JP2001347658A - Electrostatic actuator, its manufacturing method and liquid drop discharge head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic actuator for deflecting a diaphragm by an electrostatic force by impressing a voltage between the diaphragm and an electrode while an electrode substrate is set oppositely via a predetermined gap to the diaphragm which can be formed inexpensively with a high density, a method for manufacturing the electrostatic actuator and an electrostatic type discharge head. SOLUTION: A diaphragm substrate 1 and the electrode substrate 2 are directly joined without using an adhesive. Moreover, a silicon oxide film 11 for forming the gap is set to the side of the electrode substrate 2 and a join face at the side of the diaphragm substrate is made flat.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic actuator, a method of manufacturing the same, and a droplet discharge head.

[0002]

2. Description of the Related Art An ink jet head used in an ink jet recording apparatus used as an image recording apparatus such as a printer, a facsimile, a copying apparatus, etc. has a nozzle hole for discharging ink droplets and a discharge chamber (liquid chamber, pressure chamber) communicating with the nozzle hole. Chamber, pressurized liquid chamber, ink channel, etc.)
And an energy generating means (actuator) for generating energy for pressurizing the ink in the discharge chamber, and driving the actuator to pressurize the ink in the discharge chamber to discharge ink droplets from the nozzle holes. An ink-on-demand type that ejects ink droplets only when recording is necessary is the mainstream. The method is roughly classified into several methods according to a method of generating ink droplets (recording liquid) and a control method for controlling a flying direction.

Here, as an ink jet head using an electrostatic actuator, for example, Japanese Patent Laid-Open No. 4-522
No. 14, JP-A-3-293141, etc., a diaphragm which forms a liquid chamber and one wall surface of this liquid chamber by etching a first substrate (diaphragm substrate) made of a silicon substrate Is formed, and a second substrate (electrode substrate) on which an individual electrode (electrode) is formed is arranged below the first substrate, and the electrodes are opposed to each other with a predetermined gap placed on the diaphragm. An electric actuator is constructed, and by applying a voltage between the diaphragm and the electrode of the actuator, the diaphragm is flexed by electrostatic force to change the internal volume of the liquid chamber, and ink droplets from nozzles communicating with the liquid chamber. Is known.

[0004] In an ink jet head using such an electrostatic actuator, gap accuracy for utilizing electrostatic force is important. In particular, when manufacturing an ink jet head for obtaining a high-definition image, high-density dots must be realized, and the pitch that can be used as a diaphragm is reduced. When the size of the diaphragm is reduced, a large force for deforming the diaphragm is required. To generate a large force by the electrostatic actuator, a driving voltage applied between the diaphragm and the electrode is required. There is no alternative but to increase the electric field by increasing it or to increase the electric field by reducing the gap.

In this case, increasing the driving voltage requires
The drive circuit becomes expensive, and in some cases, general-purpose products cannot be used, which leads to higher costs and more problems such as an increase in power consumption. It is desired to control the gap with high precision and drive the actuator with a smaller gap.

However, for example, the nozzle density (discharge density)
In order to manufacture a high-density ink-jet head that exceeds 150 dpi, the gap between the diaphragm and the electrode must be 1 μm.
m. In order to form such a high-precision gap, it is preferable to use a semiconductor manufacturing technique such as LSI.

In this case, a method of bonding the electrode substrate and the diaphragm substrate becomes important in controlling the gap. That is, using a semiconductor manufacturing technology, the electrode substrate and
Even if a diaphragm is manufactured, a high-density ink-jet head cannot be put to practical use if the gap accuracy is deviated by the joining. Therefore, it is known to perform direct bonding using a silicon substrate.

In this direct bonding, after the surfaces of the substrates are subjected to a hydrophilization treatment, the two substrates are gently bonded to each other and heat-treated to bond the two substrates. Since the direct bonding does not require any special treatment, the surface properties of the substrate are very important. For example, surface roughness, surface undulations, etc. have a large effect on bondability, and in general,
It is said that if the surface roughness is about 1.5 nm or more, the bondability deteriorates (for example, Applied Physics Vol. 60, No. 8 (199).
1) P.I. 790).

That is, when performing direct bonding of silicon substrates, the process must not be such that the bonding surface is roughened. However, in the semiconductor manufacturing process,
During this process, processes that may damage the bonding surface, such as ion implantation, photoresist ashing, cleaning with chemicals, and etching, are repeated, so that process design becomes important.

[0010] Therefore, for example, Japanese Patent Application Laid-Open No. 5-50601
As described in Japanese Patent Application Laid-Open No. 6-71882, a method is used in which anisotropic etching is performed on a silicon substrate to form an electrode groove, and the diaphragm substrate and the electrode substrate are joined by anodic bonding. ing. Anodic bonding is 300-4
In an environment heated to about 50 ° C., a voltage of several hundred volts is applied between substrates to be bonded to perform bonding.

[0011]

However, when the diaphragm and the electrode substrate are bonded by anodic bonding as described above, when a voltage is applied at a high temperature to the semiconductor substrate on which the bonding diffusion layer is formed, a junction is generated. There is a problem that the substrate is destroyed, or one of the substrates is almost limited to a glass substrate. If the substrate is limited to glass,
Due to the problem of processing accuracy, it is difficult to form a minute gap.

