Shielding for ion implanters

Abstract

A shield for use with a rotatable platen is disclosed. The shield comprises an exposed portion and a frame for attaching the shield to the platen. The exposed portion of the shield has an arc-shaped rear surface facing the platen and an opposite exposed surface facing the ion beam. The exposed surface is designed so that the ion beam strikes the exposed surface at angles of approximately 90°, because sputtering can be reduced at these angles. The exposed surface may have various shapes, including flat, round, or inclined. Additionally, the exposed surface may comprise a plurality of exposed segments separated by connecting segments that are not exposed to the ion beam. The shield may be graphite, silicon, or silicon carbide.

Description

Technology Field

[0001] The present application claims priority to U.S. provisional application serial number 63 / 621,830 filed January 17, 2024 and U.S. patent application serial number 18 / 946,776 filed November 13, 2024, the disclosures of said applications are incorporated herein by reference in their entirety.

[0002] The present disclosure describes embodiments of a shielding member for use in an ion implanter to protect a platen. Background Technology

[0003] Semiconductor devices are manufactured using multiple processes, some of which implant ions into a workpiece. Certain implanters have the ability to monitor an ion beam directed toward the workpiece. The incoming ion beam is typically very narrow in the height direction but has a width greater than the diameter of the workpiece. This width can be achieved by using a ribbon ion beam or by scanning a spot ion beam.

[0004] Typically, the ion beam strikes the workpiece at an angle normal to the direction of the ion beam. However, in certain embodiments, it may be useful to perform the implantation at an angle not normal to the ion beam. This may be referred to as an angled implant.

[0005] When the workpiece is tilted, there is a possibility that the ion beam may strike the platen. Therefore, in certain situations, a shield may be placed around the platen to protect it from such ion beam strikes. Accordingly, the purpose of the shield is to collide with the ion beam so that the platen is not damaged by the ion beam. However, there is a possibility that situations may exist where the ion beam sputters the shield, causing undesirable particles to be generated.

[0006] Therefore, it would be beneficial if there were a shield that protects the platen but generates fewer particles when colliding with the ion beam.

[0007] A shield for use with a rotatable platen is disclosed. The shield comprises an exposed portion and a frame for attaching the shield to the platen. The exposed portion of the shield has an arc-shaped rear surface facing the platen and an opposite exposed surface facing the ion beam. The exposed surface is designed so that the ion beam strikes the exposed surface at angles of approximately 90°, because sputtering can be reduced at these angles. The exposed surface may have various shapes, including flat, round, or inclined. Additionally, the exposed surface may include a plurality of exposed segments separated by connecting segments that are not exposed to the ion beam. The shield may be graphite, silicon, silicon carbide, or other material.

[0008] According to one embodiment, an ion implanter is disclosed. The ion implanter comprises: an ion source for generating ions; a platen for supporting a workpiece to be processed by an ion beam generated from the ions—when the ion beam reaches the workpiece, the ion beam has a longer dimension in the X direction, a smaller dimension in the Y direction, and a direction of movement in the Z direction, where the Y direction is perpendicular to the X direction, and the platen is located within the process chamber of the ion implanter and includes a base and an electrostatic chuck—; and a shield for protecting the electrostatic chuck from the ion beam, wherein the shield includes a surface exposed to the ion beam, referred to as an exposed surface, and the ion beam strikes the exposed surface at an angle deviating from the normal by 20° or less when measured in the XZ plane. In some embodiments, the electrostatic chuck is maintained at an X-tilt angle of at least 60°. In some embodiments, the ion beam strikes the exposed surface at an angle deviating from the normal by 10° or less when measured in the XZ plane. In some embodiments, the ion beam strikes the exposed surface at a normal angle when measured in the XZ plane. In some embodiments, the ion beam strikes the exposed surface at an angle deviating from the normal by 20° or less when measured in the YZ plane. In some embodiments, the ion beam strikes the exposed surface at a normal angle when measured in the YZ plane. In some embodiments, the electrostatic chuck is maintained at an X-tilt angle of θ° relative to the vertical, and the angle between the top surface of the electrostatic chuck and the exposed surface in the YZ plane is (180 - θ)° or less. In some embodiments, the angle between the top surface of the electrostatic chuck and the exposed surface in the YZ plane is an acute angle. In some embodiments, the shield is made of graphite.

