JP3651923B2 - Polishing apparatus and method - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a polishing apparatus and method , and more particularly to a polishing apparatus and method for polishing a polishing object such as a semiconductor wafer in a flat and mirror-like shape.
[0002]
[Prior art]
In recent years, as semiconductor devices are highly integrated, circuit wiring is becoming finer and the distance between wirings is becoming narrower. In particular, in the case of optical lithography of 0.5 μm or less, the depth of focus becomes shallow, so that the flatness of the imaging surface of the stepper is required.
Therefore, it is necessary to flatten the surface of the semiconductor wafer, but polishing is performed by a polishing apparatus as one means of this flattening method.
[0003]
Conventionally, in this type of polishing apparatus, as shown in FIG. 1A, a top ring 4 containing a workpiece 3 is rotated while a pad 2 fixed on a rotary table 1 by adhesion or a jig is rotated. While pressing, the workpiece is polished by the relative sliding between the workpiece 3 and the pad 2 and the action of the abrasive and / or polishing liquid sprayed or impregnated on the pad surface. At that time, the arm 5 supporting the top ring 4 may be swung so that wear and clogging are not concentrated on a specific radial position of the pad (in this figure, the arm 5 is swung so as to perform a reciprocating arc motion).
[0004]
In order to improve the flatness of the object to be polished, it is important to make the pressing pressure uniform during machining and to make the sliding speed between the pad material and the work piece uniform over the whole work surface. As a device for applying a pressing force to the top ring via a spherical seat (for example, Japanese Patent Laid-Open No. 2-278822, Japanese Patent Laid-Open No. 4-19065), a device for fixing a workpiece to the top ring by vacuum suction (for example, Japanese Patent Application No. 5-256522) has been devised. As a means to make the sliding speed between the pad material and the work piece uniform over the whole work surface, when rotating the pad and the work piece at the same rotational speed in the same direction and swinging, It is well known that the rocking speed should be sufficiently lower than the rotational speed of the workpiece.
[0005]
[Problems to be solved by the invention]
The amount of polishing processing (thickness to be removed by processing) is approximately the product of the relative speed between the workpiece and the pad and the processing time, that is, the relative slip distance S of the workpiece (generally the number of rotations of the pad and the workpiece). Since the relative slip distance is substantially the same, the relative slip distance is also proportional to the work surface, but the unit slip distance (for example, 1000 m or the pad slip distance during polishing of one work piece) ) The relative slip distance L at each radial position of the pad is non-uniform as shown in FIG. This is because the arc length of the workpiece at the radial position r from the center O of the pad differs depending on the radial position r. That is, of the pad radius rp, the inner peripheral O-Oi (r≤ri) part and the outer peripheral Oo-B (r≥rp -ro) part do not contact the workpiece, and Oi-Oo. A portion (r = rm) where the relative slip distance L becomes the maximum Lmax occurs during (.DELTA.r = ro-ri).
[0006]
Deterioration of pad wear, clogging, etc. is almost proportional to the relative sliding distance of the pad, so that the processing capability of the pad decreases or increases near the pad radius r = rm, and the workpiece is convex, concave or convex. It is easy to finish in the form of a combination of two. In order to prevent this, pad dressing is required, but at least r = ro where deterioration has not progressed in order to make the pad Oi−Oo (Δr = ro−ri) uniform. And ri The vicinity is also dressed, and the life of the pad is shortened.
[0007]
On the other hand, if the pad radius is remarkably increased and the center position Oc or Ow of the workpiece is sufficiently increased or the oscillation amplitude is sufficiently increased, the relative sliding distance of the pad is reduced and the difference depending on the radial position of the pad is also achieved. Becomes smaller. However, a remarkably large pad is required, and the entire polishing apparatus becomes extremely large.
[0008]
Therefore, even if it is not an extremely large apparatus, in order to perform polishing with excellent flatness of the workpiece and to extend the life of the pad, the relative size of the pad is not increased without extremely increasing the size of the pad. It is desirable to reduce the sliding distance and the difference due to the radial position of the pad.
[0009]
The present invention has been made in view of the above circumstances, and an object thereof is to provide a polishing apparatus and method capable of reducing the relative sliding distance of the pad and reducing the difference due to the radial position of the pad.
