JP2009089006A - Method for manufacturing piezoelectric thin film vibrator and piezoelectric thin film vibrator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a piezoelectric thin film vibrator which can be manufactured simply and inexpensively. <P>SOLUTION: First, a recess part is formed on a surface of a substrate. Subsequently, a sacrifice layer which has the same thickness as a depth of the recess part and is made of a different material from an insulating film is formed on the surface of the substrate and inside the recess part by a physical vapor deposition. Thereafter, a resist mask and the sacrifice layer formed on the resist mask concerned are removed by a liftoff method. A solution containing a precursor of the insulating film is coated on the surface of the substrate by a spin coating method. The insulating film is formed on the surface of the substrate by sintering. Next, a laminated body of a lower electrode, a piezoelectric thin film and an upper electrode is formed on the surface of the substrate, and the sacrifice layer is etched to form a cavity part under the laminated body. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a method for manufacturing a piezoelectric thin film vibrator and a piezoelectric thin film vibrator.

  For example, LC filters and SAW (Surface Acoustic Wave) filters are used for various filter circuits incorporated in mobile communication terminals such as mobile phones. Compared to these filters as mobile communication terminals are further downsized. A filter (BAW (Bulk Acoustic Wave) filter) using a piezoelectric thin film resonator (piezoelectric thin film resonator) that is easy to downsize and process is attracting attention.

  Piezoelectric thin film vibrators used in this filter are classified into several types depending on the structure and manufacturing method, and among them, an FBAR (Film Bulk Acoustic Resonator) type that uses the longitudinal direction of the film thickness direction of the piezoelectric thin film. There is a piezoelectric thin film vibrator.

This piezoelectric thin film vibrator has a structure in which the upper part and the lower part of the resonance part are in contact with air in order to confine the excited elastic vibration. That is, the upper part of the resonance part naturally comes into contact with air, but the lower part of the resonance part forms a cavity part for making contact with air. There are mainly three types of methods for creating the hollow portion.
(1) A sacrificial layer is formed on a substrate, a laminated body (resonant portion) of a lower electrode, a piezoelectric thin film and an upper electrode is formed on the upper portion of the sacrificial layer, and finally the sacrificial layer is etched to create a void portion. Method (for example, refer to Patent Document 1).
(2) A gap is formed in the substrate, and the sacrificial layer fills the gap and performs CMP (Chemical Mechanical Polishing). A method of creating a cavity by creating a resonance part and finally etching a sacrificial layer (see, for example, Patent Document 2).
(3) A method of creating a cavity by creating a resonance part on a substrate and etching from the lower surface of the substrate (see, for example, Patent Document 3).

  The methods (1) to (3) described above have their merits and demerits. In the method (1), the cavity can be easily formed. However, since the sacrificial layer formed on the substrate has a step portion, a step is also generated in the resonance portion formed on the upper portion. For this reason, the piezoelectric thin film at the step portion becomes imperfect, and there is a problem that the Q value is lowered due to incomplete vibration of the piezoelectric thin film and reflection / absorption of the transverse mode of vibration at the step portion. In the method (2), since the sacrificial layer portion and the substrate portion are smooth, the problem described in the method (1) does not occur. However, by polishing the substrate, a process error, that is, a design value is obtained. There is a problem that the variation with respect to increases. The reason for this is that in the CMP process, the polishing rate depends on the concentration of the slurry, but the solid content in the slurry tends to agglomerate and settle, making it very difficult to control the concentration. As a result, the polishing rate must be stabilized. Is difficult. In CMP, there are many problems to be solved such as dishing, erosion, and scratches. Furthermore, since there is a problem of pattern dependency, that is, there is a problem that the polishing characteristics are different between the substrate region and the sacrificial layer region, CMP is more likely to cause an error than other processes. In addition, a polishing pad as a consumable member is used in the CMP apparatus, and this polishing pad is expensive. Therefore, there is a problem that the manufacturing cost is increased by replacing the polishing pad with a new one every time the polishing pad is consumed.

In the method (3), since the air gap is formed from the lower surface of the substrate, the problem described in the method (1) does not occur. However, since the substrate itself is largely etched, the strength of the resonator may be deteriorated. is there. In addition, there is a problem that it is necessary to increase the element size in order to create the cavity, and it is difficult to reduce the size (integration) of the element.
As described above, in the methods (1) to (3) described above, various problems occur depending on the method. However, the inventors form a gap in the substrate as in the method (2), and the gap The cavity is filled with a sacrificial layer to create a cavity, and then the sacrificial layer is etched to create a cavity.

