JP3346971B2 - Submount for optical semiconductor device and method of mounting the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a submount for an optical semiconductor device and a method of mounting the same, and in particular, AuSn on both the first surface on the optical semiconductor device chip mounting side and the second surface on the metal radiator die bond side. The present invention relates to a submount for an optical semiconductor element having a solder layer and a method of mounting the same, for example, used for a semiconductor laser device or the like.

[0002]

2. Description of the Related Art Optical semiconductor devices, particularly semiconductor lasers, have been put into practical use in the fields of optical information processing and optical communication, but the reliability of the devices is extremely important. In such a semiconductor laser, a driving current is used in a range of several tens mA to several hundred mA. However, since a large amount of heat is generated, a metal radiator is generally used as a heat sink. Furthermore, in order to prevent a decrease in reliability due to the influence of stress generated due to a difference in thermal expansion coefficient between the metal radiator and the semiconductor laser element substrate material,
A method is used in which a submount made of a material having a thermal expansion coefficient close to that of a semiconductor laser substrate material is arranged on a heat sink, and a semiconductor laser chip is die-bonded thereon via a solder material.

As described above, a method for mounting the optical semiconductor element, the submount, and the metal radiator is to mount the submount on the metal radiator and then mount the optical semiconductor element on the submount. In general, a gold wire is formed on the upper surface of the element and the surface of the submount in order to allow a current to flow through the optical semiconductor element.

As one example of the structure of a conventional submount for a semiconductor laser, there is a structure in which a Ti / Pt / solder layer is provided on both surfaces of a Si semiconductor substrate as disclosed in Japanese Patent Application Laid-Open No. 1-138777. The Ti / Pt layer functions as a barrier metal layer.

However, in the above structure, since the entire upper surface of the submount is a solder layer, a gold wire cannot be bonded to the upper surface of the submount. If the solder layer is removed, a Pt layer is formed. Gold wire cannot be bonded.

On the other hand, another example of the structure of a conventional submount for a semiconductor laser is disclosed in Japanese Unexamined Patent Publication No. 2-128486. As shown in FIG. A structure in which a Pt layer 3 / Au layer 4 / AuSn (gold tin) eutectic solder layer 5a is provided is known. In this case, since the AuSn eutectic solder layer 5a has higher reliability than a normal Sn solder layer, it is suitable for mounting an optical semiconductor element chip.

The above structure employs AuSn on both sides of the submount.
Since the eutectic solder layer 5a is formed, the position adjustment between the submount and the optical semiconductor element is easy. However, since the melting points of the solder layers 5a and 5a on both surfaces of the submount are the same and the solder layers 5a and 5a on both surfaces of the submount are simultaneously melted when the submount and the optical semiconductor element are mounted successively, When one of the optical semiconductor elements is moved, the other moves. Further, since the solder layers 5a and 5a are provided on the entire surface of both sides of the submount, it is impossible to bond a gold wire to the submount.

[0008]

As described above, the conventional submount for an optical semiconductor device having the AuSn eutectic solder layers having the same melting point on both surfaces of the submount, the submount and the optical semiconductor device are mounted successively. At this time, there is a problem that when one is moved, the other is moved, and that a gold wire cannot be bonded to the submount.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has improved reliability in mounting a submount for an optical semiconductor element and mounting the optical semiconductor element easily. It is an object of the present invention to provide a mounting method of a submount for an optical semiconductor device which can be realized.

[0010]

A submount for an optical semiconductor device according to the present invention comprises a submount substrate for an optical semiconductor device mount made of an electrically insulating material having high thermal conductivity, and an optical semiconductor device of the submount substrate. Both the first surface on which the chip is mounted and the second surface on which the die is bonded to the metal radiator are made of Ti or Cr on the first layer formed in order from the surface of the submount substrate. An adhesive layer, a diffusion barrier layer made of Pt as a second layer, a third Au layer and a fourth AuSn solder layer,
A third Au layer formed on the first surface side and a fourth Au layer;
The content of Sn with respect to the total amount of Au in the AuSn solder layer of the layer is Sn with respect to the total amount of Au of the third Au layer and the fourth AuSn solder layer formed on the second surface side.
Third layer A of rather greater than the content, and the second surface side
with respect to the total amount of Au in the u layer and the fourth AuSn solder layer.
Wherein the weight percentage of Sn is not more than 20% .

