JP3332565B2 - Solid phase bonding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid phase bonding method, and more particularly to a solid phase bonding method in which solids (solid phases) are bonded to each other by applying an insulating monomolecular film or a monomolecular cumulative film to a bonding surface. About.

[0002]

2. Description of the Related Art Conventionally, solid-phase bonding is generally carried out by
As described in Japanese Patent No. 53886, the bonding surfaces are cleaned by means of ion bombardment or the like in an ultra-high vacuum, and then the bonding surfaces are abutted against each other before contamination due to adsorption is caused. It is done in such a way as to reach the distance.

[0003]

However, in the above conventional example, cleaning of the bonding surface in an ultra-high vacuum (atmosphere),
And the need for a joining operation, the following inconveniences were recognized. 1) The apparatus configuration for forming an ultra-high vacuum atmosphere becomes large. 2) It is difficult to perform an alignment operation of the bonding surface in an ultra-high vacuum atmosphere. 3) The bonding accuracy is not very good.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a solid-state joining method which eliminates the disadvantages of the conventional example and performs a simple and accurate joining between solids (solid phases). is there.

[0005]

The above objects can be achieved by the present invention described below.

That is, the present invention firstly provides a method for joining at least two members, wherein a step (A) of forming a monomolecular film or a monomolecular cumulative film on at least one joint surface;
A solid-state bonding method comprising: a step (B) of bringing the members into close contact with each other via the bonding surface; and a step (C) of applying an electric field to the bonding surface. (A) forming a monomolecular film or a monomolecular cumulative film on at least one of the joining surfaces, and (B) bringing the members into close contact with each other via the joining surface. ), A step (C) of applying an electric field to the bonding surface, and a step (D) of heating the bonding surface. Third, at least two members A step of forming a monomolecular film or a monomolecular cumulative film on at least one of the joining surfaces (A), and a step of bringing the members into close contact with each other via the joining surface (B); (C) applying an electric field to the bonding surface; A solid-phase bonding method, characterized in that it comprises a step (E) of irradiating a laser beam.

[0007] In the second and third aspects of the present invention, the steps (C) and (D) or the steps (C) and (E) are executed in sequence. It may be executed or substantially simultaneously.

According to the present invention, an insulating monomolecular film or a monomolecular cumulative film, that is, L composed of a hydrophobic group or a hydrophilic group
By accumulating a single layer or more of a B film (Langmuir-Blodgett film) on the bonding surface, the bonding surfaces made of hydrophobic groups or hydrophilic groups were opposed to each other, and the bonding surfaces were overlapped and positioned. Thereafter, temporary bonding at the time of positioning is performed by lightly pressing. That is, hydrophobic groups,
Alternatively, by bonding hydrophilic groups to each other, displacement after positioning can be prevented, and handling after positioning is facilitated. After the positioning, a voltage is applied to both ends of the adhesive surface sandwiching the LB film.

For example, in FIG. 1, 1 and 2 indicate Si substrates, and 4 and 5 indicate LB films. Reference numerals 7 and 9 denote hydrophilic groups of LB film constituent molecules, and reference numerals 8 and 10 denote hydrophobic groups. Here, an electric field (V) is applied between the Si substrates 1 and 2 from the power supply 17 via the lead wire 21.

When the LB film functions as a high breakdown voltage insulating film, a high electric field V / d as shown in FIG. 1 is generated between the bonding surfaces. The following electrostatic attraction F between the bonding surfaces due to the electric field V:
Works. That is, F = ε (V / d) 2/2
··· (1) Here, ε; Dielectric coefficient of LB film V; Potential difference between bonding surfaces d; Gap between bonding surfaces (that is, thickness of LB film) Therefore, a large electric field strength is obtained from equation (1). If an LB film that can be used, that is, an LB film having as small a gap d as possible (the thickness of the LB film made of a hydrophobic group or a hydrophilic group is extremely thin) and having high insulation resistance,
It is possible to increase the electrostatic attractive force F, and it is possible to bring the bonding surfaces closer to each other on the order of the interatomic force by the electrostatic attractive force. That is, strong adhesion can be obtained.

The LB film constituting material used in the present invention has, for example, 16 to 30 carbon atoms, preferably
Fatty acids having 18 to 24 carbon atoms and derivatives thereof are mentioned. The thickness of the LB film is preferably 500 ° or less, and more preferably 200 °, because a strong electric field can be generated at a potential in a practical range.

Further, after the above, that is, after the bonding surfaces are close to each other on the order of the interatomic order, the LB film may be decomposed by heat treatment or laser beam irradiation. By decomposing and evaporating the LB film in this processing step, direct bonding between the bonding surfaces becomes possible as a result.

