JP2000349100A - Bonding material and its manufacture, and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent semiconductor chips from being broke and to reduce a failure caused by an insufficient cooling capacity, by making the heights of the laminated members uniform by adjusting the thickness of a bonding layer even if semiconductor chips or the other constituents constituting a device are different in height from each other. SOLUTION: A bonding material 6 is made of a composite material of a metal having a low melting point and a porous metal, and thus is not made completely fluid at a bonding temperature but is compositely changed by a small stress and has high wettability. Even if Si chips are different in height from each other when the top portions of the Si chips are pressed by an upper die, the bonding material 6 is compositely changed to align the heights of the Si chips with the height of the side wall of the lower die. This can align the heights of the Si chips and, when the Si chips are press-bonded to a water-cooled heat sink, this can prevent a force from being concentrated at a specified point and prevent the built-in Si chips from being broke and apply a sufficient pressing force thereto, which results in producing sufficient cooling performance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a large-capacity power semiconductor device, and more particularly to a bonding material for bonding a semiconductor chip and a plate-like member constituting the semiconductor device and a method of manufacturing the same.

[0002]

2. Description of the Related Art Power semiconductor devices have been increasing in capacity and speed, and the amount of heat generated by the devices has tended to increase further. As shown in FIG. 5, the structure of the power semiconductor device includes a plurality of plate-shaped members, that is, Cu (copper) posts 11a and 11a.
b, has a structure in which a Mo (molybdenum) material 12 and a Si (silicon) chip 13 are bonded and laminated by bonding materials 14, 15, and 16, and a multi-chip type in which this laminated body is arranged in a plurality of islands is mainly used. It has become. Since the thickness of each plate member to be laminated always varies within a tolerance range, the height of each laminate is generally not constant.

On the other hand, such a power semiconductor device generates a large amount of heat because it is used with a large current, and its cooling is an important technical point.

Thyristors (silicon controlled rectifiers, Thyr
istor, GTO (Gate Turn-0ff Thyristor), IEGT
(Injection Enhanced Gate Transistor), IGBT
(Insulated Gate Bipolar Transistor) and cooling of pressure-contact type (flat type) water-cooled elements for power are usually performed by applying a copper water-cooled heat sink to both sides of the element and applying pressure to minimize contact resistance. are doing.

The pressing force is 6 inch element (diameter 160mm)
And the element is clamped at a pressure of 1560 MPa. Under such use conditions, if the height of the stacked body of each chip of the multi-chip is uneven, a concentrated load is generated, and the Si chip 13 is damaged.
Therefore, it is necessary to adjust the variation in height.

Conventionally, as a countermeasure, a copper post 11a on one side has a columnar structure in which a groove 17 is provided, so that when a concentrated load is generated during pressurization, the copper post 11a bends and the Si chip 13 is bent. A method of alleviating the applied stress has been adopted.

However, this columnar copper post method requires a certain height of the post, which makes it difficult to cool the post side.

Therefore, the height of the copper post 11a is reduced, and the pressing force is reduced to such an extent that the Si chip 13 is not damaged. However, reducing the pressing force lowers the contact resistance between the layers (in the case of the pressure-contact type element), resulting in insufficient cooling capacity depending on the location, resulting in the stoppage of the function of the element.

[0009]

In the conventional power semiconductor device, the Si chip 13 and the constituent members 12, 16, 11
Due to the variation in the thicknesses of a and 11b, the height of the stacked body becomes uneven, and there is a problem that concentrated stress is generated when pressed against a water-cooled heat sink, which causes damage to the Si chip 13.

In order to avoid this, there is a method of relaxing the stress applied to the Si chip 13 when the concentrated stress is generated by a columnar copper post method, but this makes it difficult to cool the post side. Therefore, it is necessary to reduce the height of the copper post and reduce the pressing force to the extent that the Si chip 13 is not damaged, and the reduction of the pressing force causes the contact resistance between the layers (in the case of the pressure contact type element) to be low. In other words, there is a problem that the cooling capacity becomes insufficient depending on the location, and the function of the element stops.

