Method for detecting defects in a metal film

Abstract

The present application provides a kind of metal film defect detection method, first form on semiconductor substrate with copper precipitates metal film, then execute wet cleaning process to form the hollow corresponding with the copper precipitates on the surface of the metal film, in the process of executing wet cleaning process, the cleaning solution of wet cleaning process will occur chemical reaction with the copper precipitates on the surface of metal film and thus form the hollow, through hollow can simply, accurately and quickly obtain the defect distribution of copper precipitates on the surface of metal film.Further, by scanning the metal film to obtain the number of hollow in the predetermined area of the metal film surface, the copper precipitate defect on the surface of metal film can be quantified, so that the content of copper precipitate defect of metal film can be characterized, so as to evaluate the quality of metal film by the content of copper precipitate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor manufacturing, in particular to a method for detecting defects of a metal film. BACKGROUND

[0002] In the manufacturing process of semiconductor devices, a metal film is usually formed on a semiconductor substrate, which can serve as a metal connection line. In order to ensure the electron migration characteristics of the metal film, the material of the metal film will adopt an alloy including copper. However, when depositing the metal film, it is necessary to pass through a metal film deposition device, a metal etching device, a dry adhesive removal device, a chemical vapor deposition device, etc. Since the process has a high temperature of 200 degrees Celsius or above, if the semiconductor substrate stays for too long, copper is easy to precipitate, and copper precipitates are formed which are difficult to etch. On the one hand, the copper precipitates are difficult to etch and are more likely to cause short circuits between metal lines, thereby causing the failure of the conductive metal interconnection. On the other hand, in the subsequent cleaning process, since the chemical potentials of the alloys in the metal film are different, if the metal film is placed in an electrolyte solution, a so-called primary cell reaction will occur, causing electrochemical corrosion.

[0003] At present, the detection of copper precipitates in the metal film is analyzed and judged by a FIB (Focused Ion Beam) analysis method. FIB is a method in which an ion beam generated by a liquid metal (Ga) ion source is accelerated by an ion gun and focused to irradiate the sample surface to generate a secondary electron signal to obtain an electron image. However, since FIB has a high cost and takes a long time to operate, more importantly, it requires accurate positioning to capture copper precipitation defects. If the positioning is not accurate and the copper precipitation defect area cannot be captured, it is difficult to detect the copper precipitation defect area, which requires a lot of time and cannot be quantified, and the quality of the metal film cannot be evaluated. SUMMARY

[0004] The purpose of the present application is to provide a method for detecting defects of a metal film to simply, accurately and quickly obtain defects of copper precipitates in the metal film.

[0005] Another purpose of the present application is to quantify the copper precipitation defects of the metal film to evaluate the quality of the metal film.

[0006] To achieve the above purpose, the present application provides a method for detecting defects of a metal film, which comprises:

[0007] providing a semiconductor substrate;

[0008] forming a metal film on the semiconductor substrate, the surface of the metal film having copper precipitates;

[0009] performing a wet cleaning process to form the voids corresponding to the copper precipitates on the surface of the metal thin film;

[0010] scanning the metal thin film to obtain the number of the voids in the predetermined region on the surface of the metal thin film.

[0011] Optionally, in the method for detecting defects of the metal thin film, the material of the metal thin film is aluminum-copper alloy, and the metal thin film is formed by physical vapor deposition process.

[0012] Optionally, in the method for detecting defects of the metal thin film, the content of copper in the metal thin film is 0.1% to 0.5%.

[0013] Optionally, in the method for detecting defects of the metal thin film, the thickness of the metal thin film is 0.1 μm to 10 μm.

[0014] Optionally, in the method for detecting defects of the metal thin film, the wet cleaning process is immersion cleaning process and / or spray cleaning process.

[0015] Optionally, in the method for detecting defects of the metal thin film, the cleaning solution used in the wet cleaning process includes dilute hydrofluoric acid, hydrogen peroxide and hydrochloric acid.

[0016] Optionally, in the method for detecting defects of the metal thin film, the time for performing the wet cleaning process is 10 min to 60 min.

[0017] Optionally, in the method for detecting defects of the metal thin film, the surface of the metal thin film is a flat surface, the copper precipitates are embedded in the surface of the metal thin film, and the metal thin film has the copper precipitates inside.

