TIS optimization method based on double objective lenses

Abstract

The invention provides a TIS optimization method based on double objective lenses. The TIS optimization method comprises the following steps: step 1, measuring a TIS value corresponding to at least one test point on a wafer; wherein in the measurement process, the objective lens I and the objective lens II are fixed; the multiplying power of the objective lens I is smaller than that of the objective lens II; step 2, calculating a TIS average value TISmean; step 3, judging whether TISmean is greater than a preset value TISY or not, and if yes, executing step 4; 4, the TIS value with the maximum difference with the TISmean is screened out to serve as a to-be-optimized value TIS0; and step 5, changing the light inlet amount of the light source corresponding to the objective lens 2 when TIS0 is measured, and repeating the steps 1-2 until TIS0 is less than or equal to TISY. According to the method, the measurement precision of the alignment error TIS is improved, and the alignment error TIS can be optimized, so that the image alignment precision is improved.

Description

Technical Field

[0001] This invention belongs to the field of wafer metrology technology, and particularly relates to a TIS optimization method based on dual objectives. Background Technology

[0002] In actual front-end wafer metrology applications, it has been found that general overlay optical metrology equipment only uses two types of magnification objectives. Overlay optical metrology equipment on the market is often equipped with a 3-5 aperture objective replacement module. Figure 2 Linear objective switch or Figure 3 (The objective lens turret in the image). TIS is a key indicator for measuring the systematic error of a metrology tool. It is calculated by comparing the measurement differences of the same structure (a test point on wafer 4) in the 0° and 180° directions. TIS is a fundamental parameter for evaluating tool performance and ensuring the accuracy and reliability of measurement data.

[0003] like Figures 2-3 As shown, although the module offers more flexible configuration, the measurement accuracy of the TIS (Transmission Indicator) of the overlay optical measurement equipment is low. This is due to two main reasons: 1) objective lens exhibits in-situ jitter during the switching process; 2) after objective lens switching, there is an objective lens position error, meaning that the position of the new objective lens cannot perfectly coincide with the position of the previous objective lens. Both of these factors lead to unstable optical imaging, thus affecting TIS measurement. Summary of the Invention

[0004] The purpose of this invention is to provide a TIS optimization method based on dual objectives. During TIS measurement, the dual-objective focusing imaging device remains stationary, eliminating objective lens jitter and positional errors. This improves the measurement accuracy of the TIS index of the dual-objective focusing imaging device and allows for optimization of alignment error TIS, thereby enhancing image alignment accuracy. The technical solution adopted is as follows: A TIS optimization method based on dual objectives includes the following steps: Step 1: Measure the TIS value corresponding to at least one test point on wafer 4; During the measurement process, both objective lens 1 and objective lens 2 remain stationary; the magnification of objective lens 1 is less than the magnification of objective lens 2. Step 2: Calculate the TIS mean (TISmean); Step 3: Determine if TISmean is greater than the preset value TISY. If so, proceed to step 4. Step 4: Select the TIS value that differs the most from TISmean as the value to be optimized, TIS0; Step 5: Change the amount of light entering the light source corresponding to objective lens 2 when measuring TIS0, and repeat steps 1 to 2 until TIS0 ≤ TISY.

[0005] Preferably, step 1, which involves measuring the TIS value of a test point, specifically includes: Step 1A: Place test point A of the wafer 4 to be measured within the field of view of objective lens 1; Step 1B: Test point A is imaged in one step; The light beam is focused by objective lens 1 onto the area containing test point A and forms a light spot. The light spot is transmitted through objective lens 1 and focused to form an image. Step 1C: Move wafer 4 so that test point A is within the field of view of objective lens 2; Step 1D, Secondary imaging of test point A: The second beam is focused by the second objective lens 2 to the test point A to form a light spot. The light spot at the test point A is transmitted through the second objective lens 2 and focused to form an image, thus acquiring image P0. Step 1E: Rotate test point A 180° around the center of its image, and repeat steps 1C~1D to obtain image P180; Step 1F: Calculate the TIS value of test point A based on image P0 and image P180.

