Patent Application
20200147747
The present invention relates to an eddy current detection device and a polishing apparatus using the eddy current detection device.
In recent years, with the progress of the higher integration of semiconductor devices, circuit wiring is becoming finer, and an inter-wiring distance is becoming narrower. Therefore, it has been necessary to flatten the surface of a semiconductor wafer as a polishing target, and polishing has been performed by a polishing device as such a means of flattening the surface of the semiconductor wafer.
A polishing apparatus includes a polishing table for holding a polishing pad for polishing a polishing target, and a top ring for pressing the polishing target against the polishing pad while holding the polishing target. Each of the polishing table and the top ring is rotationally driven by a drive section (for example, a motor). A liquid containing polishing agent (slurry) is made to flow on the polishing pad, and the polishing target held by the top ring is pressed against the polishing pad, whereby the polishing target is polished.
In the polishing apparatus, when the polishing target is insufficiently polished, the insulation between circuits cannot be secured, and thus, short-circuiting may occur. Furthermore, when the polishing target is over-polished, there occurs such a problem that the resistance value of a wire increases due to reduction in the cross-sectional area of the wire, or a wire itself is completely removed, and thus a circuit itself is not formed. To cope with these problems, the polishing apparatus is required to detect an optimal polishing end point.
Then, Japanese Patent Laid-Open No. 2017-58245 describes such a technique. In this technique, an eddy current sensor using a so-called pod-type coil is used to detect a polishing end point.
PTL 1: Japanese Patent Laid-Open No. 2017-58245
In a first aspect of the present invention, a configuration is adopted in which there is provided an eddy current detection device capable of being disposed near a polishing target on which a conductive film is formed, the eddy current detection device including a plurality of eddy current sensors, the plurality of eddy current sensors being disposed near to each other, and each of the plurality of eddy current sensors includes a core section, an exciting coil disposed in the core section and configured to form an eddy current in the conductive film, and a detection coil disposed in the core section and configured to detect the eddy current formed in the conductive film.
In a second aspect, a configuration based on the eddy current detection device according to the first aspect is adopted. In this configuration, in at least one eddy current sensor of the plurality of eddy current sensors, the exciting coil and the detection coil constitute the same coil, and the exciting coil can detect the eddy current formed in the conductive film.
In a third aspect, a configuration based on the eddy current detection device according to the first aspect or second aspect is adopted. In this configuration, in at least one eddy current sensor of the plurality of eddy current sensors, the core section includes a bottom surface portion, a magnetic center portion provided at a center of the bottom surface portion, and a circumferential portion provided on a circumference of the bottom surface portion, and the exciting coil and the detection coil are disposed at the magnetic center portion.
In a fourth aspect, a configuration based on the eddy current detection device according to the third aspect is adopted. In this configuration, the exciting coil and the detection coil are disposed at the circumferential portion, in addition to the magnetic center portion.
In a fifth aspect, a configuration based on the eddy current detection device according to the third or fourth aspect is adopted. In this configuration, the circumferential portion constitutes a circumferential wall portion that is provided on a circumference of the bottom surface portion in such a manner as to surround the magnetic center portion.
In a sixth aspect, a configuration based on the eddy current detection device according to the third or fourth aspect is adopted. In this configuration, the bottom surface portion has a pillar-like shape, and the circumferential portion is disposed at both ends of the pillar-like shape.
In a seventh aspect, a configuration based on the eddy current detection device according to the third or fourth aspect is adopted. In this configuration, a plurality of circumferential portions are provided on the circumference of the bottom surface portion.
In an eighth aspect, a configuration based on the eddy current detection device according to the first or second aspect is adopted. In this configuration, in at least one eddy current sensor of the plurality of eddy current sensors, the core section includes a bottom surface portion and a plurality of pillar-like portions extending from the bottom surface portion in a normal direction towards the polishing target, and the plurality of pillar-like portions include a plurality of first pillar-like portions that can generate a first magnetic polarity and a plurality of second pillar-like portions that can generate a second magnetic polarity that is opposite to the first magnetic polarity.
In a ninth aspect, a configuration based on the eddy current detection device according to any one the first to eighth aspects is adopted. In this configuration, the plurality of eddy current sensors are disposed, to form a polygon, at vertices of the polygon and/or along sides of the polygon and/or in an interior of the polygon.
In a tenth aspect, a configuration based on the eddy current detection device according to any one of the first to eighth aspects is adopted. In this configuration, the plurality of eddy current sensors are disposed, to form a straight line, on the straight line.
In an eleventh aspect, a configuration is adopted in which there is provided a polishing apparatus including a polishing table to which a polishing pad for polishing a polishing target can be affixed, a drive section configured to rotationally drive the polishing table, a holding section configured to press the polishing target against the polishing pad by holding the polishing target, the eddy current detection device according to any one of the first to tenth aspects that is disposed in an interior of the polishing table, wherein the eddy current formed in the polishing target by the exciting coil in association with rotation of the polishing table is detected by the detection coil, and an end point detecting section configured to detect a polishing end point indicating an end of polishing of the polishing target from the detected eddy current.
Hereinafter, embodiments of the present invention will be described with reference to drawings. Note that in each of the following embodiments, like signs will be given to like or corresponding members, and the repetition of similar descriptions may be omitted. Features shown in one embodiment may be applied to the other embodiments as long as these features do not contradict one another.
