Object holder for positioning an object in a radiation beam

Abstract: In an object holder comprising an X-Y translation mechanism, both movements are determined by transporters (8, 22) which are separately moved across a supporting face of a supporting plate (2) under a pressure in a sliding fashion. The pressing force is preferably realized by means of permanent magnets (16) which are mounted on the transporters and which bear on the supporting face of the supporting plate (2) by way of preferably ductile spacers. A device for rotation and/or tilting can be simply added by rotating and/or tilting the entire supporting plate with the X-Y translation mechanism.

Description: The invention relates to an object holder according to the preamble of Claim 1 Such an object holder is known from GB 1 323 300. In known object holders a X-Y translation mechanism is constructed so that an X-transporter for translation in a X-direction carries a carriage for translation across the X-transporter in a Y-direction, the X-transporter acting as a reference and supporting face for the Y-transporter or vice versa. This results in a comparatively complex translation mechanism where errors in the second translation constitute a sum of errors in both translation systems and where a undesirable rotary movement and tilting can readily occur during the last translation motion. This is understandable because, considering the desirable low-friction movements, it is difficult to prevent a given play for each of the guides. This is extremely undesirable in object carriers where angular orientation of an object is co-decisive for the accuracy of measurements to be performed. Therefore, in the said document GB 1 323 300 it is proposed to attach a X-guide and a Y-guide directly to a supporting plate, the movements of the both guides being independent from each other. Because each of the two translatory movements separately refers directly to a supporting face of a supporting plate in the translation mechanism, a simple and inexpensive movement mechanism is achieved which offers accurate positioning and in which undesirable rotation and tilting are minimized. In the cited documents it is described that the moving parts of the translation mechanism are supported by aerostatic precision bearings. No further supporting means are disclosed in this document. Such bearings are complicated and sensitive supporting means, which moreover only function as desired when the supporting plate does not deviate too much from the horizontal state. It is therefore a object of the invention to provide a more simple and cheap way of supporting the transporters carrying the object table. To achieve this, the object holder according the invention is characterized in that a magnetic force of attraction is used for the contact pressure of the X-transporter and the supporting plate and a Y-transporter with the supporting plate. In a preferred embodiment in accordance with the invention the pressure exerted towards the supporting plate is realized by way of permanent magnets which are coupled to the X-transporter and to a support for the object table, which magnets preferably bear on the supporting face of the supporting plate via intermediate spacer which are preferably ductile to some extent. In addition to a smooth sliding contact, a desirable air gap is thus also achieved. In a further preferred embodiment, a rotation of the object table is added to the X-Y translation; this is comparatively simply achieved by mounting the supporting plate so as to be rotatable about an axis extending transversely of its supporting face. Driving can be realized by mounting a motor-driven rotation mechanism on a rear side of the supporting plate (with respect to the object table), the axis of rotation preferably extending through the centre of a substantially circular supporting plate. An object tilting mechanism for tilting the supporting face of the supporting plate can also be added to the supporting plate. If the angles of tilt need not be very large, for example no more than approximately plus and minus 10°, use can be made of a shaft in the form of a cylindrical bush which is partly open in the lateral direction, so that at that area a free passage is realized for a radiation beam extending parallel to the supporting plate. Some preferred embodiments in accordance with the invention will be described in detail hereinafter with reference to the drawing. The sole Figure of the drawing shows an object holder in accordance with the invention whereto a rotation mechanism as well as a tilting device, have been added. An object holder as shown in the Figure comprises a supporting plate 2 on which an X-guide 6 is mounted, preferably by way of a bracket 4 connected to the rear side. An X-transporter 8 is displaceable along the X-guide, for example in known manner by means of rollers 9, over a distance of up to, for example 50 mm or more. The X-transporter 8 is driven by a motor 10 via a transmission 12. In order to save space, the motor 10 is arranged parallel to the X-guide, but this is irrelevant for the invention. On a side which faces the supporting plate 2 the X-transporter 8 is provided with preferably three magnets 16 (for kinematic reasons), which magnets bear on the supporting plate via intermediate spacers 18 and are pressed against the supporting plate by the magnetic force produced by the magnets. It is thus achieved that the X-transporter always moves exactly parallel to the supporting face 14. The flatness of the supporting plate 2 at the area of the supporting face determines the accuracy of displacement. Such a plate, being made of a magnetic material in order to realize the magnetic pressing force, can be worked so as to be flat in an extremely accurate as well as comparatively inexpensive manner. A layer against corrosion of notably the supporting face can be locally provided. If desirable, in order to achieve an adjustable pressing force use can also be made of magnets to be energized by coils, a minimum energization being substained in order to prevent the transporter from coming loose from the supporting plate; this can alternatively be ensured by a permanent sub-magnet. The X-transporter supports an Y-guide 20 for guiding an Y-transporter 22 which is displaceable along the Y-guide, via wheels (not shown), in exactly the same way as the X-transporter. The Y-transporter is also pressed against the supporting face 14 of the supporting plate 2 by way of magnets 16 and spacers 18 (not separately shown). Therefore, also the Y-transporter will always move parallel to the supporting face 14 and rotation or tilting errors will not be summed. Rotations about an axis transversely of the supporting plate are determined as a function of the degree of straightness of the guides; such straightness can also be comparatively simply realized. The Y-transporter is driven by a motor 24 which drives a spindle 28 via a transmission 26. The Y-transporter supports an object table 30 on which an object, for example a wafer can be mounted, for example on supporting points 32. In the embodiment shown the object table 30 is rotatable about an axis 36 extending transversely of the supporting face 14. To this end, the supporting plate supports a gearwheel 38 which is driven by a motor 40, via a spindle 42 which is supported by a holder 44 and which realizes a rotation of, for example up to 360°. As a result of this construction, an object arranged on the object table can be rotated into any desirable X-Y position in the radiation beam path. To this end, the rotary shaft 34 of the supporting plate is connected to a support 46 for the object holder. Via this support, the object holder can be mounted on or in an apparatus, for example an X-ray analysis apparatus, a wafer inspection apparatus and the like. When the object table is mounted so as to be tiltable about an axis 48 parallel to the supporting face as shown, the rotary shaft 34 is coupled via a bracket 50. Using a drive motor not shown, the bracket 50 is tiltable, together with the supporting table and the X-Y translation mechanism, through an angle of, for example plus and minus 10° with respect to a vertical zero position of the supporting plate. In order to offer free passage to a radiation beam, bushes 52 for tilting are provided with lateral apertures 54. An object carrier in accordance with the invention can be successively used in X-ray analysis apparatus, in wafer inspection apparatus and the like where an object carrier of the described kind can be mounted on or in such an apparatus by means of the support 46. An object to be examined may then also be accommodated in a space to be evacuated.

