JP3429007B2 - Optical position measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical position measuring device, which can be used in connection with a particularly precise positioning drive.

In semiconductor manufacturing, linear motors of various construction types are often used as drive units for the precise relative positioning of various components, possible areas of use being wafer processing or so-called wafer testing. If the movable component is to be positioned not only in one dimension but also in two dimensions, then particular requirements are placed on the measuring system used to detect each movement in different coordinate directions. . Besides the detection of the displacement movement in the two coordinate directions, it is often necessary for this purpose to detect the rotational movement of the component to be positioned about a predetermined axis. In this case, for each moving phase, US Pat.
From the specification No. 1 it is known to provide a separate interferometer. In addition to problems with limited measuring range, blocking of the measuring light path, etc., the high costs of interferometers at present result in relatively high expenditures.

In addition, there is the additional problem that the periodic structure of the stator unit, which is normally present in the linear motors used here, is used for measuring purposes as well as for generating drive movements. Depending on the configuration of the linear motor used, this structure can be intended for two-dimensionally arranged toothed soft iron structures or periodically arranged permanent magnets of different or identical polarity. It is known to scan this structure by means of magnetic field-sensitive elements or a corresponding ring structure in order to generate a scanning signal which is modulated in a movement-dependent manner. The periodic structure used for generating the driving movement has a pitch period of the order of 2-3 nm. For the resulting scanning signals, the maximum resolution sometimes achievable is poorly obtained for precision use. To improve the measurement accuracy or resolution,
It is therefore proposed to arrange a known glass graduation plate on which a measuring graduation can be mounted between the movable drive units, ie for example incorporating such a drive unit with a commercially available cross grating measuring system. The drive unit, which is movable relative to the cross-grating measuring graduation, is provided with one or more suitable scanning units, via which the optical scanning of the measuring graduation and the associated rotation thereof. Corresponding determinations of the positions including the corners can be made in a known manner. In principle, such precision use also achieves sufficient resolution in positioning, since such cross gratings with graduation periods clearly located in the nm range can be produced. Is. However, in the case of stepper motors with a periodic soft iron structure, the achievable thrust force is sensitively dependent on the distance between the stator and the movable drive unit or rotor. If a predetermined distance between the two drive units which are movable relative to one another is exceeded, then no drive movement can occur. This is the case when the glass graduation plate with a thickness of 2-3 mm of a commercially available cross grating measuring system is arranged between both movable drive units of the step motor.

The object of the present invention is to devise an optical position measuring device for enabling an accurate determination of the relative position of these elements, especially in connection with a fine positioning drive unit of the various elements. The functioning method of each type of drive unit should then not be affected by the additional position measuring device. This requires a simplest possible construction of such a position measuring device.

This task is solved by an optical position measuring device having the features of claim 1.

Advantageous embodiments of the optical measuring device according to the invention result from the measures in the dependent claims.

On the basis of the shape of one of the two drive units which can be moved relative to each other and of the measuring graduation as an integral component, the distance between the two drive units is such that a specified relative movement is generated between them. It can be chosen to allow highly efficient cooperation. This also guarantees the function of the stepper motor, which operates in a relatively distance-sensitive manner. A stepper motor, for example with a soft iron stator, can also be replaced with the optical position measuring device according to the invention without impairing the way it functions. If an optical measuring scale with a scale period in the μm region is used,
At the same time, the position measuring device ensures a desired high resolution.

According to the invention with regard to the construction of the drive unit with the associated measuring scale, there are various possibilities. For example, the measuring graduation can be arranged directly on the flat surface of the drive unit or in its grading area. It is also possible to provide the measuring scale on a scale plate arranged on the flat surface of the drive unit. A series of different implementation variations
It is stated in the dependent claims.

The optical position measuring device according to the invention can then be used both for measuring one-dimensional running movements and for identifying running and / or pivoting movements in a positioning function in one plane. Sometimes, in the case of a locating function in one plane, it has proved to be advantageous to receive air bearings between drive units which are arranged movably with respect to one another, so that a friction-free positioning is possible.

