Chuck table

Abstract

This invention provides a chuck table that exhibits minimal warping due to thermal expansion and can also be kept at a lower cost. [Solution] This chuck table is configured to support a workpiece on its upper surface and comprises a porous body having numerous voids inside, made of ceramic material and having a first coefficient of thermal expansion; a first layer configured to support the lower surface of the porous body and having a second coefficient of thermal expansion; and a second layer configured to support the lower surface of the first layer and having a third coefficient of thermal expansion. The second coefficient of thermal expansion is either greater than the first and third coefficients of thermal expansion, or smaller than the first and third coefficients of thermal expansion.

Description

[Technical Field]

[0001] The present invention relates to a chuck table capable of adsorbing and fixing workpieces such as wafers. Regarding. [Background technology]

[0002] In the manufacturing of semiconductor devices, a grinding process is performed on the wafer, which is the workpiece, to thin it by grinding the back surface in a grinding machine, and a cutting process is performed in a dicing machine to cut out chip-sized pieces. Such grinding and dicing machines are equipped with a chuck table that can adsorb and fix the wafer.

[0003] Although the chuck table has a planar shape that conforms to the planar shape of the wafer, warping can occur on the surface of the chuck table due to expansion caused by thermal changes. Such warping reduces the suction and fixing performance of the chuck table and also affects the processing accuracy of the wafer.

[0004] Traditionally, to suppress such warping, chuck tables were constructed using ceramic porous material and low-linear-expansion stainless steel with similar coefficients of thermal expansion. However, with this configuration, it is difficult to perfectly match the coefficients of thermal expansion of the chuck table housing material, and there is a risk that warping of the chuck table surface cannot be completely suppressed. Alternatively, a two-layer structure consisting of ceramic porous material and a dense ceramic body with equal coefficients of thermal expansion could be considered, but this would increase the cost. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2011-159678 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In view of the above-mentioned problems, the present invention aims to provide a chuck table that exhibits minimal warping due to thermal expansion and can also be kept at a lower cost. [Means for solving the problem]

[0007] The chuck table according to the present invention comprises a porous body configured to support a workpiece on its upper surface, having numerous voids inside, made of ceramic material, and having a first coefficient of thermal expansion; a first layer configured to support the lower surface of the porous body and having a second coefficient of thermal expansion; and a second layer configured to support the lower surface of the first layer and having a third coefficient of thermal expansion. The second coefficient of thermal expansion is either greater than the first and third coefficients of thermal expansion, or smaller than the first and third coefficients of thermal expansion. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a chuck table that exhibits minimal warping due to thermal expansion and can also be kept at a lower cost. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic cross-sectional view of the chuck table 1 according to the first embodiment. [Figure 2] This is a table showing the various physical quantities of each layer 11 to 13 that constitute the chuck table 1 of the first embodiment. [Figure 3] This graph shows the simulation results of the relationship between the change in the thickness t of the stainless steel layer 12, which is layer A (horizontal axis), and the changes in the strain amounts δAB between layers A and B, and δAC between layers A and C, respectively (vertical axis). [Figure 4] This is a table showing various calculated values ​​when each layer 11-13 has the physical quantities shown in Figure 2. [Figure 5] Figure 5 is a schematic cross-sectional view of the chuck table 1 according to the second embodiment. [Figure 6]It is a table showing various physical quantities of each of the layers 11 to 13 constituting the chuck table 1 of the second embodiment. [Figure 7] It is a graph showing the result of simulating the relationship between the change in the thickness t of the stainless steel layer 12, which is layer A (horizontal axis), and the changes in the amount of strain δAB between layers A - B and δAC between layers A - C at that time (vertical axis). [Figure 8] It is a list showing various calculated values when each of the layers 11 to 13 has the physical quantities in FIG. 6. [Figure 9] It is a schematic cross - sectional view of the chuck table 1 of the third embodiment. [Figure 10] It is a table showing various physical quantities of each of the layers 11 to 13A constituting the chuck table 1 of the third embodiment. [Figure 11] It is a graph showing the result of simulating the relationship between the change in the thickness t of the Invar layer 12A, which is layer A (horizontal axis), and the changes in the amount of strain δAB between layers A - B and δAC between layers A - C at that time (vertical axis). [Figure 12] It is a list showing various calculated values when each of the layers 11 to 13A has the physical quantities in FIG. 10. [Figure 13] It is a schematic cross - sectional view of the chuck table 1 of the fourth embodiment. [Figure 14] It is a table showing various physical quantities of each of the layers 11 to 13B constituting the chuck table 1 of the fourth embodiment. [Figure 15] It is a graph showing the result of simulating the relationship between the change in the thickness t of the Invar layer 12B, which is layer A (horizontal axis), and the changes in the amount of strain δAB between layers A - B and δAC between layers A - C at that time (vertical axis). [Figure 16] It is a list showing various calculated values when each of the layers 11 to 13B has the physical quantities in FIG. 14. [Figure 17] It is a schematic cross - sectional view of the chuck table 1 of the fifth embodiment. [Figure 18] It is a table showing various physical quantities of each of the layers 11 to 13C constituting the chuck table 1 of the fifth embodiment. [Figure 19]This is a graph showing the result of simulating the relationship between the change in the thickness t of the stainless steel layer 12C, which is the A layer (horizontal axis), and the changes in the strain amounts δAB between the A - B layers and δAC between the A - C layers at that time (vertical axis). [Figure 20] This is a list showing various calculated values when each of the layers 11 - 13C has the physical quantities shown in FIG. 14. [Figure 21] This is a schematic cross - sectional view of the chuck table 1 of the sixth embodiment. [Figure 22] This is a table showing various physical quantities of each of the layers 11 - 13C constituting the chuck table 1 of the sixth embodiment. [Figure 23] This is a graph showing the result of simulating the relationship between the change in the thickness t of the stainless steel layer 12C, which is the A layer (horizontal axis), and the changes in the strain amounts δAB between the A - B layers and δAC between the A - C layers at that time (vertical axis). [Figure 24] This is a list showing various calculated values when each of the layers 11 - 13C has the physical quantities shown in FIG. 22. [Embodiments for Carrying Out the Invention]

