CN114589617A - Metal film thickness measuring method, film thickness measuring device and chemical mechanical polishing equipment - Google Patents

Metal film thickness measuring method, film thickness measuring device and chemical mechanical polishing equipment Download PDF

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Publication number
CN114589617A
CN114589617A CN202210206383.2A CN202210206383A CN114589617A CN 114589617 A CN114589617 A CN 114589617A CN 202210206383 A CN202210206383 A CN 202210206383A CN 114589617 A CN114589617 A CN 114589617A
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film thickness
phase
excitation
amplitude
induction coil
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CN114589617B (en
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王成鑫
王同庆
田芳鑫
侯映红
路新春
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Tsinghua University
Huahaiqingke Co Ltd
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Tsinghua University
Huahaiqingke Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
    • B24B37/00—Lapping machines or devices; Accessories
    • B24B37/04—Lapping machines or devices; Accessories designed for working plane surfaces
    • B24B37/07—Lapping machines or devices; Accessories designed for working plane surfaces characterised by the movement of the work or lapping tool
    • B24B37/10—Lapping machines or devices; Accessories designed for working plane surfaces characterised by the movement of the work or lapping tool for single side lapping
    • B24B37/105—Lapping machines or devices; Accessories designed for working plane surfaces characterised by the movement of the work or lapping tool for single side lapping the workpieces or work carriers being actively moved by a drive, e.g. in a combined rotary and translatory movement
    • B24B37/107—Lapping machines or devices; Accessories designed for working plane surfaces characterised by the movement of the work or lapping tool for single side lapping the workpieces or work carriers being actively moved by a drive, e.g. in a combined rotary and translatory movement in a rotary movement only, about an axis being stationary during lapping
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
    • B24B37/00—Lapping machines or devices; Accessories
    • B24B37/005—Control means for lapping machines or devices
    • B24B37/013—Devices or means for detecting lapping completion
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
    • B24B37/00—Lapping machines or devices; Accessories
    • B24B37/04—Lapping machines or devices; Accessories designed for working plane surfaces
    • B24B37/042—Lapping machines or devices; Accessories designed for working plane surfaces operating processes therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
    • B24B37/00—Lapping machines or devices; Accessories
    • B24B37/34—Accessories
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
    • B24B49/00—Measuring or gauging equipment for controlling the feed movement of the grinding tool or work; Arrangements of indicating or measuring equipment, e.g. for indicating the start of the grinding operation
    • B24B49/02—Measuring or gauging equipment for controlling the feed movement of the grinding tool or work; Arrangements of indicating or measuring equipment, e.g. for indicating the start of the grinding operation according to the instantaneous size and required size of the workpiece acted upon, the measuring or gauging being continuous or intermittent
    • B24B49/04—Measuring or gauging equipment for controlling the feed movement of the grinding tool or work; Arrangements of indicating or measuring equipment, e.g. for indicating the start of the grinding operation according to the instantaneous size and required size of the workpiece acted upon, the measuring or gauging being continuous or intermittent involving measurement of the workpiece at the place of grinding during grinding operation
    • B24B49/045—Specially adapted gauging instruments
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
    • B24B49/00—Measuring or gauging equipment for controlling the feed movement of the grinding tool or work; Arrangements of indicating or measuring equipment, e.g. for indicating the start of the grinding operation
    • B24B49/10—Measuring or gauging equipment for controlling the feed movement of the grinding tool or work; Arrangements of indicating or measuring equipment, e.g. for indicating the start of the grinding operation involving electrical means
    • B24B49/105—Measuring or gauging equipment for controlling the feed movement of the grinding tool or work; Arrangements of indicating or measuring equipment, e.g. for indicating the start of the grinding operation involving electrical means using eddy currents

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)
  • Mechanical Treatment Of Semiconductor (AREA)

Abstract

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

Description

Metal film thickness measuring method, film thickness measuring device and chemical mechanical polishing equipment
Technical Field
The invention relates to the technical field of chemical mechanical polishing, in particular to a metal film thickness measuring method, a film thickness measuring device and chemical mechanical polishing equipment.
Background
Integrated Circuits (ICs) are the core and fate of the development of the information technology industry. Integrated circuits are typically formed by the sequential deposition of conductive, semiconductive, or insulative layers on a silicon wafer. So that the surface of the wafer is deposited with a film formed by the filler layer. During the fabrication process, planarization of the filler layer is continued until the patterned top surface is exposed to form conductive paths between the raised patterns.
Chemical Mechanical Polishing (CMP) technology is the preferred planarization process in IC manufacturing. In chemical mechanical polishing, too much or too little material removal for the semiconductor device fabrication process can result in device electrical degradation and even failure. In order to improve the controllability of the chemical mechanical polishing process, improve the stability of the product, and reduce the defect rate of the product, so that each wafer can be uniformly produced, an End Point Detection (EPD) technique for chemical mechanical polishing is developed.
