JPH0964478A - Semiconductor element and method for forming the same - Google Patents

Abstract

(57) [Abstract] [Purpose] AlGaInP on Si substrate with photo detector
Provided is a laser unit having a low thermal resistance which can be formed into a laser unit by mounting a semiconductor laser chip. [Structure] By bonding the laser chip 2 to the comb 4 via the submount chip 3 having a higher thermal conductivity than Si and the heat conducting film 8, heat generated from the laser chip 2 is efficiently transmitted to the comb 4. S between the laser chip 2 and the comb 4
Since the i-substrate 17 is not present, the heat generated from the laser chip 2 can be efficiently transmitted to the comb 4.
It is possible to unitize a semiconductor laser chip that generates a lot of heat, such as a system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device including a substrate having a light receiving element such as a semiconductor laser unit or a circuit element and a heat generating element mounted on the substrate, and more particularly to a heat dissipation characteristic of the heat generating element. And a method for forming the same.

[0002]

2. Description of the Related Art Conventionally, a laser unit having an infrared semiconductor laser chip having a wavelength of 780 nm or more and a mirror for vertically reflecting a laser beam on a Si substrate having a light receiving element has been proposed and put into practical use ( Japanese Patent Application No. Sho 62-309
056). For example, as shown in FIG. 3, a concave hole 10 is formed in a part of the Si substrate 15 on which the light receiving element 6 is formed by etching, and the laser chip 7 is formed on the bottom surface of the hole 10.
Mount. Further, the (111) surface 10a having good flatness
In this configuration, the etched side surface is used as a mirror.
The concave portion is metallized with an inclination Au or the like to increase the reflectance of the mirror surface. The laser chip 7 is bonded to the bottom surface via a solder material. The details will be described below.

FIG. 3A is a plan view of the unit, and FIG. 3B is a sectional view taken along the line aa '. The light receiving element 6 is Si
It is integrated on the substrate 15. The thickness of the Si substrate 15 is 500 μm. Between the laser chip 7 and Si15, Cr (0.1 μm) is added to improve the adhesion of the solder material.
And a metallization layer of Au (0.5 μm). When the laser chip (wavelength: 780 nm) was replaced with a red semiconductor laser chip in this configuration and the thermal resistance was measured, it was 75 ° C./W, and the temperature dependence of the laser threshold value was large, and laser oscillation occurred at 40 ° C. or higher. ,
Due to thermal saturation, a light output of 10 mW or more could not be obtained. At the time of DC driving, the characteristic temperature To was only as small as 80K. When a laser chip having the same characteristics is mounted on a conventional round metal package having a diameter of 9 mm and the characteristic temperature is measured, a value of 115 K is obtained.

[0004]

However, the above-mentioned conventional technique has a problem that the heat dissipation property of the Si substrate 15 is low due to the low thermal conductivity of the Si substrate 15. This heat dissipation characteristic is the temperature rise of the laser active layer relative to the power consumption of the laser chip 7, that is, the thermal resistance (unit: ° C).
/ W). In a red semiconductor laser having a wavelength of 630 nm to 690 nm composed of an AlGaInP-based material, the heat generated from the laser chip 7 has a wavelength of 780 n.
This is larger than that of an infrared semiconductor laser near m, and this heat generation increases the threshold current and operating current of the laser.
It was difficult to construct the laser unit as described above.

The present invention provides a semiconductor element having a low thermal resistance that can be used as a laser unit in an AlGaInP-based semiconductor laser and a method for forming the same.

[0006]

In order to solve the above-mentioned conventional problems, the present invention provides a substrate on which a circuit element and a heating element accompanied by heat are formed, and a hole formed in a region where the heating element is formed. The heat generating element is formed on the hole, and the heat generating element is formed directly on the heat conducting film or through an element having a heat conductivity higher than that of the substrate.

Further, according to the present invention, a step of forming a circuit element on a substrate, a step of forming a heat conductive film on a surface opposite to a surface of the substrate on which the circuit element is formed, and a step of forming a circuit element on the surface of the substrate are described. The method further comprises a step of selectively forming holes and a step of forming a heat generating element directly on the heat conducting film or through an element having a higher heat conductivity than the substrate.

