JP2001121413A - Method of holding planar workpiece - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of holding a wafer, which can surely hold the wafer, which enables a more perfect surface reference process, and which can enhance the processing accuracy. SOLUTION: A wafer 1 is held on the upper surface of a porous plate 6 fixed to the upper surface of a turn table 2, through the intermediary of a packing pad 7 which is made of a soft porous material having opened pores so as to be permeable and elastic, and which is applied to the outer surface of the porous plate 6 with the use of a pressure sensitive adhesive double-coated tape which is similarly permeable. A cavity 31 defined between the rear surface of the porous plate 5 and the upper surface of the turn table 2 is connected to a vacuum pump through a depressurized passage 33. A nonporous zone is defined in the peripheral edge part 6a of the porous plate 6 whose lower surface side is fixed to the peripheral edge part of the turn table 2, and whose upper surface is attached to a guide ring 5 so as to surround the periphery of the wafer 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for holding a flat workpiece in planar polishing such as CMP, and more particularly to a method for holding a wafer using a vacuum chuck made of a porous plate. The present invention relates to a wafer holding method for achieving high processing accuracy when polishing the surface.

[0002]

2. Description of the Related Art In recent years, as semiconductor circuits have been miniaturized and multilayered, the beam wavelength of an exposure apparatus used for pattern formation has been shortened, and the margin of depth of focus by photolithography has been gradually narrowed. I have. For this reason,
A planarization technique for globally reducing steps on the surface of an interlayer insulating film or a metal film formed on a silicon substrate is becoming an indispensable technique for performing multilayer wiring. Therefore,
As a method for globally and accurately planarizing the surface of a silicon wafer, CMP (Chemical Mechanical) is used.
ical Polishing) is attracting attention.

[0003] In CMP, a slurry in which abrasive grains are mixed in a chemical solution or pure water (hereinafter, referred to as a polishing liquid) is provided between a polishing tool such as a polishing cloth or a grindstone and a surface to be polished of a workpiece such as a silicon wafer. Polishing tool) is supplied, and the polishing tool and the workpiece are rotated while the polishing tool is pressed against the surface to be polished, thereby polishing the workpiece. When a grindstone is used as a polishing tool, only a chemical solution or pure water may be used instead of an abrasive.

FIG. 6 shows a schematic configuration diagram of a conventional CMP apparatus. In the drawing, 1 is a wafer, 61 is a polishing cloth, 62 is a turntable, 72 is a polishing head, 73 is a top ring, and 75 is a backing pad.

The polishing cloth 61 is attached to the upper surface of the turntable 62 with a double-sided adhesive tape. The turntable 62 is fixed to the upper end of the drive shaft 63. The polishing head 72 is arranged above the turntable 62. A top ring 73 is attached to a lower end of the polishing head 72 so as to face the turntable 62. The wafer 1 to be polished is sucked and held on the lower surface of the top ring 73 via the backing pad 75. A guide ring 74 is attached to the periphery of the lower surface of the top ring 73 so as to surround the periphery of the wafer 1.

An abrasive (a slurry in which abrasive grains are suspended) is supplied from an abrasive supply nozzle 79 onto the polishing cloth 61, and the polishing head 72 rotates the wafer 1 in the same direction as the turntable 62 to polish the wafer 1. Cloth 61
, The step on the surface of the interlayer insulating film or the metal film formed on the wafer 1 is scraped off.

In the above-described CMP apparatus, since the polishing cloth 61 and the backing pad 75 are made of an elastic material, the wafer 1 having an uneven thickness or undulation is deformed following the polishing cloth 61, Since it is so-called surface reference processing, it can be processed with high accuracy. In particular, the backing pad 75 also has an effect of preventing a change in pressure distribution on the wafer due to the influence of dust or the like attached to the lower surface of the top ring 73 or the back surface of the wafer 1.

In the above-described CMP apparatus, as shown in FIG. 6, during processing, the wafer 1 includes a backing pad 75 attached to the front surface of a top ring 73 and a polishing cloth 6.
Between the two. Therefore, during processing, the holding force of the backing pad 75 works effectively, and the wafer 1 can be held only by the holding force of the backing pad 75.

On the other hand, when polishing the surface of a workpiece having a large area such as a large-diameter silicon wafer, a polishing tool having a diameter smaller than that of the surface to be polished is used. In such a CMP apparatus, the polishing tool is reciprocated within a plane parallel to the surface to be polished, and the entire surface of the surface to be polished is polished.

