JP4098561B2 - Electrode structure and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrode structure suitable for, for example, an LED (light emitting diode) and a manufacturing method thereof.
[0002]
[Prior art]
Conventionally, as an electrode structure of a compound semiconductor element, there is one disclosed in Japanese Patent Laid-Open No. 62-162327. The electrode structure disclosed in Japanese Patent Laid-Open No. 62-162327 has a Ti layer formed on a semiconductor crystal and an alloy layer (hereinafter referred to as “Au-based alloy layer”) formed on the Ti layer and mainly composed of Au. .).
[0003]
The electrode structure is manufactured as follows.
[0004]
First, a Ti layer and an Au-based alloy layer are sequentially stacked on the surface of the semiconductor crystal.
[0005]
Next, an Au-based alloy layer having a predetermined electrode pattern is obtained by performing photolithography and etching the Au-based alloy layer using a predetermined etchant. At this time, since there is a Ti layer under the Au-based alloy layer, the surface of the semiconductor crystal is not roughened by the etchant.
[0006]
Next, the Ti layer is etched using another etchant to expose the surface of the semiconductor crystal outside the electrode pattern of the Au-based alloy layer. Thereafter, heat treatment is performed to alloy the Au-based alloy layer and the semiconductor crystal.
[0007]
In the manufacturing method of such an electrode structure, when the Au-based alloy layer is etched, the thickness of the Ti layer is set to 10 nm or more in order to prevent the surface of the semiconductor crystal from being roughened by the etchant.
[0008]
However, as shown in FIG. 6, when the thickness of the Ti layer is increased, the voltage between the electrodes increases. That is, the resistance value between the electrodes increases. Therefore, in order to prevent the resistance value between the electrodes from increasing, the thickness of the Ti layer is set to 30 nm or less.
[0009]
As described above, the thickness of the Ti layer is optimally set to 10 nm to 30 nm from the viewpoint of imparting etchant resistance to the Ti layer and preventing an increase in resistance between the electrodes.
[0010]
[Problems to be solved by the invention]
FIG. 7 shows the state of alloying of the Au-based alloy layer and the semiconductor crystal 110 observed from the semiconductor crystal 110 side with an infrared microscope when the thickness of the Ti layer laminated on the surface of the semiconductor crystal 110 is set to 20 nm. Is shown schematically.
[0011]
As shown in FIG. 7, the portion A2 where the Au-based alloy layer and the semiconductor crystal 110 are alloyed does not reflect light and thus appears black. The area of the alloyed portion A2 corresponds to 90% of the area of the electrode formation region P2 where the Ti layer is to be formed on the surface of the semiconductor crystal 110. Since the area of the alloyed portion A2 is large, when a semiconductor light emitting device is formed using the semiconductor crystal 110, the light emitted from the semiconductor light emitting device is absorbed by the portion A2, and the light extraction efficiency of the semiconductor light emitting device is reduced. Problem arises.
[0012]
Accordingly, an object of the present invention is to provide an electrode structure that can prevent a decrease in light extraction efficiency of a semiconductor light emitting device and a method for manufacturing the same.
[0013]
[Means for Solving the Problems]
In order to solve the above problems, an electrode structure of the present invention is an electrode structure used for an AlGaAs-based semiconductor light-emitting device, wherein a Ti layer and a main electrode layer are formed on an electrode formation region on the surface of a semiconductor crystal made of AlGaAs. In order, the main electrode layer and the semiconductor crystal are alloyed via the Ti layer.
[0014]
The area of the alloyed portion is 20% to 50% of the area of the electrode formation region.
[0015]
When using the electrode structure of the arrangement in a semi-conductor light emitting device, since the area of the portion where the the main electrode layer and the semiconductor crystal is alloyed with Ti layer is 20% to 50% of the area of the electrode formation region Compared with the conventional case, the area of the alloyed portion is narrower. Therefore, the amount of light absorbed by the alloyed portion is small, and a decrease in light extraction efficiency of the semiconductor light emitting element can be prevented.