An advantageous embodiment according to claim 7 is characterized in that a plurality of drive units constructed according to the invention are arranged directly adjacent to one another and the scanning is via two separate scanning units arranged on a common slider. It is obtained when it is carried out.
Such an embodiment of the position-measuring device according to the invention proves to be suitable as long as large driving movements can thereby be detected and at the same time only a relatively compact drive unit is required. In principle, in such a modified configuration of the drive unit, only a single scanning unit can be provided if the predetermined requirements for the abutment points of the drive units bordering one another are met.

Further advantages and details of the optical position measuring device according to the invention result from the following description of exemplary embodiments on the basis of the drawings. That is, FIG. 1a is a cutaway plan view of a diagrammatically illustrated first embodiment of an optical position measuring device according to the present invention.

1b is a side sectional view of the position measuring device according to the invention of FIG. 1a.

FIG. 2 is a side sectional view of a second embodiment schematically showing a drive unit of an optical position measuring device according to the present invention.

3a and 3b are two views of a third embodiment of the drive unit of the optical position measuring device according to the invention.

FIG. 4 is a diagram representing another variation of the position measuring device according to the invention with immovable drive units abutting one another.

The first embodiment of the optical position measuring device according to the present invention is
It is partly shown in FIG. 1a in a schematic representation. FIG. 1b shows a side sectional view of this first embodiment along the section line drawn in FIG. 1a. The illustrated embodiment of the optical position-measuring device according to the invention can be used, for example, in semiconductor manufacturing for the precise positioning of components which can be moved relative to one another in a plane. It is shown in connection with. In this case, the drive unit is formed as a step motor having a stationary drive unit 1 and a drive unit 2 movable relative thereto. In an advantageous embodiment, the mobile drive unit 2 is friction-free mounted on the drive unit 1 via suitable air bearings. The drive unit 1 is furthermore formed in this embodiment as a soft iron stator, which is three-dimensionally configured with a cubical ridge 6 on the base body 5 and a recess 9 located between them. Has an area. For the generation of the drive movement, the mobile drive unit 2 has a plurality of excitation coils, not shown, which are controlled in a known manner, i.e. a time-specific excitation of the excitation coils. Through this, stepwise positioning of the movable drive unit 2 in the xy plane is possible. For this purpose, the movable drive unit 2 is connected via a connecting wire to a suitably formed control and evaluation unit 3. For the desired, high-resolution positioning of the mobile drive unit 2 in the xy plane, an optical position measuring device is provided in this embodiment, which produces a scanning signal which is dependent on the movement. The measuring graduation 8 associated with the drive unit 1 is scanned by one or more scanning units which are formed in a known manner and are arranged on the side of the movable drive unit 2. In the display of FIGS. 1a and 1b, only a single scanning unit 10 is visible on the side of the mobile drive unit 2, but also including the determination of the angle φ at which the mobile drive unit 2 can be pivoted about a vertical axis. For such a complete detection of movement in the xy plane, three such scanning units are provided. Each scanning unit 10 has for this purpose a light source 11 as well as at least one optronic detection element 12, which receives the light reflected from the measuring graduation 8. There are many known possibilities for the configuration of the scanning unit 10 to provide additional suitable transmission optics, scanning gratings, a plurality of suitably connected detector elements, etc. The measuring graduation 8 scanned by the reflected light or the illumination light is formed as a cross grating in the case of the two-dimensional movement of the movable drive unit 2 shown in the drawing, and the cross grating is used for obtaining the incremental position information by a known method. To be scanned. The graduation period of the measuring graduation 8 is, as already mentioned in the case of optical scanning, more than the period of the cubic ridges 6 which can be scanned to obtain position information, for example via other scanning principles. Obviously small. The meaningful graduation period of the measuring graduation 8 lies in the range of 1-100 μm. In the case of a 100 times interpolation of the scanning signal formed, this gives a possible resolution in the case of localization of 0.01 to 1 μm.