[0009] According to another embodiment, a shield for use with a platen is disclosed. The shield comprises an exposed portion; and a frame connecting the exposed portion to the platen, wherein the exposed portion comprises a rear surface configured to be adjacent to the platen and having an arc shape, and an exposed surface opposite the rear surface and adapted to be exposed to an ion beam, wherein the exposed portion has a first dimension referred to as width and is at least as wide as the platen, and the exposed surface is substantially straight along the first dimension. In some embodiments, the exposed surface is configured not to be bent, curved, or inclined by more than 10° along the first dimension. In some embodiments, the exposed surface is flat along the first dimension. In some embodiments, the exposed portion includes a top surface, and the top surface and the exposed surface form an acute angle. In some embodiments, the exposed portion is graphite. In some embodiments, the exposed portion includes a top surface, and the top surface and the exposed surface form an obtuse angle such that the exposed surface is substantially perpendicular to the ion beam in two directions.

[0010] According to another embodiment, a shielding portion for use with a platen is disclosed. The shielding portion comprises an exposed portion; and a frame connecting the exposed portion to the platen, wherein the exposed portion comprises a rear surface configured to be adjacent to the platen and having an arc shape, and an exposed surface opposite the rear surface and adapted to be exposed to an ion beam, wherein the exposed portion is referred to as width and has a first dimension at least as wide as the platen, and the exposed surface comprises a plurality of exposed segments configured to be substantially parallel to each other in the first dimension, and a plurality of connecting segments disposed between adjacent exposed segments, wherein the connecting segments form an angle of 90° or less with the adjacent exposed segments. In certain embodiments, the plurality of exposed segments are parallel to each other. In certain embodiments, the connecting segments form an angle of less than 90° with the adjacent exposed segments. In some embodiments, the exposed portion is graphite. In some embodiments, the exposed portion comprises a top surface, and the top surface and the exposed surface form an obtuse angle such that the exposed surface is substantially perpendicular to the ion beam in two directions. Brief explanation of the drawing

[0011] For a better understanding of the present disclosure, reference is made to the accompanying drawings, in which the same elements are referred to by the same reference numerals. FIG. 1 is a block diagram of an ion implanter using a shielding part according to one embodiment. Figure 2 is a block diagram of a process chamber having a platen and a shielding section. FIG. 3 illustrates the rotation and tilt of the work member on the platen. Figure 4 illustrates a process chamber with an electrostatic chuck at a large X-angle tilt. FIG. 5 illustrates a plan view of a shielding portion according to one embodiment. FIGS. 6a to 6c illustrate plan views of shielding portions according to several different embodiments. FIGS. 7a to 7c illustrate side views of a shielding portion according to several different embodiments. FIG. 8 illustrates a side view of a shielding portion according to another embodiment. Specific details for implementing the invention

[0012] FIG. 1 illustrates an ion implanter comprising a process chamber (100) including a platen and a shielding section. An ion source (200) is used to generate ions. The ion source (200) may be an indirectly heated cathode (IHC) ion source. Alternatively, the ion source (200) may be a capacitively coupled plasma source, an inductively coupled plasma source, a Bernas source, or another source. Accordingly, the type of ion source is not limited by the present disclosure. An extraction optical system (201) which may include one or more electrodes is positioned outside the extraction aperture of the ion source (200) and in close proximity to it.

[0013] A mass spectrometer (210) is positioned downstream from the extraction optical system (201). The mass spectrometer (210) uses magnetic fields to guide the path of the extracted ion beam. The magnetic fields influence the flight path of the ions according to their mass and charge. A mass decomposition device (220) having a resolving aperture (221) is placed at the output or at the origin of the mass spectrometer (210). By appropriate selection of the magnetic fields, only those ions with selected mass and charge among the extracted ion beam will be directed through the decomposition aperture (221). Other ions will strike the walls of the mass decomposition device (220) or the mass spectrometer (210) and will not move further within the system.