[0010] Hereinafter, this embodiment will be described with reference to the accompanying drawings. The accompanying drawings show embodiments in accordance with the principles of the present disclosure, but these are for the purpose of understanding the present disclosure and are not used to interpret the present disclosure in a limiting sense. The description in this specification is merely a typical example and does not limit the scope of the claims or application examples of the present disclosure in any sense. In this embodiment, the description is made in sufficient detail for those skilled in the art to implement the present disclosure, but other implementations and forms are also possible, and it is necessary to understand that changes in configuration and structure and replacement of various elements can be made without departing from the scope and spirit of the technical idea of the present disclosure. Therefore, the following description should not be construed as being limited to this.

[0011] [First Embodiment] The chuck table 1 of the first embodiment will be described with reference to Figures 1 to 4. Figure 1 is a schematic cross-sectional view of the chuck table 1. Figure 2 is a table showing various physical quantities for each layer constituting the chuck table 1.

[0012] This chuck table 1 has a three-layer structure consisting of a ceramic porous layer 11, a stainless steel layer 12, and an Invar layer 13, as viewed from the upper layer side (the side on which the wafer W is placed). In the following description, the intermediate layer of this three-layer structure may be referred to as layer A, the upper ceramic porous layer as layer B, and the lower layer which serves as the substrate as layer C.

[0013] The ceramic porous layer 11, which is the B layer, is the surface that comes into contact with the wafer, which is the workpiece, and is made of ceramic porous material (porous alumina) which has a large number of voids (pores) inside. The ceramic porous layer 11 is subjected to negative pressure applied to the contact surface through the voids from a negative pressure generating device (not shown in Figure 1), causing the wafer to adhere to it. The ceramic porous layer 11 has a first coefficient of linear expansion α1.

[0014] The stainless steel layer 12, which is layer A, is made of, for example, SUS630 and is configured to support the lower surface of the ceramic porous layer 11. The stainless steel layer 12 has a second coefficient of thermal expansion α2 which is greater than the first coefficient of thermal expansion α1. SUS630 is a precipitation-hardening stainless steel containing 15-17% chromium (Cr), 3-5% nickel (Ni), and 3-5% copper (Cu).

[0015] The Invar layer 13, which serves as the C layer, is made of Invar (an alloy consisting of iron with approximately 36% nickel added, and further containing trace amounts of manganese and carbon in amounts less than 1%), and is configured to support the lower surface of the stainless steel layer 12. The Invar layer 13 has a third coefficient of thermal expansion α3 that is smaller than the second coefficient of thermal expansion α2. That is, the second coefficient of thermal expansion α2 is larger than the first coefficient of thermal expansion α1 and the third coefficient of thermal expansion α3. The stainless steel layer 12 and the Invar layer 13 are provided with through holes for supplying negative pressure from a negative pressure generating device to the ceramic porous layer 11.

[0016] In this first embodiment, the sum of the thicknesses of each of the three layers 11 to 13 (overall thickness) is set to a specific thickness (e.g., 15 mm) according to the specifications of the chuck table 1. Preferably, the thickness of the ceramic porous layer 11 is set to 5 mm, taking into consideration the adsorption performance, and the sum of the thicknesses of the stainless steel layer 12 and the Invar layer 13 is 15 - 5 = 10 mm. Under these conditions, in the first embodiment, the thickness of each layer is set such that the amount of strain due to temperature rise between the ceramic porous layer 11 (layer B) and the stainless steel layer 12 (layer A) is in the opposite direction and approximately equal to the amount of strain due to temperature rise between the stainless steel layer 12 and the Invar layer 13. That is, in the chuck table 1 of this first embodiment, the thickness t of each layer is determined from the Young's modulus E and the coefficient of linear expansion α of each layer 11 to 13, thereby minimizing thermal deformation of the chuck table 1.