[0016]
[0017]
The electrode structure manufacturing method of the present invention is an electrode structure manufacturing method relating to a method of manufacturing an electrode structure used in an AlGaAs-based semiconductor light-emitting device, comprising a Ti layer and a main layer on the surface of a semiconductor crystal made of AlGaAs. A first step of sequentially laminating an electrode layer, and the Ti layer and the main electrode layer are sequentially processed into a predetermined electrode pattern by etching, whereby the predetermined layer is formed on the electrode formation region on the surface of the semiconductor crystal. A second step of providing a Ti layer processed into an electrode pattern and a main electrode layer processed into the predetermined electrode pattern on the Ti layer; and applying heat treatment to the main electrode layer and the semiconductor And a third step of alloying the crystal through the Ti layer.
[0018]
The thickness of the Ti layer stacked in the first step is Ri der range of 30 to 50 nm, and the area of the alloyed portion is Ru 20% to 50% der of the area of the electrode formation region .
[0019]
According to the manufacturing method of the electrode structure having the above configuration, the area of the portion where the main electrode layer and the semiconductor crystal are alloyed via the Ti layer is actually 20% to 50% of the area of the electrode formation region ( Details will be described later). Therefore, when the method for manufacturing an electrode structure is used in a method for manufacturing a semiconductor light emitting device, for example, the area of the alloyed portion is narrower than in the conventional case, so that the main electrode layer and the semiconductor crystal are alloyed. The amount of light absorbed in the converted portion is small, and a decrease in light extraction efficiency of the semiconductor light emitting element can be prevented.
[0020]
The reason why the thickness of the Ti layer laminated in the first step is set to 30 nm or more is that when the thickness of the Ti layer is less than 30 nm, the portion where the main electrode layer and the semiconductor crystal are alloyed. This is because the area becomes too large and the luminous intensity of the semiconductor light emitting element is lowered.
[0021]
On the other hand, the reason why the thickness of the Ti layer laminated in the first step is 50 nm or less is that when the thickness of the Ti layer exceeds 50 nm, the electrical resistance of the Ti layer increases, and the semiconductor light emitting device This is because the drive current increases.
[0022]
[0023]
[0024]
[0025]
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the electrode structure of the present invention and the manufacturing method thereof will be described in detail with reference to the illustrated embodiments.
[0027]
1A to 1E show a manufacturing process of an LED manufacturing method as an example of a semiconductor light emitting device. This LED is a substrate removal type AlGaAs LED, and is manufactured as follows.
[0028]
First, as shown in FIG. 1A, a P-type AlGaAs semiconductor clad layer 8, a P-type AlGaAs active layer 9, and an N-type AlGaAs semiconductor clad layer 10 are sequentially epitaxially grown on a P-type GaAs substrate 7 to form a wafer. To do. Here, the N-type AlGaAs semiconductor clad layer 10 corresponds to an example of a semiconductor crystal.
[0029]
Next, the P-type GaAs substrate 7 is completely removed from the wafer by chemical etching or the like to obtain the state shown in FIG.
[0030]
Next, as shown in FIG. 1C, an anode electrode 11 is formed under the P-type AlGaAs semiconductor clad layer 8. The anode electrode 11 is made of AuZn or the like.
[0031]
Subsequently, as shown in FIG. 1D, a cathode electrode 12 is formed on the N-type AlGaAs semiconductor clad layer 10.
[0032]
Thereafter, as shown in FIG. 1 (e), the wafer comprising the P-type AlGaAs semiconductor clad layer 8, the P-type AlGaAs active layer 9, and the N-type AlGaAs semiconductor clad layer 10 is divided into individual elements by dicing. A plurality of LEDs 100, 100,... (Only two are shown in FIG. 1 (e)) are completed.
[0033]
FIG. 2 schematically shows a cross section of the cathode electrode 12.
