JP5643151B2 - Polishing apparatus and polishing method - Google Patents

Description

  The present invention relates to a polishing apparatus and a polishing method useful for planarizing a surface of a planar workpiece such as a silicon wafer by CMP (chemical mechanical polishing).

  The CMP apparatus is used, for example, when a conductor film (for example, a copper plating film) formed on the surface of a silicon wafer is planarized by CMP to form a wiring. CMP as an example polishes the surface of the wafer by pressing a head holding the wafer against the polishing pad against a rotationally driven surface plate (platen) having a polishing pad mounted on the surface thereof.

  Vacuum suction is used as one means for holding the wafer. In order to realize this, a plurality of suction holes are provided on the suction surface of the head, and each suction hole is connected to a vacuum pump via a vacuum system flow path.

  When polishing a relatively thick wafer, the wafer can be held on the head by “water-bonding” the wafer to a backing pad mounted on the lower surface of the head main body, so that polishing can be performed without vacuum suction. In this case, in order to prevent the wafer from jumping out during polishing, a retainer attached to the peripheral edge of the lower surface of the head body is used.

  On the other hand, when a relatively thin wafer is polished, there is a risk of chipping or wafer cracking due to the wafer edge (periphery) hitting the retainer during polishing. For this reason, a retainer cannot be used, and it is necessary to perform polishing while adsorbing and holding the wafer on the head by the above-described vacuum adsorption.

  An example of a technique related to such CMP is described in Patent Document 1 below.

JP-A-9-262756

  As described above, when polishing (CMP) a relatively thin wafer using the current CMP apparatus, it is necessary to perform polishing by adsorbing the wafer to the adsorption surface (provided with a plurality of adsorption holes) of the head. There is.

  When polishing is performed while maintaining the suction, for example, as shown in FIG. 6B, the portion of the wafer near the suction hole is recessed due to the suction force. For this reason, the surface of the polishing pad does not sufficiently hit the adsorbed portion, and only that portion cannot be satisfactorily polished. Therefore, if the polishing target material is a copper wiring, Residue). That is, it is impossible to perform a uniform polishing process that is flattened over the entire surface of the wafer.

  In view of the above, it is an object of the present invention to provide a polishing apparatus and a polishing method that can prevent generation of polishing residue on a workpiece such as a silicon wafer.

According to one aspect, a surface plate having a polishing pad mounted on a surface, a head disposed on the surface plate, and the head on a surface facing the polishing pad are provided on a surface of the workpiece. A suction surface to be sucked, a first system flow path for vacuum suction formed by a plurality of concentric first grooves provided in the head and in communication with each other, and provided in the head and in communication with each other And a second channel for vacuum suction in which the second groove is arranged alternately with the first groove, and the head is provided with the second groove. A plurality of first suction holes communicating with the flow path of the first system and reaching the suction surface; and a plurality of second suction holes provided in the head and communicating with the flow path of the second system and reaching the suction surface. selective a head having a suction hole, the flow path and the flow path of the second system of the first system And a flow path switching means for switching and enabling, and selectively switching and enabling the flow path of the first system and the flow path of the second system, thereby adsorbing the head to the workpiece. There is provided a polishing apparatus characterized in that a suction position on a surface is switched between the first suction hole and the second suction hole.

According to another aspect, there is provided a method for polishing a surface of a flat workpiece using the polishing apparatus according to the above aspect, wherein the first system flow path is made effective, and the first system is used. The workpiece is sucked and held on the suction surface of the head through the plurality of first suction holes communicated with the flow path of the head, and in this state, the polishing pad on the surface plate that is driven to rotate is supported. A first step of polishing by pressing the surface of the workpiece, and enabling the second system flow path, and the plurality of second suction holes communicating with the second system flow path The workpiece is sucked and held on the suction surface of the head, and in this state, the surface of the workpiece is pressed against the polishing pad on the rotationally driven surface plate to perform polishing. It includes a two-step, and comprises carrying out by plural times between the first step and the second step are alternately Polishing method for are provided.

