JP4727486B2 - Semiconductor device - Google Patents

Description

  The present invention relates to a semiconductor device. In particular, the present invention relates to a semiconductor device that suppresses deterioration of electrical characteristics of a semiconductor element when the temperature of the semiconductor element rises.

  FIG. 1 shows the structure of a semiconductor device 10 in the prior art. The semiconductor device 10 includes a semiconductor substrate 20, a base plate 14, and a ceramic substrate 18.

  The semiconductor substrate 20 is a silicon substrate on which semiconductor elements such as MOS transistors, diodes, bipolar transistors, thyristors and IGBTs are formed.

  The ceramic substrate 18 is a DBC (Direct Bond Copper) substrate. A semiconductor substrate 20 is mounted on the surface of the ceramic substrate 18 via an adhesive layer 16a.

  The base plate 14 is formed of a metal such as copper or aluminum. A ceramic substrate 18 is mounted on the surface of the base plate 14 via an adhesive layer 16b.

  When a current flows through the semiconductor element formed on the semiconductor substrate 20, Joule heat is generated in the semiconductor element, and the temperature of the semiconductor device 10 rises. When the temperature of the semiconductor device 10 rises, the semiconductor substrate 20, the ceramic substrate 18 and the base plate 14 are thermally expanded. Since the semiconductor substrate 20, the ceramic substrate 18, and the base plate 14 have different thermal expansion coefficients, the heat determined by the difference in thermal expansion coefficient and the temperature at the joint between the components via the adhesive layers 16 a and 16 b. Stress is generated.

  In the semiconductor device 10, the thermal expansion coefficient of silicon, which is the material of the semiconductor substrate 20, is about 3.0 ppm, and the thermal expansion coefficient of aluminum, which is the material of the base plate 14, is about 20 ppm. On the other hand, the linear expansion coefficient of the DBC substrate used as the ceramic substrate 18 is about 5 to 7 ppm. Therefore, the thermal stress generated in the semiconductor substrate 20 mounted on the surface of the base plate 14 via the ceramic substrate 18 is smaller than the thermal stress generated when the semiconductor substrate 20 is mounted on the surface of the base plate 14. That is, in the semiconductor device 10, by providing the ceramic substrate 18 between the base plate 14 and the semiconductor substrate 20, thermal stress generated in the semiconductor substrate 20 can be relieved.

JP 2003-243601A

  When a large current flows through the semiconductor element formed on the semiconductor substrate 20, Joule heat generated in the semiconductor element increases, and the temperature of the semiconductor device 10 rises. In a semiconductor element, when the temperature rises, the mobility of carriers decreases and the electrical resistance of the current path increases. As a result, the conventional technology has a problem that the current that can be passed through the semiconductor element is limited at high temperatures.

  Therefore, an object of the present invention is to provide a semiconductor device that suppresses deterioration in electrical characteristics of a semiconductor element when the temperature of the semiconductor element rises.

  In a semiconductor device having a mounting substrate and a semiconductor substrate mounted on the surface of the mounting substrate via an adhesive layer, the present invention is disposed adjacent to a side surface of the semiconductor substrate, It is provided with the pressing tool provided so that sliding was possible, and the fixing tool mounted on the surface of the mounting substrate, and fixing and supporting a part of the pressing tool.

  Further, it is preferable that the pressing tool is disposed adjacent to the four side surfaces of the semiconductor substrate. In this case, when the temperature of the semiconductor device rises, the pressing tool thermally expands, and pressure is applied to the four side surfaces of the semiconductor substrate by the thermally expanded pressing tool. As a result, a compressive stress is generated in the semiconductor substrate in a direction parallel to the substrate surface. When the semiconductor element formed on the semiconductor substrate is a vertical semiconductor element having electrodes on the front surface and the back surface of the semiconductor substrate, the electrical stress of the semiconductor element due to the temperature rise due to the compressive stress generated in the semiconductor substrate. The deterioration of characteristics can be suppressed.