In metal CMP endpoint detection, eddy current detection is the most common method, and the output signal is a voltage signal, and the magnitude of the voltage signal is related to the metal film thickness on the surface of the wafer to be detected. In the prior art, different eddy current sensor coil structures can generate different measuring ranges and resolution ratios for eddy current detection, at present, the measurement is generally carried out by manually changing parameters little by little in a stepping manner, the measurement time is long, and according to empirical data, the result is easy to be inaccurate, and the use is influenced.
Disclosure of Invention
The embodiment of the invention provides a metal film thickness measuring method, a film thickness measuring device and chemical mechanical polishing equipment, and aims to at least solve one of the technical problems in the prior art.
A first aspect of an embodiment of the present invention provides a method for measuring a metal film thickness, including:
calculating an extreme point corresponding to the amplitude method or the phase method when measuring the film thickness of the metal film on the surface of the wafer based on the amplitude method or the phase method;
and adjusting the excitation frequency according to the extreme point, the measurement range and/or the measurement sensitivity, wherein the measurement range is a film thickness measurement range, the measurement sensitivity is resolution, and the excitation frequency is the frequency of an excitation signal for the film thickness measurement device.
A second aspect of the embodiments of the present invention provides a film thickness measuring apparatus, which performs film thickness measurement by using the metal film thickness measuring method described above; the film thickness measuring device comprises an eddy current sensor and a detection circuit; the eddy current sensor comprises an exciting coil and an induction coil; the exciting coil and the induction coil are both flat coils and are coaxially arranged, and the winding directions of the exciting coil and the induction coil are the same.
A third aspect of embodiments of the present invention provides a chemical mechanical polishing apparatus, including:
a polishing disk covered with a polishing pad for polishing a wafer;
the bearing head is used for holding a wafer and pressing the wafer on the polishing pad;
a film thickness measuring device for measuring a film thickness of the wafer during polishing;
and the control device is used for realizing the metal film thickness measuring method.
A fourth aspect of the embodiments of the present invention provides a control apparatus, including 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 metal film thickness measuring method as described above when executing the computer program.
A fifth aspect of embodiments of the present invention provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of the metal film thickness measuring method described above.
The embodiment of the invention has the beneficial effects that: by using the extreme point, the optimal measuring range and measuring sensitivity in an amplitude method and a phase method can be obtained.
Drawings
The advantages of the invention will become clearer and more readily appreciated from the detailed description given with reference to the following drawings, which are given by way of illustration only and do not limit the scope of protection of the invention, wherein:
FIG. 1 is a schematic structural diagram of a chemical mechanical polishing apparatus according to an embodiment of the present invention;
FIG. 2 is a schematic structural diagram of a chemical mechanical polishing apparatus according to an embodiment of the present invention;
FIG. 3 is a schematic structural diagram of a film thickness measuring apparatus according to an embodiment of the present invention;
FIG. 4 is a schematic structural diagram of an eddy current sensor according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of an eddy current sensor according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of an eddy current sensor according to another embodiment of the invention;
FIG. 7 is an equivalent circuit diagram of an eddy current sensor according to an embodiment of the invention;
FIG. 8 is an LC tank according to an embodiment of the present invention;
FIG. 9 is a schematic flow chart illustrating a method for measuring a thickness of a metal film according to an embodiment of the present invention;
FIG. 10 shows amplitude versus film thickness at different excitation frequencies;
FIG. 11 shows phase versus film thickness at different excitation frequencies;
fig. 12 shows the case where the amount of amplitude change attenuates at the edge under different excitation frequencies.
Detailed Description
The technical solution of the present invention will be described in detail with reference to the following embodiments and accompanying drawings. The embodiments described herein are specific embodiments of the present invention for the purpose of illustrating the concepts of the invention; the description is intended to be illustrative and exemplary and should not be taken to limit the scope of the invention. It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. In addition to the embodiments described herein, those skilled in the art will be able to employ other technical solutions which are obvious based on the disclosure of the claims and the specification thereof, and these technical solutions include technical solutions which make any obvious replacement or modification of the embodiments described herein. It should be understood that, unless otherwise specified, the following description of the embodiments of the present invention is made for the convenience of understanding, and the description is made in a natural state where relevant devices, apparatuses, components, etc. are originally at rest and no external control signals and driving forces are given.
Further, it is also noted that terms used herein such as front, back, up, down, left, right, top, bottom, front, back, horizontal, vertical, and the like, to denote orientation, are used merely for convenience of description to facilitate understanding of relative positions or orientations, and are not intended to limit the orientation of any device or structure.
In order to explain the technical solution of the present invention, the following description is made with reference to the accompanying drawings in combination with the embodiments.
