JP2011005606A - Polishing pad - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing pad suitable for polishing especially a notch part and its peripheral parts, and having a long product life.SOLUTION: This polishing pad 1 has a central layer 2 with highest porosity, an outer layer 3 with lowest porosity, and an intermediate layer 4 having porosity lower than the porosity of the central layer and higher than the porosity of the outer layer. The central layer 2 is positioned on a center side in a thickness direction, the outer layer 3 is positioned on an outer side in the thickness direction, and the intermediate layer 4 is positioned between the central layer 2 and the outer layer 3.

Description

  The present invention relates to a polishing pad used for polishing a wafer in a semiconductor device manufacturing process.

IC (Integrated Circuit), LSI (Large Scale Integration), VLSI (Very
Silicon wafers, which are the raw materials for integrated circuits using semiconductors such as Large Scale Integration, are plate-like materials that require extremely high flatness and parallelism. Planes are used to obtain precise dimensional accuracy in the manufacturing process. The processing is performed by a lapping machine or a polishing machine using a rotatable surface plate, or a rotatable surface plate with a polishing pad attached to the surface.

  A silicon wafer that is a single crystal is always formed with an orientation flat or a notch portion in order to indicate the crystal direction. In recent years, in order to increase the yield and yield of products, notch portions are often formed in which the loss of the wafer surface area is smaller than that of the orientation flat.

  The notch portion is a small notched portion formed at the edge portion of the outermost peripheral edge of the wafer, and the notch portion has two shapes, a U-shaped shape and a V-shaped shape. In the processing of silicon wafers, the edge part at the periphery of the surface part as well as the surface part is chamfered so as to have an obtuse angle or an arc-shaped profile for the purpose of preventing chipping and dust entrainment. Then, a mirror finish is applied.

  As a polishing pad for polishing the notch portion of such a wafer, a non-woven fabric of synthetic fibers is used as a base material, and the resin is uniformly adhered to or impregnated on the whole base material, thereby forming a single layer resin. The thing of the structure used as the adhesion pad or the resin impregnation pad is mainly used.

  However, in the polishing pad having such a configuration, the contact with the notch portion causes a large shearing force to be applied to the contact portion, so that wear progresses. There is a problem that the polishing pad cannot be used because the exposed fiber damages the wafer. In particular, the polishing pad is heavily worn by contact with the edge where the notch and the outer periphery of the wafer meet, thereby shortening the life of the polishing pad. For this reason, the demand for maintaining or improving the polishing performance and extending the life is increasing.

  As such a polishing pad for notch polishing, the outer peripheral portion is composed of an inner soft pad layer and an outer hard pad layer. The soft pad layer has a hardness (Asker C) of 80 or less and a compression ratio of 6 % Of a non-woven fabric or a suede type material, and the hard pad layer has a hardness (JIS-A) of 85 or more and a compression rate of 3% or less, and is composed of polyurethane (for example, Patent Document 1).

JP 2004-223684 A

  In notch polishing, the outer periphery of the polishing pad is worn by a shearing force, causing a shape change, and a problem called over polishing occurs in which the deformed polishing pad polishes not only the notch but also the outer periphery of the wafer. .

  The polishing pad disclosed in Patent Document 1 uses a hard pad that is hard to be worn on the outside, thereby suppressing deformation of the pad shape and avoiding overpolishing.

  However, the polishing pad disclosed in Patent Document 1 uses different types of materials for the inner soft pad layer and the outer hard pad layer, and has a structure in which these two layers are bonded together. Peeling occurs at this bonded portion. In particular, in notch polishing in which a large load is applied to the minute area of the polishing pad, large strain is likely to occur due to the difference in deformation amount of the materials constituting each of these two layers, and the penetration of slurry between the layers becomes noticeable. Peeling easily occurs at the mating part.

  In addition, in order to flexibly follow the shape of a minute part such as a notch and obtain excellent polishing performance, it is necessary to maintain a balance between the thickness of the inner soft pad layer and the outer hard pad layer. The layer thickness is limited.

