Method and equipment for determining uncertainty of wafer film thickness measurement

Abstract

The present invention provides a method and device for determining the uncertainty of wafer film thickness measurement. The method is applied to the field of high-precision measurement technology. The method comprises: obtaining uncertainty components of wafer film thickness measurement by a wafer film thickness measurement device; the uncertainty components include wavelength measurement uncertainty, refractive index measurement uncertainty, refraction angle measurement uncertainty, voltage measurement uncertainty, and uncertainty caused by calibration coefficient deviation of a standard wafer; and determining a synthetic standard uncertainty using uncertainties,,,,. The present invention improves the accuracy of voltage signals in the wafer film thickness measurement process, and further realizes precise control of the polishing process endpoint.

Description

Technical Field

[0001] The present invention relates to the field of high-precision measurement technology, and particularly relates to a method and device for determining the uncertainty of wafer film thickness measurement. Background Art

[0002] Wafer polishing is a crucial step in the semiconductor manufacturing process, and its purpose is to obtain a smooth and clean surface on the wafer surface for subsequent processes. In this process, precise control of the removal amount is crucial for ensuring the quality of the wafer. Traditional polishing endpoint detection methods mainly include the infrared method and the torque method, etc. These methods can detect the endpoint of polishing, but they cannot provide specific removal amount values, so they cannot meet the requirements for on-line monitoring of the removal amount.

[0003] To solve this problem, the film thickness detection method based on light intensity has gradually received attention. This method can obtain the relative removal amount of the wafer during the polishing process in real time and realize on-line monitoring of the polishing process. Through measurement by an optical wafer film thickness measurement device, the light beam emitted by the light source is expanded and collimated by a lens and then irradiated onto the wafer surface. After the incident light is reflected by the thin film, it is received by a photodiode and generates a photocurrent. This photocurrent has a linear relationship with the incident light intensity and is output in the form of voltage after signal amplification.

[0004] Although the film thickness detection method based on light intensity provides monitoring of the relative removal amount, it still has some deficiencies. In the film thickness measurement system, the film thickness value at the current position is mainly obtained by measuring the voltage value. However, the measured voltage is affected by various factors, resulting in a certain deviation between the actual measured voltage value and the theoretical value, and there is a problem that the deviation cannot be precisely controlled. Therefore, the endpoint detection of the polishing process still faces the problem of insufficient accuracy. Summary of the Invention

[0005] In view of this, on the one hand, the present invention provides a method for determining the uncertainty of wafer film thickness measurement, including:

[0006] Obtaining the uncertainty components of the wafer film thickness measurement by a wafer film thickness measurement device;

[0007] The wafer film thickness measurement device includes a light source, a lens, a reflector, and a photodiode. The light source is used to emit a light beam. The lens is used to expand and collimate the light beam and convert the point light source into a line light source. The reflector is used to reflect the line light source to irradiate onto the wafer surface. The photodiode is used to receive the reflected light reflected from the wafer surface and generate an electrical signal;

[0008] The uncertainty components include wavelength measurement uncertainty and refractive index measurement uncertainty and refraction angle measurement uncertainty , the uncertainty of voltage measurement , the uncertainty caused by the calibration coefficient deviation of the standard wafer ;

[0009] Utilize the uncertainty , , , , to determine the combined standard uncertainty

[0010] Optionally, calculate the uncertainty in the following manner :

[0011] Obtain the light source stability error and the wavelength calibration error of the wavelength calibration device ;

[0012] According to the light source stability error and the wavelength calibration error calculate the uncertainty .

[0013] Optionally, calculate the uncertainty in the following manner :

[0014] Utilize the refractive index error measurement device to obtain the refractive index measurement error ;

[0015] According to the refractive index measurement error calculate the uncertainty .

[0016] Optionally, calculate the uncertainty in the following manner :

[0017] Obtain the incident angle of the line light source irradiated on the wafer surface and the incident angle error ;

[0018] According to the incident angle and the incident angle error calculate the uncertainty .

