Eddy current sensor, metal film thickness monitoring system and method

Abstract

The present invention discloses an eddy current sensor, a metal film thickness monitoring system and method. The eddy current sensor comprises: an excitation module, comprising an excitation coil, a magnetic core and a first capacitor. The magnetic core comprises a receiving portion, a constriction portion and a winding portion. The receiving portion and the constriction portion are connected to form a placement cavity. The winding portion is arranged in the placement cavity. The excitation coil is wound on the winding portion. The opening of the constriction portion on the side away from the receiving portion is smaller than the opening on the side close to the receiving portion. The receiving module comprises a receiving coil and a second capacitor. The receiving coil is arranged at the opening of the constriction portion on the side away from the receiving portion. Compared with the prior art, the eddy current sensor, the metal film thickness monitoring system and method have a narrower attenuation area at the edge of the wafer and more accurate film thickness monitoring. The distortion of thickness monitoring data caused by edge effect is effectively avoided, processing accuracy is improved, and the usable area of ​​the wafer is expanded.

Description

Technical Field

[0001] The present invention relates to the technical field of metal film thickness monitoring, and in particular to an eddy current sensor, a metal film thickness monitoring system and a method. Background Art

[0002] In the integrated circuit manufacturing process, after the metal film on the wafer substrate is deposited, it is processed by chemical mechanical polishing (CMP) process, which can effectively improve the overlay accuracy of the photolithography process. Therefore, the thickness of the metal film needs to be monitored in real time during the chemical mechanical polishing process, and the grinding is stopped at the predetermined thickness value.

[0003] The existing online measurement process of metal film on the surface of wafer usually adopts non-contact eddy current sensor module integrated in process equipment. The eddy current measurement technology of 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 surface of the metal film 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 metal film thickness by associating the metal film thickness with related electrical parameters. Among them, when the eddy current sensor detects the metal film thickness at the edge of the wafer surface, the feedback signal will be attenuated within 10mm of the edge due to the eddy current edge effect. The closer to the edge, the more serious the attenuation, resulting in the feedback signal cannot reflect the actual film thickness and causing the online measurement data to be distorted. The existing technology reduces the signal attenuation generated by the eddy current edge effect to a lower level by changing the shape of the magnetic core and minimizing the lateral width of the magnetic core to obtain a better spatial resolution in the axial direction of the wafer. However, due to the limitations of the matching of multiple parameters such as the resonant frequency of the sensor coil and the quality factor Q value, the magnetic core body cannot be reduced to a sufficient size to meet the requirements of high-order processes, so there is still a problem of serious data signal attenuation in the wafer edge area. Summary of the invention

[0004] In view of this, the embodiments of the present invention provide an eddy current sensor, a metal film thickness monitoring system and method to solve the problem that the edge signal of the current mainstream eddy current sensor is severely attenuated and cannot meet high-order process requirements.

[0005] The technical solution proposed by the present invention is as follows:

[0006] A first aspect of an embodiment of the present invention provides an eddy current sensor, comprising an excitation module and a receiving module:

[0007] An excitation module, comprising an excitation coil, a magnetic core and a first capacitor, wherein the magnetic core comprises a receiving portion, a constriction portion and a winding portion, wherein the receiving portion and the constriction portion are connected to form a placement cavity, wherein the winding portion is arranged in the placement cavity, wherein the excitation coil is wound around the winding portion, wherein an opening of the constriction portion on a side away from the receiving portion is smaller than an opening on a side close to the receiving portion, and wherein the first capacitor and the excitation coil are connected to form a first LC oscillation circuit;

[0008] The receiving module comprises a receiving coil and a second capacitor, wherein the receiving coil is arranged at an opening of the bundle opening away from the accommodating portion, and the second capacitor is connected to the receiving coil to form a second LC oscillation circuit.

[0009] An eddy current sensor according to the first aspect of the embodiment of the present invention improves the existing eddy current sensor module into an excitation module and a receiving module, and realizes the functions of the excitation and receiving parts by two different modules respectively. The principle is that the magnetic core of the excitation coil is set to have a structure with a constriction part, thereby improving the spatial resolution of monitoring the edge of the metal film. Compared with the existing sensor, the magnetic core of the eddy current sensor almost completely wraps the excitation coil, so the influence of the eddy current feedback signal generated on the surface of the metal film on the excitation coil will be significantly reduced. Because the constriction part is a closing shape with one side large and the other side small, a receiving coil is added at the constriction to receive and monitor the changes in the eddy current parameters on the surface of the metal film. Since the receiving coil does not need to realize the excitation effect, it is not necessary to set a magnetic core, and its size is easy to change. Only by changing the size of the receiving coil, the data monitored on the edge of the metal film can be made narrower and more accurate. Compared with the prior art, when monitoring the thickness of the metal film of the wafer, the eddy current sensor has a narrower attenuation area at the edge of the wafer and more accurate film thickness monitoring, which effectively avoids the distortion of the thickness monitoring data caused by the edge effect, improves the processing accuracy, and expands the available area of ​​the wafer.

[0010] According to an eddy current sensor provided by a first aspect of an embodiment of the present invention, the farther the distance between the opening of the constriction portion and the accommodating portion is from the accommodating portion, the smaller the opening is.

[0011] In the embodiment of the present invention, the size of the opening of the side of the tie-mouth portion away from the accommodating portion is set according to the distance from the accommodating portion. The farther the distance, the smaller the opening, so that the structure of the tie-mouth portion is simple and easy to manufacture.

