Process for Producing Wiring Circuit Board

This invention relates to a process for producing a wiring circuit board having a fine wiring pattern on a substrate.

Heretofore, a wiring circuit board of thin film, multi-layer structure has been produced by forming a metal layer on a substrate by vacuum vapor deposition, sputtering, etc., removing unwanted parts from the metal layer by etching, thereby obtaining a desired wiring pattern, forming an insulating layer of metal oxide or metal nitride on the metal layer by sputtering, chemical vapor deposition, etc., removing predetermined parts from the insulating layer by chemical etching, thereby forming via-holes (through-holes), and then forming another wiring pattern on the insulating layer in the same manner as above. However, the wiring circuit board of thin film multi-layer structure tends to have less smooth surface with increasing number of layers owing to be formation of wiring pattern by etching. When a metal layer or an insulating layer is formed on such less smooth surface by sputtering or vapor deposition, only a smaller amount of metallic substance or insulating substance is deposited on the less smooth surface, with the result of uneven layer thickness and occurrence of disconnection or poor insulation. This leads to poor reliability and low production yield.

Furthermore, formation of a metal layer in via-holes is not satisfactory, so that the connection of wiring patterns in the individual layers is incomplete. This is a cause of disconnection. The number of layers that ensures is now limited to 2 at most.

An object of the present invention is to provide a process for producing a wiring circuit board free from occurrence of disconnection and poor insulation.

According to the present invention, an insulating layer comprising a plurality of insulating substances having different dissociation energies for metalization, including metal elements is provided on a substrate, and an energying beam is given to a predetermined position on the insulating layer, thereby metalizing one of the insulating substances to form a wiring pattern.

FIG. 1--1 to FIG. 1--4 show steps for producing a wiring circuit board of thin film multi-layer structure according to one embodiment of the present invention.

FIG. 2--2 to FIG. 2--7 show steps for producing wiring circuit board of thin film multi-layer structure according to another embodiment of the present invention.

A substrate 6 with a smooth surface made of sapphire or 99.5% Al.sub.2 O.sub.3 was heated at 400.degree.-700.degree. C. (FIG. 1--1), while Si and Cu were heated by a heater and vaporized to form a metal layer 7 consisting of a plurality of different metals, i.e. Si and Cu, on the substrate (FIG. 1--2).

Then, the metal layer 7 was heated in an O.sub.2 gas at 1,000.degree. C. to form an insulating layer 8 consisting of metal oxides, i.e. SiO.sub.2 and Cu.sub.2 O (FIG. 1--3). Cu.sub.2 O had a lower dissociation energy for oxygen than SiO.sub.2. Then, the insulating layer 8 on the substrate 6 was irradiated at predetermined positions in a hydrogen gas atmosphere with a YAG laser beam having an energy density of 0.1 J/cm.sup.2 -1.5 J/cm.sup.2 at a scanning speed of 1-20 cm/sec to deposit Cu, whereby a wiring pattern 9 was formed (FIG. 1--4).

The wiring pattern extended to a depth of 0.5-2 .mu.m and had a good electroconductivity such as 10.sup.-4 -10.sup.-5 .OMEGA..cm, whereas the non-irradiated parts had a good electric insulation such as 10.sup.10 -10.sup.13 .OMEGA..cm.

The given energy is not limited to a laser beam, and any means of locally giving an energy to the insulating layer 8 can be used.

The metal layer 7 consisting of Si and Cu can react with a gas mixture of N.sub.2 and O.sub.2 at a specific mixing ratio. In this case, insulating substances Si-N-O and Cu-O are formed, and Cu-O has a lower dissociation energy for oxygen than Si-N-O, and Cu is deposited by giving an energy to the metal layer, whereby a wiring pattern based on the deposited Cu can be obtained. Or, an insulating layer 8 consisting of insulating substances SiO.sub.2 and Cu.sub.2 O, or Si-N-O and Cu-O can be directly formed on the substrate 6 and Cu can be also deposited to obtain the desired wiring pattern.

Reference numerals used in this example refer to those shown in FIG. 1--1-FIG. 1--4 as in Example 1.