Of course, the arrangement of the optical position-measuring device according to the invention described below is not limited to the illustrated case of movement in two dimensions, i.e. also comprises a similar linear stepper motor which only allows positioning in one dimension. In this case, for example, the air bearing mechanism can be dispensed with and a separate guide of the movable drive part can be provided. As the measuring graduation, a known one-dimensional, reflection-type incremental graduation with an array of graduation structures periodic in the measuring direction is used here.

In order to ensure the functioning of the stepper motor in connection with the desired positioning, according to the invention, in the exemplary embodiment shown, a graduation plate 7 with a measuring graduation 8 is mounted as an integral part of the drive unit 1. Formation is considered. For this purpose, the recesses 9 between the ridges 6 of the drive unit 1 are provided with a filling material, so that a flat surface of the drive unit 1 is obtained. Certain requirements are taken into account for the filling material for the recess 9 used in this embodiment. First, in order not to affect the function of the step motor as much as possible,
The filling material must be non-magnetic. The material used for this guarantees the production of a surface of the drive unit 1 which is as flat as possible, i.e. must not be ground and bulged as well as possible.

Furthermore, in some cases it should ensure the best possible adhesion of the overlying layers. Furthermore, it is advantageous that the filling material used has a coefficient of thermal expansion similar to that of the material around the drive unit 1. Under this requirement, hard solder is the preferred filling material. Filling with other non-magnetic metals or synthetic resins can also be performed selectively. After filling the recesses 9 with a suitable filling material, the surface of the drive unit can be polished according to the flatness requirements in the subsequent processing steps. On the surface of the drive unit 1 which is as flat as possible, a thin layer is applied which serves as a scale plate 7. The material of the graduation plate is applied in a known manner, for example so-called spin-on glass or sol-
Gel materials can be targeted. Furthermore, for example, a thin metal layer, for example chromium, can be used as the scale plate.
The thickness of the layer used as the scale plate 7 is several nm. Subsequently, a specific measuring scale 8 is attached or configured on the scale plate 7. In this case, the measuring graduation 8 which is scanned with the illumination light is preferably a periodic structure having a reflective region of TiN and a non-reflective region of TiO ₂ , for example. Alternatively, a structure in which a reflection region made of Cr is provided on a CrO layer that does not reflect light is also possible. Scale plate 7 configured as such
Is provided. The unique structure of the various regions can then be effected via the known photolithographic techniques.

Finally, it is optionally also possible to form the scale plate as a metal film which can be constructed in a known manner, i.e. in a known manner for the production of steel measuring rules. The use of lasers or the like is also possible in this context, eg for construction. The metal film, including the scale structure disposed thereon, can then be glued onto the flat surface of the drive unit.

In contrast to simply arranging the glass plates of a commercially available cross-grating measuring system on the surface of the drive unit 1, the measures according to the invention allow between the drive wire 1 on the one hand and the exciter wheel of the movable drive part 2 on the other hand. It can be ensured that the distance d is not too large and in some cases the driving movement can no longer take place. The layer arranged on the flat surface of the drive unit 1 having the scale plate 7 and the measuring scale 9 has a thickness of 1 μm.
It has a thickness on the order of m. Thereby, in the described embodiment, it is possible to co-operate the drive unit 1 with the drive unit 2 which is movable relative thereto, and thus the specified relative movement between both drive units 1, 2. Can be generated.

A drive unit with a periodic structure can be used as a movable drive unit, in an alternative, of course, in a similar manner to the previously described variations with a periodic structure on the side of the stationary drive unit. The scale plate, including the measuring scale, is in this case attached to the movable drive unit in a manner similar to that described above.

A second embodiment of the drive unit 21 that can be used in the optical position measuring device according to the invention is represented diagrammatically in FIG. Unlike the described first embodiment,
Another periodic structure is provided on the side of the drive unit 21, which can be used for a permanent magnet-linear motor. On the base 25 of the drive unit 21, rectangular permanent magnets 26 are arranged as a periodic pattern similar to the first embodiment, in which case adjacent permanent magnets 26 have different polarities in FIG. The sequence having is made. Alternatively, these permanent magnets can be collectively arranged in the same direction. The generation of the drive movement of the relatively movable drive unit (not shown) is effected in a known manner by corresponding control of the exciter wheel in the other drive unit. As in the first embodiment,
The recesses 29 between the permanent magnets 26 are filled with a filling material, so that a flat surface of the drive unit 21 is obtained. On such a flat surface a layer is applied, which is subsequently used as a graduation plate 27, on which a further measuring graduation 28
Is provided. Reference is made to the above description for the possible configurations of the graduation plate 27, the measuring graduation 28 and the requirements for the filling material.