[0017] Figure 2 shows the Young's modulus E and the linear expansion coefficient α of each of the layers 11 to 13. The length L of each of the layers 11 to 13 is set to 150 mm, which is the radius of the chuck table for wafer adsorption in terms of calculation, and the temperature change ΔT is set to 1°C. The value of the length L can be appropriately changed according to the diameter of the table to be manufactured. Figure 3 is a graph showing the result of simulating the relationship between the change in the thickness t (horizontal axis) of the stainless steel layer 12, which is layer A, and the changes in the strain amounts δAB and δAC between layers A - B and A - C (vertical axis) (Note that the strain amounts δAB and δAC may be collectively referred to as the strain amount δ). Here, the total thickness of the stainless steel layer 12, which is layer A, and the invar layer 13, which is layer C, is set to 10 mm, and the thickness of the stainless steel layer 12, which is layer A, is changed, and the thickness of layer A where the difference in strain amounts (δAB - δAC) becomes approximately zero is being examined. Figure 4 shows various physical quantities generated by thermal expansion and the strain amount δAB between the stainless steel layer 12, which is layer A, and the ceramic porous layer 11, which is layer B, when the material, Young's modulus E, and linear expansion coefficient α are set as in Figure 2 and the difference in strain amounts becomes approximately zero as in Figure 3. Also, it shows various physical quantities generated by thermal expansion and the strain amount δAC between the stainless steel layer 12, which is layer A, and the invar layer 13, which is layer C. The difference (change amount δAB - ΔAC) between the strain amount δAB generated between layer A and layer B and the strain amount δAC generated between layer A and layer C is -2.4 nm and becomes approximately zero. The strain amount δ can be calculated as follows based on the lateral length L of the two layers, the thicknesses t1 and t2 of each layer, the longitudinal elastic modulus (Young's modulus) E, the linear expansion coefficient α, and the temperature change ΔT. [Equation 1] δ = {3L 4 , 3 , 2 , 2 , 2 ,

[0018] , 3 , , E1E2t1t2(α1 - α2)(t1 + t2)ΔT} / {E1<​​​​​​​​​​​​​​​​​​As shown in Figure 3, the difference in strain δ (change δAB-δAC) is approximately zero when the thickness t of layer A is around 2.85 mm and around 9 mm. However, in the case of 9 mm, the thickness of the Invar layer 13 becomes excessively small, making fabrication difficult, which is undesirable (10-9=1 mm or less). Furthermore, if the thickness is 10 mm or more, fabrication becomes impossible, and if the thickness t of layer A is less than 1 mm, the desired flatness cannot be obtained, making fabrication difficult (the same applies to the other embodiments described below). Therefore, in the structure of Figure 1, it is preferable to have a thickness t of layer A = 2.85 mm and a thickness of layer C = 7.15 mm.

[0019] As explained above, in this first embodiment, the chuck table is constructed with a three-layer structure consisting of a ceramic porous layer 11, a stainless steel layer 12, and an Invar layer 13. By optimizing the thickness of each layer, the amount of thermal strain can be reduced to almost zero. Between the stainless steel layer 12 (layer A) and the ceramic porous layer 11 (layer B), the former has a larger coefficient of linear expansion (α2 > α1), so as the temperature rises, warping occurs such that the ceramic porous layer 11 side becomes concave. On the other hand, between the stainless steel layer 12 (layer A) and the Invar layer 13 (layer C), the former has a larger coefficient of linear expansion, so warping occurs such that the Invar layer 13 side becomes concave. As these warping in opposite directions cancel each other out, an overall structure that does not warp regardless of temperature changes can be obtained.

[0020] [Second Embodiment] Next, the chuck table 1 of the second embodiment will be described with reference to Figures 5 to 8. Figure 5 is a schematic cross-sectional view of this chuck table 1. Figure 6 is a table showing the various physical quantities of each layer that constitutes this chuck table 1.

[0021] The chuck table 1 of this second embodiment, like the first embodiment, has a three-layer structure consisting of a ceramic porous layer 11, a stainless steel layer 12, and an Invar layer 13, as viewed from the top. The ceramic porous layer 11 of layer B may be substantially the same as the ceramic porous layer 11 of the first embodiment. However, the stainless steel layer 12 as layer A is made of SUS410 and is configured to support the lower surface of the ceramic porous layer 11. The stainless steel layer 12 has a second coefficient of thermal expansion α2 which is greater than the first coefficient of thermal expansion α1. SUS410 is a martensitic stainless steel containing about 13% chromium (Cr).

[0022] The Invar layer 13, as the C layer, is constructed from Invar material, similar to the first embodiment, and is configured to support the lower surface of the stainless steel layer 12. The Invar layer 13 has a third coefficient of thermal expansion α3 that is smaller than the second coefficient of thermal expansion α2. That is, the second coefficient of thermal expansion α2 is larger than the first coefficient of thermal expansion α1 and the third coefficient of thermal expansion α3.

[0023] In the second embodiment as well, the sum of the thicknesses of each of the three layers 11 to 13 (overall thickness) is set to a specific thickness (for example, 15 mm) according to the specifications of the chuck table 1. Preferably, the thickness of the ceramic porous layer 11 is set to 5 mm, taking into consideration the adsorption performance, and the sum of the thicknesses of the stainless steel layer 12 and the Invar layer 13 is 15 - 5 = 10 mm. Under these conditions, in the first embodiment, the thickness of each layer is set such that the amount of strain due to temperature rise between the ceramic porous layer 11 (layer B) and the stainless steel layer 12 (layer A) is in the opposite direction and approximately equal to the amount of strain due to temperature rise between the stainless steel layer 12 and the Invar layer 13. That is, in the chuck table 1 of this second embodiment, the thickness t of each layer is determined from the Young's modulus E and the coefficient of linear expansion α of each layer 11 to 13, thereby minimizing thermal deformation of the chuck table 1.

