JP2002237646A - Nitride semiconductor light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-emitting element wherein adherence of a chip is large and heat dissipating property is high. SOLUTION: In the light-emitting chip, nitride semiconductor is grown on a first main surface side of an oxide substrate having a first main surface and a second main surface, and a first heat dissipating thin film, including at least one kind of metal selected from among a group composed of Al, Ti, Zr, Cr, I, Mo, W, Ge, Si, Sn, Zn, Cu, Mn, V and Nb, is formed on a second main surface side. The light-emitting chip is die-bonded on a retainer via adhesive agent, having thermal conductivity and electric conductivity in a state with the first heat dissipating thin film facing the surface of the retainer, so that the light-emitting chip is bonded rigidly. In a part between the adhesive agent and the first heat-dissipating thin film, a second heat-dissipating thin film is formed, which contains at least one kind of metal selected from a group composed of Pt, Ti and Ni and whose thickness is nearly equal to or greater that that of the first heat-dissipating thin film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride semiconductor (In _X Al _Y G) used for a light emitting device such as an LED and an LD.
a _1- XYN, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1).

[0002]

2. Description of the Related Art High-brightness blue or pure green LEDs having a luminous intensity of 1 cd or more made of nitride semiconductors have recently been put to practical use, and are now manufactured and sold by the present applicant and are known.
These LEDs have a pn structure in which an active layer made of InGaN having a single quantum well structure is sandwiched between AlGaN and / or GaN.
It has a double heterostructure with a junction, and a nitride semiconductor is grown on a sapphire substrate. The nitride semiconductor light emitting chip grown on the sapphire substrate is die-bonded face-up (in a state where the substrate and the support face each other) to a support such as a lead frame. As an adhesive at the time of die bonding, for example, JP-A-7-86
As described in JP-A-640, a transparent insulating adhesive containing an organic substance is used.

On the other hand, as for an LD (laser diode) made of a nitride semiconductor, the present applicant has reported, for the first time in the world, pulse oscillation at room temperature of 410 nm at room temperature. (For example, Nikkei Electronics 1996.1.15 (No.653) p13
~ P15). This laser element also has In on a sapphire substrate.
An active layer having a multiple quantum well structure including GaN is formed of AlG
It has a double hetero structure sandwiched between aN, GaN, and the like.

[0004]

An LED die-bonded with a transparent insulating adhesive is very effective in improving the external quantum efficiency of the LED because the adhesive itself transmits light. is there. However, since it contains an organic substance, the organic substance may be deteriorated due to a short wavelength, and the adhesive may be discolored due to long-time use, thereby lowering the external quantum efficiency. Also, if the adhesion between the substrate and the support is insufficient,
At the time of wire bonding, the chip may be peeled off or shifted from the support.

On the other hand, although pulse oscillation has been successful in the case of LD, a completed product in which a light emitting chip is die-bonded to a support such as a heat sink has not yet been developed. L
In the case of D, unlike the LED, the calorific value of the chip is orders of magnitude larger. Therefore, in order to die-bond the light emitting chip, it is necessary to select an adhesive having excellent thermal conductivity. Further, when the light emitting chip is partially peeled off or shifted from the support during wire bonding, a gap exists between the adhesive and the substrate or between the adhesive and the support, resulting in poor adhesion. If the adhesion is poor, the heat generated by the light emitting chip is not sufficiently transmitted to the heat sink, so that the oscillation threshold value is increased and the life of the light emitting chip is extremely shortened.

Accordingly, an object of the present invention is to provide a light emitting device in which a light emitting chip made of a nitride semiconductor grown on an oxide substrate is die-bonded face-up to a support such as a heat sink or a lead frame. It is therefore an object of the present invention to provide a light emitting element having high chip adhesiveness and high heat dissipation.

