Method for constructing wafer film thickness calibration library, measurement method and polishing equipment

Abstract

The present invention provides a method for constructing a wafer film thickness calibration library, a measurement method and a polishing device. The construction method includes: obtaining a film thickness reflectivity library applicable to a single-layer film environment, wherein the reflectivity value shows a periodic change with the change of the thickness value; obtaining the electrical signals corresponding to the light intensities of the reflected lights of two wafer films with known different thicknesses for a single-wavelength beam; obtaining the electrical signals corresponding to the light intensities of the reflected lights of the two wafer films in a multi-layer film environment for the single-wavelength beam; determining a conversion coefficient according to the electrical signals, the electrical signals, the electrical signals and the electrical signals; and converting the film thickness reflectivity library into a database applicable to a multi-layer film environment by using the conversion coefficient.

Description

Technical Field

[0001] The present invention relates to the field of wafer polishing, and particularly to a method for constructing a wafer film thickness calibration library, a measurement method, and a polishing device. Background Art

[0002] In CMP (Chemical Mechanical Polishing) technology, there are various methods for detecting the thickness of a wafer and the polishing endpoint, such as the eddy current method, the optical method, etc. Since the scale involved in the polishing process is at the sub-micron or nano level, traditional contact measurement methods are no longer applicable. The eddy current method generally can only polish a conductor substrate. Therefore, the optical thin film method is widely applicable to the polishing process.

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

[0004] In actual application scenarios, when performing thickness detection in processes such as CMP, the wafer thin film to be detected is often in a complex environment. For example, there are media such as water and polishing liquid on the wafer surface, and there may also be other transparent media between the photodetector and the wafer thin film, such as glass, etc. The above complex environment is called a multi-layer film environment in this field, or the wafer thin film is in a multi-layer film state. The conventional single-beam laser measurement method cannot obtain 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 applicable to multi-layer films, including:

[0006] Obtain a film thickness reflectivity library applicable to a single-layer film environment, where the reflectivity value changes periodically with the thickness value;

[0007] Obtain the electrical signals corresponding to the light intensities of the reflected lights of two wafer thin films with known different thicknesses for a single-wavelength light beam and the electrical signals ;

[0008] Obtain the electrical signals corresponding to the light intensities of the reflected lights of the two wafer thin films for the single-wavelength light beam in a multi-layer film environment and the electrical signals ;

[0009] According to the electrical signal 、the electrical signal 、the electrical signal and the electrical signal Determine the conversion coefficient;

[0010] Use the conversion coefficient to convert the film thickness - reflectivity library into a database applicable to the multi - layer film environment.

[0011] Optionally, after obtaining the database applicable to the multi - layer film environment, it further includes:

[0012] Use the calibration coefficient to convert the reflectivity values in the film thickness - reflectivity library into electrical signal values.

[0013] Optionally, it further includes determining the calibration coefficient in the following manner :

[0014] Obtain the reflectivity of the wafer thin film with a known thickness to the single - wavelength light beam in the multi - layer film environment ;

[0015] According to the reflectivity and the electrical signal calculate the calibration coefficient .

[0016] Optionally, the electrical signal is a voltage signal, .

[0017] Optionally, it further includes determining the calibration coefficient in the following manner :

[0018] Obtain the electrical signal corresponding to the light intensity of the reflected light of the total - reflection mirror for the single - wavelength light beam in the multi - layer film environment , and obtain , where the positional relationship between the total - reflection mirror and the acquisition device when collecting the electrical signal is the same as the positional relationship between the wafer thin film and the acquisition device when collecting the electrical signal .

[0019] Optionally, determine the conversion coefficient in the following manner:

[0020] ;

[0021] where and are the conversion coefficients.

[0022] Optionally, convert the reflectivity in the film thickness - reflectivity library in the following manner:

[0023] ;

[0024] where represents the reflectivity before conversion, Represents the reflectance after conversion applicable to the multilayer film environment.

[0025] Optionally, the correspondence between the reflectance value and the thickness value is

[0026] ;

[0027] Wherein represents the reflectance value, t represents the thickness value, , A and B are constants.

[0028] Optionally, the correspondence between the electrical signal value and the thickness value is

[0029] ;

[0030] Wherein represents the electrical signal value, t represents the thickness value, represents the calibration coefficient, , A and B are constants.

