JPH06340901A - Sintering method - Google Patents

Abstract

PURPOSE:To form a line or protrusion shape on a substrate by a dry and simple process without raising the temp. of the substrate. CONSTITUTION:A substrate 1 with a circuit 2 and an insulating protective film 3 is coated with a gold vapor-deposited film 4 and a film 5 of superfine gold particles is disposed on a prescribed part of the circuit 2 and sintered by irradiation with laser light 6. The reflectance of the film 5 is measured with a reflectance measuring instrument 19 at the time of irradiation with the laser light 6, the sintered state of the film 5 is estimated from the measured value, and the output of the laser light 6 and irradiation time are controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sintering method, and more particularly to a method for forming a sintered body on a substrate without raising the substrate temperature.

[0002]

2. Description of the Related Art In the process of forming a sintered body on a substrate, various metal films and non-metal films are formed. These membranes
Mainly made by vacuum deposition method, sputtering method, CVD method or the like, and plating method or screen printing method is used depending on the manufacturing conditions.

In the process of manufacturing electronic parts, the temperature of the substrate on which the film is to be formed cannot be raised and the film thickness is from several μm to several tens.
In some cases, a film having a thickness of μm is formed and processed into a specific shape. In such a case, the vacuum vapor deposition method and the sputtering method require a long time for film formation, and when the film thickness increases, it takes a long time to etch unnecessary portions and the accuracy decreases. In the case of the method, it is not used because the substrate is heated by radiation from the evaporation source.
Screen printing is not used because it heats the entire substrate to fire the printed paste.

Therefore, the plating method is used under such conditions. In the plating method, a film can be formed without heating the substrate, but the substrate must be immersed in a plating solution. There are drawbacks such as requiring a long time for plating, complicating the whole process such as an electrode forming process and a photoresist process, making the film thickness non-uniform, and lowering the yield. Despite the high cost due to the above-mentioned drawbacks, the plating method is currently used under the above-mentioned conditions.

A technique described in Japanese Patent Laid-Open No. 57-160975 is related to the sintering technique proposed by the present invention.

[0006]

The plating method is inevitably costly because of the complexity of the process and the poor yield. In particular, the wet process is inconvenient for other manufacturing processes.

Although the sintering of ultrafine particles by laser is known in the above-mentioned publication, it is not intended to irradiate ultrafine metal powder and cannot be used for manufacturing electronic parts, for example.

An object of the present invention is to provide a method for forming a linear or projecting shape on a substrate by a dry and simple process without raising the substrate temperature.

[0009]

The above object is to provide a method of irradiating energy to a metal powder or a mixture of a metal powder and a non-metal powder arranged on a substrate to sinter the metal powder or the mixture. A black ultrafine particle is used as a part or all of the powder, and the sintered state of the metal powder or the mixture at the portion irradiated with energy is detected by a sensor as the energy absorption rate and / or reflectance, and the irradiation position is the energy absorption body. This is achieved by stopping the irradiation of energy at the time when the energy is converted into a reflector of energy.

The black ultrafine particles may be metal and / or ceramic ultrafine particles.

The energy irradiation source may be selected from laser light and light beam.

(Formation of Raw Material Coating) The ultrafine particle-containing layer is preferably applied in a paste form.

Alternatively, it is preferable that a film of a substance having a high reflectance with respect to the irradiation energy is formed on the surface of the substrate before forming the layer containing the ultrafine particles on the surface of the substrate.

Further, prior to the formation of the ultrafine particle-containing layer on the substrate surface, a film for enhancing the wettability between the sintered body obtained by the energy irradiation and the substrate may be formed on the substrate surface. desirable.

The paste is preferably applied by printing in a predetermined pattern.

On the other hand, it is also effective to irradiate the ultrafine particle-containing layer with energy and sinter it, and then remove the other unsintered portion.

(Applied Product) The present invention is applicable to electronic parts, especially TAB.
It is most suitable for bump parts of IC chip mounted products by (tape automated bonding) method, and is also effective for forming microcircuit wiring such as IC chips and conductor film and / or wiring of multilayer wiring board. is there.

