JP2004209700A - Bonding method between materials with different coefficients of thermal expansion - Google Patents

Abstract

An object of the present invention is to provide a method for bonding an insulator having different coefficients of thermal expansion to a Si substrate.
Kind Code: A1 In joining a piezoelectric (9) made of PZT formed on a film forming substrate (7) such as MgO and a semiconductor (or conductor) such as a Si substrate (1), materials having different thermal expansions from each other are used. Is formed by anodic bonding via the glass 5 serving as a thinned diaphragm, that is, the piezoelectric body 9 and the semiconductor 1 (which are different from each other in thermal expansion). Or a conductor).
[Selection diagram] Fig. 4

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method of joining glass as a diaphragm, which is anodically joined to a Si substrate constituting an ink jet head or a droplet discharge head, to a piezoelectric material having a different thermal expansion coefficient.
[0002]
[Prior art]
Conventionally, in order to utilize a small element as a small member, the element is bonded to a Si substrate or the like due to the ease of a photolithography process. However, the bonding has problems in workability, heat resistance, and the like. It is desired to perform solid layer bonding at a predetermined position at a low temperature without using an adhesive or the like, and an anodic bonding method is generally known as this solid layer bonding method.
[0003]
Therefore, conventionally, the three-layer structure using the anodic bonding method in the solid-layer bonding has been performed by bonding Si with each other via a thin film glass formed by film formation, that is, a bonding mode of Si / thin film / Si. (For example, see Patent Document 1).
[0004]
Alternatively, it has been performed in a manner in which crystals are bonded to each other via a Si thin film formed by film formation, that is, a bonding mode of crystal / Si thin film / crystal (for example, see Patent Document 2).
[0005]
Alternatively, Si is electrostatically bonded to each other via a boron silicate glass film formed by sputtering to form a three-layer structure in a bonding mode of Si / boron silicate glass / Si (for example, see Non-Patent Document 1). .
[0006]
[Patent Document 1]
JP-A-58-55732 [Patent Document 2]
JP-A-1-80832 [Non-Patent Document 1]
J. Electrochem. Soc .; SOLID-STATE SCIENCE AND TECHNOLOGY, April 1972, vol. 119, No. 4, p.545
[0007]
[Problems to be solved by the invention]
In the anodic bonding method, mobile ions are present in one of the insulators, for example, such as boron silicate glass, and the thermal expansion of both need to be substantially equal, and an insulator containing no mobile ions, for example, a PZT film is formed. Anodic bonding between an MgO substrate, which is a film-forming substrate, and a semiconductor (or a conductor) such as a Si substrate is difficult because their thermal expansion coefficients are different from each other by two times or more.
[0008]
For this reason, when joining a MgO substrate, which is a deposition substrate on which a PZT film is deposited, to a Si substrate, it is difficult to join materials having different thermal expansions unless an adhesive is used. There has been a demand for a bonding method and a bonding structure that do not use the same.
[0009]
An object of the present invention is to provide a method for bonding insulators having different coefficients of thermal expansion to a Si substrate.
[0010]
[Means for Solving the Problems]
The present invention provides a bonding structure and a bonding method of an insulator and a Si substrate having different coefficients of thermal expansion that meet the above-mentioned demands. The gist of the present invention is to perform anodic bonding of a Si substrate and glass, and after the anodic bonding. Then, the glass acting as a movable body and a structure is flaked, and an intermediate layer made of a conductive film is formed in an uneven shape on one of the insulators having different thermal expansions, and then the insulator side having a large thermal expansion is heated. A pressure is applied between the uneven intermediate layer and the glass while applying a voltage, and a bonding having a three-layer structure of a piezoelectric / glass / semiconductor is performed by using the bonding. In the structure.
[0011]
As an example of the joined body of the present invention, when a piezoelectric body made of PZT formed on a film forming substrate such as MgO and a semiconductor (or a conductor) such as a Si substrate are bonded to each other, thermal expansion of the piezoelectric body occurs. An uneven intermediate layer formed on the piezoelectric body by solid layer bonding between different materials, and anodic bonding via flaked glass, that is, the piezoelectric body and the semiconductor (or the conductive material) differ from each other in thermal expansion. Body).