Incidentally, even when a ferroelectric LB film is used in addition to the LB film having high insulation resistance, the same adhesion as described above can be obtained.

[0014]

Hereinafter, the present invention will be described in detail with reference to examples.

[Embodiment 1] FIG. 2 shows a first embodiment of the present invention, in which the features of the present invention are best shown. In FIG. Si substrate for bonding, 4 is LB formed on the surface of Si substrate 2
The film 5 is an LB film accumulated in a layer on the LB film 4,
Reference numerals 7 and 8 denote hydrophilic groups and hydrophobic groups, respectively, of the LB film 4 on the Si substrate 2, 9 and 10 denote hydrophilic groups and hydrophobic groups, respectively, of the LB film 5, and 17 denotes an electric field between the Si substrate 1 and the Si substrate 2. A power supply for generating the electric power, a switch 18 for turning on and off the electric field, a power supply 17 for the Si substrates 1 and 2,
These are lead wires for electrically connecting the switch 18.

Next, in the above configuration, first, the Si substrate 2
The LB films 4 and 5 are accumulated on the surface of the LB film 5, and then, the bonding surface of the Si substrate 1, which has been cleaned in advance, is superposed while being positioned on the LB film 5. However, Si substrates 1 and 2
Is not completely flat when viewed from the atomic level and is composed of countless irregularities, or is composed of wavy undulations.
Adhesion with the LB film 5 on the i-substrate 2 does not occur on the entire surface.
Therefore, the adhesive strength decreases.

Therefore, as shown in FIG.
1 is turned on, and an electric field is applied between the Si substrate 1 and the Si substrate 2 by the power supply 17. Since the electrostatic attraction is generated between the Si substrate 1 and the Si substrate 2 by the electric field, the Si substrate 1
The distance between the LB film 5 formed on the i-substrate 2 and the LB film 5 gradually narrows with time, and approaches the interatomic distance over the entire surface. At this time, even when the switch 18 is turned off and the electrostatic attraction is removed, if either the Si substrate 1 or the Si substrate 2 is a thin plate having low rigidity, the Si substrate 1 and the LB film 5 Means that the bonded state is maintained by the intermolecular force. As a result, the Si substrate 1 is bonded to the Si substrate 2 with the LB films 4 and 5 as the intermediate layers. Since it is necessary to increase the electrostatic attraction in order to enable bonding over the entire surface, it is desirable to use a thin film that is easy to form an extremely thin film and has a high withstand voltage. Now, in the case of this example, arachidic acid was used as the LB film for the intermediate layer,
As shown in (2), when the power supply 17 was applied at about 5 [V] for about 30 minutes, the Si substrates 1 and 2 were bonded to each other.

Note that the present invention does not change even when a ferroelectric LB film (for example, a diacetylene-based or benzene derivative-based) or a polyimide LB film is used as the LB film. Shall be.

[Embodiment 2] FIG. 3 shows a second embodiment of the present invention, in which the features of the present invention are best shown. In FIG. Si substrate for bonding, 4 is LB formed on the surface of Si substrate 2
The film 5 is an LB film accumulated in a layer on the LB film 4,
Reference numerals 7 and 8 denote hydrophilic groups and hydrophobic groups, respectively, of the LB film 4 on the Si substrate 2, 9 and 10 denote hydrophilic groups and hydrophobic groups, respectively, of the LB film 5, and 13 denotes a platen with a heater for heating the Si substrates 1 and 2. , 14 a heating power supply for heating the heater of the platen 13, 15 a switch for turning on and off the heater of the platen 13, 16 an electrical connection between the platen 13, the switch 15 and the heating power supply 14. The connected lead wire, 17 is a power supply for generating an electric field between the Si substrate 1 and the Si substrate 2, and 19 and 20 are needle-shaped electrodes electrically connected to the Si substrate 1 and the platen 13, respectively. (The platen 13 and the Si substrate 2 are electrically connected.) 21 is the needle electrodes 19 and 20, and the power source 1
7 is a lead wire electrically connecting between the lead wires 7.

Next, in the above configuration, first, the Si substrate 2
The LB films 4 and 5 are formed on the surface of the substrate 1. Thereafter, the LB films 4 and 5 are superposed while positioning the previously cleaned adhesive surface of the Si substrate 1 on the LB film 5. Thereafter, an electric field is applied between the Si substrates 1 and 2 by the power supply 17, and the electrostatic attraction generated by the electric field causes the Si substrate 1 and the LB film 5 to approach the interatomic distance.

Further, while applying an electric field between the Si substrates 1 and 2, the switch 15 is turned on at the same time, and the Si substrates 1 and 2 are heated by the platen 13 with a heater, and the LB film 4 is heated.
And 5 are decomposed and evaporated. Although the LB films 4 and 5 disappear by this decomposition and evaporation, at this time, the distance between the Si substrates 1 and 2 is close to the distance where the atomic force or the intermolecular force acts. The Si substrates 1 and 2 are directly bonded to each other.