Application examples of electronic parts represented by TAB are as follows:
The substrate is an insulating film, conductor wiring is provided on the film, the ends of the conductor wiring are connected to the upper surface of the IC chip by bumps, and the bumps are used as the sintered body.

[0019]

The operation will be described below by taking black metal ultrafine powder as an example.

By making the metal powder ultrafine, the light absorptivity was increased and the sintering by laser irradiation was facilitated.

Further, since the laser irradiation time can be shortened by grasping the sintering state with the sensor and irradiating the laser, the heating of the substrate by the laser irradiation can be suppressed. In addition, since the ultrafine metal particle film becomes a high light reflector after sintering, it is not heated more than necessary and prevents the heating of the substrate.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a method of sintering ultrafine gold powder by laser light irradiation according to an embodiment of the present invention.

In the figure, 1 is a silicon substrate, 2 is aluminum wiring, 3 is an insulating protective film, 4 is a gold vapor deposition film, 5 is a gold ultrafine powder film, and 6 is a laser beam. , And 7 are laser oscillators.

FIG. 2 is a sectional view of the substrate before the ultrafine gold film 5 is formed, and FIG. 3 is a sectional view of the substrate after the ultrafine gold film 5 is formed in FIG.

Originally, gold is a high-reflector of light and reflects about 95% of YAG laser (wavelength 1.06 μm), and C
It reflects about 98% for an O ₂ laser (wavelength 10.6 μm). However, when ultrafine particles are formed, gold becomes a light absorber having a very high absorptance. Generally, a metal becomes a high light absorber by ultra-fine atomization. Part of the present invention takes advantage of this characteristic and attempts to sinter ultrafine powder by laser irradiation.

First, as shown in FIG. 2, a gold (Au) thin film is formed on an IC chip. The forming method may be a sputtering method, a vacuum vapor deposition method, or a CVD method, and the forming method is not particularly limited.

Next, as shown in FIG. 3, a paste made of ultrafine Au powder is printed, heated to about 400 ° C. in an inert gas, N ₂ atmosphere, or air, and dried.

Next, as shown in FIG. 1, dried Au ultra-fine powder is irradiated with a laser for about a few seconds to a few seconds and sintered in an extremely short time, and the shape is about 100 μm × 100 μm and the height is about 2 μm.
A gold bump of 0 μm is formed. The laser may be a YAG laser, a CO ₂ laser or a glass laser, and there is no particular limitation. At this time, the Au vapor deposition film formed on the IC chip is
u Reflects laser light other than the ultrafine powder film to prevent temperature rise of the IC chip. Further, since Al and Au have poor wettability, if Au ultra-fine powder is directly applied to the Al wiring, even if sintering is performed by laser irradiation, sufficient adhesion can be obtained between the Al wiring and the gold bump. I can't. However, when the Au vapor deposition film is formed in advance, the Au bump and the Al wiring are sufficiently bonded. Therefore, other than the Au vapor-deposited film, the vapor-deposited film may be formed of a material (Pd or the like) that can obtain the adhesive force between the Au bump and the Al wiring.

As described above, in the present invention, the laser irradiation portion is extremely small, the laser irradiation time is extremely short, and the Au vapor deposition film on the IC chip reflects laser light other than the Au ultrafine powder film. That is, after the ultrafine gold film is sintered, it becomes a high-reflector of light, and the energy absorption after sintering is reduced, so that the Au bump can be formed at a low temperature in the IC chip.

According to this embodiment, Au bumps can be formed on the IC chip by a simple dry process with extremely high productivity.

FIG. 4 is a sectional view of the TAB mounting obtained in the above embodiment, and FIG. 5 is a plan view of the same. 8 in the figure is an IC
Chip, 9 polyimide film, 10 copper lead, 1
1 is an Au bump.