[0010]
[Means for Solving the Problems]
The present invention rotates a circular pad sprayed or impregnated with an abrasive and / or polishing liquid, and presses the work piece against the pad while rotating the work piece around a position deviated by a predetermined distance from the center of the pad. In the polishing apparatus and method for polishing a workpiece, the workpiece is oscillated so as to make a reciprocating arc motion during processing, and the ratio of the oscillation radius r s to the radius r w of the workpiece R s = r s / r w, swing angle amplitude phi (degrees), the ratio of the radius r w of eccentricity r c and the workpiece of the workpiece from the center of the pad at the center of the swing angle amplitude of workpiece Rc = When r c / r w is displayed in the R c -R s -φ orthogonal three-dimensional coordinate system, the relative slip distance of the workpiece is S, the maximum relative slip distance on the pad side is L max , and the pad The ratio R o = r o / r w between the required minimum diameter r o and the work piece radius r w (L max / S) × surrounded by the envelope to 10% increase of the minimum value of R o ^2, the space further 0.5r w + r o -r c above, was added restrictions on r s to be equal to or less than r o And the following 15 points:
(1.10, 1.50, 0) (1.60, 1.50, 0)
(2.60, 1.50, 0) (1.10, 2.10, 0)
(1.60, 2.60, 0) (2.60, 3.60, 0)
(1.10, 1.56, 20) (1.60, 1.54, 20)
(2.45, 1.53, 20) (1.15, 2.16, 20)
(1.60, 2.71, 34) (2.35, 3.44, 20)
(1.20, 1.69, 40) (1.60, 1.80, 52)
(2.25, 1.66, 40)
It is characterized by being inside a space surrounded by a curved surface passing through .
[0012]
[Action]
As described above, the maximum value Lmax / S of the relative slip distance L on the pad side per relative slip distance S of the work piece (the deterioration of the pad is most severe at the position of the radius rw at which the relative slip distance of the pad is maximum). The size of the pad needs to be increased, there is a conflict between the desire to increase the life of the pad and to perform polishing with excellent flatness, and the requirement to reduce the pad size. . Therefore, it is desirable to select a combination of the optimum pad diameter, workpiece eccentricity, swing angle amplitude, and swing radius.
[0013]
Since the polishing apparatus according to the present invention has the same configuration as that of FIG. 1A already described, the following description will be given with reference to FIG.
In order to minimize the product of Lmax / S corresponding to the degree of deterioration of the pad and ro ² corresponding to the pad area, the required minimum diameter ro of the pad, the eccentric amount rc of the workpiece, the swing angle amplitude φ, One of the means is to select the swing radius rs.
[0014]
The number of swings per unit time is set to 1/5 of the number of rotations of the workpiece (equal to the number of rotations of the pad), and the eccentricity Rc (= rc / rw) made dimensionless by the radius rw of the workpiece. FIG. 2 shows the relationship between the dynamic radius Rs (= rs / rw), the required minimum pad diameter Ro (= ro / rw), the swing angle amplitude φ, and Lmax / S. Here, 1/3 of one cycle was a constant speed and 1/6 was a constant acceleration / deceleration.
[0015]
(Lmax / S) × Ro ² is a plane curve with Rc as a variable when not rocking (φ = O) (thick solid line in FIG. 2), and a curved surface with Rc, Rs and φ as variables when rocking. (The dotted line in FIG. 2 when φ = 30 °, and the alternate long and short dash line in FIG. 2 when φ = 60 °), both of which have a minimum value. The (Lmax / S) × Ro ² becomes minimum Rc and / or Rs, phi is a Lmax / S corresponding to the degree of deterioration of the pad, the optimum condition for pressing both of the pad area low. The mounting of the workpiece, flights removed, Rc to use the high construction material marketable, Rs, to have a slight degree of freedom in the selection of phi, the ^{(Lmax / S) × Ro 2} (Lmax / and allowing up to 10% increase of the minimum value of ^{S) × Ro 2, Rc,} Rs, when determining the range of phi, indicated by a chain line envelope (one point in FIG. _{3) Y 1, Y 2,} Y 3, Y _4, the interior of the space surrounded by Y _5.
