Patent Grant
10442202
The present disclosure relates to a bonded-substrate article where multiple substrates have been bonded, a manufacturing method of the bonded-substrate article, a liquid discharge head having the bonded-substrate article, and a manufacturing method thereof.
In recent years, devices configured of bonded-substrate articles where substrates have been bonded to each other are being fabricated in functional devices such as microelectromechanical systems (MEMS) like pressure sensors, acceleration sensors, and so forth, microfluidic devices, and so forth. An example thereof is a liquid discharge head that discharges liquid.
A liquid discharge head is a device that has multiple energy generating elements, and causes liquid to be discharged from multiple discharge orifices, by energy provided from the energy generating elements. The liquid discharge head normally has a configuration where multiple substrates are bonded, such as a substrate where energy generating elements and circuits for driving these are formed, a substrate where discharge orifices are formed, a substrate where channels for liquid to be supplied to the discharge orifices are formed, and so forth. It is important in such a configuration that the substrates are bonded to each other with high precision. If the positional relation among the boards is off, this creates variation in volume of the channels and in the relative positional relation between the energy generating elements and discharge orifices, which can lead to unevenness in discharge.
Japanese Patent Laid-Open No. 9-187938 describes a liquid discharge head having a top plate that forms channels for liquid to guide the liquid to discharge orifices, and a substrate where energy generating elements are formed, wherein protrusions formed in the top plate and grooves formed in the substrate are fit one on one, and bonded by an adhesive agent. The bottoms of the grooves provided to the substrate are formed tapered, and accordingly the protrusions formed on the top plate moved along the inclination at the bottoms of the grooves, and thus are positioned in a stable manner. Accordingly, positioning of the top plate and the substrate can be performed with high precision.
In recent years, reduction in size and high density of discharge orifices have come to be demanded of liquid discharge heads. Accordingly, there is demand for positioning of substrates with even higher precision.
Even if substrates are fit to each other with the bottom of grooves tapered, such as described in Japanese Patent Laid-Open No. 9-187938, misalignment may still occur among substrates. This is due to thermal stress on the adhesive agent and substrates, due to heating when hardening the adhesive agent.
A manufacturing method for a bonded-substrate article, according to the present disclosure, where a first substrate has a first bonding region and a second bonding region that are both bonded to a second substrate, and the second substrate has a third bonding region and a fourth bonding region that are both bonded to the first substrate. The method includes: first bonding, where the first bonding region of the first substrate and the third bonding region of the second substrate are bonded at a first temperature; and second bonding following the first bonding, where the second bonding region of the first substrate and the fourth bonding region of the second substrate are bonded at a second temperature. The first temperature is lower than the second temperature.
Also, a manufacturing method for a liquid discharge head according to the present disclosure is a manufacturing method for a liquid discharge head having a bonded-substrate article where a first substrate has a first bonding region and a second bonding region that are both bonded to a second substrate, and the second substrate has a third bonding region and a fourth bonding region that are both bonded to the first substrate, and the bonded-substrate article has a liquid channel traversing the first substrate and the second substrate. The method includes: first bonding, where the first bonding region of the first substrate and the third bonding region of the second substrate are bonded at a first temperature; and second bonding, following the first bonding, where the second bonding region of the first substrate and the fourth bonding region of the second substrate are bonded at a second temperature. The first temperature is lower than the second temperature.
Further, a liquid discharge head according to the present disclosure is a liquid discharge head having a bonded-substrate article where a first substrate and a second substrate are bonded to each other, and the bonded-substrate article has a liquid channel provided traversing the first substrate and the second substrate. The bonded-substrate article is the bonded-substrate article described above.
Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
It has been found desirable to provide a manufacturing method of a bonded-substrate article and a manufacturing method of a liquid discharge head, where positioning among substrates can be performed with high precision. It also has been found desirable to provide a bonded-substrate article where boards have been bonded to each other with high precision, and a liquid discharge head having the bonded-substrate article.
The bonded-substrate article according to the present disclosure and the manufacturing method thereof will be described below, by way of example of a liquid discharge head.
The manufacturing method of the liquid discharge head according to a first embodiment will be described with reference to
Structure of Liquid Discharge Head
First, the structure of the liquid discharge head to which the manufacturing method of the bonded-substrate article and liquid discharge head according to the present embodiment is applied will be described with reference to
A channel 115 for liquid is provided to the bonded-substrate article 130, traversing the first substrate 131 and second substrate 132. A film 108 is formed on the inner wall face of the channel 115, traversing the first substrate 131 and second substrate 132. The film 108 is a film that has liquid-resistant properties, and serves to protect the inner wall face of the bonded-substrate article 130 from erosion by the liquid such as ink or the like. The channel 115 is configured of a first channel 112, a second channel 113, and a third channel 114. The first channel 112 comes into contact with the pressure chamber 102 that corresponds to one discharge orifice 101. The second channel 113 comes into contact with multiple first channels 112 within the liquid discharge head, and distributes liquid to the first channels 112. The third channel 114 is connected to the second channel 113, and has a role of narrowing the width of a channel that is externally supplied. In the present embodiment, out of the channel 115, the first channel 112 and second channel 113 are formed in the first substrate 131, and the third channel 114 is formed in the second substrate 132.
The liquid discharge head illustrated in
Manufacturing Method of Liquid Discharge Head
Next, a manufacturing method of the liquid discharge head according to the present embodiment will be described.
