JPH10146755A - Workpiece holding back film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformize the distribution of moisture of a workpiece surface, and obtain excellent flatness by forming plural grooves becoming a moving passage of water on a contact surface with a workpiece. SOLUTION: Grooves 15 are arranged on a contact surface with a workpiece of a back film 1. When a width of the grooves 15 is 2-mm, the fact that slight working nonuniformity is caused in a part corresponding to the grooves 15 can be understood. Therefore, it is desirable that the width of the grooves 15 formed on the back film is set not more than 2mm. In the back film on which a hole diameter of an independent foaming part is about 0.2mm and a compressive deformation rate of a raw material is about 30%, the occurrence of deformation of about 0.1mm in the lateral direction is calculated. Therefore, when the back film is used, there is a possibility that the width narrows 0.1mm by 0.1mm on both sides of the grooves 15. When this fact is considered, it is desirable that the width of the grooves 15 is set not less than 0.3mm to secure a movement of moisture inside of the grooves 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a back film for holding a workpiece, which is used for holding a flat workpiece such as a semiconductor substrate, glass or ceramic on a surface of the polishing apparatus in a polishing apparatus. According to.

[0002]

2. Description of the Related Art In a polishing apparatus, there are known methods of holding a flat workpiece such as a semiconductor substrate, glass or ceramics, such as a wax bonding method, a vacuum chucking method, and a water bonding method using a back film. Have been.

In the case of the wax application method, it is necessary to repeat the melting and solidification of the wax every time the workpiece is replaced, which causes a reduction in work efficiency. Also, in the case of the vacuum chuck method, the back surface of the work is vacuum-adsorbed and fixed to the surface of the chuck, so that irregularities on the back surface side of the work and between the back surface of the work and the front surface of the chuck are involved. It is easy to be affected by foreign matter and the like, and processing irregularities such as bulls and eyes are easily generated.

On the other hand, in the case of a water application method using a back film made of a flexible material such as an elastomer and having an independently foamed surface, a contact surface with a workpiece is flexibly deformed. It is less susceptible to the influence of irregularities on the back side of the workpiece or the inclusion of foreign matter. For this reason, the water bonding method using a back film is expected to be capable of polishing on a surface basis. That is, it is expected that the surface roughness, flatness, and the like can be improved according to the original surface shape of the surface to be polished.

[0005] By the way, when the area of the workpiece is large,
Alternatively, when the pressing force at the time of polishing is large, in the water bonding method using the conventional back film, the vicinity of the center of the workpiece tends to be polished more.

FIG. 6 shows that an oxide film having a target thickness of 1000 nm is formed on an 8-inch Si wafer, and this is held on a carrier by a water bonding method using a conventional back film, and is polished. This is the result of measuring the distribution of the thickness of the oxide film after polishing in the diameter direction. The pressing force at the time of polishing was 600 g / cm ² , and the rotation speed of the carrier was 23 rpm. Note that the initial deviation of the thickness of the oxide film was about several nm, and the thickness of the oxide film was almost uniform. From these results, it can be seen that the surface to be polished has a concave shape in the water bonding method using the conventional back film.
From the results of experiments, it has been confirmed that this tendency becomes more pronounced as the pressing force during polishing increases.

[0007] The reason why the vicinity of the center of the workpiece is more polished is considered to be the effect of water used in the water application method. FIG. 7 schematically shows a cross-section of a workpiece and its periphery during polishing when a conventional back film is used. In the drawing, reference numeral 4 denotes a polishing platen for forming a polishing surface, 9 denotes a workpiece, 1 denotes a back film, 2 denotes a carrier that holds the workpiece 9 via the back film 1, 5 denotes a supply nozzle of an abrasive, Numeral 11 denotes a closed foam part on the back film surface.