[0007]

Means for Solving the Problems We form a number of metal thin films on the substrate side of a light emitting chip made of a nitride semiconductor,
The discovery that die bonding increases the bonding strength, and further enumerating only those metals having a strong bonding strength, found that there is a tendency to increase the bonding strength to a specific metal element, and to form the present invention. Reached. That is, in the nitride semiconductor light emitting device of the present invention, the nitride semiconductor is grown on the first main surface side of the oxide substrate having the first main surface and the second main surface, and the second main surface side To Al, Ti, Zr, Cr,
Ni, Mo, W, Ge, Si, Sn, Zn, Cu, M
A light emitting chip on which a first heat dissipation thin film containing at least one metal selected from the group consisting of n, V, and Nb is formed, with the first heat dissipation thin film facing the support surface,
A nitride semiconductor light-emitting device that is die-bonded to a support via an adhesive having thermal conductivity and conductivity, wherein the adhesive having thermal conductivity and conductivity;
A film containing at least one metal selected from the group consisting of Pt, Ti, and Ni between the first heat dissipation thin film and a thickness substantially equal to or greater than the thickness of the first heat dissipation thin film Wherein a second heat dissipation thin film is formed.

Further, another nitride semiconductor light emitting device according to the present invention is characterized in that the first heat dissipation thin film has a thickness of 50 Å to 10 μm.

Further, in another nitride semiconductor light emitting device according to the present invention, the first heat radiation thin film is made of Ti, Cr, Ni, Zr.
And at least one metal selected from the group consisting of:

Further, another nitride semiconductor light emitting device according to the present invention is characterized in that the first heat dissipation thin film is a metal containing Ti and the second heat dissipation film is Pt.
Still further, in another nitride semiconductor light emitting device of the present invention, the adhesive having thermal conductivity and conductivity is Si, Ge,
At least one metal selected from the group consisting of Sn and Au are included. Furthermore, another nitride semiconductor light emitting device according to the present invention is characterized in that the adhesive having thermal conductivity and conductivity contains Si and Au. Still further, in another nitride semiconductor light emitting device according to the present invention, the nitride semiconductor light emitting device is a nitride semiconductor light emitting device, and the support is a heat sink.

[0011]

FIG. 1 is a schematic cross-sectional view showing one structure of a light emitting device according to the present invention. Specifically, the structure of a laser device cut in a direction perpendicular to a resonance direction of laser light is shown. Is shown. The basic structure of the light emitting chip has a double hetero structure in which an n-type layer 2, an active layer 3, and a p-type layer 4 are sequentially stacked on a first main surface of an oxide substrate 1,
Further, a ridge shape is formed above the p-type layer so that light emission is concentrated on the active layer 3 corresponding to a portion below the p-electrode 11. The light emitting chip is die-bonded in a face-up state to a heat sink or a submount serving as a support 30 via a conductive adhesive 23, and a conductive adhesive is attached to the second main surface side of the oxide substrate 1. A first thin film 21 made of a specific metal is formed for the purpose of enhancing the adhesion to the first thin film 23. The n-electrode 10 and the pad electrode 12 electrically connected to the p-electrode 11 are respectively wire-bonded with gold wires (denoted as wires in the figure).

Further, since the substrate 1 is an oxide substrate, an n-electrode cannot be formed on the back surface (second main surface) of the substrate. Therefore, the structure is such that the nitride semiconductor layer on the first main surface side is etched to extract the n-electrode 10 and the p-electrode 11 on the same surface side. In the nitride semiconductor laser device in which the n-electrode 10 and the p-electrode 11 are formed on the same surface side, as shown in FIG. By providing two n-electrodes 10 symmetrically, the threshold current tends to decrease. Further, when the n-electrode 10 is provided on almost the entire surface of the n-type layer 2 exposed by etching, the threshold voltage tends to decrease.