[0008]

According to the present invention, since the heat generating element is formed directly on the heat conducting film or through the element having a higher heat conductivity than the substrate, the heat from the heat generating element is efficiently radiated.

[0009]

【Example】

(First Embodiment) The first embodiment of the present invention will be described below.

FIG. 1 is a block diagram of a semiconductor laser unit showing a first embodiment of the present invention. FIG. 1A is a plan view,
FIG. 1B shows a sectional view taken along the line aa '. 17 in the figure
Is a Si substrate on which the light receiving element 1 is integrated. The Si substrate 17 has a thickness of 500 μm and has a double-sided mirror-polished finish. The (111) plane of the hole 5 formed by etching the Si substrate 17 is used as a mirror for reflecting the light emitted from the laser chip 2 and directing it in the vertical direction. A CVD diamond film having a film thickness of about 50 μm is formed as a heat conducting film 8 on the bottom surface of the hole 5, and the laser chip 2 is bonded onto the diamond film via the submount chip 3 of SiC (thickness 300 μm).

The creation procedure will be described below. First, on the surface of the Si substrate opposite to the surface on which the light receiving element 1 is formed, a portion other than the portion where the heat conductive film (diamond film) 8 is synthesized is covered with a SiO 2 film, and then a diamond film is formed by a microwave plasma CVD method. Since diamond nuclei are less likely to occur on SiO 2, the diamond film selectively grows only on the Si substrate. Table 1 shows the synthesis conditions of the microwave plasma CVD apparatus used in this example. The raw material gas was methane, which was diluted with hydrogen gas to 99% before use.
The thermal conductivity of the obtained film was about 1200 W / mK.

[0012]

[Table 1]

Next, by anisotropic etching of alkali, a hole 5 having a (111) plane to be a laser mirror is formed. At this time, since the diamond film is not etched, it also serves as an etching stopper. Usually as-depo
The surface of the diamond film in this state is poor in smoothness, and polishing is required when using this surface as a heat conductive film, but the surface property on the substrate side (that is, the surface obtained by removing the substrate) is rough. It follows that In this embodiment, since the mirror-polished Si substrate is used, the surface of the diamond film is smooth and need not be polished. Although it has been attempted to use diamond as a heat dissipation substrate from the past, it was not practical because the cost was increased because it was necessary to polish the surface and process it into a specific shape.

The steps of photolithography, vapor deposition, plating, etc. described above are wafer processes, and after completion of these steps, a Si substrate is produced by a dicing step. The laser chip 2 is bonded with the side of the active layer, which generates a large amount of heat, facing downward. Here, the laser chip 2 is a red semiconductor laser using an AlGaInP-based material having an oscillation wavelength of 650 nm. The rated light output of the laser is 35 mW. Finally, wiring of the laser chip 2 and the light receiving element 1 is performed by wire bonding. The submount chip 3 and the heat conductive film (diamond film) 8, and the laser chip 2 and the submount chip 3 are bonded by a solder material (Pb-Sn). At this time, the surfaces of the diamond film, the submount chip, and the laser chip are metallized with Cr (0.1 μm) and Au (0.5 μm), respectively, in order to facilitate the attachment of the solder material. When the thermal resistance was measured with this configuration, it was about 40 ° C./W, and it was found that a heat dissipation effect about twice that of the conventional case was obtained.

The submount chip 3 is not limited to SiC, but a material having a high thermal conductivity is desirable. When a diamond film is used for the heat conduction film 8, since diamond is an insulating film, it can also serve as an insulating layer for insulating between the laser chip 2 and the comb 4. Therefore, various materials can be selected as the submount material without depending on the magnitude of resistance. If the submount chip 3 is made of Cu (thickness 300 μm), the thermal resistance is about 25 ° C.
/ W, and a larger heat dissipation effect can be obtained. However, at this time, In solder (thickness 3 μm) was used for bonding the laser chip and the submount chip. This is because there is a difference in the coefficient of thermal expansion between Cu and the laser chip 2, so that the laser chip 2 is prevented from being distorted when its temperature rises to deteriorate the characteristics or break the chip.