[0031] Correspondingly, a method for measuring the thickness of a wafer thin film based on a single-wavelength light beam includes:

[0032] Obtaining an electrical signal corresponding to the light intensity of the reflected light of at least one single-wavelength light beam by the wafer thin film with an unknown thickness in a multilayer film environment;

[0033] Determining the thickness of the wafer thin film by using the database applicable to the multilayer film environment constructed by the above method.

[0034] Optionally, when multiple single-wavelength light beams are used, the wavelengths of at least two single-wavelength light beams are different, and they correspond to corresponding different databases;

[0035] In the step of determining the thickness of the wafer thin film, using the electrical signals of each single-wavelength light beam and the corresponding databases to obtain corresponding multiple thickness sets, and obtaining the thickness of the wafer thin film by taking the intersection of the multiple thickness sets.

[0036] Correspondingly, the present application provides a device for constructing a film thickness calibration library applicable to a multilayer film, including: 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 to enable the processor to execute the above method for constructing a film thickness calibration library applicable to a multilayer film.

[0037] Correspondingly, the present application provides a device for measuring the thickness of a wafer thin film based on a single-wavelength light beam, including: 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 to enable the processor to execute the above method for measuring the thickness of a wafer thin film based on a single-wavelength light beam.

[0038] The present application also provides a chemical mechanical polishing apparatus for performing chemical mechanical polishing on a wafer film and executing the above-described method for measuring the thickness of the wafer film based on a single-wavelength light beam during the polishing process.

[0039] According to the method and apparatus for constructing a film thickness calibration library provided by the present application, by measuring the same wafer film with a single-wavelength light beam respectively in a single-layer film environment and a multi-layer film environment to obtain corresponding electrical signals, the signal correspondence relationship in the two environments can be determined, and the corresponding conversion coefficient can be obtained. Using this conversion coefficient to process the film thickness reflectivity library applicable to the single-layer film, the database applicable to the multi-layer film environment can be obtained. Based on this database, the single-wavelength light beam measurement method can obtain more accurate thickness measurement results in the multi-layer film environment.

[0040] According to the chemical mechanical polishing apparatus and measurement method provided by the present application, during the process of performing chemical mechanical polishing on the wafer film, the wafer film is in a multi-layer film environment. Using the film thickness calibration library applicable to the multi-layer film, 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. Description of the Drawings

[0041] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0042] Figure 1 It is a flowchart of the method for constructing a film thickness calibration library in an embodiment of the present application;

[0043] Figure 2 It is a schematic diagram of the light beam voltage vs. thickness curve and thickness intersection in an embodiment of the present application. Detailed Embodiments

[0044] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the drawings. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0045] 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 construed as indicating or implying relative importance. In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0046] As Figure 1 shown, an embodiment of the present invention provides a method for constructing a film thickness calibration library applicable to a multilayer film. This 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:

[0047] S1. Obtain a film thickness reflectivity library applicable to a single-layer film environment, where 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 of film thickness and reflectivity applicable to an air environment.

[0048] The film thickness reflectivity library for a single-layer film environment can be generated based on a mathematical model. By specifying the film thickness, the corresponding reflectivity can be calculated.

[0049] According to the thin film optical principle, in an air environment, the following relationship exists between the film thickness and reflectivity of a wafer:

[0050] ;

[0051] where R represents the reflectivity, A, B, and are all coefficients related to the refractive index of the wafer surface material and can be obtained by substituting relevant parameters. Among them, the phase difference . n1 represents the refractive index, h represents the thickness of the wafer thin film, represents the incident light wavelength, represents the refraction angle between the incident light and the surface of the optical thin film.

[0052] 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 relational expression can be simplified as:

[0053] ;

[0054] where represents the reflectivity, t represents the thickness, , A, and B are constants.

[0055] S2. Obtain the electrical signals and electrical signal corresponding to the light intensities of the reflected light of a single-wavelength beam by two wafer thin films with known different thicknesses. and is the electrical signal collected for the wafer thin film in a single-layer film environment. Two wafer thin films with different thicknesses mean that the thicknesses of both wafer thin films are known information and they are not equal.

[0056] S3. Obtain the electrical signals corresponding to the light intensities of the reflected light of a single-wavelength light beam by two wafer thin films in a multi-layer film environment and the electrical signals . The measurement object is the same as that in step S2, with the difference that the and here are the electrical signals collected for the wafer thin film in a multi-layer film environment. The multi-layer film environment is specifically determined according to the environment faced by this solution and is used to simulate the actual measurement environment. For example, it can be adding water or polishing fluid to the surface of the wafer thin film, or installing other transparent media such as glass between the probe of the collection device and the surface of the wafer thin film.