The load/unload section 62 includes two or more (four in the present embodiment) front load units 20, in each of which a wafer cassette where many semiconductor wafers (substrates) are stocked is mounted. The front load units 20 are disposed adjacent to the housing 61 and arranged along a width direction (a direction perpendicular to a longitudinal direction) of the substrate processing apparatus. Each front load unit 20 is configured such that an open cassette, an SMIF (Standard Manufacturing Interface) pod, or an FOUP (Front Opening Unified Pod) can be installed therein. Here, the SMIF and the FOUP each constitute a hermetically sealed container that accommodates a wafer cassette therein and is covered with partition walls so as to keep an independent environment isolated from an external space.
A traveling mechanism 21 is laid out along the arrangement of the front load units 20 in the load/unload section 62. Two transport robots (loaders) 22 are installed on the traveling mechanism 21 in such a manner as to move along the direction in which the wafer cassettes are arranged. The transport robots 22 can access the wafer cassettes installed in the front load units 20 by moving on the traveling mechanism 21. Each transport robot 22 has two hands; an upper hand and a lower hand. The upper hand is used to return a processed semiconductor wafer to a wafer cassette. The lower hand is used to unload a semiconductor wafer before processing from the wafer cassette. In this way, the upper hand and the lower hand are used for the different purposes. Furthermore, the semiconductor wafer can be turned over by causing the lower hand of the transport robot 22 to turn around its shaft center.
The load/unload section 62 is a region which needs to be kept in the cleanest state. Therefore, the interior of the load/unload section 62 is always kept at a pressure higher than that in any of the outside of the substrate processing apparatus, the polishing section 63, and the cleaning section 64. The polishing section 63 is the dirtiest region because a slurry is used as a polishing liquid. Accordingly, a negative pressure is formed inside the polishing section 63 and is kept at a pressure that is lower than the pressure inside the cleaning section 64. A filter fan unit (not illustrated) having a clean air filter such as an HEPA filter, a ULPA filter, or a chemical filter is provided in the load/unload section 62. Clean air from which particles, toxic vapor, or toxic gas has been removed is always blown out from the filter fan unit.
The polishing section 63 is a region where polishing (flattening) of a semiconductor wafer is performed, and includes a first polishing unit 3A, a second polishing unit 3B, a third polishing unit 3C, and a fourth polishing unit 3D. As illustrated in
As illustrated in
Likewise, the second polishing unit 3B includes a polishing table 30B to which a polishing pad 10 is attached, a top ring 31B, a polishing liquid supply nozzle 32B, a dresser 33B, and an atomizer 34B. The third polishing unit 3C includes a polishing table 30C to which a polishing pad 10 is attached, a top ring 31C, a polishing liquid supply nozzle 32C, a dresser 33C, and an atomizer 34C. The fourth polishing unit 3D includes a polishing table 30D to which a polishing pad 10 is attached, a top ring 31D, a polishing liquid supply nozzle 32D, a dresser 33D, and an atomizer 34D.
The first polishing unit 3A, the second polishing unit 3B, the third polishing unit 3C, and the fourth polishing unit 3D have the same configuration as each other. Therefore, for the details of the polishing unit, the first polishing unit 3A will be described below.
A circular elastic pad 642 that abuts on the semiconductor wafer 16, an annular pressure sheet 643 made up of an elastic film, and a substantially disk-shaped chucking plate 644 configured to hold the elastic pad 642 are accommodated in a space formed inside the top ring main body 24 and the retainer ring 23. An upper circumferential end of the elastic pad 642 is held to the chucking plate 644, and four pressure chambers (air bags) P1, P2, P3, and P4 are provided between the elastic pad 642 and the chucking plate 644. The pressure chambers P1, P2, P3, and P4 are formed by the elastic pad 642 and the chucking plate 644. A pressurized fluid such as pressurized air is supplied to the pressure chambers P1, P2, P3, and P4 via corresponding fluid paths 651, 652, 653, and 654, or a vacuum is drawn into the pressure chambers P1, P2, P3, and P4 via the fluid paths 651, 652, 653, and 654. The pressure chamber P1 at the center is circular, and the other pressure chambers P2, P3, and P4 are annular. The pressure chambers P1, P2, P3, and P4 are concentrically arranged.
Internal pressures of the pressure chambers P1, P2, P3, and P4 can be changed independently of one another by a pressure adjusting section, which will be described below, whereby pressing forces against four regions, that is, a central portion, an inner intermediate portion, an outer intermediate portion, and a circumferential edge portion of the semiconductor wafer 16 can be independently adjusted. The entire top ring 31A is raised and lowered so that the retainer ring 23 can be pressed against the polishing pad 10 with a predetermined pressing force. A pressure chamber P5 is formed between the chucking plate 644 and the top ring main body 24 so that a pressurized fluid is supplied to the pressure chamber P5 via a fluid path 655 or a vacuum is drawn thereinto via the fluid path 655. This enables the whole of the chucking plate 644 and the elastic pad 642 to move up and down.
The circumferential edge portion of the semiconductor wafer 16 is surrounded by the retainer ring 23 so that the semiconductor wafer 16 is prevented from getting out of the top ring 31A during polishing. An opening (not illustrated) is formed at a portion of the elastic pad 642, which constitutes the pressure chamber P3, and a vacuum is drawn into the pressure chamber P3 so that the semiconductor wafer 16 can be suction held to the top ring 31A. Nitrogen gas, dried air, compressed air, or the like is supplied to the pressure chamber P3 so that the semiconductor wafer 16 is released from the top ring 31A.
