WO2007093497A1

WO2007093497A1 - Method for producing a test structure in order to test flexibility of a membrane of a micromechanical component and corresponding examination structure

Info

Publication number: WO2007093497A1
Application number: PCT/EP2007/050877
Authority: WO
Inventors: Klaus Schuette; Neil Davies; Andreas Duell; Gerhard Lammel; Matthias Neubauer; Volkmar Senz; Thomas Schnitzler
Original assignee: Robert Bosch Gmbh
Priority date: 2006-02-15
Filing date: 2007-01-30
Publication date: 2007-08-23
Also published as: DE102006006890A1

Abstract

The invention relates to a test structure for testing flexibility of a membrane (3) of a micromechanical component (10), comprising a plurality of discrete test patterns (T1-T4). Said test patterns (T1-T4) are resolved in a structurally different manner by a developing process so that the structural resolution of a respective test pattern (T1-T4) represents a measurement for the flexibility of the membrane (3) in the position of a respective test pattern (T1-T4), and to a corresponding production method. The invention also relates to an test structure for testing the flexibility of a membrane (3) of a micromechanical component (10), said test structure comprising a continuous test structure (T5), whereby the test pattern (T1-T4) is resolved in a structurally continuous manner by a developing process so that the structural resolution of the test pattern (T5) in a respective position of the pest pattern (T5) represents a measurement of the flexibility of the membrane (3) in the respective position of the test pattern (T5), in addition to a corresponding method.

Description

description

title

Method for producing a test structure for testing the deflection of a membrane of a micromechanical component and corresponding test structure

STATE OF THE ART

The present invention relates to a method for producing a test structure for testing the deflection of a membrane of a micromechanical component and a corresponding test structure.

Although applicable in principle to any micromechanical components, the present invention and the problems underlying it are explained with reference to micromechanical pressure sensors.

With the help of micromechanical process steps cavities in semiconductor substrates, such as. Semiconductor wafers (see eg DE 100 32 579 A1 or WO 02/02458). Such cavities are usually a component of a pressure sensor device or similar micromechanical components. If these cavities are closed by a thin membrane, this membrane bends through, provided that the pressure in the cavity is different from the ambient pressure. The size of the deflection is dependent, inter alia, on the pressure difference, the thickness and the size of the membrane / cavity system and on the material properties of the membrane. If the impermeability of the cavity or the deflection of the membrane is important for the function of the component, then this must be checked and ensured in later process steps.

One possibility is to perform an inspection by an optical inspection, e.g. By a microscope with phase interference contrast or infrared spectroscopy. Also conceivable is a functional check of the finished component, for example by, an electrical measurement of pressure sensors at different ambient pressures. In semiconductor technology, components are usually defined via photolithographic process steps, in particular coating of a wafer, exposure and development of the photoresist. When exposing a wafer, the wafer surface is aligned to the focal plane of the imaging optic, with an accuracy of alignment of typically about 0.1 μm can be achieved. If the wafer or part of the wafer is not exactly in the focal plane (deviation> 0.3 μm), aberrations occur. These aberrations mean that the structure widths can be reduced or minimal structures can no longer be opened.

The testing for aberrations occurs in semiconductor manufacturing, among other things with the help of resolution structures. If these dissolution structures or parts thereof are placed on bent or curved regions of the wafer, individual parts of the dissolution structures are no longer imaged depending on the distance to the focal plane.

The inventive method for producing a test structure for testing the deflection of a membrane of a micromechanical device according to claim 1 or 3 and the corresponding test structure according to claim 8 or 10 have the advantage that they provide a simple and reliable way to check the deflection of a micromechanical Create a membrane.

The idea underlying the present invention lies in the creation of a photolithographic test structure in the production of the micromechanical device, which after exposure and

Development automatically gives a measure of the size of the deflection. In a typical micromechanical manufacturing process, exposure and development steps of paint layers (so-called lithography process steps) take place for structuring individual layers. Since the structure width or the resolution depends sensitively on the focal plane of the exposure device relative to the wafer or substrate surface, critical structures on bent-through regions which lie outside the focal plane are blurred or no longer imaged. In other words, a test structure is created whose exposure quality is dependent on the size of the deflection and the size of the test structure elements. If such optical test structures are placed on a deflected membrane to be inspected, it can be easily evaluated on the basis of this structure after exposure and development whether or to what extent a deflection exists.

