JPH02290084A - Silicon carbide light emitting diode device and manufacture of silicon carbide single crystal - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a silicon carbide light emitting diode device capable of emitting blue light and a method for producing a silicon carbide single crystal.

(Explanation) Conventional technology In general, silicon carbide [3iC] has attracted attention as an environmentally resistant semiconductor material due to its physical and chemical properties such as excellent heat resistance, mechanical strength, and resistance to radiation. , Moreover, for the same chemical composition, SiC crystal has cubic,
Various hexagonal crystal structures exist, and the forbidden band width is 2.
Because it has a wide range of 39 to 3.33 eV and is capable of forming pn junctions, it is seen as a promising material for light emitting diodes that emit visible light in the entire wavelength range from red to blue. A 6H type SiC crystal with a forbidden band width of 3 eV is used as a material for blue light emitting diodes.

The growth of SiC single crystals is usually carried out by the dip method, which is a type of liquid phase epitaxial growth method, as described in the magazine "Electronic Technology, Vol. 26, No. 14, pp. 128-129, published by Nikkan Kogyo Shimbun. This device is constructed as shown in Fig. 4, in which a crucible (16) made of graphite is filled with silicon [Si] and heated in an inert gas atmosphere. The crucible (16) is completely heated by a high-frequency induction heating coil (not shown) wound around the outside of the crucible (16), and an St melt (17) is formed, and the tip of the support rod (18) made of graphite is heated. V-shaped notch (1
9) is equipped with a 6H type S + Cm crystal substrate (20),
Once fixed, the substrate (20) is immersed together with the support rod (18) in the melt (17) for a certain period of time, and a 6H type SiC single crystal grows on the surface of the substrate (20).

The growth of such a SiC single crystal is achieved by dissolving a small amount of carbon [C] into the St melt (17) from the heated crucible (16).
This is carried out by the Si melt <17) being carried near the surface of the substrate (20) by convection and reacting with St.

Further, during crystal growth, the support rod (18) is rotated as shown by the arrow in FIG. 1, and the substrate (20) is rotated in a fixed position, thereby making the growth layer uniform.

Note that during the growth of the n-type layer, silicon nitride [s:+Nil] is added to the Si melt (17) as a donor impurity, and a small amount of aluminum [A
2] is added, and during growth of the p-type layer, Ap is added as an acceptor impurity.

In addition, conventional SiC light emitting diodes are based on the electronic technology mentioned above.
As shown in Volume 26, No. 14, P128-P129, an n-type layer and a p-type layer with controlled impurity concentrations are sequentially stacked on one main surface of an n-type SiC substrate, and a p-type Al/Si on the layer surface! Au/Nit electrodes are formed on the other main surface of an n-type substrate.

(c) Problems to be Solved by the Invention However, since SiC, which is a light-emitting material, has an indirect transition type energy band structure, its luminous efficiency is lower than that of a direct transition type light-emitting material. For this reason, SiC light emitting diodes have only a weaker emission intensity than light emitting diodes made of other materials.

Therefore, the technical object of the present invention is to provide a SiC light emitting diode device and a method for manufacturing a silicon carbide single crystal that can achieve high brightness.

(2) Means for Solving the Problems The present invention provides an arrangement in which an n-type layer and a p-type layer made of silicon carbide are laminated in this order on one main surface of an n-type silicon carbide substrate. A silicon carbide light emitting device comprising a regenerated silicon light emitting diode element in which an n-type ohmic electrode and a p-type ohmic electrode are formed on a flush F and the p-type layer, respectively, and a stem for mounting and fixing the light emitting diode element. In order to solve the above problem in a diode device, the crystal growth plane of the n-type substrate has a (000 plane) plane or a (0001 plane).
The n-type ohmic electrode and the p-type ohmic electrode are formed partially with respect to the other main surface of each silicon carbide; It is characterized in that it has a substantially trapezoidal cross section with the surface of the mold layer as the base and the surface of the n-type substrate as one or two sides, and is fixed to the stem on the p-type layer side.

A more preferred feature of the present invention is that, in the above configuration, the (OO+)T) plane is used as the crystal growth plane of the n-type substrate.

Further, in the present invention, in the above configuration, the n-type substrate has a resistance of 10Ω.
In addition to having a specific resistance of less than 300 nm, the n-type electrode has a specific resistance of
It is characterized by being arranged at the corner of the other main surface of the mold substrate.

