Wafer holder

Abstract

To provide a wafer holder with a simple structure, which is used when a warped wafer is held.SOLUTION: A wafer holder includes a holding base which has a circular holding surface, in which an annular first groove and an annular second groove surrounded by the first groove are formed on a holding surface side, and which includes a plurality of first suction holes opening in an area surrounded by the first groove and the second groove on the holding surface, a plurality of second suction holes opening in an area surrounded by the second groove on the holding surface, and a suction path communicating with the first suction holes and the second suction holes and opening on the back surface opposite to the holding surface, the first and second suction holes and the suction path being formed inside the holding base. The first suction holes and the second suction holes are designed such that pressure loss in each of the first suction holes is more than pressure loss in each of the second suction holes.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a wafer holder used to hold a wafer by suction. [Background technology]

[0002] Chips for devices such as ICs (Integrated Circuits) or LSIs (Large Scale Integration) are essential components in various electronic devices such as mobile phones and personal computers. Such chips are manufactured, for example, by dividing a disk-shaped wafer on which many devices are formed into regions containing individual devices.

[0003] These wafers are typically cut from cylindrical ingots using a blade saw, wire saw, or the like. Wafers cut in this manner often warp. Furthermore, the warping can also occur due to internal stresses that arise during device formation. Therefore, during the chip manufacturing process, warped wafers may need to be processed or transported.

[0004] However, the holding surface of the wafer holder (such as a chuck table or transfer pad) used to hold a wafer by suction for processing or transporting the wafer is often flat. When a warped wafer is held using such a wafer holder, leakage may occur. In this case, the suction force acting on the wafer becomes weak, making it difficult or impossible to hold the wafer.

[0005] In view of this, it has been proposed to provide a pair of O-rings on either side of a suction hole opening in the holding surface of a wafer holder, and to provide a liquid supply means that forms a liquid seal between the wafer and the holding surface, located outside the pair of O-rings (see, for example, Patent Document 1). When such a wafer holder is used, the occurrence of leaks is suppressed and the suction force acting on a warped wafer is strengthened. Therefore, in this case, it is easy to hold the wafer in a flat state. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-90028 Summary of the Invention [Problem to be solved by the invention]

[0007] When the liquid supply means is provided on the wafer holder, the structure of the wafer holder becomes complicated, increasing the manufacturing cost of the wafer holder. Furthermore, since the liquid supply means must be operated to supply liquid in order to hold the wafer using the wafer holder, the manufacturing cost of the chips produced by dividing the wafer also increases.

[0008] In view of this, an object of the present invention is to provide a wafer holder that is used to hold a warped wafer and has a simple structure that can suppress increases in the manufacturing costs of the wafer holder itself and the manufacturing costs of chips produced by dividing the wafer. [Means for solving the problem]

[0009] According to the present invention, there is provided a wafer holder used for holding a wafer by suction, which has a circular holding surface, and on the holding surface side, a first annular groove and a second annular groove surrounded by the first groove are formed, and a plurality of first suction holes opening in an area of ​​the holding surface sandwiched between the first groove and the second groove, a plurality of second suction holes opening in an area of ​​the holding surface surrounded by the second groove, and a plurality of first suction holes opening on the holding surface in communication with the plurality of first suction holes and the plurality of second suction holes. A wafer holder is provided, which comprises a holding base having a suction passage formed therein that opens to the rear surface on the opposite side, a first elastic ring disposed in the first groove and having a portion thereof protruding from the holding surface, and a second elastic ring disposed in the second groove and having a portion thereof protruding from the holding surface, wherein the plurality of first suction holes and the plurality of second suction holes are designed so that the pressure loss in each of the plurality of first suction holes is greater than the pressure loss in each of the plurality of second suction holes.

[0010] Preferably, the suction path includes a communicating portion extending radially so as to be parallel to the holding surface, each of the plurality of first suction holes and each of the plurality of second suction holes extend linearly from the communicating portion of the suction path to the holding surface so as to be perpendicular to the holding surface, each of the plurality of first suction holes is formed in a cylindrical shape having a first diameter, and each of the plurality of second suction holes is formed in a cylindrical shape having a second diameter larger than the first diameter.