  Alternatively, it is preferable that the pressing member is disposed adjacent to each of one side surface of the semiconductor substrate and a side surface opposite to one of the side surfaces of the semiconductor substrate. In this case, the pressing tool thermally expands when the temperature of the semiconductor device rises, and pressure is applied to the two side surfaces of the semiconductor substrate by the thermally expanded pressing tool. As a result, compressive stress is generated in the semiconductor substrate in the direction sandwiched between the two side surfaces. Due to this compressive stress generated in the semiconductor substrate, it is possible to suppress a decrease in electrical characteristics of the semiconductor element accompanying a temperature increase.

  Furthermore, it is preferable that the pressing tool includes a material having a product of a linear expansion coefficient and a Young's modulus of 2 MPa / K or more. For example, the material of the pressing member is preferably any one of copper, iron, nickel, alumina, sapphire, or titania. In this case, when the temperature of the semiconductor substrate rises, the compressive stress generated in the semiconductor substrate by the presser can be increased.

  Moreover, it is preferable that the surface of the pressing tool is covered with an insulating material. In this case, even when the presser and the semiconductor substrate come into contact with each other when the temperature of the semiconductor substrate rises, electrical insulation can be maintained between the presser and the semiconductor substrate.

  In addition, it is preferable that the pressing member provided to be slidable with respect to the mounting substrate has a sliding portion protruding toward the surface of the mounting substrate. Furthermore, it is preferable that the shape of the sliding portion is a sharp shape or a shape having a curved surface, and a part of the shape of the sliding portion having a sharp shape or a curved surface is in contact with the surface of the mounting substrate. In this case, since the contact area between the surface of the mounting substrate and the pressing tool can be reduced, the slidability of the pressing tool with respect to the surface of the mounting substrate can be improved.

  Furthermore, it is preferable that the sliding portion is coated with a fluororesin or a fluororesin. In this case, the effect is remarkable in that the coefficient of friction is reduced on the surface where the surface of the mounting substrate and the sliding portion come into contact.

  The material of the adhesive layer is preferably solder. In this case, thermal stress caused by the difference in thermal expansion between the mounting substrate and the semiconductor substrate can be relaxed.

  Further, it is preferable that the mounting substrate is a ceramic substrate, and the material of the fixture is a steel material. In this case, a fixture made of a material having higher rigidity than the presser can be mounted on the mounting board.

  ADVANTAGE OF THE INVENTION According to this invention, when the temperature of a semiconductor element rises, it can suppress that the electrical property of a semiconductor element falls.

(First embodiment)
FIG. 2 is a top view of the semiconductor device 50 according to the present invention. FIG. 3 shows a cross-sectional structure diagram between A1 and A2 in FIG.

  The semiconductor device 50 includes a mounting substrate 52, a semiconductor substrate 54, an adhesive layer 56, a pressing tool 58, and a fixing tool 60.

  The semiconductor substrate 54 is a substrate made of silicon, silicon-germanium, compound semiconductor, or the like on which semiconductor elements such as MOS transistors, bipolar transistors, diodes, thyristors, and IGBTs are formed. For example, in the present embodiment, the semiconductor substrate 54 is a silicon substrate having a thickness of about 0.1 mm to 0.5 mm, and the semiconductor element formed on the semiconductor substrate 54 includes a front surface and a back surface of the semiconductor substrate 54. This is a vertical semiconductor element having an electrode (not shown).

  A semiconductor substrate 54 is mounted approximately at the center of the surface of the mounting substrate 52 via an adhesive layer 56, and a pressing tool 58 and a fixing tool 60 are mounted around the mounted semiconductor substrate 54. The material of the mounting substrate 52 is preferably an insulating material. For example, a ceramic material is used as one that can firmly restrain the fixture 60 mounted on the surface of the mounting substrate 52. Further, a metal wiring layer (not shown) such as copper or aluminum used as circuit wiring is formed on the surface of the mounting substrate 52.

  The adhesive layer 56 formed between the mounting substrate 52 and the semiconductor substrate 54 is a conductive material, and is formed in contact with the metal wiring layer formed on the surface of the mounting substrate 52. Thereby, an electrode (not shown) formed on the back surface of the semiconductor substrate 54 and the metal wiring layer formed on the surface of the mounting substrate 52 are electrically connected. As the conductive material for the adhesive layer 56, a material that can alleviate the influence of thermal stress caused by the difference in thermal expansion between the mounting substrate and the semiconductor substrate is preferable. For example, solder or a silver epoxy adhesive is used for the adhesive layer 56.