[0057] S4. Determine the conversion coefficient according to the electrical signal , the electrical signal , the electrical signal and the electrical signal . The conversion coefficient is the unknown to be solved. According to the corresponding relationship between the signals in the single-layer film environment and the signals in the multi-layer film environment, the value of the conversion coefficient can be calculated by solving equations.

[0058] The values of the above electrical signals change with the thickness of the wafer thin film. By analyzing a large amount of data, it can be determined that there is a definite corresponding relationship between the electrical signal and the electrical signal . Similarly, there is also a definite corresponding relationship between the electrical signal and the electrical signal , and the corresponding relationship is the same, that is , . The conversion coefficient is the constant required in the function f.

[0059] S5. Use the conversion coefficient to convert the film thickness reflectivity library into a database applicable to the multi-layer film environment. Since the value of the electrical signal measured by the single-wavelength light beam is obtained based on the intensity of the reflected light, and the intensity of the reflected light is affected by the reflectivity, the reflectivity in the single-layer film environment and the reflectivity in the multi-layer film environment also conform to the above corresponding relationship, that is . Therefore, by processing the reflectivity in the film thickness reflectivity library in step S1 with the conversion coefficient obtained in step S4, the value of the reflectivity in the multi-layer film environment can be obtained.

[0060] In one embodiment, based on the variation of the electrical signal with the thickness value to form a corresponding relationship curve, it is found that compared with the corresponding relationship curve between the electrical signal and the thickness in a single-layer film environment, the corresponding relationship curve between the electrical signal and the thickness in a multi-layer film environment is compressed or stretched, and at the same time the overall curve is raised or lowered. Then in this embodiment, the above corresponding relationship is determined as

[0061] ;

[0062] wherein represents "compressed or stretched", represents "raised or lowered", and are the conversion coefficients.

[0063] Similarly, the corresponding relationship of the reflectivity is also

[0064] ;

[0065] wherein represents the reflectivity before conversion (the reflectivity in a single-layer film environment), represents the reflectivity applicable to the multi-layer film environment after conversion. By processing the reflectivity in the library in a single-layer film environment in this way, it can be converted into a film thickness reflectivity library applicable to the multi-layer film environment.

[0066] In one embodiment, after obtaining the database applicable to the multi-layer film environment in step S5, the following processing is further included:

[0067] S6. Using the calibration coefficient to 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 a single-wavelength light beam and the reflectivity of the wafer thin film. The calibration coefficient is at least the value determined before step S6, and under the condition of not changing the measurement environment and the wafer material, the calibration coefficient remains unchanged at different thicknesses. As an example, assuming that at a certain thickness, the measured voltage value is 1.8V, and at the same time 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; under the condition of not changing other conditions and only changing the film thickness, for example, at another thickness, the measured voltage value = 1.5V, and at the same time the reflectivity can be determined to be 0.5, the calibration coefficient k is still 3.

[0068] 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

[0069] ;

[0070] wherein represents the value of the electrical signal, and t represents the thickness value. represents the calibration coefficient. A and B are constants.

[0071] Regarding the above calibration coefficient, in one embodiment, the calibration coefficient is determined based on a wafer thin film with a known thickness. Specifically, the following operations are included:

[0072] Obtain the reflectivity of a wafer thin film with a known thickness for a single-wavelength light beam in a multilayer film environment. Specifically, the electrical signal corresponding to the light intensity of the reflected light of a total reflector for a single-wavelength light beam in a multilayer film environment can be obtained by actual measurement. Then, the reflectivity can be obtained.

[0073] Alternatively, the theoretical calculation method can be used. First, use the theoretical model applicable to a single-layer film environment and given the thickness to calculate the reflectivity in a single-layer film environment. Then, according to the determined corresponding relationship to obtain the reflectivity in a multilayer film environment.

