A method for measuring the thickness of a metal film

Abstract

The present invention provides a method for measuring the thickness of a metal film layer, comprising: providing a reference sample with a reference film layer thickness distribution curve, wherein the horizontal coordinate is the distance from a point on the reference sample to the center, and the vertical coordinate is the actual film layer thickness; using an eddy current sensor to obtain a first film layer thickness distribution curve of the reference sample, wherein the horizontal coordinate corresponds to the reference horizontal coordinate one by one, and the vertical coordinate is the first test film layer thickness; obtaining a film layer thickness attenuation coefficient curve, wherein the horizontal coordinate is the reference horizontal coordinate, and the vertical coordinate is the attenuation coefficient, and the attenuation coefficient is the difference between the actual film layer thickness and the first test film layer thickness; using an eddy current sensor to obtain a second film layer thickness distribution curve of the test sample, wherein the horizontal coordinate corresponds to the reference horizontal coordinate one by one, and the vertical coordinate is the second test film layer thickness; obtaining a compensation film layer thickness distribution curve of the test sample, wherein the horizontal coordinate is the reference horizontal coordinate, and the vertical coordinate is the compensation film layer thickness. The present application compensates the signal at the distorted position of the eddy current signal to improve accuracy.

Description

Technical Field

[0001] The invention relates to the field of semiconductor manufacturing, and in particular to a method for measuring the thickness of a metal film layer. Background Art

[0002] The online measurement process of the metal film on the surface of the integrated circuit wafer usually uses a non-contact eddy current sensor module integrated on the process equipment. The eddy current measurement technology of the metal film thickness is to apply a certain frequency AC voltage to the sensor coil, so that the LC circuit at the sensor end forms an oscillation loop to generate an alternating magnetic field. The alternating magnetic field forms an eddy current effect on the metal film surface of the measured object, forming a magnetic field opposite to the sensor coil, changing the apparent impedance of the sensor coil, and realizing the measurement of the metal film thickness by associating the metal film thickness with related electrical parameters. By calibrating the metal film thickness corresponding to different sensor output signal values, it is concluded that the signal value and the metal film thickness are in a linear relationship.

[0003] This measurement method is heavily dependent on the accuracy of the sensor signal value, but the eddy current edge effect will cause the feedback signal to attenuate within the edge range, and the closer to the edge, the more serious the attenuation. At the same time, due to the influence of the metal components in the polishing head, the feedback signal increases near the center. In summary, when calculating the thickness of the metal film layer based on the linear relationship between the signal value and the thickness of the metal film layer, large errors will occur at the center and edge positions. Summary of the invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defect that large errors occur at the center and edge positions during the existing online measurement of the thickness of the metal film layer, and further provide a method for measuring the thickness of the metal film layer.

[0005] The present invention provides a method for measuring the thickness of a metal film layer, comprising: providing a reference sample having a reference film layer thickness distribution curve, wherein the horizontal coordinate of the reference film layer thickness distribution curve is a reference horizontal coordinate, the reference horizontal coordinate is the distance between a point on the reference sample and the center of the reference sample, and the vertical coordinate of the reference film layer thickness distribution curve is a reference vertical coordinate, and the reference vertical coordinate is the actual film layer thickness; using an eddy current sensor to obtain a first film layer thickness distribution curve of the reference sample, the horizontal coordinate of the first film layer thickness distribution curve is a first horizontal coordinate, the first horizontal coordinate corresponds to the reference horizontal coordinate one by one, the vertical coordinate of the first film layer thickness distribution curve is a first vertical coordinate, and the first vertical coordinate is the first test film layer thickness; obtaining a film layer thickness attenuation coefficient curve, the film layer The horizontal coordinate of the thickness attenuation coefficient curve is the reference horizontal coordinate, and the vertical coordinate of the film thickness attenuation coefficient curve is the attenuation coefficient, and the attenuation coefficient is the difference between the actual film thickness and the first test film thickness; an eddy current sensor is used to obtain the second film thickness distribution curve of the test sample, the horizontal coordinate of the second film thickness distribution curve is the second horizontal coordinate, the second horizontal coordinate corresponds one-to-one with the reference horizontal coordinate, the vertical coordinate of the second film thickness distribution curve is the second vertical coordinate, and the second vertical coordinate is the second test film thickness; according to the film thickness attenuation coefficient curve, the compensation film thickness distribution curve of the test sample is obtained, the horizontal coordinate of the compensation film thickness distribution curve is the reference horizontal coordinate, and the vertical coordinate of the compensation film thickness distribution curve is the compensation film thickness.