  According to the polishing apparatus according to the above aspect, the plurality of suction holes provided in the suction surface of the head are arranged separately for each flow path of the first system and the second system, and the flow paths of each system are selectively selected. Switch and enable. As a result, even if a remaining polishing portion is generated near the suction hole when the first system is polished, the remaining polishing portion is removed when the second system is polished next. Can do.

1 is a diagram schematically showing an overall configuration of a CMP apparatus according to an embodiment. It is a figure which shows the cross-sectional structure of the head used for the CMP apparatus of FIG. 1 with the structural member engaged with this. FIG. 3 is a plan view when the head is viewed along line AA in FIG. 2. FIG. 2 is a process diagram showing an example of a method for polishing a relatively thin wafer using the CMP apparatus of FIG. 1. FIG. 5 is a diagram for supplementarily explaining the polishing process shown in FIG. 4. It is explanatory drawing of the problem at the time of grind | polishing a comparatively thin wafer using the CMP apparatus of a present technology.

  First, before describing the embodiment, a preliminary matter for facilitating understanding of the embodiment will be described with reference to FIG.

  6A shows an example of a cross-sectional structure of a head used in a state-of-the-art CMP apparatus. FIG. 6B shows a state in which a relatively thin wafer is sucked and polished using this head. This is shown schematically.

  As shown in FIG. 6A, the head 60 includes a head main body 61, a casing 62, a shaft portion 63, and the like. Inside the head main body 61, a chamber 71 serving as a decompression exhaust path for vacuum suction is provided. Further, a plurality of suction holes 72 are formed so as to penetrate from the vacuum suction chamber 71 to the lower surface of the head main body 61. Further, a backing pad 64 is attached to the lower surface of the head main body 61, and a plurality of suction holes 73 are formed in the backing pad 64 at positions corresponding to the plurality of suction holes 72 provided in the head main body 61. Has been. The wafer 1a (see FIG. 6B), which is an object to be polished, is sucked and held on the lower surface of the head main body 61 through the suction holes 73 formed in the backing pad 64.

  The bottom of the casing 62 is opened, and the head body 61 is held in the opening. The head main body 61 hermetically closes the opening. A shaft portion 63 is fixed to the central portion of the upper portion of the casing 62.

  Inside the shaft portion 63, a vacuum suction tube 65 and an air introduction tube 66 are provided. One end of the vacuum suction tube 65 passes through the shaft portion 63 and is connected to the chamber 71 in the head body 61 through the casing 62, and the other end on the opposite side is connected to a vacuum pump outside the head. Has been.

  One end of the tube 66 for introducing air passes through the shaft portion 63 and is open to the inner wall surface of the upper portion of the casing 62, and the other end opposite to this is connected to a compressor (not shown) outside the head. Are combined. By filling the casing 62 with air (air) through the air introduction tube 66 from the compressor, an appropriate load can be applied to the head body 61 by the air pressure. Due to this load, the wafer 1a (FIG. 6B) attracted and held on the lower surface of the head main body 61 (backing pad 64) is applied to a polishing pad (not shown) attached on a rotationally driven surface plate. It is pressed against and its surface is polished.

  When CMP is performed while maintaining the suction of a relatively thin wafer using the head 60 (including the CMP apparatus) having such a structure, the portion of the wafer 1a near the suction hole 73 (see the arrow P in FIG. 6B). ) Is recessed due to the adsorption force. For this reason, the surface of the polishing pad does not sufficiently hit the adsorbed portion, and only that portion cannot be satisfactorily CMPed. As a result, as shown in FIG. 6B, a polishing residue RS is generated in the vicinity of the suction hole 73. That is, it is impossible to perform a uniform polishing process that is flattened over the entire surface of the wafer.

  Hereinafter, preferred embodiments of the present invention will be described.

  FIG. 1 schematically shows the overall configuration of a CMP (Chemical Mechanical Polishing) apparatus according to an embodiment. FIG. 2 shows a cross-sectional structure of a head used in this CMP apparatus together with constituent members engaged therewith, and FIG. 3 shows the head in a plan view along the line AA in FIG. The structure is shown schematically.

  First, referring to FIG. 1, in the CMP apparatus 50 of this embodiment, a polishing pad 10 made of a nonwoven fabric or the like is mounted on a flat surface of a surface plate 11, and the surface plate 11 is fixed to the upper end of a drive shaft 12. Driven by rotation. Above the polishing pad 10 on the surface plate 11, a head 20 for adsorbing and holding a flat plate-like workpiece (a relatively thin wafer 1 in this embodiment) that is an object to be polished is disposed. . Details of the head 20 will be described later.

  The wafer 1 is attracted and held on the lower surface of the head 20 via the backing pad 24 (see FIG. 2). Further, above the surface plate 11, an abrasive supply nozzle 45 for supplying an abrasive (for example, ammonium persulfate, sodium persulfate, etc.) onto the polishing pad 10, and used to remove clogging of the polishing pad 10. A dresser 46 and the like are arranged.

  For polishing the surface of the wafer 1, the surface plate 11 is rotated (the head 20 is also rotated as necessary), and an abrasive is supplied from the abrasive supply nozzle 45 onto the polishing pad 10. This is performed by pressing the surface of the polishing pad 10 against the polishing pad 10.

  Next, the configuration of the head 20 will be described.

  As shown in FIG. 2, the head 20 includes a head main body 21, a casing 22, a shaft portion 23, and the like. The head body 21 is composed of two members (a base 21a and a lid 21b) joined together, and two systems serving as a decompression exhaust path for vacuum suction are formed therein (a joint between the base 21a and the lid 21b). Channels 31 and 32 are provided. For convenience, the system of the flow path 31 is referred to as “A system”, and the system of the flow path 32 is referred to as “B system”.

  As shown in FIGS. 2 and 3, two independent grooves are formed concentrically on the upper surface side of the base 21 a constituting the head body 21. By these grooves, the A system flow path 31 and the B system flow path 32 are formed concentrically between the lower surface of the lid portion 21b. After the required two independent grooves are formed in the base portion 21a, the head main body 21 is configured by connecting a lid portion 21b to the base portion 21a.

  Further, a plurality of suctions are respectively made corresponding to the A system flow path 31 and the B system flow path 32 so as to penetrate from the respective vacuum suction flow paths 31 and 32 to the lower surface of the head body 21 (suction surface 21S). Holes 33 and 34 are formed. The other end of each suction hole 33, 34 whose one end communicates with each flow path 31, 32 is open to the lower surface (suction surface 21 </ b> S) of the head body 21.

  The vacuum suction channels 31 and 32 are formed on the same plane as shown in FIG. 2, and are formed in a required pattern shape (concentric in the example of FIG. 3) independently of each other. Each flow path 31 and 32 is formed so that each pattern may be distributed over the entire suction surface 21S of the head body 21 (FIG. 3). Preferably, each pattern is formed so that a plurality of suction holes 33 and 34 communicated with the respective flow paths 31 and 32 are arranged at substantially equal intervals on the flow path.

  Note that the pattern shapes of the flow paths 31 and 32 shown in FIG. 3 are merely examples, and it is needless to say that the pattern shapes are not limited to the illustrated pattern shapes.

  Each suction hole 33, 34 has a step so that the diameter on the suction surface 21 S side is smaller than the diameter on the side communicating with each flow path 31, 32 when viewed in cross section (see FIG. 2). It is formed in a shape. The reason for increasing the diameter of the portion (large diameter portion 33a, 34a) on the side communicating with each flow path 31, 32 of each suction hole 33, 34 is that if the diameter is small, clogging occurs and sufficient decompression occurs. This is because there is a possibility that exhausting cannot be performed (impeding vacuum adsorption). On the other hand, the reason why the diameter of the portion (small diameter portion 33b, 34b) on the side communicating with the suction surface 21S of each suction hole 33, 34 is small is that if the diameter is large, the suction force is too strong and the wafer at that portion. It is because the dent of (polishing object) increases.