[0012] A second aspect of an embodiment of the present invention provides a metal film thickness monitoring system, comprising a waveform generation module, a signal acquisition and processing module, a main control module and an eddy current sensor as provided in the second aspect of an embodiment of the present invention;

[0013] The waveform generating module, whose input end is connected to the main control module, is used to output a first AC signal and a second AC signal with two equal amplitudes and opposite directions;

[0014] The excitation module comprises a first LC oscillation circuit composed of an excitation coil and a first capacitor, wherein an input end of the first LC oscillation circuit is connected to an output end of the waveform generating module, and is used to receive the first AC signal, and based on the first AC signal, excite the metal film to generate an alternating magnetic field and output a first output signal;

[0015] The receiving module includes a second LC oscillation circuit composed of a receiving coil and a second capacitor, the input end of the second LC oscillation circuit is connected to the other output end of the waveform generating module, and is used to receive the alternating magnetic field and the second AC signal generated by the metal film to be measured, and output a second output signal based on the second AC signal and the alternating magnetic field;

[0016] The signal acquisition and processing module has one input end connected to the excitation module and another input end connected to the receiving module, and is used to acquire the first output signal and the difference signal between the first output signal and the second output signal, and output the acquired signal to the main control module;

[0017] The main control module is used to control the waveform generating module to output the first AC signal and the second AC signal, and to calculate the thickness of the metal film to be measured according to the first output signal and the difference signal.

[0018] The embodiment of the present invention adopts an eddy current sensor including an excitation module and a receiving module, and the input signals of the excitation module and the receiving module are respectively a first AC signal and a second AC signal of two equal amplitudes and opposite directions, and the functions of the excitation and receiving parts are respectively implemented by two different modules, thereby reducing signal interference and simplifying the circuit structure. In addition, the receiving coil of the present invention does not need to realize the excitation effect, so there is no need to set a magnetic core, and there is no need to consider parameter restrictions such as the resonant frequency and the quality factor Q value. Its size is easy to change, and only the size of the coil in the receiving module needs to be changed to measure the azimuth at the edge of the metal film more narrowly and more accurately, thereby reducing the influence of data attenuation in the edge area of ​​the metal film on the measurement results. Compared with the prior art, when monitoring the thickness of the metal film of the wafer, the metal film thickness monitoring system has a narrower attenuation area at the edge of the wafer and more accurate film thickness monitoring, which effectively avoids the distortion of thickness monitoring data caused by the edge effect, improves processing accuracy, and expands the available area of ​​the wafer.

[0019] According to the metal film thickness monitoring system provided by the second aspect of the embodiment of the present invention, the waveform generating module includes: a waveform generator, a power amplifier, an amplitude stabilization circuit, a reference circuit and an inverter, the waveform generator, the power amplifier and the amplitude stabilization circuit are connected in series in sequence, one input end of the amplitude stabilization circuit is connected to the reference circuit, one output end of the amplitude stabilization circuit is connected to the excitation module, and the other output end is connected to the receiving module through an inverter.

[0020] In the metal film thickness monitoring system of the embodiment of the present invention, the waveform generator realizes sinusoidal wave output according to the configuration parameters of the main control module, and amplifies the power of the input sinusoidal wave signal through the power amplifier. The function of the amplitude stabilization circuit and the reference circuit is to stabilize the sinusoidal amplitude within the set appropriate value. The function of the inverter is to excite the alternating sinusoidal waveform to produce a 180° phase shift, so that the output signal is equal to the original excitation signal in amplitude and opposite in direction.

[0021] According to the metal film thickness monitoring system provided in the second aspect of the embodiment of the present invention, the signal acquisition and processing module includes: a first acquisition module, a second acquisition module, a first differential amplifier circuit, a second differential amplifier circuit, a third differential amplifier circuit and a fourth differential amplifier circuit, the input end of the first acquisition module is connected to the excitation module, and the output end is respectively connected to the first differential amplifier circuit and the second differential amplifier circuit, the input end of the second acquisition module is connected to the receiving module, and the output end is connected to the third differential amplifier circuit, the output end of the first differential amplifier circuit is connected to an input end of the main control module, the output end of the second differential amplifier circuit is connected to an input end of the fourth differential amplifier circuit, the output end of the third differential amplifier circuit is connected to another input end of the fourth differential amplifier circuit, and the output end of the fourth differential amplifier circuit is connected to another input end of the main control module.

[0022] The metal film thickness monitoring system of the embodiment of the present invention, after the first acquisition module and the second acquisition module acquire relevant signals, amplifies the acquired signals through the first differential amplifier circuit, the second differential amplifier circuit, the third differential amplifier circuit and the fourth differential amplifier circuit, so as to facilitate the subsequent circuit use detection, and uses the differential amplifier design to filter out common mode interference from the hardware, thereby increasing the anti-interference capability.

[0023] According to the second aspect of the embodiment of the present invention, the metal film thickness monitoring system provided also includes an AD conversion module, and the AD conversion module includes a first AD conversion module and a second AD conversion module; the input end of the first AD conversion module is connected to the output end of the first differential amplifier circuit, and the output end is connected to an input end of the main control module, for converting the first output signal into a digital signal; the input end of the second AD conversion module is connected to the output end of the fourth differential amplifier circuit, and the output end is connected to another input end of the main control module, for converting the difference signal into a digital signal.

[0024] The metal film thickness monitoring system of the embodiment of the present invention converts the amplified analog signal into a digital signal through the first AD conversion module and the second AD conversion module, so as to facilitate processing by the main control module.

[0025] According to the metal film thickness monitoring system provided by the second aspect of the embodiment of the present invention, the main control module includes a host computer and a communication control unit, the communication control unit includes a waveform control module, a signal processing module and a storage module, the waveform control module is used to control the first AC signal and the second AC signal output by the waveform generating module, the signal processing module is used to perform difference processing on the first output signal and the difference signal to obtain a signal processing result, the storage module is used to store the signal processing result, and the host computer is used to obtain the measured metal film thickness based on the linear relationship analysis between the signal processing result and the metal film thickness.

[0026] A third aspect of an embodiment of the present invention provides a method for measuring the thickness of a metal film, comprising:

[0027] Generate a first alternating current signal and a second alternating current signal of equal amplitude and opposite direction;

[0028] Based on the first AC signal, the metal film under test is stimulated to generate an alternating magnetic field and generate a first output signal;

[0029] generating a second output signal based on the second AC signal and the alternating magnetic field;

[0030] collecting the first output signal and a difference signal between the first output signal and the second output signal;

[0031] The thickness of the metal film to be measured is calculated according to the first output signal and the difference signal.

