JPH10217102A - Dressing method for abrasive cloth and its device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve flatness in addition to planeness of an abrasive cloth by dressing by fixing a position of a dressing too in an abrasive cloth thickness direction continuously after a process to maintain welding pressure of the dressing tool constant. SOLUTION: A position, rotational speed and torque of a servo motor are controlled to correspond to a target value by feeding them back to a control device. At the time of dressing an abrasive cloth 1, the abrasive cloth 1 is fed while precisely controlling a position of a dresser grinding wheel 2 in an abrasive cloth thickness direction by positional control of this servo motor, and the dresser grinding wheel 2 is pressed against the abrasive cloth 1 with proper bearing. At this time, welding pressure to press the dresser grinding wheel 2 is detected by a load cell 14, and a position of the dresser grinding wheel 2 is controlled so as to make the welding pressure constant. Continuously, a clamper 16 is closed by working an air cylinder 18. Consequently, the final position of the dresser grinding wheel 2 in the abrasive cloth thickness direction is fixed by firmly constraining an elevation shaft 8 by the clamper 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a device for dressing a polishing cloth used in a polishing apparatus for flat-working a flat workpiece, and more particularly to further improving the flatness of the polishing cloth. The present invention relates to a method and an apparatus for dressing an abrasive cloth.

[0002]

2. Description of the Related Art In recent years, it has been particularly required to carry out a polishing process while maintaining a high degree of flatness, for example, in a polishing process of a semiconductor wafer. When a flat surface is created on a workpiece by a polishing apparatus used for such ultra-precision polishing, the flatness of the platen facing in parallel with the processing surface of the workpiece is excellent, and the flatness of the workpiece is high. It is necessary to increase.

In this type of polishing, the flatness of the surface plate gradually deteriorates because the surface plate itself is also polished by the abrasive. For this reason, in order to maintain the flatness of the surface plate, it is necessary to appropriately correct the shape using a grindstone.

[0004] Among the polishing apparatuses, there are elastomers, soft plastics, woven fabrics in which fibers are regularly woven, or
In a polishing apparatus that performs polishing by attaching a polishing cloth made of a nonwoven fabric or the like to a surface plate, it is necessary to appropriately dress the polishing cloth to correct its shape. However, at present, this type of polishing cloth is at the stage of finding the conditions of shape correction through trial and error, and at present, there is no established technology for the method of shape correction at present. is there.

[0005] In a process of dressing a polishing cloth while giving a rotation to a circular or ring-shaped whetstone and applying a rotational motion to the polishing cloth on a rotary platen in the same direction as the whetstone, the processing mechanism is the same. It is considered that this is basically different from the grinding of metal and hard brittle material using a grindstone. In the grinding of metals and hard and brittle materials, the amount of processing and the shape of the grinding wheel are determined by the amount of cutting of the grindstone, whereas the abrasive cloth is soft and elastically deformed by the pressing of the grindstone. This is because the processing amount and the processing shape do not correspond to the amount.

Conventionally, regarding dressing of a polishing cloth,
The fact that the processing conditions had to be determined empirically by trial and error is considered to be based on the characteristics of this polishing cloth processing.

In general, in polishing, it is considered that there is a strong correlation with the processing amount in terms of the surface pressure between the workpiece and the polishing platen and the distance over which the grindstone slides on the surface of the polishing cloth. In practice, the surface pressure / sliding distance and the processing amount are usually not proportional due to the crushing or deterioration of the abrasive material. However, in the dressing of a polishing cloth using a whetstone, the processing action is polished. It is predicted that the surface pressure and the processing amount, and the sliding distance and the processing amount are almost proportional to each other because the surface pressure and the processing amount are provided by a grindstone which is less likely to be crushed or deteriorated compared to the material. further,
Since it can be assumed that the grindstone is pressed against the polishing cloth with a constant surface pressure, the shape of the polishing cloth after dressing (dressing shape) is determined mainly by the sliding distance distribution of the dresser at each point of the polishing cloth. Conceivable.

