JPH11204704A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device correcting distortion developed by the expansion/contraction of a chip along a main face when a temperature changes and distortion developed by the change of the degree of the curvature of the chip. SOLUTION: A first layer 1a and a second layer 1b, consisting of materials different in the coefficients of thermal expansion, are stacked to constitute a heat sink 1. The coefficients of the thermal expansion of the first layer 1a and the second layer 1b are set to be values approximated to the coefficient of the thermal expansion of the laser chip 2, and the coefficient of the thermal expansion of the first laver 1a is made to be larger than that of the second layer 1b. The laser chip 2 consisting of the substrate 2b and the laser chip 2 is mounted on the first layer 1a of the heat sink 1 by making a semiconductor layer 2b-side face downward.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly, to a semiconductor device having a chip mounted on a base.

[0002]

2. Description of the Related Art Generally, when a semiconductor device is operated,
A temperature change due to heat generation of the chip (including a bar-shaped one) is inevitable, and the chip expands and contracts due to the temperature change. For this reason, in a semiconductor device in which a chip is mounted on a base such as a heat sink or a package, if the degree of expansion and contraction of the two at the junction between the chip and the heat sink differs when the temperature changes, mechanical This can cause periodic stress. The adverse effect of the distortion due to the stress on the characteristics and reliability of the semiconductor device is more serious as the area of the chip is larger.

For example, in a semiconductor laser having a laser array structure, the total length of a laser chip (or laser bar) is about 10 mm, and the temperature of the laser chip increases by about 50 ° C. during operation. In such a semiconductor laser, when copper is used as the material of the heat sink, the thermal expansion coefficient of GaAs constituting the laser chip is 6.5 ×.
Copper has a coefficient of thermal expansion of 17 while being 10 ^-6 / ° C.
Since it is 0 × 10 ⁻⁶ / ° C., the difference between the expansion of the laser chip caused by thermal expansion and the expansion of the heat sink at the portion where the laser chip is die-bonded is about 6 °.
μm, which causes the occurrence of stress. Therefore, in such a semiconductor laser, for example, aluminum nitride (AlN), copper tungsten (Cu
By forming the heat sink from a material having a thermal expansion coefficient close to the thermal expansion coefficient of the laser chip, such as W) or silicon (Si), the distortion due to this stress is corrected.

[0004]

However, a laser chip in an actual semiconductor laser has a structure in which a semiconductor layer having a composition different from that of the substrate is laminated on a substrate in order to form a laser structure. However, there are the following problems.

That is, for example, as shown in FIG.
In an lGaAs semiconductor laser, a laser chip 1
Reference numeral 01 denotes a GaAs substrate 101a and the GaAs substrate 1
And a semiconductor layer 101b, such as a plurality of AlGaAs layers, constituting a laser structure, which is stacked on one main surface of the semiconductor laser 101a. Although illustration is omitted, in the laser chip 101, electrodes are provided on the back surface of the GaAs substrate 101a and the upper surface of the semiconductor layer 101b, respectively.

In manufacturing the laser chip 101, a semiconductor layer 101b is grown on a GaAs substrate 101a at a growth temperature higher than room temperature, for example, about 800 ° C. At the growth temperature, the GaAs substrate 101a is lattice-matched. However, the composition of the GaAs substrate 101a and the composition of the semiconductor layer 101b are different from each other.
Since the thermal expansion coefficient of 01a is larger than the thermal expansion coefficient of the semiconductor layer 101b, the laser chip 101 is curved with the semiconductor layer 101b side convex at normal temperature. The degree of curvature (radius of curvature) of the laser chip 101 is
It changes depending on the difference between the growth temperature when growing the semiconductor layer 101b on the GaAs substrate 101a and the temperature of the laser chip 101. Therefore, when the temperature changes, the laser chip 101 not only expands and contracts in the direction along the main surface thereof, but also changes the degree of curvature.

FIG. 3 shows a state in which the laser chip 101 is mounted on a heat sink. As shown in FIG. 3, the laser chip 101 is die-bonded on the heat sink 102 with the semiconductor layer 101b side down using solder (not shown).

However, in the prior art in which the coefficient of thermal expansion of the heat sink 102 is made to match the coefficient of thermal expansion of the laser chip 101, the distortion caused by the expansion and contraction of the laser chip 101 in the direction along its main surface is corrected. Is possible, but the distortion caused by the change in the degree of curvature of the laser chip 101 cannot be corrected yet. For this reason, in the conventional semiconductor laser, there is a problem that the distortion caused by the change in the degree of curvature of the laser chip 101 adversely affects the characteristics and reliability of the semiconductor laser.

