JP2002240276A - Ink jet head and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that highly accurate bonding can not be effected with high accuracy. SOLUTION: A silicon substrate is employed as a channel substrate 1 for forming a diaphragm 10 and an electrode substrate 2 for forming an electrode 12. The channel substrate 1 and the electrode substrate 2 are bonded through a silicon oxide film 14 exhibiting softening properties at low temperature and a polish stopper 13 having a low polish rate is provided on the side of the electrode substrate 2 for forming a silicon oxide film 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet head and a method for manufacturing the same.

[0002]

2. Description of the Related Art In general, as an ink jet head used in an image recording apparatus (including an image forming apparatus) such as a printer, a facsimile, a copying machine, a plotter, etc., a nozzle for discharging ink droplets and a discharge for communicating with the nozzle are provided. A chamber (also referred to as an ink flow path, an ink chamber, a liquid chamber, a pressure chamber, a pressure generation chamber, a pressurized chamber, a pressurized liquid chamber, and the like) and a diaphragm serving also as a first electrode forming a wall surface of the discharge chamber And an electrode (second electrode) opposed thereto, and an electrostatic inkjet head that discharges ink droplets from nozzles by deforming and displacing a diaphragm with electrostatic force is known.

In such an electrostatic ink jet head, the mechanical deformation characteristics of the diaphragm greatly affect the ink droplet ejection characteristics, and it is necessary to reduce the thickness of the diaphragm and to control it with high precision. A high-concentration boron diffusion layer is formed on a substrate, and the silicon substrate is anisotropically etched using the high-concentration boron diffusion layer as an etching stop layer, thereby forming a thin film diaphragm with high precision thickness.

In the electrostatic ink jet head, the distance between the diaphragm and the electrodes, that is, the gap size needs to be controlled with extremely high precision. Therefore, for example, the substrate for forming the diaphragm and the substrate for forming the electrodes are required. When a silicon substrate is used, bonding is performed by using a direct bonding method that is used for manufacturing an SOI (silicon-on-insulator) wafer and that can obtain a reliable and strong bonding force.

For example, as disclosed in Japanese Patent Application Laid-Open No. 6-23986, a first silicon substrate in which a cavity to be a nozzle and a discharge chamber is formed and a second silicon substrate to be a diaphragm are formed. The second silicon substrate on which the high-concentration p-type silicon layer is formed and the first silicon substrate are bonded by a silicon-silicon direct bonding method, and the bonded second silicon substrate is subjected to alkali anisotropic etching. In some cases, a diaphragm is formed by leaving a p-type silicon layer.

Further, as disclosed in JP-A-9-267479, a high-concentration p-type silicon layer of a first silicon substrate having a high-concentration p-type silicon layer formed on one side and a nozzle are formed. In some cases, the diaphragm is formed by directly bonding the second silicon substrates to each other and bonding them together by direct bonding at a rate of temperature rise from room temperature of 5 ° C./min or less.

When such a direct bonding of silicon substrates is used, the bonding temperature is 1100 ° C. to 1200 ° C.
In order to enable bonding at a lower temperature, for example, as disclosed in Japanese Patent Application Laid-Open No. 9-286101, a silicon oxide A sodium silicate layer formed by diluting an aqueous solution of sodium silicate consisting of Na ₂ O and water using spin coating to form a sodium silicate layer. There is known a method of obtaining a bonded wafer by applying a load from the opposite side of the mating surface and performing heating in an atmosphere of 800 ° C. or more and 1200 ° C. or less.

Further, as disclosed in Japanese Patent Application Laid-Open No. 10-286954, after the first silicon substrate and the second silicon substrate are washed and dried, the polysilazane is spin-coated on the bonding surface side of the first silicon substrate. After the layer is formed and the polysilazane layer is formed, the first silicon substrate and the second silicon substrate are immediately bonded to each other, a load is applied from the opposite side of the bonding surface, and the wafer is heated at 450 ° C. for 1 hour to bond the bonded wafer. Methods of obtaining are also known.

[0009]

As described above, when the substrate on which the diaphragm is formed and the substrate on which the electrode is to be bonded are joined together, the heat resistance of the substrate on which the electrode is formed and the high-concentration boron For example, when a diffusion layer is used, the redistribution of boron directly affects the thickness and variation of the diaphragm, so it is necessary to lower the bonding temperature.