[0006] Optionally, the reference samples include reference samples with different film thicknesses.

[0007] Optionally, the step of using an eddy current sensor to obtain the first film layer thickness distribution curve of a reference sample includes: selecting a wafer with a uniform surface metal film layer thickness, and taking a fixed-point measurement method to obtain the eddy current signal values ​​output by the eddy current sensor at different positions and the corresponding actual film layer thickness.

[0008] Optionally, when the radius of the wafer is 150mm, an eddy current sensor is used to obtain the average value of the eddy current signal value output at a position 60mm-110mm from the center and the corresponding actual film thickness average value, and a point on the eddy current signal value-film thickness fitting curve is obtained, and then wafers with different surface metal film thicknesses are tested separately to obtain the eddy current signal value-film thickness fitting curve.

[0009] Optionally, the first test film layer thickness and the second test film layer thickness are obtained according to an eddy current signal value-film layer thickness fitting curve.

[0010] Optionally, after obtaining the first test film thickness according to the eddy current signal value-film thickness fitting curve, the attenuation coefficient curve of the benchmark samples with different film thicknesses is obtained, and the horizontal coordinate of the film thickness attenuation coefficient curve is the benchmark horizontal coordinate, and the vertical coordinate of the film thickness attenuation coefficient curve is the attenuation coefficient.

[0011] Optionally, in the step of obtaining a compensation film layer thickness distribution curve of the test sample according to a film layer thickness attenuation coefficient curve, the compensation film layer thickness is equal to the sum of the second test film layer thickness and the attenuation coefficient.

[0012] Optionally, in the step of obtaining a compensation film layer thickness distribution curve of the test sample according to a film layer thickness attenuation coefficient curve, an attenuation coefficient prediction model is generated according to the attenuation coefficient to obtain the compensation film layer thickness.

[0013] Optionally, the attenuation coefficient prediction model includes a broken line model or a curved surface model.

[0014] Optionally, the method for generating the broken line model includes a bilinear interpolation method, and the method for generating the surface model includes a least squares method.

[0015] The technical solution of this application has the following advantages:

[0016] The metal film thickness measurement method provided in the present application avoids the distortion of the metal film thickness data at the center and edge existing in the existing test methods by obtaining the compensation film thickness distribution curve of the test sample, compensates the eddy current signal at the distorted position of the eddy current signal, improves the measurement accuracy, and can meet the requirements for online measurement of the metal film thickness. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] 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.

[0018] Figure 1 Schematic diagram of the process of the metal film thickness measurement method of this embodiment;

[0019] Figure 2 A schematic diagram showing the relationship between the tested film thickness and the actual film thickness in the prior art;

[0020] Figure 3 This is a schematic diagram of the signal value-film thickness fitting curve of this embodiment;

[0021] Figure 4is a schematic diagram of the film thickness attenuation coefficient curve of this embodiment;

[0022] Figure 5 It is a schematic diagram of the relationship between the test film thickness in the prior art, the compensation film thickness in this embodiment and the actual film thickness. DETAILED DESCRIPTION

