Wafer film thickness calibration library construction method, measurement method and polishing equipment

Abstract

The invention provides a wafer film thickness calibration library construction method, a measurement method and polishing equipment, and the construction method comprises the steps: obtaining a film thickness reflectivity library suitable for a single-layer film environment, and enabling the reflectivity value to periodically change along with the change of the thickness value; acquiring an electric signal # imgabs0 # and an electric signal # imgabs1 # corresponding to the light intensity of reflected light of the single-wavelength light beam by two wafer films with known different thicknesses; acquiring an electric signal # imgabs2 # and an electric signal # imgabs3 # corresponding to the light intensity of the reflected light of the single-wavelength light beam by the two wafer films in the multi-layer film environment; determining a conversion coefficient according to the electric signal # imgabs4 #, the electric signal # imgabs5 #, the electric signal # imgabs6 # and the electric signal # imgabs7 #; and converting the film thickness reflectivity library into a database suitable for a multilayer film environment by using the conversion coefficient.

Description

Technical Field

[0001] The invention relates to the field of wafer polishing, and in particular to a wafer film thickness calibration library construction method, a measurement method and polishing equipment. Background Art

[0002] In CMP (Chemical Mechanical Polishing) technology, there are many methods for detecting wafer thickness and polishing endpoint, such as eddy current method, optical method, etc. Since the scale involved in the polishing process is submicron or nanometer level, the traditional contact measurement method is no longer applicable. The eddy current method can generally only be used for polishing conductor substrates. Therefore, the optical thin film method is widely used in the polishing process.

[0003] At present, the single-beam laser (single-wavelength light beam) thickness detection method based on the optical thin film method is widely used. The principle of single-beam laser thickness detection is that the light source is irradiated on the wafer for reflection, and the reflected light is irradiated into the photodetector. The photodetector converts the light intensity signal into an electrical signal, and the thickness of the wafer film is determined by the electrical signal.

[0004] In actual application scenarios, when performing thickness detection in CMP processes, the wafer film being detected is often in a complex environment, such as the presence of water, polishing liquid and other media on the wafer surface, and other transparent media such as glass between the photodetector and the wafer film. The above complex environment is called a multi-layer film environment in the art, or the wafer film is called a multi-layer film state. Conventional single-beam laser measurement methods cannot measure accurate results in this environment or state. Summary of the invention

[0005] In view of this, the present application provides a method for constructing a film thickness calibration library suitable for multilayer films, comprising: Obtain a film thickness reflectivity library suitable for a single-layer film environment, where the reflectivity value changes periodically with the thickness value; Obtain the electrical signal corresponding to the light intensity of the reflected light of a single wavelength beam from two wafer films of known different thicknesses and electrical signals ; Obtaining an electrical signal corresponding to the light intensity of the reflected light of the single wavelength light beam by the two wafer thin films in a multilayer film environment and electrical signals ; According to the electrical signal ,electric signal ,electric signal and electrical signals Determine the conversion factor; The film thickness reflectivity library is converted into a database suitable for a multilayer film environment using the conversion coefficient.

[0006] Optionally, after obtaining a database suitable for a multilayer film environment, the method further includes: Using calibration factors The reflectivity values ​​in the film thickness reflectivity library are converted into electrical signal values.

[0007] Optionally, the calibration coefficient is determined by the following method: : Get known thickness The reflectivity of the wafer film to the single wavelength beam in a multilayer film environment ; According to the reflectivity and electrical signals Calculate the calibration coefficient .

[0008] Optionally, the electrical signal is a voltage signal. .

[0009] Optionally, the calibration coefficient is determined by the following method: : Obtain the electrical signal corresponding to the light intensity of the reflected light of a single wavelength beam by a total reflector in a multilayer film environment ,get , where the electrical signal is collected The position relationship between the total reflection mirror and the collection device and the collected electrical signal At this time, the positional relationship between the wafer film and the collection device is consistent.

[0010] Optionally, the conversion coefficient is determined in the following manner: ; in and is the conversion coefficient.

[0011] Optionally, the reflectivity in the film thickness reflectivity library is converted as follows: ; in represents the reflectivity before conversion, Represents the converted reflectivity suitable for multilayer film environment.

[0012] Optionally, the corresponding relationship between the reflectivity value and the thickness value is ; in represents the reflectivity value, t represents the thickness value, , A and B are constants.

