JPH02256262A - Heat sink for semiconductor devices - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a heat sink for a semiconductor device used for heat dissipation of a semiconductor laser, a light emitting diode, or the like.

(Prior Art) Semiconductor elements (hereinafter referred to as elements) such as semiconductor lasers (LDs) and light emitting diodes (LEDs) generate heat during use. Therefore, as shown in FIG. 1, a heat sink 1 is fused to the element 2 with solder 3 so that the generated heat is released through the heat sink 1.

Materials used for heat sinks include diamond, Cu, Si, Mo, Aj! , Au, BeO, etc., but they are required to have 1) a high thermal conductivity λ, 2) a thermal expansion coefficient α close to that of the element, and 2) a low price.

Diamond is very good in ■ but does not meet ■, and Cu is good in ■ and ■ but has a problem with ■. For example, the thermal expansion coefficient α of a GaAs element is 6.63 Xl0-
'deg-', whereas the CuO thermal expansion coefficient α is 1
It is large at 6.7X10-'deg-'. Si is ■ and Cu
■ and ■ are relatively good, although slightly inferior.

In the end, considering ■～■, Cu and St were used as heat sink materials.
is often used.

By the way, when welding a heat sink to an element, the temperature should be around the melting point of the solder (280°C for Au-3n solder).
℃). However, because the thermal expansion coefficient α of the element and the heat sink are different, a large stress is generated in the element when it returns to room temperature.

For example, when a GaAs LD element is fused to a Cu heat sink using Ac+-3n solder, a stress calculated by the following formula is generated.

(Thermal expansion coefficient of Cu - Thermal expansion coefficient of GaAs)
-3n melting point of solder - room temperature) X (Young's modulus of GaAs) = (16,7X10-'deg-' -6,6X
10-'deg-') X (280°C-20°C)
X8.55X10”dyn/cm”=2X10”
dyn/cm" When electricity is applied to an element under such stress, dislocations are introduced from the element crystal surface, shortening its lifetime. Therefore, when using a heat sink with a large coefficient of thermal expansion such as Cu, it is necessary to Welding is performed using In solder, which is soft at the melting point, and the stress generated is absorbed by plastic deformation of the In.

However, a problem has arisen in that In penetrates into the interior of the crystal and deteriorates its properties.

(Problems to be Solved by the Invention) An object of the present invention is to provide a heat sink that has good heat dissipation properties and can extend the life of the element by absorbing the stress generated when the element and the heat sink are fused together.

(Means for Solving the Problem) As a result of repeated studies on means for absorbing the stress generated inside the element when a heat sink is fused to a semiconductor element, the inventor of the present invention discovered that a semiconductor If a lattice layer or two or more types of metal thin film layers are formed, those layers will expand and contract with each other and absorb the stress generated during welding, and since these layers are very thin, they will not be able to dissipate heat. I learned that there was no damage to the product.

This invention was made based on the above knowledge, and its gist is ``A heat sink used for heat dissipation of a semiconductor element, which has a semiconductor superlattice layer or two or more types of metal thin film layers formed on the element fusion surface. "Heat sink for elements".

(Function) As described above, the heat sink of the present invention is characterized by having a semiconductor superlattice layer or two or more types of metal thin film layers on the element fusion surface.

First, a heat sink having a semiconductor superlattice layer will be explained.

The superlattices forming the semiconductor superlattice layer include the following.

GaAS* P l-w /GaAs, P+-yAL
Cat-++ P/A/! , Ga1-, PA4. Cat
-x As/Affi, Cat-y AsI nx C
at-* P/I ny Cat-y PThe range of X and y in the superlattice layer is 0≦x<1.0≦y
<1. Moreover, one set of the above-mentioned superlattice is counted as two layers.

These superlattice layers expand and contract with each other to absorb stress generated during fusion and prevent it from being applied to the element.

Incidentally, the total thickness of the superlattice layer is desirably in the range of 50 to 50 seconds. If the thickness is less than 50 people, stress cannot be completely absorbed, while if it exceeds 5,000 people, heat dissipation will be poor. The number of superlattice layers is preferably six or more, and if the number of zero layers is small, stress may not be absorbed completely.

