JPH1197463A - Pressure joint semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To absorb dispersion in heigh of a contact surface, thermal resistance, and electric resistance in a contact interface, by combining a main electrode of a semiconductor element, and at least one of intermediate electrode plates through a plurality of metallic bumps. SOLUTION: In a pressure joint semiconductor device, a first main electrode 2 is formed in a first main surface of a semiconductor chip or a wafer 1, and a second main electrode 3 is formed in a second main surface. An assembly wherein the first main electrode 2 and an intermediate electrode plate 4 formed of Mo and W are joined by a metallic bump 7 is arranged in a first main surface of the wafer 1. Furthermore, a pair of Cu main electrode plates 8, 9 are arranged in an outside part of the intermediate electrode plate 4 and are pressed at once, thus bringing members into contact with each other. As a result, parallelism of intermediate electrode plates 4, 5 is corrected during junction and dispersion in height of a contact surface (irregularities due to warp, undulation, in size of members, etc.) is absorbed and thermal and electric resistance can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure contact type semiconductor device, and more particularly, to a thermal resistance between a semiconductor element and a package electrode.
The present invention relates to a press-contact type semiconductor device capable of reducing electric resistance and ensuring uniform contact, and a converter using the same.

[0002]

2. Description of the Related Art The technology of power electronics, which controls the main circuit current by making full use of the technology of semiconductor electronics, has been applied in a wide range of fields, and its application is being expanded. Thyristors, optical thyristors, gate turn-off thyristors (GT)
O), an insulated gate bipolar transistor (hereinafter abbreviated as IGBT) or a MOS field effect transistor (hereinafter abbreviated as MOSFET) which are MOS control devices.
In these devices, a main electrode (cathode, emitter electrode) is mainly formed on a first main surface of a semiconductor chip, and another main electrode (anode, collector electrode) is formed on a second main surface side.

In a high-power semiconductor device such as a GTO or an optical thyristor, elements are packaged for each wafer. The two main electrodes of the above-mentioned element are structured to be brought into pressure contact with a pair of external main electrodes of the package via a heat buffer electrode plate made of Mo or W. In order to improve the uniformity of the switching operation and the breaking characteristics of large currents, it is necessary to make the contact state between the above-mentioned element electrode, thermal buffer plate and external main electrode as uniform as possible, and to lower the contact thermal resistance and electric resistance. is important.

For this reason, measures are generally taken to increase the processing accuracy (flatness, flatness) of package components and reduce warpage and undulation. Further, with respect to the contact thermal resistance between metals, it is known that the contact thermal resistance increases as the roughness of the contact surface increases. Conventionally, from this viewpoint, countermeasures have been promoted as a method of reducing the contact thermal resistance and the electric resistance in a direction of reducing the surface roughness as much as possible.

On the other hand, in IGBTs and the like, a plurality of chips have been mounted so far mainly in a package form of an electrode connection system using wires, which is called a module type structure. In the case of such a modular package, heat generated inside the element is released only from one side of the package, that is, only from the collector side directly mounted on the metal base, so that the thermal resistance is generally large and can be mounted in one package. The number of chips (calorific value or current capacity) was limited.

Recently, in order to cope with such a problem and respond to a demand for a large capacity, a plurality of IGBT elements proposed in Japanese Patent Application Laid-Open No. 8-88240 and the like are formed in a flat type similar to a GTO package. A multi-chip parallel type pressure contact structure in which the emitter electrode and collector electrode formed on the main surface of the package are brought into surface contact with a pair of external main electrode plates provided on the package side, respectively, and pulled out in parallel in the package. Semiconductor devices are receiving attention. In this multi-chip parallel type pressure contact type semiconductor device, there is an unavoidable variation in height at each chip position due to a variation in member dimensions, which results in a problem in that the pressure is different for each chip and uniform contact cannot be obtained. there were. To cope with this problem, Japanese Patent Application Laid-Open No. 8-88240 discloses a method of interposing a thickness correcting plate made of a ductile soft metal sheet such as Ag.

