DE102008020783A1 - Filter chip with different conductive layers and method of manufacture - Google Patents

Abstract

On a piezo substrate (PS) at least two structured conductive layers (LS) are formed side by side, each realize a SAW filter. The conductive layers comprise transducer structures, reflectors and printed conductors and each have a metallization system to which a layer thickness is assigned. At least two layer thicknesses of different conductive layers deviate from one another.

Description

The The invention relates to a filter chip with SAW structures consisting of different conductive layers are formed, and a method for the production.

A Exemplary use find SAW filter in terminals of mobile communication. Modern mobile phones today have a variety of diverse bands can serve, for the usually each own filter is required. Every filter is usually built on a separate chip. Several packaged Filters can but be united to a filter bank on a module. It is possible also, several filter chips unheated to mount on a module and to encapsulate the module together. Also known are duplexers, the two filter chips in a common Package have.

task the present invention is to provide simpler solutions for such applications, which require multiple filters.

These The object is achieved by a Filter chip solved according to claim 1. Advantageous embodiments of the invention and a method for Production of the filter chip can be found in further claims.

It It is proposed to have at least two SAW filters on a common Piezo substrate to realize. Each filter is from its own structured, formed on the piezoelectric substrate conductive layer formed, each transducer structures, reflectors and conductors includes. A conductive layer has a metallization system one or more layers of metals or alloys on. On the filter chip two are different at least in one parameter Conductive layers provided, the different filters assigned are. This may be the layer thickness of the conductive layer or one of the Partial layers or even the structure and the metals used Be conductive layers or their sublayers.

It is known to have a SAW filter optimized in its properties one aimed at the passband and thus at the resonant frequency of the filter relative metallization height, So has a corresponding layer thickness of the conductive layer. at SAW filters that work in different frequency ranges, can the optimum parameters of the respective conductive layer, in particular their Differentiate between layer thicknesses.

So far it was not known, however, with more than one optimized SAW filter respectively adapted conductive layer on a common piezosubstrate to realize. The invention proposes different respectively optimized conductive layers for the at least two SAW filters to use and to each of the filters with a to the pass frequency of the filter adapted layer thickness of the conductive layer form. Furthermore allows the invention, the entire metallization to the adapt to respective filter requirements and train accordingly. Therefore, you can also the metallization of the at least two conductive layers in other parameters differ.

in the proposed filter chip can the metallization systems and the layer thicknesses of the conductive layers arbitrarily strong, as well as the transmission frequencies of the realized by SAW filters. The at least two SAW filters can be completely independent of each other be optimized and do not influence each other.

Of the Filter chip can be built into a package and encapsulated in it, so that the effort to encapsulate a second and possibly further on the one filter chip realized SAW filter is omitted since only one filter chip has to be encapsulated. On the same Filter chip can also be realized three, four or more SAW filters next to each other.

Of the Filter chip has the advantage that it is compared to a plurality of separate Filter chips, each with only one SAW filter, easier to handle is. Instead of the corresponding number of different filter chips only one filter chip has to be mounted. Likewise reduced the encapsulation effort required for the SAW filter required surface on piezosubstrate and total the dimension of the filter chip. At the same time with the filter chip also costs compared the multi-chip solution saved.

In According to an embodiment of the invention, the filter chip has a ground connection which is electrically connected to at least two of the SAW filters is. Such a common ground connection saves additional chip area and diminished over a solution with multiple filter chips and the wiring on the carrier substrate or the circuit board to mount on the filter chip or the is.

The conductive layers of the different SAW filters on the filter chip may include different metallization systems. These may differ with respect to the materials used. It may also be conductive layers in which the layer thicknesses or the layer thickness ratios of different partial layers in the different conductive layers are chosen differently. Different conductive layers can also handle a different number of sublayers believe it.

The Center frequencies of the at least two SAW filters preferably differ from each other and are each aligned to a separate frequency band. Possible However, there are also different SAW filters, although the same Center frequency work, but different specifications have, for example, with respect the bandwidth of the passband.

