CN114589617B - Metal film thickness measuring method, film thickness measuring device and chemical mechanical polishing equipment - Google Patents

Abstract

The invention discloses a metal film thickness measurement method, a film thickness measurement device and chemical mechanical polishing equipment. The method includes: when measuring the film thickness of a metal film on a wafer surface based on an amplitude method or a phase method, calculating the amplitude method or the phase method The corresponding extreme point; the excitation frequency is adjusted according to the extreme point, the measurement range and/or the measurement sensitivity, wherein the measurement range is the measurement film thickness range, the measurement sensitivity is the resolution, and the excitation frequency is The frequency of the excitation signal for the film thickness measurement device. The invention utilizes the extreme point to obtain the optimal measurement range and measurement sensitivity in the amplitude method and the phase method.

Description

Metal film thickness measurement method, film thickness measurement device and chemical mechanical polishing equipment

technical field

The invention relates to the technical field of chemical mechanical polishing, in particular to a metal film thickness measurement method, a film thickness measurement device and chemical mechanical polishing equipment.

Background technique

Integrated Circuit (IC) is the core and lifeblood of the development of the information technology industry. Integrated circuits are typically formed by sequentially depositing conductive, semiconducting, or insulating layers on a silicon wafer. Thus, a thin film formed by a filler layer is deposited on the surface of the wafer. During the fabrication process, the filler layer needs to be continuously planarized until the patterned top surface is exposed to form conductive paths between the raised patterns.

Chemical mechanical polishing (Chemical Mechanical Polishing, CMP) technology is the preferred planarization process in the IC manufacturing process. In chemical mechanical polishing, too much or too little material removal for the manufacturing process of semiconductor devices can lead to electrical degradation or even failure of the device. In order to improve the controllability of the chemical mechanical polishing process, improve the stability of the product, reduce the defect rate of the product, and achieve uniform production of each wafer, the Endpoint Detection (EPD) technology of chemical mechanical polishing came into being as the times require. .

In metal CMP endpoint detection, eddy current detection is the most commonly used method. The output signal is a voltage signal, and the magnitude of the voltage signal is related to the thickness of the metal film on the measured wafer surface. In the prior art, different eddy current sensor coil structures will produce different ranges and resolutions of eddy current detection. At present, the test is generally performed by manually changing parameters little by little. The test time is long, and based on empirical data, The results are easy to be inaccurate and affect the use.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a metal film thickness measurement method, a film thickness measurement device, and a chemical mechanical polishing device, aiming at at least solving one of the technical problems existing in the prior art.

A first aspect of the embodiments of the present invention provides a method for measuring metal film thickness, including:

When measuring the film thickness of the metal thin film on the wafer surface based on the amplitude method or the phase method, calculate the extreme point corresponding to the amplitude method or the phase method;

The excitation frequency is adjusted according to the extreme point, measurement range and/or measurement sensitivity, wherein the measurement range is the measurement range of film thickness, the measurement sensitivity is the resolution, and the excitation frequency is used for the film thickness measurement device frequency of the excitation signal.

A second aspect of the embodiments of the present invention provides a film thickness measurement device, which uses the above-mentioned metal film thickness measurement method for film thickness measurement; the film thickness measurement device includes an eddy current sensor and a detection circuit; the eddy current The sensor includes an excitation coil and an induction coil; the excitation coil and the induction coil are both flat coils and are arranged coaxially, and the excitation coil and the induction coil are wound in the same direction.

A third aspect of the embodiments of the present invention provides a chemical mechanical polishing device, comprising:

a polishing pad covered with a polishing pad for polishing the wafer;

a carrier head for holding the wafer and pressing the wafer on the polishing pad;

A film thickness measurement device for measuring the film thickness of the wafer during polishing;

The control device is used for realizing the above-mentioned metal film thickness measurement method.

A fourth aspect of the embodiments of the present invention provides a control device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, when the processor executes the computer program Carry out the steps of the metal film thickness measurement method as described above.

A fifth aspect of the embodiments of the present invention provides a computer-readable storage medium, where the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, implements the steps of the above method for measuring metal film thickness .

The beneficial effects of the embodiments of the present invention include: by using the extreme point, the optimal measurement range and measurement sensitivity in the amplitude method and the phase method can be obtained.