Further, it is electrically connected to the p-electrode 11,
The pad electrode 12 for wire bonding having a larger surface area than the electrode is formed. The pad electrode 12 is formed via an insulating film 13 formed on the surface of the nitride semiconductor layer exposed by the etching. The surface area of the p-electrode 11 is not large enough to allow wire bonding. Therefore, p
By providing a pad electrode 12 electrically connected to the electrode 11, wire bonding to the p electrode can be performed. Since the p-electrode 11 needs to make ohmic contact with the uppermost p-type layer 4, its material is limited, but the pad electrode 12 can be firmly bonded to the p-electrode 11,
Any material may be used as long as it has good conductivity.
The insulating film 13 is made of, for example, SiO ₂ , TiO ₂ , Al ₂
It can be formed of an insulating material such as O ₃ or polyimide, and has a thickness of, for example, 100 Å to 5 μm or less, except for the surface of the nitride semiconductor layer on which the n-electrode 10 and the p-electrode 11 are to be formed. Formed over the entire surface. Insulating film 13
Has the effect of preventing the pad electrode 12 from coming into contact with the n-type layer 2 and causing a short circuit, and also prevents the surface of the light emitting chip from being damaged and damaging the element.

Next, the relationship between the oxide substrate and the first thin film, which is an important point of the present invention, will be described. In the light emitting element of the present invention, an oxide is used for the substrate. Sapphire (Al ₂ O ₃ ), spinel (MgAl)
₂ O ₄ ), zinc oxide (ZnO), magnesia (MgO)
Can be used, but sapphire or spinel is generally used.

Next, the first thin film 21 formed on the second main surface side of the oxide substrate is a metal having an electronegativity of less than 2.0,
Any metal that is stable in air may be used. For example, Al = 1.
5, Ti = 1.5, Zr = 1.4, Cr = 1.6, Ni
= 1.8, Mo = 1.8, W = 1.7, Ge = 1.8,
Si = 1.8, Sn = 1.8, Zn = 1.6, Cu =
As described in 1.9, Mn = 1.5, V = 1.6, and Nb = 1.6, metals excluding alkali metals and having a melting point of 200 ° C. or more can be used, and among them, the most preferable is used. The first thin film 21 is made of at least one metal selected from the group consisting of Ti, Cr, Ni, Zr, and Mo. The first thin film 21 can be formed with a thickness of usually 50 Å to 10 μm using a normal CVD apparatus such as vapor deposition and sputtering. By forming this first thin film,
The adhesiveness between the oxide substrate 1 and the conductive adhesive 23 is improved, and the thermal conductivity is further improved. The electronegativity depends on the value of L. Pauling.

Further, as the conductive adhesive 23 for connecting the first thin film 21 and the support 30, an adhesive having a high thermal conductivity containing a metal can be used, such as a silver paste, an In paste, a Pt paste, or the like. There are Pb-Sn solder and other metal-based adhesives. Among them, a conductive adhesive containing Au and at least one metal selected from the group consisting of Si, Ge, and Sn, specifically, Au- Si, Au-Ge,
Au-Sn or the like is used. Although the composition ratio of each metal of these specific adhesives is not particularly defined, usually, when Au is contained more than Si, Ge, and Sn, stronger adhesive force and higher thermal conductivity can be obtained. When the light emitting chip is die-bonded, the conductive adhesive 23 is 50 Å to 1 Å.
In a state of a thin film of about 0 μm, it can be formed on the surface of the first thin film 21 in advance, or can be formed on the support side.

FIG. 2 is a schematic sectional view showing another embodiment of the laser device of the present invention. As in FIG. 1, a sectional view of the laser device cut in a direction perpendicular to the resonance direction of the laser beam. And the same reference numerals as those in FIG. 1 indicate the same members. This element differs from the element of FIG. 1 in that a second thin film 22 made of a metal having a higher melting point than Au is formed on the first thin film. This second thin film 22
Has the effect of preventing the conductive adhesive 23 from being mixed into the first thin film 21 and being alloyed by heating during die bonding, thereby preventing the first thin film from being altered. That is, the second thin film 22 is formed by the first thin film 21 and the conductive adhesive 2.
3 acts as a barrier layer between them and has an effect of preventing the adhesive strength from being reduced. As a material of the second thin film, for example, Pt, Ti, Ni or the like can be preferably used.
Also, the thickness of the second thin film is not particularly limited, and is desirably substantially the same as or larger than the first thin film.

