JP2010272685A - Semiconductor device and method of manufacturing semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device which can efficiently dissipate heat to the outside and is reduced in manufacturing cost, and to provide a method of manufacturing the semiconductor device. <P>SOLUTION: Disclosed is the semiconductor device which includes a semiconductor layer and a heat sink installed on the semiconductor layer. The heat sink includes: a layered structure having a high-thermal-conductivity layer, a low-thermal-conductivity layer and a high-thermal-conductivity layer laminated in this order; or a layered structure having a low-thermal-conductivity layer, a high-thermal-conductivity layer and a low-thermal-conductivity layer laminated in this order, wherein the upper part of the layered structure above its thickness-directional center part and the lower part of the layered structure below its thickness-directional center part is symmetrical with respect to the thickness-directional center part of the layered structure. The method of manufacturing the same is also disclosed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a semiconductor device and a method for manufacturing a semiconductor device.

  In recent years, for example, liquid crystal displays for displaying images are widely used in liquid crystal televisions, personal computer displays, mobile phones, car navigation systems, PDAs (Personal Digital Assistants), and the like.

  This liquid crystal display employs a backlight for irradiating light from the back side of the liquid crystal display panel to increase the brightness of the display screen.

  Conventionally, backlights using fluorescent tubes such as cold cathode fluorescent lamps (CCFLs) have been used as backlights for liquid crystal displays. Currently, however, LED (Light Emitting Diode) is used as an alternative. ) Backlights using elements are attracting attention.

  In the backlight using a fluorescent tube such as CCFL, a high voltage is required when the backlight is turned on, and the life of the fluorescent tube is shortened when the fluorescent tube is frequently turned on and off. there were.

  On the other hand, backlights using LED elements can be driven at a lower voltage compared to backlights using fluorescent tubes such as CCFLs, and have superior characteristics such as low power consumption and long life. I can expect.

  In particular, in backlights using LED elements of the three primary colors of light (red, green and blue), in order to obtain white light from wavelengths close to the three primary colors of light, compared to backlights using fluorescent tubes such as CCFLs. It is said that the characteristic that the degree of freedom of color increases can be obtained.

  Since the LED element generates heat when it emits light, a heat sink (heat radiating substrate) for dissipating the heat to the outside is separately prepared, and the heat sink is bonded to the LED element with eutectic solder. (For example, refer nonpatent literature 1).

Kanto Kanto, “Technology for improving efficiency and performance of our company's LED”, Monthly Display, February 2005, p. 51-p. 57

  However, in the method described in Non-Patent Document 1, the LED element and the heat sink are bonded together with eutectic solder, but the thickness of the eutectic solder generally requires a thickness of about several hundred μm. Therefore, the eutectic solder itself becomes a thermal resistance, and there is a problem that the heat generated in the LED element is not efficiently released to the outside through the heat sink.

  In addition, in the method described in Non-Patent Document 1, since the wettability of eutectic solder is ensured, the surface of the LED element and the surface of the heat sink are required to be plated, which increases the manufacturing cost. There was also a problem.

  Further, the above problem is not limited to the LED element, but is a problem of the entire semiconductor device including the LED element.

  In view of the above circumstances, an object of the present invention is to provide a semiconductor device and a method for manufacturing a semiconductor device that can efficiently release heat to the outside and can reduce manufacturing costs.

  The present invention includes a semiconductor layer and a heat sink disposed on the semiconductor layer, and the heat sink is a laminated structure in which a high thermal conductivity layer, a low thermal expansion layer, and a high thermal conductivity layer are laminated in this order, or It includes a laminated structure in which a low thermal expansion layer, a high thermal conductivity layer, and a low thermal expansion layer are laminated in this order, and the upper part from the central part in the thickness direction of the laminated structure and the central part in the thickness direction of the laminated structure The semiconductor device is symmetrical with respect to the central portion in the thickness direction of the laminated structure.

  Here, in the semiconductor device of the present invention, a conductive layer is preferably provided between the semiconductor layer and the heat sink.

  In the semiconductor device of the present invention, it is preferable that the thermal conductivity of the high thermal conductivity layer is 200 W / (m · K) or more.

In the semiconductor device of the present invention, it is preferable that the coefficient of linear expansion of the low thermal expansion layer is 8 × 10 ⁻⁶ (1 / K) or less.

  In addition, the present invention is a method for manufacturing the semiconductor device according to any one of the above, wherein a step of forming a high thermal conductivity layer on the semiconductor layer and a low thermal expansion layer on the high thermal conductivity layer are formed. It is a manufacturing method of a semiconductor device including a process and a process of forming a high thermal conductivity layer on a low thermal expansion coefficient layer.

  In addition, the present invention is a method for manufacturing the semiconductor device according to any one of the above, wherein the step of forming a low thermal expansion coefficient layer on the semiconductor layer and the formation of a high thermal conductivity layer on the low thermal expansion coefficient layer are provided. It is a manufacturing method of a semiconductor device including a process and a process of forming a low thermal expansion coefficient layer on a high thermal conductivity layer.

  In the method for producing a semiconductor device of the present invention, it is preferable to form at least one of a high thermal conductivity layer and a low thermal expansion layer by electrolysis of a molten salt bath.

  ADVANTAGE OF THE INVENTION According to this invention, while being able to discharge | release heat efficiently outside, the manufacturing method of the semiconductor device which can suppress manufacturing cost, and a semiconductor device can be provided.

It is typical sectional drawing of an example of the LED element which is an example of the semiconductor device of this invention. It is typical sectional drawing illustrating a part of manufacturing process of an example of the manufacturing method of the LED element of the structure shown in FIG. It is typical sectional drawing illustrating a part of manufacturing process of an example of the manufacturing method of the LED element of the structure shown in FIG. It is typical sectional drawing illustrating a part of manufacturing process of an example of the manufacturing method of the LED element of the structure shown in FIG. It is typical sectional drawing illustrating a part of manufacturing process of an example of the manufacturing method of the LED element of the structure shown in FIG. It is typical sectional drawing illustrating a part of manufacturing process of an example of the manufacturing method of the LED element of the structure shown in FIG. It is a typical block diagram which illustrates a part of manufacturing process of an example of the manufacturing method of the LED element of the structure shown in FIG. It is a typical block diagram which illustrates a part of manufacturing process of an example of the manufacturing method of the LED element of the structure shown in FIG. It is a typical block diagram which illustrates a part of manufacturing process of an example of the manufacturing method of the LED element of the structure shown in FIG.

