JP2001127375A - Submount for mounting optical semiconductor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a submount for mounting an optical semiconductor element which can prevent the breakage of the optical semiconductor element due to conveyance of thermal stress thereto as well as alloying of metallic layer elements in a brazing material layer when the brazing material layer is heated and melted to join the optical semiconductor element, and also prevent an increase in melting point due to compositional change of the brazing material layer. SOLUTION: This mounting electrode is formed by forming a joint layer in which a metallic layer 5 made of Au, Ag, Cu, or alloy made of these elements, a second diffusion prevention layer 6 and a brazing layer 7 are laminated in sequence, on a wiring layer in which an adhesive metallic layer 2, a diffusion prevention layer 3 and a main conductor layer 4 are laminated in sequence on the optical semiconductor element mounting part on a diamond substrate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a submount for mounting an optical semiconductor element such as a semiconductor laser and an optical semiconductor element carrier, and more particularly to a high-output semiconductor laser and a precise temperature control. The present invention relates to a device for mounting a semiconductor laser or the like.

[0002]

2. Description of the Related Art FIG. 2 is a partial cross-sectional view of a wiring layer for mounting an optical semiconductor element of a conventional submount for mounting an optical semiconductor element (hereinafter abbreviated as a submount) and a bonding layer for bonding an optical semiconductor element. . In the figure, 1 is a diamond substrate having excellent thermal conductivity and strength, and 2 is a Ti substrate having good adhesion.
3 is a diffusion prevention layer (hereinafter, also referred to as a barrier layer) for preventing components of the adhesion metal layer 2 from diffusing into the upper main conductor layer 4, and 4 is a main conductor layer made of Au or the like. The adhesion metal layer 2, the diffusion preventing layer 3, and the main conductor layer 4 constitute a wiring layer. Then, on the main conductor layer 4, Au—Sn for joining with a wiring layer of an optical semiconductor electronic component or the like.
A low melting point brazing material layer 7 made of an alloy or the like is laminated, and the brazing material layer 7 forms a bonding layer. Although a wiring layer and a bonding layer are laminated on one main surface of the diamond substrate 1 and a wiring layer is also formed on the other main surface, there may be no wiring layer on the other main surface.

[0003] Such a diamond substrate 1 for submount is composed entirely of diamond, or a diamond film is coated on the surface of a silicon substrate by a CVD method or the like, and then the silicon substrate is dissolved and removed to remove only the diamond film. In this case, a substrate using this diamond film as a substrate was used (see Japanese Patent Application Laid-Open No. H6-177135 and Japanese Patent Publication No. H7-54834). Then, on one main surface of the diamond substrate 1, Ti as an adhesion metal layer is formed.
Layer, Pt layer as a diffusion preventing layer, Au as a main conductor layer
A wiring layer in which layers are sequentially laminated is formed, a metal brazing material such as an Au—Sn alloy solder is partially formed on the wiring layer as a bonding layer in a predetermined pattern, and G is further formed on the bonding layer.
A semiconductor laser made of a semiconductor material such as aAs has been mounted and mounted. Further, the other main surface (back surface) side of the submount on which the semiconductor laser is mounted is Pb-S
It was bonded on the Cu-W wiring layer or the ceramic substrate as the mother substrate by n solder or the like.

The above-mentioned adhesive metal layer 2, diffusion preventing layer 3, and main conductor layer 4 constituting the wiring layer are formed by a thin film forming method such as a sputtering method or a vapor deposition method, and are processed into a desired pattern by a photolithographic method. Thus, it is formed as a wiring layer for mounting the optical semiconductor element. The wiring layer generally comprises
An adhesion metal layer made of Ti, Cr, Ta, etc., Pt, Pd,
It has a three-layer structure in which a diffusion prevention layer made of Ni or the like and a main conductor layer made of Au or the like are sequentially laminated, and a layer structure of a Ti layer, a Pt layer, and an Au layer can be adopted as a particularly good layer structure. Many.

