JPH0851235A - Manufacture of semiconductor light emitting element - Google Patents

Abstract

PURPOSE:To provide a manufacturing method of a semiconductor light emitting element whereby the generations of its crystal defects and dislocations are suppressed even with mismatching of lattice constants and the differences of thermal expansion coefficients which are present among its semiconductor layers and electrodes, and whereby the lengths and times of its manufacturing processes can be contracted. CONSTITUTION:(a) On a substrate 1, gallium nitride based compound semiconductor layers wherein at least an n-type layer 4 and a p-type layer 6 are provided and a light emitting layer 5 is formed are formed. (b) n-side and p-side electrodes 9, 8 which are connected electrically with the respective n-type and p-type layers 4, 6 are formed. (c) After the formations of both the electrodes 9, 8, the whole of the gallium nitride based compound semiconductor layers is subjected to a heat treatment at a temperature not lower than 400 deg.C. Thereby, both the annealing of the p-type layer 6 and the alloyings of the electrodes 9, 8 with the semiconductor layers are performed concurrently.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor light emitting device. More specifically, it relates to a method for manufacturing a semiconductor light emitting device using a gallium nitride based compound semiconductor suitable for blue light emission.

Here, a gallium nitride compound semiconductor is a compound of a group III element Ga and a group V element N or
A semiconductor made of a compound in which a part of Ga of the group III element is replaced with another group III element such as Al and In and / or a part of N of the group V element is replaced with another group V element such as P and As. Say.

A semiconductor light emitting device is a light emitting diode (hereinafter referred to as LED) having a double heterojunction such as a pn junction or a pin, a super luminescent diode (SLD) or a semiconductor laser diode (LD).
A semiconductor element that emits light.

[0004]

2. Description of the Related Art Conventionally, blue LEDs have a lower brightness than red and green and are difficult to put into practical use. In recent years, however, gallium nitride compound semiconductors have been used, and a low resistance p-type semiconductor layer doped with Mg has been formed. As a result, the brightness is improved and it is in the limelight.

A conventional gallium nitride-based LED manufacturing method is carried out, for example, in the steps shown in FIGS.

First, as shown in FIG. 3A, a substrate 21 made of sapphire (Al ₂ O ₃ single crystal) or the like is formed on the substrate 21.
As a metalorganic compound gas, trimethylgallium (hereinafter, referred to as TMG), ammonia (NH ₃ ) and a dopant together with a carrier gas H ₂ by a metalorganic vapor phase growth method (hereinafter, referred to as MOCVD method) at a low temperature of 00 to 700 ° C. SiH ₄ or the like is supplied to form the low-temperature buffer layer 22 made of an n-type GaN layer to a thickness of about 0.01 to 0.2 μm, and then the same gas is supplied at a high temperature of 900 to 1200 ° C. The high temperature buffer layer 23 made of GaN is formed to have a thickness of about 2 to 5 μm.

Then, a raw material gas of trimethylaluminum (hereinafter referred to as TMA) is further added to the above gas, and n
N _- type Al _x Ga _1-x N containing Si as a type dopant
A (0 <x <1) layer is formed, and an n-type cladding layer 24 for forming a double heterojunction is formed to have a thickness of about 0.1 to 0.3 μm.

Next, trimethylindium (hereinafter referred to as TMI) is introduced in place of the above-mentioned source gas TMA,
A material whose band gap energy is smaller than that of the cladding layer, for example, Ga _y In _1-y N (0 <y ≦ 1)
And the active layer 25 is formed to have a thickness of about 0.05 to 0.1 μm.

Further, cyclopentadienylmagnesium for Mg or Zn as a p-type impurity (hereinafter, referred to as a p-type impurity by replacing SiH _{4 as an} impurity source gas with the same source gas as the gas used for forming the n-type cladding layer 24). Cp ₂ Mg) or dimethylzinc (hereinafter referred to as DMZn) is added to the reaction tube, and the p-type cladding layer 26 of p-type A
The l _x Ga _1-x N layer is vapor-grown. As a result, the n-type cladding layer 24, the active layer 25, and the p-type cladding layer 26 form a double heterojunction.

Next, to form the cap layer 27, a gas similar to that used for the buffer layer 23 is used as an impurity source gas, ie, C.
By supplying p ₂ Mg or DMZn, a p-type GaN layer is grown to about 0.3 to 1 μm.

After that, a protective film 28 such as SiO ₂ is provided on the entire surface of the growth layer of the semiconductor layer (see FIG. 3B), 40.
Annealing is performed at 0 to 800 ° C. for 20 to 60 minutes (see FIG. 3C) to activate the p-type cladding layer 26 and the cap layer 27. The reason why this annealing is performed is as follows. That is, the p-type layer of the gallium nitride based compound semiconductor is doped with Mg or the like as a dopant, but Mg or the like is mixed with H _{2 of} the carrier gas or H of NH ₃ of the reaction gas at the time of doping to change the dopant High resistance without working. Therefore, an annealing process is provided to separate Mg from H and release H to reduce the resistance.