  Embodiments of the present invention will be described below. In the drawings of the present invention, the same reference numerals represent the same or corresponding parts.

<Configuration of semiconductor device>
FIG. 1 shows a schematic cross-sectional view of an example of an LED element which is an example of a semiconductor device of the present invention. Here, the LED element shown in FIG. 1 includes a heat sink 1 and an LED structure 10 installed on the heat sink 1, and the heat sink 1 and the LED structure 10 are joined by a conductive layer 21. Have.

  Here, the heat sink 1 is composed of a laminated structure in which a high thermal conductivity layer 2, a low thermal expansion layer 3, and a high thermal conductivity layer 2 are laminated in this order.

  The LED structure 10 is also disposed on the semiconductor substrate 14, the n-type semiconductor layer 13 disposed on the semiconductor substrate 14, the active layer 12 disposed on the n-type semiconductor layer 13, and the active layer 12. P-type semiconductor layer 11, translucent electrode 17 disposed on p-type semiconductor layer 11, p-electrode 15 disposed on translucent electrode 17, and n-electrode disposed on n-type semiconductor layer 13 16.

  As the high thermal conductivity layer 2 constituting the heat sink 1, it is preferable to use a layer having a thermal conductivity of 200 W / (m · K) or more at 25 ° C. When a layer having a thermal conductivity of 200 W / (m · K) or higher at 25 ° C. is used as the high thermal conductivity layer 2, the heat generated in the LED structure 10 is efficiently released to the outside through the heat sink 1. This is because the tendency to be able to do so increases.

  Among these, from the viewpoint of increasing the heat dissipation of the heat sink 1, it is preferable to use a layer containing at least one selected from the group consisting of copper, aluminum, silver, gold and diamond as the high thermal conductivity layer 2. Of these, it is more preferable to use a single layer of either copper or aluminum.

Moreover, as the low thermal expansion coefficient layer 3 constituting the heat sink 1, it is preferable to use a layer having a linear expansion coefficient of 8 × 10 ⁻⁶ (1 / K) or less. When a layer having a linear expansion coefficient of 8 × 10 ⁻⁶ (1 / K) or less is used as the low thermal expansion coefficient layer 3, deformation of the heat sink 1 due to heat generated in the LED structure 10 can be suppressed. The trend becomes larger.

  In particular, from the viewpoint of suppressing deformation due to heat of the heat sink 1, it is preferable to use a layer containing at least one selected from the group consisting of molybdenum, tungsten, nickel and iron as the low thermal expansion layer 3. It is more preferable to use a single layer of either molybdenum or tungsten, or a nickel-tungsten alloy or nickel-iron alloy.

Further, in order to suppress the warpage of the heat sink 1, the upper portion from the central portion in the thickness direction of the laminated structure constituting the heat sink 1 (in this example, a portion that is ½ of the thickness h ₂ of the low thermal expansion coefficient layer 3). The portion and the portion below the central portion in the thickness direction of the laminated structure are symmetrical with respect to the central portion in the thickness direction of the laminated structure. Note that “symmetry” means that the thickness and thickness of the layered structure constituting the heatsink is determined by the material and thickness of the layer that appears when proceeding upward in the vertical direction from the center in the thickness direction of the layered structure constituting the heatsink to the upper end surface. It means that it is about the same as the case of proceeding downward in the vertical direction from the center of the direction to the lower end surface (the absolute value of the corresponding layer thickness difference is 5 μm or less).

In addition, the thickness h ₂ of the low thermal expansion layer 3 is preferably larger than the thickness h ₁ of the high thermal conductivity layer 2. By making the thickness h ₂ of the low thermal expansion layer 3 thicker than the thickness h ₁ of the high thermal conductivity layer 2, it has both high heat dissipation characteristics and characteristics that can suppress deformation due to heat at a high level. The tendency to obtain the heat sink 1 is increased.

Further, the total thickness of the heat sink 1 (in this example, the sum of the thickness h ₁ of thickness h ₂ and the high thermal conductivity layer 2 having a thickness of h ₁ and the low thermal expansion coefficient layer 3 high thermal conductivity layer 2) Is preferably 0.2 mm or less, and more preferably 0.1 mm or less. When the total thickness of the heat sink 1 is 0.2 mm or less, particularly when it is 0.1 mm or less, the material cost can be reduced, and the workability such as cutting of the heat sink 1 is also reduced due to its thinness. In order to improve, the tendency to obtain a very useful effect becomes large.

Further, the thickness h ₁ of the high thermal conductivity layer 2 and the thickness h ₂ of the low thermal expansion layer 3 preferably satisfies the following equation (1).

5 ≦ 100 × (h ₁ ) / (h ₁ + h ₂ ) ≦ 70 (1)
When the thickness h ₁ of the high thermal conductivity layer 2 and the thickness h ₂ of the low thermal expansion layer 3 satisfies the above relational expression (1) can suppress deformation due to the characteristics and thermal excellent in heat dissipation of heat There is a greater tendency to obtain a heat sink 1 that has both characteristics at a high level.

  Further, as the conductive layer 21, a layer made of a conductive material having a higher thermal conductivity than eutectic solder can be used. For example, a metal having a low electrical resistance, a high thermal conductivity, and hardly oxidized is used. In particular, it is preferable to use a layer containing at least one selected from the group consisting of gold, silver, copper and nickel.

Here, the thickness h ₃ of the conductive layer 21 is preferably 0.1 mm or more and 0.5 mm or less. When the thickness h ₃ of the conductive layer 21 is not less than 0.1 mm and not more than 0.5 mm, the processing cost when cutting the product in the subsequent process can be suppressed.