[0006] Preferably, the focusing imaging step in step 1B includes: The light spot at test point A is incident on the dichroic mirror 31 through objective lens 1, and then transmitted through the dichroic mirror 31 and focused by the first lens 32 onto the imaging unit 33.

[0007] Preferably, the focusing imaging step in step 1D includes: The light spot at test point A is incident through objective lens 2 to another dichroic mirror, and then focused by another lens to another imaging unit.

[0008] Preferably, the first light beam in step 1 is provided by the first light-emitting module 5; the second light beam in step 1 is provided by the second light-emitting module. The structures of light-emitting module 5 and light-emitting module 2 are the same.

[0009] Preferably, the light-emitting module 5 includes: Light source 51; The second lens 52 and the reflector 53 are arranged sequentially along the direction of beam propagation; The divergent beam emitted by the light source 51 is shaped into a parallel beam by the second lens 52 and then incident on the reflector 53.

[0010] Preferably, the second lens 52 is a convex lens.

[0011] Preferably, objective lens 1 and objective lens 2 are arranged symmetrically.

[0012] Among them, "TIS" (Tool Induced Shift) refers to alignment errors caused by equipment or tools in semiconductor manufacturing.

[0013] TIS refers to the systematic differences in measurement values ​​obtained when measuring the same target from different orientations in the same measurement due to imperfections in the measuring tools themselves.

[0014] Compared with the prior art, the advantages of the present invention are: During the measurement process, the dual-objective focusing imaging device remains stationary. Therefore, during the TIS measurement, the dual-objective focusing imaging device remains stationary, and there is no objective lens jitter or objective lens position error. As a result, the measurement accuracy of the dual-objective focusing imaging device, namely the alignment error TIS, is ultimately improved. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a dual-objective focusing imaging device; Figure 2 Replace the module for the existing 3-aperture objective lens.

[0016] Figure 3 The existing technology uses a 5-aperture objective lens replacement module.

[0017] Figure 4 When test point A is located below objective lens two, Figure 1 The image of the imaging unit on the right side of the image.

[0018] Figure 5 The flowchart shows the TIS optimization method based on dual objectives. Figure 6 A comparison chart of Tis values; Figure 7 The imaging effect of imaging a certain test point in the existing technology; Figure 8 After TIS optimization of the dual-objective focusing imaging device, the dual-objective focusing imaging device was used again to... Figure 7 Imaging is performed at the same test point in the objective lens, and the imaging effect is shown in the imaging unit at objective lens 2. Figure 9 A three-dimensional view of adjustment unit one; Figure 10 This is a top view of adjustment unit one; Figure 11 This is a schematic diagram of the installation method for aperture one; Figure 12 To adjust the 3D model of the module; Figure 13 To adjust the cross-sectional view of the module; Figure 14This is a schematic diagram showing the position of the limit sensor on the Y-axis linear module. Figure 15 for Figure 14 Rear view.

[0019] Among them, 1 is objective lens one, and 2 is objective lens two. 3-Imaging optical path one, 31-Dichroic mirror, 32-Mirror number one, 33-Imaging unit, 4-Wafer to be measured 5-Light-emitting module one, 51-Light source, 52-Mirror No. 2, 53-Reflector; 6-Adjustment Unit 1, 60-Fixed base, 61-Isolation block, 62-Adjustment module, 620-X linear module, 621-Y-direction linear module, 6210-motor, 6211-Y-direction linear unit, 6212-mounting base, 6213-connector. 63-Mobile board, 7-Lead screw, 8-Nut, 9-Machine base 10-Limit sensor PCB board, 11-Limit sensor. Detailed Implementation

[0020] The dual-objective TIS optimization method of the present invention will be described in more detail below with reference to the schematic diagrams, which illustrate preferred embodiments of the invention. It should be understood that those skilled in the art can modify the invention described herein while still achieving its advantageous effects. Therefore, the following description should be understood as being of general knowledge to those skilled in the art and is not intended to limit the invention.

[0021] like Figures 1-15 As shown, a dual-objective focusing imaging device includes: Objective lens 1 is used to focus beam 1 onto the region containing the test point and transmit the light spot of the region to imaging optical path 3. Beam 1 is focused in the region containing the test point to form a light spot.