In the present application, Chemical Mechanical Polishing (Chemical Mechanical Planarization) is also called Chemical Mechanical Planarization (Chemical Mechanical Planarization), and wafer (wafer) is also called wafer, silicon wafer, substrate or substrate (substrate), which means and actually functions equivalently.
As shown in fig. 1, the chemical mechanical polishing apparatus 1 provided by the embodiment of the invention includes a carrier head 10 for holding and rotating a wafer w, a polishing disk 20 covered with a polishing pad 21, a dresser 30 for dressing the polishing pad 21, and a liquid supply portion 40 for supplying a polishing liquid.
In the chemical mechanical polishing process, the carrier head 10 sucks the wafer w by negative pressure, and presses one surface of the wafer w containing the metal film on the polishing pad 21, and the carrier head 10 performs a rotation motion and a reciprocating motion along the radial direction of the polishing disk 20 so that the surface of the wafer w contacting with the polishing pad 21 is gradually polished away, and simultaneously the polishing disk 20 rotates, and the liquid supply part 40 sprays polishing liquid to the surface of the polishing pad 21. Under the chemical action of the polishing liquid, the wafer w is rubbed against the polishing pad 21 by the relative movement of the carrier head 10 and the polishing platen 20 to perform polishing. During polishing, the dresser 30 serves to dress and activate the topography of the polishing pad 21. The use of the dresser 30 can remove foreign particles remaining on the surface of the polishing pad 21, such as abrasive particles in the polishing liquid and waste materials detached from the surface of the wafer w, and can also planarize the surface deformation of the polishing pad 21 due to polishing.
During the chemical mechanical polishing, the wafer w is pressed against the polishing pad 21 by the carrier head 20 and reciprocates with the carrier head 20 in a radial direction along the polishing pad 10, and at the same time, the carrier head 20 and the polishing pad 10 rotate synchronously, so that the surface of the wafer w contacting with the polishing pad 21 is gradually removed.
As shown in fig. 2, the chemical mechanical polishing apparatus 1 further includes a film thickness measuring device 50 for measuring the film thickness of the wafer w on-line and a control device. The film thickness measuring device 50 is installed in the polishing platen 20 below the polishing pad 21. The film thickness measuring device 50 rotates following the polishing disk 20 to realize on-line measurement of film thickness while polishing. The film thickness measuring device 50 is disposed next to the polishing pad 21, and the wafer w is placed on the polishing pad 21, so that the distance from the film thickness measuring device 50 to the wafer w is the thickness of the polishing pad 21.
In the polishing process, the film thickness change and the film thickness value of the wafer w need to be monitored in real time so as to adopt a corresponding polishing process to avoid over-polishing or incomplete polishing. The thickness of the metal film on the surface of the wafer is measured on line in the polishing process, so that the removal rate of the metal film is accurately controlled by adjusting the pressure of the carrier head 10, and better global planarization is realized. The film thickness measuring device 50 can use eddy current detection, and the principle of the eddy current detection is that when the film thickness measuring device 50 sweeps across the wafer w, the metal film layer on the surface of the wafer w induces eddy current to change the magnetic field generated by the film thickness measuring device 50, so that when the metal film layer is removed by polishing, the film thickness measuring device 50 measures the eddy current change to measure the film thickness of the metal film layer.
In one embodiment of the present invention, film thickness measuring apparatus 50 includes eddy current sensor 51 and detection circuit.
As shown in fig. 3, the detection circuit includes an oscillator, a phase shift unit, a differential amplification unit, a cosine synchronous detection unit, a sine synchronous detection unit, a first low-pass filtering and amplification unit, and a second low-pass filtering and amplification unit.
The oscillator is respectively connected with the exciting coil 511 and the phase shifting unit, the phase shifting unit is respectively connected with the cosine synchronous detection unit and the sine synchronous detection unit, the differential amplification unit is respectively connected with the induction coil 512, the cosine synchronous detection unit and the sine synchronous detection unit, the cosine synchronous detection unit is connected with the first low-pass filtering and amplification unit, and the sine synchronous detection unit is connected with the second low-pass filtering and amplification unit.
As shown in fig. 3, the working principle of the detection circuit is as follows: an excitation voltage is inputted to the excitation coil 511 and the phase shift unit through an oscillator, an output voltage at both ends of the induction coil 512 is detected by the differential amplification unit and inputted to the cosine synchronous detection unit and the sine synchronous detection unit, an original excitation voltage signal (indicated by 0 ° in fig. 3) and a phase-shifted quadrature voltage signal (indicated by 90 ° in fig. 3) are respectively input to the cosine synchronous detection unit and the sine synchronous detection unit through the phase shift unit, then, the output signal of the cosine synchronous detection unit is subjected to first low-pass filtering and amplification unit to obtain the imaginary component Y of the output voltage of the induction coil 512, the output signal of the sine synchronous detection unit is subjected to second low-pass filtering and amplification unit to obtain the real component X of the output voltage of the induction coil 512, and the real component X and the imaginary component Y are subjected to vector calculation to obtain the amplitude of the output voltage of the induction coil 512.
