Overlay mark structure, method of manufacturing the same, and overlay mark size selection method

Abstract

The present application provides a kind of overlay mark structure and its manufacturing method, overlay mark size selection method, overlay mark structure includes the mark groove formed in photoresist layer, the depth of the mark groove is less than the thickness of the photoresist layer, the groove width of the mark groove is less than 2 μm.The present application can effectively reduce the overlay measurement error caused by the morphology distortion of the overlay mark itself due to the asymmetry of the surrounding pattern by the design of narrow-width mark groove, fundamentally improves the process robustness and measurement accuracy of overlay mark, and further improves the product yield.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and in particular to an overlay marking structure and its manufacturing method, as well as a method for selecting the size of the overlay marking. Background Technology

[0002] In integrated circuit manufacturing, the alignment accuracy of photolithography directly affects device performance and yield. Excessive alignment errors can lead to defects such as leakage, open circuits, or short circuits. Therefore, high-precision alignment measurement technology has become a key link in ensuring process stability and product reliability.

[0003] Currently, the industry typically creates specific overlay marks on the chip surface and obtains overlay deviation data using optical or electron beam metrology equipment. However, in actual production, it has been found that when the pattern distribution around the overlay marks is asymmetrical, the marks themselves are prone to forming asymmetrical morphologies during photolithography and subsequent processes. This problem is particularly prominent in thick-film photoresist processes: during the baking process after exposure, the uneven generation and thermal expansion distribution of gases (such as N2) within the photoresist film lead to an asymmetrical conical structure (e.g., ...) of the overlay mark contour. Figure 1 As shown, the longitudinal section of the mark is trapezoidal and asymmetrical at the two waists (i.e., the values ​​of a and b are different), which seriously affects the accuracy of the overlay measurement. Summary of the Invention

[0004] The purpose of this invention is to provide an overlay marking structure and its manufacturing method, as well as an overlay marking size selection method, which can effectively reduce the impact of the overlay marking morphology asymmetry on measurement error while meeting the process requirements for photoresist thickness, without reducing the photoresist thickness or changing the process flow.

[0005] The present invention provides an overlay marking structure, including marking grooves formed in a photoresist layer, wherein the depth of the marking grooves is less than the thickness of the photoresist layer, and the width of the marking grooves is less than 2 μm.

[0006] In some embodiments, the width of the marking groove is 0.3 μm to 2.0 μm.

[0007] In some embodiments, the depth of the marking trench is greater than or equal to 0.15 μm and less than the thickness of the photoresist layer, wherein the thickness of the photoresist layer is greater than 2 μm.

[0008] On the other hand, the present invention also provides a method for manufacturing an overlay marking structure, the method comprising the following steps:

[0009] A photoresist layer is coated on the substrate;

[0010] Marking trenches with a width of less than 2 μm are formed in the photoresist layer using a photolithography process, wherein the depth of the marking trenches is less than the thickness of the photoresist layer.

[0011] Furthermore, the present invention also provides a method for selecting the size of overlay marks, comprising the following steps:

[0012] A test mask is provided, wherein multiple overlay mark patterns of different widths and multiple CD bar patterns of different widths are integrated on the layout of the test mask, wherein the width of the overlay mark pattern is less than 2μm;

[0013] A first substrate is provided, on which a first photoresist layer is formed. Using the test photomask and photolithography, a plurality of first marking trenches of different widths and a plurality of first CDbar trenches of different widths are formed in the first photoresist layer.

[0014] Measure the trench width of the first CD bar trench, and select the optimal photolithography conditions for the photolithography process based on the trench width;

[0015] A second substrate is provided, on which a second photoresist layer is formed. Using the test photomask and photolithography under optimal photolithography conditions, a plurality of second mark trenches of different widths and a plurality of second CDbar trenches of different widths are formed.

[0016] Measure the depth of the second marking groove, and select the target marking groove based on the groove depth.

[0017] In some embodiments, the width of the CD bar graphic ranges from 0.5μm to 4μm, and the width of the overlay mark graphic ranges from 0.3μm to 2μm.

[0018] In some embodiments, two key lithography conditions are provided during the exposure process of the photolithography process. These two key lithography conditions include focal length and exposure dose.

[0019] During exposure, the focal length varies in a set step along one direction of the first substrate, and the exposure dose varies in a set step along another direction, so as to form a series of exposure areas with different combinations of focal length and exposure dose on the first substrate, wherein the one direction is perpendicular to the other direction.

