JPH08298341A - Light emitting diode - Google Patents

Abstract

PURPOSE: To improve moistureproofness of an element surface, prevent decrease of luminous output, and improve the life of an element, by forming a thin film composed of insulating inorganic material, on the light emitting surface of a light emitting diode, and forming a thin thermosetting resin film on the thin inorganic film. CONSTITUTION: A clad layer 4 is grown on a P-type GaAs substrate 1, and further an active layer 2 and an N-type GaA As clad layer 3 are grown. An AuBe electrode 5 is formed. A thin film composed of insulating inorganic material is formed on the light emitting surface of a light emitting diode, and a thin thermosetting resin film is formed on the thin inorganic film. Resin is soft as compared with inorganic material, so that, when resin of high stress is used as a molding resin, the thin resin film as mold resin relieves the stress. Hence the stress applied to the thin inorganic film is reduced. Thereby the deterioration of luminous output due to moisture and the decrease of luminous output due to stress applied to the molding resin can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device, and more particularly to a light emitting device in which the surface of the device is protected by a specific substance to prevent deterioration of light emission output.

[0002]

2. Description of the Related Art A light emitting device using a compound semiconductor is generally called a light emitting diode (hereinafter abbreviated as LED). For example, GaP, GaAsP, GaAs, and GaAlAs are used in LEDs using III-V group compound semiconductors. However, these compound semiconductors have a drawback that the element surface is oxidized when exposed to humidity for a long time, and the oxide film makes it difficult for light to pass therethrough, so that the light emission output is reduced. When the light emitting element is used industrially, generally, the light emitting element is completely sealed with an epoxy resin, and L
Although it is used to form an ED lamp, this resin is inferior in moisture resistance and allows moisture in the atmosphere to enter, and therefore cannot prevent oxidation of the surface of the compound semiconductor light emitting device.
In particular, GaAlAs-based LEDs are easily oxidized by moisture, and as a result, the emission output is reduced, which is a major obstacle when the LEDs are used outdoors such as in displays and traffic lights. In addition, it is possible to change the epoxy resin used as a countermeasure to a highly hygroscopic and hard one, but when these resins are used for compound semiconductor crystals that have a large stress and are extremely weak against external stress. , Induces crystal defects and, conversely, reduces the light emission output. Therefore, in order to prevent surface oxidation, various studies using a surface protective film have been conducted. For example, a method of forming a natural oxide film by chemical surface treatment (for example, Proceedings of the 42nd Japan Society of Applied Physics, page 600, 9a-D-3, 1981, 44th).
Proceedings of the Japan Society of Applied Physics, 485 pages, 28a-H-3, 1
983, and JP-A-4-216683), silicon oxide,
A method of forming a protective film of silicon nitride or silicon oxynitride (see, for example, JP-A-62-20383 and JP-A-1).
-226181, Japanese Patent Laid-Open No. 4-167569, Takuo Kanno,
Semiconductor plasma process technology, industrial books, etc.) have been proposed. It is also practiced to cover the surface with a resin such as polyimide having a specific refractive index to improve the luminous efficiency. However, it is not used as a protective film due to its poor moisture resistance.

[0003]

The adhesion between the compound semiconductor surface and the oxide film interface is weak only by the method of forming a natural oxide film.
Since it is difficult to grow a dense film, it is impossible to completely prevent moisture. When silicon oxide or silicon nitride is used as the surface protection film, external stress or Ga caused by the mold resin
Since there is a difference in the thermal expansion coefficient from III-V group compound semiconductors such as As, stress is generated, crystal defects are induced on the semiconductor surface, and cracks occur in the silicon nitride film etc., and reliability that can withstand long-term use. There was a problem that I could not get. Therefore, a composite film in which a silicon oxide film is formed on a surface of a III-V group compound semiconductor and then a silicon nitride film is formed is used, or a silicon oxynitride film is adopted. It is difficult to completely compensate for the drawbacks of No. 1 and obtain a complete passivation film. In addition, the organic resin film is inferior in moisture resistance to the inorganic film, and cannot obtain long-term reliability. With the conventional method, it is difficult to protect the light-emitting element from moisture, and even if it is used for a long time in a severe environment of high temperature and high humidity, the light output is prevented from being deteriorated and the productivity is not impaired. A method for forming a protective film is desired. On the other hand, although moisture resistance can be improved to some extent by selecting a resin having low water absorption when the LED chip is sealed with a mold resin, a resin having low moisture absorption has a large stress and is a III-V group compound. Since semiconductors are weak against stress,
On the contrary, it causes stress deterioration. In addition, in extreme cases, a film of silicon oxide, silicon nitride, or the like may be cracked, which may adversely affect the moisture resistance. These measures against resin stress are also problems that must be solved in order to further improve the reliability of the light emitting diode chip. The present invention is to solve the above-mentioned problems and provides a light-emitting device that improves the moisture resistance of the device surface, prevents a decrease in light-emission output, and prolongs the life of the device and does not hinder productivity. The purpose is to do.