[0074] Calculate the calibration coefficient based on the reflectivity and the electrical signal. When a voltage signal is used,

[0075] Regarding the above calibration coefficient, in another embodiment, the calibration coefficient is determined based on a total reflector surface. Specifically, the following operations are included:

[0076] Obtain the electrical signal corresponding to the light intensity of the reflected light of a total reflector for a single-wavelength light beam in a multilayer film environment. to obtain where the position relationship between the total reflector and the acquisition device when collecting the electrical signal is the same as the position relationship between the wafer thin film and the acquisition device when collecting the electrical signal

[0077] Refer to the principle of the previous embodiment where represents the electrical signal, represents the reflectivity, and k represents the calibration coefficient. Since the reflectivity of the total reflector in this embodiment is 100%, there is that is,

[0078] Next, in combination withFigure 2 Introduce a method for measuring the thickness of a wafer thin film in a multi-layer film environment based on the above database. A method for measuring the thickness of a wafer thin film based on a single-wavelength beam includes the following operations:

[0079] Obtain the electrical signal corresponding to the light intensity of the reflected light of a single-wavelength beam by the wafer thin film with unknown thickness in a multi-layer film environment. Determine the thickness of the wafer thin film using the electrical signal and the database applicable to the multi-layer film environment constructed according to the above method.

[0080] Participate Figure 2 The middle wavelength is of the curve or the wavelength is of the curve. This curve is the visualization data of the above database. In this embodiment, it is specifically the visualization data of the film thickness electrical signal library obtained according to step S6, where the abscissa d / nm is the thickness of the wafer thin film and the ordinate U / v is the electrical signal. Taking the curve with the wavelength as an example, assuming that the value of the electrical signal measured for the wafer thin film with unknown thickness is V1, since the electrical signal changes periodically with the thickness, V1 is matched with the curve, and a thickness set d11... d1N can be obtained.

[0081] This measurement method can be applied at least to the relative thickness detection of the wafer during CMP in a multi-layer film environment. For example, at a certain moment during the CMP process, the measured thickness is d1i. Starting from this, the thickness is continuously measured, and according to the thickness d1j obtained at a later moment, calculating d1i - d1j can determine the amount by which the wafer thin film is thinned during this time period.

[0082] The above database is not limited to measuring relative thickness. In order to obtain the absolute thickness, two or more single-wavelength beams with different wavelengths can be used. Taking two different single-wavelength beams as an example, according to the above steps S1~S5 or S1~S6, two databases corresponding to the two beams can be constructed respectively.

[0083] In the step of determining the thickness of the wafer thin film, using the electrical signals of each single-wavelength beam and the corresponding database to obtain corresponding multiple thickness sets, and obtaining the thickness of the wafer thin film by taking the intersection of the multiple thickness sets.

[0084] As Figure 2 shown, for example, based on the electrical signal measured by a single-wavelength beam with a wavelength and matching it with the corresponding film thickness electrical signal library, a thickness set d11... d1N can be obtained; based on the electrical signal measured by a single-wavelength beam with a wavelength By matching with the corresponding film thickness electrical signal library, the thickness set d21... d2N can be obtained. By taking the intersection, it can be obtained that there is only one thickness value in the intersection of the two thickness sets. For example, Figure 2 as shown, d12 = d22 is the film thickness measurement result.

[0085] When only two light beams with different wavelengths are used, in order to ensure that there is only one thickness value in the intersection of the two thickness sets, 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 (the thickness sets are the same); if the two wavelengths are too different, there may be multiple thickness values in the intersection of the two thickness sets, and it is still difficult to obtain a unique measurement result. Through experiments, it is found that the ratio of the two different wavelengths to the wavelength is preferably in the range of 1.2 to 1.5, that is or .

[0086] In addition, it should be noted that Figure 2 the shown is an embodiment of using the film thickness electrical signal library (based on the result of step S6). When using the film thickness reflectivity library (based on the result of step S5), it is necessary to process the electrical signal of the wafer thin film with unknown thickness measured. Specifically, the measured electrical signal is converted into reflectivity by using the above calibration coefficient , that is , and then it is matched in the film thickness reflectivity library in the multi-layer film environment. The matching method is similar to that of the film thickness electrical signal library, which will not be elaborated here.

[0087] Those skilled in the art should understand that the embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memories, CD-ROMs, optical memories, etc.) containing computer-usable program codes.

[0088] The present invention is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram can be realized by computer program instructions, and the combination of the processes and / or blocks in the flowchart and / or block diagram can also be realized by computer program instructions. These computer program instructions can be provided to the processor of a general computer, a special computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate for realizing in the process Figure 1 one process or multiple processes and / or blocksFigure 1 means for the functions specified in one or more boxes.

[0089] These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to operate in a particular manner, such that the instructions stored in the computer-readable memory produce a manufacture including an instruction means that implements the functions specified in one or more processes and / or boxes Figure 1 one or more processes and / or boxes Figure 1 in one or more boxes.

