DE10357062B4 - System for measuring the tilt of structured surfaces - Google Patents

Abstract

System for measuring the tilting, in which an optical system throws a light beam onto a surface, which is radiated again and impinges on a detector, characterized in that
for interference-free, fast and accurate measurement of the tilt either the surface of the plane to be measured is structured, or this structuring is driven partially or completely through the tilt plane, so that the incident radiation is either reflected or transmitted at the tilt plane, the structuring the tilting plane is designed in such a way
that the beam path of the incident radiation is changed by refraction and / or diffraction, so that on the radiation-sensitive detector of the evaluation circuit for the structuring characteristic change of the spatial pattern or energy focus, the reflected from the tilt plane / transmitted radiation results.

Description

The The invention relates to a system for measuring tilting according to the preamble of Patent claim 1.

to Determination of tilting find a number of measuring principles Application. The existing systems are executed macroscopically and Almost all are inherently not for use in microsystems technology (Order of magnitude of Micrometers).

Out The prior art are measuring systems that tilt a Use electrode arrangement in an electrolyte as a measurement signal, known (P1). This principle is based on gravity and has the horizon as a frame of reference, as the surface of the Electrolytes in the case of equilibrium always due to gravity Aligns parallel to the horizon. In (P2) is also an electrolytic Sensor principle presented. Another measuring principle by means of magnetic liquid is described in (1). (P3) describes a system that the Seebeck effect uses for measuring the tilting. This system is also gravitational and has the horizon as a 0 degree reference frame.

One Another measuring system works capacitively according to the principle of an electric Capacitor. Since electric field and charge distribution as independent of dominant gravitational field can be seen, this is oriented Measuring system not on the visible horizon.

(P4) describes an optical principle for measuring position and tilt by oblique Incidence and reflection on an unstructured surface. Around, especially at very low tilting (eg 0.1 to 5 °), an in the practice good sensitivity between tilting degree and change of location of the reflected beam to reach on the PSD, must be at an angle that is different from 90 ° (this is also specified in (P4)), irradiated on the tilting surface become. The reflection of the oblique incident light beam, however, finds it on an unstructured surface instead, here the principle of simple reflection (angle of incidence equal failure angle) is used. Existing optical and capacitive Measuring systems such as Micro-Epsilon GmbH & Co KG use the diffuse scattering at the reflection plane to calculate the distance. The in (P5) only deals with the special case the tilting of two plates, which is a common Turn axis.

First is find that (P1) - (P3), macroscopic Describe systems. These systems are not for tilt measurement to use in microsystems technology. In these procedures happens In addition, the tilt measurement is not contactless, d. H. these sensors have to be applied by hand or by machine to the test object. This is in microtechnical constructions where in the micrometer range on the one hand, no manual assembly possible is and apart from the measurement object from the outside, so after the process engineering Manufacturing, often unavailable, not at all or only very limited possible. The cited thermal measuring system (P3) is also inherently sluggish and the electrolytic system very sensitive to vibration; it was because it would higher viscosity liquids which in turn increases the response time and the measuring system makes you sluggish.

These Disadvantages avoid the capacitive and optical measuring methods. she do not use lethargic or vibration-sensitive Medium and work without contact. Both methods are applicable in microsystem technology, wherein optical methods still have the advantage of being very scalable and with consistent accuracy for both macroscopic and microscopic Constructions to be suitable. Furthermore, optical and capacitive Systems with their fast response time suitable for real-time monitoring. Optical methods also have the advantage that the measuring principle insensitive to electromagnetic interference fields and she herself is not a source of electrical interference occur.

task The invention is a fast and yet highly accurate, relatively easy to integrate and universal, also in microsystem technology, to find usable measuring system. The measuring principle should be relative Easy to integrate into existing systems, look good in the scale dimensions up and down and also vertical Allow incidence of the measuring beam (eg by highly integrated beam sources as vertical surface emitting Laser (VCSEL) for to use the tilt measurement in microsystem technology).

Another object is to be able to realize with the specified in claim 1 invention, a feedback system for micro-optical application, adjusted with the tilting of micromirrors and controlled long-term stability and optionally adapted. In conjunction with this, the light beam to be switched should also be used as a measuring beam for tilting determination. It is thereby sought by each Verkippungseinheit (eg., Micromirror) otherwise notweni to save the beam source. These objects are achieved by the features listed in claim 1 such as that it is an optical measuring method with structuring of the surface of the tilt plane and the use of reflection or transmission gratings, solved.