[0018] Optionally, in the method for detecting defects of the metal thin film, the method for scanning the metal thin film includes:

[0019] scanning the predetermined region on the surface of the metal thin film by scanning electron microscope to obtain the number of the voids in the predetermined region.

[0020] Optionally, in the method for detecting defects of the metal thin film, the cross section of the predetermined region on the surface of the metal thin film in horizontal direction is rectangular, circular or triangular; and the area of the predetermined region is 100 μm2 to 1000 μm2.

[0021] In the method for detecting defects of a metal thin film provided by the present application, a metal thin film with copper precipitates is first formed on a semiconductor substrate, and then a wet cleaning process is performed to form cavities corresponding to the copper precipitates on the surface of the metal thin film. In the process of performing the wet cleaning process, the cleaning liquid of the wet cleaning process will chemically react with the copper precipitates on the surface of the metal thin film to form the cavities. Thus, the defect distribution of the copper precipitates of the metal thin film can be simply, accurately and quickly obtained through the cavities. Further, by scanning the metal thin film to obtain the number of cavities in a predetermined area on the surface of the metal thin film, the copper precipitate defects on the surface of the metal thin film can be quantified, so that the content of the copper precipitate defects of the metal thin film can be characterized, and thus the quality of the metal thin film can be evaluated through the content of the copper precipitates. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a flowchart of the method for detecting defects of a metal thin film according to an embodiment of the present application;

[0023] Figure 2 is a schematic cross-sectional view of a metal thin film in the method for detecting defects of a metal thin film according to an embodiment of the present application;

[0024] Figure 3 is a top view of a metal thin film in the method for detecting defects of a metal thin film according to an embodiment of the present application;

[0025] In the drawings, the reference signs are explained as follows:

[0026] 100 - semiconductor substrate; 110 - metal thin film; 110A - copper precipitate; 110B - cavity. DETAILED DESCRIPTION

[0027] The method for detecting defects of a metal thin film according to the present application will be further described in detail below in combination with the drawings and specific embodiments. The advantages and features of the present application will be more apparent according to the following description. It should be noted that the drawings are all very simplified and use non-precise proportions, which are only used to facilitate and clarify the purpose of assisting the description of the embodiments of the present application.

[0028] Figure 1 is a flowchart of the method for detecting defects of a metal thin film according to an embodiment of the present application. As shown in Figure 1 , the present embodiment provides a method for detecting defects of a metal thin film, which comprises:

[0029] Step S1: providing a semiconductor substrate;

[0030] Step S2: forming a metal thin film on the semiconductor substrate, the surface of the metal thin film having copper precipitates;

[0031] Step S3: performing a wet cleaning process to form holes corresponding to the copper precipitates on the surface of the metal thin film;

[0032] Step S4: scanning the metal thin film to obtain the number of holes in a predetermined region on the surface of the metal thin film.

[0033] Figure 2 is a cross-sectional view of a metal thin film in the method for detecting defects of a metal thin film according to an embodiment of the present application; Figure 3 is a top view of a metal thin film in the method for detecting defects of a metal thin film according to an embodiment of the present application. Next, the above steps will be described in more detail with reference to the accompanying drawings. Figures 2-3

[0034] As shown in step S1, a semiconductor substrate 100 is provided, which can be any suitable substrate known to those skilled in the art, for example, can be at least one of the following materials: silicon, germanium, germanium silicon, carbon silicon, carbon germanium silicon, indium arsenide, gallium arsenide, indium phosphide, silicon on insulator, silicon on germanium on insulator, or the like. In this embodiment, the semiconductor substrate 100 is a silicon substrate. Figure 2 In this embodiment, in order to better detect defects of the metal thin film 110, before forming the metal thin film 110 on the semiconductor substrate 100, the method for detecting defects of the metal thin film 110 further comprises: first, cleaning the semiconductor substrate 100 to remove contaminants such as residual particles attached to the surface of the semiconductor substrate 100, for example, the surface of the semiconductor substrate 100 can be first cleaned with a hydrofluoric acid or hydrochloric acid solution, the cleaning time can be 3-4 min, and then the surface of the semiconductor substrate 100 is rinsed with deionized water; then, drying the semiconductor substrate 100 to remove moisture attached to the surface of the semiconductor substrate 100, the drying temperature can be 250-280°C, and the drying time can be 1-2 min.

