Method for producing a polycrystalline ceramic film

Abstract

The invention relates to a method for producing a polycrystalline ceramic film on a surface (12) of a substrate (10), in which a particle stream is directed onto the surface (12) and the ceramic film is formed by deposition of the particles onto the surface (12), wherein the particle stream is directed by means of a diaphragm onto the surface (12) along a preferred direction until a first specified layer thickness is reached, the preferred direction and a surface normal of the surface (12) enclosing a specified angle of incidence. According to the invention, the diaphragm is removed from the particle stream after the specified layer thickness has been reached, and additional particles are directed onto the surface (12) until a specified second layer thickness has been reached.

Claims

1. A method for producing a polycrystalline ceramic film on a surface of a substrate, the method comprising: directing a particle stream onto the surface, the polycrystalline ceramic film being formed by deposition of particles on the surface, wherein the directing comprises: forming a first layer, the forming of the first layer comprising directing, until a first specified layer thickness is reached, the particle stream by a diaphragm in a direction onto the surface, making a specified angle of incidence with a normal to the surface, the specified angle of incidence with the normal to the surface being a non-zero angle with a maximum of 90; and after attainment of the first specified layer thickness with a desired crystalline axis orientation, directing further particles of the same particle stream of particles onto the surface with the diaphragm removed from the particle stream until a second specified layer thickness with the desired crystalline axis orientation of the first layer is reached, and wherein directing the further particles of the same particle stream of particles onto the surface comprises growing crystals from the first layer with the desired crystalline axis orientation of the first layer.

2. The method of claim 1, wherein the first specified layer thickness is 50 to 150 nm.

3. The method of claim 1, wherein the second specified layer thickness is 450 to 600 nm.

4. The method of claim 1, wherein particles of ZnO, particles of AlN, or a combination thereof is used as particles of the particle stream.

5. The method of claim 1, wherein the particle stream is provided by sputtering.

6. The method of claim 1, wherein the specified angle of incidence is selected from the range from 10 to 30.

7. The method of claim 3, wherein the first specified layer thickness is 100 nm.

8. The method of claim 3, wherein the second specified layer thickness is 540 nm.

9. The method of claim 1, wherein the substrate is made of silicon.

10. A method for producing a thin-film bulk acoustic resonator, the method comprising: directing a particle stream onto a surface of a substrate, a polycrystalline ceramic film being formed by deposition of particles on the surface, wherein the directing comprises: forming a first layer, the forming of the first layer comprising directing, by a diaphragm, the particle stream in a direction onto the surface until a first specified layer thickness is reached, the direction on to the surface making a specified angle of incidence with a normal to the surface, the specified angle of incidence with the normal to the surface being a non-zero angle with a maximum of 90; and after attainment of the first specified layer thickness with a desired crystalline axis orientation, directing further particles of the same particle stream of particles onto the surface with the diaphragm removed from the particle stream until a second specified layer thickness with the desired crystalline axis orientation of the first layer is reached, and wherein directing the further particles of the same particle stream of particles onto the surface comprises growing crystals from the first layer with the desired crystalline axis orientation of the first layer.

11. The method of claim 10, wherein the substrate is made of silicon.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a substrate wafer with a plurality of measuring points for quality control of a layer applied by one embodiment of a method.

DETAILED DESCRIPTION

(2) In order to produce a thin-film bulk acoustic resonator (FBAR), a layer of a piezoelectric ceramic (e.g., ZnO) enclosed between planar electrodes is produced on a substrate 10 (e.g., a silicon wafer). The layer is applied by deposition processes that are known (e.g., sputtering).

(3) In order to achieve the desired resonator properties, and to make the excitation of shear modes possible, the polar axis of the piezoelectric material is to make an angle with the normal to the substrate surface. For this, a seed layer of about 100 nm thickness is produced. During deposition of this seed layer, a diaphragm system is installed between a source for the particles to be deposited and the substrate surface 12, providing shadowing of certain angles of incidence, so that the particles are deposited on the substrate surface 12 in a preferred orientation with the polar axis tilted in the desired way.

(4) As soon as the desired seed layer thickness is reached, the diaphragm system may be removed, and deposition may continue undirected. Owing to the axis orientation already produced in the seed layer, further growth of the layer is also directed, so that overall the desired tilt of the polar axis is achieved. This operation is continued until a total layer thickness of about 540 nm is reached.

(5) During production of the seed layer, deposition rates of about 4 nm/min may be achieved, and after removal of the diaphragm system, these may be increased to up to 40 nm/min. In this way, the process is accelerated considerably compared to processes known from the prior art, in which a diaphragm system is used throughout the deposition operation.

(6) To verify the quality of the layer produced, at several measuring points 14 of a 6 wafer shown schematically in FIG. 1, samples of the layer are analyzed and compared with samples of a wafer fabricated by methods known from the prior art.

(7) As shown in the table, the layers produced with the embodiment of the method are far more homogeneous. The dispersion of the layer thickness, measured by the standard deviation normalized to the layer thickness, improves from 10.3% to 3%. The process time may be reduced from 132 min to 34 min. There is no notable impairment of the shear coupling coefficient.

(8) The much shorter residence time of the diaphragms in the particle stream leads to less fouling of the diaphragms and therefore to lower costs for cleaning and adjustment.

(9) TABLE-US-00001 TABLE Comparison of process and layer properties for layers produced according to the prior art and according to an embodiment Embodiment Prior art Average layer thickness [nm] 550 530 (layer thickness)/layer thickness [%] 3.0 10.3 Shear coupling coefficient [%] 11 12 Process time [min] 34 132 Proportionate diaphragm residence time [%] 17 100

(10) Thus, a method that allows rapid, economical and safe production of piezoelectric ceramic layers with a specified tilt of the axis is provided.

(11) It is to be understood that the elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present invention. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims can, alternatively, be made to depend in the alternative from any preceding or following claim, whether independent or dependent, and that such new combinations are to be understood as forming a part of the present specification.

(12) While the present invention has been described above by reference to various embodiments, it should be understood that many changes and modifications can be made to the described embodiments. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description.