The above is a problem in a semiconductor laser. A similar problem may occur in a semiconductor device in which a chip whose degree of curvature changes with temperature is mounted on a heat sink or a package. It is.

Therefore, an object of the present invention is to correct not only the distortion caused by the expansion and contraction of the chip along its main surface when the temperature changes, but also the distortion caused by the degree of the curvature of the chip. Another object of the present invention is to provide a semiconductor device capable of performing the above.

[0011]

To achieve the above object, the present invention provides a semiconductor device having a chip mounted on a base, wherein the base has a thermal expansion coefficient close to that of the chip. And has a structure in which two or more layers made of materials having different thermal expansion coefficients from each other are laminated, and when the temperature changes, the degree of the bending causes the stress due to the change in the degree of the bending of the chip. It is characterized in that it changes so as to relax.

In the present invention, a chip typically has a structure in which a layer made of a material having a different composition from that of the substrate is laminated on a substrate, and the degree of curvature of the chip changes with temperature. It is. Note that this chip may be in the form of a bar.

In the present invention, the base is typically
Two or more layers constituting this are laminated in the order of larger (or smaller) coefficient of thermal expansion.

According to the present invention configured as described above, two or more layers of the base that are made of materials having different thermal expansion coefficients have a thermal expansion coefficient close to that of the chip. Thereby, the degree of expansion and contraction of the two at the junction between the chip and the base when the temperature changes is substantially equal, and the stress generated when the chip expands and contracts along its main surface can be reduced. In addition, the base has a structure in which two or more layers made of materials having different thermal expansion coefficients are laminated, so that the degree of curvature changes depending on the temperature. Therefore, if the change in the degree of bending of the base due to the temperature change is made to follow the change in the degree of bending of the chip, the stress caused by the change in the degree of bending of the chip can also be reduced.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of the semiconductor laser according to the embodiment. This semiconductor laser is an AlGaAs-based semiconductor laser.

As shown in FIG. 1, in the semiconductor laser according to this embodiment, a heat sink 1 includes a first layer 1a and a second layer 1 made of materials having mutually different coefficients of thermal expansion.
b has a bimetallic structure bonded to the substrate.
In this case, the first layer 1a and the second layer 1b
Has a thermal expansion coefficient close to that of the laser chip 2 mounted on the heat sink 1, and the thermal expansion coefficient of the first layer 1a is larger than that of the second layer 1b. It is getting bigger. The laser chip 2 is mounted on the substrate 2
a and a semiconductor layer 2b constituting a laser structure provided on one main surface of the substrate 2a. Although not shown, in this laser chip 2,
Electrodes are provided on the back surface of the substrate 2a and the top surface of the semiconductor layer 2b, respectively. In this laser chip 2, the thermal expansion coefficient of the substrate 2a is larger than that of the semiconductor layer 2b.

Then, this laser chip 2 is
The heat sink 1 is die-bonded to a predetermined portion on the first layer 1a with the b side down using, for example, solder (not shown). Therefore, in this semiconductor laser, when the laser chip 2 is mounted on the heat sink 1, the thermal expansion coefficient of the heat sink 1 in the stacking direction and the thermal expansion coefficient of the laser chip 2 in the stacking direction are different. Matches.

Here, the substrate 2a of the laser chip 2 is made of, for example, GaAs, and the semiconductor layer 2 constituting the laser structure is formed.
b is composed of a plurality of Al _x Ga _1-x As layers (where x is, for example, 0.1 ≦ x ≦ 0.6). This laser chip 2
, The thermal expansion coefficient of the GaAs substrate 2a is 6.5 × 10 ⁻⁶ / ° C. The coefficient of thermal expansion of the semiconductor layer 2b is determined by the plurality of Al _x G
It depends on the Al composition ratio x of the a _1-x As layer. As an example, it is assumed that the Al composition ratio x of the plurality of Al _x Ga _1-x As layers is 0.5 on average. The coefficient of thermal expansion of this semiconductor layer 2b is 5.9 × 10 ⁻⁶ / ° C. In this case, the thermal expansion coefficient of the substrate 2a is larger than the thermal expansion coefficient of the semiconductor layer 2b, and the difference between the two is 0.6 × 10 ^−6.
/ ° C.