  The presser 58 has a flat plate shape. A wide surface of the pressing tool 58 is parallel to the surface of the mounting substrate, and one end surface of the flat pressing tool 58 is one of the side surfaces of the semiconductor substrate 54 mounted on the surface of the mounting substrate 52. Arranged to face each other. In the present embodiment, at least four pressing tools 58 are arranged so that one of the end faces faces each of the four side surfaces of the semiconductor substrate 54. Further, the thickness of the presser 58 is formed to be thicker than the thickness of the semiconductor substrate 54.

  For example, the pressing tool 58 is disposed on the surface of the mounting substrate 52 so that the gap with the side surface of the semiconductor substrate 54 is 5 μm or less at room temperature (10 ° C. to 30 ° C.). Further, when the thickness of the semiconductor substrate 54 is about 0.1 mm to 0.5 mm, the presser is formed with a thickness of about 0.2 mm to 0.8 mm.

  The material of the presser 58 is preferably a material that is likely to thermally expand as the temperature of the semiconductor device 50 increases, and is a material having a Young's modulus that is substantially the same as or higher than that of silicon that is the material of the semiconductor substrate 54. It is preferable. In particular, in order for pressure to be applied to the side surface of the semiconductor substrate 54 by the thermally expanded pressing tool 58 to generate a large compressive stress in the semiconductor substrate 54, the product of the linear expansion coefficient and Young's modulus of the material of the pressing tool is It is preferable that it is 2 MPa / K or more. As such a material, a conductive material such as copper, iron, nickel, or alumina or an insulating material such as sapphire or titania is used for the presser 58. When a conductive material such as copper, iron, nickel, and alumina is used for the presser 58, when it is not preferable that the presser 58 and the semiconductor substrate 54 are in electrical contact at a high temperature, the surface of the presser 58 is Covered with an insulating material.

  A part of the pressing tool 58 is in contact with the surface of the mounting substrate 52. In order to reduce the contact area and improve the slidability of the presser 58 with respect to the mounting substrate 52, the presser 58 has a sliding portion 58 a that protrudes from the presser 58 toward the surface of the mounting substrate 54. It is formed. As shown in FIG. 3, the sliding portion 58 a has a sharp shape such as a knife edge shape, and the sharp shape contacts the surface of the mounting substrate 52. Or as shown in FIG. 4, the shape which has a curved surface may be sufficient as the sliding part 58a. In this case, a part of the curved surface of the sliding portion 58 a is in contact with the surface of the mounting substrate 52.

  Further, the surface of the pressing tool 58 is made of a fluororesin such as Teflon (registered trademark) so that the pressing tool 58 can slide relative to the surface of the mounting board 54 on the surface where the pressing tool 58 and the mounting board 52 come into contact. May be coated. Or you may form the sliding part 58a which protruded from the pressing tool 58 with fluororesins, such as Teflon (trademark).

  Alternatively, as shown in FIG. 5, the pressing tool 58 and the sliding portion 62 may be formed separately. In this case, a sliding portion 62 is formed between the presser 58 and the mounting substrate 52. The sliding portion 62 is preferably formed of a fluororesin such as Teflon (registered trademark) or the surface of the sliding portion 62 is covered with a fluororesin such as Teflon (registered trademark).

  The fixing tool 60 is mounted on the surface of the mounting substrate 52, and a part of each pressing tool 58 is fixed and supported. As the material of the fixture 60, a material having a higher Young's modulus than the material of the presser 58 and being firmly fixed to the mounting substrate 52 is used. For example, a steel material is used for the fixture 60.

  In the semiconductor device 50, the presser 58 having the sliding portion 58a is slidable in a direction parallel to the surface of the mounting substrate 52 (x-axis direction or y-axis direction in FIG. 2). When the temperature of the semiconductor device 50 is a reference temperature within the range of room temperature, the presser 58 and the semiconductor substrate 54 come into contact with each other, but the pressure is not applied to the semiconductor substrate 54 by the presser 58. A case where the presser 58 is mounted on the mounting substrate 52 will be described. When the temperature of the semiconductor device 50 further increases by ΔT from the reference temperature, the presser 58 thermally expands and slides in a direction parallel to the surface of the mounting substrate 52 (x-axis direction or y-axis direction in FIG. 2). To do. As a result, pressure is applied from the presser 58 to each of the four side surfaces of the semiconductor substrate 54. As a result, compressive stress is generated in the semiconductor substrate 54 in a direction parallel to the surface of the semiconductor substrate 54 (x-axis direction or y-axis direction in FIG. 2). The magnitude σ of this compressive stress is as follows.

