JP5968179B2 - Holding pad - Google Patents

Description

  The present invention relates to a holding pad, and in particular, a soft resin sheet having foam formed by a wet film formation method and having a skin layer on the holding surface side for holding an object to be polished, and a back surface of the holding surface. It is related with the holding pad provided with the made resin base material.

  Conventionally, materials such as semiconductor wafers, glass substrates, magnetic disks, etc. (objects to be polished) are required to have high precision flatness, and therefore polishing using a polishing pad is performed. Usually, for polishing of these objects to be polished, a double-side polishing machine that simultaneously polishes both surfaces of the object to be polished and a single-side polishing machine that polishes the object to be polished one by one are used.

  In a single-side polishing machine, the holding surface plate holds one surface side of the object to be polished through the holding pad, and the other surface side of the object to be polished is supplied with the polishing liquid (slurry) by the polishing pad attached to the polishing surface plate. Polishing is performed on the (processed surface). Usually, a soft resin sheet manufactured by a wet film forming method is used for the holding pad. This soft resin sheet has a skin layer on the surface side, and foam is continuously formed inside the skin layer. Since this skin layer has a dense microporous structure and excellent contact with the object to be polished, the object to be polished can be held. When holding an object to be polished, a liquid such as water is included in the surface (holding surface) of the holding pad, and is held by adsorption by the action of the surface tension of the liquid. After the polishing process, the object to be polished is removed, but the object to be polished, especially the glass substrate, is thinned, making it difficult to remove. That is, if the adsorption force to the holding pad is too strong, the object to be polished may be damaged when the object to be polished is removed. For this reason, the holding pad is required to be easily removable while securing the object to be polished during polishing.

  In such a holding pad, since the object to be polished is attracted and held on the holding surface, the flatness of the object to be polished is expected to increase as the flatness of the holding surface increases, that is, the variation in thickness decreases. The However, in a soft resin sheet formed by a wet film formation method, thickness variation occurs due to coating unevenness when a resin solution is applied and foaming unevenness in a coagulation regeneration process. In order to reduce the thickness variation of the soft resin sheet while leaving the skin layer, for example, a technique of buffing the surface side opposite to the skin layer of the soft resin sheet, that is, the back surface side of the holding surface is disclosed. (See Patent Document 1). In addition, as a method for reducing thickness variation without performing buffing, a technique is disclosed in which a soft resin sheet is sandwiched between two smooth members and subjected to heat and pressure treatment (see Patent Document 2).

Japanese Patent No. 4455230 JP 2011-156634 A

  However, in the technique of Patent Document 1, foaming holes may be formed on the back surface by buffing, and the adhesive area between the soft resin sheet and the base material or the polishing machine is reduced, so that the adhesive force is weakened, May peel. Moreover, in the technique of patent document 2, since the surface of the soft resin sheet is hardened by the heat and pressure treatment, it becomes difficult to absorb fine irregularities on the processed surface of the object to be polished, and the flatness of the object to be polished is improved. It can be difficult. On the other hand, when the flatness of the holding surface of the soft resin sheet is improved, the adhesion with the object to be polished is increased, and therefore the adsorption force due to the surface tension of the liquid may become too high when holding the object to be polished. is there. For this reason, there is a possibility of damaging the workpiece when the workpiece is removed after the polishing process. Moreover, in the soft resin sheet by the wet film forming method, the larger the coating thickness of the resin solution, the greater the variation in the size of foam formed in the coagulation regeneration process. As a result, the thickness variation of the obtained soft resin sheet increases, and it may be difficult to improve the flatness of the object to be polished. Therefore, it is possible to ensure a good balance between the flatness of the holding surface and the holding force when adsorbing and holding the object to be polished without performing buffing or heat and pressure treatment, particularly thin glass. This is important for polishing a substrate or the like.

  An object of the present invention is to provide a holding pad capable of improving the flatness of an object to be polished and ensuring a stable holding force of the object to be polished.