Further, in the present invention, AP and N are added to a silicon melt in a crucible made of graphite, a silicon carbide single crystal substrate is immersed in the melt, and an n-type silicon carbide single crystal substrate is placed on the substrate. In a method for producing a silicon carbide single crystal in which a layer is grown in a liquid phase phase, the amount of Aρ added to the silicon form liquid is changed to a carrier of a silicon carbide single crystal obtained when only A feet are added to the silicon melt. The concentration is 5. 5 X 10" - 6 X 10"am-', and the amount of N added to the silicon melt is set to a range of The carrier concentration is 7x tQ
1 Set to a range of 7 to 5 x 1016 cm-3,
Moreover, the growth temperature is 1650 to 1800°C.

(e) Operation The device of the present invention uses a (0001) plane or a plane inclined from the (0001) plane as the crystal growth plane of the substrate, and an n-type polarizing electrode and a p-type ohmic electrode are attached to each silicon carbide surface. High-intensity blue light can be obtained by forming each light emitting diode element partially, making the light emitting diode element approximately trapezoidal in cross section so that the surface of the p-type layer has a large area, and fixing the p-type layer side to the stem.

1) Embodiment FIG. 1 shows an embodiment of the apparatus of the present invention. In the figure, (
7) shows a light emitting diode element, and the structure of such an element is as follows: (1) is a substrate made of n-type S+C (silicon capide), (2) and <3) are each a substrate (1). An n-type SiC layer and a p-type SiCJi are shown epitaxially grown on one principal surface (18) of the figure.

The light emitting diode element 7〉 has a thickness of 50 to 100ρ, for example, the surface of the n-type SiC substrate (1) is 260×26
0pm. p-type SiCffi (3) surface at 300pm
X 300pln, the cross-section has a substantially trapezoidal shape with the surface of the p-type SiC layer (3) as the bottom and the surface of the n-type SiC substrate (1) as the top.

The substrate (1) has a thickness of 30 to 80 cm, IXIO"cm-3
It has a carrier concentration above and a specific resistance below the 160Ω mark. The substrate 1> has one main surface (1a) and the other main surface (1b), and in particular, the main surface <1a> is a (0001) plane with a C (carbon) arrangement on the surface or an St (silicon) arrangement. Select the (0001) plane where is the surface, and convert that plane to <o2o>
direction or <1oTo> direction.

The above inclination angle on the life surface (1a) of the substrate is 1 to 10
6, preferably 3-10'', more preferably 3-76
In this embodiment, 5'' is adopted.

Figure 3 shows (000
The graph shows the inclination angle from the surface (1) and the emission wavelength before and after current aging of the light emitting diode element (7) manufactured using such a substrate (1).
mA, and the current application time was 50 hours. Furthermore, the emission wavelength referred to here is the light emitted from a SiC light emitting diode element, which normally has a plurality of peak wavelengths, converted into a wavelength as light of one color perceived by human vision. As is clear from the figure, in the case where the tilt angle is 0 @, the emission wavelength before energization is located on the longer wavelength side compared to the case where the inclination is allowed, and the shift width of the emission wavelength after energization is large. It has become. This is all due to the presence of many crystal defects in the growth layer formed on the substrate (1). In addition, the shift width of the emission wavelength due to energization is
Since it decreases as the tilt angle of the substrate (1) increases, it can be seen that the crystal defects in the growth layer formed on the substrate (1) decrease and the crystallinity improves. The shift width when the inclination angle is 5'' or more is approximately the same as when it is 5 degrees, so it is omitted from the table.

In this way, the selection of the tilt angle is extremely important for improving the crystallinity of the n-type SiC layer (2) on which epitaxial growth occurs and for suppressing the increase in the emission wavelength of the light emitting diode element (7). It is effective.

In addition, it is more preferable to use an inclined plane from the (000〉 plane) as the crystal growth plane in the apparatus of the present invention than the (0001) plane. Compared to the surface of This is because the shift in the emission wavelength due to energization of the die-cut element is smaller than that using an inclined plane from the (0001) plane.

The n-type SiCJi (2) has a film thickness of 5 to 10ρ, and its carrier concentration is I x 10" to 5 x 10"c+n
-', preferably 2 X 10'' to 3 X IQ'
"cm-', more preferably 5 x 10" to l x
IQ"Om-'. However, the carrier concentration in the n-type StC layer (2) is from the carrier (electron) concentration when only N is added to the carrier (hole) concentration when only A! is added.
This is the value obtained by subtracting the concentration.

Therefore, in order to obtain the carrier concentration in the n-type SiC layer 2), various combinations of the amount of N added and the amount of Al added can be considered, but the amounts of N and Al added in the present invention are as follows:
The carrier concentration can be determined as follows by converting it into the carrier concentration obtained when each is added alone.