[0014] A collimator (230) may be positioned downstream from the mass decomposition device (220). The collimator (230) receives ions from an ion beam passing through a decomposition aperture (221) and generates an ion beam (250) formed of a plurality of parallel or nearly parallel beamlets. The output or near end of the mass analyzer (210) and the input or near end of the collimator (230) may be separated by a fixed distance. The mass decomposition device (220) is positioned in the space between these two components.

[0015] An acceleration / deceleration stage (240) may be located downstream from the collimator (230). The acceleration / deceleration stage (240) is a beam-line lens component configured to independently control the deflection, deceleration, and focus of the ion beam (250). For example, the acceleration / deceleration stage (240) may be an electrostatic filter (EF). The ion beam (250) exiting the acceleration / deceleration stage (240) enters the process chamber (100).

[0016] The controller (280) may communicate with one or more of the power supply units, thereby allowing the voltage or current supplied by these power supply units to be monitored and / or modified. The controller (280) may include a processing unit, such as a microcontroller, a personal computer, a special-purpose controller, or other suitable processing unit. The controller (280) may also include a non-transient storage element, such as semiconductor memory, magnetic memory, or other suitable memory. Such a non-transient storage element may include instructions and other data that enable the controller (280) to perform the functions described herein.

[0017] In certain embodiments, the ion source (200) can generate a ribbon ion beam traveling through these components. Accordingly, while FIG. 1 illustrates a ribbon ion beam system, it is understood that an ion implantation system can utilize a scanned beam. Such an ion implanter includes an ion source that generates ions in the form of a spot ion beam. This type of ion implanter also includes a mass spectrometer and a mass decomposition device, as described above. Furthermore, a scanner, which may be electrostatic or of another type, is used to generate the scanned ion beam. Specifically, the spot beam may enter an electrostatic scanner, which is used to scan the spot beam in the width direction to form a scanned ion beam in the form of an ion beam having a width much greater than its height. Subsequently, the scanned ion beam may pass through an angle compensator. The angle compensator is designed to deflect the ions of the scanned ion beam to generate an ion beam having parallel ion trajectories, and accordingly, to focus the scanned ion beam. Specifically, an angle corrector is used to change diverging ion trajectory paths into substantially parallel paths of the ion beam (250). In some embodiments, the angle corrector may include magnetic poles spaced apart to define a gap, and a magnetic coil coupled to a power supply. The scanned ion beam passes through the gap between the magnetic poles and is deflected according to the magnetic field within the gap. In other embodiments, the angle corrector may be an electrostatic lens, sometimes referred to as a paralleling lens.

[0018] In both configurations, when the ion beam (250) reaches the workpiece, the ion beam has a larger dimension in the X direction and a smaller dimension in the Y direction. The X direction may be referred to as the width of the ion beam, while the Y direction may be referred to as the height of the ion beam. The X direction and the Y direction are perpendicular to each other. Additionally, the ion beam (250) travels in the Z direction.

[0019] FIG. 2 illustrates the process chamber (100) of FIG. 1 in more detail. The process chamber (100) includes a platen (120), on which a workpiece (110) may be placed. When in the operating position, an ion beam (250) strikes the workpiece (110). The platen (120) may include an electrostatic chuck (140) used to clamp and hold the workpiece (110) while the ion beam (250) is directed into the process chamber (100). In some embodiments, the platen (120) may be raised and lowered in the Y direction (127) through the movement of a shaft (128).

