JP6166170B2 - Composite substrate and manufacturing method thereof - Google Patents

Description

  The present invention relates to a composite substrate and a manufacturing method thereof.

  In recent years, research and development of micro electro mechanical systems (MEMS) using semiconductor manufacturing processes have been actively conducted. One of the basic structures that can be used for such MEMS includes a support substrate having a cavity and a piezoelectric thin plate bonded to the support substrate so as to cover the cavity. This basic structure can be used not only for MEMS but also for elastic wave devices and the like. For example, there are the following two methods for producing such a basic structure. The first method is a method in which a thick piezoelectric substrate is bonded to a support substrate having a cavity so as to cover the cavity, and after bonding, the piezoelectric substrate is thinly polished (see, for example, Non-Patent Document 1). In the second method, the cavity of the support substrate having cavities is filled with a sacrificial layer, the sacrificial layer side of the support substrate is bonded to a thick piezoelectric substrate, the piezoelectric substrate is polished thinly, and then the sacrificial layer is etched. It is a method to do. A technique for etching the sacrificial layer in the cavity is disclosed in Non-Patent Document 2, for example.

IEEE / MTT-S International Microwave Symposium, 2007, p873-876 RF MEMS and its applications (Kuniki Owada, Kei Labo Publishing, 2004) p. 62

  However, in the first method, when the piezoelectric substrate is polished, there is a problem that the thickness after polishing differs greatly between the portion immediately above the cavity and the portion that is not in the piezoelectric substrate. When the in-plane thickness distribution of the piezoelectric substrate is large, it is difficult to obtain desired characteristics when the piezoelectric MEMS is manufactured, which is not preferable. On the other hand, in the second method, since the cavity is filled with the sacrificial layer, the in-plane thickness distribution of the polished piezoelectric substrate is small, but a step of etching the sacrificial layer is necessary, and the sacrificial layer is completely removed. There was a risk that the element could not be removed or the piezoelectric substrate stuck in the cavity and the element did not function. For these reasons, it has been desired to develop a method for relatively easily manufacturing a composite substrate having a small in-plane thickness distribution while being a thin piezoelectric substrate.

  The present invention has been made to solve such a problem, and is a composite substrate including a piezoelectric substrate and a support substrate having a cavity, and has an in-plane thickness distribution while being a thin piezoelectric substrate. The main objective is to produce a small composite substrate relatively easily.

  The present invention adopts the following means in order to achieve the above-mentioned object.

The method for producing the composite substrate of the present invention includes:
(A) A bonded substrate is prepared by bonding a first support substrate having flat front and back surfaces and a piezoelectric substrate having flat front and back surfaces with an organic adhesive layer, and the thickness of the piezoelectric substrate of the bonded substrate is 0.1. Polishing to have a thickness of ˜3 μm;
(B) A second support substrate having a cavity is prepared, and a surface of the second support substrate on which the cavity is provided and a surface of the piezoelectric substrate opposite to the bonding surface of the first support substrate are provided. Direct bonding,
(C) obtaining a composite substrate in which the piezoelectric substrate and the second support substrate are joined by etching the organic adhesive layer to remove the first support substrate from the piezoelectric substrate;
Is included.

  In this composite substrate manufacturing method, first, in step (a), the piezoelectric substrate of the bonded substrate is polished to a thickness of 0.1 to 3 μm. As an example of polishing, the surface of the diamond slurry is polished using a lapping machine, and then precision polishing is performed by a CMP machine using colloidal silica. CMP is chemical mechanical polishing, and the polishing agent and the polishing object are affected by the surface chemical action of the polishing agent (abrasive grains) itself or the action of chemical components contained in the polishing liquid. This is a technique for increasing the mechanical polishing (surface removal) effect by relative motion and obtaining a high-speed and smooth polished surface. Since both the first support substrate and the piezoelectric substrate constituting the bonded substrate are substrates having a flat surface without a cavity or the like, the in-plane thickness distribution of the piezoelectric substrate after polishing can be made extremely small (for example, Within ± 50 nm). Next, in the step (b), the surface of the second support substrate provided with the cavity is directly bonded to the surface of the piezoelectric substrate opposite to the bonding surface of the first support substrate. Accordingly, a three-layer structure in which the piezoelectric substrate is sandwiched between the first support substrate and the second support substrate is obtained. Next, in step (c), the organic adhesive layer is etched to remove the first support substrate from the piezoelectric substrate, thereby obtaining a composite substrate in which the piezoelectric substrate and the second support substrate are bonded. The obtained piezoelectric substrate of the composite substrate maintains the in-plane thickness distribution at the end of the step (a). As described above, according to the method of manufacturing the composite substrate, it is not necessary to fill the cavity with the sacrificial layer or to remove the sacrificial layer unlike the second method described above. However, a composite substrate having a small in-plane thickness distribution can be manufactured relatively easily.