The control section 65 determines respective internal pressures of the pressure chambers P1, P2, P3, and P4 based on the monitoring signal, and issues an instruction to a pressure adjusting section 675 so that the determined internal pressures are formed in the pressure chambers P1, P2, P3, and P4. The control section 65 functions as a pressure control section that controls the internal pressures of the pressure chambers P1, P2, P3, and P4 based on the monitoring signal and an end point detecting section that detects a polishing end point.
An eddy current detection device 50 is also provided in each of the second polishing unit 3B, the third polishing unit 3C, and the fourth polishing unit 3D, as in the first polishing unit 3A. The control section 65 generates a monitoring signal from a signal transmitted from a film thickness sensor 76 of each of the polishing units 3A to 3D, and monitors the progress in polishing of the semiconductor wafer in each of the polishing units 3A to 3D. In the case where a plurality of semiconductor wafers are polished at the polishing units 3A to 3D, the control section 65 monitors monitoring signals representing film thicknesses of the semiconductor wafers during polishing and controls pressing forces of the top rings 31A to 31D so that polishing times at the polishing units 3A to 3D are substantially the same based on the monitoring signals. Thus, the pressing forces of the top rings 31A to 31D during polishing are thus controlled based on the monitoring signals, respectively, whereby the polishing times at the polishing units 3A to 3D can be leveled.
The semiconductor wafer 16 may be polished by any one of the first polishing unit 3A, the second polishing unit 3B, the third polishing unit 3C, and the fourth polishing unit 3D, or may be continuously polished by a plurality of polishing units previously selected from the polishing units 3A to 3D. For example, the first polishing unit 3A and the second polishing unit 3B may polish the semiconductor wafer 16 in this order. Alternatively, the third polishing unit 3C and the fourth polishing unit 3D may polish the semiconductor wafer 16 in this order. Furthermore, the first polishing unit 3A, the second polishing unit 3B, the third polishing unit 3C, and the fourth polishing unit 3D may polish the semiconductor wafer 16 in this order. In any case, the polishing times at all the polishing units 3A to 3D are leveled so that throughput can be improved.
The eddy current detection device 50 is preferably used when the film of the semiconductor wafer is a metallic film. In the case where the film of the semiconductor wafer is a film having light transmissivity such as an oxide film, an optical sensor can be used as a film thickness sensor in place of the eddy current detection device 50. Alternatively, a microwave sensor may be used as the film thickness sensor. The microwave sensor can be used for both a metallic film and a nonmetallic film.
Next, referring to
The lifter 11 receives a semiconductor wafer from the transport robot 22. The first linear transporter 66 transports the semiconductor wafer received from the lifter 11 among a first transport position TP1, a second transport position TP2, a third transport position TP3, and a fourth transport position TP4. The first polishing unit 3A and the second polishing unit 3B receive the semiconductor wafer from the first linear transporter 66 and polish the semiconductor wafer. The first polishing unit 3A and the second polishing unit 3B pass the polished semiconductor wafer to the first linear transporter 66.
The swing transporter 12 delivers the semiconductor wafer between the first linear transporter 66 and the second linear transporter 67. The second linear transporter 67 transports the semiconductor wafer received from the swing transporter 12 among a fifth transport position TP5, a sixth transport position TP6, and a seventh transport position TP7. The third polishing unit 3C and the fourth polishing unit 3D receive the semiconductor wafer from the second linear transporter 67 and polish the semiconductor wafer. The third polishing unit 3C and the fourth polishing unit 3D transfer the polished semiconductor wafer to the second linear transporter 67. The semiconductor wafer polished by the polishing unit 3 is placed on the temporary placement stand 180 by the swing transporter 12.
The first polishing unit 3A is a polishing unit for performing polishing between the polishing pad 10 and the semiconductor wafer 16 disposed facing the polishing pad 10. The first polishing unit 3A includes the polishing table 30A for holding the polishing pad 10, and the top ring 31A for holding the semiconductor wafer 16. The first polishing unit 3A includes a swing arm 110 for holding the top ring 31A, a swing shaft motor 14 for causing the swing arm 110 to swing, and a driver 18 that supplies drive power to the swing shaft motor 14.
According to a plurality of embodiments that will be described by reference to
The top ring (the holding section) 31A, the swing arm 110, the arm drive section (the swing shaft motor 14), and the end point detecting section form a set, and these sets are provided individually in the first polishing unit 3A, the second polishing unit 3B, the third polishing unit 3C, and the fourth polishing unit 3D.
The polishing table 30A is connected to a motor M3 (refer to
The top ring 31A includes the top ring main body 24 that presses a semiconductor wafer 16 against the polishing surface 101 and the retainer ring 23 that holds an outer circumferential edge of the semiconductor wafer 16 so as to prevent the semiconductor wafer 16 from getting out of the top ring.
The top ring 31A is connected to the top ring shaft 111. The top ring shaft 111 is caused to move up and down relative to the swing arm 110 by an up-and-down motion mechanism, which is not illustrated. The up-and-down motion of the top ring shaft 111 causes the entire top ring 31A to ascend or descend and causes it to be positioned relative to the swing arm 110.
