EDDY CURRENT END-POINT DETECTION DEVICE AND METHOD

Description

TECHNICAL FIELD

The invention belongs to the technical field of integrated circuit semiconductor equipment, and particularly relates to an eddy current end-point detection device and method.

RELATED ART

In fabrication of integrated circuit chips, chemical mechanical planarization (CMP) of metal layers needs to be detected in real time, and the CMP end-point is determined according to the values of detected features. In actual use, an eddy current method is often used for online

CMP end-point detection of metal films. Eddy current detection, as a non-contact non-destructive detection method, is suitable for the CMP process of integrated circuit chips.

In the prior art, an exciting coil and a detecting coil are often used together, wherein the exciting coil is used to generate a magnetic field at a certain frequency on the surface of a metal film, and at the same time, the detecting coil is used to detect the change of the magnetic field.

For example, CN114536214A discloses an eddy current sensor and a polishing apparatus, wherein exciting coils are disposed on end walls of a magnetic core and configured to generate an eddy current in a conductor, and a detecting coil is disposed on the central wall of the magnetic core and configured to detect the eddy current.

However, due to the circuit design, such a scheme cannot guarantee both a high frequency and a high quality factor. That is, if the frequency of the detection magnetic field is increased, the quality factor of a circuit will be decreased, leading to a low intensity of the detection magnetic field; if the quality factor is increased, the detection frequency of the circuit will be reduced, making it impossible to generate a large induced current on a high-resistivity metal film.

SUMMARY OF INVENTION

To overcome the defects in the prior art, the invention presents an eddy current end-point detection device and method, which can guarantee the frequency of a detection magnetic field and the quality factor of a circuit.

The technical solution adopted by the invention to solve the above technical problems is as follows: an eddy current end-point detection device comprises:

multiple resonant circuits connected in series, each resonant circuit generating a set frequency;

a magnetic core, inductors of all the resonant circuits being wound around the magnetic core;

according to a thickness threshold of a metal film, the corresponding resonant circuit being selected to generate a target frequency, which is applied to a surface of the metal film;

a detection unit, configured to acquire first voltage signals of two terminals of all the resonant circuits connected in series and second voltage signals of two terminals of any resonant circuits; and

a processing unit, configured to calculate a thickness of the metal film according to the detection voltage signals acquired by the detection unit.

Further, the processing unit converts current amplitude and phase signals received by the detection unit into direct-current voltage signals and then performs analog-to-digital conversion to convert the direct-current voltage signals into film thickness signals corresponding to the metal film.

Further, the processing unit performs differentiation on the first voltage signals and the second voltage signals to convert the first voltage signals and the second voltage signals into direct-current voltage signals and then performs analog-to-digital conversion to convert the direct-current voltage signals into the corresponding thickness of the metal film.

Further, a resonant frequency generated by the resonant circuits is 0.1-3 MHz.

The invention further discloses an eddy current end-point detection method, comprising the following steps:

connecting multiple resonant circuit in series, and winding inductors of the multiple resonant circuits around a same magnetic core;

selecting a target frequency according to a current thickness threshold of a detected metal film;

according to the target frequency, selecting the resonant circuit that outputs a set frequency, and applying the set frequency to a surface of the metal film;

the detection unit acquiring the first voltage signals of two terminals of all the resonant circuits connected in series and the second voltage signals of two terminals of any resonant circuits; and

the processing unit calculating the thickness of the metal film according to changes of the detection voltage signals acquired by the detection unit.

Further, the processing unit converts current amplitude and phase signals received by the detection unit into direct-current voltage signals and then performs analog-to-digital conversion to convert the direct-current voltage signals into film thickness signals corresponding to the metal film.

Further, the processing unit performs differentiation on the first voltage signals and the second voltage signals to convert the first voltage signals and the second voltage signals into direct-current voltage signals and then performs analog-to-digital conversion to convert the direct-current voltage signals into the corresponding thickness of the metal film.

Further, the eddy current end-point detection method further comprises the following step: when the thickness of the metal film falls within a set threshold, selecting a target frequency, wherein the target frequency corresponds to another resonant circuit.

Further, when the thickness of the polished metal film exceeds a thickness detection range of the current target frequency, the current target frequency is switched to a target frequency corresponding to the thickness until the thickness of the metal film reaches a target thickness, and then the target frequency will not be changed.

The invention has the following merits: (1) an exciting circuit and a detecting circuit are integrated in a same circuit, such that the detection device and method are simplified; (2) multiple resonant circuit are connected in series by coupling between multiple inductors, such that different target frequencies can be output, and detection is more flexible; (3) for metal films with a large thickness that exceeds the detection range of a high frequency, the thickness of the metal films cannot be detected; a low-frequency magnetic field has better penetrability, but it has a lower resolution to the thickness of metal films, thus not being suitable for detecting thin metal films; the detection device and method provided by the invention can guarantee a high frequency and a high quality factor and can be used for detecting the thickness of different metal films, thus being high in detection adaptability; (4) detection results can be output in real time, the detection efficiency is high, and detection is accurate; (5) the output target frequency can be changed quickly in the detection process of the same detection device.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a first circuit diagram according to the invention.

