SILICON WAFER

Abstract

A method of reducing warp imparted to a silicon wafer having a (110) plane orientation and a <111> notch orientation by anisotropic film stress of a multilayer film that is to be formed on a surface of the silicon wafer, that includes forming the multilayer film on a surface of the silicon wafer in an orientation so that a direction in which the warp of the wafer will be greatest coincides with a direction in which Young's modulus of a crystal orientation of the silicon wafer is greatest. Also, a method of reducing warp imparted to a silicon wafer having a (111) plane orientation by isotropic film stress of a multilayer film to be formed on a surface of the silicon wafer, that includes, prior to forming the multilayer film, causing the silicon wafer to have an oxygen concentration of 8.0×10.sup.17 atoms/cm.sup.3 or more (ASTM F-121, 1979).

Claims

1. A method of reducing an amount of warp imparted to a silicon wafer having a (110) plane orientation and a <111> notch orientation by anisotropic film stress of a multilayer film that is to be formed on a surface of the silicon wafer, the method comprising: forming the multilayer film on a surface of the silicon wafer in an orientation so that a direction in which the warp of the wafer will be greatest coincides with a direction in which Young's modulus of a crystal orientation of the silicon wafer is greatest.

2. The method of claim 1, wherein the silicon wafer has an oxygen concentration of 6.0×10.sup.17 atoms/cm.sup.3 or more (ASTM F-121, 1979) prior to forming the multilayer film.

3. The method of claim 1, wherein the multilayer film is for a semiconductor device layer that includes a 3DNAND flash memory.

4. A method of reducing an amount of warp imparted to a silicon wafer having a (111) plane orientation by isotropic film stress of a multilayer film that is to be formed on a surface of the silicon wafer, the method comprising: prior to forming the multilayer film, causing the silicon wafer to have an oxygen concentration of 8.0×10.sup.17 atoms/cm.sup.3 or more (ASTM F-121, 1979).

5. The method of claim 4, wherein the multilayer film is for a semiconductor device layer that includes a 3DNAND flash memory.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 is a schematic plan view illustrating the configuration of a silicon wafer according to a first embodiment of the present invention.

[0026] FIG. 2 is a schematic plan view illustrating the configuration of a silicon wafer according to a second embodiment of the present invention.

[0027] FIG. 3 is a schematic view for explaining the type of warp generated when a film stress is applied to a flat silicon wafer, in which (a) illustrates a bowl-shaped warp, and (b) illustrates a saddle-shaped warp.

[0028] FIG. 4 is a schematic view for explaining a difference in how the wafer is warped due to a film stress applied to the silicon wafer.

[0029] FIG. 5 is a schematic perspective view illustrating an example of a film formation pattern that applies an anisotropic film stress to a silicon wafer.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

[0031] FIG. 1 is a schematic plan view illustrating the configuration of a silicon wafer according to a first embodiment of the present invention.

[0032] As illustrated in FIG. 1, a silicon wafer 1A is a silicon wafer for a highly laminated semiconductor device in which there is formed a multilayered film constituting a semiconductor device layer, such as a 3DNAND flash memory, on one main surface thereof in a device process and which is warped in a bowl shape due to an isotropic film stress of the multilayered film. The plane orientation of the silicon wafer 1A is (111), and the notch orientation thereof is <110> or <112>. That is, a notch 2 is formed in a <110> or <112> direction.

[0033] The oxygen concentration of the silicon wafer 1A is preferably 8.0×10.sup.17 atoms/cm.sup.3 or more (ASTM F-121, 1979). The Young's modulus of a (111) silicon wafer has oxygen concentration dependency, and thus it is possible to enhance warp reduction effect when the oxygen concentration is 8.0×10.sup.17 atoms/cm.sup.3 or more.

[0034] FIG. 2 is a schematic plan view illustrating the configuration of a silicon wafer according to a second embodiment of the present invention.

[0035] As illustrated in FIG. 2, a silicon wafer 1B is a silicon wafer for a highly integrated semiconductor device in which there is formed a multilayered film constituting a semiconductor device layer on one main surface thereof in a device process and which is warped in a saddle shape due to an anisotropic film stress of the multilayered film. The plane orientation of the silicon wafer 1B is (110), and the notch orientation thereof is <111>. That is, a notch 2 is formed in a <111> direction.

[0036] The oxygen concentration of the silicon wafer 1B is preferably 6.0×10.sup.17 atoms/cm.sup.3 or more (ASTM F-121, 1979). The Young's modulus of a (110) silicon wafer has oxygen concentration dependency, and thus it is possible to enhance the warp reduction effect when the oxygen concentration is 6.0×10.sup.17 atoms/cm.sup.3 or more.

[0037] FIG. 3 is a schematic view for explaining the type of warp generated when a film stress is applied to a flat silicon wafer, in which (a) illustrates a bowl-shaped warp, and (b) illustrates a saddle-shaped warp.