[0011] Also, preferably, the number of the plurality of first suction holes is smaller than the number of the plurality of second suction holes.

[0012] Preferably, the second elastic ring is a V-ring. The upper end of the second elastic ring is positioned higher than the upper end of the first elastic ring. [Effects of the Invention]

[0013] The wafer holder of the present invention can be used to hold a wafer whose diameter is larger than the outer diameter of the first groove and which is warped to such an extent that it comes into contact with the second elastic ring but does not come into contact with the first elastic ring when placed on the holding surface side of the holding base. Specifically, in this wafer holder, a suction force can be applied from an external suction source to a wafer placed on the holding surface side of the holding base through the suction path, the plurality of first suction holes, and the plurality of second suction holes.

[0014] Furthermore, this wafer holder is designed so that the pressure loss in each of the plurality of first suction holes is greater than the pressure loss in each of the plurality of second suction holes, so that the suction force acting on the space near the area surrounded by the second elastic ring (second groove) on the holding surface is stronger than the suction force acting on the space near the area outside the second elastic ring on the holding surface.

[0015] When the wafer is held by this wafer holder, the area (central area) of the wafer located inside the second elastic ring is first strongly sucked, which flattens the central area of ​​the wafer so that it comes into contact with the holding surface of the holding base while pressing the second elastic ring into the second groove.

[0016] When the central region of the wafer is flattened, the region surrounding the central region of the wafer (peripheral region) also approaches the holding surface of the holding base, which brings the peripheral region of the wafer into contact with or into proximity with the first elastic ring, thereby suppressing leakage through the gap between the peripheral region of the wafer and the first elastic ring.

[0017] When leakage through the gap between the outer circumferential region of the wafer and the first elastic ring is suppressed, the suction force acting on the outer circumferential region of the wafer is strengthened. This flattens the outer circumferential region of the wafer so that it contacts the holding surface of the holding base while pressing the first elastic ring into the first groove. As a result, the wafer is held flat by this wafer holder.

[0018] The wafer holder of the present invention described above has a simpler structure than conventional wafer holders equipped with a liquid supply means for forming a liquid seal, etc., and therefore increases in manufacturing costs can be suppressed. Furthermore, when using the wafer holder of the present invention to hold a wafer, there is no need to operate special components (e.g., a liquid supply means), and therefore increases in manufacturing costs for chips produced by dividing the wafer can be suppressed. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1(A) is a top view schematically showing an example of a wafer holder, and FIG. 1(B) is a cross-sectional view showing a cross section of the wafer holder taken along line A1A2 shown in FIG. 1(A). [Figure 2] FIG. 2(A) is a top view schematically showing an example of a wafer held using a wafer holder, and FIG. 2(B) is a cross-sectional view showing a cross section of the wafer taken along line B1B2 shown in FIG. 2(A). [Figure 3] FIG. 3 is a cross-sectional view that schematically shows how a wafer is held by using a wafer holder. [Figure 4] FIG. 4 is a cross-sectional view that schematically shows how a wafer is held by using a wafer holder. [Figure 5] FIG. 5 is a cross-sectional view that schematically shows how a wafer is held by using a wafer holder. [Figure 6] FIG. 6 is a cross-sectional view that schematically shows how a wafer is held by using a wafer holder. DETAILED DESCRIPTION OF THE INVENTION

[0020] An embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1(A) is a top view showing a schematic diagram of an example of a wafer holder, and Fig. 1(B) is a cross-sectional view showing a cross section of the wafer holder taken along line A1A2 shown in Fig. 1(A). For convenience, Fig. 1(B) also shows components connected to the wafer holder simply by symbols or blocks.

[0021] 1(A) and 1(B) has a disk-shaped holding base 4. This holding base 4 is made of, for example, ceramics, and has roughly parallel circular holding surfaces 4a. In addition, on the holding surface 4a side of the holding base 4, an annular groove (first groove) 6 is formed concentrically with the outer periphery of the holding surface 4a.

[0022] The holding base 4 is designed so that the diameter of the holding surface 4a is longer than the diameter of a wafer (described later) and the outer diameter of the groove 6 is shorter than the diameter of the wafer (described later). The groove 6 is provided with an annular seal sponge (first elastic ring) 8 made of, for example, resin.

