A method for characterizing the sidewall morphology of a gel-type material

Abstract

The present invention provides a method for characterizing the sidewall morphology of a glue mold, the method comprising: providing a sample to be tested, the sample to be tested comprising a substrate and a glue layer located above the substrate, wherein a graphic opening is provided in the glue layer; cutting a preset area of ​​the sample to be tested to reveal a longitudinal section of a characteristic structure; using an image acquisition device to obtain a longitudinal section image and a surface image of the characteristic structure; obtaining a characteristic dimension of the sample to be tested based on the surface image, obtaining a glue layer thickness and a longitudinal section area value of the opening of the sample to be tested based on the longitudinal section image, and characterizing the sidewall morphology of the glue mold based on the characteristic dimension, the glue layer thickness and the longitudinal section area value of the opening. The method for characterizing the sidewall morphology of the glue mold of the present invention can be implemented based on testing with a conventional image acquisition device, and has a high tolerance for image measurement errors; moreover, it can realize efficient and accurate characterization of the sidewall morphology of a glue mold structure with a high aspect ratio, and can intuitively reflect the sidewall morphology of glue molds with various characteristic dimensions and various aspect ratio ranges.

Description

Technical Field

[0001] The invention belongs to the field of micro-nano device manufacturing and relates to a method for characterizing the morphology of a glue mold sidewall. Background Art

[0002] Photolithography is the most commonly used method in the processing of micro-nano devices and integrated circuits, and it is also one of the most important process steps. As the feature size continues to shrink, the core structures of many devices are high aspect ratio graphics with nanometer width, which puts higher requirements on the development of photolithography processes and their stability control. Especially when using photoresist (or electron beam resist) masks to achieve the transfer of high aspect ratio structural graphics with nanometer width, the sidewall morphology of photoresist (or electron beam resist) directly affects the graphics quality of subsequent processes. On the one hand, different subsequent processes after photolithography, such as plasma etching and wet stripping, have different requirements for the sidewall morphology of the resist; on the other hand, photoresists (or electron beam resists) of different properties, different exposure methods (optical exposure, electron beam exposure, etc.), and different feature sizes have different requirements for the sidewall morphology after photolithography. Therefore, the effective control of the sidewall morphology of the high aspect ratio resist is the key factor to achieve accurate transfer of mask graphics.

[0003] Lithography process optimization is usually based on experience-based traversal testing, and repeated large-scale trial and error experiments are carried out to continuously optimize the settings of lithography parameters. Not only is the development efficiency low and the cost high, but it is also very blind. Sometimes it is even difficult to find the best process window or to judge the degree of optimization of the results. Experimental design methods such as Taguchi experimental method, full factorial experimental design method, and response surface method have been widely used in parameter optimization modeling and analysis, which can provide effective and accurate assistance and guidance for lithography process parameter optimization. In experimental design, it is necessary to model and analyze the influence of different process parameters on the sidewall morphology of the mold in order to predict the sidewall morphology of the mold after lithography, which requires accurate quantitative characterization of the sidewall morphology of the mold. In the prior art, cross-sectional images are usually manually measured to obtain the sidewall inclination angle to determine the sidewall morphology, which lacks sufficient resolution and accuracy and cannot be applied to the development of high aspect ratio graphic lithography processes with nanometer line widths.

[0004] Therefore, how to provide a method for characterizing the sidewall morphology of the mold to improve the efficiency and accuracy of the characterization of the sidewall morphology of the mold has become an important technical problem that needs to be solved urgently in achieving high aspect ratio structure lithography parameter control and improving the precise transfer of graphics. Summary of the invention

[0005] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a method for characterizing the sidewall morphology of a mold, so as to solve the problems of low efficiency and low accuracy in the prior art of characterizing the sidewall morphology of a mold.