In the light emitting device of the present invention, Al, Ti, Zr, Cr, Ni, Mo,
It is not clear whether the formation of a metal thin film having an electronegativity of less than 2.0, such as W, Ge, Si, Sn, Zn, Cu, Mn, V, and Nb, improves the adhesive strength. There is a clear difference from the case where the above metal thin film is formed. The possible causes are as follows. When the light emitting chip is die-bonded, the conductive adhesive is heated to several hundred degrees Celsius.
During heating, heat is applied to the first thin film and the second thin film formed on the light emitting chip.
The metal contained in the conductive adhesive and the metal contained in the first thin film and the second thin film partially alloy or eutectic. At this time, it is presumed that a combination of a metal material of the oxide substrate material, the first thin film, and the conductive adhesive may enhance some physical adhesive force or chemical adhesive force.

[0019]

[Embodiment 1] Sapphire substrate C of 2 inch φ
An n-type contact layer made of n-type GaN, an n-type light confinement layer made of n-type AlGaN, a light guide layer made of n-type AlGaN, and InGaN
A laser wafer is prepared in which an active layer made of p-type AlGaN, a light guide layer made of p-type AlGaN, a p-type light confinement layer made of p-type AlGaN, and a p-type contact layer made of p-type GaN are stacked. The laminated structure of the nitride semiconductor is merely an example for laser oscillation, and is not limited to this structure.

Next, after forming a mask of a predetermined shape on the uppermost layer of the nitride semiconductor of this wafer, RIE (reactive ion etching) is performed using SiCl ₄ gas and Cl ₂ gas, and FIG. An n-type contact layer on which an n-electrode is to be formed is exposed in the shape as shown. After exposing the n-type contact layer, a mask is formed and etching is performed again. A part of the p-type contact layer and the p-type cladding layer are etched to form a ridge shape from the p-type cladding layer as shown in FIG. By these etchings, as shown in FIG.
The n-type contact layer symmetrical to the ridge-shaped stripe is exposed.

After exposing the n-type contact layer, an insulating film made of SiO ₂ is formed on the surface of the nitride semiconductor layer by a CVD method except for the uppermost p-type contact layer and the surface of the n-type contact layer on which the n-electrode is to be formed. To form a film having a thickness of 1 μm. After the formation of the insulating film, 2 is formed on almost the entire surface of the uppermost p-type contact layer.
A p-electrode made of Ni-Au having a stripe shape of μm is formed, and a stripe-shaped Ti
An n-electrode made of Al is formed. Then, a pad electrode made of Ni-Au is formed on the p-electrode via an insulating film as shown in FIG.

After the electrodes are formed, the sapphire substrate is wrapped to a thickness of 80 μm, polished and polished, and the polished surface is formed of a first Ti film made of Ti by CVD.
Is formed in a thickness of 0.1 μm.

Subsequently, on the first thin film made of Ti, A
A conductive adhesive layer made of u-Sn (70% -30%) is formed with a thickness of 0.5 μm.

After forming the conductive adhesive layer, the substrate is forcibly cleaved to form a nitride semiconductor.

[Outside 1] A resonance surface is formed on a surface corresponding to the surface, and a bar-shaped laser chip is manufactured. The outer surface is a side surface of a hexagonal prism (square surface, M
Surface).

Next, on the resonance surface side of the bar-shaped laser chip,
Using a plasma CVD apparatus, a dielectric multilayer film composed of SiO ₂ and TiO ₂ is formed to form a reflecting mirror, and the bar-shaped laser chip is divided by scribing at a position parallel to the n-electrode. Obtain a rectangular laser chip of × 500 μm square.

The laser chip obtained as described above is die-bonded to a heat sink heated to 400 ° C. in a face-up state using a die bonder. Thousands of laser elements die-bonded to heat sink
Randomly extract 1000 pieces from among them, and furthermore, n
The electrode and the p-electrode are each wire-bonded with a gold wire. When the laser chip was removed from the heat sink during the wire bonding step or after the wire bonding or was removed, the yield was 99% or more, and it was found that the laser element was die bonded very firmly. Further, when this laser element was oscillated by a direct current, it showed a laser oscillation of 410 nm and a life of one hour or more.