A substrate 6 made of sapphire was placed in a vacuum vapor deposition vessel having a plurality of vapor deposition source cells, and heated to 400.degree.-600.degree. C., while Si was heated by electron beams to vaporize, and Cu was heated by a heater to vaporize, and Si and Cu were vapor deposited on the substrate 6 to form a metal layer 7 consisting of Si and Cu having a layer thickness of 10 .mu.m. Then, the substrate 6 was heated in an O.sub.2 atmosphere at 1,000.degree. C. to oxidize the metal layer 7 into insulating substances SiO.sub.2 and Cu.sub.2 O, thereby forming an insulating layer 8. Then, the substrate 6 with the insulating layer 8 was placed in a vessel filled with H.sub.2, and irradiated with a YAG laser beam having an energy density of 0.1 J/cm.sup.2 -1.5 J/cm.sup.2 at a scanning speed of 1-20 cm/sec. along the desired pattern on the surface of the insulating layer 8. The parts irradiated with the laser beam extended to a depth of 0.5-2 .mu.m and had a good electroconductivity such as 10.sup.-4 -10.sup.-5 .OMEGA..cm, while the non-irradiated parts had a good electrical insulation such as 10.sup.10 -10.sup.13 .OMEGA..cm. That is, a good wiring pattern 9 was obtained. This was because Cu.sub.2 O having a lower dissociation energy for oxygen was selectively reduced to deposit Cu. Irregularity of the surface of the insulating layer 8 including the wiring pattern 9 was less than 0.1 .mu.m, and thus the surface had a very good smoothness.

Reference numerals used in this example refer to those shown in FIG. 1--1-FIG. 1--4 as in Example 1.

In the same manner as in Example 2, a metal layer 7 consisting of Si and Cu and having a layer thickness of 10 .mu.m was formed on a substrate 6 made of sapphire. Then, the metal layer was heated in a gas mixture of N.sub.2 and O.sub.2 having an O.sub.2 concentration of 10-50% at 1,000.degree. C. to change the metal layer into an insulating layer 8 consisting of insulating substances Si-N-O and Cu-O. Then, in the same manner as in Example 2, the insulating layer was irradiated with the laser beam by local scanning to change Cu-O into Cu through metalizing, whereby the desired wiring pattern 9 was obtained. The wiring pattern extended to a depth of 0.5-2 .mu.m, and had a good electroconductivity such as 10.sup.-4 -10.sup.-5 .OMEGA..cm, while the parts non-irradiated with the laser beam had a good electric insulation such as 10.sup.11 -10.sup.14 .OMEGA..cm. The thus prepared wiring circuit board had a surface irregularity of less than 0.1 .mu.m, and thus had a very good surface smoothness.

Reference numerals used in this example refer to those shown in FIG. 1--1-FIG. 1--4 as in Example 1.

A substrate 6 made of sapphire or 99.5% Al.sub.2 O.sub.3 was heated and kept at 500.degree.-800.degree. C., while SiO.sub.2 was heated by electron beams to vaporize and deposited onto the surface of the substrate 6 together with Cu.sub.2 O by chemical vapor deposition at the same time, whereby an insulating layer 8 consisting of SiO.sub.2 and Cu.sub.2 O was directly formed onto the substrate. The chemical vapor deposition of Cu.sub.2 O was carried out by heating Cu by a heater to vaporize, while irradiating the surface of substrate 6 with O.sup.+ ion beams, thereby forming Cu.sub.2 O on the substrate 6. Then, the insulating layer was irradiated with the laser beam in the same manner as in Example 2, whereby a wiring circuit pattern having a good result as in Example 2 was obtained.

A substrate 6 with a smooth surface, made of sapphire or 99.5% Al.sub.2 O.sub.3 was heated at 400.degree.-700.degree. C. (FIG. 2--1), while Si and Cu were heated by a heater to vaporize, and O.sub.2 was introduced toward the substrate 6 through a nozzle. A shower of electrons was allowed to hit Si, Cu and O.sub.2 to partially ionize them, and an insulating layer 8' consisting of SiO.sub.2 and Cu.sub.2 O was formed on the substrate 6 by ion plating (FIG. 2--2).

A gas mixture of O.sub.2 and N.sub.2 can be used in place of O.sub.2, where an insulating layer 8' consisting of Si-N-O and Cu-O can be obtained. In any case, the insulating layer 8 had a volume resistivity of 10.sup.10 -10.sup.14 .OMEGA..cm.

In the same manner as in Example 2, a wiring pattern 9 was formed by laser beam irradiation (FIG. 2--3). The irradiated parts had an electroconductivity of 10.sup.-4 -10.sup.-5 .OMEGA..cm, and had a surface irregularity of less than 0.1 .mu.m, that is, a very good surface smoothness.

Then, another insulating layer 8" was formed on the insulating layer 8' and the wiring pattern 9 in the same manner as above (FIG. 2--4), and parts corresponding to via-holes were irradiated with a laser beam to form a connecting part 10 through the insulating layer 8" (FIG. 2--5).