The present applicant simulated dressing conditions and mechanical conditions for optimizing a dressing shape. Summarizing the results, in the case of using a ring-shaped dresser grindstone having an inner diameter equal to or greater than the width of the use area of the polishing cloth, and in the case of using a circular dresser grindstone having an outer diameter equal to or less than the use area width, the dressing shape (Japanese Patent Application Nos. 8-125984 and 8-1492) are proposed.
No. 40).

FIG. 6 shows the result of simulating the sliding distance distribution of a ring-shaped dresser grindstone having an outer diameter of 240 mm and a grindstone width of 20 mm.

In FIG. 6, the vertical axis representing the sliding distance is:
The display is such that the sliding distance increases as the uppermost part is set to 0 and goes downward. The horizontal axis indicates the radial position of the polishing pad. In FIG. 6, the curve represents the sliding distance at each position in the radial direction of the polishing cloth, and the shape of the hatched portion defined by the curve is the cross-sectional shape of the polishing cloth cut by the dressing, that is, the shape of the dressing shape. Represents the features.

FIG. 7 is a view showing the actual cross-sectional shape after dressing the polishing cloth under the same conditions as those used in the simulation of FIG. As can be seen from FIGS. 6 and 7, the sliding distance distribution of the grindstone corresponds well to the actual shape of the polishing cloth after dressing.

[0012]

However, as can be seen from FIG. 7, the surface of the polishing pad is slightly convex. The convex curved surface in which the central portion of the polishing cloth is slightly higher inevitably occurs when a dresser whetstone is used. When modifying the shape of the polishing cloth, in addition to uniformity of the polishing cloth,
It is necessary to correct the flatness, but in the conventional dressing method of polishing cloth, the flatness is aside from the flatness,
At present, there was no effective way to improve it.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to improve the flatness of a polishing pad and also improve the flatness so that the central portion does not have a convex curved surface. An object of the present invention is to provide a method and an apparatus for dressing a cloth.

[0014]

In order to achieve the above object, a method of dressing a polishing pad according to the present invention comprises pressing a rotating dressing tool against a surface of a rotating polishing pad while rotating the rotating dressing tool. A first step of dressing the polishing cloth while maintaining a constant pressing force for pressing the dressing tool against the polishing cloth; and setting the position of the dresser tool to the first step.
The method is characterized by including a second step of fixing the polishing pad in a final position in the thickness direction of the polishing pad in the step, and dressing the polishing pad while maintaining this position.

In such a dressing method, the dressing shape of the polishing pad at the stage of the first step of dressing at a constant pressure is such that the central portion has a slightly convex middle-high surface.

In the subsequent second step, in order to fix the position of the dresser grindstone in the thickness direction of the polishing cloth, the pressure applied by the dresser grindstone is greatly reduced in the more advanced dressing area. Does not progress, whereas doshing proceeds on the central convex surface, and as a result, the convex curved surface at the center of the polishing pad is selectively dressed, and the flatness is improved.

The dressing method of the present invention is effective for a polishing cloth which is an elastic body made of an elastomer, a plastic, a non-woven cloth or a mixture thereof. This is because two-stage dressing of constant pressure and fixed position is effective for elastic deformation of the polishing pad.

An apparatus for carrying out such a dressing method includes a rotating platen on which a polishing cloth to be dressed is attached and which rotates at a constant rotation speed, a disk-shaped dressing tool for grinding the surface of the polishing cloth, Dressing tool rotating means for holding the dressing tool rotatably and applying a rotating motion of a predetermined number of revolutions to the dressing tool,
Means for applying a pressing force for pressing the polishing cloth to the dressing tool, pressing force control means for controlling the pressing force for pressing the dressing tool to the polishing cloth to a constant value, and polishing the dressing tool. Dressing tool moving means for moving along a control axis including an axis parallel to the thickness direction of the cloth, and position fixing means for fixing the position of the dresser tool in the thickness direction of the polishing cloth at a fixed position. Things.

According to a preferred embodiment of the present invention, the dressing tool moving means includes a ball screw mechanism for feeding the dressing tool in the thickness direction of the polishing pad, and a servomotor for driving the ball screw mechanism.

The pressure control means compares a set value with a detection value fed back from a pressure detector for detecting a pressure applied to the dresser tool so that the pressure is maintained at the set value. The position of the servomotor can be controlled.