<Semiconductor device manufacturing method>
Hereinafter, an example of a method for manufacturing the LED element having the configuration shown in FIG. 1 will be described with reference to FIGS.

  First, as shown in the schematic cross-sectional view of FIG. 2, the conductive layer 21 is formed on the surface of the semiconductor substrate 14. Here, the conductive layer 21 can be formed by, for example, sputtering, electroless plating, vapor deposition, or application of a conductive substance.

  Next, as shown in the schematic cross-sectional view of FIG. 3, the high thermal conductivity layer 2 is formed on the surface of the conductive layer 21. Here, the high thermal conductivity layer 2 can be formed as follows, for example.

  First, as shown in the schematic configuration diagram of FIG. 7, the semiconductor substrate 14 and the counter electrode 6 after the formation of the conductive layer 21 are immersed in the electroplating solution 9 accommodated in the container 7. Here, the counter electrode 6 can be used without particular limitation as long as it is a conductive electrode. For example, a metal electrode or the like can be used.

  The electroplating solution 9 is electrolyzed by applying a voltage between the electroconductive layer 21 and the counter electrode 6 with the conductive layer 21 as a cathode and the counter electrode 6 as an anode. A metal constituting the high thermal conductivity layer 2 is deposited on the surface of the conductive layer 21. Thereby, the high thermal conductivity layer 2 can be formed on the surface of the conductive layer 21.

  Here, the electroplating solution 9 contains metal atoms that constitute the high thermal conductivity layer 2, and the metal that constitutes the high thermal conductivity layer 2 can be deposited by electrolysis of the electroplating solution 9. For example, when the high thermal conductivity layer 2 is made of copper, for example, a commercially available copper sulfate plating solution can be used as the electroplating solution 9.

  In addition, the semiconductor substrate 14 after the formation of the high thermal conductivity layer 2 is taken out from the electroplating solution 9, and the electroplating solution 9 adhering to the high thermal conductivity layer 2 is washed and removed by, for example, ion exchange water. Thereafter, the oxide film formed on the surface of the high thermal conductivity layer 2 can be removed by washing with a predetermined acid, for example.

  Next, as shown in the schematic cross-sectional view of FIG. 4, the low thermal expansion layer 3 is formed on the surface of the high thermal conductivity layer 2. Here, the low coefficient of thermal expansion layer 3 can be formed as follows, for example.

  First, as shown in the schematic configuration diagram of FIG. 8, a molten salt bath 8 containing metal atoms constituting the low thermal expansion coefficient layer 3 is accommodated in a container 7.

  The molten salt bath 8 includes metal atoms constituting the low thermal expansion coefficient layer 3 and can deposit the metal constituting the low thermal expansion coefficient layer 3 by electrolysis of the molten salt bath 8. Although not particularly limited, a preferable configuration of the molten salt bath 8 when the low thermal expansion coefficient layer 3 is made of, for example, tungsten will be described later.

  Next, the semiconductor substrate 14 and the counter electrode 6 after the formation of the high thermal conductivity layer 2 are immersed in the molten salt bath 8 accommodated in the container 7.

  Next, using the conductive layer 21 as a cathode and the counter electrode 6 as an anode, a voltage is applied between the conductive layer 21 and the counter electrode 6 to electrolyze the molten salt bath 8. The metal constituting the low thermal expansion layer 3 is deposited on the surface of the high thermal conductivity layer 2 to form the low thermal expansion layer 3.

  Then, the semiconductor substrate 14 after the formation of the low thermal expansion coefficient layer 3 is taken out from the molten salt bath 8, and the molten salt bath 8 attached to the low thermal expansion coefficient layer 3 is washed and removed, for example, with ion exchange water. At the same time, the oxide film formed on the surface of the low thermal expansion coefficient layer 3 is removed by washing with a predetermined acid, for example.

  Next, as shown in the schematic sectional view of FIG. 5, the high thermal conductivity layer 2 is formed on the surface of the low thermal expansion coefficient layer 3. Here, the high thermal conductivity layer 2 can be formed as follows, for example.

  First, as shown in the schematic configuration diagram of FIG. 9, the semiconductor substrate 14 and the counter electrode 6 after the formation of the low thermal expansion layer 3 are immersed in the electroplating solution 9 accommodated in the container 7.

  Next, the electroplating solution 9 is electrolyzed by applying a voltage between the electroconductive layer 21 and the counter electrode 6 while using the electroconductive layer 21 as a cathode and the counter electrode 6 as an anode. The metal constituting the high thermal conductivity layer 2 is deposited on the surface of the low thermal expansion layer 3. As described above, the high thermal conductivity layer 2 can be formed on the surface of the low thermal expansion coefficient layer 3.

  Then, the semiconductor substrate 14 after the formation of the high thermal conductivity layer 2 is taken out from the electroplating solution 9, and the electroplating solution 9 adhering to the high thermal conductivity layer 2 is washed and removed by ion exchange water or the like, for example. Thereafter, the oxide film formed on the surface of the high thermal conductivity layer 2 can be removed by washing with a predetermined acid, for example.

  Next, after setting the semiconductor substrate 14 on which the heat sink 1 has been formed as described above, for example, in a MOCVD (Metal Organic Chemical Vapor Deposition) apparatus, as shown in the schematic cross-sectional view of FIG. An n-type semiconductor layer 13, an active layer 12, and a p-type semiconductor layer 11 are epitaxially grown in this order by, for example, the MOCVD method or the like on the surface of the semiconductor substrate 14 on the side opposite to the formation side.

  Thereafter, a part of the n-type semiconductor layer 13, the active layer 12, and the p-type semiconductor layer 11 is removed by, for example, photoetching, and then the semi-transparent electrode 17 is formed on the p-type semiconductor layer 11 by using, for example, a lift-off method. In addition, the p-electrode 15 and the n-electrode 16 are formed on the n-type semiconductor layer 13.