[0020] In some embodiments, measuring the trench width of the first CD bar trench and selecting the optimal photolithography conditions for the photolithography process based on the trench width further includes:

[0021] The first substrate is sliced ​​to prepare a first FEM structure. The CD bar pattern in each exposure area is measured using the first FEM structure to obtain the CD value under each photolithography condition.

[0022] Plot a Poisson curve for each fixed exposure dose with focal length as the x-axis and CD value as the y-axis.

[0023] The optimal photolithography conditions for the photolithography process were confirmed based on the Poisson curve.

[0024] In some embodiments, the optimal lithography conditions include optimal focal length and optimal exposure dose.

[0025] In some embodiments, selecting target marker trenches based on the trench depth further includes:

[0026] The second marking groove with a groove depth greater than 0.15 μm and the minimum value was selected as the target marking groove.

[0027] Compared with the prior art, the present invention has the following unexpected technical effects:

[0028] This invention provides an overlay marking structure and its manufacturing method, as well as a method for selecting the size of the overlay marking. The overlay marking structure includes marking grooves formed in a photoresist layer. The depth of the marking grooves is less than the thickness of the photoresist layer, and the width of the marking grooves is less than 2 μm. This invention actively controls the development depth of the overlay marking grooves by optimizing the key dimension (i.e., the groove width), rather than passively changing the overall thickness of the photoresist layer. In other words, through the narrow-width marking groove design, the overlay measurement error caused by the morphological distortion of the overlay marking itself due to the asymmetry of the surrounding pattern can be effectively reduced. This fundamentally improves the process robustness and measurement accuracy of the overlay markings, thereby increasing product yield. Attached Figure Description

[0029] Figure 1 This is a cross-sectional schematic diagram of the overprinted markings.

[0030] Figure 2 This is a schematic diagram of an overlay marking structure.

[0031] Figure 3 This is a schematic diagram of an overlay marking structure provided in an embodiment of the present invention.

[0032] Figure 4 This is a schematic flowchart illustrating a method for manufacturing an overlay marking structure according to an embodiment of the present invention.

[0033] Figure 5 This is a flowchart illustrating a method for selecting the size of overlay marks according to an embodiment of the present invention.

[0034] Explanation of reference numerals in the attached figures:

[0035] 10-Substrate; 11-Front layer marking; 20-Photoresist layer; 21-Marking trench. Detailed Implementation

[0036] The following will provide a more detailed description of an overlay marking structure, its manufacturing method, and the method for selecting the overlay marking size according to the present invention. The present invention will now be described in more detail with reference to the accompanying drawings, 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.

[0037] For clarity, not all features of the actual embodiments are described. In the following description, well-known functions and structures are not detailed in detail, as they would obscure the invention with unnecessary detail. It should be understood that in the development of any actual embodiment, numerous implementation details must be made to achieve the developer's specific objectives, such as changes from one embodiment to another according to limitations related to the system or business. Furthermore, it should be understood that such development work may be complex and time-consuming, but is merely routine work for those skilled in the art.

[0038] To make the objectives and features of the present invention more apparent and understandable, the specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that the drawings are all in a very simplified form and use non-precise ratios, and are only used to conveniently and clearly assist in illustrating the objectives of the embodiments of the present invention.

[0039] An asymmetrical, tapered structure in the overlay mark contour can severely affect the accuracy of overlay measurements. For example... Figure 2 As shown, the overlay marks located in the photoresist layer PR (the trapezoidal structure refers to...) Figure 2 The trapezoid located in the middle, where the asymmetry in the trapezoid structure is manifested in that the base of the trapezoid makes different angles with the two legs respectively. There is a clear theoretical relationship between its overlay measurement error ΔX and the overlay mark groove depth h: ΔX=1 / 2×h×(cotα-cotβ).

[0040] Where α and β are the angles (not exceeding 90°) between the base of the trapezoidal overlay mark and the angles of the two sidewalls, respectively (these angles are positive). In the PR process of thick-film photoresist layers, the h value is usually large (e.g., above 4 μm), which leads to a significant increase in ΔX, severely affecting the measurement accuracy and process window. When α-β>0, ΔX is negative, and the overlay measurement error shifts towards the sidewall corresponding to the angle β; when α-β<0, ΔX is positive, and the overlay measurement error shifts towards the sidewall corresponding to the angle α.

[0041] Therefore, how to effectively reduce the impact of the morphological asymmetry of the overlay marks on measurement errors while meeting the process requirements for photoresist thickness, without reducing the photoresist thickness or changing the process flow, has become a technical problem that urgently needs to be solved in this field.