In the present embodiment, a stearic acid accumulation film is used for the LB films 4 and 5, and about 6
When the substrate was gradually heated to 350 ° C. or more while applying the voltage of [V], the Si substrates 1 and 2
They adhered to each other. The bonded substrate was strong enough to withstand subsequent cutting by a dicing saw.

It is to be noted that a conductive substrate (for example, a substrate having a conductive film formed on an insulator surface or a substrate which has been made conductive by ion implantation) may be used instead of the Si substrate. The intention of the present invention does not change.

[Embodiment 3] FIGS. 4 and 5 show a third embodiment of the present invention, in which the features of the present invention are best shown. In both figures, 1 is a Si substrate and 3 is a Si substrate. A quartz substrate for bonding to the substrate 1, 4 and 5 LB films accumulated on the surface of the Si substrate 1, 6 LB films accumulated on the surface of the quartz plate 3,
7 and 8 are hydrophilic groups and hydrophobic groups of the LB film 4 on the Si substrate 1, 9 and 10 are hydrophilic groups and hydrophobic groups of the LB film 5, 11 and 12 are hydrophilic groups and hydrophobic groups of the LB film 6, respectively. 13 is a platen for mounting the quartz substrate 3 and the Si substrate 1, 17 is a power supply for applying an electric field between the Si substrate 1 and the quartz substrate 3, and 19 and 20 are Si, respectively.
Needle electrodes electrically connected to the substrate 1 and the quartz substrate 3 (the platen 13 is made of a conductor), and 21 electrically connects the needle electrodes 19 and 20 and the power supply 17. The lead wire 22 is a laser beam for irradiating the interface between the Si substrate 1 and the quartz substrate 3 and the LB films 4, 5, and 6.

Next, in the above configuration, first, the Si substrate 1
Then, a cumulative film of the LB films 4 and 5 and a monomolecular film of the LB film 6 are formed on the quartz substrate 3, respectively.
The LB films 5 on the Si substrate 1 are opposed to each other from above the B film 6, and are superposed while being positioned. Then, power supply 17
To apply an electric field between the Si substrate 1 and the quartz substrate 3, and the electrostatic attraction caused by the electric field causes the LB film 5 on the Si substrate 1 and the LB film 6 on the quartz substrate 3 to move between the LB film 5 and the LB film 6.
Close to the interatomic distance over the entire surface. Furthermore, Si
While applying an electric field between the substrate 1 and the quartz substrate 3, a laser beam 22 is simultaneously irradiated from above the Si substrate 1,
The membranes 4, 5 and 6 are decomposed and evaporated. The LB films 4, 5 and 6 disappear by this decomposition and evaporation, but at this time, the distance between the Si substrate 1 and the quartz substrate 3 is close to the distance where the atomic force or the intermolecular force acts. Therefore, as a result, the Si substrate 1 and the quartz substrate 3 are directly bonded.

In the case of this embodiment, a cumulative film of behenic acid is used as the LB films 4 and 5, stearylamine is used as the LB film 6, and about 200 mm is provided between the Si substrate 1 and the quartz substrate 3.
Irradiate CO ₂ laser light while applying [V] (about 5W
/ Cm ² ), the Si substrate and the quartz substrate 3 adhered after about one hour. The bonded substrate was strong enough to withstand subsequent cutting by a dicing saw.

In the case where an insulator (for example, Pyrex (trade name) glass or the like) to which a mobile ion is added as an impurity or intentionally is used instead of the above quartz substrate, the intention of the present invention is also considered. What you do is not changed.

[Embodiment 4] In this embodiment, single crystal substrates having different crystal orientations were joined to each other in substantially the same manner as in Embodiment 1. That is, a first Si substrate in which two layers of behenic acid LB film are accumulated on the (100) Si substrate surface,
After washing by boiling with a mixed acid, a second (110) Si substrate subjected to a hydrophobic treatment with 2% hydrofluoric acid was joined in the following manner. After laminating the first and second Si substrates with the LB film interposed therebetween, the substrate was heated to 200 ° C. while applying 5 V between the two substrates.
The bond was made by holding for 0 minutes.

The Si substrate bonded as described above was cut with a dicing saw, but no peeling of the substrate occurred, and it was confirmed that the substrate was firmly adhered.

Example 5 After washing by boiling with trichloroethylene, a stearylamine LB film was further deposited on the surface of an InP substrate whose surface was cleaned with a mixed aqueous solution of sulfuric acid and hydrogen peroxide. On the other hand, after the Si substrate was washed by boiling with a mixed acid, the surface was hydrophobized with 2% hydrofluoric acid. After laminating the two substrates via an LB film, the substrates were heated to 250 ° C. and held for one hour while applying 3 V between the two substrates to perform bonding.