In this example, one year old, as mentioned above, (
By using a plane inclined from the 000"'1) plane or the (0001) plane, the crystallinity of the n-type SiC layer (2> formed thereon) is improved. Therefore, the crystallinity of the n-type SiC layer (2>) formed thereon is improved. As a result, the number of donor-acceptor pairs serving as luminescence centers increases, and the luminescence intensity increases.

=11-1121 The p-type SiC layer (3) has a film thickness of 5 to 10 ρ, and its carrier concentration is I x 10" to 5 x 10"cm-"
, preferably 2 X 10" to 3 X 10" cm-
``C' is there.

(4) is a p-type ohmic electrode placed at the center of the surface of the p-type SJC layer (3) and partially provided on the surface of the p-type SiC layer (3); Viewed from the side, it consists of a laminated structure of a Ti film, an Al film, and a Ti film, and has a 7
It has an area of 10"' - 7 X IQ - 'cTII'. The electrode area of the p-type ohmic electrode (4) is effective in generating high-quality blue light without mixing with green light at a current of 5 to 50 mA that is normally used. That is, the generation wavelength is light emission M (in this example device, n-type Si
It is known that the current density changes depending on the current density in the portion of the C layer (2) that contributes to light emission. In addition, in the device of this embodiment, the carrier concentration is IXIO”~5×1016
cm-” p-type SiC layer (3) has a high resistivity and p
The current hardly spreads in the type S{Ciil (3), and the n-type SjC layer (2) and the p-type ohmic electrode (
4) is short, the current density flowing through the part of the n-type SiC layer (2) that contributes to light emission is lower than that of the p-type SiC layer (2).
3>, the current density in the p-type SiC layer (3), that is, the magnitude of the injection current and the p-type ohmic electrode (4)
It is determined by the area of As a result of experiments conducted by the present inventors with various injection currents and electrode areas, it was found that when the current was between 5 and 50 mA and the electrode area was 7 x 10 cm" or less, high-quality blue light without mixing with green light was obtained. However, when the electrode area is smaller than 7×10 cm, the concentration of t-current becomes large and the device deteriorates rapidly, resulting in a decrease in the reliability of the device. Therefore, the electrode area of the p-type ohmic electrode (4) is 7 x 10-' to 7 x IQ-'c
m'' is appropriate.

(5) is an n-type ohmic electrode located at a position offset from the center of the n-type SiC substrate (1) surface and partially provided on the n-type SiC substrate (1) surface. (1) When viewed from the side, it has a laminated structure of N i pJ and Pd films.

(6) and <6) are bonding electrodes provided on the p-type ohmic electrode (4) and the n-type ohmic electrode (5), respectively, and when viewed from each ohmic electrode, Ti film, Pd film, Au
Forms a layered structure of membranes.

(8) is a protective film made of an A j2 10 M film or a SiO film, which is deposited on the surface and side surfaces of the n-type SiC substrate (1) of the light emitting diode element (7). (9) is a silver paste, and <10) is a first stem on which a light emitting diode element (7) is mounted. The first stem (10) has a reflective part (11) surrounding a light emitting diode element (7).
It is fixed to the first stem (10) on the C layer (3) side.

The reason for this element arrangement is as follows. n-type StC layer (2
> is the part corresponding to the p-type ohmic electrode (4), so the p-type SiCJ! ! If it is fixed with the (3) side up, the light directed upward will be blocked by the p-type ohmic electrode (4) and cannot be extracted from the top of the element. Furthermore, the light transmittance of the n-type SiC substrate (1) is higher than that of the p-type SfC layer (3). Furthermore, the specific resistance of the substrate (1) is as low as 1Ω or less, and current flows easily, so the n-type ohmic electrode (5) can be placed at the corner of the other main surface (1b) of the substrate (1), which prevents radiation On the other hand, it does not substantially serve as a shield. Furthermore, in the device of the present invention, the light emitting diode element 7) has a substantially trapezoidal cross section with a wide bottom surface, so light is emitted from the n-type SiC layer (2) and passes through the n-type SiC substrate (1) to the side surface of the element. Since the incident angle with respect to the side surface of the element becomes large, the light directed toward the element reduces internal reflection and is efficiently extracted to the outside of the element.

(12) is a gold wire, (13) is a second stem, and the second stem <13) is electrically connected to the terminal electrode (6) on the n-type ohmic electrode (5) via the gold wire (12). I can connect to. (14) is an epoxy resin-based transparent resin mold that covers part of the light emitting diode element (7), the first and second stems (10), and the stems (13).