  Then, the semiconductor substrate 14 after the formation of the p-electrode 15 and the n-electrode 16 is cut by, for example, a circular rotary blade, thereby being divided into individual LED elements having a schematic cross section shown in FIG. As described above, the LED element having the configuration shown in FIG. 1 can be obtained.

<Action>
As described above, in the present invention, it is not necessary to join the heat sink 1 and the LED structure 10 using eutectic solder having a thickness of about several hundreds μm as in the prior art. It is not necessary to perform a treatment such as plating on the surface of the heat sink, the manufacturing cost can be reduced, and heat can be efficiently released to the outside because there is no thermal resistance due to the eutectic solder.

  In the present invention, the upper part from the central part in the thickness direction of the laminated structure constituting the heat sink 1 and the lower part from the central part in the thickness direction of the laminated structure are the central part in the thickness direction of the laminated structure. Therefore, it is possible to prevent the heat sink 1 from warping. Thereby, the occurrence of problems such as peeling of the heat sink 1 from the semiconductor substrate 14 due to warpage of the heat sink 1 can be avoided, the manufacturing yield can be improved, and the manufacturing cost of the semiconductor device can be reduced. it can.

  Further, in the present invention, since the heat sink having a thickness significantly reduced as compared with the prior art can be formed, the material cost of the heat sink 1 can be reduced, and the heat sink 1 can be easily cut when divided into LED elements. Therefore, workability is improved. Furthermore, the thickness of the LED element can be reduced by forming the heat sink 1 very thin.

<Other forms>
Needless to say, the heat sink 1 is not limited to the above configuration, and includes a laminated structure in which the high thermal conductivity layer 2, the low thermal expansion layer 3, and the high thermal conductivity layer 2 are laminated in this order, or There is no particular limitation as long as it includes a laminated structure in which the low thermal expansion layer 3, the high thermal conductivity layer 2, and the low thermal expansion layer 3 are laminated in this order.

  The heat sink 1 is not limited to the above three-layer structure, and may have a structure other than three layers such as five layers.

  As a preferable configuration of the heat sink 1, for example, as shown in FIG. 1, a three-layer structure in which a high thermal conductivity layer 2, a low thermal expansion layer 3, and a high thermal conductivity layer 2 are laminated in this order. In addition, there is a configuration in which the high thermal conductivity layer 2 is a layer made of copper and the low thermal expansion layer 3 is a layer made of tungsten. By adopting such a configuration, there is a greater tendency to obtain a heat sink 1 having a high level of both the characteristics of excellent heat dissipation and the characteristics of suppressing deformation due to heat.

  In the above description, the LED structure 10 includes the p-type semiconductor layer 11, the n-type semiconductor layer 13, and the active layer 12, and the active layer 12 is disposed between the p-type semiconductor layer 11 and the n-type semiconductor layer 13. In addition, any structure that emits light from the active layer 12 by current injection can be used without particular limitation. For example, a conventionally known LED structure can be used.

  For example, the n-electrode 16 of the LED element having the configuration shown in FIG. 1 is used as a cathode, the p-electrode 15 is used as an anode, a voltage is applied between the p-electrode 15 and the n-electrode 16, and p inside the LED structure 10. A current is passed from the electrode 15 toward the n-electrode 16. Then, light is emitted from the active layer 12 between the p-type semiconductor layer 11 and the n-type semiconductor layer 13 of the LED structure 10.

  The p-type semiconductor layer 11 is a semiconductor layer having a p-type conductivity type doped with a p-type impurity, and the n-type semiconductor layer 13 is an n-type conductivity type doped with an n-type impurity. Needless to say, this is a semiconductor layer. The active layer 12 may have either a p-type or n-type conductivity type, and is an undoped semiconductor layer in which neither p-type impurity nor n-type impurity is doped. Also good.

  In particular, as the LED structure 10, the p-type semiconductor layer 11, the active layer 12, and the n-type semiconductor layer 13 each include a group III element (at least one selected from the group consisting of Al, In, and Ga) and a group V. It is preferable to use a group III-V nitride semiconductor which is a compound with an element (nitrogen). In this case, blue light can be emitted from the active layer 12.

  As an example of the configuration of the LED structure 10 capable of emitting blue light from the active layer 12, for example, a GaN substrate or a sapphire substrate is used as the semiconductor substrate 14 shown in FIG. A configuration in which an n-type GaN layer is used, an undoped InGaN layer is used as the active layer 12, and an n-type GaN layer is used as the n-type semiconductor layer 13 can be exemplified.

  The semiconductor device of the present invention is not limited to an LED element, and can be applied to a semiconductor device other than an LED element such as a semiconductor laser element or a field effect transistor. Here, as the semiconductor substrate 14 used for the semiconductor device other than the LED structure 10 capable of emitting blue light from the active layer 12, for example, a silicon substrate, a silicon carbide substrate, a gallium arsenide substrate, or the like is used. Can do.

  In the above, the heat sink 1 is formed by forming the high thermal conductivity layer 2 using the electroplating solution 9 and forming the low thermal expansion layer 3 using the molten salt bath 8. Needless to say, the method of forming the layer 2 and the low thermal expansion layer 3 is not limited to these. For example, the heat sink 1 can also be formed by forming the high thermal conductivity layer 2 and the low thermal expansion layer 3 by a conventionally known vapor phase method such as sputtering. Moreover, the high thermal conductivity layer 2 may be formed by combining, for example, the formation of the electroplating solution by electrolysis and the formation of a vapor phase method such as a sputtering method. Alternatively, the formation of the molten salt bath by electrolysis and the formation by a vapor phase method such as a sputtering method may be combined.

  For example, when the high thermal conductivity layer 2 and / or the low thermal expansion layer 3 is made of a nonmetal, it can be formed by a vapor phase method such as a sputtering method.

  In the above, the conductive layer 21, the high thermal conductivity layer 2, the low thermal expansion layer 3 and the high thermal conductivity layer 2 are formed in this order, but the high thermal conductivity layer 2 and the low thermal expansion coefficient are in the opposite direction. The layer 3, the high thermal conductivity layer 2, and the conductive layer 21 may be formed in this order.