[0012]
Examples of the piezoelectric material include piezoelectric materials such as PZT, barium titanate, strontium titanate, zinc oxide, and quartz. Further, examples of the intermediate layer made of the conductive film include Ag, Al, Cu, Fe, Ge, Si, Sn, Zn, and Zr.
[0013]
In order to obtain the joined body of the present invention, a piezoelectric body such as PZT is formed on a film-forming substrate such as MgO, and furthermore, an electrode and a conductive thin film such as Al having plastic deformability are formed thereon. It is important to form an uneven intermediate layer in advance.
[0014]
On the other hand, a diaphragm made of glass such as a Pyrex glass substrate is preliminarily anodically bonded to a Si substrate, the diaphragm is thinned after the bonding, and then the intermediate layer and the diaphragm having the uneven shape are opposed to each other, The anodic bonding is performed by heating from the substrate side for film formation while applying a load, that is, from the MgO substrate side having a large thermal expansion coefficient, and simultaneously applying a voltage to the uneven intermediate layer and the Si substrate. As a result, a bonded structure having a three-layer structure consisting of the double anodic bonding intended in the present invention is obtained.
[0015]
In this case, the thermal expansion of the film-forming substrate made of MgO on which a piezoelectric body made of PZT is formed is larger than that of the diaphragm made of Si substrate and Pyrex glass. During the temperature lowering, there is a case where peeling occurs at the bonding interface due to thermal strain.
[0016]
Therefore, it was necessary to perform anodic bonding at a temperature as low as possible near room temperature. However, as the temperature decreases, the movable ions in the Pyrex glass become more difficult to move, so that it becomes necessary to apply a high voltage. Therefore, in the case of the present invention, Pyrex glass serving as a diaphragm is anodically bonded to a Si substrate, and thereafter, the diaphragm made of Pyrex glass is thinned in advance. By the thinning, that is, by thinning to about 3 μm, the applied voltage at the time of the anodic bonding can be reduced from 2000 V to 200 V. In this case, the side of the film formation substrate having a large thermal expansion coefficient is heated, and at the same time, the side of the semiconductor (or conductor) substrate formed of the Si substrate is cooled, that is, heat is applied between the side of the film formation substrate and the Si substrate. It is desirable to have a gradient. However, this does not mean that the thermal distortion has disappeared. Therefore, an intermediate layer made of an uneven conductive film having plastic deformability is formed on the piezoelectric body, and double anodic bonding is performed between the intermediate layer and the diaphragm by the above-described method.
[0017]
With this configuration and method, the thermal distortion at the bonding interface is alleviated by the uneven projections, and peeling at the bonding interface can be prevented even when the temperature is lowered to room temperature. That is, the thermal strain caused by the joining is intended to be reduced by the convex portions of the intermediate layer having the plastic deformation ability.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
(First Embodiment of the Invention)
1 to 6 show a first embodiment of the present invention, FIG. 4 is a cross-sectional view that best illustrates the features of the present invention, and FIGS. 1, 2, and 3 are cross-sectional views before double anodic bonding. 4 is a cross-sectional view of the double anodic bonding, FIG. 5 is a view as viewed from an arrow A in FIG. 3, and FIG. 6 is a view as viewed from an arrow B in FIG.
[0019]
In the figure, 1 is a Si substrate, 2 is an ink chamber processed on the Si substrate 1, 3 is an ink flow path processed on the Si substrate 1, 4 is a nozzle for discharging ink processed on the Si substrate 1, and 5 is a Si substrate. 1 is a diaphragm made of a glass substrate (Pyrex glass; registered trademark of Corning) which is anodically bonded, 6 is a bonding interface between a Si substrate and the diaphragm, 7 is a film to be formed in the order of an upper electrode, a piezoelectric body, and a lower electrode. 8 is an upper electrode made of Pt formed on the film forming substrate 7 (Ti is formed as a sublayer; not shown), and 9 is formed on the upper Pt electrode 8. Piezoelectric body having a piezoelectric effect (PZT; lead zirconate titanate), 10 is a lower electrode made of Pt formed on piezoelectric body 9, and 11 is an electrode made of Al formed on lower electrode 10 as an electrode. And an intermediate layer for bonding to play a role of relaxing thermal strain, 12 is a convex portion of the intermediate layer 11, and 13 is Concave portions between layers 11, 14 is a bonding electrode for dual anodic bonding was formed on the glass substrate 5.