[0020] Additionally, the platen (120) may rotate about different axes. FIG. 3 illustrates the platen (120) and its various rotation directions. FIG. 3 illustrates a perspective view of a rotatable platen (120), referred to as a roplat. As shown in FIG. 2, the roplat comprises a base (130) and an electrostatic chuck (140). The electrostatic chuck (140) comprises one or more electrodes that enable the electrostatic chuck to generate an electrostatic force that clamps the workpiece (110) to the clamping surface (129). The electrostatic chuck (140) is rotatably coupled to the base (130). The platen (120) may have three axes. There may be a torsional axis (121) perpendicular to the clamping surface (129) of the electrostatic chuck (140) and passing through the center of the electrostatic chuck (140). Rotation around such a torsion axis (121) is referred to as the torsion angle (122). Note that the electrostatic chuck (140) is rotatable around the torsion axis (121), while the base (130) remains fixed. There is an X-axis (123) that passes through the platen, is parallel to the clamping surface (129) of the platen (120), and is perpendicular to the torsion axis (121). The X-axis (123) is parallel to the broad dimension of the ion beam (250). The tilt with respect to the X-axis (123) is referred to as the X-tilt angle (124) and is achieved by the rotation of the electrostatic chuck (140) on the base (130). X-tilt angles are measured with respect to the vertical direction. In other words, when the clamping surface (129) is vertical as shown in FIG. 2, the X-tilt angle is defined as 0°. An X-tilt angle of 90° is defined as being in a horizontal position. Additionally, there is also a Y-axis (125) that passes through the platen (120), is parallel to the clamping surface (129) of the platen (120), and is perpendicular to the torsion axis (121) and the X-axis (123). The Y-axis (125) is parallel to the narrow dimension of the ion beam (250).The tilt with respect to the Y-axis (125) is referred to as the Y-tilt angle (126) and can be achieved by moving the base (130). For example, the Y-tilt angle (126) can be achieved by rotating the shaft (128).

[0021] In certain embodiments, the electrostatic chuck (140) can be rotated 90° around the X-axis (123) so that the clamping surface (129) of the electrostatic chuck (140) is horizontal, allowing the workpiece (110) to be placed on the platen (120). This may be referred to as the loading position. Subsequently, the electrostatic chuck (140) is rotated around the X-axis (123) to the operating position or injection position shown in FIG. 2.

[0022] Note that, as illustrated in FIG. 4, when the electrostatic chuck (140) is tilted with respect to the X-axis (123), the lowest portion of the electrostatic chuck (140) may be exposed to the incident ion beam (250). Accordingly, a shielding portion (300) may be added to protect the electrostatic chuck (140). FIG. 5 illustrates a plan view of the shielding portion (300) when the platen (120) is in the loading position. The shielding portion (300) includes an exposed portion (310) located along the lower portion of the electrostatic chuck (140). The lower portion is defined as the portion of the electrostatic chuck (140) facing the ion beam (250) when the electrostatic chuck (140) is in the loading position. The exposed portion (310) typically has a first dimension along the X direction (also referred to as width) which is wider than the electrostatic chuck (140), and a second dimension perpendicular to the first direction (also referred to as length) which is smaller than the first dimension. The second dimension is parallel to the Z direction when the platen is in the loading position. The exposed portion (310) also has a thickness perpendicular to the first and second dimensions and parallel to the Y direction when the platen is in the loading position. The exposed portion (310) also has a top surface that may be parallel to the top surface of the electrostatic chuck (140).

[0023] The exposed portion (310) has an exposed surface (311) that faces the ion beam (250) and extends along a first dimension. The exposed portion (310) also has a rear surface (312) that faces the electrostatic chuck (140). In some embodiments, the rear surface (312) is an arc shape having a diameter slightly larger than the diameter of the electrostatic chuck (140). The shielding portion (300) also includes a frame (320) used to attach the exposed portion (310) to the base (130). The frame (320) may have one or more brackets (321) for attaching the exposed portion (310) to the base (130).

[0024] The exposed portion (310) of the shielding portion (300) may be composed of graphite. It has been found that sputtering on the surface of the graphite is minimized when an ion beam strikes the graphite at an angle normal to the surface of the graphite. Additionally, sputtering increases as the angle formed between the ion beam and the graphite surface deviates from the normal. Specifically, the amount of sputtering remains low up to angles of about 20° from the normal, and increases more rapidly as the angle deviates beyond this.