  Thus, in a polishing pad having a structure in which a soft pad and a hard pad are bonded together as disclosed in Patent Document 1, peeling of the bonded portion occurs, and the product life cannot be improved. The followability to the shape of the part is also insufficient.

  An object of the present invention is to provide a polishing pad that is particularly suitable for polishing notches and their peripheral portions and has a long product life.

The present invention provides a polishing pad comprising a base material impregnated with a resin,
Located in the center in the thickness direction, the central layer with the highest porosity,
An outer layer located on the outer side in the thickness direction and having the lowest porosity,
A polishing pad, which is located between the central layer and the outer layer and includes an intermediate layer having a porosity lower than the porosity of the central layer and higher than the porosity of the outer layer. It is.

In the present invention, the porosity of the central layer and the outer layer is constant in the thickness direction,
The porosity of the intermediate layer has an inclination distribution that decreases from the central layer side to the outer layer side.

  According to the present invention, by changing the porosity indicating the degree of filling of the resin impregnated into the base material between the outer layer, the intermediate layer, and the central layer, the hardness is changed depending on each position in the thickness direction. Yes. By changing the porosity, the hardness of the outer layer is made the hardest and softened inward, thereby providing durability and followability to the shape of the part to be polished. As described above, since the porosity is changed in the thickness direction, peeling between layers due to bonding of different materials does not occur.

  From the above, it is possible to realize a polishing pad that is particularly suitable for polishing the notch portion and its peripheral portion and has a long life.

  According to the invention, the porosity of the central layer and the outer layer is constant in the thickness direction, and the porosity of the intermediate layer decreases from the central layer side to the outer layer side. Therefore, the hardness in the thickness direction changes continuously, and the stress generated inside the polishing pad due to the external force applied during polishing is dispersed in the intermediate layer. The breakage of the pad can be prevented, the followability to the shape of the portion to be polished can be further improved, and the polishing characteristics of the notch portion and its peripheral portion can be improved.

It is a mimetic diagram showing composition of polishing pad 1 which is an embodiment of the present invention. It is a figure which shows the example of a shape of the polishing pad 1 which concerns on embodiment of this invention. It is a figure which shows the cross-sectional photograph of an Example and a comparative example. It is a graph which shows the evaluation result of the porosity in five places of the thickness direction about each of an Example and a comparative example. It is a figure which shows the outline of notch grinding | polishing. It is a schematic diagram which shows the shape of the Example and comparative example in the notch part 5a vicinity.

Hereinafter, embodiments of the present invention will be described.
FIG. 1 is a schematic diagram showing a configuration of a polishing pad 1 according to an embodiment of the present invention.

  The polishing pad 1 includes a central layer 2 having the highest porosity, an outer layer 3 having the lowest porosity, and an intermediate layer having a porosity lower than the porosity of the central layer and higher than the porosity of the outer layer. 4. The central layer 2 is located on the center side in the thickness direction, the outer layer 3 is located on the outer side in the thickness direction, and the intermediate layer 4 is located between the central layer 2 and the outer layer 3. When the porosity is large, the filling rate is small, and when the porosity is small, the filling rate is large. Therefore, the filling degree of the impregnating resin of the polishing pad 1 can be shown by the distribution of the porosity.

  In the drawing, the boundary between the central layer 2 and the intermediate layer 4 and the boundary between the intermediate layer 4 and the outer layer 3 are clearly shown so that the configuration of the polishing pad 1 can be easily understood. There is no such boundary. As shown in the manufacturing method described later, the polishing pad 1 is obtained by impregnating a single substrate with a resin and solidifying, and the central layer 2, the outer layer 3, and the intermediate layer 4 have a porosity. They are distinguished only by differences.

