JPH0275210A - Manufacture of thin film resonator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a thin film resonator having a structure that disperses internal strain stress in a thin film resonator.

(Conventional technology) A conventional element of this type will be explained with reference to the drawings.

FIG. 3 is a sectional view of a conventional thin film resonator of this type. In the figure, 11 is a silicon substrate, 12 is an epitaxial layer, 13 is a SiO□ layer, 14 is a lower electrode, 15 is a piezoelectric material, for example Zn0, and 16 is an upper electrode. The operating principle of this type of element is that by applying a high frequency signal to the lower electrode 14 and the upper electrode 16, the piezoelectric body 15 repeats expansion and contraction at the period of the high frequency signal, and the thin film resonant portion, that is, the epitaxial layer 12, the SiO□ layer 13, and the thickness of the piezoelectric body 15 causes resonance.

The manufacturing method for this type of device involves forming an epitaxial layer 12 doped with boron or the like at a high concentration on a (100) silicon substrate, partially masking the back surface of the substrate, and then etching the back surface of the substrate with an anisotropic etching solution. Perform more etching. Etching is stopped at the epitaxial layer 12. Next, SiO□
The entire layer 13 is formed by uttering or the like, and the lower electrode 14 is formed by vacuum evaporation and photolithography.

The piezoelectric body 15 is formed by sputtering or the like, and the upper electrode 16
It is manufactured by forming the lower electrode 14 in the same manner as the lower electrode 14.

FIG. 4 is a sectional view of another example of this type of element.

In the drawing, 21 is a silicon substrate, 23 is a lower SiO□
layer, 24 is a lower electrode, 25 is a piezoelectric material, 26 is an upper electrode,
27 is an upper SiO□ layer, 28 is an opening, and 29 is a thin film resonator holding portion. The operating principle is the same as in Fig. 3, where the lower electrode 2
The high frequency signal applied to the two-part electrode 26 causes
The piezoelectric body 25 repeatedly expands and contracts, and the thin film resonance part, that is, the lower part S
Resonance occurs due to the thicknesses of the iO2 layer 23, the piezoelectric body 25, and the upper SiO□ layer 27.

Next, the manufacturing method of the structure shown in FIG.
Lower electrode 24, piezoelectric body 25, upper electrode 26 and 5iO7
is formed by a method similar to that shown in FIG.

Next, the device is manufactured by anisotropic etching through the opening 28 of the mask.

Here, when forming a multilayer thin film in the above manufacturing method, for example, when forming a thin film by sputtering, the substrate temperature is about 600°C, which is lowered to room temperature (about 2°C).
When the temperature is returned to 5° C.), strain stress occurs at the thin film interface due to the difference in thermal expansion. In the structure shown in FIG. 3, the thin film resonant part is asymmetrical in the thickness direction, and in the structure shown in FIG.

In this way, as shown in FIGS. 3 and 4, conventional thin film resonators all have asymmetrical portions in the thickness direction. If the film is asymmetrical in the thickness direction, the strain stress at the film interface cannot be canceled out by the multilayer film as a whole, resulting in a disadvantage that it is likely to break.

(Problems to be Solved by the Invention) In the above-mentioned thin film resonator, it has been difficult to sufficiently reduce the occurrence of cracks caused by deflection in the thin film resonator portion due to internal stress accumulated during device fabrication.

In order to solve the above-mentioned problems, the present invention provides a thin film resonator having a structure that disperses the strain stress in the thin film resonator and reduces the occurrence of deflection and cracks.

(Means for Solving the Problems) An embodiment of the thin film resonator of the present invention, which was made to solve the above problems, will be described in detail with reference to FIG. 31 is a silicon substrate, 32 is a 5i02 layer for holding, and 33 is a lower SiO
2 layers, 34 is a lower electrode, 35 is a piezoelectric body, 36 is an upper electrode, 37 is an upper 5iO7 layer, 39 is a thin film resonator holding part, 4
0 is a space layer separating the thin film resonator and the silicon substrate. Here, the piezoelectric body 35 does not need to be limited to ZnO (A7
+N etc. may also be used.

In order to operate the device of the present invention, by applying a high frequency signal between the lower electrode 34 and the upper electrode 36, the piezoelectric body 35 repeatedly expands and contracts with the period of the high frequency signal, and the thin film resonant portion, that is, the lower SiO2 layer 36 , piezoelectric body 35 and upper part 5i
O) Resonance occurs due to the thickness of the 4th layer 37.

(Example) The manufacturing method of the present invention will be explained with reference to FIG. A holding SiO2 layer is formed on the surface of the silicon substrate 31 by sputtering or the like. This thickness is equal to 2 times the thickness of the space layer 40, the thickness of the lower SiO□ layer 33, and the thickness of the piezoelectric body 35, which will be explained later.
Make the thickness equal to the sum of Si by photolithography technology
A part of O□iO□ is etched (FIG. 2(a)).

