Metal film thickness online measurement compensation method, film thickness sensor and equipment

Abstract

The invention discloses a metal film thickness online measurement compensation method, a film thickness sensor and equipment, and the method comprises the steps: obtaining the nth output quantity Sn of the film thickness sensor for measuring the thickness of a metal film in a polishing process; calculating the temperature drift compensation amount delta Ssn of the sensor by using the temperature tsn of the film thickness sensor at the moment and the temperature drift function of the film thickness sensor; calculating a wafer temperature drift compensation amount delta Swn by using the wafer temperature twn at the moment, the film thickness dn-1 measured at the (n-1) th time and a wafer temperature compensation function; calculating the output quantity S'n after compensation, wherein S'n is equal to Sn-delta Ssn-delta Swn; and obtaining the film thickness dn measured for the nth time according to a sensor output function and the compensated output quantity S'n.

Description

[0001] This application is a divisional application of the invention patent application filed on April 17, 2023 with application number 202310410608.0. Technical Field

[0002] The invention relates to the technical field of chemical mechanical polishing, and in particular to an online measurement compensation method for metal film thickness, a film thickness sensor and equipment. Background Art

[0003] Chemical Mechanical Polishing (CMP) technology is the preferred planarization process in the IC manufacturing process. In chemical mechanical polishing, for the manufacturing process of semiconductor devices, too much or too little material removal will lead to the degradation of device electrical properties or even failure. In order to improve the controllability of the chemical mechanical polishing process, enhance the stability of the product, reduce the defect rate of the product, and achieve uniform production for each wafer, the endpoint detection technology (EPD) of chemical mechanical polishing came into being.

[0004] During the CMP process, a large amount of heat is generated due to mechanical friction and chemical reactions. On the one hand, this heat will be transferred to the wafer, causing the wafer temperature to rise and the conductivity of the metal film to change; on the other hand, the heat will be transferred to the eddy current sensor through the polishing disk, causing the operating temperature of the eddy current sensor to change. The conductivity of the wafer metal film and the operating temperature of the eddy current sensor change, resulting in errors in the eddy current sensor measuring the thickness of the wafer metal film, which ultimately affects the capture of the polishing end point. Summary of the invention

[0005] The embodiments of the present invention provide a metal film thickness online measurement compensation method, a film thickness sensor and a device, aiming to solve at least one of the technical problems existing in the prior art.

[0006] A first aspect of an embodiment of the present invention provides a metal film thickness online measurement compensation method, comprising:

[0007] During the polishing process, obtain the nth output S of the film thickness sensor measuring the metal film thickness n ;

[0008] Using the film thickness sensor temperature t sn And its own temperature drift function, calculate the sensor temperature drift compensation ΔS sn ;

[0009] Using the wafer temperature t wn , the film thickness d measured for the n-1th time n-1 And the wafer temperature compensation function, calculate the wafer temperature drift compensation ΔS wn ;

[0010] Calculate the output after compensation S′ n , S′ n =S n -ΔS sn -ΔS wn ;

[0011] According to the sensor output function and the compensated output S′ n Get the film thickness d measured for the nth time n .

[0012] In one embodiment, the sensor output function is calibrated by the mapping relationship between the output of the film thickness sensor and the actual film thickness at room temperature. The sensor output function is expressed as d=f1(S), where d is the film thickness of the wafer and S is the output of the film thickness sensor.

[0013] In one embodiment, the self-temperature drift function is obtained by calibrating the mapping relationship between the output of the film thickness sensor at different temperatures and the temperature. The self-temperature drift function is expressed as ΔS s =f2(t s ), where ΔS s is the sensor temperature drift compensation, t s is the temperature of the film thickness sensor.

[0014] In one embodiment, the wafer temperature compensation function is obtained by calibrating the output of the film thickness sensor corresponding to different film thicknesses of the wafer at different temperatures. The wafer temperature compensation function is expressed as ΔS w =f3(t w , d), where ΔS w is the wafer temperature drift compensation, t w is the wafer temperature, and d is the film thickness of the wafer.