The substrates joined together as described above were cut with a dicing saw. No peeling of the substrates occurred, and it was confirmed that the substrates were firmly adhered.

As apparent from the fourth and fifth embodiments, according to the present invention, different kinds of substrates can be bonded to each other in a low-temperature region, and thus are caused by thermal stress found in the conventional method. The occurrence of crystal transition can be avoided.

[0033]

As described above, in the solid-state bonding method of the present invention, the following effects are obtained by using a monomolecular film or a monomolecular cumulative film for the bonding surface.

(1) In the solid-phase bonding, an adhesive force that does not cause the substrates to be peeled from each other is generated only by superimposing with a very small load, so that the positioning (alignment operation) is easy, and further, the positioning after the positioning is performed. Handling is also easy. Further, since the LB film has high insulation resistance and can apply a large electrostatic attraction between the bonded substrates, it is possible to further increase the adhesive force after positioning.

(2) using the LB film for the initial bonding step,
After that, the LB film is heated to the decomposition and evaporation temperature (about 300
℃ or more), the LB film disappears.
The bonding between the conductive substrates is made stronger.

(3) using the LB film for the initial bonding step,
After that, the LB film is decomposed and evaporated by laser light irradiation.
By irradiating the laser light sequentially and evenly from the center of the bonding to the outer periphery of the bonding, uniform bonding can be achieved over the entire surface.

[Brief description of the drawings]

FIG. 1 is a diagram used for describing electrostatic attraction acting between substrates.

FIG. 2 is a cross-sectional view of an adhesive embodying the present invention.

FIG. 3 is a cross-sectional view of an adhesive embodying the present invention.

FIG. 4 is a cross-sectional view of a sample before bonding according to the present invention.

FIG. 5 is a cross-sectional view of an adhesive embodying the present invention.

[Explanation of symbols]

 1, 2, Si substrate 3 Quartz crystal substrate 4, 5, 6 LB film 7, 9, 11 Hydrophilic group of LB film 8, 10, 12 Hydrophobic group of LB film 13 Platen 14 Heater power supply 15 Switch 16 Lead wire 17 For applying electric field Power supply 18 Switch 19,20 Needle electrode 21 Lead wire 22 Laser beam

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 21/02 B23K 20/00 C04B 37/00 C09J 5/00

Claims (14)

(57) [Claims] 1. A method of joining at least two members, wherein a step (A) of forming a monomolecular film or a monomolecular cumulative film on at least one joint surface, and the step of joining the members via the joint surface A solid-state bonding method comprising: a step (B) of bringing the two into close contact with each other; and a step (C) of applying an electric field to the bonding surface. 2. A method of joining at least two members, wherein a step (A) of forming a monomolecular film or a monomolecular cumulative film on at least one joining surface, and the step of joining the members via the joining surface A solid-state bonding method, comprising: a step (B) of bringing them into close contact with each other; a step (C) of applying an electric field to the bonding surface; and a step (D) of heating the bonding surface. 3. A method for joining at least two members, wherein a step (A) of forming a monomolecular film or a monomolecular cumulative film on at least one joint surface, and the step of joining the members via the joint surface A solid-state bonding method comprising: a step (B) of bringing the two into close contact with each other; a step (C) of applying an electric field to the bonding surface; and a step (E) of irradiating the bonding surface with a laser beam. 4. The solid-state bonding method according to claim 2, wherein the step (C) and the step (D) are sequentially performed. 5. The solid-state bonding method according to claim 2, wherein the steps (C) and (D) are performed substantially simultaneously. 6. The solid-state bonding method according to claim 3, wherein the step (C) and the step (E) are sequentially performed. 7. The solid-state bonding method according to claim 3, wherein the step (C) and the step (E) are performed substantially simultaneously. 8. The solid-state bonding method according to claim 1, wherein at least one of the members is a conductor. 9. The solid-state joining method according to claim 1, wherein the members are of the same quality. 10. The apparatus according to claim 1, wherein said members are different from each other.
The solid phase bonding method according to any one of Items 1 to 3. 11. The solid-state bonding method according to claim 1, wherein the monomolecular film or the monomolecular accumulation film is insulating. 12. The monomolecular film or the monomolecular cumulative film,
The solid phase bonding method according to any one of claims 1 to 3, wherein the method is a fatty acid having 16 to 30 carbon atoms and a derivative thereof . 13. The solid-state bonding method according to claim 2, wherein the heating is performed using a heater. 14. The method according to claim 3, wherein a CO ₂ laser beam is used as the laser beam.