[0022] Objective lens 2 is used to focus beam 2 onto the test point and transmit the light spot at the test point to imaging optical path 2; beam 1 is focused at the test point to form a light spot.

[0023] Among them, the magnification of objective lens 1 is different from that of objective lens 2.

[0024] In this embodiment, the magnification of objective lens 1 is less than that of objective lens 2. That is, objective lens 1 is a low-power objective lens, and objective lens 2 is a high-power objective lens.

[0025] Objective lens 1 and objective lens 2 are symmetrically arranged about the Z-axis. That is, objective lens 1 and objective lens 2 have the same structure.

[0026] Imaging optical path 1-3 and imaging optical path 2 are symmetrically set about the Z direction, that is, imaging optical path 1-3 and imaging optical path 2 are exactly the same.

[0027] Light-emitting module 1 (5) and light-emitting module 2 (2) are symmetrically arranged and have the same structure. Light-emitting module 1 (5) is used to provide light beam 1 to objective lens 1; light-emitting module 2 is used to provide light beam 2 to objective lens 2.

[0028] Specifically, imaging optical path 13 includes: The dichroic mirror 31, the first mirror 32, and the imaging unit 33 are arranged sequentially along the direction of beam propagation. The light beam emitted by the light-emitting unit 5 is reflected by the dichroic mirror 31 and then enters the objective lens 1.

[0029] Among them, lens 32 is a convex lens, and imaging unit 33 is a camera.

[0030] Specifically, the light-emitting module 5 includes: Light source 51 is used to emit a diverging beam.

[0031] The second lens 52 and the reflector 53 are arranged sequentially along the direction of beam propagation; The divergent beam emitted by the light source 51 is shaped into a parallel beam (flat beam) by the second lens 52 and then incident on the reflector 53.

[0032] Among them, lens number 52 is a convex lens.

[0033] Among them, the first light-emitting module 5 also includes an aperture 50, and the second light-emitting module also includes an aperture 2; Regarding the position of the aperture: Figure 1 An aperture stop 50 is set between the light source 51 and the second lens 52.

[0034] Similarly, Figure 1 An aperture stop, or aperture stop two, is also set between the light source on the right and the corresponding second lens.

[0035] Within the XY plane, the positions of aperture 50 and aperture 2 are adjustable. That is, both apertures can be moved along the X or Y direction.

[0036] Specifically, aperture 50 is connected to the output end of adjustment unit 6; aperture 2 is connected to the output end of adjustment unit 2; both adjustment unit 6 and adjustment unit 2 have degrees of freedom to move along the X and Y directions.

[0037] To avoid interference with the optical path, regarding adjustment unit 1 and adjustment unit 2... Figure 3Location description in the middle: Figure 1 The adjustment unit (adjustment unit 6) on the left side of the center has one end with an aperture 50 facing the light source 51. (The last sentence appears to be incomplete and possibly refers to a separate, unrelated instruction.) Figure 10 After rotating 180 degrees, place it in Figure 1 Below the light source 51.

[0038] Figure 1 The adjustment unit (adjustment unit two) on the right side of the center has one end of its aperture two facing the light source on the right. That is, adjustment unit two is... Figure 1 The placement position in the middle is as follows Figure 10 As shown.

[0039] Among them, neither adjustment unit 1 nor adjustment unit 2 was in Figure 1 As shown in the figure, the structures of adjustment unit 1 (6) and adjustment unit 2 are the same.

[0040] In step 5 of this embodiment, only the second driving unit needs to adjust the amount of light entering the body, while the first adjusting unit 6 remains stationary.

[0041] Therefore, by controlling the movement of the X and Y axes to slightly shift the center position of the aperture, the center position of the beam can be adjusted, which in turn affects the measurement accuracy after optical refraction.

[0042] like Figures 9-13 The adjustment unit 6 includes: The fixed base 60, the vibration isolation block 61, the adjustment module 62 and the movable plate 63 are connected sequentially from bottom to top by fasteners; The adjustment module 62 has degrees of freedom to move along the X and Y directions; The movable plate 63 has a mounting hole that extends through the movable plate 63 along the Z direction, and an aperture 50 is embedded in it.