The laser chip 2 is manufactured at the time of manufacture.
The semiconductor layer 2b is formed on the substrate 2a at a temperature of, for example, about 800 ° C.
Is grown, and the thermal expansion coefficient of the substrate 2a is
b is larger than the thermal expansion coefficient of the semiconductor layer 2 at room temperature.
It is curved with the b side convex.

In this semiconductor laser, the first layer 1a and the second layer 1b constituting the heat sink 1
For example, a copper tungsten alloy is used. This copper tungsten alloy has good thermal conductivity,
Since heat generation during operation can be prevented from adversely affecting the characteristics and reliability of the semiconductor laser, it is suitable as a heat sink material. The copper-tungsten alloy has a thermal expansion coefficient of 6.5 × 10 ⁻⁶ / ° C. to 8.5 × by changing the alloy ratio of copper to tungsten from 1: 9 to 2: 8, for example. It is possible to change to 10 ^-6 / ° C. This is because the difference in thermal expansion coefficient between the substrate 2a and the semiconductor layer 2b in the laser chip 2 (0.
6 × 10 ⁻⁶ / ° C.), and a value close to the thermal expansion coefficient of GaAs or Al _x Ga _{1 -x} As forming the substrate 2a and the semiconductor layer 2b. is there.

In this heat sink 1,
By forming the first layer 1a and the second layer 1b using copper tungsten alloys having different composition ratios from each other,
The thermal expansion coefficient of the first layer 1a is different from the thermal expansion coefficient of the second layer 1b. At this time, the ratio of copper in the copper-tungsten alloy forming the first layer 1a is made larger than the ratio of copper in the copper-tungsten alloy forming the second layer 1b. But the second
Is larger than the thermal expansion coefficient of the layer 1b. The first layer 1a and the second layer 1b of the heat sink 1
Is set to be substantially equal to the difference between the thermal expansion coefficients of the substrate 2a and the semiconductor layer 2b in the laser chip 2. Here, the ratio of copper in the first layer 1a is, for example, 15%.
The coefficient of thermal expansion of a is 7.2 × 10 ⁻⁶ / ° C. The ratio of copper in the second layer 1b is, for example, 10%, and the thermal expansion coefficient of the second layer 1b at this time is 6.5 × 10 ⁻⁶ /.
° C.

In the heat sink 1, the first layer 1a and the second layer 1b have different thermal expansion coefficients from each other.
It is possible to change the degree of the curvature according to the temperature change. The heat sink 1 has a first layer 1a and a second layer 1b having different thermal expansion coefficients.
Are laminated at a temperature of, for example, about 500 ° C., and at normal temperature, the second layer 1 b is curved with the convex side. At this time, in the heat sink 1, the degree of curvature of the concave surface on the first layer side on which the laser chip 2 is mounted is determined by the degree of curvature of the convex surface on the semiconductor layer 2b side of the laser chip 2. By making the degree substantially equal to the degree, the adhesion when mounting the curved laser chip 2 is improved. Note that such a heat sink 1 may be manufactured by changing the composition ratio at the stage of manufacturing the copper-tungsten alloy.

This semiconductor laser is manufactured by die bonding a laser chip 2 at a temperature of, for example, 250 ° C. to 350 ° C. on the heat sink 1 configured as described above.

In the semiconductor laser configured as described above, when the laser chip 2 is mounted on the heat sink 1, the relationship between the magnitudes of the thermal expansion coefficients in the stacking direction of the heat sink 1 and the size of the laser chip 2 in the stacking direction are different. Since the magnitude relationship between the coefficients of thermal expansion coincides with each other, if the temperature changes due to, for example, heat generation during operation or a change in environment, the degree of curvature of the heat sink 1 will be
It changes following the change in the degree of curvature of the laser chip 2, and the stress caused by the change in the degree of change in the curvature of the laser chip 2 can be reduced.

At this time, the difference in the coefficient of thermal expansion between the first layer 1a and the second layer 1b in the heat sink 1 is calculated as follows:
Since the difference between the thermal expansion coefficients of the substrate 2a and the semiconductor layer 2b in the laser chip 2 is substantially equal,
Within the range of temperature change when this semiconductor laser is used in a normal environment, the amount of change in the degree of curvature of the heat sink 1 and the amount of change in the degree of curvature of the laser chip 2 are set to be substantially equal. I have. Further, the thermal expansion coefficients of the first layer 1a and the second layer 1b of the heat sink 1 are as follows:
Since the value is close to the coefficient of thermal expansion of the laser chip 2, the degree of expansion and contraction of the heat sink 1 and the laser chip 2 at the joint is almost equal, and therefore the laser chip 2 expands and contracts in the direction along its main surface. It is also possible to alleviate the stress caused by the above.