[0024] Figure 6 shows the Young's modulus E and the coefficient of linear expansion α of each layer 11-13. Similar to the first embodiment, the length L of each layer 11-13 is set to 150 mm, which is the radius of the 300 mm wafer suction chuck table calculated, and the temperature change ΔT is set to 1°C. The value of length L can be appropriately changed according to the diameter of the table being manufactured. Figure 7 is a graph showing the simulation results of the relationship between the change in thickness t of the stainless steel layer 12, which is layer A (horizontal axis), and the changes in the strain amount δAB between layers A and B, and the strain amount δAC between layers C (vertical axis). Here, assuming that the sum of the thicknesses of the stainless steel layer 12, which is layer A, and the Invar layer 13, which is layer C, is 10 mm, the thickness of the stainless steel layer 12, which is layer A, is changed to investigate the thickness of layer A at which the difference in strain amount (δAB-δAC) becomes approximately zero. Figure 8 shows the various physical quantities and strain amounts δAB that occur due to thermal expansion between the stainless steel layer 12 (layer A) and the ceramic porous layer 11 (layer B) when the material, Young's modulus E, and coefficient of thermal expansion α are set as in Figure 6, and the difference in strain amounts is approximately zero as in Figure 7. It also shows the various physical quantities and strain amounts δAC that occur due to thermal expansion between the stainless steel layer 12 (layer A) and the Invar layer 13 (layer C). The difference (change δAB-δAC) between the strain amount δAB that occurs between layers A and B and the strain amount δAC that occurs between layers A and C is -40.4 nm, which is approximately zero.

[0025] As shown in Figure 7, the difference in strain δAB-δAC (change) becomes approximately zero when the thickness t of layer A is around 2.55 mm and around 9 mm. However, in the case of 9 mm, the thickness of the Invar layer 13 becomes excessively small, making it difficult to manufacture, which is undesirable (10-9 = 1 mm or less). Therefore, in the structure of Figure 5, it is preferable to have a thickness of layer A of t = 2.55 mm and a thickness of layer C of 7.45 mm.

[0026] As explained above, in this second embodiment as well, the chuck table is constructed with a three-layer structure consisting of a ceramic porous layer 11, a stainless steel layer 12, and an Invar layer 13. By optimizing the thickness of each layer, the amount of thermal strain can be reduced to almost zero. Between the stainless steel layer 12 (layer A) and the ceramic porous layer 11 (layer B), the former has a larger coefficient of linear expansion, so as the temperature rises, the ceramic porous layer 11 side warps, becoming concave. On the other hand, between the stainless steel layer 12 (layer A) and the Invar layer 13 (layer C), the former has a larger coefficient of linear expansion, so the Invar layer 13 side warps, becoming concave. These warps in opposite directions cancel each other out, resulting in a structure that remains warp-free regardless of temperature changes.

[0027] [Third Embodiment] Next, the chuck table 1 of the third embodiment will be described with reference to Figures 9 to 12. Figure 9 is a schematic cross-sectional view of this chuck table 1. Figure 10 is a table showing various physical quantities for each layer constituting this chuck table 1.

[0028] The chuck table 1 of this third embodiment has a three-layer structure, viewed from the upper side, consisting of a ceramic porous layer 11, an Invar layer 12A, and a stainless steel layer 13A. The ceramic porous layer 11 of layer B may be substantially the same as the ceramic porous layer 11 of the first embodiment, except for its thickness. However, the Invar layer 12A, which is layer A, is made of Invar and is configured to support the lower surface of the ceramic porous layer 11. The Invar layer 12A has a second coefficient of thermal expansion α2 that is smaller than the first coefficient of thermal expansion α1. In other words, in this chuck table 1, the Invar layer 12A is the upper layer (layer A) and the stainless steel layer 13A is the lower layer (layer B), which is the reverse of the order in the above embodiment.

[0029] The stainless steel layer 13A, which serves as layer C, is constructed using SUS630 as an example, and is configured to support the lower surface of the Invar layer 12A. The stainless steel layer 13A has a third coefficient of thermal expansion α3 that is greater than the second coefficient of thermal expansion α2. That is, the second coefficient of thermal expansion α2 is smaller than the first coefficient of thermal expansion α1 and the third coefficient of thermal expansion α3.

[0030] In the third embodiment as well, the sum of the thicknesses of each of the three layers 11 to 13A (overall thickness) is set to a specific thickness (for example, 15 mm) according to the specifications of the chuck table 1. Preferably, the thickness of the ceramic porous layer 11 is set to 3 mm, taking into consideration the adsorption performance, and the sum of the thicknesses of the Invar layer 12A and the stainless steel layer 13A is 15 - 3 = 12 mm. Under these conditions, in the third embodiment, the thicknesses of each of the layers 11 to 13A are set such that the amount of strain due to temperature rise between the ceramic porous layer 11 (layer B) and the Invar layer 12A (layer A) is in the opposite direction and approximately equal to the amount of strain due to temperature rise between the Invar layer 12A and the stainless steel layer 13A. That is, in the chuck table 1 of this third embodiment, the thickness t of each layer is determined from the Young's modulus E and the coefficient of linear expansion α of each of the layers 11 to 13A, thereby minimizing thermal deformation of the chuck table 1.