The present invention has been made in view of the above points, and has as its object to provide an inexpensive and high-density electrostatic actuator, a method of manufacturing the same, and a droplet discharge head.

[0013]

According to a first aspect of the present invention, there is provided an electrostatic actuator comprising: a diaphragm substrate on which a diaphragm is formed; and an electrode substrate on which an electrode is formed. In an electrostatic actuator in which a diaphragm is deformed by applying a voltage between an electrode and a diaphragm, a diaphragm substrate and an electrode substrate are not bonded to each other without using an adhesive. Direct joining, and
A silicon oxide film for forming a gap was provided on the electrode substrate side, and the bonding surface on the diaphragm substrate side was flat.

According to a second aspect of the present invention, there is provided a method of manufacturing an electrostatic actuator according to the first aspect of the present invention, wherein the diaphragm substrate has a high height on the side of the joint surface with the electrode substrate. Using a silicon wafer into which a high concentration impurity has been implanted, an oxide film is formed on the bonding surface side of the silicon wafer, and then the silicon wafer is bonded to the electrode substrate.

According to a third aspect of the present invention, there is provided a method of manufacturing an electrostatic actuator according to the first aspect of the present invention, wherein the diaphragm substrate has a height higher than that of the surface to be joined to the electrode substrate. An oxide film layer and a compound layer generated on the surface of the silicon wafer to be bonded to the electrode substrate are removed by using a silicon wafer into which impurities of a concentration are implanted, and then the silicon wafer is bonded to the electrode substrate.

According to a fourth aspect of the present invention, there is provided a method of manufacturing an electrostatic actuator according to the first aspect, wherein a semiconductor substrate having an SOI structure is used as a diaphragm substrate. Then, after a silicon oxide film is formed on the bonding surface of the semiconductor substrate with the electrode substrate by a thermal oxidation method, the semiconductor substrate is bonded to the electrode substrate.

According to a fifth aspect of the present invention, there is provided a method of manufacturing an electrostatic actuator according to the first aspect, wherein a semiconductor substrate having an SOI structure is used as a diaphragm substrate. After removing a natural oxide film formed on the bonding surface of the semiconductor substrate with the electrode substrate, the semiconductor substrate is bonded to the electrode substrate.

According to a sixth aspect of the present invention, in the method of manufacturing an electrostatic actuator according to the first aspect, a silicon wafer is used as an electrode substrate. A silicon oxide film is formed by thermal oxidation, etched to a depth corresponding to the thickness of the electrode and the thickness of the gap layer, an electrode is formed in the etched region, and then joined to the diaphragm substrate. did.

According to a seventh aspect of the present invention, there is provided a method of manufacturing an electrostatic actuator according to the first aspect, wherein the silicon wafer is used as an electrode substrate. After a silicon nitride film is formed in a portion other than the electrode formation region, the oxide film is grown by selectively thermally oxidizing the electrode formation region until the required gap layer and electrode thickness are obtained. Then, a gap layer is formed on the silicon substrate by removing the nitride film, and then a surface oxidation, which is a sacrificial oxidation, is performed. Then, the oxide film is removed. After forming a silicon oxide film to a thickness necessary for the insulation, an electrode is formed and the structure is joined to the diaphragm substrate.

In the droplet discharge head according to the present invention, the actuator is an electrostatic actuator according to the present invention.

[0021]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic cross-sectional view in the longitudinal direction of a diaphragm showing an ink jet head which is a droplet discharge head according to the present invention provided with the electrostatic actuator according to the present invention, and FIG. It is a schematic cross section explanatory view.

This ink jet head includes a diaphragm substrate 1, an electrode substrate 2 provided below the diaphragm substrate 1,
A plurality of nozzles 5 for discharging ink droplets, comprising: a nozzle plate 3 provided above the diaphragm substrate 1;
And a common ink flow path 8 for supplying ink to the liquid chamber 6 via a fluid resistance portion 7.

The diaphragm substrate 1 is made of a silicon substrate, and is formed by using a silicon substrate, a concave portion forming a liquid chamber 6 and a diaphragm 10 forming a bottom surface of the liquid chamber 6, a groove portion forming a fluid resistance portion 7, a common ink flow path. 8 are formed. The diaphragm substrate 1 can be formed using, for example, an SOI substrate in which a silicon substrate is bonded via an oxide film. In this case, the diaphragm 10 can be formed with high accuracy by using the oxide film as an etch stop layer by etching the concave portion serving as the liquid chamber 6 using an etching solution such as a KOH aqueous solution. Also, the diaphragm 10 can be formed with high precision by forming a high-concentration P-type impurity diffusion layer, for example, a boron diffusion layer on a silicon substrate, and performing an etch stop using the boron diffusion layer as an etching stop layer.

On the electrode substrate 2, a silicon oxide film 11 is formed on the surface using a silicon substrate, an electrode forming groove 12 is formed in the silicon oxide film 11, and the diaphragm substrate 1 is formed on the bottom of the electrode forming groove 12. The electrode 13 opposing the diaphragm 10 via a gap 14 is provided. These diaphragms 10
The electrode 13 constitutes an electrostatic actuator which is a microactuator for deforming and displacing the vibration plate 7 by electrostatic force to pressurize ink in the liquid chamber 6 and discharge ink droplets from the nozzle 5.