  As described above, the porosity is different in the central layer 2, the outer layer 3, and the intermediate layer 4, and the hardness at each position in the thickness direction of the polishing pad 1 is also different depending on the difference in the porosity. In the polishing pad 1, the porosity of the central layer 2 is the highest, and the intermediate layer 4 and the outer layer 3 are configured to decrease in order from the central layer 2 toward the outer side in the thickness direction. As for the hardness at each position, the central layer 2 is the softest, and the intermediate layer 4 and the outer layer 3 become harder in this order from the central layer 2 toward the outer side in the thickness direction.

  By increasing the hardness of the outermost layer that is in direct contact with the object to be polished, that is, the outer layer 3, high durability is achieved in polishing notches where a large shear force is applied, and deformation in the thickness direction of the pad is also achieved. Suppressed. Further, by making the central layer 2 soft, the polishing pad 1 as a whole has flexibility, and as shown in FIG. 1, the notch portion can be obtained by following the shape of a minute portion such as the notch portion 5a of the wafer 5. This improves the polishing characteristics. Further, by providing an intermediate layer 4 having a hardness between the outer layer 3 and the central layer 2, the hardness gradually changes in the thickness direction inside the polishing pad 1, and polishing is performed particularly by polishing the notch portion. Even when a large external force is sometimes applied to the outer layer 3, stress is dispersed in the intermediate layer 4 of the polishing pad 1, and the destruction of the polishing pad 1 due to stress concentration can be prevented.

  The polishing pad 1 constitutes each layer of the central layer 2, the outer layer 3, and the intermediate layer 4 by impregnating a single base material such as a non-woven fabric with a resin and providing a difference in porosity in the thickness direction. Therefore, there is no portion in the polishing pad 1 of the present invention where peeling occurs, such as an interface between different materials.

  As described above, the polishing pad 1 is particularly suitable for polishing the notch portion and its peripheral portion, and can realize a long-life polishing pad.

  The central layer 2 and the outer layer 3 have a certain porosity in the thickness direction, and the intermediate layer 4 has an inclination distribution such that the porosity decreases from the central layer 2 side to the outer layer 3 side. Is preferred.

  When the porosity of the intermediate layer 4 has a gradient distribution, the hardness in the thickness direction of the polishing pad 1 continuously changes. Even when a large external force is applied at the time of polishing such as polishing of the notch portion, stress is dispersed in the intermediate layer 4 and the destruction of the polishing pad 1 due to stress concentration can be prevented. In addition, the intermediate layer 4 having a gradient in the porosity can further improve the followability to the shape of the object to be polished and improve the polishing characteristics of the notch portion.

  FIG. 2 shows a shape example of the polishing pad 1 according to the embodiment of the present invention. 2A, FIG. 2B, FIG. 2C, and FIG. 2D all show a plan view on the upper side and a sectional view on the lower side.

  Although the shape of the whole polishing pad is not particularly limited, it is mainly produced in a ring shape, a disk shape or the like. The notch portion is, for example, a V-shaped cut portion, and the shape of the peripheral portion that contacts the notch portion during polishing is preferably a shape that matches the notch shape of the notch portion.

  In the shape example shown in FIG. 2A, the polishing pad 1 is ring-shaped, the cross-sectional shape in the thickness direction of the peripheral edge portion is substantially V-shaped, and the tip portion is flat. In the shape example shown in FIG. 2B, the polishing pad 1 is ring-shaped, and the cross-sectional shape in the thickness direction of the peripheral edge portion is U-shaped. In the shape example shown in FIG. 2 (c), the polishing pad 1 has a ring shape, the cross-sectional shape in the thickness direction of the peripheral edge portion is substantially V-shaped similar to FIG. 2 (a), and the tip portion has an acute angle. Or may be formed at an obtuse angle. In the shape example shown in FIG. 2D, the polishing pad 1 has a ring shape, and the cross-sectional shape in the thickness direction of the peripheral edge portion is a rectangular shape.