In order to solve the above-described problems, the present invention provides a soft resin sheet having a skin layer on a holding surface side for holding an object to be polished, in which foam is formed by a wet film forming method, and the holding surface of the soft resin sheet. And a resin base material having a substantially flat surface on the side facing the back surface, and the soft resin sheet has an average thickness of 0.2 mm to 0 mm. The standard deviation of thickness is 0.01 mm or less in a range of .8 mm, and the soft resin sheet is formed by coagulation of a resin solution coated on the base material. Holding characterized in that when water is dropped at a rate of 50 mg per 1 cm ^{2 of the} holding surface and left for a certain period of time, the ratio of the absorbed water mass to the dropped water mass is 0.1% or less. It is a pad.

  In this case, the thickness range represented by the difference between the maximum value and the minimum value of the thickness of the soft resin sheet can be set to 0.02 mm to 0.08 mm. The adsorption force when the glass substrate is adsorbed on the holding surface of the soft resin sheet via water can be set in the range of 250N to 390N. The soft resin sheet may be made of polyurethane resin. At this time, the 100% modulus of the polyurethane resin can be in the range of 4 MPa to 10 MPa. The surface roughness Ra of the substantially flat surface of the substrate may be in the range of 0.4 μm to 0.7 μm. At this time, it is good also considering the average value of the thickness of a base material as the range of 0.1 mm-0.5 mm.

  According to the present invention, the soft resin sheet is formed by coagulation of a resin solution coated on a substrate having a substantially flat surface, and the average thickness is 0.2 mm to 0.8 mm. Due to the range, since the variation in the size of the formed foam becomes small, the standard deviation of the thickness becomes 0.01 mm or less and a flat holding surface is formed. Since the proportion of water that is dripped onto the holding surface is absorbed by 0.1% or less, the unevenness of moisture in the holding surface is suppressed when holding the polishing object. It is possible to obtain an effect that a stable holding force can be secured.

It is sectional drawing which shows typically the holding pad of embodiment to which this invention is applied. The positional relationship of a holding pad, a surface plate, and a to-be-polished object when evaluating the adsorption | suction power of a holding pad is shown typically, (A) is sectional drawing, (B) is a top view.

  Embodiments of a holding pad to which the present invention is applied are described below with reference to the drawings.

(Constitution)
As shown in FIG. 1, the holding pad 10 of the present embodiment includes a polyurethane sheet 2 as a soft resin sheet formed of a polyurethane resin by a wet film forming method. The polyurethane sheet 2 is formed by coagulating a resin solution applied onto a substrate 6 having a substantially flat surface during wet film formation and regenerating the polyurethane resin.

  The polyurethane sheet 2 has a skin layer 2a formed on the surface side by a wet film forming method. The surface of the skin layer 2a constitutes a holding surface S for holding an object to be polished. The skin layer 2a is formed in a fine microporous shape (not shown). Inside the polyurethane sheet 2 on the inner side of the skin layer 2 a, a foam 3 having a triangular cross section (conical shape) rounded along the thickness direction of the polyurethane sheet 2 is formed. The pore diameter of the foam 3 is formed such that the size on the holding surface S side is smaller than the back side of the holding surface S. Although the foam 3 has variations in the length of the polyurethane sheet 2 in the thickness direction, the foam 3 has a generally uniform size. In the polyurethane resin between the foams 3, foam (not shown) having a pore diameter smaller than that of the foam 3 is formed. The foam 3 and the foam (not shown) are communicated in a three-dimensional mesh shape with a communication hole (not shown). In other words, the polyurethane sheet 2 has a continuous foam structure in which foaming is continuously formed.

The polyurethane sheet 2 is adjusted so that the average thickness is in the range of 0.2 to 0.8 mm and the standard deviation of the thickness is 0.01 mm or less. The thickness range R represented by the difference between the maximum value and the minimum value of the thickness of the polyurethane sheet 2 is 0.02 to 0.08 mm. The thickness of the polyurethane sheet 2 can be adjusted by the coating amount of the resin solution applied during wet film formation. In the polyurethane sheet 2, when water is dropped on the holding surface S at a rate of 50 mg per 1 cm ^{2 of the} holding surface S and left for a certain period of time, the ratio of the absorbed water mass to the dropped water mass is 0.1% or less is shown. The mass of water absorbed by the polyurethane sheet 2 can be determined by the mass change of the polyurethane sheet 2 before and after dropping.

