Electrostatic chuck with rotary section current transmitting mechanism

Abstract: A rotary section current transmitting mechanism includes a rotary member having an outer wall of a circular cross-section and a stationary member provided around the rotary member with separation from the rotary member by ring-shaped space so as to form concentric circles with the rotary member, and having an inner wall of a circular cross-section. The ring-shaped space accommodates a film-shaped wire. Both ends of the film-shaped wire are fixed in the same direction respectively to wire fixing sections of the rotary member and of the stationary member, and the film-shaped wire curves between the both ends. The film-shaped wire has a configuration in which conductors are sandwiched between insulating films. This configuration enables electric current to be stably transmitted from the stationary member to the rotary member which rotates forward and backward within a predetermined angle.

Description: FIELD OF THE INVENTION The present invention relates to a rotary section current transmitting mechanism for transmitting current between an inner member and an outer member which rotates forward and backward within a limited angle relatively to the inner member. The rotary section current transmitting mechanism is applicable to a semiconductor manufacturing machine, such as an ion implantation machine, an industrial robot, and so on. BACKGROUND OF THE INVENTION Conventionally, slip rings have been used for providing electric power to rotary members in semiconductor manufacturing machines and industrial robots. The slip ring is mainly composed of a sliding ring and a brush. Electric wire, as well as such a slip ring, is sometimes used for a rotary member rotating forward and backward within a predetermined angle. The wire is designed to be of such a length as to follow the rotary member in any position during the rotation, and is slack when the rotary member is in certain positions. Nonetheless when the slip ring is used for providing electric power to the rotary member, the sliding ring and the brush abrade, which causes various problems such as dust, inadequate contact, and noise. As a result, such a slip ring is not very reliable, needs frequent maintenance, and wears out easily. Especially, in the semiconductor manufacturing machine, reduction of dust and noise which affects its control system is strongly demanded. Besides, the wire in the above configuration may break off and tangle, and is therefore not very reliable and not applicable for a wide rotation angle. SUMMARY OF THE INVENTION According to the present invention, there is provided an electrostatic chuck, comprising: a holder section, having at least two electrodes, for attracting and holding a substance placed on a surface with an electrostatic force produced by voltage applied across the electrodes; and a rotary section current transmitting mechanism for transmitting electric current to the electrodes, wherein said rotary section current transmitting mechanism includes: a rotary member connected directly or indirectly to said holder section, having an outer wall whose cross-sectional shape is circular, and being rotatable forward and backward within a limited angle; a stationary member provided around and concentric with the rotary member, separated from the rotary member by a ring-shaped space, and having an inner wall whose cross-sectional shape is circular; and a flexible belt accommodated in the ring-shaped space, said belt curving between both ends thereof which are fixed in the same direction respectively to the outer wall of the rotary member and to the inner wall of the stationary member, wherein said belt has at least one conductor provided in a film-shaped insulating material. In view of the above problems, it is an advantage that the rotary section current transmitting mechanism may be dust free, highly reliable, lasting and almost maintenance free. According to the above arrangement, if the relative angle between the inner member and the outer member changes within a predetermined range, for example, due to rotation of the inner member in a certain direction, the belt is wound around the outer wall of the inner member. If the inner member rotates in the other direction, the belt is stretched along the inner wall of the outer member. The ring-shaped space between the inner member and the outer member serves during rotation in any direction as a guide for preventing the belt from being rubbed or broken. Consequently, the belt moves (rolls in and out) smoothly in the ring-shaped space with its ends fixed to the inner and outer members. The belt, having at least one conductor provided on or in the insulating material, is, for example, a film-shaped wire having copper foil or other materials in a film made of polyimide. When the belt rolls in and out as above, the conductor (e.g., copper foil provided in the belt) allows the relative rotation angle between the inner member and the outer member to change, and also allows electric current to be transmitted between the inner member and the outer member. Consequently, there occurs little abrasion due to sliding motion between the belt and the outer and inner walls; hence the amount of dust is reduced. Besides, since the belt receives no strong force, there is almost no