WO2001058015A2

WO2001058015A2 - Method for producing a component that comprises a piezoelectric substrate and a surface acoustic wave identification mark

Info

Publication number: WO2001058015A2
Application number: PCT/DE2001/000379
Authority: WO
Inventors: Stefan Berek; Ulrich Knauer; Markus Mohr; Gerd Scholl
Original assignee: Siemens Aktiengesellschaft
Priority date: 2000-02-01
Filing date: 2001-01-31
Publication date: 2001-08-09
Also published as: DE10004282A1; WO2001058015A3

Abstract

The invention relates to a method for producing a component that comprises a piezoelectric substrate and a surface acoustic wave identification mark. According to the inventive method, a component (T, T', T*) is produced from a blank (B) that is provided with an piezoelectric substrate (S) and a plurality of conductive sub-structures (W, R, I, O) attached thereto. The inventive method is further characterized in that at least one of the sub-structures (W, R, I, O) is deactivated and/or removed in an individualization step.

Description

description

Method for producing a component with a piezoelectric substrate and surface wave identification mark

The invention relates to a method for producing a component with a piezoelectric substrate and conductive substructures attached to it, in particular surface wave (OF) components, a method for producing a set of several components and a surface wave identification mark ("OF -ID -Day") .

A method for producing an electroacoustic SAW filter is described in "Reproducable fabrication of surface acoustic wave filters", by.-E. Bulst and E. Willibald-Riha, Telecom Report, _10 (1987) 247. It comprises a single-crystalline piezoelectric substrate with an active surface on which metallic structures are attached. These structures include an electroacoustic transducer, which mediates a clear relationship between an electrical signal at this transducer and a surface acoustic wave on the active surface and other structures. These further structures serve to modify an acoustic surface wave propagating on the active surface, which occurs in particular through partial reflection.

For the use of an electroacoustic SAW component as a filter, reference is also made to the article "Surface acoustic wave filters for digital radio ^ relay systems" by G. Riha, H. Stocker and P. Zebis, Telecom Report, 10 (1987) 241.

SAW components are not only suitable as filters, but can also be used as sensors and identification tags ("ID tags"). See also the article "Acoustic Surface Waves - Technology for Innovations" by W. -E. Bulst and C. Ruppel, Siemens magazine Spezial, spring 1995, p. 2 and the essay "RF-powered wellness SAW sensors" by G. Scholl, F. Schmidt, T. Ostertag, 0. Sczesny and C. Seisenberger; RF-Powered Wireless SAW Sensors. Sensor99 Proceedings, Vol. 2 (1999) C7.2, Ξ. 227-232).

So far SAW components have been manufactured in such a way that their varying SAW substructures are placed individually in a lithography process, i. H. one exposure step is carried out for each substructure or different masks are used for different SAW components. Since the dimensions of the structures to be produced are generally in the micrometer or submicrometer range, high-resolution and expensive lithography is necessary to expose them. Each exposure step per component causes increased manufacturing costs or a low component throughput.

This is particularly disadvantageous in the case of surface wave identification marks ("SAW ID tags"), which often have to be individually coded within an area of application. For example, in the case of an SAW ID tag, the coding is generally represented by the individual placement of reflectors or transducers, the number of possible reflectors or transducers determining the strength of the coding. Larger SAW components can have 30 or more single exposures.

It is the object of the present invention to provide a possibility for the simple and fast production of components with a piezoelectric substrate and conductive substructures attached thereon.

The object is achieved by means of the method according to one of the claims 1 or 9 and by means of a device according to one of the claims 11 or 12.

The manufacturing process is based on a blank, the at least one piezoelectric substrate and several includes conductive substructures to be further processed in an individualization process in such a way that at least one of the substructures present on the blank is deactivated or removed.

Typically, the blank has many substructures, e.g. B. more than twenty reflectors on a SAW ID tag blank. A part is deactivated and / or removed from the set of existing partial structures and thus individualized in relation to the blank. For example, after the individualization of a SAW ID tag blank, there is a component in the form of a coded SAW ID tag. The method is not limited to SAW ID tags, but also covers other applications of components of the type mentioned, e.g. B. SAW filter.

When a partial structure is removed in the individualization process, it is removed from the piezoelectric substrate using suitable methods. When deactivated, the substructures are deactivated in such a way that they can no longer perform the intended function on the component. This can e.g. B. by cutting or partial removal of the substructures, e.g. B. lines happen.

This method has the advantage that the areas for deactivating or removing the unused substructures are generally larger than the substructures themselves, and therefore the individualization process needs to be less high-resolution than the basic process for producing the substructures on the blank , It follows that the customization process can be carried out using standard methods that are quick and comparatively inexpensive.