  Further, in the polyurethane sheet 2, the adsorption force when the glass substrate is adsorbed and held on the holding surface S via water is adjusted in the range of 250 to 390N. The adsorption force is obtained as follows. That is, after water is sprayed onto the holding surface S and water is infiltrated into the skin layer 2a, the glass substrate is pressed and adsorbed at a constant pressure. The force when the glass substrate is pulled in the horizontal direction and the glass substrate is displaced from the holding surface S is obtained as the adsorption force.

  As for the base material 6, the average value of thickness is set to the range of 0.1-0.5 mm. The base material 6 has a substantially flat surface on the polyurethane sheet 2 side, and the surface roughness Ra on the surface is in the range of 0.4 to 0.7 μm. In this example, the substrate 6 is made of polyethylene terephthalate (hereinafter abbreviated as PET) and has flexibility. In the holding pad 10, the polyurethane sheet 2 is formed by applying a resin solution on the substantially flat surface of the substrate 6. In other words, the polyurethane sheet 2 is bonded to the substrate 6 by a wet film forming method. It is formed so as to be integrated.

  As shown in FIG. 1, the holding pad 10 has a double-sided tape 7 attached to the surface of the base 6 opposite to the polyurethane sheet 2 for attaching the holding pad 10 to a polishing machine. In the double-sided tape 7, for example, an adhesive layer (not shown) such as an acrylic adhesive is formed on both sides of a tape base material (not shown) of a flexible film such as a PET film. The double-sided tape 7 is bonded to the substrate 6 with an adhesive layer on one side of the tape substrate, and the adhesive layer on the other side (the side opposite to the substrate 6) is covered with a release paper (not shown). Yes.

(Manufacturing)
In manufacturing the holding pad 10, the polyurethane sheet 2 is produced on the substrate 6 by a wet film forming method, and the double-sided tape 7 is bonded to the surface of the substrate 6 opposite to the polyurethane sheet 2. In the wet film-forming method, a resin solution in which a polyurethane resin is dissolved in an organic solvent is continuously applied to the substrate 6, the resin solution is solidified in an aqueous coagulation liquid, and the polyurethane resin is regenerated into a sheet and washed. After drying, a belt-like (long shape) polyurethane sheet 2 is produced in an integrated state with the substrate 6. Hereinafter, it demonstrates in order of a process.

  In the preparation step, the polyurethane resin is dissolved by mixing a polyurethane resin and a water-miscible organic solvent capable of dissolving the polyurethane resin. As the polyurethane resin, a soft resin having a 100% modulus in the range of 4 to 10 MPa is used among resins such as polyester, polyether, and polycarbonate. As the organic solvent, N, N-dimethylformamide (hereinafter abbreviated as DMF), N, N-dimethylacetamide, or the like can be used. In this example, DMF is used. The polyurethane resin is dissolved so that the concentration is 20 to 50%. If the concentration of the polyurethane resin is less than 20%, the bulk density of the resulting polyurethane sheet will be low. On the other hand, if it exceeds 50%, the viscosity will be too high and the desired thickness and flatness will not be obtained. . In addition, the resin solution includes a pigment such as carbon black that adjusts the size and amount (number) of foam 3 to stabilize foam formation, a hydrophilic activator that promotes foaming, and a hydrophobic that stabilizes coagulation regeneration of polyurethane resin. Additives such as an active agent can be added. The obtained solution is degassed under reduced pressure to obtain a resin solution.

  In the coating process, the resin solution prepared in the preparation process is applied to the belt-like substrate 6 at a normal temperature by a coating apparatus such as a knife coater. At this time, the coating thickness (coating amount) of the resin solution is adjusted by adjusting the gap (clearance) of the coating apparatus. In this example, the coating thickness is adjusted to a range of 0.20 to 0.80 mm. If the coating thickness is less than 0.20 mm, it is difficult to apply a uniform thickness. Conversely, if the coating thickness exceeds 0.80 mm, the resin solution becomes an aqueous coagulating liquid. Before dipping, liquid dripping and coating unevenness are likely to occur, and foaming unevenness is likely to occur.