[0031] Figure 10 shows the Young's modulus E and the coefficient of linear expansion α for each layer 11-13A. The length L of each layer 11-13A is set to 150 mm, which is the radius of the 300 mm wafer chuck table used in the calculation, and the temperature change ΔT is set to 1°C. The value of length L can be changed as appropriate according to the diameter of the table being manufactured. Figure 11 is a graph showing the simulation results of the relationship between the change in thickness t of the Invar layer 12A (layer A) (horizontal axis) and the changes in the strain δAB between layers A and B, and the strain δAC between layers C (vertical axis). Here, assuming that the sum of the thicknesses of the Invar layer 12A (layer A) and the stainless steel layer 13A (layer C) is 12 mm, the thickness of the Invar layer 12A (layer A) is varied to investigate the thickness of layer A at which the difference in strain (δAB-δAC) becomes approximately zero. Figure 12 shows the various physical quantities and strain amounts δAB that occur due to thermal expansion between the Invar layer 12A (layer A) and the ceramic porous layer 11 (layer B) when the material, Young's modulus E, and coefficient of thermal expansion α are set as in Figure 10, and the difference in strain amounts is approximately zero as in Figure 11. It also shows the various physical quantities and strain amounts δAC that occur due to thermal expansion between the Invar layer 12A (layer A) and the stainless steel layer 13A (layer C). The difference (change δAB-δAC) between the strain amount δAB that occurs between layers A and B and the strain amount δAC that occurs between layers A and C is approximately zero, which is 0.9 nm.

[0032] As shown in Figure 12, the difference in strain δ (change δAB-δAC) is approximately zero when the thickness t of layer A is around 2.78 mm and around 11.5 mm. However, in the case of 11.5 mm, the thickness of the stainless steel layer 13A becomes excessively small, making it difficult to manufacture, which is undesirable (12-11.5=0.5 mm or less). Therefore, in the structure shown in Figure 9, it is preferable to have a thickness t of layer A = 2.78 mm and a thickness of layer C = 9.22 mm.

[0033] As explained above, in this third embodiment as well, the chuck table is constructed with a three-layer structure consisting of a ceramic porous layer 11, an Invar layer 12A, and a stainless steel layer 13A. By optimizing the thickness of each layer, the amount of thermal strain can be reduced to almost zero. Between the Invar layer 12A (layer A) and the ceramic porous layer 11 (layer B), the former has a smaller coefficient of linear expansion, so as the temperature rises, the ceramic porous layer 11 side warps, becoming convex. On the other hand, between the Invar layer 12A (layer A) and the stainless steel layer 13A (layer C), the former has a smaller coefficient of linear expansion, so the stainless steel layer 13A side warps, becoming convex. These warps in opposite directions cancel each other out, resulting in an overall structure that is free from warping. [Fourth Embodiment] Next, the chuck table 1 of the fourth embodiment will be described with reference to Figures 13 to 16. Figure 13 is a schematic cross-sectional view of this chuck table 1. Figure 14 is a table showing various physical quantities for each layer constituting this chuck table 1.

[0034] The chuck table 1 of this fourth embodiment has a three-layer structure, viewed from the upper side, consisting of a ceramic porous layer 11, an Invar layer 12B, and a stainless steel layer 13B, and in this respect it is common to the second embodiment. The ceramic porous layer 11 of layer B (first coefficient of thermal expansion α1) may be substantially the same as the ceramic porous layer 11 of the first embodiment. However, the Invar layer 12B as layer A is made of Invar and is configured to support the lower surface of the ceramic porous layer 11. The stainless steel layer 12B has a second coefficient of thermal expansion α2 which is smaller than the first coefficient of thermal expansion α1.

[0035] The stainless steel layer 13B, which serves as layer C, is constructed using SUS630 as an example, and is configured to support the lower surface of the Invar layer 12A. The stainless steel layer 13B has a third coefficient of thermal expansion α3 that is greater than the second coefficient of thermal expansion α2.

[0036] In this fourth embodiment, as in the second embodiment, the sum of the thicknesses of each of the three layers 11 to 13B (overall thickness) is set to a specific thickness (for example, 15 mm) according to the specifications of the chuck table 1. Preferably, the thickness of the ceramic porous layer 11 is set to 3 mm, taking into consideration the adsorption performance, and the sum of the thicknesses of the Invar layer 12A and the stainless steel layer 13B is 15 - 3 = 12 mm. Under these conditions, in the fourth embodiment, the thickness of each layer is set such that the amount of strain due to temperature rise between the ceramic porous layer 11 (layer B) and the Invar layer 12B (layer A) is in the opposite direction and approximately equal to the amount of strain due to temperature rise between the Invar layer 12B and the stainless steel layer 13A. That is, in the chuck table 1 of this fourth embodiment, the thickness t of each layer is determined from the Young's modulus E and the coefficient of linear expansion α of each layer 11 to 13B, thereby minimizing thermal deformation of the chuck table 1.

