US20150183084A1

US20150183084A1 - Polishing end point detection method and polishing end point detection apparatus

Info

Publication number: US20150183084A1
Application number: US14/583,505
Authority: US
Inventors: Ban ITO; Naoshi Sakuma; Akihiro Kajita; Tadashi Sakai
Original assignee: Ebara Corp
Current assignee: Ebara Corp
Priority date: 2013-12-27
Filing date: 2014-12-26
Publication date: 2015-07-02
Also published as: TW201524674A; KR20150077337A; JP2015126179A

Abstract

There is provided a polishing end point detection method of improving the accuracy of detecting a polishing end point. The polishing end point detection method emits light toward a polishing object including a hybrid film made of a nanocarbon material and a light-transmissive material while polishing the polishing object (Step S102). Then, the polishing end point detection method receives light reflected from the polishing object (Step S103). Then, the polishing end point detection method subjects the received reflected light to signal processing (Step S104). Then, the polishing end point detection method determines the polishing end point of the polishing object based on the result of the signal processing (Step S105), and detects the polishing end point (Step S106).

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2013-271413, filed on Dec. 27, 2013, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a polishing end point detection method and a polishing end point detection apparatus.
2. Description of the Related Art
Examples of conventional wiring materials for semiconductor circuits and the like include copper, tungsten, and the like. A reduction in size of such a semiconductor circuit involves an increase in electrical resistance of such a wiring material. As a result, a reduction in current capacity may cause a problem of reduction in reliability. In light of this, as a next generation wiring material, attention has been paid to a nanocarbon material expected to have low resistance and high reliability even for thin line widths.
Examples of the nanocarbon material include a multilayer graphene (MLG) made of graphene sheets stacked thereon and a carbon nanotube (CNT). The MLG is used, for example, as a horizontal wiring of the semiconductor circuit. The carbon nanotube is used, for example, as a vertical wiring (via) of the semiconductor circuit.
The surface of a substrate such as a semiconductor wafer containing a wiring of the nanocarbon material is polished by a polishing apparatus such as a chemical mechanical polishing (CMP) apparatus. When the substrate is polished by the polishing apparatus, the polishing end point is determined.
To this end, according to a conventional technique disclosed in Japanese Patent Laid-Open No. 10-202523, the polishing end point is visually inspected by a human operator. More specifically, when a predetermined time has elapsed since polishing started, the operator stops polishing and visually inspects the surface of the substrate (e.g., for the color and the like of the substrate surface). If the operator determines that polishing is insufficient as a result of visual inspection, the operator starts polishing again. Then, when a predetermined time has elapsed since polishing started, the operator stops polishing and visually inspects the surface of the substrate. According to such a conventional technique, an optimal polishing end point is determined by repeating the polishing and the visual inspection.

