JPH0376578B2 - - Google Patents

Description

[Detailed description of the invention]

[Purpose of the Invention] (Field of Industrial Application) The present invention relates to a semiconductor device in which semiconductor pellets are directly die-bonded to a copper material, and particularly provides advantages such as no cracking in the pellets even when large-sized pellets are used. This is a semiconductor device having a (Prior art) Conventionally, when die bonding is performed by directly soldering a small silicon pellet of approximately 6 mm or less to a copper piece (for example, a stem) that will serve as a collector electrode, the temperature is 180 to 350 °C. Even when the soldering temperature is returned to room temperature, cracks do not occur because the pellet size is small. For example, the pellet size is 6mm, and the soldering temperature is 275mm.
When calculating the difference in thermal contraction when the temperature is ℃, the thermal expansion coefficient α of silicon pellets is α=7.3×10 ^-6
℃ ^-1 , so it shrinks by about 11 μm, while copper α=
Since the temperature is 17.0×10 ^-6 °C ^-1 , it shrinks by about 25.5 μm, and the difference in thermal shrinkage between the two is about 14 μm. According to such a difference in thermal shrinkage, the silicon pellet should be warped in a convex shape, but this distortion is alleviated by the elastic and plastic deformation of the solder layer, and in reality it is not long enough to cause a crack. It does not reach. However, when the silicon pellet becomes larger than approximately 7 mm, the strain becomes large due to the difference in thermal contraction between copper and silicon, and the stress applied to the silicon pellet exceeds its elastic limit, causing it to collapse during cooling after die bonding or afterwards. Pellet cracks occur during the temperature cycling of the process. For this reason, conventionally, die bonding has been carried out between the copper material and the silicon pellet through a thermal buffer plate such as a Mo plate or W plate, which has a coefficient of thermal expansion α close to that of silicon. To explain this with reference to FIG. 1, it consists of a pellet 1, a Mo plate 2 for thermal buffering, a copper plate 3 serving as a collector electrode, a ceramic liquid-absorbing plate 4, and a copper base 5 for heat dissipation, and these include solder layers 7 to 10, etc. It is fixed by. In this case, the silicon pellet is 10mm
Assuming that the soldering temperature is 275℃,
In the same way as above, silicon pellet 1 and Mo
When calculating the difference in thermal contraction between the plate 2 and the plate 2, the thermal expansion coefficient α of Mo is 4.9 to 5.1×10 ⁻⁶ ° C. ⁻¹ , so the difference in thermal contraction is approximately 5.4 μm. Similar Mo plate 2 and copper plate 3
The difference in thermal shrinkage between the two is approximately 30 μm. Therefore, the stress applied to the silicon pellet is small, so no cracks occur, and the Mo plate is subjected to a large stress, but it has a large longitudinal elastic modulus and is much thicker than the silicon pellet, with a thickness of 0.5 to 1.0 mm or more. Because it is thick, it is possible to suppress the occurrence of cracks and warping. As described above, when semiconductor pellets are directly die-bonded to a copper material, there is a risk that distortion or cracks may occur in the pellets. In addition, Mo board and W
When die bonding is performed through a thermal buffer plate such as a plate, when the semiconductor element is actually operated and generates heat, a loss occurs in thermal conductivity due to the thermal buffer plate. Also
Since Mo boards are expensive, it is inevitable that the cost of the equipment will increase. (Problems to be Solved by the Invention) An object of the present invention is to provide a semiconductor device including a conductive material made of copper or a copper alloy, in which the substantial coefficient of thermal expansion of the copper material is close to that of the semiconductor pellet. It is in. Another object is to provide a semiconductor device that can be directly die-bonded to a copper material without causing distortion or cracks in the pellet, even if the semiconductor pellet is particularly large in size, and to provide a semiconductor device that can be die-bonded directly to a copper material, even if it is a large-sized semiconductor pellet. The object of the present invention is to provide a semiconductor device with good characteristics. [Structure of the Invention] (Means for Solving the Problems) Copper and a nonmetallic refractory material such as ceramics have already been placed in contact with each other, and a eutectic produced by heating in a reactive atmosphere has been utilized. It is known that the two can be strongly joined, that a circuit pattern can be formed from the joined material, and that this method can be used to create an airtight seal between nonmetallic refractory materials (Japanese Patent Laid-Open No. 49/1999).