[0007]

In a package such as the above-mentioned GTO, the element size (wafer size) has been increased in order to increase the capacity in the future. Parts) tend to increase.

[0008] There is a limit in the processing to increase the processing accuracy (flatness, flatness) of the package parts as described above to reduce warpage and undulation, and to further reduce the surface roughness. The problem in terms of aspect is also great. Therefore, it has become increasingly difficult to ensure uniform contact between the wafer and package components (electrodes) over the entire element size (wafer size), and to reduce thermal resistance and electrical resistance.

On the other hand, the above-described method of sandwiching a soft metal sheet disclosed as a method for coping with the problem of uniform contact between chips in a multi-chip parallel type pressure contact type semiconductor device is as follows.
According to the study of the present inventors, at least in a practical pressure range where the semiconductor chip is not destroyed, the deformation amount is very small (only deformation due to elastic deformation), and the height between the chips (and the intermediate electrode member sandwiching the chip is reduced). It was found that when the variation in height included was large, the thickness variation absorption capacity was insufficient. When applying pressure in the thickness direction to the soft metal sheet surface to cause plastic deformation in the horizontal direction, the frictional force (friction resistance) generated at the interface between the soft metal sheet and the electrode member sandwiches the soft metal material. Is considered to be due to the fact that the deformation resistance in the lateral direction becomes extremely large. Even if the pressing force is increased for deformation, the plastic deformation does not easily occur because the frictional force also increases in proportion to the pressure. Especially when the thickness is very small compared to the area receiving the resistance like the sheet shape, the influence of the frictional force generated on this surface becomes dominant, so it exceeds the yield stress of commonly known materials Even if pressure is applied, practically no plastic deformation (flow) occurs, and the thickness of the soft metal sheet hardly changes. A first object of the present invention is to increase the size of a package by increasing the diameter of a wafer as described above, and to increase the number of chips in a large area, which becomes increasingly difficult with the parallelization of elements corresponding to the increase in capacity. A method of ensuring a uniform pressure contact state, that is, variations in the height of the contact surface (warpage, undulation,
It is intended to provide a method capable of absorbing thermal resistance and electrical resistance at the contact interface by absorbing variation in member dimensions.

A second object of the present invention is to provide a converter particularly suitable for a large-capacity system by using the semiconductor device obtained as described above.

[0011]

SUMMARY OF THE INVENTION The object of the present invention is to provide a semiconductor device having at least a first main electrode on a first main surface and a second main electrode on a second main surface, wherein an intermediate electrode is arranged on each main surface. Further, in a press-contact type semiconductor device in which these are incorporated between a pair of main electrode plates, it can be realized by a structure in which at least one of the main electrode and the intermediate electrode plate of the semiconductor element is joined by a plurality of metal bumps.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows an example in which the present invention is applied to the basic structure of a pressure contact type semiconductor device. In a press-contact type semiconductor device, a first main electrode 2 is formed on a first main surface of a semiconductor chip or a wafer 1, and a second main electrode 3 is formed on a second main surface.
An assembly in which a first main electrode 2 and an intermediate electrode plate 4 made of Mo or W are joined to each other by a metal bump 7 on a first main surface of the wafer 1 is further provided. This is a pressure-contact type semiconductor device in which Cu main electrode plates 8 and 9 are arranged, and are pressed together and each member is brought into contact.

In the present invention, among the interfaces formed in this embodiment, the first and second main electrodes 2 and 3 and the intermediate electrode plates 4 and 5 made of Mo or W are formed on the first main surface of the wafer 1. The first main electrode 2 and the intermediate electrode plate 4 made of Mo or W are bonded to the first main surface of the wafer 1 by a plurality of metal bumps 7, and the main electrode plate 8 , 9 and the intermediate electrode plates 4, 5 are pressed against each other.

When a pressing force is applied in this state (shown below), the first main electrode 2 and Mo are applied to the first main surface of the wafer 1.
The plurality of metal bumps 7 joining the intermediate electrode plate 4 made of W and W are compressed and deformed, and come into contact with the surfaces of the intermediate electrode plates 4 and 5 and the main electrode plates 8 and 9 to provide a good contact between the two surfaces. Contact is completed.

