JPS61296779A - Formation of back electrode of light emitting diode - Google Patents

Abstract

PURPOSE:To obtain excellent yield of production of the title electrode by a method wherein, on the stripe-like electrode formed by vapor-deposition, another stripe-like electrode is formed again placing an angle for the stripe of the electrode using a metal mask for formation of the stripe-like electrode, and a reticulate electrode is formed without using a photoetching method. CONSTITUTION:A metal mask, whereon stripe-formed holes of 50mum wide and 3cm long are formed in line at the pitch of 100mum, is manufactured and the prescribed electrode material mainly composed of gold is vapor-deposited on a GaAs infrared ray light-emitting diode epitaxial wafer. Then, either of said wafer and metal mask is rotated at an angle of 90 deg., and the same vapor- deposition method is performed again. Subsequently, a sintering is conducted on the above-mentioned material at the prescribed temperature for the prescribed period of time, and it in formed into the indivisually cut pellets of 400mumX400mum, and the manufacture of light-emitting diode pellet is completed. As a result, the pellet having the total electrode area percentage for the pellet back side of 75% can be formed without using a photoetching method.

Description

[Detailed Description of the Invention] [Industrial Field of Application] Light emitting diodes have the advantages of long life, low power consumption, and high speed, so they have been used in various fields in recent years, and have been used in various displays, home appliances, etc. It is also widely used as a light source for remote control devices. The present invention relates to the structure of the light emitting diode, and 51% relates to a method for forming a back electrode.

[Conventional technology]

Light emitting diodes generally have a substrate 1 made of GaP, GaAs, etc.
Homogeneous layer or GaAsx-xPx, GaAlt-x on top
After forming predetermined electrodes on the front surface 4 and the back surface of a wafer in which a ternary compound semiconductor layer 2 such as Asx is epitaxially grown to form a PN junction, the wafer is separated into pellets of predetermined dimensions. (Figure 2) In addition, the back electrode 3 on the side to be bonded is designed to reduce the area of the back electrode in order to reduce the absorption of light generated by the PN junction on the back surface, and generally has a diameter of 50 to 100 BTrLφ. A method has been adopted in which a plurality of circular minute dot electrodes are deposited.

(Fig. 3 (a)) [Problem to be solved by the invention] The formation of the circular microelectrode described above involves etching a thin metal plate made of molybdenum or the like to provide a large number of holes in the required electrode shape. Generally, the back surface of the wafer is tightly covered with a metal mask for vapor deposition, and a predetermined electrode material is directly vapor-deposited thereon. However, the metal mask vapor deposition method has limitations in terms of metal mask manufacturing when it is desired to increase the total electrode area by increasing the diameter of the circular electrode and the number of electrodes.

That is, in view of the etching accuracy of the metal mask and the mechanical strength of the mask itself, the closest distance between adjacent holes is limited to 50 .mu.m for a plate thickness of 25 to 30 .mu.m which is normally used. In addition, dot electrodes have the disadvantage that all the back dot electrodes on each node may not come into uniform contact with the mounting material (mainly silver paste), which is a problem in light emitting diodes. However, it is especially suitable for use as a remote control source in the large current range (100
GaAs-based infrared light emitting diodes, which are often used in
C. Current concentration may occur with the mounting material, and contact resistance may be added in series, leading to a large increase in forward voltage in one current. Therefore, in a constant-voltage light emitting diode that uses a dry battery as a power source, although the output has been increased by making the back electrode smaller, the effect of reducing the conducting current due to the increase in forward voltage at large currents is large. This caused deterioration of the linearity of the output as a whole. Therefore, it was necessary to find the optimal value by considering the balance between electrode area and output.

Therefore, in order to improve the two problems of difficulty due to the increase in the number of electrode gate structures and poor contact with the mounting material, the mesh electrode shown in FIG. 3(b) has been adopted.

This manufacturing method also uses photoetching on the back electrode side.
It is formed by partially removing an electrode of an arbitrary area. However, since the mesh electrode is formed by a photoetching method, it requires an additional process compared to the metal mask method, and also requires additional steps due to photoresist coating.
- Breakage of the substrate and uneven etching of the back electrode, which is mainly made of gold, which lowers the yield rate, remain unavoidable drawbacks.

[Means for solving problems]

The present invention eliminates the drawbacks of the conventional method by forming a back electrode of a light emitting diode (in order to form a mesh electrode, a metal mask for forming a stripe electrode is used, and the stripe electrode is formed by vapor deposition on top of the electrode). In this method, striped electrodes are formed again by vapor deposition at an angle to the stripes of the electrodes, thereby forming a mesh electrode without using a photo-etching method.

〔Example〕

Next, the present invention will be explained based on examples.

As mentioned above, the mask used in the metal mask method is mainly made of molybdenum and has a plate thickness of 25 to 30 μm. In this case, it is difficult to reduce the closest distance between the holes to 50 μm or less. It is. Therefore, in this embodiment, the width is 50μ7.
FIX length 3cIrL striped hole 100μm
A metal mask arranged at pitches is manufactured and a predetermined electrode material mainly composed of gold is vapor-deposited onto a Gaps-based infrared light emitting diode epitaxial wafer. Further, either the wafer or the metal mask is rotated 90',
The same vapor deposition is performed again. Thereafter, sintering is performed at a predetermined temperature and time to form individual pellets of 400 μm×400 μm, thereby completing the light emitting diode pellets according to the present invention.

As a result, an electrode having a ratio of the total electrode area to the back surface of the pellet of 75% can be formed without using the photoetching method.

〔Effect of the invention〕

As explained above, for backside polarization, by depositing striped electrodes twice so that they intersect with each other, it is possible to form a net-like electrode without using the photoetching method, which is a process called double deposition. Nevertheless, the second vapor deposition only requires rotating the metal mask or wafer by about 90 degrees, and the yield is good, and the yield can be maintained at the same level as that of conventional dot electrodes. Furthermore, since the dot electrodes are composed of multiple microelectrodes, some of the electrodes may have poor contact with the mounting material, which directly affects the forward voltage of the light emitting diode. However, with this mesh electrode 2, even if there are parts that have poor contact with the silver paste of the mounting material, the entire electrode is connected, so contact is made with the entire back electrode, and the light emitting diode Needless to say, no current concentration occurs when the current is applied, and the linearity of the light emission output is not impaired. In addition, in this example, stripes with a width of 50 μm were provided at a pitch of 100 μm, but the width and pitch could be adjusted within the limit that the closest distance between each stripe was 50 μm.
By changing the width and pitch, it is also possible to arbitrarily change the ratio of the electrode area to the back surface area of one pellet.

[Brief explanation of drawings]

FIG. 1 shows a top view of the back electrode on the die bonding side of a light emitting diode according to the present invention, FIG. 2 is a sectional view showing the most general structure of a light emitting diode, and FIG. 3 is a top view of a back electrode according to the prior art. The figures show (a) a circular dot electrode formed by a metal mask method, and (b) a mesh electrode formed by a photoetching method. Sensei /I! I (cL) (6-) Kaya 3 Figure

Claims (1)

[Claims] In the back electrode of a light emitting diode, in particular, a striped electrode is formed by vapor deposition in a mesh electrode formation method, and then
A method for forming a back electrode, which comprises forming a stripe-like electrode again by vapor deposition at an angle so as to intersect with the electrode to form a mesh-like electrode.