In this case, in the case where water glass (sodium silicate solution) is used for bonding the two substrates in order to lower the bonding temperature, this material shows good bonding at a low temperature, but has a low water content. Due to the large content, the influence of gas (such as water vapor) emitted from the film cannot be avoided. Further, in the case of using polysilazane for bonding the two substrates, although the reliability is excellent, the problem of outgassing is inherent.

Also, the surface properties (surface roughness: Ra) of the bonding surface of both substrates are very strict (Ra <0.2n).
m or less), and it is difficult to obtain high bonding reliability in bonding substrates having undergone various processes.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide an ink jet head realizing low cost, high accuracy, high density, and high reliability, and a method of manufacturing the same.

[0013]

In order to solve the above-mentioned problems, in the ink jet head according to the present invention, the first substrate on which the vibration plate is provided and the second substrate on which the electrodes are provided are a silicon substrate, and the first substrate and the first substrate are provided. The two substrates are bonded together via a silicon oxide film which is soft at low temperature, and a polishing stopper having a small polishing rate is provided on the substrate side on which the silicon oxide film is provided.

Here, it is preferable that the silicon oxide film has a composition exhibiting softness at a temperature not exceeding 1000 ° C. Preferably, the silicon oxide film contains phosphorus and / or boron. Further, it is preferable that the polishing stopper is a silicon nitride film.

A method for manufacturing an ink jet head according to the present invention is a method for manufacturing an ink jet head according to the present invention, wherein a substrate surface on which a silicon oxide film is provided is flattened by a CMP polishing step in which polishing is stopped by a polishing stopper. This is a configuration that can be used.

The method for manufacturing an ink-jet head according to the present invention is a method for manufacturing an ink-jet head according to the present invention, wherein the silicon oxide film is subjected to a heat treatment at a temperature equal to or higher than the reflow property. The first substrate and the second substrate are joined by heating at a temperature of less than or less than 1000 ° C.

[0017]

Embodiments of the present invention will be described below with reference to the accompanying drawings. First, an embodiment of an inkjet head to which the present invention is applied will be described with reference to FIGS. 1 is an exploded perspective view of the head, FIG. 2 is a top view of the same head excluding a nozzle plate, FIG. 3 is a cross-sectional view of the same head in a longitudinal direction of the diaphragm, and FIG. It is principal part enlarged sectional explanatory drawing of a board short direction.

This ink jet head has a flow path substrate 1 as a first substrate using a single crystal silicon substrate, and an electrode as a second substrate using a single crystal silicon substrate provided below the flow path substrate 1. It has a structure in which a substrate 2 and a nozzle plate 3 which is a third substrate provided on the upper side of the flow path substrate 1 are laminated, a plurality of nozzles 4 for discharging ink droplets, and an ink flow path through which each nozzle 4 communicates. A certain discharge chamber 6, a common liquid chamber 8 communicating with each discharge chamber 6 via a fluid resistance portion 7 also serving as an ink supply path, and the like are formed.

In the flow path substrate 1, there are formed a plurality of discharge chambers 6 with which the nozzles 4 communicate with each other, and a concave portion forming a diaphragm 10 (also serving as an electrode) which is a bottom which is a wall surface of the discharge chamber 6. . A silicon oxide film (S) for preventing a short circuit between electrodes is formed on the surface of the diaphragm 10 in the out-of-plane direction (the electrode substrate 2 side).
An insulating film 11 made of an iO ₂ film) is formed.

Here, the flow path substrate 1 is, for example, (110)
When a single-crystal silicon substrate having a plane orientation is used, a high-concentration p-type impurity (for example, boron) is implanted in advance in the thickness of the diaphragm to form a high-concentration boron diffusion layer serving as an etching stop layer. After that, the concave portion which becomes the discharge chamber 6 is K
By performing anisotropic etching using an alkaline etching solution such as an OH aqueous solution, the high-concentration boron diffusion layer becomes an etching stop layer at this time (the etch rate becomes extremely small), and the diaphragm 10 is formed with high precision. Is done.
Examples of the high-concentration P-type impurity include gallium and aluminum in addition to boron, but boron is generally used in the semiconductor field.

As the flow path substrate 1, an SOI (Silic) in which a base substrate and an active layer substrate are bonded via an oxide film.
On On Insulator) substrates can also be used.
Currently, for the purpose of manufacturing high-performance semiconductor devices,
A wafer having a silicon active layer of about 3 μm (this active layer is used for the diaphragm 10 in an ink jet head) can be easily obtained, and cost can be reduced.