[0019] Optionally, calculate the uncertainty in the following manner :

[0020] Obtain the true film thickness value of the standard wafer through the film thickness measurement device and obtain the corresponding reflectivity ;

[0021] Obtain the known true film thickness value multiple times The voltage value corresponding to the standard wafer, and calculate the standard deviation s of the voltage value;

[0022] According to the number of times of the repeatability measurement results And the true film thickness values of the standard wafer obtained multiple times Calculate the average voltage value of the repeatability measurement results corresponding to the voltage values ;

[0023] According to the number of times of the repeatability measurement results , the standard deviation s and the average voltage value Calculate the uncertainty .

[0024] Optionally, calculate the uncertainty in the following way :

[0025] According to the average voltage value , the uncertainty one caused by the fitting error of the film thickness-voltage curve, the uncertainty two caused by the film thickness measurement instrument error, the uncertainty three caused by the line noise error, and the uncertainty four caused by the AD conversion error, calculate the uncertainty .

[0026] Optionally, calculate the uncertainty in the following way :

[0027] ;

[0028] Among them, Is the uncertainty one, Is the uncertainty two, Is the uncertainty three, Is the uncertainty four.

[0029] Optionally, determine the combined standard uncertainty in the following way :

[0030] ;

[0031] Among them, Represents the wafer film thickness, Represents the wavelength of the light source, Represents the refractive index of the wafer thin film, Is the angle refracted to the surface of the wafer thin film, Represents the voltage, Represents the calibration coefficient.

[0032] In a second aspect of the present invention, there is provided an apparatus for determining the uncertainty of wafer film thickness measurement, the apparatus comprising: a processor and a memory connected to the processor; wherein the memory stores instructions executable by the processor, and when the instructions are executed by the processor, the processor is caused to execute the above-mentioned method for determining the uncertainty of wafer film thickness measurement.

[0033] The present invention obtains in detail each uncertainty component of the wafer film thickness measurement by a wafer film thickness measurement device, including wavelength measurement error, refractive index error, refraction angle measurement error, and voltage measurement error, to evaluate various error sources affecting the measurement result; and uses these uncertainty components to calculate the combined standard uncertainty to comprehensively evaluate the overall accuracy of the measurement result for deviation correction, thereby improving the accuracy of the voltage signal in the wafer film thickness measurement process and ultimately achieving precise control of the end point of the polishing process. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] 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 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, other drawings can be obtained based on these drawings without creative efforts.

[0035] Figure 1 It is a diagram of a wafer film thickness measurement device in an embodiment of the present invention;

[0036] Figure 2 It is a flowchart of the method for determining the uncertainty of wafer film thickness measurement in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] The following will clearly and completely describe the technical solutions of the present invention with reference to 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 based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention.

[0038] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present invention. In addition, the terms "first", "second", and "third" are only used for descriptive purposes and should not be construed as indicating or implying relative importance.

[0039] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can also be the communication inside two components. It can be a wireless connection or a wired connection. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0040] 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.

[0041] As Figure 1 shown, an embodiment of the present invention provides a wafer film thickness measurement device, which includes a light source 1, a lens 2, a mirror 3, and a photodiode 4. The light source 1 is used to emit a light beam. After the lens 2 expands and collimates the light beam, the point light source is converted into a line light source. The mirror 3 is used to reflect the line light source so as to irradiate the surface of the wafer 5. The photodiode 4 is used to receive the reflected light reflected from the wafer surface and generate an electrical signal.

[0042] The specific working principle of the wafer film thickness measurement device is as follows: The wafer film thickness measurement device is arranged at the bottom of the polishing disc. The wafer to be polished is placed on the polishing pad of the polishing disc. The wafer film thickness measurement device is turned on. The light source 1 emits a light beam. After passing through the lens 2, the light beam is expanded and collimated, and the point light source is converted into a line light source, and is reflected by the mirror 3 and irradiated onto the surface of the wafer 5. The line light source beam passes through the wafer film and is reflected on the substrate. The reflected light is irradiated into the photodiode 4 of the wafer film thickness measurement device. The photodiode 4 receives the reflected light signal and generates a photocurrent. The magnitude of the photocurrent has a linear relationship with the magnitude of the light intensity incident on the photodiode 4. After the photocurrent passes through the photoelectric conversion circuit and the signal amplification circuit in the wafer film thickness measurement device, it is output in the form of a voltage to obtain an electrical signal.