ここで、α₁は半導体基板５４の線膨張係数，α₂は押さえ具の線膨張係数，Ｅ₁は半導体基板５４のヤング率，Ｅ₂は押さえ具のヤング率，ｌ₁は半導体基板５４の長さ，ｌ₂は押さえ具５８の長さである。

Here, α ₁ is the linear expansion coefficient of the semiconductor substrate 54, α ₂ is the linear expansion coefficient of the presser, E ₁ is the Young's modulus of the semiconductor substrate 54, E ₂ is the Young's modulus of the presser, and l ₁ is the semiconductor substrate 54. The length l ₂ is the length of the presser 58.

For example, the material of the semiconductor substrate 54 is silicon (α ₁ = 3 × 10 ⁻⁶ K ⁻¹ , E ₁ = 170 × 10 ⁹ Pa), and the material of the presser 58 is copper (α ₂ = 17 × 10 ^−6). K ⁻¹ , E ₂ = 120 × 10 ⁹ Pa), when the length l ₁ of the semiconductor substrate 54 is 10 mm and the length l ₂ of the presser 58 is 10 mm, when ΔT = 125 ° C., about A compressive stress of 205 MPa is generated in the semiconductor substrate 54.

In the semiconductor device 50, the main current path of the vertical semiconductor element formed in the semiconductor substrate 54 is the z-axis direction shown in FIG. Further, the compressive stress generated in the semiconductor substrate 54 has an x-axis direction component and a y-axis direction component. Assuming that the magnitude of stress in each direction is σ _x and σ _y , the electrical resistivity ρ _z of the current path of the semiconductor element changes as follows by the piezoresistance effect.

ここで、式（２）の左辺は、半導体素子の電流経路の電気抵抗率ρ_zの変化率である。また、Π_Vは、半導体基板５４において発生した応力の方向と垂直な方向に対するピエゾ抵抗係数である。また、応力の大きさσ_x，σ_yは、圧縮応力の場合を負とし、引張応力の場合を正とする。

Here, the left side of Equation (2) is the rate of change of the electrical resistivity ρ _z of the current path of the semiconductor element. Also, [pi _V is a piezoresistive coefficient for the direction perpendicular to the direction of stress generated in the semiconductor substrate 54. The magnitudes of stress σ _x and σ _y are negative in the case of compressive stress and positive in the case of tensile stress.

In the above example, σ _x and σ _y are each about −205 MPa, and the piezoresistance coefficient Π _v in silicon is 53.4 × 10 ⁻¹¹ Pa ⁻¹ , so Δρ _z / ρ _z is about -22%. That is, when the temperature change ΔT of the semiconductor device 50 is 125 ° C., the electrical resistivity of the current path of the vertical semiconductor element formed on the semiconductor substrate 54 is reduced by about 22%.

  As described above, according to the configuration of the present invention, when the temperature of the semiconductor device 50 rises, a compressive stress is generated in the semiconductor substrate 54 by the presser 58, and the electrical characteristics are lowered due to the change in carrier mobility. Is suppressed.

  When the temperature of the semiconductor device 50 is lower than room temperature, the carrier mobility increases and the electrical resistance decreases in the vertical semiconductor element formed on the semiconductor substrate 54. At this time, the semiconductor substrate 54 and the presser 58 are each thermally contracted due to a decrease in temperature. Therefore, a gap between the side surface of the semiconductor substrate 54 and the pressing tool 58 is widened. As a result, the electrical resistance of the current path of the vertical semiconductor element formed on the semiconductor substrate 54 is not affected by the presser 58. Further, the occurrence of a gap between the semiconductor substrate 54 and the pressing member 58 at a low temperature is advantageous in terms of ensuring module reliability.