  In the method for producing a composite substrate of the present invention, in the step (b), before joining the second support substrate and the piezoelectric substrate, electrodes are formed on the piezoelectric substrate, and the cavity of the second support substrate is formed. The second support substrate and the piezoelectric substrate may be directly bonded so that the electrode is included therein. In this way, it is possible to easily produce a structure having electrodes on the cavity-side surface of the piezoelectric substrate. In such a composite substrate manufacturing method, the second support substrate may include a plurality of the cavities, and the electrodes of the piezoelectric substrate may be formed corresponding to the cavities. In this way, a large number of micro-sized composite substrates can be manufactured by dicing the composite substrate for each cavity.

The composite substrate of the present invention is
A support substrate having a cavity;
A piezoelectric substrate that is directly bonded to the support substrate so as to cover the cavity, has a thickness of 0.1 to 3 μm, and an in-plane thickness distribution within ± 50 nm;
An electrode formed on a surface of the piezoelectric substrate located in the cavity of the support substrate;
It is equipped with.

  This composite substrate is obtained by the above-described composite substrate manufacturing method. The manufacturing method of the composite substrate described above is significantly different from the conventional manufacturing method. By this manufacturing method, a composite substrate having a very small in-plane thickness distribution of ± 50 nm can be obtained even though the thickness of the piezoelectric substrate is as thin as 0.1 to 3 μm. As a result, desired characteristics can be obtained when a piezoelectric MEMS, an acoustic wave device, or the like is manufactured using the composite substrate.

FIG. 3 is a cross-sectional view schematically showing the composite substrate 10. FIG. 3 is a cross-sectional view schematically showing a manufacturing process of the composite substrate 10. Explanatory drawing of the grinding | polishing apparatus 120. FIG.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing the composite substrate 10.

  The composite substrate 10 includes a support substrate 22 and a piezoelectric substrate 12. The support substrate 22 has a cavity 24. The piezoelectric substrate 12 is directly bonded to the support substrate 22 so as to cover the cavity 24. An electrode 14 having a predetermined pattern is formed on the surface of the piezoelectric substrate 12 facing the support substrate 22. Hereinafter, the support substrate 22 may be referred to as a second support substrate 22.

  The material of the support substrate 22 is silicon, sapphire, aluminum nitride, alumina, alkali-free glass, borosilicate glass, quartz glass, lithium tantalate, lithium niobate, lithium niobate-lithium tantalate solid solution single crystal, lithium borate , Langasite, crystal and the like. Further, the size of the support substrate 22 is not particularly limited, but for example, the diameter is 50 to 150 mm, the thickness is 100 to 1000 μm, and preferably 150 to 500 μm.

  Examples of the material of the piezoelectric substrate 12 include lithium tantalate, lithium niobate, lithium niobate-lithium tantalate solid solution single crystal, lithium borate, langasite, and quartz. Although the magnitude | size of the piezoelectric substrate 12 is not specifically limited, For example, a diameter is 50-150 mm and thickness is 0.1-3 micrometers. The in-plane thickness distribution of the piezoelectric substrate 12 is, for example, within ± 50 nm.

  The composite substrate 10 can be used as a piezoelectric MEMS or an acoustic wave device by forming an electrode pattern on the exposed surface of the piezoelectric substrate 12.

  A process for manufacturing such a composite substrate 10 will be described below with reference to FIG. FIG. 2 is a cross-sectional view schematically showing the manufacturing process of the composite substrate 10. Here, the steps (a) to (c) will be described separately.

・ Process (a)
A bonded substrate 50 in which a first support substrate 21 having a thickness of 100 to 1000 μm and a piezoelectric substrate 12 having a thickness of 100 to 1000 μm are bonded together with an organic adhesive layer 30 is prepared. Both the front and back surfaces of the first support substrate 21 and the piezoelectric substrate 12 are flat surfaces having no cavities or the like. The material of the first support substrate 21 is the same as that exemplified for the support substrate 22. The first support substrate 21 and the support substrate 22 may be made of the same material or different materials. Examples of the organic adhesive layer 30 include an epoxy resin and an acrylic resin. Polishing is performed so that the thickness of the piezoelectric substrate 12 of the bonded substrate 50 becomes 0.1 to 3 μm. Since both the first support substrate 21 and the piezoelectric substrate 12 constituting the bonded substrate 50 are substrates having a flat surface without a cavity or the like, the in-plane thickness distribution of the polished piezoelectric substrate 12 is very small ( For example, within ± 50 nm). As an example of polishing, the surface of the diamond slurry is polished using a lapping machine, and then precision polishing is performed by a CMP machine using colloidal silica.