[0037] Figure 14 shows the Young's modulus E and the coefficient of linear expansion α for each layer 11-13B. The length L of each layer 11-13B is set to 150 mm, which is the radius of the 300 mm wafer suction chuck table in the calculation, and the temperature change ΔT is set to 1°C. The value of length L can be changed as appropriate according to the diameter of the table being manufactured. Figure 15 is a graph showing the simulation results of the relationship between the change in thickness t of the Invar layer 12B, which is layer A (horizontal axis), and the changes in the strain amount δAB between layers A and B, and the strain amount δAC between layers C (vertical axis). Here, too, assuming that the sum of the thicknesses of the Invar layer 12B, which is layer A, and the stainless steel layer 13B, which is layer C, is 12 mm, the thickness of the stainless steel layer 12, which is layer A, is varied to investigate the thickness of layer A at which the difference in strain amount (δAB-δAC) is approximately zero. Figure 16 shows the various physical quantities and strain amounts δAB that occur due to thermal expansion between the Invar layer 12B (layer A) and the ceramic porous layer 11 (layer B) when the settings shown in Figure 14 are made, and also shows the various physical quantities and strain amounts δAC that occur due to thermal expansion between the Invar layer 12B (layer A) and the stainless steel layer 13B (layer C). The difference (change δAB-δAC) between the strain amount δAB that occurs between layers A and B and the strain amount δAC that occurs between layers A and C is -2.2 nm, which is approximately zero.

[0038] As shown in Figure 15, the difference in strain δ (change δAB-δAC) is approximately zero when the thickness t of layer A is around 3 mm and around 11.5 mm. However, in the case of 11.5 mm, the thickness of the stainless steel layer 13A becomes excessively small, making it difficult to manufacture, which is undesirable (12-11.5=0.5 mm or less). Therefore, in the structure shown in Figure 13, it is preferable to have a thickness t of layer A = 3 mm and a thickness of layer C = 9 mm.

[0039] As explained above, in this fourth embodiment as well, the chuck table is constructed with a three-layer structure consisting of a ceramic porous layer 11, an Invar layer 12B, and a stainless steel layer 13B. By optimizing the thickness of each layer, the amount of thermal strain can be reduced to almost zero. Between the Invar layer 12B (layer A) and the ceramic porous layer 11 (layer B), the former has a smaller coefficient of linear expansion, so as the temperature rises, the ceramic porous layer 11 side warps, becoming convex. On the other hand, between the Invar layer 12B (layer A) and the stainless steel layer 13B (layer C), the former has a smaller coefficient of linear expansion, so the stainless steel layer 13B side warps, becoming convex. These warps in opposite directions cancel each other out, resulting in a structure that does not warp regardless of temperature changes.

[0040] [Fifth Embodiment] Next, the chuck table 1 of the fifth embodiment will be described with reference to Figures 17 to 20. Figure 17 is a schematic cross-sectional view of this chuck table 1. Figure 18 is a table showing various physical quantities for each layer constituting this chuck table 1.

[0041] The chuck table 1 of this fifth embodiment has a three-layer structure, viewed from the upper side, consisting of a ceramic porous layer 11 as layer B, a stainless steel layer 12C as layer A, and a stainless steel layer 13C as layer B. That is, both layer A and layer B are stainless steel layers, which is different from the above embodiment. The ceramic porous layer 11 of layer B (first coefficient of thermal expansion α1) may be substantially the same as the ceramic porous layer of the first embodiment. The stainless steel layer 12C as layer A is, in this example, made of SUS303 and is configured to support the lower surface of the ceramic porous layer 11. The stainless steel layer 12C has a second coefficient of thermal expansion α2 which is larger than the first coefficient of thermal expansion α1. SUS303 is an austenitic stainless steel containing 17-19% chromium (Cr), 8-10% nickel (Ni), and trace components such as phosphorus (P), sulfur (S), manganese (Mn), and silicon (Si).

[0042] The stainless steel layer 13C, which serves as layer C, is constructed using SUS410 as an example, and is configured to support the lower surface of the stainless steel layer 12C. The stainless steel layer 13C has a third coefficient of thermal expansion α3 that is smaller than the second coefficient of thermal expansion α2.

[0043] In the fifth embodiment as well, the sum of the thicknesses of each of the three layers 11 to 13C (total thickness) is set to a specific thickness (e.g., 15 mm) according to the specifications of the chuck table 1. Preferably, the thickness of the ceramic porous layer 11 is set to 5 mm, taking into consideration the adsorption performance, and the sum of the thicknesses of the stainless steel layer 12 and the Invar layer 13C is 15 - 5 = 10 mm. Under these conditions, in the first embodiment, the thickness of each layer is set such that the amount of strain due to temperature rise between the ceramic porous layer 11 (layer B) and the stainless steel layer 12C (layer A) is in the opposite direction and approximately equal to the amount of strain due to temperature rise between the stainless steel layer 12C and the stainless steel layer 13C. That is, in the chuck table 1 of this fifth embodiment, the thickness t of each layer is determined from the Young's modulus E and the coefficient of linear expansion α of each layer 11 to 13, thereby minimizing thermal deformation of the chuck table 1.

