JPH01304797A - Aluminum nitride multilayer interconnection substrate and manufacture of it - Google Patents

Abstract

PURPOSE:To increase a heat dissipation property by using the material having a lower melting point that a sintered temperature of aluminum nitride as a conductive material and by forming at least one conductive layer in an aluminum nitride substrate. CONSTITUTION:A ceramic layer 1 is made of the polycrystalline substrate which consists of aluminum nitride. A conductive layer 2 is formed by putting the melted material such as copper, silver, gold, aluminum, zinc or lead which has a lower specific resistance than molybdenum and tungsten into a cavity which is formed in the ceramic by the optical lithography technology. Therefore, it is easy to form a highly integrated circuit having a low resistant conductor including a signal line and a power supply layer. This method also makes it possible to make a high thermal conductive multilayer ceramic substrate which is effective to a heat dissipation property.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to the structure and manufacturing method of a multilayer ceramic substrate, particularly a highly thermally conductive multilayer ceramic substrate.

(Prior Art) With the dramatic progress of the semiconductor industry, ICs and LSIs have come to be widely used for industrial and civilian purposes.

Along with this, high-speed operation LSI with high integration density
Multilayer ceramic substrates are attracting attention as mounting substrates. Generally, alumina is mainly used as the material for this ceramic substrate, and it is effective for high-density packaging because '1M and f41 multilayer wiring is possible.

(Problems to be Solved by the Invention) In recent years, there has been a strong demand for electronic devices and equipment to be smaller and more dense, and the packaging density of circuit boards has become higher.

On the other hand, in LSI chips, there is a tendency for the chips to generate more heat as they operate at higher speeds and become more densely packed.

As a result, the heat generated by the substrate increases significantly, and a problem arises in that the alumina substrate does not have sufficient heat dissipation properties.

Therefore, there is a need for an insulating substrate that has higher thermal conductivity and better heat dissipation than an alumina substrate.

Therefore, a ceramic substrate mainly composed of silicon carbide was developed as a material with excellent heat dissipation properties (Japanese Patent Laid-Open No. 57
-180006). However, silicon carbide itself electrically belongs to a semiconductor, has a specific resistance of about 1 to 10 Ω·am, and has no electrical insulation properties, so it cannot be used as an insulating substrate. Furthermore, since silicon carbide has a high melting point and is very difficult to sinter, it is usually sintered using a so-called hot press method in which a small amount of sintering aid is added and pressure is applied at high temperature. When beryllium oxide or boron nitride is used as this sintering aid, it is effective not only for the sintering aid but also for electrical insulation, and the specific resistance of the sintered substrate mainly composed of silicon carbide is 1.
0.010 Ωcm or more. However, the dielectric constant, which is one of the important factors in mounting boards such as LSI, is 4 at IMHz.
Even with the addition of additives, the insulation between particles rapidly decreases when the voltage reaches about 5V, so there is also a problem with the withstand voltage.

Furthermore, although it is possible to create a multilayer ceramic substrate using Be○ powder, it is difficult in practice because of its toxicity.

On the other hand, from a process point of view, a hot press method must be applied, which not only requires a complicated apparatus, but also makes it difficult to increase the shape of the substrate, and there are many problems with surface smoothness. Furthermore, in the case of ceramic substrates using silicon carbide, it is extremely difficult to use alumina multilayer ceramic substrate technology using the conventional green sheet method in terms of process.

The green sheet multilayer ceramic substrate technology referred to herein is the following technology. Also, the ceramic powder is mixed with an organic vehicle to form a slurry. A sheet having a thickness of about 10 pm to 40,011 m is formed on an organic filter using this slurry by a casting film forming method.

After cutting the sheet into a predetermined size and forming through holes for establishing electrical conduction between each layer, a predetermined conductor pattern is formed by thick film printing. The ceramic green sheets on which each of these conductor patterns have been formed are laminated and pressed, subjected to a binder removal process, and then fired.

The main properties that a high-density mounting board should have are (
1) Low dielectric constant with respect to electrical properties, low dielectric loss, and excellent electrical insulation, (2) Sufficient mechanical strength, (3) High thermal conductivity, ( 4)
It is necessary to have a coefficient of thermal expansion close to that of a silicon chip, etc., (5) to have excellent surface smoothness, and (6) to be able to easily increase the density.

Research and development is being conducted on aluminum nitride as a substrate material that can satisfy these requirements. Aluminum nitride almost satisfies the required substrate properties, but has the drawback that it is difficult to increase the density of multiple layers because of its high sintering temperature of 1900°C or higher.

For example, an example of the development of an aluminum nitride multilayer wiring board using the green sheet method is shown in Figure 2, Microelectronics Symposium Proceedings, pp. 185-188 (July 1987).
has been reported.

As is clear from this report, since the sintering temperature of aluminum nitride is high, it is necessary to use a material with a high melting point such as tungsten as a conductor.As a result, the conductor resistance is extremely high at 20 mΩ10, and high speed is required. There is a problem with the wiring board used for this purpose.

