Ion irradiation method

Abstract

To suppress a mask from shifting in position relative to a semiconductor substrate.SOLUTION: An ion irradiation method comprises: positioning a semiconductor substrate and a mask plate in overlapping relation (S12); temporarily fixing the semiconductor substrate and mask plate by applying first fixing force in the direction in which the semiconductor substrate and mask plate overlap each other (S14); using a fixing tool to apply second fixing force smaller than the first fixing force in the direction in which the semiconductor substrate and mask plate overlap each other with the first fixing force applied (S16); removing the first fixing force and then fixing the semiconductor substrate and mask plate with the fixing tool applying the second fixing force (S18); and irradiating the semiconductor substrate with ions through the mask plate fixed with the fixing tool (S20).SELECTED DRAWING: Figure 16

Description

[Technical Field]

[0001] The present invention relates to an ion irradiation method. [Background technology]

[0002] A technique for improving the characteristics of a semiconductor device by irradiating a semiconductor substrate on which a semiconductor device is formed with light ions such as hydrogen or helium to form defects in the semiconductor substrate is known. To form defects only in a partial region of the semiconductor substrate, a mask with an opening formed in a partial region is used. For example, the mask is positioned relative to the semiconductor substrate by using a magnet to fix the mask holder that holds the mask to a wafer holder that holds the semiconductor substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6914600 Summary of the Invention [Problem to be solved by the invention]

[0004] When a magnet is used to secure the wafer holder and mask holder, the magnetic force acting in the in-plane direction along the surface of the semiconductor substrate immediately before the holder is secured can cause the mask holder to shift in the in-plane direction relative to the wafer holder. If the mask is secured in a position that is misaligned in the in-plane direction relative to the semiconductor substrate, defects cannot be formed in the desired area, leading to a decrease in the yield of the ion irradiation process.

[0005] An exemplary object of an embodiment of the present invention is to provide a technique for suppressing misalignment of a mask with respect to a semiconductor substrate. [Means for solving the problem]

[0006] An ion irradiation method according to one embodiment of the present invention includes aligning a semiconductor substrate and a mask plate so that they overlap; applying a first fixing force in the direction in which the semiconductor substrate and the mask plate overlap to temporarily fix the semiconductor substrate and the mask plate; while the first fixing force is applied, applying a second fixing force smaller than the first fixing force in the direction in which the semiconductor substrate and the mask plate overlap using a fixing jig; releasing the first fixing force and fixing the semiconductor substrate and the mask plate using the fixing jig that applies the second fixing force; and irradiating ions toward the semiconductor substrate through the mask plate fixed by the fixing jig.

[0007] Any combination of the above components or mutual substitution of the components or expressions of the present invention between methods, devices, systems, etc. are also valid aspects of the present invention. [Effects of the Invention]

[0008] According to one aspect of the present invention, it is possible to suppress misalignment of a mask with respect to a semiconductor substrate. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating a schematic configuration of an ion irradiation system. [Figure 2] FIG. 10 is a diagram showing an example of a transport plate that supports a masked wafer. [Figure 3] FIG. 1 is a plan view schematically showing a masked wafer according to an embodiment. [Figure 4] 1 is a cross-sectional view schematically showing a masked wafer according to an embodiment. [Figure 5] FIG. 2 is a plan view schematically illustrating a wafer holder. [Figure 6] FIG. 2 is a perspective view schematically illustrating a fixing jig. [Figure 7] 10 is a cross-sectional view schematically illustrating an enlarged portion of a fixture including a protruding member. [Figure 8] FIG. 1 is an external view schematically illustrating an alignment device. [Figure 9]FIG. 2 is a plan view schematically showing the configuration of the lower surface of the mask holder. [Figure 10] 10A to 10C are diagrams illustrating a temporary fixing step using an alignment device. [Figure 11] 10A to 10C are diagrams schematically illustrating a process of attaching a fixing jig. [Figure 12] FIG. 2 is a plan view schematically showing a transport plate. [Figure 13] FIG. 4 is a side view schematically showing a part of the transport plate. [Figure 14] FIG. 2 is a plan view schematically showing pin holes of a wafer holder. [Figure 15] FIG. 2 is a plan view schematically showing a masked wafer attached to a transport plate. [Figure 16] 3 is a flowchart illustrating an example of an ion irradiation method according to an embodiment. [Figure 17] FIG. 10 is a cross-sectional view schematically showing a masked wafer according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments for carrying out the present invention will be described in detail. Note that the configurations described below are examples and do not limit the scope of the present invention in any way. Furthermore, in the description of the drawings, the same elements are given the same reference numerals, and duplicate explanations will be omitted as appropriate. Furthermore, in the drawings referred to in the following description, the size and thickness of each component are for the convenience of explanation and do not necessarily represent the actual dimensions or ratios.

[0011] 1 is a diagram illustrating a schematic configuration of an ion irradiation system 10. The ion irradiation system 10 includes an accelerator 12, a wafer transport device 14, and a beam transport duct 16. The ion irradiation system 10 is configured to irradiate a wafer 26, which is a semiconductor substrate, with ions.

[0012] The accelerator 12 accelerates the ion beam and emits it to the outside. The accelerator 12 may be, for example, a cyclotron-type or Van de Graaff-type device. The wafer transport device 14 includes a storage unit (not shown) that stores multiple transport plates 18, an irradiation chamber 20 in which one transport plate 18 removed from the storage unit is irradiated with an ion beam, and a moving mechanism 22 that moves the transport plate 18 between the storage unit and the irradiation chamber 20. The transport plate 18 can carry multiple wafers 26. In the irradiation chamber 20, the multiple wafers 26 loaded on the transport plate 18 are sequentially irradiated with the ion beam. The beam transport duct 16 guides the ion beam extracted from the accelerator 12 to the wafer transport device 14. The beam transport duct 16 includes a vacuum pump that maintains a vacuum inside the duct through which the ion beam is transported, and an electromagnetic coil for correcting the irradiation direction of the ion beam.