[0043] Set the relative film thickness value to be removed , and record the voltage value of the current electrical signal before polishing . After the polishing process starts, the relative change trend of the voltage during the polishing process will be recorded, the increasing and decreasing states will be recorded, and based on the recorded states and the mathematical model pre-stored in the controller MCU, the voltage value and the relative change trend at the polishing end point will be determined. When it is monitored that the real-time voltage value reaches the voltage value at the polishing end point , and is consistent with the theoretical change trend, it indicates that the polishing process reaches the end point, and the polishing can be stopped.

[0044] Then, the mathematical model for film thickness information analysis is used to analyze and process the electrical signals received by the wafer film thickness measuring device, and the wafer film thickness information is output.

[0045] Since the measured voltage is affected by various factors, there is a deviation between the actually measured film thickness and the film thickness at the theoretical polishing end point. Therefore, it is necessary to eliminate the deviation. For example, Figure 1 As shown, the embodiment of the present invention provides a method for determining the uncertainty of wafer film thickness measurement, which specifically includes:

[0046] S1, obtaining the uncertainty components of the wafer film thickness measurement by the wafer film thickness measuring device, and the uncertainty components include wavelength measurement uncertainty , refractive index measurement uncertainty , refraction angle measurement uncertainty , voltage measurement uncertainty , and the uncertainty caused by the calibration coefficient deviation of the standard wafer .

[0047] S2, using the uncertainties , , , , to determine the combined standard uncertainty.

[0048] In this embodiment, by obtaining in detail the various uncertainty components of the wafer film thickness measurement by the wafer film thickness measuring device, including wavelength measurement error, refractive index error, refraction angle measurement error, and voltage measurement error, various error sources affecting the measurement result are evaluated; and the combined standard uncertainty is calculated using these uncertainty components to comprehensively evaluate the overall accuracy of the measurement result, which is used for deviation correction, thereby improving the accuracy of the voltage signal in the wafer film thickness measurement process and ultimately achieving precise control of the polishing process end point.

[0049] It should be noted that this calculation method is only for explaining how to calculate a total component by combining multiple uncertainty components, and does not mean that all the above components must be introduced in actual application. Those skilled in the art can select the components that affect the measurement result according to the actual situation. For different devices, there may be different errors, and selection and calculation should be based on the actual situation.

[0050] Specifically, error analysis is performed on the mathematical model pre-stored in the MCU. Since there is a specific relationship between the wafer film thickness and the reflectivity, through experimental verification and data fitting and derivation, it can be known that the relationship between the wafer film thickness and its reflectivity can be approximately expressed by a cosine function. Therefore, assuming the wafer film thickness is t and the reflectivity of the wafer is R, taking the incident angle of 15° as an example, the following relational expression exists:

[0051] ;

[0052] where both A and B are constants, is the angle of incidence The angular velocity value of the cosine model under the condition of 15 degrees, where the angular velocity can be expressed as:

[0053] ;

[0054] where represents the refractive index of the wafer film, is the angle after refraction to the surface of the wafer film, is the wavelength of the light source. The refraction angle can be expressed as:

[0055] ;

[0056] where is the refractive index of air.

[0057] Before the experiment starts, in order to calibrate and correct the mathematical model, a standard wafer with a film thickness of 200 nm can be used for calibration by a film thickness measuring device. The thickness of this standard wafer can be 200 nm or a wafer with other thicknesses. When measuring the reflectivity of the standard wafer under specific conditions, the current standard voltage value is obtained. Since the voltage V and the reflectivity R are linearly related, that is V = kR , the coefficient k between voltage and reflectivity can be obtained through the calibration process. Then, substituting the cosine relationship between the wafer film thickness and the reflectivity R into the linear relationship between voltage and reflectivity, the relationship between film thickness and voltage can be obtained as:

[0058] ;

[0059] Therefore, when the polishing end point is reached, the relative film thickness value removed at this time can be expressed as:

[0060] ;

[0061] where is the wafer film thickness at the polishing end point, is the wafer film thickness measured last time, is the voltage corresponding to the polishing end point, is the voltage corresponding to the last measurement.

