JP2014154570A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device which can remove generated heat of a semiconductor chip and inhibit a heat stress generated in the semiconductor chip.SOLUTION: A semiconductor device comprises a semiconductor chip 10 having a rectangular planar shape and a sub-mount 20 on which the semiconductor chip 10 is mounted. The sub-mount 20 includes a plurality of sheet-like graphites 21 which are laminated along a direction substantially orthogonal to a thickness direction of the semiconductor chip 10, in which a linear thermal expansion coefficient α1 of a lamination plane of the sheet-like graphites 21 in a surface direction and a linear thermal expansion coefficient α2 of the lamination plane of the sheet-like graphites 21 in a normal direction have values different from each other, and an angle θ between a long side direction of a plane of the semiconductor chip 10 and a normal direction of the lamination plane of the sheet-like graphites 21 is 35-65°.

Description

  The present invention relates to a semiconductor device in which a semiconductor chip is mounted on a submount.

  In a semiconductor device, heat is generated in the semiconductor chip during use, and the characteristics of the semiconductor chip change due to temperature changes caused by the heat generation. For example, in a semiconductor laser device, the oscillation wavelength changes or the emission intensity changes due to temperature changes. In the semiconductor laser device, in order to dissipate the heat generated in the laser chip at the time of use with high efficiency, there is a technology that uses a material having high thermal conductivity as a material constituting the submount on which the laser chip is mounted. Are known. For example, Patent Document 1 discloses a semiconductor laser device having a submount made of diamond. Patent Document 2 discloses a semiconductor laser device having a submount in which a plurality of sheet-like graphites are stacked along a plane intersecting a contact surface with a laser chip.

JP 2001-127375 A JP 2011-23670 A

However, when diamond is used as the material constituting the submount, the diamond has a linear thermal expansion coefficient that is equal to that of the material constituting the laser chip, such as a gallium arsenide compound or a gallium nitride compound. On the other hand, the difference is large. Therefore, in the manufacturing process of the semiconductor laser device, for example, a large thermal stress is generated in the laser chip by heating when the laser chip is bonded to the submount by AuSn solder.
Further, even when a laminate of sheet-like graphite is used as the material constituting the submount, the sheet-like graphite and the linear thermal expansion coefficient in the plane direction and the linear thermal expansion coefficient in the thickness direction are greatly different. Therefore, a large thermal stress is generated in the laser chip.
And when a thermal stress arises in a laser chip, there exists a problem that a crack will arise in a laser chip or a laser characteristic will be impaired.

  The present invention has been made based on the above circumstances, and an object thereof is a semiconductor capable of removing heat generated by a semiconductor chip and suppressing thermal stress generated in the semiconductor chip. To provide an apparatus.

The semiconductor device of the present invention is a semiconductor device comprising a semiconductor chip having a rectangular planar shape and a submount on which the semiconductor chip is mounted,
The submount is formed by laminating a plurality of sheet-like graphites along a direction substantially orthogonal to the thickness direction of the semiconductor chip, and a linear thermal expansion coefficient α1 in the surface direction of the lamination surface of the sheet-like graphite and the lamination surface. And the linear thermal expansion coefficient α2 in the normal direction are different from each other,
An angle θ between a long side direction in the plane of the semiconductor chip and a normal direction of the laminated surface of the sheet-like graphite is 35 to 65 °.

In the semiconductor device of the present invention, when the main material of the semiconductor chip is gallium arsenide (GaAs) or gallium nitride (GaN), the long side direction in the plane of the semiconductor chip and the laminated surface of the sheet-like graphite The angle θ formed with the normal direction is preferably 40 to 55 °.
The main material of the semiconductor chip may be silicon (Si).

According to the semiconductor device of the present invention, the submount is formed by laminating sheet-like graphite having a high thermal conductivity in the plane direction along a direction substantially orthogonal to the thickness direction of the semiconductor chip. The exotherm can be removed.
The submount has a linear thermal expansion coefficient α1 in the plane direction of the laminated surface of the sheet-like graphite and a linear thermal expansion coefficient α2 in the normal direction of the laminated surface, and the plane of the semiconductor chip. Since the angle θ formed by the long side direction and the normal direction of the laminated surface of the sheet-like graphite is in a specific range, the thermal stress generated in the semiconductor chip can be suppressed. Therefore, it is possible to prevent the semiconductor chip from being cracked or from damaging the characteristics of the semiconductor chip.