[0006] To achieve the above-mentioned and other related purposes, the present invention provides a method for characterizing the sidewall morphology of a mold, comprising the following steps:

[0007] Providing a sample to be tested, the sample to be tested comprising a substrate and a glue layer located above the substrate, wherein the glue layer is provided with a patterned opening;

[0008] Cutting a predetermined area of ​​the sample to be tested to reveal a longitudinal section of a characteristic structure;

[0009] Using an image acquisition device to acquire a longitudinal section image and a surface image of the characteristic structure;

[0010] The characteristic dimension CD of the sample to be tested is obtained based on the surface image, the glue layer thickness h of the sample to be tested and the longitudinal cross-sectional area value S of the opening are obtained based on the longitudinal cross-sectional image, and the glue sidewall morphology is characterized based on the characteristic dimension CD, the glue layer thickness h and the longitudinal cross-sectional area value S of the opening.

[0011] Optionally, the step of characterizing the glue mold sidewall morphology based on the characteristic dimension CD, the glue layer thickness h and the longitudinal cross-sectional area value S of the opening includes:

[0012] Calculate the cross-sectional profile area difference ΔS, where ΔS = Sh × CD;

[0013] The morphology of the glue sidewall is characterized based on the size of the cross-sectional contour area difference ΔS, wherein, if ΔS>0, it is judged that the longitudinal section of the opening is a regular trapezoidal shape; if ΔS=0, it is judged that the longitudinal section of the opening is a rectangular shape; if ΔS<0, it is judged that the glue layer is not exposed or insufficiently developed.

[0014] Optionally, the method for obtaining the characteristic dimension CD, the glue layer thickness h and the longitudinal cross-sectional area value S of the opening includes: converting the analog image obtained by the image acquisition device into a digital image, and after determining the contours of the cross-sectional area to be observed and the surface area to be observed, obtaining the characteristic dimension CD, the glue layer thickness h and the longitudinal cross-sectional area value S of the opening.

[0015] Optionally, before using an image acquisition device to acquire a longitudinal section image and a surface image of the characteristic structure, the method further includes forming a conductive layer in a cross-sectional area to be observed and a surface area to be observed.

[0016] Optionally, the conductive layer includes a metal film, and a method of forming the conductive layer includes a physical vapor deposition method.

[0017] Optionally, the thickness of the conductive layer is 3-5 nm.

[0018] Optionally, the glue layer includes a photoresist layer or an electron beam resist layer.

[0019] Optionally, the opening comprises a grating, a rod or an array of holes.

[0020] Optionally, the method of cutting the preset area of ​​the sample to be tested includes mechanical cutting or ion beam cutting.

[0021] Optionally, the image acquisition device comprises a scanning electron microscope

[0022] As described above, the method for characterizing the sidewall morphology of the mold of the present invention can be implemented based on testing with a conventional image acquisition device, without adding complex process flows, image processing or dedicated high-end measurement and characterization equipment, and has a high tolerance for image measurement errors; moreover, it can achieve efficient and accurate characterization of the sidewall morphology of a high aspect ratio mold structure, and can intuitively reflect the sidewall morphology of molds with various feature sizes and various aspect ratio ranges. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram showing the process of the method for characterizing the sidewall morphology of the mold according to the present invention.

[0024] Figure 2 Schematic diagram of the structure showing the colloid sidewall morphology with a regular trapezoidal opening.

[0025] Figure 3 Schematic diagram of the structure showing the morphology of the colloid sidewall with a rectangular opening.

[0026] Figure 4 Schematic diagram of the structure showing the incompletely developed colloid sidewall morphology.

[0027] Figure 5 Shown is a longitudinal cross-sectional scanning electron microscope image of the first group of samples in an embodiment of the present invention.

[0028] Figure 6 Shown is a longitudinal cross-sectional scanning electron microscope image of the second group of samples in the embodiments of the present invention.

[0029] Figure 7 Shown is a longitudinal cross-sectional scanning electron microscope image of the third group of samples in the examples of the present invention.