[0016]
By the way, in selecting Rc, Rs and φ, the axis of the arm 5 (not shown) for supporting or swinging the workpiece and the outer peripheral thickness of the top ring 4 holding the workpiece are also taken into consideration. Since the distance between the required radius ro of the pad and the arm shaft rotation center is 0.5 rw or more, the lower limit of rs is limited. Further, if the length of the arm is increased unnecessarily, the polisher device becomes larger and the object of the present invention is impaired. Therefore, the upper limit of rs is limited to the required radius (ro) of the pad or less.
[0017]
The result of adding the above-mentioned restriction of rs to the range of Rc, Rs, and φ indicated by the envelope (the chain line) is the inside of the space indicated by the thick line in FIG. In FIG. 3, the coordinates of points A to S on the spatial boundary surface indicated by the bold lines are as follows in the Rs-Rs-φ coordinate system.
A: (1.10, 1.50, 0), A: (1.60, 1.50, 0),
C: (2.60, 1.50, 0), D: (1.10, 2.10, 0),
E: (1.60, 2.60, 0), F: (2.60, 3.60, 0),
G: (1.10, 1.56, 20), K: (1.60, 1.54, 20),
K: (2.45, 1.53, 20), K: (1.15, 2.16, 20),
S: (1.60, 2.71, 34), S: (2.35, 3.44, 20),
S: (1.20, 1.69, 40), C: (1.60, 1.80, 52),
Seo: (2.25, 1.66, 40)
[0018]
If Rc, Rs, and φ are selected so as to be within the space surrounded by the coordinates of A to S, the product of the pad's relative sliding distance and the pad area corresponding to the degree of deterioration of the pad can be reduced. Therefore, a polishing apparatus that can simultaneously reduce the size of the pad and the deterioration of the pad is realized.
[0019]
Specifically, when the rocking is not performed, Rc is set within the range of straight lines a to c in FIG. 3, that is, 1.1 ≦ Rc ≦ 2.6, and when rocking, Rc, Rs, φ are shown in FIG. Select so that it is inside space 3 of the space.
[0020]
【Example】
Assuming a mirror polishing of a silicon wafer coated with silicon dioxide (SiO ₂ ) having a diameter of 200 mm (r w = 100 mm ) as a workpiece, in FIG. 1 (a), rc = 150 mm, rs = 270 mm, A polishing apparatus was prototyped with φ = 22 degrees. The combination of rc / rw = Rc, rs / rw = Rs, and φ was selected so as to be in the space as shown in FIG. The pad 2 on the turntable 1 is made of a polyurethane-impregnated polyester nonwoven fabric having a hardness of 73, and an abrasive liquid containing 0.5% selenium oxide fine particles is used as the abrasive liquid. In both cases, the mirror polishing process of the SiO ₂ layer was performed with 100 rpm, the swing period of the arm 5 being 5 seconds, and the pressing pressure of the wafer against the pad 2 being 300 g / cm ² .
[0021]
As a result, the processing (removal in the thickness direction of the SiO ₂ layer) speed is 3500 to 4000 angstroms / minute, and the variation in the remaining SiO ₂ thickness after processing is 10 to 15% on average at 18 points in the wafer surface. Flatness and workability were obtained.
[0022]
During the processing, the back of the wafer contact portion of the pad surface was cleaned with clean water jet to clean the pad surface and shape the fibers forming the pad, but after being used for more than 1200 minutes with a takt time of 3 minutes, There was no significant difference between the flatness of the object and the processing speed, and no sign of deterioration of the specific radial position of the pad was observed, either visually or with an electron microscope.
[0023]
【The invention's effect】
As described above, according to the present invention, the maximum value Lmax of the relative slip distance on the pad side per the relative slip distance S of the workpiece, that is, the degree of deterioration of the pad (deterioration of a specific radial position in the pad). As the process progresses, the flatness of the workpiece is impaired, and the ratio L0 (= ro / rw) of the parameter Lmax / S corresponding to the required pad radius ro corresponding to the pad area and the radius rw of the workpiece. The eccentric distance rc on the pad at the center of rotation of the workpiece and / or the rocking radius rs and the rocking angle so that the product of the squared value (Ro ² ) is within 1.1 times its minimum value Since the amplitude φ is set, the relative sliding distance of the pad can be reduced with an appropriate pad size, and the difference depending on the radial position of the pad can be reduced. Therefore, the flatness of the workpiece can be stabilized for a long time and excellent polishing can be realized. In addition, the life of the pad can be kept long.