An oxide film (thermal oxide film) 2a is formed on the electrode substrate 2 by a thermal oxidation method using a single crystal silicon substrate, and a silicon oxide film 11 and a vibration plate 10 are formed on the thermal oxide film 2a. Opposing electrodes 12 are formed on the same plane, and a polishing stopper 13 having a small polishing rate is formed on the silicon oxide film 11.
A silicon oxide film 14 having a composition exhibiting softening properties at a low temperature is provided through the substrate, a recess 16 serving as a gap 15 between the diaphragm 10 and the electrode 12 is formed in the silicon oxide film 14, and a predetermined ( Gap 1 (for example, about 0.3 μm)
An electrostatic microactuator is constituted by the vibration plate 10 and the electrode 12 which face each other via 5. Note that the bottom of the recess 16 formed in the silicon oxide film 14 becomes the electrode protection film 17 on the electrode 12, and the portion other than the recess 16 becomes the gap spacer portion.

Here, the electrode 12 has a two-layer structure of a tungsten side film and a polysilicon film, as will be described later. In addition to this, gold or Al, which is generally used in a process of forming a semiconductor element, is used. A metal material such as Cr or Ni, a high melting point metal such as Ti or TiN, or a polycrystalline silicon film doped with impurities can also be used. The electrode 12 extends to the outside to form an electrode pad portion 12a, an opening 18 corresponding to the electrode pad portion 12a is formed in the silicon oxide film 14, and a driver as an electrode head driving circuit is formed in the electrode pad portion 12a. An FPC cable on which the IC 19 is mounted by wire bonding or the like is connected via an anisotropic conductive film or the like.

A silicon nitride film is used as the polishing stopper 13 formed on the silicon oxide film 11, that is, on the side of the electrode substrate 2 of the silicon oxide film 14 having a composition exhibiting softness at a low temperature. The polishing stopper 13 is provided in a portion of the surface of the silicon oxide film 11 where the distance between the electrodes 12 is wide (the electrode pattern is sparse). This polishing stopper 1
After the formation of the silicon oxide film 3, the surface on the electrode substrate 2 side (the surface of the silicon oxide film 11) is subjected to CMP (chemical-mechani
By flattening by cal-polishing (chemical mechanical polishing), the surface of the electrode substrate 2 can be evenly flattened.

Further, as the silicon oxide film 14 having a composition exhibiting softening properties at low temperature, for example, a silicon oxide film containing boron (BSG) (BSG film: Boro-Silicate)
Glass) is used, but it does not contain boron and contains phosphorus (PSG film: Phospho-Silicate Glass),
Alternatively, a silicon oxide film containing phosphorus and boron (BPSG)
Membrane: BoroPhospho-Silicate Glass) can also be used. The silicon oxide film containing phosphorus and / or boron is a silicon oxide film having a composition exhibiting softness at 1000 ° C. or lower.

The electrode substrate 2 has an ink inlet 9 for supplying ink to the common liquid chamber 8. By bonding and connecting an ink supply pipe to the ink intake port 9, the common liquid chamber 8, the discharge chamber 6, and the like can be filled with ink supplied from the ink tank (not shown) through the ink intake port 9. It becomes possible. The ink to be used is prepared by dissolving or dispersing a surfactant such as ethylene glycol and a dye or pigment in a main solvent such as water, alcohol and toluene. Further, if a heater or the like is attached to the inkjet head, hot melt ink can be used.

The nozzle plate 3 has a large number of nozzles 4 and a groove for forming a fluid resistance portion 7 for communicating the common liquid chamber 8 and the discharge chamber 6. here,
A water-repellent film is formed on the ink ejection surface (nozzle surface side). The nozzle plate 3 is made of a glass substrate, a plastic plate, stainless steel or Kovar (Fe29-Ni-17).
A metal plate such as Co) or a silicon substrate can be used.

The flow path substrate 1 and the electrode substrate 2 are directly joined via a silicon oxide film 14 having a composition exhibiting softness at a low temperature. As described above, by joining the flow path substrate 1 and the electrode substrate 2 via the silicon oxide film 14 having a composition exhibiting softness at a low temperature, particularly 1000 ° C. or lower,
After the silicon oxide film 14 is formed, reflow is performed by a heat treatment at a temperature equal to or higher than the melting point, thereby obtaining a surface property that enables good direct bonding.