[0030] Component number description

[0031] 10 Substrate

[0032] 20 glue layer

[0033] CD characteristic size

[0034] CD1 Characteristic dimensions of the first group of samples

[0035] CD2 The second group of sample characteristic dimensions

[0036] CD3 The third group of sample characteristic dimensions

[0037] h Adhesive layer thickness

[0038] h1 The first group of sample adhesive layer thickness

[0039] h2 The thickness of the adhesive layer of the second group of samples

[0040] h3 The thickness of the adhesive layer of the third group of samples

[0041] S Opening longitudinal section area value

[0042] Steps S1 to S4 DETAILED DESCRIPTION

[0043] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0044] See also Figures 1 to 7 It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0045] As described in the background technology, in the modeling analysis and optimization, it is necessary to model and analyze the effects of different process parameters on the side wall morphology of the glue type in order to predict the side wall morphology of the glue type after photolithography, and then achieve the purpose of forming a preset structure. In the prior art, the steepness or slope of the colloid side wall is usually used to describe the side wall morphology characteristics, that is, quantitative characterization is performed by measuring the inclination angle of the side wall of the colloid cross section. For example, for the stripping process, it is generally required to form an inverted trapezoidal structure, and the inclination angle of the cross-sectional morphology of the glue type is less than 90 degrees, which is conducive to the stripping and detachment of the metal layer from the colloid; for most etching processes, the inclination angle of the cross-sectional morphology of the glue type tends to be equal to or greater than 90 degrees, so as to ensure that the etching atmosphere or etching solution can fully react or corrode the material during the etching process, and ensure the accurate transfer of the pattern.

[0046] However, the inventors found that in the process of developing photolithography, the experimental design modeling using the sidewall morphology inclination angle as the process parameter optimization has obvious limitations: First, the sidewall inclination angle cannot fully describe the three states of underexposure, ideal exposure, and overexposure in the model. The inclination angle can reflect the two photolithography results of ideal exposure and overexposure, but for underexposure, the bottom of the gel structure after development is usually arc-shaped. Although the cross-section observation of the gel can determine that it is underexposure, it is impossible to quantitatively describe the underexposure through the sidewall inclination angle. Secondly, there are technical challenges in accurately characterizing the change in the sidewall inclination angle of the cross-section of the high aspect ratio gel using the inclination angle measurement method. For the high aspect ratio structure, the ratio of the gel thickness to the characteristic line width is usually above 8, resulting in a difference in the angles of the steep and inverted trapezoidal sidewalls, but the angle difference is not particularly large. For example, for a high aspect ratio structure with a gel thickness of 450nm and a line width of 50nm, when the line width at the bottom of the cross section increases from 20nm to 30nm relative to the line width at the top, the sidewall inclination angle changes by only 0.7 degrees. This places extremely stringent requirements on the measurement accuracy of the inclination angle and the resolution of the characterization equipment, requiring complex graphics processing technology or dedicated characterization equipment. Finally, the actual sidewall morphology of the colloid is not a straight line, but has a certain curvature. In addition, after the high aspect ratio structure is developed, the colloid is prone to tilt and deform to one side under the action of surface tension. The left and right sidewalls of the colloid or spacing structure are asymmetrical, that is, the left and right inclination angles are inconsistent. Therefore, modeling and analysis using a single bottom sidewall angle cannot accurately reflect the actual sidewall morphology.

[0047] Based on the above analysis, this embodiment provides a method for characterizing the sidewall morphology of a mold to improve the efficiency and accuracy of characterizing the sidewall morphology of a mold. Figure 1 , shown as a process flow chart of the method, comprising the following steps:

[0048] S1: providing a sample to be tested, wherein the sample to be tested comprises a substrate and a glue layer located above the substrate, wherein the glue layer is provided with a patterned opening;

[0049] S2: cutting a predetermined area of ​​the sample to be tested to reveal a longitudinal section of a characteristic structure;

[0050] S3: using an image acquisition device to obtain a longitudinal section image and a surface image of the characteristic structure;

[0051] S4: Acquire the characteristic dimension CD of the sample to be tested based on the surface image, acquire the glue layer thickness h of the sample to be tested and the longitudinal cross-sectional area value S of the opening based on the longitudinal cross-sectional image, and characterize the glue type sidewall morphology based on the characteristic dimension CD, the glue layer thickness h and the longitudinal cross-sectional area value S of the opening.