The top ring shaft 111 is connected to a rotary cylinder 112 via a key (not illustrated). The rotary cylinder 112 includes a timing pulley 113 provided on an outer circumferential portion thereof. A top ring motor 114 is fixed to the swing arm 110. The above-described timing pulley 113 is connected to a timing pulley 116 provided on the top ring motor 114 via a timing belt 115. As the top ring motor 114 rotates, the rotary cylinder 112 and the top ring shaft 111 integrally rotate via the timing pulley 116, the timing belt 115, and the timing pulley 113, and thus the top ring 31A rotates.
The swing arm 110 is connected to a rotation shaft of the swing shaft motor 14. The swing shaft motor 14 is fixed to a swing arm shaft 117. Therefore, the swing arm 110 is rotatably supported by the swing arm shaft 117.
The top ring 31A can hold a substrate such as a semiconductor wafer 16 to an undersurface thereof. The swing arm 110 can turn around the swing arm shaft 117. The top ring 31A that holds the semiconductor wafer 16 to its undersurface is moved from a receiving position of a semiconductor wafer 16 to a position above the polishing table 30A as the swing arm 110 turns. Then, the top ring 31A is caused to descend to press the semiconductor wafer 16 against the surface (polishing surface) 101 of the polishing pad 10. At this time, each of the top ring 31A and the polishing table 30A is caused to rotate. At the same time, the polishing liquid is supplied onto the polishing pad 10 from the polishing liquid supply nozzle provided above the polishing table 30A. In this way, the surface of the semiconductor wafer 16 is polished by bringing the semiconductor wafer 16 into sliding contact with the polishing surface 101 of the polishing pad 10.
The first polishing unit 3A includes a table drive section (not illustrated) that drives to rotate the polishing table 30A. The first polishing unit 3A may include a table torque detection section (not illustrated) configured to detect table torque applied to the polishing table 30A. The table torque detection section can detect table torque from the current of the table drive section, which is a rotation motor. The control section 65 may detect a polishing end point indicating an end of polishing only from the eddy current detected by the eddy current detection device 50 or may detect a polishing end point indicating an end of polishing in taking arm torque detected by an arm torque detection section or the table torque into consideration.
Referring to
Here, disposing the eddy current detection sensors 56 near to one another means disposing the plurality of eddy current sensors 56 near to one another so that a strong magnetic field having a required predetermined strength can be generated in a desired narrow area on the semiconductor wafer 16 by the plurality of eddy current sensors 56. A specific example where the strong magnetic field having the required predetermined strength is generated in the desired narrow area will be described later by reference to
In this embodiment, the plurality of eddy current sensors are disposed near to each other, and each of the plurality of eddy current sensors includes the core section, the exciting coil disposed in the core section and configured to form the eddy current, and the detection coil disposed in the core section and configured to detect the eddy current. As a result, although the eddy current is formed only one eddy current sensor in the conventional technique, since the eddy current is formed by the plurality of eddy current sensors disposed near to each other, the magnetic field formed in the polishing target becomes stronger than that formed by the conventional technique. The number of eddy current sensors to be provided only needs to be plural, and hence, two, three, four, eight, twelve, and so on eddy current sensors can be provided. In order to evaluate a film thickness highly accurately over a wide area, more than twelve eddy current sensors can also be used.
Additionally, in the embodiment, since the exciting coil and the detection coil are disposed in the same core section, the detection coil can detect the eddy current formed by the exciting coil with good efficiency. In the case where the detection coil is not disposed in the core section where the exciting coil is disposed, the detection coil cannot detect the eddy current with good efficiency. This is because an inverse magnetic field by the eddy current formed by the exciting coil becomes the greatest in the core section where the exciting coil is provided.
As a specific example where the plurality of eddy current sensors 56 are disposed near to one another, for example, in the case where the individual eddy current sensors 56 have a circular shape as illustrated in
In the case where the individual eddy current sensors 56 are a polygon, for example, in consideration of a circle or an oval that the polygon is inscribed in or circumscribed on, the eddy current sensors 56 can be disposed in the ways described above. In
Each of the plurality of eddy current sensors 56 includes a pot core 60 (a core section), exciting coils 860, 862 disposed in the pot core 60 and configured to form an eddy current in the conductive film, and detection coils 864, 866 disposed in the pot core 60 and configured to detect the eddy current formed in the conductive film. How to dispose the exciting coils 860, 862 and the detection coils 864, 866 in the pot core 60 will be described later.
As illustrated in
In one case, metal is distributed widely into the form of a plane (in bulk) on the surface of a polishing target, and in the other case, fine wirings of copper or the like exist partially on the surface of a polishing target. In the case where fine wirings exist partially on the surface of a polishing target, the density of an eddy current that flows in the polishing target is required to be greater, that is, a magnetic field formed in the polishing target by the eddy current sensor is required to be stronger than that of the case where metal is distributed widely into the form of a plane.
One aspect of the present invention provide an eddy current detection device in which a stronger magnetic field is formed in a polishing target and a polishing apparatus using the eddy current detection device.
Referring to
In
In the state in
The timing at which the strength of the magnetic field that the exciting coils 860, 862 generate is changed when the conductivity of the semiconductor wafer 16 changes may not be when the state in
In order to increase the strength of the magnetic field that the exciting coils 860, 862 generate, a current caused to flow to the exciting coils 860, 862 is increased or a voltage applied to the exciting coils 860, 862 is increased. As another method of increasing the strength of the magnetic field, a state where only one of the exciting coil 860 and the exciting coil 862 is used may be changed to the state where both the exciting coil 860 and the exciting coil 862 are used.