The method of forming the diamond film is not limited to the microwave plasma CVD method. As already reported, the diamond film formed by any of the hot filament method, the plasma jet method and the direct current discharge plasma CVD method has the same effect in the constitution of the present invention.

(Second Embodiment) Next, a second embodiment of the present invention will be described. The structure is exactly the same as that of the first embodiment, but a carbon film in which diamond bonds and graphite bonds are mixed is used as the heat conduction film 8 (thickness 40 μm). This film was synthesized by the microwave plasma CVD method described in Example 1 under the condition that the dilution ratio of hydrogen was low, and had a configuration in which graphite and amorphous carbon were mixed in the diamond particles. Since graphite is mixed in this film, the film formation rate is higher than that of the diamond film, and the internal stress of the film is small. Therefore, it has excellent productivity and there is little risk of distorting the film or substrate. (Table 2) shows the synthesis conditions.

[0018]

[Table 2]

The thermal conductivity of this film is 300 W / mK, which is only about 1/4 that of a polycrystalline diamond film.
When measuring the thermal resistance of the laser unit (Table 3)
Were obtained.

[0020]

[Table 3]

By selecting the material and the thickness of the submount in this way, it was possible to realize the heat radiation characteristics higher than those of the conventional round metal package.

The material of the heat conducting film is not limited to the diamond film of Example 1 or the carbon film of Example 2 in which diamond and graphite are mixed. It is selected according to the substrate material of the element and the shape of the submount.
In the element using i as the substrate, it is desirable that the material has a thermal conductivity of 200 W / mK or more and the film thickness is less than 100 μm. This is because a material having a thermal conductivity of less than 200 W / mK has a large thermal resistance and cannot sufficiently radiate heat. Further, when the film thickness is 100 μm or more, the substrate and the film are distorted or damaged due to the difference in thermal expansion from the substrate for any material.

(Embodiment 3) A third embodiment of the present invention will be described below.

FIG. 2 is a block diagram of a semiconductor laser unit showing a third embodiment of the present invention. FIG. 2A is a plan view,
FIG. 2B shows a sectional view taken along the line aa '. In the figure, a Si substrate 16 on which the light receiving element 12 is integrated is shown. The Si substrate 16 has a thickness of 500 μm. On this substrate, a laser chip 13 and a mirror 11 for reflecting the emitted light from the laser chip 13 and directing it in the vertical direction are bonded. In the portion where the laser chip 13 and the mirror 11 are bonded, Ti 0.1 μm and Au0.
5 μm is deposited. The mirror 11 is made of Si, and the reflecting mirror surface uses a surface having an inclination angle of 45 degrees formed by mechanical polishing. Mirror surface and bottom part are T
It is metallized with a deposited film of i 0.1 μm and Au 0.5 μm, and Pb solder containing 30% Sn is vapor-deposited 2 μm on the bottom surface for bonding. The laser chip 13 is bonded onto the diamond film 15 provided on the bottom surface of the hole formed in the Si substrate 16 via a submount (material Cu, thickness 500 μm) 17.

The creation procedure will be described below. First, after covering the portion of the Si substrate opposite to the surface on which the light receiving element 12 is formed with a portion other than the portion for synthesizing the diamond film with the SiO2 film
A diamond film is formed by the microwave plasma CVD method. Since diamond nuclei are less likely to occur on SiO 2, the diamond film selectively grows only on the Si substrate. The film forming apparatus and conditions were the same as in Example 1, and the thermal conductivity of the obtained film was about 1200 W / mK.