[0005]

However, in the above-mentioned conventional submount, thermal stress is generated between the diamond substrate 1 and the mounted optical semiconductor element due to a difference between their thermal expansion coefficients and a temperature difference during driving. There has been a problem that a semiconductor laser or the like made of a brittle compound semiconductor material such as a GaAs single crystal is broken by the thermal stress. For example, the coefficient of thermal expansion of the diamond substrate 1 is 2.3 × 10
^- to ⁶ / ° C. about a of the thermal expansion coefficient of the optical semiconductor element comprising a GaAs single crystal 6.5 × 10 ^- because it is about ⁶ / ° C., the difference is 4.2 × 10 ^- becomes ⁶ / ° C. approximately, Large thermal strain was generated, and large thermal stress was generated between the diamond substrate 1 and the optical semiconductor element.

In the case where a diamond thin film is formed on another substrate by a plasma CVD method (hereinafter, referred to as a CVD method), the diamond thin film is made of a polycrystal oriented in a thickness direction. When there is such an orientation, there is a property that it is easily broken by a tensile stress or a compressive stress. For this reason, the diamond substrate 1 made of a diamond thin film formed by the CVD method is easily broken due to thermal stress between the diamond substrate 1 and another ceramic substrate, a metal substrate, or a package on which the diamond substrate 1 is mounted. There was also.

Accordingly, the present invention has been completed in view of the above circumstances, and an object of the present invention is to provide a GaAs substrate having a thermal expansion coefficient difference between a diamond substrate and an optical semiconductor element mounted thereon and a thermal stress caused by a temperature difference during driving. An object of the present invention is to prevent a semiconductor laser or the like made of a brittle compound semiconductor material such as a single crystal from being broken.

[0008]

A submount for mounting an optical semiconductor device according to the present invention is a wiring in which an adhesion metal layer, a diffusion prevention layer, and a main conductor layer are sequentially laminated on an optical semiconductor device mounting portion on a diamond substrate. A mounting electrode formed by forming a bonding layer in which a metal layer made of Au, Ag, Cu or an alloy thereof, a second diffusion prevention layer, and a brazing material layer are sequentially formed on the layer is provided. And

According to the present invention, when a large thermal strain occurs between the diamond substrate and the mounted optical semiconductor element, the soft metal layer easily deforms and absorbs thermal stress due to the thermal strain. . Therefore, since a large thermal stress is hardly transmitted to the optical semiconductor element side, the optical semiconductor element is hardly damaged by the thermal stress. In addition, since the second diffusion prevention layer exists between the metal layer and the brazing material layer, when the brazing material layer is heated and melted to join the optical semiconductor elements, the metal layer component is contained in the brazing material layer. There is no melting and alloying, and no increase in the melting point due to a change in the composition of the brazing material layer. As a result, good bondability can be obtained.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A submount according to the present invention will be described below. FIG. 1 is a partial cross-sectional view of a submount according to the present invention, wherein 1 is a diamond substrate, 2 is Ti, Cr, N
An adhesion metal layer made of i-Cr, Ta, etc., 3 is Pt, P
d, a diffusion preventing layer made of Ni-Cr, Ti-W, etc., 4 is a main conductor layer made of Au or the like, 5 is a metal layer made of Au, Ag, Cu or an alloy thereof, 6 is Pt, Rh, Ru, etc. A second diffusion prevention layer made of Au-Sn alloy brazing material, Au-Ge alloy brazing material, Pb-Sn solder, In-S
This is a brazing material layer made of n solder or the like for joining optical semiconductor elements. The adhesion metal layer 2, the diffusion preventing layer 3, and the main conductor layer 4 constitute a wiring layer, and the metal layer 5, the second diffusion preventing layer 6, and the brazing material layer 7 form a bonding layer for bonding an optical semiconductor element. Is configured. Then, an electrode for mounting the optical semiconductor element, which is formed by forming a bonding layer on a part of the wiring layer, is provided.