On the surface of the electrode 13 of the electrode substrate 2, an oxide-based insulating film such as a SiO ₂ film or a nitride-based film such as a Si ₃ N ₄ film is used to prevent damage due to contact with the diaphragm 10. A protective film (insulating film) 15 made of an insulating film is formed.

Here, the diaphragm substrate 1 and the electrode substrate 2 are directly joined without using an adhesive, and the diaphragm 10 and the electrode substrate 1 are joined together.
The silicon oxide film 11 defining the gap with the electrode substrate 3 is provided on the electrode substrate 2 side, and the bonding surface of the diaphragm substrate 1 with the electrode substrate 2 is made flat (surface roughness Ra = 1.4 nm or less).

The nozzle plate 3 has a nozzle 5 formed of a metal layer, a laminated member in which a metal layer and a polymer layer are directly joined, a resin member, nickel electroforming, or the like. : Ejection surface), in order to ensure water repellency with the ink, a water repellent film is formed by a known method such as a plating film or a water repellent coating.

In the ink jet head configured as described above, the diaphragm 10 is used as a common electrode, and the electrode 13 is used as an individual electrode. The diaphragm 10 is deformed and displaced toward the electrode 13 due to an electrostatic force generated between the electrode 13 and the diaphragm 10. By returning the electric charge between the diaphragm 10 and the electrode 13 from this state, the diaphragm 10 is returned and deformed.
When the internal volume (volume) / pressure of the liquid chamber 6 changes, ink droplets are ejected from the nozzles 5.

In this ink jet head, the diaphragm substrate 1 and the electrode substrate 2 are directly joined without using an adhesive, and the silicon oxide film 11 defining the gap between the diaphragm 10 and the electrode 13 is covered with the electrode. Since it is provided on the substrate 2 side and the bonding surface of the diaphragm substrate 1 with the electrode substrate 2 is flat, when manufacturing an actuator using a semiconductor process, the bonding surface of the diaphragm substrate 1 and the electrode substrate 2 is used. It is possible to obtain an actuator portion by direct bonding without causing any warpage, thereby improving gap accuracy and obtaining a higher density inkjet head.

Further, since a silicon substrate is used for the diaphragm substrate 1 and the electrode substrate 2, stress such as thermal expansion is hardly received, and bonding reliability is improved. Furthermore, since the bonding surface on the diaphragm substrate 1 side is flat, all the bonding surfaces on the electrode substrate side can contribute to bonding, and the bonding strength is improved.

Next, a method for manufacturing an ink jet head according to the present invention by applying the first embodiment of the method for manufacturing an electrostatic actuator according to the present invention will be described with reference to FIGS. FIG. 3 is an explanatory view for explaining a manufacturing process of a silicon substrate to be a diaphragm substrate, FIG. 4 is an explanatory view for explaining a manufacturing process of an electrode substrate, and FIG. FIG. 4 is an explanatory diagram illustrating a process of forming a head.

First, a process for manufacturing a silicon substrate serving as a diaphragm substrate will be described with reference to FIG. As shown in FIG. 1A, as a silicon substrate 21 serving as a diaphragm substrate,
A silicon substrate having a P-type polarity and a crystal plane orientation of (110) and both surfaces mirror-polished is used. The reason why such a silicon substrate 21 is used is to obtain a processed shape with high accuracy by utilizing the plane anisotropy of the wet etching rate of silicon.

Then, as shown in FIG. 2B, the surface of the silicon substrate 21 which is to be bonded to the electrode substrate is formed by a solid diffusion method, a coating diffusion method, an ion implantation method, or the like.
High concentration boron is implanted to form a high concentration boron layer 22. The thickness of the high-concentration boron layer 22 is
It diffuses to a thickness of zero.

The surface of the silicon substrate 21 on the side where boron is implanted is subjected to the boron diffusion layer 22 during the thermal diffusion process.
A compound layer 23 of silicon and boron is formed on the surface of the semiconductor layer, and a silicon oxide film 24 containing boron is formed on the compound layer 23. The silicon oxide film 24 containing this impurity may be used for bonding as it is, but if it is left as it is, the compound layer 23 remains on the surface on which the diaphragm is formed. It becomes difficult.

Then, as shown in FIG. 3C, the silicon substrate 21 is immersed in a hydrogen fluoride solution to remove the silicon oxide film 24 on the surface, and then mixed with a hydrogen fluoride solution and an aqueous nitric acid solution. By dipping in the liquid, the silicon and boron compound layer 23 formed on the surface of the silicon substrate 21 is removed. At this time, the surface of the boron diffusion layer 22 of the silicon substrate 21 is slightly etched.

In this case, by optimizing the diffusion conditions,
Although the roughness of the surface of the boron diffusion layer 22 of the silicon substrate 21 can be reduced, here, as shown in FIG.
The surface is polished using such a technique. In the present CMP technology, if the polishing amount is 0.1 μm, the surface roughness can be finished to a Ra value of about 0.2 nm (mirror finish of a level that enables direct bonding sufficiently), and the polishing amount is reduced. By setting the diffusion conditions in consideration of the above, the diaphragm can be formed with high accuracy.

As described above, by using a silicon wafer in which a high-concentration impurity is implanted into the vibration substrate on the bonding surface side with the electrode substrate, an oxide film layer formed on the bonding surface side of the silicon wafer with the electrode substrate is used. Also, by removing the compound layer and then bonding to the electrode substrate, vibration design becomes easy.