Incidentally, in the state in
As to the size of the eddy current sensors 56, in many cases, a sensor having a diameter of about 15 mm or smaller is regarded as a sensor of a small size, and a sensor having a diameter of greater than 15 mm is regarded as a sensor of a great size. Although the size is expressed by the diameter of an external shape (an outer circumference) of the eddy current sensor 56 in many cases, the size may be expressed by a representative length of the eddy current sensors 56. For sensors of a small size, sensors of a diameter ranging from 1 to 15 mm can be used in accordance with process applications. Sensors of a diameter of smaller than 1 mm can be fabricated using the micro-fabrication technique.
Superposing magnetic fields 922 generated individually by the three eddy current sensors 56 on one another results in the magnetic field 924. The magnetic field 920 and the magnetic field 924 are magnetic fields that are generated in the conductive layer 890 lying on the surface of the semiconductor wafer 16 that corresponds to the center line 928 illustrated in
The magnetic field 920 has a wide range of magnetic field, in the magnetic field 924, a narrow range of magnetic field is generated. In comparison with the outside diametric size of the large eddy current sensor 58 (for example, with a diameter of 20 mm), when an area occupied by the metal in the conductive layer 890 is not the bulk, for example, when the area occupied by the metal is only 50% (when a few metallic areas, each being a 5-mm square, exist in a 20-mm square), it may be difficult for the eddy current sensor 58 to detect a change in film thickness. At this time, in comparison with the eddy current sensor 58, the eddy current detection device 50 including the small eddy current sensors 56 having the narrow range of magnetic field has the following advantages.
In the small eddy current sensor 56 (whose diameter is, for example, 5 mm) having the narrow range of magnetic field, in the area described above, since the area occupied by the metal in the range of the eddy current sensor 56 (whose diameter is 5 mm) becomes, for example, 100%, the eddy current sensor 56 can detect a change in thickness of the film. However, with one small eddy current sensor 56 in which the range of the magnetic field 922 is narrow, when comparing with the magnetic field 920 generated by the eddy current sensor 58, as illustrated in
With the present embodiment, the problem described above is solved by installing the plurality of eddy current sensors 56 in the same eddy current detection device 50. According to the present embodiment, (1) a spot is made smaller by a coil that is smaller than that of the eddy current sensor 58, and (2) the magnetic field can be made stronger by a plurality of small coils. The magnetic field 924 that is generated by the plurality of eddy current sensors 56 illustrated in
When compared with the magnetic field 920, in the magnetic field 924, an area where the strength of the magnetic field is great is narrow. That is, an area 934 of the magnetic field 924 where the strength is greater than a predetermined strength 10 is narrower than an area 926 of the magnetic field 920 where the strength is greater than the predetermined strength 10. Then, the strength of the magnetic field of the area 926 is almost the same as the strength of the magnetic field of the area 934. Thus, as described above, in the case where there exist a few metallic areas of a 5-mm square in a 20-mm square, these metallic areas of a 5-mm square cannot be detected by the magnetic field 920 but can be detected by the magnetic field 924.
In the present embodiment, although the eddy current sensor 56 is described as being small, the eddy current sensor 56 can be said to be so small in a relative comparison with the eddy current sensor 58 that is greater in size. When the eddy current sensor 58 is said to cause a problem due to its great size, that is not because the area occupied by the metal in the conductive layer 890 is considered to be the bulk when compared with the size of the eddy current sensor 56 but because the area occupied by the metal in the conductive area 890 is considered to be the bulk when compared with the size of the eddy current sensor 58. In the case where the area occupied by the metal in the conductive layer 890 is reduced further, the area occupied by the metal in the conductive layer 890 is not considered to be the bulk when compared with the size of the small eddy current sensor 56, and hence, an eddy current sensor 56 that is smaller than the eddy current sensor 56 is considered to be necessary.
According to the eddy current detection device 50, there are provided such advantages that the magnetic field that is generated by the exciting coils 860, 862 towards the semiconductor wafer 16 can be increased, increasing the density of the eddy current (1), and that the detection coils 864, 866 can obtain more a demagnetizing field (an interlinking magnetic flux) that is generated by the eddy current (2), and in addition, there is also provided an advantage that since the pot core 60 has the relatively small diameter, other influence (external influence) than the film on the surface of the semiconductor wafer 16 can be made smaller. This will be described in greater detail later by reference to
Although the conductive layer 890 illustrated in
Next, the eddy current detection device 50 including the polishing apparatus according to the present invention will be described in greater detail by reference to the drawings. As illustrated in
The plurality of eddy current sensors 56 may be disposed along an inner circumference of the eddy current detection device 50. For example, when the external shape of the eddy current detection device 50 is a circle, the plurality of eddy current sensors 56 may be disposed on a circumference along the inner circumference of the eddy current detection device 50. A film thickness may be measured by using only part of the plurality of eddy current sensors 56 that is included in the eddy current detection device 50. For example, nine eddy current sensors 56 are disposed by disposing three eddy current sensors 56 along each of three rows in an eddy current detection device 50 having a polygonal external shape. That is, the total of nine eddy current sensors 56 arranged in three rows of three eddy current sensors 56 are provided in an interior of the eddy current detection device 50. A film thickness may be measured by using only part or all of the nine eddy current sensors 56. Which of the nine eddy current sensors 56 is or are used is determined in accordance with a fine circuit on a semiconductor wafer 16, which is a measuring target.