[0023] The cross section of this seal sponge 8 is circular with a diameter shorter than the width of the groove 6. The seal sponge 8 may be replaced with an O-ring made of resin. The thickness of the seal sponge 8 is greater than the depth of the groove 6. Therefore, the upper end of the seal sponge 8 protrudes from the holding surface 4a of the holding base 4.

[0024] Furthermore, an annular groove (second groove) 10 surrounded by groove 6 is also formed on the holding surface 4a side of the holding base 4. This groove 10 is concentric with the outer periphery of the holding surface 4a and is deeper than groove 6. A V-ring (second elastic ring) 12 is provided in groove 10.

[0025] This V-ring 12 has a main body portion 12a having a trapezoidal cross section with each side slightly shorter than the width of the groove 10, a hinge portion 12b provided at the upper inner end of the main body portion 12a, and a lip portion 12c extending linearly from the hinge portion 12b to above the outer end of the main body portion 12a.

[0026] The thickness of the V-ring 12 is greater than the depth of the groove 10. That is, the lip portion 12c protrudes from the holding surface 4a of the holding base 4. The position of the tip of the lip portion 12c is higher than the position of the upper end of the seal sponge 8.

[0027] In addition, inside the holding base 4, there are formed a plurality of (here, four) suction holes (first suction holes) 14 that open in the area sandwiched between grooves 6 and 10 on the holding surface 4a, and a plurality of (here, thirteen) suction holes (second suction holes) 16 that open in the area surrounded by grooves 10 on the holding surface 4a.

[0028] Specifically, the openings of the plurality of suction holes 14 are positioned at approximately equal intervals along the circumferential direction of the holding base 4. The plurality of suction holes 16 include suction hole 16a that opens at the center of the holding surface 4a, four suction holes 16b that are at a first distance from the center of the holding surface 4a, four suction holes 16c that are at a second distance that is longer than the first distance, and four suction holes 16d that are at a third distance that is longer than the second distance. The openings of the four suction holes 16b, 16c, and 16d that are at the same distance from the center of the holding surface 4a are positioned at approximately equal intervals along the circumferential direction of the holding base 4.

[0029] Each of the plurality of suction holes 14 and each of the plurality of suction holes 16 are formed in a cylindrical shape and extend at equal lengths so as to be perpendicular to the holding surface 4a. Furthermore, the diameter of each of the plurality of suction holes 16 is larger than the diameter of each of the plurality of suction holes 14.

[0030] Suction paths 18 are also formed inside the holding base 4. These suction paths 18 extend radially and have communication portions 18a that communicate with the plurality of suction holes 14 and the plurality of suction holes 16, and an opening portion 18b that extends perpendicular to the holding surface 4a and opens on the back surface 4b opposite the holding surface 4a. The wafer holder 2 can also communicate with a suction source 22, such as an ejector, via a pipe and a valve 20 that are connected to the opening portion 18b of the suction paths 18.

[0031] The plurality of suction holes 14 and the plurality of suction holes 16 formed inside the holding base 4 of the wafer holder 2 are designed so that the pressure loss in each of the plurality of suction holes 14 is greater than the pressure loss in each of the plurality of suction holes 16.

[0032] Specifically, the pressure loss (Δp) of each suction hole 14, 16 is quantified by the Darcy-Weisbach equation:

number

[0033] In the above equation, λ is the friction coefficient of each suction hole 14, 16, d is the diameter of each suction hole 14, 16, l is the length of each suction hole 14, 16, ρ is the density of the fluid supplied to each suction hole 14, 16, and v is the velocity of the fluid supplied to each suction hole 14, 16.

[0034] Here, since each of the suction holes 14, 16 is formed inside the holding base 4, the friction coefficients of each of the suction holes 14, 16 are equal. As described above, each of the suction holes 14, 16 has the same length. As described above, each of the suction holes 14, 16 communicates with the suction path 18, the density and velocity of the fluid supplied to each of the suction holes 14, 16 are also equal.