[0013] Optionally, the corresponding relationship between the electrical signal value and the thickness value is: ; in represents the electrical signal value, t represents the thickness value, represents the calibration coefficient, , A and B are constants.

[0014] Accordingly, a wafer film thickness measurement method based on a single-wavelength light beam comprises: Acquire an electrical signal corresponding to the light intensity of the reflected light of at least one single wavelength light beam by a wafer thin film of unknown thickness in a multilayer film environment; The thickness of the wafer film is determined using the database suitable for the multilayer film environment constructed using the above method.

[0015] Optionally, when multiple single-wavelength light beams are used, at least two of the single-wavelength light beams have different wavelengths and correspond to different databases; In the step of determining the wafer film thickness, the electrical signal of each single-wavelength light beam and the corresponding database are used to obtain corresponding multiple thickness sets, and the thickness of the wafer film is obtained by taking the intersection of the multiple thickness sets.

[0016] Accordingly, the present application provides a device for constructing a film thickness calibration library suitable for multilayer films, comprising: a processor and a memory connected to the processor; wherein the memory stores instructions executable by the processor, and the instructions are executed by the processor so that the processor executes the above-mentioned method for constructing a film thickness calibration library suitable for multilayer films.

[0017] Accordingly, the present application provides a wafer thin film thickness measurement device based on a single wavelength light beam, comprising: a processor and a memory connected to the processor; wherein the memory stores instructions executable by the processor, and the instructions are executed by the processor so that the processor executes the above-mentioned wafer thin film thickness measurement method based on a single wavelength light beam.

[0018] The present application also provides a chemical mechanical polishing device for performing chemical mechanical polishing on a wafer film and executing the above-mentioned wafer film thickness measurement method based on a single wavelength light beam during the polishing process.

[0019] According to the film thickness calibration library construction method and equipment provided in the present application, by using a single-wavelength light beam to measure the same wafer thin film in a single-layer film environment and a multi-layer film environment respectively, the corresponding electrical signal can be obtained, thereby determining the signal correspondence between the two environments and obtaining the corresponding conversion coefficient. The film thickness reflectivity library suitable for single-layer films is processed using this conversion coefficient to obtain a database suitable for a multi-layer film environment. Based on this database, the single-wavelength light beam measurement method can obtain more accurate thickness measurement results in a multi-layer film environment.

[0020] According to the chemical mechanical polishing equipment and measurement method provided in the present application, during the chemical mechanical polishing process of the wafer film, the wafer film is in a multi-layer film environment. By using a film thickness calibration library suitable for multi-layer films, the thickness of the wafer film can be measured in real time and in situ during the polishing process, thereby improving the efficiency of the polishing work. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 This is a flow chart of a method for constructing a film thickness calibration library in an embodiment of the present application; Figure 2 Schematic diagram of the beam voltage and thickness curve and the intersection of thickness in an embodiment of the present application. DETAILED DESCRIPTION

[0023] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] In the description of the present invention, it should be noted that the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0025] like Figure 1 As shown, an embodiment of the present invention provides a method for constructing a film thickness calibration library applicable to a multilayer film. The method can be executed by a chemical mechanical polishing device for a wafer, or by an electronic device such as a computer or a server, and includes the following operations: S1, obtaining a film thickness reflectivity library applicable to a single-layer film environment, wherein the reflectivity value changes periodically with the thickness value. The film thickness reflectivity library applicable to a single-layer film environment refers to a theoretical relationship library between film thickness and reflectivity applicable to an air environment.

[0026] The film thickness reflectivity library of a single-layer film environment can be generated based on a mathematical model, and the corresponding reflectivity can be calculated by giving the film thickness.

[0027] According to the principles of thin film optics, in an air environment, there is the following relationship between the film thickness and reflectivity of the wafer: ; Where R represents reflectivity, A, B and are coefficients related to the refractive index of the wafer surface material and can be obtained by substituting relevant parameters. . n1 represents the refractive index, h represents the thickness of the wafer film, is the wavelength of incident light, Represents the refraction angle between the incident light and the surface of the optical film.

[0028] From the above relationship, it can be seen that in a single-layer film environment, the film thickness reflectivity curve changes in a sine and cosine law, and its relationship can be simplified as follows: ; in represents reflectivity, t represents thickness, , A and B are constants.

