JP4341228B2 - Nitride-based optical element and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical element using a nitride semiconductor used for a light emitting element such as a light emitting diode or a laser diode, or a light receiving element such as an optical sensor or a solar cell, and more specifically, a flip-chip type nitride semiconductor optical. It relates to an element.
[0002]
[Prior art]
At present, optical elements using nitride semiconductors capable of emitting short wavelengths such as blue light are attracting attention, and high-intensity blue LEDs and blue-green LEDs have been put to practical use in displays, signal lights, and the like. To mount a nitride semiconductor optical element on a mounting substrate, for example, flip chip in which the semiconductor layer of the optical element is on the lower side and the positive electrode and the negative electrode of the optical element are connected to the wiring electrodes on the mounting substrate. A type mounting method is used.
[0003]
Optical elements used in the flip chip mounting method are connected to an n-type nitride semiconductor layer and a p-type nitride semiconductor layer formed on a substrate, and the n-type nitride semiconductor layer and the p-type nitride semiconductor layer, respectively. A positive electrode and a negative electrode formed on the same plane side on the substrate, and mounting on the mounting substrate is performed with the p-type nitride semiconductor layer and the n-type nitride semiconductor layer on the lower side, and the positive electrode and the negative electrode This can be done by making the electrode face the wiring electrode on the mounting substrate and pressing and connecting to the wiring electrode through the metal bump.
[0004]
Here, in order to form a metal bump, the tip of the metal wire is melted into a ball shape, and the ball is pressure-bonded to the positive electrode and the negative electrode, or a thick film is used to ensure adhesion with the metal bump. A method using a positive electrode and a method of providing a thick pad electrode on a thin positive electrode are conceivable.
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 2000-183400
[Problems to be solved by the invention]
However, the method of melting the tip of the metal wire to form a ball requires that the ball be pressure-bonded for each electrode, and it takes time to position the electrode, so that it takes a long time to produce the metal bump. There's a problem. On the other hand, there is an electrolytic plating method as a method for simultaneously forming a large number of metal bumps. However, it is necessary to provide a current-carrying electrode for flowing a plating current in the electrolytic plating method, and it is difficult to apply to an optical element using an insulating substrate.
[0007]
In addition, when a thick positive electrode is used to improve the adhesion to the metal bump, the sheet resistance of the positive electrode is lowered, and the problem is that the emission intensity distribution is not uniform. A possible reason for this is that the sheet resistance of the n-type nitride semiconductor layer is larger than the sheet resistance of the positive electrode. That is, even if the sheet resistance of the positive electrode is reduced, if the sheet resistance of the n-type semiconductor layer is larger than that, the current can easily flow around the negative electrode having a small resistance, and the light is bright around the negative electrode. It will be darker as you leave. In the case where the pad electrode is provided, the pad electrode needs to be thick in order to facilitate bonding, and the same problem can be considered.
[0008]
Therefore, the present invention solves the above-mentioned problems, improves the adhesion between the metal bumps, the electrode and the nitride semiconductor layer while maintaining uniform light emission characteristics, and produces the metal bumps efficiently, It is an object of the present invention to provide a nitride semiconductor optical element having excellent properties and light emission characteristics and a method for manufacturing the same.
[0009]
[Means for Solving the Problems]
The present applicant has eagerly studied to produce metal bumps using an electroless plating method that can be produced at low cost and can be expected to have high productivity, and as a result, a metal formed by electroless plating. The present invention has been completed by finding a nitride semiconductor optical element having excellent adhesion to a bump.
That is, the nitride semiconductor optical element of the present invention has an n-type nitride semiconductor layer and a p-type nitride semiconductor layer stacked on a substrate, and a positive electrode connected to the p-type nitride semiconductor layer, the positive electrode a flip chip-type nitride semiconductor optical device to be connected to the mounting substrate via the metal bumps, the positive electrode is made of two or more metal layers, said two or more metal layers, said having a first metal layer in contact with the p-type nitride semiconductor layer, a second metal layer in contact with the metal bumps, the first metal layer has a thickness of 200Å~1000Å, Rh, Pd and Pt And the second metal layer has a thickness of 50 to 3000 mm and any one metal selected from Au, Ag, Cu, Rh, Pd and Pt has, the first and second metal layers the metal bumps Ri consists large metal ductile than the metal constituting the metal ductility constituting the first metal layer being greater than the ductility of the metal constituting the second metal layer.