1. Process for Preparing First Substrate and Second Substrate
The first substrate 131 where the energy generating element 104 for generating energy used for discharging liquid and the surface membrane layer 103 have been formed is prepared, as illustrated in
Various types of substrates suitable for forming the energy generating element 104 and wiring film can be used as the first substrate 131. The first substrate 131 preferably includes any one selected from a group made up of silicon, silicon carbide, silicon nitride, glass (quartz glass, borosilicate glass, alkali-free glass, soda glass), alumina, gallium arsenide, gallium nitride, aluminum nitride, and aluminum alloy. Out of these, a silicon substrate is suitably used for the first substrate 131. The first substrate 131 worked to reduce thickness from the rear face if necessary. Techniques to reduce thickness include grinding and wet etchings using an etchant such as hydrofluoric acid. The rear face of the first substrate 131 is also subjected to smoothing, to facilitate a bonding process with the second substrate 132, which will be described later. Techniques for smoothing include grinding with a grinding stone of a large grain size, dry polishing, grinding by chemical-mechanical polishing (CMP), dry etching using reactive gas, and wet etchings using an etchant such as hydrofluoric acid.
Next, the first channel 112 and second channel 113 are formed in the first substrate 131, as illustrated in
Next, the rear face of the first substrate 131 (the bonding face with the second substrate 132) is worked, to form a first bonding region 121 and a second bonding region 122, as illustrated in
The reason why the bonding face is divided into the first bonding region 121 and second bonding region 122 is for functional separation of the bonding face. That is to say, two-stage bonding is performed in the later-described bonding processing in the present embodiment, so bonding regions corresponding to the bonding processes is preferable. Details of the bonding process will be described later.
The following method can be exemplified for working the bonding face into a protruding form. First, an etching mask is formed on the bonding face of the first substrate 131 where the second channel 113 is to be formed. Laminating and transferring a resist formed into a dry film onto the bonding face is preferable as a technique for forming the etching mask on the bonding face of the first substrate 131, since the etching mask can be formed relatively easily even if there is a large opening such as the third channel 114. An etching mask for forming the step on the bonding face of the first substrate 131 may be formed beforehand, before forming the second channel 113. The material of the etching mask preferably has high thermal stability, and is stable with regard to the working process on the second channel 113. Examples of such a material include resist, an organic resin that is insoluble in stripping solution, and an inorganic film such as a silicon oxide film or a silicon nitride film formed by vapor growth. Thereafter, the substrate is etched over the etching mask, thereby forming the first bonding region 121 and second bonding region 122. Thereafter, the etching mask is removed by a stripping solution, oxygen plasma ashing, dry etching, or some like technique. At this time, the bonded-substrate article may be cleansed using a stripping solution for removing etching deposits, to remove etching deposits adhered to the surface of the inner walls of the channels and the bonding face.
The second substrate 132 is prepared, as illustrated in
Next, the third channel 114 is formed by a technique the same as described above, as illustrated in
2. Process of Bonding First Substrate and Second Substrate
Next, the first substrate 131 and second substrate 132 are bonded to each other. This bonding includes at least the two processes of a process of bonding the first bonding region 121 of the first substrate 131 and the third bonding region 123 of the second substrate 132 (first bonding process), and following the first bonding process, a process of bonding the second bonding region 122 of the first substrate 131 and the fourth bonding region 124 of the second substrate 132.
The first bonding process is performed to precisely fix the first substrate 131 and second substrate 132 beforehand, before the second bonding process. On the other hand, the second bonding process is performed to strongly bond the substrates to each other, and is performed at a relatively high temperature. If there is not process such as the first bonding process before the second bonding process to fix the substrates to each other, the positions of the substrates will deviate due to thermal stress applied to the substrates in the second bonding process. Thus, the first bonding process where the substrates are fixed to each other at a lower temperature (first temperature) than the temperature of the second bonding process (second temperature) is performed in the present embodiment before the second bonding process. Accordingly, positional deviation among the substrates does not readily occur even through a high-temperature process such as the second bonding process.
The first bonding region 121 and third bonding region 123 are bonded by direct bonding in the first embodiment. Direct bonding is normally performed at a low temperature, so there is no thermal stress or the like on the substrates, and the substrates can be quickly and precisely fixed to each other. Also, adhesive agent itself is not used, so positional deviation due to adhesive agent does not occur, and further the two substrates can be quickly and strongly fixed at the instant of contact.
In a case where the bonding portions of the substrates are exposed in the channel 115 for liquid, as in the liquid discharge head according to the present embodiment, if the substrates are bonded to each other using adhesive agent, the adhesive agent may be altered by the liquid such as ink, and adhesion strength between the substrates may deteriorate. However, the bonding process according to the present embodiment bonds the first bonding region 121 and third bonding region 123 at the channel 115 side using direct bonding, so contact between liquid and adhesive agent does not readily occur, and deterioration in adhesion between the substrates due to alteration of adhesive agent. Moreover, and advantage is that the adhesion material can be optimized only by bonding capabilities, without having to take into consideration liquid resisting properties when selecting an adhesive agent.