Next, after removing the protective film 28, in order to form an n-side electrode, a resist is applied and patterning is performed to partially remove each of the grown semiconductor layers as shown in FIG. 4 (d). N-type Ga removed by dry etching
The buffer layer 23, which is the N layer, is exposed. Then, A
A metal film of u, Al or the like is formed by sputtering or the like to form both the p-side and n-side electrodes 29, 30 and the LED chip is formed by dicing.

Next, in order to make ohmic contact between the electrode metal such as Al and the gallium nitride based compound semiconductor, heat treatment is carried out at about 300 ° C. in an H ₂ atmosphere to form an alloy (FIG. 4 (e)). reference).

[0014]

In the conventional method for manufacturing a semiconductor light emitting device using a gallium nitride based compound semiconductor, it is necessary to perform the heat treatment twice, that is, the annealing treatment and the alloying treatment as described above. Moreover, the sapphire substrate and the gallium nitride-based semiconductor crystal have large differences in the lattice constant and the thermal expansion coefficient, and repeated thermal shock of returning to room temperature by heat treatment causes repeated expansion and contraction, resulting in a buffer contact with the sapphire substrate. Crystal defects such as cracks and dislocations are generated in the layer, and the crystal defects and dislocations also propagate to the clad layer and the active layer, which are the operating layers, and the luminous efficiency is reduced and the life is also shortened.

The present invention solves such a problem, suppresses the generation of crystal defects and dislocations due to the mismatch of lattice constants and the difference in thermal expansion coefficient, and can shorten the manufacturing process. The purpose is to provide a manufacturing method.

[0016]

According to the method of manufacturing a semiconductor light emitting device of the present invention, (a) a gallium nitride compound semiconductor layer having at least an n-type layer and a p-type layer and having a light emitting layer is laminated on a substrate. And (b) forming an n-side electrode and a p-side electrode electrically connected to the n-type layer and the p-type layer, and (c) annealing the p-type layer by performing heat treatment after forming the both electrodes. And alloying the electrode and the semiconductor layer at the same time.

In the method of manufacturing the semiconductor light emitting device, a sapphire substrate is used as the substrate, and the n-side electrode or the p-side electrode is used.
An n-type layer in which one of the side electrodes is formed on the surface of the stacked compound semiconductor layer, the other electrode is formed by etching a part of the stacked compound semiconductor layer, and is electrically connected to the other electrode. Alternatively, it can be formed on the exposed surface of the p-type layer.

It is difficult to remove N and Ga in the gallium nitride based compound semiconductor layer by coating the surface of the compound semiconductor layer with a protective film before the heat treatment, and even if the melting point of the electrode material is lower than the annealing temperature. It is preferable because the electrode material is melted and held without flowing.

[0019]

According to the manufacturing method of the present invention, both the n-side electrode and the p-side electrode can be alloyed with the surface of the compound semiconductor layer at the same time when annealing is performed. Therefore, the annealing step and the electrode alloying step can be performed. Can be combined into one, and man-hours can be reduced. Further, since it is not necessary to raise the temperature of the compound semiconductor layer once lowered to high temperature again, the gallium nitride based compound semiconductor layer generated by repeated expansion and contraction of gallium nitride based compound semiconductors laminated on the substrate of different materials Generation of crystal defects and dislocations can be suppressed.

[0020]

Next, a method for manufacturing a semiconductor light emitting device of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing the steps of an embodiment of a method for manufacturing a semiconductor light emitting device of the present invention, and FIG. 2 is a sectional view of an LED chip manufactured by the manufacturing method of FIG.

First, as shown in FIG. 1A, a low temperature buffer layer 2 and a high temperature buffer layer 3 made of a gallium nitride based semiconductor layer such as n-type GaN are formed on a substrate 1 made of sapphire by MOCVD. Of 0.01 to 0.2 μm and 2 to 5 μm, respectively. After that, the n-type cladding layer 4, the non-doped or n-type or p-type active layer 5, the p-type cladding layer 6, and the cap layer 7 are sequentially formed. The clad layers 4 and 6 are usually 0.1 to 0.3.
The active layer 5 is formed to have a thickness of about 0.05 μm and a thickness of about 0.05 to 0.1 μm. The film formation of these gallium nitride based semiconductor layers is performed by introducing the same raw material gas as described in the prior art and reacting it to grow.

In order to form the above-mentioned cladding layer 4 into an n-type, Si, Ge, Te, etc. are replaced with SiH ₄ , GeH ₄ , T.
In order to form the cladding layer 6 into a p-type by mixing it as a gas such as eH _{4 into the} reaction gas, Mg or Zn is added to Cp ₂ Mg.
It is mixed in the source gas as an organic metal gas such as DMZn or DMZn.
The cap layer 7 is for reducing the contact resistance with the electrode and is made of p-type GaN or the like, and is formed to a thickness of 0.2 μm or more.

