JP4664617B2 - Polishing apparatus and method - Google Patents

Description

  The present invention relates to the field of semiconductor manufacturing technology, and in particular to a method for inspecting a polished material surface.

  In this type of technical field, a multilayered element structure is required from the viewpoint of high performance and miniaturization of the device, and the demand is particularly great in the next generation LSI. For this reason, the planarization technique in the manufacturing process is particularly important, and in recent years, a chemical mechanical polishing (CMP) method has attracted attention. The CMP method can reduce processing strain by advancing chemical etching simultaneously with physical (mechanical) polishing.

There are several ways to detect the polishing endpoint by inspecting the polished substrate surface. For example, a method of inspecting a substrate to be processed by irradiating a laser beam and utilizing the intensity of the reflected light, a method of inspecting a vibration change of a polishing body (surface plate), a method of inspecting a torque change of the polishing body, etc. is there. For example, Patent Document 1 discloses a method for inspecting a torque change of a polishing body and detecting a polishing end point.
JP 2003-318140 A

  By the way, since planarization by CMP includes mechanical polishing, if foreign matter enters between the substrate to be processed (wafer) and the polishing cloth, the surface of the substrate to be processed may be scratched and a defective product may be generated. There is. Such foreign matters are, for example, diamond particles for cutting the polishing cloth from a conditioner that appropriately adjusts the condition of the surface of the polishing cloth, or metal powder or other dust falling from the sliding part of the device. May occur.

  In the conventional method for detecting scratches attached to the substrate to be processed, the substrate to be processed is taken out of the polishing apparatus, and a surface inspection process using a special detection device for detecting the scratch is performed. In the continuous manufacturing process, the polishing process for the next group of substrates to be processed is performed while the surface inspection process for the substrates to be processed after polishing is performed. For this reason, when it is detected that the substrate to be processed is scratched in the surface inspection process, many subsequent substrates to be processed are already polished and scratched, resulting in a lot of damage. Problems can arise. This problem becomes more serious as the number of substrates to be polished at a time increases and the size of the substrate increases. Although it may be possible not to perform the polishing step and the surface inspection step at the same time, another problem arises in that the throughput is sacrificed.

With the above polishing end point detection method, it is difficult to find such scratches on the substrate to be processed. In conventional polishing end point detection, it is possible to detect macroscopic (macroscopic) changes such as whether or not the entire substrate surface is flat, but it is possible to detect microscopic changes such as the presence or absence of scratches on a substantially flat substrate surface. This is because it is difficult to detect a (microscopic) change.
The present invention has been made to address at least one of the above-mentioned problems, and the object thereof is to provide an inspection method capable of detecting an abnormality of a polished material surface at an early stage. is there.

The method for inspecting the surface of a polished material according to the present invention includes:
A polishing step of contacting the material to be processed and the polishing pad and rotating the material to be processed or the polishing pad; and
And an inspection step of examining a torque signal representing torque for rotating the material to be processed or the polishing pad in the process of separating the material to be processed from the polishing pad.

  According to the present invention, it is possible to detect an abnormality of the polished material surface at an early stage.

  According to one aspect of the present invention, a torque signal indicating torque for rotating the material to be processed or the polishing pad in the process of separating the material to be processed from the polishing pad is checked, and an alarm is issued according to the check result. For this reason, it becomes possible to grasp | ascertain whether a grinding | polishing surface is satisfactorily flat, without attaching a to-be-processed material to another test | inspection apparatus.

  According to one aspect of the present invention, an alarm indicating that there is an abnormality on the surface of the material to be processed is issued when the amount of change in the torque signal in the process of separating the material to be processed from the polishing pad does not exceed a threshold value. . For this reason, it becomes possible to discover at an early stage that there is an abnormality such as a scratch on the polished surface of the material to be processed.

  According to one aspect of the invention, the torque signal represents a moving averaged torque. For this reason, it becomes possible to reliably detect abnormality of the polished surface.