The blanks can conveniently be made in stock, e.g. B. from a specialized manufacturer, and later shipped to the end customer and customized depending on the order. There is a further advantage that standard manufacturing methods only need to be expanded by one coding process.

It is advantageous if a first spatial resolution in the individualization process is less than a second spatial resolution in the basic process for producing the substructures of the blank that are to be removed and / or deactivated. The customization is thus shifted from an expensive to an inexpensive structuring. For example, a high-resolution lithography may be required to produce the partial structures in the basic process, but a lower-resolution, and thus faster and cheaper, lithography may be used to remove the partial structures in individualization.

It is advantageous if the partial structures are produced with a smallest dimension determined by the first spatial resolution of the individual process, and so the first spatial resolution is matched to the required fineness of the partial structures. A typical minimum structure size is 0.3 μm.

It is advantageous if a lithography method is used in the individualization process for deactivating and / or removing partial structures, because this is reliable, accurate and comparatively inexpensive, e.g. B. compared to mechanical methods such as micromachining.

It is particularly advantageous if the individualization process is preceded by the basic process for the production of the blank without intermediate storage as a process step for the production of the component, because the transition from the basic process to the individualization process can thus take place at low cost, e.g. B. within a production line. For example, an additional etching process can be saved and no additional process steps or systems are required. Typically in the lithography process for individualization, the blanks are first coated, e.g. B. with positive or negative resist, and then exposed. After the exposure, the latent image is developed, then the structures exposed by the exposure process are etched away, usually by wet chemical etching processes or dry etching processes. After stripping, the individualized component is available.

It is advantageous if in the case of lithography fast pattern generators, which are usually used in the

Mask manufacturing can be used, fast steppers, - programmable masks can be used in standard exposure systems or freely programmable laser lithography systems. In general, however, other lithography methods for 2D structuring can also be used, e.g. B. electron beam process.

In the case of thinner conductive layers, the structures released for the etching attack can be etched away when the etching mask is developed with an alkaline developer (organic or inorganic). Depending on the frequency and application, the thickness of the thinner conductive layers is typically less than 100 nm.

The blank to be individualized is advantageously selected from a set of identical blanks, in particular after a quality control.

The object is also achieved in that a set with several components of the type described above is produced from a set of several similar blanks, and at least one partial structure per blank is deactivated and / or removed in the subsequent individualization process for each of these blanks. This can e.g. B. happen that on a Several blanks are produced within a basic process and then individualized after a wafer or other substrate. This can be followed by a separation. However, it is also advantageous to process already isolated blanks at the same time.

For example, 3 inch or 4 inch wafers are used. Typical component sizes are (2 x 2) mm ² for SAW high-frequency filters, (7.3 x 2.4) mm ² for 20-bit SAW ID tags and (11.5 x 1.5) mm ² for 32-bit SAW ID tags. Typical SAW speeds are 3000 m / s to 4000 m / s at 50 MHz to 2.5 GHz. Of course, the method is not restricted to components with these values.

It is also preferred if a different set of substructures is deactivated and / or removed for each of the blanks treated simultaneously within the individualization process. This z. B. allows ongoing coding in one step, z. B. with 16 4-bit SAW ID tags, the encodings from 0 (binary 0000) to 15 (binary 1111).

It is advantageous if the component is a surface wave identification mark ("SAW ID tag") which is produced by one of the methods mentioned. Due to the generally individual coding of the SAW ID tag, particularly efficient production is possible.

It is particularly advantageous if at least one partial structure in the form of an input / output converter for converting electromagnetic waves into surface waves and vice versa, as well as several locally varying partial structures in the form of reflectors, a coding being determined by a position of the reflectors , At least one reflector is removed during manufacture. It is also favorable if at least one substructure is an input transducer for converting electromagnetic waves into surface waves, and several substructures are in the form of output transducers, a coding being determined by a position of the output transducers. At least one output converter is removed during manufacture.

It is particularly preferred if at least one partial structure, in particular all partial structures, is present in the OFW-ID tag using thin-film technology, in particular with a thickness of less than 100 nm, because an etching process can be saved in this way.

In the following exemplary embodiments, a method for producing individualized components in the form of SAW ID tags and a SAW ID tag produced therewith are shown schematically in more detail.

FIG. 1 shows a flowchart of the process sequence for individualizing SAW ID tags,

FIG. 2 shows an individualized SAW ID tag and its signal response when actuated, FIG. 3 shows a blank B for producing the SAW ID tags, FIGS. 4 to 6 each show a SAW ID tag.

FIG. 2 above shows a top view of an individualized SAW ID tag T in the form of a reflective SAW delay line, as is shown, for example, in FIG. B. for remote readable identification of objects.