[0062] The uncertainty evaluation is carried out for the thickness values within a certain specific range. According to the above content, the thickness t can be expressed by the following relationship.

[0063] ;

[0064] Therefore, the measurement uncertainty of the film thickness at the end point of wafer polishing can be expressed as:

[0065] ;

[0066] wherein,

[0067] ;

[0068] ;

[0069] ;

[0070] ;

[0071] ;

[0072] The measurement uncertainty of the film thickness at the end point of wafer polishing is obtained from five uncertainty components, namely the measurement uncertainty of wavelength , the measurement uncertainty of refractive index , the measurement uncertainty of refraction angle , the measurement uncertainty of voltage , and the uncertainty caused by the deviation of the calibration coefficient of the standard wafer .

[0073] In one embodiment, the uncertainty is calculated in the following manner :

[0074] Obtain the light source stability error and the wavelength calibration error of the wavelength calibration device ;

[0075] According to the light source stability error and the wavelength calibration error calculate the uncertainty .

[0076] Specifically, the measurement uncertainty of wavelength comes from the wavelength calibration error and the light source stability error. Among them, the wavelength calibration error comes from a wavelength calibration device with higher precision, and the light source stability comes from the temperature drift of the wavelength, the wavelength indication error, the resolution, etc. Let the wavelength stability error be , and the wavelength calibration error be , then the measurement uncertainty of the wavelength of the light wave is

[0077] ;

[0078] wherein, is the coverage factor under uniform distribution, used to convert the uncertainty range of uniform distribution into standard uncertainty, and the meanings used in subsequent calculations are the same.

[0079] This embodiment comprehensively considers the main error sources of wavelength measurement, thereby evaluating and optimizing the measurement accuracy of the wafer film thickness measurement device, and improving the precise control of the polishing process endpoint.

[0080] In one embodiment, the uncertainty is calculated in the following manner :

[0081] Obtain the refractive index measurement error using a refractive index error measurement device ;

[0082] According to the refractive index measurement error calculate the uncertainty .

[0083] Specifically, the refractive index is mainly related to the basic properties of the material and can be obtained through devices such as a spectrometer and an Abbe refractometer. Let the obtained error be , then the measurement uncertainty of the refractive index is

[0084] ;

[0085] Among them, is the coverage factor under uniform distribution, used to convert the uncertainty range of uniform distribution into standard uncertainty.

[0086] This embodiment obtains the refractive index measurement error by using devices such as a spectrometer and an Abbe refractometer , calculates the measurement uncertainty of the refractive index according to the refractive index measurement error, and provides a reliable measurement benchmark and accuracy guarantee for the subsequent precise control of the polishing endpoint.

[0087] In one embodiment, the uncertainty is calculated in the following manner :

[0088] Obtain the incident angle of the line light source irradiated on the wafer surface and the incident angle error ;

[0089] According to the incident angle and the incident angle error calculate the uncertainty .

[0090] Specifically, the refraction angle is mainly related to the following factors: the magnitude of the incident angle, the refractive index of air and the refractive index of the wafer thin film Among them, the influence of the air refractive index and the thin film refractive index on the refraction angle can be ignored. Therefore, the main source of its measurement uncertainty is related to the incident angle, and the incident angle is related to the position of the mirror and the height difference between the measurement system and the wafer. Therefore, the error sources of the incident angle are: the optical path installation angle error, the flatness error of the measurement system and the wafer plane, and the height error caused by environmental vibration. Let the influence of the above errors on the magnitude of the incident angle be , then the measurement uncertainty of the refractive index can be expressed as:

[0091] ;

[0092] In this embodiment, by quantifying the main sources of refraction angle error, such as the optical path installation angle error, the flatness error between the measurement system and the wafer, and the error caused by environmental vibration, the measurement uncertainty of the refraction angle is accurately calculated . This method not only comprehensively considers various influencing factors in the measurement process, improves the accuracy and reliability of the evaluation of the measurement uncertainty of the refraction angle, and improves the accuracy of the uncertainty analysis of the wafer film thickness measurement, thus ensuring the precise control of the polishing process end point.

[0093] Among them, is the coverage factor under uniform distribution, which is used to convert the uncertainty range of uniform distribution into standard uncertainty.