The method of mounting a submount for an optical semiconductor device according to the present invention includes a step of die-bonding a submount substrate of the submount for an optical semiconductor device according to the present invention to a metal radiator; The temperature of the third surface of the first surface side of the
Melting the Au layer and the fourth AuSn solder layer, lowering the temperature of the submount substrate, and die-bonding the optical semiconductor element chip to a chip mounting region of the submount substrate. It is characterized by the following.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a cross-sectional structure according to a first embodiment of a submount for an optical semiconductor device of the present invention, and FIG. 2 shows an example of the mounted state.

The submount 1 of the present embodiment uses a submount substrate having a thickness of, for example, 300 μm and made of, for example, aluminum nitride; AlN, which is an electrically insulating material having high thermal conductivity.

The optical semiconductor element 6 mounted on the submount 1 is, for example, a semiconductor laser chip of 300 μm × 100 μm □, and the surface on the mount side (lower side in the drawing) is covered with an Au layer.

The first surface of the sub-mount 1 on which the semiconductor laser chip 6 is mounted and the second surface of the sub-mount 1 on which the semiconductor laser chip 6 is die-bonded to the metal radiator 7 are arranged in order from the surface of the sub-mount substrate. Ti (or C
r), a diffusion barrier layer made of Pt as a second layer, an Au layer as a third layer, and an AuSn solder layer as a fourth layer.

That is, as shown in FIG.
Side of the metal radiator (the lower side of the submount 1 in the drawing)
A Ti layer 2a having a thickness of 0.1 μm, a Pt layer 3a having a thickness of 0.1 μm, and an Au layer 4a having a thickness of 1 μm are formed in this order from the submount surface.
Au (80 wt%) Sn (20 wt%) layer 5 a
Are formed on the entire surface.

On the semiconductor laser chip 6 side of the submount 1 (the upper surface side of the submount 1 in the drawing), a Ti layer (or Cr layer) 2b, 0 .1 μm thick Pt layer 3b,
An Au layer 4b having a thickness of 0.5 μm is formed, and a region (300) for mounting the semiconductor laser chip 6 is formed.
5 μm thick Au (77 wt%) Sn (2 μm □).
3 wt%) layer 5b is formed. The Au layer 4b and the AuSn (23 wt%) layer 5b are formed in such an amount that almost AuSn (20 wt%) is formed when the Au layer 4b and the AuSn (23 wt%) layer are heated and reacted.

The mount of the semiconductor laser chip 6 is usually made of Au (80 wt%) Sn (20 wt%) having a melting point of 278 ° C.
%), An Au layer 4a and an Au layer 4a are provided on the surface of the submount 1 on the side of the metal radiator 7 in this example.
(80 wt%) Sn (20 wt%) layer 5 a is formed, and A
u layer 4b and Au (77 wt%) Sn (23 wt%) layer 5
The eutectic solder b is formed.

Next, an example of an assembling process of a semiconductor laser using the submount for an optical semiconductor device will be described with reference to a sectional view shown in FIG. 2 and a phase diagram of AuSn shown in FIG.

First, the AuSn on the surface of the submount 1 on the side of the metal radiator 7 on which the layers are stacked as described above.
(20 wt%) The solder layer 5 a is soldered to the metal heat sink 7. At this time, the AuSn (20 wt%) layer 5a and the Au layer 4a react with each other and become Au-rich after a certain period of time, and the submount 1 and the metal heat sink 7 are firmly bonded.

That is, the melting point of the AuSn (20 wt%) layer 5a on the metal radiator side surface of the submount 1 is 278 ° C.
AuSn on the surface of the submount 1 on the side of the semiconductor laser chip
The melting point of the (23 wt%) layer 5 b is about 300 ° C. Therefore, when mounting the metal radiator 7 and the submount 1, the AuSn on the metal radiator side surface of the submount 1 is mounted.
(20 wt%) layer 5a is melted at 278 ° C., but AuSn (2
(3 wt%) The layer 5b does not melt.

At this time, since the submount moves during the time when the AuSn (20 wt%) layer 5a and the Au layer 4a on the surface of the submount 1 on the side of the metal heat radiator react with each other, the submount can be easily positioned.