[0032] The embodiment of the present invention outputs two first AC signals and second AC signals with equal amplitude and opposite directions, and excites the metal film to generate an alternating magnetic field and outputs a first output signal based on the first AC signal; outputs a second output signal based on the second AC signal and the alternating magnetic field, and implements the functions of the excitation and receiving parts with two different modules respectively, thereby reducing signal interference. In addition, the second output signal is output based on the second AC signal and the alternating magnetic field, so the receiving coil of the second output signal does not need to be provided with a magnetic core, and does not need to consider parameter restrictions such as the resonant frequency and the quality factor Q value. Its size is easy to change, and only the size of the coil in the receiving module needs to be changed to measure the azimuth at the edge of the metal film, which is narrower and more accurate. Compared with the prior art, when monitoring the thickness of the metal film of the wafer, the metal film thickness monitoring method has a narrower attenuation area at the edge of the wafer and more accurate film thickness monitoring, which effectively avoids the distortion of the thickness monitoring data caused by the edge effect, improves the processing accuracy, and expands the available area of ​​the wafer.

[0033] According to a third aspect of an embodiment of the present invention, a method for measuring the thickness of a metal film is provided, wherein the thickness of the metal film to be measured is calculated according to the first output signal and the difference signal, and includes:

[0034] Performing difference processing on the first output signal and the difference signal to obtain a signal processing result;

[0035] Performing edge compensation on the signal processing result to obtain a compensated signal processing result;

[0036] The linear relationship between the signal processing result and the thickness of the metal film is pre-stored, and the thickness of the metal film is obtained according to the compensated signal processing result and the linear relationship.

[0037] According to a third aspect of an embodiment of the present invention, a metal film thickness measurement method is provided, wherein edge compensation is performed on the signal processing result to obtain a compensated signal processing result, including:

[0038] Pre-calibrating to obtain compensation coefficients of the signal processing results at metal films of different thicknesses and at different edge positions, the compensation coefficients being the ratio of the actually measured signal processing results to the nominal thickness feedback signal;

[0039] Obtain the resonant frequency, standard thickness and edge position information of the current signal processing result, and obtain the corresponding compensation coefficient according to the resonant frequency, standard thickness and edge position information;

[0040] The current signal processing result is divided by the corresponding compensation coefficient to obtain the compensated signal processing result.

[0041] The embodiment of the present invention adds edge compensation to the signal processing result, which can reduce the influence of edge loss on the measurement result, improve edge detection accuracy, and meet high-order process requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly express the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0043] Figure 1 is a cross-sectional view of an eddy current sensor according to an embodiment of the present invention;

[0044] Figure 2 It is a schematic diagram of the structure of an eddy current sensor in an embodiment of the present invention;

[0045] Figure 3 is a cross-sectional view of another eddy current sensor according to an embodiment of the present invention;

[0046] Figure 4 It is a schematic diagram of the structure of another eddy current sensor in an embodiment of the present invention;

[0047] Figure 5 This is a diagram showing the eddy current influence area of ​​the eddy current sensor in the prior art;

[0048] Figure 6 For the present invention Figure 1 The eddy current sensor shows the eddy current influence area;

[0049] Figure 7 For the present invention Figure 1 A comparison chart of edge attenuation data of the eddy current sensor in the embodiment and the eddy current sensor in the prior art;

[0050] Figure 8 A block diagram of a metal film thickness monitoring system according to an embodiment of the present invention;

[0051] Fig. 9 : is a circuit schematic diagram of a metal film thickness monitoring system according to an embodiment of the present invention;

[0052] Fig.10 Flow chart of a method for measuring thickness of a metal film according to an embodiment of the present invention;

[0053] Fig.11 It is a schematic diagram of attenuation data at different thicknesses in an embodiment of the present invention. DETAILED DESCRIPTION

[0054] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. 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.

[0055] The embodiment of the present invention provides an eddy current sensor to solve the problem that the edge signal of the current mainstream eddy current sensor is severely attenuated when detecting the metal film thickness at the edge of the wafer surface and cannot meet the requirements of high-order processes.

[0056] See also Figure 1 and Figure 2 , the eddy current sensor includes an excitation module and a receiving module:

[0057] An excitation module includes an excitation coil L1, a magnetic core 1 and a first capacitor (not shown in the figure), the magnetic core 1 includes a housing portion 12, a constriction portion 13 and a winding portion 11, the housing portion 12 and the constriction portion 13 are connected to form a placement cavity, the winding portion 11 is arranged in the placement cavity, the excitation coil L1 is wound on the winding portion 11, the opening of the constriction portion 13 on a side away from the housing portion 12 is smaller than the opening on a side close to the housing portion 12, and the first capacitor and the excitation coil L1 are connected to form a first LC oscillation circuit;

[0058] The receiving module includes a receiving coil L2 and a second capacitor (not shown in the figure). The receiving coil L2 is arranged at the opening of the bundle mouth portion 13 on the side away from the accommodating portion 12. The second capacitor and the receiving coil L2 are connected to form a second LC oscillation circuit.

[0059] Specifically, the first capacitor and the second capacitor can be arranged at any place of the eddy current sensor, and are electrically connected to the excitation coil L1 and the receiving coil L2 respectively to form an LC oscillation circuit.

[0060] In an optional embodiment, the magnetic core 1 includes a housing portion 12, a collar portion 13 and a winding portion 11, which are an integrated structure. The winding portion 11 is columnar and is arranged on the inner side of the top of the housing portion 12. Of course, in other embodiments, the housing portion 12, the collar portion 13 and the winding portion 11 can also be detachable structures, and the winding portion 11 can also be in other shapes such as a cube, an L-shape, etc., and the setting position can also be the side wall of the housing portion 12 or the collar portion 13, etc.

[0061] In an alternative embodiment, see Figure 1 and Figure 2The cross-sectional shapes of the accommodating portion 12 and the constricting portion 13 are both circular. The accommodating portion 12 is a cylinder with an opening at the bottom, the constricting portion 13 is a circular funnel, and the winding portion 11 is a cylinder, which is arranged on the inner side of the top of the accommodating portion 12.

[0062] In an alternative embodiment, see Figure 3 and Figure 4 The cross-sectional shapes of the accommodating portion 12 and the constricting portion 13 are both rectangular. The accommodating portion 12 is a square shell with an opening at the bottom, the constricting portion 13 is a square funnel, and the winding portion 11 is a cuboid and is arranged on the inner side of the top of the accommodating portion 12.