Figure BDA0003529324680000061
And phase
Figure BDA0003529324680000062
And finally, the output of the detection circuit transmits the amplitude and the phase to an upper computer through a data acquisition module and a communication module.
As shown in fig. 4, the eddy current sensor 51 includes an excitation coil 511, an induction coil 512, a bobbin 513, and a shield case 514. Experiments verify that the double-coil structure has better edge measurement performance than a single coil.
As shown in fig. 4, the coil frame 513 is used to support and fix the induction coil 512 and the excitation coil 511, and insulate the two coils, the induction coil 512 and the excitation coil 511 are wound on the coil frame in the same direction, and four leads of the two coils are led out from one side of the coil frame 513, and the material of the coil frame 513 may be organic glass or PPS engineering plastic.
As shown in fig. 4, a shielding shell 514 made of permalloy or aluminum and having a thickness of 0.2mm to 0.5mm is provided around the coil bobbin 513. The shielding shell 514 can reduce the influence of the change of the external magnetic field environment on the performance of the eddy current sensor 51. In one embodiment, the core layer of the shield shell 514 is made of a metallic material and the surface is coated with a non-metallic material layer to prevent metal ion contamination.
In one embodiment, the excitation coil 511 and the induction coil 512 are both flat coils and are coaxially arranged, and the winding direction of the excitation coil 511 is the same as that of the induction coil 512. The coil can be wound by adopting an enameled wire winding process and can also be manufactured by a PCB (printed Circuit Board) or MEMS (micro-electromechanical System) process.
As shown in fig. 5, as an embodiment, the excitation coil 511 and the induction coil 512 are both annular flat coils, and the excitation coil 511 and the induction coil 512 are arranged in parallel and coaxially. Specifically, in the chemical mechanical polishing apparatus 1, the excitation coil 511 is located below the induction coil 512, and the spacing between the excitation coil 511 and the induction coil 512 is less than 0.9 mm. The inner diameter of the exciting coil 511 is larger than 1mm, the outer diameter is smaller than 5mm, and the number of turns is smaller than 200 turns. The inner diameter of the induction coil 512 is larger than 1mm, the outer diameter is smaller than 8mm, and the number of turns is not larger than 600 turns and not smaller than that of the excitation coil 511. In one embodiment, the exciting coil 511 has an inner diameter of 2mm, an outer diameter of 4.2mm, and a number of turns of 50 turns, and the induction coil 512 has an inner diameter of 2mm, an outer diameter of 8mm, and a number of turns of 350 turns.
As shown in fig. 6, as another possible embodiment, the excitation coil 511 and the induction coil 512 are both annular flat coils, the excitation coil 511 and the induction coil 512 are coaxially and parallelly disposed, the excitation coil 511 is located in the ring of the annular induction coil 512, and the induction coil 512 wraps the outer diameter of the excitation coil 511. The inner diameter of the exciting coil 511 is larger than 1mm, the outer diameter is smaller than 5mm, and the number of turns is smaller than 100 turns. The inner diameter of the induction coil 512 is not less than the outer diameter of the excitation coil 511, the outer diameter of the induction coil 512 is less than 8mm, and the number of turns is not more than 600 turns and not less than the number of turns of the excitation coil 511. In one embodiment, the exciting coil 511 has an inner diameter of 1mm, an outer diameter of 3mm, and 50 turns, and the induction coil 512 has an inner diameter of 4mm, an outer diameter of 7mm, and 300 turns.
The mounting position of the eddy current sensor 51 is as shown in fig. 2, and the lift-off height of the eddy current sensor 51 from the metal film is defined as the distance from the induction coil 512 to the metal film, and is not more than 4 mm. The upper surface of eddy current sensor 51 should be as close to polishing pad 21 as possible during use, typically with an initial thickness of polishing pad 21 of 3.5mm or less and a maximum lift-off height of typically 3.5 mm. .
The eddy current sensor 51 is a core part of the film thickness measuring apparatus 50, and is mainly used for exciting an alternating electromagnetic field and inducing a change in induced electromotive force due to a mutual inductance effect caused by inducing different metal thin films. Under the condition that other conditions are not changed, the induced electromotive force and the thickness of the metal film have a one-to-one correspondence relationship.
The exciting coil 511 is mainly used for introducing an alternating current signal with a fixed frequency to generate an alternating magnetic field, so that induced electromotive force is generated in the metal film and the induction coil 512, and a coupled electromagnetic induction relationship exists among the exciting coil 511, the induction coil 512 and the metal film. As shown in fig. 7, using the transformer model, the coupling relationship can be solved.