[0013] The ion irradiation system 10 is configured to be able to adjust various parameters related to the ion beam, such as the ion species, acceleration energy, ion irradiation amount (beam current, irradiation time), and ion irradiation direction. The ion species used for ion irradiation include ionized atoms of at least one type selected from the group consisting of H, He, B, C, N, O, Ne, Si, Ar, Kr, and Xe. Specifically, for example, 1 H + , 2 H + , 3 He 2+ , 4 He 2+ The ion irradiation system 10 may irradiate ions at an acceleration energy of 0.001 MeV or more, or 0.1 MeV or more. The ion irradiation system 10 may irradiate ions at an acceleration energy of 100 MeV or less, or 30 MeV or less.

[0014] The wafer 26 onto which the ions are irradiated is typically a circular silicon wafer, but the shape and material of the wafer 26 are not limited thereto. The wafer 26 may have a diameter of, for example, 300 mm or less, such as 300 mm, 250 mm, 200 mm, or 150 mm. The wafer 26 may have a thickness of, for example, 0.05 mm to 1.50 mm.

[0015] When ions are irradiated onto the wafer 26, the ions reach a certain depth within the wafer. At this time, lattice defects are formed in the vicinity of the ions, disrupting the crystal regularity (periodicity). In such regions with many lattice defects, electrons are more likely to scatter, hindering their movement. In other words, the resistivity increases in regions where localized lattice defects are generated by ion irradiation. By adjusting the above-mentioned parameters in the ion irradiation system 10, the in-plane position, depth position, depth width, and resistivity of the defect layer within the wafer can be appropriately set. The defect layer obtained by ion irradiation can be used for various purposes, such as forming a carrier lifetime control layer in addition to forming a high-resistivity region.

[0016] 2 is a diagram showing an example of a transfer plate 18 supporting a masked wafer 23. The transfer plate 18 is configured to transfer a plurality of masked wafers 23 in an upright position for ion irradiation. The plurality of masked wafers 23 are arranged in a horizontal row and held at respective predetermined positions on the transfer plate 18.

[0017] The masked wafer 23 is formed by a wafer holder 24, a mask plate 25, and a wafer 26. The wafer holder 24 supports the mask plate 25 and the wafer 26. The mask plate 25 is positioned so as to overlap the wafer 26. The wafer 26 is positioned between the wafer holder 24 and the mask plate 25. The mask plate 25 and the wafer 26 are fixed to the wafer holder 24 by a fixing jig (not shown in FIG. 2 ), which will be described later. The wafer holder 24 supports the mask plate 25 and the wafer 26, which are fixed by the fixing jig, to form the masked wafer 23. A plurality of masked wafers 23 can be loaded on one transfer plate 18.

[0018] The mask plate 25 is a disk-shaped member large enough to cover the wafer 26. The mask plate 25 is made of metals such as aluminum (Al), stainless steel (SUS), nickel (Ni), tungsten (W), molybdenum (Mo), titanium (Ti), and alloys thereof, as well as silicon (Si), resins, and the like. However, the shape and material of the mask plate 25 are not limited to these. For example, if the wafer 26 has a rectangular or other planar shape, the mask plate 25 may also have a planar shape that matches this.

[0019] The mask plate 25 has an aperture pattern that allows the irradiated ions to pass toward the wafer 26, and an alignment aperture that is used for alignment with the wafer 26. An alignment mark is provided on the front surface of the wafer 26 (the surface that is irradiated with ions). The mask plate 25 and the wafer 26 are aligned so that the alignment mark on the wafer 26 matches the position of the alignment aperture on the mask plate 25. The aligned mask plate 25 and wafer 26 are fixed to the wafer holder 24 while maintaining this aligned state.

[0020] The moving mechanism 22 is configured to move the transfer plate 18 at least in the horizontal direction. The moving mechanism 22 can move the transfer plate 18 so that all of the wafers 26 mounted on the transfer plate 18 are sequentially irradiated with the ion beam. When the ion irradiation process is completed, the moving mechanism 22 engages the shaft end 32a of the transfer shaft 32 with the engagement portion 30 provided at the end of the transfer plate 18, and returns the transfer plate 18 to the accommodation portion. Then, the moving mechanism 22 loads the next transfer plate 18 into the irradiation chamber 20.

[0021] The wafer holder 24 is supported by the transfer plate 18 so as to stand perpendicular to the horizontal plane. The mask plate 25 and wafer 26 fixed to the wafer holder 24 are also supported by the transfer plate 18 so as to stand perpendicular to the horizontal plane. The ion beam is incident on the mask plate 25 along the horizontal plane and is irradiated onto the wafer 26 through the mask plate 25. If necessary, the transfer plate 18 may be configured to transfer the wafer holder 24, mask plate 25, and wafer 26 so as to stand at an angle to the horizontal plane.

[0022] 3 is a plan view schematically showing a masked wafer 23 according to an embodiment. The masked wafer 23 includes a wafer holder 24, a mask plate 25, a wafer 26, and a plurality of fixing jigs 28. In the example shown, two fixing jigs 28 are provided, and the two fixing jigs 28 are attached to both sides of the center C of the wafer holder 24. One fixing jig 28 is located on the upper edge 24a when the wafer holder 24 is upright, and the other fixing jig 28 is located on the lower edge 24b. The two fixing jigs 28 are located at both ends of the diameter of the mask plate 25 and the wafer 26.