JP 2005-338065 A JP 2002-140075 A JP 2002-76824 A

  The present invention has been made in view of such circumstances, and an object thereof is to form a laminate of a lower electrode, a piezoelectric thin film, and an upper electrode on the surface of the substrate so as to cover a recess on the surface of the substrate, A method of manufacturing a piezoelectric thin film vibrator in which a cavity is formed by a recess and a lower surface of a laminate, and a method of manufacturing a piezoelectric thin film vibrator that can be manufactured easily and inexpensively, and a piezoelectric device manufactured by this method An object is to provide a thin film vibrator.

In the present invention, a laminated body of a lower electrode, a piezoelectric thin film and an upper electrode is formed on the surface of the substrate so as to cover the concave portion of the surface of the substrate, and a cavity is formed by the lower surface of the concave portion and the laminated body. A method of manufacturing a piezoelectric thin film vibrator,
Forming a resist mask having an opening corresponding to the recess on the surface of the substrate;
Etching the substrate exposed from the resist mask to form a recess on the surface of the substrate;
Forming a sacrificial layer made of a material different from the insulating film having the same thickness as the depth of the recesses on the surface of the substrate and in the recesses by physical vapor deposition;
Thereafter, a step of removing the resist mask and the sacrificial layer formed on the resist mask by a lift-off method,
Next, a step of applying a solution containing a precursor of the insulating film on the surface of the substrate by a spin coating method and further baking to form an insulating film on the surface of the substrate;
Next, forming a laminate of a lower electrode, a piezoelectric thin film and an upper electrode on the surface of the substrate;
And then forming a resist mask having an opening for etching the sacrificial layer on the surface of the substrate, and etching the sacrificial layer using the mask to form a cavity under the stacked body. It is characterized by that.

In the method for manufacturing the piezoelectric thin film vibrator, the insulating film is preferably a film containing, for example, silicon oxide as a main component.
The piezoelectric thin film vibrator of the present invention is manufactured by the above-described method for manufacturing a piezoelectric thin film vibrator.

  According to the present invention, the sacrificial layer forming step is not performed by the film formation and CMP process of the entire substrate including the concave portion, but by the lift-off method and the spin coating method, so that the process error can be reduced. The manufacturing process can be simplified and the manufacturing cost can be reduced. Further, since the sacrificial layer forming process is performed in the lift-off process and the spin coating process, the generation of a step between the sacrificial layer and the substrate can be suppressed as much as possible. Accordingly, it is possible to reduce a decrease in Q value caused by an incomplete portion of the piezoelectric thin film due to a step of the sacrificial layer.

An example of a piezoelectric thin film vibrator manufactured by the manufacturing method according to the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view schematically showing a piezoelectric thin film vibrator according to the present embodiment. A reference numeral 30 in FIG. 1 denotes a rectangular silicon substrate, and a rectangular recess 31 having a size that protrudes slightly to the left and right of the lateral width of the piezoelectric thin film 33 is formed at a substantially central portion of the substrate 30. . An SOG film (SiO ₂ film) 32 that is an insulating film is formed on the surface of the substrate 30 by a spin coating method as will be described later. A lower electrode 33 is formed on the surface of the SOG film 32. In this example, a region where the lower electrode 33 is formed extends slightly from the one end side of the substrate 30 across the concave portion 31 to the other edge side of the concave portion 31. It is formed to the position beyond.

  In addition, a rectangular piezoelectric thin film 34 is formed on the surfaces of the lower electrode 33 and the substrate 3, and the formation region of the piezoelectric thin film 34 is formed in a substantially central portion of the substrate 30 so as to cover the recess 31 in this example. Has been. Further, an upper electrode 35 is formed on the surfaces of the piezoelectric thin film 34 and the substrate 30, and the formation region of the upper electrode 35 is the other end of the substrate 10 from one end side to the other end side of the piezoelectric thin film 34 in this example. It is formed to the side. As described above, the laminated body 3 of the lower electrode 33, the piezoelectric thin film 34 and the upper electrode 35 is positioned on the concave portion 31, so that a cavity 36 is formed below the laminated body 3. Further, an electrode pad 37 a is formed on the surface of the lower electrode 33 located on one end side of the substrate 30, and an electrode pad 37 b is formed on the surface of the upper electrode 35 located on the other end side of the substrate 30.