Here, the inductance of the exciting coil 511 is defined as L1The internal resistance of the exciting coil 511 is R1The excitation voltage of the excitation signal inputted to the excitation coil 511 is U1The excitation current of the excitation signal is I1The angular frequency of the excitation signal is ω; the output voltage across the induction coil 512 is U2The internal resistance of the induction coil 512 is R2Inductance of the induction coil 512 is L2(ii) a Of thin metal films or the likeEffective inductance of LtThe equivalent resistance of the metal thin film is RtThe induced current of the metal film is It(ii) a The mutual inductance between the exciting coil 511 and the metal thin film is M1tThe mutual inductance between the exciting coil 511 and the metal thin film is k1t(x) The mutual inductance between the exciting coil 511 and the induction coil 512 is M12The mutual inductance between the exciting coil 511 and the induction coil 512 is k12The mutual inductance between the induction coil 512 and the metal film is M2tThe mutual inductance between the induction coil 512 and the metal film is k2t(x)。
Assuming that the induction coil 512 is open-circuited and neglecting the influence of mutual inductance of the exciting coil 511 by the metal film, according to kirchhoff's voltage law, it can be obtained that:
I1(R1+jωL1)＝U1 1)
RtLt+jωLtIt＝jωM1tI1 2)
R2I2+jωL2I2+jωM12I1-jωM2tIt＝U2 3)
the mutual inductance can be expressed as:
Figure BDA0003529324680000081
Figure BDA0003529324680000082
Figure BDA0003529324680000083
wherein x is the lift-off height. Mutual inductance factor only with distance under the condition of coil other parameter determinationRelated, in other words, k1t(x) In relation to the vertical distance between the exciting coil 511 and the metal thin film, k2t(x) In relation to the vertical distance between the induction coil 512 and the metal film. Based on the dual-coil structure of eddy current sensor 51 in the embodiment of the present application, as shown in fig. 5 or fig. 6, the distance between excitation coil 511 and induction coil 512 is fixed, so k is12Is a constant number, k1t(x) And x2t(x) Can be expressed as a function of lift-off height x. And, k12、k1t(x) And k2t(x) The values of (A) are all between 0 and 1.
According to the equivalent eddy current ring theory, when the thickness of the conductor film is extremely thin, the following can be obtained:
Figure BDA0003529324680000091
Lt＝μ0·S(r2，r1) (8)
wherein t is the film thickness, μ0For relative permeability, σ is the electrical conductivity, r1Is equivalent to the inner diameter of the swirl ring, r2Is the outer diameter of the equivalent swirl ring, S (r)2，r1) Is a function of the inner and outer diameters of the equivalent vortex ring. When the coil structure is fixed, the outer diameter r of the equivalent eddy current ring2Inner diameter r1And S (r)2，r1) The value of (c) may be considered fixed.
Defining a constant G, which can be expressed as:
Figure BDA0003529324680000092
by combining the above equations, an output voltage of:
Figure BDA0003529324680000093
when the eddy current sensor 51 is placed in the space without the sample to be measured, the measured air voltage value is:
Figure BDA0003529324680000094
in fact, the variation of the voltage, i.e. the effective signal, is:
ΔU＝U2-Uair (12)
can be further expressed as:
Figure BDA0003529324680000101
the voltage variation has two characteristic quantities, namely amplitude and phase, and can be expressed as:
Figure BDA0003529324680000102
Figure BDA0003529324680000103
it can be seen that the magnitude | Δ U | and phase
Figure BDA0003529324680000104
Relating only to the lift-off height x and the thickness t of the metal film, when the lift-off height x is fixed, the amplitude | Δ U | and the phase
Figure BDA0003529324680000105
The amplitude | Δ U | and the phase are determined only in relation to the film thickness t, in the case where the structure of the coil, the kind of the metal thin film, the excitation voltage, and the like are determined
Figure BDA0003529324680000106
Can be used to measure the variation of the metal film thickness t. The method of obtaining the film thickness by solving the amplitude | Δ U | may be called an amplitude method, and the method of obtaining the film thickness by solving the phase
Figure BDA0003529324680000107
The method for obtaining the film thickness may be referred to as a phase method.
As the thickness t of the metal film changes, the amplitude | Delta U | has an extreme point, and the thickness corresponding to the extreme point determines the range of the thickness measured by the amplitude method. As the film thickness increases, the amplitude increases and then decreases, and the extreme point of the amplitude | Δ U | can be expressed as:
Figure BDA0003529324680000108
for the phase method, when k12-k1t(x)k2t(x)<Time 0, phase
Figure BDA0003529324680000109
The value of (b) monotonically increases with the increase in film thickness. When k is12-k1t(x)k2t(x)>Time 0, phase
Figure BDA00035293246800001010
There is an extreme point in the value of (b), and as the film thickness increases, the phase value decreases first and then increases. Phase position
Figure BDA00035293246800001011
The extreme points of (A) are:
Figure BDA00035293246800001012
when the eddy current sensor 51 has both the amplitude and phase extremes, there is the following equation:
Figure BDA0003529324680000111
if it is not
Figure BDA0003529324680000112
Method for measuring film thickness in range larger than phase position by amplitude methodOtherwise, it is smaller. When the coil structure parameters, the metal film material to be measured and the lift-off height are determined, the measurement sensitivity and the measurement range of an amplitude method and a phase method can be adjusted by adjusting the excitation frequency.