[0023] Fixing jig 28 sandwiches wafer holder 24, mask plate 25, and wafer 26, thereby fixing mask plate 25 and wafer 26 to wafer holder 24. Fixing jig 28 has protruding members 35 that can protrude toward mask plate 25, and when protruding members 35 abut against mask plate 25, wafer holder 24, mask plate 25, and wafer 26 are sandwiched between fixing jig 28. The magnitude of the fixing force by fixing jig 28 is controlled, for example, by the amount of protrusion of protruding members 35.

[0024] The wafer holder 24 has an extension 36 on the outside of the mask plate 25. The extension 36 extends to the left and right of the wafer holder 24 and is divided into a left region 36a and a right region 36b, with the location of the fixing jig 28 as the boundary. An opening 38 is provided in the left region 36a near the top edge 24a. The left region 36a has a thin elongated portion 40 that extends radially outward from the opening 38 (to the upper left of the wafer holder 24). The thin elongated portion 40 can be used as a handle when an operator holds the wafer holder 24.

[0025] The wafer holder 24 is provided with a plurality of pin holes 42. One of the two pin holes 42 is formed in the right region 36b near the top edge 24a, and the other pin hole 42 is formed in the left region 36a near the bottom edge 24b. The two pin holes 42 are positioned equidistant from the center C of the wafer holder 24. In this way, the pin holes 42 are arranged diagonally in the extension portion 36 of the wafer holder 24.

[0026] Fig. 4 is a cross-sectional view showing a schematic diagram of a masked wafer according to an embodiment. Fig. 4 corresponds to the cross section AA in Fig. 3. Fig. 5 is a schematic plan view of wafer holder 24. Fig. 5 shows wafer holder 24 with mask plate 25, wafer 26, and fixture 28 removed.

[0027] As shown in FIG. 4, the wafer holder 24 has a bottom portion 24c and an outer frame portion 24d. As shown in FIG. 5, the outer periphery of the wafer holder 24 is formed by the outer frame portion 24d and an extension portion 36. The wafer holder 24 is a plate-like member in which the bottom portion 24c, the outer frame portion 24d, and the extension portion 36 are integrally formed. The extension portion 36 is a portion that is located outside the mask plate 25 in a plan view when the mask plate 25 is fixed to the wafer holder 24 by the fixing jig 28 and does not overlap with the mask plate 25. The outer frame portion 24d is a portion that overlaps with the mask plate 25 or the fixing jig 28 and is a portion that is not visible from the outside in FIG. 4. As shown in FIG. 5, a left region 36a and a right region 36b of the extension portion 36 are connected by the outer frame portion 24d.

[0028] The mask plate 25 has a mask front surface 25a, a mask back surface 25b, and a mask side surface 25c. The mask front surface 25a is the surface onto which the ion beam is incident and is located on the opposite side from the wafer holder 24. The mask back surface 25b is the surface facing away from the mask front surface 25a and faces the wafer 26. The mask side surface 25c connects the mask front surface 25a and the mask back surface 25b and determines the outer shape of the mask plate 25.

[0029] The wafer 26 has a wafer front surface 26a, a wafer back surface 26b, and a wafer side surface 26c. The wafer front surface 26a is the surface onto which the ion beam is incident and faces the mask back surface 25b. A semiconductor device (e.g., an integrated circuit) including semiconductor elements such as transistors and diodes is formed on the wafer front surface 26a. The wafer back surface 26b is the surface facing away from the wafer front surface 26a and faces the bottom 24c of the wafer holder 24. The wafer side surface 26c connects the wafer front surface 26a and the wafer back surface 26b and determines the outer shape of the wafer 26.

[0030] In the wafer holder 24, a wafer holder recess 46 capable of accommodating a wafer 26 is formed by a bottom 24c and an outer frame 24d. The wafer holder recess 46 has an opening corresponding to the outer diameter of the wafer 26, and the wafer side surface 26c is in contact with the outer frame 24d or is surrounded by the outer frame 24d with a small gap. The depth of the wafer holder recess 46 is, for example, approximately 1 mm to 5 mm.

[0031] The wafer holder recess 46 is provided with a wafer holder protrusion 48 that is formed integrally with and adjacent to the bottom 24c and outer frame 24d of the wafer holder 24. The wafer holder protrusion 48 is formed in a ring shape that corresponds to the outer diameter of the wafer 26. The wafer holder protrusion 48 contacts the outer peripheral region of the wafer back surface 26b. The wafer holder protrusion 48 separates the wafer back surface 26b from the bottom 24c of the wafer holder 24, preventing the wafer back surface 26b and the bottom 24c of the wafer holder 24 from contacting each other. The height of the wafer holder protrusion 48 is, for example, approximately 0.5 mm to 2 mm.

[0032] The masked wafer 23 further includes a spacer member 44 disposed between the outer peripheral region of the wafer 26 and the mask plate 25. The spacer member 44 is a ring-shaped member corresponding to the outer diameter of the wafer 26. The inner diameter of the spacer member 44 is smaller than the outer diameter of the wafer 26. The outer diameter of the spacer member 44 is the same as or larger than the outer diameter of the wafer 26. The radial width of the spacer member 44 is, for example, approximately 2 mm to 6 mm. In this case, the inner diameter of the spacer member 44 is approximately 2 mm to 6 mm smaller than the outer diameter of the wafer 26, and the outer diameter of the spacer member 44 is approximately 2 mm to 6 mm larger than the outer diameter of the wafer 26.