[0023] A method for measuring the thickness of a metal film layer. When an eddy current sensor is close to the metal film layer to be detected, an excitation voltage is provided to the eddy current sensor through an excitation power supply. The voltage applied to the eddy current sensor will generate a gradually increasing excitation current, and the excitation current will generate eddy currents in the metal film layer to be measured. Then the excitation power supply is disconnected. As the excitation power supply is disconnected, the eddy currents in the metal film layer to be detected will change. After the excitation voltage is disconnected, the eddy currents in the metal to be measured will generate a freewheeling current in the excitation coil of the eddy current sensor. At this time, the eddy current changes in the metal film layer to be detected are detected by the eddy current sensor and converted into a voltage signal. The voltage signal fed back by the eddy current sensor is collected. Since the eddy current gradually decreases, the voltage signal also gradually decays. Since the voltage signal decay rate and decay time of metal film layers of different thicknesses are different, the thickness of the metal to be measured can be judged based on the decay curve and decay time of the voltage signal. However, if Figure 2 As shown in the figure, the eddy current edge effect will cause the feedback signal to attenuate within the edge range, and the closer to the edge, the more serious the attenuation. At the same time, due to the influence of the metal components in the polishing head, the feedback signal increases near the center. Therefore, it is necessary to compensate and correct the feedback signals near the center and the edge.

[0024] 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.

[0025] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are 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 therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0026] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" 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 it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0027] 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.

[0028] This embodiment provides a method for measuring the thickness of a metal film layer. Figure 1 As shown, the following steps are included:

[0029] Step S1: providing a reference sample having a reference film thickness distribution curve, wherein the abscissa of the reference film thickness distribution curve is a reference abscissa, which is the distance between a point on the reference sample and the center of the reference sample, and the ordinate of the reference film thickness distribution curve is a reference ordinate, which is the actual film thickness;

[0030] Step S2: using an eddy current sensor to obtain a first film layer thickness distribution curve of a reference sample, wherein the abscissa of the first film layer thickness distribution curve is a first abscissa, and the first abscissa corresponds one-to-one with the reference abscissa, and the ordinate of the first film layer thickness distribution curve is a first ordinate, and the first ordinate is the first test film layer thickness;

[0031] Step S3: obtaining a film thickness attenuation coefficient curve, wherein the abscissa of the film thickness attenuation coefficient curve is the reference abscissa, the ordinate of the film thickness attenuation coefficient curve is the attenuation coefficient, and the attenuation coefficient is the difference between the actual film thickness and the first test film thickness;

[0032] Step S4: using an eddy current sensor to obtain a second film layer thickness distribution curve of the test sample, the abscissa of the second film layer thickness distribution curve is a second abscissa, the second abscissa corresponds one-to-one with the reference abscissa, the ordinate of the second film layer thickness distribution curve is a second ordinate, and the second ordinate is the second test film layer thickness;

[0033] Step S5: obtaining a compensation film thickness distribution curve of the test sample according to the film thickness attenuation coefficient curve, wherein the abscissa of the compensation film thickness distribution curve is the reference abscissa, and the ordinate of the compensation film thickness distribution curve is the compensation film thickness.

[0034] The metal film thickness measurement method provided in this embodiment avoids the distortion of the metal film thickness data at the center and edge in the existing test method by obtaining the compensation film thickness distribution curve of the test sample, and compensates the eddy current signal at the distorted position of the eddy current signal, thereby improving the measurement accuracy and meeting the requirements for online measurement of the metal film thickness. At the same time, swapping the horizontal and vertical coordinates of the reference film thickness distribution curve, the first film thickness distribution curve, the attenuation coefficient curve, the second film thickness distribution curve or the compensation film thickness distribution curve is also within the protection scope of this application.

[0035] In this embodiment, the reference samples include reference samples with different film thicknesses. The eddy current signal value-film thickness fitting curve can be easily obtained through the reference samples with different film thicknesses.

[0036] In this embodiment, the step of using an eddy current sensor to obtain a first film thickness distribution curve of a reference sample includes: selecting a wafer with a uniform thickness of a surface metal film layer, and taking a fixed-point measurement method to obtain the eddy current signal value output by the eddy current sensor at different positions and the corresponding actual film thickness. The selection of fixed points includes the central area, the edge area, and the area between the central area and the edge area. This is because the first test film thickness in the central area is greater than the actual film thickness, the first test film thickness in the edge area is less than the actual film thickness, and the first test film thickness in the area between the central area and the edge area is similar to the actual film thickness.