[0043] The bottom vibration isolation block 61 is made of foamed aluminum alloy, which reduces the vibration interference of the moving mechanism and helps to improve the measurement accuracy of this type of optical system.

[0044] In this embodiment, the adjustment module 62 forms the output terminal of the adjustment unit 6.

[0045] like Figure 12 The adjustment module 62 includes: X-direction linear module 620, which has the degree of freedom to move along the X direction; And the Y-direction linear module 621, which has the degree of freedom to move along the Y direction; The moving end of the X-axis linear module 620 is connected to the Y-axis linear module 621; The moving end of the Y-axis linear module 621 is connected to a moving plate 63.

[0046] In other embodiments, the adjustment module 62 may also employ... Figure 6 Other structures besides those shown.

[0047] like Figure 12 The Y-axis linear module 621 includes: The motor 6210 is threadedly connected to the mounting base 6212 via the connector 6213, and the mounting base 6212 is connected to the moving end of the X-direction linear module 620.

[0048] And the Y-axis linear unit 6211 is connected to the output end of the motor 6210.

[0049] The mounting base 6212 comprises two integrally formed parts: one part is threadedly connected to the connector 6213, and the other part is the part indicated by the mark 6212.

[0050] In addition, such as Figure 9 As shown, a limit sensor PCB board 10 is provided on the machine base 9; The limit sensor PCB board 10 is connected to the machine base 9 by fasteners, and the baffle 12 is connected to the mounting base 6212 by fasteners.

[0051] Three limit sensors 11 are soldered to the position sensor PCB board 10. Among them, the limit sensors 11 are photoelectric sensors.

[0052] Along the Y direction, when any limit sensor 11 moves to the position where it is blocked by the baffle 12, it reaches the set position.

[0053] like Figure 13 As shown, the Y-direction linear element 6211 includes: Lead screw 7 is connected to the output terminal of motor 6210.

[0054] Nut 8 is fitted onto lead screw 7 and connected to machine base 9 by fasteners.

[0055] Among them, the lead screw 7 and the nut 8 form a lead screw sliding transmission.

[0056] In the use of overlay optical measurement equipment, a situation may be encountered, for example, when 9 test points are selected on a wafer, after measuring the 9 points, it is found that the TIS values ​​of 8 points are reasonable, but one point is abnormal. This may be caused by the characteristics of that point on the wafer itself. It is necessary to first adjust the aperture position of this point through software, and then recalculate whether the TIS value is reasonable.

[0057] The TIS optimization method based on dual objectives includes the following steps: Step 1: Measure the TIS values ​​corresponding to the 5 test points on wafer 4; During the measurement process, both objective lens 1 and objective lens 2 remain stationary; the magnification of objective lens 1 is less than that of objective lens 2. For each test point, the amount of light entering each light source required during the measurement process is preset and stored in the record.

[0058] Step 2: Calculate the TIS mean (TISmean); Step 3: Determine if TISmean is greater than the preset value TISY. If so, proceed to step 4. Step 4: Select the TIS value that differs the most from TISmean as the value to be optimized, TIS0; Step 5: Change the amount of light entering the light source corresponding to objective lens 2 when measuring TIS0 by adjusting unit 2, that is, change the position of aperture 2, and repeat steps 1 to 2 until TIS0 ≤ TISY.

[0059] Figure 6 As shown, the Tis values ​​of the dual-objective structure exhibit a smaller fluctuation range.

[0060] Figure 6 In the middle: each green square represents a test point, and the gray circle represents the field of view.

[0061] by Figure 6 Take the middle right image as an example: In this embodiment, TIS values ​​were measured at 5 test points, with each test point corresponding to one TIS value, thus a total of 5 TIS values ​​were obtained.

[0062] Among them, there are 5 TIS values, including a maximum value of 1.2551nm, a minimum value of 0.67265nm, and 3 other values ​​not shown.

[0063] The arithmetic mean of the summation of the five TIS values ​​was obtained, resulting in TISmean = 1.0234 nm.

[0064] Among them, the difference between the minimum value of 0.67265nm and TISmean is the largest, so 0.67265nm is taken as the value to be optimized, TIS0.