[0042] Based on the above analysis, this embodiment provides an overlay marking structure for overlay alignment measurement in integrated circuit photolithography, and aims to solve the measurement distortion problem caused by the asymmetry of the overlay marking contour in thick film photolithography. The overlay marking structure includes marking trenches formed in a photoresist layer, wherein the depth of the marking trenches is less than the thickness of the photoresist layer, and the width of the marking trenches is less than 2 μm.

[0043] This embodiment, through the design of a narrow-width marking groove, can effectively reduce the overlay measurement error caused by the shape distortion of the overlay mark itself due to the asymmetry of the surrounding pattern. This fundamentally improves the process robustness and measurement accuracy of the overlay mark, thereby increasing the product yield.

[0044] like Figure 3 As shown, the overlay marking structure is formed in the photoresist layer 20, which is coated on the substrate 10. The width W of the marking trench 21 is optimized to be in the range of 0.3 μm to 2.0 μm. The depth of the marking trench 21 is limited to be less than the thickness of the photoresist layer 20 (e.g., 2 μm) and greater than or equal to 0.15 μm.

[0045] In this embodiment, the substrate 10 can be a silicon substrate 10 or a substrate 10 with a device layer already formed thereon. A front layer mark 11 has been formed in the substrate 10, and the front layer mark 11 and the mark trench 21 together constitute the overlay mark structure. The thickness of the photoresist layer is greater than 2 μm, for example, 4 μm.

[0046] In a preferred embodiment, the trench depth H of the marking trench 21 is controlled to be close to 0.15 μm, that is, the width W of the marking trench 21 is optimized to be in the range of 0.3 μm to 2.0 μm. Compared with the trench depth of about 4 μm commonly seen in traditional thick-film photoresist processes, the trench depth H is reduced by more than 96%.

[0047] According to the basic formula for overlay measurement error ΔX = 1 / 2 × H × (cotα - cotβ) (where α and β are the angles between the base of the trapezoidal shape between the two overlay grooves and the two sidewalls, that is, the acute angles between the sidewalls of the two adjacent overlay grooves facing each other and the base), when angles α and β remain constant, the sharp decrease in groove depth H directly leads to a significant reduction in the theoretical measurement error ΔX. Therefore, without changing the thickness of the photoresist layer 20 itself (i.e., a thick-film photoresist layer 20 can still be used to meet other process requirements), the structural design of the overlay marking structure reduces the measurement error caused by the asymmetry of the groove sidewalls from a physical source. Here, angles α and β affect the direction of deviation of the theoretical measurement error ΔX, that is, the deviation shifts towards the side with the smaller angle.

[0048] like Figure 4 As shown, this embodiment also provides a method for manufacturing an overlay marking structure, including the following steps:

[0049] Step S11: Coat a photoresist layer on the substrate;

[0050] Step S12: A marking trench with a width of less than 2 μm is formed in the photoresist layer by photolithography, wherein the depth of the marking trench is less than the thickness of the photoresist layer.

[0051] Please see Figure 2 In step S11, a substrate is first provided, and adhesive is applied to the substrate. Specifically, a thick photoresist layer 20 is spin-coated onto the substrate with the completed previous layer pattern. The thickness of the photoresist layer 20 can be set according to process requirements, for example, 4 μm.

[0052] In step S12, a photolithography machine is used to expose and develop the photoresist layer 20 through a photomask containing a narrow-width overlay marking pattern (pattern width less than 2 μm), so as to form marking trenches 21 with a trench width of less than 2 μm in the photoresist layer 20. The key control in this step is the focus position and energy of the exposure to ensure clear imaging of narrow lines.

[0053] This manufacturing method does not introduce any additional or special process equipment or materials. It achieves the fabrication of markers with reduced measurement errors simply by synergistically optimizing the exposure pattern (width of the marking trench 21) and photolithography conditions in existing photolithography processes. This significantly reduces the cost of technology upgrades and facilitates rapid implementation and application on existing production lines.

[0054] like Figure 5 As shown, this embodiment also provides a method for selecting the size of the overlay mark, including the following steps:

[0055] Step S21: Provide a test mask, wherein the test mask has multiple overlay mark patterns of different widths and multiple CD bar patterns of different widths integrated on its layout, wherein the width of the overlay mark pattern is less than 2μm;

[0056] Step S22: Provide a first substrate on which a first photoresist layer is formed. Using the test photomask and photolithography, form a plurality of first marking trenches and a plurality of first CD bar trenches of different widths in the first photoresist layer.