[0035] As shown in step S2, a metal thin film 110 is formed on the semiconductor substrate 100, which can be any suitable material known to those skilled in the art, for example, can be at least one of the following materials: copper, aluminum, titanium, tungsten, molybdenum, nickel, platinum, gold, silver, palladium, or the like. In this embodiment, the metal thin film 110 is a copper thin film.

[0036] Figure 2 ​​As shown, in step S2, a metal film 110 is formed on the semiconductor substrate 100, and the surface of the metal film 110 has copper precipitates 110A. The surface of the metal film 110 is a flat surface, the copper precipitates 110A are embedded in the surface of the metal film 110, and the copper precipitates 110A are also in the interior of the metal film 110. Specifically, the metal film 110 is a copper-doped aluminum film, and the metal film 110 is formed by a physical vapor deposition process. The metal film 110 can be used as a metal layer in an interconnection structure to electrically connect devices on the semiconductor substrate 100. In addition, a transistor and / or a dielectric layer are formed between the semiconductor substrate 100 and the metal film 110. In this embodiment, the transistor and / or the dielectric layer between the semiconductor substrate 100 and the metal film 110 are omitted for better illustration of the present application, and the corresponding illustrations of the transistor and / or the dielectric layer between the semiconductor substrate 100 and the metal film 110 are omitted in the accompanying drawings. Figures 2-3

[0037] In the process of forming the metal film 110, the semiconductor substrate 100 is placed in a chamber of a physical vapor deposition process machine, and parameters such as temperature and power are set. For example, the temperature can be set to 400-700°C, and the power can be set to 5000-8000W. The greater the power, the faster the rate of forming the metal film 110. In this embodiment, the thickness of the metal film 110 is 0.1-10μm.

[0038] The metal film 110 can be formed by vacuum evaporation, sputtering, or ion plating in a physical vapor deposition process. In vacuum evaporation, the metal material to be evaporated is heated and evaporated in a vacuum chamber, and the evaporated atoms or atomic groups are condensed on a substrate at a lower temperature to form the metal film 110. In sputtering, the surface of a solid target (i.e., a metal material) is bombarded with charged ions under the action of an electromagnetic field to obtain sufficient energy, and the plasma sputtered from the surface of the target is shot at the surface of the semiconductor substrate 100 with a certain kinetic energy to form the metal film 110 on the semiconductor substrate 100. In ion plating, under vacuum conditions, gas discharge is used to partially ionize the gas or evaporated material, and the evaporated material or its reaction product is deposited on the semiconductor substrate 100 under the bombardment of gas ions or evaporated material particles to form the metal film 110.

[0039] ​For example, the metal thin film 110 is a copper-doped aluminum film, and the aluminum target contains 0.1% to 0.5% of copper. In this embodiment, the aluminum target contains 0.5% of copper. When the metal thin film 110 is formed on the semiconductor substrate 100, the plasma of aluminum and copper is sputtered on the surface of the semiconductor substrate 100 to form the metal thin film 110 on the surface of the semiconductor substrate 100. Since the metal thin film 110 is a copper-doped aluminum film, the thermal accumulation of the copper-doped aluminum increases with the accumulation of the film thickness at high temperature, which seriously affects the lattice size of the metal thin film 110, and causes copper to precipitate in the solid solution to form copper precipitates (i.e., copper-rich phase) 110A on the surface and inside of the metal thin film 110 after the metal thin film 110 is cooled. The copper precipitates 110A are distributed in the form of particles on the surface and inside of the metal thin film 110. It should be understood that the distribution of the copper precipitates 110A is uneven, and the distribution is more dense in some areas and more dispersed in other areas.

[0040] As shown in FIG. 3, in step S3, a wet cleaning process is performed to form cavities 110B corresponding to the copper precipitates 110A on the surface of the metal thin film 110. In this embodiment, the wet cleaning process is a soaking cleaning process and / or a spraying cleaning process. Figure 3

[0041] Preferably, the wet cleaning process is performed by using a soaking cleaning process. Specifically, the semiconductor substrate 100 is soaked in a cleaning solution. Since the metal thin film 110 is a copper-doped aluminum film, and the electric potential of copper is different from that of aluminum, if the metal thin film 110 composed of copper and aluminum is placed in an electrolyte solution, a galvanic cell reaction will occur, causing electrochemical corrosion. The cleaning solution includes at least one of dilute hydrofluoric acid, hydrogen peroxide, and hydrochloric acid. The corrosion rate of the copper precipitates 110A is higher than that of aluminum in the dilute hydrofluoric acid, hydrogen peroxide, or hydrochloric acid. Therefore, during the wet cleaning process, the cleaning solution reacts with the copper precipitates 110A on the surface of the metal thin film 110, thereby forming cavities 110B on the copper precipitates 110A on the surface of the metal thin film 110.