The TAB mounting method enables thinning, miniaturization, and multi-pinning of IC elements, and is essential for OA devices and calculators that have become thinner in recent years, especially for IC cards that need to be thinned. It is a technology.

First, according to the conventional technique, a copper thin plate is adhered on a polyimide film, and a copper lead is formed by etching.

On the other hand, on the aluminum wiring of the IC chip to be connected to the copper lead, the thickness A of about 20 μm is plated.
Form u bumps. The Au bump and the copper lead are bonded by the bonding method, and the IC chip is mounted on the polyimide film. Since the IC chip cannot raise the temperature above about 450 ° C., the bump on Au must be formed by a plating method that does not raise the substrate temperature. However, as described above, the steps of the general plating method are complicated in (1) formation of electrodes for plating, (2) photoresist step, (3) plating step, (4) removal of photoresist, and (5) electrode etching. Therefore, a long time is required, and because the height of the Au bumps is not uniform, a defective connection with a copper lead is likely to occur, resulting in a poor yield.

The above-mentioned drawbacks of the prior art are eliminated by adopting the embodiments of FIGS.

Next, an outline of a process of forming Au bumps on copper leads according to an embodiment of the present invention will be described with reference to FIGS.

6 and 7, 10 is a copper lead, and 9 is
Is a polyimide film, 12 is a Sn vapor deposition film, 5 is an Au ultrafine powder film, 13 is a copper block, 6 is a laser beam, and 7 is a laser oscillator.

Like the IC chip, the polyimide film cannot withstand a temperature of about 450 ° C. or higher, so that Au bumps must be formed at a low temperature.

First, as shown in FIG. 6, S is formed on the copper lead.
An evaporated film is formed. The method for forming the Sn vapor deposition film may be vacuum vapor deposition, sputtering, or plating, and is not particularly limited.

Next, as shown in FIG. 7, a paste made of ultrafine Au powder is printed, heated to about 400 ° C. in an N ₂ gas atmosphere which is an inert gas, and dried. Next, as shown in FIG. 7, the copper leads are sandwiched between the copper blocks from above and below, and the ultrafine Au film is irradiated with a laser for about a few seconds to a few seconds in an inert gas atmosphere such as N ₂ or Ar to sinter. , Au bumps are formed. At this time, the copper block absorbs heat generated by the laser light irradiation and prevents the polyimide film from being heated. Further, the Sn vapor-deposited film causes a eutectic reaction with the Au bumps and produces a sufficient adhesive force.

At the time of laser light irradiation, an inert gas atmosphere such as N ₂ or Ar must be used in order to prevent oxidation of the copper leads and the Sn vapor deposition film.

FIG. 8 shows an embodiment. In FIG. 8, 1
0 is a copper lead formed with a Sn vapor-deposited film, 9 is a polyimide film, 5 is an ultrafine powder film of gold, 13 is a copper block, 14 is a rectangular cylindrical copper block, 7 is a laser oscillator, 15 is a pipe, and 6 is a laser beam. Is. The copper leads to be irradiated with laser are sandwiched between the copper blocks from above and below, and N ₂ or Ar is blown into the inside of the rectangular cylindrical copper block from a pipe, and only the periphery of the laser-irradiated portion is made into an N ₂ or Ar atmosphere. According to this method, Au bumps can be formed on the copper leads according to this embodiment even in the atmosphere.

As described above, in this embodiment, the laser irradiation portion is extremely small and the irradiation time is short, the heat is taken away by the copper block, and the ultrafine gold film has an increased reflectance after sintering and absorption. Due to such a decrease in the rate, the Au bumps can be formed with good productivity while keeping the polyimide film at a low temperature.

Next, still another embodiment will be described with reference to FIGS.

When the electrodes are to be connected after the IC chip is completed, it is inefficient to form the Al wiring by the steps of ordinary photoresist, Al vapor deposition and etching. Also I
Since the C chip is completed, the substrate temperature cannot be raised and an efficient screen printing method cannot be used.