Example 2 In Example 1, a second thin film made of Pt was placed on top of the first thin film made of Ti.
It is formed with a thickness of 2 μm, and Au-S is formed on the second thin film.
A conductive adhesive layer made of i is similarly formed. Otherwise, the laser chip was die-bonded in the same manner as in Example 1, and the electrodes were wire-bonded. The yield was 99.5.
%, And no laser chip was peeled off from the heat sink. Further, the life of the laser element was almost the same as that of Example 1.

[Example 3] In Example 1, a spinel substrate was used as the substrate, a nitride semiconductor was grown on the first main surface of the spinel substrate, and after growth, the polished spinel substrate was polished on the second main surface side. Then, a first thin film made of Cr is formed to a thickness of 0.1 μm, and an Au- thin film is formed on the first thin film made of Cr.
A laser chip was obtained and wire-bonded in the same manner except that a conductive adhesive layer made of Ge (70% -30%) was also formed with a thickness of 0.5 μm, and the yield was also 99%. As described above, the life of the laser element was almost equal to that of the first embodiment.

[Embodiment 4] In the third embodiment, a second thin film made of W is formed on the first thin film made of Cr by 0.2.
μm, and Au—Si on the second thin film.
A conductive adhesive layer made of the same is formed in the same manner. Otherwise, after die bonding the laser chip in the same manner as in Example 1,
When the electrodes were wire-bonded, the yield was 99.5% or more, and no laser chip was peeled off from the heat sink. Further, the life of the laser element was almost the same as that of Example 1.

Example 5 In Example 1, a spinel substrate was used as the substrate, a nitride semiconductor was grown on the first main surface of the spinel substrate, and after growth, the second main surface of the polished spinel substrate was polished. First, a first thin film made of Ni is formed to a thickness of 0.1 μm, and an Au- thin film is formed on the first thin film made of Ni.
A laser chip was obtained and wire-bonded in the same manner except that a conductive adhesive layer made of Si (70% -30%) was also formed with a thickness of 0.5 μm, and the yield was also 99%. As described above, the life of the laser element was almost equal to that of the first embodiment.

[Embodiment 6] In Embodiment 1, a first thin film made of Zr is formed to a thickness of 0.1 μm on the polished sapphire substrate on the second principal surface side, and the first thin film made of Zr is formed.
A laser chip was obtained and wire-bonded in the same manner as above except that a conductive adhesive layer made of Au-Sn (70% -30%) was also formed on the thin film with a thickness of 0.5 μm. Similarly, the yield was 99% or more, and the life of the laser element was almost the same as that of the first embodiment.

[Embodiment 7] In the first embodiment, a first thin film made of Mo is formed to a thickness of 0.1 μm on the polished sapphire substrate on the second main surface side, and the first thin film made of Mo is formed. A laser chip was obtained and wire-bonded in the same manner except that a conductive adhesive layer made of Au-Sn (70% -30%) was formed with a thickness of 0.5 μm on the same. The yield was 99% or more, and the life of the laser element was almost the same as that of the first embodiment.

[Embodiments 8 to 16] In the first embodiment, Al was added to the polished sapphire substrate on the second main surface side.
(Example 8), W (Example 9), Si (Example 10), Sn (Example 1)
1), Zn (Example 12), Cu (Example 13), Mn (Example 1)
4) A first thin film made of V (Example 15) and Nb (Example 16) is formed to a thickness of 0.1 μm, and Au-Sn (70% -30%) is formed on the first thin film. A laser chip was obtained and wire-bonded in the same manner except that the conductive adhesive layer was formed to a thickness of 0.5 μm, and the yield was 93 to 95% as compared with Example 1. Although slightly reduced as described above, the life of the laser element was almost equal to that of the first embodiment.

[Comparative Example 1] In Example 1, Pd (electronegativity =
A first thin film of 2.2 is formed to a thickness of 0.1 μm, and Au-Sn (70% -30%) is formed on the first thin film.
%), And a laser chip was obtained in the same manner as above, except that the conductive adhesive layer was formed with a thickness of 0.5 μm, and wire bonding was performed. The yield also decreased to 85%.