[0094] In one embodiment, the uncertainty is calculated in the following manner :

[0095] Obtain the true film thickness value of the standard wafer through the film thickness measurement device and obtain the corresponding reflectivity .

[0096] Obtain the voltage values corresponding to the standard wafers with known true film thickness values multiple times, and calculate the standard deviation s of the voltage values;

[0097] According to the number of times of the repeated measurement results and the true film thickness values of the standard wafers obtained multiple times, calculate the average voltage value of the repeated measurement results;

[0098] According to the number of times of the repeated measurement results, the standard deviation s and the average voltage value calculate the uncertainty .

[0099] Specifically, the error may also come from the error during the calibration of the standard wafer with a nominal film thickness of 200 nm at the beginning, that is, the coefficient kThere is an error in the calibration coefficient of the standard wafer k The specific analysis of the deviation is:

[0100] First, use the film thickness measurement equipment to measure the film thickness of the standard wafer with a nominal value of 200nm to obtain its true value , and calculate the true film thickness value of the standard wafer The corresponding reflectivity is , then the 200nm standard wafer is placed in the wafer film thickness measurement device of the present invention, and the voltage generated at the photodiode is repeatedly measured. The repeatedly measured voltage value is the true film thickness value The corresponding voltage value, assuming the number of repeatable measurements is N, calculate the voltage average value based on the repeatability N and the voltage value of each measurement, expressed as , standard deviation is s, then the calibration coefficient is k can be expressed as

[0101] ;

[0102] Due to the calibration factor k The uncertainty caused by the deviation is:

[0103] ;

[0104] This embodiment uses standard deviation s and voltage average value and the number of measurements N to calculate the uncertainty caused by the deviation of the correlation coefficient , thereby evaluating and optimizing the measurement accuracy of wafer film thickness measurement devices and improving the precise control of the polishing process endpoint.

[0105] The uncertainty of wafer polishing endpoint film thickness measurement also includes the uncertainty of voltage measurement , although the relationship between voltage and film thickness is obtained, in practical applications, due to various experimental conditions and measurement errors, the voltage value calculated directly by the theoretical relationship may be different from the actual measured value. In order to more accurately describe the relationship between voltage and film thickness, the Fourier fitting method is used to fit the theoretical film thickness-voltage curve under a single wavelength. In the fitting process, a point is taken every 5nm as the measurement sample data (taking the number of samples as 200 as an example). Each sample point contains the wafer film thickness and its corresponding voltage value. By calculating these sample points, the fitted film thickness information analysis mathematical model, that is, the film thickness-voltage mathematical model, is obtained. This model can more accurately reflect the actual relationship between voltage and film thickness, but there is still a certain error. This error may come from the limitations of the fitting algorithm itself.

[0106] Therefore, the uncertainty caused by the film thickness-voltage curve fitting error is calculated as follows:

[0107] A film thickness-voltage mathematical model is established using multiple measurement samples, which are voltage values converted from single-wavelength reflected light collected for wafer films of different thicknesses. The mathematical model for film thickness information analysis is specifically the film thickness-voltage mathematical model.

[0108] Calculate the standard deviation of the film thickness-voltage mathematical model.

[0109] Calculate uncertainty one based on the standard deviation of the film thickness-voltage mathematical model and the number of multiple measurement samples.

[0110] Specifically, for the error of the fitting algorithm, the standard deviation of the fitting curve of the mathematical model is calculated to be 0.0295. The uncertainty brought by this curve fitting error is:

[0111] ;

[0112] where is uncertainty one.

[0113] In this embodiment, a film thickness-voltage mathematical model is established using the voltage values of single-wavelength reflected light converted from multiple wafer films of different thicknesses. Since the error of this mathematical model affects the measurement of wafer film thickness, the standard deviation of this mathematical model is calculated to evaluate the fitting error, forming uncertainty one, which provides a reliable measurement benchmark and accuracy guarantee for the precise control of the subsequent polishing end point.