In addition, as a manufacturing method for multilayer wiring boards that can use conductors with low conductor resistance as wiring materials using alumina, zirconia, beryllia, etc., cavities are formed in ceramic.
A manufacturing method has been proposed in which metals such as silver and copper are injected in a molten state.

(Special Publication No. 44-27102, No. 6l-229549
) However, in these manufacturing methods, the cavity for forming the circuit pattern is formed by screen printing, so it is difficult to reduce the width of the wiring to 10,011 m or less, and there is a limit to the formation of a high-density wiring board. Yes. Furthermore, the thickness of the wiring is about 10 pm at most, and when making fine wiring, the cross-sectional area of the conductor is small, about 101000 p, so even if a material with low conductor resistance is used, the resistance of the wiring becomes high, which is a problem as a wiring board for high frequency pulses. There is.

The inventors of the present invention have invented an aluminum nitride multilayer ceramic substrate and a method for manufacturing the same, paying particular attention to high thermal conductivity and high multilayer density while keeping these substrate properties in mind.

(Means for solving the problem) In the present invention, the ceramic layer is composed of a polycrystalline material mainly composed of aluminum nitride, and the conductor layer is made of molybdenum such as copper, silver, gold, aluminum, lead, zinc, etc. A multilayer ceramic wiring board with high thermal conductivity, which is formed by melting and injecting a material with a lower specific resistance than tungsten into a cavity formed using lithography technology in ceramic.

(Function) The present invention solves the problems of the prior art by the above-mentioned means. First, aluminum nitride, which has high thermal conductivity, was used as the insulating ceramic material constituting the multilayer ceramic substrate. After firing, the material forms a dense structure of polycrystalline aluminum nitride. In order to obtain high thermal conductivity, it is preferable that the amount of oxygen contained in the sintered body is small, and therefore it is preferable to add a reducing agent as an additive.

Next, regarding the conductor layer, multiple power supply layers, ground layers, fine signal lines, and other conductor layers are formed on the ceramic layer made of aluminum nitride, and these multiple conductor layers are provided within the ceramic layer. It is electrically connected via a peer hole.

Therefore, the wiring density of the mounting board can be greatly increased, and the heat generated from elements such as LSI can be efficiently dissipated to the outside.

Because the conductor layer to be formed can use materials with low resistance, it is possible to use high-frequency pulses, and optical lithography technology allows the formation of fine conductor patterns with a small cross-sectional area, without increasing the resistance of the wiring.
It is possible to miniaturize wiring patterns.

(Example) Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is an explanatory diagram showing an embodiment of a highly thermally conductive multilayer ceramic substrate according to the present invention. Reference numeral 1 denotes an insulating ceramic layer, which is mainly composed of polycrystalline aluminum nitride. Reference numeral 2 denotes a conductor layer for signal lines, power supply, etc., which is mainly made of copper, and electrically connects the layers through peer holes 3 formed in the insulating ceramic layer. A die pad 4 and a bonding pad 5 are formed on the multilayer ceramic substrate configured in this way so that an LSI chip can be mounted, and for extracting signals from the mounting board or inputting signals into the board. An I10 pad 6 is formed on the back surface of the substrate.

Heat generated from the LSI chip mounted on the substrate is diffused into the ceramic substrate via the die pad 4. The high thermal conductivity of the ceramic substrate allows for effective thermal diffusion, thereby preventing the LSI chip from increasing in temperature due to heat generation.

The method for manufacturing the wiring board of this example is as follows.

FIG. 2 shows the process of the present invention. A pattern corresponding to a circuit pattern is formed on a photosensitive resin sheet by a photolithography process. First, a photosensitive resin is uniformly coated onto a carrier film such as polyester to a predetermined thickness. A photomask with a predetermined circuit pattern formed thereon is closely attached to the photosensitive resin sheet thus produced, and after exposure, a development process is performed to form a hole pattern corresponding to the predetermined circuit pattern. .

On the other hand, as the ceramic material constituting the substrate of the present invention, an example is shown in which CaC2 is mixed as an additive in order to improve the sinterability of aluminum nitride. First, aluminum nitride powder and CaC2 powder were weighed and wet mixed in an organic solvent using a ball mill for 48 hours. At this time CaC2
was set at 1.0 wt%.

This mixed powder is dispersed in a solvent together with an organic binder that is easily decomposed in a nitrogen atmosphere, such as polycabralactone or polyacrylate resin, and the viscosity is 3000 to 700.
Creates a slurry in the 0cp range. A green sheet is formed from the slurry onto an organic film using a casting method so as to have a uniform thickness of about 10 pm to 20,011 m.

Next, after four organic films are peeled off from this green sheet, peer holes are formed for electrically connecting each layer. The pier holes formed here were punched out mechanically using a punch and die, but they can also be punched out by other methods such as laser machining.

Next, on the green sheet with the pier holes formed thereon, a paste of materials such as garbon powder, graphite powder, acrylic powder, etc., which are scattered during firing due to combustion, sublimation, etc., is filled into the pier holes using a screen printing method, and the temperature is 80°C. Dry with.