  The oscillating operation of the piezoelectric thin film vibrator configured as described above is an elastic vibration excited in the thickness direction of the piezoelectric thin film 34 by applying a voltage to the upper electrode 35 and the lower electrode 33 via the electrode pads 37a and 37b. Is reflected at the boundary surface between the upper electrode 35 and air and the boundary surface between the lower electrode 33 and the recess 31, and resonance occurs at a resonance frequency determined by the film thickness of the piezoelectric thin film 34.

  Next, a method for manufacturing the piezoelectric thin film vibrator shown in FIG. 1 will be described with reference to FIGS. First, after polishing and cleaning the cut silicon substrate 30 (FIG. 2A), a resist film 40 is formed on the surface of the silicon substrate 30, and the recess 31 shown in FIG. 1 is formed by photolithography. The corresponding portion of the resist film 40 is removed (FIG. 2B). In this example, the silicon substrate 30 is used. However, for example, a glass substrate or a quartz substrate may be used in addition to the silicon substrate 30. Subsequently, dry etching or wet etching is performed using the resist film 40 as a mask to etch the substrate 30 not covered with the resist film 40 (anisotropic etching), thereby forming a recess 31 on the surface of the substrate 30 (see FIG. FIG. 2 (c)).

  Next, germanium (Ge) is formed on the surface of the substrate 30 as a sacrificial layer material by PVD (Physical Vapor Deposition) method by vapor deposition or sputtering. In the deposition of the sacrificial layer 41, the deposition time is controlled, and the sacrificial layer 41 having the same thickness as the depth of the recess 31 is formed on the surface of the substrate 30 and in the recess 31 formed on the substrate 30. (FIG. 2D). That is, the surface of the substrate 30 and the surface of the sacrificial layer 41 formed in the recess 31 are flush with each other. The sacrificial layer 41 may be made of metal such as Si or W in addition to Ge.

  The state of the surface of the substrate 30 and the surface of the substrate 30 after the sacrificial layer 41 is formed in the recess 31 as described above will now be described. As shown in FIG. A gap 50 is formed between the side surface of the recess 31 and the side surface of the sacrificial layer 41 without being in contact with the sacrificial layer 41. This is because in the case of vapor deposition, since the film forming material goes straight, the film forming material cannot be deposited on the shadowed portion or the side wall of the resist film 40. That is, when the sacrificial layer 41 is formed on the surface of the substrate 30 by the PVD method, the gap 50 is formed between the side surface of the recess 31 and the side surface of the sacrificial layer 41.

  After the sacrificial layer 41 is formed on the surface of the substrate 30 and in the recess 31, the sacrificial layer 41 formed on the resist film 40 is peeled off by a lift-off method. That is, first, the substrate 30 is immersed in a chemical solution for dissolving a resist, for example, acetone, and ultrasonic waves are applied to dissolve the resist film 40, thereby removing the sacrificial layer 41 on the resist film 40 (FIG. 2E). ).

Thereafter, an SOG film 32, which is an insulating film, is formed on the surface of the substrate 30 by spin coating. This process will be described in detail. First, a solution containing a powdery precursor of SiO ₂ film (insulating film made of silicon and oxygen) at the center of the surface of the substrate 30 by a nozzle while rotating the substrate 30 at a low speed, in this example Then, an SOG solution is applied. The SOG solution supplied from the nozzle to the central portion of the substrate 30 spreads toward the periphery by centrifugal force and spreads over the entire surface. At this time, the SOG solution 60 flows into the gap 50 between the side surface of the recess 31 and the side surface of the sacrificial layer 41 (FIG. 3). In this way, the SOG solution 60 is embedded in the gap 50, and the step between the substrate 30 and the sacrificial layer 41 is eliminated. After applying the SOG solution to the surface of the substrate 30, the substrate 30 is heated to cure the SOG solution, and an SOG film 32 is formed on the surface of the substrate 30 (FIG. 4A). As a result, the surfaces of the substrate 30 and the sacrificial layer 42 are planarized by the SOG film 32.

  Next, a metal film having a film thickness of, for example, 0.1 to 0.3 μm is formed on the surface of the substrate 30 by a magnetron sputtering method or the like, and patterned by lithography and wet etching to form the lower electrode 33 (FIG. 4B). )). As this metal film, for example, a metal such as molybdenum (Mo), aluminum (Al), titanium (Ti), platinum (Pt), copper (Cu), chromium (Cr), tungsten (W), tantalum (Ta) is used. It is done.