[0033] The spacer member 44 contacts the outer peripheral region of the wafer front surface 26a and the outer peripheral region of the mask back surface 25b. The spacer member 44 separates the mask back surface 25b and the wafer front surface 26a, preventing them from contacting each other. The upper surface of the spacer member 44 that contacts the mask back surface 25b is slightly higher than the outer frame portion 24d of the wafer holder 24. The spacer member 44 has a thickness of, for example, about 0.5 mm to 2 mm.

[0034] Here, the peripheral region of wafer 26 refers to a region approximately 1 mm to 3 mm from wafer side surface 26c, where no semiconductor devices are formed. Therefore, even if spacer member 44 or wafer holder protrusion 48 contacts wafer 26 in the peripheral wafer region, there is little effect on the semiconductor devices formed on wafer 26. Furthermore, providing spacer member 44 and wafer holder protrusion 48 prevents wafer holder 24 and mask plate 25 from contacting the inner wafer region where the semiconductor devices are formed, and thus preventing damage to the inner wafer region.

[0035] Fixing jig 28 is attached so as to sandwich the outer peripheries of mask plate 25 and wafer holder 24. Fixing jig 28 fixes mask plate 25 and wafer 26 to wafer holder 24 so as not to displace relative to each other in the in-plane direction, thereby forming masked wafer 23. Fixing jig 28 has a U-shape or a sideways U-shape. Fixing jig 28 includes protruding member 35, wafer holder-side arm 50, mask-side arm 52, and arm connecting portion 54. FIG. 6 is a perspective view schematically showing fixing jig 28.

[0036] The wafer holder side arm 50 is a portion that comes into contact with the bottom 24c of the wafer holder 24, and extends in the in-plane direction of the wafer 26. The mask side arm 52 is a portion that extends in the in-plane direction of the wafer 26, away from the mask front surface 25a of the mask plate 25. The mask side arm 52 is provided with a protruding member 35 that protrudes toward the mask plate 25. The arm connection portion 54 is a portion that connects the wafer holder side arm 50 and the mask side arm 52, and extends in the thickness direction of the wafer holder 24, mask plate 25, and wafer 26.

[0037] The masked wafer 23 further includes a protective plate 34. The protective plate 34 is provided between the protruding members 35 and the mask plate 25, and contacts the outer peripheral region of the mask front surface 25a and the tip members 35b of the protruding members 35. The protective plate 34 prevents the tip members 35b of the protruding members 35 from contacting the mask front surface 25a. The protective plate 34 prevents the tip members 35b of the protruding members 35 from hitting the mask front surface 25a, thereby causing scratches or dents on the mask front surface 25a. The protective plate 34 has a thickness of, for example, about 0.2 mm to 1 mm.

[0038] The protruding member 35 can protrude from the mask-side arm 52 toward the protective plate 34. The protruding member 35 can protrude along an axis extending in the direction in which the wafer 26 and the mask plate 25 overlap (i.e., the thickness direction). The protruding member 35 is provided at a position overlapping the outer circumferential region of the wafer 26. The wafer holder protrusion 48, the wafer outer circumferential region, the spacer member 44, the mask outer circumferential region, the protective plate 34, and the protruding member 35 are aligned on the axis extending in the protruding direction of the protruding member 35. This allows the fixing jig 28 to firmly clamp and fix the wafer holder 24, the wafer 26, the spacer member 44, the mask plate 25, and the protective plate 34.

[0039] 7 is a cross-sectional view schematically showing an enlarged portion of the fixing jig 28 including the protruding member 35. The mask side arm 52 has a screw hole 52a. The protruding member 35 includes a main body member 35a that is a screw that screws into the screw hole 52a, and a tip member 35b that abuts against the protective plate 34. When the protruding member 35 is rotated relative to the mask side arm 52 as indicated by arrow 62, the protruding member 35 screws into the screw hole 52a and protrudes toward the protective plate 34, and when rotated in the opposite direction, the protruding member 35 moves away from the protective plate 34.

[0040] A recess is formed at the lower end of the main body member 35a to accommodate the tip member 35b. The tip member 35b has a flat upper surface, a flat lower surface, and a convex curved (e.g., spherical) side surface connecting the upper and lower surfaces. The tip member 35b is a flat ball with a so-called anti-reversal mechanism and can swing relative to the recess in the main body member 35a. When the main body member 35a protrudes from the mask-side arm 52, the flat lower surface of the tip member 35b abuts against the protective plate 34. The tip member 35b comes into contact with and presses against the protective plate 34, so that the tip member 35b is held stationary by the frictional force between the wafer 26 and the protective plate 34.

[0041] Because the tip member 35b can swing independently of the main member 35a, it is possible to prevent or reduce misalignment of the mask plate 25 and the wafer 26 due to screw rotation. Furthermore, because the tip member 35b is in surface contact with the protective plate 34, the fixing force per unit area applied from the protruding member 35 to the protective plate 34 is smaller than in the case of point contact. Furthermore, because the protective plate 34 is inserted between the tip member 35b and the mask front surface 25a, the fixing force per unit area applied from the protruding member 35 to the mask front surface 25a is smaller than in the case where the protective plate 34 is not present. This makes it possible to prevent or reduce damage to the mask plate 25 that may occur when the protruding member 35 hits the mask plate 25.

