Thin film stress testing method and substrate thereof

Abstract

This invention discloses a thin film stress testing method and its application substrate, belonging to the technical solution of the thin film field. Its core lies in polishing the measurement surface of the substrate, then measuring the radius of curvature R'0 before coating and the radius of curvature #imgabs0#R' after coating using an optical lever method. Substituting these values ​​into the formula yields the thin film stress σ, where E s V is the elastic modulus of the substrate. s H is the Poisson's ratio of the substrate. s Let f be the thickness of the substrate, and let f be the thickness of the thin film. R0 = -(R'0 - H) s ), wherein R = -(R' - H s Therefore, this method does not require the reflectivity of the thin film. As long as the measurement surface of the substrate is polished, the thin film stress σ can be obtained by using the optical rod method, which solves the problem that the existing technology requires the thin film to be reflective in order to measure the thin film stress.

Description

Technical Field

[0001] The invention relates to a stress testing method, in particular to a film stress testing method and a substrate used therein. Background Art

[0002] Thin film materials are widely used in many fields such as microelectronics, semiconductors, photovoltaic energy, aerospace, automobiles, mechanical processing, etc., and their importance is becoming increasingly prominent. Most key development areas are closely related to thin film material technology. Therefore, vigorously carrying out relevant research on thin film materials is of great significance to promoting the development of key national industries.

[0003] The interfacial bonding strength and thermal fatigue resistance of thin film materials are closely related to the film stress. Super-hard and wear-resistant coating materials often have strong covalent bond characteristics. Thin films prepared by chemical vapor deposition or physical vapor deposition processes generally have residual stresses of several GPa or even up to more than ten GPa. In severe cases, this can cause the film to peel off and affect its performance. Therefore, during the development and preparation of the film, its stress must be tested and fed back to the film development and preparation process to obtain a thin film material with the required stress.

[0004] Currently, the main stress testers generally use the optical lever principle for testing. The test principle is to measure the change in substrate curvature before and after film deposition by collecting the movement of laser on the film surface and the change in the position of the laser reflected by the film on the receiver, and then apply the Stoney formula to calculate the film stress.

[0005] However, existing methods of using the optical lever method to test film stress all require that the film surface is smooth enough to reflect a light beam of sufficient intensity. For films with surfaces that are not smooth enough, such as diamond films prepared by the CVD method, or for films that are not smooth enough to ensure bonding strength, resulting in the film surface not being reflective, the optical lever method cannot be used to test film stress. Summary of the invention

[0006] The object of the present invention is to provide a thin film stress testing method and a substrate used therein, so as to solve the problem in the prior art that the thin film must reflect light in order to measure the film stress.

[0007] In order to solve the above technical problems, the present invention provides a thin film stress testing method, comprising the following steps:

[0008] Step A, the substrate comprises a measuring surface and a coating surface which are arranged opposite to each other, and the measuring surface of the substrate is polished;

[0009] Step B, using an optical lever method to measure the curvature radius of the measuring surface of the substrate to obtain R'0;

[0010] Step C, coating a thin film on the coating surface of the substrate, and then measuring the curvature radius of the measuring surface of the substrate by using an optical lever method to obtain R';

[0011] Step D: Substitute the measured data into the formula Calculate to obtain the membrane stress σ;

[0012] Among them, E s is the elastic modulus of the substrate, V s is the Poisson's ratio of the substrate, H s is the thickness of the substrate, f is the thickness of the film, and R0=-(R'0-H s ), wherein R=-(R'-H s ).

[0013] Wherein, the thickness of the substrate is at least 100 times the thickness of the film.

[0014] The thickness f of the film is measured using a scanning electron microscope.

[0015] Wherein, in step A, the measuring surface of the substrate is chemically polished.

[0016] Wherein, in step A, the measuring surface of the substrate is polished to a roughness of less than 0.04 μm.

[0017] Wherein, in step A, it is necessary to perform coating pretreatment on the coating surface of the substrate.

[0018] Wherein, in step C, the measuring surface of the substrate is first shielded, and then the film is plated on the coating surface of the substrate.

[0019] Wherein, in step C, the substrate is clamped on a plane fixture, the measuring surface of the substrate is fitted with the plane fixture, and then the thin film is plated on the coating surface of the substrate. After the thin film is plated, the substrate is removed from the plane fixture, and the optical lever method is used to measure the curvature radius of the measuring surface of the substrate to obtain R'.