On the surface of the back film 1, a workpiece 9
In order to enhance the function of adsorbing and holding, a closed cell portion 11 is usually formed. Water 8 for absorbing the workpiece 9 is held in the independent foaming portion 11. Workpiece 9
Is adsorbed by the back film 1, and the surface of the workpiece 9 is pressed against the polishing platen 4 forming the polishing surface to make relative movement, whereby polishing is performed. At this time, the workpiece 9
The water retained in the independent foamed portion in the region indicated by reference numeral 22 or 23 corresponding to the peripheral portion of the water gradually flows out to the outside due to vibration or the like at the time of polishing, and becomes an amount corresponding to the pressing force. And stable. On the other hand, the water retained in the independent foamed portion in the region indicated by the reference numeral 21 near the center of the workpiece 9 hardly moves toward the periphery because the resistance of the outflow path is large, and most of the water is retained. However, as a result of being trapped in the vicinity of the center, an excessive amount of water with respect to the average pressing force remains in the vicinity of the center 21. On the other hand, the back film 1 itself is deformed with a change in volume due to the pressure, but the water 8 does not change in volume because the water 8 is incompressible. For this reason, the reaction force generated with respect to the average pressing force due to the trapped water becomes higher in the vicinity of the center 21 as compared with the peripheral portions 22 and 23. That is, the surface pressure distribution on the surface to be polished increases as it approaches the center of the workpiece, so that the amount of polishing near the center of the workpiece 9 increases.

FIG. 8 shows experimental results for supporting the above hypothesis. FIG. 8 is a view of the workpiece after polishing when a through-hole penetrating through the back film 1 and the carrier 2 is provided at the center of the workpiece 9 for convenience of attaching and detaching and transporting the workpiece 9. Surface shape (directly,
(Thickness distribution of the oxide film).

The surface of the workpiece is convex near the center where the through-hole is provided, and it can be seen that the surface pressure is reduced. At this time, the size of this through hole is set to 0.
Although it was changed between 6 mmφ and 2.0 mmφ, almost no change was recognized in the shape of the surface of the workpiece. From this, it can be considered that this is not the effect of the loss due to the through hole formed in the back film 1. Therefore, as described above, it can be interpreted that the phenomenon in which water flows out from the through-hole and excessive water is confined in the vicinity of the center of the back surface of the workpiece does not occur.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to hold a flat workpiece by a water bonding method using a back film. It is an object of the present invention to provide a back film structure capable of obtaining a good flatness by making the distribution of water on the surface of a workpiece uniform when polishing by polishing.

[0012]

SUMMARY OF THE INVENTION A back film for holding a workpiece according to the present invention is a back film used for sucking and holding a flat workpiece in a polishing apparatus. A plurality of grooves serving as a movement path of water are formed on a contact surface with the water.

[0013] Preferably, the width of the groove is 0.3 mm or more and 2 mm or less. Further, preferably, the groove,
The grooves are arranged at intervals of 10 times or more and 40 mm or less of the groove width.

[0014] Preferably, at least one of the grooves is formed so as to pass through the center of the contact surface and reach a position near the periphery of the contact surface. Preferably, at least one of the grooves is formed so as to pass through a center portion of the contact surface and reach outside a peripheral portion of the contact surface.

Preferably, a plurality of through holes are formed in the thickness direction in addition to the grooves. In order to hold a flat workpiece in the polishing apparatus, if a back film according to the present invention in which a plurality of grooves are formed on the contact surface with the workpiece, when polishing the workpiece, Water retained on the contact surface between the workpiece and the back film can be dispersed to the surroundings through these grooves, so that water is not trapped in a part of the contact surface, and the polished surface The surface pressure distribution can be made uniform.

The width of the groove is 0.3 mm
Above, an effect of facilitating the movement of water can be obtained.
When the thickness is 2 mm or less, it is possible to prevent the shape of the groove from being transferred to the surface of the workpiece.

Further, since the range affected by the groove is a distance of about 20 mm from the groove, the distance between the grooves is set to 40 mm.
When the thickness is not more than mm, uniformity of the surface pressure distribution on the polished surface can be ensured. It is appropriate that the interval between the grooves is at least 10 times the groove width.

Further, at least one of the grooves is
If it is formed so as to reach just before the periphery of the contact surface through the center of the contact surface, or to reach outside the periphery of the contact surface through the center of the contact surface, the center of the contact surface Because the water near the part can easily flow to the peripheral part,
It is possible to effectively prevent the phenomenon that excessive moisture is trapped in the vicinity of the center.