Description of drawings

The advantages of the present invention will become clearer and easier to understand through the detailed description in conjunction with the following drawings, but these drawings are only schematic and do not limit the protection scope of the present invention, wherein:

1 is a schematic structural diagram of a chemical mechanical polishing apparatus according to an embodiment of the present invention;

2 is a schematic structural diagram of a chemical mechanical polishing apparatus according to an embodiment of the present invention;

3 is a schematic structural diagram of a film thickness measurement device provided by an embodiment of the present invention;

FIG. 4 is a schematic structural diagram of an eddy current sensor provided by an embodiment of the present invention;

FIG. 5 is a schematic diagram of an eddy current sensor provided by an embodiment of the present invention;

6 is a schematic diagram of an eddy current sensor provided by another embodiment of the present invention;

7 is an equivalent circuit diagram of an eddy current sensor provided by an embodiment of the present invention;

FIG. 8 is an LC resonant circuit provided by an embodiment of the present invention;

9 is a schematic flowchart of a method for measuring metal film thickness provided by an embodiment of the present invention;

Figure 10 shows the relationship between the amplitude and the film thickness under different excitation frequencies;

Figure 11 shows the relationship between phase and film thickness under different excitation frequencies;

Figure 12 shows that the amplitude variation is attenuated at the edge under different excitation frequencies.

Detailed ways

The technical solutions of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings. The embodiments described herein are specific embodiments of the present invention, used to illustrate the concept of the present invention; these descriptions are all explanatory and exemplary, and should not be construed as limiting the embodiments of the present invention and the protection scope of the present invention . It should be noted that the embodiments in the present application and the features of the embodiments may be combined with each other in the case of no conflict. In addition to the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims of the present application and the description thereof, and these technical solutions include adopting any modifications made to the embodiments described herein. Obvious alternative and modified technical solutions. It should be understood that, unless otherwise specified, for ease of understanding, the following descriptions of the specific embodiments of the present invention are based on the natural state that the relevant equipment, devices, components, etc. are in the original static state without external control signals and driving forces. describe.

In addition, it should be noted that the terms used in this application, such as front, rear, upper, lower, left, right, top, bottom, front, back, horizontal, vertical, etc., are used for the purpose of To aid in the understanding of relative positions or orientations, it is not intended to limit the orientation of any device or structure.

In order to illustrate the technical solutions of the present invention, the following description will be made with reference to the accompanying drawings and in conjunction with the embodiments.

In this application, chemical mechanical polishing (Chemical Mechanical Polishing) is also called chemical mechanical planarization (Chemical Mechanical Planarization), wafer (wafer) is also called wafer, silicon wafer, substrate or substrate (substrate), its meaning and The actual effect is equivalent.

As shown in FIG. 1 , the main components of the chemical mechanical polishing apparatus 1 provided by the embodiment of the present invention include a carrier head 10 for holding the wafer w and driving the wafer w to rotate, a polishing pad 20 covered with a polishing pad 21, The dresser 30 for dressing the polishing pad 21, and the liquid supply part 40 for supplying the polishing liquid.

During the chemical mechanical polishing process, the carrier head 10 sucks the wafer w through negative pressure, and presses the side of the wafer w containing the metal film on the polishing pad 21 , and the carrier head 10 rotates and rotates along the radial direction of the polishing pad 20 . The reciprocating movement causes the surface of the wafer w in contact with the polishing pad 21 to be gradually thrown away, while the polishing disc 20 rotates, and the liquid supply part 40 sprays the polishing liquid on the surface of the polishing pad 21 . Under the chemical action of the polishing liquid, the wafer w is rubbed against the polishing pad 21 through the relative movement of the carrier head 10 and the polishing disc 20 to perform polishing. During polishing, the conditioner 30 is used to condition and activate the surface topography of the polishing pad 21 . The use of the conditioner 30 can remove the impurity particles remaining on the surface of the polishing pad 21, such as abrasive particles in the polishing liquid and the waste material falling off the surface of the wafer w, etc., and can also flatten the surface deformation of the polishing pad 21 caused by grinding. .

During the chemical mechanical polishing process, the wafer w is pressed on the polishing pad 21 by the carrier head 20, and reciprocates along the radial direction of the polishing disk 10 with the carrier head 20. At the same time, the carrier head 20 rotates synchronously with the polishing disk 10, so that the The surface of the wafer w that the polishing pad 21 contacts is gradually removed.

As shown in FIG. 2 , the chemical mechanical polishing apparatus 1 further includes a film thickness measuring device 50 and a control device for measuring the film thickness of the wafer w online. The film thickness measuring device 50 is installed in the polishing disc 20 below the polishing pad 21 . The film thickness measuring device 50 rotates following the polishing disc 20 to realize on-line measurement of the film thickness while polishing. The film thickness measuring device 50 is disposed next to the polishing pad 21 , and the wafer w is placed on the polishing pad 21 . Therefore, the distance between the film thickness measuring device 50 and the wafer w is the thickness of the polishing pad 21 .