The method for forming the semiconductor superlattice layer on the heat sink includes:
It can be formed relatively easily using a metal organic chemical vapor deposition method (MOCVD method) or a molecular beam epitaxial method (M'BE method).

Next, a heat sink having two or more types of metal thin film layers will be described.

Suitable metals for forming the thin film layer include MOLTa, W, Cr, and Pt, which have a coefficient of thermal expansion close to α of the element material, and Cu, Au, Ag, and A1, which have a high thermal conductivity λ. When two or more of these metals are layered alternately to form a thin film layer, they expand and contract with each other and absorb the stress that occurs when fusing the heat sink and the element, but a single layer does not have this effect. .

The total thickness of the metal thin film layer is preferably in the range of 500 to 10,000. If it is thinner than this, stress cannot be absorbed, and if it is thicker than this, resistance increases and heat dissipation becomes poor. The thickness of one layer is preferably 50 to 1,000 people. It is difficult to form a group with less than 50 people, 1.
If it is thicker than 0.001 mm, it will not be effective in absorbing stress. In order to completely absorb stress, it is preferable that the number of layers is 10 or more while satisfying the conditions of thickness of all layers and one layer.

Methods for forming a metal thin film on a heat sink include methods such as electron beam evaporation and sputtering, and either method can easily form a uniform metal thin film.

Now, with a heat sink that has a superlattice layer or metal thin film layer as described above, even if the temperature is raised to the melting point of the solder together with the element and fused, the stress generated at that time will be completely absorbed by the superlattice layer and metal thin film layer. It gets absorbed into. Therefore, even if current is applied to the semiconductor element connected to the heat sink, no dislocations are introduced into the element crystal, so its characteristics will not deteriorate or its life will end prematurely.

Hereinafter, the semiconductor superlattice layer and gold W of the present invention will be described in Examples.
, a heat sink having a TiJ film layer will be explained.

(Example 1) This example is a case of a heat sink in which a semiconductor superlattice layer is formed on the element fusion surface.

As shown in FIG. 2, the heat sink 11 having the semiconductor superlattice layer of the present invention has a length II, a width IIfi11, and a thickness of 3.
It consists of an n-type Si substrate 11a with a thickness of 00 μm and a semiconductor superlattice layer 11b with 101 layers formed thereon. The superlattice layer 11b has 10 layers of Ga 6.7 A j2o, 3 A S with a thickness of 50 nm and GaAs with a thickness of 50 nm alternately deposited by metal organic vapor phase epitaxy.
The layers (total thickness 500 people) are formed.

Thermal conductivity of the semiconductor superlattice layer (0.3 W/cm/de
g) is less than one-fourth of that of Si (1.45 W/cm/deg), but since the thickness is very thin at 500 mm, its influence can be ignored. Note that the semiconductor superlattice layer 11
On the element side of b, there is an Au-Ge-GaAs ohmic electrode with a thickness of 2,000 to facilitate the flow of current.
Ni is vapor-deposited, and Si is also deposited on the heat sink side for the same purpose.
2,000 thick Au-3b which is an ohmic electrode of
is deposited.

The heat sink 11 has a length of 300 μm and a width of 150 μm.
μl, 801m thick GaAj2As/GaAS system L
The D element 2 is fused with Au-5n solder 3 (thickness s, ooo thick).

Further, in this embodiment, only the thickness of the Si substrate 11a is 350 μm, which is different from the above heat sink (thickness 300 μm).
A heat sink made of μm and 400 μm steel was manufactured and fused to an LD element using Au Sn solder. Furthermore, in order to clarify the effect of the heat sink of the present invention, an LD element was fused with Au-3n solder to three types of conventional heat sinks (Si substrate with thicknesses of 300 μm, 350 μn+, and 400 μm) shown in FIG. I made something.

The following stresses are generated in the heat sink and the LD element, which are fused together using Au-3n solder.

(Thermal expansion coefficient of LD element - 3i substrate thermal expansion coefficient)
Melting point of AuSn solder - room temperature) x LDLD element rate =
(6,63Xl0-'deg-'-2,5X10-
'deg-') X (280°C-20°C) X 8
．． 55 XIO"dyn/co+" = 9.2xlO
” dyn/c+mz and the LD element with the above heat sink fused to it is biased as shown in Figure 2, and the temperature is 50°C.
Changes in operating current were examined while maintaining the output at 5 mW.