In order to further improve the measuring sensitivity of the induction coil, an LC resonant circuit shown in fig. 8 is used at both ends of the induction coil, where R2 is the internal resistance of the induction coil, and C is the parallel resonant capacitance. At a frequency f of the excitation signal, the resonant capacitance may take:
Figure BDA0003529324680000113
due to the skin effect, the intensity of the eddy current in the conductor decreases exponentially with the depth into the conductor, and for non-magnetic materials, the skin depth is calculated as
Figure BDA0003529324680000114
Where f is the excitation frequency, which is also the resonant frequency of the LC tank. In order to accurately measure the thickness of the metal film, the skin depth at the operating frequency f is selected to be greater than the maximum thickness of the metal film, i.e., the electromagnetic field completely penetrates through the measured metal film. In addition, due to the existence of the parasitic parameters of the coil, the self-resonant frequency f of the induction coil with the excitation frequency f less than 0.7 times is generally requiredseThis improves the stability of the eddy current sensor 51. Specifically, the excitation frequency f may take 300kHZ to 10 MHz.
Based on the above analysis, another embodiment of the present invention further provides a method for measuring a metal film thickness, which is suitable for measuring a film thickness of a wafer w by using the eddy current type film thickness measuring apparatus 50, wherein a surface film layer of the wafer w is made of a metal material, such as copper, tungsten, aluminum, tantalum, titanium, and the like. The film thickness of the wafer w may be 0 to 3 um.
As shown in fig. 9, the method for measuring a metal film thickness according to the embodiment of the present invention includes:
step S1, when the film thickness of the metal film on the surface of the wafer is measured based on the amplitude method or the phase method, the extreme point corresponding to the amplitude method or the phase method is calculated.
The amplitude method is a method of obtaining the film thickness from the amplitude of the signal output from the film thickness measuring apparatus 50, and the phase method is a method of obtaining the film thickness from the phase of the signal output from the film thickness measuring apparatus 50. Specifically, the extreme points corresponding to the amplitude method or the phase method may be calculated according to the above equations (16) and (17).
And step S2, adjusting the excitation frequency according to the extreme point, the measurement range and/or the measurement sensitivity, wherein the measurement range is the range of the measured film thickness, the measurement sensitivity is the resolution, and the excitation frequency is the frequency of the excitation signal for the film thickness measuring device.
It can be understood that the larger the measurement range is, the smaller the measurement sensitivity is, the smaller the measurement range is, the larger the measurement sensitivity is, the contradiction between the measurement range and the measurement sensitivity is, and how to obtain the optimal combination is a troublesome problem.
In one embodiment, step S2 includes: and adjusting the excitation frequency according to the calculated extreme point, thereby adjusting the measurement sensitivity and the measurement range of the amplitude method and the phase method to obtain the optimal combination of the measurement sensitivity and the measurement range.
Further, the required measured film thickness range is known, where the measured film thickness range is the thickness of the metal film to be removed, for example, the metal film on the wafer surface has a thickness of 2 μm and needs to be removed completely, and then the required measured film thickness range is 0-2 μm. In order to make the measurement range cover the required measurement film thickness range, the extreme point should be made to fall outside the required measurement film thickness range, and then a range of excitation frequencies can be calculated, taking the maximum value in the range to maximize the measurement sensitivity.
Specifically, step S2 includes:
1) adjusting the extreme point to be out of the required film thickness measuring range so as to realize that the measuring range covers the required film thickness measuring range;
2) the range of the corresponding excitation frequency is calculated, and the maximum value of the range of the excitation frequency is obtained to maximize the measurement sensitivity.
The embodiment of the invention can adjust the size of the excitation frequency according to the calculated extreme point, thereby adjusting the measurement sensitivity and the measurement range of the amplitude method and the phase method and obtaining the optimal combination of the measurement sensitivity and the measurement range.
Fig. 10 and 11 show the relationship between the amplitude and phase at different excitation frequencies and the thickness of the copper film to be measured, respectively. It can be seen that both amplitude and phase sensitivity increase with increasing excitation frequency. In the measurement of an amplitude method, when the resonant frequency is 1.18MHz, the film thickness corresponding to an extreme point is between 1250nm and 1460 nm. Assuming that the film thickness corresponding to the extreme point is 1350nm, according to the formula (16), it can be obtained that the film thickness corresponding to the extreme point is 3670nm and 2048nm respectively when the excitation frequency is 434kHz and 778 kHz. As can be seen from FIG. 10, the measurable film thickness range also gets larger and larger as the frequency is decreased, and the extreme point disappears between the 50nm-2000nm that we need. This effectively demonstrates that equation (16) can be used to guide the adjustment of the sensitivity and range of dual coil sensor amplitude measurements by adjusting the resonant frequency of the resonant tank of the induction coil. In addition, the phase variation monotonically increases along with the increase of the film thickness in the range of measurement range, no extreme point appears, and the film thickness measuring characteristic is better.