FIG. 2 is a second circuit diagram according to the invention.

FIG. 3 is a schematic diagram of a magnetic core where inductors are wound according to the invention.

DESCRIPTION OF EMBODIMENTS

To allow those skilled in the art to gain a better understanding of the technical solutions of the invention, the technical solutions in the embodiments of the invention will be clearly and completely described below in conjunction with accompanying drawings of these embodiments. Obviously, the embodiments described below are merely illustrative ones, and are not all possible ones of the invention. All other embodiments obtained by those ordinarily skilled in the art based on the following ones without creative labor should also fall within the protection scope of the invention.

An eddy current end-point detection device may be arranged below a metal film and comprises:

multiple resonant circuits connected in series, wherein each resonant circuit is formed by an inductor L and a capacitor C which are connected in series or in parallel; as shown in FIG. 1, a resonant circuit L₁C₁ is formed by an inductor L₁ and a capacitor C₁ which are connected in parallel, a resonant circuit L₂C₂ is formed by an inductor L₂ and a capacitor C₂ which are connected in series; as shown in FIG. 2, a resonant circuit L₁C₁ is formed by an inductor L₁ and a capacitor C₁ which are connected in parallel, and a resonant circuit L₂C₂ is formed by an inductor L₂ and a capacitor C₃ which are connected in parallel; each resonant circuit generates a set frequency and generates an alternating-current signal with a resonant frequency of 0.1-3 MHz; that is to say, each inductor L is connected with a capacitor C in series or in parallel, and the inductors L are connected in series;

a magnetic core 1, wherein the inductors 2 of all the resonant circuits are wound around the magnetic core 1 to converge and conduct a magnetic field; in this embodiment, the cross-section of the magnetic core 1 is E-shaped, and the inductors 2 may be wound around protrusions of the magnetic core 1 as shown in FIG. 3, or may be wound around bottom joints;

according to a thickness threshold of the metal film, the corresponding resonant circuit is selected to generate a target frequency, which is applied to a surface of the metal film; in this embodiment, the thickness threshold of the metal film may be 4 um-10 nm;

a detection unit, wherein the detection unit is configured to acquire first voltage signals of two terminals of all the resonant circuits connected in series and acquire second voltage signals of two terminals of any resonant circuits; and

a processing unit, wherein the processing unit is configured to calculate a thickness of the metal film according to the detection voltage signals acquired by the detection unit;

specifically, the processing unit converts current amplitude and phase signals received by the detection unit into direct-current voltage signals and then performs analog-to-digital conversion to convert the direct-current voltage signals into film thickness signals corresponding to the metal film;

more specifically, the processing unit performs differentiation on the first voltage signals and the second voltage signals to convert the first voltage signals and the second voltage signals into direct-current voltage signals and then performs analog-to-digital conversion to convert the direct-current voltage signals into the corresponding thickness of the metal film, wherein the differentiation comprises digital differentiation and analog differentiation.

An eddy current end-point detection method comprises the following steps:

connecting multiple resonant circuit in series, winding inductors 2 of the multiple resonant circuits around a same magnetic core 1, and selecting a target frequency according to a current thickness threshold of a detected metal film;

selecting, according to the target frequency, the resonant circuit that outputs a set frequency, and applying the set frequency to a surface of the metal film;

acquiring, by a detection unit, first voltage signals of two terminals of all the resonant circuits connected in series and second voltage signals of two terminals of any resonant circuits; and

calculating, by a processing unit, a thickness of the metal film according to changes of the detection voltage signals acquired by the detection unit.

More specifically, the detection unit measures the first voltage signals of the two terminals of all the resonant circuits connected in series (that is, the detection unit detects voltage signals of a main circuit formed after all the inductors are connected) and measures the second voltage signals of the two terminals of any resonant circuits (that is, the second voltage signals are voltage signals at any nodes of joints of a plurality of inductors in the middle, not including the two terminals of all the inductors that are connected); the processing unit performs differentiation on the first voltage signals and the second voltage signals to convert the first voltage signals and the second voltage signals into direct-current voltage signals and then performs analog-to-digital conversion to convert the direct-current voltage signals into the thickness of the metal film.

The differentiation comprises digital differentiation and analog differentiation.

when the obtained thickness of the metal film falls within a set threshold, a target frequency is selected again, wherein the target frequency corresponds to another resonant circuit.

Of course, the eddy current end-point detection method may also comprise a step of continuous polishing, wherein when the thickness of the polishing metal film exceeds the thickness detection range of the currently selected target frequency, the currently selected target frequency is switched to a target frequency corresponding to the thickness of the polished film, that is, when the polished metal film reaches a second thickness, the target frequency is changed into a second target frequency; once the thickness of the polished metal film exceeds the thickness detection range of the current second target frequency, the second target frequency is switched to a third target frequency unit the thickness of the metal film reaches a target thickness, at this moment, the target frequency will not be changed anymore, and polishing is stopped.

The above specific embodiments are used to explain the invention and are not intended to limit the invention. Any modifications and transformations made to the invention based on the spirit of the invention and within the protection scope of the claims should fall within the protection scope of the invention.