JPS6347758B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of bonding two members to be bonded, one of which is a solid that is transparent to light, such as glass or dielectric crystal.

Technologies for bonding different materials using extremely thin adhesives are used, for example, to create communication devices that use sound waves that propagate in solids, electroacoustic transducers in optoelectronic devices, and glass when manufacturing cells in liquid crystal display devices. This technique is needed in many fields such as gluing plates and crystal plates.

One method that has been commonly used to fabricate cells for liquid crystal display devices is to use screen printing technology to apply thermosetting resin adhesive to the periphery of the main surfaces of two glass plates used as substrates. print on,
This is a method of bonding them together, applying pressure, and heating them to about 100 to 150°C to harden them. The characteristics of a liquid crystal cell, such as the required applied voltage and display speed, are greatly influenced by the thickness of the cell into which the liquid crystal is injected. Therefore, in order to minimize variations in these characteristics within the display surface and also to reduce variations among fabricated elements, a sophisticated technique for bonding the substrates is required. The voltage must be applied to all substrates to a constant thickness, and moreover, to a constant thickness evenly within the substrate surface. Further, the load applied during thermal curing needs to be delicately adjusted in consideration of thermal deformation of the glass substrate. In recent years, the materials used for substrates are not only the same glass materials, but also silicon crystal plates,
There is an increasing need for adhesion between different materials, such as substrates with photoconductive thin films. Since the materials used here have different coefficients of thermal expansion, the substrate is likely to warp or deform, or the thin film provided on the substrate may peel off when the temperature is lowered after thermosetting. In addition, in order to improve the above-mentioned properties, it is necessary to further reduce the cell thickness, but with conventional bonding methods such as screen printing, it is difficult to apply adhesive accurately with little variation. It is.

Some of the fields that require advanced adhesive technology include:

There are many devices that utilize ultrasonic motion ranging from megahertz (MHz) to gigahertz (GHz), such as ultrasonic delay lines, ultrasonic microscopes, and acousto-optic devices. Many devices require methods to efficiently excite sound waves over a wide frequency range. To excite plane wave sound waves in a solid, a porcelain or crystal body having magnetostrictive, electrostrictive, or piezoelectric effects is usually adhered to the solid surface, and a high-frequency electric field is applied to an electrode provided on the porcelain or crystal. The piezoelectric effect of dielectric crystals, especially the piezoelectric effect of dielectric crystals, is currently being used because of their ease of handling and good properties. A commonly used method is to apply an electric field in the thickness direction of a thin dielectric crystal plate and use it near the resonance frequency determined by this thickness. The conventional method for bonding a piezoelectric crystal plate to a solid body in which it is desired to excite sound waves is to use a thermosetting resin, or to attach indium, a low melting point metal, to both by vapor deposition or the like, and heat it to near the melting point of indium. There are known methods for welding. As is well known, resin absorbs large sound waves and is inconvenient for use in the high frequency range mentioned above, and indium also has a 1 GHz transverse wave of 160,000 dB/cm and a longitudinal wave of 80,000 dB/cm.
It is as large as cm. Therefore, heat generation occurs due to absorption, leading to changes in the acoustic and optical characteristics of the element. Furthermore, since indium is easily oxidized by air and susceptible to many chemical liquids and their vapors, there are concerns about the long-term reliability of the device. A gold film and an indium film are provided on both the piezoelectric crystal and the solid to which it is attached by vapor deposition as described above, and the indium surfaces of both are placed in a vacuum and pressure is applied for a long period of time at room temperature. A known method is to bond indium together and then raise the temperature to the melting point of indium to form an alloy of indium and gold. An alloy of indium and gold has a high melting point of over 400 degrees Celsius, and its absorption of sound waves is lower than that of indium itself, increasing the reliability of the device. However, since the processing steps must be performed in a vacuum, productivity is low, and it is not possible to use a method such as forming patterns on the deposited film using a mask or the like and aligning the patterns. In addition, since the element is heated above 156°C, which is the melting point of indium, when forming the alloy, when the temperature is lowered to room temperature after processing, heat is generated due to the difference in thermal expansion coefficient between the piezoelectric material and the solid material to which it is bonded. If the strain becomes too large, both may be destroyed. For example, when a lithium niobate crystal is used as a piezoelectric crystal, and fused silica, which is a material with excellent light transmission properties, is used as a medium to bond the piezoelectric crystal and excite sound waves, the thermal expansion coefficient of the lithium niobate crystal is 16.7× 10 ^-6 /℃,
That of fused silica is 5.5×10 ^-7 /°C, which is two orders of magnitude different.
For this reason, even after heating to around 150℃, after cooling down,
Thermal distortion occurs and cracks occur in the lithium niobate crystal. Also, sometimes the fused silica itself is destroyed. The coefficient of thermal expansion of most piezoelectric crystals, not just lithium niobate, is approximately 10×10 ^-6 /°C. For this reason, bonding with fused silica, which has a small coefficient of expansion, has conventionally been achieved only by methods using organic adhesives or indium, which can absorb strain differences to some extent through the softness of the material. For this reason, it has become difficult to achieve high performance with a wide acoustic bandwidth and low heat generation due to acoustic absorption with elements using fused silica.

