JPS61296780A - Formation of back electrode of light-emitting diode - Google Patents

Abstract

PURPOSE:To increase the area of electrode as well as to enhance the percentage of electrode to the maximum of 50% or thereabout by a method wherein, in the formation of the back electrode of a light-emitting diode, the electrode is formed into a rectangle or a polygon when a metal mask vapor-deposition method is performed. CONSTITUTION:The enlargement of electrode area is achieved by changing the shape of electrode from the conventional round shape to a rectangular shape. A metal mask, whereon a plurality of rectangular holes of 100mum by 200mum are arranged leaving the interval of 50mum when extremely approached, is manufactured, a prescribed electrode material mainly composed of gold is vapor-deposited on a GaAs infrared ray light-emitting diode epitaxial wafer, the electrode material formed into the individually cut pellet form of 400mum by 400mum, and the light-emitting diode pellets are completed. In the case of the used metal mask, the percentage of the area of an electrode 42 to the whole area of the back side of a pellet is 50%.

Description

[Detailed Description of the Invention] [Industrial Field of Application] Light emitting diodes have the advantages of long life, low power consumption, and quick turn off, so in recent years they have been used in various fields, including various displays and home appliances. It is widely used as a light source for remote control devices such as.

The present invention relates to the structure of the above-mentioned light emitting diode, and particularly to a method for forming a back electrode.

[Conventional technology]

Light emitting diodes are generally made of GaP as shown in Figure 2.
, a similar layer on a substrate l such as GaAs or GaAs+-x
Px, GaA1. ->(After epitaxially growing ternary compound semiconductor layers 1 and 2 such as Asx and forming a PN junction, predetermined electrodes are formed on the front and back surfaces of a wafer, and then separating into pellets of predetermined dimensions. Furthermore, in order to reduce the absorption of light generated by the PN junction on the back surface of the back electrode 4 on the die bonding side, the area of the back electrode 4 is made small, and is generally 50 to 100 μm.
A method has been adopted in which a plurality of circular minute dot electrodes of φ are deposited. Note that 5 is a surface electrode.

[Problem that the invention seeks to solve]

The above-mentioned circular microelectrodes are formed by etching a thin metal plate made of molybdenum or the like, and then using a metal mask for vapor deposition, which has many holes in the shape of the necessary electrodes, to closely cover the back surface of the wafer. This is generally done by vapor depositing a predetermined electrode material directly onto the electrode. However, the metal mask deposition method has limitations in terms of metal mask manufacturing when it is desired to increase the diameter of the circular electrode and increase the number of electrodes to increase the area of the line electrode.

This is because, due to 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 commonly used plate thickness of 25 to 30 .mu.m. For example, in the case of a 4002 m x 400 μm pellet, in the case of a circular dot electrode with a diameter of 50 to 100 μm, the ratio of the electrode area to the total area of the back surface is at most 30%.
limited to. Therefore, light emitting diodes can be used as a source for remote control, especially in the large current range (more than xoomA).
In the case of GaAs-based infrared light emitting diodes, which are often used in , the back electrode area is small, leading to an increase in forward voltage at large currents. As a result, in constant-voltage light-emitting diodes that use dry batteries as a power source, the back electrode has to be made smaller, and even though the output has been increased, the effect of reducing the current flowing due to the increase in forward voltage at large currents is significant. However, this caused a deterioration in 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.

In addition, in order to eliminate the above-mentioned problems, the photoresist method is used to form a mesh-like electrode structure 4 as shown in Fig. 3.
1 can be adopted to increase the electrode area. However, compared to the metal mask method, the photoresist method not only requires a longer process and increases the number of sheaths, but also has the problem that the effective electrode area partially varies due to unevenness caused by etching. Ta.

Means for Solving Problem C] In order to eliminate the drawbacks of the conventional back electrode of a light emitting diode, the present invention changes the shape of the electrode from the conventional circular shape to a rectangular or polygonal shape in the metal mask evaporation method. The present invention provides a method in which the area of the back electrode can be selected from a wide range without reducing the yield depending on the purpose of use of the light emitting diode even in the metal mask evaporation method.

〔Example〕

Examples As mentioned above, the mask used in the metal mask evaporation method is mainly made of molybdenum and generally has a thickness of 25 to 30 μm. In this case, the closest distance between the holes should be 50 μm or less. That is difficult.

Therefore, we attempted to increase the stain electrode area by changing the electrode shape from the conventional circular shape to a rectangular shape. In the non-implemented example, Fig. 1 (a
), a metal mask in which a plurality of 100 μm x 200 μm strip-shaped rectangular holes are arranged at intervals of 50 μm closest to each other is manufactured, and predetermined electrodes mainly made of gold are applied to the GaAs-based infrared light emitting diode epitaxial wafer. The material was deposited. Thereafter, the pellets were cut into pieces of 400 μm×400 μm to complete a light emitting diode pellet according to the present invention.

In the case of the metal mask used in this example, the area of the electrode 42 accounts for 50% of the total area of the back surface of the pellet.

Example Z This example is an example in which the shape of the back electrode is a regular hexagon. As shown in Figure 1(b), each side is 100μ
A metal mask in which regular hexagonal holes of m in size are arranged in a comb pattern in three directions at intervals of 50 μm was fabricated, and predetermined electrodes mainly made of gold were placed on a GaAs-based infrared light emitting diode epitaxial wafer as in Example 1. The material was deposited. Thereafter, it was cut into 400 μm×400 μm pellets. In the case of the metal mask used in this example, the ratio Pi of the area of the electrode 42 to the total area of the back surface of the pellet was 50.
It is 6%.

[Effects of the Invention] As explained above, when forming the east electrode of a light emitting diode, it is possible to increase the stain pole area by making the electrode shape rectangular or polygonal even in the metal mask evaporation method. , 400μ by changing the side dimensions
In the case of m×400 μm pellets, the electrode ratio can be increased up to about 50%. According to the present invention, a light emitting diode with an increased back electrode area and a low forward voltage even when a large current is applied can be manufactured without using the photoetching method. The voltage value is G a A, which was a conventional product with a circular electrode and showed L70V at forward current Ir = 400 mA.
s The infrared light emitting diode in both Examples 1 and 2 of the present invention was lowered to L60V, and the mesh-like t
It became equivalent to the value of & (electrode ratio 50%).

Furthermore, since the metal mask evaporation method is used, it goes without saying that the number of man-hours is reduced and the yield is improved compared to the photoetching method.

[Brief explanation of drawings]

1(a) and Φ) show a plan 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.
The figure shows a plan view of a back electrode according to the prior art, and (a) is a nine-circular dot electrode formed by a metal mask method, Φ).
shows a mesh electrode formed by photoetching. 4.41.42... Back electrode, 5...
Back electrode. Agent Patent Attorney Uchihara 2 ・〜ゝku

Claims (1)

[Claims] In the electrode of a light-emitting diode, especially the back electrode on the side to which die bonding is performed, in the so-called metal mask evaporation method, in which the electrode material is vapor deposited by closely contacting the metal mask directly to the substrate on which the electrode is to be formed, the holes in the metal mask are A method for forming a backside electrode of a light emitting diode, characterized in that the area of the electrode portion occupies 30% or more of the total area of the backside by making the shape rectangular or polygonal.