  FIG. 1 shows a partial schematic view of a polishing apparatus capable of using an inspection method according to an embodiment of the present invention. The polishing apparatus 100 is an apparatus for performing chemical mechanical polishing (CMP). In order to simplify the description, a case where a wafer for a semiconductor device is polished will be described as an example. However, the present invention is not limited to the polishing of a wafer, and can be widely applied to applications in which any material is mechanically polished. The polishing apparatus 100 includes a surface plate 102, a polishing cloth 104, a conditioner 106, a header 108, and a slurry supply unit 112 including a slurry nozzle 110. The header 108 holds a wafer 114 that is a substrate to be processed. The polishing apparatus 100 includes a motor 116 that rotates the surface plate 102, a torque analysis unit 118, and a controller 120.

  The surface plate 102 has a disk shape, for example, and is rotated by a motor 116. The platen is also referred to as “platen”.

  The polishing cloth 104 is provided on the surface plate 102 and rotates together with the surface plate 102. The polishing cloth 104 includes, for example, an independent / continuous foam, a suede type, and the like, but the present invention is not limited to a specific polishing cloth material. Abrasive cloth is also widely referred to as a “polishing pad”.

  The conditioner 106 is an element for appropriately maintaining the surface state of the polishing pad 104. For example, the conditioner 106 can cut the polishing cloth 104 using a disk interspersed with diamond particles. However, if the diamond particles fall off and enter the polishing cloth 104, there is a risk of scratching the surface of the substrate to be processed.

  The header 108 holds the wafer 114 during the polishing process. Details of the header 108 are described in connection with FIG. The header 108 can be rotated along an arrow 113 or moved horizontally or vertically along arrows 115 and 117 by a mechanism (not shown).

  The slurry supply unit 112 causes a slurry (abrasive) 111 to flow between the polishing cloth 104 and the wafer 114 through the slurry nozzle 110. In this embodiment, a liquid slurry is used. However, any slurry can be used in the present invention.

  The motor 116 can rotate the surface plate 102. The motor 116 gives a torque signal representing the torque for driving the surface plate 102 to the torque analyzer 118. The torque signal may be a signal representing the torque value itself, or may be a voltage or current that determines the torque value.

  The torque analyzer 118 receives the torque signal of the surface plate and / or the torque signal of the header, and monitors the change of the torque signal. The header torque signal is a signal that represents the torque that rotates the header 108, and may be a signal that represents the torque value itself, or a voltage or current that determines the torque value. The torque signals of both the surface plate and the header may be given to the torque analysis unit 118, or only one of the torque signals may be given. The torque analysis unit 118 gives an abnormality detection signal to the controller 120 when the change (analysis result) of the torque signal matches a predetermined condition. The predetermined condition is, for example, a case where the change of the torque signal is below a certain threshold, but is not limited to this. These torque signals may be instantaneous torque signals. However, from the viewpoint of ensuring the accuracy of abnormality detection, the torque signals are averaged by moving averages and torque signals leveled by various filters. Analysis based on this is desirable.

  The controller 120 outputs a control signal for controlling the operation of the motor 116 and other elements according to the abnormality detection signal. For example, an alarm that interrupts the polishing process can be issued in response to the abnormality detection signal. Other elements include, for example, the header 108, the slurry supply unit 112, and the like.

  FIG. 2 shows an enlarged view of the header 108. The header 108 includes a main body 201 having a shallow cylindrical shape with one end closed, and a holding unit 202 that holds the wafer 114 or the like in the cylindrical opening of the main body 201. The holding part 202 is made of resin in this embodiment. The holding part 202 is also referred to as “retainer ring”. On the wafer 114, a seal 206 having a disk shape matching the shape of the wafer 114 is provided. In this embodiment, the seal 206 is formed of a thin rubber film. Further, a metal wafer support 204 is provided on the seal 206. The wafer support 204 has a ring-shaped protrusion 205 around the wafer support 204, and can form some gap with the wafer 114 when the wafer 114 is attracted. The substantially disk-shaped wafer support 204 has a plurality of through holes (not shown) that penetrate in the thickness direction of the disk. Therefore, the space 203 is sealed by the main body 201, the holding part 202, and the seal 206. The header 108 is provided with a mechanism (not shown) for increasing or decreasing the pressure of the space 203.