[0020]
Next, in the above configuration, first, as shown in FIG. 1, an ink chamber 2, an ink flow path 3, and a nozzle 4 are formed in a Si substrate 1 by isotropic etching and anisotropic etching using a photolithography process, respectively. Thereafter, a diaphragm 5 made of a glass substrate (Pyrex glass; a registered trademark of Corning Incorporated) is anodically bonded to the Si substrate 1. Further, after the anodic bonding, the diaphragm 5 is polished and thinned to about 3 μm, and thereafter, a bonding electrode 14 is formed as shown in FIGS. On the other hand, the piezoelectric body 9 for bonding to the diaphragm 5 is formed as follows. That is, first, an upper electrode 8 made of Pt is formed on the film forming substrate 7, and a piezoelectric body 9 made of PZT (lead zirconate titanate) is formed on the upper electrode 8. A lower electrode 10 made of Pt is formed thereon, and an intermediate layer 11 made of Al is formed on the lower electrode 10 in an uneven shape through a photolithography process and a film forming process as shown in FIG. Then, as shown in FIG. 3, after the diaphragm 5 and the intermediate layer 11 are opposed to each other and the positions thereof are aligned, the diaphragm 5 and the convex portion 12 of the intermediate layer 11 are brought into close contact with each other, and the film forming substrate 7 and the Si The convex portion 12 was plastically deformed while applying a load from both sides of the substrate 1, and simultaneously or thereafter, the convex portion 12 and the diaphragm 5 were anodically bonded to each other, that is, double anodic bonding. In this double anodic bonding, the bonding electrode 14 was used as the positive electrode, and the Si substrate 1 was used as the negative electrode (not shown in the double anodic bonding). As a result, the convex portion 12 bridges the bonding strength between the two substrates, that is, between the film-forming substrate 7 and the Si substrate 1. Since the convex portion 12 has a columnar shape, it has a degree of freedom in a direction parallel to the bonding surface as compared with the bonding between the flat plates. Therefore, in the anodic bonding between materials having different coefficients of thermal expansion, after the anodic bonding, Even when the temperature was lowered from the anodic bonding temperature (150 ° C.) to room temperature, the bonding was firmly performed without peeling.
[0021]
After the above-mentioned bonding, only the film forming substrate 7 made of the MgO substrate used for forming the PZT film is removed by etching in hot phosphoric acid, and then the upper electrode 8 made of Pt is removed by photolithography and dry etching. Thus, a piezoelectric body 9 made of PZT is formed by etching into a shape similar to that of the upper electrode 8. That is, the piezoelectric body 9 made of PZT immediately below the upper electrode 8 is left, and the other piezoelectric bodies 9 made of PZT are removed. Thereafter, the disk was cut out from the middle of the nozzle 4 by a disc cutter, so that droplets from the nozzle could be discharged.
[0022]
When a pulsed voltage was applied (not shown) between the upper electrode and the lower electrode of the bonded structure formed by the above bonding method, droplets could be discharged from the nozzle 4.
[0023]
In the present embodiment, Pyrex G. (registered trademark of Corning) is used as the diaphragm 5 made of glass, but other materials such as borosilicate glass, soda glass, and aluminosilicate glass may be used.
[0024]
Furthermore, although PZT was used as the piezoelectric body, any material having a perovskite structure may be used. For example, barium titanate may be used instead of PZT.
[0025]
Further, in the present embodiment, Al is used as the intermediate layer, but other materials such as Ag, Cu, Cr, Fe, Ge, Si, Sn, Zn, and Zr may be used, or these compounds may be used.
[0026]
In other words, any conductor may be used as long as the conductor has plastic deformability, and the intention of the present invention does not change at all.
[0027]
(Second embodiment of the invention)
FIGS. 1 to 5 and 7 show a second embodiment of the present invention. FIG. 4 is a cross-sectional view which best illustrates the features of the present invention. FIGS. 4 is a cross-sectional view of the double anodic bonding, FIG. 5 is a view as viewed from an arrow A in FIG. 3, and FIG. 7 is a view as viewed from an arrow B in FIG.