Specifically, immediately after the film formation, the surface roughness Ra value was about 1 to 3 nm in the evaluation of the surface properties using the AFM. The surface property which can be obtained was obtained. Further, moisture, hydrogen gas, and the like are released, and if the temperature does not exceed the heat treatment temperature in the subsequent bonding process, bonding failure due to outgassing does not occur. Also,
By setting the bonding temperature to 1000 ° C. or less, the electrode 12
In this case, it is possible to prevent an adverse effect when the diaphragm 10 is formed of a high-concentration impurity diffusion layer.

As the silicon oxide film 14, a silicon oxide film containing phosphorus and / or boron, for example, a BSG film, P
By using an SG film, a BPSG film, or the like, the melting point of the silicon oxide film can be easily reduced to form a silicon oxide film having a composition exhibiting softening properties at 1000 ° C. or less. Thereafter, by performing reflow by heat treatment, surface properties that enable good direct bonding are obtained.

By providing the polishing stopper 13 having a small polishing rate on the electrode substrate 2 side on which the silicon oxide film 14 is provided, the electrode substrate 2 side can be flattened with high precision. By using the low melting point silicon oxide film 14 containing phosphorus and / or boron, the bonding temperature can be lowered, and the surface properties of the bonding surface (surface roughness: R <0.3)
temperature range that does not require strict specifications of about 10 nm or less, avoids poor bonding (unbonded) due to poor planarization of the substrate, and does not affect the electrode 12 or the diaphragm 10 made of a high-concentration impurity diffusion layer. In this way, highly reliable bonding can be achieved.

In this case, by using a silicon nitride film having a high polishing selectivity with respect to the silicon oxide film 11 as the polishing stopper 13, the side of the electrode substrate 2 on which the silicon oxide film 14 is provided with high precision, that is, with high controllability, is flattened. Will be able to

In this ink jet head, since the opening of the gap 15 on the electrode pad 12a side is also hermetically sealed with the silicon oxide film 14, moisture and foreign matter enter the gap 15 and the vibration plate 10 is moved. Displacement is prevented, and a change in the displacement characteristic of the diaphragm 10 due to the flow of air is prevented. At this time, by setting the gap 15 in a substantially vacuum state, extra energy such as compression of gas in the gap 15 at the time of deformation of the diaphragm is not required, so that low voltage driving can be achieved.

The operation of the ink jet head thus configured will be briefly described. The vibration plate 10 is used as a common electrode, the electrode 12 is used as an individual electrode, and the vibration plate 10 and the electrode 12 are used.
When a driving waveform is applied from the driver IC 19 to the diaphragm 10, an electrostatic force (electrostatic attraction) is generated between the diaphragm 10 and the electrode 12, and the diaphragm 10 is deformed and displaced toward the electrode 12. As a result, the internal volume of the discharge chamber 6 is expanded and the internal pressure is reduced, so that the ink is filled from the common liquid chamber 8 into the discharge chamber 6 via the fluid resistance portion 7.

Next, when the voltage application to the electrode 12 is stopped,
The electrostatic force stops working, and the diaphragm 10 is restored by its own elasticity. With this operation, the internal pressure of the ejection chamber 6 increases, and ink droplets are ejected from the nozzles 5. When a voltage is applied to the electrode again, the diaphragm 10 is drawn toward the electrode 12 again by the electrostatic attraction force. Therefore, by applying a drive voltage between the diaphragm 10 and the electrode 12 according to the recorded image, ink droplets can be ejected according to the recorded image.

Next, a method for manufacturing an ink jet head according to the present invention will be described with reference to FIGS. First, as shown in FIG. 5A, a silicon substrate having a thickness of about 625 μm and a crystal plane orientation of (100) is used as the electrode substrate 2, and a thermal oxide film 2 a is formed on one side of the electrode substrate 2. To a thickness of 2 μm.

Then, a polysilicon film 21 is deposited to a thickness of 200 nm on the entire surface of the thermal oxide film 2a by the CVD method, and phosphorus or arsenic is ion-implanted and heat treatment for activation is performed. Although the method of ion implantation is used here, the polysilicon film 21 may be doped with phosphorus glass or the like by spin coating or heat treatment.

Further, a 150-nm tungsten silicide film 22 is formed on the surface of the polysilicon film 21 by sputtering.
m. Before the sputtering of the tungsten silicide film 22, the surface of the polysilicon film 21 is reverse-sputtered (etched) with Ar to be cleaned (removal of a natural oxide film or the like), whereby the polysilicon film 21 and the tungsten silicide film 22 are removed. Therefore, it is preferable to continuously perform the removal of the natural oxide film and the formation of the tungsten silicide film 22 using a multi-chamber sputtering apparatus because the adhesion of the tungsten oxide film can be improved and high reliability can be secured.