In a package, the filter chip preferably in a flip-chip arrangement be mounted on the top of a multilayer substrate. The latter points then solderable on its underside Outdoor connections, the above a wiring realized inside the multilayer substrate with connection surfaces on the top of the multilayer substrate and these in turn via bumps can be connected to the filter chip.

One on a carrier substrate in flip-chip assembly mounted filter chip can therefore with a on the back side of the filter chip and the adjacent surface of the carrier substrate Be sealed cover that formed one or more layers can be. The cover can be a laminated single or multi-layered Be film that includes plastic. Alternatively or additionally the cover include a metallization. About this single or multi-layered Cover can over it In addition, the filter chip still be covered with a potting compound. On the carrier substrate can Also, other chips may be mounted together with the filter chip result in a module. The filter chip and the other chips can work together be encapsulated in the module, for example, by a common over all Chips overlying cover that is tight with the carrier substrate concludes.

It Other covers are possible, for. B. with a potting compound applied directly to the filter chip is.

The Production of a filter chip with different SAW filters with different Conductive layers succeed in a process in which the different Conductive layers sequentially one behind the other and independently getting produced. For this purpose, a piezo substrate is first a first structured conductive layer which produces a first SAW filter formed. This includes transducer structures, reflectors and printed conductors. For this first conductive layer for the first SAW filter can be any Metallization and structuring techniques are used.

Subsequently, will the conductive layer for applied the second SAW filter. This is done in a first variant according to a Lift-off technology first the whole area a photoresist layer is applied and patterned. Subsequently, will the second conductive layer over the entire surface of the structured resist layer applied and in particular vapor-deposited. in the next Step is the structured photoresist including the areas of applied conductive layer, which rests directly on the photoresist, lifted from the piezosubstrate, so we speak here of lift-off. The not lifted off remaining on the piezo substrate Leitschichtstrukturen form the structures of the second SAW filter, which also includes transducer structures, reflectors and tracks.

In another later executed step can Pads, which are also common connection pads for the at least two SAW filters can be, be generated. For the connection pads can be used a metallization system, which differs from that of the first and second SAW filter layers different. In particular, the connection pads are preferably in larger layer thickness as the transducer structures and tracks produced. Preferably at least the connection pads for ground - the ground pads - so applied, that they over Tracks at the same time as the ground connections of the first and second SAW filters are connected.

In similar or the same as the second conductive layer can still on the piezoelectric substrate applied further Leitschichten and structured to other SAW filters become. Basically allowed It's the proposed method, any number of SAW filters to realize on a common piezosubstrate.

For the lift-off procedure it is advantageous if the resist structures to be removed have a to the top, so away from the piezoelectric substrate away cross-section exhibit. Such z. B. conical cross section prevents anisotropic deposition of the conductive layer that attaches to the metal then overhanging faces the resigned resist structures precipitates. This causes that between the not To be lifted directly deposited on the piezo substrate surface areas the conductive layer on the one hand and on the other hand the surface areas, which are deposited on the resist structures, not metallic Connections exist. This is a clean peel off the Resist structures along with deposited surface areas of the conductive layer possible. Become non-lifted structures remaining on the substrate not damaged and therefore have clean and smooth edges even after lifting on.

Photoresist structures with conical upwardly extending cross-section can help with a suitable phototechnology can be generated. For this purpose, an optionally multi-stage process with possibly several resist systems or layers may be used so that the remaining structures assume a conical cross-section or at least have an overhanging structure.

In a variant of the application of the conductive layer successively a first T and a second sub-layer of the conductive layer applied, z. B. vapor-deposited. The first sub-layer can in particular a the Liability intermediary layer be.

For each SAW filter becomes the layer thickness of the respective partial or conductive layer controlled during application and to a respective individual, the SAW filter assigned value and thus optimized. This can be done with a quartz crystal, in the deposition area the metal deposition is arranged and its resonance frequency depends on the applied metal layer thickness. If necessary, can also in addition or Alternatively, a trim process can be used to determine the layer thickness reduce after application.

The Application of the conductive layers can be the application of several partial layers include that applied in different layer forming processes be selected could be from sputtering and vapor deposition. For different conductive layers the sub-layers differ in at least one feature, selected from sequence of partial layers, material of the partial layers and layer thickness the sublayers.

at the lift-off technique can be the lifting of the photoresist including the on it Overlying areas of the conductive layer by treating with a solvent take place, which can dissolve or dissolve the resist structures.

