DE10216559B4 - Acoustic surface acoustic wave device and method for its production - Google Patents

Abstract

acoustic Surface acoustic wave device with stripe structures of a thin-film metallization system as finger electrodes, where at least the stripe structures partly or completely with a thin film are coated on the basis of Ta and Si.

Description

The The invention relates to a method for producing power SAW Components (Power SAW Devices) with a novel Metallisierungssytem based on copper thin films. For this Copper SAW technology are thin Barrier layers to prevent interdiffusion of fabric required. Especially against oxygen and copper diffusion.

For the production of SAW components, international metallization systems are used for the production of finger electrodes based on Al, Al alloys and Al layer systems. For this purpose, one or more metal layers (multilayers _{) are} deposited on a piezoelectric substrate (quartz, LiNbO ₃ , LiTaO ₃ , ZnO layers or the like) on which there is a resist mask using known deposition methods, advantageously electron beam evaporation or magnetron sputtering, and then structured by detachment of the resist mask (lift-off technique).

A other principle possibility structuring is the etching technology (either dry or wet chemical etching), where the wafers complete coated with metal and the electrode part to be obtained covered with a mask while the places to be removed etched become. In this way, two finger-like structured, into each other produces gripping electrodes whose individual fingers have a defined Distance from each other and a certain overlap area (aperture) and have a well-defined geometry.

Another principle possibility of producing structured metal finger structures is given by the CMP method. CMP3 (chemical metal polishing) was originally developed as a planarization process for SiO ₂ . When applied to three-dimensionally deposited metal layers in the so-called damascene technology, the planarizing effect of the process leads to their structuring, which makes CMP an alternative structuring method for metals. Due to the chemical and physical mode of action and the wide range of variation of the chemicals and additives, this process offers the possibility to process a wide range of applications, even of very hard coatings. For this purpose, the required layer sequence is introduced into a trench structure, which may be located preferably in the silicon oxide or else in the substrate, and planarized in alternation with the coating with the CMP process (Z: Stavreva, Dissertation, Dresden (1998)).

By applying a high-frequency voltage to the finger electrode pair, a time-dependent electric field strength is generated between two oppositely poled electrode fingers, resulting in a location-dependent displacement of the grating components in the piezoelectric substrate material. A surface acoustic wave is generated which, depending on geometric and material-specific conditions, has a specific propagation characteristic that can be calculated in principle. With good adhesion of the metallization on the substrate, this mechanical distortion of the substrate material translates as local strain (mechanical tension) or compression (mechanical pressure) on the finger electrodes. By constantly changing the polarity of the adjacent electrodes in the frequency of the applied electrical voltage in this way creates a high dynamic mechanical bending-tensile alternating stress (high cyclic fatique loading). This cyclic loading at high frequency causes at high amplitudes of the SAW and / or temperatures, ie at high power densities, in the electrode material detectable by microscopic methods stress-induced mass transfer, visible depending on the material at a more or less pronounced hole and hill formation or partial delamination the metal layer, especially pronounced in Al base systems. This process is known in the literature as akustomigration (N. Kimura, et al., IEEE Ultrasonics Symp. Proc., 1998, pp. 315-318; W. Ruile, et al., IEEE Ultrasonics Symp. Proc. 2000, pp. 275-278; workshop S. Menzel, among others, Proc 6 ^th Int; S. Menzel, among others, Proceedings of the 12 ^th European Congress on Electron Microskopy, Vol II, Physical Sciences, July 2000, Brno, Czech, pp 541-542.... Phenomena in Metallization, Ithaca 2001; H. Schmidt, IEEE Ultrasonics Symp. 2001, Atlanta submitted). It has been experimentally proven that this mass transport correlates with a change in the electrical signal behavior of SAW devices. For example, a significant non-reversible shift of the resonance frequency and a change in the amplitude in the admittance curve could in filter components are detected (p Menzel, among others, Proceedings of the 12 ^th European Congress on Electron Microskopy, Vol. II, Physical Sciences, July 2000, Brno, Czech, pp. 541-542, H. Schmidt, et al., IEEE Ultrasonics Symp., 2001, Atlanta submitted). The intensity of damage caused by hole and hill formation is dependent not only on the power but also on the operating time (for a given power) of the components, which results in a connection to the service life even at low power densities. In case of severe damage, the component fails in its function.

It is known after the US 5,343,107 A a surface acoustic wave device including a diamond layer and a piezoelectric thin film, between which epitaxially grown copper electrodes are interposed.