[0038] The silicon wafer can be warped in a bowl shape or a saddle shape. When an isotropic film stress is applied to a flat silicon wafer, a bowl-shaped warp is generated as illustrated in FIG. 3(a); while when an anisotropic film stress is applied to a flat silicon wafer, a saddle-shaped warp is generated as illustrated in FIG. 3(b). The bowl shape refers to a shape in which the entire outer periphery of the wafer is displaced upward or downward relative to the center portion of the wafer. The saddle shape refers to a shape in which both end portions of the wafer in one of the X-and Y-directions thereof are displaced upward (or downward) relative to the center portion of the wafer and both end portions in other one of the X- and Y-directions are displaced downward (or upward) relative to the center portion.

[0039] The bowl shape refers to a shape in which the entire outer periphery of the wafer is displaced upward or downward relative to the center portion of the wafer. The saddle shape refers to a shape in which both end portions of the wafer in one of the X-and Y-directions thereof are displaced upward (or downward) relative to the center portion of the wafer and both end portions in other one of the X- and Y-directions are displaced downward (or upward) relative to the center portion.

[0040] FIG. 4 is a schematic view for explaining a difference in how the wafer is warped due to a film stress applied to the silicon wafer.

[0041] As illustrated in FIG. 4, when a laminated film such as a wiring layer constituting a semiconductor device is formed on the surface of the silicon wafer, a film stress is generated in the silicon wafer, whereby a bowl-shaped warp as illustrated in (a) or a saddle-shaped warp as illustrated in (b) is generated. When such a warp of the wafer increases, various problems arise in the subsequent processes.

[0042] The reason that the silicon wafer is warped into a saddle shape during a device process is that the signs of the film stresses of the films formed on the silicon wafer differ from each other to generate anisotropy of the film stress. For example, as illustrated in FIG. 4, when, in addition to a wiring layer in which a compressive stress in the X-direction is dominant, a wiring layer having a tensile stress in the Y-direction perpendicular to the X-direction is formed, the compressive stress in the X-direction is intensified, with the result that the silicon wafer is warped in a saddle shape.

[0043] The Young's modulus of a silicon crystal varies depending on a crystal orientation, that is, it has orientation dependency. Specifically, the Young's modulus of a silicon crystal is 130 MPa in a [100] direction, 170 MPa in a [110] direction, and 189 MPa in a [111] direction. The smaller the Young's modulus is, the easier deformation occurs. When the wafer is warped in a saddle shape, coincidence between a direction in which the warp is maximum and the direction of a crystal orientation in which Young's modulus is small makes the wafer more apt to be warped to increase the warp amount. Conversely, coincidence between the direction in which the warp is maximum and the direction of a crystal orientation in which Young's modulus is large makes the wafer less likely to be warped to reduce the warp amount.

[0044] Thus, in the present embodiment, when the wafer is warped in a saddle shape in a device process, the silicon wafer 1B in which the plane orientation having a large orientation dependency of the warp is (110) and the notch direction is <111> is used (see FIG. 2). Normally, a semiconductor device is formed in accordance with the notch direction in a device process, so that by matching the direction of the wiring layer to the notch direction, it is possible to make a direction in which the warp of the wafer becomes large coincide with the direction of a crystal orientation in which Young's modulus is large, whereby an effect of reducing the saddle-shaped warp can be enhanced.

[0045] Further, when the wafer is warped in a bowl shape in a device process, the silicon wafer 1A in which the plane orientation having no orientation dependency of the warp is (111) is used (see FIG. 1). By making the Young's modulus of the silicon wafer isotropic in conformity to the isotropic film stress to be applied in a device process, an effect of reducing the bowl-shaped warp can be enhanced.

[0046] While the present invention has been described based on the preferred embodiment, the present invention is not limited to the above embodiment, and various modifications may be made within the scope of the present invention. Accordingly, all such modifications are included in the present invention.

[0047] For example, although the silicon wafer manufacturing method suitable for manufacture of a 3DNAND has been described in the above embodiment, the present invention is not limited to this but may be applied to silicon wafers for various semiconductor devices in which the wafer may be warped due to the film stress.

EXAMPLES

Example 1

[0048] Silicon wafer samples #1 to #16 having different plane orientations and different notch orientations were prepared. Each of the wafer samples was grown by a CZ method and had a diameter of 300 mm and a thickness of 775 μm. The plane orientations of the wafer samples were of three types of (100), (110), and (111). The notch orientation of the wafer having the (100) plane orientation included two types of <110> and <100>. The notch orientation of the wafer having the (110) plane orientation included two types of <110> and <111>. The notch orientation of the wafer having the (111) plane orientation included two types of <110> and <112>. Variations in both the plane orientation and notch orientation among the wafers used were within ±1°.

[0049] Then, the oxygen concentration of each wafer was measured. The oxygen concentration was measured using a Fourier transform infrared spectroscopy (FT-IR) defined in ASTM F-121, 1979.

[0050] Then, a silicon oxide film having a thickness of 2 μm was formed on the main surfaces of the wafer samples #1 to #16 by a CVD process. As a result, a convex bowl-shaped warp was generated. The measurement results concerning the warp amounts (WARP) of the wafer samples are shown in Table 1.