The particular advantages of the invention are that the basic principle of (P4) is extended so that the optical measuring principle of reflection at a tilt plane used with techniques and methods of microsystems technology will, as the process engineering requirements and opportunities Microsystems technology a simple scaling down the principle off (P4). Furthermore elevated the presented invention, the accuracy of the measurement by increasing the angle change of the emergent beam, by both diffraction and reflection be used, resulting in a larger location change of the measuring beam on the detector and thus a higher resolution of the Tilting is accompanied. Furthermore, the simple reflection principle on unstructured surfaces extended by the structuring so that even vertically irradiating measuring beams not back to yourself be reflected, but (for example, for higher order diffraction orders, or especially for vertically structured diffractive structures) under one clearly of 0 degrees different angle reflected on the position detector can be. This opens options for the Use of so-called vertical surface emitting lasers (VCSEL) for tilt measurement in microsystems technology and offers immense Advantages in terms of integration density, assembly and connection technology, Positioning accuracy and manufacturing costs. Another advantage the invention presented here is that in optical applications, the radiation to be switched simultaneously used as a measuring beam source can be and thus an extra beam source for tilt measurement is unnecessary. Possible this is done by structuring the tilt plane as a transmission grating.

The Invention is both macro- and microtechnically usable and easy to integrate into existing designs. About the freely selectable structuring the surface Is it possible, Specify specifically specific reflection and / or transmission behavior. This not only results in "clean" reflection behavior (in contrast to unstructured reflection behavior) surfaces with diffuse reflection), but the formal relationship of tilting degree and beam path can also be precisely defined over the selected structuring adjusted or formally derived. In addition, one benefits from one high reproducibility of the critical parameters, such as the Adjustment of the beam source or the accuracy of the lattice constants (Grid structures can be produced very accurately and reproducibly). In addition, the presented measuring method does not depend on the geometry depends on the particular structure; in contrast z. B. to the capacitive measuring systems, where the measuring principle fundamentally depends on the geometry of the capacitor formed.

A advantageous embodiment of the invention is in claim 2 given. The development according to claim 2 allows a Highly accurate, continuous yet cost effective and easy to implement Evaluation of the physical reflection and diffraction principle.

drawing

In The drawing shows an embodiment is shown and will be closer in the following described.

It demonstrate:

1 Measuring principle in reflection (side view)

101

sideview the tilt axis

102

Verkippungsebene in the untilted state

103

Verkippungsebene tilted by the angle α

104

Verkippungsebene tilted by the angle β

105

Beam path of the diffracted / reflected measuring beam in the untilted state ( 102 )

106

Beam path of the bent / reflected measuring beam in the tilted state β (FIG. 104 )

107.110

Tilt-dependent position change on the detector

 108

Beam path of the diffracted / reflected measuring beam in the untilted state ( 102 )

109

Beam path of the diffracted / reflected measuring beam in the tilted state α ( 103 )

111, 112

position Sensitive radiation detectors

113

beam source

2 Surface structure principle

201

Verkippungsebene in the supervision

202

surface structure the tilt plane (here a line grid)

3 Transmission grille in side view

301

incident beam

302

Verkippungsebene in the untilted state

303

diffraction peak zeroth order (straight-line passage)

304 305

beam path the diffraction maxima ± 1. order

306

Verkippungsebene in the tilted state

307 308

Beam path of the diffraction maxima ± 1. Order in the tilted state ( 306 )

4 Tiltable micromirror with transmissive measuring principle

401

Verkippungsebene in the untilted state

402

transmission grid (Amplitude grating)

403

incident radiation

404

diffraction peak zeroth order (straight-line passage)

405 406

beam path the diffraction maxima ± 1. order

407 408

beam path the diffraction maxima ± 1. order with tilting

409 410

position Sensitive Radiation detectors (eg PSDs or CCDs)

5 Tiltable micromirror with reflective measuring principle

501

Verkippungsebene in the untilted state

502

reflective Grid (phase grid)

503

incident Radiation or diffraction maximum 0th order

504 505

beam path the diffraction maxima ± 1. order with tipped mirror

506 507

beam path the reflected diffraction maxima ± 1. Okay (tilted mirror)

508

beam path of the diffraction maximum of 0th order with tilted plane

509 510

position Sensitive Radiation detectors (eg PSDs or CCDs)