[0034]
As shown in FIG. 2, the cathode electrode is formed on an N-type AlGaAs semiconductor cladding layer 10 on a semiconductor crystal surface roughening prevention layer 1, a contact layer 2, a first barrier layer 3, a second layer as an example of a Ti layer. The barrier layer 4 and the bonding pad layer 5 are sequentially laminated. This contact layer 2 corresponds to an example of a main electrode layer. The roughening prevention layer 1 is made of Ti, the contact layer 2 is made of an Au-based alloy layer such as AuSi, the first barrier layer 3 is made of TiN, etc., the second barrier layer 4 is made of Ti, and the bonding pad layer 5 is made of Each is made of Al. In order to maintain the bonding performance, the second barrier layer 5 barriers the bonding pad layer 5 from the alloyed contact layer metal. Further, since the second barrier layer 4 is made of Ti, the adhesion to the first barrier layer 3 made of TiN is good and the adhesion to the bonding pad layer 5 made of Al is also good.
[0035]
Hereinafter, a method for forming the cathode electrode 12 will be described.
[0036]
First, before the roughening prevention layer 1 is formed, the surface of the N-type AlGaAs semiconductor clad layer 10 is pretreated to clean the surface of the N-type AlGaAs semiconductor clad layer 10.
[0037]
Next, immediately after the above pretreatment, the roughening prevention layer 1 is laminated on the surface of the N-type AlGaAs semiconductor clad layer 10 by sputtering.
[0038]
Next, the contact layer 2 is laminated on the surface of the roughening prevention layer 1 by sputtering. The contact layer 2 is made of an Au-based alloy such as AuSi to which Si is added, for example, and can easily make ohmic contact with the N-type AlGaAs semiconductor clad layer 10.
[0039]
Subsequently, a first barrier layer 3 and a second barrier layer 4 are sequentially laminated on the surface of the contact layer 2. The first barrier layer 3 is made of TiN, and the second barrier layer 4 is made of Ti.
[0040]
Thereafter, the bonding pad layer 5 is laminated on the surface of the second barrier layer 4 by sputtering or vapor deposition. The bonding pad layer 5 is made of Al and can be wire bonded.
[0041]
Next, a resist having a predetermined electrode pattern is formed on the surface of the bonding pad layer 5 by a normal photolithography process.
[0042]
Next, wet etching using an etchant is performed to sequentially process the bonding pad layer 5, the second barrier layer 4, the first barrier layer 3, and the contact layer 2 into a predetermined electrode pattern. Thereafter, the exposed portion of the roughening prevention layer 1 is removed by etching using another etchant.
[0043]
Next, heat treatment is performed, and the contact layer 2 and the N-type AlGaAs semiconductor clad layer 10 are alloyed via the roughening prevention layer 1 to complete the cathode electrode 12.
[0044]
In such a method of forming the cathode electrode 12, the thickness of the roughening prevention layer 1 laminated on the surface of the N-type AlGaAs semiconductor clad layer 10 is an important condition for controlling the electrode alloying ratio.
[0045]
FIG. 3 shows a graph of the relationship between the thickness of the laminated anti-roughening layer 1 and the luminous intensity of the LED 100, and FIG. 4 shows the thickness of the laminated anti-roughening layer 1 and the VF (forward voltage) of the LED 100. The relationship graph is shown. The VF is a value measured by passing a current of 20 mA between the anode electrode 11 and the cathode 12.
[0046]
In FIG. 3, the thickness of the laminated anti-roughening layer 1 is changed to 20 nm, 40 nm, and 80 nm, and the luminous intensity of each LED 100 manufactured using the anti-roughening layer 1 is measured. When the thickness of the laminated anti-roughening layer 1 is set to 40 nm and 80 nm, the luminous intensity is improved by 10% or more compared to the case where the laminated anti-roughening layer 1 is set to 20 nm. However, when the thickness of the roughening prevention layer 1 is set to 80 nm, the resistance of the roughening prevention layer 1 increases and VF increases.