[0057] Step S23: Measure the trench width of the first CD bar trench, and select the optimal photolithography conditions for the photolithography process based on the trench width;

[0058] Step S24: Provide a second substrate on which a second photoresist layer is formed. Using the test photomask and photolithography under optimal photolithography conditions, form a plurality of second marking trenches of different widths and a plurality of second CD bar trenches of different widths.

[0059] Step S25: Measure the groove depth of the second marking groove, and select the target marking groove according to the groove depth.

[0060] The overlay mark size selection method in this embodiment directly addresses the relationship between overlay measurement error and trench depth H. Through scientific experiments, it finds the optimal width W that achieves the shallowest trench depth H, thereby minimizing the theoretical measurement error ΔX at its source and significantly improving the overlay measurement accuracy in thick-film processes. Furthermore, this method requires only one additional experimental fabrication and data analysis to determine the optimal design rules applicable in the long term for a specific technology node, avoiding the high costs and time delays caused by repeated trial and error and iteration, thus reducing R&D costs and cycle time.

[0061] The following provides a detailed description of the overlay mark size selection method provided in this embodiment.

[0062] First, step S21 is performed to provide a test mask. The test mask has multiple overlay marking patterns of different widths and multiple CD bar patterns of different widths integrated on its layout. The width of the overlay marking patterns is less than 2 μm.

[0063] In detail, a dedicated test mask is designed and manufactured. The layout of the test mask includes a CD bar (Critical Dimension bar) graphic and overlay marking graphics. The width of the CD bar graphic ranges from 0.5μm to 4μm. The overlay marking graphics include BIB (Box-In-Box) and AIM (Advanced Imaging Measurement Marker) markings. The core feature of these overlay marking graphics is that their widths W vary, but all fall within the optimization range of interest in this invention, i.e., all are less than 2μm. In a preferred embodiment, the width W of the overlay marking graphics ranges from 0.3μm to 2μm, in increments of 0.1μm (i.e., W = 0.3, 0.4, 0.5, ..., 1.8, 1.9, 2.0μm), comprising a total of 18 overlay marking graphics of different widths. All overlay markings and CD bar patterns are set in the cut track area of ​​the test mask, and at least one CD bar pattern is distributed around the overlay marking pattern. All the overlay markings are asymmetrically arranged around the overlay marking pattern.

[0064] Next, step S22 is performed, providing a first substrate on which a first photoresist layer is formed. Using the test photomask and photolithography, a plurality of first marking trenches of different widths and a plurality of first CD bar trenches of different widths are formed in the first photoresist layer.

[0065] This step specifically includes:

[0066] First, a silicon substrate with specifications identical to that of the mass-produced product is provided as the first substrate. Then, photoresist is spin-coated onto the first substrate using the same coating equipment and process parameters as the mass production line to form the first photoresist layer.

[0067] Next, using the test photomask, multiple first marking trenches and multiple first CD bar trenches of different widths are formed in the first photoresist layer through photolithography. Specifically, the test photomask is first used with the same lighting system settings (such as lighting shape, σ value, etc.) as the actual product manufacturing process to expose the first substrate, thereby forming multiple marking trenches of different widths. During exposure, two key photolithography conditions are provided: focal length and exposure dose. Typically, the focal length varies in set steps along one direction (e.g., the X direction) of the first substrate, and the exposure dose varies in set steps along another direction (e.g., the Y direction). This forms a series of exposure areas with different combinations of focal length and exposure dose on the first substrate. One direction (e.g., the X direction) and the other direction (e.g., the Y direction) are perpendicular to each other.

[0068] Next, step S23 is executed to measure the trench width of the first CD bar trench and select the optimal photolithography conditions for the photolithography process based on the trench width.

[0069] In detail, firstly, the first substrate is sliced ​​to prepare a first FEM (Focus Energy Matrix) structure. The CD bar pattern within each exposure area is measured using the first FEM structure to obtain the critical dimension (CD) value under each photolithography condition. Then, a Poisson curve is plotted with focal length as the x-axis and CD value as the y-axis for each fixed exposure dose to visually demonstrate the sensitivity of CD to focal length variations. Next, the optimal photolithography conditions for the process, i.e., the optimal focal length and optimal exposure dose, are determined based on the Poisson curve.

[0070] Next, step S24 is performed, providing a second substrate on which a second photoresist layer is formed. Using the test photomask and photolithography under optimal photolithography conditions, multiple second marking trenches of different widths and multiple second CD bar trenches of different widths are formed.