  In the coagulation regeneration process, the resin solution coated on the substrate 6 in the coating process is immersed in a coagulation liquid (water-based coagulation liquid) whose main component is water that is a poor solvent for the polyurethane resin. In the coagulation liquid, first, a skin layer 2a having a thickness of about several μm is formed on the surface side of the resin solution. As the substitution of DMF and coagulating liquid proceeds, the resin solution coagulates and the polyurethane resin is regenerated into a sheet on the substrate 6. That is, DMF is desolvated from the resin solution, and DMF and the coagulating liquid are substituted to form foam 3 and foam (not shown) inside the skin layer (in the polyurethane resin). A communication hole (not shown) that communicates in a mesh shape is formed. Since the PET base material 6 does not allow water to permeate, solvent removal occurs on the skin layer 2a side, and foam 3 is formed on the base material 6 side that is larger than the skin layer 2a side.

  Here, the formation of the foam 3 will be described. In general, in a polyurethane sheet formed by a wet film forming method, the larger the coating thickness of the resin solution, the greater the variation in the size of foam formed during coagulation regeneration. This is presumably because the replacement of DMF with the coagulating liquid takes time because the thickness of the coated resin solution is increased. In this example, the coating thickness of the resin solution is adjusted to a range of 0.20 to 0.80 mm. For this reason, since the replacement of the DMF and the coagulating liquid proceeds in a relatively short time, the foam 3 having a substantially uniform size is formed to be evenly dispersed in the polyurethane resin inside the skin layer 2a. .

  In the washing / drying step, the DMF remaining in the polyurethane sheet 2 is removed by washing the polyurethane sheet 2 coagulated and regenerated on the substrate 6 in the coagulation regenerating step in a cleaning solution such as water. After washing, the polyurethane sheet 2 is dried by passing it through a hot air dryer. In the hot air dryer, hot air is circulated and supplied to the inside, and the polyurethane sheet 2 formed on the substrate 6 is dried by passing it in a state where the width direction is fixed by a tentering device such as a tenter.

  In the laminating process, the surface of the substrate 6 opposite to the polyurethane sheet 2 and the double-sided tape 7 are bonded together. Then, it is cut into a desired shape such as a circle, and inspection such as confirming that there is no adhesion of dirt or foreign matter is performed to complete the holding pad 10.

  When polishing the object to be polished with the obtained holding pad 10, the holding pad 10 is mounted on a holding surface plate of a single-side polishing machine, and the object to be polished is held in contact with the holding surface S through water. Let When the holding pad 10 is attached, the release paper of the double-sided tape 7 is peeled off and attached with the exposed adhesive layer. In addition, when holding the object to be polished, the object to be polished is pressed by adding an appropriate amount of water to the holding surface S of the holding pad 10. Since the surface tension of water infiltrated into the skin layer 2a on the holding surface S side acts between the holding pad 10 and the object to be polished, the object to be polished is held. At the time of polishing, a polishing pad is mounted on a polishing surface plate disposed opposite to a holding surface plate, and a polishing liquid (slurry) containing abrasive particles is supplied between the object to be polished and the polishing pad, and pressure is applied to the object to be polished. The processed surface of the workpiece is polished by rotating the polishing platen or holding platen while applying.

(Action etc.)
Next, the operation and the like of the holding pad 10 of this embodiment will be described.

  In the holding pad 10 of the present embodiment, the polyurethane sheet 2 is formed by coagulation of a resin solution coated on the substrate 6, and the average thickness is in the range of 0.2 to 0.8 mm. It has been adjusted. For this reason, since the variation in the size of the foam 3 formed inside becomes small, the thickness of the polyurethane sheet 2 can be formed in a variation range where the standard deviation is 0.01 mm or less. Thereby, since the flat holding surface S is configured, the object to be polished is held flat, so that the flatness of the object to be polished can be improved by polishing.