[0025] Accordingly, in one embodiment, the exposed surface (311) of the shielding portion (300) is flat along its width (i.e., X direction) and perpendicular to the incident ion beam (250) in the XZ plane, as shown in FIG. 6a. In this embodiment, note that the ion beam (250) is perpendicular to the exposed surface (311) in the XZ plane over the entire width over which the ion beam (250) strikes the exposed surface (311). In other words, when viewed from above, the ion beam is perpendicular to the exposed surface (311).

[0026] However, as mentioned above, as long as the angle of incidence does not deviate more than 20° from the normal, the amount of sputtering is kept low. Accordingly, in another embodiment illustrated in FIG. 6b, the exposed surface (311) is not flat in the X direction but has a curve or slope. However, the radius of the curve or slope is selected so that the ion beam (250) does not strike the exposed surface (311) at an angle of less than 70° or greater than 110° (when measured in the XZ plane). In another embodiment, the angle of incidence does not deviate more than 10° from the normal. Accordingly, the radius of the curve or slope is selected so that the ion beam (250) does not strike the exposed surface (311) at an angle of less than 80° or greater than 100° (when measured in the XZ plane). In other words, the exposed surface (311) is substantially straight. In the present disclosure, the term “substantially straight” indicates that the exposed surface (311) is configured not to bend, curve, or bevel by more than 20° in any direction along the width exposed to the ion beam (250). Additionally, in certain embodiments, the exposed surface (311) is configured not to bend, curve, or bevel by more than 10° in the width direction or thickness direction.

[0027] Note that FIGS. 6a and 6b include a large exposed portion. In other embodiments, the size of the exposed portion (310) is reduced. FIG. 6c illustrates one such embodiment. In this embodiment, the exposed surface (311) includes a plurality of exposed segments (313), each of which is normal to the incident ion beam (250) in the XZ plane. There are connecting segments (314) between adjacent exposed segments (313). The connecting segments (314) may form angles perpendicular to the adjacent exposed segments (313). In other embodiments, the connecting segments (314) may form acute angles with both adjacent exposed segments (313). In this way, the connecting segments (314) are not exposed to the ion beam (250). In another embodiment, the exposed segments (313) form an angle that deviates from the normal to the ion beam (250) in the XZ plane by 20° or less. In other words, the exposed segments (313) may be substantially parallel to each other. The term "substantially parallel" indicates that the orientation of each exposed segment (313) is within 20° of the orientation of any other exposed segment (313) and within 20° of the normal to the ion beam (250). In certain embodiments, as illustrated in FIG. 6c, the exposed segments (313) are parallel to each other and normal to the ion beam (250) in the XZ plane.

[0028] Although FIGS. 6a through 6c illustrate several different embodiments, the present disclosure is not limited to those exemplified herein. Rather, any shielding portion (300) may be utilized such that the exposed surface (311) exposed to the ion beam (250) creates an angle of 70° to 110° with the ion beam (250) in the XZ plane.

[0029] However, the exposed surface (311) also has a thickness in the Y direction when the platen (120) is in the loading position. Accordingly, in some embodiments, as illustrated in FIGS. 7a and 7b, the shielding portion (300) is configured such that the exposed surface (311) is perpendicular to the ion beam (250) in the YZ plane. Note that the electrostatic chuck (140) can be positioned at different X-tilt angles. FIG. 7a illustrates an electrostatic chuck (140) at an X-tilt angle of 80°, and a shielding portion (300) having an exposed surface (311) perpendicular to the incident ion beam (250) in the YZ plane.

[0030] FIG. 7b illustrates an electrostatic chuck (140) at an X-tilt angle of 60° and a shield (300) having an exposed surface (311) perpendicular to the incident ion beam (250) in the YZ plane. Note that different shields are used for each X-tilt angle to have an exposed surface (311) perpendicular to the ion beam (250) in the YZ plane.

[0031] Accordingly, in one embodiment, a set of shielding members is disclosed, wherein each shielding member has an exposed surface (311) configured such that the ion beam (250) does not strike the exposed surface (311) at an angle of less than 70° or greater than 110° (when measured in the XZ plane). Additionally, each shielding member is configured for a specific X-tilt angle such that the exposed surface (311) is perpendicular to the ion beam (250) in the YZ plane.