[0004]

The inventors of the present invention have conducted extensive studies to solve the above problems, and as a result, as a result, a thin film made of an inorganic material such as silicon oxide, silicon nitride or silicon oxynitride is formed on the surface of the compound semiconductor other than the electrode region. The inventors have found that the above problems can be solved by forming a thin film of thermosetting resin on the surface of which a polyimide, a cyclic olefin resin, or the like is formed, and completed the present invention.

The semiconductor substrate used in the present invention is GaA.
A commonly used semiconductor substrate for a light emitting diode such as s, GaP or InP can be used. As the structure of the LED, GaAlAs, AlInG are used for the active layer and the clad layer.
The one having a layer containing an Al component such as aP or AlGaN is most effective, but GaAs or GaP homojunction or GaAlAs / GaAs used in a normal LED is used.
There is no problem in application even with a heterojunction such as. The thickness of the active layer is preferably 0.5 to 30 μm, but in the clad layer,
2 μm or more is desirable. As the growth method, the liquid phase epitaxial growth method is optimal in terms of cost, but a halide vapor phase epitaxial growth method, a MOCVD method using an organic metal, or an MBE method can also be used. The electrode can be made of any material as long as it has ohmic characteristics and does not impair the bonding.

A protective film such as silicon oxide or silicon nitride is generally C
It is formed by a vapor phase method called VD. Among various CVDs, the plasma CVD method, which has a low reaction temperature, is excellent in terms of adhesion, but the thermal decomposition CVD method may be used, and the optimum thickness is in the range of 0.02 μm to 0.5 μm. If it is thin, it may not function as a passivation film, and if it is thick, there is a concern that cracks may occur due to stress strain. Alternatively, a chemical solution in which an inorganic silicon resin such as glass resin is dispersed in a solvent may be uniformly applied to the wafer surface by a spinner or the like and sintered at high temperature to be used as a protective film. The thermosetting resin film formed thereon is required to have a high heat resistance resin having a glass transition point of 160 ° C. or higher, assuming that the LED chip is put into a bonding process, a reflow process and the like. In that sense, a polyimide-based resin having a high heat-resistant temperature is most preferable among ordinary resins. When a photosensitive polyimide resin having a photosensitive group is used as the polyimide resin, a pattern can be formed by an ordinary photolithography method after coating the entire surface of the wafer, and the process can be simplified. However, a general polyimide resin may be formed into a sheet on the surface of the chip and then etched with hydrazine or the like for use. Incidentally, those having a photosensitive group require curing in order to accelerate the imide bond reaction,
It is necessary to perform the treatment at a temperature and for a time such that the imidization ratio becomes 60% or more. The thickness of the thermosetting resin is 0.2 to 2
0 μm is desirable. If it is thinner than 0.2 μm, the effect as a protective film is not sufficient, and if it is thicker than 20 μm, peeling easily occurs due to a difference from the coefficient of thermal expansion. It is effective that the protective film completely covers the entire surface of the chip from the side surface of the chip to the upper surface of the chip, but even if the protective film is formed only on the upper surface of the chip, the effect is not impaired.

[0007]

[Function] By forming a resin thin film on an inorganic thin film, even if a high stress resin is used as the molding resin, the resin is softer than the inorganic resin, so the resin thin film relieves the stress of the molding resin. The stress applied to the inorganic thin film is reduced. Therefore, the occurrence of cracks in the inorganic thin film is reduced, and even if a few cracks occur, the resin thin film is formed on the cracks, so that the thin film is protected. Although the stress relaxation of the mold resin by the resin thin film is the same without the inorganic thin film, the moisture resistance is not sufficient only with the resin thin film. It is possible to effectively prevent deterioration of the light emission output due to humidity and reduction of the light emission output due to the stress of the molding resin only after forming the resin thin film on the inorganic thin film.

[0008]

【Example】

Example 1 As an example, an example in which a plurality of LED elements are formed on a GaAlAs light emitting diode epitaxial substrate will be described. Its sectional structure is shown in FIG. As the epitaxial substrate, a Zn-doped p-type GaAlAs clad layer (20 μm) 4 was grown on a p-type GaAs substrate 1 having a plane orientation (100) by a liquid phase epitaxial method, and a Zn-doped p-type GaAlAs layer as an active layer was formed thereon. (1 μm) 2 was grown, and a Te-doped n-type GaAlAs clad layer (40 μm) 3 was further grown thereon to create the layer. The Al mixed crystal ratio of the active layer is set so that the emission wavelength is 660 nm.
_It was adjusted to _0.35 Ga _0.65 As.