possibility that the belt breaks off. Therefore the belt is almost maintenance free. In addition, the inner and outer members are always electrically connected to each other via the conductor in the belt. The connection includes no sliding part, and therefore has more stable and reliable electric conductivity. Consequently, the present invention may provide an electrostatic chuck with a rotary section current transmitting mechanism which is almost dust free, noise free, maintenance free and highly reliable. Moreover, the conductor is fixed on or in the insulating material, and a plurality of conductors therefore can be held easily at a predetermined interval (insulation distance). Those conductors are insulated from each other by the film-shaped insulating material made of, for example, polyimide. Consequently, the number of circuits of the current transmitted by the rotary section current transmitting mechanism can be easily increased by increasing the number of conductors in the belt. In addition, since the mechanism has a configuration primarily utilizing the ring-shaped space around the inner member, the internal structure of the inner member is not limited: for example, the inside, of the inner member may be either empty or filled. As a result, the mechanism can be easily installed around a movable section already provided in various devices. In the arrangement, a wall insulating part made of insulating material, such as silicon rubber and polyacetal copolymer resin, is preferably adhered to a wall of the inner member and/or to a wall of the outer member which are walls facing the ring-shaped space so as to insulate the conductors in the belt from the walls. Therefore, even if the main body of the inner member or of the outer member is conductive, the conductors are prevented from being short-circuited with each other. Similarly, even if the conductors in the belt are exposed, the conductors are prevented from being short-circuited with each other, it is thus possible to prevent devices electrically connected to the conductors from being damaged. Alternatively, in the arrangement, a wall of the inner member and/or a wall of the outer member which are walls facing the ring-shaped space preferably have electric insulating property by being coated with fluororesin (fluorocarbon polymers). Or, at least one of the walls may have an electric insulating property with an anodic oxide film formed by anodic oxidation technique. In addition, after the anodic oxide film is provided on the wall(s), fluororesin may be also impregnated and/or coated on the wall(s) in order to enhance characteristics such as insulation and abrasion resistance. For example, when the inner and outer members are made of aluminum or aluminum alloy, a porous, hard and corrosion-resistive oxide film is formed first with anodic oxidation technique on the entire walls facing the ring-shaped space or a designated part of the walls. Then, the oxide film is impregnated (or, impregnated and coated) with fluororesin, such as polytetrafluoroethylene(PTFE). Such walls, having the aluminum surface provided with the hard oxide film which is impregnated (or, impregnated and coated) with fluororesin, have the following useful characteristics: (1) The walls have necessary electric insulating property and can prevent the conductors in the belt from being short-circuited with each other. (2) The walls have excellent abrasion resistance, and the wall surfaces do not peel. In other words, the wall surfaces are smooth and thus there occurs less friction (the coefficient of friction is smaller). Therefore, the belt is more lasting and moves more smoothly. Moreover, since the surface of the aluminum composing the main body is directly processed to form the wall surface into a film, i.e., a hard oxidized-aluminum film which is impregnated (or, impregnated and coated) with fluororesin, there is little possibility that the wall surface peels while the belt is moving. Consequently, the amount of particles (dust) is better reduced. (3) The walls are hard enough to be handled with ease and less likely to break or be damaged. (4) The walls have good heat resistance property, which can prevent unwelcome events such as deformation and denaturation caused by heat. Besides, the walls have good properties in corrosion resistance, precise scale workability and so on. For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view, showing an embodiment in accordance with the present invention, of a rotary section current transmitting mechanism of an electrostatic chuck of the embodiment. Fig. 2 is a cross-sectional view along the axis of the electrostatic chuck. Fig. 3 is a cross-sectional view of a film-shaped wire of the rotary section current transmitting mechanism. Fig. 4 is an enlarged and detailed cross-sectional view of the section P in Fig. 1, showing a wire fixing section of the film-shaped wire. Fig. 5 is an enlarged and detailed cross-sectional view of the section Q in Fig. 2, showing walls of a rotary member and a stationary member of the rotary section current transmitting mechanism. Fig. 6 is an explanatory drawing showing operation of the rotary section current transmitting mechanism. Fig. 7 is an explanatory drawing showing the relationship between size and rotation angle of the rotary section current transmitting mechanism. Fig. 