The proposed lifting method allows the production of a second, third and optionally further conductive layers in an analogous manner, wherein the material systems and material thicknesses for the conductive layers for each conductive layer chosen differently can be. An already applied and structured conductive layer disturbs this the generation of the other conductive layers not so that different Conductive layers or SAW filters structured from them are completely independent of each other can be produced.

The Connection pads for Signal connections and ground terminals be final produced after the production of the last conductive layer. This can also a lift-off technique can be used. Single connection and ground pads can simultaneously with several SAW filters or with structures of several SAW filter be connected.

to Making a common connection pad for two different SAW filters can be the structured with the SAW filters interconnects are structured so that their ends are brought close together. About the two ends can be then apply a connection pad so that it overlaps both tracks and an electrical contact to the two associated SAW structures manufactures.

in the Below, the invention will be described with reference to embodiments and the related Figures closer explained. The figures are solely illustrative of the invention and are therefore designed only schematically and not true to scale. The Figures can therefore neither absolute nor relative measurements are taken.

1 shows in cross-section a piezosubstrate with two structured, different conductive layers applied thereto,

2 shows a schematic plan view of a filter chip indicated structures for here three realized on the substrate SAW filter,

3 shows in schematic cross section the production of a filter chip with two different structured conductive layers during different process stages,

4 shows an alternative method of making the first conductive layer.

1 schematically shows a first embodiment of a filter chip according to the invention, are structured on the two different conductive layers to two SAW filters. On the piezo substrate PS, which is preferably monocrystalline, a first conductive layer LS1 is patterned into a first SAW filter. The structures are arranged in a first filter area FB1 on the piezo substrate PS. A second conductive layer LS2, which is shown here with a layer thickness differing from the first conductive layer, is arranged and structured in a second filter region FB2 on the same piezo substrate PS.

2 shows in plan view and only schematically indicated an exemplary structure of three SAW filters that can be generated according to the invention together on the same piezo substrate PS. Each SAW filter is arranged in a separate filter area FB. The relative arrangement of the different SAW filters to each other is preferably such that signal terminals and ground can be used together without the need for an elaborate or long trace guidance on the surface of the piezosubstrate. Each SAW filter here has, for example, interdigital transducers W which are arranged in an acoustic track. Each acoustic track is terminated on both sides with two reflectors R and can each have one or more transducers. The interdigital transducers W are connected to signal connections SA and / or ground connections MA and / or to each other. One of the ground connections MP is designed as a common ground pad for two different, directly juxtaposed SAW filters. For example, the common ground pad MP12 serves as a ground terminal for structures of second and third SAW filters arranged in the second and third filter areas FB2, FB3. The ground pad MP23 serves as a common ground terminal for structures of the second and third SAW filters in the second and third filter area FB2, FB3.

The first SAW filter is formed for example from a first strain gauge track, at the six interdigital transducers W between two reflectors R are arranged. Two transducers serving as input are parallel interconnected, as well as two each serving as an output converter, so that the filter is symmetrical / unbalanced and thus operated as a BALUN can be. Electrically in series with the DMS track is another acoustic track, which formed as a two-port resonator is. The two exits the DMS track are each equipped with an interdigital transducer of the two-port resonator connected. The two exits of the first SAW filter are at the respective busbar of the converter of Two-OR resonator arranged.

As Shown in the figure, the second SAW filter can be a similar or even the same structure, but preferably finger pitches the transducer and the conductive layers of the first and second SAW filters are formed differently. Also the third SAW filter can a similar Structure, in which case a DMS filter in series with a One-port resonator is switched while another one-port resonator is connected in parallel with the serial resonator. To the common used mass pad MP23 can Reflectors and grounded busbars of the converters of both Be connected to SAW filters. In addition, only be provided to the respective SAW filter associated with Massepads.

in principle Is it possible, to realize SAW filters of different filter types on the filter chip. So, for example DMS filters and reactance filters, which are formed, for example, of one-port resonators are realized side by side on a common filter chip become. The inventive method allows structures for create different filter types on the common chip and is in this regard therefore not limited.

