Thickness measurement method and equipment for wafer thin film polishing process

Abstract

The present invention provides a thickness measurement method and device for a wafer film polishing process, the method comprising: in the process of polishing the wafer film, obtaining an electrical signal corresponding to the light intensity of the reflected light of the wafer film to a single-wavelength light beam; calculating the reflectivity of the wafer film to the single-wavelength reflected light according to the electrical signal and a calibration coefficient; determining the thickness and reflectivity corresponding data of a cycle including the thickness at the previous moment; matching the data of the cycle according to the reflectivity to obtain two groups of data; comparing the larger thickness of the two groups of data with the thickness, when the larger thickness of the two groups of data is greater than the thickness, taking the smaller thickness of the two groups of data as the thickness at the current moment; when the larger thickness of the two groups of data is less than the thickness, taking the larger thickness as the thickness at the current moment.

Description

Technical Field

[0001] The invention relates to the field of wafer feature measurement, and in particular to a thickness measurement method and equipment used in a wafer thin film polishing process. Background Art

[0002] In the polishing EPD (End Point Detection) project based on optical measurement methods, there are two methods for measuring the thickness of wafer thin films: the first method is to invert the film thickness through the different spectral characteristic information of multiple wavelengths in the spectrometer under different film thicknesses, which is referred to as the multi-wavelength beam measurement method; the second method is to judge the relative thickness of the wafer thin film by converting the light intensity signal of the received reflected light into an electrical signal under a single wavelength light source, which is referred to as the single-wavelength beam measurement method.

[0003] However, when performing EPD endpoint detection on a CMP (Chemical Mechanical Polishing) machine, it is difficult to obtain accurate film thickness information using the multi-wavelength beam measurement method when the film thickness is small, because there is no peak characteristic information in the wide spectrum wavelength range, and the change in the spectrum shape with film thickness is less obvious than that with large film thickness.

[0004] The defect of the single-wavelength beam method is that, since the output electrical signal varies periodically with the film thickness value, this method can only obtain the relative measurement value of the film thickness, and cannot obtain the absolute value of the film thickness. Summary of the invention

[0005] In view of this, the present application provides a thickness measurement method for a wafer thin film polishing process, comprising:

[0006] In the process of polishing the wafer film, an electrical signal corresponding to the light intensity of the reflected light of the wafer film to the single wavelength light beam is obtained. ;

[0007] According to the electrical signal and calibration coefficient Calculate the reflectivity of the wafer film to a single wavelength beam of light ;

[0008] Determine the thickness including the previous moment The thickness and reflectivity corresponding data of a period including , wherein the period is the period in which the reflectivity changes with the thickness;

[0009] According to the reflectivity Two sets of data are obtained by matching the data of one cycle, and the reflectivity and reflectivity in the two sets of data are Same, different values ​​of thickness;

[0010] Compare the larger thickness of the two sets of data with the thickness , when the larger thickness of the two sets of data is greater than the thickness When the thickness of the two sets of data is smaller, the thickness at the current moment is taken as ; When the larger thickness of the two sets of data is less than the thickness When the larger thickness is taken as the thickness at the current moment .

[0011] Optionally, determine the thickness including The thickness and reflectivity corresponding data of a period include:

[0012] Use thickness The thickness and reflectivity corresponding data of a period are calculated using the thickness and reflectivity corresponding relationship model.

[0013] Optionally, the thickness and reflectivity correspondence model is:

[0014]

[0015] in represents reflectivity, t represents thickness, , A and B are constants.

[0016] Optionally, the thickness-reflectivity correspondence model is a model applicable to a multilayer film environment; the method further comprises:

[0017] The conversion factor is used to convert the model applicable to the single-layer film environment into a model applicable to the multi-layer film environment.

[0018] Optionally, determine the thickness including The thickness and reflectivity corresponding data of a period include:

[0019] Use thickness The thickness and reflectivity corresponding data of a period are determined with a reference database, wherein the reference database includes different thicknesses and their corresponding reflectivities.

[0020] Optionally, the relationship between thickness and reflectivity in the reference database is a quasi-sinusoidal function.

[0021] Optionally, the reference database is applicable to a multilayer film environment; the method further comprises:

[0022] The conversion factor is used to convert the reference database applicable to the single-layer film environment into a reference database applicable to the multi-layer film environment.