[0015] In one embodiment, the specific calculation process includes:

[0016] ΔS sn =f2(t sn )

[0017] ΔS wn =f3(t wn , d n-1 )

[0018] S′ n =S n -ΔS sn -ΔS wn

[0019] d n =f1(S′ n )

[0020] Among them, f2 is the self-temperature drift function, f3 is the wafer temperature compensation function, and f1 is the sensor output function.

[0021] In one embodiment, the output of the film thickness sensor is a resonance frequency.

[0022] A second aspect of an embodiment of the present invention provides a film thickness sensor, which uses the above-mentioned metal film thickness online measurement and compensation method to measure film thickness; the film thickness sensor includes an eddy current module, a detection circuit and a temperature measurement module.

[0023] A third aspect of an embodiment of the present invention provides a chemical mechanical polishing device, comprising:

[0024] A polishing plate, which is covered with a polishing pad for polishing a wafer;

[0025] A carrier head, used for holding the wafer and pressing the wafer onto the polishing pad, wherein a temperature detection unit is provided on the carrier head;

[0026] The film thickness sensor as described above is used to measure the film thickness of the wafer during polishing;

[0027] A control device is used to implement the above-mentioned metal film thickness online measurement compensation method.

[0028] A fourth aspect of an embodiment of the present invention provides a control device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above-mentioned metal film thickness online measurement compensation method when executing the computer program.

[0029] A fifth aspect of an embodiment of the present invention provides 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 steps of the above-mentioned metal film thickness online measurement compensation method are implemented.

[0030] The beneficial effects of the embodiments of the present invention include: being able to compensate for the influence of temperature change on film thickness measurement, and significantly improving the accuracy and precision of film thickness measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The advantages of the present invention will become clearer and easier to understand through the detailed description made in conjunction with the following drawings, but these drawings are only schematic and do not limit the scope of protection of the present invention, wherein:

[0032] Figure 1 A chemical mechanical polishing device provided by an embodiment of the present invention is shown;

[0033] Figure 2A film thickness sensor provided by an embodiment of the present invention is shown;

[0034] Figure 3 The relationship curve between film thickness and film thickness sensor output is shown;

[0035] Figure 4 The relationship between the output of the film thickness sensor and the temperature is shown;

[0036] Figure 5 The output of the film thickness sensor is shown as a binary curve of the film thickness and temperature;

[0037] Figure 6 A method for online measurement and compensation of metal film thickness provided by an embodiment of the present invention is shown;

[0038] Figure 7 A comparison chart of the film thickness sensor before and after temperature compensation is shown. DETAILED DESCRIPTION

[0039] The technical scheme of the present invention is described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments recorded herein are specific embodiments of the present invention, which are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary, and should not be understood as limitations on the embodiments of the present invention and the scope of protection of the present invention. It should be noted that, in the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. In addition to the embodiments recorded herein, those skilled in the art can also adopt other obvious technical solutions based on the contents disclosed in the claims of this application and its specification, which include technical solutions that adopt any obvious replacements and modifications to the embodiments recorded herein. It should be understood that, unless otherwise specified, for ease of understanding, the following description of the specific embodiments of the present invention is based on the description of the relevant equipment, devices, components, etc. in the original static natural state without external control signals and driving forces.

[0040] In addition, it should be noted that the terms used in this application to indicate orientation, such as front, back, up, down, left, right, top, bottom, front, back, horizontal, vertical, etc., are merely for convenience of description to help understand relative positions or directions, and are not intended to limit the orientation of any device or structure.

[0041] In order to illustrate the technical solution of the present invention, the following description will be given with reference to the accompanying drawings and in combination with embodiments.

[0042] In this application, chemical mechanical polishing is also referred to as chemical mechanical planarization, and wafer is also referred to as chip, silicon wafer, base wafer or substrate, etc., and their meanings and actual functions are equivalent.