Next, the manufacturing process of the electrode substrate will be described with reference to FIG. As shown in FIG. 1A, a silicon substrate 31 serving as the electrode substrate 2 has a P-type polarity, has a crystal plane orientation of (100), and has a mirror-finished surface to be bonded to the diaphragm substrate. A silicon substrate, here, a silicon wafer is used. By using such a silicon substrate 31, the electrode substrate can be formed from the most common and widely used silicon wafer, and the cost can be reduced.

Therefore, as shown in FIG. 2B, the silicon substrate 31 is oxidized by a thermal oxidation method such as a pyro-oxidation (wet oxidation) method or a dry oxidation method, and a silicon oxide film 11 is formed on the surface of the silicon substrate 31. A silicon oxide film 32 is formed. The thickness of the silicon oxide film 32 is determined by the gap length (about 500 nm in the present embodiment) which is the distance between the vibration plate 10 and the electrode 13 of the electrostatic actuator, and the thickness of the electrode material (the electrode in the present embodiment). (The thickness of about 150 nm + the thickness of the protective film 150 nm) and the thickness (about 500 nm in the present embodiment) at which electrical insulation between the electrode 13 and the electrode substrate 2 (silicon substrate 31) can be ensured. Min thickness. Here, the thickness of the silicon oxide film 32 is set to about 1500 nm.

Next, a photoresist is applied to the surface of the silicon oxide film 32, and thereafter, exposure and development are performed to form an electrode forming groove on the bonding surface side of the silicon oxide film 32, as shown in FIG. A photoresist pattern 33 having an opening 34 corresponding to 12 is formed.

Then, as shown in FIG. 3D, using the photoresist pattern 33 as a mask, a silicon oxide film 32 is formed by using a hydrogen fluoride solution having a concentration of about 5% to about 8%.
The electrode forming groove 12 is formed by wet etching to a depth of 00 nm. Here, the variation in the depth direction of the wet etching is about 1%, and does not affect the function of the actuator.

Next, the photoresist pattern 33 is removed. The removal of the photoresist pattern 33 is preferably a process using a remover specified by a photoresist maker. For example, a photoresist ashing apparatus using oxygen plasma may be used. In this case, RCA cleaning is performed to prevent the silicon oxide film 32 from being damaged (surface roughness, residual resist ash, etc.). It is necessary to perform wet cleaning that can be performed.

Subsequently, as shown in FIG.
3 is formed by sputtering or the like, and an electrode insulating protective film 1 is formed on the titanium nitride layer 35.
A silicon oxide film 36 serving as No. 5 is deposited, a photoresist (not shown) is applied on the silicon oxide film 36, and the photoresist is exposed and developed to form a resist pattern for masking a portion corresponding to the electrode 13. .

Then, using this resist pattern as a mask, the silicon oxide film 36 is etched with a hydrogen fluoride solution, and further using the remaining silicon oxide film 36 as a mask, the titanium nitride layer 35 is etched with ammonia and hydrogen peroxide solution. By etching with an aqueous solution, an electrode 13 made of titanium nitride and an insulating film 15 made of a silicon oxide film are formed in an electrode forming groove 12 of a silicon oxide film 11 made of a silicon oxide film 32 as shown in FIG. The obtained electrode substrate 2 is obtained.

At this time, the titanium nitride film 35 on the electrode substrate 2 made of the silicon substrate 31 is removed. At this time, the aqueous solution of ammonia and hydrogen peroxide as the etchant is mixed with the SC-1 cleaning solution in the RCA cleaning. Similarly, even after the titanium nitride layer 35 disappears, the surface of the silicon oxide film 11 serving as a bonding surface is not roughened.
Here, titanium nitride is used as the electrode material, but other conductive ceramics, high melting point metals, or polysilicon having conductivity may be used.

As described above, using a silicon wafer as the electrode substrate, a silicon oxide film is formed on the entire surface of the silicon wafer by the thermal oxidation method, and the silicon oxide film is etched to the depths of the individual electrodes and the gap layer. After the individual electrodes are formed in the etched region and then joined to the diaphragm substrate, a high-precision gap can be formed at a low cost by a simple process.

Next, a description will be given, with reference to FIG. 5, of a bonding process between the silicon substrate 21 serving as the diaphragm substrate 1 and the electrode substrate 2 using the silicon substrate. First, the silicon substrate 21 and the electrode substrate 2 are cleaned. Here, cleaning using ammonia water + hydrogen peroxide water + water was performed to remove dust on the wafer surface. Then, a treatment for imparting hydrophilicity is performed for the purpose of improving the bonding property at room temperature. Here, a chemical solution treatment using sulfuric acid + hydrogen peroxide solution was performed.

Next, alignment is performed using an orientation flat formed on the silicon substrate 21 and the electrode substrate 2 using an aligner or the like, and gently bonded together. Subsequently, it is determined whether or not initial voids are generated.
After inspection using an R inspection device or the like, the sample is placed in a heating furnace such as a diffusion furnace and heated, and as shown in FIG.
The silicon substrate 21 serving as the diaphragm substrate 1 and the silicon substrate serving as the electrode substrate 2 are directly bonded via the silicon oxide film 11. The conditions at this time are as follows:
Performed at 50 ° C. for 2 hours.