[0029] S2, obtain the electrical signal corresponding to the light intensity of the reflected light of the single wavelength light beam from two wafer films of known different thicknesses and electrical signals In this step and It is an electrical signal collected from a wafer film in a single-layer film environment. The two wafer films with different known thicknesses refer to the fact that the thicknesses of the two wafer films are known information and they are not equal.

[0030] S3, obtaining the electrical signal corresponding to the light intensity of the reflected light of the single wavelength light beam by the two wafer thin films in the multilayer film environment and electrical signals The measurement object is the same as that in step S2, except that and It is the electrical signal collected from the wafer thin film in a multi-layer film environment. The multi-layer film environment is determined according to the environment faced by this scheme and is used to simulate the actual measurement environment. For example, water or polishing liquid can be added to the surface of the wafer thin film, or other transparent media such as glass can be installed between the probe of the collection device and the surface of the wafer thin film.

[0031] S4, according to the electrical signal ,electric signal ,electric signal and electrical signals Determine the conversion coefficient. The conversion coefficient is an unknown number to be solved. According to the corresponding relationship between the signal in the single-layer film environment and the signal in the multi-layer film environment, the value of the conversion coefficient can be calculated by solving the equation.

[0032] The value of the above electrical signal varies with the thickness of the wafer film. By analyzing a large amount of data, the electrical signal can be determined. With electrical signal There is a certain correspondence between them. Similarly, electrical signals With electrical signal There is also a certain corresponding relationship between them, and the corresponding relationship is the same, that is, , , the conversion coefficient is the constant required in function f.

[0033] S5, using the conversion coefficient, converts the film thickness reflectivity database into a database suitable for a multilayer film environment. Since the value of the electrical signal measured by a single wavelength beam is based on the intensity of the reflected light, the intensity of the reflected light is affected by the reflectivity, and the reflectivity in a single-layer film environment is Reflectivity in multilayer environments It also conforms to the above correspondence, that is, , Therefore, the reflectivity in the film thickness reflectivity library in step S1 is processed using the conversion coefficient obtained in step S4 to obtain the reflectivity value in the multilayer film environment.

[0034] In one embodiment, based on the corresponding relationship curve formed by the change of the electrical signal with the thickness value, it is found that compared with the corresponding relationship curve of the electrical signal and the thickness in the single-layer film environment, the corresponding relationship curve of the electrical signal and the thickness in the multi-layer film environment is compressed or stretched, and the curve is raised or lowered as a whole. In this embodiment, the above corresponding relationship is determined as ; in Represents "compression or tension", Meaning "to raise or lower", and This is the conversion factor.

[0035] Similarly, the corresponding relationship of reflectivity is ; in represents the reflectivity before conversion (reflectivity in a single-layer film environment), Indicates the converted reflectivity suitable for a multilayer film environment. By processing the reflectivity in the library under a single-layer film environment in this way, it can be converted into a film thickness reflectivity library suitable for a multilayer film environment.

[0036] In one embodiment, after obtaining the database applicable to the multilayer film environment in step S5, the following processing is further included: S6, using calibration coefficients Convert the reflectivity value in the film thickness reflectivity library into an electrical signal value. The role of the calibration coefficient is to establish the connection between the electrical signal measured by the single-wavelength beam and the reflectivity of the wafer film. The calibration coefficient is at least the value determined before step S6. Without changing the measurement environment and the wafer material, the calibration coefficient at different thicknesses remains unchanged. As an example, assuming that the voltage value measured at a certain thickness is 1.8v, and the reflectivity can be determined to be 0.6, the calibration coefficient is the ratio of the voltage value to the reflectivity, that is, the calibration coefficient k=1.8 / 0.6=3; without changing other conditions and only changing the film thickness, for example, the voltage value measured at another thickness is 1.5v, and the reflectivity can be determined to be 0.5, the calibration coefficient k is still 3.

[0037] After the processing of step S6, the database is converted into a film thickness electrical signal library. The corresponding relationship between the electrical signal value and the thickness value in the film thickness electrical signal library is: ; in represents the electrical signal value, t represents the thickness value, represents the calibration coefficient, , A and B are constants.

[0038] Regarding the above calibration coefficients, in one embodiment, the calibration coefficients are determined based on a wafer film of known thickness. , including the following operations: Get known thickness The reflectivity of the wafer film to a single wavelength beam in a multilayer film environment Specifically, the electrical signal corresponding to the light intensity of the reflected light of a single wavelength light beam by a total reflector in a multilayer film environment can be obtained by actual measurement. , and then the reflectivity .