[0043] like Figure 1 As shown, the main components of the chemical mechanical polishing equipment provided by the embodiment of the present invention include a carrier head 10 for holding a wafer w and driving the wafer w to rotate, a polishing disk 20 covered with a polishing pad 21, a dresser 30 for dressing the polishing pad 21, and a liquid supply part 40 for providing a polishing liquid.

[0044] During the chemical mechanical polishing process, the carrier head 10 absorbs the wafer w through negative pressure, and presses the side of the wafer w containing the metal film onto the polishing pad 21, and the carrier head 10 performs a rotational motion and a radial reciprocating motion along the polishing disk 20 so that the surface of the wafer w in contact with the polishing pad 21 is gradually polished, while the polishing disk 20 rotates, and the liquid supply unit 40 sprays the polishing liquid onto the surface of the polishing pad 21. Under the chemical action of the polishing liquid, the relative movement of the carrier head 10 and the polishing disk 20 causes the wafer w to rub against the polishing pad 21 for polishing. During polishing, the dresser 30 is used to dress and activate the surface morphology of the polishing pad 21. The dresser 30 can be used to remove foreign particles remaining on the surface of the polishing pad 21, such as abrasive particles in the polishing liquid and waste materials falling off the surface of the wafer w, and can also be used to flatten the surface deformation of the polishing pad 21 caused by grinding.

[0045] During the chemical mechanical polishing process, the wafer w is pressed onto the polishing pad 21 by the carrier head 20 and reciprocates radially along the polishing disk 10 with the carrier head 20. At the same time, the carrier head 20 and the polishing disk 10 rotate synchronously, so that the surface of the wafer w in contact with the polishing pad 21 is gradually polished away.

[0046] like Figure 2 As shown, the chemical mechanical polishing equipment also includes a film thickness sensor 50 and a control device for online measuring the film thickness of the wafer w. The film thickness sensor 50 is installed in the polishing plate 20 and is located below the polishing pad 21. The film thickness sensor 50 rotates with the polishing plate 20 to achieve online film thickness measurement while polishing. The film thickness sensor 50 is set next to the polishing pad 21, and the wafer w is placed on the polishing pad 21. Therefore, the distance between the film thickness sensor 50 and the wafer w is the thickness of the polishing pad 21.

[0047] During the CMP polishing process, it is necessary to monitor the film thickness change and film thickness value of the wafer w in real time so as to adopt the corresponding polishing process to avoid over-polishing or incomplete polishing. During the polishing process, the metal film thickness on the surface of the wafer w is measured online, so as to accurately control the removal rate of the metal film by adjusting the pressure of the carrier head 10 to achieve better global flattening. The film thickness sensor 50 can adopt eddy current detection. The principle of eddy current detection is that when the film thickness sensor 50 scans the wafer w, the metal film layer on the surface of the wafer w will induce eddy currents and change the magnetic field generated by the film thickness sensor 50. Therefore, when the metal film layer is removed by polishing, the film thickness sensor 50 measures the eddy current changes to measure the film thickness of the metal film layer.

[0048] Since a lot of heat is generated during the CMP polishing process, the temperature of the wafer w rises, and the working temperature of the film thickness sensor 50 is inconsistent with the calibrated temperature, resulting in temperature drift. Therefore, the output change of the film thickness sensor 50 during the polishing process consists of three parts: one is the output change caused by the change in the film thickness of the measured metal film, and the change curve is as follows: Figure 3 As shown; the second is the output change of the film thickness sensor 50 caused by the temperature change, the change curve is as shown Figure 4 As shown; the third is the output change caused by the change in conductivity of the measured metal film due to temperature change, the change curve is shown in Figure 5 Finally, the output of the film thickness sensor 50 is coupled together by these three parts.