[0042] The wafer holder 24 includes a notch 56 as shown in FIG. 5. When the fixing jig 28 is attached to the wafer holder 24, the notch 56 contacts the wafer holder 24 but prevents the fixing jig 28 from contacting the mask side surface 25c. The notch 56 has a fixing jig abutment surface 58 located radially outward from the designed position of the mask side surface 25c when the mask plate 25 is fixed to the wafer holder 24. The fixing jig abutment surface 58 contacts the inner surface of the arm connection portion 54 to position the fixing jig 28 in the radial direction of the wafer holder 24. As shown in FIG. 4, because the fixing jig 28 does not contact the mask side surface 25c, a gap 59a is formed between the arm connection portion 54 and the mask side surface 25c. Therefore, when the fixing jig 28 is attached, the fixing jig 28 does not press the mask plate 25 in the in-plane direction, preventing misalignment of the mask plate 25.

[0043] The fixing jig 28 does not come into contact with the mask front surface 25a and the protective plate 34, except for the protruding member 35. That is, a gap 59b is also formed between the lower surface of the mask-side arm 52 and the protective plate 34. When attaching the fixing jig 28, the fixing jig 28 is inserted into the notch 56 while the wafer holder-side arm 50 of the fixing jig 28 is abutting against the wafer holder 24, so that the fixing jig 28 can be attached without coming into contact with the mask plate 25 and the protective plate 34. To facilitate this attachment, the length of the wafer holder-side arm 50 is longer than the length of the mask-side arm 52. The length by which the wafer holder-side arm 50 extends from the arm connecting portion 54 is longer than the length by which the mask-side arm 52 extends from the arm connecting portion 54. First, the extended portion of the wafer holder-side arm 50 is abutted against the notch 56 from the bottom 24c side of the wafer holder 24, and then the fixing jig 28 can be inserted radially inward.

[0044] The cutout portion 56 further has a pair of fixture guide surfaces 60 shown in FIG. 5. The fixture guide surfaces 60 extend radially outward on both sides of the fixture abutment surface 58. The fixture guide surfaces 60 connect the fixture abutment surface 58 to the upper side 24a (or the lower side 24b). When the fixture 28 is inserted into the cutout portion 56, the fixture guide surfaces 60 guide the arm connection portion 54 in the radial direction of the wafer holder 24 along both sides of the arm connection portion 54. Since the installation location of the fixture 28 is determined in this manner, the installation work is easy.

[0045] The extension portion 36 of the wafer holder 24 extends radially outward beyond the fixture abutment surface 58. The diameter of the wafer holder 24 is larger than that of the mask plate 25 along its entire periphery. The wafer holder 24 has an excess area outside the mask plate 25 where the pin holes 42 and the elongated portions 40 that serve as handles are provided. An operator can hold this excess area when setting the wafer holder 24 on or removing it from the transfer plate 18. Because there is no need to touch the mask plate 25 with one's hands during this operation, the possibility of accidentally touching the mask plate 25 and causing misalignment is reduced.

[0046] Next, an alignment device for fixing the mask plate 25 and the wafer 26 to the wafer holder 24 will be described. Fig. 8 is a schematic external view of an alignment device 80. The alignment device 80 includes a stage 82 that supports the wafer holder 24, a mask holder 83 that holds the mask plate 25, supports 84 that support the mask holder 83, and a camera 85 that detects the alignment mark on the wafer 26 through an alignment opening in the mask plate 25.

[0047] The stage 82 is configured to be movable in the X and Y directions along the upper surface of the stage and in the θ direction around the Z axis perpendicular to the upper surface of the stage. The stage 82 moves the wafer 26 supported by the wafer holder 24 placed on the upper surface of the stage in the X, Y, and θ directions, and aligns the wafer 26 in the in-plane direction with respect to the mask plate 25 held by the mask holder 83. The stage 82 is configured to be movable in the Z direction by an elevator device 86. A compression spring 87 is provided between the stage 82 and the elevator device 86. The compression spring 87 absorbs the impact generated when the stage 82 is raised toward the mask plate 25 and the spacer member 44 placed on the wafer 26 is pressed against the mask plate 25.

[0048] The mask holder 83 is disposed above the stage 82. The mask holder 83 is divided into left and right halves, a left mask holder 83a and a right mask holder 83b. The mask plate 25 is held by the suction force of suction pads 88 provided on the undersides of the left mask holder 83a and the right mask holder 83b. The suction pads 88 are connected to a vacuum pump (not shown).

[0049] 9 is a plan view schematically showing the configuration of the underside of the mask holder 83. The mask holder 83 is formed with a holding recess 89 for holding the outer peripheral region of the mask plate 25. The holding recess 89 extends in an arc shape corresponding to the outer diameter of the mask plate 25. The holding recess 89 is formed by a left holding recess 89a formed in the left mask holder 83a and a right holding recess 89b formed in the right mask holder 83b. A gap 83c is provided between the left holding recess 89a and the right holding recess 89b for inserting the fixing jig 28. A suction pad 88 is provided in the holding recess 89.

[0050] Next, a method for fixing a mask using an alignment device 80 will be described. First, as shown in Fig. 8, the wafer holder 24 is placed on the alignment device 80, the wafer 26 is placed on the wafer holder 24, and the spacer member 44 is placed on the wafer 26. The mask plate 25 is placed on the mask holder 83 and is held suspended above the stage 82 by the suction force of the suction pad 88. A protection plate 34 is attached to a part of the mask front surface 25a. The attachment position of the protection plate 34 corresponds to the attachment position of the fixing jig 28.