[0032] For the exposed surface (311) to be perpendicular to the ion beam (250) in the YZ plane, if the X-tilt angle is given as θ, the angle formed (in the YZ plane) by the top surface of the electrostatic chuck (140) and the exposed surface of the shield (300) is given as 180 - θ. Since θ is always less than 90°, the angle formed between the exposed surface of the shield (300) and the top surface may be obtuse.

[0033] Note that the angle at which the ion beam (250) strikes the exposed surface (311) may deviate from the normal in the YZ plane. As described above, if the angle deviates from the normal by less than 20°, the amount of sputtering is small. Accordingly, in some embodiments, the exposed surface (311) is substantially perpendicular to the ion beam in two directions. The term "substantially perpendicular" indicates that the edge of the exposed surface (311) contacted by the ion beam is within 20° of the normal to the ion beam (250) in the YZ and XZ planes.

[0034] Accordingly, a shielding portion (300) comprising an exposed surface (311) forming a 70° angle with the top surface of the electrostatic chuck (140) in the YZ plane can be used for injections having tilt angles of 50° to 90°. Accordingly, a certain range of tilt angles can be provided by a single shielding portion.

[0035] Additionally, in some embodiments, it may be desirable for the angle to deviate from the normal so that the ion beam (250) is deflected downward from the exposed surface (311). FIG. 7c illustrates an embodiment in which the shielding portion (300) of FIG. 7a is positioned on the electrostatic chuck (140) at an angle of inclination of 60°. The beamlet (251) strikes the shielding portion (300) and is deflected downward away from the work member (110). Accordingly, in these embodiments, the angle formed between the top surface of the electrostatic chuck (140) and the exposed surface of the shielding portion (300) (in the YZ plane) is less than 180 - θ, where θ is the X-angle of inclination.

[0036] In this scenario, a shield designed for an X-tilt angle of θ can be used with an electrostatic chuck (140) having an X-tilt angle of less than θ. However, in certain embodiments, the reverse may not be true, and thus a shield designed for an X-tilt angle of θ may not be used with an electrostatic chuck (140) having an X-tilt angle greater than θ.

[0037] In certain embodiments, the angle between the top surface of the electrostatic chuck (140) and the exposed surface (311) in the YZ plane may be an acute angle, as shown in FIG. 8. In these embodiments, beamlets (251) from the ion beam (250) striking the exposed surface (311) will be deflected downward toward the base (130).

[0038] Although the exposed portion (310) is described as being graphite, it is understood that other materials, such as single-crystal silicon, silicon carbide, nickel, yttrium, zirconium, and doped diamond-like carbon (DLC), may also be used.

[0039] This system has many advantages. Traditional shields have exposed surfaces that are arc-shaped. Accordingly, the ion beam strikes the exposed surface at different angles along the X direction. In the middle of the ion beam, the ion beam may be perpendicular to the exposed surface, but the closer it is to the edges of the ion beam, the smaller the contact angle can be. As described above, the amount of sputtering on the shield can be related to the angle at which the ion beam strikes the exposed surface. By modifying the design of the shield so that the exposed surface of the shield where the ion beam strikes is substantially perpendicular to the ion beam, the amount of particles generated by sputtering on the shield can be reduced. Additionally, this design can be accommodated in the space currently used by the current shield.

[0040] The scope of this disclosure should not be limited by the specific embodiments described herein. In fact, in addition to those described herein, various other embodiments of this disclosure and modifications to this disclosure will be apparent to those skilled in the art from the foregoing description and the accompanying drawings. Accordingly, such other embodiments and modifications are intended to fall within the scope of this disclosure. Furthermore, although this disclosure has been described herein in the context of a specific implementation in a specific environment for a specific purpose, those skilled in the art will recognize that the usefulness of this disclosure is not limited thereto and that this disclosure may be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be interpreted in the full scope and spirit of this disclosure as described herein.