[0028]
In the figure, 1 is a Si substrate, 2 is an ink chamber processed on the Si substrate 1, 3 is an ink flow path processed on the Si substrate 1, 4 is a nozzle for discharging droplets processed on the Si substrate 1, and 5 is a Si. A diaphragm made of a glass substrate (SD2; registered trademark of HOYA) anodically bonded to the substrate 1, 6 is a bonding interface between the Si substrate 1 and the diaphragm 5, 7 is a film-forming substrate made of an MgO substrate, and 8 is a film-forming substrate. An upper electrode made of Pt formed on the substrate 7 for use (Ti is formed as an undercoat layer; not shown), and 9 is a piezoelectric substance (lead zirconate titanate) having a piezo effect formed on the Pt electrode 8. Reference numeral 10 denotes a lower electrode made of Pt formed on the piezoelectric body 9, and reference numeral 11 denotes an electrode made of Sn formed on the lower electrode 10, which serves as an electrode and serves to reduce thermal strain. An intermediate layer, 12 is a bonding portion composed of a convex portion serving as a bonding portion of the intermediate layer 11, 13 is a concave portion of the intermediate layer 11, and 14 is a glass substrate 5. It is a bonding electrode for double anodic bonding formed above.
[0029]
Next, in the above configuration, first, as shown in FIG. 1, an ink chamber 2, an ink flow path 3, and a nozzle 4 are formed in a Si substrate 1 by isotropic etching and anisotropic etching using a photolithography process, respectively. Thereafter, a diaphragm 5 made of glass (SD-2; a registered trademark of HOYA) is anodically bonded to the Si substrate 1. Further, after the bonding, the diaphragm 5 is polished and thinned to about 3 μm, and thereafter, a bonding electrode 14 is formed as shown in FIGS. On the other hand, the other substrate for double anodic bonding to the diaphragm 5 is formed as follows. That is, first, an upper electrode 8 made of Pt is formed on a film forming substrate 7 made of an MgO substrate, and a piezoelectric body 9 made of lead zirconate titanate is formed on the upper electrode 8. A lower electrode 10 made of Pt is formed on the lower electrode 10, and an intermediate layer 11 made of Sn is formed on the lower electrode 10 in an uneven shape through a film forming process and a photolithography process as shown in FIGS. Form. The protrusion 12 was formed in a columnar shape so that the intermediate layer 11 made of Sn had a greater plastic deformation ability.
[0030]
In this case, it is preferable that the columnar aspect ratio of the projection 12, that is, the vertical length ratio, be as large as possible.
[0031]
Then, as shown in FIG. 3, after the diaphragm 5 and the intermediate layer 11 are opposed to each other and the positions thereof are aligned, the diaphragm 5 and the protruding portions 12 of the intermediate layer 11 are brought into close contact with each other, and the substrate for film formation is removed from the MgO substrate. The convex portion 12 was plastically deformed while applying a load from both sides of the silicon substrate 7 and the Si substrate 1, and at the same time or thereafter, the convex portion 12 and the diaphragm 5 were anodically bonded to each other. That is, double anodic bonding was performed. In this double anodic bonding, the bonding electrode 14 was used as a positive electrode, and the Si substrate 1 was used as a negative electrode (not shown). As a result, the columnar projections 12 bridge the bonding strength between the two substrates, that is, between the film-forming substrate 7 and the Si substrate 1. Since the convex portion has a columnar shape, displacement by plastic deformation in a direction parallel to the substrate surface is facilitated as compared with a flat intermediate layer whose periphery is restricted. That is, the thermal strain caused by the difference in thermal expansion coefficient can be reduced by the displacement. In the present embodiment, even when the temperature was lowered from the anodic bonding temperature of 150 ° C. to the room temperature after the anodic bonding, the bonding was firm without peeling.
[0032]
After the bonding, only the MgO substrate 7 used for forming the PZT film is removed by etching in hot phosphoric acid, and then the upper electrode 8 is present only on the ink flow path 3 by using a photolithography process and a dry etching process. Then, a piezoelectric body 9 made of PZT is formed in the same shape as the upper electrode 8 by etching. That is, the piezoelectric body 9 immediately below the upper electrode 8 is left, and the other piezoelectric bodies 9 are removed.