  When the space 203 is depressurized, the seal 206 is sucked through the through hole of the wafer support 204, and a slightly depressed shape is formed in accordance with the through hole. For this reason, the gap between the seal 206 and the wafer 114 is also decompressed, and the wafer 114 is also sucked toward the wafer support 204 side. On the other hand, when the space 203 is pressurized, the seal 206 and the wafer 114 try to move away from the wafer support 204. In addition to adjusting the pressure of the space 203, the holding force for holding the wafer 114 (and the wafer support 204 and the seal 206) of the holding unit 202 is adjusted, so that the vertical direction of the wafer 114 and the like (arrow 117 in FIG. 1). It is also possible to adjust the position of the direction.

  FIGS. 3 to 5 are views (Nos. 1 to 3) showing respective steps for explaining the inspection method according to the embodiment of the present invention. For convenience of explanation, it is assumed that the header 108 and the surface plate 102 (polishing cloth 104) are rotated at 50 to 100 times / min throughout the entire process shown in FIGS. Then, a torque signal representing torque for rotating the header 108 and / or the surface plate 102 is transmitted to the torque analysis unit 118 (see FIG. 1) and monitored. FIG. 3 shows an accretion process, and shows a state before (upper figure) and after (lower figure) that the header 108 supporting the wafer 114 is deposited on the polishing pad 104. The header 108 can be moved in the vertical direction by an air cylinder, for example. As shown in the upper diagram, the holding portion 202 is separated from the polishing pad 104 before landing. The pressure in the space 203 is reduced, and the wafer 114 is attracted to the wafer support 204 side. An arrow 302 in the drawing indicates the direction of stress acting on the seal 206 when the space 203 is depressurized. Even after landing as shown in the figure below, the pressure in the space 203 is reduced, and the seal 206 and the wafer 114 are attracted to the wafer support 204 side. At this stage, the holding unit 202 is in contact with the polishing pad 104, but the wafer 114 is not in contact.

  FIG. 4 shows a polishing process showing a state during the polishing. The polishing process in the present embodiment is performed by dividing it into a main polishing process (upper figure) and a post-polishing process (lower figure). In this polishing step, the pressure in the space 203 is increased so that the stress as shown by the arrow 402 acts on the seal 206. As a result, the wafer 114 comes into contact with the polishing pad 104 (strongly pressed), and the contact surface of the wafer 114 with the polishing pad 104 is polished. In this case, the slurry 111 (FIG. 1) is introduced. As the polishing proceeds, the polished surface is flattened. The end point of polishing can be detected by using various existing techniques as described in the background section.

  In the post-polishing step (below), the pressure in the space 203 is reduced as compared with the main polishing step, that is, the magnitude of the stress acting on the seal 206 is weakened as indicated by an arrow 404. As a result, the friction between the wafer 114 and the polishing pad 104 is reduced, and the progress of polishing can be slowed or substantially stopped. In this embodiment, at this stage, the supply of the slurry 111 is interrupted and pure water is supplied to the polishing pad 104. As a result, the slurry 111 remaining on the polished surface of the wafer 114 can be cleaned.

  FIG. 5 shows the suction and separation process, and shows the state of the suction process (upper figure) and the separation process (lower figure) before the header and wafer are removed. As shown in the upper diagram, the space 203 is depressurized while the holding portion 202 is in contact with the polishing pad 104, and stress acts on the seal 206 as indicated by an arrow 502. As a result, the seal 206 and the wafer 114 are attracted to the wafer support 204 side (adsorption process). Further, the holding unit 202 is pulled away from the polishing pad 104 while the wafer 114 is attracted to the wafer support 204 side (detachment process).

  As described above, the torque signal related to the header 108 and / or the surface plate 102 is analyzed and monitored by the torque analysis unit 118 (FIG. 1). Therefore, the torque signal of the header 108 and / or the surface plate 102 before and after the separation is also analyzed and monitored. It is assumed that the polished surface of the wafer 114 is not scratched and the polished surface has a very high flatness. In this case, since the wafer 114 and the polishing pad 104 are in close contact with each other, a large resistance is applied in the process of separating the wafer 114 from the polishing pad 104, that is, the torque signal changes greatly (the torque increases). On the other hand, if there is a scratch on the polished surface of the wafer 114, the adhesion between the wafer 114 and the polishing pad 104 is weakened. For this reason, the resistance force in the process of separating the wafer 114 from the polishing pad 104 is reduced, and the change in the torque signal is also reduced.