FIG. 9, FIG. 10 and FIG. 11 show the outline of the process of forming Au wiring on the IC chip according to this embodiment.
In each figure, 8 is an IC chip, 16 and 17 are electrodes to be connected by Au wiring, 18 is an insulating protective film, 5 is Au ultrafine powder film, 6 is laser light, and 7 is a laser oscillator.

First, as shown in FIG. 10, an ultrafine Au film is applied between the electrodes to be connected. In this case, only Au ultrafine powder may be applied, or a paste using Au ultrafine powder may be used. After forming the Au ultrafine powder film, the laser beam or the IC chip is moved, and the laser beam is irradiated so as to connect the electrodes to sinter only the wiring part connecting the electrodes. After the laser irradiation, the unsintered part of the Au ultrafine particle film is removed with water or an organic solvent as shown in FIG.

As described above, according to the present embodiment, since the laser irradiation time is short and the Au ultrafine powder film becomes a high light reflector after sintering and does not absorb extra heat, the substrate temperature is kept low. The Au wiring having an arbitrary shape can be efficiently formed. Further, in the case of forming the Au wiring, similarly to the Au bump forming method described above, even if only the wiring portion is printed, dried and then sintered by laser irradiation, it can be similarly efficiently formed.

Looking at the external appearance photograph of the Au ultrafine particle film sintered by this method, the Au ultrafine particle film was applied on the silicon substrate on which the Au vapor deposition film was formed, and the laser beam was irradiated to obtain a diameter of about 1 mm.
According to the Au thin film sintered in a circular shape of mm, the gold-colored circular portion is the Au thin film sintered by laser irradiation, and the surrounding black portion is the unsintered Au ultrafine particle film. The laser used at this time is a YAG laser, and the irradiation time is about 1 second. The adhesive strength with the substrate after sintering was strong, and the tape test did not cause peeling.

Although Au bumps are formed on the Al wirings in this example, conductive metal wirings other than Al, such as Cu, Sn, Ag and Au, are symmetrical. The bump material is not only Au but also A
Ultrafine particles of g, Cu, Al and the like may be black as long as they become black and are reflective after sintering.

In the wiring method described in the examples of FIGS. 9 to 11, it is also possible to form a multilayer wiring by this method by further forming an insulating layer and then repeating the same wiring.

Further, in FIG. 10, a metal film can be formed by scanning a wide area by scanning a laser beam or a chip.

This example was explained using laser light, but a heat source (electron beam,
Infrared, plasma, light beam, etc.) may be used.

FIG. 12 shows the relationship between the light reflectance and the ultrafine particle diameter when gold ultrafine particles are applied in a film form. ● indicates the reflectance for light with a wavelength of 0.9 to 1.1 μm, ○ indicates a wavelength of 9
It is the reflectance for light of ˜11 μm. Average particle size about 10
The 0Å gold ultrafine film has a YAG laser wavelength (1.06 μm).
The light equivalent to is completely absorbed. It is also a high absorber for light corresponding to the CO ₂ laser wavelength (10.6 μm). For comparison, the reflectance of bulk gold (mirror surface) for light of the same wavelength is shown in the same figure. Bulk gold has extremely high reflectance for light of both wavelengths. In the present embodiment, the characteristics of the reflectance and the characteristics of the low temperature sinterability of the ultrafine metal particles are utilized to sinter by laser irradiation.

FIG. 13 shows a modification of FIG. Reference numeral 19 in the drawing is a reflectance measuring device (sensor).

Originally, gold is a high-reflector of light.
As shown in No. ₂ , about 95% is reflected also to the YAG laser (wavelength 1.06 μm) and the CO ₂ laser (wavelength 10.6 μm)
For m), about 98% is reflected. However, when made into ultrafine particles, gold becomes a high absorber of light. In general, a metal becomes a high light absorber by ultra-fine atomization.

This example is different from that shown in FIG. 1 in that the sensor is used to appropriately grasp the progress of sintering by utilizing this characteristic.