The present invention has a structure in which the first main electrode 2 and the intermediate electrode plate 4 made of Mo or W are bonded to the first main surface of the wafer 1 by a plurality of metal bumps 7. The parallelism of the intermediate electrode plates 4 and 5 is corrected, and variations in the height of the contact surface (due to warpage, undulation, variations in member dimensions, etc.) are absorbed, and the number of contact interfaces is reduced, so that thermal resistance and electrical resistance can be reduced. . Further, the pressing force applied to the pressing-type semiconductor device can be reduced.

FIG. 2 is a model diagram showing a process of manufacturing the press contact type semiconductor device of the present invention. 2A shows a state in which the second main electrode 3 and an intermediate electrode plate 5 made of Mo or W are joined to the second main surface of the wafer 1 by thermocompression bonding, and FIG. (C) heats the first main electrode 2 and the plurality of metal bumps 7 of the intermediate electrode plate 4 made of Mo or W on the first main surface of the wafer 1. The state joined by crimping is shown.

FIG. 3 shows, as a modification of FIG. 2, (a) a second main electrode 3 and an intermediate electrode plate 5 made of Mo or W joined to the second main surface of the wafer 1 by thermocompression bonding. State,
(B) shows a state in which a plurality of metal bumps 7 are formed on the first main surface of the wafer 1 by bonding to the first main electrode 2, and (c) shows a state where the first main electrode 2 is formed on the first main surface of the wafer 1. 2 shows a state in which a plurality of metal bumps 7 provided by bonding and an intermediate electrode plate 4 made of Mo or W are joined by thermocompression bonding.

According to FIGS. 2 and 3, as shown in FIGS. 2 and 3A, the second main electrode 3 and the M
The intermediate electrode plate 5 made of o or W is joined by thermocompression bonding. Next, as shown in FIGS. 2 and 3 (b), a plurality of metal bumps 7 are provided on the first main electrode 2 on the intermediate electrode plate 4 or the first main surface of the wafer 1 by bonding. Further, as shown in FIGS. 2 and 3 (c), the intermediate electrode plate 4 is provided via a plurality of metal bumps 7 provided by bonding.
And the first main electrode 2 on the first main surface by thermocompression bonding or ultrasonic bonding to manufacture an assembly.

In this assembly, a plurality of metal bumps 7 are deformed at the time of joining, correct the parallelism of the whole assembly and form a joint, so that the number of contact interfaces is smaller than in the prior art, so that thermal resistance and electric resistance are reduced. it can. Further, when the number of the metal bumps 7 is further increased, the thermal resistance and the electric resistance can be reduced.

Finally, it is possible to deform the metal bumps 7 sufficiently to completely fill the bonding interface, but in reality, it is impossible to completely fill them due to the limitation of the load. Thus, a non-contact portion remains, but there is no problem in electrical resistance and the like.

As described above, the optimum number of metal bumps 7 and the amount of deformation in the thickness direction depend on whether the thermal resistance, the electric resistance, or the improvement of the deformability is prioritized according to the usage mode of the semiconductor device. It is preferred to select

The metal bumps have the necessary thermal resistance, electrical resistance,
The optimum value and method are determined according to the height change amount. The material of the metal bump is made of a soft metal such as gold, silver, copper, aluminum, nickel or solder, and is particularly preferable because it is easily deformed. In particular, if the core material is made of a plastic resin and the surface layer is made of a metal bump having a composite structure made of a metal, the core material is a plastic resin. It can be used.

For example, when a plurality of semiconductor chips are incorporated in parallel in the above-mentioned press-contact type package, the dimensional accuracy (in the height direction) of the assembly can be obtained by using the assembly of the present invention.
Is preferable because it is good.