The adhesion metal layer 2, diffusion prevention layer 3, main conductor layer 4, metal layer 5, second diffusion prevention layer 6, and brazing material layer 7 are formed as follows. First, a resist film is formed on a portion other than the portion where the wiring layer is formed by a known two-layer resist method. Thereafter, an adhesion metal layer 2, a diffusion preventing layer 3, and a main conductor layer 4 are sequentially laminated on the entire surface of the resist film by a thin film forming method such as an evaporation method or a sputtering method. After completion of the film formation, the excess resist film is lifted off by immersing the diamond substrate 1 in a resist stripping solution, and a wiring layer having a desired pattern is formed. The lift-off method is not limited to the two-layer resist method, but may be a three-layer resist method, an image inversion resist method, or the like. Similarly, the metal layer 5, the second diffusion prevention layer 6, and the brazing material layer 7 are partially formed on the wiring layer.
Is formed.

In the present invention, the thickness of the close contact metal layer 2, the diffusion preventing layer 3, and the main conductor layer 4 is not particularly limited, but the thickness of the close contact metal layer 2 is about 60 to 1200 nm. The thickness of the prevention layer 3 is 500 to 2500 nm.
And the thickness of the main conductor layer 4 is 200 to 5000 nm.
It is about.

The thickness of the metal layer 5 is preferably 1.0 μm or more. If the thickness is less than 1.0 μm, the effect of absorbing the thermal stress of the metal layer 5 is not sufficient, so that the optical semiconductor element is easily broken.
If the thickness exceeds 5.0 μm, the cost is increased. Therefore, the thickness is more preferably 1.0 to 5.0 μm. The thickness of the second diffusion prevention layer 6 is preferably 0.1 μm or more. If the thickness is less than 0.1 μm, there is no sufficient diffusion prevention effect. Since the five components are diffused and melted, the melting point of the brazing material layer 7 increases, and the bondability deteriorates.
If the thickness exceeds 0.5 μm, the cost is increased. Therefore, the thickness is more preferably 0.1 to 0.5 μm.

The thickness of the brazing material layer 7 is preferably 2 to 10 μm.
If the thickness is less than 2 μm, the volume of the metal brazing material is small, so that voids, that is, unnecessary vacancies in the metal brazing material are likely to be generated between the optical semiconductor elements. If it exceeds 10 μm, it becomes difficult to form a pattern of the brazing material layer 7 by a lift-off method or the like.

The metal layer 5 of the present invention is made of Au, Ag, Cu,
Or, it is composed of an alloy of any two or more of these metal elements, and these metal elements and alloys are 300 to 40.
It is a soft metal having an elongation at break of 30% or more with respect to the maximum tensile stress of 0 MPa (megapascal). It is difficult to react with oxygen or the like after forming a thin film and has excellent chemical stability. Other soft metals such as Sn and In have melting points that are too low, and Ni and the like harden after forming a thin film.

The brazing material layer 7 of the present invention has a low melting point (130
To 450 ° C.), and the reaction time with the main conductor layer 4 hardly occurs by shortening the heating time.

FIGS. 3 and 4 show a state where the semiconductor laser 8 is mounted on the wiring layer and the bonding layer of the submount. In these figures, reference numeral 8 denotes a semiconductor laser, 8a denotes a back metal layer for bonding on the lower surface of the semiconductor laser 8, 8b denotes an input wiring layer for inputting drive signals and the like, and 8c denotes a light emitting unit.
In FIG. 4, reference numeral 10 denotes an optical semiconductor element mounting portion;
Is a mounting electrode.

FIGS. 3 and 4 show the submount of the present invention.
It goes without saying that the present invention can be applied not only to the submount for an optical semiconductor device such as the semiconductor laser 8 as described in the above, but also to a submount and a wiring board on which an LSI, an IC, etc. are mounted. Further, as shown in FIGS. 3 and 4, the wiring layer of the present invention has an electrode and the like of an optical semiconductor element placed and bonded thereon via a bonding layer, but the wiring layer is more complicated. A pattern may be formed. Furthermore, the submount of the present invention is suitable for an optical semiconductor device made of a brittle semiconductor material such as GaAs, but it goes without saying that the submount can be applied to an optical semiconductor device made of a semiconductor material other than GaAs.