Thereafter, as shown in FIG. 5B, the silicon wafer 21 side of the bonded wafer is polished to a predetermined thickness. At this time, the bonded wafer did not peel off, and had sufficient bonding strength. In this embodiment, in order to obtain the ejection characteristics of the ink jet head, the bonded wafers are polished. However, if the required ejection characteristics can be obtained, the polishing process can be omitted.

Further, a silicon nitride film 41 is deposited on the entire surface of the wafer (silicon substrate 21 and electrode substrate 2) after polishing by CVD or the like, and a photoresist is applied to the silicon nitride film 41. The photoresist is patterned in accordance with the liquid chamber pattern corresponding to the electrode pattern by the IR transmission method, and as shown in FIG.
After the opening 42 is formed by patterning the silicon nitride film 41 by a method such as dry etching, the photoresist is removed.

Next, as shown in FIG. 2D, using the patterned silicon nitride film 41 as a mask, a high concentration alkali metal hydroxide solution (for example, a 30% -KOH solution heated to 80 ° C.). The joining member of the silicon substrate 21 and the electrode substrate 2 is immersed therein, and the silicon substrate 21 is selectively etched to form the diaphragm substrate 1 in which the concave portion 43 serving as the liquid chamber 6 is formed.

At this time, when the etching of the silicon substrate 21 reaches the region of the boron layer implanted at a high concentration, the etching is stopped spontaneously. Can produce well. Here, the diaphragm 10 having a thickness of about 2 μm was formed. Further, due to the etching anisotropy of the silicon substrate 21 itself, the liquid chamber 6 (the concave portion 43) could be etched with an accuracy within ± 1 μm.

In this case, the alignment using the orientation flat was performed. However, if polishing or the like is not required, a pattern for gap formation (particularly, alignment) is formed on the surface of the silicon substrate 21 with a silicon nitride film or the like in advance. A pattern may be formed.), And an engraving pattern (particularly, a pattern for alignment may be formed) indicating the electrode region of the electrode substrate 2.
A method of taking alignment and bonding gently can also be used.

Thereafter, although not shown, as described above,
The ink jet head is completed by joining the nozzle plate 3 to the diaphragm substrate 1.

Next, a manufacturing process of a silicon substrate serving as a diaphragm substrate in a second embodiment of the method of manufacturing an electrostatic actuator according to the present invention will be described with reference to FIG. Also in this case, as shown in FIG. 3A, a silicon substrate having a P-type crystal plane orientation of (110) and both surfaces mirror-polished is used as a silicon substrate 21 serving as a diaphragm substrate.

Then, as shown in FIG. 2B, the surface of the silicon substrate 21 which is to be joined to the electrode substrate is formed by a solid diffusion method, a coating diffusion method, an ion implantation method, or the like.
High concentration boron is implanted to form a high concentration boron layer 22. The thickness of the high-concentration boron layer 22 is
It diffuses to a thickness of zero.

The surface of the silicon substrate 21 on the side where boron is implanted is subjected to the boron diffusion layer 22 during the thermal diffusion process.
A compound layer 23 of silicon and boron is formed on the surface of the semiconductor layer, and a silicon oxide film 24 containing boron is formed on the compound layer 23. The silicon oxide film 24 containing this impurity may be used for bonding as it is, but if it is left as it is, the compound layer 23 remains on the surface on which the diaphragm is formed. It becomes difficult.

Then, as shown in FIG. 3C, the silicon substrate 21 is immersed in a hydrogen fluoride solution to remove the silicon oxide film 24 on the surface, and then mixed with a hydrogen fluoride solution and an aqueous nitric acid solution. By dipping in the liquid, the silicon and boron compound layer 23 formed on the surface of the silicon substrate 21 is removed.

Next, as shown in FIG.
(Chemical Mechanical Polishing) or the like, and the surface is polished. In the present CMP technology, if the polishing amount is 0.1 μm, the surface roughness can be finished to a Ra value of about 0.2 nm (mirror finish of a level that enables direct bonding sufficiently), and the polishing amount is reduced. By setting the diffusion conditions in consideration of the above, the diaphragm can be formed with high accuracy.

Thereafter, as shown in FIG. 3E, the entire wafer is oxidized by a thermal oxidation method to form a silicon oxide film 25 on the entire surface of the silicon substrate 21 (including the high-concentration boron diffusion layer 22). At this time, the thickness of the silicon oxide film 25 was grown to about 200 nm.

Next, a process of manufacturing an electrode substrate in a third embodiment of the method of manufacturing an electrostatic actuator according to the present invention will be described with reference to FIG. Here, as shown in FIG. 1A, a silicon substrate 5 serving as an electrode substrate 2 is formed.
As one, it has P-type polarity and its crystal plane orientation is (10
In (0), a silicon substrate, whose surface to be bonded to the diaphragm substrate is mirror-finished, here, a silicon wafer is used.

Then, as shown in FIG. 3B, a silicon oxide film 52 serving as a buffer oxide film is formed on the surface of the silicon substrate 51 by a thermal oxidation method. Subsequently, as shown in FIG. 3C, a silicon nitride film 53 is deposited on the silicon substrate 51 by a method such as CVD, and a photoresist is applied on the silicon nitride film 53.