It is a perspective view which shows the structure in an example of the semiconductor laser apparatus concerning this invention. FIG. 2 is a plan view of the semiconductor laser device shown in FIG. 1. It is AA sectional drawing of the semiconductor laser apparatus shown in FIG. It is a graph which shows the relationship between the perpendicular stress which arises in the laser chip calculated | required in Experimental example 1, and the angle which the long side direction of a laser chip and the lamination direction of a sheet-like graphite make. It is a graph which shows the relationship between the perpendicular stress which arises in the laser chip calculated | required in Experimental example 2, and the angle which the long side direction of a laser chip and the lamination direction of a sheet-like graphite make. It is a graph which shows the relationship between the perpendicular stress which arises in the laser chip calculated | required in Experimental example 3, and the angle which the long side direction of a laser chip and the lamination direction of a sheet-like graphite make. It is a graph which shows the relationship between the perpendicular stress which arises in the laser chip calculated | required in Experimental example 4, and the angle which the long side direction of a laser chip and the lamination direction of a sheet-like graphite make.

Hereinafter, embodiments of a semiconductor device according to the present invention will be described by taking as an example a case where the semiconductor device is implemented as a semiconductor laser device.
1 is a perspective view showing a configuration of an example of a semiconductor laser device according to the present invention, FIG. 2 is a plan view of the semiconductor laser device shown in FIG. 1, and FIG. 3 is an AA view of the semiconductor laser device shown in FIG. It is sectional drawing.
This semiconductor laser device has a plate-like laser chip 10 having a rectangular planar shape. The laser chip 10 is mounted on the surface of a rectangular plate-shaped submount 20 by being bonded via a first bonding layer 25 made of, for example, AuSn eutectic solder. On the back surface of the submount 20, a heat sink 30 made of, for example, copper is bonded via a second bonding layer 26 made of, for example, SnAgCu eutectic solder.

In the laser chip 10, a plurality of planar circular light emitters 15 each emitting light are linearly arranged in a line along the longitudinal direction of the laser chip 10 inside a plate-like substrate 11 having a rectangular planar shape. They are arranged side by side. A plurality of light extraction portions 12 for extracting light emitted from the light emitter 15 to the outside are formed on the surface of the base 11 in the laser chip 10. These light extraction portions 12 are arranged so as to be aligned in a straight line along the longitudinal direction of the base 11 corresponding to each of the light emitters 15.
As a material constituting the base 11, a semiconductor material such as gallium arsenide (GaAs), gallium nitride (GaN), or silicon (Si) can be used.

The submount 20 is configured by laminating a plurality of sheet-like graphites 21 along a direction substantially orthogonal to the thickness direction of the semiconductor chip.
The thickness of the submount 20 is preferably 0.5 to 1.2 mm.
The thermal conductivity in the surface direction of the sheet-like graphite 21 in the submount 20 is preferably 1500 W / m ° C. or higher. If this thermal conductivity is too low, it may be difficult to remove the heat generated by the laser chip 10 with high efficiency.
The thermal conductivity in the thickness direction of the sheet-like graphite 21 in the submount 20 is, for example, 5 to 9 W / m ° C.

In the submount 20, the linear thermal expansion coefficient α1 in the surface direction of the laminated surface of the sheet-like graphite 21 and the linear thermal expansion coefficient α2 in the normal direction of the laminated surface are different from each other.
The linear thermal expansion coefficient α1 in the surface direction of the laminated surface of the sheet-like graphite 21 in the submount 20 is, for example, −1 × 10 ⁻⁶ to 1 × 10 ⁻⁶ K ⁻¹ .
The linear thermal expansion coefficient α2 in the normal direction of the laminated surface of the sheet-like graphite 21 in the submount 20 is, for example, 20 × 10 ^{−6 to} 35 × 10 ⁻⁶ K ⁻¹ .
The linear thermal expansion coefficient of the material constituting the substrate 11 of the laser chip 10, for example, gallium arsenide (GaAs), gallium nitride (GaN), silicon (Si), etc. is larger than the linear thermal expansion coefficient α1, and the line It is smaller than the thermal expansion coefficient α2.