Claims

Claim 1 An ion implanter comprising: an ion source for generating ions; a platen for supporting a workpiece to be processed by an ion beam generated from said ions—when the ion beam reaches said workpiece, said ion beam has a longer dimension in the X direction, a smaller dimension in the Y direction, and a direction of movement in the Z direction, said Y direction being perpendicular to said X direction, said platen being located within a process chamber of said ion implanter and comprising a base and an electrostatic chuck—; and a shield for protecting said electrostatic chuck from said ion beam, said shield comprising a surface exposed to said ion beam, said surface, said ion beam striking said exposed surface at an angle deviating from the normal at 20° or less when measured in the XZ plane. Claim 2 An ion implanter according to claim 1, wherein the electrostatic chuck is maintained at an X-tilt angle of at least 60°. Claim 3 An ion implanter according to claim 1, wherein the ion beam strikes the exposed surface at an angle deviating from the normal by 10° or less when measured in the XZ plane. Claim 4 In claim 1, the ion implanter, wherein the ion beam strikes the exposed surface at a normal angle when measured in the XZ plane. Claim 5 An ion implanter according to claim 1, wherein the ion beam strikes the exposed surface at an angle deviating from the normal by 20° or less when measured in the YZ plane. Claim 6 In claim 1, the ion beam strikes the exposed surface at a normal angle when measured in the YZ plane, an ion implanter. Claim 7 An ion implanter according to claim 1, wherein the electrostatic chuck is maintained at an X-tilt angle of θ° with respect to the vertical, and the angle between the uppermost surface of the electrostatic chuck and the exposed surface in the YZ plane is (180 - θ)° or less. Claim 8 An ion implanter according to claim 1, wherein the angle between the uppermost surface of the electrostatic chuck and the exposed surface in the YZ plane is an acute angle. Claim 9 In claim 1, the shielding part is made of graphite, an ion implanter. Claim 10 A shielding portion for use with a platen, comprising: an exposed portion; and a frame connecting the exposed portion to the platen, wherein the exposed portion comprises a rear surface configured to be adjacent to the platen and having an arc shape, and an exposed surface opposite to the rear surface and adapted to be exposed to an ion beam, wherein the exposed portion has a first dimension referred to as width and is at least as wide as the platen, and the exposed surface is substantially straight along the first dimension. Claim 11 In claim 10, the exposed surface is configured not to be bent, curved, or inclined by more than 10° along the first dimension, a shielding portion. Claim 12 In item 10, the exposed surface is a shielded portion that is flat along the first dimension. Claim 13 In item 10, the above-mentioned exposed portion includes an uppermost surface, and the uppermost surface and the above-mentioned exposed surface form an acute angle, a shielding portion. Claim 14 In item 10, the shielding part, the exposed portion is graphite. Claim 15 In paragraph 10, the exposed portion comprises an uppermost surface, and the uppermost surface and the exposed surface form an obtuse angle such that the exposed surface is substantially perpendicular to the ion beam in two directions, a shielding portion. Claim 16 A shielding portion for use with a platen, comprising: an exposed portion; and a frame connecting the exposed portion to the platen, wherein the exposed portion comprises a rear surface configured to be adjacent to the platen and having an arc shape, and an exposed surface opposite to the rear surface and adapted to be exposed to an ion beam, wherein the exposed portion has a first dimension referred to as width and is at least as wide as the platen, and the exposed surface comprises a plurality of exposed segments configured to be substantially parallel to each other at the first dimension, and a plurality of connecting segments disposed between adjacent exposed segments, wherein the plurality of connecting segments form an angle of 90° or less with the adjacent exposed segments. Claim 17 In paragraph 16, the plurality of exposed segments are shielded, parallel to each other. Claim 18 In paragraph 16, the plurality of connecting segments form an angle of less than 90° with the adjacent exposed segments, a shielding portion. Claim 19 In Clause 16, the shielding part, the exposed portion is graphite. Claim 20 In paragraph 16, the exposed portion comprises an uppermost surface, and the uppermost surface and the exposed surface form an obtuse angle such that the exposed surface is substantially perpendicular to the ion beam in two directions, a shielding portion.

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