WO1992008102A1

WO1992008102A1 - Device for measuring linear dimensions on a patterned surface

Info

Publication number: WO1992008102A1
Application number: PCT/EP1991/002089
Authority: WO
Inventors: Karlheinz Bartzke; Rolf Thiemer; Erhard Mende; Bernhard Retschke; Wolfgang Krausse; Manfred Weihnacht; Günter HELKE; Joachim Heim; Eike Wehrsdorfer
Original assignee: Jenoptik Carl Zeiss Jena Gmbh
Priority date: 1990-11-05
Filing date: 1991-11-05
Publication date: 1992-05-14
Also published as: DE4035084A1

Abstract

The device proposed, which is designed to measure linear dimensions on the patterned surface (8) of a body (9), has a pointed sensor tip (7) coupled to a resonator (5) which is connected in turn to an oscillator circuit (10). The device also includes a control circuit (12) which is connected to resonator-position control elements (1, 2) acting at right angles to the surface (8), a shock isolator (6) connected to the control circuit (12) being located between the sensor tip (7) and the resonator (5).

Description

Name of the invention

Arrangement for measuring linear dimensions on a structured surface of a measurement object

10

Technical field

The invention relates to an arrangement for measuring linear dimensions on a structured surface of a measurement object, in which one is arranged perpendicularly movable relative to the surface of the measurement object

,, - probe tip is coupled to a resonator which is connected to an oscillator circuit, a control circuit also being provided which is connected to actuating elements for the resonator acting perpendicularly to the surface of the test object. The invention is particularly applicable to two-coordinate measuring devices, measuring devices for ultra-precision machining technology, probe cutters, measuring devices for measuring microelectronic semiconductor structures, roughness measuring devices, profile measuring devices and for producing microstructures on surfaces.

5

State of the art

For the measurement of linear dimensions of semiconductor structures, optical arrangements are known which achieve a linear resolution of approximately 0.7 μm 0 with the aid of optical imaging systems and optoelectronic receivers.

A significant increase in the lateral resolution below 0.7 μm is not possible due to the wave character of the light. As a result of optical diffraction phenomena, which falsify the actual position of the structure edges for each measuring point, measurement errors arise, in particular when measuring ₅ structure widths below 1 μm (cf. journal "Feingerätetechnik" 32 (1 983),

No. 9, pp. 402-406; Journal "Technisches Messen" 54 (1987), No. 6, p. 243-252; Journal "Journal for optics and precision mechanics" 35 (1988), pp. 196-235).

Furthermore, electron microscope measuring arrangements are known in which the objects to be measured must have an electrically conductive surface layer.

The measuring process takes place in a vacuum, so that the vacuum clamping which is customary for wafers cannot be used, and therefore measurements on wafers with these arrangements can only be carried out to a limited extent. As with an optical measuring arrangement, measurement errors arise here due to electron-optical imaging errors (Reimer, L .; Pfefferkorn, G .: "scanning electron microscopy",

Springer-Verlag Berlin, 1 77).

In the case of measuring arrangements based on the principle of scanning tunnel microscopy (STM) or atomic force microscopy (AFM), a nanometer-fine tip made of tungsten, gold, diamond or the like is used. guided at a distance of a few nanometers over the surface of the test specimen, so that a tunnel current of a few nanoamperes is formed between the tip and the surface either at a voltage of a few millivolts (STM) or interatomic forces become effective (AFM), which are kept constant by a distance controller become. These solutions have the disadvantage that the test specimen surface at the STM must be electrically conductive due to the tunnel current.

The arrangements are so sensitive that only areas of a few micrometers in size can be scanned and the scanning speeds are very slow. During these scans, the measurement processes on the test object produce traces (Proceedings of SPIE, Vol. 897, 1988, pp. 8-15;

EP 0 338 083 AI; "Physical Review Letter" 56 (1986) 9, pp. 930-933). For atomic force microscopy (AFM), an arrangement is known in which a stylus is attached to a piezo oscillator, the tip of which probes the surface of the test specimen with high frequency vibration. An electrical measuring circuit determines the shift in the resonance frequency of the piezoelectric oscillator, which is caused by touching the test specimen surface with the stylus.

A control circuit connected to the measuring circuit and an actuating unit carrying the piezo oscillator are used to determine the profile. A disadvantage of this arrangement is that the cube-shaped geometry of the piezo oscillator shown in the measuring arrangement does not produce a harmonic oscillation enables and that the probe needle, which is massive in comparison to the piezo oscillator, dampens the natural resonance of the piezo oscillator.