[0044] Figure 18 shows the Young's modulus E and the coefficient of linear expansion α for each layer 11-13C. Similar to the first embodiment, the length L of each layer 11-13C is set to 150 mm, which is the radius of the 300 mm wafer suction chuck table calculated, and the temperature change ΔT is set to 1°C. The value of length L can be appropriately changed according to the diameter of the table being manufactured. Figure 19 is a graph showing the simulation results of the relationship between the change in thickness t of the stainless steel layer 12C, which is layer A (horizontal axis), and the changes in the strain amount δAB between layers A and B, and the strain amount δAC between layers C and D (vertical axis). Here, assuming that the sum of the thicknesses of the stainless steel layer 12C, which is layer A, and the stainless steel layer 13C, which is layer C, is 10 mm, the thickness of the stainless steel layer 12, which is layer A, is changed to investigate the thickness of layer A at which the difference in strain amount (δAB-δAC) becomes approximately zero. Figure 20 shows the various physical quantities and strain amounts δAB that occur due to thermal expansion between the stainless steel layer 12C (layer A) and the ceramic porous layer 11 (layer B), given the material, Young's modulus E, and coefficient of thermal expansion α as shown in Figure 18. It also shows the various physical quantities and strain amounts δAC that occur due to thermal expansion between the stainless steel layer 12C (layer A) and the stainless steel layer 13C (layer C). The difference (change δAB-δAC) between the strain amount δAB occurring between layers A and B and the strain amount δAC occurring between layers A and C is -1315.8 nm, which is not close to zero, but it is minimized to the point where the strain amount can be ignored.

[0045] As shown in Figure 19, when the thickness t of layer A is around 7 mm, the difference in strain amount δ (change amount δAB - δAC) is minimized, and the amount of strain can be made negligible.

[0046] As described above, in this fifth embodiment as well, the chuck table is constructed with a three-layer structure consisting of a ceramic porous layer 11, a stainless steel layer 12C, and a stainless steel layer 13C. By optimizing the thickness of each layer, the amount of thermal strain can be minimized to a negligible level.

[0047] [Sixth Embodiment] Next, the chuck table 1 of the sixth embodiment will be described with reference to Figures 21 to 24. Figure 21 is a schematic cross-sectional view of this chuck table 1. Figure 22 is a table showing the various physical quantities of each layer constituting this chuck table 1.

[0048] The chuck table 1 of this sixth embodiment has a three-layer structure, viewed from the upper side, consisting of a ceramic porous layer 11 as layer B, a stainless steel layer 12C as layer A, and a stainless steel layer 13C as layer B. In this respect, it is common with the fifth embodiment. The ceramic porous layer 11 of layer B (first coefficient of linear expansion α1) may be substantially the same as the ceramic porous layer of the first embodiment. The stainless steel layer 12C as layer A is, in this example, made of SUS303 and is configured to support the lower surface of the ceramic porous layer 11. The stainless steel layer 12C has a second coefficient of linear expansion α2 which is larger than the first coefficient of linear expansion α1.

[0049] The stainless steel layer 13C, which serves as layer C, is constructed using SUS410 as an example, and is configured to support the lower surface of the Invar layer 12A. The stainless steel layer 13C has a third coefficient of thermal expansion α3 that is smaller than the second coefficient of thermal expansion α2.

[0050] In the sixth embodiment, the sum of the thicknesses of each of the three layers 11 to 13C (overall thickness) is set to a specific thickness (e.g., 15 mm) according to the specifications of the chuck table 1. Preferably, the thickness of the ceramic porous layer 11 is set to 3 mm, taking into consideration the adsorption performance, and the sum of the thicknesses of the stainless steel layer 12C and stainless steel layer 13C is 15 - 3 = 12 mm. Under these conditions, in the sixth embodiment, the thickness of each layer is set such that the amount of strain due to temperature rise between the ceramic porous layer 11 (layer B) and the stainless steel layer 12C (layer A) is in the opposite direction and approximately equal to the amount of strain due to temperature rise between the stainless steel layer 12C and the stainless steel layer 13C. That is, in the chuck table 1 of this sixth embodiment, the thickness t of each layer is determined from the Young's modulus E and the coefficient of linear expansion α of each layer 11 to 13C, thereby minimizing thermal deformation of the chuck table 1.

[0051] Figure 22 shows the Young's modulus E and the coefficient of linear expansion α for each layer 11-13C. Similar to the first embodiment, the length L of each layer 11-13C is set to 150 mm, which is the radius of the 300 mm wafer suction chuck table calculated, and the temperature change ΔT is set to 1°C. The value of length L can be appropriately changed according to the diameter of the table being manufactured. Figure 23 is a graph showing the simulation results of the relationship between the change in thickness t of the stainless steel layer 12C, which is layer A (horizontal axis), and the changes in the strain amount δAB between layers A and B, and the strain amount δAC between layers C and D (vertical axis). Here, assuming that the sum of the thicknesses of the stainless steel layer 12C, which is layer A, and the stainless steel layer 13C, which is layer C, is 12 mm, the thickness of the stainless steel layer 12, which is layer A, is changed to investigate the thickness of layer A at which the difference in strain amount (δAB-δAC) becomes approximately zero. Figure 24 shows the various physical quantities and strain amounts δAB generated by thermal expansion between the stainless steel layer 12C (layer A) and the ceramic porous layer 11 (layer B) when the settings are as shown in Figure 22 and the difference in strain amounts is approximately zero as shown in Figure 23. It also shows the various physical quantities and strain amounts δAC generated by thermal expansion between the stainless steel layer 12C (layer A) and the stainless steel layer 13C (layer C). The difference (change δAB-δAC) between the strain amount δAB generated between layers A and B and the strain amount δAC generated between layers A and C can be made approximately zero, at 3.1 nm.