[0010]
According to the present invention, when producing a metal bump, at least the first metal layer in contact with the p-type nitride semiconductor layer of the positive electrode and the second metal layer in contact with the metal bump are more ductile than the metal constituting the metal bump. By constituting the metal with a large metal, the stress of the metal bump is relieved, and the metal bump is prevented from peeling from the positive electrode or the positive electrode bonded to the metal bump from the p-type nitride semiconductor layer. Can be increased. Thereby, since it is not necessary to increase the thickness of the positive electrode, the difference between the sheet resistance of the positive electrode and the sheet resistance of the n-type nitride semiconductor layer does not increase, and the uniformity of the emission intensity can be maintained. Here, the metal having a large ductility refers to a metal having a large plastic deformation that has occurred until breakage. For example, a metal having a larger elongation at break as defined in JIS Z 2241 than a metal constituting the metal bump.
[0011]
In the present invention, Ni or Cu can be used for the metal constituting the metal bump. In that case, it is preferable that the first metal layer has at least one metal selected from Rh, Pd, and Pt. The second metal layer preferably contains at least one metal selected from Au, Ag, Cu, Rh, Pd, and Pt.
[0012]
In the nitride semiconductor optical element of the present invention, the negative electrode is composed of two or more metal layers, and the second metal layer in contact with the metal bump is at least Au, Ag, Al, Cu, Rh, Pd, and It is preferable to have any one metal selected from Pt.
[0013]
Moreover, the metal bump can be a plating bump formed by electroless plating.
[0014]
The nitride semiconductor optical element of the present invention can be produced, for example, by the following method. That is, the method for manufacturing a nitride semiconductor optical element of the present invention includes a step of laminating an n-type nitride semiconductor layer and a p-type nitride semiconductor layer on a substrate, and a positive electrode connected to the p-type nitride semiconductor layer. As described above, any one selected from Au, Ag, Cu, Rh, Pd and Pt, and a first metal layer having a thickness of 200 to 1000 mm having any one metal selected from Rh, Pd and Pt. A step of sequentially forming a second metal layer having a thickness of 50 to 3000 mm having a seed metal, and Ni plating in contact with the second metal layer and having a lower ductility than the metal constituting the second metal layer Or forming a Cu plating and connecting to the mounting substrate through the plating, and the ductility of the metal constituting the first metal layer is greater than the ductility of the metal constituting the second metal layer. Is also large.
[0015]
Further, after forming the electrode, it is preferable to anneal at a temperature of 400 ° C. or higher in a non-oxidizing atmosphere. Here, the non-oxidizing atmosphere refers to an atmosphere that does not substantially contain oxygen.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic cross-sectional view showing an example of the structure of a nitride semiconductor optical element (hereinafter abbreviated as an optical element) according to an embodiment of the present invention. 1 is formed on the upper surface of an n-type nitride semiconductor layer 3 and a p-type nitride semiconductor layer 4 that are sequentially formed on a substrate 2 and an n-type nitride semiconductor layer 3 with one end exposed. The negative electrode 6 is formed on a substantially entire upper surface of the p-type nitride semiconductor layer 4 and includes a positive electrode 5 having a bonding surface on a part of the upper surface, and an insulating protective film 7. The insulating protective film 7 is continuous over the upper surface of the positive electrode 5 other than the bonding surface, the upper surface of the negative electrode 6 other than the bonding surface, and the upper surface of the substrate 2 exposed around the n-type nitride semiconductor layer 3. The positive electrode 5 and the negative electrode 6 are separated and insulated. Further, plating bumps 8 and 9 are formed on the bonding surfaces of the positive electrode 5 and the negative electrode 6 by electroless plating. The positive electrode 5 includes an uppermost metal layer 5a that is a second metal layer in contact with the plating bump, and a lowermost metal layer 5c that is a first metal layer in contact with the p-type nitride semiconductor layer 4. The intermediate layer 5b is a third metal layer between the uppermost layer and the lowermost metal layer. The negative electrode 6 includes an uppermost metal layer 6a that is a second metal layer in contact with the plating bump, and a lowermost metal layer 6c that is a first metal layer in contact with the n-type nitride semiconductor layer 3. It is configured.