Formation of further insulating layers and connecting parts were repeated to the desired thickness, as required (FIG. 2--6).

By laser beam irradiation of the surface of insulating layer 8 by scanning, the desired wiring patterns 9 and 9' were connected to each other through the connecting part 10 to obtain a wiring circuit board of two-wiring layer structure (FIG. 2--7).

To increase the number of layers, steps of FIG. 2--4 to FIG. 2--7 must be repeated, where the uppermost layer can always have a smooth surface and the thickness of wiring patterns can be kept even. Furthermore, the thickness of an insulating layer between any two layers of wiring patterns can be kept even. By repeating the steps of FIG. 2--4 and FIG. 2--5, an insulating layer can have a satisfactory thickness for the desired electric insulation. It is necessary to repeat the steps of FIG. 2--4 and FIG. 2--5, because, when too thick an insulating layer 8" is formed in the step of FIG. 2--4, it will take much time in forming the connecting part 10 through the insulating layer 8" and also because it is difficult to form a wiring pattern with a good precision due to the dissipation of heat within the insulating layer 8" during the formation of the connecting part. Thus, this insulating layers 8" must be formed one after another, while forming a connecting part 10 at a position corresponding to the via-hole in each insulating layer, so that a wiring pattern can be formed with good precision.

Reference numerals used in this example refer to those shown in FIG. 2--1-FIG. 2--7 as in Example 5.

A substrate 6 made of 99.5% Al.sub.2 O.sub.3 was placed in an Ar atmosphere containing 10% O.sub.2, and an insulating layer consisting of Al.sub.2 O.sub.3, SiO.sub.2 and Cu.sub.2 O and having a layer thickness of 2 .mu.m was formed on the surface of Al.sub.2 O.sub.3 substrate 6 from a mixture of Al.sub.2 O.sub.3, SiO.sub.2 and Cu.sub.2 O as a target material by sputtering. Then, in the same manner as in Example 2, Cu was deposited from Cu.sub.2 O by laser beam irradiation to form a wiring pattern 9.

Then, another insulating layer 8" consisting of Al.sub.2 O.sub.3, SiO.sub.2 and Cu.sub.2 O and having a layer thickness of 2 .mu.m was formed thereon by sputtering, and the surface of insulating layer 8" was irradiated at the position corresponding to via-hole with a laser beam in the same manner as in Example 2 to deposit Cu from Cu.sub.2 O, whereby a connecting part 10 was formed. The steps of forming the insulating layer 8" having the layer thickness of 2 .mu.m and irradiating the position corresponding to the via-hole with the laser beam were repeated until the overall insulating layer 8 had a thickness of 10 .mu.m. Then, the surface of insulating layer 8 was irradiated with a laser beam in the same manner as in Example 2 to form a wiring pattern consisting of 9 and 9'.

In this embodiment, the parts irradiated with the laser beam had a good electroconductivity such as 10.sup.-4 -10.sup.-5 .OMEGA..cm, while the non-irradiated parts had a good electric insulation such as 10.sup.11 -10.sup.14 .OMEGA..cm. The insulating layer 8' consisting of Al.sub.2 O.sub.3, SiO.sub.2 and Cu.sub.2 O had a surface irregularity of less than 0.1 .mu.m, that is, a very good surface smoothness. Thus, the insulating layer 8" consisting of the same insulating substances could be suppressed to a thickness fluctuation of less than 3%, and thus had a surface irregularity of less than 0.1 .mu.m.

In place of the laser beam used as an energizing means for locally metalizing the insulating layer in the foregoing Examples 2 to 6, an electron beam could be used with equivalent good results. Also aqueivalent good results could be obtained with a beam of metal ions of low resistivity such as ions of Cu, Au, Ag, Al, etc. when irradiated with an energy of 1-400 Ke.

In the foregoing Examples, the insulating substance is metalized with an energizing beam, and thus no photomask is required for patterning of wiring. Furthermore, an insulating layer consisting of a plurality of insulating substance is used and other insulating substances than the specific one are prevented from metalizing even by irradiation of the beam, and thus the metalized parts will not unduly extend from the beam-irradiated parts, that is, a fine wiring pattern can be formed with an increasing density in the individual layers. Furthermore, the thickness of wiring pattern in the individual layers and that of the insulating layer between the wiring patterns can be kept even, and thus the number of layers can be considerably increased, as compared with the conventional art.