FIG. 7 shows a schematic configuration diagram of a CMP apparatus using a polishing tool having a smaller diameter than the surface to be polished. In the figure, 1 is a wafer, 2 is a turntable, 5 is a backing pad, 11 is a polishing tool, and 12 is a tool holder.

The turntable 2 is fixed to an upper end of the drive shaft 3. A wafer 1 to be processed is held on a top surface of a turntable 2 via a backing pad 5. A guide ring 4 is attached to the periphery of the upper surface of the turntable 2 so as to surround the periphery of the wafer 1.

A tool holder 12 is arranged so as to face the upper surface of the turntable 2, and a polishing tool 11 is mounted on the lower surface of the tool holder 12. The tool holder 12 includes a motor 16
The housing of the motor 16 is attached to the distal end of an arm 21 via an air cylinder 17 and a linear guide 18. The motor 16 drives the tool holder 12 to rotate, and the air cylinder 17 moves the tool holder 12 in the vertical direction, and presses the polishing tool 11 against the wafer 1 during polishing. The arm 21 reciprocates on a swivel path around the column 22, thereby reciprocating the tool holder 12 in a plane parallel to the surface to be polished. Tool holder 1
A nozzle 19 for supplying an abrasive is disposed adjacent to the outer peripheral portion of the nozzle 2. By dropping the abrasive around the polishing tool 11 from the nozzle 19, the abrasive is supplied between the surface to be polished and the polishing tool 11.

As described above, when a polishing tool having a diameter smaller than the diameter of the wafer is used, the pressure of the polishing tool 11 acts on only a part of the surface of the wafer 1, so that the wafer 1 is backed. It is difficult to hold only the pad 5. As a result, the wafer 1 may jump out of the turntable 2 during processing and may be damaged. For this reason, when a polishing tool having a diameter smaller than the diameter of the wafer is used, it is necessary to vacuum-suction the wafer 1 onto the turntable 2 in order to secure a sufficient suction force during processing. Have been done.

FIG. 8 shows a state in which the wafer 1 is held by using a general vacuum chuck 81 made of a perforated plate having a plurality of suction holes 83 for vacuum suction. As shown in FIG. 8, the wafer 1 is in close contact with the vacuum chuck 81 immediately above the suction hole 83 for vacuum suction (part Z in the drawing).
3, the adhesion between the vacuum chuck 81 and the wafer 1 becomes insufficient (Y part in the figure). Like this
If processing is performed in a state where the close contact state in the plane of the wafer 1 is not uniform, a difference in processing speed occurs in the plane of the wafer 1 and the processing accuracy is impaired.

Further, when the wafer 1 is directly sucked onto the surface of the vacuum chuck 81, the back side reference processing (processing based on the back side of the wafer) is performed, so that the thickness of the wafer 1 before processing is not sufficient. Uniformity appears on the surface, and sufficient processing accuracy cannot be obtained. Further, there is also a problem that the pressure distribution on the wafer 1 changes due to dust or the like attached to the back surface of the wafer 1 or the surface of the vacuum chuck 81, and the processing accuracy is reduced.

FIG. 9 shows a state in which the wafer 1 is held by using the vacuum chuck 81 and the conventional backing pad 85 shown in FIG. As shown in FIG. 9, in this example, a backing pad 85 is attached to the surface of a vacuum chuck 81, and the wafer 1 is vacuum-sucked via the backing pad 85. Thus, since the surface reference processing is performed, the unevenness of the thickness of the wafer 1 before processing and the influence of undulation can be suppressed. Furthermore, wafer 1
The problem that the pressure distribution on the wafer 1 changes due to dust or the like attached to the back surface of the wafer or the surface of the vacuum chuck 81 and the processing accuracy is reduced is also solved.

However, around the through hole 86 formed on the backing pad 85 side corresponding to the suction hole 83 for vacuum suction, the backing pad 85 is crushed and its thickness is reduced (Z in the figure). Portion) and a portion (the Y portion in the figure) apart from the through hole 86, a difference in thickness occurs. If the processing of the wafer 1 is performed in such a state, a difference occurs in the processing speed in the plane of the wafer 1 and the processing accuracy is impaired.

FIG. 10 shows a vacuum chuck 91 made of a porous material.
Shows a state in which the wafer 1 is held by using. Since the vacuum chuck 91 made of a porous body can uniformly suction the wafer 1 within the suction surface, there is no difference in processing speed due to uneven suction force.