−17381). Furthermore, the present inventors have confirmed that copper or copper alloy containing an appropriate amount of oxygen and a nonmetallic refractory material are bonded by a similar eutectic even when contact heating is performed in an inert gas atmosphere. There is. The present inventors have found that the coefficient of thermal expansion of copper bonded to a nonmetallic refractory material by such eutectic material is extremely close to that of semiconductor pellets such as silicon, and that large-sized pellets with a diameter of 40 mm without intervening thermal buffer plates can be used. The present inventors have discovered that pellet cracks do not occur even when the pellets are die-bonded directly onto the copper surface of a bonding substrate, and that heat dissipation from the pellets is improved, and the present invention has been completed. That is, the semiconductor device of the present invention is as described in the claims.
The first to third conductive materials made of copper or copper alloy having a thickness of The first feature is that it has a laminated substrate bonded via a cuprous oxide eutectic. Of the first to third conductive materials bonded to the laminated board, a heat sink is bonded to the copper or copper alloy surface of the first conductive material bonded to the first surface of the nonmetallic fireproof material plate by soldering or welding. The copper or copper alloy of the second conductive material bonded to the second surface of the nonmetallic refractory material plate is loaded with at least one semiconductor pellet with a diameter of 7 mm or more by soldering or welding, and the second conductive material is bonded to the second surface of the nonmetallic refractory material plate. The copper or copper alloy surface of the third conductive material joined to the semiconductor pellet is electrically connected to the semiconductor pellet by a lead wire, and external terminals are connected to the second conductive material and the third conductive material, respectively. This is the second characteristic. The second invention of claim 2 is provided with a plurality of sets of second and third conductive materials corresponding to a plurality of element units, and the third invention of claim 3 is a non-conductive material. A first conductive material having the same shape as the first conductive material is bonded to the entire first surface of the metal refractory material plate. (Function) The function of the present invention will be specifically explained below. First, a eutectic produced by heating will be explained using a eutectic of copper and oxygen as an example. Oxygen 0.008% by weight
When copper containing less than 0.39% by weight is heated to 1065°C, a eutectic of α-copper and Cu ₂ O (oxygen content at that temperature is 0.39% by weight) and solid α-copper coexist. This coexistence state is maintained within the range of 1065 to 1083°C. In this state of coexistence, the copper sheet retains its original shape and its surface becomes wetted by the eutectic. If this coexisting copper conductive material (sheet) is brought into contact with a nonmetallic refractory material plate such as ceramic and cooled, the eutectic on the surface of the sheet becomes a eutectic of α copper and Cu ₂ O. The copper sheet can then be bonded to the ceramic. As such a eutectic, in addition to the above-mentioned copper/oxygen eutectic, it is disclosed in JP-A No. 17381/1989 that eutectic with copper/phosphorus, copper/sulfur, and other elements can be used. Further, instead of copper, copper alloys with beryllium, nickel, silver, aluminum, zinc, tin, lead, etc. can also be used. Elements such as oxygen for eutectic formation are disclosed in JP-A-49