[0035] On the other hand, as described above, the diameter of each of the plurality of suction holes 16 is larger than the diameter of each of the plurality of suction holes 14. Therefore, in the wafer holder 2, the pressure loss in each of the plurality of suction holes 14 is larger than the pressure loss in each of the plurality of suction holes 16.

[0036] FIG. 2(A) is a top view showing a schematic example of a wafer held using wafer holder 2, and FIG. 2(B) is a cross-sectional view showing a cross section of the wafer taken along line B1B2 shown in FIG. 2(A).

[0037] 2(A) and 2(B) is made of a single-crystal semiconductor material such as silicon (Si), silicon carbide (SiC), or gallium arsenide (GaAs). The wafer 11 is warped. That is, the wafer 11 has one surface 11a that is curved in a concave shape and the other surface 11b that is curved in a convex shape.

[0038] The side surface 11c of the wafer 11 may be chamfered, or may have a notch or an orientation flat formed thereon to indicate a specific crystal orientation. Furthermore, a device such as an IC or an LSI may be formed on one surface 11a or the other surface 11b of the wafer 11.

[0039] 3 to 6 are cross-sectional views that schematically show how wafer 11 is held by wafer holder 2. When wafer 11 is held by wafer holder 2, first, the other surface 11b of wafer 11 is placed on holding surface 4a of holding base 4 (see FIG. 3).

[0040] In this case, the tip of the lip portion 12c of the V-ring 12 protruding from the holding surface 4a comes into contact with the other surface 11b of the wafer 11, and the V-ring 12 supports the wafer 11. In addition, since the other surface 11b of the wafer 11 is curved so as to protrude, the seal sponge 8 and the wafer 11 are separated from each other.

[0041] Therefore, in this case, the multiple suction holes 16 are connected to the space S1 sealed by the wafer 11 and the V-ring 12, and the multiple suction holes 14 are connected to the open space S2 through the gap between the wafer 11 and the seal sponge 8.

[0042] Next, with the suction source 22 operating, the valve 20 is opened (see FIG. 4). As a result, a suction force acts on the spaces S1 and S2 via the suction path 18, the plurality of suction holes 14, and the plurality of suction holes 16. That is, a suction force acts on the wafer 11 to bring the other surface 11b of the wafer 11 into contact with the holding surface 4a of the holding base 4.

[0043] Here, wafer holder 2 is designed so that the pressure loss in each of multiple suction holes 14 is greater than the pressure loss in each of multiple suction holes 16. Therefore, the suction force acting on space S1 is stronger than the suction force acting on space S2.

[0044] In this case, first, a region (central region) of the wafer 11 located inside the V ring 12 is strongly sucked. As a result, the lip portion 12c of the V ring 12 is pressed into the groove 10 by the central region of the wafer 11. As a result, the central region of the wafer 11 is flattened so as to come into contact with the holding surface 4a of the holding base 4 (see FIG. 5).

[0045] When the central region of the wafer 11 is flattened, the region surrounding the central region of the wafer 11 (peripheral region) also approaches the holding surface 4a of the holding base 4. As a result, the peripheral region of the wafer 11 comes into contact with or approaches the seal sponge 8, and leakage through the gap between the peripheral region of the wafer 11 and the seal sponge 8 is suppressed.

[0046] When leakage through the gap between the outer peripheral region of the wafer 11 and the seal sponge 8 is suppressed, the suction force acting on the outer peripheral region of the wafer 11 increases, causing the seal sponge 8 to be pressed into the groove 6 by the outer peripheral region of the wafer 11 so that the cross section becomes elliptical.

[0047] Furthermore, the lip portion 12c of the V ring 12 is pressed into the groove 10 from the outside by the outer circumferential region of the wafer 11. As a result, the outer circumferential region of the wafer 11 is flattened so as to come into contact with the holding surface 4a of the holding base 4 (see FIG. 6).

[0048] The above-described wafer holder 2 has a simpler structure than conventional wafer holders equipped with a liquid supply means for forming a liquid seal, etc., and therefore increases in manufacturing costs can be suppressed. Furthermore, when using wafer holder 2 to hold wafer 11, there is no need to operate special components (e.g., a liquid supply means), so increases in manufacturing costs for chips manufactured by dividing wafer 11 can be suppressed.