[0051] Next, the lifting device 86 is used to raise the stage 82, bringing the mask back surface 25b and the wafer front surface 26a closer to each other so that the distance d between them becomes a predetermined distance. This brings the alignment mark on the wafer front surface 26a within the focal depth of the camera 85, enabling alignment of the wafer 26 with respect to the mask plate 25. At this time, there is a gap between the mask back surface 25b and the spacer member 44, and they are not in contact with each other. The distance d between the mask back surface 25b and the wafer front surface 26a during alignment is approximately 1 mm to 3 mm, which is slightly larger than the thickness of the spacer member 44. In this state, the stage 82 is moved in the X, Y, and θ directions, thereby aligning the mask plate 25 and the wafer 26.

[0052] FIG. 10 is a schematic diagram illustrating a temporary fixing process using an alignment device 80. After the mask plate 25 and wafer 26 are aligned, the stage 82 is raised by the elevator device 86 as indicated by arrow 90, bringing the outer peripheral region of the mask back surface 25b into contact with the spacer member 44. The drive shaft of the elevator device 86 is further raised from the state in which the mask plate 25 and the spacer member 44 are in contact, thereby compressing the compression spring 87 provided between the stage 82 and the elevator device 86. This applies a first fixing force between the stage 82 and the mask holder 83 according to the compression amount δ of the compression spring 87. The magnitude of the first fixing force is, for example, approximately 60 N to 100 N. The first fixing force is applied to the outer peripheral region of the wafer where the wafer holder 24, wafer 26, spacer member 44, and mask plate 25 overlap. The first fixing force generates a frictional force at the interfaces between these members, temporarily fixing the wafer 26 and mask plate 25 while maintaining their alignment.

[0053] 11 is a diagram schematically illustrating the process of attaching the fixing jig 28. The fixing jig 28 is attached with the wafer 26 and the mask plate 25 positioned by the first fixing force. As described above, the fixing jig 28 is inserted into the cutout portion 56 (see FIG. 5) of the wafer holder 24 with the wafer holder-side arm 50 in contact with the underside of the wafer holder 24. Thereafter, the protruding member 35 provided on the mask-side arm 52 is caused to protrude toward the protective plate 34, so that the tip of the protruding member 35 abuts against the protective plate 34, and the fixing jig 28 is attached to the wafer holder 24.

[0054] The fixing jig 28 is attached so that a second fixing force is applied between the wafer holder 24 and the protruding member 35. When the main body member 35a of the protruding member 35 is a screw, the tightening torque of the main body member 35a can be controlled to a predetermined value by rotating the main body member 35a using, for example, a torque driver with an idle rotation. This allows the application of a second fixing force corresponding to the tightening torque. The magnitude of the second fixing force is smaller than the magnitude of the first fixing force. The magnitude of the second fixing force is, for example, approximately 30 N to 50 N. The magnitude of the second fixing force is, for example, approximately 50% to 80% of the first fixing force. By making the second fixing force smaller than the first fixing force, it is possible to prevent misalignment of the wafer 26 and the mask plate 25 when attaching the fixing jig 28. For example, if the second fixing force is larger than the first fixing force, excessive force is applied in the direction of rotation of the protruding member 35, making it impossible to maintain the temporary fixation provided by the first fixing force, which could result in misalignment of the wafer 26 and the mask plate 25.

[0055] After the fixing jig 28 is attached, the stage 82 is lowered using the elevator 86, thereby releasing the first fixing force applied by the compression spring 87. When the first fixing force is released, the wafer holder 24, wafer 26, spacer member 44, mask plate 25, and protection plate 34 are fixed by the fixing jig 28, which applies a second fixing force. When the first fixing force is released, the second fixing force is applied to the wafer 26 and mask plate 25 by the fixing jig 28 in the thickness direction, but no force is applied in the in-plane direction that could contribute to misalignment between the wafer 26 and mask plate 25. Therefore, the wafer 26 and mask plate 25 are aligned and the fixing by the fixing jig 28 is completed, thereby forming the masked wafer 23. The masked wafer 23 is then attached to the transfer plate 18.

[0056] 12 is a plan view schematically illustrating the transfer plate 18. The transfer plate 18 includes a wafer holder mounting surface 64, a plurality of pins 66, a plurality of pin seats 68, and a plurality of openings 70. In the example of FIG. 12, the transfer plate 18 is configured to support three masked wafers 23.

[0057] The wafer holder mounting surface 64 is a flat surface that contacts the bottom 24c of the wafer holder 24 and supports the wafer holder 24 in a fixed position. A plurality of pins 66 engage with pin holes in the wafer holder 24 to position and support the wafer holder 24 in a fixed position. The plurality of pins 66 are provided in a number and arrangement that corresponds to the pin holes 42 in the wafer holder 24. Two pins 66 are arranged diagonally, corresponding to the two pin holes 42 in one wafer holder 24. Pin seats 68 are provided on the wafer holder mounting surface 64 and fix the bases of the pins 66. Openings 70 are formed in the transfer plate 18 to receive the fixture 28 when the wafer holder 24 contacts the wafer holder mounting surface 64.

[0058] 13 is a side view that schematically shows a portion of the transfer plate 18, and illustrates the structure of the pins 66 and pin seats 68. The pins 66 have an inverted cone shape extending from the pin seats 68. The pins 66 are provided perpendicular to the wafer holder mounting surface 64.