In
The size of the area 934 illustrated in
In
Next, the eddy current sensor 56 will be described. A core of the eddy current sensor 56 can have an arbitrary shape. That is, the core can have a cylindrical shape like that of a solenoid coil, a pod core shape, or E-like shape or the like. In the cylindrical shape, the pod core shape, and E-like shape, since the pod core shape is preferable because a thin magnetic flux can be generated by the pod core shape. In the case of the pod core shape, the core section normally includes a bottom surface portion, a magnetic center portion provided at a center of the bottom surface portion, and a circumferential portion provided on a circumference of the bottom surface portion. The exciting coils and the detection coils can be disposed at the magnetic center portion.
The exciting coils and the detection coils can also be disposed at the circumferential portion, in addition to the magnetic center portion. The circumferential portion constitutes a circumferential wall portion that is provided along the circumference of the bottom surface portion in such a manner as to surround the magnetic center portion.
In the six coils 860, 862, 864, 866, 868, 870, the central coils 860, 862 are exciting coils that are connected together by an alternating-current signal source 52, which will be described later. These exciting coils 860, 862 form an eddy current in a metallic film (or a conductive film) mf on a semiconductor wafer 16 disposed near to the exciting coils 860, 862 by a magnetic field that is formed by a voltage supplied by the alternating-current signal source 52. The detection coils 864, 866 are disposed on metallic film sides of the exciting coils 860, 862, respectively, to detect a magnetic field that is generated by the eddy current formed in the metallic film. Dummy coils 868, 870 are disposed on opposite sides of the exciting coils 860, 862, respectively, to the sides where the detection coils 864, 866 are disposed. One coil may function as an exciting coil and a detection coil.
The exciting coil 860 is disposed on an outer circumference of the magnetic center portion 61b and is an internal coil that can generate a magnetic field, forming an eddy current in the conductive film. The exciting coil 862 is disposed on an outer circumference of the circumferential wall portion 61c and is an external coil that can generate a magnetic field, forming an eddy current in the conductive film. The detection coil 864 is disposed on the circumference of the magnetic center portion 61b and can detect a magnetic field, detecting an eddy current formed in the conductive film. The detection coil 866 is disposed on the outer circumference of the circumferential wall portion 61c and can detect a magnetic field, detecting an eddy current formed in the conductive film.
The eddy current sensor includes the dummy coils 868, 870 configured to detect an eddy current formed in the conductive film. The dummy coil 868 is disposed on the outer circumference of the magnetic center portion 61b and can detect a magnetic field. The dummy coil 870 is disposed on the outer circumference of the circumferential wall portion 61c and can detect a magnetic field. In the present embodiment, although the detection coils and the dummy coils are disposed on the outer circumference of the magnetic center portion 61b and the outer circumference of the circumferential wall portion 61c, the detection coil and the dummy coil may be disposed only one of the outer circumference of the magnetic center portion 61b and the outer circumference of the circumferential wall portion 61c.
An axial direction of the magnetic center portion 61b intersects the conductive film on the substrate at right angles, and the detection coils 864, 866, the exciting coils 860, 862, and the dummy coils 868, 870 are disposed in different positions in the axial direction of the magnetic center portion 61b. The detection coils 864, 866, the exciting coils 860, 862, and the dummy coils 868, 870 are disposed sequentially from a position lying nearer to the conductive film on the substrate towards a position lying farther from the conductive film on the substrate in the axial direction of the magnetic center portion 61b in that order. Lead wires (not shown) are drawn out from the detection coils 864, 866, the exciting coils 860, 862, and the dummy coils 868, 870 for connection with exteriors of the eddy current sensor.
A conductor used for the detection coils 864, 866, the exciting coils 860, 862, and the dummy coils 868, 870 is a copper wire, a manganin wire, or a nichrome wire. A change in electric resistance or the like by temperature change is reduced by using a manganin wire or a nichrome wire, whereby the temperature properties are improved.
In the present embodiment, since the exciting coils 860, 862 are formed by winding a wire material around an outer side of the magnetic center portion 61b, which is made of a magnetic element such as ferrite, and an outer side of the circumferential wall portion 61c, the density of an eddy current flowing to a measuring target can be enhanced. In addition, since the detection coils 864, 866 are also formed on the outer side of the magnetic center portion 61b and the outer side of the circumferential wall portion 61c, the detection coils 864, 866 can collect a demagnetizing field (an interlinking magnetic flux) generated with good efficiency. In the case where the exciting coil and the detection coil are disposed at the circumferential portion in addition to the magnetic center portion, compared with the case where the exciting coil and the detection coil are disposed only at the magnetic center portion, the eddy current that can be formed by the exciting coil can be concentrated on to a narrow area, whereby the magnetic field formed on the polishing target becomes stronger.
In order to increase the density of the eddy current flowing to the measuring target, in the present embodiment, further, the exciting coil 860 and the exciting coil 862 are connected parallel as illustrated in
As illustrated in
Since the magnetic field 876 and the magnetic field 878 that are shown in an area 880 are directed in the same direction, the two magnetic fields are added to each other, resulting in a greater magnetic field. Compared with the conventional case where only the magnetic field 876 that the exciting coil 860 generates exists, in the present embodiment, the magnetic field is increased by such an extent that the magnetic field 878 is generated by the exciting coil 862.