The position fixing means includes a clamp means for fixing the feeding mechanism when the dresser tool is at a predetermined position, and can fix the position of the dresser tool at a fixed position during the second step.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method and an apparatus for dressing a polishing pad according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an apparatus for carrying out a polishing cloth dressing method according to the present invention. In FIG. 1, reference numeral 1 denotes a polishing cloth, and 2 denotes a dresser whetstone used as a dressing tool.

The polishing cloth 1 is, for example, a woven cloth in which an elastomer or a soft plastic fiber is regularly knitted or a polishing cloth made of these nonwoven cloths. An adhesive or the like is used at a concentric position on the upper surface of the rotating platen 3. It can be pasted. The rotating surface plate 3 is connected to a rotation driving mechanism incorporated in the machine base 4.

On the other hand, as a dresser whetstone 2 for correcting the shape of the polishing pad 1, a disk-shaped whetstone is used. In this embodiment, the outer diameter of the dresser whetstone 2 is larger than the annular use area width R of the polishing pad 1. The dresser grindstone 2 constitutes a dressing tool rotating means, and is held at a tip of a rotating shaft of a dresser rotating head 5 containing a motor. The rotation speed of the rotating platen 3 and the dresser grindstone 2 can be set and controlled to an arbitrary rotation speed by a control device (not shown).

At the time of dressing, the rotating platen 3 rotates in the same direction as the dresser grindstone 2, whereby the polishing cloth 1 is given a rotational movement in the same direction as the dresser grindstone 2.

The dresser rotary head 5 is attached to the tip of an arm 6, and the other end of the arm 6 has a dresser lifting mechanism 7 which constitutes a dressing tool moving means.
It is connected to.

FIG. 2 is a view showing the structure of the dresser elevating mechanism 7, wherein 8 denotes an elevating shaft, and 9 denotes a base on which the elevating shaft is slidably supported. A ball nut 10 is attached to a lower end portion of the elevating shaft 8, and the ball nut 10 is screwed to a ball screw 11. The ball screw 11 is directly connected to the servo motor 12. The position, the rotation speed, and the torque of the servomotor 12 are fed back to the control device, and are controlled so as to coincide with the target value. Therefore, when the polishing cloth 1 is dressed, the position of the dresser grindstone 2 in the thickness direction of the polishing cloth is fed by accurately controlling the position of the dresser grindstone 2 by the position control of the servomotor 12.
Is pressed against the polishing pad 1 with an appropriate surface pressure. that time,
The pressing force for pressing the dresser grindstone 2 is detected by the load cell 14 shown in FIG. 1, and the position of the dresser grindstone is controlled so that the pressing force becomes constant.

In FIG. 1, a half ring type clamper 16 is mounted on the elevating shaft 8, and the clamper 16 is tightened by an air cylinder 18. When the clamper 16 is tightened, the elevating shaft 8 is restrained and locked by the clamper 16, and the position of the dresser grindstone 2 at this time is fixed. The arm 6 is pivotable, and is fixed at a predetermined dressing position on the polishing pad 1 during dressing. When the dresser whetstone 2 is not used, the arm 6 is moved away from the rotary platen 3. It can be turned and retracted.

Although the dressing apparatus of this embodiment does not employ a swing mechanism as a mechanism for causing the dresser grindstone 2 to reciprocate in the radial direction on the polishing pad 1, a dresser grindstone having a small diameter is used. In this case, it is preferable to use a swinging mechanism or a mechanism for giving a linear reciprocating movement in the radial direction to give the dresser grindstone a radial movement.

Next, the dressing method of the present invention, which is carried out using the above-described apparatus, will be described below.
This will be described in detail. FIG. 3 is a diagram illustrating changes in the position and the pressing force of the dresser whetstone 2 in the dressing process of the polishing pad 1.

This dressing method uses a dresser whetstone 2
A first step of performing dressing while executing a constant pressure control for keeping the pressing force for pressing the polishing pad 1 against the polishing cloth 1 constant (time T1 to T2), and the dresser whetstone 2 in the first step.
And a second step (time T2 to T3) of performing dressing while fixing the final position (P2) in the polishing cloth width direction.