Further, by providing a through hole in the thickness direction of the back film in addition to these grooves, water on the contact surface can flow out to the back surface side of the back film. The effect of making the surface pressure distribution uniform can be enhanced.

[0020]

FIG. 1 shows an example of a back film according to the present invention. In each of these examples, the back film 1
A groove 15 is provided on the contact surface with the workpiece 9 of
FIG. 1A shows an example in which grooves are radially provided, FIG. 1B shows an example in which grooves are provided in a grid pattern, and FIG. 1C shows an example in which substantially radial grooves formed by curves are provided. 1 (d) represents an example in which radial grooves and concentric grooves are combined.

The groove 15 is formed when the back film 1 is manufactured.
It is made by a method of forming an independent foam layer except for the groove 15 portion. Alternatively, the groove 15 may be formed by forming a closed foam layer on the entire surface and then processing the groove 15 by heat melting, cutting, etching, or the like.

FIG. 2 shows another example of the back film according to the present invention. In each of these examples, the grooves 15 are formed on the contact surface of the back film 1 with the workpiece 9 and the through holes 16 are formed in the thickness direction. FIG. 2A shows an example in which one hole is provided in the center and four through holes around the center in addition to the radial grooves, and FIG. FIG. 2C shows an example in which four through-holes are provided around one and the center, and FIG. 2C shows an example in which three through-holes are provided around the center in addition to the radial grooves. a)
Represents an example in which, in addition to the radial grooves, one through-hole is provided at the center and several through-holes are provided around the center.

The through hole 16 is used not only for attaching / detaching / transferring the workpiece, but also for facilitating the outflow of water existing on the contact surface with the workpiece 9. Regarding the width of the groove and the interval between the adjacent grooves, the following was found as a result of the experiment.

Polishing was performed using two types of back films having a groove width of 1 mm and 2 mm.
In the case of mm, it was found that slight processing unevenness occurs in a portion corresponding to the groove. Therefore, the width of the groove formed in the back film is desirably 2 mm or less.

When the back film is used, swelling due to moisture and pressing force cause deformation in the lateral direction, and the width of the groove is reduced. For example, the pore diameter of the independent foam part is 0.2m
m, it is calculated that a deformation of about 0.1 mm occurs in the lateral direction in the back film having a compression deformation rate of the material of 30%. Therefore, when using the back film, 0.1 m on both sides of the groove
The width may be reduced by m. In consideration of this, it is desirable that the width of the groove be 0.3 mm or more in order to secure the movement of moisture inside the groove.

When the range affected by the groove was examined, the range where the uniformity of the processing amount was ± 1% was a region of about 18 mm width around the groove, and the range where the uniformity was ± 5% was the groove. Was found to be a region of about 45 mm centered at. Therefore,
When arranging a plurality of grooves, the distance between them is 40 m.
m or less. The interval is 20m
If it is less than m, higher flatness can be obtained.

However, if the interval between the grooves is too narrow, the contact area with the workpiece decreases, and the holding force of the workpiece decreases.
Therefore, in order to suppress the decrease in the contact area within about 10%, it is desirable that the interval between the grooves is set to be at least 10 times the width of the groove.

[0028]

FIG. 3 shows the thickness of an oxide film on the surface of a workpiece after polishing when polishing is performed using a back film having a groove on the contact surface shown in FIG. 1 (b). It is an example of the result of measuring the distribution of the diameter in the diameter direction. The workpiece is placed on an 8-inch Si wafer with a target thickness of 1000 nm.
And an oxide film is formed at a pressure of 600 g / c.
m ² , and the carrier rotation speed was 23 rpm. The conditions for the above polishing are the same as those shown in FIG.

As compared with the results shown in FIG. 1, it can be seen that the flatness after polishing is greatly improved. FIG.
Shows the distribution in the diameter direction of the thickness of the oxide film on the surface of the workpiece after polishing when polishing is performed using the back film provided with the grooves and through holes shown in FIG. It is an example of the measurement result. The polishing conditions are the same as those shown in FIGS.