SUMMARY OF THE INVENTION

The conventional technique does not consider improving the accuracy of detecting the polishing end point.
Specifically, in the conventional technique, polishing end points vary because the operator visually inspects the polishing end point. In addition, the visual inspection by the operator may increase man-hours because the operator needs to repeat polishing and visual inspection. Alternatively, in order to check the polished state, destruction observation using cross-sectional SEM may conventionally be used to inspect the film thickness of the substrate. However, this method involves destruction of the substrate and hence cannot be used in a step of producing actual products.
It is therefore an object of an aspect of the present invention to improve the accuracy of detecting the polishing end point.
An aspect of a polishing end point detection method of the present invention has been made in view of the above problem and comprises the steps of: emitting light to a polishing object including a hybrid film made of a nanocarbon material and a light-transmissive material while polishing the polishing object; and detecting a polishing end point of the polishing object based on light reflected from the polishing object.
In an aspect of the polishing end point detection method of the present invention, the step of detecting the polishing end point of the polishing object may detect the polishing end point of the polishing object using optical interferometry for measuring a film thickness of the polishing object based on a phase difference in light reflected from the polishing object.
In an aspect of the polishing end point detection method of the present invention, the step of detecting the polishing end point of the polishing object may detect the polishing end point of the polishing object based on a change in intensity of a composite wave obtained by combining the light reflected from a plurality of reflecting surfaces of the polishing object and a polishing rate of the polishing object.
In an aspect of the polishing end point detection method of the present invention, the step of detecting the polishing end point may detect the polishing end point of the polishing object based on a change in optical spectrum of the light reflected from the polishing object.
In an aspect of the polishing end point detection method of the present invention, the step of detecting the polishing end point may detect the polishing end point of the polishing object based on a result of comparison between a preset optical spectrum waveform and an optical spectrum waveform of the light reflected from the polishing object.
In an aspect of the polishing end point detection method of the present invention, the nanocarbon material may include a graphene sheet or a carbon nanotube.
An aspect of a polishing end point detection apparatus of the present invention comprises: a light emitting unit configured to emit light toward a polishing object including a hybrid film made of a nanocarbon material and a light-transmissive material; a light receiving unit configured to receive light reflected from the polishing object; and a detection unit configured to detect the polishing end point of the polishing object based on the light received by the light receiving unit.
In an aspect of the polishing end point detection apparatus of the present invention, the detection unit may detect the polishing end point of the polishing object using optical interferometry for measuring a film thickness of the polishing object based on a phase difference in light reflected from the polishing object.
In an aspect of the polishing end point detection apparatus of the present invention, the detection unit may detect the polishing end point of the polishing object based on a change in intensity of a composite wave obtained by combining the light reflected from a plurality of reflecting surfaces of the polishing object and a polishing rate of the polishing object.
In an aspect of the polishing end point detection apparatus of the present invention, the detection unit may detect the polishing end point of the polishing object based on a change in optical spectrum of the light reflected from the polishing object.
In an aspect of the polishing end point detection apparatus of the present invention, the detection unit may detect the polishing end point of the polishing object based on a result of comparison between a preset optical spectrum waveform and an optical spectrum waveform of the light reflected from the polishing object.
In an aspect of the polishing end point detection apparatus of the present invention, the nanocarbon material may include a graphene sheet or a carbon nanotube.
Such an aspect of the present invention can improve the accuracy of detecting the polishing end point.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view schematically illustrating an entire structure of the polishing apparatus and the polishing end point detection apparatus;

FIG. 2A is a view for describing a measurement principle of optical interferometry;

FIG. 2B is a view for describing the measurement principle of optical interferometry;

FIG. 3 is a view for describing the measurement principle of optical interferometry;

FIG. 4A is a view illustrating an outline of processing of a signal processing unit;

FIG. 4B is a view illustrating an outline of processing of the signal processing unit;

FIG. 4C is a view illustrating an outline of processing of the signal processing unit;

FIG. 5 is a view illustrating an outline of wiring using an MLG and a carbon nanotube;

FIG. 6A is a view schematically illustrating an example of a circuit using the carbon nanotubes;

FIG. 6B is a view schematically illustrating an example of the circuit using the carbon nanotubes;

FIG. 6C is a view schematically illustrating an example of the circuit using the carbon nanotubes;

FIG. 7 is a view simply modeling the example of the circuit using the carbon nanotubes;

FIG. 8 is a flowchart illustrating a flow of a process of detecting a polishing end point;

FIG. 9A is a graph illustrating a change in optical spectrum of reflected light from a substrate modeled in FIG. 7, which has been polished seven times while polished repeatedly, each process of polishing the substrate continuing for 240 seconds;

FIG. 9B is a graph illustrating a change in optical spectrum of reflected light from a substrate modeled in FIG. 7, which has been polished seven times while polished repeatedly, each process of polishing the substrate continuing for 240 seconds;

FIG. 9C is a graph illustrating a change in optical spectrum of reflected light from a substrate modeled in FIG. 7, which has been polished seven times while polished repeatedly, each process of polishing the substrate continuing for 240 seconds; and

FIG. 10 is a graph illustrating an example of detecting the polishing end point using a spectral index waveform.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a polishing end point detection method and a polishing end point detection apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a view schematically illustrating an entire structure of the polishing apparatus and the polishing end point detection apparatus. The description starts with the polishing apparatus.
As illustrated in FIG. 1, a polishing apparatus 100 includes a polishing table 110, on an upper surface of which a polishing pad 108 can be mounted so as to polish a substrate 102 such as a semiconductor wafer. The polishing apparatus 100 further includes a first electric motor 112 rotationally driving the polishing table 110. The polishing apparatus 100 furthermore includes a top ring 116 capable of holding the substrate 102. The polishing apparatus 100 still further includes a second electric motor 118 rotationally driving the top ring 116.
The polishing apparatus 100 further includes a slurry line 120 on an upper surface of the polishing pad 108. The slurry line 120 supplies a polishing liquid containing a polishing agent. The polishing apparatus 100 furthermore includes a polishing apparatus control unit 140 outputting various control signals about the polishing apparatus 100.
When the substrate 102 is polished, the polishing apparatus 100 supplies polishing slurry containing abrasive grains onto the upper surface of the polishing pad 108 through the slurry line 120 and the first electric motor 112 rotationally drives the polishing table 110. Then, the polishing apparatus 100 presses the substrate 102 held by the top ring 116 against the polishing pad 108 in a state in which the top ring 116 is rotated about a rotation axis eccentric to a rotation axis of the polishing table 110. This allows the substrate 102 to be polished and planarized by the polishing pad 108 holding the polishing slurry.
The description now focuses on the polishing end point detection apparatus. As illustrated in FIG. 1, a polishing end point detection apparatus 200 includes an optical sensor 210. The polishing end point detection apparatus 200 further includes an end point detection apparatus body 220 connected to the optical sensor 210 through rotary joint connectors 160 and 170.
The present embodiment uses optical interferometry to measure the film thickness of the substrate 102 and to detect the polishing end point of the substrate 102. Here, the measurement principle of the optical interferometry will be briefly described.
FIGS. 2A, 2B, and 3 each are a view for describing the measurement principle of the optical interferometry. An example used herein assumes that a polishing film 320 to be polished is stacked on a silicon substrate 310. First, as illustrated in FIG. 2A, after incident light (n0) is emitted from the optical sensor 210, reflected light R1 is reflected on a surface of the polishing film 320 and reflected light R2 is transmitted through the polishing film 320 and reflected on an interface between the polishing film 320 and the silicon substrate 310. Then, the reflected light R1 is combined with the reflected light R2. Note that the reflected light R1 and the reflected light R2 have the same phase.
Next, as illustrated in FIG. 2B, even after the film thickness of the polishing film 320 is changed, the reflected light R1 is reflected on a surface of the polishing film 320 and the reflected light R2 is transmitted through the polishing film 320 and reflected on an interface between the polishing film 320 and the silicon substrate 310. Then, the reflected light R1 is combined with the reflected light R2. Note that the reflected light R1 and the reflected light R2 have reverse phases to each other. Thus, it is understood from FIGS. 2A and 2B that a change in the film thickness of the polishing film 320 due to polishing generates a phase shift between the reflected light R1 and the reflected light R2.
FIG. 3 is a graph illustrating a transition in the signal intensity of a composite wave obtained by combining the reflected light R1 and the reflected light R2. In FIG. 3, the abscissa axis represents the film thickness of the polishing film 320, and the ordinate axis represents the signal intensity of the composite wave obtained by combining the reflected light R1 and the reflected light R2. A change in the film thickness of the polishing film 320 due to polishing generates a phase shift between the reflected light R1 and the reflected light R2 according to a change in the film thickness. This, in turn, leads to a periodic change in the reflection intensity of the composite wave as illustrated in FIG. 3. Note that in FIG. 3, (1) represents a portion where the reflected light R1 and the reflected light R2 have the same phase as illustrated in FIG. 2A, and (2) represents a portion where the reflected light R1 and the reflected light R2 have reverse phases to each other as illustrated in FIG. 2B.