  By polishing the notch using the polishing pad 1 having the shape shown in FIG. 2, the surface on one side in the thickness direction of the polishing pad 1 polishes the inner surface on the one side of the cut portion, and the thickness of the polishing pad 1 The surface on the other side in the direction will polish the inner surface on the other side of the cut portion. Since the polishing pad 1 is configured so that the hardness gradually becomes softer from the outer side in the thickness direction toward the center, the contact between the surface on one side and the other side in the thickness direction of the polishing pad 1 and the inner surface of the cut portion Even if a large external force is applied to the portion, the hard outer layer 3 realizes a high durability. Further, by making the central layer 2 soft, the polishing characteristics of the notch portion are improved due to the followability to the shape of the object to be polished.

  Further, since the difference in porosity at each position in the thickness direction of the polishing pad 1 can be obtained without any structural boundary, the shape of the polishing pad can be corrected using a diamond dresser or the like. The life can be further extended. By further extending the product life of the polishing pad 1, a dresser is installed on the opposite side of the wafer to the polishing pad being polished, and the polishing pad shape can be corrected simultaneously with polishing.

  The substrate constituting the polishing pad 1 of the present invention may be appropriately selected depending on the type of the object to be polished and desired polishing characteristics, and examples thereof include polyester fibers, nylon fibers, polypropylene fibers, polyvinyl alcohol fibers, and polyamide fibers. The comprised nonwoven fabric can be used suitably.

  The resin to be impregnated into the substrate may be appropriately selected depending on the kind of the object to be polished and desired polishing characteristics. For example, a synthetic resin such as a urethane resin, an acrylic resin, a melamine resin, a phenol resin, or an epoxy resin is preferably used. Can be used.

Next, an example of the manufacturing method of the polishing pad 1 will be described.
(1) Impregnation solution preparation step of urethane resin In this step, the impregnation solution is prepared by dissolving the urethane resin in a solvent. A wet urethane resin is mixed with a solvent such as dimethylformamide (DMF) to dissolve the urethane resin, thereby preparing a urethane resin solution as an impregnation solution.

  As the urethane resin as the impregnation solution, a urethane resin such as polyester, polyether or polycarbonate may be used, and two different types of urethane resins may be used in combination.

  As a solvent for dissolving the urethane resin, a solvent such as dimethyl sulfoxide, tetrahydrofuran, dimethylacetamide or the like can be used in addition to the above-mentioned dimethylformamide.

(2) Impregnation step In this step, a nonwoven fabric such as felt is used as the base material of the polishing pad 1, and the base material is impregnated in the urethane resin impregnation solution prepared in the impregnation solution preparation step.

  The nonwoven fabric is dipped in the urethane resin impregnation solution filled in the container, pulled up after a lapse of a predetermined time, and the excess impregnation solution is removed with a drawing device such as a mangle.

(3) Curing step The nonwoven fabric impregnated with an appropriate amount of impregnation solution is coagulated in coagulated water, the urethane resin is wet coagulated, and an outer layer composed of a porous body having a low porosity, and a porosity higher than that of the outer layer. And a middle layer composed of a porous body having a porosity higher than that of the outer layer and lower than that of the center layer.

  Then, after washing with water to remove the solvent of the impregnation solution, the front and back surfaces of the nonwoven fabric impregnated and solidified with urethane resin are subjected to surface grinding (buffing) to obtain a porous polishing pad 1. The coagulated water is a liquid for solidifying and fixing the urethane resin on the base material which is a non-woven fabric, and is not particularly limited. However, considering use in the manufacturing process of semiconductor devices, for example, pure water, ultrapure Water, ion-exchanged water, distilled water and the like are preferable, and DMF may be added as necessary.

  As for a specific method for changing the porosity in the thickness direction of the polishing pad 1, for example, a nonwoven fabric is impregnated with urethane resin from one side in the thickness direction, impregnated to a predetermined depth, and then the nonwoven fabric is inverted to the other side of the nonwoven fabric. In a method of impregnating from both sides by impregnating from, a method of curing the outer layer part by applying heat from the outside after impregnation with urethane resin, or a five-layer structure in which the center layer is sandwiched between the intermediate layers from both sides and further sandwiched between the outer layers Instead of simple bonding, a method of welding the joint surface between the central layer and the intermediate layer and the joint surface between the intermediate layer and the outer layer with heat or chemical components to make the layers seamless may be used.