  In the semiconductor laser device of the present invention, the angle θ formed by the long side direction X in the plane of the laser chip 10 and the normal direction (hereinafter also referred to as “lamination direction”) S of the laminated surface of the sheet-like graphite. 35 to 65 °. In particular, when the main material of the laser chip 10, specifically, the material constituting the substrate 11 is gallium arsenide (GaAs) or gallium nitride (GaN), the long-side direction X in the plane of the laser chip 10 and The angle θ formed with the stacking direction S of the sheet-like graphite 21 is preferably 40 to 55 °. When the angle θ formed is too small or too large, it is difficult to suppress the thermal stress generated in the laser chip 10. As a result, the thermal stress generated in the laser chip 10 causes cracks in the laser chip 10 or damages the laser characteristics.

Such a semiconductor laser device can be manufactured, for example, as follows.
A rectangular parallelepiped laminate material in which a large number of sheet-like graphites are laminated is produced. Next, when the laser chip 10 is mounted on the submount 20 at a required angle between the stacking direction S and the longitudinal direction of the submount 20 to be formed with one side surface perpendicular to the stacking surface of the stack material as the surface. Then, the laminate material is cut into a rectangular plate shape so that the angle θ between the lamination direction S and the long side direction X of the laser chip 10 is obtained. Then, the target submount 20 is obtained by polishing the cut laminate material.

  Next, the laser chip 10 is disposed on the surface of the submount 20 via, for example, an AuSn eutectic solder material. Then, after the AuSn eutectic solder material is melted by heating to a temperature equal to or higher than its melting point, for example, 320 ° C., the AuSn eutectic solder material is cooled and solidified to form a first joint on the surface of the submount 20. The laser chip 10 is bonded via the layer 25. Thereafter, the heat sink 30 is disposed on the back surface of the submount 20 via a SnAgCu eutectic solder material. Then, after the SnAgCu eutectic solder material is heated to a temperature equal to or higher than its melting point, the SnAgCu eutectic solder material is cooled and solidified, whereby the second bonding layer 26 is formed on the back surface of the submount 20. The semiconductor laser device shown in FIG. 1 is manufactured.

In the above, the laser chip 10 can be bonded to the submount 20 by a known method such as reflow or die bonding.
In joining the laser chip 10, the laser chip 10 and the submount 20 are heated and cooled together with the AuSn eutectic solder material. At this time, the laser chip 10 and the submount 20 are deformed (expanded and contracted) in accordance with their respective thermal expansion coefficients. Therefore, thermal stress is generated in the cooled laser chip 10 due to a difference in thermal expansion coefficient from the submount 20. However, according to the semiconductor laser device of the present invention, since the angle θ between the long side direction X of the laser chip 10 and the stacking direction S of the sheet-like graphite 21 is in a specific range, the thermal stress generated in the laser chip 10. Is suppressed.

  In the semiconductor laser device according to the present invention, when electric energy is supplied to the laser chip 10, part of the electric energy is converted into light energy, and light is emitted from each light emitter 15. Further, a part of the electric energy supplied to the laser chip 10 is converted into heat energy, thereby generating heat in the laser chip 10. Thus, the sheet-like graphite 21 has a high thermal conductivity in the surface direction, and the submount 20 is formed by laminating the sheet-like graphite 21 along a direction substantially perpendicular to the thickness direction of the semiconductor chip. Therefore, heat generated in the laser chip 10 is conducted in the thickness direction of the submount 20, is transmitted to the heat sink 30 through the second bonding layer 26, and is removed from the bottom of the heat sink 30 to the outside.

As described above, according to the semiconductor laser device according to the present invention, the submount 20 has the sheet-like graphite 21 having a high thermal conductivity in the plane direction stacked along the direction substantially orthogonal to the thickness direction of the laser chip 10. Therefore, the heat generated in the laser chip 10 can be removed.
Further, in the sheet-like graphite 21, the linear thermal expansion coefficient α1 in the plane direction of the laminated surface and the linear thermal expansion coefficient α2 in the normal direction of the laminated surface are different from each other, and the long side in the plane of the laser chip 10 Since the angle θ between the direction and the normal direction of the laminated surface of the sheet-like graphite 21 is in a specific range, the thermal stress generated in the laser chip 10 can be suppressed. Therefore, it is possible to prevent the laser chip 10 from being cracked or the characteristics of the laser chip 10 from being impaired.

