Wafer film stress adjustor and preparation method thereof

Abstract

The invention provides a wafer film stress adjustor and a preparation method thereof, and belongs to the technical field of microelectronic metrology, and the method comprises the steps: calculating the curvature radius RB of a grown film according to a formula (1); glass is selected as a growth substrate, coarse grinding, accurate grinding and polishing are carried out according to the calculated curvature radius RB, and a substrate with the upper surface curvature radius RB is obtained; coating a film on the upper surface of the substrate to obtain a stress adjustor with the curvature radius of RB; in the formula (1), sigma film is a preset stress value of the thin film growing on the substrate; delta is a constant; rA is the curvature radius value of the thin film grown in an ideal state, and the thin film is a horizontal plane in the ideal state, so that RA is infinite; rB is the curvature radius of the actually grown film. The wafer film stress adjustor prepared by the invention can accurately adjust a film tester and ensure the accuracy of a test result of the tester.

Description

Technical Field

[0001] The invention belongs to the technical field of microelectronic metrology, and in particular relates to a wafer film stress adjuster and a preparation method thereof. Background Art

[0002] Thin films play an important role in the semiconductor field due to their unique conductive properties and mature implementation process. They are not only used in integrated circuits and micro-electromechanical systems (MEMS), but also as the basic materials for RF chips, thin-film sensors, optical devices and flexible electronic components (such as flexible electronic displays, thin-film solar panels, etc.). For example: RF chips, as the king of chips in the 5G era, are the "nerve center" of information equipment and greatly affect the performance of information equipment. In the preparation process of RF chips, thin films are widely used, whether they are semiconductor films, dielectric films, or metal films. They are indispensable.

[0003] The thickness of the film is generally only in the micrometer or even nanometer range. Its own mechanical strength alone cannot meet the use requirements. It needs to be attached to a substrate to form a film base structure, referred to as a film-based structure. The film-based structure will be subjected to more complex load conditions during service, including tension, compression, bending, impact, and temperature loads. Therefore, it is very important to conduct research on the generation mechanism, distribution law, and testing of wafer film stress.

[0004] At present, a thin film stress tester is used to test the curvature change of the substrate during the thin film deposition process. The tester uses an optical lever measurement method to realize the conversion of the curvature radius of the wafer surface and the laser angle to obtain the average stress of the film. During operation, the position changes of position sensors, reflectors and laser components, the changes in laser light intensity, the accuracy of the lead screw movement, etc. become the key to measurement accuracy. In order to verify the change in the measurement accuracy of the instrument, the instrument needs to be calibrated in time, otherwise the test result will be too large. However, there is currently no device for calibrating the tester, and it is impossible to calibrate the wafer thin film stress tester. Summary of the invention

[0005] The embodiment of the present invention provides a wafer film stress adjuster and a preparation method thereof, which solves the problem of adjusting a wafer film stress tester.

[0006] To achieve the above object, the technical solution adopted by the present invention is: to provide a method for preparing a wafer thin film stress regulator, the method comprising:

[0007] The curvature radius R of the growing film is calculated according to formula (1): B ;

[0008]

[0009] Glass is selected as the growth substrate, and the curvature radius R is calculated. B Rough grinding, fine grinding and polishing are performed to obtain the upper surface curvature radius R B substrate;

[0010] The film is deposited on the upper surface of the substrate to obtain a curvature radius of R B Stress adjuster;

[0011] In formula (1), σ film is the preset stress value of the film grown on the substrate; Δ is a constant;

[0012] R A is the radius of curvature of the film grown under ideal conditions. In ideal conditions, the film is horizontal, so R A is infinite;

[0013] R B is the radius of curvature of the actual grown film.

[0014] In combination with the first aspect, in an achievable manner, the rough grinding process includes: fixing the selected substrate on a workbench, using a curvature radius R B The coarse spherical grinding wheel performs preliminary grinding on the substrate.

[0015] In combination with the first aspect, in an achievable manner, the fine grinding process includes: after cleaning the grinding debris by flushing, replacing the grinding wheel with a curvature radius R B The substrate is finely ground by a fine spherical grinding wheel.

[0016] In combination with the first aspect, in one achievable manner, the mesh number of the coarse spherical grinding wheel is smaller than the mesh number of the fine spherical grinding wheel; the mesh number of the coarse spherical grinding wheel is 36 meshes, and the mesh number of the fine spherical grinding wheel is ≥100 meshes.