Next, an electric configuration of the eddy current sensor 56 will be described.
There may be situations where the output characteristics of the plurality of eddy current sensors 56 within one eddy current detection device 50 vary. When the variation in the output characteristics needs to be reduced, one or more of a plurality of methods below can be used to deal with the required reduction. i) Output characteristics of a plurality of eddy current sensors 56 are individually measured before the plurality of eddy current sensors 56 are built into one eddy current detection device 50, and a plurality of eddy current sensors 56 having similar output characteristics are selected to be built into one eddy current detection device 50.
ii) A control circuit or a control program is provided to control individually output characteristics of a plurality of eddy current sensors 56 of one eddy current detection device 50 so that the output characteristics become similar to one another. The control circuit or the control program is a circuit or a program for measuring output characteristics or the like of the individual eddy current sensors 56 in advance and changing the output characteristics or the like of the individual eddy current sensors 56 based on the results of the measurements. Changing the output characteristic of the eddy current sensor 56 may include, for example, setting a weighted output for the eddy current sensor 56 in question.
The specific contents (for example, setting a weighted output) of i) and ii) may be changed in accordance with the characteristics (for example, a material, an electric characteristic of a circuit formed, and the like) of the semiconductor wafer 16, which is a measuring target. That is, there may be situations where when the characteristics of the semiconductor wafer 16, which is the measuring target, are changed, the specific contents of the methods of i) and ii) are desirably changed accordingly.
As illustrated in
The eddy current sensor 56 is of a frequency type or an impedance type. In the eddy current sensor 56 of the frequency type, an oscillation frequency changes when an eddy current is generated in the metallic film (or the conductive film), whereby the metallic film (or the conductive film) is detected from the change in frequency. In the eddy current sensor 56 of the impedance type, an impedance changes when an eddy current is generated in the metallic film (or the conductive film), whereby the metallic film (or the conductive film) is detected from the change in impedance. That is, in the eddy current sensor 56 of the frequency type, in the equivalent circuit illustrated in
In the eddy current sensor of the impedance type, signal outputs X, Y, a phase, and a combined impedance Z are fetched as will be described later. Measurement information on the metallic film (or the conductive film) of Cu, Al, Au, or W is obtained from a frequency F, or impedances X, Y, and the like. The eddy current sensor 56 can be incorporated in a position lying in the vicinity of the surface in the interior of the polishing table 30A and is positioned in such a manner as to face the semiconductor wafer 16, which is the polishing target, via the polishing pad 10 as illustrated in
A single wave, a mixed wave, an AM modulating wave, an FM modulating wave, a sweep output of a function generator, or a plurality of oscillation frequency sources can be used for the frequency of the eddy current sensor, and an oscillation frequency or a modulation method with good sensitivity is preferably selected to match the type of the metallic film.
Hereinafter, the eddy current sensor 56 of the impedance type will be described specifically. The alternating-current signal source 52 is an oscillator of a fixed frequency of the order of 2 to 30 MHz, and for example, a crystal oscillator is used for the eddy current sensor 56. A current I1 is caused to flow to the eddy current sensor 56 by an alternating-current voltage that is supplied by the alternating-current signal source 52. When the current flows to the eddy current sensor 56 disposed near the metallic film (or the conductive film) mf, a resultant magnetic flux is interlinked with the metallic film (or the conductive film) mf, whereby a mutual inductance M is formed therebetween, and an eddy current I2 flows in the metallic film (or the conductive film) mf. Here, R1 denotes an equivalent resistance on a primary side that includes the eddy current sensor, and L1 denotes an self-inductance of the primary side that includes the eddy current sensor. On the metallic film (or the conductive film) mf side, R2 denotes an equivalent resistance corresponding to an eddy current loss, and L2 denotes a self-inductance thereof. The impedance Z seen from terminals a, b of the alternating-current signal source 52 toward an eddy current sensor side changes based on the magnitude of the eddy current loss formed in the metallic film (or the conductive film) mf.
The detection coils 864, 866 and the dummy coils 868, 870 form the series circuit in the opposite phase as described above and are connected to a bridge circuit 77 that includes a variable resistance 76 at ends thereof. The exciting coils 860, 862 are connected to the alternating-current signal source 52 and form an eddy current in the metallic film (or the conductive film) mf that is disposed near the exciting coils 860, 862 by generating an alternating magnetic flux. An output voltage of the series circuit made up of the detection coils 864, 866 and the dummy coils 868, 870 can be controlled so as to become zero when no metallic film (or no conductive film) exists by controlling a resistance value of the variable resistance 76. Signals of L1, L3 are controlled so as to have the same phase by the variable resistance 76 (VR1, VR2) that is connected parallel to the detection coils 864, 866 and the dummy coils 868, 870. That is, the variable resistances VR1 (=VR1-1+VR1-2) and VR2 (=VR2-1+VR2-2) are controlled so that the following expression (1) holds in an equivalent circuit illustrated in
VR1-1×(VR2-2+jωL3)=VR1-2×(VR2-1+jωL1) (1).
