarization beam splitter (5) and the objective lens (7) and is used to adjust the illumination light beam into circularly polarized light; the second quarter wave plate (11) and the third quarter wave plate (12) are arranged between the corresponding right-angle prism and the second polarization beam splitter (8) and are used to convert the light beam into S-polarized light or P-polarized light; The measurement light beam output by the self-reference interference mirror group in combination with the second quarter wave plate (11) and the third quarter wave plate (12) of the interference adjustment mirror group is a superimposed light beam with orthogonal polarization states and wavefronts that are 180° mirror-symmetrical to each other.

6. The overlay error measurement device according to claim 5, characterized in that: The imaging adjustment light group comprises an eliminator mirror group (13), a half-wave plate (14) and a third polarization beam splitter (15); the eliminator mirror group (13) comprises a compensation mirror, a plurality of lenses and a measuring aperture, and is used to eliminate eliminators of an emitted measuring light beam; the half-wave plate (14) is used to rotate the polarization direction of the passing measuring light beam by 45 degrees; and the third polarization beam splitter (15) is used to split the measuring light beam into S-polarized light and P-polarized light which are destructively and constructively interfered in two directions.

7. The overlay error measurement device according to claim 6, characterized in that: The detector (16) comprises a plurality of detection units, and is used for receiving a multi-order mixed measurement light beam of a plurality of wavelengths after being adjusted and split by the imaging adjustment light group.

8. The overlay error measurement device according to claim 1, characterized in that: The alignment grating adopts a reflective rectangular phase grating with aluminum film coated on the surface.

9. An overlay error measurement method based on the overlay error measurement device according to any one of claims 1 to 8, characterized in that: Overlay error measurement methods include: Place the wafer, and place the wafer with the alignment grating on the motion adjustment stage (400), the grating period of the alignment grating is , the initial position is , the reflection coefficient is r, f is the duty cycle of the grating, is the grating deformation; Pre-positioning the wafer and preliminarily adjusting the wafer so that the wafer notch is aligned with the initial position on the motion adjustment stage (400); Grating interferometry adjustment, multi-band selection and weighting of the grating interferometry system (100), thereby obtaining optimized optical measurement conditions; The overlay error is measured by optical interferometry. A selected multi-band combined light source (1) is used to illuminate the alignment grating, and the overlay error is calculated based on the assigned weights.

10. The overlay error measurement method according to claim 9, characterized in that: The overlay error measurement method also includes: The auxiliary measurement system (200) is turned on to emit pulses to the alignment grating buried in the wafer, and a diffraction image formed by the pulsed acoustic field radiation or a thermal electron temperature gradient image formed by thermal radiation is obtained, thereby achieving position determination of the alignment grating and overlay error measurement.

Images