  Further, a backing pad 24 is mounted on the lower surface of the head body 21, and a plurality of suction holes are provided on the backing pad 24 at positions corresponding to the suction holes 33 and 34 provided in the head body 21. 35 and 36 are formed. The wafer 1 (see FIG. 2), which is an object to be polished, is sucked and held on the lower surface (suction surface 21S) of the head body 21 through suction holes 35 and 36 formed in the backing pad 24.

  The casing 22 constituting a part of the head 20 has an opening at the bottom, and the head body 21 is held in the opening. The head body 21 hermetically closes the opening. A shaft portion 23 is fixed to the upper central portion of the casing 22.

  Inside the shaft portion 23, two systems (A system and B system) of vacuum suction tubes 25 and 26 and an air introduction tube 27 are provided. One end of each of the tubes 25 and 26 for vacuum suction passes through the shaft portion 23 and is connected to the corresponding flow paths 31 and 32 in the head body 21 through the casing 22, and the other end on the opposite side is These are coupled to the vacuum pump 40 via individual flow path opening / closing valves 41 and 42, respectively. Reference numeral 43 denotes a wafer detachment valve, which is interposed between the vacuum pump 40 and the flow path opening / closing valves 41 and 42. The valve 43 is used when releasing the suction holding by the head 20 after the desired polishing of the wafer 1 is finished.

  One end of the tube 27 for introducing air passes through the shaft portion 23 and is open to the inner wall surface of the upper portion of the casing 22, and the other end opposite to this is connected to a compressor (not shown) outside the head. Are combined. By filling the casing 22 with air (air) from the compressor through the air introduction tube 27, an appropriate load can be applied to the head body 21 by the air pressure. With this load, the wafer 1 (FIG. 1) sucked and held on the lower surface of the head main body 21 (backing pad 24) is pressed against the polishing pad 10 mounted on the surface plate 11 that is rotationally driven. The surface is polished.

  In addition, as a material of the head main body 21, for example, stainless steel (SUS) is preferably used. As a material for the backing pad 24, for example, polyurethane (which is an elastic body and has excellent mechanical properties, weather resistance, and particularly wear resistance) is preferably used. In addition, as a material for the casing 22 and the shaft portion 23, a plastic material is used.

  Although not shown in FIG. 2, a retainer is attached in a ring shape along the peripheral edge of the lower surface of the head main body 21. This retainer is used to prevent the wafer from popping out when polishing a relatively thick wafer as described above. When polishing a relatively thin wafer 1 as in this embodiment, the retainer is appropriately retracted to a position where the polishing pad 10 does not hit.

  Next, a method for polishing a relatively thin wafer using the CMP apparatus 50 (FIGS. 1 to 3) of the present embodiment will be described with reference to FIG. To do.

  First, a relatively thin wafer 1 (for example, 200 μm or less) that is an object to be polished is prepared. In this embodiment, as an example, a case where a copper (Cu) wiring pattern is formed on a silicon wafer by a dual damascene method will be described as an example, as illustrated in FIGS.

  In the Cu wiring formation by the dual damascene method, a required wiring 2 is formed on a silicon wafer, an insulating film 3 is formed so as to cover the wiring 2, and the insulating film 3 is etched to be connected to the lower wiring 2. A contact hole groove 4 and a wiring groove 5 are formed. Next, after a barrier metal layer 6 (for example, TiN) is formed on the entire surface, copper (Cu) 7 is embedded in the grooves 4 and 5 by CVD, plating, or the like. Thereafter, unnecessary portions of Cu7 and barrier metal layer 6 are planarized while being removed by CMP to form wiring 7a.

  This CMP method will be described with reference to FIG.