The polishing end point detection apparatus 200 measures the film thickness of the polishing film 320 and detects the polishing end point of the polishing film 320 based on the transition in the signal intensity of the composite wave. For example, if the relationship between the polishing rate of the polishing film 320 and the period of the transition in the signal intensity of the composite wave is known, the polishing end point detection apparatus 200 can measure the polishing amount of the polishing film 320 and detect the polishing end point of the polishing film 320.
Referring now back to FIG. 1, the polishing end point detection apparatus 200 will be specifically described. The optical sensor 210 includes a light emitting unit emitting light toward the substrate 102; and a light receiving unit receiving light reflected from the substrate 102. Here, a hole is formed in the polishing table 110 and the polishing pad 108 so as to insert the optical sensor 210 thereinto from a rear surface side of the polishing table 110. The optical sensor 210 is inserted into the hole formed in the polishing table 110 and the polishing pad 108. The optical sensor 210 emits light toward the substrate 102 and receives light reflected from the substrate 102.
The end point detection apparatus body 220 includes a spectroscope 230, a signal processing unit 240, and a polishing end point detection unit 250. The spectroscope 230 receives the reflected light from the optical sensor 210. The spectroscope 230 splits the reflected light for each wavelength (e.g., 400 nm to 800 nm).
The signal processing unit 240 calculates the spectral index representing the intensity of the reflected light for each predetermined interval (e.g., one rotation of the polishing table 110) along the polishing time. The signal processing unit 240 calculates the spectral index waveform obtained by plotting the calculated spectral index in time sequence.
The description will now focus on the processing of the signal processing unit 240. FIGS. 4A, 4B, and 4C each are a view illustrating an outline of processing of the signal processing unit 240. First, as illustrated in FIG. 4A, the signal processing unit 240 calculates the signal intensity of the reflected light of each wavelength for each predetermined interval (e.g., one rotation of the polishing table 110) along the polishing time. Then, as illustrated in FIG. 4B, the signal processing unit 240 calculates the spectral index for each predetermined interval based on the signal intensity of the reflected light of each wavelength for each predetermined interval. Then, as illustrated in FIG. 4C, the signal processing unit 240 calculates the spectral index waveform by plotting the spectral index of each predetermined interval in time sequence.
Referring back to FIG. 1 again, the polishing end point detection unit 250 detects the polishing end point of the substrate 102 based on the light received by the optical sensor 210 (light receiving unit). Specifically, the polishing end point detection unit 250 detects the polishing end point of the substrate 102 using optical interferometry for measuring the film thickness of the substrate 102 based on the phase difference in light reflected from the substrate 102. For example, as described above in FIG. 3, the polishing end point detection unit 250 may detect the polishing end point of the polishing object based on the change in intensity of the composite wave obtained by combining the light reflected from a plurality of reflecting surfaces of the polishing object and the polishing rate of the polishing object.
Alternatively, the polishing end point detection unit 250 may detect the polishing end point of the substrate 102 based on the change in the optical spectrum of the light reflected from the substrate 102. For example, the polishing end point detection unit 250 compares a preset optical spectrum waveform with the optical spectrum waveform of the light reflected from the polishing object. Then, the polishing end point detection unit 250 may detect the polishing end point of the polishing object based on the result of comparison. This method will be described later.
The polishing end point detection unit 250 is connected to a polishing apparatus control unit 140 performing various controls about the polishing apparatus 100. When the polishing end point of the substrate 102 is detected, the polishing end point detection unit 250 outputs a signal to that effect to the polishing apparatus control unit 140. When the signal indicating the polishing end point is received from the polishing end point detection unit 250, the polishing apparatus control unit 140 stops polishing by the polishing apparatus 100.
The description will now focus on the substrate 102 to be polished in the present embodiment. According to the present embodiment, the substrate 102 includes a hybrid film made of a nanocarbon material and a light-transmissive material.