[0033]
When a voltage was applied between the upper electrode and the lower electrode of the bonded structure formed by the above bonding method, droplets could be discharged from the nozzle 4.
[0034]
In the present embodiment, the piezoelectric body 9 is made of PZT, but in addition, barium titanate or lead titanate can also produce a piezo effect, and can be used instead of PZT.
[0035]
Further, although the convex portion 12 is formed in a columnar shape, a rectangular column may be used, and there is no change in what is intended by the present invention.
[0036]
Although two embodiments of the present invention have been shown and described above, those skilled in the art will appreciate that the spirit and scope of the present invention are not limited to the specific description and drawings in this specification, but may be applied to the present invention. It will be understood that various modifications and changes are set forth which are all set forth in the following claims.
[0037]
Examples of embodiments of the present invention are listed below.
[0038]
An embodiment of the present invention relates to a method of forming a piezoelectric body formed on a film formation substrate for forming an epitaxial layer in a droplet discharge head, and a semiconductor (or a conductor) formed with an ink flow path. In the bonding method, a double anodic bonding is performed through glass serving as a diaphragm, a bonding method including the following steps:
(1) Anodically bonding a semiconductor (or a conductor) and glass,
(2) Thin the glass,
(3) forming an intermediate layer made of a conductive film on the surface of the piezoelectric body,
(4) The thinned glass and the intermediate layer on the surface of the piezoelectric body are opposed to each other and brought into close contact with each other,
(5) Heat the side with large thermal expansion,
(6) During heating, a voltage is applied between the semiconductor (or the conductor) and the intermediate layer on the surface of the piezoelectric body to perform anodic bonding;
A film forming method comprising joining a semiconductor (or a conductor) having an ink flow path formed thereon and a piezoelectric body via glass serving as a diaphragm of a droplet discharging head, comprising the above steps. This is a bonding method of performing double anodic bonding for forming a three-layer structure of a piezoelectric / glass / semiconductor (or conductor) on a substrate.
[0039]
According to the present embodiment, a diaphragm is anodic-bonded on the ink flow path formed on the semiconductor, and a piezoelectric body is further directly anodic-bonded on the diaphragm via an intermediate layer. Further, it is possible to form a simple joint structure between a semiconductor and a piezoelectric body having different thermal expansion coefficients without using an adhesive.
[0040]
Further, the glass to be the diaphragm is anodically bonded, and thereafter, the diaphragm made of glass is thinned in advance. By this thinning, that is, by thinning to about 3 μm, the applied voltage at the time of the anodic bonding can be reduced from 2000 V to 200 V.
[0041]
In the present invention, the film formation substrate is preferably made of MgO.
[0042]
Further, in the present invention, the crystal structure of the piezoelectric body is preferably a perovskite structure, more preferably barium titanate or lead zirconate titanate.
[0043]
In the present invention, the glass is preferably borosilicate glass, soda-lime glass, or aluminosilicate glass.
[0044]
In the present invention, the thinning of the glass is preferably for reducing the rigidity of the glass, reducing the spring constant of the piezoelectric body and the glass which are integrated by joining, and thereby increasing the displacement. .
[0045]
In the present invention, the intermediate layer is preferably any one of Ag, Al, Ge, Zr, Zn, Si, Sn, Cr, Ti, Fe, and Cu.
[0046]
Further, in the present invention, it is preferable that the intermediate layer has an uneven shape, and is in close contact with and bonded to the glass at the convex portion.
[0047]
According to the present embodiment, the thermal distortion at the bonding interface is alleviated by the convex and concave portions, and peeling at the bonding interface can be prevented even when the temperature is lowered to room temperature. That is, the thermal strain caused by the joining is intended to be reduced by the convex portions of the intermediate layer having the plastic deformation ability.
[0048]
In the present invention, the heating temperature is preferably 150 ° C. or lower.