The AuSn (20 wt%) layer 5a
When the reaction progresses to the Au layer 4a for a certain time, the state becomes Au-rich, and as can be seen from FIG. 3, the melting point sharply rises (in the direction B in FIG. 3) and the metal radiator 7 and the submount 1 is fixed.

Next, the temperature of the support for fixing the metal heat sink 7 on which the submount 1 is mounted is lowered to about 280.degree. Then, the semiconductor laser chip 6 is mounted on the mounter.
While holding the semiconductor laser chip 6, the mounter is operated to hold the semiconductor laser chip 6 near the submount 1.
A of the surface of the submount 1 fixed on the metal heat sink 7
By blowing heated nitrogen gas on the uSn layer 5b, the AuSn (23 wt%) layer 5b is melted at 300 ° C.
When the temperature is temporarily increased (heated) to the extent, AuS
The n (23 wt%) layer 5b reacts with the Au layer 4b to lower the melting point.

At this time, when the reaction of both proceeds, AuSn
(23 wt%) The reaction proceeds from the layer 5b to the Au layer 4b,
u become rich. Even if the heated nitrogen gas is stopped, A
Since the uSn (23 wt%) layer 5b is in a molten state, the semiconductor laser chip 6 sucked and held by the mounter can be easily positioned.

The AuSn (23 wt%) layer 5b
And the Au layer 4b react with each other to lower the melting point (in the direction A in FIG. 3) to form an Au (.about.80 wt%) Sn layer having a melting point of 278.degree.
Semiconductor laser chip 6 in the state of Sn (20 wt%) eutectic
Can be held for a time sufficient for the positioning of.

Then, the semiconductor laser chip 6 is mounted on a desired position on the submount 1 to fix the semiconductor laser chip 6, and the AuSn layer is rapidly cooled by blowing a cooling nitrogen gas to be hardened. The submount 1 is fixed, and the mounting is completed.

At this time, the positioning of the metal radiator 7 and the submount and the semiconductor laser chip 6 is extremely easy, and the Au between the metal radiator 7 and the submount is very easy.
Sn becomes Au-rich and its melting point decreases (see FIG. 3).
Since the melting point rises very rapidly (in the direction B in FIG. 3) as compared with the case of the middle and the direction A, there is no movement when the semiconductor laser chip 6 and the submount 1 are mounted. As a result, the problem that one moves when the other moves while maintaining the ease of position adjustment can be overcome.

Also, as shown in FIG. 1, by forming the AuSn solder layer 5b only on the mounting area of the semiconductor laser chip 6, the A
The rise of the uSn solder is prevented, and the reliability of the element is improved. In addition, since the Au layer is exposed on the surface of the submount, bonding using an Au wire or the like is easy.

In a series of operations for mounting the semiconductor laser chip 6 on the submount 1 as described above, the submount 1 and the metal heat sink 7 are Au-rich AuS
n and does not move because the melting point is rapidly rising. For this reason, the operation of mounting the semiconductor laser chip 6 on the submount 1 has excellent positioning accuracy and can be performed extremely easily.

Further, by forming AuSn only in the mounting region of the semiconductor laser chip 6, not only the reliability of the element is improved, but also a gold wire can be easily bonded to the Au layer 4b.

That is, according to the above-described embodiment, the Ti / Pt / Au /
AuSn (20 wt%) [melting point 278 ° C.] is formed, and Ti /
Pt / Au / AuSn (23 wt%) [Melting point 300 ° C]
Are formed, Au / AuSn reacts when the metal heat radiator is mounted, resulting in Au-rich and a sharp rise in melting point.

This makes it possible to accurately adjust the mounting position without moving the submount when mounting the optical semiconductor element, and to temporarily raise the temperature to Au / Au.
The melting point is lowered by reacting Sn (23 wt%) [melting point 27
8 ° C.], the AuSn can be held in a molten state for a long time, the mounting position of the optical semiconductor element can be adjusted, and the optical semiconductor element can be mounted at a desired place with high accuracy, and the efficiency of the mounting operation can be increased.

Further, since AuSn is formed only in the mounting region of the optical semiconductor element, the Au
The swelling of the Sn solder is prevented, and the element reliability is improved. Further, since the Au layer is exposed on the surface of the submount, there is also an effect that bonding by an Au wire or the like is easy.

