DD264943A1 - PROCESS FOR THE ADHESIVE METALLIZATION OF PIEZOELECTRIC MATERIALS - Google Patents

Abstract

The invention relates to a method for adherent metallization of piezoelectric substrate materials for the production of electronic components. An adherent metallization, for example with aluminum, by vapor deposition is inventively achieved in that initially the substrate material is coated in combination with a glow treatment with a thin intermediate layer of chromium or SiO. The ganzflaechige adhesion of the subsequent applied metallization is thereby increased so that after appropriate tests at any point of the substrate Schichtabhebungen occur. Such adherent metallizations are a prerequisite to be able to produce by means of piezoelectric materials high quality and reliable electronic components with high production yield.

Description

Field of application of the invention

The invention relates to a method for producing adhesion-resistant metallization on piezoelectric materials, which are used for the production of filters, resonators and delay lines in electronics.

Characteristic of the known state of the art

Filters, resonators, delay lines and other electronic components produced on piezoelectric substrates are increasingly being used in communications engineering. For the production of frequency-selective component), in particular monocrystalline lithium niobate (LiNbOj) is used as the piezoelectric material for surface acoustic wave filters. The function of surface wool fillers is based on the excitation, propagation, and reception of surface acoustic wave on piezoelectric substrate materials. In order to excite and receive the surface wave generated and propagated on the piezoelectric material, interdigitated comb-like electrodes are fabricated as interdigital transducers by photolithography from a vapor deposited metal layer. The properties of the filter are determined by the structure widths and the transducer geometry. The pattern widths are on the order of less than 3 pm to about 15 mm. Zi-r vapor deposition of the metallization vo voices is preferably used aluminum. High demands are placed on the adhesive strength of the vapor-deposited metal layer, as it depends on the production yield of components as well as their quality and reliability. Furthermore, this layer must also be bondable for the electrical connection.

Due to special cut bonbons in the LiNBOj crystal, deviating from the usual YZ cut, a minimization of the component size is possible. However, such cut crystal disks can have very high static charges, whereby the adhesive strength of the deposited metal layer is impaired.

Prerequisite for a perfect metallization is a clean substrate surface. It is known that in order to avoid reactions between the substrate and the metal layer, an intermediate layer can be vapor-deposited as a diffusion barrier, since the reaction products can impair the adhesion of the layer and its function. In the Federal Republic of Germany patents P 2238925.9, P 2631671.2-35 and P 2431620.0, SiO and Cr interlayers are used to increase the quality of the output signal and to affect the through-charging characteristic of a surface acoustic wave filter on piezoelectric material.

To date, there has been no attempt to deposit reproducible, all-over adherent and bondable metal layers, such as aluminum, on single-crystalline piezoelectric materials, in particular on LiNbOj substrate wafers, which are produced differently from the YZ cut. This results in difficulties in the realization of technically possible small feature sizes for the interdigital transducer and economic disadvantages due to the non-optimal use of the entire substrate wafer for chips for component production

Object of the invention

The aim of the invention is on piezoelectric substrate materials that can charge statically, such as single-crystalline LiNbOi, provided by a process reproducible with a very large surface adherent metallization in vacuo, so that increases the chip yield per substrate wafer, the feature widths reduced for the interdigital transducer and the quality and reliability of the components manufactured

Explanation of the essence of the invention

The technical object of the invention is to apply a very adhesive metallization on piezoelectric materials such as LiNbOj, over the entire surface and reproducibly by a suitable method in a vacuum, which can be subsequently structured and is bondable.

According to the invention, the method consists of vacuum-depositing, in combination with a glow discharge, an intermediate layer between the piezoelectric material and the motorization in a vacuum which does not adversely affect device design and function. It has been found that for metallization with aluminum old interlayer in combination with a glow discharge chromium and SiO are particularly suitable. The glow discharge is absolutely necessary

before the vapor deposition of chromium and SiO as an intermediate layer. While no repetition of the glow discharge is required for the subsequent metallization with aluminum in the chromium intermediate layer, a further glow discharge must take place when aluminum is vapor-deposited onto the SiO intermediate layer.

The glow discharge in the fore-vacuum region obviously causes, in addition to the known activation of the substrate surface also a Discharge or transhipment of the static charge on the substrate surface, whereby, with the cooperation of the intermediate layer a

significantly higher adhesion of the metallization is achieved. A diene of the intermediate layer of 20 nm is sufficient and it should not be thicker than 50 nm.

Have comparative studies. _U d / eigt that other materials for the intermediate layer, such as nickel, Tungsten or ZnO, garkeine or only slightly improve the adhesion of the metallization. Ausfülirungsbeisplel For metallization, the piezoelectric materials, such as polished single crystal LiNbOj substrate slices,

Thoroughly clean according to known methods.

The metallization is carried out in a vacuum system in such a way that in the region of the pre-vacuum that arranged in the recipient Suspend substrates for at least 30 seconds from a glow blast with a glow current of approximately 4 amperes. After that

is generated in the recipient for the vapor deposition of the intermediate layer high vacuum of less than 6 · 10 ' ¹ Pa and

Chromium or SiO evaporates in known manner, so that an intermediate layer of these materials on the substrate of 20 nm

to 50nm thickness arises.

On the intermediate chrome plate, immediately after its deposition from a second evaporator for metallization,

For example, aluminum, are deposited in the thickness required for bonding.

Bui the use of SiO as an intermediate layer is after their vapor deposition a gas inlet to repeat the Glimmbohandiung of at least 30 seconds at 4A glow current necessary. Then again high vacuum is to be generated

and rum example aluminum as metallization to evaporate.

The metallization vapor-deposited by the process according to the invention is extremely adherent, so that also conventional Schichtablöcungen from the substrate after entsp ".., ienden test procedures do not occur.

Claims (3)

1. A method for adherent metallization of piezoelectric materials, in particular of polished monocrystalline LiNbOa substrates, by vacuum evaporation of, for example, aluminum, characterized in that an intermediate layer is applied in combination with a glow discharge before the actual metallization. 2. The method according to claim 1, characterized in that the intermediate layer consists of chromium or SiO and is at least 20 nm thick. 3. The method according to claim 1 and 2, characterized in that prior to the application eggs interlayer there is a glow treatment of the substrates and this glow treatment is repeated before the application of the actual metallization, at least in the SiO intermediate layer.