8 is an enlarged and detailed cross-sectional view, showing another embodiment in accordance with the present invention, of walls of rotary and stationary members of a rotary section current transmitting mechanism which are walls facing a ring-shaped space in accordance with the present invention. DESCRIPTION OF THE EMBODIMENTS [FIRST EMBODIMENT] Referring to Figs. 1 through 7, the following description will discuss an embodiment in accordance with the present invention. An electrostatic chuck of the present embodiment is used in an ion implantation machine in order to attract and hold, for example, a wafer. A holder surface which attracts a wafer is provided so as to rotate both forward and backward within a predetermined angle to perform an operation, such as step implantation in which ion is implanted from various angles. As shown in Fig. 2, the electrostatic chuck includes a rotary section current transmitting mechanism 1. The rotary section current transmitting mechanism 1 has a rotary member 2 (an inner member) which rotates, and a stationary member 3 (an outer member), and is capable of transmitting positive and negative direct currents from the stationary member 3 to the rotary member 2. A holder base 4 of a disk shape is fixed on the upper surface of the rotary member 2. On the holder base 4, the main body 6 of the electrostatic chuck is disposed. The electrostatic chuck main body 6 (holder section), being of a disk shape, attracts and holds a substance 5, such as a wafer. The substance 5 which is attracted and held receives, for example, ion implantation treatment. Meanwhile, the rotary member 2 is fixed at the lower surface thereof on top of a rotation shaft 7 through which driving forces are transmitted from, for example, a direct drive motor (not shown). The stationary member 3 is fixed to a stationary section supporting member 8. In the present embodiment, the rotation shaft 7 is a power output shaft of a direct drive motor, while the stationary section supporting member 8 is a stationary section of the direct drive motor. In the present embodiment, the electrostatic chuck main body 6 is of a bipolar type, composed of a ceramics dielectric body 9 and two electrodes 10a and 10b. The electrodes 10a and 10b are of a half circle shape in its plan view, provided side by side in the dielectric body 9, and connected to the rotary section current transmitting mechanism 1 via wiring (not shown). As a d.c. voltage of, for example, about ± 350 v is applied by an external power source 11 across the electrodes 10a and 10b via the rotary section current transmitting mechanism 1, dielectric polarization occurs in the dielectric body 9 covering the electrodes 10a and 10b, thus producing electrostatic force, i.e, the attractive force. The electrostatic chuck main body 6 attracts and holds with the attractive force the substance 5 placed on the electrostatic chuck main body 6. Claws 12 for detaching the substance 5 are disposed at the circumference of the holder surface of the electrostatic chuck main body 6. The claws 12 reciprocate in the vertical direction with a driving force from, for example, an air cylinder (not shown), thus being capable of lifting and lowering the substance 5. The substance 5 lifted by the claws 12 is transported by, for example, a transport robot. Such an electrostatic chuck main body 6 can hold the substance 5 while preventing any material from touching the upper surface of the substance 5. Therefore, the electrostatic chuck main body 6 is useful in preventing particle adhesion to the surface of the substance 5 during, for example, ion implantation treatment. Referring to Figs. 1 and 2, the following description will discuss the rotary section current transmitting mechanism 1 in detail. Fig. 1 is a horizontal cross-sectional view at the X-X line in Fig. 2. As shown in Fig. 1, the rotary member 2 of the rotary section current transmitting mechanism 1 is of a disk shape, and has an outer wall 2a on the lower side thereof. The outer wall 2a has a circular shape in its horizontal cross-section, and the central axis thereof is designed to agree with the central axis of the rotation shaft 7 fixed on the lower surface of the rotary member 2. The stationary member 3 is made to be of a ring shape in its plan view and of an L-like shape in its vertical cross-sectional view. An inner wall 3a of the stationary member 3 has a circular shape in its horizontal cross-section, and is disposed around the rotary member 2 so that the central axis of the inner wall 3a agrees with the central axis of the outer wall 2a of the rotary member 2. Consequently, the inner wall 3a of the stationary member 3 and the outer wall 2a of the rotary member 2 face each other, and ring-shaped space 14 is formed therebetween. In the present embodiment, the rotary member 2 and the stationary member 3 are both made of aluminum alloy. A film-shaped thin and elastic electric wire 15 (belt) is accommodated in the ring-shaped space 14. An end of the film-shaped wire 15 is fixed to a wire fixing section 16 provided to the stationary member 3, whereas the other end is fixed to a wire fixing section 16 provided to the rotary member 2. The film-shaped wire 15 is fixed in the same direction at the wire fixing sections 16, and curves between the both ends. The curved part is shown as 15a