[0063] It should be noted that the cross-sectional shapes of the accommodating portion 12 and the constricting opening 13 are not limited to circular and rectangular, and may also be square, straight-slot-shaped, and the like.

[0064] In an optional embodiment, the opening of the tie mouth 13 away from the accommodating portion 12 is smaller as the distance from the accommodating portion 12 increases. For example, the tie mouth 13 may be funnel-shaped or bowl-shaped, so that the tie mouth 13 has a simple structure and is easy to manufacture.

[0065] In an optional embodiment, the material of the magnetic core 1 is ferrite, which has a resistivity much greater than that of general metal magnetic materials and has the advantage of small eddy current loss. Of course, other common magnetic core materials can also be selected in other embodiments.

[0066] When using the eddy current sensor of this embodiment to monitor the thickness of the metal film on the surface of the wafer, two first AC signals and second AC signals with equal amplitudes and opposite directions are applied to the excitation coil L1 and the receiving coil L2 respectively. The eddy current sensor is first calibrated to the air so that the sampling voltage output by the receiving coil L2 is zero, and then the receiving module is aligned with the metal film on the surface of the wafer. When the metal film on the surface of the wafer approaches the sensor, the excitation coil L1 excites the metal film to generate eddy current. At the same time, the eddy current in the metal film will generate an induced electromotive force inside the receiving coil again. At this time, the sampling voltage output by the receiving coil L2 is equivalent to the induced electromotive force that the eddy current in the metal film will generate inside the receiving coil again. By correlating the induced electromotive force with the thickness of the metal film, the thickness of the metal film can be obtained by processing the induced electromotive force.

[0067] Compared with the existing eddy current sensors, the eddy current sensor of the embodiment of the present invention can significantly reduce the eddy current influence area on the metal film surface, thereby improving the spatial resolution and effectively reducing the signal attenuation caused by the edge effect of the eddy current at the edge of the wafer. Taking the copper film as an example, Figure 5 The eddy current sensor of the prior art, the ferrite core 1 without a tie and the receiving coil L2, the eddy current generated on the surface of the copper film of the wafer, Figure 6This is a comparison of the embodiments of the present invention under the same parameters. The affected area obviously has a higher spatial accuracy. Figure 7 : is the edge signal attenuation value of the eddy current sensor in the prior art and the embodiment of the present invention. From the comparison shown, it can be seen that the attenuation ratio of the eddy current feedback signal at the edge of the wafer is significantly reduced, and setting a suitable receiving coil L2 will obtain better edge monitoring data.

[0068] An eddy current sensor according to the first aspect of the embodiment of the present invention improves the existing eddy current sensor module into an excitation module and a receiving module, and realizes the functions of the excitation and receiving parts by two different modules respectively. The principle is to improve the spatial resolution of monitoring the edge of the metal film by setting the magnetic core 1 of the excitation coil L1 to have a structure with a constriction portion 13. Compared with the existing sensors, the magnetic core 1 of the eddy current sensor almost completely wraps the excitation coil L1, so the influence of the eddy current feedback signal generated on the surface of the metal film on the excitation coil L1 will be significantly reduced. Because the constriction portion 13 is a closing shape with one side larger and the other side smaller, a receiving coil L2 is added at the constriction to receive and monitor the changes in the eddy current parameters on the surface of the metal film. Since the receiving coil L2 does not need to realize the excitation effect, the magnetic core 1 does not need to be set, and its size is easy to change. Only by changing the size of the receiving coil L2, the data monitored on the edge of the metal film can be made narrower and more accurate. Compared with the existing technology, when monitoring the thickness of the metal film on the wafer, the eddy current sensor has a narrower attenuation area at the edge of the wafer and more accurate film thickness monitoring, which effectively avoids the distortion of thickness monitoring data caused by edge effects, improves processing accuracy, and expands the available area of ​​the wafer.

[0069] The embodiment of the present invention also provides a metal film thickness monitoring system, such as Figure 8 As shown, the metal film thickness monitoring system includes a waveform generating module, a signal acquisition and processing module, a main control module and an eddy current sensor as provided in the above embodiment.

[0070] The waveform generating module has an input end connected to the main control module and is used to output a first AC signal and a second AC signal with two equal amplitudes and opposite directions.

[0071] In an exemplary embodiment, the waveform generation module includes: a waveform generator, a power amplifier, an amplitude stabilization circuit, a reference circuit and an inverter. The waveform generator, the power amplifier and the amplitude stabilization circuit are connected in series in sequence. One input end of the amplitude stabilization circuit is connected to the reference circuit, one output end of the amplitude stabilization circuit is connected to the excitation module, and the other output end is connected to the receiving module through an inverter. Exemplarily, in this embodiment, the waveform generator uses an arbitrary waveform generator based on direct digital synthesis technology (Direct Digital Synthesis, DDS), the power amplifier uses an OPA power amplifier, and the amplitude stabilization circuit uses an automatic gain control (Automatic Generation Control, AGC) amplitude stabilization circuit. In other embodiments, these circuits can be set according to actual needs as long as they can meet the corresponding functions.

[0072] Specifically, the waveform generator realizes sinusoidal output according to the configuration parameters of the main control module, and amplifies the power of the input sinusoidal wave signal through the power amplifier. The function of the amplitude stabilization circuit and the reference circuit is to stabilize the sinusoidal amplitude within the set appropriate value. The function of the inverter is to excite the alternating sinusoidal waveform to produce a 180° phase shift, so that the output signal is equal to the original excitation signal in amplitude and opposite in direction.

[0073] like Fig. 9 As shown, the excitation module includes a first LC oscillation circuit composed of an excitation coil L1 and a first capacitor C1. The input end of the first LC oscillation circuit is connected to an output end of the waveform generating module, and is used to receive a first AC signal, and based on the first AC signal, excite the metal film under test to generate an alternating magnetic field and output a first output signal.

[0074] The receiving module includes a second LC oscillation circuit composed of a receiving coil L2 and a second capacitor C2. The input end of the second LC oscillation circuit is connected to another output end of the waveform generating module, and is used to receive the alternating magnetic field and the second AC signal generated by the metal film under test, and output a second output signal based on the second AC signal and the alternating magnetic field.