Thereafter, the photoresist is patterned so as to be opened only in a region to be the electrode forming groove 12 for forming the electrode 10, and the photoresist is used as a mask.
After etching the silicon nitride film 53 to form a mask of the silicon nitride film 53 having the opening 54, the photoresist is removed.

Then, using the silicon nitride film 53 as a mask, thermal oxidation such as pyro-oxidation (wet oxidation) or dry oxidation is performed to selectively oxidize the opening 54 of the silicon nitride film 53 (LOCOS: Local Oxidation). of
Silicon). At this time, the silicon oxide film 55 is
It was grown to a thickness of 000 nm. Such LOC
When the OS is performed, the thickness at which the silicon substrate 51 is oxidized (the oxidized region 56 of the silicon substrate 51) and the thickness of the portion where the silicon oxide film 55 protrudes from the surface of the silicon substrate 53 become approximately 1: 1.

Thereafter, when the silicon oxide film 55 is completely removed by dipping in a hydrogen fluoride solution, a groove 57 having a depth of about 1500 nm is formed in the silicon substrate 53. Further, the silicon substrate 51 is subjected to thermal oxidation (sacrifice oxidation) such as pyro-oxidation (wet oxidation) or dry oxidation to form a silicon oxide film having a thickness of about 200 nm. As shown in (1), the silicon oxide film is completely removed with a hydrogen fluoride solution.

The purpose of this sacrificial oxidation is to eliminate the problem of bonding with the diaphragm substrate caused by forming a gentle slope 58 at the end of the groove formed in the silicon substrate 51 by the LOCOS method. .

That is, on a surface such as an end of a groove formed in the silicon substrate 51 by the LOCOS method, where a predetermined crystal plane is not formed, a surface having a high oxidation rate protrudes and is oxidized. It is difficult to obtain a proper oxide film thickness, and in general, it tends to have a shape protruding above the bonding surface at a corner.

When a surface close to such a line is formed,
The temperature (1200 ° C.) is such that the area that can be directly bonded to the diaphragm substrate becomes very narrow and the silicon oxide film itself is thermally deformed.
If the bonding temperature is not increased to about (above the level), bonding will not be achieved. However, if the temperature is increased to such a temperature that the silicon oxide film itself is thermally deformed, the silicon oxide film itself is deformed, so that it is difficult to obtain the gap accuracy of the actuator, and it is possible to withstand such a high temperature. It becomes difficult to select an electrode material.

Therefore, in the present invention, by performing sacrificial oxidation before forming the gap layer, a surface higher than the bonding surface is prevented from being generated. By performing the sacrificial oxidation in this way, the silicon substrate 51 itself is also oxidized more in the portion where the oxidation rate is high, and after the sacrificial oxide layer is removed, as shown in FIG. So that the thickness of the silicon substrate 5
When 1 is oxidized, the silicon substrate 51 can be an electrode substrate having no region protruding from the joint surface with the diaphragm.

After that, the electrode 13 and the insulating film 15 are formed on the silicon substrate 51. In addition, the diaphragm board 1 after that
This step is performed in the same manner as described above.

As described above, by using a silicon wafer as an electrode substrate, forming a silicon nitride film on a portion other than the electrode formation region of the silicon wafer, and selectively thermally oxidizing the electrode formation region, After growing the oxide film until the thickness of the gap layer and the electrode is reached, the oxide film and the nitride film are removed to form a gap layer on the silicon substrate, and then, after performing a surface oxidation that is a sacrificial oxidation, This oxide film is removed, and a silicon oxide film is further formed on the entire surface to a thickness necessary for insulation between the electrode and the silicon substrate by a thermal oxidation method, and then the electrode is formed and joined to the diaphragm substrate. In addition, a low-cost electrode substrate can be formed by a simple process, and a highly accurate gap can be obtained.

Next, the manufacturing process of the diaphragm substrate in the fourth embodiment of the manufacturing method of the electrostatic actuator according to the present invention will be described with reference to FIG. Here, SOI (Silicon On I) is used as a silicon substrate serving as a diaphragm substrate.
(SOI) wafer (S)
OI substrate) 61 is used.

In the SOI substrate 61, the silicon surface 62 for engraving the diaphragm (forming a concave portion serving as a liquid chamber) has P-type polarity, its crystal plane orientation is (110), and The silicon surface 63 serving as the diaphragm is finished to have a thickness of the diaphragm (about 2 μm in this case), and has a crystal plane orientation of (100). These silicon surfaces 62
The silicon oxide film 64 which is an insulating layer between
A 00 nm SOI substrate was used. In addition, both surfaces are polished to a mirror surface.

When the SOI substrate 61 is used, as shown in FIG.
After etching, a concave portion serving as a liquid chamber is carved in the silicon surface 62 by etching, and etching is stopped using the silicon oxide film 64 as an etching stop layer.
0 is obtained.

By using the SOI wafer in this manner, the vibration plate 10 and the electrode substrate 2 can be bonded with a good surface roughness of the bonding surface, and the direct bonding with the electrode substrate 2 is improved. be able to. Also, since the intermediate insulating layer of the SOI wafer can be used as an etching stop layer,
The surface roughness of the diaphragm 10 on the opposite electrode side (liquid chamber side) is also reduced, and a diaphragm having vibration characteristics close to ideal conditions can be obtained.