in Fig. 1. As shown in Fig. 3, in order to apply positive and negative d.c. voltages to the electrostatic chuck main body 6, the film-shaped wire 15 has two conductors 17 disposed side by side with a predetermined spacing therebetween. The film-shaped wire 15 has a configuration in which the two conductors 17 are sandwiched between insulating films 18 and 19 (film-shaped insulating material) serving, respectively, as a base and a cover, and the conductors 17 and the insulating films 18 and 19 are all bonded by insulating adhesive 20. Although the conductors 17 are usually made of copper foil, stainless steel and aluminum are sometimes used instead. The insulating films 18 and 19, made of polyimide or polyester for insulation, mechanical strength and elasticity purposes, insulate the two conductors 17 from each other, the conductors 17 from the outer wall 2a of the rotary member 2, and the conductors 17 from the inner wall 3a of the stationary member 3. Although the width of the film-shaped wire 15 is not limited in principle, the width and the thickness of the conductors 17 are determined by the electric current to be carried by the conductors 17. The insulation distance between the conductors 17 is determined by the applied voltage and the material of the insulating films 18 and 19. The flex breakage number, an indicator for lifetime of the film-shaped wire 15, depends upon the thickness of the film-shaped wire 15 and the radius R of the curvature of the curved part 15a of the film-shaped wire 15. More specifically, as the film-shaped wire 15 becomes thicker, the flex breakage number becomes smaller: and as the radius R of the curvature becomes shorter, the flex breakage number becomes smaller. If the film-shaped wire 15 is required to have a certain predetermined flex breakage number, the radius R of the curvature can be made shorter by making the conductors 17 and the insulating films 18 and 19 thinner. The size of the rotary section current transmitting mechanism 1 as a whole can be hence made smaller. The radius R of the curvature is given by the following equation: R = (R 2 - R 1 ) / 2, where, as shown in Fig. 1, R 1 is the radius of the outer wall 2a of the rotary member 2, and R 2 is the radius of the inner wall 3a of the stationary member 3. The film-shaped wire 15 of the present embodiment has the following specifications. The insulating films 18 and 19 are made of polyimide and specified to have a thickness of 25 µm. The conductors 17 are made of rolled copper foil of 35 µm in thickness and 3 mm in width. The spacing (insulation distance) between the conductors 17 is specified to be 3 mm. This allows the film-shaped wire 15 to have a thickness of about 145 µm. In the present embodiment, the radius R 1 of the outer wall 2a of the rotary member 2 is specified to be 58.5 mm: the radius R 2 of the inner wall 3a of the stationary member 3 is specified to be 78 mm: the radius R of the curvature is specified to be 9.75 mm. An experiment have shown that these specifications result in a flex breakage number of the film-shaped wire 15 of more than 10 10 times. As shown in Fig. 4, an insulating reinforcing plate 21 is provided for a reinforcement purpose at each connecting part of the film-shaped wire 15 and the wire fixing sections 16. Each end part of the film-shaped wire 15 is folded parallelly to its sideline so as to sandwich the reinforcing plate 21, and fixed at the connecting part. The reinforcing plates 21 are so fixed by screws (not shown) to the wire fixing sections 16 that the conductors 17 in the film-shaped wire 15 are not affected. Each of the conductors 17 is electrically connected to wiring (not shown) in the wire fixing section 16 via a soldered joint 22 made of, for example, solder filling a hole formed in the insulating film 19. The wiring in the wire fixing section 16 of the rotary member 2 is connected to the electrodes 10a and 10b shown in Fig. 2. The wiring between the wire fixing section 16 and the electrodes 10a and 10b is not shown. Meanwhile, the wiring in the wire fixing section 16 of the stationary member 3 is connected to the external power source 11. The wire fixing sections 16 preferably have an insulating function if the rotary member 2 and the stationary member 3 shown in Fig. 2 are made of metal. As shown in Fig. 5, an insulating sheet 23 is provided as a wall insulating part to the outer wall 2a of the rotary member 2 and to the inner wall 3a of the stationary member 3. The insulating sheets 23 are, for example, made of silicon rubber. An insulating plate 24 is provided as a wall insulating part to an end surface of the rotary member 2 which is the upper surface of the ring-shaped space 14 and to an end surface of the stationary member 3 which is the lower surface of the ring-shaped space 14. The insulating plates 24 are made of, for example, polyacetal copolymer resin. Fig. 6 shows operation of various parts when the rotary member 2 rotates clockwise. The arrow B in Fig. 6 represents the rotation direction and rotation angle of the rotary member 2. The ring-shaped space 14 between the rotary member 2 and the stationary member 3 also serves in the rotary section current transmitting mechanism 1 as a guide for preventing the film-shaped wire 15 from being rubbed or broken. When the rotary member 2 rotates in the direction B, the