[0020] Wherein, in step C, the thin film is deposited on the coating surface of the substrate by using physical vapor deposition method.

[0021] A substrate is used in the above-mentioned thin film stress side-view method, the substrate comprises a measuring surface and a coating surface which are arranged oppositely, and the measuring surface is a polished surface.

[0022] The beneficial effects of the present invention are as follows:

[0023] In the embodiment of the present invention, the measuring surface of the substrate is polished, and then the optical lever method can be used to measure the radius of curvature of the measuring surface of the substrate to obtain R'0 (before thin film coating) and R' (after thin film coating), and finally the film stress σ can be obtained by substituting it into the formula. Therefore, this method has no requirements on the reflective ability of the film. As long as the measuring surface of the substrate is polished, the optical lever method can be used to obtain the film stress σ, thereby solving the problem in the prior art that the film must be reflective in order to measure the film stress. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solution of the present invention, the drawings required for use in the implementation mode will be briefly introduced below. Obviously, the drawings described below are only some implementation modes of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 It is a schematic diagram of the substrate structure provided by a preferred embodiment of the thin film stress testing method of the present invention;

[0026] Figure 2 It is a schematic diagram of the measurement principle provided by the preferred embodiment of the thin film stress testing method of the present invention.

[0027] The reference numerals are as follows:

[0028] 1. Substrate; 11. Measuring surface; 12. Coating surface. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0030] from Figure 1 and 2 It can be seen that the film stress testing method described in the embodiment of the present invention includes the following steps:

[0031] Step A: The substrate comprises a measuring surface and a coating surface which are arranged opposite to each other, and the measuring surface 11 of the substrate 1 is polished;

[0032] Step B, using an optical lever method to measure the curvature radius of the measuring surface 11 of the substrate 1 to obtain R'0;

[0033] Step C, coating a thin film on the coating surface 12 of the substrate 1, and then measuring the curvature radius of the measuring surface 11 of the substrate 1 by using an optical lever method to obtain R';

[0034] Step D: Substitute the measured data into the formula Calculate to obtain the membrane stress σ;

[0035] Among them, E s is the elastic modulus of the substrate 1, V s is the Poisson's ratio of the substrate 1, H s is the thickness of the substrate 1, f is the thickness of the film, and R0=-(R'0-H s ), wherein R=-(R'-H s ).

[0036] In summary, this method has no requirements on the reflective ability of the film. As long as the measuring surface 11 of the substrate 1 is polished, the optical lever method can be used to obtain the film stress σ, thereby solving the problem in the prior art that the film must be reflective in order to measure the film stress.

[0037] For E s The value of 1E of substrates of different materials can be obtained by reading relevant reference books or searching online. s Value; Similarly, for V s The value of 1V of substrates of different materials can be obtained by reading the corresponding reference books or searching the Internet. s Value; for H s The value of can be measured using a vernier caliper or height gauge; the value of f can be measured using a microscope.

[0038] An improvement to the thin film stress testing method according to the embodiment of the present invention may be as follows: the thickness of the substrate 1 is at least 100 times the thickness of the thin film.

[0039] Because different films have different thicknesses, selecting a substrate 1 of corresponding thickness according to the thickness of different films can further improve the accuracy of film stress measurement. Therefore, when the thickness of the substrate 1 is at least 100 times the thickness of the film, the accuracy of film stress measurement can be better guaranteed.

[0040] Therefore, according to the thickness of the existing film, the thickness H of the substrate 1 can be s Set it to 0.1~1mm, which can meet most testing needs.

[0041] An improvement to the film stress testing method in the embodiment of the present invention may be as follows: a scanning electron microscope is used to measure the thickness f of the film.

[0042] Since the thickness of the film is very small, it is difficult for general measuring tools to accurately measure its thickness; the scanning electron microscope mainly uses secondary electron signal imaging to observe the surface morphology of the sample, that is, a very narrow electron beam is used to scan the sample, and various effects are produced through the interaction between the electron beam and the sample, among which the main effect is the secondary electron emission of the sample. The secondary electrons can produce an enlarged morphological image of the sample surface. This image is established in a time sequence when the sample is scanned, that is, the enlarged image is obtained by using the point-by-point imaging method. Its advantages are:

[0043] 1. It has a high magnification, which can be adjusted continuously between 200,000 and 200,000 times;

[0044] 2. It has a large depth of field, a wide field of view, and a three-dimensional image, and can directly observe the fine structure of the uneven surface of various samples;

[0045] 3. Sample preparation is simple.