In this embodiment, a large-diameter dresser whetstone 2 is used.
Therefore, in the first step, the position in the polishing cloth radial direction is set so as not to move. For example, rotating platen 3
Is rotated at about 30 rpm. Dresser whetstone 2 also about 30
The entire arm 6 is lowered while rotating at rpm. Thus, dressing is started while pressing the dresser whetstone 2 with a pressing force of, for example, 100 g / cm ² .

At the beginning of the dressing (T1), the position of the dresser whetstone 2 in the polishing cloth thickness direction is P1.
Thereafter, when the dressing is continued, the entire surface of the polishing pad 1 is worn down, and the dressing proceeds while the position of the dresser grindstone 2 moves slightly downward. Under the above conditions, a dressing amount of about 0.8 to 1.7 μm can be obtained in one minute.

During this dressing, the load cell 14
The pressure is detected from the output signal of (1), and the position of the servo motor 12 for lowering the dresser grindstone 2 is controlled so that the pressure is kept constant.

When the dresser grindstone 2 descends to P2 in this manner, the dressing shape of the polishing pad 1 at this stage becomes a shape in which the central portion has a slightly high convex surface as shown in FIG.

In the second step performed after the first step, the clamper 16 is closed by the operation of the air cylinder 18 in order to fix the position of the dresser whetstone 2 in the polishing cloth thickness direction at the height P2. As a result, since the clamper 16 firmly restrains the elevating shaft 8, the position of the dresser whetstone 2 in the polishing cloth thickness direction is fixed so as not to be shifted up and down from P2.

Thereafter, while this position is maintained, the dresser grindstone 2 rotates and the dressing is continued. During this time, the position of the dresser whetstone 2 does not lower and does not change, so that as the wear of the polishing pad progresses, the pressing force decreases. In the dressing in which such a fixed position is maintained, in a region where dressing is further advanced in a portion closer to the outer peripheral portion and the central portion of the polishing cloth in FIG. On the other hand, the sliding of the dresser grindstone advances the dressing on the convex curved surface at the central portion, and as a result, the convex curved surface at the middle height of the polishing cloth is selectively dressed. In addition, the closer to the center, the greater the amount of dressing, so that the dressing is performed so as to increase the flatness.

In the embodiment described above, in order to keep the pressure of the dresser grinding stone 2 in the first step constant, the pressure is detected by the load cell 14 and the servomotor 12 is controlled so that the pressure becomes constant. Although the position control described above is performed, the constant pressure control of the pressing force can be executed by controlling the torque of the servo motor 12.

The clamper 16 is used as a means for fixing the position of the dresser whetstone 2 in the second step.
The position may be fixed by using both the position control of the servomotor 12 and the electromagnetic brake.

Next, another embodiment of the dressing method according to the present invention will be described with reference to FIG. In this embodiment, a small-diameter grindstone is used as a dresser grindstone, and dressing is performed while moving the small-diameter dresser grindstone in the radial direction of the polishing pad. FIG. 4 is a schematic view showing the movement positional relationship between the polishing pad 1 and the dresser grindstone 20 when the small-diameter dresser grindstone 20 is used.

In the polishing cloth 1, a concentric area having a width W in the radial direction is a polishing cloth use area, and its center is Od. In the dressing method of this embodiment, in order to dress the entire use area, in the first first step, the pressure of the use area width W is kept constant while the pressure of the dresser grindstone 20 is kept constant, as in the first embodiment. The center Od is moved to the outermost position a in the radius direction from the starting point, and then reversed, and after reaching the innermost position b, the position is reversed again to return to the initial position Od.

In the subsequent second step, dressing is performed while fixing the final position of the dresser grindstone 20 in the polishing cloth thickness direction in the first step.

Each change in the position of the dresser grindstone 20 and the pressing force in this dressing step is the same as in FIG. 3 described above, and the dresser grindstone 20 is moved to the initial position O.
After returning to d and descending to the position P2, the dressing shape of the polishing pad obtained by the dressing for keeping the pressing force constant in the first step is, as shown in FIG. The result is that the pitch varies depending on the diameter of the dresser whetstone 20.