During the polishing process, it is necessary to monitor the film thickness change and the film thickness value of the wafer w in real time, so as to adopt a corresponding polishing process to avoid over-polishing or incomplete polishing. During the polishing process, the thickness of the metal film on the wafer surface is measured online, so that the removal rate of the metal film can be precisely controlled by adjusting the pressure of the carrier head 10 to achieve better global planarization. The film thickness measurement device 50 can use eddy current detection. The principle of the eddy current detection is that when the film thickness measurement device 50 sweeps across the wafer w, the metal film layer on the surface of the wafer w will induce eddy currents, so that the film thickness measurement device 50 generates an eddy current. The magnetic field of the metal film changes, so that when the metal film layer is removed by polishing, the film thickness measuring device 50 measures the eddy current change to measure the film thickness of the metal film layer.

In one embodiment of the present invention, the film thickness measurement device 50 includes an eddy current sensor 51 and a detection circuit.

As shown in FIG. 3 , the detection circuit includes an oscillator, a phase shift unit, a differential amplifying unit, a cosine synchronous detection unit, a sine synchronous detection unit, a first low-pass filtering and amplifying unit, and a second low-pass filtering and amplifying unit.

The oscillator is connected to the excitation coil 511 and the phase-shifting unit respectively, the phase-shifting unit is respectively connected to the cosine synchronous detection unit and the sine synchronous detection unit, and the differential amplifier unit is respectively connected to the induction coil 512, the cosine synchronous detection unit and the sine synchronous detection unit , the cosine synchronous detection unit is connected with the first low-pass filtering and amplifying unit, and the sine synchronous detection unit is connected with the second low-pass filtering and amplifying unit.

与相位

最后，检测电路的输出通过数据采集模块和通讯模块将该幅值和相位送至上位机。As shown in FIG. 3 , the working principle of the detection circuit is as follows: the excitation voltage is respectively input to the excitation coil 511 and the phase shift unit through the oscillator, the output voltage across the induction coil 512 is detected by the differential amplifier unit and the output voltage is input to the cosine The synchronous detection unit and the sine synchronous detection unit respectively input the original excitation voltage signal (represented by 0° in Figure 3) and the phase-shifted quadrature voltage signal (represented by 90° in Figure 3) to the cosine synchronization unit through the phase shift unit The detection unit and the sine synchronous detection unit, then, the output signal of the cosine synchronous detection unit is subjected to the first low-pass filtering and amplification unit to obtain the imaginary component Y of the output voltage of the induction coil 512, and the output signal of the sine synchronous detection unit is filtered by the second low-pass filter. The real component X of the output voltage of the induction coil 512 is obtained through the filtering and amplifying unit, and the magnitude of the output voltage of the induction coil 512 is obtained through the vector calculation of the real component X and the imaginary component Y.

with phase

Finally, the output of the detection circuit sends the amplitude and phase to the upper computer through the data acquisition module and the communication module.

As shown in FIG. 4 , the eddy current sensor 51 includes an excitation coil 511 , an induction coil 512 , a bobbin 513 and a shielding case 514 . It is experimentally verified that the structure of the double coil has better edge measurement performance than the single coil.

As shown in FIG. 4 , the coil bobbin 513 is used to support and fix the induction coil 512 and the excitation coil 511 and to insulate the two coils. The induction coil 512 and the excitation coil 511 are wound on it in the same direction. The four leads of the two coils are drawn from one side of 513, and the material of the coil bobbin 513 can be plexiglass or PPS engineering plastic.

As shown in FIG. 4 , around the coil bobbin 513 is a circle of shielding shells 514 , which can be made of permalloy or aluminum, with a thickness of 0.2 mm to 0.5 mm. The shielding case 514 can reduce the influence of the change of the external magnetic field environment on the performance of the eddy current sensor 51 . In one embodiment, the core layer of the shielding shell 514 is made of a metal material, and the surface is coated with a non-metallic material layer to prevent metal ion contamination.

In one embodiment, the excitation coil 511 and the induction coil 512 are both flat coils and are arranged coaxially, and the excitation coil 511 and the induction coil 512 are wound in the same direction. The coil can be wound by enameled wire winding process, or can be produced by PCB or MEMS process.