As described above, according to the semiconductor laser according to this embodiment, when the temperature changes, the distortion caused by the expansion and contraction of the laser chip 2 can be corrected. Since it is also possible to correct the distortion caused by the change in the degree of curvature of the laser chip 2, it is impossible to minimize the adverse effects of these distortions on the characteristics and reliability of the semiconductor laser. Is possible.

Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications based on the technical idea of the present invention are possible. For example, the numerical values, materials, structures, and the like described in the embodiments are merely examples, and the present invention is not limited thereto.

In the above-described embodiment, when the laser chip 2 is mounted on the heat sink 1, the semiconductor layer 2b side of the laser chip 2 is located on the first layer 1a side of the heat sink 1. It is also possible for the substrate 2a side of the laser chip 2 to be on the second layer 1b side of the heat sink 1.

Further, the heat sink 1 in the above-described embodiment may be formed by laminating three or more layers made of materials having different thermal expansion coefficients from each other. In this case, these three or more layers are stacked, for example, in descending order of the coefficient of thermal expansion.

In the above-described embodiment, the first layer 1a and the second layer 1b constituting the heat sink 1 are formed.
Is used as a material for the first layer 1a and the second layer 1b, for example, a copper molybdenum alloy, AlSiC, or the like may be used.

In the present invention, the package is formed by laminating two or more layers made of materials having a thermal expansion coefficient close to that of a chip mounted thereon and having different thermal expansion coefficients from each other. It may be constituted by doing.

Further, in the above-described embodiment, the case where the present invention is applied to a semiconductor laser has been described. However, the present invention is not limited to a semiconductor laser using a material other than AlGaAs-based materials, and the chip may be a heat sink or a package. A semiconductor device mounted on a base, specifically, for example, a power MOSFET, or two (plural) laser structures are provided on the same substrate, and a laser beam is emitted from one laser to the other laser. Monolithic optical amplifier (Monolithic Optical P
It can also be applied to power amplifiers (OWER Amplifier, MOPA) and the like.

[0033]

As described above, according to the present invention, the base has two or more materials made of materials having different thermal expansion coefficients from each other and having a thermal expansion coefficient close to that of the chip. In addition to having a structure in which the layers are stacked, when the temperature changes, the degree of curvature changes so as to reduce stress caused by the change in the degree of curvature of the chip, so that the chip changes when the temperature changes. Since the distortion caused by expansion and contraction and the distortion caused by the change in the degree of curvature of the chip can be corrected together, the adverse effects of these distortions on the characteristics and reliability of the semiconductor device can be minimized. It is possible to suppress.

[Brief description of the drawings]

FIG. 1 is a sectional view of a semiconductor laser according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a laser chip of a semiconductor laser for describing a problem of the related art.

3 is a cross-sectional view illustrating a state where the laser chip illustrated in FIG. 2 is mounted on a heat sink, for describing a problem of the related art.

[Explanation of symbols]

1 ... heat sink, 1a ... first layer, 1b ...
A second layer, 2 ... laser chip, 2a ... substrate,
2b ... Semiconductor layer

Claims (7)

[Claims] 1. A semiconductor device having a chip mounted on a base, wherein the base has a coefficient of thermal expansion close to the coefficient of thermal expansion of the chip and is made of a material having different coefficients of thermal expansion from each other. A semiconductor device having a structure in which one or more layers are stacked, and wherein, when the temperature changes, the degree of curvature changes so as to reduce stress caused by the change in the degree of curvature of the chip. . 2. The base according to claim 2, wherein the base has a thermal expansion coefficient close to the thermal expansion coefficient of the chip, and has a structure in which two layers made of materials having different thermal expansion coefficients are stacked. 2. The semiconductor device according to claim 1, wherein a thermal expansion coefficient of the layer on which the chip is mounted is larger than a thermal expansion coefficient of the other layer. 3. The semiconductor device according to claim 1, wherein the amount of change in the degree of curvature of the chip when the temperature changes is substantially equal to the amount of change in the degree of curvature of the base. 4. The method according to claim 1, wherein the degree of curvature of the tip is substantially equal to the degree of curvature of the base.
13. The semiconductor device according to claim 1. 5. The semiconductor device is a semiconductor laser,
2. The semiconductor device according to claim 1, wherein said chip is a laser chip or a laser bar. 6. The semiconductor device according to claim 1, wherein said base is a heat sink. 7. The semiconductor device according to claim 1, wherein said base is a package.