Although it may be supplied from a reactive gas atmosphere as in No. 17381, copper containing 0.008% by weight or more and less than 0.39% by weight of oxygen is pre-contained in a copper sheet so that it is heated in a non-reactive atmosphere. It is easier to mass-produce this method, and a high-quality bonded substrate can be obtained. Non-metallic refractory materials include alumina, beryllia, forsterite, zircon, magnesia,
Examples include quartz, spinel, etc., and eutectic exhibits good bonding to all these nonmetallic refractory materials. Among the above, those whose thermal expansion coefficient is close to or smaller than that of semiconductor pellets are preferred. In the semiconductor device shown in FIG.
is a 96% Al ₂ O ₃ ceramic plate (thickness 1.0 mm) 21
Electrolytic copper foil with an oxygen content of 0.04% by weight (thickness 250μ
m) 22 in close contact with each other, placed in a conveyor-type heating furnace, held at 1070℃ for 10 minutes in a _N2 stream, slowly cooled, and taken out.The copper foil is firmly bonded to the ceramic plate. It is. When the thermal expansion coefficient α of the copper surface on this substrate 20 was measured, it was approximately 11×10 ⁻⁶ ° C. ⁻¹ . This is due to alumina where α=7.7×10 ^-6 ℃ ^-1 .
= 17.0×10 ^-6 °C ^-1 copper has a substantially lower coefficient of thermal expansion. Calculating the difference in thermal contraction at a temperature difference of 250°C between the copper on the substrate, which has a coefficient of thermal expansion of 11×10 ^-6 °C ^-1 , and the silicon pellet with a diameter of 15 mm, it is approximately 14 μm. If the value is around this level, it can be expected that pellet cracks will not occur. And it did not break even after actual die bonding, and the temperature cycle test (-55℃ to 150℃)
However, no abnormality in the characteristics of the semiconductor device was observed. The reduction in the coefficient of thermal expansion of the copper on the substrate is primarily determined by the thickness of the copper sheet and the thickness of the ceramic plate. The decrease is almost the same depending on the type of eutectic, and the level only differs depending on the type of copper/copper alloy or ceramic. Figure 3 shows alumina (1
The relationship between the coefficient of thermal expansion when the copper thickness is changed is shown using the mm thickness curve A and the 2 mm thickness curve B. As can be seen in Figure 3, when the copper thickness becomes less than 0.6 mm (probably because it exceeds the elastic limit of copper), the coefficient of thermal expansion approaches that of ceramic. Therefore, an example of the most preferable combination of copper and ceramic is a combination of 2 mm thick ceramic and 50 μm thick copper foil,
In this case, it has been found that if the pellets are soldered ideally so that no distortion occurs, it is possible to die-bond pellets with a diameter of 40 mm or more without a thermal buffer plate. Next, the copper thickness is 1 mm, which is the same thickness as ceramic.
When this copper is bonded to one side of ceramic, ±
Warpage of about 1% occurs. When the copper thickness exceeds the ceramic thickness, the warpage becomes even greater and pellet cracks occur. One countermeasure in this case is to simultaneously bond copper foils 22 and 23 (preferably the two copper foils have the same thickness) to both sides of the ceramic plate to prevent warping, as shown in Figure 2. It can be avoided. Another measure is
In order to bond 1 mm thick copper, it is also possible to stack and bond two 0.5 mm thick copper foils. However, when bonding copper on both sides, if the thickness of the copper is much thicker than the thickness of the ceramic, of course there will be no warping, but there is a risk of damage to the ceramic plate during die bonding or subsequent temperature cycling. The type of semiconductor pellet to be die bonded in the present invention is not limited. This is because the present invention takes advantage of copper's altered coefficient of thermal expansion. And also soldering, eutectic bonding, brazing, organic adhesive bonding, etc.
The present invention is not limited by the die bonding method either. Table 1 shows specific ranges of combinations of pellet size, copper thickness, and ceramic thickness that have been confirmed to be practical in terms of not causing cracks or warping of pellets or ceramic plates.