On the three surfaces of the n-type GaAlAs cladding layer, AuGe / Au (thickness: 1000 A / 60, respectively).
00A) electrode material is formed by vacuum evaporation method, and p-type GaAs
An AuBe (thickness: 6000A) electrode 5 was formed on the surface of the substrate by a vacuum deposition method. The electrode 5 on the n side has a diameter of 130 μm
The region of φ was protected by a resist material or the like by photolithography, and the region other than the above region was removed by etching. The p-side electrode on the back surface was a solid electrode. After removing the resist material, 5 at 420 ° C. under N ₂ atmosphere
After alloying for minutes, ohmic electrodes were formed on the front and back surfaces. Plasma C made from silane and nitrous oxide
Silicon oxide was deposited to a thickness of 0.25 μm by the VD method. In addition, a photosensitive polyimide (PIM manufactured by Asahi Kasei
An EL series and a glass transition point of 355 ° C.) were uniformly applied with a spin coater. A pattern was formed by a photolithography method so as to protect the electrode region and the region other than the dicing street portion 9, and the silicon oxide in the electrode region and the dicing street portion was removed with an HF-ammonium fluoride aqueous solution. To cure the resin, heat treatment was performed at 350 ° C. for 60 minutes in a nitrogen atmosphere. The film thickness of polyimide is 3 μm.

The element is cut with a dicing saw and the LED
A chip was formed. The plan view is shown in FIG. After the chip was die-mounted on the lead frame, wire bonding was performed with a gold wire of 25 μm, and further molding was performed with an epoxy resin to produce a lamp. High temperature / high humidity energization test (temperature: 60 ° C, humidity: 95% R) for 100 samples
H, current; 13 mA continuous energization) was performed. In the LED lamps obtained by this method, 100% of the LED lamps satisfy the standard of the residual brightness rate of 85% or more after 1000 hours. The property maintains a high survival rate. In this embodiment,
AlGaAs / GaAs LED was used, but GaAs
Similar effects were obtained with infrared LEDs and GaP visible LEDs.

[Embodiment 2] As an embodiment, an example in which a plurality of LED elements are formed on a GaAlAs light emitting diode epitaxial substrate will be described. The process up to the formation of the ohmic electrode is the same as in Example 1. Silicon nitride was deposited to a thickness of 0.1 μm by the plasma CVD method using silane and ammonia as raw materials. Furthermore, a photosensitive cyclic olefin resin (Z-Coat series manufactured by Nippon Zeon, glass transition point 168)
(° C.) was evenly applied with a spin coater. A pattern was formed by a photolithography method so as to protect regions other than the electrode region and the dicing street part, and silicon nitride in the electrode region and the dicing street part was removed with an HF-ammonium fluoride aqueous solution. In order to cure the resin, heat treatment was performed at 300 ° C. for 60 minutes in a nitrogen atmosphere. The film thickness of the cyclic olefin resin was 2 μm.

The element is cut with a dicing saw and the LED
A chip was formed. The sectional structure before cutting is the same as that of FIG. 1 except that silicon oxide 7 is replaced by silicon nitride 8 in FIG. The plane of the chip after cutting is shown in FIG. After the chip was die-mounted on the lead frame, wire bonding was performed with a gold wire of 25 μm, and further molding was performed with an epoxy resin to produce a lamp. High temperature / high humidity current test (temperature: 60 ° C, humidity: 95% RH,
Current: 13 mA continuous energization) was performed. With the LED lamp obtained by this method, the residual brightness rate after 1000 hours was 8
Those satisfying the standard of 5% or more were 100%. The property maintains a high survival rate. In this embodiment, AlG
We used aAs / GaAs LED, but GaAs infrared L
Similar effects were obtained for ED and GaP visible LEDs.

COMPARATIVE EXAMPLE 1 As an example, an example in which a plurality of LED elements are formed on an epitaxial substrate for a GaAlAs light emitting diode will be shown. The process up to the formation of the ohmic electrode is the same as in Example 1. Silicon oxide was deposited to a thickness of 0.25 μm by the plasma CVD method using silane and nitrous oxide as raw materials. A resist pattern was formed by a photolithography method so as to protect regions other than the electrode region and the dicing street part, and silicon oxide in the electrode region and the dicing street part was removed with an HF-ammonium fluoride aqueous solution.