[0052] First, step S1 is performed: providing a sample to be tested, wherein the sample to be tested includes a substrate 10 and a glue layer 20 located above the substrate 10 , wherein the glue layer 20 is provided with a patterned opening.

[0053] As an example, the substrate 10 includes a semiconductor substrate, a metal substrate or other suitable substrates, which are selected according to the target device and are not limited in this embodiment.

[0054] As an example, the glue layer 20 includes a photoresist layer or an electron beam anti-etching agent layer, which is selected according to actual needs. For example, when optical exposure is adopted, a photoresist layer is selected, and the photoresist layer includes positive photoresist and negative photoresist; when electron beam exposure is adopted, an electron beam resist layer is selected, and the electron beam resist layer includes positive resist and negative resist.

[0055] As an example, the graphical structure of the opening is defined according to actual needs, depending on the design of the photolithography pattern, including gratings, pillars or hole arrays, etc.

[0056] Then, step S2 is performed: cutting is performed at a predetermined area of ​​the sample to be tested to reveal a longitudinal section of the characteristic structure.

[0057] As an example, the preset area is the area to be observed, and cutting is performed to reveal the longitudinal cross-sectional morphology of the characteristic structure for subsequent observation.

[0058] As an example, the method of cutting the preset area of ​​the sample to be tested includes mechanical cutting, ion beam cutting or other suitable cutting methods.

[0059] Specifically, in this embodiment, a diamond tool is used to perform cutting along the XZ plane.

[0060] Then, step S3 is performed: a longitudinal section image and a surface image of the characteristic structure are acquired by using an image acquisition device.

[0061] As an example, the surface image is an upper surface image of the adhesive layer 20 .

[0062] As an example, the image acquisition device includes a scanning electron microscope to obtain a surface scanning electron microscope image and a longitudinal section scanning electron microscope image containing the characteristic structure.

[0063] As an example, before the step of using an image acquisition device to obtain a longitudinal cross-sectional image and a surface image of the characteristic structure, a step of forming a conductive layer on the surface of the cross-sectional area to be observed and the surface area to be observed is also included. The conductive layer increases the electron contrast of the adhesive layer 20 to collect high-quality scanning electron microscope images and reduces the damage to the characteristic structure caused by electron bombardment. The thickness of the conductive layer is in the range of 3-5nm.

[0064] As an example, the conductive layer includes a metal thin film layer, which is formed by physical vapor deposition methods such as evaporation. The material of the conductive layer includes but is not limited to platinum, gold, silver, copper, aluminum, nickel or titanium and other thin film layers with good conductive properties. This embodiment uses a platinum metal layer.

[0065] As an example, the particle size of the conductive layer is extremely small, reaching 10 -10 m to 10 -9 In the photolithography process of micro-nano devices, a conductive layer with a small particle size is beneficial to the conformal of the graphic structure of the adhesive layer 20. If the conductive layer has a large particle size, it is easy to form a "hole seal" on the opening surface of the graphic structure such as a grating, a hole array, etc., thereby destroying the graphic opening structure.

[0066] Then execute step S4: obtain the characteristic dimension CD of the sample to be tested based on the surface image, obtain the glue layer thickness h of the sample to be tested and the longitudinal cross-sectional area value S of the opening based on the longitudinal cross-sectional image, and characterize the glue sidewall morphology based on the characteristic dimension CD, the glue layer thickness h and the longitudinal cross-sectional area value S of the opening.