There are several techniques for direct bonding. One example of direct bonding is plasma activated bonding. Plasma activated bonding involves forming hydroxyl groups on each of the bonding faces by plasma irradiation, and bonding the substrates to each other by hydrogen bonding and dehydration condensation reaction among the hydroxyl groups. A second example of direct bonding involves forming hydroxyl groups on each of the bonding faces by oxidizing the bonding faces by an oxidizing liquid such as ozone water or a hydrogen peroxide solution, and bonding the substrates to each other by hydrogen bonding and dehydration condensation reaction among the hydroxyl groups. A third example of direct bonding is room-temperature bonding, where the outermost surfaces of the bonding faces are etched in a vacuum, and thereafter the bonding faces are brought into contact with each other. Note that the third example is advantageous in that a high bonding strength can be obtained at room temperature. Of these, plasma activated bonding and room-temperature bonding are preferable, since bonding can be performed at relatively low temperatures. The processes of bonding the first substrate 131 and second substrate 132 will be described below in order, according to an example of plasma activated bonding.
2-1. Pre-Processing Process
Pre-processing is performed before the first bonding process and second bonding process. The bonding faces are preferably clean and smooth for performing direct bonding. Accordingly, the bonding faces of the first substrate 131 and the bonding faces of the second substrate 132 are preferably cleansed before the first bonding process, to remove foreign matter present on the bonding faces. Smoothing the bonding faces to increase planarity of the bonding faces also is preferable.
An example of a cleaning method is physical cleaning using cleaning by physical shock. Specific examples include megasonic cleaning, two fluid cleaning where liquid is broken by a nitrogen jet, high pressure liquid jet cleaning, and brush scrub cleaning. Examples of liquid used therein include pure water, ozone water, hydrogen water, ammonia water, and hydrogen fluoride water. Another example of cleaning methods is chemical cleaning, where the substrates are dipped in a liquid or the bonding faces of the substrates are coated with a liquid, and cleansing is performed by causing a chemical reaction between the substrates and the liquid. Specific examples of chemical cleaning include a cleaning method using a mixed solution of ammonia and a hydrogen peroxide solution, a cleaning method using a mixed solution of sulfuric acid and a hydrogen peroxide solution, and a cleaning method where hydrogen fluoride water and ozone water are alternately coated.
Examples of techniques for smoothing the bonding faces include grinding with a grinding stone of a fine grain size, dry polishing, polished by CMP, dry etching using reactive gas, and wet etchings using an etchant such as hydrofluoric acid, as described above. The surface roughness of the bonding faces after smoothing preferably is 20 nm or less, and more particularly is 1 nm or less. The term “surface roughness” as used here refers to the arithmetic average roughness (Ra) of a roughness curve stipulated in Japan Industrial Standards (JIS) B0601:2001. Note that the smoothing of the bonding faces may be performed before performing the first bonding process, may be performed immediately before forming the channels in the substrates, or both may be performed.
Thereafter, when performing the direct bonding, pre-processing is executed in accordance with the type of direct bonding. The pre-processing differs according to the type of direct bonding. In the case of pre-processing for plasma activated bonding, at least one bonding face of the first substrate 131 and second substrate 132 is irradiated by plasma formed by discharging using nitrogen gas, oxygen gas, or argon gas, in a vacuum. The plasma-irradiated faces may be cleaned with pure water following plasma irradiation, to increase the number of hydroxyl groups on the bonding faces.
2-2. Process of Coating Adhesive Agent
Next, an adhesive agent 152 is coated on the second bonding region 122 of the first substrate 131, as illustrated in
A material that has high adhesion to the substrates is preferably used for the adhesive agent 152. A material that has little inclusion of bubbles and high coatablity is preferable, and a material that has low viscosity, enabling a thinner layer of adhesive agent 152 to be formed, is preferable. The adhesive agent 152 is preferably includes a resin selected from a group made up of acrylic resin, epoxy resin, silicone resin, benzocyclobutene resin, polyamide resin, polyimide resin, and urethane resin. Benzocyclobutene resin is more preferably included, since a high bonding strength for the adhesive agent 152 can be obtained. Examples of the method of hardening the adhesive agent 152 include thermal hardening and retarded UV curing. Note that in a case where either of the substrates is UV-transmissive, fast UV curing can be used.
An example of a technique to coat with the adhesive agent 152 is adhesive agent transfer by substrate. Specifically, a transferring substrate is prepared, and the adhesive agent is thinly and uniformly coated onto the transferring substrate by spin coating or slit coating. Thereafter, the bonding faces of the first substrate 131 are brought into contact with the coated adhesive agent, thereby transferring the adhesive agent onto just the bonding faces of the first substrate 131. The size of the transferring substrate suitably is the same dimensions as the first substrate 131 or larger, and the material suitably is silicon or glass.
It is sufficient for the adhesive agent 152 to be coated on at least one of the second bonding region 122 of the first substrate 131 and the fourth bonding region 124 of the second substrate 132, and may be coated on the fourth bonding region 124 of the second substrate 132 side. In a case of coating the adhesive agent by adhesive agent transfer, the second bonding region 122 of the first substrate 131 side, which is the top face of the protruding portion, is preferably coated, from the perspective of ease of coating.