[0059] FIG. 14 is a plan view schematically illustrating the pin hole 42 of the wafer holder 24. The pin hole 42 has a so-called potbellied shape. The pin hole 42 has a first arc-shaped contour 42a and a second arc-shaped contour 42b. Both ends of the first arc-shaped contour 42a are connected to both ends of the second arc-shaped contour 42b. The first arc-shaped contour 42a has a first center 74 and a first radius 75, and the second arc-shaped contour 42b has a second center 76 and a second radius 77. The second center 76 is eccentric downward from the first center 74, and the second arc-shaped contour 42b is offset downward from the first arc-shaped contour 42a. The pin hole 42 is symmetrical with respect to a line 78 connecting the first center 74 and the second center 76. The second radius 77 is larger than the first radius 75. The first radius 75 is smaller than the radius of the tip of the pin 66 and larger than the radius of the root of the pin 66. The second radius 77 is larger than the radius of the tip of the pin 66.

[0060] FIG. 15 is a plan view schematically illustrating a masked wafer 23 attached to the transfer plate 18. When attaching the masked wafer 23 to the transfer plate 18, a pin 66 can be inserted into the second arcuate contour 42b of the pin hole 42. The pin 66 then fits into the first arcuate contour 42a due to the weight of the wafer holder 24. The pin 66 is thickest at its tip and gradually tapers toward the pin base 68. Therefore, when the pin 66 is placed in the pin hole 42 of the wafer holder 24, the wafer holder 24 moves downward due to its own weight along the inverse tapered surface (i.e., inverse conical surface) of the pin 66, approaching the transfer plate 18 and ultimately hitting the wafer holder mounting surface 64. This allows the wafer holder 24 to be quickly attached to the transfer plate 18, and the masked wafer 23 to be reliably positioned in a fixed position. Furthermore, because the wafer holder 24 is supported by two diagonally arranged pins 66, its position is stable even during transfer by the transfer plate 18. Such shapes of the pins 66 and pin holes 42 prevent the masked wafer 23 from falling off during transport and suppress vibrations. Furthermore, when the masked wafer 23 is to be removed from the transport plate 18 after ion irradiation, it can be easily removed by simply lifting the wafer holder 24 slightly.

[0061] After ion irradiation, the masked wafer 23 may be released from the fixed wafer 26 and mask plate 25 using an alignment device 80. First, a camera 85 of the alignment device 80 may be used to check whether the alignment between the wafer 26 and the mask plate 25 is correct. By rechecking the alignment after ion irradiation, it can be confirmed whether ion irradiation was performed at the appropriate position, and the yield in subsequent processes can be increased.

[0062] After confirming the alignment, the fixing jig 28 can be removed from the masked wafer 23 to release the wafer 26 and the mask plate 25. At this time, the fixing jig 28 may be removed while the first fixing force is applied. For example, the masked wafer 23 is placed on the stage 82, and the stage 82 is raised to accommodate the mask plate 25 in the holding recess 89 of the mask holder 83. After the mask plate 25 contacts the mask holder 83, the stage 82 is further raised to apply the first fixing force between the stage 82 and the mask holder 83. With the first fixing force applied, the screws of the protruding members 35 are reversely rotated to separate the protruding members 35 from the protective plate 34, and the fixing jig 28 is removed. After the fixing jig 28 is removed, the stage 82 is lowered to release the first fixing force. At this time, the mask plate 25 may be held by the suction force of the suction pads 88 of the mask holder 83, or may remain placed on the wafer holder 24. Thereafter, the spacer member 44 and the wafer holder 24 are removed from the wafer holder 24. Note that the fixing jig 28 may be removed without applying the first fixing force.

[0063] FIG. 16 is a flowchart showing an example of an ion irradiation method according to an embodiment. First, a semiconductor substrate and a mask plate are brought close to each other and aligned (S10). Next, a first fixing force is applied in the direction in which the semiconductor substrate and the mask plate overlap, temporarily fixing the semiconductor substrate and the mask plate (S12). While the first fixing force is being applied, a second fixing force smaller than the first fixing force is applied in the direction in which the semiconductor substrate and the mask plate overlap using a fixing jig (S14). After the fixing jig is attached, the first fixing force is released, and the semiconductor substrate and the mask plate are fixed using a fixing jig that applies the second fixing force (S16). The semiconductor substrate and the mask plate fixed by the fixing jig are set on a transfer plate and transported to an irradiation chamber, where ions are irradiated toward the semiconductor substrate through the mask plate (S18). After ion irradiation, the semiconductor substrate and the mask plate fixed by the fixing jig are removed from the transfer plate, and it is checked whether the semiconductor substrate and the mask plate are misaligned (S20). Then, the semiconductor substrate and the mask plate are released from the fixing jig (S22).

[0064] 17 is a cross-sectional view schematically showing a masked wafer 93 according to another embodiment. The masked wafer 93 includes a mask plate 25, a wafer 26, a protective plate 34, a spacer member 44, and a wafer holder 94. The wafer holder 94 includes a fixture 96 that fixes the mask plate 25 and the wafer 26. The wafer holder 94 is configured similarly to the above-described wafer holder 24, but differs from the above-described embodiment in that it includes the fixture 96.

[0065] The wafer holder 94 has a bottom portion 94c, an outer frame portion 94d, and a fixture support portion 94e. The bottom portion 94c and the outer frame portion 94d are configured similarly to the bottom portion 24c and the outer frame portion 24d described above. The bottom portion 94c and the outer frame portion 94d form a wafer holder recess 46 that accommodates the wafer 26. The wafer holder recess 46 is provided with a wafer holder protrusion 48 that is integrally formed adjacent to the bottom portion 94c and the outer frame portion 94d.

[0066] The fixing jig support portion 94e is provided radially outward from the outer frame portion 94d. The fixing jig support portion 94e is provided on the outer periphery of the wafer holder 94, for example, at the position of the cutout portion 56 shown in Fig. 5. A fixing jig 96 is attached to the fixing jig support portion 94e.