[0037] For example, when the radius of the wafer is 150 mm, an eddy current sensor can be used to obtain the average value of the eddy current signal output at a position 60 mm-110 mm from the center, that is, the area between the center area and the edge area, and the corresponding actual film thickness average value, and obtain a point on the eddy current signal value-film thickness fitting curve, and then test wafers with different surface metal film thicknesses respectively to obtain the following: Figure 3 The eddy current signal value-film thickness fitting curve shown, Figure 3 The horizontal axis is the eddy current signal value, and the vertical axis is the film thickness, in angstroms, and the linear relationship between the film thickness and the eddy current signal value is obtained by fitting. The mean value of the actual film thickness can be obtained through the reference film thickness distribution curve or direct measurement.

[0038] After the eddy current signal value-film layer thickness fitting curve is obtained, the first test film layer thickness and the second test film layer thickness can be calculated from the eddy current signal value obtained by the test.

[0039] In this embodiment, after obtaining the first test film thickness according to the eddy current signal value-film thickness fitting curve, the attenuation coefficient curves of the reference samples with different film thicknesses are obtained, such as Figure 4As shown, the horizontal coordinate of the film thickness attenuation coefficient curve is the reference horizontal coordinate, with a unit of millimeters. The reference horizontal coordinate represents the distance of a point on the reference sample from the center of the reference sample. The vertical coordinate of the film thickness attenuation coefficient curve is the attenuation coefficient, with a unit of angstroms. Figure 4 The different line shapes represent the benchmark samples with film thickness of 2000 angstroms, 6000 angstroms, 8000 angstroms and 12000 angstroms respectively.

[0040] In an optional embodiment, in the step of obtaining the compensation film thickness distribution curve of the test sample according to the film thickness attenuation coefficient curve, the compensation film thickness is equal to the sum of the second test film thickness and the attenuation coefficient. The film thickness of a wafer with a radius of 150 mm and a known true thickness distribution is tested using the prior art and the method of the present application. The test results are as follows: Figure 5 shown. Figure 5 The horizontal axis is the reference horizontal axis, in millimeters, and the vertical axis is the thickness, in angstroms. Figure 5 It can be seen that the edge area thickness measured by the prior art is much smaller than the actual thickness, the center area thickness measured by the prior art is much larger than the actual thickness, and the thickness measured by the method of the present application is similar to the actual thickness in the entire region.

[0041] In an optional embodiment, in the step of obtaining the compensation film layer thickness distribution curve of the test sample according to the film layer thickness attenuation coefficient curve, an attenuation coefficient prediction model is generated according to the attenuation coefficient to obtain the compensation film layer thickness.

[0042] Specifically, the attenuation coefficient prediction model includes a broken line model or a curved surface model.

[0043] Exemplarily, the method for generating the polyline model includes bilinear interpolation. When the attenuation coefficient of the calibration point is known, the specific attenuation coefficient of the non-calibration point is obtained by the bilinear interpolation algorithm. Assuming that the attenuation coefficients of the adjacent grid coordinates of the four existing calibration data are known to be (x, y), (x+1, y), (x, y+1), (x+1, y+1), respectively, the calculation method is as follows:

[0044] f(x+u,y+v)=(1-u)(1-v)f(x,y)

[0045] +(1-u)vf(x,y+1)

[0046] +u(1-v)f(x+1,y)

[0047] +uvf(x+1,y+1)

[0048] Exemplarily, the method for generating the surface model includes the least square method. It is known that there are enough standard points, and it is required to fit all coordinates with the following bivariate polynomial function: Right now

[0049]

[0050] set up

[0051]

[0052] Then the function can be expressed as f(x,y)=X T AY, the goal of fitting is to find the coefficient matrix A. When a new point (u, v) is obtained, f(u, v) can be found according to the fitting function.