2-3. First Bonding Process
Next, the bonding faces of the substrates are made to face each other, aligned by a bonding alignment device or the like, and the first bonding region 121 of the first substrate 131 and the third bonding region 123 of the second substrate 132 are bonded by direct bonding, as illustrated in
An example of an alignment method includes a technique of using an optical microscope to align one substrate at a time. First, one substrate is loaded to an alignment device, and adjusted so that alignment marks are in the field of view of the optical microscope. Thereafter, the optical microscope and the one substrate are fixed, and the device is caused to remember the alignment mark positions. Next, another substrate is loaded to the alignment device, and this other substrate is disposed between the one substrate and the optical microscope, with the bonding face of one substrate and the bonding face of the other substrate facing each other. Positioning is performed while observing using the optical microscope, so that the alignment marks provided on the opposite side of the other substrate from the bonding face matches the alignment mark position of the one substrate. When alignment is completed, the other substrate and the one substrate are fixed, thereby completing alignment. An example of the fixing method is clamping with a clamp jig. When the two substrates are fixed, these are transported to a bonding device along with the jig that is fixing them. In a case where alignment and bonding can be performed in the same device, bonding may be performed in the same device after alignment is completed.
Another example of an alignment method is a technique to bring the substrates into close proximity while facing each other, and position the alignment marks on each using infrared light that that can pass through the substrates, while observing through a microscope. Another method is to prepare two microscopes provided so as to sandwich the two substrates facing each other, and to perform positioning while viewing alignment marks provided on each of the two substrates.
Direct bonding is performed by pressurizing the substrates at room temperature, and bringing the first bonding region 121 and third bonding region 123 into contact. When the bonding faces come into contact, the hydroxyl groups on the bonding faces exhibit hydrogen bonding, and the substrates are fixed to each other. Pressurizing can be performed in a vacuum or in the ambient atmosphere. Note that in order to raise the bonding strength of the bonding portions between the first bonding region 121 and the third bonding region 123, after bonding, thermal processing may be performed at a low temperature where the adhesive agent 152 will not harden, to promote dehydration condensation reaction.
It is sufficient for the temperature in the first bonding process (first temperature) to be lower than the temperature in the second bonding process (second temperature). Specifically, the first temperature preferably is 200° C. or lower, particularly preferably is 150° C. or lower, and further preferably is 50° C. of lower. Although the lower limit of the first temperature is not restricted in particular, 0° C. or higher, and particularly 20° C. or higher is preferable. Note that the temperature referred to here is the temperature of the bonded-substrate article.
2-4. Second Bonding Process
Next, the adhesive agent 152 coated on the second bonding region 122 is hardened, thereby bonding the second bonding region 122 of the first substrate 131 and the fourth bonding region 124 of the second substrate 132. The role of a bonding portion 154 between the second bonding region 122 and the fourth bonding region 124 is to exhibit high bonding strength, and to suppress occurrence of bonding voids and guarantee bonding reliability. Heating at high temperature is performed in the second bonding process, to form such a bonding portion 154. Although the temperature depends on the type of adhesive agent, heating is performed at 100° C. or higher but 300° C. or lower, and more particularly 150° C. or higher but 300° C. or lower. Note that the temperature referred to here is the temperature of the bonded-substrate article.
In a case where the adhesive agent 152 is a thermosetting type, the substrates fixed beforehand by the first bonding process are placed in a bonding device, and after the substrates are heated to a predetermined temperature within the bonding device, the adhesive agent 152 is sufficiently hardened at a predetermined temperature, time, and pressure. The second bonding process is preferably performed while pressurizing. This suppresses thermal expansion when heating and thermal contraction when cooling of the adhesive agent 152 and substrates, thereby suppressing positional device between the substrates even further. Although the hardening reaction may be completed within the bonding device, the substrates may be extracted from the bonding device at a state where the adhesive agent 152 has hardened to a certain extent, and separately heated in an oven. This enables the hardening reaction to be performed in a short time.
In the case that the adhesive agent 152 is a retarded UV curing type, the adhesive agent 152 is irradiated by a stipulated amount of ultraviolet rays before the first bonding process, and the substrates are then further heated in the second bonding process after the first bonding process, to sufficiently harden the adhesive agent 152. In a case where the adhesive agent 152 is a fast UV curing type, the adhesive agent 152 is irradiated by a stipulated amount of ultraviolet rays through the transparent substrates, and thereafter the adhesive agent 152 is sufficiently hardened by heating the substrates in an oven or the like.
In either case, the adhesive agent 152 is preferably hardened sufficiently in the second bonding process. Specifically, hardening is preferably performed until the hardness of the adhesive agent 152 is 60% or higher, and more particularly 80% or higher. Now, the hardness of the adhesive agent is calculated as follows by a differential scanning calorimeter. Around 1 to 10 mg samples are taken from adhesive agent before hardening and after the second bonding process. The temperature of the samples is raised to 300° C. at a rate of 10° C. per minute, the calorific value (J/g) at this time is measured by the differential scanning calorimeter, and the hardness is calculated from the measured calorific value according to the following expression.
Hardness (%)={(calorific value of adhesive agent before hardening)−(calorific value of adhesive agent after hardening)}/(calorific value of adhesive agent before hardening)
As described above, according to the first bonding process and the second bonding process according to the present embodiment, position can be performed precisely by direct bonding in the first process, and high bonding strength with occurrence of bonding voids and the like suppressed can be obtained by the second process. That is to say, according to the above-described bonding process, high positioning precision and bonding reliability, which were both difficult with direct bonding alone or adhesive agent bonding along, can be achieved.