As a result, as illustrated in
Then, when the metallic film (or the conductive film) exists near the detection coils 864, 866, a magnetic field generated by an eddy current formed in the metallic film (or the conductive film) is interlined with the detection coils 864, 866 and the dummy coils 868, 870. However, since the detection coils 864, 866 are disposed in a position lying nearer to the metallic film (or the conductive film), a balance between an induced voltage generated in the detection coils 864, 866 and an induced voltage generated in the dummy coils 868, 870 is collapsed, whereby an interlinked magnetic flux generated by the eddy current in the metallic film (or the conductive film) can be detected by this collapse in the balance of the induced voltages. That is, a zero point control can be executed by separating the series circuit of the detection coils 864, 866 and the dummy coils 868, 870 from the exciting coils 860, 862 that are connected to the alternating-current signal source and controlling the balance by the resistance bridge circuit. Consequently, since the eddy current flowing to the metallic film (or the conductive film) can be detected from a zero state, the detection sensitivity of eddy current in the metallic film (or the conductive film) is enhanced. As a result, the magnitude of the eddy current generated in the metallic film (or the conductive film) can be detected over a wide dynamic range.
As described above, the signal source 52, which is configured to supply an alternating-current signal to the eddy current sensor 56 disposed near the semiconductor wafer 16 on which the metallic film (or the conductive film) constituting the detection target is formed, is the oscillator of the fixed frequency that is made up of a crystal oscillator and supplies a voltage of a fixed frequency of, for example, 2 MHz, 8 MHz, or 16 MHz. Alternating-current voltage formed by the signal source 52 is supplied to the eddy current sensor 56 via the signal source 52. A cos component and a sin component of a signal detected at the terminals of the eddy current sensor 56 are fetched by a synchronous detection section that is made up of a cos synchronous detection circuit 85 and a sin synchronous detection circuit 86 via a high-frequency amplifier 83 and a phase shift circuit 84. Here, as an oscillation signal formed by the signal source 52, two signals of an in-phase component (0°) and an orthogonal component (90°) of the signal source 52 are formed by the phase shift circuit 84 and are introduced into the cos synchronous detection circuit 85 and the sin synchronous detection circuit 86 respectively, whereby the synchronous detection is executed as described above.
Unnecessary high frequency components that are equal to or greater than the signal components are removed from the signals that are synchronously detected by low-pass filters 87, 88, whereby a resistance component (R) output, which is a cos synchronous detection output, and a reactance component (X) output, which is a sin synchronous detection output, are fetched. In addition, an amplitude output (R2+X2)1/2 is obtained from the resistance component (R) output and the reactance component (X) output by a vector computing circuit 89. Similarly, a phase output (tan−1R/X) is obtained from the resistance component output and the reactance component output by a vector computing circuit 90. Here, various types of filters are provided on a measuring device main body to remove noise components of sensor signals. The various filters have cutoff frequencies that are set individually therefor. For example, by setting cutoff frequencies of the low-pass filters in a range from 0.1 to 10 Hz, a noise component mixed into a sensor signal at the time of polishing is removed, thereby making it possible to measure the metallic film (or the conductive film), which is the measuring target, highly accurately.
Next, a difference between an embodiment of an eddy current sensor 56 in which the exciting coil 860 is wound only around the inner magnet center section 61b and an embodiment of an eddy current sensor 56 in which the exciting coils are wound both around the inner magnetic center portion 61b and the outer circumferential wall portion 61c will be described by reference to
In the eddy current sensor 56 illustrated in
In the eddy current sensor 56 illustrated in
The eddy current sensor 56 illustrated in
Next, a different example will be described in which a circumferential magnetic element differs from the wall portion illustrated in
Next, referring to
As illustrated in
The shape of the bottom surface portion 944, the shape of the first pillar-like portion 946a, and the shape of the second pillar-like portion 946b are not limited to the cylindrical shape and hence may take the form of an oval pillar, a disk, or a prism. Additionally, the shape of the eddy current detection device 50 is not limited to the circular shape and hence may be an oval or a polygon. The number of pillar-like portions 946 that one eddy current sensor 56 includes is not limited to four and hence only needs to be two or more and in an even number or an odd number. The numbers of first pillar-like portions 946a and second pillar-like portions 946b that one eddy current sensor 56 includes are not limited to two and hence only need to be one or more.
A coil 948 is wound around the pillar-like portion 946. As the coil 948, an exciting coil and a detection coil may be provided separately, or one coil 948 may function as an exciting coil and a detection coil. That is, an exciting coil and a detection coil can constitute the same coil, and the exciting coil can be configured to detect an eddy current that is formed in a conductive film on a semiconductor wafer 16. The configuration in which the exciting coil and the detection coil constitute the same coil can also be applied to a combination of the exciting coil 860 and the detection coil 864 or a combination of the exciting coil 862 and the detection coil 866 illustrated in
Thus, while the examples of the embodiments of the present invention have been described heretofore, the embodiments of the present invention that have been described heretofore are intended to facilitate the understanding of the present invention but are not intended to limit the present invention. The present invention can be modified or improved without departing from the spirit and scope thereof, and its equivalents are, of course, included in the present invention. Additionally, the constituent elements described in claims below and the description can arbitrarily be combined or omitted as long as at least a part of the problems described above is solved or at least a part of the effects described above is realized.
This application claims priority under the Paris Convention to Japanese Patent Application No. 2018-210865 filed on Nov. 8, 2018. The entire disclosure of Japanese Patent Laid-Open No. 2017-58245 including specification, claims, drawings and summary is incorporated herein by reference in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 210865/2018 | Nov 2018 | JP | national |