<Preferred configuration of molten salt bath>
An example of a preferable configuration of the molten salt bath 8 used in the present invention will be described below, but the molten salt bath 8 used in the present invention is not limited to the following configuration.

  For example, in the case where the low thermal expansion layer 3 made of tungsten is formed using the molten salt bath 8, a molten material containing lithium atoms, sodium atoms, potassium atoms, tungsten atoms, oxygen atoms, and chlorine atoms. A salt bath 8 is preferably used.

  Here, sodium atoms are contained in the molten salt bath 8 at a ratio of 25 to 400 atoms with respect to 100 atoms of lithium atoms. Further, potassium atoms are contained in the molten salt bath 8 at a ratio of 25 atoms or more and 185 atoms or less with respect to 100 atoms of lithium atoms. Further, tungsten atoms are contained in the molten salt bath 8 at a ratio of 10 to 40 atoms with respect to 100 total atoms of lithium atoms, sodium atoms and potassium atoms. Further, oxygen atoms are contained in the molten salt bath 8 at a ratio of 40 atoms or more and 160 atoms or less with respect to a total of 100 atoms of lithium atoms, sodium atoms, and potassium atoms. Furthermore, chlorine atoms are contained in the molten salt bath 8 at a ratio of 20 atoms or more and 80 atoms or less with respect to a total of 100 atoms of lithium atoms, sodium atoms, and potassium atoms.

  The molten salt bath 8 does not contain sodium atoms in a proportion of 25 to 400 atoms with respect to 100 atoms of lithium atoms, and 25 to 185 atoms of potassium atoms with respect to 100 atoms of lithium atoms. If it is not contained in a proportion of atoms or less, the melting point of the molten salt bath 8 rises, and the adverse effect of heat on the base material on which tungsten is deposited (for example, the high thermal conductivity layer 2) increases. It tends to be unsuitable for a molten salt bath for precipitation.

  In the molten salt bath 8, when the content of tungsten atoms exceeds 40 atoms with respect to 100 atoms in total of lithium atoms, sodium atoms, and potassium atoms, the melting point of the molten salt bath 8 Rises and the viscosity of the molten salt bath 8 increases, so that the supply of tungsten ions to a substrate on which tungsten is deposited (for example, the high thermal conductivity layer 2 and the like) is suppressed, and a tungsten precipitate having a smooth surface is formed. It tends not to be obtained. Further, in this case, undissolved salt floats in the molten salt bath 8 and becomes a cause of defects such as being taken into the tungsten precipitate, so that it tends to be unsuitable for a molten salt bath for tungsten precipitation.

  Further, in the molten salt bath 8 described above, when the content of tungsten atoms is less than 10 atoms with respect to the total number of atoms of lithium atoms, sodium atoms and potassium atoms of 100 atoms, Since the tungsten concentration in the substrate is low, tungsten ions are not sufficiently supplied to the base material on which tungsten is deposited (for example, the high thermal conductivity layer 2), and the tungsten precipitate tends to be dendritic. It tends to be unsuitable for a molten salt bath.

  Further, in the molten salt bath 8 described above, when the oxygen atom content exceeds 160 atoms with respect to the total number of atoms of lithium atoms, sodium atoms and potassium atoms being 100 atoms, the viscosity of the molten salt bath 8 is Since it becomes too high, the supply of tungsten ions to the surface of the substrate (for example, the high thermal conductivity layer 2 or the like) is delayed. This makes it easy to obtain dendritic tungsten precipitates, oxygen atoms are easily taken into the tungsten precipitates, and the content of oxygen in the tungsten precipitates increases, resulting in an increase in impurities. Tend not to be suitable for molten salt baths.

  Further, in the molten salt bath 8 described above, when the content of oxygen atoms is less than 40 atoms with respect to 100 atoms in total of lithium atoms, sodium atoms, and potassium atoms, the coordination state of tungsten is Instead, the smoothness of the surface of the low thermal expansion coefficient layer 3 made of tungsten precipitates is deteriorated, so that it tends to be unsuitable for a molten salt bath for tungsten precipitation.

  In the molten salt bath 8, when the content of chlorine atoms exceeds 80 atoms with respect to the total number of atoms of lithium atoms, sodium atoms, and potassium atoms, the coordination state of tungsten changes. Since the smoothness of the surface of the low thermal expansion layer 3 made of tungsten precipitates deteriorates, it tends to be unsuitable for a molten salt bath for tungsten precipitation.

  In the molten salt bath 8, when the chlorine atom content is less than 20 atoms with respect to 100 atoms in total of lithium atoms, sodium atoms, and potassium atoms, the viscosity of the molten salt bath 8 is Increases, the supply of tungsten ions to the base material (for example, the high thermal conductivity layer 2) is suppressed, and the low thermal expansion layer 3 made of tungsten precipitates with a smooth surface cannot be obtained. It tends to be unsuitable for a molten salt bath.

  In the molten salt bath 8, sodium atoms are preferably contained in a proportion of 70 to 85 atoms with respect to 100 atoms of lithium atoms. When the content of sodium atoms in the molten salt bath 8 is in the range of 70 atoms or more and 85 atoms or less with respect to 100 atoms of lithium atoms, a low thermal expansion coefficient layer comprising a tungsten precipitate having high surface smoothness 3 tends to be obtained.

  Moreover, in said molten salt bath 8, it is preferable that a potassium atom is contained in the ratio of 40 to 50 atoms with respect to 100 atoms of lithium atoms. When the content of potassium atoms in the molten salt bath 8 is in the range of 40 to 50 atoms with respect to 100 atoms of lithium atoms, an increase in the melting point of the molten salt bath 8 can be suppressed, There is a tendency to obtain a low coefficient of thermal expansion layer 3 made of a tungsten precipitate having a high surface smoothness.