  CMP is performed using a polishing apparatus 120 shown in FIG. The polishing apparatus 120 includes a disk-shaped surface plate 122 with a large diameter, a disk-shaped substrate carrier 126 with a small diameter, and a pipe 129 for supplying a slurry containing an abrasive onto the surface plate 122. The surface plate 122 includes a shaft 122a at the center of the back surface, and rotates when the shaft 122a is rotationally driven by a drive motor (not shown). The surface plate 122 has a polishing cloth 124 made of a nonwoven fabric or the like attached to the surface. The substrate carrier 126 has a shaft 126a at the center of the upper surface, and rotates when the shaft 126a is rotationally driven by a drive motor (not shown). A recess 126 b is formed on the lower surface of the substrate carrier 126. The substrate carrier 126 is arranged at a position shifted from the center of the surface plate 122. The pipe 129 is disposed in the vicinity of the substrate carrier 126 and serves to supply a slurry containing an abrasive to the polishing cloth 124. A method of using the polishing apparatus 120 will be described. First, the first support substrate side of the bonded substrate 50 is fixed to the recess 126b provided on the lower surface of the substrate carrier 126 using wax. Next, the surface plate 122 and the substrate carrier 126 are axially rotated while supplying the slurry from the pipe 129 to the polishing cloth 124 with the piezoelectric substrate 12 of the bonded substrate 50 in contact with the polishing cloth 124. Then, polishing is performed until the piezoelectric substrate 12 has a predetermined thickness.

・ Process (b)
An electrode 14 is formed on the surface of the piezoelectric substrate 12 opposite to the side bonded to the first support substrate 21. The electrode 14 can be formed by a photolithography technique. Subsequently, a second support substrate 22 having a thickness of 100 to 500 μm and having a cavity 24 is prepared. The second support substrate 22 and the piezoelectric substrate 12 are arranged so that the electrode 14 is included in the cavity 24 of the second support substrate 22. Then, the surface of the second support substrate 22 where the cavity 24 is provided and the surface of the piezoelectric substrate 12 opposite to the bonding surface of the first support substrate 21 are directly bonded. The direct bonding is performed by activating the bonding surfaces of the piezoelectric substrate 12 and the second support substrate 22 and then pressing the substrates 12 and 22 with the bonding surfaces facing each other. Examples of the activation of the bonding surface include irradiation of an ion beam of an inert gas (such as argon) to the bonding surface, irradiation of plasma or a neutral atom beam, and the like. Thereby, a three-layer structure 60 in which the piezoelectric substrate 12 is sandwiched between the first support substrate 21 and the second support substrate 22 is obtained.

・ Process (c)
The composite substrate 10 in which the piezoelectric substrate 21 and the second support substrate 22 are bonded together by etching the organic adhesive layer 30 of the three-layer structure 60 using an etchant and removing the first support substrate 21 from the piezoelectric substrate 12. Get. The etchant is not particularly limited as long as it can dissolve the organic adhesive layer 30. For example, the etchant may be an acidic liquid or an alkaline liquid. Examples of the acidic liquid include hydrofluoric acid, hydrofluoric acid, nitric acid, sulfuric acid, hydrochloric acid, and a mixture thereof. These may be appropriately diluted with water as necessary. Examples of the alkaline solution include a KOH aqueous solution and a NaOH aqueous solution. Further, in the case where the etching in the state as it is takes time, half-dicing may be performed from the first support substrate side and the organic adhesive layer 30 may be cut and then etched. This facilitates etching. Alternatively, it is also possible to mechanically peel off by putting a blade at the bonding interface of the adhesive.

  According to the manufacturing method of the composite substrate 10 of the present embodiment described in detail above, the composite substrate 10 having a small in-plane thickness distribution can be manufactured relatively easily even though the piezoelectric substrate 12 is thin. Specifically, unlike the second method described in the background art section, it is not necessary to fill the sacrificial layer into the cavity 24 or to remove the sacrificial layer.

  In addition, a structure having the electrode 14 on the surface on the cavity 24 side of the piezoelectric substrate 12 can be easily manufactured.

  It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

  For example, as the second support substrate 22 of the above-described embodiment, a substrate having a plurality of cavities 24 is used, and a plurality of electrodes 14 of the piezoelectric substrate 12 are formed corresponding to each of the cavities 24. Also good. In this way, by dicing the composite substrate 10 for each cavity 24, a large number of micro-sized composite substrates can be manufactured.