Thus, according to the present invention, when a large thermal strain occurs between the diamond substrate and the mounted optical semiconductor element, the metal layer is easily deformed to absorb the thermal stress caused by the thermal strain, and The optical semiconductor element is less likely to be damaged. In addition, when the brazing material layer is heated and melted to join the optical semiconductor elements, the metal layer component does not melt into the brazing material layer to form an alloy, and the melting point rises due to a change in the composition of the brazing material layer. However, as a result, there is an operational effect that good bonding properties can be obtained.

It should be noted that the present invention is not limited to the above embodiment, and that various changes may be made without departing from the spirit of the present invention.

[0021]

Embodiments of the present invention will be described below.

(Example) The submount of FIG. 1 was constructed as follows. A diamond film having a thickness of 300 μm was formed on a silicon substrate by a CVD method, and the silicon substrate was dissolved and removed with a potassium hydroxide solution to obtain a diamond film. Each diamond substrate 1 was cut out from the diamond substrate to produce a 2 mm square diamond substrate 1.

On one main surface of the diamond substrate 1,
A resist film is formed in a portion other than the portion where the wiring layer is to be formed by the two-layer resist method, and a pattern is formed by the two-layer resist method.
, A diffusion preventing layer 3 made of Pt having a thickness of 0.1 μm, and a main conductor layer made of Au having a thickness of 1.0 μm were sequentially laminated by a sputtering method. Then
The resist layer was stripped and removed, and pattern processing was performed to obtain a desired pattern.

Similarly, as shown in Table 1, metal layers 5 of various thicknesses and compositions and second layers of various thicknesses and compositions were partially formed on the wiring layer by a two-layer resist method and a sputtering method. Diffusion prevention layer 6, Au-Sn alloy solder (melting point 2
(80 ° C.) were sequentially laminated, and lift-off was performed to perform pattern processing to obtain a desired pattern. 1 mm × 1 mm × 0.1 m on this brazing material layer 7
A semiconductor laser using GaAs of m as a semiconductor material was bonded and mounted as described below, and a thermal stress breakdown test by a temperature cycle test and an evaluation of solder wettability were performed. The results are shown in Table 1.

[0025]

[Table 1]

In Table 1, the thermal stress fracture test (thermal stress characteristic test) and the evaluation of solder wettability were performed as follows.
The submount is mounted on a heater block which is maintained at a temperature about 20 to 50 ° C. higher than the melting point of the brazing material layer 7.
After 0 seconds, a thickness of 0.1 μm
m Ti layer, 0.1 μm thick Pt layer, 0.1 μm thick
Was mounted on the bonding layer of the submount. After maintaining that state for one second,
After scrubbing the semiconductor laser for 2 seconds to allow the metal brazing material to spread well, remove the semiconductor laser from the heater block,
Cooled to room temperature.

Then, the above-mentioned temperature cycle test was performed on ten samples of the same kind. The condition is -40
The temperature was raised from 85 ° C. to 85 ° C. in 10 minutes, the temperature was maintained at 85 ° C. for 20 minutes, and the temperature was lowered from 85 ° C. to −40 ° C. in 10 minutes.
Maintaining 0 ° C. for 20 minutes is defined as one cycle,
00 cycles were performed. After the temperature cycle test, the presence or absence of breakage of the semiconductor laser was observed.

One sample was placed on a heater block heated to 340 ° C., and the melting state of the brazing material layer 7 was observed for 120 seconds to evaluate solder wettability. 120
A double circle indicates that the solder was melted even after 2 seconds, a circle indicates that the solder was melted for 60 seconds or more, a triangle indicates that the solder was melted for 20 seconds or more, and a cross indicates that the solidified in less than 20 seconds. And In Table 1, the barrier metal means the second diffusion prevention layer 6.