[0065] Find the test point corresponding to 0.67265nm, and find the amount of light entering the light source used for that test point. Then change the amount of light entering the light source corresponding to objective lens 2.

[0066] The light source corresponding to objective lens 2, i.e. Figure 1 The light source is located on the right side of the center.

[0067] like Figure 5 As shown, the steps for measuring the TIS value at any test point (test point A) include: Step 1A: Place wafer 4 on the machine and below the dual objective lens focusing imaging device, so that test point A of wafer 4 is located below objective lens 1 and within the field of view of objective lens 1.

[0068] The purpose of step 1A is to initially locate test point A.

[0069] Specifically: By observing the imaging unit 33, it can be determined whether the test point A is within the field of view of objective lens 1.

[0070] Among them, the magnification of objective lens 1 is less than that of objective lens 2; Step 1B: Image test point A onto imaging unit 3 corresponding to objective lens 1.

[0071] In this embodiment, both light sources are always on.

[0072] The specific imaging process (beam propagation direction) is as follows: (1) Figure 1 The direction of beam propagation on the left side: Light source 51 emits a diverging light beam, which is shaped by lens 52 and then incident on mirror 53. After being reflected by mirror 53, the beam is incident on dichroic mirror 31. Lens 52 is a convex lens.

[0073] The light beam enters the objective lens 1 after being reflected by the dichroic mirror 31.

[0074] Objective lens 1 focuses the light beam onto the area containing test point A and forms a light spot. The light spot passes through objective lens 1 and is incident on dichroic mirror 31. After being transmitted through dichroic mirror 31, it is focused by lens 32 onto imaging unit 33.

[0075] (2) Figure 1 The direction of beam propagation on the right side: It propagates in the exact same direction as the beam on the left.

[0076] The difference is that, since both light sources are always on, the image detected by the imaging unit corresponding to objective lens 2 is not the image of test point A.

[0077] Step 1C: Move wafer 4 so that test point A is within the field of view of objective lens 2.

[0078] Among them, wafer 4 can be translated or rotated around the Z-axis, so that the pilot A is moved into the field of view of objective lens 2 and below objective lens 2.

[0079] Wafer 4 can be translated or rotated around the Z-axis, both of which are existing technologies.

[0080] Specifically: through observation Figure 1The imaging unit on the right can determine whether test point A is within the field of view of objective lens 2.

[0081] Step 1D: Image test point A onto the imaging unit corresponding to objective lens 2, and obtain image P0.

[0082] The imaging effect of image P0 is as follows Figure 4 The left image is shown in the diagram. In the left image, the smaller square represents the image of test point A.

[0083] The beam propagation direction during the imaging process is the same as the beam propagation direction on the right side in step 2. The difference is that the imaging unit corresponding to objective lens 2 detects the image of test point A.

[0084] Therefore, the image detected by imaging unit 33 in step 2, and the image detected by imaging unit (in step 4) Figure 1 On the right side (i.e., the imaging unit on imaging optical path two), the detected images are all corresponding to test point A.

[0085] Step 1E: Rotate test point A 180° around the center of its image, and repeat steps 1C~1D to obtain image P180; The imaging effect of image P180 is... Figure 4 As shown in the right figure.

[0086] Step 1F: Calculate the TIS value of test point A based on image P0 and image P180.

[0087] Step 1F is the prior art.

[0088] The most classic and common scenario is when using optical overlap error measurement equipment: when measuring a structure (such as a Box-in-Box structure formed by two overlapping photolithographic layers), the wafer will be rotated in two directions, 0° and 180°.

[0089] First measurement: The wafer (test point) is in its initial position (e.g., denoted as 0° orientation).

[0090] Second measurement: The wafer is rotated 180 degrees, that is, the test point is rotated 180 degrees around the center of its image.

[0091] Theoretically, it should be expected that due to the 180-degree rotation, the two measurements should yield completely opposite but equal-absolute overlap error values. For example, if the actual overlap error is X nanometers, then the measurement value corresponding to 0° might be X+Δ, and the measurement value corresponding to 180° should be -X+Δ (where Δ is the systematic error of the tool, which is known).

[0092] Among them, by Figure 4 Obtaining overlap error values ​​from images is a current technology.