Another embodiment of the optical position measuring device according to the invention is
It is represented diagrammatically in two partial views, FIGS. 3a and 3b.
The measurement scale 58 is further attached to the drive unit 51,
The drive unit is similar to the first embodiment and has a periodic structure with the ridges 56 and the recesses 59 located between them on the base body 55, ie of the drive unit 51 formed as a soft iron stator. The movable drive unit which is arranged above and which has an exciter wheel, as well as the drive unit or units used for the illumination light scanning of the measuring scale 58 on the drive unit 51, are:
Not shown. Unlike both embodiments described above, the measuring graduation 58, which is formed as a cross grid as an integral component of the stationary drive unit 51, can be arranged directly on the flat or flat component. It is done, i.e. no separate scale plate is required.

Corresponding surface planarization takes place as described above, ie by filling the recesses 56 with a filling material, for example hard solder. The surface is then polished to give the measuring graduation 58 before any intrinsic structure formation takes place. At that time, the measuring scale 58 is composed of periodically arranged reflecting regions such as TiN / TiO ₂ and non-reflecting regions. As an alternative to the variants shown, the measuring graduations can only be applied in a partial region of the surface of the drive unit according to the respective measuring requirements, for example only on a flat surface such as a ridge.

A particularly advantageous embodiment of the optical position-measuring device according to the invention is represented diagrammatically in acid 4. In this case, two separate drive units 31.1, 31.2 arranged adjacent to each other
It is shown. The configuration of both drive units 31.1, 31.2 is
Corresponding to the drive unit of the first embodiment described in FIGS. 1a and 1b, that is to say on the surface of the drive units 31.1, 31.2 are crossed measuring scales 38.1, 38.2 as integral parts of the drive units, respectively. A grid is arranged. Above both drive units 31.1 and 31.2, xy
A movable drive unit 32 is provided which can be positioned in the plane. The mobile drive unit 32 in the illustrated embodiment has in particular two scanning units 40.1, 40.2, which are arranged on both lateral sides of the drive unit 32 and by means of which cross-grating measurement is carried out. Optical scanning of the scale is performed. In addition to determining the amount of movement in the xy plane, the rotation of the movable drive unit 32 about a vertical axis oriented in the z direction can also be detected by the mechanism shown. Through this embodiment, a large driving range of the movable drive unit can also be realized with such a drive unit according to the invention, and at the same time an optical position measuring device with high resolution is possible. For this purpose, a plurality of small drive units, which are collectively constructed in the manner described, can be aligned with one another. For that purpose, it is not necessary to make a single large-area drive unit containing a large-area measuring graduation, and a predetermined stator size, which is correspondingly aligned according to the required travel area, can be used. In the embodiment shown in FIG. 4, the scanning units 40.1, 40.2 are arranged on the side surface of the movable drive unit 32 at two intervals, that is, they are separated from each other by one of the scanning units 40.1, 40.2. There is no passage over the abutment points of the drive units 31.1, 31.2 that touch. To this end, in another embodiment, the selectively movable drive unit has only a single scanning unit in the modular construction of the drive unit. In this case, furthermore, in order to ensure an accurate positioning also at this point, certain requirements are set at the abutment point which can be passed by the scanning unit. In a first variant, a sufficiently precise production of the measuring graduation ensures that no erroneous measurements occur at this point, especially in the region of the abutment point of the drive unit that directly borders. In a second variation with only a single scanning unit in this area, it is possible to provide a certain amount of distance between the drive units which selectively border each other. This specific distance can be adjusted during assembly of the entire drive unit of individual modules via a suitable optical adjustment device. Even in this case, it is ensured that no error occurs in the position determination when the scanning unit passes through the abutting point.