Next, in the second step, the first position of the dresser grindstone 20 in the polishing cloth thickness direction is fixed to the position P2, and the first step is performed.
In the same manner as in the process, dressing is continuously performed by reciprocating the dresser grindstone 20 in the polishing cloth radial direction.

In the second step, the convex surface 22 is selectively dressed in the same manner as in the case of using a large-diameter dressing grindstone, and the amount of dressing is closer to the center of each convex surface 22. As a result, the flatness of the finally obtained dressing shape can be further improved as a whole.

[0046]

As is apparent from the above description, according to the present invention, following the step of keeping the pressure of the dressing tool constant, the dressing is performed by fixing the position of the dressing tool in the polishing cloth thickness direction. By doing so, the convex surface of the polishing cloth can be selectively dressed, so that in addition to the flatness of the polishing cloth, the flatness can be improved so that the central portion does not become a convex curved surface.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of an apparatus for carrying out a dressing method of a polishing pad according to the present invention.

FIG. 2 is a sectional view of an elevating mechanism constituting the dressing tool moving means.

FIG. 3 is a diagram showing a change in a position of a dressing tool in a thickness direction of a polishing cloth and a pressing force in a dressing method according to the present invention.

FIG. 4 is a view showing a movement direction of a dressing tool according to another embodiment of the dressing method of the present invention.

FIG. 5 is a view showing a dressing shape of a polishing pad when a small-diameter dressing tool is used.

FIG. 6 is a diagram showing a distribution of a sliding distance of a dressing tool in a polishing cloth.

FIG. 7 is a diagram showing a dressing shape of a polishing pad when a large-diameter dressing tool is used.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Polishing cloth 2 Dressing tool 3 Rotating surface plate 4 Machine stand 5 Dresser rotating head (dressing tool rotating means) 6 Arm 7 Dresser elevating mechanism (dressing tool moving means) 8 Elevating shaft 9 Base part 10 Ball nut 11 Ball screw 12 Servo motor 14 load cell 16 clamper (clamping means) 18 air cylinder 20 dressing tool 22 convex surface

Claims (7)

[Claims] 1. A dressing method for correcting the shape of the polishing cloth by pressing the rotating dressing tool against the surface of the rotating polishing cloth while rotating the polishing tool, wherein the pressing force for pressing the dressing tool against the polishing cloth is kept constant. A first step of dressing the polishing cloth while dressing; and a second step of dressing the polishing cloth while fixing the position of the dresser tool at the final polishing cloth thickness direction position in the first step and holding this position. A dressing method for a polishing cloth, characterized by comprising: 2. The dressing method according to claim 1, wherein the polishing cloth is an elastic body made of an elastomer, a plastic, a non-woven cloth, or a mixture thereof. 3. A rotating platen on which a polishing cloth to be dressed is mounted and rotates at a constant rotation speed, a disc-shaped dressing tool for grinding the surface of the polishing cloth, and a rotatably holding the dressing tool. A dressing tool rotating means for applying a predetermined number of rotations to the dressing tool, a means for applying a pressing force for pressing the polishing cloth to the dressing tool, and pressing the dressing tool against the polishing cloth. Pressure control means for controlling the pressure of the polishing cloth constant, dressing tool moving means for moving the dressing tool along a control axis including an axis parallel to the thickness direction of the polishing cloth, and a polishing cloth of the dresser tool. And a position fixing means for fixing the position in the thickness direction to a fixed position. 4. The polishing machine according to claim 3, wherein said dressing tool moving means includes a ball screw mechanism for feeding the dressing tool in a polishing cloth thickness direction, and a servo motor for driving said ball screw mechanism. Cloth dressing equipment. 5. The pressure control means compares a detection value fed back from a pressure detector for detecting a pressure applied to the dresser tool with a set value, and controls the pressure so that the pressure is maintained at the set value. 4. The dressing apparatus for polishing cloth according to claim 3, wherein the servomotor is position-controlled. 6. The dressing apparatus for an abrasive cloth according to claim 3, wherein said position fixing means includes a clamp means for fixing a ball screw mechanism when said dresser tool is at a predetermined position. 7. The dressing apparatus for polishing cloth according to claim 3, wherein said pressure control means executes torque control of said servomotor to keep the pressure constant.