3 shows by means of schematic cross sections through a piezoelectric substrate different process stage in the production of a filter chip with at least two conductive layers, which are associated with two SAW filters.

On a piezo substrate PS is first a first conductive layer LS1 applied and to structures of a first Structured SAW filters. The first conductive layer can be structured with lift-off technology. Is possible However, it also, a large-scale first conductive layer to generate and over a resist mask by etching to structure.

Over the piezosubstrate PS with the first conductive layer LS1, a layer of a photoresist PR2 is subsequently applied over the whole area, for example by spin-coating. (please refer 3B ).

3C shows the photoresist layer after the photopatterning, consisting of exposure, temperature and developer processes. Resist structures remain which have a larger cross section in the upper layer region than in the lower layer region.

Then be the whole area one or more optionally different, metallic sublayers MS2 for applied the second conductive layer. This can be done by vapor deposition take the metallic sublayer.

As the 3D shows, resting on the resist layer areas of the metal layer MS2 and on other surfaces such. B. the piezosubstrat PS lying layer portions of the metal layer separated from each other and not connected by laterally adhering to the resist structures metal structures. In the next step, this makes it possible to cleanly remove the complete structure of the photoresist layer PR2 together with the layer regions of the metal layer MS2 resting thereon, for example by treatment with solvent.

3E shows the arrangement with ready-structured second conductive layer LS2, which is formed in a second filter area FB2 next to the first filter area FB1 on the piezoelectric substrate. First and second conductive layers differ in at least one feature selected from layer thickness, material or layer sequence.

An alternative method by which the first conductive layer for the first SAW filter can be applied and patterned is described below from 4 explained. Here, first of all, a metal layer MS1 is applied to the upper side of the piezo substrate PS. This can be done by sputtering and / or vapor deposition. The conductive layer may comprise a plurality of optionally different partial layers. One or more of the sublayers may comprise aluminum and / or copper. It is also possible to realize multi-layer constructions in which aluminum or aluminum-containing layers and layers of a harder and / or heavier metal alternate. It is advantageous, for example, to provide at least one copper layer in the multi-layer structure.

With the aid of a photoresist layer applied over the entire surface, which may be a positive or negative-working lacquer, and a subsequent photolithography, an etching mask is then produced, as used, for example, in US Pat 4B is shown. The regions of the metal layer which are covered by the resist mask ERST remain free of erosion in the subsequent etching step, which is carried out, for example, by means of a dry etching process. Subsequently, the photoresist layer is removed and optionally cleaned the surface of other paint residues.

4C shows the resulting first conductive layer LS1 directly on the piezo substrate.

After the structuring of the first conductive layer LS1 by means of an etching process, the next and possibly further subsequent conductive layers can be produced using the lifting method already described. In principle, however, it is also possible to also produce further conductive layers by the etching process. For this it is necessary, after the in 4C process step shown to deposit an etch stop layer at least in the region of the first conductive layer LS1 and to structure. The piezosubstrate PS provided with an etching stop layer over the first conductive layer is then used as substrate for the production of the second conductive layer in the region not covered by the etching stop layer. For this purpose, a further metal layer is generated over the entire surface and structured by means of a photolithography and a further etching step. The etch stop layer over the first conductive layer LS1 prevents the first conductive layer from being damaged when the structure of the second conductive layer LS2 is etched.

Further Conductive layers can in the same way by repeating the described process steps be applied and structured. After creating the last Conductive layer on the piezo substrate PS is also here in a common step is the generation of connection pads that are used for electrical Contacting individual or common contacts of several Leitschichten can be used.

In the variant with patterning by etching, the etching stop layer is first photolithographically structured in such a way that it is removed in the region of the connection pads to be produced. The connection pads themselves can be generated and patterned by means of etching technology. For this purpose, a metal layer is first applied over the entire surface and patterned photolithographically to the desired pad. In structuring, it is possible for the connection pads to be applied only partially to the piezosubstrate and to the exposed conductor tracks which are connected to the conductive layers LS. For producing the metallization for the connections, preferably two partial layers are applied, one comprising predominantly aluminum. However, the preparation of the connection pads is also possible by the lift-off, as they are based on the first embodiment and according to 3 was explained.