FIG. 4 shows an example in which the present invention is applied to the basic structure of a pressure contact type semiconductor device. In a press-contact type semiconductor device, a first main electrode 2 is formed on a first main surface of a semiconductor chip or a wafer 1, and a second main electrode 3 is formed on a second main surface.
An assembly in which the two electrode surfaces and the intermediate electrode plates 4 and 5 made of Mo or W are joined by a metal bump 7 is arranged. Further, a pair of Cu main electrode plates 8 and 9 are provided on the outer portion of the intermediate electrode plate. This is a press-contact type semiconductor device which is arranged, pressurized at once, and brought into contact with each other.

In the present invention, of the interfaces formed in this embodiment, the first main electrodes 2 and 3 and the intermediate electrode plates 4 and 5 made of Mo or W are joined to the first main surface of the wafer 1. In particular, both electrode surfaces 2 and 3 of the wafer 1 are
And the intermediate electrode plates 4 and 5 made of Mo or W are joined by a plurality of metal bumps 7, and the main electrode plates 8 and 9 and the intermediate electrode plates 4 and 5 are pressed against each other. Features.

When the press-contact type semiconductor device of the present invention is used, the press-contact force during operation can be reduced as compared with the conventional press-contact type semiconductor device.

FIG. 5 shows a flywheel diode (F) connected in anti-parallel with a switching device using IGBT10.
This shows an example in which the present invention is applied to a reverse conduction type switching device incorporating WD) 11. FIG. 5 shows a partial cross section from the outermost part of the press-contact type semiconductor device at the right end to the middle toward the center. The IGBT chip 10 has an emitter electrode 12 formed on almost the entire first main surface on the upper surface side and a collector electrode 13 on the second main surface on the lower surface side, and further has a control electrode (gate) on the first main surface. An electrode 14 is formed. In the FWD 11, an anode electrode 15 is formed on the upper surface side of the silicon substrate, and a cathode electrode 16 is formed on the lower surface side.

In each of these semiconductor chips, intermediate electrodes 4 and 5 made of Mo for both heat dissipation and electrical connection are joined to the main electrodes on the chip by metal bumps 7 and joining layers 6, respectively. Further, a first common main electrode plate (Cu) 8
And a second common main electrode plate (Cu) 9.

Incidentally, the common main electrodes 8, 9 and the intermediate electrodes 4,
The surface contacting with No. 5 is Rmax 1 μm.

The semiconductor chip and the intermediate electrode are fixed to each other by a Teflon frame 17. Also, IGBT
The gate electrode is connected to the gate electrode wiring board 19 by the spring pin of the chip 10, the connection terminal 20 wiring is drawn out by the wire bond 18, and the gate electrode wiring is put out of the package by the sealed wiring 22 penetrating the outer cylinder 21. Drawn out. The space between the pair of common main electrode plates 8 and 9 is externally insulated by an insulating outer cylinder 21 made of ceramic or the like, and the space between the common main electrode plates 8 and 9 and the insulating outer cylinder 21 is inside the package by a flange 23. Is hermetically sealed.

Then, the on-voltage was measured with the applied pressure between the intermediate electrode plate and the main electrode plate being 0.3 kg / mm ^2. As a result, it was found that the electric resistance was reduced by about 30% as compared with the conventional semiconductor device having the pressure contact structure. Was completed. Also, the thermal resistance was reduced by about 20%.

As the material of the intermediate electrode, a material having a thermal expansion coefficient between Si and the external main electrode material and having good thermal conductivity and electric conductivity is used. Specifically, tungsten
Metal such as (W) and molybdenum (Mo), or Cu-W, Ag-W, Cu-M using them as main constituent materials
o, Ag-Mo, Cu-FeNi or other composite materials or alloys, and further, composite materials of metals and ceramics or carbon, such as Cu / SiC, Cu / C, Al / SiC,
Al / AlN and the like are preferable.

On the other hand, it is preferable to use copper or aluminum having good electrical conductivity and thermal conductivity, or the above-mentioned alloy or composite material containing them for the main electrode.