[0046] Therefore, using a scanning electron microscope to measure the thickness f of the film not only makes the measurement process simple, but also has high measurement accuracy, providing important assistance for the entire measurement process.

[0047] An improvement to the thin film stress testing method according to the embodiment of the present invention may be as follows: in step A, the measuring surface 11 of the substrate 1 is subjected to chemical polishing.

[0048] Polishing can be roughly divided into two types:

[0049] 1. Physical polishing, using mechanical methods to flatten the surface of an object, such as grinding;

[0050] 2. Chemical polishing, which uses chemical corrosion to level the surface of an object, such as cleaning the metal surface with sulfuric acid added with a leveling agent.

[0051] However, compared with chemical polishing, physical polishing may cause stress on the polished surface, which may affect the accuracy of thin film stress measurement. Therefore, chemical polishing of the measurement surface 11 of the substrate 1 can eliminate this interference factor.

[0052] An improvement of the thin film stress testing method in the embodiment of the present invention may be as follows: in step A, the measuring surface 11 of the substrate 1 is polished to a roughness less than 0.04 μm.

[0053] In order to ensure that the optical lever method can be used to measure thin film stress, it should be ensured that the measuring surface 11 of the substrate 1 can reflect light of sufficient intensity. When the roughness of the measuring surface 11 of the substrate 1 is less than 0.04μm, it can meet the requirement for necessary reflection of light, thus providing a guarantee for the measurement of thin film stress.

[0054] An improvement to the thin film stress testing method according to the embodiment of the present invention may be as follows: in step A, the coating surface 12 of the substrate 1 needs to be subjected to coating pretreatment.

[0055] After the coating surface 12 of the substrate 1 is pretreated, the film can be more stably coated on the coating surface 12 of the substrate 1, which provides a guarantee for the measurement of film stress. Among them, the purification treatment of the coating surface 12 of the substrate 1 is a basic pretreatment. The purification treatment can be carried out by cleaning liquid. The commonly used cleaning liquid can be:

[0056] 1. Softened water or water-containing systems, such as water containing detergents, dilute acids or alkalis;

[0057] 2. Anhydrous organic solvents, such as ethanol, isopropanol, ketone, acetone, etc.;

[0058] 3. Petroleum distillates, chlorinated or fluorinated hydrocarbons;

[0059] 4. Emulsion or solvent vapor;

[0060] 5. Metal cleaning agents. Metal cleaning agents can be divided into three categories: acidic, alkaline and neutral alkaline. Their uses are as follows: acidic ones are used to clean oxides, rust and corrosion products; alkaline ones contain surfactants and are used to remove light oil stains; neutral alkaline ones can avoid damage to the surface by acids and alkalis.

[0061] An improvement to the thin film stress testing method described in the embodiment of the present invention may be as follows: in step C, the measuring surface 11 of the substrate 1 is first shielded, and then the thin film is plated on the coating surface 12 of the substrate 1 .

[0062] Before thin film coating, by shielding the measuring surface 11 of the substrate 1, it is possible to prevent the thin film from being mistakenly plated on the measuring surface 11 of the substrate 1, thereby avoiding affecting the measurement accuracy of the thin film stress due to mistaken plating, and providing an important guarantee for the accuracy of the thin film stress measurement.

[0063] An improvement to the thin film stress testing method described in the embodiment of the present invention may be as follows: in step C, the substrate 1 is clamped on a planar fixture, the measuring surface 11 of the substrate 1 is in contact with the planar fixture, and then the thin film is plated on the coating surface 12 of the substrate 1. After the thin film is plated, the substrate 1 is removed from the planar fixture, and the optical lever method is used to measure the curvature radius of the measuring surface 11 of the substrate 1 to obtain R'.

[0064] When thin film coating is performed, since the measuring surface 11 of the substrate 1 is in a fitted state with the planar fixture, the thin film cannot be mistakenly plated onto the measuring surface 11 of the substrate 1, thereby avoiding affecting the measurement accuracy of the thin film stress due to mistaken plating, and providing an important guarantee for the accuracy of the thin film stress measurement.