  In the molten salt bath 8 described above, tungsten atoms are preferably contained in a proportion of 20 to 30 atoms with respect to 100 total atoms of lithium atoms, sodium atoms, and potassium atoms. When the content of tungsten atoms in the molten salt bath 8 is 20 atoms or more and 30 atoms or less with respect to a total of 100 atoms of lithium atoms, sodium atoms, and potassium atoms, electrolysis is performed at a relatively low temperature range. Tend to be able to. Even when the temperature during electrolysis is the same, since the viscosity of the molten salt bath 8 is lower than that of other molten salt baths, tungsten ions can be supplied to the base material (for example, the high thermal conductivity layer 2). It becomes faster and the range of current density for depositing tungsten tends to widen.

  In the molten salt bath 8, oxygen atoms are preferably contained in a proportion of 80 atoms or more and 120 atoms or less with respect to 100 atoms in total of lithium atoms, sodium atoms, and potassium atoms. When the content of oxygen atoms in the molten salt bath 8 is in the range of 80 atoms or more and 120 atoms or less with respect to 100 atoms in total of lithium atoms, sodium atoms and potassium atoms, the molten salt bath 8 The viscosity of is low, the coordination state of tungsten is suitable for electrolysis, and the range of current density for depositing tungsten tends to widen.

  In the molten salt bath 8 described above, the chlorine atoms are preferably contained in a proportion of 40 to 60 atoms with respect to a total of 100 atoms of lithium atoms, sodium atoms, and potassium atoms. When the content of chlorine atoms in the molten salt bath 8 is in the range of 40 to 60 atoms with respect to 100 atoms of lithium atoms, the viscosity of the molten salt bath 8 is low and the coordination state of tungsten is low. It is suitable for electrolysis and tends to widen the range of current density for depositing tungsten.

  The molten salt bath 8 preferably further contains fluorine atoms in addition to the above atoms. Here, in the molten salt bath 8, fluorine atoms are more preferably contained in a proportion of 5 to 165 atoms with respect to 100 atoms of tungsten atoms, and 10 atoms with respect to 100 atoms of tungsten atoms. More preferably, it is contained in a proportion of 20 atoms or less.

  When the molten salt bath 8 contains fluorine atoms, the smoothness of the surface of the low coefficient of thermal expansion layer 3 made of tungsten precipitates deposited by electrolyzing the molten salt bath 8 tends to be improved. In particular, when the fluorine atom content in the molten salt bath 8 is 5 atoms or more and 165 atoms or less with respect to 100 atoms of lithium atoms, it is particularly 10 atoms or more and 20 atoms or less with respect to 100 atoms of tungsten atoms. In this case, the smoothness of the surface of the low coefficient of thermal expansion layer 3 made of the tungsten precipitate deposited by electrolyzing the molten salt bath 8 tends to be further improved.

  The form of the lithium atom, sodium atom, potassium atom, tungsten atom, oxygen atom, chlorine atom and fluorine atom in the molten salt bath 8 is not particularly limited. For example, it exists as an ion or forms a complex May exist. Further, atoms other than oxygen atoms constituting the molten salt bath 8 can be detected by performing ICP spectroscopic analysis (inductively coupled plasma spectrometry) on a sample obtained by dissolving the molten salt bath of the present invention in water. .

  The oxygen atoms in the molten salt bath 8 can be confirmed by using an inert gas melting infrared absorption method for the molten salt bath 8. Here, the inert gas melting infrared absorption method can be performed, for example, as follows.

  First, after the molten salt bath 8 is accommodated in a carbon crucible in a helium gas atmosphere, oxygen is generated from the molten salt bath 8 by heating the carbon crucible. Then, this oxygen reacts with the carbon in the carbon crucible to produce carbon monoxide and carbon dioxide. Next, infrared rays are irradiated in the atmosphere containing the generated carbon monoxide and carbon dioxide. Finally, the presence and content of oxygen in the molten salt bath 8 can be confirmed by investigating the attenuation amount of infrared rays generated by the absorption of carbon monoxide and carbon dioxide in the atmosphere.

  The molten salt bath 8 can be produced, for example, by mixing at least lithium tungstate, sodium tungstate, potassium tungstate, and alkali metal chloride.

  Here, the alkali metal chloride is preferably at least one selected from the group consisting of lithium chloride, sodium chloride and potassium chloride.

  Then, lithium tungstate, sodium tungstate, potassium tungstate, and alkali metal chloride are mixed to prepare a mixture, and the mixture is heated and melted, whereby the above molten salt bath 8 is prepared. Can be manufactured.

  When lithium tungstate, sodium tungstate, potassium tungstate, and alkali metal chloride are not in solid form but in a molten state, lithium tungstate, sodium tungstate, tungstic acid The molten salt bath 8 can be produced simply by mixing the potassium melt and the alkali metal chloride melt.

  In the molten salt bath 8, for example, sodium tungstate is mixed in an amount of 24 to 400 substances with respect to 100 substances of lithium tungstate, and potassium tungstate is mixed in an amount of 5 to 184 substances. Can be produced. In addition, the alkali metal chloride can be mixed, for example, at a ratio of 115 to 1770 substances with respect to 100 substances of lithium tungstate.

  In addition, when the molten salt bath 8 contains a fluorine atom, the above-described component includes, for example, at least one alkali metal selected from the group consisting of lithium fluoride, sodium fluoride, and potassium fluoride. It can produce by mixing the fluoride of.

  The low thermal expansion coefficient layer 3 made of tungsten precipitates deposited by electrolyzing the molten salt bath 8 is characterized by improved surface smoothness.

In the present invention, as the molten salt bath 8, in addition to the above, for example, potassium fluoride (KF), boron oxide (B ₂ O ₃ ), and tungsten oxide (WO ₃ ), for example, 67: 26: 7 It is also possible to use a molten salt bath or the like prepared by melting a mixture mixed at a molar ratio of

<Preparation of Heat Sink of Example 1>
First, one sapphire substrate having a circular surface with a diameter of 100 mm and a thickness of 500 μm was prepared.

  Next, a nickel layer having a thickness of about 50 nm was formed on one surface of the sapphire substrate by sputtering to form a conductive layer.