The assembly mounting system of the present invention can be used for a pressure-contact type semiconductor device consisting of only a switching semiconductor such as an IGBT without a diode. Of course is also effective. In the above embodiments, the IGBT is used as the semiconductor device with the control electrode. However, the present invention provides a semiconductor device having at least a first main electrode on a first main surface and a second main electrode on a second main surface. It is intended for the whole, including insulated gate transistors (MOS transistors) other than IGBTs,
The present invention can be similarly applied to a semiconductor element with a control electrode such as an insulated gate thyristor (MOS control thyristor) including an IGCT (Insulated Gate Controlled Thyristor), a diode, and the like. Further, the present invention is similarly effective for compound semiconductor devices such as SiC and GaN other than the Si device.

In the pressure contact type semiconductor device of the present invention, a stable contact interface between the electrodes can be obtained even when the size is increased, so that a semiconductor device having a small electric resistance and a small thermal resistance can be obtained. Therefore, by using this press-contact type semiconductor device, the converter volume,
In addition, a large-capacity converter whose cost is greatly reduced can be realized. Further, according to the present invention, uniform contact can be obtained even with a lower pressing force than in the prior art, so that the stack structure and the like can be simplified.

The pressure-contact type semiconductor device of the present invention is not particularly limited to the above example, and is particularly suitable for a self-excited large-capacity converter used in a power system or a large-capacity converter used as a converter for a mill.
Variable speed pumped storage power generation, substation facilities in buildings, substation facilities for railways,
It can also be used in converters for sodium-sulfur (NaS) battery systems and vehicles.

[0038]

According to the present invention, uniformity over a large area becomes increasingly difficult with the increase in the size of the package due to the increase in the diameter of the wafer and the parallelization of elements corresponding to the increase in the capacity. Pressure welding can be easily realized with relatively low pressure, that is, it absorbs variations in the height of the contact surface sufficiently,
In addition, the thermal resistance and electric resistance at the contact interface can be reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view of a press-contact type semiconductor device shown as an embodiment of the present invention.

FIG. 2 is a view for explaining a manufacturing process of the press-contact type semiconductor device of FIG. 1;

FIG. 3 is a view for explaining a manufacturing process of the press contact type semiconductor device of FIG. 1;

FIG. 4 is a cross-sectional view showing an application example of the press contact type semiconductor device of the present invention.

FIG. 5 is a cross-sectional view of an IGBT shown as an example of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Wafer, 2, 3 ... 1st and 2nd main electrode, 4, 5 ... Intermediate electrode plate, 6 ... Bonding layer, 7 ... Metal bump, 8, 9 ... Main electrode plate, 10 ... IGBT, 11 ... Flywheel Diode, 12: Emitter electrode, 13: Collector electrode, 14 ...
Gate electrode, 15: Anode electrode, 16: Cathode electrode, 17: Teflon frame, 18: Wire bond, 19: Gate electrode wiring board, 20: Connection terminal, 21: Insulated outer cylinder, 2
2: airtight through wiring, 23: flange.

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Mamoru Sawahata 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd.

Claims (4)

[Claims] An intermediate electrode plate is disposed on each of the main surfaces of a semiconductor device having a first main electrode on a first main surface and a second main electrode on a second main surface. A press-contact type semiconductor device incorporated between plates, wherein at least one of a main electrode of a semiconductor element and an intermediate electrode plate is joined by a plurality of metal bumps. 2. The method according to claim 1, wherein the metal bumps are made of Ag, Ag alloy, Au,
Au alloy, Cu, Cu alloy, Al, Al alloy, Ni, N
2. The pressure-contact type semiconductor device according to claim 1, wherein the semiconductor device is one of an i-alloy and a solder. 3. A semiconductor device having a first main electrode on the first main surface and a second main electrode on a second main surface, wherein a plurality of semiconductor elements are juxtaposed and incorporated between a pair of main electrode plates. 2. The pressure-contact type semiconductor device according to claim 1, wherein: 4. The semiconductor device is an insulated gate device having a first main electrode and a control electrode on a first main surface, and a second main electrode on a second main surface. 2. A flywheel diode having a first main electrode on one main surface and a second main electrode on a second main surface, and a plurality of flywheel diodes are respectively incorporated in anti-parallel with the insulated gate element. Pressure contact type semiconductor device.