An input / output transducer W applied to a piezoelectric substrate S transmits surface waves via the substrate S in the direction of metallic reflectors R, which are attached to the substrate S one behind the other, that is to say locally varying. When the surface waves hit the A portion of the surface waves is reflected in each case by reflectors R and is then detected in the input / output converter W.

The substrate S is single-crystal of lithium niobate (LiNb0 ₃ ), which is preferably used for SAW ID tags T and temperature sensors. In general, quartz can also be used, in particular for frequency-accurate components with a low temperature response and mechanical sensors, or lithium tantalate (Li-Ta0 ₃ ), in particular for HF filters, the reflectors R are made of aluminum. For high performance, the substructures can also consist of Al-Cu-Al layer systems.

The typical relative layer thickness of the substructures, based on the acoustic wavelength, is 1% to 3% for surface wave resonators and 8% to 12% for high-frequency filters

FIG. 2 below shows the reflection signal corresponding to the upper partial image as a plot of the reflection in the time domain (S11) against a time t. The reflection signals are given as reflection peaks P.

Each reflection peak P corresponds to a (partial) reflection and thus to the presence of a reflector R. The position of each reflection peak P is, ideally linear, correlated with the transit time of the signal and from it with the distance to the input / output converter W (arrows ). The positions of the individual reflection peaks P and their combination correspond to a special code or identification number that can be designed individually for each component.

General methods can be used for coding, e.g. B. pulse position coding, on-off coding or a combination of these methods. For example, an existing be a reflector R to be interpreted as an "on" state, and the absence of a reflector R accordingly as an "off" state. Bit pattern coding can be achieved in this way.

As a rule, each SAW ID tag T is coded differently. This uniqueness distinguishes it from many common SAW components such as SAW filters, so that the processes known in SAW technology cannot be easily transferred to the manufacture of SAW ID tags.

Such an SAW ID tag T has so far been produced by conventional, time-consuming and costly application of the substructures.

A process flow for the individualization of SAW ID tags T is shown as a flow chart in FIG.

To the left of the dashed line are work steps for standard production for SAW mass components, to the right of these work steps for the individualization process, in particular for coding ID tags.

A typical manufacturing process of an SAW ID tag T comprises the following steps:

(1) At the start of production, a set of several blanks B is manufactured in a basic process ("front end"), typically by means of lithography on a 3-inch or 4-inch wafer. The structurally identical blanks B have all possible partial structures within a construction type, e.g. B. all possible reflectors R, which are combined in a reflector array A. The blanks B can be processed immediately or stored temporarily. (2) For blank B it is decided whether it should be individualized. If the decision is negative, blank B is placed in the assembly where it is isolated and checked ("backend", see (8)). If the decision is positive, blank B is individualized. The decision to individualize can depend on a selection of blanks B, e.g. B. via a quality control.

The individualization decision can e.g. B. also look so that when a suitable blank B is individualized, when another workpiece is present it is not individualized.

(3) As a first step in the individualization process, the wafer on which a set of blanks B or the reflector arrays A are located is coated. This can be done, for example, using a high-speed resist and a softbake in a variable temperature profile.

(4) There follows an exposure of the reflectors R to be removed from the reflector array A with an I-line stepper.

(5) The latent paint image is then developed using an organic developer (puddle development). The exposed illuminators R are etched away by an extended puddie time.

(6) Stripping the wafers in the stripper NMP.

(7) Optical inspection of the individualized SA components T.

After individualization, e.g. B. (8) Structure of the SA components T by separating and checking them ("backend")

connect. This type of individualization offers, in addition to the possibility of using fast and inexpensive standard processes with a comparatively low resolution, the advantages that an additional etching process with preparatory process steps such as heating the photoresist after development is saved, and the etching process is a sub-process of the structural development and therefore no additional process steps or plants are required.

This method is of course not limited to SAW ID tags, but can also be used for other SAW components, such as SAW filters, mechanical sensors or temperature probes.

Figure 3 shows a blank B after supervision (step 1). For better comparison with FIG. 2 (top) it is shown individually and not on the wafer.

With this type of component, 4 different positions are possible for each of the 4 reflectors R, which are combined in a reflector array A. The reflector array A is divided into 4 sub-arrays PA1, PA2, PA3, PA4, from each of which a reflector R is selected for coding. The other reflectors R are deactivated or removed. This can e.g. B. correspond to a bit pattern (from left to right: 1000 0100 0001 1000). However, other types of coding are also possible.

FIG. 4 shows a supervision of an individualized SAW ID tag T after work step (5). The photoresist is represented by slashes. You can see the exposed, developed and etched away areas on which there is no longer any photoresist. For each partial array PA1, PA2, PA3, PA4, three reflectors R were removed, the former position of which is shown in broken lines. The reflectors R under the photoresist and the input / output converter W are also available.

After removal of the photoresist, the SAW ID tag T shown in FIG. 2 results.