Furthermore, the measurement method used for the resonance frequency difference measurement is slow in time and relatively insensitive and is therefore less suitable as a highly dynamic and at the same time highly sensitive measurement principle (EP 0 290 647).

For the mechanical scanning of semiconductor structures and for roughness measurements, probe cutters are known which, with a diamond tip as a probe tip, achieve a lateral resolution of 6 nm depending on the probe tip geometry and measuring force. A disadvantage of these conventional stylus devices is that due to dynamic effects, e.g. Jumping the stylus, only low measuring speeds are possible, which require long measuring times. The constant contact of the diamond tip and the surface of the test specimen requires measuring forces of at least 10 N, the traces of injury on the

Can generate surface of the target. (Special print from "Control" 1 1/12, 1 987).

Furthermore, stylus cutters are known, the stylus tip of which is attached to a piezoelectric seignette crystal with a large piezo effect. The crystal acts as a spiral spring, which generates electrical voltages when the probe tip is moved over the surface of a measurement object, which voltages are further processed to form the measurement value. A disadvantage of these solutions is that only a low measuring speed is possible and that the measuring forces of the probe tip are too great (Perthen, J .: "Checking and measuring the surface shape", Carl Hanser Verlag, Munich, 1949, p.118 -1 1 9).

Also known is an arrangement in which, for roughness measurement, a piezo crystal is integrated in a lever that scans the surface with a tip, the measuring forces of which it is loaded are used for signal acquisition. Disadvantages are the large measuring forces, which make it difficult to scan microstructures without damaging them, and the only low permissible ones

Measuring speeds through the quasi-static measuring method

(DE 8 600 738.6 Ul).

For the hardness measurement and as a modification to the surface profile determination, a contact detector is known, in which the contact to the surface is determined by a piezoelectric rod resonator, on the front side of which a probe tip, preferably made of diamond, is attached. The Stαbresonαtor is excited via lateral electrodes by a generator or oscillator in natural resonance. An electronic measuring circuit evaluates the frequency or amplitude changes of the resonator that occur when the probe tip touches the measuring surface as a contact signal

Connection with an actuator can serve to determine the profile. The disadvantage of this arrangement is that the rod resonator produces high measuring forces and has low resonance frequencies, so that the measuring surface can be damaged and only low measuring speeds can be achieved (WO 89/00672 AI). Another known scanning probe device works according to an impulse scanning method, in which a stylus is raised and lowered in a pulsed manner from the surface of the measurement object. The device works quasi statically. Raising the stylus serves to reduce frictional and tangential forces in the bearing points of the measuring mechanism. In this device it is disadvantageous that the pulse speed is low and that the

Measuring forces are too high (Lehmann, R .: "Guide to Length Measurement", VEB Verlag, Technik Berlin, 1 60, p. 277).

Description of the invention

The invention has for its object to further develop a generic measuring arrangement so that the measuring accuracy is still improved, the measuring speed is increased and the measuring forces are reduced.

This object is achieved in that a shock absorber is provided in an arrangement of the generic type between the probe tip and the resonator, which is connected to a control circuit. The measuring arrangement according to the invention allows the surface of the test object (test object) to be scanned with high frequency using low pressure forces with the aid of a piezoelectric resonator.

Any suitable material with piezoelectric or electrostrictive properties can be used for the shock absorber. Sputtered and textured zinc oxide, piezoelectric polymer film, lithium niobate and Piezokerαmik particularly suitable.

In terms of measurement technology, it is advantageous if the resonator is designed as a piezoelectric, prismatic rod oscillator made of quartz, lithium niobate or piezoceramic, on the end of which faces the surface of the measurement object, a shock absorber is attached, the shock absorbers being electrically connected in difference.

The advantageous effect of the arrangement according to the invention is based on the fact that when the vibrating probe tip touches the surface to be tested in the shock absorber, electrical measurement pulses are generated in the shock absorber, which form the input variable for the control circuit after amplification.

The output signal of the control circuit controls the control elements, which the

Wear the resonator and the probe tip, the probe tip being brought into contact with the surface of the test specimen in such a way that the contact shocks of the probe tip always have a constant, very low force in the order of 10 N M 2. The shock absorber can have a pressure sensitivity of approx. 10 V / N, so that the contact shocks between the probe tip and the surface of the measurement object cause mechanical effects on the surface which are only a few nanometers. The high resonance of the resonator enables high measuring speeds.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is explained in more detail below by way of example with reference to the drawing. Show it:

Fig. 1 shows a push button with piezoceramic bending plate in a basic representation and

2 shows a pushbutton sensor with rod oscillator made of quartz, likewise in a basic representation.