In order to form a thin film resonance part, the etched part is filled with a material (etching material) that can be easily etched later, such as ZnO (FIG. 2(b)).

A lower SiO□ layer 33 is formed by sputtering or the like, and a lower electrode 34 is formed by vacuum evaporation and photolithography (FIG. 2(C)). The piezoelectric body 35 is formed by sputtering or the like, and patterned by etching or the like (
Figure 2(d)). An upper electrode 36 is formed in the same manner as the lower electrode 34, and an upper SiO□ layer 37 is formed by sputtering or the like (FIG. 2(e)). Masking the thin film resonance part, the holding SiO□ layer 32, the lower SiO□ layer 33 and the upper SiO
□ Etch the layer 37 with hydrofluoric acid etc. to form a retaining SiO□
The end face of the etching material such as ZnO buried in the etched portion of layer 32 is exposed.

(Figure 2(f)). The ZnO layer of the etching material buried in the etched portion of the holding SiO□ layer 32 is etched with diluted hydrochloric acid or the like to form a space layer 40 separating the thin film resonant portion and the silicon substrate (see FIG. 2(g)). )).

At this time, the ZnO equivalent piezoelectric material sandwiched between the electrode materials and the thin film resonator section whose upper and lower surfaces are sandwiched between 5i02 are separated from the Si substrate by the space layer 40 and configured. Furthermore, by setting the thickness of the holding SiO□ layer 32 to approximately the sum of the thickness of the space layer 40, the thickness of the lower SiO□ layer 33, and the thickness of the piezoelectric body 35, thin film resonance can be achieved. The central plane of the portion can be made to substantially coincide with the surface of the holding SiO□ layer and its extension line.

When manufactured in this way, the thickness of the electrode thin film is usually sufficiently thin compared to other thin films, so the entire thin film resonant part is almost symmetrical in the thickness direction, and the strain stress at the film interface is canceled out by the entire multilayer, resulting in bending and cranking. The occurrence can be significantly reduced.

Here, 31 is a silicon substrate, but 5iO
Similarly, substrates made of materials that cannot be etched with the Z etching solution, or substrates whose surfaces are coated with materials that cannot be etched with the 5iOz etching solution, such as silicon substrates and SiO It is clear that it can be significantly reduced.

In addition, here we have shown a structure in which the upper and lower surfaces of the piezoelectric material such as ZnO in the thin film resonance part are sandwiched between SiO□ layers, but in particular, the upper and lower S
It is clear that a thin film resonator having a thin film resonator without an iO□ layer can similarly deflect and significantly reduce the occurrence of cranking.

(Effects of the Invention) As explained above, since the thin film resonator according to the present invention has a structure and a manufacturing method that disperse strain stress in the thin film resonator, the occurrence of deflections, cracks, etc. that have been problems with conventional methods can be significantly reduced. It has a high mechanical strength and has the effect of reducing
A thin film resonator with less characteristic deterioration during resonance can be provided.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a thin film resonator of the present invention, FIG. 2 is an explanatory diagram of a method of manufacturing a thin film resonator of the present invention, and FIGS. 3 and 4 are sectional views of a conventional thin film resonator. 1], 21.31...Silicon substrate, 12...Epitaxial layer, 13...SiO□ layer, 14. , 2
,1. , 34...lower electrode, 15.25.35...
・Piezoelectric body, 16°26.36...Top electrode, 23.3
3... Lower part 5i02 layer, upper part 27.37... Main part SiO□ layer, 28... Opening part,
29° 39... Thin film resonant part holding part, 32... SiO□ layer for holding, 40... Space layer.

Claims (2)

[Claims] 1. means for forming a holding SiO_2 layer on the substrate surface;
A part of the holding SiO_2 layer is etched, and the etched part is covered with a material that can be easily etched later (such as ZnO).
means for filling with a piezoelectric material such as ZnO whose upper and lower surfaces are sandwiched between electrode materials, or a thin film resonator whose upper and lower surfaces are further sandwiched between SiO_2 layers; 1. A method for manufacturing a thin film resonator, comprising means for separating the thin film resonator and a substrate by etching an etching material buried in the etching portion to create a space layer. 2. In the thin film resonator according to claim 1, the thickness of the SiO_2 layer formed on the substrate surface is made thicker than 1/2 of the thickness of the thin film resonant part, and the depth after filling the etched part with an etching material is A method of manufacturing a thin film resonator, characterized in that the thickness of the thin film resonator is approximately 1/2 of the thickness of the thin film resonator.