[0017]
As the metal constituting the plating bump, Ni or Cu that can be electrolessly plated and has high conductivity can be used. Electroless plating is preferable because Ni has a high deposition rate and can form plating bumps in a short time and is low in cost. The thickness of the plating bump is 1 to 150 μm, more preferably 1 to 50 μm. Further, the plating bump may be a two-layer structure in which electroless Au plating is provided on electroless Ni plating. For example, when electroless Ni is formed to a height of 1 to 150 μm and electroless Au plating is formed on the electroless Ni plating at a height of 5000 mm or less, the bonding property with the wiring board is good, which is preferable.
[0018]
The plating bump can be formed by the following method, for example. That is, after the positive electrode and the negative electrode are separated and insulated using an insulating protective film, a resist layer is formed on the entire surface of the optical element. Next, the resist layer is exposed using a predetermined mask so that the bonding surfaces of the positive electrode and the negative electrode are exposed, and the bonding layer is exposed by removing the resist layer on the bonding surface. Next, the wafer on which the optical element is formed is washed with an acid solution, and the wafer is immersed in an electroless plating bath containing a predetermined plating metal at a predetermined temperature for a predetermined time, so that plating bumps are formed on the bonding surface. Grow. The thickness of the plating bump can be adjusted by changing the immersion time, the pH and temperature of the plating bath, the number of immersions, and the like. Here, a known plating bath can be used as the plating bath. For example, a Ni-P system or a Ni-B system can be used for Ni plating, but the deposition rate is high and high hardness is obtained. Ni-P-based plating baths that are low in cost are preferable.
[0019]
In addition, after forming a positive electrode and a negative electrode, before performing electroless plating, it is 400 degreeC or more in the presence of a non-oxidizing atmosphere, Preferably nitrogen gas or argon gas, Preferably it is 400 degreeC or more and 600 degrees C or less, and an optical element Is preferably annealed. This is because oxidation of the uppermost layer metal can be prevented and adhesion with the plating bump can be improved.
[0020]
As the metal constituting the positive electrode, it is necessary to use a metal having a higher ductility than the metal constituting the plating bump. It is preferable to use at least one metal selected from Rh, Pd, and Pt as the metal constituting the lowermost metal layer. In any case, ohmic contact with the p-type nitride semiconductor layer is possible, and furthermore, the reflectance of light from the light emitting layer is high. In particular, Rh is preferable because of good adhesion to the p-type nitride semiconductor layer. The thickness of the lowermost metal layer is 200 to 1000 mm, more preferably 200 to 800 mm. This is because the adhesiveness is insufficient if it is smaller than 200 mm, and the sheet resistance of the n-type nitride semiconductor layer is smaller than 1000 mm.
[0021]
Moreover, it is preferable to use at least one metal selected from Au, Ag, Cu, Rh, Pd, and Pt as the metal constituting the uppermost metal layer of the positive electrode. The thickness of the uppermost layer is 50 to 3000 mm, more preferably 100 to 1000 mm. In particular, when Ni is used for the plating bump, it is preferable to use Pd. This is because when the Pd layer becomes a seed layer and electroless Ni plating is performed, the activation process is not necessary.
[0022]
The intermediate layer of the positive electrode ensures good adhesion between the uppermost layer and the lowermost metal layer, and the adhesion between the plating bump, the positive electrode, and the p-type nitride semiconductor layer. It has a function to ensure. At least one metal selected from Pt, Au, Ir and Pd can be used as the metal constituting the metal layer of the intermediate layer, and Ir is preferable. The intermediate layer has a thickness of 200 to 1000 mm, more preferably 200 to 500 mm. The intermediate layer can be omitted depending on the combination of the uppermost layer and the lowermost layer.
[0023]
Here, it is preferable that the ductility of the metal constituting the lowermost layer of the positive electrode is larger than the ductility of the metal constituting the uppermost layer. This is because the adhesion to the p-type nitride semiconductor layer can be further enhanced. For example, when Ni is used for the metal constituting the plating bump, the uppermost layer / intermediate layer / lowermost layer is Pd / Ir / Rh, Pd / Rh, Pt / Ir / Rh, Au / Ir / Rh, Pt / Rh. A combination of / Au / Rh can be mentioned. In particular, a combination of Pd / Ir / Rh is preferable.