film-shaped wire 15 is wound around the outer wall 2a of the rotary member 2. When the rotary member 2 rotates in the other direction (the opposite direction from the direction B), the film-shaped wire 15 is stretched along the inner wall 3a of the stationary member 3. The rotary member 2 rotating clockwise operates as shown in Fig. 6, while the rotary member 2 rotating anti-clockwise operates backwards in Fig. 6. Note that Figs. 1 through 7 show the film-shaped wire 15 touching neither the outer wall 2a nor the inner wall 3a. This, however, is for a better illustration of the film-shaped wire 15. The film-shaped wire 15 actually touches both the outer wall 2a and the inner wall 3a. As shown in Fig. 7, the maximum allowable rotation angle  [degree] depends upon factors, such as the radius R 1 of the outer wall 2a of the rotary member 2, the radius R 2 of the inner wall 3a of the stationary member 3, and the length L of the film-shaped wire 15. With the thickness of the film-shaped wire 15 ignored, the rotation angle  is given by the following equation (1):  = (180/π) (R 1 + R 2 ) {L - π (R 2 - R 1 ) / 2} / R 1 R 2 The equation (1) is derived as explained below. As shown in Fig. 7, let Y 1 [rad] represent the rotation angle of the rotary member 2, and Y 2 [rad] represent the winding angle of the film-shaped wire 15 stretched along the stationary member 3. As already mentioned, the radius R of the curvature of the curved part 15a of the film-shaped wire 15 is: R = (R 2 - R 1 ) / 2. Assuming that this does not change, and that the rotary member 2 is rotating as in Fig. 7, the following equations (2) and (3) hold. Y 2 R 2 = (Y 1 - Y 2 ) R 1 Y 2 = {R 1 / (R 1 + R 2 )} Y 1 The equation (3) is obtained by rearranging the equation (2). Meanwhile, referring to Fig. 7, assuming that the rotary member 2 is in its extreme position in the anti-clockwise rotation, the following equations (4), (5) and (6) hold: L 2 = L - L 3 = L - π (R 2 - R 1 ) / 2 Y 2 R 2 = L 2 Y 2 = {L - π (R 2 - R 1 ) / 2} / R 2 where L 2 represents the winding length of the film-shaped wire 15 stretched along the stationary member 3, L 3 represents the length of the curved part 15a of the film-shaped wire 15, and it is taken into consideration that L 3 = π (R 2 - R 1 ) / 2. The equation (6) is derived from the equations (4) and (5). The equation (3) is rearranged into the equation (7) in order to give the rotation angle Y 1 of the rotary member 2: Y 1 = {(R 1 + R 2 ) / R 1 } Y 2 The following equation (8) is obtained by substituting the equation (6) into the equation (7): Y 1 = (R 1 + R 2 ) {L - π (R 2 - R 1 ) / 2} / R 1 R 2 The equation (1) can be obtained by changing the unit of the equation (8) (i.e, radial) into degree. For example, in the present embodiment, the radius R 1 of the outer wall 2a of the rotary member 2 is specified to be 58.5 mm: the radius R2 of the inner wall 3a of the stationary member 3 is specified to be 78 mm: and the length L of the film-shaped wire 15 is specified to be 475 mm. Therefore, the maximum allowable rotation angle  obtained from the equation (1) is 761.6°. As discussed so far, the film-shaped wire 15 moves, without slipping, on the surfaces of the outer wall 2a of the rotary member 2 and of the inner wall 3a of the stationary member 3. Consequently, there occurs little abrasion due to sliding motion between the film-shaped wire 15 and the outer and inner walls 2a and 3a; hence there occurs little dust. Besides, since the outer and inner walls 2a and 3a guide the film-shaped wire 15, the film-shaped wire 15 smoothly rolls in and out. Since the film-shaped wire 15 receives no strong force, there is almost no possibility that the film-shaped wire 15 breaks off. Consequently, the film-shaped wire 15 is lasting and almost maintenance free. In addition, the film-shaped wire 15 does not tangle, and the film-shaped wire 15 placed closer to the rotation shaft 7 allows a greater maximum allowable rotation angle than conventionally used slack wires. In the film-shaped wire 15, the insulating films 18 and 19 relieve the tension applied to the conductors 17, and thus protect the conductors 17. In addition, since the insulating films 18 and 19 have better flex resistance than the metal composing the conductors 17, the film-shaped wire 15 seldom breaks at the curved part 15a shown in Fig. 1. Consequently, such a film-shaped wire 15 is more durable and reliable. Moreover, since the film-shaped wire 15 seldom breaks, the radius R of the curvature of the curved part 15a of the film-shaped wire 15 can be shortened. For example, if the film-shaped wire 15 is about 145 µm in thickness as in the present embodiment, a radius of curvature of not less than approximately 10 mm provides the film-shaped wire 15 with a long enough lifetime. Consequently, it is also possible to reduce the ring-shaped space 14, and hence reduce the rotary section current transmitting mechanism 1 in size. Meanwhile, the wire fixing sections 16 of the rotary member 2 and of the stationary member 3 are always electrically connected to each other via the conductors 17 in the film-shaped wire 15. The connection includes no sliding part, and therefore has more stable and reliable electric conductivity. For the same reason, the connection also reduces noise. Especially since semiconductor manufacturing machines are sensitive