[0039] Theoretical calculations can also be used, using a theoretical model suitable for a single-layer film environment. , given thickness Calculate the reflectivity under single-layer film environment , and then according to the determined correspondence , and the reflectivity under the multilayer film environment is obtained .

[0040] According to the reflectivity and electrical signals Calculate the calibration factor , when using voltage signal, .

[0041] Regarding the above calibration coefficients, in another embodiment, the calibration coefficients are determined based on the total reflection mirror surface. , including the following operations: Obtain the electrical signal corresponding to the light intensity of the reflected light of a single wavelength beam by a total reflector in a multilayer film environment ,get , where the electrical signal is collected The position relationship between the total reflection mirror and the collection device and the collected electrical signal At this time, the positional relationship between the wafer film and the collection device is consistent.

[0042] Referring to the principle of the previous embodiment ,in Indicates electrical signal, represents the reflectivity, k represents the calibration coefficient. Since the reflectivity of the total reflection mirror in this embodiment is 100%, ,Right now .

[0043] Combine the following Figure 2 A method for measuring wafer film thickness in a multilayer film environment based on the above database is introduced. A wafer film thickness measurement method based on a single wavelength beam includes the following operations: The electrical signal corresponding to the light intensity of the reflected light of a single wavelength beam of a wafer film of unknown thickness in a multilayer film environment is obtained, and the thickness of the wafer film is determined using the electrical signal and a database suitable for a multilayer film environment constructed according to the above method.

[0044] join Figure 2 The medium wavelength is The curve or wavelength is The curve is the visualization data of the above database. In this embodiment, it is the visualization data of the film thickness electrical signal library obtained according to step S6, where the horizontal axis d / nm is the wafer film thickness and the vertical axis U / v is the electrical signal. Taking the curve as an example, assuming that the value of the electrical signal measured for a wafer film of unknown thickness is V1, since the electrical signal changes periodically with the thickness, by matching V1 with the curve, we can get the thickness set d11...d1N.

[0045] This measurement method can at least be applied to relative thickness detection when performing CMP on wafers in a multi-layer film environment. For example, the thickness is measured as d1i at a certain moment in the CMP process, and the thickness is measured continuously from then on. Based on the thickness d1j obtained at the next moment, d1i-d1j is calculated to determine the amount of wafer film thinning during this time period.

[0046] The above database is not limited to measuring relative thickness. In order to obtain absolute thickness, two or more single-wavelength light beams with different wavelengths can be used. Taking two different single-wavelength light beams as an example, according to the above steps S1 to S5 or S1 to S6, two databases corresponding to the two light beams can be constructed respectively.

[0047] In the step of determining the wafer film thickness, the electrical signals of each single-wavelength light beam and the corresponding database are used to obtain corresponding multiple thickness sets, and the thickness of the wafer film is obtained by taking the intersection of the multiple thickness sets.

[0048] like Figure 2 As shown, for example, based on the wavelength The electrical signal measured by a single wavelength beam By matching with the corresponding film thickness electrical signal library, the thickness set d11…d1N can be obtained; based on the wavelength The electrical signal measured by a single wavelength beam By matching with the corresponding film thickness electrical signal library, we can get the thickness set d21...d2N. By finding the intersection, we can get that the intersection of two thickness sets has only one thickness value, such as Figure 2 The d12=d22 shown is the film thickness measurement result.

[0049] When only two light beams with different wavelengths are used, in order to ensure that the intersection of the two thickness sets has only one thickness value, the ratio between the two wavelengths used should be within a certain range. If the two wavelengths are too close, it is difficult to distinguish the difference in the measurement results (same thickness set); if the two wavelengths differ too much, multiple thickness values ​​may appear in the intersection of the two thickness sets, and it is still difficult to obtain a unique measurement result. It has been found through experiments that two different wavelengths With wavelength The ratio range is preferably 1.2~1.5, that is or .

[0050] It should also be noted that Figure 2The embodiment shown is using the film thickness electrical signal library (based on the result of step S6). When the film thickness reflectivity library is used (based on the result of step S5), the electrical signal of the wafer film of unknown thickness needs to be processed, specifically using the calibration coefficients mentioned above. The measured electrical signal is converted into reflectivity, that is, , and then match it in the film thickness reflectivity library under the multilayer film environment. The matching method is similar to the film thickness electrical signal library and will not be repeated here.