[0114] In one embodiment, the following method is used to calculate uncertainty two caused by the error of the film thickness measuring instrument:

[0115] According to the number of times of repeated measurement results and the true film thickness values of the standard wafers obtained multiple times calculate the average voltage value of the repeated measurement results corresponding to the voltage values ;

[0116] Obtain the measurement accuracy of the film thickness measuring device, and calculate the voltage fluctuation value caused by the measurement accuracy deviation when the film thickness measuring device measures the standard wafer;

[0117] According to the average voltage value and the voltage fluctuation value, calculate uncertainty two caused by the error of the film thickness measuring instrument.

[0118] The error of the mathematical model for film thickness information analysis may also come from the error of the film thickness measurement device when measuring the film thickness of a standard wafer with a nominal value of 200 nm. Since the measurement accuracy of the film thickness measurement device in this embodiment is 0.1 nm, the established mathematical model for film thickness information analysis will have errors. According to the voltage fluctuation corresponding to a 0.1 nm deviation being 0.5 mV, that is, when there is a 0.1 nm deviation between the true value and the nominal value (200 nm) of the wafer film thickness, the voltage output generated by the wafer film thickness measurement device will fluctuate by 0.5 mV. Therefore, the uncertainty generated by the error of the film thickness measurement instrument is

[0119] ;

[0120] where is the second uncertainty, is the coverage factor under uniform distribution, which is used to convert the uncertainty range of uniform distribution into standard uncertainty.

[0121] In this embodiment, by quantifying the corresponding relationship between voltage fluctuation and film deviation, the influence of device accuracy on voltage measurement results is evaluated, improving the accuracy of uncertainty analysis for wafer film thickness measurement, thereby ensuring precise control of the polishing process end point.

[0122] In one embodiment, the following method is used to calculate the third uncertainty generated by line noise error:

[0123] Calculate the third uncertainty according to the average voltage and the line noise error value. The average voltage is the number of times of repeated measurement results as mentioned above and the true film thickness values of the standard wafer obtained multiple times The corresponding voltage values are used to calculate the average value.

[0124] Specifically, analyze the line noise error: Noise is inevitably generated in the circuit. When the line generates noise, it will cause voltage fluctuations, thereby affecting the voltage measurement results. The line noise error is conservatively estimated to be 2 mV (which can be set according to past experience). The resulting uncertainty is:

[0125] ;

[0126] where is the third uncertainty, is the coverage factor under uniform distribution, which is used to convert the uncertainty range of uniform distribution into standard uncertainty.

[0127] In this embodiment, by analyzing the line noise error in the wafer film thickness measuring device, the influence of line noise on the voltage measurement result is obtained, so as to accurately calculate the uncertainty three caused by line noise. This method improves the recognition and control of the influence of noise in the voltage measurement process, ensures the accuracy of the measurement result, and thus ensures the precise control of the end point of the polishing process.

[0128] In one embodiment, the uncertainty four caused by the AD conversion error is calculated by the following method:

[0129] Calculate the resolution of the AD conversion element within the range of the AD conversion element;

[0130] According to the average voltage and the resolution of the AD conversion element, calculate the uncertainty four.

[0131] Specifically, in the optoelectronic conversion circuit, the resolution of the AD conversion element adopted is 12 bits. For a voltage with a range of 2.5 V, its resolution is:

[0132] ;

[0133] The uncertainty caused by the AD conversion error is

[0134] ;

[0135] where is the uncertainty four, is the coverage factor under uniform distribution, which is used to convert the uncertainty range of uniform distribution into standard uncertainty.

[0136] In this embodiment, the uncertainty four caused by the AD conversion error is evaluated through the resolution of the AD conversion element. This method quantitatively evaluates the precision limitation of the AD conversion element in signal processing, helps to improve the accuracy of the voltage measurement result, and further improves the film thickness measurement result, thus ensuring the precise control of the end point of the polishing process.

[0137] Therefore, the uncertainty is calculated by the following method:

[0138] According to the average voltage 、the uncertainty one caused by the fitting error of the film thickness-voltage curve, the uncertainty two caused by the film thickness measuring instrument error, the uncertainty three caused by the line noise error, and the uncertainty four caused by the AD conversion error, calculate the uncertainty .