Although such a problem is conspicuous in a multi-chip, even in the case of a flat element, there is a problem that the cooling performance is deteriorated due to uneven contact of the heat sink due to uneven thickness.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems. Even if the thickness of a semiconductor chip or other components constituting the device varies, the thickness of the bonded body layer can be reduced. By adjusting the height of the stacked body by adjusting the thickness of the semiconductor device, it is possible to reduce failure due to damage to the semiconductor chip and insufficient cooling capacity, and a bonding material for bonding the stacked body of such a semiconductor device. It is an object of the present invention to provide a manufacturing method thereof.

[0013]

Means for Solving the Problems In order to achieve the above object, a feature of the present invention is a bonding material having a mixed structure of two or more metals for bonding a material to be bonded. It consists of a metal phase for maintaining the thickness accuracy of the bonding material layer and a metal phase for fusion bonding.

According to a second aspect of the present invention, in the bonding material according to the first aspect, the yield stress of the metal phase that maintains the thickness accuracy of the bonding material layer at the melting point of the metal phase to be melt-bonded is increased by the bonding strength. It is to be used in a combination lower than the fracture stress of the material.

According to a third aspect of the present invention, in the bonding material according to the first aspect, the metal phase for maintaining the thickness accuracy of the bonding material layer of the bonding material is formed in a mesh shape, a porous shape, or a particle dispersed shape. It is located.

According to a fourth aspect of the present invention, in the bonding material according to the first aspect, the metal phase for maintaining the thickness accuracy of the bonding material layer of the bonding material has a thermal conductivity of about 70 W / mK or more near room temperature. It is to be.

According to a fifth aspect of the present invention, in the bonding material according to the first aspect, the metal phase for maintaining the thickness accuracy of the bonding material layer of the bonding material is Cu, Ag, Au, Mn, Ni, Fe, or the like.
It consists of at least one kind of Zn metal or an alloy thereof.

According to a sixth aspect of the present invention, in the joining material according to the first aspect, the melting point of the metal phase to be melt-joined is 12 or more.
It is below 00 ° C.

According to a seventh aspect of the present invention, in the bonding material according to the first aspect, the bonding material is stacked between the materials to be bonded, and heated to a bonding temperature while being pressed to a predetermined height. .

A feature of the invention according to claim 8 is that the metal powder of the metal phase which maintains the thickness accuracy of the bonding material layer of the bonding material according to claim 1, the metal powder of the metal phase to be melt-bonded, and the binder. Paste is applied to the material to be joined.

According to a ninth aspect of the present invention, a sheet of a porous sintered body of a metal phase which maintains the thickness accuracy of the bonding material layer of the bonding material according to the first aspect is impregnated with the molten bonding metal. is there.

According to a tenth aspect of the present invention, the fusion bonding metal is formed on a net, a woven fabric, or an aggregate of a metal phase of a metal phase which maintains the thickness accuracy of the bonding material layer of the bonding material according to the first aspect. Impregnation.

A feature of the invention according to claim 11 is that a sponge sheet of a metal that maintains the thickness accuracy of the bonding material layer of the bonding material according to claim 1 is impregnated with the molten bonding metal.

According to a twelfth aspect of the present invention, there is provided a method of applying the molten joining metal of the joining material according to the first aspect to the material to be joined, and thereafter, a metal powder or a fine wire which maintains the thickness accuracy of the joining material layer. And embedding at least one kind of porous body.

A thirteenth aspect of the present invention resides in that a semiconductor chip and other components are joined by using the joining material of the first aspect.

It is a necessary condition that the joining material of the present invention does not become a complete fluid at the joining temperature but undergoes plastic deformation with low stress and high wettability. When the laminate of the semiconductor elements is joined using the same, the laminate is heated to a joining temperature and pressed using a jig so that the height of the laminate is constant. This stress is at such a low level that the laminate constituting material is not damaged. Thereby, the joining material is plastically deformed, and the height of each laminate becomes uniform. In order to satisfy the above-mentioned requirements for the bonding material, the bonding material of the present invention is composed of a composite material of a low melting point metal for lowering the bonding temperature and ensuring wettability, and a metal porous body having plastic deformation. is there.