  Next, outside the glove box, the sapphire substrate after the formation of the conductive layer is placed in a copper sulfate plating solution (Rebco EX manufactured by Uemura Kogyo Co., Ltd.) contained in a Pyrex (registered trademark) beaker. One sapphire substrate and the counter electrode were immersed together with the counter electrode made of phosphorous copper one by one.

Then, with the temperature of the copper sulfate plating solution maintained at 30 ° C., a current of 20 mA (milliampere) per 1 cm ² of the surface of the conductive layer on the counter electrode as the anode and the sapphire substrate as the cathode (current density 20 mA / cm ^2). ) Was allowed to flow for 45 minutes between the anode and cathode.

  By conducting electrolysis of the copper sulfate plating solution under such conditions, copper is deposited on the surface of the conductive layer on the sapphire substrate, which is the cathode, to form a high thermal conductivity layer (first layer) made of copper precipitates. It was formed to a thickness of 20 μm.

  Next, outside the above glove box, the sapphire substrate after the formation of the high thermal conductivity layer is taken out from the copper sulfate plating solution, and the copper sulfate plating solution adhering to the high thermal conductivity layer is washed and removed with ion exchange water. At the same time, the oxide film formed on the surface of the high thermal conductivity layer was removed by washing with an acid.

Next, a mixture is prepared by mixing potassium fluoride (KF) powder, boron oxide (B ₂ O ₃ ) powder and tungsten oxide (WO ₃ ) powder in a molar ratio of 67: 26: 7, and the mixture is made of SiC. The crucible made by Aswan Co., Ltd. was used.

Here, potassium fluoride (KF) powder, boron oxide (B ₂ O ₃ ) powder, and tungsten oxide (WO ₃ ) powder are each weighed in a glove box in an Ar (argon) atmosphere, and alumina in the same glove box. It was put into a made crucible.

  Next, the alumina crucible charged with the above mixture was heated to 850 ° C. using a mantle heater to melt the above mixture, and the molten salt bath of Example 1 was produced.

  Next, in the above-mentioned glove box, the conductive layer (cathode) on the sapphire substrate after the formation of the high thermal conductivity layer is opposed to the molten salt bath of Example 1 together with the counter electrode (anode) made of a tungsten plate. It was immersed so as to face the electrode.

  Here, a nickel wire is welded to each of the anode and the cathode, and a current can be supplied from the nickel wire between the anode and the cathode.

In the state where the temperature of the molten salt bath of Example 1 is maintained at 850 ° C., a current (current density of 30 mA / cm ² ) of 30 mA (milliampere) flows per 1 cm ^{2 of the} anode surface while the anode and the cathode are swung. As described above, a current was passed between the anode and the cathode for 204 minutes.

  By conducting the electrolysis of the molten salt bath of Example 1 under such conditions, tungsten is deposited on the surface of the high thermal conductivity layer on the conductive layer which is the cathode, and the low thermal expansion coefficient layer (2 Layer) was formed to a thickness of 60 μm.

  Next, outside the glove box, the sapphire substrate after the formation of the low thermal expansion layer is taken out from the molten salt bath of Example 1, and the molten salt bath is attached to the low thermal expansion layer by ion exchange water. After washing and removing, the oxide film formed on the surface of the low thermal expansion layer was removed by washing with acid.

  Next, outside of the glove box, the sapphire substrate after the formation of the low thermal expansion layer is a copper sulfate plating solution contained in a Pyrex (registered trademark) beaker (Rebco EX manufactured by Uemura Kogyo Co., Ltd.). The sapphire substrate and the counter electrode were immersed together with the counter electrode made of one sheet of phosphorous copper.

Then, with the temperature of the copper sulfate plating solution maintained at 30 ° C., a current of 20 mA (milliampere) per 1 cm ² of the surface of the conductive layer on the counter electrode as the anode and the sapphire substrate as the cathode (current density 20 mA / cm ^2). ) Was allowed to flow for 45 minutes between the anode and cathode.

  By electrolyzing the copper sulfate plating solution under such conditions, copper is deposited on the surface of the low thermal expansion layer formed on the sapphire substrate, which is the cathode, and a high thermal conductivity layer (three layers) made of a copper precipitate is formed. Eyes) was formed to a thickness of 20 μm.

  Next, outside the above glove box, the sapphire substrate after the formation of the high thermal conductivity layer is taken out from the copper sulfate plating solution, and the copper sulfate plating solution adhering to the high thermal conductivity layer is washed and removed with ion exchange water. At the same time, the oxide film formed on the surface of the high thermal conductivity layer was removed by washing with an acid.

  As described above, a high thermal conductivity layer (first layer) made of copper having a thickness of 20 μm, a low thermal expansion layer (second layer) made of tungsten having a thickness of 60 μm, and a low thermal expansion layer (3) made of copper having a thickness of 20 μm. The heat sink (total thickness: 100 μm) of Example 1 consisting of a laminated structure in which the layers) were laminated in this order was obtained.

<Preparation of Heat Sink of Example 2>
A heat sink of Example 2 was produced in the same manner as Example 1 except for the following (1) to (3).

(1) Sapphire, which is a cathode, by electrolyzing a copper sulfate plating solution by flowing a current density of 20 mA / cm ² for 23 minutes between a counter electrode as an anode and a conductive layer on a sapphire substrate as a cathode. A high thermal conductivity layer (first layer) made of a copper precipitate was formed to a thickness of 10 μm on the surface of the conductive layer on the substrate.

(2) Electrolysis of the molten salt bath of Example 1 is performed by flowing a current of 30 mA / cm ² for 102 minutes between the counter electrode as the anode and the conductive layer on the sapphire substrate as the cathode. The low thermal expansion coefficient layer (second layer) made of tungsten precipitates was formed to a thickness of 30 μm on the surface of the high thermal conductivity layer on the conductive layer.