[Comparative Example 2] In Example 1, Pt (electronegativity =
A second thin film of 2.2 is formed with a thickness of 0.1 μm, and a conductive adhesive layer of silver paste is formed on the first thin film with a thickness of 0.5 μm. When a laser chip was obtained in the same manner and wire bonding was performed, the yield was reduced to 60%.

[Comparative Example 3] In Example 1, Au (electronegativity =
A first thin film of 2.4) is formed with a thickness of 0.1 μm, and a conductive adhesive layer of Au—Ge is formed on the first thin film with a thickness of 0.5 μm. Otherwise, a laser chip was obtained in the same manner and wire bonding was performed. As a result, the yield was reduced to 88%.

[0037]

As described above, in the nitride semiconductor device of the present invention, a thin film made of a specific metal is formed on the substrate side where no nitride semiconductor layer is formed, and this specific metal is formed. In this state, by bonding to the support via a conductive adhesive such as Au-Sn while heating,
The adhesiveness of the light emitting chip is improved. Further, when a second thin film made of a high melting point metal is formed on the first thin film, the barrier effect is enhanced and the adhesiveness is further improved. Furthermore,
In the light emitting device of the present invention, since the bonding material uses a material having good heat conductivity including all metals, the life of the device is improved especially when used for a light emitting device requiring heat radiation such as a laser device. It is very convenient in making it work. As described above, the laser element has been described as the light emitting element of the present invention.
It is also possible to apply to an element.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating one structure according to a light emitting element of the present invention.

FIG. 2 is a schematic cross-sectional view showing another structure according to the light emitting element of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Oxide substrate 2 ... N-type layer 3 ... Active layer 4 ... P-type layer 10 ... N-electrode 11 ... P-electrode 12 ... Pad electrode 13: insulating film 21: first thin film 22: second thin film 23: conductive adhesive 30: support

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Ikuizumi Ikuizumi 491, Kaminakacho Oka, Anan-shi, Tokushima Prefecture Inside Nichia Chemical Industry Co., Ltd. 100 Nichia Kagaku Kogyo Co., Ltd. 5F073 AA11 AA83 CA07 CB05 DA25 DA32 DA33 FA22

Claims (7)

[Claims] An oxide substrate having a first main surface and a second main surface, wherein a nitride semiconductor is grown on the first main surface side;
Al, Ti, Zr, Cr, Ni, Mo, W,
The light-emitting chip on which the first heat-dissipating thin film containing at least one metal selected from the group consisting of Ge, Si, Sn, Zn, Cu, Mn, V, and Nb is formed, comprises a first heat-dissipating thin film and a support surface. And a nitride semiconductor light emitting device die-bonded to a support via an adhesive having thermal conductivity and conductivity, wherein the adhesive having thermal conductivity and conductivity is provided. , The first
A first heat radiation thin film that includes at least one metal selected from the group consisting of Pt, Ti, and Ni between the first heat radiation thin film and the first heat radiation thin film; 2. A nitride semiconductor light emitting device, wherein the heat dissipation thin film is formed. 2. The nitride semiconductor light emitting device according to claim 1, wherein said first heat dissipation thin film has a thickness of 50 Å to 10 μm. 3. The method according to claim 1, wherein the first heat radiation thin film is made of Ti, Cr, N
3. The nitride semiconductor light emitting device according to claim 1, comprising at least one metal selected from the group consisting of i and Zr. 4. The nitride semiconductor light emitting device according to claim 1, wherein said first heat radiation thin film is a metal containing Ti, and said second heat radiation film is Pt. . 5. The method according to claim 1, wherein the adhesive having heat conductivity and conductivity contains Au and at least one metal selected from the group consisting of Si, Ge, and Sn. The nitride semiconductor light emitting device according to any one of the above. 6. The nitride semiconductor light emitting device according to claim 1, wherein the adhesive having thermal conductivity and electrical conductivity contains Si and Au. 7. The nitride semiconductor light emitting device according to claim 1, wherein said nitride semiconductor light emitting device is a nitride semiconductor light emitting device, and said support is a heat sink.