The nanocarbon material used herein includes a graphene sheet or a carbon nanotube. The graphene sheet is a sheet-like substance having a hexagonal lattice structure like honeycomb made of carbon atoms and their bonds. For example, a multilayer graphene (MLG) made of graphene sheets stacked thereon is used for horizontal wiring of a semiconductor circuit.
In addition, the carbon nanotube is a substance of the graphene sheet with a single-layered or multilayered coaxial tubular shape. The carbon nanotubes are used, for example, as a vertical wiring (via) of the semiconductor circuit.
FIG. 5 is a view illustrating an outline of wiring using an MLG and a carbon nanotube. As illustrated in FIG. 5, the wiring of the semiconductor circuit includes horizontal wirings 410 containing MLG and vertical wirings (vias) 420 containing carbon nanotubes.
The description will now focus on a specific circuit structure. FIGS. 6A, 6B, and 6C each are a view schematically illustrating an example of the circuit using the carbon nanotubes.
As illustrated in FIG. 6A, the circuit includes a metal film 510 made of copper (Cu), tungsten (W), or the like; a nitride film 520 stacked on the metal film 510; and an oxide film 530 stacked on the nitride film 520. A hole (via) for vertical wiring is formed in part of the oxide film 530. An underlying film 540 (e.g., Ti or TiN) is formed on the oxide film 530 and in a portion of the oxide film 530 where the hole is formed. A catalyst layer 550 (e.g., Ni or Co) for growing carbon nanotubes is formed on the underlying film 540. Carbon nanotubes 560 are formed grown in a vertical direction on the catalyst layer 550. Further, a hybrid layer 570, in which the carbon nanotubes 560 have been impregnated with a light-transmissive material 590 (e.g., spin on glass (SOG)), is formed on the catalyst layer 550. Furthermore, an SOG layer 580, which is a single layer of the light-transmissive material 590, is formed on the hybrid layer 570. The SOG film used in the hybrid layer 570 and the SOG layer 580 is an example of the light-transmissive material 590. Note that the present embodiment has described an example of using an SOG film for the hybrid layer 570 and the SOG layer 580, but not limited thereto, and any substance can be used as long as the substance can transmit light and can impregnate the carbon nanotubes 560 therewith. Note also that the following description will focus on detecting the polishing end point of a substrate including the carbon nanotubes and the light-transmissive material, but not limited thereto, and the present embodiment can be applied to detecting the polishing end point of a substrate including other carbon nanotube material (such as MLG) and the light-transmissive material.
Here, assume that the substrate is polished in the order of FIGS. 6A, 6B, and 6C, until the polishing end point is reached at the state of FIG. 6C. FIG. 7 is a view simply modeling the example of the circuit using the carbon nanotubes.
As illustrated in FIG. 7, the modeled circuit includes a silicon substrate 610; a TEOS (insulating film) layer 620 stacked on the silicon substrate 610; and an underlying layer 630 made of TiN and Ti stacked on the TEOS layer 620. The modeled circuit further includes a catalyst layer 660 made of Ni stacked on the underlying layer 630. The modeled circuit furthermore includes a hybrid layer 640 mixing the carbon nanotubes and SOG and being stacked on the catalyst layer 660. The modeled circuit still furthermore includes an SOG layer 650 stacked on the hybrid layer 640. Note that the catalyst layer 660 is a very thin layer (e.g., 2 to 3 nm) and is turned into fine particles when carbon nanotubes are grown. For this reason, the catalyst layer 660 has little effect on detection of the polishing end point according to the present embodiment.
The description will now focus on the process of detecting the polishing end point in the modeled circuit. FIG. 8 is a flowchart illustrating a flow of the process of detecting the polishing end point. First, the polishing apparatus control unit 140 starts polishing the substrate 102 (Step S101). Then, the optical sensor 210 emits light from the light emitting unit (Step S102). Then, the light receiving unit of the optical sensor 210 receives light reflected from the substrate 102 (Step S103).
Then, the signal processing unit 240 subjects the reflected light to signal processing (Step S104). Specifically, as illustrated in FIG. 4A, the signal processing unit 240 calculates the signal intensity of the reflected light of each wavelength for each predetermined interval (e.g., one rotation of the polishing table 110) along the polishing time. Then, as illustrated in FIG. 4B, the signal processing unit 240 calculates the spectral index for each predetermined interval based on the signal intensity of the reflected light of each wavelength for each predetermined interval. Then, as illustrated in FIG. 4C, the signal processing unit 240 calculates the spectral index waveform by plotting the spectral index of each predetermined interval in time sequence.