  First (see FIG. 4A), with the flow path on / off valve 42 closed with the wafer detachment valve 43 (FIG. 2), the flow path on / off valve 41 is opened and the vacuum pump 40 is activated. As a result, the air in the flow path is evacuated through the tube 25 from the flow path 31 communicating with the A system adsorption hole 33 (35). As a result, as shown in FIG. 4A, the portion of the wafer 1 near the suction hole 35 is recessed due to the suction force.

  In this state (see FIG. 4B), when the wafer 1 is polished (CMP) by being pressed against the polishing pad 10 on the rotationally driven surface plate 11 (FIG. 1), the adsorbed portion (arrow P1) Since the surface of the polishing pad 10 does not sufficiently hit the portion indicated by), only that portion cannot be satisfactorily polished. As a result, as shown in FIG. 4B, a polishing residue RS is generated at the location of the wafer 1 near the suction hole 35. FIG. 5C conceptually shows the state of the polishing residue RS at this time.

  Next (see FIG. 4C), with the vacuum pump 40 activated, this time the flow path on / off valve 42 is opened and the flow path on / off valve 41 is closed. As a result, the air in the flow path is evacuated through the tube 26 from the flow path 32 communicating with the B system adsorption hole 34 (36). As a result, as shown in FIG. 4C, the portion of the wafer 1 in the vicinity of the suction hole 36 (the portion indicated by the arrow P2 in FIG. 4B) was recessed due to the suction force, and was recessed until then. The portion of the wafer 1 near the suction hole 35 is relatively projected. That is, the portion where the polishing residue RS is generated is projected.

  In this state (see FIG. 4D), when the wafer 1 is polished (CMP) by pressing against the polishing pad 10 in the same manner as described above, the surface of the polishing pad 10 is placed on the protruding portion of the polishing residue RS. In order to reliably hit, the portion of the polishing residue RS is polished. As a result, as shown in FIG. 4D, the portion of the polishing residue RS generated at the location of the wafer 1 near the suction hole 35 is removed cleanly.

  After removing the portion of the polishing residue RS in this way, when vacuum suction is stopped, a uniformly flattened wafer 1 having no polishing residue over the entire surface is obtained (FIG. 4E). reference). The vacuum suction is stopped by stopping the vacuum pump 40 and opening both the flow path opening / closing valves 41 and 42. When the wafer detachment valve 43 is further opened in this state, the wafer 1 is released from the suction holding by the head 20.

  In the CMP method shown in FIG. 4, for simplification of explanation, the adsorption and polishing processes are performed once for each of the A system and the B system. However, in the actual switching mode, the A system and the B system are used. CMP is performed by alternately switching the system a plurality of times. For example, when the polishing rate for copper (Cu) is 1 μm / min and the copper (Cu) film 7 is formed on the wiring groove 5 (see FIG. 5) with a thickness of about 5 μm, adsorption and polishing processes are performed for the A system and the B system, respectively. By repeating the process five times alternately, a uniform polishing process with no polishing residue can be performed.

    As described above, according to the CMP apparatus 50 and the polishing method using the same according to the present embodiment, the plurality of suction holes 33 (35) and 34 (34) provided in the suction surface 21S of the head 20 (head body 21). 36) are divided into two channels (system A and system B) for vacuum suction flow paths 31 (25) and 32 (26) (FIG. 3), and are arranged by vacuum pump 40 and flow path opening / closing valves 41 and 42. , A channel and B channel 31 (25), 32 (26) are selectively switched to be effective.

  As a result, even if a portion of the polishing residue RS is generated at the location of the wafer 1 near the suction hole 35 when polishing (CMP) is performed in the A system as illustrated in FIG. When CMP is performed, the portion of the polishing residue RS can be removed. Preferably, by performing CMP by alternately switching between the A system and the B system a plurality of times, it is possible to perform a uniform polishing process with no polishing residue over the entire surface of the wafer 1.