[Brief description of the drawings]
FIG. 1 (a) is a plan view showing a basic configuration of a polishing apparatus according to the present invention and a conventional example, and FIG. 1 (b) is a graph showing a relative sliding distance L of a pad at a radial position.
FIG. 2 is a diagram showing a relationship of (Lmas / S) × Ro ² with dimensions and swinging methods of the polishing apparatus according to the present invention.
FIG. 3 is a view showing an appropriate dimension range of the polishing apparatus according to the present invention.
[Explanation of symbols]
1 Rotary table 2 Pad 3 Work piece 4 Top ring 5 Arm φ Oscillation angle amplitude rc Eccentric distance rw of work piece when φ = o Workpiece radius rs Oscillation radius ro Minimum required pad radius Lmax Pad Relative slip distance S of the workpiece R relative slip distance Rc = rc / rw
Rs = rs / rw
Ro = ro / rw

Claims (2)

A circular pad sprayed or impregnated with an abrasive and / or polishing liquid is rotated, and the workpiece is polished by pressing against the pad while rotating the workpiece about a position decentered by a predetermined distance from the center of the pad. In the polishing apparatus, the workpiece is swung in a reciprocating arc motion during machining, the ratio Rs = rs / rw of the rocking radius rs to the workpiece radius rw, and the swing angle amplitude φ (degrees). The ratio Rc = rc / rw of the work piece eccentric distance rc and the work piece radius rw from the center of the pad at the center within the swing angle amplitude of the work piece is Rc-Rs-φ orthogonal three-dimensional. When displayed in the coordinate system, the relative sliding distance of the workpiece is S, the maximum value of the relative sliding distance on the pad side is Lmax, and the ratio of the required minimum diameter ro of the pad to the radius rw of the workpiece Ro = ro / as rw and (Lmax / S) 10% increase of the minimum value of × Ro ² That is surrounded by the envelope, further 0.5rw + ro-rc above, a space obtained by adding a restriction to rs such that ro less, the following 15 points:
(1.10, 1.50, 0) (1.60, 1.50, 0)
(2.60, 1.50, 0) (1.10, 2.10, 0)
(1.60, 2.60, 0) (2.60, 3.60, 0)
(1.10, 1.56, 20) (1.60, 1.54, 20)
(2.45, 1.53, 20) (1.15, 2.16, 20)
(1.60, 2.71, 34) (2.35, 3.44, 20)
(1.20, 1.69, 40) (1.60, 1.80, 52)
(2.25, 1.66, 40)
A polishing apparatus characterized by being inside a space surrounded by a curved surface passing through. A circular pad sprayed or impregnated with an abrasive and / or polishing liquid is rotated, and the workpiece is polished by pressing against the pad while rotating the workpiece about a position decentered by a predetermined distance from the center of the pad. In the polishing method, the workpiece is swung in a reciprocating arc motion during machining, the ratio Rs = rs / rw between the rocking radius rs and the workpiece radius rw, and the swing angle amplitude φ (degrees). The ratio Rc = rc / rw of the work piece eccentric distance rc and the work piece radius rw from the center of the pad at the center within the swing angle amplitude of the work piece is Rc-Rs-φ orthogonal three-dimensional. When displayed in the coordinate system, the relative sliding distance of the workpiece is S, the maximum relative sliding distance on the pad side is Lmax, and the ratio of the required minimum diameter ro of the pad to the radius rw of the workpiece Ro = ro / as rw and (Lmax / S) 10% increase of the minimum value of × Ro ² That is surrounded by the envelope, further 0.5rw + ro-rc above, a space obtained by adding a restriction to rs such that ro less, the following 15 points:
(1.10, 1.50, 0) (1.60, 1.50, 0)
(2.60, 1.50, 0) (1.10, 2.10, 0)
(1.60, 2.60, 0) (2.60, 3.60, 0)
(1.10, 1.56, 20) (1.60, 1.54, 20)
(2.45, 1.53, 20) (1.15, 2.16, 20)
(1.60, 2.71, 34) (2.35, 3.44, 20)
(1.20, 1.69, 40) (1.60, 1.80, 52)
(2.25, 1.66, 40)
A polishing method characterized by being inside a space surrounded by a curved surface passing through.

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