Then, as shown in FIG. 2B, the tungsten silicide film 22 and the polysilicon film 21 are patterned into an electrode shape by a known photolithography technique and a dry etching technique, and are formed on the thermal oxide film 2a of the electrode substrate 2. Then, an electrode 12 having a laminated structure of a polysilicon film 21 and a tungsten silicide film 22 is formed. Note that the thickness of the tungsten silicide film 22 is set to 150 nm.
The sheet resistance of the electrode 12 is 10Ω / □
It becomes below. Further, as a material of the electrode 12, as described above, another high melting point metal or a laminated structure of these metals may be used.

Next, as shown in FIG.
A silicon oxide film 11 is deposited to a thickness of 350 nm on the entire surface of the electrode substrate 2 on which is formed by CVD. At this time, a protrusion 11a and a recess 11b are formed in the silicon oxide film 11 depending on the presence or absence of the electrode 12 on the electrode substrate 2. As the silicon oxide film 11, an oxide film (reflow film) containing impurities such as B (boron) and / or P (phosphorus) can be used similarly to the silicon oxide film 14.

Further, after a silicon nitride film 23 is deposited on the surface of the silicon oxide film 11 to a thickness of 20 μm, it is patterned by a well-known photolithography technique and a dry etching technique as shown in FIG. ,
A polishing stopper 1 made of a silicon nitride film 23 at a portion where the distance between the electrodes 12 and 12 is large (the electrode pattern is sparse).
Form 3

Thereafter, as shown in FIG.
The silicon oxide film 11 on the surface of the electrode substrate 2 is flattened by polishing. In this CMP polishing step, as shown in FIG. 7, a polishing pad 31 provided on a polishing plate 30 rotating at a predetermined table speed is rotated against a wafer W attached to a polishing head 32 rotating at a predetermined carrier speed. Then, the surface to be polished (the surface of the silicon oxide film 11) of the electrode substrate 2) is pressed with a predetermined pressure, and the polishing is performed while the slurry liquid 33 is dropped.

Here, the slurry liquid 33 is SS2
5 (manufactured by Cabot Corp., trade name) diluted 1: 1 with ultrapure water.
/ Suba400 (a laminated structure of rigid polyurethane foam / polyester fiber nonwoven fabric).

In this case, the polishing conditions were such that table speed / carrier speed = 40 rpm / 29 rpm and polishing pressure = 200 g / cm ² .

At this time, the polishing proceeds from the polishing of the projections 11a of the silicon oxide film 11 and reaches the polishing stopper 13, but the silicon nitride film forming the polishing stopper 13 is hardly polished because the polishing rate is small. So
The portion of the concave portion 11b located between the electrodes 12, 12 is not polished, and the surface of the silicon oxide film 11 of the electrode substrate 2 is flattened with high precision. In this case, the polishing pad 31 comes into contact with the polishing stopper 13 so that the torque of the carrier 34 increases. Therefore, by detecting the increase in the torque and stopping the polishing, the polishing amount can be controlled with high precision.

On the other hand, when the polishing stopper 13 is not provided, as shown in FIG. 8, as the polishing proceeds, the concave portion 11 between the electrodes 12 of the silicon oxide film 11 is formed.
b is also polished, and after polishing, the silicon oxide film 11 of the electrode substrate 2 is formed in a portion where the distance between the electrodes 12 is wide (the electrode pattern is sparse).
Since the concave portion 11c is formed on the surface, defective bonding in direct bonding with the flow path substrate 1 in a later step is likely to occur.

As described above, the gap between the electrodes 12 is buried with the silicon oxide film 11 for flattening, and the silicon oxide film 14 for forming a gap spacer portion and a gap concave portion is laminated on the silicon oxide film 11 as described later. By providing a polishing stopper 13 made of a material having a smaller polishing rate and a larger rate difference than the silicon oxide film 11 as the buried oxide film, the surface of the electrode substrate 2 provided with the electrodes 12 is flattened with high precision. Therefore, it is possible to prevent the occurrence of defective direct bonding.

In this case, when a silicon nitride film is used as the polishing stopper 13, the polishing rate of the silicon nitride film is much lower than that of the silicon oxide film 11 (about 1/20), so that the CMP polishing is effectively stopped. And highly accurate flattening can be performed.