to noise and dust, they greatly benefit from the reduction thereof. For these reasons, the rotary member 2 can rotate both forward and backward within a limited angle, while the current can be stably transmitted between the rotary member 2 and the stationary member 3. Therefore, as shown in Fig. 2, the external power source 11 can provide electric power to the electrostatic chuck main body 6 rotating forward and backward within the predetermined angle. The uniformity in treatment of the substance 5 can be improved, and ion can be implanted uniformly to a side-wall of a groove part formed on the substance 5, by rotating forward and backward the substance 5 attracted by the electrostatic chuck main body 6. Furthermore, as shown in Fig. 3, the conductors 17 are sandwiched by the insulating films 18 and 19, and fixed with the insulation distance therebetween. Since the conductors 17 do not tangle and are insulated from each other, a plurality of conductors 17 are easily provided in the film-shaped wire 15. In addition, since the conductors 17 are covered with the insulating films 18 and 19, the conductors 17 are insulated from both the outer wall 2a of the rotary member 2 and the inner wall 3a of the stationary member 3. Note that the conductors 17 may be configured with no insulating film 19 so that the conductors 17 are placed on the insulating film 18 with a suitable insulating distance between the conductors 17 and then bonded by the insulating adhesive 20. In this configuration, even if the rotary and stationary members 2 and 3 have conductivity, the conductors 17 can be prevented from being short-circuited from each other by the insulating sheets 23 and the insulating plates 24. The conductors 17 in this configuration, however, need to be designed to have a suitable thickness so as not to be damaged and/or broken. Incidentally, Japanese Laid-Open Patent Application No. 8-96915/1996 (Tokukaihei 8-96915) filed by the same inventors of the present invention and published on 12.04.1996, has disclosed a configuration in which a conductor belt is used as a belt. In such a configuration, it is necessary to increase the number of the conductor belts if the number of circuits of the current transmitted by the rotary section current transmitting mechanism is to be increased. Therefore, the ring-shaped space 14 needs to be so divided according to the number of the conductor belts that each of the divided spaces can accommodate one conductor belt in order to prevent contact and ensure insulation among the conductor belts. The ring-shaped space 14 is divided by, for example, ring-shaped insulating partitions made of insulating material. In contrast, in the present embodiment, the number of conductors 17 in the film-shaped wire 15 can be increased in order to increase the number of circuits. Therefore, the film-shaped wire 15 need not be increased in number. As a result, the ring-shaped space 14 need not be divided by, for example, insulating partitions, and the number of circuits of the current transmitted by the rotary section current transmitting mechanism 1 can be thus easily increased. Moreover, the film-shaped wire 15 can also be configured so that a plurality of conductors 17 are provided in the thickness direction of the film-shaped wire 15. The configuration, realized by alternately stacking an insulating film and a conductor 17, allows the number of circuits of the current transmitted by the rotary section current transmitting mechanism 1 to be increased even more. In addition, the conductor belt as described above, is made of, for example, metal. The conductor belt is therefore hard to some extent and may break when the radius R of the curvature is too short. In the present embodiment, however, the thickness of the conductors 17 is specified to be considerably thin. The insulating films 18 and 19 are, as well as specified to be very thin, made of materials with better flexibility and flex resistance than those of metal of the same thickness. For these reasons, the film-shaped wire 15 lasts even longer. In addition, since the mechanism has a configuration primarily utilizing the ring-shaped space 14 around the rotary member 2, the internal structure of the rotary member 2 is not limited: for example, the inside of the rotary member 2 may be either empty or filled. As a result, the mechanism can be easily installed around a movable section already provided in various devices. Moreover, even when the conductors 17 are in an exposed state, the conductors 17 can be insulated from the rotary member 2 and the stationary member 3 by providing the insulating sheets 23 and the insulating plates 24 to the walls of the rotary member 2 and of the stationary member 3 which are walls facing the ring-shaped space 14. If the conductors 17 are in an exposed state, the exposed conductors 17 may become short-circuited and allow undesirably high current to flow, which is likely to break the rotary section current transmitting mechanism 1, the external power source 11 and/or loads connected to the rotary section current transmitting mechanism 1. The present embodiment, however, prevents such damages. Note that in the present embodiment, the rotary member 2 and the rotation shaft 7 are two separate members: however, the rotary member 2 may also serve as the rotation shaft 7. Besides, the