Then, based on a result of the signal processing in Step S104, the polishing end point detection unit 250 determines the polishing end point (Step S105). For example, the polishing end point detection unit 250 may determine the polishing end point of the substrate 102 based on the change in the optical spectrum of the reflected light.
The above process will be described as follows. FIGS. 9A, 9B, and 9C each are a graph illustrating a change in optical spectrum of reflected light from the substrate modeled in FIG. 7, which has been polished seven times while polished repeatedly, each process of polishing the substrate continuing for 240 seconds. In FIGS. 9A, 9B, and 9C, the abscissa axis represents the wavelength of light, and the ordinate axis represents the signal intensity of the reflected light. Note that according to the present embodiment, the film thickness of the TEOS layer 620 in the central portion of the substrate was checked by a film thickness measuring device at the end of each polishing. As a result, it was found that the TEOS layer 620 in the central portion of the substrate was hardly scraped at the end of the sixth polishing, but was largely scraped at the end of the seventh polishing. This leads to considering that the CNT-SOG hybrid layer 640, the catalyst layer 660, the underlying layer 630, and the TEOS layer 620 in the central portion of the substrate were scraped off in the seventh polishing.
FIG. 9A is a graph illustrating the waveform of optical spectrum plotted every 10 rotations from the 10th rotation to the 190th rotation in the 7th polishing. In FIG. 9A, the optical spectrum waveform has an up and down amplitude at a relatively small period.
Then, FIG. 9B is a graph illustrating the waveform of optical spectrum plotted every 10 rotations from the 200th rotation to the 250th rotation in the 7th polishing. In FIG. 9B, the optical spectrum waveform has a less up and down amplitude at a small period, and has an up and down amplitude at a large period.
Further, FIG. 9C is a graph illustrating the waveform of optical spectrum plotted every 10 rotations from the 260th rotation to the 710th rotation in the 7th polishing. In FIG. 9C, the optical spectrum waveform has little up and down amplitude at a small period, and has an up and down amplitude at a large period.
Such a change in the waveform of optical spectrum leads to considering that, although roughly, the waveform like FIG. 9A appears when the CNT-SOG hybrid layer 640 is polished; the waveform like FIG. 9B appears when the catalyst layer 660 or the underlying layer 630 is polished; and the waveform like FIG. 9C appears when the TEOS layer 620 is polished.
In light of this, when the optical spectrum waveform like FIG. 9C is detected, the polishing end point detection unit 250 determines that the TEOS layer 620 has started to be polished. When a preset predetermined time has elapsed since it was determined that the TEOS layer 620 started to be polished, the polishing end point detection unit 250 may determine as the polishing end point being reached (detect the polishing end point). For example, the optical spectrum waveform like FIG. 9C is preset, and then the polishing end point detection unit 250 compares the preset optical spectrum waveform with the optical spectrum waveform calculated by the signal processing unit 240. When the degree of matching between the preset optical spectrum waveform and the optical spectrum waveform calculated by the signal processing unit 240 is greater than or equal to a preset threshold, the polishing end point detection unit 250 may determine that the TEOS layer 620 has started to be polished.
Alternatively, the polishing end point detection unit 250 may detect the polishing end point based on a spectral index waveform. FIG. 10 is a graph illustrating an example of detecting the polishing end point using the spectral index waveform.
In FIG. 10, the abscissa axis represents the polishing time, and the ordinate axis represents the reflection intensity. For example, the frequency of the spectral index waveform obtained when the TEOS layer 620 is polished is preset. When the spectral index waveform of the preset frequency appears and a minimum value 710 of the waveform is detected, the polishing end point detection unit 250 may determine as the polishing end point being reached. Alternatively, when a maximum value 720, not limited to the minimum value 710, is detected, the polishing end point detection unit 250 may determine as the polishing end point being reached. Still alternatively, when the minimum value 710 or the maximum value 720 is detected a plurality of times, the polishing end point detection unit 250 may determine as the polishing end point being reached. Further, when a predetermined time has elapsed since the minimum value 710 or the maximum value 720 was detected (for example, a predetermined time α has elapsed since the maximum value 720 was detected), the polishing end point detection unit 250 may determine as the polishing end point being reached.