[0065] An improvement to the thin film stress testing method described in the embodiment of the present invention may be as follows: in step C, the thin film is deposited on the coating surface 12 of the substrate 1 by using a physical vapor deposition method.

[0066] Chemical vapor deposition is a vapor phase growth method for preparing materials. It is a process technology that introduces one or more compounds or single gases containing thin film elements into a reaction chamber where a substrate is placed, and deposits a solid thin film on the surface of the substrate with the help of spatial vapor phase chemical reactions.

[0067] Physical vapor deposition refers to the process of transferring atoms or molecules from a source to the surface of a substrate by using a physical process to achieve material transfer. Its function is to spray certain particles with special properties (high strength, wear resistance, heat dissipation, corrosion resistance, etc.) on a matrix with lower performance, so that the matrix has better performance. Its basic methods include: vacuum evaporation, sputtering, ion plating (hollow cathode ion plating, hot cathode ion plating, arc ion plating, active reaction ion plating, radio frequency ion plating, DC discharge ion plating, etc.).

[0068] Compared with the chemical vapor deposition process, the physical vapor deposition process has a low processing temperature and has no effect on the bending strength of the material below 600°C; the internal stress state of the film is compressive stress, which is more suitable for coating of cemented carbide precision and complex products; the physical vapor deposition process has no adverse effect on the environment and is in line with the development direction of modern green manufacturing; the current physical vapor deposition coating technology has been widely used in the coating treatment of cemented carbide end mills, drills, step drills, oil hole drills, reamers, taps, indexable milling inserts, turning inserts, special-shaped tools, welding tools, etc.

[0069] from Figure 1 and 2 It can be known that the substrate 1 described in the embodiment of the present invention is used for the above-mentioned thin film stress side-view method, and the substrate 1 includes a measuring surface 11 and a coating surface 12 arranged oppositely, and the measuring surface 11 is a polished surface.

[0070] By using this substrate 1, the curvature radii R'0 and R' can be measured before and after coating the coating surface 12, and then the film stress σ can be obtained by substituting them into the above-mentioned related formula, thereby solving the problem that the film stress can only be measured by reflecting light in the prior art.

[0071] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A film stress testing method, characterized in that The following steps are included: Step A, the substrate comprises a measuring surface and a coating surface which are arranged opposite to each other, and the measuring surface of the substrate is polished. In the step A, the measuring surface of the substrate is polished to a roughness of less than 0.04 μm; Step B, using an optical lever method to measure the curvature radius of the measuring surface of the substrate to obtain R'0; Step C, coating a thin film on the coating surface of the substrate, and then measuring the curvature radius of the measuring surface of the substrate by using an optical lever method to obtain R'. In the step C, the measuring surface of the substrate is first shielded, and then the thin film is coated on the coating surface of the substrate; Step D: Substitute the measured data into the formula Calculate to obtain the membrane stress σ; Among them, E s is the elastic modulus of the substrate, V s is the Poisson's ratio of the substrate, H s is the thickness of the substrate, f is the thickness of the film, and R0=-(R'0-H s ), wherein R=-(R'-H s ).

2. The thin film stress testing method according to claim 1, characterized in that: The thickness of the substrate is at least 100 times the thickness of the film.

3. The thin film stress testing method according to claim 1, characterized in that: The thickness f of the film was measured using a scanning electron microscope.

4. The thin film stress testing method according to claim 1, characterized in that: In step A, a chemical polishing process is performed on the measurement surface of the substrate.

5. The thin film stress testing method according to claim 1, characterized in that: In step A, the coating surface of the substrate needs to be pre-treated.

6. The thin film stress testing method according to claim 5, characterized in that: In step C, the substrate is clamped on a planar fixture, the measuring surface of the substrate is in contact with the planar fixture, and then the thin film is coated on the coating surface of the substrate. After the thin film is coated, the substrate is removed from the planar fixture, and the optical lever method is used to measure the curvature radius of the measuring surface of the substrate to obtain R'.

7. The thin film stress testing method according to claim 1, characterized in that: In step C, the thin film is deposited on the coating surface of the substrate by using physical vapor deposition.

8. A substrate, characterized in that The substrate is used in the thin film stress testing method according to any one of claims 1 to 7, and the substrate comprises a measuring surface and a coating surface which are arranged opposite to each other, and the measuring surface is a polished surface.

Images