It can clearly be seen that the dimension of the exposure area required for the individualization is significantly larger than the maximum dimension of a partial structure, here at least one reflector R. This is particularly noticeable if the partial structure itself still has an internal structure.

FIG. 5 shows a further individualized SAW ID tag T 'after work step (5). The photoresist is represented by slashes.

In contrast, in this SAW ID tag T ', which was produced from the same set of the same blanks B as that in FIG. 4, a different set of substructures was removed. This can e.g. B. correspond to a binary bit pattern (from left to right: 0100 0100 1000 0001).

FIG. 6 shows a supervision of an SAW ID tag T * using several output converters 0 for coding.

The SAW ID tag T * has been individualized and coded analogously to the SAW ID tag T in FIG. In this figure, the SAW ID tag T * now comprises partial structures 1.0 in the form of an input converter I and a plurality of output converters 0. Surface waves are introduced into the SAW ID tag T * by means of the input converter I, which is equipped with an antenna L1. These waves are picked up by the output transducers 0 and forwarded to an output antenna L2 via a common busbar G. The position of the output transducers 0 relative to the output antenna L2 determines the chronological sequence of the signals radiated via the output antenna L2, by means of which coding can be implemented.

There were four subarrays PA1 *, ..., PA4 * each with four output converters on the blank. As a result of the individualization process, three output converters per partial array PA1 *, ..., PA4 * have been removed (dashed lines) and one output converter 0 remains.

Instead of removing the three output converters per sub-array PA1 *, ..., PA4 *, they can also be deactivated, e.g. B. by interrupting the connection to one or both busbars G.

The SAW ID tag T * with output converters 0 is not limited to the configuration shown in this figure. Rather, others, e.g. B. parallel and / or serially wired output converters 0 can be used, for example by using only one antenna with parallel connection of input and output converters 1.0. Reflectors R and output converter 0 can also be present together on an SAW ID tag.

Claims

claims

1. A method for producing a component (T, T ', T *) from a blank (B) which has a piezoelectric substrate (S) and attached to it several conductive substructures (W, R), characterized in that ß in an individualization process at least one of the substructures (W, R, 1,0) is deactivated and / or removed.

2. The method according to claim 1, wherein a first spatial resolution in the individualization process is less than a second spatial resolution in a basic process for producing the substructures of the blank (B) to be removed and / or deactivated.

3. The method according to claim 2, wherein the substructures (W, R, 1,0) are produced with a minimum dimension determined by the first spatial resolution.

4. The method according to any one of the preceding claims, in which at least one partial structure (R, 0) is removed in the individualization process by means of a lithography method.

5. The method according to any one of the preceding claims, wherein the blank (B) from a set comprising a plurality of identical blanks (B) is selected.

6. The method according to any one of the preceding claims, wherein the component (T, T ', T *) is a surface wave identification mark,

7. The method according to claim 6, wherein

a substructure (W) is an input / output converter (W),

- at least one partial structure (R) is a reflector (R), - At least one reflector (R) is deactivated and / or removed in the individualization process.

8. The method according to claim 6, wherein - a substructure (W) is an input converter (I),

- at least one substructure (R) is an output converter (0),

- At least one output converter (0) is deactivated and / or removed in the individualization process.

9. Method for producing a set of several components (T, T ', T *) from a set of several identical blanks (B), each of which has a respective piezoelectric substrate (1) and a plurality of conductive partial structures applied thereon ( W, R, 1.0), characterized in that ß is deactivated and / or removed in each of the blanks (B) in the subsequent individualization process at least one substructure (W, R, 1.0) per blank (B).

10. The method according to claim 9, wherein in the individualization process for each blank (B) a different set of substructures is deactivated and / or removed.

11. Surface wave identification mark (T, T '), having

- a piezoelectric substrate (S),

- At least one partial structure in the form of an input / output transducer (W), - At least one conductive partial structure in the form of a reflector (R), through whose position on the substrate (S) a coding can be determined, characterized in that the surface waves -Identification mark (T, T ') from a blank (B) with several reflectors (R) was made so that at least one reflector (R) of the blank (B) by means of of an individualization process has been deactivated and / or removed.

12. Surface wave identification mark (T *), comprising - a piezoelectric substrate (S),

- at least one partial structure in the form of an input converter (I),

- At least one conductive substructure in the form of an output transducer (0), through whose position on the substrate (S) a coding can be determined, characterized in that the surface wave identification mark (T *) is produced from a blank with a plurality of output transducers (0) was that at least one output converter (0) of the blank (B) was deactivated and / or removed by means of an individualization process.

13. Surface wave identification mark (T, T ^f , T *) according to one of claims 11 or 12, in which the partial structures are present in thin-film technology, in particular in a thickness of less than 100 nm.