[0052] As shown in Figure 23, the difference (change) in strain δ becomes approximately zero when the thickness t of layer A is around 7.1 mm and around 9.5 mm. However, in the case of 9.5 mm, the stainless steel layer 13C, which serves as the substrate layer B, becomes excessively small, making it difficult to manufacture and therefore undesirable (12 - 9.5 = 2.5 mm or less). Therefore, in the structure shown in Figure 24, it is preferable to have a thickness t of layer A = 7.1 mm and a thickness of layer C = 4.9 mm.

[0053] As explained above, in this sixth embodiment as well, the chuck table is constructed with a three-layer structure consisting of a ceramic porous layer 11, a stainless steel layer 12C, and a stainless steel layer 13C. By optimizing the thickness of each layer, the amount of thermal strain can be minimized to a negligible level. Between the stainless steel layer 12C (layer A) and the ceramic porous layer 11 (layer B), the former has a larger coefficient of linear expansion, so as the temperature rises, warping occurs such that the ceramic porous layer 11 side becomes concave. On the other hand, between the stainless steel layer 12C (layer A) and the stainless steel layer 13C (layer C), the former has a larger coefficient of linear expansion, so warping occurs such that the stainless steel layer 13C side becomes concave. As these warping in opposite directions cancel each other out, an overall structure without warping can be obtained.

[0054] In the sixth embodiment, an example was shown in which the second coefficient of thermal expansion of the stainless steel layer 12, which is layer A, is larger than the first and third coefficients of thermal expansion. However, as in the third embodiment, a configuration in which the second coefficient of thermal expansion is smaller than the first and third coefficients of thermal expansion can also be adopted.

[0055] The present invention is not limited to the embodiments described above, and includes various modifications. For example, the embodiments described above are described in detail to make the present invention easier to understand, and are not necessarily limited to those having all the configurations described. Furthermore, it is possible to replace parts of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add configurations from other embodiments to the configuration of one embodiment. In addition, it is possible to add, delete, or replace parts of the configuration of each embodiment with other configurations. [Explanation of Symbols]

[0056] 1... Chuck table 11…Ceramic porous layer 12, 12B, 12C, 13A, 13B, 13C…Stainless steel layer 12A, 12B, 13... Invar layer

Claims

1. A porous body configured to support a workpiece on its upper surface, having numerous voids inside, made of ceramic material, and having a first coefficient of linear expansion, A first layer having a second coefficient of linear expansion is configured to support the lower surface of the porous body, A second layer having a third coefficient of thermal expansion is configured to support the lower surface of the first layer. Equipped with, A chuck table in which the second coefficient of thermal expansion is greater than the first coefficient of thermal expansion and the third coefficient of thermal expansion, or less than the first coefficient of thermal expansion and the third coefficient of thermal expansion.

2. The chuck table according to claim 1, wherein the thicknesses of the porous body, the first layer, and the second layer are set such that the amount of strain between the porous body and the first layer due to temperature changes is equal to the amount of strain between the first layer and the second layer in the opposite direction.

3. The first layer is made of stainless steel, The chuck table according to claim 1, wherein the second layer is made of Invar material.

4. The thickness of the porous material is 5 mm. The sum of the thicknesses of the first and second layers is 10 mm. The chuck table according to claim 3, wherein the thickness of the first layer is set such that the amount of strain due to temperature rise between the porous body and the first layer is equal to the amount of strain due to temperature rise between the first layer and the second layer.

5. The material of the first layer is SUS630. The chuck table according to claim 4, wherein the thickness of the first layer is 2.85 mm.

6. The material of the first layer is SUS410. The chuck table according to claim 4, wherein the thickness of the first layer is 2.55 mm.

7. The first layer is made of Invar material, The chuck table according to claim 1, wherein the second layer is made of stainless steel.

8. The thickness of the porous material is 3 mm. The sum of the thicknesses of the first and second layers is 12 mm. The chuck table according to claim 7, wherein the thickness of the first layer is set such that the amount of strain due to temperature rise between the porous body and the first layer is equal to the amount of strain due to temperature rise between the first layer and the second layer.

9. The material of the second layer is SUS630. The chuck table according to claim 8, wherein the thickness of the first layer is 2.78 mm.

10. The material of the second layer is SUS430. The chuck table according to claim 8, wherein the thickness of the first layer is 3.13 mm.

11. The first layer is made of a first stainless steel material, The chuck table according to claim 1, wherein the second layer is made of a second stainless steel different from the first stainless steel.

12. The thickness of the porous material is 3 mm. The sum of the thicknesses of the first and second layers is 12 mm. The chuck table according to claim 11, wherein the thickness of the first layer is set such that the amount of strain between the porous body and the first layer due to the temperature rise is equal to the amount of strain between the first layer and the second layer.

13. The material of the first layer is SUS303. The material of the second layer is SUS410. The chuck table according to claim 11, wherein the thickness of the first layer is 7 mm.

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