To WO 00/33394 is a surface acoustic wave device known, which consists of a metallized piezoelectric substrate consists, wherein between the substrate and metallization electrodes are arranged. These electrodes consist of a first layer of pure titanium and a second layer of an aluminum and titanium alloy.

A surface acoustic wave device has also been proposed in which metallic strip structures made of a copper base material are coated or surrounded by one or more diffusion barrier layers ( DE 102 06 480 A1 ).

task The invention relates to the provision of surface acoustic wave devices where little or no interdiffusion of substances occurs and a simple process for their preparation.

The Invention is solved by the invention specified in the claims. further developments are the subject of the dependent claims.

The acoustic according to the invention Surface Acoustic Wave Components have strip structures from a thin-film metallization system as finger electrodes, where at least the stripe structures partially or completely with a thin film are coated on the basis of Ta and Si.

advantageously, consists of the thin-film metallization system from a Cu thin-film system.

Also Advantageously, there is the thin film on the basis of Ta and Si from 20-80 atom% Ta, from 15-50 atom% Si and from 0 to 60 atom% N.

Especially Advantageously, there is the thin film based on Ta and Si from 25-35 at.% Ta, from 15-25 at.% Si and from 45 to 60 atom% N.

Farther It is advantageous if the thin film is amorphous on the basis of Ta and Si.

Also It is advantageous if the thin layer based on Ta and Si, the finger electrodes completely sheathed.

Also It is advantageous if the thin layer based on Ta and Si is a conductive layer.

But It is also advantageous if the strip structures covered in total are and the covering thin film is formed insulating on the basis of Ta and Si.

Farther the task is solved by a method for producing surface acoustic wave components, at a cluster plant on an unstructured or in a cluster plant trenches of a patterned wafer, the thin film metallization system and the thin film on the basis of Ta and Si as a two-layer system or as a multilayer system be deposited.

advantageously, The finger electrodes and the thin film are based on Ta and Si deposited on a piezoelectric substrate.

Also advantageously, the deposition is carried out on a piezoelectric substrate made of quartz, LiNbO ₃ , LiTaO ₃ , ZnO, KNbO ₃ , GaPO ₄ Li ₂ B ₄ O ₇ or La ₃ Ga ₅ SiO ₁₄ .

Also Advantageously, the finger electrodes are made of a Cu thin film system by means of magnetron sputtering, electrochemical processes, MOCVD or evaporation deposited.

It is also beneficial if the thin films from TaSiN by reactive sputtering from a TaSi target under nitrogen atmosphere be deposited. It is likewise advantageous if the deposition is performed by means of magnetron sputtering without vacuum interruption.

It is also advantageous when the deposited thin film metallization system and / or the thin film be tempered on the basis of Ta and Si.

And it is likewise advantageous if the thin-film metallization system and the thin film based on Ta and Si in trenches of a patterned wafer be deposited.

a higher Resistance to acoustomigration show thin-film metallization systems on the base from Cu. For These technologies are the use of the sheath according to the invention very cheap, because this sheath acts as a diffusion barrier and diffusion of copper in the substrate and also the reaction with oxygen with the generally uncovered finger electrodes largely or Completely prevented.

With the invention advantageous amorphous deposited thin film system TaSiN achieves very good properties of the surface acoustic wave components. In particular, such devices according to the invention are far above SAW operating temperatures and for intermediate technological treatments necessary temperatures stable.

The Chemical composition can vary within a wide range.

in the Furthermore, the invention is explained in more detail in several embodiments.

example 1

TaSiN layers have been deposited on a Cu layer by means of magnetron sputtering and without vacuum interruption in a cluster system on a LiNbO ₃ wafer. The TaSiN layers encapsulated the Cu layers, which are in the form of finger electrodes.

there shows

1a) a result of an AES examination for samples tempered at 400 ° C. with the layer sequence according to the invention TaSiN (50 nm) / Cu (150 nm) / TaSiN (50 nm)
in comparison shows

image 1b) a layer sequence of Ti (50 nm) / Cu (150 nm) / Ta (50 nm).

at the layer sequence according to the invention is still at 400 ° C due to the amorphous state of the sheath layer a very good barrier effect.