Compared with the results shown in FIGS. 6 and 8, the flatness after polishing is greatly improved. FIG. 5 shows the polishing rate and the uniformity of the polishing with respect to the case where polishing was performed using the back film according to the present invention and the case where polishing was performed using the back film having the conventional structure. 2 shows the results of comparison. The evaluation value used here is defined by the following equation.

Processing rate = average processing amount / pressing time (nm / min) Processing amount uniformity = (maximum processing amount−minimum processing amount) / (maximum processing amount + minimum processing amount) × 100 (%) The larger the value of the rate, the higher the throughput is obtained, and the smaller the value of the uniformity of the processing amount, the better the flatness.

In FIG. 5, "grooved (a)" and "grooved (b)" used the back film having grooves formed on the contact surfaces shown in FIGS. 1 (a) and 1 (b), respectively. The result of the polishing process in the case is shown. “Groove / Hole (a)” indicates the result of polishing when a back film having grooves and through holes formed on the contact surface shown in FIG. 2A is used.

FIG. 5 shows that the back film having the grooves formed on the contact surface can maintain the processing rate equivalent to that of the conventional back film and can suppress the processing amount uniformity to 10% or less.

[0034]

According to the back film for holding a workpiece according to the present invention, by providing a groove on the contact surface with the workpiece, the movement of water existing on the contact surface is facilitated, and as a result, the working surface pressure is reduced. The uniformity increases, and as a result, the uniformity of the polishing amount can be improved without lowering the processing rate.

[Brief description of the drawings]

FIG. 1 is a view showing an example of the shape of a back film according to the present invention, and (a) to (d) are views showing various examples of the arrangement of grooves provided on a contact surface of the back film.

FIG. 2 is a view showing another example of the shape of the back film according to the present invention, and (a) to (d) show various examples of the arrangement of grooves and through holes provided on the contact surface of the back film. Figure representing.

FIG. 3 is a diagram illustrating a surface shape of a workpiece when polishing is performed using a back film in which a groove is formed according to the present invention.

FIG. 4 is a diagram illustrating a surface shape of a workpiece when polishing is performed using a back film in which grooves and through holes are formed according to the present invention.

FIG. 5 is a diagram showing a comparison of processing rate and processing amount uniformity when polishing is performed using various types of back films.

FIG. 6 is a diagram illustrating a surface shape of a workpiece when a conventional back film is used.

FIG. 7 is a schematic view showing a conventional back film during polishing and a cross section around the back film.

FIG. 8 is a diagram illustrating a surface shape of a workpiece when a conventional back film provided with through holes is used.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Back film, 2 ... Carrier, 4 ... Polishing surface plate which comprises a polishing surface, 5 ... Abrasive supply nozzle, 8 ... Water, 9 ... Workpiece, 11: Independent foam part, 15: Groove, 16: Through-hole.

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[Procedure amendment]

[Submission date] December 4, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 3

[Correction method] Change

[Correction contents]

Claims (6)

[Claims] 1. A back film used for sucking and holding a plate-shaped workpiece in a polishing apparatus, wherein a plurality of grooves serving as a movement path of water are provided on a contact surface with the workpiece. A back film for holding a workpiece, wherein the back film is formed. 2. The groove has a width of 0.3 mm or more,
2. The back film for holding a workpiece according to claim 1, wherein the thickness is not more than mm. 3. The groove has a width of 10 times and a width of 40 mm.
2. The device according to claim 1, wherein the components are arranged at the following intervals.
Or the back film for holding a workpiece according to any one of claims 2 to 6. 4. The device according to claim 3, wherein at least one of the grooves is formed so as to pass through a center portion of the contact surface and reach a position short of a peripheral portion of the contact surface. The back film for holding a workpiece as described in the above. 5. The method according to claim 3, wherein at least one of the grooves is formed so as to pass through a center portion of the contact surface and reach outside a peripheral portion of the contact surface. The back film for holding a workpiece as described in the above. 6. A plurality of through holes are formed in a thickness direction in addition to the grooves.
3. The back film for holding a workpiece according to claim 1.