[0017] In combination with the first aspect, in one achievable manner, after the rough grinding process, a rough grinding radius of curvature of the upper surface of the substrate is obtained using a profile measuring instrument; and the duration and rotation speed of the fine spherical grinding wheel are adjusted according to the obtained rough grinding radius of curvature.

[0018] In combination with the first aspect, in one achievable manner, the polishing process includes: evenly sprinkling polishing liquid on the grinding disc, placing the upper surface of the substrate upside down on the grinding disc, and polishing the upper surface of the substrate by rotating the grinding disc.

[0019] In combination with the first aspect, in one achievable manner, after the rough grinding process, a rough grinding radius of curvature of the upper surface of the substrate is obtained using a profile measuring instrument; and the duration and rotation speed of the fine spherical grinding wheel are adjusted according to the obtained rough grinding radius of curvature.

[0020] In combination with the first aspect, in one achievable manner, the coating on the upper surface of the substrate is completed by using a semiconductor sputtering process.

[0021] In combination with the first aspect, in one achievable manner, the film has a thickness of 20 nm to 25 nm and is made of Cr.

[0022] In combination with the first aspect, in one achievable manner, the preset film stress value is 10 MPa to 300 MPa.

[0023] In a second aspect, an embodiment of the present invention further provides a wafer thin film stress regulator, which is manufactured using the wafer thin film stress regulator manufacturing method.

[0024] Compared with the prior art, the preparation method of the wafer thin film stress regulator provided by the present invention has the beneficial effect that: according to the preset film stress value, the curvature radius of the film to be processed on the substrate is calculated, and then according to the radius, the substrate with the curvature radius is processed through rough grinding, fine grinding and polishing, and then the curved surface of the substrate is uniformly coated to obtain a standard regulator, thereby solving the calibration problem of the tester and ensuring the accuracy of the test results of the tester. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of the structure of a wafer film provided by an embodiment of the present invention;

[0026] Figure 2 A schematic diagram of the structure of a wafer thin film stress adjuster (Part A) provided in an embodiment of the present invention;

[0027] Figure 3 A schematic diagram of the structure of a wafer thin film stress adjuster (Part B, a product prepared in this application) provided in an embodiment of the present invention;

[0028] Figure 4 It is a profile test curve diagram after rough grinding and fine grinding in the preparation process of the wafer thin film stress adjuster provided by the present invention;

[0029] Figure 5 A process flow chart of the preparation of a wafer thin film stress regulator provided by an embodiment of the present invention;

[0030] Description of reference numerals:

[0031] 1. Substrate; 2. Oxide layer; 3. Thin film. DETAILED DESCRIPTION

[0032] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0033] Please also read Figures 1 to 3 , Figure 5 Now, the preparation method of the wafer thin film stress regulator provided by the present invention is described. The preparation method of the wafer thin film stress regulator comprises:

[0034] The curvature radius R of the growing film 3 is calculated according to formula (1): B ;

[0035]

[0036] Glass is selected as the growth substrate, and the curvature radius R is calculated. B Rough grinding, fine grinding and polishing are performed to obtain the upper surface curvature radius R B substrate;

[0037] The film is deposited on the upper surface of the substrate to obtain a curvature radius of R B Stress adjuster;

[0038] In formula (1), σ film is the preset stress value of the film grown on the substrate; Δ is a constant;

[0039] R A is the radius of curvature of the film grown under ideal conditions. In ideal conditions, the film is horizontal, so R A is infinite;

[0040] R B is the radius of curvature of the actual grown film.

[0041] Compared with the prior art, the preparation method of the wafer thin film stress regulator provided by the present invention has the beneficial effect that: according to the preset thin film stress value, the curvature radius of the thin film that needs to be processed on the substrate is calculated, and then according to the radius, the substrate with the curvature radius is processed through rough grinding, fine grinding and polishing, and then the curved surface of the substrate is uniformly coated to obtain a standard regulator, thereby solving the calibration problem of the tester and ensuring the accuracy of the test results of the tester.

[0042] The present application uses glass as the substrate, cuts the material, rolls it into a round shape, and then performs rough grinding, fine grinding, and polishing. After polishing, the centering and edge grinding are performed, and then coating is performed to complete the production of the adjuster.