3. Process of Forming Film
Next, the film 108 having the function of protecting the inner walls of channels from liquid such as ink is formed as necessary, as illustrated in
The film 108 is formed over the first substrate 131, second substrate 132, and the bonded portion of the first substrate 131 and second substrate 132 (a bonded portion 153 of the first bonding region 121 and second bonding region 122). Thus, forming the film 108 over the bonded portion 153 enables the bonding reliability between substrates to be improved. Even if slight bonding voids (around 0.1 μm in height) are present within the bonded portion 153 bonded by direct bonding, and a minute path to the adhesive agent 152 is formed from the channel 115, this minute path is easily closed off by the film 108. Accordingly, the adhesive agent 152 can be protected from liquid such as ink or the like even further, and deterioration in adhesion between the substrates due to alteration of the adhesive agent 152 can be suppressed.
The film 108 is preferably formed by atomic layer deposition. A deposition process and an exhaust process are alternately repeated in atomic layer deposition. In the deposition process, precursor molecules serving as the material and water molecules are fed into the substrate in a vacuum chamber, and the substrate surface adsorbs molecules for around one molecule layer worth. At this time, functional groups in the precursor are adsorbed by the hydroxyl groups present on the surface of the substrates. The functional groups rob the hydroxyl groups of hydrogen atoms and break away as volatile molecules. Thereafter, the remaining oxygen atoms and inorganic elements within the precursor are bonded by covalent bonding. In the exhaust process, molecules retained within the chamber without being adsorbed on the surface of the substrates are discharged. A strong bond is formed by covalent bonding in atomic layer deposition, so a film with high adhesion strength can be formed. The mean free path of molecules is great in atomic layer deposition, so groves and holes having high aspect ratios are well covered by the film. Accordingly, the material forming the film finds its way into gaps from the channel side, and a uniform film can be formed on the entire wall within the gap.
On the other hand, depending on the material of the face on which the film is formed, there are cases where the film formed by atomic layer deposition does not have good adhesion with that face. For example, adhesion between the surface of adhesive agent and a film formed by atomic layer deposition is not good, and in a case of the bonded portion 153 being bonded by adhesive agent and the film 108 being formed on the adhesive agent, the film 108 readily peels off. This is because there are few hydroxyl groups as compared to the surface of a substrate formed of a material such as silicon, and the functional groups of the precursor molecules do not readily react. As a result, a great number of unreacted functional groups remain at the interface between the adhesive agent and the film formed by atomic layer deposition, and flaws readily occur. Exposing a bonded-substrate article having such a film to liquid such as ink for prolonged periods can lead to faulty adhesion between the substrates, due to the film formed by atomic layer deposition peeling away and the adhesive agent being altered or liquid intruding into the interface between the adhesive agent and the substrates.
However, according to the present embodiment, the bonded portion 153 is bonded by direct bonding that does not use adhesive agent, so a film 108 with few flaws is strongly bonded to the substrates. As a result, the film 108 does not readily peel off of the inner walls of the channel 115.
The film 108 has liquid-resistant properties and is relatively stable even if exposed to liquid, and functions to protect the adhesive agent and substrates from liquid filled in the channel 115. The film 108 preferably includes an elemental form, an oxide, a nitride, or a carbide, of an element selected from a group made up of tantalum (Ta), titanium (Ti), zirconium (Zr), niobium (Nb), vanadium (V), hafnium (Hf), and silicon (Si). Of these, an oxide of an element selected from the group made up of Ta, Ti, Zr, Nb, V, Hf, and Si is preferably included.
The film 108 may be formed by methods other than atomic layer deposition, as long as gaps are well covered by the film. Examples include chemical vapor deposition (CVD) such as thermal CVD, plasma CVD, catalytic CVD, and so forth. Other methods that can be used include sputtering, vacuum deposition, ion beam deposition, and so forth. These methods are poorer as compared with atomic layer deposition with regard to covering well, but the film formation rate is high, and a film with few impurities, such as carbon, hydrogen, water, and so forth can be formed.
After the process of forming the film 108 has ended, unnecessary portions of the film 108 formed on the bonded-substrate article are removed. An example of an unnecessary portion of the film 108 is a portion formed on electrode pads that are present on the surface of the first substrate 131. The following is an example of a technique that can be used to remove unnecessary portions of the film 108. First, resist that has been formed into a dry film is laminated onto the surface side of the bonded-substrate article, and an etching mask is formed on portions other than the unnecessary portions of the film 108. Thereafter, the unnecessary portions of the film 108 are removed by dry etching or wet etching. After etching, the etching mask is removed by a solvent or the like.
4. Process of Forming Discharge Orifice Forming Member
Next, the discharge orifice forming member 107 is formed on the first substrate 131. First, a dry film resist where photo-setting resin has been coated on a film substrate is adhered onto the first substrate 131. Thereafter, the dry film resist is exposed and developed, thereby patterning the side wall 106 of the discharge orifice forming member 107. Next, the top plate 105 of the discharge orifice forming member 107 is patterned in the same way using dry film resist. Finally, discharge orifices 101 and pressure chambers 102 are formed by developing the unexposed portions, thereby completing the liquid discharge head.