Next, an example of a method for manufacturing the device of this embodiment will be explained with reference to FIG.

Figure 2(a) shows the first step, and shows the (000th) plane or (
An n-type SiC substrate (1) with a thickness of 350 to 500 sm is prepared. Then, the (000 plane) or (0001) plane of such SjC substrate (1) is
Polish in the grass 0> direction or <10 work 0> direction, 1 to 1
Tilt 0°. =15--16= After that, the inclined surface was polished for 400 minutes to remove the polishing damage.
~500'C (7) KOH melt b Louis 41:
Etching treatment at 1500 to 1800'C t7) H atmosphere. The obtained inclined surface is the whole surface of the substrate (1) (
1a).

FIG. 2<b> shows the second step, using the apparatus shown in FIG.
n-type SiCJ at ~1800°C, preferably 1650-1800°C, for example 1700°C! t(2), p-type SiC layer (
3) are sequentially grown by liquid phase epitaxial growth. At this time, when growing the n-type SiC layer (2) and the p-type SiC layer (3),
The amount of impurities added into the i-melt (17) is determined to obtain the carrier concentration described. For example, in an n-type SiC layer
2) Carrier concentration IXIO”~5×10’”c
m-” 1.3X10-”~
3. OX 10-”wt%, Al 0.2-12.
Oat. % may be added respectively. In addition, p-type SjC layer (
3) Carrier concentration 1×1017 to 5×101″On-
'To obtain Al, 045-20. Oat. % may be added.

After growing each layer, the other main surface of the n-type SiC substrate (1) is polished to make the thickness of the entire laminated substrate 50 to ioom.

FIG. 2(e) shows the third step, in which a Ti film with a thickness of 300 or more, for example, a Ti film with a thickness of 500 and an A! A Ti film with a thickness of 4,000 yen was vacuum deposited in this order to form a p-type ohmic electrode (4).
A film with a thickness of 300 mm is formed on the other main surface (1b) of the n-type SiC substrate (1).
A Ni film with a thickness of 0 and a Pd film with a thickness of 5000 are vacuum deposited in this order to form an n-type ohmic electrode (5). Here, the p-type ohmic electrode (4) will be located at 7 in the center of the device when the multilayer substrate is separated into devices in the future (indicated by the broken line in the figure).
Using a metal mask, partially form on the surface of the p-type SiC layer (3) of each element so that it has an area of be done. Further, the n-type ohmic electrode ai (5) is arranged so as to be offset from the center of the element, and is partially formed on the surface of the n-type SiC substrate (1) of each element.

Thereafter, such a laminated substrate is exposed to vacuum or Ar, Ha. Nt
, He or a mixed atmosphere of 900
Apply heat treatment at ~1000°C. As a result, each ohmic 1t pole obtains ohmic properties with SiC.

FIG. 2(d) shows the fourth step, in which the p-type ohmic electrode (
4) On top and n-type ohmic electrode 5〉, film thickness 100
Ti film of 0 people, Pd film of 2000 people, thickness 5000
The Au films are vacuum-deposited in this order to form bonding electrodes (6) and (6), respectively.

After that, the laminated substrate is coated with Ar, H2, N,
, He or a mixed atmosphere of 30
Heat treatment is performed at 0 to 500°C.

FIG. 2(e) shows the fifth step, in which the n-type S
Grooves (15), (15), etc. for element isolation having a depth of 20 to 70 − are formed by dicing on the iC substrate (1) side. At this time, the grooves (15) (15)... are formed in a wedge shape, so each element separated in the future will have the surface of the p-type SiC layer (3) as the bottom and the n-type SiC substrate (1> as the top). The cross section is approximately trapezoidal.

FIG. 2(f) shows the sixth step, where grooves (15) (15)
Groove (15)<15)... is formed on the laminated substrate with...
Mechanically separate each light emitting diode element (7〉
get.

After each light-emitting diode element (7) is organically cleaned, the n-type SiC substrate (1) of the light-emitting diode element (7) is cleaned by Ar sputtering with the n-type SiC substrate (1) on the source side.
Al10. Or Si
A protective film (8) consisting of an n2 film is deposited.

Figure 2(g) shows the final process, in which the light emitting diode element (
7〉 p-type SiC layer (3) side to the first stem (10〉),
Place it through silver paste (9) and apply it to 130-17
Heat treatment at 0°C. Next, the bonding electrode (6) and the second stem (13) on the side of the n-type SiC substrate (1) are wire bonded with a gold wire (12). At this time, a protective film 8 is placed on the bonding electrode (6) on the n-type SiC substrate (1) side.
), but if the film thickness is less than about 2000, the gold wire (12) will break through the protective film (8) by wire bonding and be connected to the bonding electrode (6). If the film (8) is too thick to be pierced by the wire bonding, the protective film (8) on the pounding electrode 6> may be mechanically removed before wire bonding.

Finally, a part of the light emitting diode element (7) and the first and second stems (10) and (13) are covered with an epoxy resin transparent resin mold (14) not shown, as shown in FIG. The SiC light emitting diode device is completed.

According to the above manufacturing method, an n-type SiC substrate (1) with a carrier concentration of 8 x 101F CTI1-'' is used, and its crystal growth plane is set to be a plane inclined by 5 degrees in the <ti2o> direction from the (000 plane) plane. Each layer was formed under the following conditions, and the SIC
A light emitting diode device was manufactured.

Also, the area of the p-type ohmic electrode (4) is 4X10-'
It was designated as cITl2.

The emission wavelength of the SiC light emitting diode device manufactured in this way is 4B2 nm, and the emission intensity is 20 nm when the driving current is 20 nm.
It was 10-12 mcd at mA.

(g) Effects of the Invention According to the apparatus of the present invention, an n-type SiC layer with excellent crystallinity can be formed by using a plane inclined from the (000 plane> plane or <0001) plane as the crystal growth plane of the substrate. Therefore, a large amount of impurities can be added without impairing crystallinity. As a result, the number of donor-acceptor pairs serving as luminescence centers increases, and the luminescence intensity increases. Further, an n-type ohmic electrode and a p-type ohmic electrode are partially formed on each SiC surface, and a light emitting diode element is formed with the p-type SiC layer surface as the bottom side and the n-type SiC substrate surface as the top side. By making it trapezoidal in cross section and fixing it to the stem on the p-type SiC layer side, light can be efficiently extracted to the outside.

As described above, in the device of the present invention, the emission intensity can be increased to 10 to 12 mcd at a driving current of 20 mA,
It is possible to turn that light into high-quality blue light without any green light mixed in. Further, according to the present invention, high-intensity blue light with a small long-wavelength shift width of the emission wavelength due to current aging can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one embodiment of the device of the present invention, FIG. 2 is a sectional view showing an example of the manufacturing method of the device of the present invention, and FIG.
The figure is a characteristic diagram showing the tilt angle of the substrate and the emission wavelength of the light emitting diode element before and after energization aging, and FIG. 4 is a cross-sectional view of the crystal growth apparatus used for manufacturing the apparatus of the present invention.

Claims (4)

[Claims] (1) An n-type layer and a p-type layer made of silicon carbide are laminated in this order on one main surface of an n-type silicon carbide substrate, and an n-type layer and a p-type layer are respectively stacked on the other main surface of the n-type substrate and on the p-type layer. In a silicon carbide light emitting diode device comprising a silicon carbide light emitting diode element on which a type ohmic electrode and a p type ohmic electrode are formed, and a stem for mounting and fixing the light emitting diode element, the crystal growth surface of the n type substrate is Ha(000@
1@) plane or a plane inclined from the (0001) plane, the n-type ohmic electrode and the p-type ohmic electrode are formed partially on each silicon carbide surface, and the light emitting diode element has a substantially trapezoidal cross section with the surface of the p-type layer as the base and the other main surface of the n-type substrate as the top, and is fixed to the stem on the p-type layer side. silicon carbide light emitting diode device. (2) On the crystal growth surface of the above n-type substrate (000@1@)
2. The silicon carbide light emitting diode device according to claim 1, wherein a surface inclined from the surface is used. (3) The n-type substrate has a specific resistance of 1.0 Ωcm or less, and the n-type ohmic electrode is arranged at a corner of the other main surface of the n-type substrate. Silicon carbide light emitting diode device. (4) Al and N are added to a silicon melt in a crucible made of graphite, a silicon carbide single crystal substrate is immersed in the melt, and an n-type layer made of silicon carbide single crystal is formed on the substrate. In the method for producing a silicon carbide single crystal grown by liquid phase epitaxial growth, A added to the silicon melt
The carrier concentration of the silicon carbide single crystal obtained when only Al is added to the silicon melt is 5.5 × 1.
When only N is added to the silicon melt, the amount of N added to the silicon melt is set to a range of 0^1^6 to 6 x 10^1^7 cm^-^3. The carrier concentration of the silicon carbide single crystal obtained is 7×10^1^7 ~
A method for producing a silicon carbide single crystal, characterized in that the growth temperature is set in a range of 5 x 10^1^8 cm^-^3 and the growth temperature is set at 1650 to 1800°C.