Based on the arrangement according to the invention, in connection with different stepper motor variants, the high resolution allowed,
A set of feasibility is obtained which guarantees optical positioning.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Allgauer Michael, Federal Republic of Germany, D-83371 Stein, Keenbergstraße, 24 (72) Inventor, Karimitsian Christian, Federal Republic of Germany, D-83714 Mies Bach, Anger 25 (56) Reference JP 63-148856 (JP, A) JP 63-148855 (JP, A) JP 3-124255 (JP, A) JP 8-191564 (JP, A) ) JP-A-2-65652 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H02K 41/03 G01B 11/00 G01D 5/34 H02P 7/00

Claims (10)

(57) [Claims] 1. Two mutually movable drive units (1,
2; 21; 31.1,31.2,32; 51,52), an optical position-measuring device for a drive device for precise positioning, comprising M1) both drive units (1,2; 21; 31.1, 31.2, 32; 51, 52)
One of which is a three-dimensionally structured region having ridges (6; 26; 56) and recesses (9; 29; 59) between the three-dimensionally arranged regions which are periodically arranged in one or two dimensions. And M2) This one drive unit (1; 21; 31.1,31.2; 51)
Is a measurement scale (8; 28; 38.1,3 as an integral component
8.2; 58), the measuring scale being scanned by a scanning unit (10; 40.1,40.2) coupled to the other drive unit (2; 32; 52) for the generation of a position-dependent output signal, M3) The measuring graduations (8; 28; 38.1,38.2; 58) on the layer serving as graduation supports (7; 27) are provided on the one drive unit (1; 2).
1; 31.1,31.2; 51) on a flat surface, including the measuring graduations (8; 28; 38.1,38.2) and serving as graduation supports (7; 27) That is, the scanning unit (10; 40.1,40.2) of the other drive unit (2; 32; 52) to which the one drive unit (1; 21; 31.1,31.2; 51) is relatively movable. ), And M4) scale support (7; 27) and measuring scale (8; 28; 38.1,38.
2) the one drive unit (1; 21; 31.1,31.2; 5)
The recess (9; 29; 59) is provided with a filling material for flattening the surface of (1), and the filling material is provided in the one drive unit (1; 21; 31.1,3).
1.2; 51) to allow the formation of a flat surface and yet to ensure good adhesion of the layers arranged thereon, both drive units (1, 2; 21; 31.1,31.2,32; 51, 52) The optical position measuring device, which does not affect the interaction of 52). 2. A drive unit (1; 21; 3) for the one of the fillers.
1.1, 31.2; 52) having the same coefficient of thermal expansion as the surrounding material. 3. Spin-on glass is selected as a material for the scale support (7; 27).
The optical position measuring device according to. 4. The optical position measuring device according to claim 1, wherein a sol-gel material is selected as a material of the scale support (7; 27). 5. Optical position measuring device according to claim 1, characterized in that the scale support (7; 27) is formed as a thin metal film. 6. The metal film has a reflective region and a non-reflective region as a scale.
The optical position measuring device according to. 7. A precision positioning device for components movable in a plane, the device comprising two adjacently arranged optical position measuring devices according to claim 1. Or more drive units (31.1, 31.2) and at least one scanning unit (4
0.1, 40.2) and a movable drive unit (32), and the scanning unit includes the other drive unit (31.1,
31.2) A device as defined above, which is designed for optical scanning of measuring graduations (38.1, 38.2) arranged on it. 8. Device according to claim 7, characterized in that the movable drive unit comprises two scanning units (40.1, 40.2) spaced apart. 9. The movable drive unit has a single scanning unit, the movable drive units with graduations are arranged in direct contact with each other, and the movable drive units are separated from each other at an abutting point. 8. The device according to claim 7, wherein the measuring graduations are connected to one another exactly. 10. The movable drive unit according to claim 7, wherein the drive units having a single scanning unit and carrying the measuring scale are arranged at mutually specified intervals. The described device.