Returning to FIG. 6B, after the surface of the silicon oxide film 11 of the electrode substrate 2 is flattened as described above, the BPSG film 14a as the silicon oxide film 14 having a composition exhibiting softness at a low temperature. Is deposited to a thickness of about 300 nm over the entire surface of the wafer using a technique such as CVD (phosphorus concentration 4.5%, boron concentration 4.0%). In this case, the BPSG film 14a also has a role of protecting the electrode 12 and preventing oxidation.

It should be noted that the concentrations of phosphorus and boron are not limited to the above concentrations, and the silicon oxide film 14 may be a PSG film not containing boron or a BSG film not containing phosphorus.
As described above, an SG film or the like can be used. The emphasis here is on lowering the melting point by incorporating phosphorus and / or boron into the silicon oxide film.

Thereafter, the BPSG film 14a is heated at a temperature equal to or higher than the softening point and in a heat treatment for direct bonding (temperature 900
Reflow at a temperature higher than (° C). Due to this heat treatment, even when a very small step occurs due to the polishing stopper 13, the surface of the BPSG film 14a is flattened, and moisture, hydrogen gas, and the like contained in the BPSG film 14a are released. If the heat treatment temperature is not exceeded, no bonding failure due to outgassing will occur. Here, heat treatment was performed at 950 ° C. for 60 minutes for reflow. Immediately after the formation of the BPSG film 14a, the surface roughness Ra was about 1 to 3 nm in the evaluation of the surface properties using AFM. Surface properties were obtained.

Then, as shown in FIG.
The concave portion 1 is formed on the G film 14a by photolithography and etching so as to have a predetermined gap depth.
6, and an opening 18 is formed in a portion corresponding to the electrode pad portion 12a. In addition, even if the etching is wet etching using a hydrofluoric acid aqueous solution or the like,
Well-known dry etching may be used. Alternatively, the concave portion 16 in which the gap shape is in a non-parallel state may be formed by giving an inclination to the resist shape and performing etching using an argon (Ar) gas or the like. Also, the electrode pad portion 1
The opening 18 corresponding to 2a is not formed here, but the BPSG film 14a on the electrode pad 12a is formed in a later step.
May be formed when etching is removed by dry etching or the like.

Next, steps from bonding with the flow path substrate to completion of the ink jet head will be described with reference to FIGS. First, as the flow path substrate 1, FIG.
As shown in (a), a silicon substrate 41 having a crystal plane orientation of (110) and a thickness of 500 μm is used to diffuse boron into the silicon substrate 41 by a solid diffusion method to form a high-concentration boron diffusion layer 42. I do. The diffusion method is BB
A vapor diffusion method using r ₃ , an ion implantation method, a coating diffusion method in which B ₂ O ₃ is dispersed in an organic solvent and spin-coated on a wafer, or the like may be used.

For example, the silicon substrate 41 and the solid diffusion source are arranged facing each other and set in a furnace at 750 ° C. Nitrogen mixed with 0.25% oxygen is flowed into the furnace. The temperature of the furnace was raised to 1125 ° C. at a rate of 8 ° C./min, and held in that state for 50 minutes, and then lowered to 750 ° C. at a rate of 8 ° C./min. The formed silicon substrate 41 is obtained.

After that, the B ₂ O ₃ layer formed on the surface of the silicon substrate 41 is removed with hydrofluoric acid. A compound layer of silicon and boron is formed under the B ₂ O ₃ layer, and when it is removed, it can be removed by hydrofluoric acid by oxidizing. However, even if the compound layer is removed by fluorination and oxidized in this way, the silicon surface in which boron is diffused is roughened, and cannot be joined by direct joining performed later.

Therefore, the surface properties that can be directly bonded by CMP polishing (Ra = 5 μm area measured using AFM)
0.2 nm or less). In CMP polishing, the outermost surface is 1
Since it can be polished uniformly in the plane below 000Å,
The change of the high-concentration boron diffusion layer 42 is very small, and it is easy to determine the diffusion conditions in consideration of the polishing amount. Also, after oxidizing and treating with hydrofluoric acid to remove the compound layer, C
MP polishing may be performed, or the oxidized oxide film 11 may be
The oxide film 9 having good surface properties may be formed by MP polishing. Here, good surface properties (surface roughness Ra = 0.3) are obtained by thermally oxidizing a silicon substrate (high-concentration boron diffusion layer 42) provided with good surface properties by CMP.
nm or less).