Unlike the first embodiment, a second embodiment performs bonding using adhesive agent in the first bonding processing, and not direct bonding. In the present embodiment, a first adhesive agent 151 that hardens at low temperature is coated on at least one of the first bonding region 121 of the first substrate 131 and the third bonding region 123 of the second substrate 132. The first adhesive agent 151 is then hardened at a lower temperature than a second adhesive agent 152 is hardened at in the second bonding process. In the same was as in the first embodiment, the substrates are fixed to each other beforehand at a lower temperature than the second bonding process in the present embodiment, so positional deviation amount the substrates due to stress occurring in the adhesive agent and substrates due to high temperature in the second bonding process does not readily occur.
The manufacturing method of the bonded-substrate article and liquid discharge head according to the present embodiment will be described in order with reference to
1. Process for Preparing First Substrate and Second Substrate
The first substrate 131 is worked to form the first channel 112, second channel 113, first bonding region 121, and second bonding region 122, in the same way as in the first embodiment, as illustrated in
2. Process of Bonding First Substrate and Second Substrate
2-1. Pre-Processing Process
The bonding faces may be cleaned and smoothed as necessary, in the same way as in the first embodiment.
2-2. Process of Coating Adhesive Agents
The first adhesive agent 151 is then coated on at least one of the first bonding region 121 and the third bonding region 123, and the second adhesive agent 152 is coated on at least one of the second bonding region 122 and the fourth bonding region 124, as illustrated in
Examples of the hardening method of the first adhesive agent 151 include thermosetting and retarded UV curing. In a case where either of the substrates is UV-transmissive, fast UV curing can be used.
The first adhesive agent 151 serves to fix the first substrate 131 and second substrate 132 in the later-described first bonding process, and is an adhesive agent that hardens at a lower temperature than the temperature at which the second adhesive agent 152 used in the second bonding process is hardened at. Further, the first adhesive agent 151 preferably has good removability, since removing at least part in a subsequent process can be expected.
The first adhesive agent 151 preferably includes a resin selected from a group made up of acrylic resin, epoxy resin, cyclized rubber resin, and phenol resin. Adhesive agents including these resins can be hardened at lower temperatures of 50° C. or above to 200° C. or lower, and thus are suitable. The first adhesive agent 151 more preferably includes an alicyclic epoxy resin.
The first adhesive agent 151 preferably is coated on to the third bonding region 123 of the second substrate 132. The third bonding region 123 of the second substrate 132, which is the top face of the recessed form of the bonding face, is preferably coated, from the perspective of ease of coating. The adhesive agent transfer method described in the first embodiment can be used as a coating method. The thickness of the first adhesive agent 151 preferably is as thin as possible from the perspective of improving the positioning precision even further, and specifically, preferably is 2.0 μm or less. Coating the first adhesive agent 151 at a thickness of 2.0 μm or less enables the positional deviation of the substrates in the horizontal direction ΔX and ΔY, and the positional deviation of the substrates in the vertical direction ΔZ, to be suppressed to within 2.0 μm. The thickness of the first adhesive agent 151 is even more preferably 1.0 μm or less since positional deviation can be further suppressed. The second adhesive agent 152 preferably has a certain thickness for fixing the substrates to each other, and specifically is 0.1 μm or more.
The second adhesive agent 152 is an adhesive agent that exhibits a high bonding strength at the bonding portion 154 between the second bonding region 122 and fourth bonding region 124 by being hardened in the second bonding process. An adhesive agent the same as that used in the first embodiment can be used for the second adhesive agent 152.
The second adhesive agent 152 is preferably coated on the second bonding region 122 of the first substrate 131. The second bonding region 122 of the first substrate 131, which is the top face of the protruding portion of the bonding face, is preferably coated, from the perspective of ease of coating. The adhesive agent transfer method, the same as in the first embodiment, can be suitably used. The thickness of the second adhesive agent 152 normally is thicker than the first adhesive agent 151. This is because the second adhesive agent 152 is bonding to guarantee bonding reliability of the substrates, and preferably has a certain thickness, in contrast to the first adhesive agent 151 that preferably is as thin as possible. It is preferable that the thickness of the second adhesive agent 152 specifically is 1.0 μm or more. The reason is that when the thickness of the second adhesive agent 152 is 1.0 μm or more, the adhesive agent can flow and cover any foreign matter, scratches, or surface roughness that might have occurred on the bonding surface, and defective bonding such as voids can be suppressed and a highly-reliable bonding can be obtained. On the other hand, if the thickness of the second adhesive agent 152 is excessively great, the bonding strength of the first adhesive agent 151 can be affected due to the influence of stress, so the thickness of the second adhesive agent 152 preferably is 30.0 μm or less.
2-3. First Bonding Process
Next, the bonding faces of the substrates are made to face each other, as illustrated in
2-4. Second Bonding Process
Next, the second bonding region 122 and the fourth bonding region 124 are bonded by hardening the second adhesive agent 152 coated on the second bonding region 122, while still in the bonding device. The role of the bonding portion 154 of the second bonding region 122 and fourth bonding region 124 is to exhibit a high bonding strength, and to guarantee bonding reliability by suppressing occurrence of bonding voids. The second bonding process involves heating at high temperatures to form such a bonding portion 154. Although the temperature depends on the type of second adhesive agent, the heating is performed specifically at a temperature of 100° C. or higher but 300° C. or lower, and more particularly 150° C. or higher but 300° C. or lower.