[0042] ​In the cleaning process of the wet cleaning, one cleaning solution can be used to complete at the same temperature, but in this case, the reaction rate of the copper precipitate 110A with the cleaning solution will gradually decrease with the consumption of the cleaning solution, and the reaction rate of the copper precipitate 110A with the cleaning solution will decrease with the increase of the soaking time. Therefore, in order to improve the reaction rate of the copper precipitate 110A with the cleaning solution, one cleaning solution can be used and heated from 20°C to 50°C, or multiple cleaning solutions can be used according to the reaction rates of different cleaning solutions at different temperatures, and the order of changing the cleaning solutions is from low to high according to the optimal cleaning temperature of different cleaning solutions.

[0043] For example, there are three cleaning solutions in this embodiment: the first cleaning solution is optimal at 20°C, the second cleaning solution is optimal at 30°C, and the third cleaning solution is optimal at 40°C. The steps of the wet cleaning process are as follows: first, soak the semiconductor substrate 100 with the metal film 110 in the first cleaning solution at 20°C for a certain time, then change to the second cleaning solution to soak the semiconductor substrate 100 at 30°C for a certain time, and then change to the third cleaning solution to soak at 40°C for a certain time. The first cleaning solution can be dilute hydrofluoric acid, the second cleaning solution can be hydrogen peroxide, and the third cleaning solution can be hydrochloric acid.

[0044] In the process of performing the wet cleaning, the cleaning solution can penetrate from the surface of the copper precipitate 110A on the surface of the metal film to the inside of the copper precipitate 110A, thereby forming a cavity 110B on the surface of the metal film 110. In this embodiment, the time for performing the wet cleaning process is 10-60 minutes, for example, 20 minutes, to ensure that the cleaning solution and the copper precipitate 110A can produce sufficient chemical reaction, so that the cavity 110B in the metal film 110 has a certain size. If the size of the cavity 110B is small, it is not easy to be found in the subsequent scanning, thereby causing the problem of inaccurate detection results.

[0045] In another embodiment, the wet cleaning process is performed using a spray cleaning process, which refers to spraying at least one of dilute hydrofluoric acid, hydrogen peroxide and hydrochloric acid to the surface of the metal film 110, and the cleaning solution reacts with the copper precipitate 110A on the surface of the metal film 110 to form a cavity 110B on the surface of the metal film 110.

[0046] In step S4, the metal thin film 110 is scanned to obtain the number of voids 110B within a predetermined region L on the surface of the metal thin film 110. Specifically, the method for scanning the metal thin film 110 includes scanning the predetermined region L on the surface of the metal thin film 110 using a scanning electron microscope (SEM) to obtain the number of voids 110B within the predetermined region L. The defect distribution of copper precipitates 110A on the metal thin film 110 can be obtained simply, accurately, and quickly through the voids 110B. Furthermore, by scanning the metal thin film 110 to obtain the number of voids 110B within the predetermined region L on the surface of the metal thin film 110, the defects of copper precipitates 110A on the surface of the metal thin film 110 can be quantified, thereby characterizing the content of copper precipitates 110A defects in the metal thin film 110, and thus assessing the quality of the metal thin film 110 through the content of copper precipitates 110A.

[0047] In this embodiment, the predetermined area L on the surface of the metal thin film 110 has a rectangular, circular, or triangular cross-section in the horizontal direction. This embodiment uses a rectangular cross-section on the surface of the metal thin film 110 as an example (e.g.,...). Figure 3 (As shown). The area of ​​the predetermined region L is 100 μm. 2 ~1000μm 2 It should be noted that the area of ​​the predetermined region on the surface of the metal thin film 110 can be determined based on the distribution of voids 110B. If a certain region on the surface of the metal thin film 110 is selected for scanning, and the number of voids 110B in that region is large, the area of ​​that region can be narrowed. If the number of voids 110B in that region is small, the area of ​​that region can be expanded to ensure that the quality of the metal thin film 110 can be accurately evaluated through the voids 110B. By evaluating the quality of the metal thin film 110, the formation process of the metal thin film 110 can be modified to form a metal thin film 110 of higher quality, thereby optimizing the reliability of the interconnect structure.