Analogously, a resistive electrical test structure can be realized whose value is influenced by the lithographic resolution due to the deflection. In the case of optically evaluated test structures, the evaluation of the deflection can be made simpler and safer by the test structure, or image recognition can be automated, which results in cost savings and improved quality. If electrical test structures are implemented, then optical methods can be replaced by electrical measurements, which can be evaluated faster and more reliably. If these electrical test structures are included in an evaluation circuit, entire work steps can be omitted. Both methods have the advantage that rejects can be detected in earlier process steps, which also brings a cost savings.

As a result, the optical evaluation can be simplified or an optical evaluation can be replaced by a simple electrical evaluation. The evaluation can be done essentially without additional effort if it is done visually, and realized with little additional effort, if it is done electrically.

In the dependent claims are advantageous developments and improvements of the respective subject of the invention.

According to a preferred development, the developed test patterns comprise a photoresist area in which photoresist-free ladder-type area is embedded with a plurality of photoresist-free ladder rungs, the number of photoresist-free ladder rungs being the measure for deflection of the membrane at the position of a respective test pattern.

According to a further preferred development, the developed test pattern comprises a photoresist region in which the strip-like region is embedded, wherein the width of the strip-like region is the measure for deflection of the membrane at the position at the respective position of the test pattern.

DRAWINGS

Embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description.

Show it: 1 a, b is a schematic cross-sectional view and plan view of a test structure for testing the deflection of a membrane of a micromechanical device according to a first embodiment of the present invention;

FIG. 2 is a flow chart for explaining a method for manufacturing a test structure for testing the deflection of a diaphragm of a micromechanical device according to the first and a second embodiment of the present invention; FIG. and

3a, b are two schematic plan views of a test structure for testing the deflection of a membrane of a micromechanical device according to the second embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

In the figures, the same reference numerals designate the same or functionally identical components.

1a, b are a schematic cross-sectional view and a top view of a test structure for testing the deflection of a membrane of a micromechanical device according to a first embodiment of the present invention.

In Fig. 1, reference numeral 1 denotes a silicon semiconductor substrate. Provided in the semiconductor substrate 1 is a cavity 2. The cavity 2 is spanned by a membrane 3, which due to a pressure difference in the cavity 2 with respect to the environment has a deflection of the height .DELTA.h of 1 micron. Discrete test patterns T1-T4, which occupy different positions with respect to the maximum deflection Δh of the membrane 3, are provided at different locations of the membrane 3 and at a location on the surrounding surface O of the substrate 1.

These test patterns T1-T4 have been exposed by means of an exposure apparatus, wherein the surface O of the surrounding substrate has been selected for the optical focal plane OFP of the exposure apparatus. Thereafter, a conventional development for removing the exposed positive photoresist

(or the unexposed photoresist in the case of negative photoresist).

As can be seen from FIG. 1b, the developed test patterns T1-T4 comprise one after the photoresist area U, into which a photoresist-free area B1, B2, S1-S4 having a plurality of photo-lacquer-free areas Ladder rungs S1-S4 is embedded. The ladder rungs S1-S4 have a critical dimension, whereas the ladder legs Bl, B2 have a much larger dimension. Due to the variable position of the various test patterns with respect to the optical focal plane OFP, the test patterns T1-T4 have been structurally differently resolved during development so that the structural resolution of a respective test pattern is a measure of the deflection of the diaphragm 3 at the respective position of a respective test pattern.

In particular, the number of photoresist-free ladder rungs is the measure of the deflection of the membrane 3 at the position of a respective test pattern. In the test pattern T4, which lies on the surface O of the associated substrate 1, which coincides with the optical focal plane OFP, all ladder rungs S1-S5 are resolved. For the test pattern T3, only the rungs S1-S4, only the rungs S1-S3 for the test pattern T2 and only the rungs S1 and S2 for the test pattern T1. With increasing deviation of the local height of a respective test pattern from the optical focal plane OFP, therefore, the number of ladder rungs developed decreases substantially continuously.