[0023] Optionally, before calculating the reflectivity, the method further includes:

[0024] For known thickness The wafer film collects the electrical signal corresponding to the light intensity of the reflected light of the single wavelength beam ;

[0025] According to thickness Calculate the reflectivity of the wafer film to the single wavelength reflected light ;

[0026] According to the reflectivity and electrical signals Calculate the calibration coefficient .

[0027] Optionally, the electrical signal is a voltage signal, and the calibration coefficient ; .

[0028] Accordingly, the present application provides a thickness measurement device for a wafer thin film polishing process, 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 thickness measurement method for a wafer thin film polishing process.

[0029] The thickness measurement method and device provided in the present application for the wafer thin film polishing process use a predetermined calibration coefficient to convert the electrical signal measured by a single wavelength light beam into a reflectivity, and determine the thickness and reflectivity correspondence data of one cycle based on the law that the reflectivity changes periodically with the thickness in combination with the thickness information of the previous moment, and use the reflectivity at the current moment to match two thickness values ​​in the data of one cycle, and finally combine the matched thickness value with the thickness value of the previous moment to obtain a unique thickness value, so that the single wavelength light beam measurement method can measure the absolute thickness of the wafer thin film during the polishing process. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] 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.

[0031] Figure 1 This is a flow chart of a thickness measurement method for a wafer thin film polishing process in an embodiment of the present application;

[0032] Figure 2 A schematic diagram of matching wafer film thickness in an embodiment of the present application;

[0033] Figure 3 A schematic diagram of another method for matching wafer film thickness in an embodiment of the present application. DETAILED DESCRIPTION

[0034] 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 the embodiments. 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.

[0035] 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.

[0036] like Figure 1 As shown, an embodiment of the present invention provides a thickness measurement method for a wafer thin film polishing process, which can be performed by an electronic device such as a computer or a server, and includes the following operations:

[0037] S1, in the process of polishing the wafer film, obtain the electrical signal U corresponding to the light intensity of the reflected light of the wafer film to the single wavelength light beam 1n Specifically, a light source emitting single-wavelength light is used to emit light to the surface of the wafer film. The incident light can be perpendicular to the surface of the wafer film or obliquely incident on the surface of the wafer film at a certain angle. The reflected light from the surface of the wafer is received by the photoelectric sensor and converted into an analog electrical signal. After optional processing such as analog-to-digital conversion, filtering, and amplification, a digital electrical signal is obtained.

[0038] The thickness of the wafer film can affect the intensity of the reflected light, and the intensity of the light can affect the value of the digital electrical signal. According to the measurement results at different thicknesses, it can be found that the electrical signal shows a periodic change with the change of thickness.

[0039] S2, according to the electrical signal U 1n And the calibration coefficient k is used to calculate the reflectivity R of the wafer film to the single wavelength reflected light. 1n , reflectivity The reflectivity also changes periodically with the thickness. With electrical signal The relationship between is a linear correspondence, and the specific correspondence depends on the electrical signal The type of data (such as voltage or current), usually the voltage value.

[0040] The function of the calibration coefficient k is to establish the connection between the electrical signal and the reflectivity of the wafer film. The calibration coefficient k is at least the value determined before step S2B. Without changing the measurement environment and the wafer material, the calibration coefficient remains unchanged at different thicknesses. For example, assuming that the voltage value measured at one thickness is 1.8v, and the reflectivity can be determined to be 0.6, then 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, then the calibration coefficient k=1.5 / 0.5=3.

[0041] Determine the calibration factor There are many ways to calculate the calibration coefficient. According to the above examples, as long as the reflectivity can be determined, the calibration coefficient can be calculated. If the reflectivity needs to be determined, the thickness of the wafer film needs to be determined. There are many ways to measure the thickness. Specifically, for example, the thickness of the wafer film can be determined by using a contact or non-contact measurement tool before performing the wafer film polishing process; or it can be measured in situ or offline during the wafer film polishing process.

[0042] S3, determine the corresponding data of thickness and reflectivity of a period including the thickness at the previous moment, where the period is the period of change of reflectivity with thickness. The corresponding relationship between thickness and reflectivity is known. According to the principle of thin film optics, in an air environment, there is the following relationship between the film thickness and reflectivity of the wafer:

[0043] ;

[0044] 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.