[0048] In summary, the metal thin film defect detection method provided by this invention first forms a metal thin film with copper precipitates on a semiconductor substrate. Then, a wet cleaning process is performed to form voids corresponding to the copper precipitates on the surface of the metal thin film. During the wet cleaning process, the cleaning solution reacts chemically with the copper precipitates on the metal thin film surface to form these voids. Therefore, the defect distribution of copper precipitates in the metal thin film can be obtained simply, accurately, and quickly through these voids. Furthermore, by scanning the metal thin film to obtain the number of voids within a predetermined area on the surface of the metal thin film, the copper precipitate defects on the metal thin film surface can be quantified. This allows for characterization of the copper precipitate defect content in the metal thin film, thereby assessing the quality of the metal thin film through the copper precipitate content.

[0049] The above description is only description of the preferred embodiments of the present application, and is not any limitation to the scope of the present application. Any change, modification made by the person of ordinary skill in the art according to the above disclosure is within the protection scope of the claims.

Claims

1. A method of detecting defects in a metal film, characterized by, The method for detecting defects of the metal film comprises the following steps: providing a semiconductor substrate; forming a metal film on the semiconductor substrate, the surface of the metal film having copper precipitates; the metal film is a copper-doped aluminum film, and the metal film is formed by a physical vapor deposition process; performing a wet cleaning process to form cavities corresponding to the copper precipitates on the surface of the metal film, the wet cleaning process using a cleaning liquid having a higher corrosion rate for the copper precipitates than for aluminum; scanning the metal film to obtain the number of cavities in a predetermined area of the surface of the metal film.

2. The method for detecting defects in metal thin films as described in claim 1, characterized in that, The content of copper in the metal film is 0.1% to 0.5%.

3. The method of detecting defects in a metal film according to any one of claims 1 to 2, wherein The thickness of the metal film is 0.1 μm to 10 μm.

4. The method of claim 1, wherein the metal thin film defect is detected by using a light source having a wavelength of 400 nm or less. The wet cleaning process is a soaking cleaning process and / or a spraying cleaning process.

5. The method for detecting defects in metal thin films as described in claim 4, characterized in that, The cleaning liquid used in the wet cleaning process comprises at least one of dilute hydrofluoric acid, hydrogen peroxide and hydrochloric acid.

6. The method of claim 1, wherein the metal thin film defect is detected by using a light source having a wavelength of 400 nm or less. The wet cleaning process is performed for 10 min to 60 min.

7. The method of claim 1, wherein the step of detecting defects in the metal thin film is performed by using a method selected from the group consisting of a surface inspection method, a defect review method, and a defect classification method. The surface of the metal film is a flat surface, the copper precipitates are embedded in the surface of the metal film, and the metal film has the copper precipitates inside.

8. The method of claim 1, wherein the metal thin film defect is detected by using a light source having a wavelength of 400 nm or less. The method for scanning the metal film comprises the following steps: scanning a predetermined area of the surface of the metal film by a scanning electron microscope to obtain the number of cavities in the predetermined area. The content of copper in the metal film is 0.1% to 0.5%. The thickness of the metal film is 0.1 μm to 10 μm. The wet cleaning process is a soaking cleaning process and / or a spraying cleaning process. The cleaning liquid used in the wet cleaning process comprises at least one of dilute hydrofluoric acid, hydrogen peroxide and hydrochloric acid. The wet cleaning process is performed for 10 min to 60 min. The surface of the metal film is a flat surface, the copper precipitates are embedded in the surface of the metal film, and the metal film has the copper precipitates inside. The method for scanning the metal film comprises the following steps: scanning a predetermined area of the surface of the metal film by a scanning electron microscope to obtain the number of cavities in the predetermined area.

9. The method for detecting defects in metal thin films as described in claim 8, characterized in that, The predetermined region of the metal thin film surface has a rectangular, circular or triangular cross section in the horizontal direction; the area of the predetermined region is 100 μm 2 ~ 1000 μm 2 .

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