[0049] In order to accurately measure the temperature change during polishing, such as Figure 1 and Figure 2 As shown, in one embodiment of the present invention, a temperature detection unit 11 is provided on the carrier head 10 for obtaining the temperature of the wafer w or the surface temperature of the polishing pad near the wafer w, so as to achieve wafer temperature compensation. Figure 2 As shown, the film thickness sensor 50 includes an eddy current module 51, a detection circuit and a temperature measurement module 52, wherein the eddy current module 51 is used to realize metal film thickness detection, and the temperature measurement module 52 is used to detect the temperature change of the film thickness sensor 50 itself to realize the temperature drift compensation of the film thickness sensor 50 itself.

[0050] Based on the above chemical mechanical polishing equipment and the film thickness sensor 50, as shown in FIG. Figure 6 As shown, an embodiment of the present invention further provides a metal film thickness online measurement compensation method, comprising:

[0051] Step S1, during the polishing process, obtain the nth output value S of the film thickness sensor 50 measuring the metal film thickness n The output of the film thickness sensor 50 is the resonant frequency. The sampling frequency and output frequency of the film thickness sensor 50 are generally fixed, and its output is continuously output at a certain interval. The output Sn It is data directly output by the film thickness sensor 50 at the nth time, where n is a natural number.

[0052] Step S2, using the film thickness sensor temperature t sn And its own temperature drift function, calculate the sensor temperature drift compensation ΔS sn The temperature sensor temperature t is collected by using the temperature measurement module 52. sn The self-temperature drift function is obtained by calibrating the mapping relationship between the output of the film thickness sensor 50 at different temperatures and the temperature. The self-temperature drift function can be expressed as ΔS s =f2(t s ), ΔS s is the sensor temperature drift compensation, t s is the temperature of the film thickness sensor.

[0053] Step S3, using the wafer temperature t wn , the film thickness d measured for the n-1th time n-1 And the wafer temperature compensation function, calculate the wafer temperature drift compensation ΔS wn The temperature detection unit 11 is used to collect the wafer temperature t wn The wafer temperature compensation function is obtained by calibrating the output of the film thickness sensor 50 corresponding to different film thicknesses of the wafer at different temperatures. The wafer temperature compensation function can be expressed as ΔS w =f3(t w , d), ΔS w is the wafer temperature drift compensation, t w is the wafer temperature, and d is the film thickness of the wafer.

[0054] Step S4, calculate the output after compensation S' n , S′ n =S n -ΔS sn -ΔS wn .

[0055] Step S5, according to the sensor output function and the compensated output S' n Get the film thickness d measured for the nth time n The sensor output function is calibrated by the mapping relationship between the output of the film thickness sensor and the actual film thickness at room temperature. The sensor output function can be expressed as d=f1(S), where d is the film thickness of the wafer and S is the output of the film thickness sensor.

[0056] It can be understood that the sensor output function f1, the self-temperature drift function f2 and the wafer temperature compensation function f3 mentioned above can all be represented by a relationship curve, a data calibration table or a fitting function.

[0057] In one embodiment, when executing Figure 6 Before the online measurement and compensation method of metal film thickness is shown, a calibration process is required, including:

[0058] The mapping relationship between the output of the film thickness sensor at room temperature and the actual film thickness is calibrated to obtain the output function d=f1(S) of the film thickness sensor. For example, at an ambient temperature of 24°C and a fixed lift-off height, Cu film wafers with different film thicknesses are placed on the film thickness sensor 50 to obtain the sensor output function f1(S) at the calibration temperature, as shown in FIG. Figure 3 A curve showing the relationship between film thickness and output, which can represent the sensor output function f1(S), is shown.

[0059] Calibrate the mapping relationship between the output and temperature of the film thickness sensor at different temperatures to obtain the film thickness sensor's own temperature drift function ΔS s =f2(t s Specifically, the film thickness sensor 50 is placed in a precise temperature control device, and the relationship between the output of the film thickness sensor and the temperature is calibrated, thereby obtaining its own temperature drift function f2(t s ),like Figure 4 The graph shows the relationship between the output of the film thickness sensor and the temperature when it is unloaded.