【table】

[Table] As described above, since the copper on the substrate of the present invention is bonded by eutectic, the coefficient of thermal expansion of the copper on the substrate approaches that of the nonmetallic refractory material plate. , can be utilized in relation to the coefficient of thermal expansion of the semiconductor pellet. One of its uses is that conventional silicon pellets with a size of about 6 mm or less, which could be directly die bonded to copper without going through a thermal buffer plate, can now be directly die bonded to copper with a diameter of about 7 mm or more, for example, 40 mm. Can be bonded. This simplifies the process and reduces expensive
This greatly contributes to reducing the cost of semiconductor devices by eliminating the need for Mo plates. Furthermore, since the device of the present invention does not have a thermal buffer plate and there is no adhesive layer such as a solder layer between the copper and the ceramic plate serving as the insulating layer, the copper under the pellet is relatively thin. However, it has high thermal conductivity and good heat dissipation from the pellets. Specifically, the thermal resistance R _th(JC) of the conventional example shown in FIG. 4a is 0.17 to 0.22°C/W, and the thermal resistance R _th(JC) of the reference example shown in FIG. °C/W, thermal resistance R _th(JC) of the example shown in Fig. 4c = 0.22 to 0.26 °C/
It was W. However, 41 is a silicon pellet with a 13.6mm opening, 42 is a 0.5mm thick Mo plate, and 43 is 3.5mm.
Thick Cu plate, 44 is 0.5mm thick alumina plate, 45 is 3mm thick Cu base, 46 is Cu sheet, 0.25mm/
This is a eutectic bonded substrate according to the present invention consisting of a 0.5 mm alumina plate/0.25 mm Cu sheet, and S is a fixed solder layer. (Example) As an example of the device of the present invention, a power module having the circuit configuration shown in FIG. 5a and the structure shown in FIG. 5b will be described. That is _, in FIG. 5b, as in the case of _FIG .
A 0.04% by weight electrolytic copper foil (thickness 250 μm) was placed in close contact with the copper foil, placed in a conveyor type heating furnace, and placed in a _N2 gas stream.
It was obtained by holding it at 1070℃ for 10 minutes, slowly cooling it, and then taking it out.The copper foil was firmly bonded to the ceramic plate. The joined conductive materials include, on the second surface of the ceramic plate, a set of second conductive material 22, third conductive material 24, and third conductive material 25, and second conductive material 22',
This is a set of third conductive material 24' and third conductive material 25', and the first conductive material (23 in FIG. 2) is bonded to the entire first surface (back surface) of the ceramic plate. Reference numerals 1 and 1' designate semiconductor pellets each forming an element circuit within the range surrounded by the dashed line in FIG. 5a. The semiconductor pellets 1, 1' are shown in FIG. 5b.
As shown in FIG.
2', and predetermined electrode pads of pellets 1, 1' are connected to third conductive members 24, 24' and third conductive members 25, 25' by lead wires. In addition
C ₁ and C ₂ are external terminals connected to the second conductive material, and B ₁ , B ₂ , E ₁ , and E ₂ are external terminals connected to the third conductive material. At this time, the set of conductive members, that is, the lead-out portion of the second conductive member 22, the third conductive member 24, and the third conductive member 25, are arranged along each side of the substrate around the semiconductor pellet 1, and Conductive material 24 and third conductive material 2
By aligning the lead wires 5 in parallel in one direction and arranging the conductive members 22', 24', and 25' in the same arrangement, the multi-element module can be made into an external structure with a simple shape. Preferable for connecting via terminals. [Effects of the Invention] According to the semiconductor device of the present invention, thermal expansion of the surface of copper or copper alloy in a substrate in which a conductive material of copper or copper alloy is bonded to a nonmetallic refractory material plate by cuprous oxide eutectic is particularly effective. Since the coefficient is substantially reduced, there is no risk of pellet cracking even when semiconductor pellets are die-bonded to the copper or copper alloy surface without a thermal buffer plate, and the heat generated in the pellets is well dissipated, making the manufacturing process easier. It is simple and has many advantages, such as not requiring an expensive thermal buffer plate.

[Brief explanation of drawings]

FIG. 1 is a side view showing a conventional semiconductor device that requires a thermal buffer plate, FIG. 2 is a side view of a semiconductor device according to an embodiment of the present invention, and FIG. 3 is a side view of a semiconductor device according to an embodiment of the present invention. A graph showing the relationship between the coefficient of thermal expansion of the upper copper surface, Fig. 4 is an explanatory diagram of the thermal resistance test samples of the conventional example (a in the same figure), the reference example (b in the same figure), and the example (c in the same figure), Fig. 5 The figures are a circuit configuration diagram (a in the same figure) and an exploded perspective view (b in the same figure) of an embodiment of the present invention. 1, 1'... Semiconductor pellet, 5... Heat sink,
20... Laminated board, 21... Nonmetallic fireproof material plate,
22, 22'... second conductive material, 23... first conductive material, 24, 24', 25, 25'... third conductive material,
C ₁ , C ₂ , B ₁ , B ₂ , E ₁ , E ₂ ...external terminals.