In the second bonding process, the substrates are heated to a predetermined temperature in the bonding device, and then subjected to a predetermined temperature and pressure, for a predetermined amount of time to sufficiently harden the second adhesive agent 152, in the same way as with the first embodiment. Sufficiently hardening the second adhesive agent 152 in this way increases the adhesion of the bonding portion 154, and a highly-reliable bond can be obtained.
3. Process of Forming Film
Next, the film 108 having the function of protecting the adhesive agent and the inner walls of channels from liquid such as ink is formed as necessary.
3-1. Process of Removing Adhesive Agent
In a case of forming the film 108, the first adhesive agent 151 is preferably removed from the channel side as illustrated in
Examples of techniques to remove the first adhesive agent 151 and cause the edge portion 155 of the adhesive agent to regress include oxygen plasma ashing and etching. When removing by ashing, first, the bonded-substrate article is placed in an ashing chamber, and oxygen ions and oxygen radicals are generated by high-frequency plasma while applying a flow of oxygen gas. The oxygen ions and oxygen radicals intrude into the channel from the opening portion of the first channel and the third channel of the bonded-substrate article. The oxygen ions and oxygen radicals in the channel only slightly oxidize the surface of substrate materials such as silicon or the like, but react with the carbon that is the primary component of the adhesive agent and causes it to volatilize, so the adhesive agent is isotopically removed.
An example of removal by etching is wet etching. In this case, the adhesive agent is etched by immersing the bonded-substrate article in an etchant. An appropriate etchant is selected in accordance with the type of adhesive agent. Examples of the etchant in a case where the adhesive agent includes epoxy resin include concentrated sulfuric acid, chromic acid, and alkaline permanganate. The etchant in a case where the adhesive agent includes polyimide resin is preferably an alkaline aqueous solution, examples thereof including hydrazine, caustic alkali, and organic amine compounds.
The regression width L of the edge portion 155 of the adhesive agent from the edge face A-A′ of the bonded portion 153 can be decided as appropriate. Setting the regression width L to be great enables a contact width W (see
3-2. Process of Forming Film
Next, the film 108 is formed from the first substrate 131 to the second substrate 132 on the inner wall face of the channel 115, as illustrated in
The materials and film forming methods listed in the first embodiment can be used for formation of the film 108. The film 108 starts adhering to the bonding face of the first substrate 131 and the bonding face of the second substrate 132 within the gap 141, and eventually these films become one, thereby closing off the gap 141. At this time, the film 108 almost completely fills the gap 141 and becomes one. In order to sufficiently fill in the gap 141, the thickness t of the film 108 and the height h of the gap 141 preferably satisfies the relation of h<t. In the present embodiment, positional deviation in the vertical direction of the substrates is suppressed by the above-described two-sage bonding process, so the height of the gap 141 formed in the above process of removing the adhesive agent can be strictly controlled. As a result, the amount of film formation of the film 108 necessary to close off the gap 141 in this process of forming the film 108 can be accurately predicted, and a liquid discharge head having a uniform film 108 in the channel can be easily manufactured.
4. Process of Forming Discharge Orifice Forming Member
Next, the side wall 106 and top plate 105 of the discharge orifice forming member 107 are formed on the first substrate 131 in the same way as in the first embodiment, and the liquid discharge head is complete.
An arrangement where the bonding face of the first substrate 131 is a protruding form and the bonding face of the second substrate 132 is a recessed form has been described in the above-described two embodiments, but an arrangement may be made where the bonding face of the first substrate 131 is a recessed form and the bonding face of the second substrate 132 is a protruding form. However, in a case where the bonding face of the first substrate 131 (rear side) has a larger area than the bonding face of the second substrate 132 (front side), as in the above embodiments, the recessed form is preferably formed on the second substrate 132 side that has a wider bonding face. The reason is that the narrower the width of the bonding face is, the more difficult it is to continuously cover with resist uniformly from the edge of the bonding face, and forming the resist for forming the recessed portion is difficult. Particularly, in a case of a liquid discharge head having the shape illustrated in
Although a step has been provided between the first bonding region 121 and second bonding region 122 in the first substrate 131 in the above-described two embodiments, two bonding regions may be provided on the same plane. Particularly, in the second embodiment, the first bonding region 121 and second bonding region 122 are both bonded to the second substrate 132 by adhesive agent, so the two bonding regions may be on the same plane, as long as the thickness of the adhesive agent is maximally matched. On the other hand, in the first embodiment, the first bonding region 121 is bonded to the second substrate 132 by direct bonding, while the second bonding region 122 is bonded to the second substrate 132 by adhesive agent. Accordingly, a step of a size at least equivalent to the thickness of the adhesive agent is preferably provided between the first bonding region 121 and second bonding region 122.
Also, in the above-described two embodiments, the first bonding region 121 that is bonded in the first bonding process is provided at the channel side, and the second bonding region 122 bonded in the second bonding process is provided on the inner side of the bonded-substrate article 130. However, the positions of the first bonding region 121 and second bonding region 122 may be inverted, and the bonding regions on the inner side of the bonded-substrate article 130 may be bonded first in the first bonding process.