As shown in Table 1, NO. 1-4, 17, 19, 2
In Nos. 1 and 23, the thickness of the metal layer 5 was 0.5 μm, so that the semiconductor laser was destroyed in the temperature cycle test and became unsuitable. On the other hand, NO. When the thickness of the metal layer 5 was 1.0 μm or more as in 5 to 16, the semiconductor laser was not broken in the temperature cycle test. Therefore, it was found that the thickness of the metal layer 5 was preferably 1.0 μm or more. In addition, the solder wettability changed depending on the thickness of the barrier metal, and good results were shown when the thickness was 0.1 μm or more. Note that A
Similar properties were obtained as a result of the same examination for any two or more alloys of u, Ag, and Cu.

As a comparative example, when there is no metal layer 5 and no barrier metal (NO. 33), when the barrier metal is Ni (NO. 34), and when there is no barrier metal (NO. 35), Table 2 shows the results of the temperature cycle test and the evaluation of the solder wettability for the three types in the same manner as described above.

[0031]

[Table 2]

From Table 2, it can be seen that NO. In No. 33, the temperature cycle test was unsuitable because the metal layer 5 was not provided.
Solder wettability was good under the influence of the t layer. NO. In No. 34, the temperature cycle test was suitable, indicating that the presence of the barrier metal was effective, but the solder wettability was poor. This indicates that Ni is not suitable as a barrier metal material. In addition, NO. In 35, since the metal layer 5 component and the brazing material layer 7 component are alloyed, the metal layer 5 hardens during the temperature cycle test and becomes unsuitable.
The solder wettability was poor due to the rise in the melting point of the brazing material layer 7 and the non-eutectic point of the composition.

[0033]

According to the present invention, Au, Ag, Cu or any of these is formed on a wiring layer in which an adhesion metal layer, a diffusion prevention layer, and a main conductor layer are sequentially laminated on an optical semiconductor element mounting portion on a diamond substrate. By providing a mounting electrode formed by forming a bonding layer in which a metal layer made of an alloy, a second diffusion prevention layer, and a brazing material layer are sequentially laminated, a large heat is generated between the diamond substrate and the optical semiconductor element. When distortion occurs, the metal layer is easily deformed, absorbs thermal stress due to thermal strain, and it is difficult for the large thermal stress to be transmitted to the optical semiconductor element side, so that the optical semiconductor element is less likely to be damaged. In addition, since the second diffusion prevention layer exists between the metal layer and the brazing material layer, when the brazing material layer is heated and melted to join the optical semiconductor elements, the metal layer component is contained in the brazing material layer. There is no melting and alloying, and no increase in the melting point due to a change in the composition of the brazing material layer. As a result, good bondability can be obtained.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of a wiring layer and a bonding layer of a submount for mounting an optical semiconductor element of the present invention.

FIG. 2 is a partial sectional view of a wiring layer and a bonding layer of a conventional optical semiconductor element mounting submount.

FIG. 3 is a partial sectional view of a wiring layer and a bonding layer of a submount for mounting an optical semiconductor element of the present invention on which a semiconductor laser is mounted.

FIG. 4 is a plan view of an optical semiconductor element mounting submount of the present invention on which a semiconductor laser is mounted.

[Explanation of symbols]

 1: Diamond substrate 2: Adhesive metal layer 3: Diffusion prevention layer 4: Main conductor layer 5: Metal layer 6: Second diffusion prevention layer 7: Brazing material layer 8: Semiconductor laser

Claims (1)

[Claims] 1. A metal layer made of Au, Ag, Cu or an alloy thereof on a wiring layer in which an adhesion metal layer, a diffusion preventing layer and a main conductor layer are sequentially laminated on an optical semiconductor element mounting portion on a diamond substrate. A submount for mounting an optical semiconductor element, comprising: a mounting electrode formed by forming a bonding layer in which a layer, a second diffusion prevention layer, and a brazing material layer are sequentially laminated.