  As described above, the embodiments of the semiconductor device according to the present invention have been described by taking the case where the semiconductor device is implemented as a semiconductor laser device. However, the present invention is not limited to the semiconductor laser device, for example, a semiconductor device including an LED chip, The present invention can be applied to a semiconductor device including a power semiconductor chip such as a power MOSFET or IGBT.

<Experimental example 1>
On a submount in which a plurality of sheet-like graphites are laminated along a direction substantially perpendicular to the thickness direction, a thickness of 5 μm made of AuSn eutectic solder having a mass ratio of gold to tin of 80:20 is interposed. Then, a laser chip having a size of 8 mm × 1 mm × 0.07 mm, a size of 12 mm × 3.5 mm × 0.8 mm, and a base material of gallium arsenide (GaAs) was disposed.
Next, the AuSn eutectic solder was heated to 280 ° C. (eutectic point of the AuSn eutectic solder) and then cooled to −40 ° C., whereby the laser chip was bonded onto the submount.
In the above, as the submount, the angle θ between the long side direction of the laser chip and the lamination direction of the sheet-like graphite is 0 °, 10 °, 20 °, 30 °, 40 °, 45 °, 50 °, 60 Those having angles of 70, 80, and 90 degrees were used.
The physical properties of gallium arsenide (GaAs), submount and AuSn eutectic solder constituting the base of the laser chip are shown in Table 1 below.
The vertical stress generated in each of the long side direction and the short side direction of the laser chip when cooled to −40 ° C. with the stress at 280 ° C. being 0 at the joint surface of the laser chip with the submount is defined as a finite element. It was obtained from the structural analysis by the method. FIG. 4 shows the relationship between the vertical stress generated in the laser chip and the angle θ between the long side direction of the laser chip and the stacking direction of the sheet-like graphite.

<Experimental example 2>
A laser chip was obtained in the same manner as in Experimental Example 1 except that a laser chip having a size of 12 mm × 3.5 mm × 0.8 mm and a base material of gallium nitride (gallium nitride (GaN)) was used. The vertical stress generated in each of the long side direction and the short side direction of the laser chip was obtained by bonding on the submount. FIG. 5 shows the relationship between the vertical stress generated in the laser chip and the angle θ between the long side direction of the laser chip and the stacking direction of the sheet-like graphite.
The physical properties of gallium nitride (GaN) constituting the base of the laser chip are shown in Table 1 below.

<Experimental example 3>
The laser chip was bonded onto the submount in the same manner as in Experimental Example 1 except that a laser chip having a size of 12 mm × 3.5 mm × 0.8 mm and a base material of silicon (Si) was used. The normal stress generated in each of the long side direction and the short side direction of the laser chip was obtained. FIG. 6 shows the relationship between the vertical stress generated in the laser chip and the angle θ between the long side direction of the laser chip and the stacking direction of the sheet-like graphite.
The physical properties of silicon (Si) constituting the base of the laser chip are shown in Table 1 below.

<Experimental example 4>
A laser chip was used in the same manner as in Experimental Example 1 except that a laser chip having a size of 6 mm × 3.5 mm × 0.8 mm and a base material of gallium arsenide (gallium arsenide (GaAs)) was used. The chip was bonded onto the submount, and the normal stress generated in each of the long side direction and the short side direction of the laser chip was determined. FIG. 7 shows the relationship between the vertical stress generated in the laser chip and the angle θ between the long side direction of the laser chip and the stacking direction of the sheet-like graphite.

In the graphs shown in FIGS. 4 to 7, the horizontal axis indicates the angle θ between the long side direction of the laser chip and the lamination direction of the sheet-like graphite, and the vertical axis indicates the value of the vertical stress.
As is apparent from the results shown in these drawings, in the long side direction of the bonding surface of the laser chip, when the value of θ is 0 °, negative vertical stress, that is, compressive stress is generated. This is because, when cooled from 280 ° C. to −40 ° C., the contraction rate in the long side direction of the base of the laser chip is smaller than the contraction rate in the long side direction (sheet-like graphite lamination direction) of the submount. . On the other hand, in the short side direction of the bonding surface of the laser chip, when the value of θ is 0 °, positive vertical stress, that is, tensile stress is generated. This is because, when cooled from 280 ° C. to −40 ° C., the shrinkage rate in the short side direction of the laser chip substrate is larger than the shrinkage rate in the short side direction (surface direction of the sheet-like graphite) in the submount. .