[0024]
Moreover, the total film thickness of the metal layer which comprises a positive electrode is 200-5000 mm, More preferably, it is 200-1000 mm. This is because if it exceeds 5000 mm, the sheet resistance decreases and the difference from the sheet resistance of the n-type nitride semiconductor layer becomes too large. Moreover, it is because adhesiveness with a plating bump will become inadequate when smaller than 200 mm.
[0025]
The negative electrode can also be composed of two or more metal layers. The metal constituting the lowermost metal layer in contact with the n-type nitride semiconductor layer is not particularly limited as long as ohmic contact with the n-type nitride semiconductor is possible. Preferably, at least one metal selected from Pt, Ti, Al, Ni, Au, W, and V can be used. The thickness of the lowermost metal layer is 50 to 500 mm, more preferably 100 to 200 mm.
[0026]
Further, at least one metal selected from Au, Ag, Al, Cu, Rh, Pd, and Pt can be used as the metal constituting the uppermost metal layer of the negative electrode. The thickness of the uppermost layer is 50 to 3000 mm, more preferably 100 to 1000 mm. Further, as described above, when Ni is used for the plating bump, it is preferable to use Pd. This is because when the Pd layer becomes a seed layer and electroless Ni plating is performed, the activation process is not necessary.
[0027]
【Example】
Example 1.
(Production of optical elements)
On the insulating substrate 1 made of sapphire, an n-type nitride semiconductor layer 2, a p-type nitride semiconductor layer 3, and a light emitting layer were formed by the MOVPE method. After annealing, the wafer was taken out of the reaction vessel, an insulating film made of SiO ₂ was formed on the surface of the uppermost p-type nitride semiconductor layer, and a resist film having a predetermined shape was formed on the surface of the insulating film. Next, etching was performed from the p-type nitride semiconductor layer side with an RIE (reactive ion etching) apparatus to expose the surface of the n-type nitride semiconductor layer forming the negative electrode. Next, after peeling off the insulating film with acid, Rh, Ir, and Pd are stacked in this order in a thickness of 400 mm / 200 mm / 1000 mm on the entire surface of the p-type nitride semiconductor layer to form a positive electrode. Formed. On the other hand, on the surface of the n-type nitride semiconductor layer exposed by etching, W and Al were laminated in this order at a film thickness of 200 mm / 3500 mm to form a negative electrode. After forming the positive electrode and the negative electrode, the optical element was heat-treated at 400 ° C. in a nitrogen gas atmosphere.
[0028]
Next, after exposing only the bonding surface of the positive electrode and the negative electrode by patterning, an insulating protective film made of SiO ₂ was formed so as to cover the entire element other than the bonding surface.
[0029]
(Plating bump formation)
Next, the wafer was immersed in a plating solution containing nickel ions and sodium hypophosphite in the reducing agent, and nickel was deposited to form 50 μm-thick plating bumps on the bonding surfaces of the positive electrode and the negative electrode.
[0030]
(Evaluation of adhesion)
The adhesion between the plating bump and the positive electrode and the p-type nitride semiconductor layer is determined by performing a peel test using a tensile tester and measuring the shear force when the plating bump peels from the positive electrode or the p-type nitride semiconductor layer. Evaluation was made by measuring.
[0031]
(Evaluation of luminous characteristics)
FFP measurement was performed to evaluate the light emission distribution of the optical element.
[0032]
Comparative Example Using Ni / Pt (film thickness: 100 mm / 500 mm) as the positive electrode, Pt (film thickness: 7000 mm) as the pad electrode is laminated on the positive electrode, and W / Al (film thickness: 200 mm / 2000 mm) is used as the negative electrode. A nitride semiconductor optical element was produced by the same method as in Example 1 except that.
[0033]
(result)
As a result of the peel test, the shear force increased greatly to 420 gf in Example 1 compared to 50 gf of the comparative example, and the adhesion was greatly improved.
In addition, compared with the comparative example, in Example 1, the emission intensity distribution was more uniform.