[0067] As an example, the method for obtaining the characteristic dimension CD, the adhesive layer thickness h and the longitudinal cross-sectional area value S of the opening includes: using image processing software to convert the scanning electron microscope image obtained in step S3 into a digital image, and after finding and determining the contours of the cross-sectional area to be observed and the surface area to be observed, the characteristic line width and cross-sectional contour area value of the target structure can be obtained. Of course, the image processing software can also be used to measure the scanning electron microscope image to obtain the characteristic line width and cross-sectional contour area value of the target structure.

[0068] As an example, the step of characterizing the sidewall morphology of the glue layer by the characteristic dimension CD, the glue layer thickness h and the longitudinal cross-sectional area value S of the opening includes:

[0069] (i) calculating the cross-sectional profile area difference ΔS, where ΔS=Sh×CD, i.e., the cross-sectional profile area difference ΔS is equal to the longitudinal cross-sectional area of ​​the opening minus the product of the characteristic dimension and the adhesive layer thickness;

[0070] (ii) characterizing the sidewall morphology of the adhesive layer based on the size of the cross-sectional profile area difference ΔS, wherein if ΔS>0, it indicates that the longitudinal section of the opening is in the shape of a regular trapezoid, and the structure has an undercut feature, such as Figure 2 If ΔS = 0, it indicates that the longitudinal section of the opening is rectangular with steep side walls, such as Figure 3 If ΔS<0, it indicates that the glue layer is not fully exposed or underdeveloped. Figure 4By comparing the ΔS values, the cross-sectional morphology of the mold after different photolithography process conditions can be significantly distinguished, which can be used to determine whether the exposure results are consistent with the model prediction.

[0071] It should be noted that, compared with the sidewall profile inclination angle measurement in the prior art, the glue mold sidewall morphology characterization method provided in this embodiment realizes the efficient and accurate characterization of the sidewall morphology of the glue mold structure, and can intuitively reflect the glue mold sidewall morphology of various feature sizes and various aspect ratio ranges. For example, in the process of developing micro-nano devices such as zone plates, photonic crystals, polarizers, and X-ray diffraction elements with typical high aspect ratio structures, the response surface method can be used to establish a corresponding relationship between multiple process variable inputs (exposure dose, light intensity, glue thickness, development time / temperature, design line width, etc.) and the cross-sectional profile area difference, so as to quickly optimize the exposure process parameters with high resolution, high aspect ratio and high steepness, which can solve the problem of high cost and low efficiency of traditional traversal experimental methods.

[0072] As an example, the present invention can be implemented based on conventional image acquisition device testing, without adding complex process flows, image processing or dedicated high-end measurement characterization equipment, and has a high tolerance for image measurement errors.

[0073] Specifically, Figures 5 to 7 As shown, in this embodiment, three groups of samples were prepared and characterized, wherein the adhesive layer 20 used a positive resist layer, electron beam exposure was used to form a patterned grating structure, diamond tool slices were used, and scanning electron microscopes were used to collect surface images and longitudinal cross-sectional images of the characteristic structure. For each group of samples, the characteristic size, adhesive layer thickness, and longitudinal cross-sectional area of ​​the opening were obtained by averaging 10 groups of data to reduce errors. Please refer to Figure 5 , showing the longitudinal section scanning electron microscope image of the first group of samples. The characteristic size CD1 of the first group of samples is 63.8nm, the thickness of the glue layer h1 is 435.8nm, and the longitudinal section area value S1 of the opening is 3.42×10 4 nm 2 According to the cross-sectional area difference formula: ΔS = S-CD × h, ΔS1 is calculated to be 6396.0 nm 2 ; see Figure 6 , showing the longitudinal section scanning electron microscope image of the second group of samples. The characteristic size CD2 of the second group of samples is 31.6nm, the thickness of the glue layer h2 is 438.9nm, and the longitudinal section area value S2 of the opening is 1.48×10 4 nm 2 , ΔS2 is calculated to be 930.8nm 2 ; see Figure 7, showing the longitudinal section scanning electron microscope image of the third group of samples. The characteristic size CD3 of the third group of samples is 30.7nm, the thickness of the glue layer h3 is 431.0nm, and the longitudinal section area value S3 of the opening is 1.20×10 4 nm 2 , ΔS3 is calculated to be -1231.7nm 2 .contrast Figures 5 to 7 It can be seen that the values ​​of the three sets of cross-sectional profile area differences can correctly characterize the morphology of the colloid cross-sectional sidewall.