  Further, in the holding pad 10 of the present embodiment, the surface roughness Ra of the substrate 6 has a range of 0.4 to 0.7 μm. Since the polyurethane sheet 2 is directly formed on the substantially flat surface of the base material 6, it is possible to improve the uniform thickness of the base material 6 and the polyurethane sheet 2 as a whole. Thereby, the flatness of the workpiece can be improved.

  Furthermore, in the holding pad 10 of the present embodiment, the rate of absorption of water dropped on the holding surface S is adjusted to 0.1% or less. For this reason, when the amount of water absorbed on the holding surface S side is reduced, the water present on the holding surface S is unevenly distributed in the surface when the object to be polished is held by the surface tension of the water. Therefore, it is difficult to cause uneven adsorption, and the holding force can be stabilized. When the rate of water absorption increases, the moisture present on the holding surface S of the polyurethane sheet 2 is likely to be unevenly distributed in the surface, and as a result, the adsorptive power may vary. Considering the stability of the holding force of the holding surface S, it is preferable that the ratio of water absorbed is 0.06% or less.

  Furthermore, in the holding pad 10 of the present embodiment, the thickness expressed by the difference between the maximum value and the minimum value of the thickness in addition to the standard deviation of the thickness of the polyurethane sheet 2 being adjusted to the above-described range. The range R is adjusted to a range of 0.02 to 0.08 mm. For this reason, by improving the flatness of the holding surface S, it is possible to improve the flatness of the workpiece by polishing.

  Furthermore, in the holding pad 10 of the present embodiment, the adsorption force when the glass substrate is adsorbed to the holding surface S of the polyurethane sheet 2 via water shows a range of 250 to 390N. For this reason, during the polishing process, the object to be polished is held with an appropriate adsorption force, so that the object to be polished can be prevented from falling off.

  In addition, by setting the thickness of the polyurethane sheet 2 in the above-described range, even if a polishing pressure is applied during the polishing process, the sinking of the workpiece to the holding pad 10 side is suppressed. For this reason, since it is suppressed that the polyurethane sheet 2 follows the unevenness | corrugation of the surface of to-be-polished material too much, the adhesiveness between the polyurethane sheet 2 and to-be-polished material is restrict | limited. Thereby, the removal operation | work of a to-be-polished object can be made easy. Furthermore, in the holding pad 10 of the present embodiment, a polyurethane resin having a 100% modulus in the range of 4 to 10 MPa is used for producing the polyurethane sheet 2. For this reason, even if the holding pad 10 has the above-described thickness range and the sinking of the object to be held to the holding pad 10 side is suppressed, the polyurethane sheet 2 is soft. It can be absorbed by the holding surface S.

  In the present embodiment, an example in which the average value of the thickness of the polyurethane sheet 2 is in the range of 0.2 to 0.8 mm is shown. If the average value of the thickness is less than 0.2 mm, it becomes difficult to obtain a uniform thickness by the wet film forming method. Conversely, if the thickness exceeds 0.8 mm, uneven foaming tends to occur. In consideration of uniform thickness and suppression of foaming unevenness, it is preferable that the average thickness is in the range of 0.2 to 0.4 mm. Moreover, if the standard deviation of the thickness of the polyurethane sheet 2 is 0.005 mm or less, the flatness of the object to be polished by the polishing process can be further improved.

  Moreover, in this embodiment, although the polyurethane sheet 2 made from a polyurethane resin was illustrated, this invention is not limited to this. Examples of the resin that can be used other than the polyurethane resin include a polyester resin. If the 100% modulus is in the range of 4 to 10 MPa, the flatness on the holding surface is the same as the polyurethane sheet 2 described above. Thus, it is possible to ensure a good balance between the retention of the object to be polished.

  Furthermore, in this embodiment, although the example which bonds the double-sided tape 7 which has an adhesive layer on both surfaces of a tape base material on the surface on the opposite side to the polyurethane sheet 2 of the base material 6 was shown, this invention is limited to this. Is not to be done. For example, it is possible to use only an adhesive without using a tape base material. Moreover, in this embodiment, although the base material 6 made from PET was shown, the present invention is not limited to this. As the base material 6, thickness and surface roughness Ra should just be the range mentioned above, for example, polyethylene, a polypropylene, etc. may be used.