FIG. 2 is a flow chart for explaining a method of manufacturing a test structure for testing the deflection of a diaphragm of a micromechanical device according to the first and a second embodiments of the present invention.

2, the provision of a photo lacquer layer on the membrane 3 and the surrounding surface O of the substrate 1. In step S2, the photoresist layer with the test structure with the plurality of discrete test patterns T1-T4, which, as in Figure Ia represented, assume different positions with respect to the deflection of the membrane 3 and with respect to the optical focal plane OFP during exposure, exposed via a mask.

Continuing with reference to step S3, the development of the photoresist layer takes place with the plurality of exposed test patterns T1-T4, which results in the structurally differently resolved test patterns T1-T4 according to FIG.

The thus produced first embodiment of a test structure for testing the deflection of a

Membrane of a pressure sensor can be evaluated optically (variant a) in Fig. 2). More specifically, with reference to step S4a, an optical inspection simply counts the number of remaining sprouts in the respective test patterns T1-T4. The test pattern T4 serves only as a reference. 3a, b are two schematic plan views of a test structure for testing the deflection of a membrane of a micromechanical device according to the second embodiment of the present invention.

In FIG. 3 a, reference symbol T5 denotes a continuous test pattern which has a strip-like, photoresist-free region WS with a width b.sub.O which is guided from a first corner E1 to a second diagonally opposite corner E2 over the membrane. The remaining surface O is photoresist region U '.

In FIG. 3 a, the case of a lack of bending of the membrane 3 is shown. In this case, the width bθ of the strip-like region WS does not change over the membrane 3. In other words, in the exposure, all the dots of the stripe-like photoresist-free region WS were within the optical focus plane OFP coincident with the upper surface O of the surrounding substrate 1, so that the structural resolution is the same everywhere.

With further reference to FIG. 3b, the membrane 3 is deflected analogously to the illustration in FIG. 1a by the maximum height difference Δh, so that the developed test pattern T5 is structurally resolved in a continuously changing manner. The structurally variable resolution of the test pattern T5 at a respective position of the test pattern T5 is a measure of the deflection of the membrane 3 at the respective position of the test pattern T5. In other words, the width of the stripe-like photoresist-free region WS 'varies from the maximum width bl at the ends El and E2 to the minimum width bθ in the center of the diaphragm 3, d. H. the highest area.

In principle, such a structure can also be optically evaluated according to FIG. 2 (variant a), step S4a), but in such a continuous test structure an electrical evaluation is also suitable. In this case, according to variant b) in FIG. 2, in step S4b an electrical doping of the membrane 3 by means of foreign ions in the strip-like region WS 'and the production of electrical contacts at the ends E1, E2 of the strip-shaped region WS' takes place. Depending on the deflection of the membrane, the resistance value measured at the ends E1, E2 will be different. In the case of a lack of deflection according to Figure 3 a, the electrical resistance will be the lowest, and in the case of a desired deflection according to Figure 3b highest. The current deflection can be determined either by calibration or by comparison with a flat resistance strip introduced in the surface O (analogous to FIG. 3 a). If you integrate such a derstand directly into an evaluation circuit, the deflection can be tested without further effort in testing the relevant micromechanical device. The electrical evaluation of such resistors can also be carried out by means of more complex evaluation circuits, for example, if additionally a van der Pauw structure is implemented. Doping variations of the resistors can thus be eliminated.

Although the present invention has been described above with reference to a preferred embodiment, it is not limited thereto, but modifiable in many ways.

In particular, the present invention has been described in terms of a micromechanical pressure sensor having a membrane capped cavity, but of course it is applicable to any curved membrane structures. For example, the membrane could take on an open tent-like shape. Also, the shown geometry of the discrete test pattern according to FIG. 1a, b or the continuous test pattern according to FIG. 3a, b can only be varied by way of example and as desired.