In the above embodiment, AlN is used as the material of the submount 1. However, a material having good thermal conductivity, such as SiC, Si, or diamond, may be used. Further, as for the solder, a material that easily reacts with Au (AuGe, AuSi, InPb, or the like) can be used.

In the above embodiment, AuSn (2
Although 0% by weight and AuSn (23% by weight) have been described as examples, the amount of Sn in the AuSn solder is not limited to this. That is, in the submount and the mounting method of the present invention, the third Au layer 4b and the fourth AuS layer formed on the first surface side of the submount 1 are formed.
The content of Sn with respect to the total amount of Au in the n solder layer 5b is different from the total amount of Au in the third Au layer 4a and the fourth AuSn solder layer 5a formed on the second surface.
Greater than the content of

In this case, the third surface formed on the first surface side
Au layer 4b as a fourth layer and AuSn solder layer 5b as a fourth layer
Is preferably 15% or more and 40% or less with respect to the total amount of Au. It is preferable that the weight percentage of Sn relative to the total amount of Au in the third Au layer 4a and the fourth AuSn solder layer 5a on the second surface side is 20% or less. The third Au layer and the fourth AuSn solder layer may be interchanged.

[0038]

As described above, according to the present invention, the submount for an optical semiconductor device with improved reliability and the mounting position can be easily adjusted, and the mounting work of the submount and the optical semiconductor device can be made more efficient. A method for mounting a submount for an optical semiconductor element can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a submount for an optical semiconductor device according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing an example of a mounted state of the optical semiconductor element submount of FIG. 1;

FIG. 3 is a phase diagram of AuSn.

FIG. 4 is a sectional view showing an example of the structure of a conventional optical semiconductor element submount.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Submount base | substrate, 2a, 2b ... Ti layer, 3a, 3b ... Pt layer, 4a, 4b ... Au layer, 5a ... AuSn (20Wt%) layer, 5a ... AuSn (23Wt%) layer, 6 ... Semiconductor laser chip , 7 ... Metal radiator plate.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-190973 (JP, A) JP-A-6-326210 (JP, A) JP-A-5-48213 (JP, A) 145181 (JP, A) JP-A-2-128486 (JP, A) JP-A-6-21577 (JP, A) JP-A-4-25088 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 5/00-5/50 H01L 23/373

Claims (5)

(57) [Claims] 1. A submount base for mounting an optical semiconductor element made of a high thermal conductive electrically insulating material, a first surface of the submount base on which an optical semiconductor element chip is mounted, and a metal radiator. A bonding layer made of Ti or Cr as a first layer, a diffusion barrier layer made of Pt as a second layer, and a second layer formed in order from the surface of the submount substrate. Third
A third Au layer formed on the first surface side and a fourth Au layer and a fourth AuSn solder layer.
The content of Sn with respect to the total amount of Au in the AuSn solder layer of the layer is Sn with respect to the total amount of Au of the third Au layer and the fourth AuSn solder layer formed on the second surface side.
Third layer A of rather greater than the content, and the second surface side
with respect to the total amount of Au in the u layer and the fourth AuSn solder layer.
Wherein the weight percentage of Sn is 20% or less . 2. The optical semiconductor element submount according to claim 1, wherein the third Au layer and the fourth AuSn solder layer are interchanged. For submount. 3. The submount for an optical semiconductor device according to claim 1, wherein the weight percentage of Sn relative to the total amount of Au in the third Au layer and the fourth AuSn solder layer on the first surface side is A submount for an optical semiconductor device, wherein the submount is 15% or more and 40% or less. 4. The optical semiconductor device submount according to claim 1, wherein the fourth AuSn solder layer on the first surface is formed in a region where a chip of the optical semiconductor device is mounted. Characteristic submount for optical semiconductor devices. 5. A step of die-bonding the optical semiconductor element submount base according to claim 1 to a metal radiator, and thereafter, temporarily increasing the temperature of the submount base to reduce the temperature of the submount base. After melting the third Au layer and the fourth AuSn solder layer on the first surface side, the temperature of the submount substrate is lowered to move the chip of the optical semiconductor element to the chip mounting area of the submount substrate. And a step of die bonding.