As the value of θ increases from 0 °, the compressive stress generated in the long side direction of the laser chip bonding surface decreases, and then a positive normal stress, that is, tensile stress occurs. And as the value of θ approaches 90 °, the tensile stress generated in the long side direction of the joining surface of the laser chip increases.
Further, as the value of θ increases from 0 °, the tensile stress generated in the short side direction of the bonding surface of the laser chip decreases, and thereafter negative vertical stress, that is, compressive stress occurs. As the value of θ approaches 90 °, the compressive stress generated in the short side direction of the bonding surface of the laser chip increases.

  From the results shown in FIG. 4, when the laser chip whose substrate is made of gallium arsenide (GaAs) is mounted on the submount, the length of the bonding surface of the laser chip when the value of θ is about 40 °. The normal stress generated in the side direction is zero. Further, when the value of θ is about 55 °, the vertical stress generated in the short side direction of the bonding surface of the laser chip is zero. Accordingly, if the value of θ is in the range of 35 to 65 °, particularly 40 to 55 °, the stress generated in the laser chip is suppressed, and the laser chip is cracked or the characteristics of the laser chip are impaired. It is understood that it can be prevented.

  Further, from the results shown in FIG. 5, when a laser chip whose base is made of gallium nitride (GaN) is mounted on the submount, it is the same as when a laser chip whose base is made of gallium arsenide (GaAs) is mounted. If the value of θ is in the range of 35 ° to 65 °, particularly 40 ° to 55 °, the stress generated in the laser chip is suppressed, and the laser chip is prevented from cracking or from damaging the characteristics of the laser chip. It is understood that you can.

  Further, from the results shown in FIG. 6, when a laser chip whose substrate is made of silicon (Si) is mounted on the submount, when the value of θ is about 35 °, the long side direction of the bonding surface of the laser chip The normal stress generated in is zero. Further, when the value of θ is about 65 °, the vertical stress generated in the short side direction of the bonding surface of the laser chip is zero. Accordingly, when the value of θ is in the range of 35 to 65 °, the stress generated in the laser chip is suppressed, and it is possible to prevent the laser chip from being cracked or from damaging the characteristics of the laser chip. Understood.

  4 and 7, even when the ratio of the long side dimension to the short side dimension in the laser chip is different, the value of θ is in the range of 35 to 65 °, particularly 40 to 55 °. It is understood that the stress generated in the laser chip can be suppressed, and it is possible to prevent the laser chip from being cracked or from damaging the characteristics of the laser chip.

DESCRIPTION OF SYMBOLS 10 Laser chip 11 Base | substrate 12 Light extraction part 15 Optical emitter 20 Submount 21 Sheet-like graphite 25 1st joining layer 26 2nd joining layer 30 Heat sink

Claims (3)

A semiconductor device comprising a semiconductor chip having a rectangular planar shape and a submount on which the semiconductor chip is mounted,
The submount is formed by laminating a plurality of sheet-like graphites along a direction substantially orthogonal to the thickness direction of the semiconductor chip, and a linear thermal expansion coefficient α1 in the surface direction of the lamination surface of the sheet-like graphite and the lamination surface. And the linear thermal expansion coefficient α2 in the normal direction are different from each other,
An angle θ formed by a long side direction in a plane of the semiconductor chip and a normal direction of a laminated surface of the sheet-like graphite is 35 to 65 °.   The main material of the semiconductor chip is gallium arsenide (GaAs) or gallium nitride (GaN), and the angle θ formed by the long side direction in the plane of the semiconductor chip and the normal direction of the laminated surface of the sheet-like graphite is The semiconductor device according to claim 1, wherein the angle is 40 to 55 °.   The semiconductor device according to claim 1, wherein a main material of the semiconductor chip is silicon (Si).

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