[0047]
FIG. 5 schematically shows an alloyed state of the contact layer 2 and the N-type AlGaAs semiconductor clad layer 10 when the roughening prevention layer 1 to be laminated is set to 40 nm. This alloyed state is obtained by observing from the N-type AlGaAs semiconductor clad layer 10 side with an infrared microscope. Further, in FIG. 5, the alloyed portion of the cathode electrode 12 appears black because it does not reflect light.
[0048]
In the conventional example of FIG. 7, the area of the alloyed portion A2 is 90% of the area of the electrode formation region P2, but as shown in FIG. 5, the thickness of the laminated anti-roughening layer 1 is set to 40 nm. The total area of the alloyed portions A1,... Is 30% of the area of the electrode formation region P1. Here, the alloyed portions A1,... Indicate portions where the contact layer 2 and the N-type AlGaAs semiconductor clad layer 10 are alloyed via the roughening prevention layer 1. The electrode forming region P1 refers to a region where the roughening prevention layer 1 is to be formed on the surface of the N-type AlGaAs semiconductor clad layer 10.
[0049]
Although not shown, when the thickness of the roughening preventing layer 1 to be laminated is set to 80 nm, the area of the alloyed portion is 10% of the area of the electrode formation region P1.
[0050]
As a result of further changing the thickness of the anti-roughening layer 1 to be laminated as described above, the thickness of the anti-roughening layer 1 to be laminated is set to 30 nm to 50 nm, so that the contact layer 2 and the N-type AlGaAs The area where the semiconductor clad layer 10 is alloyed does not become too large. Therefore, the amount of light absorbed by the alloyed portion in the roughening prevention layer 1 is small, and a decrease in the light extraction efficiency of the LED 100 can be prevented.
[0051]
Further, if the thickness of the laminated anti-roughening layer 1 is less than 30 nm, the area where the contact layer 2 and the N-type AlGaAs semiconductor clad layer 10 are alloyed becomes too large, so that light absorption by the cathode electrode 12 is prevented. As a result, the light extraction efficiency of the LED 100 decreases. That is, the luminous intensity of the LED 100 decreases.
[0052]
On the other hand, if the thickness of the laminated anti-rough layer 1 exceeds 50 nm, the electrical resistance of the cathode electrode 12 increases, and the drive current of the LED 100 increases.
[0053]
The heat treatment for the roughening prevention layer 1, the contact layer 2, the first barrier layer 3, the second barrier layer 4 and the bonding pad layer 5 is preferably performed at 400 ° C. to 500 ° C. for 5 minutes to 20 minutes. By performing the heat treatment at 400 ° C. to 500 ° C. for 5 minutes to 20 minutes, the area of the portion where the contact layer 2 and the N-type AlGaAs semiconductor clad layer 10 are alloyed can be surely contained within a predetermined range.
[0054]
If the heat treatment is less than 400 ° C. or less than 5 minutes, alloying of the contact layer 2 and the N-type AlGaAs semiconductor clad layer 10 becomes insufficient. That is, the area of the alloyed portion becomes too narrow.
[0055]
If the heat treatment exceeds 500 ° C. or the heat treatment exceeds 20 minutes, alloying between the contact layer 2 and the N-type AlGaAs semiconductor clad layer 10 proceeds excessively. That is, the area of the alloyed portion becomes too large.
[0056]
In the above embodiment, the bonding pad layer 5 is made of Al, but may be made of Au, an alloy containing Au, an alloy containing Al, or the like. For example, a bonding pad layer made of an alloy of Au and Al may be used.
[0057]
In the said embodiment, Si concentration in AuSi of the said contact layer 2 is set to 1-5 wt%, for example.
[0058]
The dividing method for forming the wafer into an element may be a mesa etching method in which dicing is performed after PN junction partial disconnection by wet etching after performing photolithography.
[0059]
Further, the area of the portion where the roughening prevention layer 1 and the N-type AlGaAs semiconductor cladding layer 10 are alloyed is 20% to 50% of the area of the roughening prevention layer 1 in contact with the N-type AlGaAs semiconductor cladding layer 10. May be.