[0045] According to the above correspondence, the reflectivity shows a periodic change with the change of thickness. Figure 2 and Figure 3 As shown, in one embodiment, the corresponding relationship between the reflectivity R and the thickness d is a quasi-sine function relationship. The period of the reflectivity R is known to be T. For example, from the beginning of polishing (the thickness changes in the direction of the arrow in the figure), the known initial thickness is used as the thickness at the previous moment. , take first There are many ways to intercept the data of a thickness period, as long as the thickness at the current moment is within this period, for example, Figure 2 The thickness of the previous moment is As the upper limit, take the data of one period T downward, that is, da~ Thickness and its corresponding reflectivity value; you can also use Figure 3 The thickness of the previous moment is As the middle value, take the data of half a period T upward and downward respectively, that is, db~dc thickness and its corresponding reflectivity value.

[0046] S4, according to the reflectivity R 1n Two sets of data are obtained by matching the data of one cycle. The reflectivity and reflectivity R in the two sets of data are 1n The same, but different thickness values, the thickness of the two sets of data is one large and one small. Figure 2 or Figure 3 The reflectivity R 1n Corresponding thickness and .

[0047] S5, compare the larger thickness of the two sets of data with the thickness at the previous moment , determine whether the larger thickness of the two sets of data is greater than the thickness at the previous moment , when the larger thickness of the two sets of data is greater than the thickness When the larger thickness of the two sets of data is less than the thickness , execute step S7.

[0048] S6, take the smaller thickness of the two sets of data as the current thickness Since the thickness at the current moment in the polishing process must be smaller than the thickness at the previous moment, when the larger thickness of the two sets of data exceeds the thickness at the previous moment, the smaller thickness is determined to be the thickness at the current moment. Figure 3 The relationship shown > > , then determine the thickness at the current moment is .

[0049] S7, take the larger thickness as the current thickness When the thickness in both sets of data is smaller than the thickness at the previous moment, the larger thickness is closer to the thickness at the previous moment, so the larger thickness is the thickness at the current moment. Figure 2 The relationship shown > > , then determine the thickness at the current moment is .

[0050] The calibration coefficient k can be calculated as follows before step S2:

[0051] For known thickness The wafer film collects the electrical signal corresponding to the light intensity of the reflected light of the single wavelength beam For example, before polishing begins, electrical signals can be collected for the wafer film at the initial thickness. .

[0052] According to thickness Calculate the reflectivity of wafer film for single wavelength reflected light . Calculation based on theoretical model, given thickness The unique reflectivity can be calculated .

[0053] According to the reflectivity and electrical signals Calculate the calibration factor The electrical signal is preferably a voltage signal, and the calibration coefficient , in step S2B, .

[0054] The above step S3 includes at least two implementation modes. The first implementation mode is to use the thickness The thickness and reflectivity corresponding data of a period are calculated by using the thickness and reflectivity corresponding model. An available thickness and reflectivity corresponding model is

[0055] ;

[0056] in represents reflectivity, t represents thickness, , A and B are constants.

[0057] This embodiment adopts a theoretical mathematical model, based on the thickness at the last moment A thickness cycle including the current thickness is determined, and the corresponding reflectivity can be calculated by substituting it into the above model, thereby obtaining the corresponding data of thickness and reflectivity of a cycle.

[0058] The second implementation method is to use thickness The thickness and reflectivity corresponding data of one period are determined with a reference database, wherein the reference database includes different thicknesses and their corresponding reflectivities, and the reference database is data of more than one period.

[0059] The difference between the reference database and the theoretical model is that the thickness and reflectivity in the reference database are measured data, and the relationship between the two may be very close but not completely consistent with the theoretical model, for example, appearing to be close to a relationship with a sine function (a quasi-sine function relationship).

[0060] In some embodiments, the reference database or theoretical model used in step S3 is based on a single-layer film environment. A single-layer film means that there is only one medium (such as air) between the photodetector and the wafer surface. During the polishing process, it is necessary to add polishing liquid to the wafer surface and continuously flush it with water. There are also other transparent media such as glass and PU between the photodetector and the wafer surface. This complex environment is called a multi-layer film environment in the art, or the wafer film is called a multi-layer film state. The reference database or theoretical model obtained based on a single-layer film environment is not suitable for measuring the thickness of a wafer film in a multi-layer film environment.

[0061] In order to adapt to the multi-layer film environment, this embodiment further includes the following operations in the above step S3:

[0062] The conversion coefficient is used to convert the model or reference database applicable to the single-layer film environment into the model or reference database applicable to the multi-layer film environment.