Claims (1)

[Claims] 1. The first surface of the first conductive material made of copper or copper alloy is placed in contact with the first surface of the nonmetallic refractory material plate, and the oxidized metal is heated in a non-oxidizing atmosphere. a laminated board in which the nonmetallic refractory material plate and the first conductive material are bonded via a single copper eutectic, and a second conductive material made of at least one copper or copper alloy, the second conductive material being a second conductive material of the nonmetallic refractory material plate; The second one on two sides
The first surface of the conductive material is placed in contact with the non-metallic refractory material plate through a cuprous oxide eutectic produced by heating in a non-oxidizing atmosphere, and at least one copper or copper alloy. a third conductive material, which is separated from the second conductive material, and a first conductive material of the third conductive material on the second surface of the nonmetallic refractory material plate;
The second surface of the first conductive material is bonded to the nonmetallic refractory material plate through a cuprous oxide eutectic produced by heating in a non-oxidizing atmosphere, and solder or A heat dissipation plate joined by welding; at least one semiconductor pellet having a diameter of 7 mm or more mounted on the second surface of the second conductive material by soldering or welding; and at least one semiconductor pellet connecting the semiconductor pellet and the third conductive material. one lead wire, an external terminal connected to the second conductive material, and an external terminal connected to the third conductive material, and the first to third conductive materials have a thickness of 0.25 to 0.5 mm. What is claimed is: 1. A semiconductor device characterized in that the nonmetallic refractory material plate is thicker than the first conductive material to the third conductive material. 2. Place the first surface of the first conductive material of copper or copper alloy in contact with the first surface of the nonmetallic refractory material plate, and heat it in a non-oxidizing atmosphere to form a cuprous oxide eutectic. a laminated board in which the non-metallic fireproof material plate and the first conductive material are joined together, a heat dissipation plate joined to the second surface of the first conductive material by soldering or welding, and a plurality of component combination units on the laminated board. is constructed, and the member combination unit is at least one second conductive material of copper or copper alloy, and the second conductive material is attached to the second surface of the non-metallic refractory material plate.
The first surface of the conductive material is placed in contact with the non-metallic refractory material plate through a cuprous oxide eutectic produced by heating in a non-oxidizing atmosphere, and at least one copper or copper alloy. a third conductive material, which is separated from the second conductive material, and a first conductive material of the third conductive material on the second surface of the nonmetallic refractory material plate;
The second conductive material is bonded to the nonmetallic refractory material plate via a cuprous oxide eutectic produced by heating in a non-oxidizing atmosphere, and the second conductive material is bonded to the second surface with solder or At least one semiconductor pellet with a diameter of 7 mm or more mounted by welding, at least one lead wire connecting the semiconductor pellet and the third conductive material, an external terminal connected to the second conductive material, and the third conductive material. and an external terminal connected to a third conductive material, wherein the first to third conductive materials have a thickness of 0.25 to 0.5 mm, and the nonmetallic refractory material plate connects the first to third conductive materials. A semiconductor device characterized by being thicker than the material itself. 3 The first surface of the first conductive material of copper or copper alloy is placed in contact with the first surface of the nonmetallic refractory material plate, and the first surface of the first conductive material of copper or copper alloy is placed in contact with the first surface of the nonmetallic refractory material plate, and the first surface is heated in a non-oxidizing atmosphere to form a cuprous oxide eutectic. a laminated substrate in which the non-metallic refractory material plate and the first conductive material are joined together, and at least one second conductive material of copper or copper alloy, the second conductive material being connected to the second surface of the non-metallic refractory material plate;
The first surface of the conductive material is placed in contact with the non-metallic refractory material plate through a cuprous oxide eutectic produced by heating in a non-oxidizing atmosphere, and at least one copper or copper alloy. a third conductive material, which is separated from the second conductive material, and a first conductive material of the third conductive material on the second surface of the nonmetallic refractory material plate;
The second surface of the first conductive material is bonded to the nonmetallic refractory material plate through a cuprous oxide eutectic produced by heating in a non-oxidizing atmosphere, and solder or A heat dissipation plate joined by welding; at least one semiconductor pellet having a diameter of 7 mm or more mounted on the second surface of the second conductive material by soldering or welding; and at least one semiconductor pellet connecting the semiconductor pellet and the third conductive material. one lead wire, an external terminal connected to the second conductive material, and an external terminal connected to the third conductive material, and the first to third conductive materials have a thickness of 0.25 to 0.5 mm. and the nonmetallic refractory material plate is thicker than the first to third conductive materials, and the first conductive material is a sheet having the same shape as the nonmetallic refractory material plate. Device.