(Second embodiment)
FIG. 6 is a top view of the semiconductor device 70 according to the present invention. Since the cross-sectional structure between B1 and B2 in FIG. 6 is the same as that in FIG. 3 shown in the first embodiment, the illustration is omitted here. Further, the same components as those of the semiconductor device 50 are denoted by the same reference numerals as those of the semiconductor device 50, and detailed description thereof is omitted.

  In the present embodiment, the semiconductor element formed on the semiconductor substrate 54 is a lateral semiconductor element having a current path in the y-axis direction of FIG.

  There are two flat pressing members 58 mounted on the surface of the mounting substrate 52, and one of the side surfaces of the semiconductor substrate 54 and the other side surface of the semiconductor substrate 54 on the side opposite to the side surfaces. One end face of each presser 58 is arranged so as to face each other.

When the temperature of the semiconductor device 70 is a reference temperature within the range of room temperature, the presser 58 and the semiconductor substrate 54 are in contact with each other. However, the pressure is not applied to the semiconductor substrate 54 by the presser 58, so that the pressure is not applied to the semiconductor substrate 54. A case where the tool 58 is mounted on the mounting substrate 52 will be described. When the temperature of the semiconductor device 70 further increases by ΔT from the reference temperature, pressure is applied to each of the two side surfaces of the semiconductor substrate 54 by the presser 58 thermally expanded in the x-axis direction. As a result, a compressive stress in the x-axis direction is generated in the semiconductor substrate 54. The magnitude σ _x of this compressive stress is the same as that in Equation (1).

For example, the material of the semiconductor substrate 54 is silicon (α ₁ = 3 × 10 ⁻⁶ K ⁻¹ , E ₁ = 170 × 10 ⁹ Pa), and the material of the presser 58 is copper (α ₂ = 17 × 10 ^−6). K ⁻¹ , E ₂ = 120 × 10 ⁹ Pa), when the length l ₁ of the semiconductor substrate 54 is 10 mm and the length l ₂ of the presser 58 is 10 mm, when ΔT = 125 ° C., about A compressive stress of 205 MPa in the x-axis direction is generated in the semiconductor substrate 54.

  In the semiconductor device 70, the current path of the lateral semiconductor element formed on the semiconductor substrate 54 is in the y-axis direction shown in FIG. 6, and therefore the change in the electrical resistivity ρ of this current path is expressed by the following equation due to the piezoresistance effect. It becomes like this.

ここで、式（３）の左辺は、半導体素子の電流経路の電気抵抗率ρの変化率である。また、Π_Vは、半導体基板５４において発生した応力の方向と垂直な方向に対するピエゾ抵抗係数である。また、応力の大きさσ_xは、圧縮応力の場合を負とし、引張応力の場合を正とする。

Here, the left side of Equation (3) is the rate of change of the electrical resistivity ρ of the current path of the semiconductor element. Also, [pi _V is a piezoresistive coefficient for the direction perpendicular to the direction of stress generated in the semiconductor substrate 54. The stress magnitude σ _x is negative in the case of compressive stress and positive in the case of tensile stress.

In the above example, σ _x is about −205 MPa, and the piezoresistance coefficient Π _v in silicon is 53.4 × 10 ⁻¹¹ Pa ⁻¹ , so Δρ / ρ is about −22%. That is, when the temperature change ΔT of the semiconductor device 70 is 125 ° C., the electrical resistivity of the current path in the y-axis direction of the lateral semiconductor element formed on the semiconductor substrate 54 is reduced by about 22%.

  As described above, when the temperature of the semiconductor device 70 rises, a compressive stress in the uniaxial direction is generated in the semiconductor substrate 54 by the presser 58, and the carrier moves in a direction orthogonal to the direction of the compressive stress. The deterioration of the electrical characteristics accompanying the change in the degree is suppressed.