[0067] Fixing jig 96 is a so-called toggle clamp, and has an arm 96a on which protruding member 95 is provided, and a lever 96b for moving arm 96a. Arm 96a is attached to the outer periphery of wafer holder 94 and extends from the outer periphery of wafer holder 94. Arm 96a is rotatable about a shaft 96c provided on the outer periphery of wafer holder 94.

[0068] The protruding member 95 has a main body member 95a and a tip member 95b. The tip member 95b is configured similarly to the tip member 35b described above. The tip member 95b is supported by the main body member 95a so as to be able to swing relative to the main body member 95a. A recess is formed at the lower end of the main body member 95a to accommodate the tip member 95b. The tip member 95b has a flat upper surface, a flat lower surface, and a side surface that is a convex curved surface (e.g., a spherical surface) connecting the upper and lower surfaces.

[0069] The protruding member 95 can protrude toward the protective plate 34 by moving the arm 96a via the lever 96b. By moving the tip of the arm 96a toward the mask plate 25, the protruding member 95 comes into contact with and presses the protective plate 34. When the tip member 95b of the protruding member 95 abuts against the protective plate 34, a second fixing force is applied between the wafer holder 94 and the tip member 35b. When the tip of the arm 96a is moved upward away from the mask plate 25, the second fixing force applied by the protruding member 95 is released.

[0070] Using the wafer holder 94 according to this embodiment, the mask plate 25 and the wafer 26 can be fixed using the same process as in the above-described embodiment. First, the wafer holder 94 is placed on the stage 82, and with the arm 96a raised, the wafer 26 and the spacer member 44 are placed on the wafer holder 94. The mask plate 25 and the wafer 26 held by the mask holder 83 are then aligned, and the stage 82 is raised to apply a first fixing force to the mask plate 25 and the wafer 26, temporarily fixing them together. While the first fixing force is being applied, the arm 96a is moved downward via the lever 96b, allowing the protruding member 95 to apply a second fixing force to the mask plate 25 and the wafer 26. The stage 82 is then lowered to release the first fixing force, thereby fixing the mask plate 25 and the wafer 26 with the fixing jig 96, which applies the second fixing force.

[0071] In yet another embodiment, a magnet may be used as the fixing jig that applies the second fixing force to the mask plate 25 and the wafer 26. For example, by forming the wafer holder protrusions 48 from a magnetic material and making at least the tip of the protruding member a magnet, the second fixing force can be generated between the protruding member and the wafer holder protrusions 48 by magnetic force.

[0072] The present invention has been described above based on examples. It will be understood by those skilled in the art that the present invention is not limited to the above-described embodiments, and that various design changes and modifications are possible, and that such modifications are also within the scope of the present invention. [Explanation of symbols]

[0073] 10...Ion irradiation system, 18...Transport plate, 23...Wafer with mask, 24...Wafer holder, 25...Mask plate, 26...Wafer, 28...Fixing jig, 34...Protective plate, 35...Protruding member, 44...Spacer member, 80...Alignment device, 82...Stage, 83...Mask holder, 86...Lifting device, 87...Compression spring.

Claims

1. Aligning the semiconductor substrate and the mask plate so that they overlap; applying a first fixing force in a direction in which the semiconductor substrate and the mask plate overlap, thereby temporarily fixing the semiconductor substrate and the mask plate; applying a second fixing force smaller than the first fixing force in a direction in which the semiconductor substrate and the mask plate overlap each other using a fixing jig while applying the first fixing force; fixing the semiconductor substrate and the mask plate by the fixing jig that releases the first fixing force and applies the second fixing force; irradiating ions toward the semiconductor substrate through the mask plate fixed by the fixing jig.

2. further comprising disposing a spacer member between the peripheral region of the semiconductor substrate and the mask plate; The ion irradiation method according to claim 1 , wherein the first fixing force and the second fixing force are applied to positions where the semiconductor substrate, the spacer member, and the mask plate overlap.

3. further comprising disposing a protection plate between the fixture and the mask plate; The ion irradiation method according to claim 1 , wherein the second fixing force is applied to a position where the semiconductor substrate, the mask plate, and the protection plate overlap each other.

4. The ion irradiation method according to claim 3 , wherein the first fixing force is applied to a position where the semiconductor substrate, the mask plate, and the protection plate do not overlap with each other.

5. 5. The ion irradiation method according to claim 1, wherein the temporary fixing includes using an elevator device to move a stage supporting the semiconductor substrate toward the mask plate held by a mask holder, and controlling the magnitude of the first fixing force by a compression amount of a compression spring provided between the stage and the elevator device.

6. The ion irradiation method according to claim 5 , wherein the mask holder holds the mask plate above the stage by a suction force that attracts an outer peripheral region of the mask plate.

7. the fixing jig includes a protruding member that can protrude toward the mask plate, The ion irradiation method according to claim 1 , wherein applying the second fixing force includes controlling the magnitude of the second fixing force by a protrusion amount of the protrusion member.

8. The ion irradiation method according to claim 1 , wherein the fixing jig sandwiches and fixes the semiconductor substrate, the mask plate, and a bottom of a wafer holder that accommodates the semiconductor substrate.

9. 8. The ion irradiation method according to claim 1, wherein the fixing jig includes an arm attached to an outer periphery of a wafer holder that accommodates the semiconductor substrate, and the semiconductor substrate and the mask plate are sandwiched and fixed between the wafer holder and the arm.

Images