Example 2

1. Lithography for structuring the SAW components:

• Apply the paint on the front of the substrate
• Drying of the paint
• Exposure of the paint with appropriate mask
• hardening of the paint

2. Dry cleaning of the substrate surface ICP cleaning process parameters: Performance (Target): 200 W Power (Substrate): 50 W Working gas: Ar Ar-Flow: 10 sec Working pressure: 1 mTorr Resulting bias voltage: 135 v Cleaning time: 3 min 3. Reactive RF magnetron sputtering of the TaSiN copper barrier (50 nm). Process parameters of the deposition: Performance (Target): 1000W Power (Substrate): 0 W Target material: Ta ₅ Si ₃ Working gas: Ar Ar-Flow: 5 sec Reaction gas: N N ₂ flow: 4 sec Working pressure: 1.2 mTorr Resulting bias voltage: 110V sputtering: 2:06 min Substrate temperature: ° C 25 4. DC magnetron sputtering of the Cu power layer (150 nm). Process parameters of the deposition: Performance (Target): 4000W Target material: Cu Working gas: Ar Ar-Flow: 3 sec Working pressure: 0.9 mTorr sputtering: 0:45 min Substrate temperature: ° C 25 5. Reactive RF Magnetron Sputtering of the TaSiN Oxygen Barrier (50 nm) Process Parameters of Deposition: Performance (Target): 1000W Power (Substrate): 0 W Target material: Ta ₅ Si ₃ Working gas: Ar Ar-Flow: 5 sec Reaction gas: N N ₂ flow: 4 sec Working pressure: 1.2 mTorr Resulting bias voltage: 110V sputtering: 2:06 min Substrate temperature: ° C 25

6. Wet paint removal (lift off)

• Removal of the paint with acetone bath and ultrasound (10 min)
• Removal of the paint residue with ethanol bath and ultrasound (5 min)
• Dry the substrate

following becomes composition and resistivity of the TaSiN layers described with varied nitrogen content.

By varying the N ₂ flow during the sputtering process, the nitrogen content in the TaSiN layer is deliberately changed. The change in the composition influences the microstructural properties (eg the resistivity) of the barrier layer (see Figure 2). The composition was determined by Rutherford Back Scattering.

Of the specific electrical resistance increases with increasing nitrogen content (see Figure 3). Be more than 50% nitrogen in the TaSiN layer introduced, so they are electrically insulating.

there shows

Figure 2 shows the composition of the barrier layer as a function of the N ₂ flow

image 3 the electrical resistance as a function of the nitrogen content

Claims (16)

Acoustic surface wave device with stripe structures from a thin-film metallization system as finger electrodes, where at least the stripe structures partially or completely with a thin film are coated on the basis of Ta and Si. The device of claim 1, wherein the thin film metallization system from a Cu thin-film system consists. The device of claim 1, wherein the thin film on the basis of Ta and Si from 20-80 atom% Ta, from 15-50 atom% Si and from 0 to 60 atom% N exists. A device according to claim 3, wherein the thin film based on Ta and Si from 25-35 at.% Ta, from 15-25 at.% Si and from 45 to 60 atom% N. The device of claim 1, wherein the thin film is amorphous on the basis of Ta and Si. The device of claim 1, wherein the thin film based on Ta and Si, the finger electrodes completely sheathed. The device of claim 1, wherein the thin film based on Ta and Si is a conductive layer. Component according to Claim 1, in which the strip structures are covered in total and the covering thin film on the basis of Ta and Si is formed insulating. Method for producing surface acoustic wave components according to at least one of the claims 1 to 8, in which in a cluster plant on an unstructured or in trenches a structured wafer, the thin-film metallization system and the thin film on the basis of Ta and Si as a two-layer system or as a multilayer system be deposited. The method of claim 9, wherein the finger electrodes and the thin film based on Ta and Si on a piezoelectric substrate be deposited. The method of claim 10, wherein the deposition on a piezoelectric substrate made of quartz, LiNbO ₃ , LiTaO ₃ , ZnO, KNbO ₃ , GaPO ₄ Li ₂ B ₄ O ₇ or La ₃ Ga ₅ SiO _{14 is} made. The method of claim 9, wherein the finger electrodes from a Cu thin-film system using magnetron sputtering, electrochemical methods, MOCVD or Vaporizing be deposited. The method of claim 9, wherein thin films from TaSiN by reactive sputtering from a TaSi target under nitrogen atmosphere be deposited. The method of claim 9, wherein the deposition is performed by means of magnetron sputtering without vacuum interruption. The method of claim 9, wherein the deposited Thin-film metallization and / or the thin film be tempered on the basis of Ta and Si. The method of claim 9, wherein the thin film metallization system and the thin film based on Ta and Si in trenches of a patterned wafer be deposited.