  Furthermore, in this embodiment, the knife coater is exemplified for the application of the resin solution. However, for example, a reverse coater, a roll coater, or the like may be used, as long as the substrate 6 can be applied to a substantially uniform thickness. There is no particular limitation. In the present embodiment, the hot air dryer is exemplified for drying the polyurethane resin. However, the present invention is not limited to this, and for example, a cylinder dryer or the like may be used.

  Hereinafter, examples of the holding pad 10 manufactured according to the present embodiment will be described. The holding pad of the comparative example manufactured for comparison is also shown.

Example 1
In Example 1, a polyester MDI (diphenylmethane diisocyanate) polyurethane resin having a 100% modulus of 6 MPa was used as the polyurethane resin. A resin solution is prepared by mixing 47 parts of DMF for viscosity adjustment and 20 parts of a DMF dispersion containing 20% of pigment carbon black to 100 parts of a DMF solution in which polyurethane resin is dissolved at 30% by mass. did. As shown in Table 1 below, the coating device clearance was set to 0.50 mm when the obtained resin solution was applied to the PET substrate 6. As the substrate 6, a substrate having a thickness of 0.25 mm and a surface roughness Ra of 0.47 μm was used. After washing and drying, the holding pad 10 was manufactured by pasting together with the double-sided tape 7.

(Example 2 to Example 5)
As shown in Table 1, in Example 2 to Example 4, the holding pad 10 was manufactured in the same manner as Example 1 except that the clearance of the coating apparatus was changed. The clearance was set to 0.55 mm in Example 2, 0.77 mm in Example 3, 0.90 mm in Example 4, and 1.02 mm in Example 5.

(Comparative Examples 1 to 2)
As shown in Table 1, in Comparative Examples 1 and 2, a holding pad was manufactured in the same manner as in Example 1 except that the clearance of the coating apparatus was changed. The clearance was set to 0.42 mm in Comparative Example 1 and 1.21 mm in Comparative Example 2, respectively.

(Evaluation)
About the holding pad of an Example and a comparative example, thickness, a water absorption rate, and adsorption power were measured. The thickness was measured using a thickness gauge (minimum scale 0.001 mm) and applying a load of 100 g / cm ² . A holding pad measuring 1 m in length and 1 m in width was read at a pitch of 10 cm in length and width, and the average value of thickness, standard deviation σ, and the difference between the maximum thickness and the minimum thickness were determined as range R. The water absorption ratio was measured by the following method using a measurement sample cut to 10 cm × 10 cm from each holding pad, that is, 5 g (5 ml) of distilled water on the holding surface S of the measurement sample in which the mass before water absorption was measured in advance. Was dropped and left for 5 minutes. The moisture on the holding surface S was wiped off, and the mass after water absorption was measured. The difference in mass before and after adding distilled water was determined, and the ratio of the added distilled water to the mass was calculated as a percentage. Adsorption force was measured by the following method. As shown in FIGS. 2A and 2B, the holding pad 10 was mounted on a surface plate 81 having a substantially flat surface with an adhesive layer of the double-sided tape 7. After spraying water onto the holding surface S of the holding pad 10 with a spray, the water on the surface was lightly removed with a wiper. Next, a glass plate 82 having a length of 10 cm and a width of 10 cm was placed on the holding surface S. A wire is attached to the glass plate 82 at a central portion of one side with an interval of 5 cm. A weight 83 is placed on the entire upper surface of the glass plate 82 so that a load of 75 g / cm ² is applied evenly and left for 1 minute, then the weight 83 is removed, and the air storage state between the holding pad 10 and the glass plate 82 is visually observed. Judged by. When air storage was observed, the glass plate 82 was removed and the process was repeated. After confirming that there is no air storage, the glass plate 82 is pulled with a wire in the horizontal (horizontal) direction (arrow A direction), and the peak value (maximum value) of the tensile force when the glass plate 82 is displaced from the holding pad 10. Was measured. The measurement was performed three times, and the average value was calculated as the adsorption force, and the polishing object retention was evaluated. Table 1 shows the measurement results of thickness, water absorption ratio, and adsorption force.