Next, the steps up to the completion of the ink jet head will be described. As shown in FIG.
The silicon substrate 41 to be formed and the electrode substrate 2 are directly bonded.
Specifically, after cleaning each substrate 41, 2 using a substrate cleaning method known as RCA cleaning, a volume ratio of sulfuric acid and hydrogen peroxide (a mixed solution of sulfuric acid and hydrogen peroxide 2: 1 at a temperature of 100 ° C. or more) is used. ) To make the bonding surface hydrophilic so that the surface can be directly bonded. Then, after drying the substrates 41 and 42,
Pre-bonding is completed by superimposing the substrates 41 and 2 under reduced pressure (room temperature) and pressing them under reduced pressure.

Here, the important point is that the surface of the silicon oxide film 14, which is the bonding surface of the electrode substrate 2, has good surface properties (R
a: about 0.2 nm), and the surface of the oxide film 9 which is the bonding surface of the silicon substrate 41 to be the flow path substrate 1 also has good surface properties (Ra: 0.2 nm or less). That is, if the surface properties of the bonding surfaces of the substrates 41 and 2 to be bonded are not good, pre-bonding does not occur at room temperature, and bonding with high reliability cannot be performed.

After that, the bonded wafer (the silicon substrate 41 and the electrode substrate 2) is placed in a nitrogen gas atmosphere under a B gas atmosphere.
BPS at a temperature equal to or higher than the melting point of the PSG film 14a
900 ° C. lower than the heat treatment temperature (950 ° C.) of the G film 14 a
And baked for 2 hours. As a result, strong joining without joining defects (unjoined portions) was obtained.

Next, as shown in FIG.
The silicon substrate 41 of 0 μm is thinned by polishing to a predetermined liquid chamber height of 100 μm in thickness, and LP-
Silicon nitride films 43a and 43b are formed by CVD.

Subsequently, as shown in FIG. 2D, the silicon nitride film 43b on the electrode substrate 2 is patterned by photolithography and dry etching.
The silicon substrate of the electrode substrate 2 is anisotropically etched at a temperature of 90 ° C. with a 25 wt% aqueous solution of potassium hydroxide. With this etching solution, etching of the plane having the crystal plane orientation (100) proceeds at a speed of 2.5 μm / min. When the etching proceeds and reaches the thermal oxide film 2a, the etching is stopped because the etch rate of the thermal oxide film 2a is very small. Here, a groove 44 serving as the ink inlet 19 is formed in the silicon substrate of the electrode substrate 2.

Then, as shown in FIG. 10A, the silicon nitride film 43a is patterned by a photolithography technique and a dry etching technique.
Is performed on the silicon substrate 41 to be formed. At this time, etching proceeds from the concave portion on the patterned side, and when the boron concentration reaches a depth of 1E20 / cm ³ , the etching is stopped (the etch rate is extremely lowered), and the high-concentration boron diffusion layer (high-concentration boron doping) is formed. The flow path substrate 1 in which the vibration plate 10 made of the silicon layer 42 and the concave portions that become the ejection chamber 6 and the common ink chamber 8 are formed is obtained.

Subsequently, as shown in FIG. 6B, the thermal oxide film 2 corresponding to the groove 44 serving as the ink inlet 20 is formed.
a, the silicon oxide film 11, the BPSG film 14b, and the oxide film 9 are sequentially etched and removed with a hydrofluoric acid aqueous solution or the like. In addition, the silicon nitride films 43a and 43b are removed by wet etching using hot phosphoric acid or the like or by dry etching. Here, the silicon nitride film 43a
And 43b may be left without being removed.

Then, the wafer is cut into a head chip size by dicing at a position indicated by a dashed line in the figure. After that, the high-concentration boron diffusion layer 42 on the side of the flow path substrate 1 corresponding to the ink intake port 20 is placed on the
Removed from the side by dry etching, ink inlet 2
0 is formed.

Next, as shown in FIG. 3C, a metal mask is placed over the flow path substrate 1 so as to protect the discharge chamber 6 and the common liquid chamber 8 from the flow path substrate 1 side. The BPSG film 14a protecting the concentration boron diffusion layer 42 and the electrode pad portion 12a is removed by dry etching.

Finally, the ink jet head is completed by joining the nozzle plate 3 on which the nozzles 4 and the fluid resistance portions 7 are formed on the flow path substrate 1 using an epoxy adhesive or the like.

In the above embodiment, the present invention is applied to a side shooter type ink jet head in which the diaphragm displacement direction and the ink droplet ejection direction are the same, but the diaphragm displacement direction is perpendicular to the ink droplet ejection direction. The present invention can be similarly applied to an edge shooter type inkjet head. Further, the present invention can also be applied to, for example, a droplet discharge head that discharges a liquid resist for patterning.