That is, as shown in FIG. 13, dried A
The ultrafine powder film is irradiated with a laser for about a few seconds to a few seconds and sintered in an extremely short time to form a gold bump having a shape of about 100 μm × 100 μm and a height of about 20 μm. At the time of laser irradiation, the reflectance of the gold ultrafine particle film is measured by a reflectance meter. Estimate the sintering condition of the ultrafine particle film from the reflectance,
The output of laser light and the irradiation time are controlled. The subsequent procedure is based on the first embodiment.

In the above embodiments, an example using a paste composed of Au ultrafine particles is shown. However, it is not necessary that all Au particles in the paste are ultrafine particles, and a mixture of gold fine particles and gold ultrafine particles, or It may be a paste composed of a mixture of ceramic powder, fine gold particles and ultrafine gold particles.

[0061]

According to the present invention, it is possible to easily form a film having a film thickness of several tens of μm under the condition that the substrate temperature cannot be raised, which can be formed only by a plating method which requires complicated steps. It can be formed in a drying process with extremely high productivity.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an electronic component in which a gold bump is formed by laser light irradiation according to an example of a sintering method of the present invention.

2 is a cross-sectional view of a substrate which is a material of the embodiment of FIG.

FIG. 3 is a cross-sectional view of a substrate coated with a gold ultrafine particle film in FIG.

FIG. 4 is a cross-sectional view of IC chip mounting obtained by the embodiment of FIG.

5 is a perspective view showing a mounting state of FIG. 4. FIG.

FIG. 6 is a cross-sectional view of a base body which is a material of the embodiment of FIG.

FIG. 7 is a cross-sectional view of an electronic component in which gold bumps are formed by laser light irradiation according to an example of the sintering method of the present invention.

FIG. 8 is a partial perspective view of an electronic component in which a gold bump is formed by laser light irradiation by an example of the sintering method of the present invention.

FIG. 9 is a perspective view of a substrate for providing micro wiring according to an example of the sintering method of the present invention.

FIG. 10 is a perspective view of the substrate of FIG. 9 during irradiation with laser light.

11 is a perspective view of a wiring-provided base body obtained in the process of FIG.

FIG. 12 is a characteristic diagram comparing the reflectance of the ultrafine particle film and the reflectance of the bulk.

FIG. 13 is a cross-sectional view of an electronic component in which gold bumps are formed by laser light irradiation according to an example of the sintering method of the present invention.

[Explanation of symbols]

1 ... Silicon substrate, 2 ... Aluminum wiring, 3 ... Insulation protective film,
4 ... Gold vapor deposition film, 5 ... Gold ultrafine particle film, 6 ... Laser light, 7 ...
Laser oscillator, 8 ... IC chip, 9 ... Polyimide film, 10 ... Copper lead, 11 ... Gold bump, 12 ... Tin vapor deposition film, 13, 14 ... Copper block, 19 ... Reflectance measuring device, 2
0, 21 ... Object to be joined, 22 ... Gold vapor deposition film, 23 ... Substrate, 2
4 ... Detector, 25 ... Protective film.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication location H01L 21/3205 21/321 (72) Inventor Susumu Hioki 502 Kandachi-cho, Tsuchiura-shi, Ibaraki Prefecture Tate Seisakusho Mechanical Research Center

Claims (3)

[Claims] 1. In a method of irradiating energy to a metal powder or a mixture of a metal powder and a non-metal powder arranged on a substrate to sinter the metal powder or mixture, part or all of the metal powder is black. Using ultrafine particles, the sensor detects the sintered state of the metal powder or mixture at the energy irradiation portion as the energy absorption rate and / or reflectance, and the irradiation position is converted from the energy absorption body to the energy reflection body. A sintering method characterized in that the irradiation of energy is stopped at a time point. 2. The sintering method according to claim 1, wherein the black ultrafine particles are metal and / or ceramic ultrafine particles. 3. The sintering method according to claim 1, wherein the energy irradiation source is selected from a laser beam and a light beam.