Next, the manufacturing process of the diaphragm substrate in the fifth embodiment of the method of manufacturing the electrostatic actuator according to the present invention will be described with reference to FIG. Also in this case, as shown in FIG. 13A, the same SOI wafer (SOI substrate) 61 as in the fourth embodiment is used as a starting material, and as shown in FIG. Oxidation is performed to a thickness of about 200 nm by pyro-oxidation (wet oxidation) or dry oxidation, and a silicon oxide film 65 is formed on the bonding surface side.

The silicon oxide film 65 can prevent the characteristic deterioration due to the discharge between the vibration plate 10 and the electrode 13 vibrating due to the electrostatic force, and can stabilize the long-term vibration characteristic.

However, when the silicon oxide film is formed on the electrode side surface of the diaphragm 10 and the direct bonding with the silicon oxide film on the electrode substrate side is performed, the bonding temperature becomes high. That is, when the direct bonding of the silicon wafer is performed, the bonding surface is made of silicon and silicon, the silicon and silicon oxide film, or the silicon oxide film and silicon oxide film. The temperatures are different, and the temperature is usually lowest in the case of silicon and silicon, followed by silicon and the silicon oxide film, and then in the case of the silicon oxide film and the silicon oxide film at the highest temperature of about 1100 ° C. Temperature is needed. Also, in the case of bonding silicon and silicon, voids are likely to occur due to a bonding reaction at the interface during bonding,
Also in this case, it is necessary to fire at a temperature at which voids do not occur.

In each of the above embodiments, an example was described in which the electrostatic actuator according to the present invention was applied to a droplet discharge head. However, the present invention is not limited to this. For example, droplets other than ink, such as The present invention can also be applied to a droplet discharge head that discharges the liquid resist described above, or can be applied to an actuator portion of a micromotor as an electrostatic actuator.

Also, the droplet discharge head has been described as a side shooter system in which the diaphragm displacement direction and the nozzle droplet discharge direction are the same, but a side shooter system in which the diaphragm displacement direction and the nozzle droplet discharge direction are orthogonal to each other. You can also.

[0081]

As described above, according to the electrostatic actuator of the first aspect, the silicon substrate for directly joining the diaphragm substrate and the electrode substrate without using an adhesive and for forming a gap. An oxide film is provided on the electrode substrate side, and the bonding surface on the diaphragm substrate side is configured to be flat.
The entire joining surface can be used directly for joining, so that joining strength and gap accuracy are improved, and a low-cost, high-density actuator can be obtained.

According to the method of manufacturing an electrostatic actuator of claim 3, the semiconductor substrate is formed by using a silicon wafer in which a high-concentration impurity is implanted on the vibration substrate on the side of the semiconductor substrate bonded to the electrode substrate. After removing an oxide film layer or a compound layer formed on the side of the joint surface with the electrode substrate, the structure is joined to the electrode substrate, so that the electrostatic actuator according to the present invention can be manufactured at low cost.

According to the method of manufacturing an electrostatic actuator of the fourth aspect, a semiconductor substrate having an SOI structure is used as a diaphragm substrate, and silicon oxide is formed on a bonding surface of the semiconductor substrate with an electrode substrate by a thermal oxidation method. Since the film is formed and then joined to the electrode substrate, the electrostatic actuator according to the present invention can be manufactured, and the characteristics of the diaphragm are improved.

According to the method of manufacturing an electrostatic actuator of the fifth aspect, a semiconductor substrate having an SOI structure is used as a diaphragm substrate, and a natural oxide film formed on a joint surface of the semiconductor substrate with an electrode substrate is formed. After removal, the structure is joined to the electrode substrate, so that the electrostatic actuator according to the present invention can be manufactured and the characteristics of the diaphragm are improved.

According to the method of manufacturing an electrostatic actuator of the sixth aspect, a silicon wafer is used as an electrode substrate, and a silicon oxide film is formed on the entire surface of the silicon wafer by a thermal oxidation method. Etching to a depth that is small, electrodes are formed in the etched region, and then the structure is joined to the diaphragm substrate, so that the electrostatic actuator according to the present invention can be manufactured at low cost. And the gap accuracy is improved.

According to the method of manufacturing an electrostatic actuator of the present invention, a silicon wafer is used as an electrode substrate, and a silicon nitride film is formed on a portion other than the electrode formation region of the silicon wafer. By selectively oxidizing thermally, after growing an oxide film to the required thickness of the gap layer and the electrode, by removing the oxide film and the nitride film,
After forming a gap layer on the silicon substrate, and then performing surface oxidation as a sacrificial oxidation, the oxide film is removed, and the entire surface is further thermally oxidized to a thickness necessary for insulation between the electrode and the silicon substrate. After the silicon oxide film is formed, the electrodes are formed and the structure is joined to the diaphragm substrate, so that the electrostatic actuator according to the present invention in which the diaphragm and the electrodes are not parallel can be manufactured at low cost. .

According to the droplet discharge head of the present invention, since the electrostatic actuator is constituted by the electrostatic actuator of the present invention, a low-cost and high-density ink jet head can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view in the longitudinal direction of a diaphragm of an inkjet head having an electrostatic actuator according to the present invention.