[0060] Calibrate the output of the film thickness sensor corresponding to different film thicknesses at different temperatures of the wafer to obtain the wafer temperature compensation function ΔS w =f3(t w Specifically, the film thickness sensor 50 and Cu film wafers with different film thicknesses are placed in a precise temperature control device, and the lift-off height between the film thickness sensor 50 and the Cu film wafer is kept constant, and the wafer temperature compensation function f3 (t w , d). Since the conductivity of metal changes with temperature, the output of the film thickness sensor also changes with the temperature under the same thickness of metal film, such as Figure 5 As shown in the figure, the binary variation curve of the film thickness sensor output and the metal film thickness and temperature.

[0061] In specific applications, the nth output S of the film thickness sensor n When making compensation, the film thickness d measured last time (n-1) must be used. n-1 , the specific calculation process includes:

[0062] (1) Calculate the self-drift of the film thickness sensor: ΔS sn =f2(t sn );

[0063] (2) Calculate the drift caused by wafer temperature change: ΔS wn =f3(t wn , dn-1 );

[0064] (3) Eliminate drift to obtain the compensated output: S′ n =S n -ΔS sn -ΔS wn ;

[0065] (4) Calculate the actual film thickness using the compensated output: d n =f1(S′ n ).

[0066] During the polishing process, the chemical mechanical polishing equipment has not yet undergone a violent chemical reaction and the temperature has not risen. The temperature at this time is consistent with the calibration temperature, and the output S1 of the film thickness sensor is correct and does not require temperature compensation. The film thickness d1 can be directly obtained. Subsequently, due to the heat generated by the chemical reaction during the polishing process, the temperature detection unit 11 is used to obtain the temperature change of the wafer surface in real time, and the temperature measurement module 52 is used to collect the temperature change of the film thickness sensor in real time, so as to perform temperature compensation calculation according to the above calculation process.

[0067] For ease of understanding, the following example illustrates the specific implementation process:

[0068]

[0069] By analogy with the calculation rules in the above table, the accurate film thickness after each compensation can be obtained.

[0070] like Figure 7 As shown, the applicant has verified the technical effect of the metal film thickness online measurement compensation method provided by the embodiment of the present invention through experiments. The Cu film thickness of the sample measured by the four-probe instrument is like Figure 7 As shown in the figure, within the temperature range of 15 to 35°C, if there is no temperature compensation, the measurement accuracy of the film thickness sensor is After adding temperature compensation, the measurement accuracy of the film thickness sensor is The measurement accuracy is improved by 10 times. In addition, the above-mentioned metal film thickness online measurement compensation method is also applicable to the CMP wafer surface flattening and endpoint stop of W and AL processes.

[0071] As described above, the metal film thickness online measurement compensation method provided by the embodiment of the present invention can compensate for the influence of temperature change on film thickness measurement, thereby significantly improving the accuracy and precision of film thickness measurement.

[0072] The embodiment of the present invention further 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 following is achieved: Figure 6The method steps shown. The control device refers to a terminal with data processing capabilities, including but not limited to computers, workstations, servers, and even some high-performance smart phones, PDAs, tablet computers, personal digital assistants (PDAs), smart TVs, etc. The control device is generally installed with an operating system, including but not limited to: Windows operating system, LINUX operating system, Android operating system, Symbian operating system, Windows mobile operating system, and iOS operating system, etc. The above lists specific examples of the control device in detail, and those skilled in the art can realize that the control device is not limited to the above-listed examples.

[0073] The embodiment of the present invention further provides 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 following is implemented: Figure 6 The method steps shown. The computer program may be stored in a computer-readable storage medium, and when the computer program is executed by a processor, the steps of each of the above method embodiments may be implemented. Wherein, the computer program includes computer program code, and the computer program code may be in source code form, object code form, executable file or some intermediate form, etc. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, USB flash drive, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signal, telecommunication signal and software distribution medium, etc.