[0034]
【The invention's effect】
As described above, in the nitride semiconductor optical element of the present invention, at least one of the positive electrode and the negative electrode is composed of two or more metal layers, and the lowest layer in contact with at least the p-type nitride semiconductor layer of the positive electrode. Since the metal having higher ductility than the metal constituting the metal bump is used for the uppermost metal layer in contact with the metal layer and the metal bump, the uppermost metal layer and the lowermost metal layer alleviate the stress of the metal bump, The adhesion between the metal bump, the positive electrode, and the p-type nitride semiconductor layer can be improved. Further, since it is not necessary to use a thick positive electrode and a pad electrode, the difference between the sheet resistance of the positive electrode and the sheet resistance of the n-type nitride semiconductor layer does not increase, and the light emission intensity is uniform. It becomes possible to maintain sex. As a result, it is possible to provide a flip-chip type nitride semiconductor optical element excellent in productivity and light emission characteristics.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing the structure of a nitride semiconductor optical element according to an embodiment of the present invention.
[Explanation of symbols]
1 optical element, 2 substrate, 3 n-type nitride semiconductor layer, 4 p-type nitride semiconductor layer, 5 positive electrode, 5a top layer, 5b intermediate layer, 5c bottom layer, 6 negative electrode, 6a top layer, 6c bottom layer , 7 Insulating protective film, 8, 9 Plating bump.

Claims (8)

An n-type nitride semiconductor layer and a p-type nitride semiconductor layer stacked on a substrate, and a positive electrode connected to the p-type nitride semiconductor layer, the positive electrode being mounted on a mounting substrate via a metal bump Flip chip type nitride semiconductor optical element to be connected,
The positive electrode is composed of two or more metal layers, and the two or more metal layers include a first metal layer in contact with the p-type nitride semiconductor layer and a second metal layer in contact with the metal bump. Have
The first metal layer has a thickness of 200 to 1000 mm, has any one metal selected from Rh, Pd, and Pt, the second metal layer has a thickness of 50 to 3000 mm, Au , Having any one metal selected from Ag, Cu, Rh, Pd and Pt,
The first and second metal layers are made of a metal having a higher ductility than the metal constituting the metal bump, and the ductility of the metal constituting the first metal layer is the ductility of the metal constituting the second metal layer. Larger nitride semiconductor optical element.   A third metal layer is provided between the first metal layer and the second metal layer, and the third metal layer has a thickness of 200 mm to 1000 mm and is selected from Pt, Au, Ir, and Pd The nitride semiconductor optical element according to claim 1, comprising any one kind of metal.   The nitride semiconductor optical element according to claim 1 or 2, wherein the metal constituting the metal bump is Ni or Cu. The metal constituting the metal bump is Ni, and the combinations of the second metal layer / the third metal layer / the first metal layer are Pd / Ir / Rh , Pt / Ir / Rh and Au. The nitride semiconductor optical element according to claim 2, which is any one selected from the combination of / Ir / Rh. A negative electrode connected to the n-type nitride semiconductor layer and formed on the same side as the positive electrode;
The negative electrode includes a first metal layer in contact with the n-type nitride semiconductor layer and a second metal layer in contact with the metal bump, and the second metal layer includes at least Au, Ag, Al 5. The nitride semiconductor optical element according to claim 1, comprising any one metal selected from Cu, Rh, Pd, and Pt.   6. The nitride semiconductor light emitting device according to claim 1, wherein the metal bump is a plated bump formed by electroless plating. Laminating an n-type nitride semiconductor layer and a p-type nitride semiconductor layer on a substrate;
As a positive electrode connected to the p-type nitride semiconductor layer, a first metal layer having a thickness of 200 mm to 1000 mm having any one metal selected from Rh, Pd, and Pt, Au, Ag, Cu A step of sequentially forming a second metal layer having a thickness of 50 mm to 3000 mm having any one metal selected from Rh, Pd and Pt;
Forming a Ni plating or Cu plating that is less ductile than the metal constituting the second metal layer in contact with the second metal layer , and connecting to the mounting substrate through the plating, and
A method for manufacturing a nitride semiconductor optical element, wherein the ductility of the metal constituting the first metal layer is greater than the ductility of the metal constituting the second metal layer.   Forming a third metal layer between the first metal layer and the second metal layer, wherein the third metal layer has a thickness of 200 mm to 1000 mm; Pt, Au, Ir The manufacturing method of Claim 7 which has any one kind of metal selected from Pd.

Images