JPH03238888A - Electrode structure of semiconductor laser - Google Patents

Abstract

PURPOSE:To make it possible to secure a necessary electrode strength while keeping an electrode area small sufficiently, by a method wherein a part of a metal film forming a bonding pad is shaped in indentation and a distance between the fore end of a projecting part of the film and a contact part of a bonding wire with the bonding pad is specified. CONSTITUTION:The area of a metal film 21 being smaller than that of an insulating film 3, a part of the metal film 21 projecting from a stripe contact part 12 thereof toward the outer periphery of a chip 1 and forming a bonding pad 22 reaches the outer periphery 222 of the chip and/or the part of the metal film 21 forming the bonding pad 22 is shaped in indentation, a distance between the fore end of the projecting part and a contact part of a bonding wire 4 with the bonding pad 22 being set to be 50mum or above. By this method, a necessary electrode strength can be secured while the area of the bonding pad 22 being kept small.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to the structure of a semiconductor laser.

[Conventional technology]

It has been a long time since semiconductor lasers have been put into practical use as light sources for optical fiber communications. In particular, as a light source for trunk optical fiber communications, distributed feedback semiconductor lasers that oscillate in a single axis mode have been put into practical use in recent years, and modulation speeds range from the IGbps band to 2Gbps.
I'm trying to move up to the bps band.

Various structural improvements are adopted in semiconductor lasers used for such applications in order to improve response speed. The most common method is to reduce the parasitic capacitance that constitutes a high-frequency current circuit that does not pass through the active layer, and is a structure in which both sides of the active layer stripe are buried with high-resistance insulating layers; A structure in which the reverse bias layer of a normal buried heterostructure is removed leaving only the vicinity of the active layer stripe; a structure that uses a stripe contact structure and further limits the area of the metal film to be smaller than that of the insulating film. This is a typical example.

FIG. 3 shows a schematic diagram of a semiconductor laser chip 1 employing one of the above-described structures. The buried heterostructure reverse bias layers (not shown in the figure) on both sides of the active layer 11 are separated by structures 13 and 14, and the metal film 21 forming the stripe contact 12 is basically It is confined to the upper part of the mesa containing the active layer 11, from which a portion extends outward to form a bonding pad 22 in the flat part.

[Problem to be solved by the invention]

The above-described conventional semiconductor laser in which the electrode area is limited has the following drawbacks.

The parasitic capacitance of the semiconductor laser chip decreases as the area of the metal film on the insulating film decreases. Reducing the area of the metal film on the mesa including the active layer is limited by the process of forming it, and the minimum size required for the bonding pad is relatively large, approximately 100 mm. The reduction in the area of the entire R film is mainly achieved by narrowing the bonding pad.As a result, the bonding pad is located on the chip flat part 15 as shown in FIG.
It has a rectangular or semicircular shape with one side touching the groove 14. By bonding the wire to this,
The outer periphery of the bonding pad tends to lift up, and even during bond pull tests, the electrode often peels off from the outer periphery of the bonding pad. This tendency becomes even more pronounced when a bonding method such as US-NTC, which is particularly suitable for automation, is used. To avoid this phenomenon,
Experiments have revealed that the distance from the contact area between the bonding wire and the bonding pad to the outer periphery of the bonding pad must be 50 μm or more.

The present invention provides a method for reducing the area of the bonding pad by 50 mm from the contact area between the bonding pad and the bonding wire, that is, from the area that is subjected to stress during bonding, without increasing the area of the bonding pad.
The present invention provides an electrode structure that allows a distance of .mu.m or more.

[Means to solve the problem]

The electrode structure of the semiconductor laser of the present invention is a semiconductor laser chip having a stripe contact structure including an insulating film in contact with a semiconductor crystal and a metal film in contact with the insulating film.
The area of the metal film is smaller than the area of the insulating film, and a part of the metal film that protrudes from the stripe contact portion of the metal film toward the chip outer periphery to form a bonding pad reaches the chip outer periphery, and/or A part of the metal film forming the bonding pad has an uneven shape, and the distance between the tip of the protrusion and the contact portion between the bonding wire and the bonding pad is 50 μm or more.

[Example 1] Next, the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of a semiconductor laser which is an embodiment of the present invention. A portion of the bonding pad 22 extends outward,
It has reached the chip outer periphery 222. In the figure, the size of the semiconductor laser chip 1 is approximately 300 μm square, which is a first-class distributed feedback semiconductor laser, and the outermost edge 222 of the bonding pad 22 on the flat part 15 is the contact area with the bonding wire 4. It is clear that the distance from 223 is 50 μm or more. As a similar embodiment, there is also a structure shown in FIG. 4, in which the bonding pad 22 is partially
22 has reached the outer periphery of the chip.

[Example 2] Next, other embodiments of the present invention will be described.

FIG. 2 is a schematic diagram of a semiconductor laser according to another embodiment of the present invention. The bonding pad 22 has an uneven shape, and the tip 224 of the convex portion is at least 50 μm away from the contact portion 223 between the bonding wire 4 and the bonding pad 22, and the area of the bonding pad 22 is as shown in FIG. It can be kept as small as the conventional example. In this embodiment, since the metal film 21 does not cover the outer periphery of the chip, there is an advantage that scribing is easy when forming a chip from a cleaved bar. [Effects of the Invention] As described above, the present invention has the advantage that scribing is easy when forming a chip from a cleaved bar. In a semiconductor laser chip in which the electrode area is limited for the purpose of increasing speed, the present invention has the effect of ensuring the necessary electrode strength while keeping the electrode area sufficiently small.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a semiconductor laser which is an embodiment of the present invention, FIG. 2 is a schematic diagram of a semiconductor laser which is another embodiment of the invention, and FIG. 3 is a schematic diagram of a conventional semiconductor laser. FIG. 4 is a schematic diagram of a semiconductor radar according to another embodiment of the present invention. l... Semiconductor laser chip, 11...
Active layer, 21... Metal film, 22... Bonding pad, 3... Insulating film, 4...
...Bonding wire.

Claims (1)

[Claims] In a semiconductor laser chip having a stripe contact structure including an insulating film in contact with a semiconductor crystal and a metal film in contact with the insulating film, the area of the metal film is smaller than the area of the insulating film, and the area from the stripe contact portion of the metal film to the chip outer periphery is A part of the metal film that protrudes toward the surface and forms a bonding pad reaches the outer periphery of the chip, and/or a part of the metal film that forms the bonding pad has an uneven shape, and the protrusion is uneven. An electrode structure for a semiconductor laser, characterized in that a distance between a tip and a contact portion between a bonding wire and the bonding pad is 50 μm or more.