  Needless to say, the present invention is not limited to the above-described embodiment, and the design can be changed without departing from the gist of the present invention.

(Example)
As an Example, the polishing pad 1 was created using the polyester fiber nonwoven fabric (EXBS1000L, Kanai Important Industry Co., Ltd.), and using the urethane resin (L-315, Mitsui Takeda Chemical Co., Ltd.) for impregnation resin. A cross-sectional photograph of the polishing pad 1 of the example is shown in FIG.

(Comparative example)
In the comparative example, an existing product GSBB180 (manufactured by Nitta Haas Co., Ltd.) was used.

(Evaluation methods)
First, the porosity of the polishing pad was evaluated.

  The void ratio is a ratio (%) occupied by a void portion in a predetermined region of a photographed cross-sectional image, and was calculated using image processing software (WinROOF, manufactured by Mitani Corporation).

<WinROOF measurement conditions>
Contrast: 100, Brightness: 50, Threshold: 0-200, Measurement area: Divided into 5 equal parts in the thickness direction

  FIG. 4 is a graph showing the evaluation results of the porosity at five locations in the thickness direction for each of the example and the comparative example. In the graph, the first layer to the fifth layer are sequentially arranged from one side in the thickness direction.

  As shown in FIG. 4, it can be seen that the porosity of the comparative example shown in the graph B is substantially the same from the first layer to the fifth layer, and the porosity is constant in the thickness direction of the polishing pad. On the other hand, the porosity of the example shown in graph A is the lowest in the first layer and the fifth layer, the highest in the third layer, and the filling rate is the highest in the first layer and the fifth layer. It can be seen that the layer is the lowest. The porosity of the second layer has a gradient distribution that decreases from the third layer side to the first layer side, and the porosity of the fourth layer decreases from the third layer side to the fifth layer side. The second layer has a gradient distribution such that the filling rate of the second layer increases from the third layer side to the first layer side, and the fourth layer has a filling rate from the third layer side. It can be seen that it has a gradient distribution that increases toward the fifth layer side. Moreover, it turns out that an Example is higher than the filling rate of a comparative example as a whole.

  Thus, in the embodiment, the first layer and the fifth layer are the outer layer 3 having the lowest porosity, the third layer is the central layer 2 having the highest porosity, and the second layer and the fourth layer. Is the intermediate layer 4 in which the porosity has a gradient distribution.

  In the comparative example, the polishing pad has substantially uniform hardness in the entire thickness direction, whereas in the example, the first layer (outer layer 3) to the second layer (intermediate layer 4), the third layer The hardness decreases step by step in the order of the layer (center layer 2), and step by step in the order of the fourth layer (intermediate layer 4) and the fifth layer (outer layer 3) beyond the third layer (center layer 2). It can be seen that the hardness increases. Moreover, it turns out that it is harder than a comparative example as a whole.

Next, as the evaluation of notch polishing, the pad life and the waveform defect rate were evaluated.
FIG. 5 is a diagram showing an outline of notch polishing. In the notch polishing, the ring-shaped polishing pad 1 is held and rotated by the polishing pad jig 6, and polishing is performed by bringing the peripheral portion of the polishing pad 1 into contact with the notch portion 5 a of the wafer 5.

<Polishing conditions>
Polishing pad rotation speed: 700 rpm
Processing pressure: 1.5 kg / cm ²
Slurry: Edge mirror V (made by Nitta Haas Co., Ltd.)

  In the notch polishing, the pad life is a comparative example of the time until the polishing pad becomes unusable by comparing the example and the comparative example.