Referring to fig. 10 and 11, as the excitation frequency increases, the film thickness corresponding to the extreme point decreases, that is, the measurement range decreases, but the measurement sensitivity increases. The measurement range and the measurement sensitivity are a pair of contradictory parameters, and the measurement sensitivity is reduced by adjusting the measurement range to be larger, and the measurement range is reduced by adjusting the measurement sensitivity to be larger, so that how to obtain the optimal solution under the competitive condition of the measurement range and the measurement sensitivity is a troublesome problem. If a value is manually used for testing, the test is not only troublesome and long in test time, but also easy to cause excessive or insufficient conditions. The embodiment of the invention deduces a specific formula for calculating the extreme point based on the specific structure of the double coils, calculates the extreme point according to the formula, and can quickly and accurately obtain the optimal measuring range and measuring sensitivity in an amplitude method and a phase method by using the extreme point.
Fig. 12 shows the case where the amount of amplitude change is attenuated at the edge at three different excitation frequencies. Wherein, the normalized attenuation value refers to the amplitude of a measured signal at a position between 130mm and 150mm in radius divided by the amplitude of a signal at 130mm on the surface of a copper-plated wafer with the diameter of 300mm and the edge of 2.5 mm. It can be seen that the higher the excitation frequency, the slower the edge decay. In consideration of the measurement range, sensitivity, and edge measurement characteristic of the film thickness measuring device 50, in this embodiment, the excitation frequency may be appropriately 750kHz to 800 kHz.
An 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. The processor realizes the method steps as shown in fig. 9 when executing the computer program. The control device refers to a terminal with data processing capability, and includes but is not limited to a computer, a workstation, a server, and even some Smart phones, palm computers, tablet computers, Personal Digital Assistants (PDAs), Smart televisions (Smart TVs), and the like with excellent performance. The control device is generally installed with an operating system, including but not limited to: windows operating system, LINUX operating system, Android (Android) operating system, Symbian operating system, Windows mobile operating system, and iOS operating system, among others. Specific examples of control devices are listed above in detail, and those skilled in the art will appreciate that control devices are not limited to the listed examples.
An embodiment of the present invention further provides a computer-readable storage medium, in which a computer program is stored, and the computer program, when executed by a processor, implements the method steps shown in fig. 9. The computer program may be stored in a computer readable storage medium, which when executed by a processor, may implement the steps of the various method embodiments described above. Wherein the computer program comprises computer program code, which may be in the form of source code, object code, an 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 disk, removable hard disk, magnetic disk, optical disk, computer Memory, Read-Only Memory (ROM), Random Access Memory (RAM), electrical carrier wave signals, telecommunications signals, software distribution medium, and the like.
Those of ordinary skill in the art will appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, or combinations of computer software and electronic hardware. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
The above-mentioned embodiments are only used for illustrating the technical solutions of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications and substitutions do not substantially depart from the spirit and scope of the embodiments of the present invention, and are intended to be included within the scope of the present invention.

Claims (16)

1. A method for measuring a thickness of a metal film, comprising:
calculating an extreme point corresponding to the amplitude method or the phase method when measuring the film thickness of the metal film on the surface of the wafer based on the amplitude method or the phase method;
and adjusting the excitation frequency according to the extreme point, the measurement range and/or the measurement sensitivity, wherein the measurement range is a film thickness measurement range, the measurement sensitivity is resolution, and the excitation frequency is the frequency of an excitation signal for the film thickness measurement device.
2. The method of claim 1, wherein the excitation frequency is adjusted based on the calculated extreme point, thereby adjusting the measurement sensitivity and the measurement range of the amplitude method and the phase method to obtain an optimal combination of the measurement sensitivity and the measurement range.
3. The method according to claim 2, wherein the extreme point is adjusted to fall outside the desired range of the measured film thickness to achieve a measurement range covering the desired range of the measured film thickness;
the range of the corresponding excitation frequency is calculated, and the maximum value of the range of the excitation frequency is obtained to maximize the measurement sensitivity.
4. The method of claim 1, wherein the amplitude method is a method of obtaining the film thickness by the amplitude of the signal output when the film thickness measuring device detects the metal thin film, and the phase method is a method of obtaining the film thickness by the phase of the signal output when the film thickness measuring device detects the metal thin film.