However, since the wafer 1 is directly adsorbed on the surface of the vacuum chuck 91 made of a porous body, the back surface processing is performed, and the unevenness of the thickness of the wafer 1 before processing appears on the surface. , Sufficient processing accuracy cannot be obtained. Further, there is also a problem that the pressure distribution on the wafer 1 changes due to dust or the like attached to the back surface of the wafer 1 or the surface of the vacuum chuck 91 made of a porous body, and the processing accuracy decreases.

FIG. 11 shows a vacuum chuck 91 made of a porous material.
5 shows a state in which the wafer 1 is held using a conventional backing pad 85. As shown in FIG. 11, in this example,
A backing pad 85 is adhered to the surface of a vacuum chuck 91 made of a porous material, and the wafer 1 is vacuum-sucked through the backing pad 85. Thus, since the surface reference processing is performed, the unevenness of the thickness of the wafer 1 before processing and the influence of undulation can be suppressed. Further, the problem that the pressure distribution on the wafer 1 changes due to dust or the like attached to the back surface of the wafer 1 or the surface of the porous body chuck 91 and the processing accuracy is reduced is also solved.

However, around the through hole 86 formed in the backing pad 85, the backing pad 85 is crushed and its thickness is reduced (part Z in the figure). (Y portion). When processing the wafer 1 in such a state,
A difference occurs in the processing speed in the plane of the wafer 1, and the processing accuracy is impaired.

FIG. 12 is a schematic view of a cross section near the end of a conventional backing pad 85. As shown in FIG. The conventional backing pad 85 is configured by attaching a double-sided adhesive tape 88 to the back surface of an elastic body 87 such as polyurethane. On the suction surface of the elastic body 87, there are many holes 89 opening toward the surface. When the wafer 1 is pressed against the suction surface of the elastic body 87, these holes 89 function as suction cups, so that the wafer 1 is sucked.

However, since the material of the conventional backing pad 85 itself does not have air permeability, when it is used by attaching it to the surface of a vacuum chuck (81, 91), the material shown in FIG. 9 or FIG. Thus, it is necessary to provide the through hole 86. For this reason, as described above, when the wafer 1 is sucked, the backing pad 85 is crushed around the through-hole 86 to reduce the thickness, and the thickness between the backing pad 85 and the portion remote from the through-hole 86 is reduced. , And as a result, wafer 1
This is a factor that causes the processing speed of the surface to vary.

[0024]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of a method for holding a wafer by a vacuum chuck using a backing pad, and an object of the present invention is to surely hold a wafer. It is an object of the present invention to provide a method of holding a wafer, which enables more complete surface reference processing at the same time as holding, and realizes high processing accuracy.

[0025]

According to the present invention, there is provided a method for holding a plate-shaped workpiece, wherein the workpiece is vacuum-adsorbed and held from a back surface when the surface of the workpiece is polished. The suction surface is vacuum-adsorbed on the surface of the vacuum chuck formed of a porous plate, through a backing pad made of a soft porous material having open pores and air permeability, and vacuum-adsorbing the workpiece. I do.

According to the method for holding a work material of the present invention, the work material is vacuum-adsorbed by using a vacuum chuck formed of a porous plate and a backing pad made of a soft porous material. The force for attracting the workpiece from the back surface can be evenly distributed. Furthermore, since a soft backing pad is interposed between the vacuum chuck and the workpiece, the pressure distribution on the wafer changes even when dust adheres to the surface of the vacuum chuck or the back of the workpiece. Less likely to give. Therefore, according to the method for holding a work material of the present invention, surface reference processing is performed in a more complete form, and high processing accuracy can be realized.

As the soft porous body constituting the backing pad, for example, polyurethane foam can be used.

The backing pad can be attached to the surface of the porous plate using, for example, a double-sided adhesive tape. In this case, as the double-sided pressure-sensitive adhesive tape, a double-sided pressure-sensitive adhesive tape having air permeability (for example, a perforated film having a large number of fine through-holes, or a film having open pores and air permeability) is used.

Preferably, a region having no air permeability is formed in a ring shape on the backing pad from the outer periphery to a position near the outer diameter of the workpiece.

Instead of using a soft porous material as described above as the backing pad, a perforated sheet made of a soft plastic such as polyurethane having a large number of fine through holes can be used. . in this case,
The thickness of the backing pad is 0.1 mm or more and 2.0 mm or less from the viewpoint of flexibility, strength, and workability of the through-hole, and the through-hole suppresses the influence of the hole to uniformly distribute the attraction force.
The 2.0mm below the through-hole diameter or more 0.3 mm, 5 per unit area / cm ² to 800 / cm ² or be formed by the following density.