Together with the connection pads can more passive structures on the surface of the piezoelectric substrate PS generated become. So it is possible in particular to create passive structures used to adapt the SAW filters and over existing ones or to be structured tracks with the conductive layers or the filter structures realized therefrom electrically connect to. Such passive structures have a function or a property over that which goes out of a track. You can use capacitors, inductors, interdigital transducers or reflectors.

Is possible however, such matching elements together with the structured conductive layers in a common process. It can be matching elements for a first SAW filter also together with the conductive layer of a second of them different SAW filters are generated, with the corresponding Conductive layer can be used to produce the matching elements. decisive for the Selection is the layer thickness or composition of the respective Conductive layer, wherein that conductive layer for the realization of the matching elements selected that's going to be the conductive layer is best suited. Decisive for the selection is the layer thickness / composition or the minimum realizable structure width.

Each conductive layer is preferably deposited simultaneously at the wafer level for a plurality of filter structures of different filters / filter chips to be formed on the wafer. In the last step, which is also considered in terms of time, an underbump metallization (UBM) is finally produced on the connection pads or in the area of the connection pads as further metallization. Subsequently, entwe the singulation of the individual filter chips from the wafer, or it is produced at wafer level a parallel made for all filter chips encapsulation.

On Wafer level are suitable for this process, in which preferably rigid cover materials over the wafer or over the individual filter chips are applied. A direct contact to the conductive layers is avoided if previously spacer elements generated between the filter areas or at the edge of the filter chips become. These spacers can for example in the form of the conductive layers enclosing frame and in particular be produced in the form of metal frames. The metal frame can all Conductive layers and elements of a filter chip structured therefrom enclose. Possible However, it is also, the frame formed as spacers only to guide mechanically sensitive areas and in particular the connection pads release.

Subsequently, will the cover, which is made of glass, ceramic or another sufficiently rigid material exists on the spacer structures put on and connected to these. Subsequently, the cover layer structured and, where appropriate, by further measures, in particular by sealed further layer generation against the piezoelectric substrate PS become.

Is possible however, it also, after the production of the conductive layers, connection pads and UBMs to separate the filter chips and individually on large-area carrier substrates with integrated metallization and wiring. Suitable carrier substrates include multilayer integrated wiring and optionally integrated passive component substrates from LTCC, HTCC or a PCB, for example made of laminate.

Becomes used as a mounting method flip-chip technology, so are the conductive layers to the carrier substrate turned and after mounting in a cavity between piezosubstrate and carrier substrate protected. The carrier substrate with it mounted in flip-chip assembly filter chips can then with a large area be provided a cover. Since the backs of the filter chips against a Mass stress are insensitive, this can be a lamination technique used in combination with other Schichtabscheideverfahren become. Possible However, it is also the filter chips by layer deposition suitable Layers, in particular metallic and inorganic insulation layers cover. Possible However, it is also insulating layers of organic materials and in particular of plastic films or potting compounds and these organic materials also with layer deposits to combine inorganic insulating materials.

With the method according to the invention can Filter chips are generated, which has a plurality of SAW filters to unite a chip. Such filter chips can be used as filter banks for all those Applications are used that require a larger number of filters. In particular, such filter banks used as filter banks are front-end modules of terminals mobile communication suitable, especially for terminal cell-bound Mobile communications.

Of the However, the proposed filter chip can also be a duplexer, triplexer, Be multiplexer or other integrated device in which the different SAW filters realized on the filter chip electrically connected to each other. This is the case with the filter chip possible, to apply a radio frequency signal to a terminal and in response to it To assign frequency to a specific signal path, so that the signal so over a particular SAW filter is filtered.

The The invention is not limited to the exemplary embodiments described in the figures limited. In particular, you can the described process steps and structural elements arbitrarily with each other be combined. decisive is always to provide a filter chip with different conductive layers, at least with regard to an essential parameter and in particular with regard to Different layer thickness of the conductive layer.