  Next, a piezoelectric thin film having a film thickness of 0.5 to 3.0 μm, for example, is formed on the surface of the substrate 30 by RF magnetron sputtering, and patterned by lithography and wet etching to form the piezoelectric thin film 34 (FIG. 4). (C)). The film thickness of the piezoelectric thin film 34 is set so as to obtain a desired resonance frequency. For example, aluminum nitride (AlN) or zinc oxide (ZnO) is used as the piezoelectric thin film.

  After patterning the piezoelectric thin film 34, a metal film having a film thickness of, for example, 0.1 to 0.3 μm is formed on the surface of the substrate 30 by a magnetron sputtering method or the like, and patterned by lithography and wet etching to form the upper electrode 35. Then, electrode pads 37a and 37b for electrical connection to the outside are formed by a lift-off method (FIG. 4D). Finally, a resist pattern having an opening for etching the Ge sacrificial layer 41 embedded in the cavity 36 by the PVD method is formed by lithography, and the Ge sacrificial layer 41 is etched with hydrogen peroxide (FIG. 4E). ). Thus, the cavity 36 is formed under the lower electrode 33, and the piezoelectric thin film vibrator shown in FIG. 1 is completed.

  According to the above-described embodiment, the formation process of the sacrificial layer 41 is not performed in the film formation and CMP process of the entire substrate including the recesses 31, but is performed by the lift-off method and the spin coating method. Thus, the manufacturing process can be simplified and the manufacturing cost can be reduced. In addition, since the sacrificial layer forming process is performed in the lift-off process and the spin coating process, the generation of a step between the sacrificial layer 41 and the substrate 30 is suppressed as much as possible. Therefore, it is possible to reduce a decrease in the Q value caused by an incomplete portion of the piezoelectric thin film 34 due to the step of the sacrificial layer 41.

  In the above-described embodiment, a silicate gas (BPSG) film may be used instead of the SOG film 32 as the insulating film. In this case, in the spin coating process, a solution containing a powdery precursor of an insulating film made of silicon, oxygen, boron and phosphorus is applied.

  The piezoelectric thin film vibrator described above can be used for a band-pass filter that is an electronic component. An equivalent circuit diagram of this filter is shown in FIG. In FIG. 5, this filter includes input terminals Vin1 and Vin2, output terminals Vout1 and Vout2, the above-described piezoelectric thin film vibrators 81, 82, and 83 that form series arms, and the above-described piezoelectric thin film vibrator 84 that forms parallel arms. 85.

1 is a schematic cross-sectional view showing a piezoelectric thin film vibrator according to an embodiment of the present invention. It is explanatory drawing of the manufacturing process of the said piezoelectric thin film vibrator. It is explanatory drawing which shows a mode that an SOG solution is formed in the substrate surface in the said manufacturing process. It is 2nd explanatory drawing of the said manufacturing process. It is an equivalent circuit diagram of the band pass filter concerning an embodiment of the invention.

Explanation of symbols

3 Stack 30 Substrate 31 Recess 32 SOG Film 33 Lower Electrode 34 Piezoelectric Thin Film 35 Upper Electrode 36 Cavity 37a, 37b Electrode Pad 41 Sacrificial Layer 50 Gap 60 SOG Solution

Claims (3)

A piezoelectric thin film vibrator in which a laminated body of a lower electrode, a piezoelectric thin film, and an upper electrode is formed on the surface of the substrate so as to cover a concave portion on the surface of the substrate, and a cavity is formed by the lower surface of the concave portion and the laminated body A method of manufacturing
Forming a resist mask having an opening corresponding to the recess on the surface of the substrate;
Etching the substrate exposed from the resist mask to form a recess on the surface of the substrate;
Forming a sacrificial layer made of a material different from the insulating film having the same thickness as the depth of the recesses on the surface of the substrate and in the recesses by physical vapor deposition;
Thereafter, a step of removing the resist mask and the sacrificial layer formed on the resist mask by a lift-off method,
Next, a step of applying a solution containing an insulating film precursor to the surface of the substrate by a spin coating method and further baking to form an insulating film on the surface of the substrate;
Next, forming a laminate of a lower electrode, a piezoelectric thin film and an upper electrode on the surface of the substrate;
And then forming a resist mask having an opening for etching the sacrificial layer on the surface of the substrate, and etching the sacrificial layer using the mask to form a cavity under the stacked body. A method of manufacturing a piezoelectric thin film vibrator.   The method for manufacturing a piezoelectric thin film vibrator according to claim 1, wherein the insulating film is a film containing silicon oxide as a main component.   A piezoelectric thin film vibrator manufactured by the method for manufacturing a piezoelectric thin film vibrator according to claim 1.

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