[0075] The signal acquisition and processing module has one input end connected to the excitation module and another input end connected to the receiving module, and is used to acquire the first output signal and the difference signal between the first output signal and the second output signal, and output the acquired signal to the main control module.

[0076] It should be noted that the signal acquisition and processing module includes two parts, one part is used to acquire the first output signal of the excitation module, and the other part is used to acquire the first output signal of the excitation module and the second output signal of the receiving module, and to make a difference between them to obtain a difference signal. After acquiring the signal, in different implementations, the signal acquisition and processing module can amplify these signals, filter noise, etc. according to actual needs.

[0077] The main control module is used to control the waveform generation module to output the first AC signal and the second AC signal, and to calculate the thickness of the metal film to be measured according to the first output signal and the difference signal.

[0078] Specifically, the first output signal and the difference signal are subjected to difference processing, and the difference after difference processing has a certain linear relationship with the thickness of the metal film on the wafer surface. The corresponding relationship between the difference and the thickness is stored in the main control module in advance, and the thickness of the measured metal film is obtained based on the difference and the corresponding relationship.

[0079] The embodiment of the present invention improves the existing eddy current sensor module into an excitation module and a receiving module. The input signals of the excitation module and the receiving module are respectively a first AC signal and a second AC signal with two equal amplitudes and opposite directions. The functions of the excitation and receiving parts are respectively implemented by two different modules, which reduces signal interference and simplifies the circuit structure. In addition, the receiving coil L2 of the present invention does not need to realize the excitation effect, so there is no need to set the magnetic core 1, and there is no need to consider the parameter restrictions such as the resonant frequency and the quality factor Q value. Its size is easy to change. It only needs to change the size of the coil in the receiving module to measure the azimuth at the edge of the metal film. The result is narrower and more accurate, and the influence of the data attenuation in the edge area of ​​the metal film on the measurement result is reduced. Compared with the prior art, when monitoring the thickness of the metal film of the wafer, the metal film thickness monitoring system has a narrower attenuation area at the edge of the wafer and more accurate film thickness monitoring, which effectively avoids the distortion of the thickness monitoring data caused by the edge effect, improves the processing accuracy, and expands the available area of ​​the wafer.

[0080] In one embodiment, the signal acquisition and processing module includes: a first acquisition module, a second acquisition module, a first differential amplifier circuit, a second differential amplifier circuit, a third differential amplifier circuit and a fourth differential amplifier circuit. The input end of the first acquisition module is connected to the excitation module, and the output end is respectively connected to the first differential amplifier circuit and the second differential amplifier circuit. The input end of the second acquisition module is connected to the receiving module, and the output end is connected to the third differential amplifier circuit. The output end of the first differential amplifier circuit is connected to an input end of the main control module, the output end of the second differential amplifier circuit is connected to an input end of the fourth differential amplifier circuit, the output end of the third differential amplifier circuit is connected to another input end of the fourth differential amplifier circuit, and the output end of the fourth differential amplifier circuit is connected to another input end of the main control module.

[0081] Specifically, Fig. 9 As shown, the first acquisition module includes an adjustable resistor RS1, one fixed end of the adjustable resistor RS1 is respectively connected to the excitation module, the positive input end of the first differential amplifier circuit and the positive input end of the second differential amplifier circuit, and the other fixed end is grounded. The second acquisition module includes an adjustable resistor RS2, one fixed end of the adjustable resistor RS2 is respectively connected to the receiving module and the positive input end of the third differential amplifier circuit, and the other fixed end is grounded. The first differential amplifier circuit, the second differential amplifier circuit, the third differential amplifier circuit and the fourth differential amplifier circuit are respectively composed of operational amplifiers U1-U4 and their peripheral circuits, wherein the negative input ends of the first differential amplifier circuit, the second differential amplifier circuit and the third differential amplifier circuit are all grounded through a resistor, the first differential amplifier circuit, the second differential amplifier circuit and the third differential amplifier circuit are all used to amplify the positive input signal, the input ends of the fourth differential amplifier circuit are respectively the first output signal and the second output signal amplified by the second differential amplifier circuit and the third differential amplifier circuit, and the fourth differential amplifier circuit is used to amplify the difference signal between the first output signal and the second output signal again.

[0082] The metal film thickness monitoring system of the embodiment of the present invention, after the first acquisition module and the second acquisition module acquire the first output signal and the second output signal, amplifies the acquired signals through the first differential amplifier circuit, the second differential amplifier circuit, the third differential amplifier circuit and the fourth differential amplifier circuit, so as to facilitate the subsequent circuit use detection, and uses the differential amplifier design to filter out common mode interference from the hardware, thereby increasing the anti-interference capability.

[0083] In an optional embodiment, an AD conversion module is also included, and the AD conversion module includes a first AD conversion module and a second AD conversion module; the input end of the first AD conversion module is connected to the output end of the first differential amplifier circuit, and the output end is connected to an input end of the main control module, for converting the first output signal into a digital signal; the input end of the second AD conversion module is connected to the output end of the fourth differential amplifier circuit, and the output end is connected to another input end of the main control module, for converting the difference signal into a digital signal.

[0084] Furthermore, before the collected signal is input into the first AD conversion module and the second AD conversion module, it is also necessary to perform AC-DC conversion. Since the collected signal is in the form of a sine wave, the first output signal needs to pass through the diode D1 and the capacitor C4, and the difference signal needs to pass through the diode D2 and the capacitor C6 to become a DC pulsation. The capacitor C value is adjusted so that the pulsation value becomes a corresponding DC voltage value, which is convenient for the first AD conversion module and the second AD conversion module to sample. Then, the amplified analog signal is converted into a digital signal through the first AD conversion module and the second AD conversion module, which is convenient for the main control module to process.

[0085] In an optional embodiment, the main control module includes a host computer and a communication control unit, the communication control unit includes a waveform control module, a signal processing module and a storage module, the waveform control module is used to control the first AC signal and the second AC signal output by the waveform generating module, the signal processing module is used to perform difference processing on the first output signal and the difference signal to obtain a signal processing result, the storage module is used to store the signal processing result, and the host computer is used to obtain the thickness of the measured metal film based on the linear relationship analysis between the signal processing result and the thickness of the metal film.