[0031]

FIG. 1 is a schematic structural view of a vacuum chuck using a method for holding a workpiece according to the present invention.

The wafer 1 is held on the upper surface of the porous plate 6 via the backing pad 7. The porous plate 6 is fixed on the turntable 2, and the turntable 2 is
It is fixed to the upper end of the drive shaft 3. Backing pad 7
Is made of a soft porous body having open pores and having air permeability and elasticity. The backing pad 7 is attached to the surface of the porous plate 6 with a double-sided adhesive tape having air permeability, as described later. A guide ring 4 is attached to the periphery of the upper surface of the porous plate 6 so as to surround the periphery of the wafer 1.

A hollow portion 31 is formed between the back surface of the porous plate 6 and the upper surface of the turntable 2.
Is connected to an external vacuum pump (not shown) via a pressure reducing path 33 formed in the center of the turntable 2 and the drive shaft 3. The peripheral portion 6a of the porous plate 6
Is formed with a region having no air permeability, and the lower surface side of the peripheral portion 6 a is fixed to the peripheral portion of the turntable 2. The guide ring 4 is mounted on the upper surface side of the peripheral portion 6a. An O-ring 35 is inserted between the upper end surface of the drive shaft 3 and the lower surface of the turntable 2 to seal the inside of the pressure reducing path 33.

FIG. 2 is a partially enlarged sectional view of an example of the backing pad used in the method for holding a workpiece according to the present invention.

In this example, the backing pad 7 is made of a porous material (thickness: 0.5 mm) made of polyurethane having open pores and air permeability. The backing pad 7 is attached to the surface of the porous plate 6 (FIG. 1) via the double-sided adhesive tape 9. For this double-sided adhesive tape 9, a perforated film made of PET is used in order to ensure air permeability between the porous plate 6 and the backing pad 7. The perforated film (thickness: 0.1 mm), the through hole 9a of diameter 0.5 mm, 100 pieces / cm ²
It is formed with the density of.

Further, along the peripheral edge of the backing pad 7, a region 7a having no air permeability is formed in a ring shape. The inner diameter of the non-breathable region 7a is set slightly smaller than the diameter of the wafer held via the backing pad 7. By configuring the backing pad 7 in this way, it is possible to prevent the outside air from entering the hollow portion 31 (FIG. 1) from the peripheral portion of the wafer and to reduce the suction force.

FIG. 3 is a partially enlarged sectional view of another example of the backing pad. The backing pad 7 is made of the same porous material made of polyurethane as in the example shown in FIG. 2, and is provided with a porous plate 6 (FIG. 1) via a double-sided adhesive tape 10.
Affixed to the surface of In this example, the double-sided pressure-sensitive adhesive tape 10 is made of a porous film (thickness: 0.1 mm) made of PET having open pores and air permeability.

FIG. 4 is a partially enlarged sectional view of another example of the backing pad. In this example, the backing pad 8
Is constituted by a perforated sheet made of polyurethane. In this perforated sheet (thickness: 0.1 mm), through holes having a diameter of 0.5 mm are formed at a density of 100 / cm ² . In addition, similarly to the example shown in FIG. 2, the region 8a having no air permeability is formed along the peripheral portion of the backing pad 8.
Are formed in a ring shape. The double-sided adhesive tape 9
Uses the same perforated film made of PET as in the example shown in FIG.

FIG. 5 is a partially enlarged sectional view of another example of the backing pad. In this example, the same perforated sheet made of polyurethane as in the example shown in FIG. 4 is used for the backing pad 8, and the same porous film 10 made of PET as in the example shown in FIG. Is used.

[0040]

According to the method for holding a work material of the present invention,
A vacuum chuck made of a porous plate is used to vacuum-suction a work material through a soft porous backing pad, so that a force for sucking the work material from the back surface can be uniformly distributed. . Furthermore, since a soft backing pad is interposed between the vacuum chuck and the workpiece,
Even when dust or the like adheres to the front surface of the vacuum chuck or the back surface of the workpiece, the wafer is less likely to be deformed.

Therefore, according to the method for holding a workpiece of the present invention, it is possible to reliably hold a wafer and at the same time realize high processing accuracy.

Although the present invention is particularly effective in a CMP apparatus using a polishing tool having a smaller diameter than the surface to be polished as shown in FIG. 7, the diameter of the polishing tool as shown in FIG. It is also applicable to a CMP apparatus.

[Brief description of the drawings]

FIG. 1 is an axial sectional view of a vacuum chuck to which a method for holding a workpiece according to the present invention is applied.