[0090] These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus, such that a series of operation steps are performed on the computer or other programmable apparatus to produce a computer-implemented process, whereby the instructions executed on the computer or other programmable apparatus provide steps for implementing the functions specified in one or more processes and / or boxes Figure 1 one or more processes and / or boxes Figure 1 in one or more boxes.

[0091] Obviously, the above embodiments are only examples for clear illustration and are not limitations on the implementation manners. For those of ordinary skill 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 enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for constructing a film thickness calibration library applicable to multilayer films, characterized in that, including: obtaining a film thickness reflectivity library applicable to a single-layer film environment, wherein the reflectivity values change periodically with the change of the thickness values; Obtain the electrical signals corresponding to the light intensities of the reflected light of a single-wavelength beam by two wafer films with known different thicknesses and the electrical signals ; Obtain the electrical signals corresponding to the light intensities of the reflected light of the single-wavelength beam by the two wafer films in a multilayer film environment and the electrical signals ; Based on the electrical signal and the electrical signal and the electrical signal and the electrical signal determine the conversion coefficient; converting the film thickness reflectivity library into a database applicable to a multi-layer film environment by using the conversion coefficient.

2. The method according to claim 1, wherein After obtaining the database applicable to the multi-layer film environment, it further includes: Using the calibration coefficient Convert the reflectivity value in the film thickness reflectivity library into an electrical signal value.

3. The method according to claim 2, wherein It also includes determining the calibration coefficient in the following manner : Obtain the reflectance of the wafer thin film with a known thickness for the single-wavelength light beam in a multilayer film environment ; Calculate the calibration coefficient according to the reflectivity and the electrical signal .

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

5. The method according to claim 2, wherein It also includes determining the calibration coefficient in the following manner : Obtain the electrical signal corresponding to the light intensity of the reflected light of a total reflection mirror for a single-wavelength light beam in a multi-layer film environment , obtain , where the electrical signal is collected The positional relationship between the total reflection mirror and the acquisition device when collecting the electrical signal is the same as the positional relationship between the wafer film and the acquisition device when collecting the electrical signal .

6. The method according to any one of claims 1-5, characterized in that, determining the conversion coefficient in the following manner: ； wherein and are the conversion coefficients.

7. The method according to claim 6, characterized in that converting the reflectivity in the film thickness reflectivity library in the following manner: ； wherein represents the reflectivity before conversion, represents the reflectivity after conversion and applicable to the multilayer film environment.

8. The method according to claim 1, wherein the correspondence between the reflectivity value and the thickness value is ； where represents the reflectivity value, t represents the thickness value, and A and B are constants.

9. The method according to claim 2, wherein the correspondence between the electrical signal value and the thickness value is ； wherein represents an electrical signal value, t represents a thickness value, represents a calibration coefficient, and A and B are constants.

10. A method for measuring the thickness of a wafer thin film based on a single-wavelength light beam, characterized in that, including: obtaining an electrical signal corresponding to the light intensity of the reflected light of at least one single-wavelength beam of a wafer thin film with an unknown thickness in a multi-layer film environment; determining the thickness of the wafer thin film by using the electrical signal and the database applicable to the multi-layer film environment constructed by the method according to any one of claims 1-9.

11. The method according to claim 10, characterized in that, When multiple single-wavelength beams are used, the wavelengths of at least two single-wavelength beams are different, and they correspond to different databases; in the step of determining the thickness of the wafer thin film, using the electrical signals of each single-wavelength beam and the corresponding databases to obtain corresponding multiple thickness sets, and obtaining the thickness of the wafer thin film by taking the intersection of the multiple thickness sets.

12. A film thickness calibration library construction device applicable to multi-layer films, characterized in that, including: 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 to enable the processor to execute the method for constructing a film thickness calibration library applicable to a multi-layer film according to any one of claims 1-9.

13. A wafer thin film thickness measuring device based on a single-wavelength light beam, characterized in that, including: 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 to enable the processor to execute the method for measuring the thickness of a wafer thin film based on a single-wavelength beam according to claim 10 or 11.

14. A chemical mechanical polishing apparatus, characterized in that, used for chemically mechanical polishing a wafer thin film and executing the method for measuring the thickness of a wafer thin film based on a single-wavelength beam according to claim 10 or 11 during the polishing process.

Images