Referring now back to FIG. 8, the polishing end point detection unit 250 repeats the process in step S105 until the polishing end point is detected (Step S106: No). If the polishing end point is detected (Step S106: Yes), the polishing end point detection unit 250 sends a message indicating that the polishing end point has been detected, to the polishing apparatus control unit 140 (Step S107).
When the message indicating that the polishing end point has been detected is received from the polishing end point detection unit 250, the polishing apparatus control unit 140 stops polishing the substrate (Step S108).
As described above, the present embodiment can improve the accuracy of detecting the polishing end point. Conventional technique for detecting the polishing end point of a substrate such as a semiconductor wafer containing a nanocarbon material wiring has been visually implemented by a human operator, resulting in variations in detection of the polishing end point.
In contrast to the above conventional technique, the present embodiment emits light toward a polishing object including a hybrid film made of a nanocarbon material and a light-transmissive material while polishing the polishing object, and detects the polishing end point of the polishing object based on the light reflected from the polishing object. Therefore, the present embodiment eliminates the need for an operator to perform visual inspection, and thus can improve the accuracy of detecting the polishing end point. In addition, the present embodiment eliminates the need for the operator to repeatedly perform polishing and visual inspection, and thus can reduce man-hours.
In particular, the nanocarbon material is generally black, and thus hardly reflects light but absorbs light. For this reason, the nanocarbon material alone has a problem in that it may be difficult to measure the film thickness using optical interferometry. In contrast to this, the present embodiment uses optical interferometry to measure the polishing object including the hybrid film made of a nanocarbon material and a light-transmissive material. Therefore, the present embodiment can reflect part of light on a surface of the light-transmissive material, thus allowing for measurement of the film thickness using optical interferometry.
Examples of the method of detecting the polishing end point include using rotation torque of the polishing table 110. Specifically, the rotation torque of the polishing table 110 correlates with the current flowing in the first electric motor 112 for rotationally driving the polishing table 110. For example, assume a case of polishing a polishing object with a first layer and a second layer stacked thereon, whose polishing rates differ greatly from each other. In this case, a change in the polishing object from the first layer to the second layer greatly changes the current flowing in the first electric motor 112. Thus, the detection of the change in the current may detect the start of polishing of the second layer.
In this regard, the substrate to be polished in the present embodiment was such that the SOG layer 650 had a polishing rate of 180 to 200 nm/min, the CNT-SOG hybrid layer 640 had a polishing rate of 150 to 180 nm/min, the underlying layer 630 had a polishing rate of 90 to 110 nm/min, and the TEOS layer 620 had a polishing rate of 90 to 110 nm/min.
As described above, according to the substrate to be polished in the present embodiment, the polishing rate of each layer did not differ so much, and thus the current flowing in the first electric motor 112 did not greatly change. Therefore, according to the substrate to be polished in the present embodiment, it is difficult to apply the method of detecting the polishing end point using the rotation torque of the polishing table 110.
Note that the polishing rate of the CNT-SOG hybrid layer 640 may change according to the density of carbon nanotubes. An increase in the density of carbon nanotubes reduces the polishing rate. In this case, this leads to an increase in difference in the polishing rate between the CNT-SOG hybrid layer 640 and the underlying layer, which may change the electric motor torque due to polishing of the underlying layer, but it is considered that torque change is difficult to occur for the reason described below.
In general, the nanocarbon material has a low friction coefficient, and hence is used as lubricant. When the nanocarbon material is used as lubricant, carbon residues occur during polishing and remain on the polishing pad surface, leaving the surface in a slippery state. For this reason, the torque values are small as a whole, leading to a possibility that the change is less visible even when the underlying layer is exposed to the polishing surface.
In contrast to this, the present embodiment employs a method of detecting the polishing end point using optical interferometry. Thus, as illustrated in FIG. 9, a change in the layer to be polished causes the optical spectrum waveform to be greatly changed. As a result, the present embodiment can accurately detect the polishing end point.