The results are shown in Figure 3. In Figure 3, lines a, b, and c are for the LD element to which the heat sink of the present invention is fused, and lines d,
Lines e and f are for an LD element using a conventional heat sink. As is clear from this figure, in the case of the LD element using the heat sink of the present invention in which the superlattice layer is fused, the operating current hardly changes even after a long period of time. In other words, no deterioration occurred in the LD element. This means that the stress generated during fusion is absorbed by the superlattice layer and does not reach the element. On the other hand, when using a conventional heat sink in which the superlattice layer is not fused, stress remains in the element and dislocations are introduced into the crystal, causing deterioration of the element and causing a sudden increase in operating current.

(Example 2) This example is a case of a heat sink in which a metal thin film layer is formed on the element fusion surface.

A heat sink 2 having a metal thin film layer as shown in FIG.
1 is a C with m 1 am, width 2aua, and thickness 1.5mm.
U substrate 21a and five metal thin film layers 2 formed thereon
1b. The metal thin film layer 21b is made up of 10 layers (100-thick Cu thin film and 100-thick Mo thin film alternately deposited by electron beam evaporation).
The total thickness is 1000 mm).

In this example, Cu and Mo were used for the metal thin film layer because the thermal conductivity λ of Cu is as large as 4.01 W/cm/deg, and the thermal expansion coefficient α(5, OXl0-'deg-
') is that of the element (GaAs) (6,6X10-'de
This is because it is close to g-').

Then, on the heat sink 21, a length of 300 μm and a width of 25
0ym, thickness 80urs, D element 2 (GaAs)
were fused using Au-3n solder 3 (thickness: 5000). Further, in order to understand the effect of the heat sink having a metal thin film layer according to the present invention, a conventional heat sink 1 shown in FIG.

The following stress is generated between the heat sink and the LD element due to the fusion using Au-5n solder.

(Thermal expansion coefficient of Cu substrate - Thermal expansion coefficient of LD element)
Au-3n solder melting point - room temperature) XLDLD element rate -
(16,7Xl0-'deg-' 6.6 Xl0-
'deg-') X (280'C20°C)
8.55 x 10th dyn/cm” = 2 XIO' d
yn/cm" In order to find out how much influence this stress has on the LD element, an element using the heat sink of the present invention and an element using a conventional heat sink were biased as shown in Fig. 4.
An energization test was conducted at a temperature of 50° C. and an output of 5 mW.

The results are shown in Figure 5. In Figure 5, the g-line shows the case of the element in which the heat sink having the metal thin film layer of the present invention is fused, and the h-line shows the case of using the conventional heat sink without the metal thin film layer. It shows. As is clear from this figure, the device using the heat sink of the present invention operates stably even after approximately 5,000 hours. On the other hand, elements using conventional heat sinks deteriorate after about 200 hours and the operating current starts to increase, and after 300 hours the deterioration becomes even more severe.
As it progressed, heat generation increased and operation stopped.

(Effect of the invention 5 As explained above, when a heat sink in which a semiconductor superlattice layer or a gold WA thin film layer is formed on the element fusion surface is used, it is possible to completely absorb the stress generated when the element and the heat sink are fused. Therefore, the introduction of dislocations during energization can be prevented and the device life can be significantly extended.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a state in which a conventional heat sink and an LD element are fused together, FIG. 2 is a diagram showing a state in which a heat sink having a semiconductor superlattice layer of the present invention and an LD element are fused together, and FIG. 4 is a diagram showing the change in operating current of an LD element using a heat sink having a semiconductor superlattice layer of the present invention and a conventional heat sink. FIG. FIG. 5 is a diagram showing changes in operating current of an LD element using a heat sink having a metal thin film layer of the present invention and a conventional heat sink. 1.11.21 is a heat sink, 2 elements, 3 is solder,
11a is a Si substrate, llb is a semiconductor superlattice layer, 21a is a Cu substrate, and 21b is a metal thin film layer. Ya / (2) Ya 2 Figure Threat 30 1jLt Ginro (A)

Claims (1)

[Claims] A heat sink used for heat dissipation of a semiconductor element, which has a semiconductor superlattice layer or two or more types of metal thin film layers formed on the element fusion surface.