As shown in FIG. 5 , as an embodiment, the excitation coil 511 and the induction coil 512 are both annular flat coils, and the excitation coil 511 and the induction coil 512 are arranged side by side up and down and coaxially. Specifically, in the chemical mechanical polishing apparatus 1, the excitation coil 511 is located below the induction coil 512, and the distance between the excitation coil 511 and the induction coil 512 is less than 0.9 mm. The inner diameter of the excitation coil 511 is larger than 1 mm, the outer diameter is smaller than 5 mm, and the number of turns is smaller than 200 turns. The inner diameter of the induction coil 512 is larger than 1 mm, the outer diameter is smaller than 8 mm, and the number of turns is not larger than 600 and not smaller than the number of turns of the excitation coil 511 . In a specific embodiment, the inner diameter of the excitation coil 511 is 2 mm, the outer diameter is 4.2 mm, and the number of turns is 50 turns. The inner diameter of the induction coil 512 is 2 mm, the outer diameter is 8 mm, and the number of turns is 350 turns.

As shown in FIG. 6 , as another embodiment, the excitation coil 511 and the induction coil 512 are both annular flat coils, the excitation coil 511 and the induction coil 512 are coaxial and arranged in parallel, and the excitation coil 511 is located in the annular induction coil 512 Inside the ring, the induction coil 512 wraps the outer diameter of the excitation coil 511. The inner diameter of the excitation coil 511 is larger than 1 mm, the outer diameter is smaller than 5 mm, and the number of turns is smaller than 100 turns. The inner diameter of the induction coil 512 is not smaller than the outer diameter of the excitation coil 511 , the outer diameter of the induction coil 512 is smaller than 8 mm, and the number of turns is not more than 600 and not less than the number of turns of the excitation coil 511 . In a specific embodiment, the inner diameter of the excitation coil 511 is 1 mm, the outer diameter is 3 mm, and the number of turns is 50 turns. The inner diameter of the induction coil 512 is 4 mm, the outer diameter is 7 mm, and the number of turns is 300 turns.

The installation position of the eddy current sensor 51 is shown in FIG. 2 . The lift-off height between the eddy-current sensor 51 and the metal film is defined as the distance from the induction coil 512 to the metal film, and the lift-off height is not greater than 4 mm. In use, the upper surface of the eddy current sensor 51 should be as close to the polishing pad 21 as possible. Generally, the initial thickness of the polishing pad 21 is less than or equal to 3.5 mm, and the maximum lift-off height is generally 3.5 mm. .

As the core part of the film thickness measuring device 50, the eddy current sensor 51 is mainly used to excite the alternating electromagnetic field and induce the change of the induced electromotive force caused by the mutual inductance effect of different metal thin films. When other conditions remain unchanged, there is a one-to-one correspondence between the induced electromotive force and the metal film thickness.

The excitation coil 511 is mainly connected with an AC signal of a fixed frequency to generate an alternating magnetic field, and then an induced electromotive force is generated in the metal film and the induction coil 512. There is a coupled electric current between the excitation coil 511, the induction coil 512 and the metal film. Magnetic induction relationship. As shown in Figure 7, using the transformer model, the coupling relationship can be solved.

Defined here, the inductance of the excitation coil 511 is L ₁ , the internal resistance of the excitation coil 511 is R ₁ , the excitation voltage of the excitation signal input to the excitation coil 511 is U ₁ , the excitation current of the excitation signal is I ₁ , the angle of the excitation signal is The frequency is ω; the output voltage at both ends of the induction coil 512 is U ₂ , the internal resistance of the induction coil 512 is R ₂ , and the inductance of the induction coil 512 is L ₂ ; the equivalent inductance of the metal film is L _t , and the equivalent of the metal film is L 2 . The resistance is R _t , the induced current of the metal film is I _t ; the mutual inductance coefficient between the excitation coil 511 and the metal film is M _1t , the mutual inductance factor between the excitation coil 511 and the metal film is k _1t (x), and the excitation coil 511 The mutual inductance coefficient between the induction coil 512 and the induction coil 512 is M ₁₂ , the mutual inductance factor between the excitation coil 511 and the induction coil 512 is k ₁₂ , the mutual inductance coefficient between the induction coil 512 and the metal film is M _2t , and the induction coil 512 and the metal film are M 2t . The mutual inductance factor between is k _2t (x).

Assuming that the induction coil 512 is open, and the influence of the mutual inductance of the metal film on the excitation coil 511 is ignored, according to Kirchhoff's voltage law, it can be obtained:

I ₁ (R ₁ +jωL ₁ )=U ₁

1)

R _t L _t +jωL _t I _t =jωM _1t I ₁

2)

R ₂ I ₂ +jωL ₂ I ₂ +jωM ₁₂ I ₁ -jωM _2t I _t =U ₂

3)

The mutual inductance can be expressed as:

where x is the lift-off height. When other parameters of the coil are determined, the mutual inductance factor is only related to the distance. In other words, k _1t (x) is related to the vertical distance between the excitation coil 511 and the metal film, and k _2t (x) is related to the distance between the induction coil 512 and the metal film. of the vertical distance. Based on the double-coil structure of the eddy current sensor 51 in the embodiment of the present application, as shown in FIG. 5 or FIG. 6 , the distance between the excitation coil 511 and the induction coil 512 is fixed, so k ₁₂ is a constant, k _1t ( Both x) and x _2t (x) can be expressed as functions related to the lift-off height x. Also, the values of k ₁₂ , k _1t (x) and k _2t (x) are all between 0 and 1.