[0043] It is inevitable that the film will generate stress during the coating process. Therefore, it is necessary to reversely calculate the curvature radius of the product based on the stress value of the film after coating, and process the adjuster based on the curvature radius to adjust the tester. Figure 1 As shown, taking the thin film oxidation process as an example, the oxide layer 2 and substrate 1 are at a relatively high temperature during the oxidation process. After the growth of the thin film 3 is completed, the entire thin film system is cooled to room temperature. Since the thermal expansion coefficient of silicon dioxide is smaller than that of silicon material, the contraction mismatch causes strain, which in turn generates stress. Without considering the plastic deformation of the silicon substrate and the oxide film, the strain caused by temperature change is:

[0044]

[0045] Among them, ε t represents the film strain caused by temperature change; α Si and Represent the thermal expansion coefficients of the oxide film and the silicon substrate, respectively, and ΔT represents the temperature change. According to the theory of elastic mechanics, the stress generated by the film strain is:

[0046]

[0047] in, and represent the elastic modulus and Poisson's ratio of the oxide film, respectively.

[0048] like Figure 2 and Figure 3 As shown in FIG. 1 , the design process of the stress adjuster is as follows: the wafer film stress adjuster is designed in the form of A+B, using a glass substrate to simulate the film growth process of a 4-inch wafer (diameter D), with a thickness of 12 mm. Part A is used as a substrate to simulate the flat wafer before film growth, and part B is used as a structure with a curvature radius after coating, representing that after film growth, due to the different materials and expansion coefficients of the film and the substrate, the entire structure is slightly bent and has a certain curvature radius. The curvature radius of part A is R. A (Ideal state, no stress bending), the curvature radius of part B is R B The substrate may also be a silicon substrate.

[0049] The thin film stress adjuster of this application is mainly prepared by ultra-precision spherical cold processing technology and semiconductor technology. The stress adjuster has the characteristics of high spherical accuracy and good uniformity, and requires accurate control of parameters such as the radius of curvature. Ultra-precision spherical cold processing technology has the following advantages: (1) It can achieve very high spherical accuracy and surface quality to meet applications with extremely high requirements for optical performance; (2) Good surface finish, the processed spherical surface has low roughness, which helps to reduce light scattering and absorption and improve the efficiency of the optical system; (3) Good repeatability. It can repeatedly produce spherical surfaces with the same accuracy and quality.

[0050] In some embodiments, the rough grinding process using the ultra-precision spherical cold processing technology includes: fixing the selected substrate on a workbench, using a curvature radius R B The rough spherical grinding wheel performs preliminary grinding on the substrate. After rough grinding, the substrate has a preliminary geometric shape, but the roughness is relatively large. The test results of the profile of the adjuster after rough grinding can be found in Figure 4 Left curve graph.

[0051] The fine grinding process using ultra-precision spherical cold processing technology includes: after washing and cleaning the grinding chips, replace the curvature radius R B The substrate is finely ground by a fine spherical grinding wheel. The test results of the adjuster profile after fine grinding are shown in Figure 4 The right side of the graph.

[0052] Among them, the mesh number of the coarse spherical grinding wheel is smaller than the mesh number of the fine spherical grinding wheel; for example, the mesh number of the coarse spherical grinding wheel is 36 mesh, 46 mesh, 60 mesh or 80 mesh, and the mesh number of the fine spherical grinding wheel is ≥100 mesh, which can be 100 mesh or 120 mesh.

[0053] The mesh number of a grinding wheel refers to the size of the abrasive grains. Specifically, the higher the mesh number, the smaller the abrasive grains, and the lower the surface roughness of the workpiece during grinding. The mesh number of a grinding wheel is closely related to the surface roughness of the workpiece during grinding. Grinding wheels with smaller mesh numbers are suitable for coarse grinding because they have a large grinding allowance and require a larger surface roughness value. Using grinding wheels with smaller mesh numbers can reduce clogging and heating problems. The relationship between the mesh number of a grinding wheel and the size of abrasive grains.

[0054] In summary, the selection of commonly used grinding wheel mesh is related to the grinding effect and surface finish of the grinding wheel. The larger the mesh, the smaller the sand particles, the finer the grinding effect and the higher the surface finish. Different grinding wheel meshes are suitable for different grinding and dressing work. Choosing the appropriate grinding wheel mesh according to actual needs can improve work efficiency and product quality.

[0055] After the rough grinding process, the rough grinding radius of curvature of the surface of the substrate is obtained by using a profilometer; according to the obtained rough grinding radius of curvature, the duration and speed of the fine spherical grinding wheel are adjusted. The profilometer is a contact surface topography measuring instrument, which is mainly used to accurately measure the surface profile of the material. Its working principle is to directly contact the surface of the object to be measured through the stylus. When the stylus slides along the surface, the tiny peaks and valleys on the surface will cause the stylus to move up and down, reflecting the profile of the surface. The sensor will convert the displacement of the stylus into an electrical signal. The electrical signal will then be converted into a digital signal and analyzed and processed by software to finally obtain detailed data of the surface profile.