[0053] 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 present invention.

Claims

1. A method for measuring the thickness of a metal film, characterized in that: include: Providing a reference sample having a reference film thickness distribution curve, wherein the abscissa of the reference film thickness distribution curve is a reference abscissa, which is the distance between a point on the reference sample and the center of the reference sample, and the ordinate of the reference film thickness distribution curve is a reference ordinate, which is the actual film thickness; An eddy current sensor is used to obtain a first film layer thickness distribution curve of a reference sample, wherein the abscissa of the first film layer thickness distribution curve is a first abscissa, and the first abscissa corresponds one-to-one with the reference abscissa, and the ordinate of the first film layer thickness distribution curve is a first ordinate, and the first ordinate is the first test film layer thickness; Obtaining a film thickness attenuation coefficient curve, wherein the abscissa of the film thickness attenuation coefficient curve is the reference abscissa, the ordinate of the film thickness attenuation coefficient curve is the attenuation coefficient, and the attenuation coefficient is the difference between the actual film thickness and the first test film thickness; The eddy current sensor is used to obtain a second film layer thickness distribution curve of the test sample, wherein the abscissa of the second film layer thickness distribution curve is a second abscissa, and the second abscissa corresponds to the reference abscissa one-to-one, and the ordinate of the second film layer thickness distribution curve is a second ordinate, and the second ordinate is the second test film layer thickness; A compensation film layer thickness distribution curve of a test sample is obtained according to a film layer thickness attenuation coefficient curve, wherein the horizontal coordinate of the compensation film layer thickness distribution curve is the reference horizontal coordinate, and the vertical coordinate of the compensation film layer thickness distribution curve is the compensation film layer thickness. In the step of obtaining the compensation film layer thickness distribution curve of the test sample according to the film layer thickness attenuation coefficient curve, an attenuation coefficient prediction model is generated according to the attenuation coefficient to obtain the compensation film layer thickness, and the attenuation coefficient prediction model includes a broken line model or a surface model, and a method for generating the broken line model includes a bilinear interpolation method, and a method for generating the surface model includes a least squares method.

2. The method for measuring the thickness of a metal film according to claim 1, characterized in that: The reference samples include reference samples with different film thicknesses.

3. The method for measuring the thickness of a metal film according to claim 1, characterized in that: The steps of using an eddy current sensor to obtain the first film layer thickness distribution curve of a reference sample include: selecting a wafer with a uniform surface metal film layer thickness, and taking a fixed-point measurement method to obtain the eddy current signal value output by the eddy current sensor at different positions and the corresponding actual film layer thickness.

4. The method for measuring the thickness of a metal film layer according to claim 3, characterized in that: When the radius of the wafer is 150mm, an eddy current sensor is used to obtain the average value of the eddy current signal output at a position 60mm-110mm away from the center and the corresponding actual film thickness average value, and a point on the eddy current signal value-film thickness fitting curve is obtained. Then, wafers with different surface metal film thicknesses are tested separately to obtain the eddy current signal value-film thickness fitting curve.

5. The method for measuring the thickness of a metal film layer according to claim 4, characterized in that: The first test film thickness and the second test film thickness are obtained according to the eddy current signal value-film thickness fitting curve.

6. The method for measuring the thickness of a metal film layer according to claim 5, characterized in that: After obtaining the first test film thickness according to the eddy current signal value-film thickness fitting curve, the attenuation coefficient curve of the benchmark samples with different film thicknesses is obtained, the horizontal coordinate of the film thickness attenuation coefficient curve is the benchmark horizontal coordinate, and the vertical coordinate of the film thickness attenuation coefficient curve is the attenuation coefficient.

7. The method for measuring the thickness of a metal film layer according to claim 1, characterized in that: In the step of obtaining the compensation film layer thickness distribution curve of the test sample according to the film layer thickness attenuation coefficient curve, the compensation film layer thickness is equal to the sum of the second test film layer thickness and the attenuation coefficient.

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