  In notch polishing, the inner surface of the notch portion of the wafer and the vicinity of the intersection of the notch portion and the outer peripheral portion of the wafer are polished. In particular, the vicinity of the intersection of the notch portion and the outer peripheral portion and the side surface of the polishing pad are polished. The contact portion of the polishing pad breaks due to the contact with the near portion, and there is a possibility that a part of the broken pad damages the outer peripheral portion of the wafer. Therefore, it is determined that the polishing pad cannot be used when a breakage that damages the outer periphery of the wafer occurs.

  The waveform defect rate indicates the result of the defect inspection based on an image taken using a CCD camera.

  Table 1 shows the evaluation results of the waveform defect rate and the pad life for each of the example and the comparative example.

  As is apparent from Table 1, as an evaluation result, the pad life of the example was improved to 1.3 times that of the comparative example, and the waveform defect rate could be reduced to about half.

  FIG. 6 is a schematic diagram showing the shapes of the example and the comparative example in the vicinity of the notch portion 5a. 6A shows the polishing pad 1 of the example, and FIG. 6B shows the polishing pad 10 of the comparative example. In the polishing pad 1 of the embodiment, the hardness gradually changes in the thickness direction, and the intermediate layer 4 is composed of an inclined layer, whereby the inner surface of the notch portion 5a and the notch portion 5a and the outer peripheral portion of the wafer 5 are formed. It is considered that a uniform shape change was shown in the contact area with the intersection neighboring portion 5b, the shape of the notch portion 5a and the intersection neighboring portion 5b was satisfactorily followed, and the waveform defect could be greatly reduced. Further, even when a large external force is applied locally in notch polishing, the stress generated in the polishing pad 1 is moderately dispersed due to the characteristics of the intermediate layer 4, and breakage occurs particularly in the contact area with the intersection 5 b. It is considered that the pad life is reduced and the pad life is extended.

  On the other hand, the polishing pad 10 of the comparative example has a configuration in which the hard layer 11 and the soft layer 12 are bonded together, and the deformation of the polishing pad 10 does not follow the shape of the notch portion 5a. Produce. Specifically, the pad surface does not come into contact with the tip of the notch portion 5a, and the pad surface comes into contact with the outer peripheral portion in the portion 5b near the intersection of the notch portion 5a and the outer peripheral portion of the wafer 5, and is indicated by a two-dot chain line. Stress concentration occurs in the region. This stress concentration portion is excessively polished as compared with other portions, and it is considered that a waveform defect occurred in the comparative example.

  Unlike the conventional extreme deformation such as a two-layer structure made of different materials, the peripheral layer where the amount of deformation increases according to the notch portion of the wafer is bordered by the intermediate layer and the central layer having a high porosity. By having a monolithic structure without any cracks, it was possible to suppress the breakage that occurred in the portion near the side surface of the polishing pad that would cause the peeling of the polishing pad or damage the outer peripheral portion of the wafer, thereby extending the product life.

  In this way, by using a porous urethane resin whose porosity increases stepwise from the outside to the inside of the polishing pad, it is possible to suppress polishing pad wear and reduce the corrugated defect rate. it can. Further, the outer layer, the intermediate layer, and the central layer have a single structure, whereby the strength is improved, and the product life can be further extended by the gentle deformation according to the distribution of the porosity.

DESCRIPTION OF SYMBOLS 1,10 Polishing pad 2 Center layer 3 Outer layer 4 Intermediate layer 5 Wafer 5a Notch part 6 Polishing pad jig | tool

Claims (2)

In the polishing pad formed by impregnating the base material with resin,
Located in the center in the thickness direction, the central layer with the highest porosity,
An outer layer located on the outer side in the thickness direction and having the lowest porosity,
A polishing pad, which is located between the central layer and the outer layer and includes an intermediate layer having a porosity lower than the porosity of the central layer and higher than the porosity of the outer layer. . The porosity of the central layer and the outer layer is constant in the thickness direction,
The polishing pad according to claim 1, wherein the porosity of the intermediate layer has an inclination distribution that decreases from the center layer side to the outer layer side.