As described above, all conventional bonding methods have drawbacks. The purpose of the present invention is to eliminate the above-mentioned difficulties and provide a method for bonding solid materials having different coefficients of thermal expansion with high performance, high reliability, simplicity, and excellent productivity without exposing samples to high temperatures. It is something.

The gist of the present invention is to provide two solid materials to be bonded, one of which is provided with a low-melting point metal film, and the other with a thin film of a metal that undergoes a solid phase reaction with the low-melting point metal at low temperatures. The method involves applying a load so that the entire vapor deposition surface is in contact with the two metals, irradiating a laser beam through either member, and causing alloying between the two metals by a solid phase reaction to bond them. The present invention will be explained in more detail based on the following.

FIG. 1 is a diagram for explaining one embodiment of the present invention, and is a diagram showing a cross-sectional structure before bonding, where 1 is a first substrate such as glass or dielectric crystal, and 2 is a first substrate. This is the second substrate to be bonded. An indium film 3 is provided on the first substrate 1 to a desired thickness by vacuum evaporation or the like. In order to strengthen the adhesion of the indium film 3 to the first substrate, a thin film 5 of chromium, nichrome, or the like is similarly provided by a method such as vapor deposition, if necessary. Similarly, a thin film 5 of chromium or the like and a gold film 4 are provided on the second substrate 2 by vapor deposition or the like. As shown in FIG. 2, the vapor deposition surfaces of both substrates are brought into contact with each other in air at room temperature, and a light weight is applied between both substrates so that the entire vapor deposition surfaces are in uniform contact. A pulsed laser beam 6 focused on the deposited film is irradiated by a lens 7 from the substrate 2 side. Pulsed laser beam 6
Examples include argon laser light, YAG laser light,
Uses CO ₂ laser light, etc. The light transmitted through the substrate 2, which has almost no light absorption, passes through the thin vapor deposited films 3, 4, 5.
, which increases the temperature of the deposited film. Indium and gold have a melting point lower than indium's melting point of 165℃.
It alloys in a solid state without melting at around 120℃. The pulsed laser light uses pulsed light with wide pulse intervals and high peak intensity. Because only the very localized deposited film irradiated with light is alloyed instantly and at a low temperature, much lower energy light intensity is required than with laser processing equipment such as a laser trimmer or scriber, and the substrates 1 and 2 are does not cause temperature rise. By irradiating the entire contact surface with laser light using a scanning means, adhesion of the entire surface is completed. Once the alloy is reacted, its melting point rises to over 400°C, so even if the same spot is irradiated with laser light, it will not melt. Therefore, a highly accurate scanning means is not required.

In the present invention, the substrates 1 and 2 are brought into contact at room temperature, and the laser beam is irradiated locally for a short period of time and with low energy enough to cause a solid phase reaction, so the temperature of the substrates does not increase. Good adhesion is achieved even if the coefficient of thermal expansion is large.

In the description of this embodiment, the laser beam is irradiated from the substrate 2 side, but it is of course possible to irradiate the laser beam from the substrate 1 side. Further, although it has been described that indium is used as the low melting point metal, other metals such as tin may be used as long as one of the films has a low melting point metal. Although gold was used as a metal that causes a solid phase reaction with a low melting point metal at low temperatures, other metals such as silver can have the same effect as in this example as long as they cause a solid phase reaction with a low melting point metal at low temperatures. Needless to say.

As described above, according to the present invention, it is possible to obtain a high-performance, highly reliable bonding method with a thin adhesive phase, as well as a simple and highly productive bonding method.

[Brief explanation of drawings]

1 and 2 are structural sectional views of an embodiment of the present invention, in which 1 and 2 are substrates to be bonded, 3 is a low melting point metal film, 4 is a gold thin film, and 6 is a pulsed laser beam.

Claims (1)

[Claims] 1. A first member having a thin film of indium or tin, which is a low melting point metal, on the adhesive surface, and an alloy formed by causing a solid phase reaction with the low melting point metal at a low temperature on the surface to which the first member is to be adhered. A second member provided with a thin film of gold or silver to be formed is brought into contact with each other at an adhesive surface, pressure is applied to the member substantially perpendicular to the adhesive surface, and further a laser beam is irradiated through one of the members. An adhesion method characterized by: