JPH04112583A - Manufacture of sic blue light-emitting diode - Google Patents

Abstract

PURPOSE:To improve the efficiency of extraction of blue light by reducing absorption in an N-type substrate of blue light emission. CONSTITUTION:The thickness (a) of an N-type layer 2 extends from 0.5mum to 20mum in either case. An N-type substrate 1 is removed until thickness (c) reaches 30mum. The substrate 1 may be taken off completely. 50mum or more are required for handling a sample because 50mum or more are needed as the total thickness a+b+c of the N-type substrate 1 and the N-type layer 2 and a P-type layer 3. However, 1mum or more are required as (b) for efficiently injecting currents. These diodes are manufactured through processes in which the N-type layer 2 is homoepitaxial-grown on the N-type substrate 1, the P-type layer 3 is homoepitaxial-grown on the layer 2, one part or the whole of the N-type substrate 1 is removed and electrodes 4, 5 are formed. Accordingly, an SiC blue light-emitting diode having the high efficiency of extraction of blue light can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a SiC blue light emitting diode.

(Prior art) 6H type 5iC (hereinafter referred to as 5iC) has a band gap of approximately 3
．． 0 electron volts, p-n both! It is expected to be used as a material for blue light emitting diodes because it is easy to control gas conductivity.

SiC blue light emitting diode, Journal Of'
ApP1ied Physics Volume 53, Page 6962 (
As reported in 1982), it is known that light is emitted from an n-type epitaxial growth layer of a pn junction. Further IEBE TRANSACTIONS ON ELB
CTRON DBVICBS BD-30 volume 277 (
(1983), aluminum-doped p-type SiC and undoped n-type SiC are different from aluminum-doped p-type SiC.
It has been reported that C has lower blue light transmittance.

From these points, aluminum-doped n-type SiC single crystal substrate (hereinafter, n-type SiC single crystal substrate is referred to as p-type substrate)
As an example of the structure of a SiC blue light emitting diode using an aluminum doped p-type homoepitaxial growth layer (hereinafter referred to as a p-type homoepitaxial growth layer), as shown in FIG. (hereinafter referred to as a p-type layer) 3, an n-type homoepitaxially grown layer (hereinafter, an n-type homoepitaxially grown layer is referred to as a 1-type layer) 2 in nitrogen 1, and a p-side down layer. It is known that the site is introduced using the n-site up method. Note that 4 is a T] type electrode and 5 is a p type electrode. In this structure, since the n-type layer 2, which is a blue light emitting layer, is the outermost surface, when blue light is extracted from the surface, the blue light is not absorbed by the n-type layer 3 or the n-type substrate 6, resulting in high light extraction efficiency. Be expected. As mentioned above, since the blue light transmittance of aluminum-topped p-type SiC is low, it is not preferable to assemble it in the n-side-down/n-site-up method as shown in FIG. 2(b).

However, the Institute of Electrical Engineers of Japan Electronic Materials Study Group material EFill
Although there are reports on p-type SiC bulk single crystal growth for the purpose of creating n-type substrates, such as p.-88-2423 (September 1988), no n-type substrates have actually been supplied.
It is difficult to obtain. Therefore, it is difficult to stably manufacture a SiC blue light emitting diode having the structure shown in FIG. 2(a).

An example of an available SiC single crystal substrate is an undoped n-type SiC single crystal produced by the Acheson method. As shown in FIG.
When a blue light emitting diode is manufactured by sequentially homoepitaxially growing the 3-doped p-type layer 3, it can be grown by the p-side-down/n-site-up method as shown in Figure (a), or by the p-side down/n-site up method as shown in Figure (a).
Assemble using the n side down/n site up method as shown in b). On page 25 of the May 1989 issue of Electronics, an n-type layer thickness of 3 to 5 μm and a p-type layer thickness of 6 μm using an n-type substrate are described.
~13 μm blue light emitting diodes have been reported, with p
It is reported that the site-down method improves blue light extraction efficiency by 70 to 8096 points compared to the n-site up method. The reason for this is not explained in the same document, but
Said 18EE TRANSACTIONS ON BL
Considering the report in ECTRON DBVICES BD-30, page 277 (1983), one of the reasons is that in the case of the n-site up method, part of the blue light is absorbed by the n-type layer 3 on the surface. . However, even in an undoped n-type SiC single crystal, the transmittance of blue light is not 100%, and a portion of the blue light is absorbed. Therefore, even with the p-side down type diode shown in Figure 3(a), which is reported to have improved light extraction efficiency, the thicker the n-type substrate 1, the more blue light is absorbed there. becomes high, which is one of the causes of a decrease in blue light extraction efficiency.

Therefore, when using the p-side down method using an undoped n-type substrate, it is desirable to reduce absorption of blue light emitted from the n-type epitaxial growth layer by the n-type substrate.

(Problems to be Solved by the Invention) The present invention provides a SiC blue light emitting diode using an n-type substrate, which improves the efficiency of blue light extraction by reducing the absorption of blue light emitted from the n-type epitaxial growth layer by the n-type substrate. Provided is a method for manufacturing a SiC blue light emitting diode that can improve the performance of the SiC blue light emitting diode.

(Means for Solving the Problems) The present invention provides an n-type Si substrate having a thickness a on an n-type SjC single crystal substrate.
After homoepitaxially growing a C single crystal layer and an n-type SiC single crystal layer with a thickness b in sequence so as to satisfy the following formula, the n-type SiC single crystal substrate was removed to a thickness C, and a p-side down method was applied. This is a method of manufacturing a SiC blue light emitting diode, which is characterized by assembling the SiC blue light emitting diode.

However, 0.5μm≦a≦20μm 1μm≦b Oμm≦c≦30μm 5 (Iμm≦a+b+c (for Ri) Hereinafter, the present invention will be explained in detail using the drawings.

FIGS. 1(a) and 1(b) are cross-sectional views of a blue light emitting diode showing an embodiment of the present invention, in which 1 is an n-type substrate, 2 is a nitrogen-doped n-type layer, and 3 is an aluminum-doped layer. The arrows in the figure indicate blue light extracted from the n-type layer 2 to the outside. The thickness a of the n-type layer 2 is 0.5 μm or more and 20 μm in both cases.
m or less.

If it is less than 0.5 μm, it is too thin and a part of the injected current cannot contribute to the recombination of holes and electrons, resulting in inefficient light emission. If the thickness exceeds 20 μm, the excess portion cannot contribute to the recombination of holes and electrons, and conversely absorbs blue light, reducing light extraction efficiency. The thickness C of the n-type substrate 1 is removed to 30 μm as shown in FIG. Furthermore, as shown in FIG. 4(b), the thickness may be 0 μm, that is, it may be completely removed.

When the thickness is 30 μm or less, the transmittance of blue light is improved and the light extraction efficiency is increased. n-type substrate l・n-type layer 2・
The reason why the total thickness a+b+c of the n-type layer 3 is required to be 50 μm or more is because 50 μm or more is required for handling the sample in the steps after liquid phase epitaxial growth. therefore,
In the same figure (b), for example, if a is 0.5 μm, b is 49
．． If a is 20 μm, then b is 30 μm or more. However, in order to inject the current efficiently, b is 1μ.
m or more is required. In the case of these blue light emitting diodes in the same figure (a), the thickness C of the n-type substrate l on the front surface is 30 μm.
The transmittance of blue light is high because it is below, and in the case of FIG. 3B, since the n-type layer 2 is on the outermost surface, there is no absorption by the n-type substrate 1, and the blue light extraction efficiency is high in both cases.

These diodes are manufactured by homoepitaxial growth of an n-type layer 2 on an n-type substrate I, further homoepitaxial growth of an n-type layer 3 thereon, removal of part or all of the n-type substrate I, and formation of an electrode 4.5. It is manufactured through the process of

For homoepitaxial growth of the n-type layer 2 and n-type layer 3, for example, Journal of Applied Phys.
It is most common to use a liquid phase epitaxial growth method as reported in Vol. 47, p. 4546 (1976). This is a method in which silicon is melted in a graphite crucible to saturate it with carbon, and a SiC substrate is immersed in the low temperature part of the melt. When growing the n-type layer 2, an n-type layer using nitrogen as a donor can be obtained by adding silicon nitride into silicon. When growing the p-type layer 3, a p-type layer with aluminum as an acceptor can be obtained by doping aluminum into silicon. However, since the blue light emission of a SiC blue light emitting diode is dominated by light emission by a donor-acceptor pair, when growing the n-type layer 2, not only silicon nitride but also aluminum is added to the silicon within a range that does not reverse the electrical conductivity type. Added.

In the liquid phase epitaxial growth method, it is necessary to stably hold the SiC substrate, so the SiC substrate used has a thickness of several hundred μm or more at the time of liquid phase epitaxial growth inside the shell. Therefore, after sequentially homoepitaxially growing the n-type layer 2 on the n-type substrate 1 with a thickness of 0.5 μm or more and 20 μm or less, and the n-type layer 3 with a thickness of Ium or more to form a pn bond, until the n-type substrate l becomes 30 μm or less. Some or all of it needs to be removed. Polishing is used as the method, but etching may also be used, or both may be used in combination.

Polishing can be performed using a polishing device using a diamond abrasive, a boron carbide abrasive, or the like.

Since SiC has a high hardness, the polishing materials and polishing devices that can be used are limited, but by selecting an appropriate polishing material and polishing device, it can be polished to a thickness of 30 μm or less with high precision.

Etching, for example, Journal of Ap
pliedPhysics Volume 48, Page 4831 (197
A method using an etching gas such as that reported in 1997 is applicable.

Note that when the n-type substrate l is completely removed as shown in FIG. 1(b), the electrical conductivity type of the substrate does not need to be n-type.

The thickness a of the n-type layer 2 is an optimal thickness determined from the properties of the n-type layer 2 (impurity concentration, blue light transmittance, diffusion length, etc.), which is within the range of 0.5 μm or more and 20 μm or less. Just do it. However, when the n-type substrate 1 is completely removed as shown in FIG. 1(b), it is desirable to grow the n-type layer 2 thicker depending on the accuracy of polishing and etching.

The thickness b of the n-type layer 3 may be at least the minimum necessary thickness determined from the conditions of 1 μm or more and the overall thickness of 50 μm or more. However, if it is too thick, depending on the resistivity of the n-type layer 3, problems may occur, such as the diode becoming highly resistive and the drive voltage becoming high, and the growth of the n-type layer 3 taking a long time. Considering the above, the total thickness is 100
Approximately μW is appropriate.

For the n-type electrodes 4 and the like, well-known nickel can be used, and for the n-type electrode 5, a well-known aluminum-silicon alloy can be used.

When a current is passed through the above blue light emitting diode 1ζ with the n-type electrode 5 side set as positive and the n-type electrode 4 side set as negative, n
Blue light is emitted from the mold layer 2. Blue light is shown in Figure 1 (a)
, (b), the thinner the n-type substrate 1 on the front surface is, the more n If the mold substrate 1 is completely removed, the light extraction efficiency can be further increased.

(Example) An example will be explained using FIG. 1.

A blue light emitting diode was manufactured as described below.

As the n-type substrate 1, a SiC single crystal made by the Acheson method and made into a parallel flat plate with a thickness of 1 mm was used. The above liquid phase epitaxial method was used for the homoepitaxial growth of the n-type layer 2 and the n-type layer 3.

The carrier concentrations of both n-type layer 2 and n-type layer 3 are approximately 10
"cm flat.The pn junction is... ■a=5μm, b=IOμm.

■a=5. czm, b=65μm.

(3) Three types were prepared, a=5 μm and b=85 μm, and polished so that the overall thickness was constant at 90 μm. Therefore, the n-type substrate I remaining after polishing is: (1) c - 75 μm 1 (2) c = 20 μm 1 (3) c = 0 μm (completely removed).

■ corresponds to FIG. 1(a), ■ corresponds to FIG. 1(b), and ■ corresponds to a comparative example. The n-type electrode (AI-3i) 5 is formed on the entire surface of the p-type layer 3 side, and the n-type electrode (Ni) 4 is formed on the n-type substrate l side (■
(in the case of n-type layer 2 side), a circular shape with a diameter of 100 μm was formed. After forming the electrodes, the sample was diced into squares with a size of 300 μm×300 μm so that the n-type electrode 4 was located at the center to obtain a blue light emitting diode chip.

The obtained diode chip was fixed to the stem using the p-site down method, that is, with the n-type electrode 5 side facing down, and a circular n
A bonding wire for current injection was connected to the mold electrode 4, and a current of 20 mA was passed with the n-type electrode 5 side as positive and the n-type electrode 4 side as negative, causing blue light to be emitted, and the luminous intensity was measured on the top surface of the chip. As a result, in case (2), the intensity of the extracted blue light is 1.
In the case of 6 to 2.0 times, the intensity of the extracted blue light is 2.
It was 0 to 2.4 times. This is because by making the n-type substrate 1 thinner or removing it, absorption of blue light by the n-type substrate 1 can be reduced and blue light extraction efficiency can be increased.

(Effects of the Invention) As described above, according to the present invention, a SiC blue light emitting diode with high blue light extraction efficiency can be manufactured.

[Brief explanation of drawings]

FIGS. 1(a) and (b) are cross-sectional views showing an embodiment of manufacturing the SiC blue light emitting diode of the present invention, and FIGS. 2(a) and (b)
) is a cross-sectional view showing an example of the structure of a SiC blue light emitting diode using an aluminum-doped substrate;
FIG. 2 is a cross-sectional view showing an example of the structure of an iC blue light emitting diode. l...n-type substrate, 2...nitrogen-doped n-type layer, 3...
Aluminum-doped p-type layer, 4...n-type electrode, 5...
- N-type electrode, 6...aluminum doped type substrate.

Claims (1)

[Claims] (1) After sequentially homoepitaxially growing an n-type SiC single-crystal layer with a thickness a and a P-type SiC single-crystal layer with a thickness b on an n-type SiC single-crystal substrate so as to satisfy the following formula, the n-type A method for manufacturing a SiC blue light emitting diode, characterized in that a SiC single crystal substrate is removed to a thickness of c and assembled using a p-side down method. However, 0.5μm≦a≦20μm 1μm≦b 0μm≦c≦30μm 50μm≦a+b+c