FIG. 2 is a partially enlarged sectional view showing an example of a backing pad according to the present invention.

FIG. 3 is a partially enlarged cross-sectional view showing another example of the backing pad according to the present invention.

FIG. 4 is a partially enlarged sectional view showing another example of the backing pad according to the present invention.

FIG. 5 is a partially enlarged sectional view showing another example of the backing pad according to the present invention.

FIG. 6 is a schematic diagram showing a configuration of a conventional CMP apparatus.

FIG. 7 is a schematic diagram showing a configuration of a CMP apparatus that uses a polishing tool having a smaller diameter than a surface to be polished.

FIG. 8 is a view for explaining an example of a conventional wafer holding method using a vacuum chuck.

FIG. 9 is a diagram illustrating another example of a conventional wafer holding method using a vacuum chuck.

FIG. 10 is a diagram illustrating an example of a wafer holding method using a vacuum chuck made of a porous body.

FIG. 11 is a diagram illustrating another example of a wafer holding method using a vacuum chuck made of a porous body.

FIG. 12 is a schematic view of a cross section near an end of a conventional backing pad.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Wafer, 2 ... Turntable, 3 ... Drive shaft, 4 ... Guide ring, 5 ... Backing pad, 6 ... Porous plate 7 ... Backing pad (Soft 8: backing pad (perforated sheet), 9: double-sided adhesive tape (perforated film), 10: double-sided adhesive tape (porous film), 11: polishing tool, 12: Tool holder, 16: Motor, 17: Air cylinder, 18: Linear guide, 19: Nozzle, 21: Arm, 22: Column, 31 ... Cavity part, 33 ... decompression path, 35 ... O-ring, 61 ... polishing cloth, 62 ... turntable, 63 ... drive shaft, 72 ... polishing head, 73 ... top Ring, 74 , 75: backing pad, 79: abrasive supply nozzle, 81: vacuum chuck, 83: suction hole, 85: backing pad, 86: through hole, 87: elasticity Body: 88 Double-sided adhesive tape 89: Hole, 91: Vacuum chuck (porous body).

Claims (12)

[Claims] 1. A method for vacuum-sucking and holding a work material from a back surface when polishing the surface of a plate-like work material, wherein the suction surface is a surface of a vacuum chuck formed of a porous plate. To
A method for holding a plate-shaped workpiece, wherein the workpiece is vacuum-sucked through a backing pad made of a soft porous material having open pores and air permeability. 2. The method according to claim 1, wherein the backing pad is made of a porous material made of polyurethane. 3. The flat plate-shaped workpiece according to claim 1, wherein the backing pad is attached to a surface of the porous plate using a double-sided adhesive tape having air permeability. Method. 4. The backing pad according to claim 1, wherein a region having no air permeability is formed in a ring shape from an outer periphery thereof to a position near an outer diameter of the workpiece. 4. The method for holding a plate-shaped workpiece according to the above. 5. A backing pad made of a soft porous material having open pores and air permeability. 6. A backing pad made of a polyurethane porous material having open pores and air permeability. 7. A method for vacuum-sucking and holding a workpiece from its back surface when polishing the surface of a flat workpiece, wherein the suction surface is a surface of a vacuum chuck formed of a porous plate. A soft plastic perforated sheet having a thickness of 0.1 mm or more and 2.0 mm or less, and a diameter of 0.3 m
2.0mm below the through-hole or m is, through the backing pad formed 5 per unit area / cm ² to 800 / cm ² or below the density, characterized in that vacuum suction workpiece A method for holding a flat workpiece. 8. The method according to claim 7, wherein the backing pad is made of a perforated sheet made of polyurethane. 9. The flat plate-shaped workpiece according to claim 7, wherein the backing pad is attached to the surface of the porous plate using a double-sided adhesive tape having air permeability. Method. 10. The backing pad has a ring-shaped region having no air permeability from an outer periphery to a position near an outer diameter of the workpiece. 4. The method for holding a plate-shaped workpiece according to the above. 11. A perforated sheet made of a soft plastic having a thickness of 0.1 mm or more and 2.0 mm or less, and through holes having a diameter of 0.3 mm or more and 2.0 mm or less per unit area is 5 / cm. A backing pad formed at a density of ² or more and 800 / cm ² or less. 12. A polyurethane perforated sheet having a thickness of 0.1 mm or more and 2.0 mm or less and a diameter of 0.1 mm or more.
A backing pad in which through holes having a size of 3 mm or more and 2.0 mm or less are formed at a density of 5 pieces / cm ² or more and 800 pieces / cm ² or less per unit area.