[Example 1]
A Si (111) substrate having a thickness of 500 μm was prepared as a first support substrate, and a LiNbO ₃ substrate (LN substrate) having a thickness of 230 μm was prepared as a piezoelectric substrate. The LN substrate was bonded to the Si substrate using an acrylic adhesive to obtain a bonded substrate. A polishing apparatus (see FIG. 3) provided with a surface plate and a ceramic substrate carrier is prepared, and the Si substrate side of the bonded substrate is fixed to the substrate carrier with wax so that the thickness of the LN substrate is 1.0 μm. One side polishing was performed by CMP until it became. When the in-plane thickness distribution of the polished LN substrate was measured, it was found that a high-precision thin film of ± 50 nm could be realized in the plane. The bonded substrate was peeled from the substrate carrier, and sufficient cleaning was performed using an organic solvent and pure water.

  A photolithography process was performed on the LN substrate side of the bonded substrate using a photomask prepared in advance to form a large number of electrodes. In addition, a via hole having a diameter of 15 μm was simultaneously formed in the LN substrate in order to draw the wiring from the electrode. Next, an alkali-free glass substrate having a thickness of 200 μm in which many cavities having a size of 1 mm square and a depth of 50 μm were formed was prepared as a second support substrate. The cavity was formed so as to correspond to the electrode on a one-to-one basis. Subsequently, the bonded substrate and the glass substrate were directly installed in the bonding apparatus. Then, the surface of the bonded substrate and the cavity forming surface of the glass substrate were irradiated with an argon ion beam to activate the surfaces, and both substrates were bonded under a load of about 200 kg. As a result, a three-layer structure in which the LN substrate was sandwiched between the Si substrate and the glass substrate was obtained.

  The three-layer structure was taken out from the apparatus, the glass substrate side was attached to a dicing tape, and half dicing was performed. Thereafter, the acrylic adhesive layer was etched by dipping in an aqueous KOH solution (40 wt%) for about 10 minutes. As a result, the Si substrate was completely peeled off to obtain a composite substrate in which the LN substrate was bonded onto the glass substrate having a cavity. The composite substrate includes a glass substrate having a cavity, an LN substrate that is directly bonded to the glass substrate so as to cover the cavity, and has a thickness of 1.0 μm and an in-plane thickness distribution within ± 50 nm, and among the LN substrates, a glass substrate And an electrode formed on the surface located in the cavity. Furthermore, photolithography was performed on the LN substrate of the composite substrate, and necessary electrodes were formed to obtain a piezoelectric element using an LN thin film. Such a piezoelectric element can be used as a resonator, for example.

DESCRIPTION OF SYMBOLS 10 Composite substrate, 12 Piezoelectric substrate, 14 Electrode, 21 1st support substrate, 22 2nd support substrate (support substrate), 24 cavity, 30 Organic adhesive layer, 50 Bonded substrate, 60 3 layer structure, 120 Polishing apparatus, 122 surface plate, 122a shaft, 124 polishing cloth, 126 substrate carrier, 126a shaft, 126b recess, 129 pipe.

Claims (5)

(A) A bonded substrate is prepared by bonding a first support substrate having flat front and back surfaces and a piezoelectric substrate having flat front and back surfaces with an organic adhesive layer, and the thickness of the piezoelectric substrate of the bonded substrate is 0.1. Polishing to have a thickness of ˜3 μm;
(B) A second support substrate having a cavity is prepared, and a surface of the second support substrate on which the cavity is provided and a surface of the piezoelectric substrate opposite to the bonding surface of the first support substrate are provided. Direct bonding,
(C) obtaining a composite substrate in which the piezoelectric substrate and the second support substrate are joined by etching the organic adhesive layer to remove the first support substrate from the piezoelectric substrate;
Of composite substrate containing In the step (b), before joining the second support substrate and the piezoelectric substrate, an electrode is formed on the piezoelectric substrate so that the electrode is included in the cavity of the second support substrate. Directly bonding the second support substrate and the piezoelectric substrate;
The method for producing a composite substrate according to claim 1. The second support substrate has a plurality of the cavities,
The electrodes of the piezoelectric substrate are formed corresponding to the cavities,
The manufacturing method of the composite substrate of Claim 2. In the step (c), half etching is performed from the first support substrate side before etching the organic adhesive layer, and a cut is made to the organic adhesive layer.
The manufacturing method of the composite substrate of any one of Claims 1-3. A support substrate having a cavity;
A piezoelectric substrate that is directly bonded to the support substrate so as to cover the cavity, has a thickness of 0.1 to 3 μm, and an in-plane thickness distribution within ± 50 nm;
An electrode formed on a surface of the piezoelectric substrate facing the support substrate;
Composite substrate with

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