[0086] Specifically, the communication control unit is an FPGA unit, which is connected to the host computer through a communication interface. The waveform control module includes a waveform generator control module, a clock control generation module and a frequency sweep drive module. First, the resonant frequency of the first LC oscillation circuit is determined according to the impedance matching of the circuit and the magnetic core 1 and the load power range during wafer detection. The resonant frequency is generally in the range of 200kHZ to 1MHZ. The formula for determining the resonant frequency is: L is the equivalent inductance value inside the sensor, and C is the equivalent capacitance value inside the sensor. The waveform generator generates excitation sinusoidal logic through the waveform generator control module, the clock control generation module, and the sweep frequency drive module, so that the waveform generator generates the required sinusoidal wave, further excites the coil L1 to reach the resonant state and locks the resonant frequency f0.

[0087] The signal processing module includes a data filtering channel 1, a data filtering channel 2 and a difference module. The data filtering channel 1 and the data filtering channel 2 filter the signals output from the first AD conversion module and the second AD conversion module respectively. The difference module differs the filtered signals to obtain a signal processing result.

[0088] The storage module uses a first-in-first-out (FIFO) memory to store the signal processing results and send the signal processing results to the host computer. The host computer obtains the measured metal film thickness based on the linear relationship analysis between the signal processing results and the metal film thickness.

[0089] In an optional embodiment, the host computer includes: a linear relationship storage unit, which is used to pre-store the linear relationship between the signal processing result and the metal film thickness; a compensation coefficient storage unit, which is used to pre-calibrate and obtain the compensation coefficient of the signal processing result for metal films of different thicknesses and different edge positions, wherein the compensation coefficient is the ratio of the actually measured signal processing result to the nominal thickness feedback signal; a compensation coefficient acquisition unit, which is used to obtain the resonant frequency, standard thickness and edge position information of the current signal processing result measurement, and obtain the corresponding compensation coefficient according to the resonant frequency, standard thickness and edge position information; a compensation result acquisition unit, which is used to divide the current signal processing result by the corresponding compensation coefficient to obtain the compensated signal processing result; a thickness acquisition unit, which is used to obtain the thickness of the metal film according to the compensated signal processing result and the linear relationship.

[0090] By adding edge compensation to the signal processing results, the host computer can reduce the impact of edge loss on the measurement results, improve edge detection accuracy, and meet high-order process requirements.

[0091] The working principle of the metal film thickness monitoring system of the embodiment of the present invention is:

[0092] Before measuring the thickness of the metal film on the wafer surface, the eddy current sensor is first calibrated in the air. During the air calibration, the receiving coil L2 and the excitation coil L1 are not aligned with the metal film, so no eddy current is generated. At this time, the second output signal generated by the receiving coil L2 is the vector sum of the self-voltage divider U1 and the excitation coil L1 mutual inductance coupling voltage U2, that is: Uo = U1 + U2. Since the self-voltage divider U1 and the excitation mutual inductance coupling voltage U2 are vectors, adjusting the resistance values ​​of resistors RS1 and RS2 can make the Uo value zero. That is, Uo = U1 + U2 = 0.

[0093] The first output signal Us output by the excitation coil L1 and the second output signal Uo of the receiving coil L2 are Uso after passing through the second differential amplifier circuit, the third differential amplifier circuit, the fourth differential amplifier circuit and the second AD conversion module. Therefore, when the eddy current sensor is calibrated in the air, Uso=nUs-nUo=nUs, where n is the total amplification factor of the second differential amplifier circuit, the third differential amplifier circuit and the fourth differential amplifier circuit.

[0094] Assume that the value after passing through the first AD conversion module is DATA1, and the value after passing through the second AD conversion module is DATA2. It is only necessary to make the amplification factor of the first differential amplifier circuit equal to the total amplification factor of the second differential amplifier circuit, the third differential amplifier circuit and the fourth differential amplifier circuit, that is, the amplification factor of the first differential amplifier circuit is n, then DATA1=nUs, DATA2=Uso=nUs, and the difference can be zero inside the main control module, that is, DATA1-DATA2=ΔDATA=0.

[0095] When measuring the thickness of the metal film on the wafer surface, the eddy current sensor is placed close to the metal film on the wafer surface. The excitation coil L1 generates eddy current in the metal film. At the same time, the eddy current in the metal film will generate an induced electromotive force U3 inside the receiving coil L2 again. At this time, the second output signal Uo' generated by the receiving coil L2 is the superposition vector sum of its own voltage divider U1, the mutual inductance coupling voltage U2 of the excitation coil L1, and the induced electromotive force U3 generated again inside the receiving coil L2 by the eddy current in the metal film, that is: Uo'=U1+U2+U3.

[0096] At this time, the first output signal Us output by the exciting coil L1 and the second output signal Uo of the receiving coil L2 are Uso'=nUs-nUo' after passing through the second differential amplifier circuit, the third differential amplifier circuit, the fourth differential amplifier circuit and the second AD conversion module.

[0097] Because U1+U2=0, Uso'=nUs-nU3, DATA1'-DATA2'=nUs-Uso'=nU3=ΔDATA≠0. The value of ΔDATA is linearly related to the wafer thickness under certain conditions. The main control module pre-stores the corresponding relationship between the value of ΔDATA and the thickness of the wafer metal film, and then the wafer metal film thickness can be obtained according to the measured value of ΔDATA.

[0098] like Fig.10 As shown, an embodiment of the present invention further provides a method for measuring the thickness of a metal film, comprising:

[0099] Step S1, generating a first AC signal and a second AC signal with equal amplitude and opposite directions;

[0100] Step S2, based on the first AC signal, exciting the metal film to generate an alternating magnetic field and generate a first output signal;

[0101] Step S3, generating a second output signal based on the second AC signal and the alternating magnetic field;

[0102] Step S4, collecting the first output signal and the difference signal between the first output signal and the second output signal;

[0103] Step S5, calculating the thickness of the metal film to be measured according to the first output signal and the difference signal.