[0068]

As described above, according to the ink jet head according to the present invention, the first substrate on which the vibration plate is provided and the second substrate on which the electrodes are provided are silicon substrates, and the first substrate and the second substrate are separated from each other. Bonding is performed via a silicon oxide film that is soft at low temperatures, and a polishing stopper with a small polishing rate is provided on the substrate side on which the silicon oxide film is provided, so that the substrate on which the silicon substrate is provided can be flattened with high precision. Can,
Highly reliable bonding can be performed in a temperature range that does not affect the electrodes and diaphragm at low temperatures.
It is possible to increase the density and improve the reliability.

Here, a silicon oxide film of 1000 ° C.
By using a material having a composition exhibiting softening property at a temperature not exceeding the above, it is possible to reliably prevent the adverse effect when the diaphragm is formed by the electrodes and the high-concentration impurity diffusion layers. Also,
When the silicon oxide film contains phosphorus and / or boron, it is possible to easily obtain a silicon oxide film having softness at a low temperature. Further, by using a silicon nitride film as a polishing stopper, a polishing stopper having a small polishing rate can be easily formed.

According to the method of manufacturing an ink jet head according to the present invention, the surface of the substrate on which the silicon oxide film is to be formed is flattened by the CMP polishing process in which the polishing is stopped by the polishing stopper, so that the substrate surface is flattened with high precision. be able to.

According to the method of manufacturing an ink jet head according to the present invention, the silicon oxide film is subjected to a heat treatment at a temperature not lower than the reflow property and at a temperature lower than the reflow property and not higher than 1000 ° C. Since the first substrate and the second substrate are joined by heating at a high temperature,
Highly reliable bonding can be performed.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of an inkjet head according to the present invention.

FIG. 2 is an explanatory top view of the head excluding a nozzle plate;

FIG. 3 is an explanatory cross-sectional view of the head in the longitudinal direction of the diaphragm.

FIG. 4 is an enlarged sectional explanatory view of a main part of the head in the transverse direction of the diaphragm.

FIG. 5 is an explanatory sectional view for explaining a manufacturing process of the electrode substrate of the head.

FIG. 6 is an explanatory sectional view illustrating a step following FIG. 5;

FIG. 7 is an explanatory view illustrating the polishing step of FIG. 5;

FIG. 8 is an explanatory sectional view illustrating a comparative example having no polishing stopper;

FIG. 9 is an explanatory sectional view illustrating a step following FIG. 6;

FIG. 10 is an explanatory sectional view illustrating a step following FIG. 9;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Flow path board, 2 ... Electrode board, 3 ... Nozzle plate, 4 ... Nozzle, 6 ... Discharge chamber, 7 ... Fluid resistance part, 8 ... Common liquid chamber, 10
... vibration plate, 11 ... silicon oxide film, 12 ... electrodes, 13 ...
Polishing stopper, 14: silicon oxide film, 15: gap.

Claims (6)

[Claims] 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 an electrode facing the vibration plate; In an ink jet head that displaces and deforms by force to discharge ink droplets from the nozzle, a first substrate on which the vibration plate is provided and a second substrate on which the electrode is provided are a silicon substrate, and the first substrate and the second substrate are provided. Are joined via a silicon oxide film that shows softening properties at low temperatures,
An ink jet head, wherein a polishing stopper having a small polishing rate is provided on the substrate side on which the silicon oxide film is provided. 2. The ink jet head according to claim 1, wherein said silicon oxide film has a composition exhibiting softening properties at a temperature not exceeding 1000 ° C. 3. The ink jet head according to claim 1, wherein said silicon oxide film contains phosphorus and / or boron. 4. An ink jet head according to claim 1, wherein said polishing stopper is a silicon nitride film. 5. The method for manufacturing an ink jet head according to claim 1, wherein a substrate surface on which the silicon oxide film is provided is flattened by using a CMP polishing step in which polishing is stopped by the polishing stopper. A method for manufacturing an ink jet head, comprising: 6. The method for manufacturing an ink jet head according to claim 1, wherein the silicon oxide film is subjected to a heat treatment at a temperature equal to or higher than the reflow property and lower than the temperature indicating the reflow property. At the temperature of 1
A method for manufacturing an ink jet head, wherein the first substrate and the second substrate are joined by heating at a temperature not exceeding 000 ° C.