5. The method of claim 4, wherein the effective signal output by the film thickness measuring device when detecting the metal thin film is:
Figure FDA0003529324670000011
where Δ U is the effective signal of the output voltage across the induction coil, ω is the angular frequency of the excitation signal input to the excitation coil, k1t(x) Is a mutual inductance factor, k, between the exciting coil and the metal film2t(x) Is the mutual inductance factor between the induction coil and the metal film, x is the lift-off height, RtIs the equivalent resistance of the metal film, LtIs an equivalent inductance, k, of a metal film12Is the mutual inductance between the exciting coil and the induction coil, L1To excite the inductance of the coil, L2Is the inductance of the induction coil, I1Is the excitation current of the excitation signal.
6. The method according to claim 5, wherein the metal film thickness is measured by a measuring unit,
Figure FDA0003529324670000021
Lt＝μ0·S(r2,r1)
wherein t is the film thickness, σ is the electrical conductivity, r2Is the outer diameter of the equivalent swirl ring, r1To the inner diameter of the equivalent swirl ring, mu0For relative permeability, S (r)2，r1) Is a custom function.
7. The method of claim 6, wherein the amplitude of the valid signal is:
Figure FDA0003529324670000022
wherein the content of the first and second substances,
Figure FDA0003529324670000023
wherein | Δ U | is the amplitude of the effective signal, and G is a custom constant.
8. The metal film thickness measuring method according to claim 7, wherein the extreme points of the amplitude of the effective signal are:
Figure FDA0003529324670000024
wherein, tUIs the extreme point of the amplitude of the effective signal.
9. The method of claim 6, wherein the phase of the valid signal is:
Figure FDA0003529324670000031
wherein the content of the first and second substances,
Figure FDA0003529324670000032
wherein the content of the first and second substances,
Figure FDA0003529324670000033
g is a self-defined constant for the phase of the effective signal.
10. The method according to claim 9, wherein the phase of the effective signal has an extreme value of:
Figure FDA0003529324670000034
wherein the content of the first and second substances,
Figure FDA0003529324670000035
is the extreme point of the phase of the effective signal.
11. A film thickness measuring apparatus, characterized in that a film thickness measurement is performed by the metal film thickness measuring method according to any one of claims 1 to 10; the film thickness measuring device comprises an eddy current sensor and a detection circuit; the eddy current sensor comprises an exciting coil and an induction coil; the exciting coil and the induction coil are both flat coils and are coaxially arranged, and the winding directions of the exciting coil and the induction coil are the same.
12. The film-thickness measuring apparatus according to claim 11, wherein the detection circuit includes an oscillator, a phase shift unit, a differential amplification unit, a cosine synchronous detection unit, a sine synchronous detection unit, a first low-pass filtering and amplification unit, and a second low-pass filtering and amplification unit;
the oscillator is respectively connected with the exciting coil and the phase shifting unit, the phase shifting unit is respectively connected with the cosine synchronous detection unit and the sine synchronous detection unit, the differential amplification unit is respectively connected with the induction coil, the cosine synchronous detection unit and the sine synchronous detection unit, the cosine synchronous detection unit is connected with the first low-pass filtering and amplification unit, and the sine synchronous detection unit is connected with the second low-pass filtering and amplification unit.
13. The film thickness measuring apparatus according to claim 12, wherein the oscillator inputs the excitation voltage to the excitation coil and the phase shift unit, respectively, the differential amplification unit detects the output voltage at both ends of the induction coil and inputs the output voltage to the cosine synchronous detection unit and the sine synchronous detection unit, the phase shift unit inputs the original excitation voltage signal and the phase-shifted quadrature voltage signal to the cosine synchronous detection unit and the sine synchronous detection unit, respectively, the output signal of the cosine synchronous detection unit is subjected to a first low-pass filtering and amplification unit to obtain the imaginary component Y of the output voltage of the induction coil, the output signal of the sine synchronous detection unit is subjected to a second low-pass filtering and amplification unit to obtain the real component X of the output voltage of the induction coil, and the real component X and the imaginary component Y are vector-calculated to obtain the amplitude of the output voltage of the induction coil.
Figure FDA0003529324670000041
And phase
Figure FDA0003529324670000042
14. A chemical mechanical polishing apparatus, comprising:
a polishing disk for covering a polishing pad for polishing a wafer;
the bearing head is used for holding a wafer and pressing the wafer on the polishing pad;
a film thickness measuring device for measuring a film thickness of the wafer during polishing;
a control device for implementing the method of measuring a metal film thickness according to any one of claims 1 to 10.
15. A control apparatus 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 method for measuring a metal film thickness according to any one of claims 1 to 10 when executing the computer program.
16. A computer-readable storage medium, characterized in that the computer-readable storage medium stores a computer program which, when executed by a processor, implements the steps of the metal film thickness measuring method according to any one of claims 1 to 10.
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