[0027]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of the semiconductor device of the present invention. The semiconductor device has a structure in which a heat sink 2, a heat compensator 3, and a Si chip (semiconductor chip) 4 are stacked in a lower mold 1 and pressed by an upper mold 7. 2 and a bonding material 5 between the Si chip 4 and the heat compensator 3.
It is joined by.

Next, a method of adjusting the height of the Si chip 4 will be described. First, heat sink 2 is placed in lower mold 1.
(Cu post or Al post) and heat compensator 3 (usually M
o, AlN or W is used), and a Si chip 4
Are mounted, and the stacked elements are placed between them with the bonding material 5 and the bonding material 6 interposed therebetween.

In this state, there is a difference in the height of the Si chip 4 as shown in FIG.

Next, the upper mold 7 is placed on the lower mold 1 and the above-mentioned laminate. Thereafter, the bonding materials 5 and 6 are heated to a melting temperature in a protective atmosphere such as vacuum, argon gas, hydrogen gas, and nitrogen gas. When the temperature is increased while applying pressure by the weight of the upper mold 5 as described above, the bonding materials 5 and 6 are crushed as shown in FIG. 3, and the height of all the laminates is uniformly equal to the height of the side wall of the lower mold 1. Adjusted.

Here, the depth of the side wall of the lower mold 1 is set according to the desired height of the laminate. That is,
The height is set in consideration of the thermal expansion at the joining temperature, and the height around the entire side wall is uniform.

Thereafter, even when the semiconductor device is cooled to room temperature, the uniform height of the stacked body is maintained.

According to the present embodiment, the joining material 5, 6 which does not become a complete fluid at the joining temperature, undergoes composition deformation with low stress, and has high wettability, and the weight of the upper mold 7 is reduced. Thus, the height of the semiconductor chip 4 can be made equal to the height of the side wall of the upper die 7 by adjusting the thickness of the bonding materials 5 and 6. Thereby, the concentrated load is not applied at the time of pressing the water-cooled heat sink, and the breakage of the Si chip 4 can be prevented.
Sufficient pressure can be applied, and sufficient cooling performance can be obtained.

In order to make the entire multilayer body of the multi-chip type element uniform in height by the above method, the joining material does not flow out to the periphery at the joining temperature, and the strength for maintaining the shape under the stress caused by the pressurization is reduced. It is a necessary condition to obtain the bonding material to be retained. With ordinary solder or brazing material, wetness spreads on the peripheral surface of the materials to be joined due to wettability and fluidity, and the distance between the materials to be joined cannot be controlled.

Therefore, as the bonding materials 5 and 6 of the above embodiment, a bonding material having a composite structure of a porous metal body and a low melting point alloy is used to satisfy the above conditions. This will be described below with reference to FIG.

FIG. 4 shows a composite bonding material (bonding material) 43 composed of a low melting point metal material 41 and a porous metal body 42 manufactured by the bonding material of the present invention and the manufacturing method thereof. The main purpose of the porous metal body 42 is to use a low melting point metal
In addition to preventing the outflow due to the wetting with 1, it functions as a structure that is not crushed by the weight of the material to be joined thereon. However, it is necessary that the pressurization for the purpose of height adjustment be deformable.

Therefore, the porous metal body 42 has a small bonding area ratio between the metal particles, a low apparent density, and a preferable density is 15 to 70%. However, the bonding area ratio between the particles is determined not by the density but by the required range of the compressive strength of the porous metal body 42 according to the use conditions.

The pressing force when used in a power semiconductor device can be applied only with a stress less than the bending strength of a relatively fragile Si chip or AlN (aluminum nitride) plate.
The compressive strength of the porous metal body 42 must be set sufficiently lower than the bending strength of the Si chip or AlN plate.