  FIG. 6 is a diagram illustrating a measurement result of a torque signal in a series of polishing steps. In this measurement, the process (horizontal axis) described in FIG. 3 to FIG. 5 is performed on a plurality of wafers whose polishing surfaces are sufficiently flattened in a mirror shape, and the torque signal (vertical axis) of the surface plate in the meantime. Is measured. The torque signal is expressed by a voltage (millivolt) of a control signal for driving the motor, and the torque is larger as the absolute value is larger. The torque signal is moving averaged. The total number of wafer samples is 11, and the torque signal for each is represented by 11 lines. Two of the samples (indicated by the thick line graph) have scratched the polished oxide film in advance, and the other nine (indicated by the thin line graph) have no scratch.

  In the landing process (FIG. 3), the torque before landing is small, but as the header 108 is gradually pressed against the polishing pad 104 and the friction increases, the torque gradually increases. In the main polishing step (upper side in FIG. 4), the wafer 114 is polished while being pressed relatively strongly against the polishing pad 104. However, since the planarization of the wafer 114 used in this experiment has been substantially completed, the torque during this process has not changed substantially. In the post-polishing step (the lower side in FIG. 4), the polishing surface is cleaned while the wafer 114 is pressed relatively weakly against the polishing pad 104. Since the friction between the wafer 114 and the polishing pad 104 is reduced, the torque is also reduced. In the adsorption process (upper side in FIG. 5), the wafer 114 is sucked toward the wafer support 204, and in the separation process (lower side in FIG. 5), the wafer 114 and the header 108 are separated from the polishing pad 104. In this case, in the sample (thin line graph) having no scratch on the polished surface, the torque decreases rapidly after the torque gradually increases. As described above, this is due to the high adhesion between the wafer 114 and the polishing pad 104. On the other hand, in the sample (thick line graph) having scratches on the polished surface, the torque is not greatly changed in the adsorption process and the separation process. This is because the adhesion between the wafer 114 and the polishing pad 104 is small as described above.

  Accordingly, by monitoring the torque signal in the process of pulling the wafer 114 away from the polishing pad 104, it is possible to detect whether or not the polishing surface of the wafer 114 has an abnormality such as a scratch. For example, the polishing surface is good when the change in torque signal before and after the separation of the wafer 114 changes so much as to exceed a predetermined threshold, but when the change is below the threshold, there is some abnormality on the polishing surface. It can be determined that there is. Such a threshold value is arbitrarily set according to the application. When an abnormality is detected, an abnormality detection signal is notified from the torque analysis unit 118 to the controller 120, and the controller 120 can send a control signal to the motor 116 and other elements of the surface plate 102. In response to this control signal, for example, it is possible to take measures such as interrupting the polishing process or collecting the polished wafer.

  In the above example, the abnormality detection signal is generated when the change in the torque signal is small. However, the present invention is not limited to such an embodiment. In the process of separating the wafer 114 from the polishing surface 104, the torque signal does not change so much when the polishing surface is uneven, and the torque signal changes greatly when the polishing surface is flat. Therefore, by monitoring the torque signal in the process of separating the wafer 114 from the polishing surface 104, it is possible to determine whether or not the substrate surface is in a good mirror state. Therefore, for example, the end point of polishing can be detected. In this case, when the torque signal changes greatly, the polishing is completed, and otherwise, it is possible to find that the polished surface is uneven.

  As described above, according to the embodiment of the present invention, without removing the wafer 114 from the polishing apparatus (from the header) or without remounting the wafer 114 to another apparatus for inspecting scratches or the like. It is possible to detect at an early stage whether or not the polished surface is abnormal and whether or not the polished surface is in a good mirror state.

  Hereinafter, the means taught by the present invention will be listed as an example.

(Appendix 1)
A polishing step of contacting the material to be processed and the polishing pad and rotating the material to be processed or the polishing pad; and
A method for inspecting a surface of a polished material, comprising: an inspection step of examining a torque signal representing torque for rotating the material to be processed or the polishing pad in the process of separating the material to be processed from the polishing pad.