[0074] Those skilled in the art will appreciate 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. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0075] The embodiments described above 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 may be replaced by equivalents. Such 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, and should all be included in the protection scope of the present invention.

Claims

1. A chemical mechanical polishing device, characterized in that: include: A polishing plate, which is covered with a polishing pad for polishing a wafer; A carrier head, used for holding the wafer and pressing the wafer onto the polishing pad, wherein a temperature detection unit is provided on the carrier head for detecting temperature changes on the surface of the wafer; A film thickness sensor, used to measure the film thickness of the wafer during polishing, the film thickness sensor comprising an eddy current module, a detection circuit and a temperature measurement module, the temperature measurement module being used to detect temperature changes of the film thickness sensor; A control device is provided for removing the change in the wafer surface temperature and the change in the film thickness sensor output caused by the change in the film thickness sensor temperature from the film thickness sensor output, thereby determining the film thickness of the wafer.

2. The chemical mechanical polishing equipment according to claim 1, characterized in that: The film thickness sensor is installed in the polishing plate, below the polishing pad and adjacent to the polishing pad.

3. The chemical mechanical polishing equipment according to claim 2, characterized in that: The control device removes the change in the wafer surface temperature and the change in the film thickness sensor output caused by the change in the film thickness sensor temperature from the film thickness sensor output, thereby determining the film thickness of the wafer, including: Determining a wafer temperature compensation amount according to the wafer surface temperature change; determining a temperature drift compensation amount of the film thickness sensor according to a temperature change of the film thickness sensor; Compensating the film thickness sensor output according to the wafer temperature compensation amount and the temperature drift compensation amount to determine a compensated output amount; The film thickness of the wafer is determined based on the compensated output.

4. The chemical mechanical polishing equipment according to claim 3, characterized in that: Determining the wafer temperature compensation amount according to the wafer surface temperature change includes: calibrating the output of the film thickness sensor corresponding to different film thicknesses of the wafer at different temperatures, obtaining a wafer temperature compensation function and calculating the wafer temperature compensation amount ΔS w , the wafer temperature compensation function is expressed as ΔS w =f3(t w , d), where t w is the wafer temperature, and d is the film thickness of the wafer.

5. The chemical mechanical polishing equipment according to claim 4, characterized in that: Determining the temperature drift compensation amount of the film thickness sensor according to the temperature change of the film thickness sensor includes: calibrating the mapping relationship between the output of the film thickness sensor at different temperatures and the temperature, obtaining the temperature drift function of the film thickness sensor itself and calculating the sensor temperature drift compensation amount ΔS s , the self-temperature drift function is expressed as ΔS s =f2(t s ), where t s is the temperature of the film thickness sensor.

6. The chemical mechanical polishing equipment according to claim 5, characterized in that: The compensating the film thickness sensor output according to the wafer temperature compensation amount and the temperature drift compensation amount to determine the compensated output amount comprises: Get the nth output S of the film thickness sensor n ; Using the film thickness sensor temperature t sn And the temperature drift function of the sensor, calculate the temperature drift compensation value ΔS sn ; Using the wafer temperature t wn , the film thickness d measured for the n-1th time n-1 And the wafer temperature compensation function, calculate the wafer temperature drift compensation amount ΔS wn ; Calculate the output after compensation S n ′ n,S n ′ =S n -ΔS sn -ΔS wn .

7. The chemical mechanical polishing equipment according to claim 6, characterized in that: Determining the film thickness of the wafer according to the compensated output comprises: Calibrate the mapping relationship between the output of the film thickness sensor at room temperature and the actual film thickness, and obtain the output function d=f1(S) of the film thickness sensor; Using the compensated output S n ′ The output function of the sensor is used to calculate the film thickness d measured for the nth time. n .

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