According to the equivalent eddy current ring theory, when the conductor film thickness is extremely thin, it can be obtained:

L _t =μ ₀ ·S(r ₂ , r ₁ ) (8)

where t is the film thickness, μ ₀ is the relative permeability, σ is the electrical conductivity, r ₁ is the inner diameter of the equivalent eddy current ring, r ₂ is the outer diameter of the equivalent eddy current ring, and S(r ₂ , r ₁ ) is A function of the inner and outer diameters of the equivalent swirl ring. When the coil structure is fixed, the values of the outer diameter r ₂ , the inner diameter r ₁ , and S(r ₂ , r ₁ ) of the equivalent eddy current ring can be considered to be fixed.

Define the constant G, which can be expressed as:

By combining the above equations, the output voltage can be obtained as:

When the eddy current sensor 51 is placed in the space without the sample to be measured, the measured air voltage value is:

In fact, the amount of change in voltage, the effective signal, is:

ΔU=U ₂ -U _air (12)

It can be further expressed as:

The variation of voltage has two characteristic quantities, namely amplitude and phase, which can be expressed as:

仅仅与提离高度x和金属膜厚t有关，当提离高度x固定不变的时候，幅值|ΔU|和相位

仅仅与膜厚t有关，在线圈的结构、金属薄膜种类、激励电压等确定的情况下，幅值|ΔU|和相位

可以用来测量金属膜厚t的变化。通过解算幅值|ΔU|来获取膜厚的方法可以称为幅值法，通过解算相位

来获取膜厚的方法可以称为相位法。It can be seen that the magnitude |ΔU| and the phase

It is only related to the lift-off height x and the metal film thickness t. When the lift-off height x is fixed, the amplitude |ΔU| and the phase

It is only related to the film thickness t. When the structure of the coil, the type of metal thin film, the excitation voltage, etc. are determined, the amplitude |ΔU| and the phase

It can be used to measure the change of metal film thickness t. The method of obtaining the film thickness by solving the amplitude |ΔU| can be called the amplitude method. By solving the phase

The method to obtain the film thickness may be called the phase method.

With the change of the metal film thickness t, the amplitude |ΔU| has an extreme point, and the size of the film thickness corresponding to this extreme point determines the range of thickness measurement by the amplitude method. As the film thickness increases, the amplitude first increases and then decreases, and the extreme point of the amplitude |ΔU| can be expressed as:

的值随着膜厚的增大而单调增大。当k₁₂-k_1t(x)k_2t(x)>0时，相位

的值存在极值点，随着膜厚的增加，相位值先减小后增大。相位

的极值点为：For the phase method, when k ₁₂ -k _1t (x)k _2t (x)<0, the phase

The value of , increases monotonically with the increase of film thickness. When k ₁₂ -k _1t (x)k _2t (x)>0, the phase

There is an extreme point in the value of , and with the increase of film thickness, the phase value first decreases and then increases. phase

The extreme point is:

When the eddy current sensor 51 has extreme points of amplitude and phase at the same time, there is the following formula:

幅值法的膜厚测量范围大于相位法，否则小于。当线圈结构参数、被测金属膜材料、提离高度确定的情况下，可以通过调节激励频率的大小来调节幅值法和相位法的测量灵敏度和测量量程大小。if

The film thickness measurement range of the amplitude method is larger than that of the phase method, otherwise it is smaller. When the coil structure parameters, the measured metal film material, and the lift-off height are determined, the measurement sensitivity and measurement range of the amplitude method and the phase method can be adjusted by adjusting the excitation frequency.