  As shown in Table 1, in Comparative Example 1 in which the clearance during coating was set to 0.42 mm, the average value of thickness, standard deviation σ, and range R were 0.149 mm, 0.0021 mm, and 0.013 mm, respectively. Yes, the adsorptive power was 247N. For this reason, in the holding pad of Comparative Example 1, although the thickness variation is small and the object to be polished can be held flat, the thickness of the polyurethane sheet is too small and the cushioning property is poor. As a result, the unevenness of the glass plate 82 could not be followed, and the adsorbing power decreased, so that the glass plate 82 was easily peeled off. On the other hand, in Examples 1 to 5, the clearance was set to be 0.50 to 1.02 mm thicker than Comparative Example 1. Accordingly, the average value of thickness, standard deviation σ, range R, and adsorption force were all larger than Comparative Example 1. Although the thickness variation was larger than that of Comparative Example 1, it had sufficient flatness as a holding pad, and the glass plate 82 could be held flat. Moreover, since the adsorption force was larger than that of Comparative Example 1 and had an appropriate adsorption force, the glass plate 82 was easily attached and detached.

  On the other hand, in Comparative Example 2 in which the clearance was set to 1.21 mm, the average value of thickness, the standard deviation σ, the range R, and the attractive force were all larger than those in each of the examples, but three attractive force tests The difference between the maximum value and the minimum value of the adsorption force measurement result was large. Since the thickness variation of Comparative Example 2 is larger than that of Examples 1 to 5, the flatness accuracy is low, and the polyurethane sheet is thicker than those of Examples 1 to 5, so that the cushioning property is increased. Was exerted and the adsorptive power increased. For this reason, the adsorption | suction with respect to the glass plate 82 became strong, and attachment / detachment became difficult. In Comparative Example 2, the water absorption ratio was 0.12%, which was higher than those of Comparative Example 1 and Examples 1 to 5. This is probably because the standard deviation σ and the range R are large, and the amount of water remaining in the recessed portion of the holding surface is increased. For this reason, the water | moisture content which exists on a holding surface changes with places, As a result, the adsorption | suction force varied. Considering the holding force stability of the holding pad, the water absorption ratio is preferably 0.06% or less.

  The present invention provides a holding pad that can improve the flatness of an object to be polished and ensure a stable holding force of the object to be polished, and thus contributes to the manufacture and sale of the holding pad. Have sex.

S Holding surface 2 Polyurethane sheet (soft resin sheet)
2a Skin layer 3 Foam 6 Base material 10 Holding pad

Claims (7)

A soft resin sheet having a skin layer on the holding surface side to hold the object to be polished, in which foam is formed by a wet film formation method;
A resin base material disposed so as to face the back surface of the holding surface of the soft resin sheet, and having a substantially flat surface on the surface side facing the back surface;
With
The soft resin sheet has an average thickness in the range of 0.2 mm to 0.8 mm, and a standard deviation in thickness of 0.01 mm or less.
The soft resin sheet is formed by coagulation of a resin solution coated on the substrate. Water is dropped onto the holding surface at a rate of 50 mg per 1 cm ^{2 of the} holding surface and left for a certain period of time. A holding pad, wherein the ratio of the mass of absorbed water to the mass of dripped water is 0.1% or less.   The holding pad according to claim 1, wherein the soft resin sheet has a thickness range represented by a difference between a maximum value and a minimum value of 0.02 mm to 0.08 mm.   The holding pad according to claim 2, wherein the soft resin sheet has an adsorption force in a range of 250N to 390N when a glass substrate is adsorbed to the holding surface through water.   The holding pad according to claim 1, wherein the soft resin sheet is made of a polyurethane resin.   The holding pad according to claim 4, wherein the polyurethane resin has a 100% modulus in a range of 4 MPa to 10 MPa.   The holding pad according to claim 1, wherein the substrate has a surface roughness Ra of the substantially flat surface in a range of 0.4 μm to 0.7 μm.   The holding pad according to claim 6, wherein the base material has an average thickness in a range of 0.1 mm to 0.5 mm.

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