REFERENCE SIGNS LIST

100 polishing apparatus
102 substrate
140 polishing apparatus control unit
200 polishing end point detection apparatus
210 optical sensor
220 end point detection apparatus body
230 spectroscope
240 signal processing unit
250 polishing end point detection unit
510 metal film
520 nitride film
530 oxide film
540 underlying film
550 catalyst layer
560 carbon nanotube
570 hybrid layer
580 SOG layer
590 light-transmissive material
610 silicon substrate
620 TEOS layer
630 underlying layer
640 hybrid layer
650 SOG layer

Claims

What is claimed is:

1. A polishing end point detection method comprising the steps of:

emitting light to a polishing object including a hybrid film made of a nanocarbon material and a light-transmissive material while polishing the polishing object; and

detecting a polishing end point of the polishing object based on light reflected from the polishing object.

2. The polishing end point detection method according to claim 1, wherein

the step of detecting the polishing end point of the polishing object detects the polishing end point of the polishing object using optical interferometry for measuring a film thickness of the polishing object based on a phase difference in light reflected from the polishing object.

3. The polishing end point detection method according to claim 1, wherein

the step of detecting the polishing end point of the polishing object detects the polishing end point of the polishing object based on a change in intensity of a composite wave obtained by combining the light reflected from a plurality of reflecting surfaces of the polishing object and a polishing rate of the polishing object.

4. The polishing end point detection method according to claim 1, wherein

the step of detecting the polishing end point detects the polishing end point of the polishing object based on a change in optical spectrum of the light reflected from the polishing object.

5. The polishing end point detection method according to claim 4, wherein

the step of detecting the polishing end point detects the polishing end point of the polishing object based on a result of comparison between a preset optical spectrum waveform and an optical spectrum waveform of the light reflected from the polishing object.

6. The polishing end point detection method according to claim 1, wherein

the nanocarbon material includes a graphene sheet or a carbon nanotube.

7. A polishing end point detection apparatus comprising:

a light emitting unit configured to emit light toward a polishing object including a hybrid film made of a nanocarbon material and a light-transmissive material;

a light receiving unit configured to receive light reflected from the polishing object; and

a detection unit configured to detect the polishing end point of the polishing object based on the light received by the light receiving unit.

8. The polishing end point detection apparatus according to claim 7, wherein

the detection unit detects the polishing end point of the polishing object using optical interferometry for measuring a film thickness of the polishing object based on a phase difference in light reflected from the polishing object.

9. The polishing end point detection apparatus according to claim 7, wherein

the detection unit detects the polishing end point of the polishing object based on a change in intensity of a composite wave obtained by combining the light reflected from a plurality of reflecting surfaces of the polishing object and a polishing rate of the polishing object.

10. The polishing end point detection apparatus according to claim 7, wherein

the detection unit detects the polishing end point of the polishing object based on a change in optical spectrum of the light reflected from the polishing object.

11. The polishing end point detection apparatus according to claim 10, wherein

the detection unit detects the polishing end point of the polishing object based on a result of comparison between a preset optical spectrum waveform and an optical spectrum waveform of the light reflected from the polishing object.

12. The polishing end point detection apparatus according to claim 7, wherein

the nanocarbon material includes a graphene sheet or a carbon nanotube.

13. The polishing end point detection method according to claim 2, wherein

14. The polishing end point detection method according to claim 2, wherein

15. The polishing end point detection method according to claim 3, wherein

16. The polishing end point detection apparatus according to claim 8, wherein

17. The polishing end point detection apparatus according to claim 8, wherein

18. The polishing end point detection apparatus according to claim 9, wherein