[0056] In some embodiments, the polishing process includes: evenly spreading polishing liquid on the grinding disc, placing the upper surface of the substrate upside down on the grinding disc, and polishing the upper surface of the substrate by rotating the grinding disc to obtain a final tuner product.

[0057] In some embodiments, after the rough grinding process, a profile meter is used to obtain the rough grinding radius of curvature of the upper surface of the substrate; according to the obtained rough grinding radius of curvature, the duration and speed of the fine spherical grinding wheel are adjusted. Controlling pressure and speed helps reduce wear on the workpiece surface and ensures that the finish of the final product meets the highest standards. In order to achieve the above goals, special attention should be paid to the pressure and speed control of grinding during precision grinding. Using lower pressure and speed than rough grinding, lower pressure helps reduce damage to the workpiece, avoids scratches or dents on the surface, and can effectively slow down the temperature rise of the material during processing. A properly reduced speed can distribute the wear pressure more evenly, ensure grinding uniformity, and reduce the impact of thermal effects on processing accuracy; achieve minimal roughness.

[0058] The coating is mainly completed by semiconductor sputtering process. The basic principle of sputtering process is: in a vacuum environment, high-energy particles accelerated by electric field bombard metal target material, causing metal atoms to escape from the surface of target material and deposit on the surface of substrate to form a dense film. In order to reduce the influence of coating on the curvature radius and improve the hardness of stress adjuster surface, a layer of 20nm thick Cr is sputtered on the upper surface of stress adjuster to obtain 10MPa~300MPa stress adjuster.

[0059] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0060] Based on the same inventive concept, an embodiment of the present application also provides a wafer thin film stress regulator, which is manufactured using the wafer thin film stress regulator manufacturing method.

[0061] By utilizing the wafer film stress adjuster provided by the present invention, the tester can be adjusted to ensure the accuracy of the test results of the tester.

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a wafer thin film stress regulator, characterized in that: The method comprises: The curvature radius R of the growing film is calculated according to formula (1): B ; Glass is selected as the growth substrate, and the curvature radius R is calculated. B Rough grinding, fine grinding and polishing are performed to obtain the upper surface curvature radius R B substrate; The film is deposited on the upper surface of the substrate to obtain a curvature radius of R B Stress adjuster; In formula (1), σ film is the preset stress value of the film grown on the substrate; Δ is a constant; R A is the radius of curvature of the film grown under ideal conditions. In ideal conditions, the film is horizontal, so R A is infinite; R B is the radius of curvature of the actual grown film.

2. The method for preparing a wafer thin film stress regulator according to claim 1, characterized in that: The rough grinding process includes: fixing the selected substrate on a workbench, using a curvature radius of R B The coarse spherical grinding wheel performs preliminary grinding on the substrate.

3. The method for preparing a wafer thin film stress regulator according to claim 2, characterized in that: The fine grinding process includes: after washing and cleaning the grinding debris, replacing the curvature radius R B The substrate is finely ground by a fine spherical grinding wheel.

4. The method for preparing a wafer thin film stress regulator according to claim 3, characterized in that: The mesh number of the coarse spherical grinding wheel is smaller than the mesh number of the fine spherical grinding wheel; the mesh number of the coarse spherical grinding wheel is 36 meshes, and the mesh number of the fine spherical grinding wheel is ≥100 meshes.

5. The method for preparing a wafer thin film stress regulator according to claim 1, wherein: After the rough grinding process, a rough grinding curvature radius of the upper surface of the substrate is obtained by using a profile measuring instrument; and the duration and rotation speed of the fine spherical grinding wheel are adjusted according to the obtained rough grinding curvature radius.

6. The method for preparing a wafer thin film stress regulator according to claim 5, characterized in that: The polishing process includes: evenly spreading polishing liquid in the grinding disc, placing the upper surface of the substrate upside down on the grinding disc, and polishing the upper surface of the substrate by rotating the grinding disc.

7. The method for preparing a wafer thin film stress regulator according to claim 1, characterized in that: The coating on the upper surface of the substrate is completed by using a semiconductor sputtering process.

8. The method for preparing a wafer thin film stress regulator according to claim 1, characterized in that: The film has a thickness of 20nm-25nm and is made of Cr.

9. The method for preparing a wafer thin film stress regulator according to claim 1, characterized in that: The preset film stress value is 10MPa to 300MPa.

10. A wafer film stress adjuster, characterized in that: The device is manufactured by the method for preparing a wafer thin film stress regulator as described in any one of claims 1 to 9.

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