(3) Sapphire, which is a cathode, by electrolyzing a copper sulfate plating solution by flowing a current of 20 mA / cm ² for 23 minutes between a counter electrode as an anode and a conductive layer on a sapphire substrate as a cathode. A high thermal conductivity layer (third layer) made of copper precipitates was formed to a thickness of 10 μm on the surface of the low thermal expansion coefficient layer formed on the substrate.

<Preparation of Heat Sink of Example 3>
A heat sink of Example 3 was produced in the same manner as Example 1 except for the following (4) to (6).

(4) Electrolysis of a copper sulfate plating solution is performed by flowing a current of 20 mA / cm ² for 27 minutes between a counter electrode as an anode and a conductive layer on a sapphire substrate as a cathode, whereby sapphire as a cathode A high thermal conductivity layer (first layer) made of copper precipitates was formed to a thickness of 12 μm on the surface of the conductive layer on the substrate.

(5) Electrolysis of the molten salt bath of Example 1 is conducted by flowing a current of 30 mA / cm ² for 102 minutes between the counter electrode as the anode and the conductive layer on the sapphire substrate as the cathode. The low thermal expansion coefficient layer (second layer) made of tungsten precipitates was formed to a thickness of 30 μm on the surface of the high thermal conductivity layer on the conductive layer.

(6) Sapphire, which is the cathode, by electrolyzing the copper sulfate plating solution by flowing a current density of 20 mA / cm ² for 23 minutes between the counter electrode as the anode and the conductive layer on the sapphire substrate as the cathode. A high thermal conductivity layer (third layer) made of copper precipitates was formed to a thickness of 10 μm on the surface of the low thermal expansion coefficient layer formed on the substrate.

<Production of LED elements of Examples 1 to 3>
An LED structure was formed on the surface of the sapphire substrate to which the heat sink of Examples 1 to 3 obtained as described above was bonded, on the opposite side of the heat sink.

  In the LED structure, an n-type GaN layer, an undoped InGaN layer, and a p-type GaN layer are epitaxially grown in this order on the surface of the sapphire substrate by MOCVD, and then the surface of the n-type GaN layer is subjected to photoetching. The n-type GaN layer, the undoped InGaN layer, and the p-type GaN layer are partially removed until a part of the n-type GaN layer is exposed, and an n-electrode on the n-type GaN layer, a translucent electrode on the p-type GaN layer, and A p-electrode on a translucent electrode was formed.

  Next, the heat sink and the LED structure of Examples 1 to 3 after the formation of the n electrode and the p electrode were divided into LED elements having a square surface of 10 mm × 10 mm with a circular rotary blade. The LED elements of Examples 1 to 3 were obtained.

<Evaluation of LED elements of Examples 1 to 3>
A copper plate and a tungsten plate are joined together by pressure welding, and a heat sink composed of a laminated structure of copper (20 μm) / tungsten (60 μm) / copper (20 μm) having a total thickness of 100 μm and an LED structure are several hundreds of μm thick. The LED element of the reference example was produced in the same manner as described above except that the LED element was formed by bonding with eutectic solder.

  And when the light emission characteristic of the LED element of Examples 1-3 produced above and the LED element of said reference example was compared, the light emission characteristic was equivalent.

  However, since the LED elements of Examples 1 to 3 are joined to the heat sink and the LED structure without using eutectic solder having a thickness of about several hundreds μm, the heat generated in the LED structure is absorbed by the heat sink. In addition, the manufacturing cost can be reduced because it is not necessary to perform a treatment such as plating on the surface of the LED element or the surface of the heat sink.

  Moreover, since the heat sink thicknesses of the LED elements of Examples 1 to 3 are 100 μm, 50 μm, and 52 μm, respectively, it is easy to cut the heat sink and the LED structure with a circular rotary blade, and the workability is improved. Was also confirmed.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  ADVANTAGE OF THE INVENTION According to this invention, while being able to discharge | release heat efficiently outside, the manufacturing method of the semiconductor device which can suppress manufacturing cost, and a semiconductor device can be provided.

  1 heat sink, 2 high thermal conductivity layer, 3 low thermal expansion layer, 6 counter electrode, 7 container, 8 molten salt bath, 9 electroplating solution, 10 LED structure, 11 p-type semiconductor layer, 12 active layer, 13 n-type Semiconductor layer, 14 semiconductor substrate, 15 p electrode, 16 n electrode, 17 translucent electrode.

Claims (7)

A semiconductor layer;
A heat sink installed on the semiconductor layer,
The heat sink is a laminated structure in which a high thermal conductivity layer, a low thermal expansion layer, and a high thermal conductivity layer are laminated in this order, or a low thermal expansion layer, a high thermal conductivity layer, and a low thermal expansion layer in this order. Including a laminated structure laminated,
A semiconductor device in which a portion above the central portion in the thickness direction of the multilayer structure and a portion below the central portion in the thickness direction of the multilayer structure are symmetrical with respect to the central portion in the thickness direction of the multilayer structure .   The semiconductor device according to claim 1, further comprising a conductive layer between the semiconductor layer and the heat sink.   The semiconductor device according to claim 1, wherein the high thermal conductivity layer has a thermal conductivity of 200 W / (m · K) or more. 4. The semiconductor device according to claim 1, wherein the low thermal expansion coefficient layer has a linear expansion coefficient of 8 × 10 ⁻⁶ (1 / K) or less. 5. A method of manufacturing a semiconductor device according to any one of claims 1 to 4,
Forming a high thermal conductivity layer on the semiconductor layer;
Forming a low thermal expansion coefficient layer on the high thermal conductivity layer;
Forming a high thermal conductivity layer on the low thermal expansion coefficient layer. A method of manufacturing a semiconductor device according to any one of claims 1 to 4,
Forming a low thermal expansion layer on the semiconductor layer;
Forming a high thermal conductivity layer on the low thermal expansion layer;
Forming a low thermal expansion coefficient layer on the high thermal conductivity layer.   7. The method of manufacturing a semiconductor device according to claim 5, wherein at least one of the high thermal conductivity layer and the low thermal expansion layer is formed by electrolysis of a molten salt bath.

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