Next, a part of each semiconductor layer, for example, C
The high temperature buffer layer 3 is exposed by performing dry etching with l ₂ plasma. Then, a metal film made of Au, Al, or the like is formed by sputtering or the like and patterned to form p on the surface of the stacked compound semiconductor layers.
A p-side electrode 8 electrically connected to the mold layer and an n-side electrode 9 electrically connected to the n-type layer on the exposed surface of the high temperature buffer layer 3 are formed (see FIG. 1B).

After forming the electrodes 8 and 9, SiO ₂ and Si ₃ N
CVD of a protective film 10 made of ₄ or the like on the surface of the semiconductor layer
Method, PCVD method or the like (see FIG. 1C), and an annealing treatment is performed (see FIG. 1D). The annealing treatment is performed in an N ₂ atmosphere at 400 to 800 ° C. for about 0.5 to 1 hour. According to this method, N and Ga are less likely to escape from the gallium nitride-based compound due to the presence of the protective film 10. However, the method is to place it under a high pressure of N ₂ atmosphere of about 10 atm and anneal at about 400 to 800 ° C. However, the same effect can be obtained. However, it is preferable that the protective film is formed because even if the melting point of the electrode material is lower than the heat treatment temperature, it does not flow down during the heat treatment and alloying is sufficiently performed. As a result, the junction between Mg and H, which are the dopants of the p-type layer, is cut and activation is achieved, and the resistance of the p-type layer is reduced. In addition, alloying between the electrode and the semiconductor layer can be performed at the same time, and ohmic contact can be obtained.

When the annealing treatment is completed, the protective film 10 is removed by etching with a hydrofluoric acid solution, and the chips are separated into semiconductor light emitting device chips as shown in FIG.

The semiconductor light emitting device chip is placed on a lead frame, wire bonded, and then molded with an epoxy resin to complete an LED.

In the above-mentioned example, the electrodes 8 and 9 are formed on the surface side of the cap layer 7.
If a semiconductor substrate made of aN-based or the like is used, it can be made conductive, and an electrode can be formed on the back surface of the compound semiconductor layer, that is, the substrate 1 side.

In the above embodiment, Al _x Ga _1-x N,
Although it was a Ga _y In _{1 -y} N double heterojunction LED, it is a normal homo or hetero pn junction LED or a laser diode formed by forming a stripe with the above-mentioned structure, and the material is a gallium nitride compound. In order to satisfy the relationship of refractive index and band gap energy in semiconductors, Al _p
Ga _q In _1-pq N (0 ≦ p <1, 0 <q ≦ 1, 0 <p
+ Q ≦ 1) having a different composition in the general formula, and a part or all of N in the general formula being substituted with As and / or P or the like can be produced in the same process.

[0030]

According to the method of manufacturing the semiconductor light emitting device of the present invention, the annealing process for the p-type compound semiconductor layer and the alloying process for the electrodes can be completed by a single heat treatment. Can prevent defects and dislocations,
It is possible to obtain a highly reliable semiconductor light emitting device with high luminous efficiency. Further, since the heat treatment step is only required once, the heat treatment step can be reduced and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a process sectional view showing an example of a method for manufacturing a semiconductor light emitting device of the present invention.

FIG. 2 is a cross-sectional view of an LED chip manufactured by the manufacturing process of FIG.

FIG. 3 is a process sectional view showing an example of a conventional method for manufacturing a semiconductor light emitting device.

FIG. 4 is a process sectional view showing an example of a conventional method for manufacturing a semiconductor light emitting device.

[Explanation of symbols]

 1 substrate 2 low temperature buffer layer 3 high temperature buffer layer 4 n-type clad layer 5 active layer 6 p-type clad layer 7 cap layer 10 protective film

Claims (3)

[Claims] 1. A method comprising: (a) laminating a gallium nitride-based compound semiconductor layer having at least an n-type layer and a p-type layer and having a light emitting layer on a substrate; and (b) electrically connecting the n-type layer and the p-type layer. An n-side electrode and a p-side electrode that are electrically connected, (c)
A method for manufacturing a semiconductor light emitting device, characterized in that a heat treatment is performed after the formation of the both electrodes to anneal the p-type layer and alloy the electrode and the semiconductor layer at the same time. 2. A sapphire substrate is used as the substrate, one of the n-side electrode and the p-side electrode is formed on the surface of the laminated compound semiconductor layer, and the other electrode is formed of the laminated compound semiconductor layer. 2. The method for manufacturing a semiconductor light emitting device according to claim 1, wherein the portion is etched and formed on the exposed surface of the n-type layer or p-type layer electrically connected to the other electrode. 3. The method for producing a semiconductor light emitting device according to claim 1, wherein the surface of the compound semiconductor layer and the electrode are covered with a protective film before the heat treatment.