FC

filter chip

FB

filter area

PS

piezosubstrate

MS

metal layer

LS

conductive layer

W

converter

LB

conductor path

R

reflector

PR

Photoresist layer

PRS

Photoresist structures

MA

ground connection

MP

common Mass Pads

SA

signal connection

Claims (19)

Filter chip - with a piezo substrate (PS) on which at least two structured conductive layers (LS) are formed side by side, each realize a SAW filter - wherein the conductive layers transducer structures, reflectors and interconnects (LB) comprise - each conductive layer, a metallization and a layer thickness assigned, - At least two layer thicknesses of different conductive layers differ from each other. Filter chip according to claim 1, which ground connections (MP) which are connected to at least two SAW filters. Filter chip according to claim 1 or 2, wherein at least two metallization systems of different conductive layers (LS) differ from each other. A filter chip according to any one of claims 1-3, wherein the at least two SAW filters have different center frequencies. Filter chip according to one of claims 1-4, which in flip-chip arrangement mounted on top of a multilayer substrate that is on its bottom solderable Has external connections, wherein in the interior of the multi-layer substrate, a multi-layer wiring is arranged, the filter chip (FC) and the realized thereon SAW filter electrically connects to the external connections. Method for producing a filter chip with at least two SAW filters - at on a piezo substrate (PS) applied a first conductive layer (LS) that becomes - one first associated with SAW filters - transducer structures, reflectors and tracks is or is structured, - in which subsequently on the piezosubstrat over the entire surface a layer of a photoresist (PRS) applied and patterned becomes - at a second conductive layer over the entire surface of the gas phase over the structured resist layer and the exposed piezosubstrate is applied, - at the photoresist with directly on top of lying areas of the lifted second Leitschicht in a lift-off from the piezoelectric substrate is, with a second SAW filter associated transducer structures, Reflectors and traces remain on the piezosubstrate. Method according to claim 6, in which common electrical Connection Pads (MPA) for the at least two SAW filters are generated. Method according to claim 6 or 7, - in which the photoresist over an overlying mask (PM) or a reticle is exposed, - in which optionally multi-stage exposure, tempering and development steps be done so that after development remaining photoresist structures in the upper layer area a larger structure width have as in the lower layer region. A method according to any one of claims 6-8, wherein for application the conductive layer (LS) or other metallic layers one or several partial layers are evaporated. A method according to claim 9, wherein as a sub-layer a layer comprising aluminum, titanium or copper is vapor-deposited becomes. Method according to one of claims 6-10, - in which the lifting of the photoresist (PRS) along with directly lying on top of the conductive layer Treat with a solvent he follows. A method according to any one of claims 6-11, wherein after manufacturing the second conductive layer (LS) a third structured conductive layer is generated, wherein the method steps for generating the second Conductor be repeated. The method of claim 12, wherein a fourth and optionally further conductive layers (LS) in the same way how to make second and third conductive layers, one associated with fourth or further SAW filters. Method according to one of claims 6-13, wherein also the first Similar to conductive layer (LS) as the second conductive layer produced and structured in lift-off becomes. Method according to one of claims 6-14, in the after the Production of a desired Number of conductive layers (LS) for a corresponding number of juxtaposed SAW filters the electrical connection pads for the SAW filters in one step be generated, and for this purpose the lift-off technique is used, being the connection pads be generated so that they at least partially with the ends of Overlap conductor tracks, which are electrically connected to the transducer structures of the SAW filters are. Method according to one of claims 6-15, wherein the layer thickness the respective conductive layer during application controlled and on set an individual value assigned to the respective SAW filter becomes. A method according to any one of claims 6-16, wherein for the manufacture the conductive layers are applied several sub-layers, at at least one characteristic selected from the composition of Partial layers, sequence of partial layers and layer thickness of the partial layers differentiates between two different SAW filters. Method according to one of claims 6-17, wherein at least two, different SAW filters associated conductor tracks with a common m connecting pad by the two tracks are brought together close together and the connection pad is then applied so that it overlaps both tracks. Method according to claims 6-18, wherein a conductive layer, which is assigned to a first filter, in the range of a second one Filter is used for the realization of passive elements.