In order to further improve the measurement sensitivity of the induction coil, the LC resonant circuit shown in Figure 8 is used at both ends of the induction coil, where R2 is the internal resistance of the induction coil, and C is the parallel resonance capacitor. When the frequency of the excitation signal is f, the resonant capacitor is desirable:

其中，f是激励频率，也是LC谐振回路的谐振频率。为了能够准确的测量金属薄膜的厚度，所选取的工作频率f下的趋肤深度要大于金属薄膜的最大厚度，即使得电磁场完全穿透被测金属薄膜。此外，由于线圈自身寄生参数的存在，一般还要使得激励频率f小于0.7倍的感应线圈自谐振频率f_se，这样可提升电涡流传感器51的稳定性。具体地，激励频率f可以取300kHZ至10MHz。Due to the skin effect, the eddy current intensity in the conductor decreases exponentially with the depth of the conductor. For non-magnetic materials, the formula for calculating the skin depth is:

where f is the excitation frequency, which is also the resonant frequency of the LC tank. In order to accurately measure the thickness of the metal film, the selected skin depth at the operating frequency f should be greater than the maximum thickness of the metal film, that is, the electromagnetic field completely penetrates the measured metal film. In addition, due to the existence of parasitic parameters of the coil itself, it is generally necessary to make the excitation frequency f less than 0.7 times the self-resonant frequency f _se of the induction coil, which can improve the stability of the eddy current sensor 51 . Specifically, the excitation frequency f can be 300kHz to 10MHz.

Based on the above analysis, another embodiment of the present invention also provides a method for measuring the thickness of a metal film. The method is suitable for measuring the film thickness of the wafer w using the eddy current film thickness measurement device 50, and the film layer on the surface of the wafer w is Metal materials such as copper, tungsten, aluminum, tantalum, titanium, etc. The film thickness of the wafer w may be 0 to 3 um.

As shown in FIG. 9 , the metal film thickness measurement method provided by the embodiment of the present invention includes:

Step S1, when measuring the film thickness of the metal thin film on the wafer surface based on the amplitude method or the phase method, calculate the extreme point corresponding to the amplitude method or the phase method.

The amplitude method obtains the film thickness from the amplitude of the signal output from the film thickness measuring device 50 , and the phase method obtains the film thickness from the phase of the signal output from the film thickness measuring device 50 . Specifically, the extremum points corresponding to the amplitude method or the phase method can be calculated according to the above formulas (16) and (17).

In step S2, the excitation frequency is adjusted according to the extreme point, the measurement range and/or the measurement sensitivity, wherein the measurement range is the measurement range of film thickness, the measurement sensitivity is the resolution, and the excitation frequency is used for the film thickness. The frequency of the excitation signal of the thickness measurement device.

It can be understood that the larger the measurement range, the smaller the measurement sensitivity, the smaller the measurement range and the higher the measurement sensitivity, the contradiction between the measurement range and the measurement sensitivity, and how to get the optimal combination is a difficult problem.

In one embodiment, step S2 includes: adjusting the size of the excitation frequency according to the calculated extreme point, thereby adjusting the measurement sensitivity and measurement range of the amplitude method and the phase method, so as to obtain the optimal measurement sensitivity and measurement range The combination.

Further, the required measurement film thickness range is known. The measurement film thickness range here is the thickness of the metal film that needs to be removed. For example, the metal film on the wafer surface is 2 μm thick and needs to be completely removed. Then, the required measurement The film thickness range is 0 to 2 μm. In order to make the measurement range cover the required measurement film thickness range, the extreme point should be outside the required measurement film thickness range, then a range of excitation frequencies can be calculated to obtain the maximum value in this range, so that the Maximum measurement sensitivity.

Specifically, step S2 includes:

1) Adjust the extreme point so that it falls outside the required measurement film thickness range, so as to achieve the measurement range covering the required measurement film thickness range;

2) Calculate the range of the corresponding excitation frequency, and obtain the maximum value of the range of excitation frequency to maximize the measurement sensitivity.

The embodiment of the present invention can adjust the size of the excitation frequency according to the calculated extreme point, thereby adjusting the measurement sensitivity and measurement range of the amplitude method and the phase method, and can obtain an optimal combination of measurement sensitivity and measurement range.

Figure 10 and Figure 11 show the relationship between the amplitude and phase under different excitation frequencies and the measured copper film thickness. It can be seen that both the amplitude sensitivity and the phase sensitivity will increase with the increase of the excitation frequency. In the amplitude method measurement, when the resonant frequency is 1.18MHz, the film thickness corresponding to the extreme point is between 1250nm and 1460nm. Assuming that the film thickness corresponding to the extreme point is 1350nm, then according to formula (16), it can be obtained that when the excitation frequency is 434kHz and 778kHz, the film thickness corresponding to the extreme point is 3670nm and 2048nm, respectively. As can be seen from Figure 10, when the frequency decreases, the measurable film thickness range becomes larger and larger, and the extreme point disappears between the 50nm-2000nm we need. This effectively proves that equation (16) can be used as a guide to adjust the sensitivity and range of the dual-coil sensor amplitude method measurement by adjusting the resonant frequency of the induction coil resonant circuit. In addition, the phase change increases monotonically with the increase of the film thickness in the range, and there is no extreme point, which has good thickness measurement characteristics.