(Appendix 2)
The method according to appendix 1, wherein an alarm is issued according to an inspection result in the inspection step.

(Appendix 3)
The method according to claim 1, wherein an alarm is issued according to a change amount of the torque signal in a process of separating the material to be processed from the polishing pad.

(Appendix 4)
The method according to claim 1, wherein when the amount of change in the torque signal in the process of separating the material to be processed from the polishing pad does not exceed a threshold value, an alarm indicating that there is an abnormality on the surface of the material to be processed is issued. .

(Appendix 5)
The method according to claim 1, wherein the torque signal represents a moving averaged torque.

(Appendix 6)
The method according to claim 1, wherein the polishing step and the inspection step are performed by a chemical mechanical polishing apparatus.

(Appendix 7)
Contacting the wafer supported by the wafer header with a polishing cloth provided on the surface plate;
A polishing step of rotating the wafer header or surface plate;
A method for detecting an abnormality of the wafer surface, comprising: a separation step for separating the wafer and the polishing, and examining a change in the separation step of a torque signal representing a torque for rotating the wafer header or the surface plate.

(Appendix 8)
A surface plate with a polishing cloth on the surface;
A conditioner for cutting the polishing cloth;
A header sandwiching the wafer and having a space on the back surface of the wafer;
Means for increasing or decreasing the pressure of the space;
Means for landing or detaching the header with respect to the surface plate;
A torque analyzer for monitoring changes in the rotational torque signal of the surface plate and / or the rotational torque signal of the head;
A polishing apparatus comprising: a controller that generates a control signal in accordance with a change in the torque signal generated by reducing the pressure in the space.

(Appendix 9)
9. The polishing apparatus according to claim 8, wherein the controller generates a control signal in accordance with a change in the torque signal generated when the head is detached from the surface plate.

FIG. 2 shows a partial schematic view of a polishing apparatus capable of using the inspection method according to the present invention. It is a figure which shows the enlarged view of a header. It is FIG. (The 1) which shows each process for demonstrating the inspection method by one Example of this invention. It is FIG. (The 2) which shows each process for demonstrating the inspection method by one Example of this invention. It is FIG. (The 3) which shows each process for demonstrating the inspection method by one Example of this invention. It is a figure which shows the measurement result of the torque signal in a series of grinding | polishing processes.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Polishing apparatus 102 Surface plate 104 Polishing cloth 106 Conditioner 108 Header 110 Slurry nozzle 111 Slurry 112 Slurry supply part 113,115,117 Movement direction of header 114 Wafer 116 Motor 118 Torque signal analysis part 120 Controller 201 Main part 202 Holding part 203 Space 204 Wafer support 205 Projection 206 Seal 302, 402, 404, 502 Stress

Claims (4)

A polishing step of contacting the material to be processed and the polishing pad and rotating the material to be processed or the polishing pad; and
A method for inspecting a surface of a polished material, comprising: an inspection step of examining a torque signal representing torque for rotating the material to be processed or the polishing pad in the process of separating the material to be processed from the polishing pad. The method according to claim 1, wherein an alarm is issued according to a change amount of the torque signal in a process of separating the material to be processed from the polishing pad. Contacting the wafer supported by the wafer header with a polishing cloth provided on the surface plate;
A polishing step of rotating the wafer header or surface plate;
A method for detecting an abnormality of the wafer surface, comprising: a separation step of separating the wafer and the polishing cloth , and examining a change in the separation step of a torque signal representing a torque for rotating the wafer header or the surface plate. A surface plate with a polishing cloth on the surface;
A conditioner for cutting the polishing cloth;
Means pressure or the pressure of the header and the space of the wafer to hold the depressurizing the backside of the wafer by providing a space,
Means for landing or detaching the header with respect to the surface plate;
A torque analyzer for monitoring changes in the rotational torque signal of the surface plate and / or the rotational torque signal of the head;
A polishing apparatus comprising: a controller that generates a control signal according to a change in the torque signal when the pressure in the space is reduced and the wafer is pulled away from the polishing cloth .

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