FIG. 2 is a schematic cross-sectional explanatory view of the head in a lateral direction of a diaphragm.

FIG. 3 is an explanatory view illustrating a process of manufacturing a silicon substrate to be a diaphragm substrate in the first embodiment of the method of manufacturing an electrostatic actuator according to the present invention.

FIG. 4 is an explanatory view for explaining a manufacturing process of the electrode substrate.

FIG. 5 is an explanatory view similarly illustrating a process of joining a diaphragm substrate and an electrode substrate to form an ink jet head.

FIG. 6 is an explanatory view illustrating a manufacturing process of a silicon substrate to be a diaphragm substrate in a second embodiment of the method of manufacturing an electrostatic actuator according to the present invention.

FIG. 7 is an explanatory view illustrating a process of manufacturing an electrode substrate in a third embodiment of the method of manufacturing an electrostatic actuator according to the present invention.

FIG. 8 is an explanatory view illustrating a silicon substrate serving as a diaphragm substrate in a fourth embodiment of the method of manufacturing an electrostatic actuator according to the present invention.

FIG. 9 is an explanatory view illustrating a process of manufacturing a silicon substrate to be a diaphragm substrate in a fifth embodiment of the method of manufacturing an electrostatic actuator according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... diaphragm board, 2 ... electrode board, 3 ... nozzle plate,
Reference numeral 5: nozzle, 6: liquid chamber, 7: fluid resistance portion, 8: common ink channel, 11: silicon oxide film, 12: electrode forming groove, 1
3 ... electrode, 14 ... gap, 15 ... insulating protective film, 21,
31: silicon substrate; 61: SOI substrate.

Claims (8)

[Claims] 1. A diaphragm substrate on which a diaphragm is formed and an electrode substrate on which individual electrodes are formed are joined by forming a gap with a silicon oxide film serving as an insulating film, and a voltage is applied between the electrode and the diaphragm. In the electrostatic actuator in which the diaphragm is deformed by applying pressure, the diaphragm substrate and the electrode substrate are directly bonded without using an adhesive, and a silicon oxide film for forming the gap is formed. An electrostatic actuator provided on the electrode substrate side, wherein a joint surface on the diaphragm substrate side is flat. 2. A method of manufacturing an electrostatic actuator according to claim 1, wherein the method includes the steps of:
Using a silicon wafer in which a high-concentration impurity is implanted on the side of the diaphragm substrate to be bonded to the electrode substrate, forming an oxide film on the side of the silicon wafer to be bonded to the electrode substrate, A method for manufacturing an electrostatic actuator, comprising: 3. The method of manufacturing an electrostatic actuator according to claim 1, wherein a silicon wafer in which a high-concentration impurity is implanted on the vibration substrate on a bonding surface side with the electrode substrate. A method for manufacturing an electrostatic actuator, comprising removing an oxide film layer and a compound layer generated on a bonding surface side of the silicon wafer with the electrode substrate, and then bonding the silicon wafer to the electrode substrate. 4. The method for manufacturing an electrostatic actuator according to claim 1, wherein a semiconductor substrate having an SOI structure is used as the diaphragm substrate, and the semiconductor substrate is bonded to the electrode substrate. A method for manufacturing an electrostatic actuator, comprising: forming a silicon oxide film on a surface by a thermal oxidation method; and bonding the silicon oxide film to the electrode substrate. 5. The method for manufacturing an electrostatic actuator according to claim 1, wherein a semiconductor substrate having an SOI structure is used as the diaphragm substrate, and the semiconductor substrate is bonded to the electrode substrate. A method for manufacturing an electrostatic actuator, comprising removing a natural oxide film formed on a surface and then bonding the same to the electrode substrate. 6. The method for manufacturing an electrostatic actuator according to claim 1, wherein a silicon oxide film is formed on the entire surface of the silicon wafer by a thermal oxidation method using a silicon wafer as the electrode substrate. Etching to a depth corresponding to the thickness of the individual electrode and the thickness of the gap layer, forming the individual electrode in the etched region, and then bonding to the diaphragm substrate. Manufacturing method of die-type actuator. 7. The method for manufacturing an electrostatic actuator according to claim 1, wherein a silicon wafer is used as the electrode substrate, and a silicon nitride film is formed on a portion of the silicon wafer other than the electrode formation region. After the formation, by selectively thermally oxidizing the electrode forming region, an oxide film is grown until the required gap layer and the thickness of the individual electrode are obtained, and then the oxide film and the nitride film are removed. Forming a gap layer on a silicon substrate, and then performing surface oxidation as a sacrificial oxidation, removing the oxide film, and further performing thermal oxidation on the entire surface to insulate the individual electrodes from the silicon substrate. A method for manufacturing an electrostatic actuator, comprising: forming a silicon oxide film to a thickness, forming the individual electrodes, and bonding the individual electrodes to the diaphragm substrate. 8. An actuator comprising a nozzle for discharging ink droplets, a discharge chamber communicating with the nozzle, a vibration plate forming a wall surface of the discharge chamber, and individual electrodes arranged opposite to the vibration plate with a predetermined gap therebetween. 11. A droplet discharge head that discharges ink droplets from the nozzles by applying a voltage between the diaphragm and the individual electrodes, wherein the actuator includes the electrostatic actuator according to claim 1. A droplet discharge head comprising a mold actuator.