Referring to Figure 10 and Figure 11, it can be seen that as the excitation frequency increases, the film thickness corresponding to the extreme point decreases, that is, the measurement range decreases, but the measurement sensitivity increases. Measurement range and measurement sensitivity are a pair of contradictory parameters. Increasing the measurement range will reduce the measurement sensitivity, while increasing the measurement sensitivity will reduce the measurement range. Therefore, it is difficult to obtain the optimal solution under the competition of the two. question. If it is manually tested one value at a time, it will not only be troublesome, take a long time to test, but also prone to excess or deficiency. Based on the specific structure of the double coil, the embodiment of the present invention derives a specific formula for calculating the extreme point, calculates the extreme point according to the formula, and then uses the extreme point to quickly and accurately obtain the amplitude method and the phase method. Optimum measurement range and measurement sensitivity.

Figure 12 shows the attenuation of the amplitude variation at the edges for three different excitation frequencies. Among them, the normalized attenuation value refers to the measured signal amplitude at the position between the radius of 130mm and 150mm divided by the signal amplitude at 130mm on the surface of a copper-plated wafer with a diameter of 300mm and an edge of 2.5mm. It can be seen that the higher the excitation frequency, the slower the edge decay. In consideration of the range, sensitivity and edge measurement characteristics of the film thickness measuring device 50, in this embodiment, it is appropriate to select an excitation frequency of 750 kHz to 800 kHz.

An embodiment of the present invention also provides a control device, which includes: a processor, a memory, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the method steps shown in FIG. 9 are implemented. The control device refers to a terminal with data processing capabilities, including but not limited to computers, workstations, servers, and even some smart phones, PDAs, tablet PCs, personal digital assistants (PDAs), smart TVs (Smart TVs) with excellent performance. )Wait. An operating system is generally installed on the control device, including but not limited to: a Windows operating system, a LINUX operating system, an Android (Android) operating system, a Symbian operating system, a Windows mobile operating system, an iOS operating system, and the like. The specific examples of the control device are listed above in detail, and those skilled in the art can realize that the control device is not limited to the above listed examples.

An embodiment of the present invention further provides a computer-readable storage medium, where the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method steps shown in FIG. 9 are implemented. The computer program can be stored in a computer-readable storage medium, and when the computer program is executed by the processor, the steps of the above-mentioned method embodiments can be implemented. Wherein, the computer program includes computer program code, and the computer program code may be in the form of source code, object code, executable file or some intermediate form, and the like. The computer-readable medium may include: any entity or device capable of carrying the computer program code, a recording medium, a U disk, a removable hard disk, a magnetic disk, an optical disk, a computer memory, a read-only memory (ROM, Read-Only Memory) , Random Access Memory (RAM, Random Access Memory), electric carrier signal, telecommunication signal and software distribution medium, etc.

Those of ordinary skill in the art can realize that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Skilled artisans may implement the described functionality using different methods for each particular application, but such implementations should not be considered beyond the scope of the present invention.

The above-mentioned embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it is still possible to implement the foregoing implementations. The technical solutions described in the examples are modified, or some technical features thereof are equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the within the protection scope of the present invention.

Claims (15)

1. a metal film thickness measurement method, is characterized in that, comprises: When measuring the film thickness of the metal thin film on the wafer surface based on the amplitude method or the phase method, calculate the extreme point corresponding to the amplitude method or the phase method; The excitation frequency is adjusted according to the extreme point, measurement range and/or measurement sensitivity, wherein the measurement range is the measurement range of film thickness, the measurement sensitivity is the resolution, and the excitation frequency is used for the film thickness measurement device the frequency of the excitation signal; The effective signal output when the film thickness measuring device detects the metal thin film is:

Among them, ΔU is the effective signal of the output voltage at both ends of the induction coil, ω is the angular frequency of the excitation signal input to the excitation coil, k _1t (x) is the mutual inductance factor between the excitation coil and the metal film, and k _2t (x) is the induction The mutual inductance factor between the coil and the metal film, x is the lift-off height, R _t is the equivalent resistance of the metal film, L _t is the equivalent inductance of the metal film, k ₁₂ is the mutual inductance factor between the excitation coil and the induction coil, L ₁ is the inductance of the excitation coil, L ₂ is the inductance of the induction coil, and I ₁ is the excitation current of the excitation signal. 2. The method for measuring metal film thickness as claimed in claim 1, wherein the size of the excitation frequency is adjusted according to the calculated extreme point, thereby adjusting the measurement sensitivity and the measurement range of the amplitude method or the phase method, to Get the best combination of measurement sensitivity and measurement range. 3. The metal film thickness measurement method according to claim 2, wherein the extreme point is adjusted to fall outside the required measurement film thickness range, so as to realize the measurement range covering the required measurement film thickness range; Calculate the range of the corresponding excitation frequency and obtain the maximum value of the range of excitation frequencies to maximize the measurement sensitivity. 4 . The method for measuring metal film thickness according to claim 1 , wherein the amplitude method is to obtain the film thickness by the amplitude of the signal output when the film thickness measuring device detects the metal film, and the phase The method is to obtain the film thickness by detecting the phase of the signal output when the metal thin film is detected by the film thickness measuring device. 5. The method for measuring metal film thickness according to claim 1, wherein,