Next, holes are formed by etching. At this time, since the diamond film is not etched, it also serves as an etching stopper. Normally, the surface of a diamond film in the as-depo state is poor in smoothness and polishing is required when using this surface as a heat conductive film, but the surface properties on the substrate side (that is, the surface obtained by removing the substrate) Is based on the roughness of the substrate. In this embodiment, since the mirror-polished Si substrate is used, the surface of the diamond film is smooth and need not be polished. The above-mentioned steps such as photolithography, vapor deposition, and plating are wafer processes, and after completion of these steps, a Si substrate is created by a dicing step. The laser chip is bonded on the diamond film 15 via the submount with the active layer side, which generates a large amount of heat, facing downward. Here, the laser chip is a red semiconductor laser using an AlGaInP-based material with an oscillation wavelength of 650 nm. The rated light output of the laser is 35 mW. Finally, wiring of the laser chip and the light receiving element is performed by wire bonding. The submount and the diamond film, and the laser chip and the submount are bonded by a solder material (Pb-Sn). At this time, the surfaces of the diamond film, the submount, and the laser chip are metallized with Cr (0.1 μm) and Au (0.5 μm) in order to facilitate the attachment of the solder material. When the thermal resistance was measured with this configuration, it was about 42 ° C./W, and it was confirmed that a heat radiating effect about twice that of the conventional case was obtained, and it was found that the same effect as in Example 1 was obtained.

The red semiconductor laser having a wavelength of 630 nm to 690 nm composed of an AlGaInP-based material has been described above as an example, but the present invention is not limited to this, and any electric / electronic element such as an IC that generates heat is generated. It is also effective.

[0028]

According to the present invention, since the heat generating element is formed directly on the heat conducting film or through the element having a heat conductivity higher than that of the substrate, the heat generating element does not come into contact with the substrate and heat from the heat generating element is not contacted. Is efficiently radiated. Therefore, since the heating element does not come into contact with the substrate, it is possible to provide a semiconductor element having good heat dissipation characteristics with a low thermal resistance even if the heating element generates a large amount of heat.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a semiconductor device according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a semiconductor device according to a third embodiment of the present invention.

FIG. 3 is a configuration diagram of a semiconductor device in a conventional example.

[Explanation of symbols]

 1 Light receiving element 2 Laser chip 3 Submount chip 4 Com 5 Hole 8 Thermal conductive film 17 Si substrate

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Isao Kidoguchi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (8)

[Claims] 1. A substrate provided with a circuit element and a heating element that generates heat, a hole provided in a region where the heating element is formed, and a heat conductive film provided in the hole, A semiconductor device characterized in that the device is formed directly on the heat conducting film or via a device having a heat conductivity higher than that of the substrate. 2. A substrate is a Si substrate, holes are selectively formed in a region of the Si substrate different from a region in which circuit elements are formed, a heat conductive film is formed on a bottom surface of the holes, and a heating element is formed. The semiconductor element according to claim 1, further comprising a semiconductor laser chip formed on the heat conductive film, and further comprising a mirror that reflects laser light emitted from the semiconductor laser chip. 3. The substrate is a Si substrate, the holes are selectively formed in a region different from the region of the Si substrate on which circuit elements are formed, and have a tapered slope, and the heat conducting film is the hole. A semiconductor laser chip formed on the bottom surface of the heat-conducting film is used as the heating element, and the laser light emitted from the semiconductor laser chip is reflected by the tapered slope of the hole and taken out above the substrate. The semiconductor device according to claim 1, wherein: 4. The semiconductor device according to claim 2, wherein the heat conducting film is made of a material having a heat conductivity of 200 W / mK or more. 5. The semiconductor device according to claim 2, wherein the heat conducting film is composed of a single crystal diamond plate or a polycrystalline diamond film. 6. The heat conductive film is composed of a carbon film having diamond bonds (SP3 bonds) or a mixture of diamond bonds (SP3 bonds) and graphite bonds (SP2 bonds). Semiconductor device. 7. The semiconductor device according to claim 2, wherein the heat conductive film has a thickness of 100 μm or less. 8. A step of forming a circuit element on a substrate, a step of forming a heat conductive film on a surface opposite to a surface of the substrate on which the circuit element is formed, and selectively from a surface of the substrate on which the circuit element is formed. A method of forming a semiconductor device, comprising: forming a hole; and forming a heat-generating element on the heat-conducting film directly or through an element having a higher thermal conductivity than the substrate.