[0063] Based on the corresponding relationship curve formed by the change of reflectivity with thickness value, it is found that compared with the corresponding relationship curve of reflectivity and thickness in the single-layer film environment, the corresponding relationship curve of reflectivity and 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

[0064] ;

[0065] in, represents the reflectance in the reference database under the single-layer film environment (reflectance before conversion), and is the conversion factor, Represents the reflectance (converted reflectance) from a reference database suitable for a multilayer film environment.

[0066] In the embodiment using the reference database, this step uses the pre-calibrated conversion coefficients and The reflectance in the reference database is processed; in the embodiment using the theoretical model, this step uses the conversion coefficient and Theoretical model of modified monolayer environment:

[0067] ;

[0068] Furthermore, the conversion coefficient can be adjusted as follows: and To perform calibration:

[0069] S01, obtain the reflectivity of two wafer films of different known thicknesses to the reflected light of a single wavelength beam in a multilayer film environment and reflectivity The two wafer films having different known thicknesses refer to the fact that the thicknesses of the two wafer films are both known information and they are not equal.

[0070] S02, obtaining the reflectivity of the reflected light of the two wafer films to the single wavelength beam in a single-layer film environment and reflectivity The measurement object is the same as that in step S01, except that the environment is different.

[0071] S03, according to reflectivity , reflectivity , reflectivity and reflectivity Determine the conversion coefficient. According to the corresponding relationship between the reflectivity in a multilayer film environment and the reflectivity in a single-layer film environment, the value of the conversion coefficient can be calculated by solving the equation:

[0072] ;

[0073] The above steps S01 and S02 can be performed in an experimental environment, and the conversion coefficient can be calibrated through the actual measured reflectivity.

[0074] It will be appreciated by those skilled in the art that 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. Furthermore, 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, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0075] 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 1A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0076] 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.

[0077] 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 A step that specifies a function in one or more boxes.

[0078] 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 measuring the thickness of a wafer thin film during polishing, characterized in that: include: For known thickness The wafer film collects the electrical signal corresponding to the light intensity of the reflected light of the single wavelength beam ; According to thickness Calculate the reflectivity of the wafer film to the single wavelength reflected light ; According to the reflectivity and electrical signals Calculate the calibration factor , wherein the electrical signal is a voltage signal, and the calibration coefficient ; During the polishing process of the wafer film, an electrical signal corresponding to the light intensity of the reflected light of the wafer film to the single wavelength beam is obtained. ; According to the electrical signal and calibration coefficient Calculate the reflectivity of the wafer film to a single wavelength beam , ; Determine the thickness including the previous moment The thickness and reflectivity corresponding data of a period including , wherein the period is the period in which the reflectivity changes with the thickness; According to the reflectivity Two sets of data are obtained by matching the data of one cycle, and the reflectivity and reflectivity in the two sets of data are Same, different values ​​of thickness; Compare the larger thickness of the two sets of data with the thickness , when the larger thickness of the two sets of data is greater than the thickness When the thickness of the two sets of data is smaller, the thickness at the current moment is taken as ; When the larger thickness of the two sets of data is smaller than the thickness When the larger thickness is taken as the thickness at the current moment .

2. The method according to claim 1, characterized in that Determine including thickness The thickness and reflectivity corresponding data of a period include: Use thickness The thickness and reflectivity corresponding data of a period are calculated using the thickness and reflectivity corresponding relationship model.

3. The method according to claim 2, characterized in that The relationship model between thickness and reflectivity is: ； in represents reflectivity, t represents thickness, , A and B are constants.

4. The method according to claim 2 or 3, characterized in that: The thickness-reflectivity correspondence model is a model suitable for a multilayer film environment; the method further comprises: The conversion factor is used to convert the model applicable to the single-layer film environment into a model applicable to the multi-layer film environment.

5. The method according to claim 1, characterized in that Determine including thickness The thickness and reflectivity corresponding data of a period include: Use thickness The thickness and reflectivity corresponding data of a period are determined with a reference database, wherein the reference database includes different thicknesses and their corresponding reflectivities.

6. The method according to claim 5, characterized in that The relationship between thickness and reflectivity in the reference database is a quasi-sine function.

7. The method according to claim 5 or 6, characterized in that: The reference database is applicable to a multilayer film environment; the method further comprises: The conversion factor is used to convert the reference database applicable to the single-layer film environment into a reference database applicable to the multi-layer film environment.

8. A thickness measuring device for wafer thin film polishing process, 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 thickness measurement method for wafer thin film polishing process as described in any one of claims 1-7.

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