inside of the rotary member 2 may be either empty or filled. Furthermore, the periphery of the stationary member 3 may take any shape as long as the cross-section of its inner wall 3a is circular. Moreover, in the rotary section current transmitting mechanism 1 of the present embodiment, the stationary member 3 provided along the outer circumference is fixed, while the rotary member 2 provided inside rotates. The rotary section current transmitting mechanism 1 may, however, be configured so that its outer part rotates and the inner part is fixed, because the relationships between a stationary member and a rotary member are relative. The mechanism may be also configured so that neither the outer part nor the inner part is fixed. The rotary section current transmitting mechanism 1 can also be employed for wiring of other purposes, apart from electricity feeding. [SECOND EMBODIMENT] Referring to Fig. 8, the following description will discuss another embodiment in accordance with the present invention. Here, for convenience, members of the second embodiment that have the same arrangement and function as members of the first embodiment, and that are mentioned in the first embodiment are indicated by the same reference numerals and description thereof is omitted. In the first embodiment, the insulating sheets 23 and the insulating plates 24 are adhered as wall insulating parts to the walls of the rotary member 2 and of the stationary member 3 which are walls facing the ring-shaped space 14. In this arrangement, however, since the insulating sheets 23 and the insulating plates 24 are adhered, they may peel when the film-shaped wire 15 moves. In other words, since the film-shaped wire 15 touches, during its movement, the insulating sheets 23 and the insulating plates 24, the film-shaped wire 15 repeatedly comes in and goes out of contact with the insulating sheets 23 and insulating plates 24. As a result, a strong stress may cause abrasion and/or peeling. This is not preferable in terms of durability and reliability because if peeling-off of, for example, the insulating sheet 23 ever happens, it causes particles (dust) to occur in the ring-shaped space 14. In contrast, in a rotary section current transmitting mechanism of the present embodiment, as shown in Fig. 8, the walls themselves have electric insulating property by being forming into insulating films 30, instead of adhering the insulating sheets 23 and the insulating plates 24 to the walls. The insulating film 30 is formed as explained below. The rotary member 2 and the stationary member 3 are made of aluminum alloy as in the first embodiment. The insulating film 30 is formed on designated wall surfaces of the rotary member 2 and of the stationary member 3. The designated wall surfaces refer to either the whole wall surfaces or part of the wall surfaces facing the ring-shaped space 14. More specifically, they refer to either (1) the outer wall 2a, the inner wall 3a, an end surface of the rotary member 2 which is the upper surface of the ring-shaped space 14, and an end surface of the stationary member 3 which is the lower surface of the ring-shaped space 14, or (2) part of those walls and surfaces. In order to form the insulating film 30, a porous hard oxide film is formed first with anodic oxidation technique on the designated wall surfaces. A hard oxidized aluminum film formed in such a manner already has good corrosion resistance and electric insulating property. Nonetheless, in order to form the insulating film 30 having even better characteristics, including insulation property, the oxide film is then impregnated (or, impregnated and coated) with fluororesin, such as polytetrafluoroethylene (PTFE). The insulating film 30, formed in the above-explained manner, has the following useful characteristics: (1) The insulating film 30 has necessary electric insulating property and can prevent the conductors 17 in the film-shaped wire 15 from being short-circuited with each other. For example, it is possible to realize a good electric insulating property with insulating resistance of 2 × 10 10 Ω and withstand voltage of 2800 V by forming the insulating film 30 having a thickness of 30 µm to 60 µm. (2) The insulating film 30 has excellent abrasion resistance, and does not peel. The insulating surface 30 has a small coefficient of friction, or in other words, the wall where the insulating film 30 is formed is smooth. Moreover, since the insulating film 30 is an oxidized aluminum film impregnated (or, impregnated and coated) with fluororesin, there is little possibility that the insulating film 30 peels while the film-shaped wire 15 is moving. Consequently, the amount of particles (dust) is surely suppressed. (3) The insulating film 30 is hard enough to be less likely to break or be damaged, and to be handled with ease. (4) The insulating film 30 has a good heat resistance property, and therefore does not deform or denature due to heat. Apart from the characteristics above, the insulating film 30 has good characteristics in corrosion resistance, non-stickiness, precise scale workability and so on. Therefore, it is possible to obtain a rotary section current transmitting mechanism of high durability and reliability by forming the insulating film 30 on the designated wall surfaces of the rotary member 2 and of the stationary