[0074] In summary, the characterization method of the mold sidewall morphology of the present invention can be implemented based on conventional image acquisition device testing, without adding complex process flow, image processing or dedicated high-end measurement and characterization equipment, and has a high tolerance for image measurement errors; and can achieve efficient and accurate characterization of the sidewall morphology of high aspect ratio mold structures, and can intuitively reflect the mold sidewall morphology of various feature sizes and various aspect ratio ranges. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has a high industrial utilization value.

[0075] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for characterizing the sidewall morphology of a mold, characterized in that: The following steps are involved: Providing a sample to be tested, the sample to be tested comprising a substrate and a glue layer located above the substrate, wherein the glue layer is provided with a patterned opening; Cutting a predetermined area of ​​the sample to be tested to reveal a longitudinal section of a characteristic structure; Using an image acquisition device to acquire a longitudinal section image and a surface image of the characteristic structure; Acquire a characteristic dimension CD of the sample to be tested based on the surface image, acquire a glue layer thickness h of the sample to be tested and a longitudinal cross-sectional area value S of the opening based on the longitudinal cross-sectional image, and characterize the glue mold sidewall morphology based on the characteristic dimension CD, the glue layer thickness h and the longitudinal cross-sectional area value S of the opening; The step of characterizing the glue mold sidewall morphology based on the characteristic dimension CD, the glue layer thickness h and the longitudinal cross-sectional area value S of the opening includes: Calculate the cross-sectional profile area difference ΔS, ΔS=Sh×CD; The morphology of the side wall of the glue type is characterized based on the size of the cross-sectional contour area difference ΔS. If ΔS>0, it is judged that the longitudinal section of the opening is a regular trapezoidal shape; if ΔS=0, it is judged that the longitudinal section of the opening is a rectangular shape; if ΔS<0, it is judged that the glue layer is not exposed or underdeveloped.

2. The method for characterizing the sidewall morphology of a mold according to claim 1, characterized in that: The method for obtaining the characteristic dimension CD, the glue layer thickness h and the longitudinal cross-sectional area value S of the opening includes: converting the analog image obtained by the image acquisition device into a digital image, and after determining the contours of the cross-sectional area to be observed and the surface area to be observed, obtaining the characteristic dimension CD, the glue layer thickness h and the longitudinal cross-sectional area value S of the opening.

3. The method for characterizing the sidewall morphology of a mold according to claim 1, characterized in that: Before using the image acquisition device to obtain the longitudinal section image and the surface image of the characteristic structure, the method further includes the step of forming a conductive layer in the cross-sectional area to be observed and the surface area to be observed.

4. The method for characterizing the sidewall morphology of a mold according to claim 3, characterized in that: The conductive layer includes a metal film, and a method of forming the conductive layer includes a physical vapor deposition method.

5. The method for characterizing the sidewall morphology of a mold according to claim 3, characterized in that: The thickness of the conductive layer is 3-5 nm.

6. The method for characterizing the sidewall morphology of a mold according to claim 1, characterized in that: The glue layer includes a photoresist layer or an electron beam resist layer.

7. The method for characterizing the sidewall morphology of a mold according to claim 1, characterized in that: The openings may comprise gratings, posts or arrays of holes.

8. The method for characterizing the sidewall morphology of a mold according to claim 1, characterized in that: The method of cutting the preset area of ​​the sample to be tested includes mechanical cutting or ion beam cutting.

9. The method for characterizing the sidewall morphology of a mold according to claim 1, characterized in that: The image acquisition device includes a scanning electron microscope.

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