On the other hand, in the case of the joining materials 5 and 6 in FIG.
The strength of the structure of the upper mold 7 on them is required so as not to be crushed by the load due to the weight. The breaking strength of the Si chip 4 is about 100 MPa, and that of the AIN plate is about 300 MPa. Calculated by the plate pressure used. From the above conditions, the compressive strength of the porous metal body 42 in a normal semiconductor device is in the range of 0.2 to 5 MPa.

Another purpose of the porous metal body 42 is to serve as a medium for heat transfer. The background of the present invention is to improve the cooling performance of a semiconductor device, and it is required that the thermal conductivity of the bonding material itself be improved. Therefore, it is a condition that the material of the porous metal body 42 is a metal having high thermal conductivity, and accordingly, Cu, Al, Ag, Au, M
Metals such as n, Fe, and Zn or alloys thereof are suitable. These are good conductive materials having a thermal conductivity of 70 W / mK or more.

As an example of the porous metal body 42, in addition to the above-mentioned sintered body of low-density particles, a porous body made of a sponge metal, a wire, or a net can be used. The outflow of the low-melting metal liquid can be suppressed by dispersing the metal particles not in the porous metal body but in the low-melting metal.

In the joining method of adjusting the height described with reference to FIGS. 2 and 3, if joining can be performed under the condition that the viscosity of the low-melting metal material 41 is high, a joining material of a particle dispersion type can be used.

Next, as the low melting point metal material 41, a commonly used solder material or brazing material can be used. In the case of a semiconductor device, a relatively high-temperature solder is selected for bonding including a Si chip. For example, Pb, Ag, and Sn-based solders are generally used.

Next, a method for manufacturing the bonding material of the present invention will be described. As a method of producing the porous metal body 42 or the particle-dispersed composite bonding material 43 using metal particles, a paste made of metal particles, a low-melting-point metal powder, and an organic binder is prepared, and screen printing technology or coating is used. One of the materials to be joined is coated in advance, and the joining method shown in FIG. At the time of joining, it is necessary to remove the binder of the paste by heating. This method is a method applicable particularly when the bonding material layer such as a semiconductor element is a thin layer having a thickness of several tens of μm.

As another embodiment, a porous metal body 42 is formed by a sintering method, and a porous body processed to a predetermined size and shape by rolling, forging or cutting is prepared, and a low melting point is obtained at the time of joining. There is a method in which impregnation and joining are performed simultaneously by overlapping with a metal sheet. In this method, the porous metal body 42 may be a sponge metal or an aggregate of fine wires, a net, or a woven fabric.

It should be noted that the bonding material of the present invention can be used not only for bonding semiconductor devices but also for manufacturing various electronic elements and electronic devices, and similar effects can be obtained.

[0047]

According to the joining material and the method of manufacturing the same according to the present invention described above, the joining material is a composite joining material of a low melting point metal material and a porous metal body, so that a complete fluid can be obtained at the joining temperature. It is possible to obtain a bonding material that has a high wettability while being deformed at a low stress and has a high wettability. In addition, the bonding material layer is not unnecessarily crushed even when pressurized by the porous metal body. Since the flow of the low-melting-point metal liquid is suppressed, a predetermined bonding layer thickness can be obtained, and the height of the multi-chip type semiconductor element can be made uniform. Furthermore, by setting the material of the porous metal body to a good conductive metal, the thermal conductivity of the bonding layer can be improved, and the cooling performance of the semiconductor element can be improved.

According to the semiconductor device of the present invention, the height of the semiconductor chip can be made uniform by adjusting the thickness of the bonding material layer used when laminating the semiconductor chip together with other components. A concentrated load is not applied when the water-cooled heat sink is pressed, so that the built-in Si chip can be prevented from being damaged and a sufficient pressing force can be applied, so that sufficient cooling performance can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a semiconductor device of the present invention.

FIG. 2 is an explanatory view showing a manufacturing process of the device shown in FIG.