Detailed description of the drawings

The arrangement according to FIG. 1 shows a coarse divider 1 connected in series and fine dividers 2, which are mounted on a frame 3. A piezoceramic bending plate 5 and a shock absorber 6 with a probe tip 7 are attached to the fine adjuster 2 as a resonator via a spacer ring 4. The probe tip 7 is in contact with a surface 8 of a measurement object 9.

The bending plate 5 is with an oscillator circuit 10 and the shock absorber

6 connected to an evaluation circuit 1 1, the latter being connected to a control circuit 12. The outputs of the control circuit 12 are connected to the coarse adjuster 1 and the fine adjuster 2. In the arrangement according to FIG. 2, a prismatic rod oscillator 13, which is held in the vibration node by means of a flange 13 and is arranged e.g. can consist of piezoceramic, lithium niobate or quartz. It is advisable to orient a rod oscillator 15 made of quartz in such a way that the rod axis is inclined by +71 32 'to the z axis in the yz crystal plane and the excitation electrodes for the oscillation process on the yz side surfaces of the rod

14 are applied. Then the end faces of the rod 14 perform favorable, piston-shaped vibrations. The electrical leads for the measuring electrodes of the shock absorber 6 are then also led favorably over the sides of the rod 14 not occupied by electrodes to the flange 13.

Due to the alternating field between the excitation electrodes of the rod 14, which generates an oscillator, not only is the rod 14 excited to longitudinal vibrations, but the measuring leads are additionally subjected to interference voltages due to induction. The measurement signal is therefore electronically, e.g. obtained from the signal mixture by a filter amplifier.

In the shock absorber 6, not only do the measurement voltages caused by the impact forces arise, but also interference voltages which are caused by the inertial forces of the shock absorber 6 and its probe tip 7 caused by the acceleration of the rod oscillator 14. This one

Interference voltages linear with the dead weight of shock absorber 6 and probe tip

7 and increase quadratically with the resonance frequency of the rod oscillator 14, these influencing parameters are to be kept as small as possible or to be designed.

A variant of the interference compensation is to occupy both end faces of the rod transducer 14 by means of a shock absorber 6 with a probe tip 7, one side of the measurement signal acquisition and the other of the St -. _: _ gnαlkompensαtion serves. For this purpose, the signals from both shock absorbers

6 electrically switched in difference, so that the interference signals are compensated.

Suitable test specimen surface elements must be scanned for certain measuring tasks, for which the arrangements according to FIG. 1 or 2 are not applicable. For these cases, the ends of the rod transducer 14 are pointed according to FIG. 2 or there are passive tips, which in turn are shock absorbers 14 and

Wear stylus tips 7, placed on their end faces.

The resonators are preferably made from sputtered and textured zinc oxide, from piezoelectric polymer film, lithium niobate or piezoceramic and are designed in the form of rod oscillators.

About the control circuit 12, the resonator and the probe tip 7 carrying actuating elements 1 and 2 are controlled so that the contact shocks

Probe tip 7 always have an essentially constant force of about 10 N against the surface 8 of the measurement object (9). The bumper

2 6 is designed with a pressure sensitivity of 10 V / N.

Claims

1. Arrangement for measuring linear dimensions on a structured surface (8) of a measurement object (9), in which a probe tip (7), which is relative to the

Surface (8) of the measurement object (9) is arranged vertically movable, is coupled to a resonator (5) which is connected to an oscillator circuit (10), and in which a control circuit (12) is provided which is perpendicular to the surface (8) acting control elements for the resonator (5) is connected, characterized in that between the probe tip (7) and

Resonator (5) is arranged a shock absorber (6) which is connected to the control circuit (12).

2. Arrangement according to claim 1, characterized in that a piezoelectric or an electrostrictive or a magnetostrictive

Shock absorber (6) is provided.

3. Arrangement according to claim 1 or 2, characterized in that the resonator (5) is designed as a piezoelectric, prismatic rod oscillator made of quartz or piezoceramic, on the surface (8) of which

Object (9) facing end face a shock absorber (6) and on the other end face a second shock absorber is fastened, the shock absorbers being electrically connected in difference.

4. Arrangement according to one of claims 1 to 3, characterized in that the shock absorber (6) consists of sputtered and textured zinc oxide or of piezoelectric polymer film or of lithium niobium or of piezoceramic.