[0071] In detail, a second substrate identical to the first substrate is first provided, and a photoresist layer, identical to that on the first substrate, is formed on it, i.e., the second photoresist layer. Then, using the same test mask and the aforementioned optimal critical process parameters, the second substrate is exposed and subjected to subsequent processes. This results in the formation of a second CD bar trench and a second marker trench within the second photoresist layer. All patterns are formed under optimal and most stable process conditions; therefore, any performance differences between them can be uniquely attributed to their different design widths. The type and thickness of the second photoresist layer are the same as those of the first photoresist layer.

[0072] Next, step S25 is executed to measure the groove depth of the second marking groove and select the target marking groove based on the groove depth.

[0073] In detail, firstly, the second substrate is sliced ​​using SEM to prepare a second FEM structure. The trench depth of second marking trenches of different widths is measured using the first FEM structure. The second marking trench with a depth greater than 0.15 μm and the minimum value (i.e., closest to 0.15 μm) is selected and used as the target marking trench. Then, the overlay marking pattern corresponding to the target marking trench is found. Finally, a product photomask is prepared, and the overlay marking pattern of the product photomask adopts the overlay marking pattern corresponding to the target marking trench.

[0074] This invention provides an overlay marking structure, its manufacturing method, and a method for selecting the size of the overlay marking. The overlay marking structure includes marking grooves formed in a photoresist layer. The depth of the marking grooves is less than the thickness of the photoresist layer, and the width of the marking grooves is less than 2 μm. This invention, through the design of narrow-width marking grooves, effectively reduces overlay measurement errors caused by morphological distortion of the overlay marking itself due to asymmetry of the surrounding pattern. This fundamentally improves the process robustness and measurement accuracy of the overlay markings, thereby increasing product yield.

[0075] Furthermore, it should be noted that, unless otherwise specified or indicated, the terms "first" and "second" in the specification are used only to distinguish the various components, elements, steps, etc. in the specification, and are not used to indicate the logical or sequential relationships between the various components, elements, steps, etc.

[0076] It is understood that although the present invention has been disclosed above with reference to preferred embodiments, these embodiments are not intended to limit the present invention. For any person skilled in the art, many possible variations and modifications can be made to the technical solutions of the present invention based on the disclosed technical content, or equivalent embodiments can be modified accordingly, without departing from the scope of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for selecting the size of an overlay mark, characterized in that, Includes the following steps: A test mask is provided, wherein multiple overlay mark patterns of different widths and multiple CD bar patterns of different widths are integrated on the layout of the test mask, wherein the width of the overlay mark pattern is less than 2μm; A first substrate is provided, on which a first photoresist layer is formed. Using the test photomask and photolithography, a plurality of first marking trenches of different widths and a plurality of first CD bar trenches of different widths are formed in the first photoresist layer. Measure the trench width of the first CD bar trench, and select the optimal photolithography conditions for the photolithography process based on the trench width; A second substrate is provided, on which a second photoresist layer is formed. Using the test photomask and photolithography under optimal photolithography conditions, a plurality of second mark trenches of different widths and a plurality of second CD bar trenches of different widths are formed. Measure the depth of the second marking groove, and select the target marking groove based on the groove depth.

2. The method for selecting the size of the overlay mark as described in claim 1, characterized in that, The width of the CD bar graphic ranges from 0.5μm to 4μm, and the width of the overlay mark graphic ranges from 0.3μm to 2μm.

3. The method for selecting the size of the overlay mark as described in claim 1, characterized in that, In the photolithography process, two key photolithography conditions are provided: focal length and exposure dose. During exposure, the focal length varies in a set step along one direction of the first substrate, and the exposure dose varies in a set step along another direction, so as to form a series of exposure areas with different combinations of focal length and exposure dose on the first substrate, wherein the one direction is perpendicular to the other direction.

4. The method for selecting the size of the overlay mark as described in claim 1, characterized in that, Measuring the trench width of the first CD bar trench and selecting the optimal photolithography conditions for the photolithography process based on the trench width further includes: The first substrate is sliced ​​to prepare a first FEM structure. The CD bar pattern in each exposure area is measured using the first FEM structure to obtain the CD value under each photolithography condition. Plot a Poisson curve for each fixed exposure dose with focal length as the x-axis and CD value as the y-axis. The optimal lithography conditions for the lithography process were confirmed based on the Poisson curve.

5. The method for selecting the size of the overlay mark as described in claim 1 or 4, characterized in that, The optimal lithography conditions include the optimal focal length and the optimal exposure dose.

6. The method for selecting the size of the overlay mark as described in claim 1, characterized in that, Target marking trenches are further selected based on the trench depth, including: The second marking groove with a groove depth greater than 0.15 μm and the minimum value was selected as the target marking groove.

Images