FIG. 3 is an explanatory diagram showing a manufacturing process of the device shown in FIG.

FIG. 4 is a cross-sectional view showing one embodiment of the structure of the bonding material of the present invention.

FIG. 5 is a cross-sectional view illustrating a configuration example of a conventional semiconductor device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 lower mold 2 heat sink (Cu post) 3 heat compensator (Mo material) 4 Si chip (semiconductor) 5, 6 bonding material 7 upper die 41 low melting point metal material (solder) 42 porous metal body 43 composite bonding material

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Takanori Nishimura 1 Toshiba-cho, Fuchu-shi, Tokyo Inside the Toshiba Fuchu Plant, Inc. (72) Inventor Atsushi Yamamoto 1-Toshiba-cho, Fuchu-shi, Tokyo Inside the Fuchu Plant, Toshiba ( 72) Inventor Takashi Kusano 1 Toshiba-cho, Fuchu-shi, Tokyo Inside the Fuchu Plant, Toshiba Corporation (72) Inventor Hiroshi Ishiwatari 2-4 Suehirocho, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture F-term in the Toshiba Keihin Works (reference) 5F047 BA06 BB11 BB13 BB16 BC31 BC35 JA06 JA07

Claims (13)

[Claims] 1. A joining material having a mixed structure of two or more kinds of metals for joining a material to be joined, comprising: a metal phase for maintaining the thickness accuracy of a joining material layer of the joining material; and a metal phase for fusion joining. A joining material characterized by being formed. 2. The joining material according to claim 1, wherein the yield stress of the metal phase that maintains the thickness accuracy of the joining material layer is lower than the fracture stress of the material to be joined at the melting point of the metal phase to be melt-joined. A bonding material characterized by being used in combination. 3. The bonding material according to claim 1, wherein the metal phase for maintaining the thickness accuracy of the bonding material layer of the bonding material is:
A bonding material characterized by being arranged in a network, a porous state or a particle dispersed state. 4. The bonding material according to claim 1, wherein the metal phase for maintaining the thickness accuracy of the bonding material layer of the bonding material is:
A bonding material having a thermal conductivity of about 70 W / mK or more near room temperature. 5. The bonding material according to claim 1, wherein the metal phase for maintaining the thickness accuracy of the bonding material layer of the bonding material is C.
A bonding material comprising at least one of u, Ag, Au, Mn, Ni, Fe and Zn metals or alloys thereof. 6. The bonding material according to claim 1, wherein the melting point of the metal phase to be melt-bonded is 1200 ° C. or less. 7. The bonding material according to claim 1, wherein the bonding material is sandwiched between the materials to be bonded and stacked, and heated to a bonding temperature while being pressed to a predetermined height. 8. A mixed paste of a metal powder of a metal phase for maintaining the thickness accuracy of the bonding material layer of the bonding material according to claim 1, a metal powder of the metal phase to be melt-bonded, and a binder, to the material to be bonded. A method for producing a bonding material, characterized by applying. 9. A method for manufacturing a bonding material, comprising: impregnating a sheet of a porous sintered body of a metal phase which maintains the thickness accuracy of the bonding material layer of the bonding material according to claim 1 with the molten bonding metal. Method. 10. A method for impregnating a net, a woven fabric, or an aggregate of a metal phase thin metal wire for maintaining the thickness accuracy of the bonding material layer of the bonding material according to claim 1, with the molten bonding metal. Manufacturing method of the joining material. 11. A method for manufacturing a bonding material, comprising: impregnating a sponge sheet of a metal that maintains the thickness accuracy of the bonding material layer of the bonding material according to claim 1 with the molten bonding metal. 12. The joining material according to claim 1, which is applied to the material to be joined, and thereafter, at least one of a metal powder, a fine wire, and a porous body that maintains the thickness accuracy of the joining material layer. A method for manufacturing a bonding material, characterized by embedding types. 13. A semiconductor device comprising a semiconductor chip and other components joined by using the joining material according to claim 1.