L _t =μ ₀ ·S(r ₂ ,r ₁ ) Wherein, t is the film thickness, σ is the electrical conductivity, r ₂ is the outer diameter of the equivalent eddy current ring, r ₁ is the inner diameter of the equivalent eddy current ring, μ ₀ is the relative permeability, S(r ₂ , r ₁ ) is a custom function. 6. The metal film thickness measurement method according to claim 5, wherein the amplitude of the effective signal is:

in,

Wherein, |ΔU| is the amplitude of the effective signal, and G is a self-defined constant. 7. The method for measuring metal film thickness according to claim 6, wherein the extreme point of the amplitude of the effective signal is:

Wherein, t _U is the extreme point of the amplitude of the effective signal. 8. The method for measuring metal film thickness according to claim 5, wherein the phase of the effective signal is:

in,

in,

is the phase of the effective signal, and G is a self-defined constant. 9. The method for measuring metal film thickness according to claim 8, wherein the extreme point of the phase of the effective signal is:

in,

is the extreme point of the phase of the effective signal. 10. A film thickness measurement device, characterized in that the film thickness measurement is performed by using the metal film thickness measurement method according to any one of claims 1 to 9; the film thickness measurement device comprises an eddy current sensor and a detection circuit; The eddy current sensor includes an excitation coil and an induction coil; the excitation coil and the induction coil are both flat coils and are arranged coaxially, and the excitation coil and the induction coil are wound in the same direction. 11. The film thickness measurement device according to claim 10, wherein the detection circuit comprises an oscillator, a phase shift unit, a differential amplification unit, a cosine synchronous detection unit, a sine synchronous detection unit, a first low-pass filter and a an amplifying unit and a second low-pass filtering and amplifying unit; The oscillator is respectively connected with the excitation coil and the phase shifting unit, the phase shifting unit is respectively connected with the cosine synchronous detection unit and the sine synchronous detection unit, the differential amplification unit is respectively connected with the induction coil, the cosine synchronous detection unit and the sine synchronous detection unit, and the cosine synchronous detection unit is respectively connected with the sine synchronous detection unit. The synchronous detection unit is connected with the first low-pass filtering and amplifying unit, and the sinusoidal synchronous detection unit is connected with the second low-pass filtering and amplifying unit. 12 . The film thickness measurement device according to claim 11 , wherein the oscillator inputs an excitation voltage to the excitation coil and the phase shifting unit respectively, and the differential amplifier unit detects the output voltage at both ends of the induction coil and inputs the output voltage. 13 . To the cosine synchronous detection unit and the sine synchronous detection unit, the phase shift unit inputs the original excitation voltage signal and the phase-shifted quadrature voltage signal to the cosine synchronous detection unit and the sine synchronous detection unit respectively, and the output signal of the cosine synchronous detection unit is processed by the first A low-pass filtering and amplifying unit obtains the imaginary component Y of the output voltage of the induction coil, and the output signal of the sine synchronous detection unit obtains the real component X of the output voltage of the induction coil through the second low-pass filtering and amplifying unit, and the real component The magnitude of the output voltage of the induction coil is obtained by vector calculation of X and the imaginary component Y

with phase

13. A chemical mechanical polishing equipment, characterized in that, comprising: A polishing disc, which is used to be covered with a polishing pad for polishing the wafer; a carrier head for holding the wafer and pressing the wafer on the polishing pad; A film thickness measurement device for measuring the film thickness of the wafer during polishing; The control device is used for realizing the metal film thickness measurement method according to any one of claims 1 to 9. 14. A control device, characterized in that it comprises a memory, a processor, and a computer program stored in the memory and executable on the processor, the processor implementing the computer program as claimed in the claims Steps of the metal film thickness measurement method described in any one of 1 to 9. 15. A computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the metal film according to any one of claims 1 to 9 is implemented Steps of the Thickness Measurement Method.

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