Claims: An object holder for positioning an object in a radiation beam, comprising an X-Y translation mechanism which comprises an X-guide (6) and an X-transporter (8), which X-guide (6) is connected to a flat supporting plate (2) in order to guide the X-transporter (8) which is translatable across the supporting plate (2) under contact pressure, the X-Y translation mechanism further comprising a Y-guide (20) and a Y-transporter (22), which Y-guide (20) is connected to said X-transporter (8), for guiding an object table (30), characterized in that magnetic forces of attraction are used for the contact pressures of the X-transporter (8) with the supporting plate (2) on the one hand and the Y-transporter (22) with the supporting plate (2) on the other hand. An object holder as claimed in Claim 1, characterized in that the magnetic attraction force between the X-transporter (8) and the supporting plate (2) is produced by permanent magnets (16) which are secured to the X-transporter and which bear on a supporting face (14) of the supporting plate (2) via intermediate sliding pieces (18). An object holder as claimed in Claim 1 characterized in that it comprises a rotation mechanism for rotating the supporting plate (2) about an axis (34) extending transversely of a supporting face (14) thereof. An object holder as claimed in Claim 3, characterized in that rotation is possible through at least 360°. An object holder as claimed in Claim 1, characterized in that it also comprises a tilt mechanism (50, 52) for tilting the supporting plate (2) about an axis (48) extending parallel to a supporting face (14) thereof. An object holder as claimed in Claim 5, characterized in that bushes (52) for the tilting movement are provided with cut-outs (54) which act as passages for a radiation beam.

Inventors: BOKSEM JAAP, BOKSEM, JAAP
Applicants: PHILIPS NV, N.V. PHILIPS' GLOEILAMPENFABRIEKEN
Application year: 1989
Main classification: G02B21
IPC codes: G12B5, G02B21, G02B7, G21K5, G01N1