[0060]
Needless to say, the electrode structure of the present invention can be applied to various semiconductor light emitting devices.
[0061]
【The invention's effect】
As is clear from the above, when the electrode structure of the present invention is used in, for example, a semiconductor light emitting device, the area of the portion where the main electrode layer and the semiconductor crystal are alloyed via the Ti layer is 20% of the area of the electrode formation region. From 50% to 50%, the amount of light absorbed by the alloyed portion is small, and the reduction of the light extraction efficiency of the semiconductor light emitting element can be prevented.
[0062]
In the electrode structure manufacturing method of the present invention, the thickness of the Ti layer laminated on the surface of the semiconductor crystal is set within a range of 30 to 50 nm, so that the main electrode layer and the semiconductor crystal are interposed via the Ti layer. The area of the alloyed portion is 20% to 50% of the area of the electrode formation region. Therefore, when the method for manufacturing an electrode structure is used, for example, in a method for manufacturing a semiconductor light emitting device, the amount of light absorbed by the alloyed portion of the main electrode layer and the semiconductor crystal is small, and the light extraction efficiency of the semiconductor light emitting device is reduced. Can be prevented.
[0063]
Further, when the manufacturing method of the electrode structure is used in, for example, a manufacturing method of a semiconductor light emitting device, alloying is performed by setting the thickness of the Ti layer laminated on the surface of the semiconductor crystal within a range of 30 to 50 nm. Since the area of the portion does not vary, the defect in the luminous intensity of the semiconductor light emitting element can be reduced and the manufacturing yield can be improved.
[Brief description of the drawings]
FIGS. 1A to 1E are process diagrams of manufacturing an LED to which an electrode structure according to an embodiment of the present invention is applied.
FIG. 2 is a schematic cross-sectional view of the cathode electrode of the LED.
FIG. 3 is a graph showing the relationship between the luminous intensity of the LED and the thickness of the roughening prevention layer.
FIG. 4 is a graph showing the relationship between the VF of the LED and the thickness of the roughening prevention layer.
FIG. 5 is a schematic view showing an alloyed state of the cathode electrode.
FIG. 6 is a graph showing the relationship between the interelectrode voltage of the conventional electrode structure and the thickness of the Ti layer.
FIG. 7 is a schematic view showing an alloyed state of an electrode prepared by the above-described conventional electrode structure manufacturing method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Roughening prevention layer 2 Contact layer 10 N-type AlGaAs semiconductor cladding layer A1 Alloyed part P1 Roughening prevention layer part in contact with N-type AlGaAs semiconductor cladding layer

Claims (2)

An electrode structure used in an AlGaAs semiconductor light emitting device,
In an electrode structure in which a Ti layer and a main electrode layer are sequentially provided on an electrode formation region on the surface of a semiconductor crystal made of AlGaAs, and the main electrode layer and the semiconductor crystal are alloyed via the Ti layer.
The area of the alloyed portion is 20% to 50% of the area of the electrode forming region. An electrode structure manufacturing method relating to a method of manufacturing an electrode structure used in an AlGaAs-based semiconductor light emitting device,
A first step of sequentially laminating a Ti layer and a main electrode layer on the surface of a semiconductor crystal made of Al GaAs, and sequentially processing the Ti layer and the main electrode layer into a predetermined electrode pattern by etching ; A Ti layer processed into the predetermined electrode pattern is provided on the electrode formation region on the surface of the semiconductor crystal, and a main electrode layer processed into the predetermined electrode pattern is provided on the Ti layer . In a method for manufacturing an electrode structure comprising: a step; and a third step of alloying the main electrode layer and the semiconductor crystal through the Ti layer by performing a heat treatment,
The thickness of the Ti layer stacked in the first step is Ri der range of 30 to 50 nm, and the area of the alloyed portion is Ru 20% to 50% der of the area of the electrode formation region An electrode structure manufacturing method characterized by the above.

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