[0049]
Another embodiment of the present invention relates to a piezoelectric body formed on a film formation substrate for forming an epitaxial layer in a droplet discharge head, and a semiconductor (or a conductor) having a flow path formed therein. The double anodic bonding of the above-described embodiment is performed via a glass serving as a vibration plate, and the piezoelectric / glass / semiconductor (or conductor) on the film formation substrate is bonded by the bonding method. A bonded structure characterized by forming a bonded structure having a three-layer structure and thereafter removing only a film-forming substrate.
[0050]
【The invention's effect】
As described above, the present invention has the following effects.
[0051]
In anodic bonding between materials having different coefficients of thermal expansion, an uneven intermediate layer having conductivity and plastic deformability is formed on one substrate by film formation, and the other substrate, ie, a semiconductor (or conductor) is formed on the other substrate. The glass is then anodically bonded, then the intermediate layer and the glass are opposed to each other, the position between the two substrates is aligned, and a voltage is applied between the intermediate layer and the Si substrate, and the glass and the intermediate Since it is a bonding method of performing double anodic bonding between the protrusions of the layer and a three-layer bonding structure formed by the bonding method,
1. Thermal distortion between materials caused by a difference in thermal expansion coefficient, that is, distortion in a direction parallel to the substrate is alleviated by plastic deformation at the projection.
[0052]
2. Since the joining electrode can be used as an extraction electrode for the lower electrode of the piezoelectric body, the structure is simple.
[0053]
3. Easy to handle because solid layer bonding is possible regardless of whether it is in vacuum or air.
[0054]
4. The diaphragm is anodically bonded to the ink chamber (groove) processed on the Si substrate, and the piezoelectric body is bonded directly to the diaphragm via a double layer anode via an intermediate layer. A simple structure can be formed without using an agent.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view when anodically bonding glass to a Si substrate having an ink flow path according to the first and second embodiments.
FIG. 2 is a cross-sectional view of the first and second embodiments when glass is anodically bonded to a Si substrate having an ink flow path and then the glass is flaked and polished.
FIG. 3 is a cross-sectional view of one of the first and second embodiments, in which one substrate, that is, a film-forming substrate made of a MgO substrate on which a piezoelectric material is formed, and the other substrate, that is, a Si substrate in which glass is anodically bonded, FIG. 4 is a cross-sectional view of a state in which alignment is performed facing each other before double anodic bonding.
FIG. 4 is a cross-sectional view of one of the first and second embodiments, in which one substrate, that is, a film-forming substrate made of a MgO substrate on which a piezoelectric material is formed, and the other substrate, that is, a Si substrate in which glass is anodically bonded, It is sectional drawing at the time of heavy anode joining.
FIG. 5 is a view on arrow A of FIG. 3 in the first and second embodiments.
FIG. 6 is a view on arrow B in FIG. 3 in the first embodiment.
FIG. 7 is a view on arrow B of FIG. 3 in the second embodiment.
[Explanation of symbols]
1 Si substrate (semiconductor)
2 Ink chamber 3 Ink flow path 4 Nozzle 5 Glass serving as vibration plate 6 Bonding interface 7 Deposition substrate 8 Upper electrode 9 Piezoelectric body 10 Lower electrode 11 Intermediate layer 12 Convex part 13 Concave part 14 Joining electrode

Claims (1)

In a method of joining a piezoelectric body formed on a film formation substrate for forming an epitaxial layer in a droplet discharge head with a semiconductor (or a conductor) having an ink flow path,
A double anodic bonding is performed through glass serving as a diaphragm, a bonding method including the following steps:
(1) anodically bonding the semiconductor (or conductor) and the glass,
(2) thinning the glass,
(3) forming an intermediate layer made of a conductive film on the surface of the piezoelectric body;
(4) The thinned glass and the intermediate layer on the surface of the piezoelectric body are opposed to each other and brought into close contact with each other,
(5) Heat the side with large thermal expansion,
(6) During the heating, a voltage is applied between the semiconductor (or the conductor) and the intermediate layer on the surface of the piezoelectric body to perform anodic bonding;
The semiconductor (or conductor) having an ink flow path formed thereon and the piezoelectric body are joined via a glass serving as a diaphragm of a droplet discharging head, comprising the above-described respective steps. A bonding method in which double anodic bonding for forming a three-layer structure of the piezoelectric body / the glass / the semiconductor (or the conductor) on a deposition substrate is performed.

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