[0093] TIS Calculation: TIS is defined as the average of the measurements taken in the 0° and 180° directions in the same measurement.

[0094] Figure 7 The image shows the imaging effect of the imaging unit corresponding to objective lens 2 in the prior art; the square in the red circle is the image corresponding to a test point on wafer 4.

[0095] Figure 8 The imaging effect of the imaging unit corresponding to objective lens two after optimization of the dual-objective focusing imaging device; the image where the yellow crosshair is located and the image in the red circle are images of the same test point.

[0096] The comparison shows that, Figure 7 The image shadows (image edges) in the image are heavier (thicker), while Figure 8 The shadow in the image becomes noticeably narrower and thinner.

[0097] Therefore, after Tis optimization, the graphic shape is more uniform and clear.

[0098] The above are merely preferred embodiments of the present invention and do not constitute any limitation on the present invention. Any equivalent substitutions or modifications made by those skilled in the art to the technical solutions and content disclosed in the present invention without departing from the scope of the present invention shall be deemed to have remained within the protection scope of the present invention.

Claims

1. A TIS optimization method based on dual objectives, characterized in that, Includes the following steps: Step 1: Measure the TIS value corresponding to at least one test point on the wafer (4); During the measurement process, both objective lens 1 (1) and objective lens 2 (2) remain stationary; the magnification of objective lens 1 (1) is less than the magnification of objective lens 2 (2); Step 2: Calculate the TIS mean (TISmean); Step 3: Determine if TISmean is greater than the preset value TISY. If so, proceed to step 4. Step 4: Select the TIS value that differs the most from TISmean as the value to be optimized, TIS0; Step 5: Change the amount of light entering the light source corresponding to objective lens 2 (2) when measuring TIS0, and repeat steps 1 to 2 until TIS0 ≤ TISY.

2. The TIS optimization method based on dual objectives according to claim 1, characterized in that, Step 1, which involves measuring the TIS value at a test point, specifically includes: Step 1A: Place the test point A of the wafer (4) to be measured within the field of view of objective lens (1); Step 1B: Test point A is imaged in one step; The light beam is focused by objective lens (1) onto the area containing test point A and forms a light spot. The light spot is transmitted through objective lens (1) and focused to form an image. Step 1C: Move the wafer (4) so ​​that test point A is within the field of view of objective lens 2 (2); Step 1D, Secondary imaging of test point A: The second beam is focused onto the test point A by the second objective lens (2) to form a light spot. The light spot at the test point A is transmitted through the second objective lens (2) and focused to form an image, thus acquiring the image P0. Step 1E: Rotate test point A 180° around the center of its image, and repeat steps 1C~1D to obtain image P180; Step 1F: Calculate the TIS value of test point A based on image P0 and image P180.

3. The TIS optimization method based on dual objectives according to claim 1, characterized in that, The focusing imaging steps in step 1B include: The light spot at test point A is incident on the dichroic mirror (31) through objective lens (1), and then transmitted through the dichroic mirror (31) and focused by lens (32) to the imaging unit (33).

4. The TIS optimization method based on dual objectives according to claim 2, characterized in that, The focusing imaging steps in step 1D include: The light spot at test point A is incident through objective lens 2 (2) onto another dichroic mirror and then focused onto another imaging unit by another lens.

5. The TIS optimization method based on dual objectives according to claim 1, characterized in that, The first beam in step 1 is provided by the first light-emitting module (5); the second beam in step 1 is provided by the second light-emitting module. The structures of the first light-emitting module (5) and the second light-emitting module are the same.

6. The TIS optimization method based on dual objectives according to claim 5, characterized in that, The light-emitting module one (5) includes: Light source (51); The second lens (52) and the reflector (53) are arranged sequentially along the direction of beam propagation; Among them, the divergent beam emitted by the light source (51) is shaped into a parallel beam by the second lens (52) and incident on the reflector (53).

7. The TIS optimization method based on dual objectives according to claim 6, characterized in that, The second lens (52) is a convex lens.

8. The TIS optimization method based on dual objectives according to claim 5, characterized in that, Objective lens one (1) and objective lens two (2) are symmetrically arranged.

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