Claims

claims

1. A method for producing a test structure for testing the deflection of a membrane (3) of a micromechanical component (10), comprising the steps of:

Providing (Sl) a photoresist layer on the membrane (3) and a surrounding surface

(O) an associated substrate (1);

Exposing (S2) the photoresist layer to a test structure having a plurality of discrete test patterns (Tl -T4) which assume different positions with respect to the deflection of the membrane (3) and with respect to an optical focal plane (OFP) during exposure (S2);

Developing (S3) the photoresist layer with the plurality of exposed test patterns (T1-T4), wherein the test patterns (T1-T4) are structurally differently resolved during development (S3) so that the structural resolution of a respective test pattern (T1-T4) a measure of deflection of the membrane (3) at the position of a respective test pattern (T1-T4).

2. The method according to claim 1, characterized in that the developed test pattern (T1-T4) comprise a photo paint area (U), in the photo-paint-free area (B 1, B2, S 1 -S5) with a plurality of photo paint-free ladder rungs (SL

S4) is embedded, wherein the number of photo varnish-free ladder rungs (S1-S4) is the measure of deflection of the membrane (3) at the position of a respective test pattern (T1-T4).

3. A method for producing a test structure for testing the deflection of a membrane (3) of a micromechanical component (10) with the steps:

Providing (Sl) a photoresist layer on the membrane (3) and a surrounding surface (O) of an associated substrate (1); Exposing (S2) the photoresist layer to a test pattern having a continuous test pattern (T5) which assumes a continuously changing position with respect to the deflection of the diaphragm (3) and with respect to an optical focal plane (OFP) during exposure (S2);

Developing (S3) the photoresist layer with the continuous test pattern (T5), wherein the

Test pattern (T5) is developed to develop structurally (S3) continuously changing, so that the structural resolution of the test pattern (T5) at a respective position of the test pattern (T5) is a measure of deflection of the membrane (3) at the respective position of the test pattern (T5) is.

A method according to claim 3, characterized in that the developed test pattern (T5) comprises a photoresist area (U ') in which a strip-like area (WS') is embedded, wherein the width (bl, b2) of the strip-like area (WS ') ) the amount of deflection of the membrane (3) at the position at the respective position of the

Test pattern (T5) is.

5. The method according to claim 5, characterized in that in the strip-like region (WS ') changing width (bl, b2) foreign ions for electrical doping in the membrane (3) are introduced and the doped strip-like region (WS') for a resistance measurement made contactable in the region of its ends (El, E2).

6. The method according to any one of the preceding claims, characterized in that the optical focal plane (OFP) coincides with the surrounding surface (O) of the associated substrate (1).

7. The method according to any one of the preceding claims, characterized in that the membrane covers a in the substrate (1) provided cavity (2).

8. test structure for testing the deflection of a membrane (3) of a micromechanical device (10) having a plurality of discrete test patterns (T1-T4), wherein the test patterns (T1-T4) by structuring (S3) are structurally differently resolved, so that the structural resolution of a respective test pattern (Tl -T4) is a measure of deflection of the membrane (3) at the position of a respective test pattern (Tl -T4).

9. test structure according to claim 8, characterized in that the developed test pattern (T1-T4) comprise a photo paint area (U), in the photo paint-free area (Bl, B2, S1-S5) with a plurality of photo paint-free ladder rungs ( sl-

S4) is embedded, wherein the number of photo lacquer-free ladder rungs (S1-S4) is the measure of deflection of the membrane (3) at the position of a respective test pattern (Tl -T4).

10. test structure for testing the deflection of a membrane (3) of a micromechanical device (10) with a continuous test pattern (T5), wherein the test pattern (T5) by

Developing (S3) structurally resolved continuously changing, so that the structural resolution of the test pattern (T5) at a respective position of the test pattern (T5) is a measure of deflection of the membrane (3) at the respective position of the test pattern (T5).

11. A test structure according to claim 10, characterized in that the developed test pattern (T5) comprises a photoresist area (U ') in which a strip-like area (WS') is embedded, wherein the width (bl, b2) of the strip-like area (WS ') is the measure of deflection of the membrane (3) at the position at the respective position of the test pattern (T5).

12. Use of a test structure according to one of claims 8 to 11 for the optical and / or electrical testing of the deflection of a membrane (3) of a micromechanical pressure sensor.