member 3. As discussed above, the wall surfaces may have some electric insulating property with a hard oxide film formed by anodic oxidation technique on the designated wall surfaces of the rotary member 2 and of the stationary member 3. Alternatively, the wall surfaces may have some electric insulating property only by coating the wall surfaces with fluororesin, instead of forming the oxide film. The insulating film 30 may be formed in this manner, as long as the wall surfaces are provided with necessary characteristics, including electric insulating property. As discussed above, in the present embodiment, the insulating film 30 is formed by impregnating (or, impregnating and coating), with fluororesin, the porous hard oxide film made of aluminum with anodic oxidation technique. This is because various characteristics, such as abrasion resistance and durability in terms of peeling-off as well as the electric insulating property, are comprehensively taken into consideration in the present embodiment. The fluororesin may only impregnate the oxide film, or alternatively, the fluororesin may both impregnate and coat the oxide film. In addition, although the PTFE is used as the fluororesin in the present embodiment, other kinds of fluororesin may be also used. Moreover, even when the rotary member 2 and/or the stationary member 3 are/is not made of aluminum alloy, the insulating film 30 may be formed, so as to provide electric insulating property to the wall surfaces, by making the wall surfaces porous and then impregnating and coating the porous wall surfaces with fluororesin, or simply by coating the wall surfaces with fluororesin. As discussed above, the insulating film 30 formed at the designated wall surfaces of the rotary member 2 and of the stationary member 3 provides the wall surfaces themselves with enough electric insulating property to prevent the conductors 17 from being short-circuited with each other, and better reduces the amount of particles (dust). The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations may not be regarded as a departure from the scope of the invention, as defined in the following claims.

Claims: An electrostatic chuck, comprising: a holder section (4), having at least two electrodes (10a, 10b), for attracting and holding a substance (5) placed on a surface with an electrostatic force produced by voltage applied across the electrodes (10a, 10b); and a rotary section current transmitting mechanism (1) for transmitting electric current to the electrodes (10a, 10b), wherein said rotary section current transmitting mechanism (1) includes: a rotary member (2) connected directly or indirectly to said holder section (4), having an outer wall (2a) whose cross-sectional shape is circular, and being rotatable forward and backward within a limited angle; a stationary member (3) provided around and concentric with the rotary member (2), separated from the rotary member by a ring-shaped space (14), and having an inner wall (3a) whose cross-sectional shape is circular; and a flexible belt (15) accommodated in the ring-shaped space (14), said belt curving between both ends (16) thereof which are fixed in the same direction respectively to the outer wall (2a) of the rotary member (2) and to the inner wall (3a) of the stationary member (3), wherein said belt (15) has at least one conductor (17) provided in a film-shaped insulating material (18, 19). The electrostatic chuck as defined in claim 1, wherein a wall insulating part (23, 24) made of insulating material is provided on a wall of the rotary member (2) and/or on a wall of the stationary member (3) which are walls facing the ring-shaped space (14). The electrostatic chuck as defined in claim 1, wherein a wall surface (30) of said rotary member (2) and/or a wall surface of said stationary member (3) which are a whole or part of wall surfaces facing the ring-shaped space (14) have/has an electric insulating property. The electrostatic chuck as defined in claim 1, wherein the conductor (17) is made of copper foil. The electrostatic chuck as defined in claim 1, wherein the film-shaped insulating material (18, 19) is made of polyimide. The electrostatic chuck as defined in claim 2, wherein the wall insulating part (23, 24) is made of silicon rubber or polyacetal copolymer resin. The electrostatic chuck as defined in claim 3, wherein the wall surface (30) is made of an insulating film, and the insulating film is either a hard anodic oxide film, a fluororesin-coated film, or a hard anodic oxide film impregnated and/or coated with fluororesin. The electrostatic chuck as defined in claim 7, wherein at least parts of said rotary (2) and stationary members (3) which are in the neighborhood of the ring-shaped space (14) are made of aluminum or aluminum alloy, and the insulating film (30) is a hard anodic oxidized-aluminium film impregnated and/or coated with the fluororesin. The electrostatic chuck as defined in claim 8, wherein the fluororesin is polytetrafluoroethylene (PTFE).

Inventors: NOGAMI TAKASHI, TANAKA YOSHIHIRO, NOGAMI, TAKASHI, TANAKA, YOSHIHIRO, Nogami, Takashi, c/o Nissin Electric Co., Ltd., Tanaka, Yoshihiro, c/o Nissin Electric Co., Ltd.
Applicants: NISSIN ELECTRIC CO LTD, NISSIN ELECTRIC COMPANY, LIMITED
Application year: 1996
Main classification: H02G11
IPC codes: B60R16, H01R35, H01L21