[0104] The embodiment of the present invention outputs two first AC signals and second AC signals of equal amplitude and opposite directions, and excites the metal film to generate an alternating magnetic field and outputs a first output signal based on the first AC signal; outputs the second output signal based on the second AC signal and the alternating magnetic field, and implements the functions of the excitation and receiving parts with two different modules respectively, thereby reducing signal interference. In addition, the second output signal is output based on the second AC signal and the alternating magnetic field, so the receiving coil L2 of the second output signal does not need to be provided with a magnetic core 1, and does not need to consider parameter restrictions such as the resonant frequency and the quality factor Q value, and its size is easy to change. It only needs to change the size of the coil in the receiving module to measure the azimuth at the edge of the metal film, and the result is narrower and more accurate. Compared with the prior art, when monitoring the thickness of the metal film of the wafer, the metal film thickness monitoring method has a narrower attenuation area at the edge of the wafer and more accurate film thickness monitoring, which effectively avoids the distortion of the thickness monitoring data caused by the edge effect, improves the processing accuracy, and expands the available area of ​​the wafer.

[0105] In one embodiment, calculating the thickness of the metal film to be measured according to the first output signal and the difference signal includes:

[0106] Performing difference processing on the first output signal and the difference signal to obtain a signal processing result;

[0107] Performing edge compensation on the signal processing result to obtain a compensated signal processing result;

[0108] The linear relationship between the signal processing result and the metal film thickness is pre-stored, and the metal film thickness is obtained according to the compensated signal processing result and the linear relationship.

[0109] Specifically, edge compensation is performed on the signal processing result to obtain the compensated signal processing result, including:

[0110] First, the compensation coefficient of the signal processing result at different thicknesses of metal films and different edge positions is obtained in advance through calibration, wherein the compensation coefficient is the ratio of the actually measured signal processing result to the nominal thickness feedback signal.

[0111] Specifically, firstly, the resonant frequency of the eddy current sensor oscillation circuit is determined according to the impedance matching of the circuit and the magnetic core 1 and the load power range during wafer detection (the resonant frequency is generally in the range of 200kHZ to 1MHZ). Specifically, the resonant frequency L is the equivalent inductance value inside the eddy current sensor, and C is the equivalent capacitance value inside the eddy current sensor. Because different resonant frequency oscillation circuits have different characteristic curves when measuring changes in metal film thickness, when the no-load resonant frequency is determined, the sensor in use will only change slightly near the resonant frequency and will not have a significant impact on the thickness and eddy current characteristic curve. At the same resonant frequency, there is a unique confirmed compensation coefficient relationship between metals of different thicknesses and edge positions. Specifically, For example, Where T 147mm is the signal value of the eddy current sensor at the position of 147mm after attenuation compensation, S 147 is the original eddy current signal value at the 147mm position, Ψ (147mm，500nm) is the attenuation coefficient of the eddy current sensor at the 147mm position of the 500nm thick copper film and 300mm diameter wafer. The specific data of the attenuation coefficient is obtained by querying the attenuation coefficient table obtained by prior calibration. Different resonant frequencies have different attenuation coefficient tables. First, obtain the corresponding attenuation coefficient table according to the resonant frequency, and then query the attenuation coefficient according to the attenuation coefficient table. The attenuation coefficient table is obtained by the calibration process. The specific calibration process is as follows: 1. Select standards of different thicknesses and measure the edge thickness at intervals of 1mm (the deviation is less than 2%); 2. Use a fixed-point measurement method, for example, take the center of the calibration standard wafer as the 0 point, establish the XY coordinates, measure the XY axis at intervals of 1mm, and compare the eddy current signal feedback values ​​of the corresponding points of -135mm~-150mm and 135mm~150mm with the ratio of the nominal thickness feedback signal of the calibration piece; 3. After the ratio is normalized, the attenuation ratio of the edge position corresponding to different thicknesses is the ratio of the edge coordinate position feedback signal to the nominal thickness feedback signal. The edge compensation calibration is completed and the attenuation data table is obtained, such as Fig.11 In the figure, 2000A-20000A represents the attenuation ratio of the corresponding edge position of wafers with different thicknesses.

[0112] According to the attenuation data table, when the attenuation coefficient of the calibration point is known, the specific attenuation coefficient of the non-calibration point is obtained by the bilinear difference algorithm (y = f (x1, x2), where x1 is the position coordinate, x2 is the wafer thickness, y is the attenuation coefficient, f uses bilinear interpolation, and the calibrated thickness and position are known data points). The calculation method is as follows (assuming that the adjacent grid coordinates of the four existing calibration data are known to be (0,0), (0,1), (1,0), (1,1)):

[0113]

[0114] The attenuation coefficients of other coordinate points within the grid coordinates (0,0), (0,1), (1,0), (1,1) of the calibration data can be obtained through bilinear interpolation, without the need to measure each point, thus improving the calibration efficiency. Through calibration and bilinear interpolation, the edge attenuation coefficients of different thicknesses and different positions can be obtained in real time during the measurement process, and the real-time compensation of the edge thickness measurement attenuation can be completed.

[0115] Secondly, the resonance frequency, standard thickness and edge position information of the metal film measured by the current signal processing result are obtained, and the corresponding compensation coefficient is obtained according to the resonance frequency, standard thickness and edge position information.

[0116] The compensation coefficient has been obtained through the above steps. It is only necessary to obtain the corresponding attenuation data table according to the resonant frequency, and then obtain the corresponding compensation coefficient from the attenuation data table using the standard thickness and edge position information.

[0117] Finally, the current signal processing result is divided by the corresponding compensation coefficient to obtain the compensated signal processing result.

[0118] The embodiment of the present invention adds edge compensation to the signal processing results, which can reduce the impact of edge loss on the measurement results, improve edge detection accuracy, and meet high-order process requirements. The attenuation area at the edge of the wafer is narrower and the film thickness monitoring is more accurate, which effectively avoids the distortion of thickness monitoring data caused by edge effects, improves processing accuracy, and expands the available area of ​​the wafer. Taking a 300mm copper wafer as an example, the metal film thickness measurement method used in the present invention can reduce the edge attenuation from 140mm to 150mm to 145 to 150mm when the error is required to be less than 3% without algorithm compensation. When the process requires the wafer to be de-edged by 5mm, it can directly meet the use requirements; when the high-order process requires de-edging of 2mm to 3mm, data compensation is required for the range of 145mm to 148mm.