6 Surface structure principle

601

Verkippungsebene

602

presentation the principle of surface structuring (Diffr. Optical element)

603

Perpendicular incident beam

604

reflected Measuring beam (angle not equal to 90 °, z. Higher Diffraction maximum)

7 Reflective principle of reflection (2α) and diffraction (β)

701

incident beam

702

Verkippungsebene in the untilted initial state

703-705

Diffraction maxima 0. or ± 1. Order in the initial state ( 702 )

706

Verkippungsebene in the tilted state

707-709

Diffraction maxima 0. or ± 1. Order in the tilted state ( 706 )

description of the embodiment

1 shows like a measuring beam starting from a beam source ( 113 ) on the test object ( 102 ) fällthier a still unabilted plane whose tilt is to measure. The beam can either by oblique incidence (angle of incidence not equal to 90 °) or perpendicular to the plane. At the location where the measuring beam meets the tilting plane, the surface is structured (eg in the manner of 2 or 6 ). This structuring can be more refractive (lenses, prisms), more diffractive (eg optical gratings of all types) or mixed refractive-diffractive types. A simple example of a diffractive optical element is in 2 and 6 shown. The principle of a possible reflexive diffractive structuring is in the 5 . 6 and especially in 7 shown in detail. α and β symbolize tilting and γ corresponding diffraction angles caused thereby. Even when the beam is incident perpendicularly, the measuring beam (here, for example, the 1st order diffraction maximum) is not reflected back to the incident beam - as would be the case with a plane of reflection - but reflected at another defined angle. This depends on the nature of the surface structuring (eg the period of the optical grating) and the wavelength of the radiation. If you now tilt the plane ( 102 ) by arbitrary angles α ( 103 ) or β ( 104 ) about the axis of rotation 101 , so also the angle of reflection with respect to the incident radiation changes and the reflected measuring beam moves from the initial position ( 105 ) (respectively. ( 108 )) to the place ( 106 ) (respectively. ( 109 )). Is the formal relationship between the tilt angles (α, β) and the position difference Δx ( 107 ) 110 ) at the detector ( 111 ) 112 ), it is possible from the path differences ( 107 ) 110 ) to infer tilt angle and direction. The tilting when measured in reflection thereby causes both a change in the phase relationship of the reflected radiation at the diffractive element - and thus characteristic diffraction angles for the different diffraction orders - as well as the superimposed reflection behavior according to the known law of reflection (angle of incidence equal to the angle of reflection; Verkippungsebene). The angle of reflection of the measuring beam (eg a 1st or 2nd order diffraction maximum) is in the case of reflection measurement thus composed of the reflection angle α (relative to the surface normal, or 2α with respect to the incident beam) and the diffraction angle γ ( conditioned by the tilt-dependent phase shift). This is in 7 shown in detail. In the case of tilt measurement in transmission, on the other hand, only a tilt-dependent change in the diffraction angle occurs. In 2 is the supervision of an example with a simple line grid ( 202 ) structured tilt plane ( 201 ). The structuring ( 202 ) consists here as an example of a simple binary amplitude grating - ie a regular alternating sequence of defined radiopaque (absorbing / reflecting) webs and radiation-permeable openings. In this case, this lattice structure is not only superficially applied, but completely driven through the tilt planes, so that the incident stratum, or at least part of it, can be transmitted to the back (in this case, it is essentially intended for applications in microtechnology). Since the lattice structure is continuous through the irradiated plane ( 3 ), incident radiation ( 301 ), which exits on the back ( 303 ) - ( 305 ), bent at this lattice (on the front bent and reflected). Part of the radiation is absorbed or reflected on the lands of the front and the rest of the surface and also diffracted at the grille on the front, while the other falls into the permeable openings and exits the back. At the rear, the elementary waves of this transmitted radiation interfere - diffraction occurs. Depending on the type of grating, different interference patterns are created on the detector, which can be used to determine the tilt state of the plane. In the simple case, clear diffraction maxima zeroth ( 303 ), first ( 304 ) 305 ) and higher order, which change their position depending on the tilt. 3 schematically illustrates the side view of 2 , A beam ( 301 ) meets the structured level ( 302 ). In the initial state ( 302 ), the diffraction maxima are formed (shown here are the maxima zeros ( 303 ) and plus / minus first order ( 304 ) 305 ). In tilted condition ( 306 ), due to the tilting path, the phase relation of the elementary waves to each other changes, and the imaging points of the first (and higher order) diffraction maxima travel on the detector, which in ( 307 ) respectively. ( 308 ) is displayed. The changes in the maxima generally do not behave symmetrically. This means that z. B. the maximum first order right ( 307 ) with the tilt of the plane ( 302 ) in z. B. the Verkippungszustand ( 306 ) not symmetric to the maximum of the first order left ( 308 ) behaves. This makes it possible, among other things, to determine the direction of the tilt from the measurement signal. The detector itself is then z. B. again as in 1 constructed as a PSD (Position Sensitive Detector). The embodiment of the structuring of the tilt plane is kept variable and can contain both diffractive and refractive or mixed diffractive-refractive optical elements.