Although the liquid discharge head in the above-described two embodiments is a bonded article of substrates having channels, this is not restrictive. The bonded-substrate article according to the present embodiment can be applied to a bonded article of substrates at any position within a liquid discharge head. For example, in a case where the discharge orifice forming member is formed by two or more substrates being bonded, the above-described bonded-substrate article can be applied to the discharge orifice forming member. A case where the discharge orifice forming member is formed by two or more substrates being bonded is a case where the discharge orifice forming member 107 is configured of the top plate 105 forming the discharge orifice 101, and the side wall 106 forming the pressure chamber 102, as illustrated in
A liquid discharge head was fabricated using the method illustrated in
Next, a mask was formed to form the first bonding region 121 and second bonding region 122 on the rear face side of the first substrate 131. First, a polyamide resin solution (product name HIMAL, manufactured by Hitachi Chemical Company, Ltd.) was coated on the entire rear face of the first substrate 131 to a thickness of 2.0 μm by spin coating, and hardened by thermal treatment at 250° C. for one hour. Thereafter a novolak resist was coated thereupon, and the resist was patterned by exposing by a two-sided alignment exposing device, and developing by a developing device. Dry etching was performed over the resist using plasma discharging into O2 gas and CF4 gas, thereby working the mask to a desired form. After etching, the resist was removed, completing the mask. Further, a mask for shaping the second channel 113 was from on the mask for forming the first bonding region 121 and second bonding region 122 on the rear face of the first substrate 131.
Next, a groove to serve as the second channel 113 was formed by etching, as illustrated in
Protective tape was then applied to the rear face of the first substrate 131 and a mask was formed on the front face in the same was as described above, and the first channel 112 made up of multiple holes was formed by dry etching from the front face side of the substrate. After etching, the protective tape was removed, and resist and deposits were removed by a stripping solution.
Following this, a protruding form to serve as the first bonding region 121 and second bonding region 122 was formed, as illustrated in
Next, a silicon substrate 500 μm thick was prepared as the second substrate 132, as illustrated in
A mask was then formed on the front side (mirror face) of the second substrate 132, silicon anisotropic etching by SF6 plasma was performed to a depth of 11 μm, working the bonding face into a recessed form. Further, a protective film was applied to the front face side of the second substrate 132, a mask was formed on the rear face, and the third channel 114 was formed by the Bosch process. Thereafter, the protective film was peeled away, and resin and deposits were removed by a stripping solution.
As a pre-preparation to the bonding process, the rear face of the first substrate 131 and the front face of the second substrate 132 were cleaned. Cleaning was performed by combined use of a cleaning fluid that was a mixture of 8% by weight of ammonia, 8% by weight of a hydrogen peroxide solution, and 84% by weight of pure water, and an ultrasonic vibrator. Further, as pre-preparation to the direct bonding, the rear face of the first substrate 131 and the front face of the second substrate 132 were subjected to irradiation, by N2 plasma in a vacuum, using a radio frequency (RF) discharge device. The plasma power was 100 W, and the irradiation time was 30 seconds.
Next, the adhesive agent 152 was coated on the second bonding region 122 on the rear face of the first substrate 131, as illustrated in
Next, for alignment of the first substrate 131 and second substrate 132 using a bonding alignment device, two positions at the substrate ends were temporarily fixed by pressurizing using a clamp jig. Minute spacer jigs, 5 mm long and 200 μm thick, were inserted to multiple positions on the perimeter portion of the substrates until implementing direct bonding, so that the first substrate 131 and second substrate 132 would not come into contact and direct bonding start.
The temporarily fixed substrates where then transported into a bonding device which was then drawn to a vacuum, and the first bonding region 121 and third bonding region 123 were brought into contact by pressurizing at room temperature, and bonded by plasma activated bonding (first bonding process), as illustrated in
Next, the film 108 was formed on the inner wall faces of the channels of the bonded-substrate article 130 as illustrated in
Next, dry film resist configured of a positive resist was laminated onto the front face of the first substrate 131 of the bonded-substrate article 130, forming a mask. Unnecessary film 108 on contact pads was removed by dry etching using plasma from a gas mixture of CF4, O2, and Ar.
Next, the discharge orifice forming member 107 was formed, as illustrated in
A liquid discharge head was fabricated using the method illustrated in
Next, the first adhesive agent 151 was coated onto the third bonding region 123 of the second substrate 132, and the second adhesive agent 152 onto the second bonding region 122 of the first substrate 131, as illustrated in
Next, the first substrate 131 and second substrate 132 were aligned and temporarily fixed, in the same way as in Example 1. The fixed substrates were transported into a bonding device, pressurized for 30 minutes at 70° C. in a vacuum, and thereafter pressurized for 20 minutes at 130° C., thereby hardening the first adhesive agent 151 (first bonding process), as illustrated in
The first adhesive agent 151 exposed at the inner wall faces of the channel was etched in an etching device, as illustrated in
Next, the film 108 was formed on the inner walls of the channels of the bonded-substrate article 130 by atomic deposition layering, as illustrated in
Finally, the discharge orifice forming member 107 was formed in the same way as in Example 1, as illustrated in
While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2017-114250 filed Jun. 9, 2017, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-114250 | Jun 2017 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5871657 | Nelson | Feb 1999 | A |
| 6406636 | Vaganov | Jun 2002 | B1 |
| 6871942 | Emery | Mar 2005 | B2 |
| 8460794 | Zheng | Jun 2013 | B2 |
| Number | Date | Country |
|---|---|---|
| H09187938 | Jul 1997 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20180354267 A1 | Dec 2018 | US |