In the semiconductor device 70, even if the semiconductor element formed on the semiconductor substrate 54 is a vertical semiconductor element having a current path in the z-axis direction, the direction of the compressive stress generated in the semiconductor substrate 54 and the current The path is orthogonal. Furthermore, in silicon, when stress in the x-axis direction is generated in the semiconductor substrate 54, the piezoresistance coefficient that affects the electrical resistivity of the current path in the z-axis direction is the electric current in the current path in the y-axis direction. It is the same as the piezoresistance coefficient Π _v that affects the resistivity. Therefore, in the semiconductor device 70, even when the semiconductor element formed on the semiconductor substrate 54 is a vertical semiconductor element, the change in the electrical resistivity of the current path is expressed by Expression (3). As a result, when the temperature of the semiconductor device 70 rises, a reduction in electrical characteristics of the vertical semiconductor element is suppressed by the compressive stress generated in the semiconductor substrate 54 by the presser 58.

  Further, when the temperature of the semiconductor device 70 is lower than room temperature, in the horizontal semiconductor element or the vertical semiconductor element formed on the semiconductor substrate 54, the carrier mobility with respect to the direction of the current path increases, and the electric resistance is small. Become. At this time, the semiconductor substrate 54 and the presser 58 are thermally contracted due to a decrease in temperature, so that a gap between the side surface of the semiconductor substrate 54 and the presser 58 is widened. As a result, the electrical resistance of the current path of the horizontal semiconductor element or the vertical semiconductor element formed on the semiconductor substrate 54 is not affected by the presser 58. Further, the occurrence of a gap between the semiconductor substrate 54 and the pressing member 58 at a low temperature is advantageous in terms of ensuring module reliability.

It is a figure which shows the structure of the semiconductor device 10 in a prior art. 1 is a top view of a semiconductor device 50 according to a first embodiment of the present invention. 1 is a side sectional view of a semiconductor device 50 according to a first embodiment of the present invention. 1 is a side sectional view of a semiconductor device 50 according to a first embodiment of the present invention. 1 is a side sectional view of a semiconductor device 50 according to a first embodiment of the present invention. It is a top view of the semiconductor device 70 which concerns on 2nd embodiment of this invention.

Explanation of symbols

  10, 50, 70 Semiconductor device, 14 Base plate, 16a, 16b, 56 Adhesive layer, 18 Ceramic substrate, 20, 54 Semiconductor substrate, 52 Mounting substrate, 58 Presser, 58a, 62 Sliding part, 60 Fixing tool.

Claims (11)

In a semiconductor device having a mounting substrate and a semiconductor substrate mounted on the surface of the mounting substrate via an adhesive layer,
A pressing tool for pressing the semiconductor substrate, which is disposed adjacent to the side surface of the semiconductor substrate and is slidable with respect to the mounting substrate;
A fixture that is mounted on the surface of the mounting substrate and fixes and supports a part of the presser;
A semiconductor device comprising: The semiconductor device according to claim 1,
The semiconductor device according to claim 1, wherein the pressing member is disposed adjacent to four side surfaces of the semiconductor substrate. The semiconductor device according to claim 1,
The semiconductor device according to claim 1, wherein the pressing member is arranged adjacent to each of one side surface of the semiconductor substrate and a side surface opposite to one of the side surfaces of the semiconductor substrate. The semiconductor device according to any one of claims 1 to 3,
The said pressing tool contains the material whose product of a linear expansion coefficient and a Young's modulus is 2 Mpa / K or more, The semiconductor device characterized by the above-mentioned. The semiconductor device according to claim 4,
The material of the pressing tool is any one of copper, iron, nickel, alumina, sapphire, or titania. The semiconductor device according to any one of claims 1 to 5,
The surface of the said pressing tool is coat | covered with an insulating material, The semiconductor device characterized by the above-mentioned. The semiconductor device according to any one of claims 1 to 6,
The semiconductor device according to claim 1, wherein the pressing member provided to be slidable with respect to the mounting substrate has a sliding portion protruding toward the surface of the mounting substrate. The semiconductor device according to claim 7,
A shape of the sliding portion is a sharp shape or a shape having a curved surface, and a part of the shape of the sliding portion having a sharp shape or a curved surface is in contact with the surface of the mounting substrate. apparatus. The semiconductor device according to claim 7 or 8,
The semiconductor device according to claim 1, wherein the sliding portion is coated with fluororesin or fluororesin.   10. The semiconductor device according to claim 1, wherein the material of the adhesive layer is solder. 11. The semiconductor device according to any one of claims 1 to 10,
The mounting substrate is a ceramic substrate, and the material of the fixture is a steel material.

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