In the 4 and 5 Two possible microtechnical versions are shown. The silicon wafer is typically structured on the reverse side by means of KOH etching. An advantageous embodiment uses a material which is transparent to the radiation used (typically Pyrex) as the distance between the micromirror ( 401 ) 501 ) and the radiation detectors ( 409 ) 410 ) 509 ) 510 ). In the case of the transmissive measuring principle after 4 falls incident radiation ( 403 ) (coherent or partially coherent) to a tiltable (mirror) structure ( 401 ) whose surface is completely or partially micro-optically structured (here an optical grating ( 402 )). Im un tilted state form below the mirror in transmission, the characteristic diffraction maxima. Shown here are the maxima of zeroth ( 404 ) as well as ± first order ( 405 . 406 ). In the tilted state changes due to the tilt, with respect to the incident radiation ( 403 ), the phase relationship of the elementary waves emitted on the backside. In contrast to the tilt-independent passage of the zero-order diffraction maximum ( 404 ) change the radiation angle of the maxima of higher order. Shown is the behavior of the first order diffraction maxima ( 407 ) and ( 408 ). From the change of the radiation behavior z. B. the maxima of first order (( 405 ) goes over in ( 407 ) and ( 406 ) to ( 408 )) can now measure the direction and size of the tilting highly accurate.

5 also represents a possible micro-technical embodiment of a tiltable micromirror. The micromirror ( 501 ) is only one-sided with an optical grating ( 502 ) structured. The grid ( 502 ) is not driven through the Verkippungsebene through, but only over a defined depth and therefore works as a phase grating. Since incident (partially) coherent radiation ( 503 ) and the detector units ( 509 ) 510 ) on the same page, this example system works in reflection. As in the case of 4 form in the untilted state ( 501 ) Diffraction maxima first ( 504 ) 505 In the case of a simple line grating, the zero-order maximum is reflected in the direction of the incident radiation when perpendicular incidence occurs ( 503 ). If the micromirror is tilted, it changes on the one hand as in the transmissive case (in 4 represented) the phase relationship of the radiated elementary waves and on the other hand, the reflection angle, which obeys the law of reflection (angle of incidence equal to the angle of reflection). Both angle effects (diffraction and reflection) come to bear, which is reflected in a significantly larger beam angle and also in a much larger tilt-dependent angle change. In tilted condition (as in 5 illustrated) goes the left intensity maximum 504 in 506 above; the right ( 505 ) in contrast (in 507 ). Since the diffraction-related emission angle of the zero-order diffraction maximum does not change with the tilting (see transmissive measurement principle in FIG 4 ), the zero-order maximum at the tilting angle α with respect to the perpendicular is reflected onto the tilting plane (or 2α with respect to the incident radiation) and thus enters into the tilting case 5 from the condition ( 503 ) in ( 508 ) and in 7 from state ( 703 ) to ( 707 ) above. The reflection-only emission angle α of the zero-order maximum therefore only occurs in reflection in the case of the tilt measurement in this type of grating. A detailed description of the general diffractive principle in reflection is given in 7 shown. The change of the reflection angle of the maximum of the first order, for example (from ( 704 ) to ( 708 )) is composed of the pure reflection angle (or tilt angle) α and the diffraction angle γ, which itself depends on the tilt angle.