[0119] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A metal film thickness monitoring system, characterized in that: It includes a waveform generation module, a signal acquisition and processing module, a main control module and an eddy current sensor, wherein the eddy current sensor includes an excitation module and a receiving module; The waveform generating module, whose input end is connected to the main control module, is used to output a first AC signal and a second AC signal with two equal amplitudes and opposite directions; The excitation module comprises a magnetic core and a first LC oscillation circuit composed of an excitation coil and a first capacitor, the magnetic core comprises a housing portion, a constriction portion and a winding portion, the housing portion and the constriction portion are connected to form a placement cavity, wherein the farther the distance between the opening of the constriction portion and the housing portion is, the smaller the opening is; the winding portion is arranged in the placement cavity, the excitation coil is wound on the winding portion, the opening of the constriction portion on the side away from the housing portion is smaller than the opening on the side close to the housing portion, the input end of the first LC oscillation circuit is connected to an output end of the waveform generating module, for receiving the first AC signal, and based on the first AC signal, exciting the metal film to be measured to generate an alternating magnetic field and output a first output signal; The receiving module comprises a second LC oscillation circuit composed of a receiving coil and a second capacitor, wherein the receiving coil is arranged at an opening of the bundle portion on a side away from the accommodating portion, the second capacitor and the receiving coil are connected to form the second LC oscillation circuit, and the input end of the second LC oscillation circuit is connected to another output end of the waveform generating module, and is used to receive the alternating magnetic field and the second AC signal generated by the metal film to be measured, and output a second output signal based on the second AC signal and the alternating magnetic field; The signal acquisition and processing module has one input end connected to the excitation module and another input end connected to the receiving module, and is used to acquire the first output signal and the difference signal between the first output signal and the second output signal, and output the acquired signal to the main control module; The main control module is used to control the waveform generating module to output the first AC signal and the second AC signal, and to calculate the thickness of the metal film to be measured according to the first output signal and the difference signal.

2. The metal film thickness monitoring system according to claim 1, characterized in that: The waveform generating module comprises: a waveform generator, a power amplifier, an amplitude stabilizing circuit, a reference circuit and an inverter. The waveform generator, the power amplifier and the amplitude stabilizing circuit are connected in series in sequence. An input end of the amplitude stabilizing circuit is connected to the reference circuit, an output end of the amplitude stabilizing circuit is connected to the excitation module, and the other output end is connected to the receiving module via an inverter.

3. The metal film thickness monitoring system according to claim 1, characterized in that: The signal acquisition and processing module includes: a first acquisition module, a second acquisition module, a first differential amplifier circuit, a second differential amplifier circuit, a third differential amplifier circuit and a fourth differential amplifier circuit. The input end of the first acquisition module is connected to the excitation module, and the output end is respectively connected to the first differential amplifier circuit and the second differential amplifier circuit. The input end of the second acquisition module is connected to the receiving module, and the output end is connected to the third differential amplifier circuit. The output end of the first differential amplifier circuit is connected to an input end of the main control module, the output end of the second differential amplifier circuit is connected to an input end of the fourth differential amplifier circuit, the output end of the third differential amplifier circuit is connected to another input end of the fourth differential amplifier circuit, and the output end of the fourth differential amplifier circuit is connected to another input end of the main control module.

4. The metal film thickness monitoring system according to claim 3, characterized in that: It also includes an AD conversion module, wherein the AD conversion module includes a first AD conversion module and a second AD conversion module; The input end of the first AD conversion module is connected to the output end of the first differential amplifier circuit, and the output end is connected to an input end of the main control module, and is used for converting the first output signal into a digital signal; The input end of the second AD conversion module is connected to the output end of the fourth differential amplifier circuit, and the output end is connected to another input end of the main control module, and is used to convert the difference signal into a digital signal.

5. The metal film thickness monitoring system according to claim 1, characterized in that: The main control module includes a host computer and a communication control unit, and the communication control unit includes a waveform control module, a signal processing module and a storage module. The waveform control module is used to control the first AC signal and the second AC signal output by the waveform generating module. The signal processing module is used to perform difference processing on the first output signal and the difference signal to obtain a signal processing result. The storage module is used to store the signal processing result. The host computer is used to obtain the thickness of the measured metal film based on the linear relationship analysis between the signal processing result and the thickness of the metal film.

6. A metal film thickness measurement method, applied to the metal film thickness monitoring system according to any one of claims 1 to 5, characterized in that: include: Generate a first alternating current signal and a second alternating current signal of equal amplitude and opposite direction; Based on the first AC signal, the metal film under test is stimulated to generate an alternating magnetic field and generate a first output signal; generating a second output signal based on the second AC signal and the alternating magnetic field; collecting the first output signal and a difference signal between the first output signal and the second output signal; The thickness of the metal film to be measured is calculated according to the first output signal and the difference signal.

7. A method for measuring the thickness of a metal film according to claim 6, characterized in that: Calculating the thickness of the metal film to be measured according to the first output signal and the difference signal includes: Performing difference processing on the first output signal and the difference signal to obtain a signal processing result; Performing edge compensation on the signal processing result to obtain a compensated signal processing result; The linear relationship between the signal processing result and the thickness of the metal film is pre-stored, and the thickness of the metal film is obtained according to the compensated signal processing result and the linear relationship.

8. A method for measuring the thickness of a metal film according to claim 7, characterized in that: The performing edge compensation on the signal processing result to obtain a compensated signal processing result includes: Pre-calibrating to obtain compensation coefficients of the signal processing results at metal films of different thicknesses and at different edge positions, the compensation coefficients being the ratio of the actually measured signal processing results to the nominal thickness feedback signal; Obtain the resonant frequency, standard thickness and edge position information of the current signal processing result, and obtain the corresponding compensation coefficient according to the resonant frequency, standard thickness and edge position information; The current signal processing result is divided by the corresponding compensation coefficient to obtain the compensated signal processing result.

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