TABLE-US-00001 TABLE 1 Oxygen concentration Wafer Wafer plane Notch (×10.sup.17 Warp amount sample orientation orientation atoms/cm.sup.3) (μm) #1 (100) <110> 8.5 612 #2 (100) <110> 13.2 608 #3 (100) <100> 8.4 611 #4 (100) <100> 13.0 605 #5 (110) <110> 7.2 789 #6 (110) <110> 12.9 762 #7 (110) <111> 8.2 785 #8 (110) <111> 13.5 765 #9 (111) <110> 6.3 507 #10 (111) <110> 8.1 451 #11 (111) <110> 10.6 443 #12 (111) <110> 12.5 441 #13 (111) <110> 13.8 448 #14 (111) <112> 6.0 501 #15 (111) <112> 8.2 436 #16 (111) <112> 11.9 440

[0051] As is clear from Table 1, in the wafer samples #1 to #4 having the (100) plane orientation, a large warp of about 600 μm is generated irrespective of the substrate oxygen concentration and notch orientation.

[0052] In the wafer samples #5 to #8 having the (110) plane orientation, a large warp of about 770 μm is generated irrespective of the substrate oxygen concentration and notch orientation. Although the warp amount is smaller as the oxygen concentration becomes higher, there is found no significant difference.

[0053] In the wafer samples #9 to #16 having the (111) plane orientation, the warp amount is reduced as compared to the wafers having the (100) and (110) plane orientations, irrespective of the notch orientation. Further, the wafer warp has oxygen concentration dependency, and the warp reduction effect is particularly high when the oxygen concentration is 8.0×10.sup.17 atoms/cm.sup.3 or more. This is presumably because increase in the oxygen concentration improves the Young's modulus of a silicon crystal.

[0054] The Young's modulus of a silicon crystal has orientation dependency in which it varies depending on the crystal orientation, so that when such a film stress with little anisotropy as to cause a bowl-shaped warp is applied, resistance to deformation is thought to be changed depending on the plane orientation. From the above results, it can be said that it is possible to suppress the warp to be a problem in a device process by using the (111) wafer.

Example 2

[0055] As in Example 1, silicon wafer samples #17 to #31 having different plane orientations and different notch orientations were prepared, and the oxygen concentrations thereof were measured.

[0056] Then, a silicon oxide film having a thickness of 1 μm was formed on the main surfaces of the wafer samples #17 to #31 by a CVD process, followed by partial etching using a mask, and then a silicon nitride film having a thickness of 0.7 μm was formed by a CVD process, followed by partial etching using a mask, whereby a film as illustrated in FIG. 5 was produced. For example, in a (100) wafer of sample #17, the silicon oxide film has a rectangular pattern elongated in a <110> direction, and the silicon nitride film has a rectangular pattern elongated in a direction perpendicular to the longitudinal direction of the silicon oxide film. By the pattern obtained by synthesizing the silicon oxide and nitride patterns, an anisotropic film stress is generated in the silicon wafer, causing a saddle-shaped warp. The measurement results concerning the warp amounts (WARP) of the wafer samples are shown in Table 2.

TABLE-US-00002 TABLE 2 Oxygen concentration Wafer Wafer plane Notch (×10.sup.17 Warp amount sample orientation orientation atoms/cm.sup.3) (μm) #17 (100) <110> 5.7 478 #18 (100) <110> 13.1 464 #19 (100) <100> 5.5 618 #20 (100) <100> 13.3 621 #21 (110) <110> 5.7 553 #22 (110) <110> 7.8 559 #23 (110) <110> 12.9 552 #24 (110) <111> 5.6 398 #25 (110) <111> 6.3 325 #26 (110) <111> 10.9 318 #27 (110) <111> 12.9 312 #28 (111) <110> 5.4 513 #29 (111) <110> 12.1 520 #30 (111) <112> 5.9 516 #31 (111) <112> 12.3 512

[0057] As is clear from Table 2, in the wafer samples #17 to #20 having the (100) plane orientation, the warp amount varies depending on the substrate oxygen concentration or notch orientation. Particularly, the warp reduction effect is higher in the <110> notch than in the <100> notch. However, the <110> notch of the (100) wafer is the standard orientation of a wafer.

[0058] In the wafer samples #21 to #27 having the (110) plane orientation, the warp amount varies depending on the substrate oxygen concentration or notch orientation. Particularly, the warp reduction effect is high in the <111> notch. Further, among the wafer samples #24 to #27 having the <111> notch, the samples #25, #26, and #27 having an oxygen concentration of 6×10.sup.17 atoms/cm.sup.3 or more have a particularly high warp reduction effect.

[0059] In the wafer samples #28 to #31 having the (111) plane orientation, a large warp of about 500 μm is generated irrespective of the substrate oxygen concentration and notch orientation. However, the <110> notch of the (111) wafer is the standard orientation of a wafer.

DESCRIPTION OF THE SYMBOLS

[0060] 1A, 1B Silicon wafer [0061] 2 notch