[0049] In the wafer holder 2, the V ring 12 may be replaced with another elastic ring such as a seal sponge or an O-ring. That is, in the wafer holder 2, there is no limitation on the structure provided in the groove 10 as long as the structure can support the wafer 11 and be pressed into the groove 10. However, in the present invention, it is preferable to provide the V ring 12 in the groove 10 because the upper end is positioned high, making it easy to seal the space S1, and the V ring 12 can be pressed into the groove 10 relatively easily.

[0050] Furthermore, in wafer holder 2, seal sponge 8 may be replaced with another elastic ring such as a V-ring. That is, in wafer holder 2, there is no limitation on the structure provided in groove 6 as long as a structure that can be pressed into groove 6 is provided in groove 6. However, in the present invention, it is preferable to provide seal sponge 8 or an O-ring in groove 6, as this facilitates flattening up to the region very close to the outer periphery of wafer 11.

[0051] Furthermore, in the wafer holder 2, the number of the suction holes 14 may be greater than the number of the suction holes 16. However, in the present invention, it is preferable that the number of the suction holes 14 is less than the number of the suction holes 16, since this makes it easier to flatten the central region of the wafer 11.

[0052] Furthermore, in the wafer holder 2, there are no restrictions on the structure of the multiple suction holes 14 and the multiple suction holes 16, as long as they are designed so that the pressure loss in each of the multiple suction holes 14 is greater than the pressure loss in each of the multiple suction holes 16.

[0053] Furthermore, in the wafer holder 2, grooves that communicate with the plurality of suction holes 14 and / or the plurality of suction holes 16 may be formed on the holding surface 4a side of the holding base 4. When such grooves are formed, it becomes easier to apply a suction force uniformly to the wafer 11.

[0054] In addition, the structures and methods according to the above-described embodiments can be modified as appropriate without departing from the scope of the present invention. [Explanation of symbols]

[0055] 2: Wafer holder 4: Holding base (4a: holding surface, 4b: back side) 6: Groove (first groove) 8: Seal sponge (first elastic ring) 10: Groove (second groove) 11: Wafer (11a: one side, 11b: other side, 11c: side) 12: V-ring (second elastic ring) (12a: main body, 12b: hinge, 12c: lip) 14: Suction hole (first suction hole) 16: Suction hole (second suction hole) (16a, 16b, 16c, 16d: suction hole) 18: Suction path (18a: communication path, 18b: opening) 20: Valve 22: Suction source

Claims

1. A wafer holder used to hold a wafer by suction, a holding base having a circular holding surface, and having a first annular groove and a second annular groove surrounded by the first groove formed on the holding surface side, and having formed therein a plurality of first suction holes opening in a region of the holding surface sandwiched between the first groove and the second groove, a plurality of second suction holes opening in a region of the holding surface surrounded by the second groove, and suction paths communicating with the plurality of first suction holes and the plurality of second suction holes opening on a back surface opposite the holding surface; a first elastic ring disposed in the first groove and having a portion protruding from the holding surface; a second elastic ring disposed in the second groove and having a portion protruding from the holding surface; the plurality of first suction holes and the plurality of second suction holes are designed so that a pressure loss in each of the plurality of first suction holes is greater than a pressure loss in each of the plurality of second suction holes.

2. the suction path includes a communication portion extending radially so as to be parallel to the holding surface, each of the plurality of first suction holes and each of the plurality of second suction holes extend linearly from the communication portion of the suction path to the holding surface so as to be perpendicular to the holding surface; Each of the plurality of first suction holes is formed in a cylindrical shape having a first diameter, 2. The wafer holder according to claim 1, wherein each of the plurality of second suction holes is formed in a cylindrical shape having a second diameter larger than the first diameter.

3. 3. The wafer holder according to claim 1, wherein the number of the first suction holes is smaller than the number of the second suction holes.

4. 4. The wafer holder according to claim 1, wherein the second elastic ring is a V-ring.

5. A wafer holder as described in any one of claims 1 to 4, characterized in that the position of the upper end of the second elastic ring is higher than the position of the upper end of the first elastic ring.

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