• [1] Olaru R., Coate C. Tilt sensor with magnetic liquid Sensors and Actuators A-Physical 59 (1–3): 133–135, 1997
• [P1] Barsky B. E., Burgess, L. E., Kull, F. R. "Electrolytic tilt sensor having a metallic envelope" US 6 249 984 B1
• [P2] Beitzer, G. W. "Tilt sensor and method of assembly" US 4 536 967
• [P3] Crossan, W. R. "Thermocouple tilt sensing device" US 6 453 571 B1
• [P4] Stoeckl, G. "Vorrichtung zur gleichzeitigen Messung des Abstandes und der Verkippung" DE 34 07 074 C2
• [P5] Hauser, Karl-Heinz "Vorrichtung zur Vermessung der Verkippung zweier Körper" DE 41 05 202 C1

If the further system-technical structure allows it, then the reflective measuring principle is advantageous since, per degree of tilting, it brings about a significantly greater change in the angle of the radiation emitted onto the detector or detectors. The advantage of the tilt measurement in transmission, on the other hand, is the clear spatial separation of the side on which the radiation is incident (and, for example, further processed) and the position on which the position-sensitive detectors are positioned, which has structural advantages since the Front, z. B. in the application, optical switch, is not reduced by the space requirement of the detectors. This is particularly advantageous in the case of (multi-dimensional) arrays of such micromirrors in optical switches (so-called optical crossconnects).

• [1] Olaru R., Coate C. Tilt sensor with magnetic liquid sensors and actuators A-Physical 59 (1-3): 133-135, 1997
• [P1] Barsky BE, Burgess, LE, Kull, FR "Electrolytic tilt sensor having a metallic envelope" US Pat. No. 6,249,984 B1
• [P2] Beitzer, GW "Tilt sensor and method of assembly" US 4,536,967
• [P3] Crossan, WR "Thermocouple tilt sensing device" US 6,453,571 B1
• [P4] Stoeckl, G. "Device for the simultaneous measurement of the distance and the tilting" DE 34 07 074 C2
• [P5] Hauser, Karl-Heinz "Device for measuring the tilting of two bodies" DE 41 05 202 C1

Claims (10)

System for measuring the tilting, in which an optical system throws a light beam onto a surface, this is radiated again and hits a detector, characterized in that for trouble-free, fast and accurate measurement of the tilting either the surface of the plane to be measured is structured or this structuring is driven partially or entirely through the tilt plane, so that the incident radiation is either reflected or transmitted at the tilt plane, the structuring of the tilt plane being designed such that the beam path of the incident radiation is refracted and / or diffracted is changed, so that on the radiation-sensitive detector of the evaluation circuit characteristic of the structuring change of the location pattern or energy focus, the Verkip Pungsebene reflected / transmitted radiation results. System according to claim 1, characterized in that the evaluation circuit for determining the tilt-dependent change the energy center of the reflected or transmitted radiation, the measurement signals of a one-dimensional or multi-dimensional position-sensitive Photodetector (Position Sensitive Device, PSD) evaluates. System according to claim 1, characterized in that the evaluation circuit for determining the tilt-dependent change the spatial pattern of the reflected or transmitted radiation, the Measuring signals of a single or multi-dimensional digital sensor (CCD) evaluates. System according to one or more of claims 1 to 3 characterized in that it is for the integrated determination of Tilting of microtechnical products is suitable. System according to one or more of claims 1 to 3, characterized in that it is for trouble-free, contactless and long - term stable integrated control and adaptation of the tilting of microsystem technology products is suitable. System according to one or more of claims 1 to 3; characterized in that it is mainly due to the principle of optical transmission grating on the tilt plane to be controlled Light beam can simultaneously use as a measuring beam. System according to one or more of claims 1 to 3, characterized in that it consists of a tiltable micromirror exists to target incoming light under a different than that Reflect angle of incidence and in the use of diffraction effects on the tilt plane of the micromirror, at which the reflection takes place, an optical grid is attached, the whole or is partially driven through the mirror surface to be tilted and depending on the version on the front or back a spatially resolving Photodetector is attached, which is a tilt-dependent characteristic Detects and evaluates part of the light diffracted at the grating. System according to claim 7, characterized in that as a carrier material for the or the micromirrors monocrystalline or polycrystalline silicon and SU-8, to increase the reflectivity Chromium / gold or aluminum metallizations as connectors and spacers between mirror and photodetector glass (Pyrex) and ITO (indium tin oxide) for Realization of transparent control electrodes are used. System according to claim 7, characterized in that the tiltable micromirror dimensions in the range of a few microns to millimeters, typically 0.1-1 mm, on the tilt plane of the micromirror mounted optical grating grating periods of typically 1-5 microns. System according to one or more of claims 1 to 3, characterized in that it is for measuring the tilt of microsystem-technical products even with normal incidence of the measuring beam is used on the tilting plane to vertically emitting Laser (VCSEL) in microsystem technology to use.