  In the above-described embodiment, the plurality of suction holes 33 (35) and 34 (36) for sucking the object to be polished (wafer 1) are arranged in two systems, and the flow paths 31 and 32 of each system are arranged. Although the case where CMP is performed while switching has been described as an example, the two systems are not necessarily required. It is also possible to perform CMP by dividing into three or more systems as necessary.

  Further, in the above-described embodiment, when CMP is performed while switching the two channels 31 and 32, the respective channels 31 and 32 are completely switched and the wafer 1 is adsorbed. It is not limited. For example, the suction may be performed by switching the strength of suction between the two channels 31 and 32.

  In the above-described embodiment, the case of performing CMP on copper (Cu) in a wiring groove formed by a damascene method has been described as an example (FIGS. 4 and 5). However, the target material of CMP is not limited to metal. Of course. As in the above damascene method, if the substrate has a structure in which an opening such as a groove is formed in the base material and a material different from the base material is embedded in the opening, for example, a silicon oxide film, polysilicon, etc. Similarly, planarization can be achieved by applying CMP to an insulating material such as a film or a silicon nitride film.

  In the above-described embodiment, the case where the silicon wafer 1 (silicon plate) is polished as a workpiece has been described as an example. However, other materials such as a glass plate, a ceramic plate, and a resin plate are polished. It is possible to select the target appropriately.

  DESCRIPTION OF SYMBOLS 1 ... Wafer (plate-shaped workpiece), 10 ... Polishing pad, 11 ... Surface plate (platen), 20 ... Head, 21 ... Head main body, 22 ... Casing, 23 ... Shaft part, 24 ... Backing pad, 25, 26 ... Tube for vacuum adsorption, 27 ... Tube for air introduction, 31, 32 ... Channel for vacuum adsorption (decompression exhaust path), 33-36 ... Adsorption hole, 40 ... Vacuum pump, 41, 42 ... Channel Open / close valve, 43 ... Valve for wafer removal, 45 ... Abrasive supply nozzle, 46 ... Dresser, 50 ... Polishing (CMP) device, RS ... Polishing residue.

Claims (4)

A surface plate with a polishing pad on the surface;
A head disposed on the surface plate;
An adsorption surface that is provided in the head on the surface facing the polishing pad and adsorbs a workpiece;
A first channel for vacuum suction formed in the head and formed by a plurality of concentric first grooves communicating with each other;
A second system for vacuum suction, which is provided in the head, is formed from a plurality of concentric second grooves communicating with each other, and the second grooves are alternately arranged with the first grooves. A flow path;
A plurality of first suction holes provided in the head and communicating with the flow path of the first system to the suction surface;
A head provided in the head and having a plurality of second suction holes communicating with the flow path of the second system and leading to the suction surface;
A flow path switching means for selectively switching the flow path of the first system and the flow path of the second system to enable,
By selectively switching the flow path of the first system and the flow path of the second system and making it effective, the suction location of the suction surface of the head with respect to the workpiece is changed to the first suction hole and the first flow path. A polishing apparatus characterized by switching between two suction holes.   2. The polishing apparatus according to claim 1, wherein in the head, the first suction holes and the second suction holes are arranged so as to be distributed over the entire suction surface.   The flow path switching means is coupled to each of the flow paths via the flow path on-off valves respectively interposed in the flow paths of the first system and the second system. The polishing apparatus according to claim 1, further comprising a vacuum pump. A method for polishing a surface of a flat workpiece using the polishing apparatus according to any one of claims 1 to 3 ,
By enabling the flow path of the first system, the work piece is sucked and held on the suction surface of the head via the plurality of first suction holes communicated with the flow path of the first system. Then, a first step of performing polishing by pressing the surface of the workpiece against the polishing pad on the surface plate to be rotationally driven,
The second system flow path is made effective, and the work piece is sucked and held on the suction surface of the head via the plurality of second suction holes communicated with the second system flow path. A second step of performing polishing by pressing the surface of the workpiece against the polishing pad on the surface plate that is rotationally driven;
Including
A polishing method, wherein the first step and the second step are alternately performed a plurality of times .

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