The element is cut with a dicing saw and the LED
A chip was formed. Its sectional structure is shown in FIG. After the chip was die-mounted on the lead frame, wire bonding was performed with a gold wire of 25 μm, and further molding was performed with an epoxy resin to produce a lamp. High temperature / high humidity energization test (temperature: 60 ° C, humidity: 95% R) for 100 samples
H, current; 13 mA continuous energization) was performed. Among the LED lamps obtained by this method, 92% of the LED lamps satisfy the specification of the residual brightness rate of 85% or more after 1000 hours.
Among the LED lamps of the conventional method obtained by this method, there were some lamps that did not satisfy the standard of the residual brightness ratio after 1000 hours. The reliability is inferior to that of the embodiment of the present invention.

[Comparative Example 2] An example in which a plurality of LED elements are formed on an epitaxial substrate for a GaAlAs light emitting diode will be shown as an example. The process up to the formation of the ohmic electrode is the same as in Example 1. Photosensitive polyimide (Asahi Kasei
PIMEL series (manufactured by PIMEL, glass transition point 355 ° C.) was uniformly applied with a spin coater. A pattern was formed by photolithography so as to protect regions other than the electrode region and the dicing street portion. To cure the resin, heat treatment was performed at 350 ° C. for 60 minutes in a nitrogen atmosphere. The film thickness of polyimide is 3 μm.

The element is cut with a dicing saw and the LED
A chip was formed. Its sectional structure is shown in FIG. After the chip was die-mounted on the lead frame, wire bonding was performed with a gold wire of 25 μm, and further molding was performed with an epoxy resin to produce a lamp. High temperature / high humidity energization test (temperature: 60 ° C, humidity: 95% R) for 100 samples
H, current; 13 mA continuous energization) was performed. 90% of the LED lamps obtained by this method satisfy the standard of the residual brightness rate of 85% or more after 1000 hours.

Among the conventional LED lamps obtained by this method, there were some lamps which did not meet the standard of the residual brightness rate after 1000 hours. The reliability is inferior to that of the embodiment of the present invention.

[0018]

According to the present invention, by forming a composite film composed of an inorganic thin film such as silicon oxide and a thermosetting resin thin film such as polyimide on the semiconductor surface, a silicon oxide single layer or a polyimide single layer is formed. The highly reliable moistureproof property that cannot be obtained is obtained. High reliability characteristics are obtained in high temperature and high humidity current test.

[Brief description of drawings]

FIG. 1 is a plan view of LED elements of Examples 1 and 2.

FIG. 2 is a cross-sectional view of LED elements of Examples 1 and 2.

FIG. 3 is a sectional view of an LED element of Comparative Example 1.

FIG. 4 is a sectional view of an LED element of Comparative Example 2.

[Explanation of symbols]

 1 GaAs substrate 2 active layer 3 n clad layer 4 p clad layer 5 ohmic electrode 6 thermosetting resin 7 silicon oxide 8 silicon nitride 9 dicing street

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiko Usuda 1505 Shimokagemori, Chichibu, Saitama Prefecture Showa Denko Co., Ltd. Chichibu Factory (72) Takayuki Kamemura 1505 Shimokagemori, Chichibu, Saitama Showa Denko Co., Ltd. Chichibu Inside the factory (72) Inventor Atsushi Yoshioka 1505 Shimokagemori, Chichibu, Saitama Prefecture Showa Denko Co., Ltd.Inside Chichibu factory (72) Inventor Takuro Sugawara 1505 Shimokagemori, Chichibu, Saitama Inside Showa Denko Co., Ltd.

Claims (7)

[Claims] 1. A light emitting diode comprising a thin film made of an insulating inorganic material formed on a light emitting surface of the light emitting diode, and a thermosetting resin thin film formed on the thin film. 2. The light emitting diode according to claim 1, wherein the thermosetting resin is a resin having an imide bond. 3. The light emitting diode according to claim 1, wherein the thermosetting resin is a resin having a photosensitive group. 4. The glass transition point of the thermosetting resin is 160 ° C.
It is above, The light emitting diode in any one of Claims 1-3. 5. The light emitting diode according to claim 1, wherein the inorganic thin film is at least one of silicon oxide, silicon nitride, and silicon oxynitride. 6. The thickness of the inorganic thin film is from 0.05 to 0.1.
5 μm, the thickness of the thermosetting resin thin film is 0.2 to 20 μm
The light emitting diode according to any one of claims 1 to 5. 7. The light emitting diode according to claim 1, wherein the light emitting layer or the light emitting surface is formed of a compound semiconductor crystal containing aluminum.