[0139] Specifically, the voltage measurement uncertainty can be expressed as:

[0140] ;

[0141] In this embodiment, by comprehensively considering multiple factors (such as the fitting error of the film thickness-voltage curve, the error of the film thickness measuring instrument, the line noise error, the AD conversion error, etc.), the uncertainty of voltage measurement is comprehensively evaluated, ensuring the comprehensiveness and accuracy of the uncertainty evaluation, ensuring the accuracy of the voltage signal during the wafer film thickness measurement, guaranteeing the precision and stability of the process control, and thus ensuring the precise control of the polishing process end point.

[0142] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memory, CD-ROM, optical memory, etc.) that contain computer-usable program code.

[0143] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to the embodiments of the present invention. It should be understood that each flow and / or block in the flowchart and / or block diagram, as well as the combination of flows 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 the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing devices generate means for implementing the specified functions in Figure 1 one or more flows and / or blocks Figure 1 one or more blocks.

[0144] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory generate a manufactured article including instruction means that implement the specified functions in Figure 1 one or more flows and / or blocks Figure 1 one or more blocks.

[0145] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process, and thus the instructions executed on the computer or other programmable device provide steps for implementing the specified functions in Figure 1 one or more flows and / or blocks Figure 1 one or more blocks.

[0146] Obviously, the above embodiments are merely examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or alterations can be made based on the above description. It is not necessary and impossible to enumerate all implementation manners here. And the obvious changes or alterations derived therefrom still fall within the protection scope of the present invention.

Claims

1. A method for determining the uncertainty of wafer film thickness measurement, characterized in that: include: Obtaining uncertainty components of wafer film thickness measurement by a wafer film thickness measurement device; The wafer film thickness measuring device comprises a light source, a lens, a reflector and a photodiode, wherein the light source is used to emit a light beam, the lens is used to expand and collimate the light beam, and then convert the point light source into a line light source, the reflector is used to reflect the line light source to irradiate the wafer surface, and the photodiode is used to receive the reflected light reflected from the wafer surface and generate an electrical signal; The uncertainty components include the wavelength measurement uncertainty , Refractive index measurement uncertainty , Refraction angle measurement uncertainty , Voltage measurement uncertainty , Uncertainty caused by deviation of calibration coefficient of standard wafer ; Using uncertainty , , , , Determine the combined standard uncertainty; The uncertainty is calculated as follows: : Get the light source stability error and wavelength calibration error of the wavelength calibration device ; According to the light source stability error and the wavelength calibration error Calculation uncertainty ; The uncertainty is calculated using the following method: : Obtain the true film thickness value of the standard wafer through film thickness measurement equipment And get the corresponding reflectivity ; Obtain known true film thickness values ​​multiple times The voltage value corresponding to the standard wafer is calculated, and the standard deviation s of the voltage value is calculated; According to the number of repeatability measurements And obtain the actual film thickness value of the standard wafer multiple times The corresponding voltage value calculates the voltage average value of the repeatability measurement result ; According to the number of repeatability measurements , standard deviation s and voltage average value Calculation uncertainty ; The uncertainty is calculated using the following method: : According to the average voltage 1. Uncertainty caused by film thickness-voltage curve fitting error 2. Uncertainty caused by line noise error 3. Uncertainty caused by AD conversion error 4. Calculation uncertainty ; The combined standard uncertainty is determined by : ; in, Indicates the wafer film thickness, represents the wavelength of the light source, represents the refractive index of the wafer film, is the angle after being refracted to the wafer film surface, Indicates voltage, Indicates the calibration factor.

2. The method according to claim 1, characterized in that The uncertainty is calculated using the following method: : Obtaining refractive index measurement error using refractive index error measurement equipment ; According to the refractive index measurement error Calculation uncertainty .

3. The method according to claim 1, characterized in that The uncertainty is calculated using the following method: : Obtain the incident angle of the line light source irradiating the wafer surface and incident angle error ; According to the incident angle and the incident angle error Calculation uncertainty .

4. The method according to claim 1, characterized in that: The uncertainty is calculated using the following method: : ; in, is the uncertainty one, is the second uncertainty, is uncertainty three, is uncertainty four.

5. A device for determining the uncertainty of wafer film thickness measurement, 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 determining the uncertainty of wafer film thickness measurement as described in any one of claims 1-4.

Images