[0051] It should be understood by those skilled in the art that the embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CDROM, optical storage, etc.) containing computer-usable program code.

[0052] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0053] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0054] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0055] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for constructing a film thickness calibration library suitable for multilayer films, characterized in that: include: Obtain a film thickness reflectivity library suitable for a single-layer film environment, where the reflectivity value changes periodically with the thickness value; Obtain the electrical signal corresponding to the light intensity of the reflected light of a single wavelength beam from two wafer films of known different thicknesses and electrical signals ; Obtaining an electrical signal corresponding to the light intensity of the reflected light of the single wavelength light beam by the two wafer thin films in a multilayer film environment and electrical signals ; According to the electrical signal ,electric signal ,electric signal and electrical signals Determine the conversion factor; The film thickness reflectivity library is converted into a database suitable for a multilayer film environment using the conversion coefficient.

2. The method according to claim 1, characterized in that After obtaining a database suitable for a multilayer film environment, it also includes: Using calibration factors The reflectivity values ​​in the film thickness reflectivity library are converted into electrical signal values.

3. The method according to claim 2, characterized in that It also includes determining the calibration coefficient using the following method : Get known thickness The reflectivity of the wafer film to the single wavelength beam in a multilayer film environment ; According to the reflectivity and electrical signals Calculate the calibration coefficient .

4. The method according to claim 3, characterized in that The electrical signal is a voltage signal, .

5. The method according to claim 2, characterized in that: It also includes determining the calibration coefficient using the following method : Obtain the electrical signal corresponding to the light intensity of the reflected light of a single wavelength beam by a total reflector in a multilayer film environment ,get , where the electrical signal is collected The position relationship between the total reflection mirror and the collection device and the collected electrical signal At this time, the positional relationship between the wafer film and the collection device is consistent.

6. The method according to any one of claims 1 to 5, characterized in that The conversion factor is determined as follows: ； in and is the conversion coefficient.

7. The method according to claim 6, characterized in that The reflectivity in the film thickness reflectivity library is converted as follows: ； in represents the reflectivity before conversion, Represents the converted reflectivity suitable for multilayer film environment.

8. The method according to claim 1, characterized in that The corresponding relationship between reflectivity value and thickness value is: ； in represents the reflectivity value, t represents the thickness value, , A and B are constants.

9. The method according to claim 2, characterized in that: The corresponding relationship between the electrical signal value and the thickness value is: ； in represents the electrical signal value, t represents the thickness value, represents the calibration coefficient, , A and B are constants.

10. A wafer film thickness measurement method based on a single wavelength light beam, characterized in that: include: Acquire an electrical signal corresponding to the light intensity of the reflected light of at least one single wavelength light beam by a wafer thin film of unknown thickness in a multilayer film environment; The thickness of the wafer thin film is determined using the electrical signal and a database suitable for a multilayer film environment constructed according to the method of any one of claims 1 to 9.

11. The method according to claim 10, characterized in that When multiple single-wavelength light beams are used, at least two of the single-wavelength light beams have different wavelengths and correspond to different databases; In the step of determining the wafer film thickness, the electrical signal of each single-wavelength light beam and the corresponding database are used to obtain corresponding multiple thickness sets, and the thickness of the wafer film is obtained by taking the intersection of the multiple thickness sets.

12. A device for constructing a film thickness calibration library suitable for multilayer films, characterized in that: include: A processor and a memory connected to the processor; wherein the memory stores instructions executable by the processor, and the instructions are executed by the processor so that the processor executes the method for constructing a film thickness calibration library suitable for multilayer films as described in any one of claims 1 to 9.

13. A wafer film thickness measurement device based on a single wavelength light beam, characterized in that: include: A processor and a memory connected to the processor; wherein the memory stores instructions executable by the processor, and the instructions are executed by the processor so that the processor executes the wafer thin film thickness measurement method based on a single wavelength light beam as described in claim 10 or 11.

14. A chemical mechanical polishing device, characterized in that: The method is used for performing chemical mechanical polishing on a wafer film, and performing the wafer film thickness measurement method based on a single wavelength light beam as claimed in claim 10 or 11 during the polishing process.

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