A green sheet in which the pier holes are filled with carbon paste or the like is laminated and bonded to a pattern forming holes corresponding to a circuit pattern formed by a photophosphorography process.

Here, heat can be applied along with pressure as necessary.

The laminate created in this way is cut into predetermined dimensions as necessary, and then the pore pattern and organic matter present in the ceramic green sheet are oxidized in a debinding process or slowly heated in a neutral atmosphere. and decomposes and disappears. Normally, these organic substances are completely decomposed and oxidized by 500°C to 600°C, but if the temperature is rapidly raised to the decomposition temperature, the laminate will be damaged, so the temperature should be kept at 25°C/hour or slower. By increasing the temperature at a rising speed and maintaining the temperature at 500°C to 600°C for a sufficiently long time, organic substances are completely disappeared.

Since no organic matter remains in the laminate after the binder removal process, the pore pattern portions remain in the laminate as cavities.

In this way, an aluminum nitride substrate is produced in which a fine cavity corresponding to a wiring pattern is formed in the aluminum nitride substrate.

The cavity inside this board is always connected to the outside of the board via a peer hole. Note that the pier holes are filled with carbon paste, etc., so that space is maintained even during crimping, and cavities are also formed to connect each circuit pattern.

After the binder removal step, it is fired in a non-oxidizing atmosphere at a temperature of 1800 to 2000°C.

A cavity corresponding to a circuit pattern is three-dimensionally formed in the aluminum nitride ceramic substrate fired in this manner. The dimensions of the cavity can be designed by the dimensions of the cavity formation pattern.

A ceramic substrate like this was heated at 1200°C under a nitrogen atmosphere.
immersion in molten liquid steel under atmospheric pressure. While immersed in liquid steel, the pressure in the space containing the liquid steel and the crucible containing it is reduced to 10' torr and maintained for 10 minutes. Thereafter, nitrogen is introduced to return the pressure to atmospheric pressure, which is then held for another 30 minutes, and then the ceramic substrate is pulled out of the liquid steel, the temperature is lowered, and the ceramic substrate is taken out into the air.

Copper was injected into the cavity formed by such a method and solidified to obtain an aluminum nitride multilayer wiring board using copper as a conductive material.

The conductor width and conductor thickness of the multilayer wiring board thus obtained were 50 pm x 50 pm, and the wiring pitch was 110 pm.
It was 0p.

Furthermore, this conductor resistance was also very small, 2.0×10 −6 Ωcm or less.

The characteristics of the produced board were that the thermal conductivity was 160 w/mk and the resistance of the conductor was 1.8 PΩ·cm.

Furthermore, the results of creating similar substrates using silver, gold, lead, aluminum, nickel, and zinc-tin instead of copper are shown in the first report.
Shown in the table. The amount of CaC2 shown here is a value based on the weight of aluminum nitride and CaC2. As a result of measuring the electrical characteristics of the created board, the insulation resistance was I
It is 1013 Ωcm or more, and the dielectric constant is 8.8 (IMHz
), and the dielectric loss was less than lXl0-3 (IMHz). It can be seen that the electrical characteristics are also at least the same as those of conventional boards, and are sufficient as a mounting board.

(Effects of the Invention) As is clear from the examples, by having the structure of the present invention, it is possible to easily form a high-density circuit having low resistance conductors including signal lines, power supply layers, etc. A highly thermally conductive multilayer ceramic substrate that is also very effective in terms of heat dissipation can be obtained.

The thermal conductivity of the conventionally used alumina substrate is 20W.
/nk, and the thermal conductivity of the substrate of the present invention is very high as shown in Table 1.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a highly thermally conductive multilayer ceramic substrate showing an embodiment of the present invention. l... Insulating ceramic layer, 2... Conductor layer, 3...
Pier hole, 4...Die pad, 5...Punching pad, 6...I10 pad. FIG. 2 is a process flowchart showing the process of the manufacturing method of the present invention. ,4 patent attorney Susumu Uchi

Claims (2)

[Claims] (1) An aluminum nitride multilayer wiring board characterized by using a material having a melting point lower than the sintering temperature of aluminum nitride as a conductor material and having a structure in which at least one conductor layer is formed in the aluminum nitride substrate. (2) A step of forming a pattern identical to the required multilayer wiring circuit using a photosensitive function, and a material that is scattered by combustion or sublimation during the firing stage to form through holes drilled at predetermined locations in the raw ceramic sheet. a step of stacking the pattern made of the photosensitive resin and the green ceramic sheet filled with the through hole through the through hole so that the upper and lower circuit patterns overlap, and firing this, A process of forming the same cavity as the multilayer wiring circuit connected inside the ceramic substrate, and injecting a liquid metal with a melting point lower than the sintering temperature of aluminum nitride into the cavity, and cooling it to produce the required amount. A method for manufacturing an aluminum nitride multilayer wiring board, comprising a step of forming a multilayer wiring circuit.