JP2001210905A - Method of manufacturing nitride semiconductor light- emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new manufacturing method of a chip of which cut surface is smooth, from a wafer where nitride semiconductor is grown on a sapphire substrate, manufacture nitride semiconductor light-emitting elements with a high yield, and realize a light-emitting element which can be turned into a laser element. SOLUTION: After nitride semiconductor containing a light-emitting active layer is grown on a surface A of the sapphire substrate, the substrate is split at an angle of 58±5 deg. or 40±5 deg. from the direction which is perpendicular to the C axis of the sapphire substrate surface, so that plane divided surfaces, which are in parallel with each other, can be obtained. As a result, a laser element using the surfaces as resonance surfaces can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

This invention relates to a nitride semiconductor (InXAlYGa1-X-YN, 0 ≦ X, 0 ≦
Y, X + Y ≦ 1) stacked light emitting diode (LE
D), a method for manufacturing a light emitting element such as a laser diode (LD).

[0002]

2. Description of the Related Art As a material for light emitting devices such as LDs and LEDs, a wide band gap semiconductor nitride semiconductor (InN) is used.
XAlYGa1-X-YN, 0≤X, 0≤Y, X + Y≤1) are known. This semiconductor is usually MO on a sapphire substrate.
It grows using vapor phase growth methods, such as VPE (organic metal vapor phase epitaxy) and MBE (molecular beam vapor phase epitaxy). Sapphire has a plane orientation such as an A plane, a C plane, an R plane, and an M plane, but a nitride semiconductor is exclusively grown on the C plane.

[0003] Generally, a nitride semiconductor wafer grown on a sapphire substrate has a lower cleavability than a GaAs, Si, GaP or other wafer having a cleavable substrate because the sapphire substrate does not have the cleavage. Therefore, there is a problem that it is very difficult to form a chip. Furthermore, since sapphire is a substance having a Mohs luminous intensity of 9 or more, even when cut with a dicer, so-called chipping such as chip breakage or chipping occurs on the cut surface, and it is difficult to obtain a chip with a flat cut surface. Was.

[0004] By the way, various laser devices made of a nitride semiconductor have been proposed. In the case of a laser device, it is necessary to form a resonance surface that reflects the light of the active layer inside. G
In the case of an infrared or red laser using an aAs substrate, a cleavage plane using the cleavage of the substrate is used as a resonance plane. However, since a nitride semiconductor wafer having a sapphire C-plane as a substrate has almost no cleavage property, it has been very difficult to form a resonance surface by breaking the substrate.

[0005]

When a wafer of a nitride semiconductor light emitting device using sapphire as a substrate is divided into chips, it is preferable that the chip division surface is a smooth surface free from chipping. If the chip can be divided into a smooth surface, the chip yield will be improved. Furthermore, in a laser device, the resonance surface must be a parallel mirror,
For that purpose, it is desirable that the chip dividing plane is a parallel and smooth plane. Accordingly, the present invention has been made in view of such circumstances, and an object thereof is to provide a new chip having a smoother cut surface than a wafer having a nitride semiconductor grown on a sapphire substrate. Provide a simple manufacturing method,
While producing nitride semiconductor light emitting devices with good yield,
Another object is to realize a light-emitting element that can be a laser element.

[0006]

SUMMARY OF THE INVENTION We have found that the above problem can be solved by growing a nitride semiconductor on a specific sapphire substrate surface and then cracking the substrate in a specific direction. Was. That is, the method for manufacturing a nitride semiconductor light emitting device of the present invention uses the sapphire substrate A
After growing a nitride semiconductor including a light emitting active layer on the surface, the surface of the substrate A is divided at an angle of 58 ± 5 ° or 40 ± 5 ° from a direction perpendicular to the C axis.

Further, a method of manufacturing a light emitting device according to the present invention is characterized in that after a substrate on which a nitride semiconductor has been grown is split, a reflection mirror is formed on the split surface to form an optical resonance surface.

FIG. 2 is a unit cell diagram showing the plane orientation of the sapphire single crystal. Sapphire has a rhombohedral structure to be precise, but can be approximated by a hexagonal system as shown in this figure. In the manufacturing method of the present invention, a nitride semiconductor is grown on the A-plane of sapphire as shown by the hatched portion in the figure. As shown in FIG. 2, the A-plane can be represented by, for example, six types of plane orientations as shown in FIG. 2, but all represent the same plane.

(Equation 1) It can be shown.

After a nitride semiconductor is grown on the A-plane of sapphire, the direction perpendicular to the C-axis of the A-plane and the vertical direction of the A-plane shown in FIG. Break the board at an angle of ゜. A preferred direction is 58 ± 5 ° to obtain a smoother divided surface than 40 ± 5 °. Note that 58 ° corresponds to approximately the R surface of sapphire. FIG. 1 is a plan view of a sapphire substrate. In this figure, the sapphire substrate A surface is a growth surface, and the orientation flat surface is a C surface. In the present invention, if the orientation flat surface is a direction perpendicular to the C axis, that is, if the orientation flat surface is the C surface, the orientation flat surface corresponds to a direction perpendicular to the C axis, and the broken line indicated by an angle θ with respect to the orientation flat surface. Crack the board. In this case, if θ is, for example, 58 °, it substantially corresponds to the R plane. In this drawing, the orientation flat surface is a C-plane. However, the method of the present invention specifies that the crystal growth surface is the A-plane, but does not specify the orientation flat surface.

For breaking the substrate, a usual wafer cutting apparatus such as scribing and dicing can be used. In dicing, a cut line is made in a state where the sapphire substrate side on which the nitride semiconductor is not formed is not cut completely but the sapphire substrate side on which the nitride semiconductor is not formed is cut in half without cutting. The wafer can be separated into chips by breaking the wafer with an external force.
When cutting lines by scribing, dicing, etc.,
As described above, it is desirable to put the nitride semiconductor on the side where the nitride semiconductor is not grown. When the nitride semiconductor layer side is scribed or cut in half, the nitride semiconductor layer is easily damaged, and it is difficult to obtain a surface that becomes a resonance surface of a laser element, for example. When a scriber is used, before scribing the substrate side, the substrate on which the nitride semiconductor is not grown is polished to reduce the thickness of the substrate to 200.
It is desirable that the thickness be not more than 150 μm, more preferably not more than 150 μm, and most preferably not more than 100 μm. When the substrate is polished and thinned, the substrate is easily broken straight when the substrate is split from the scribe line.

A second feature of the present invention is that an optical resonance surface serving as a reflecting mirror for reflecting light of the active layer is formed on the divided surface of the substrate divided as described above. This is a very effective manufacturing method for manufacturing a laser device made of a nitride semiconductor. The reflecting mirror serving as the optical resonance surface is, for example, T
A dielectric multilayer film in which thin films of iO2, SiO2, ZrO2 and the like are laminated, and a metal thin film made of a metal that reflects light of the active layer are formed. The reflecting mirror is formed on the divided surface of the substrate to form a resonance surface, and resonates light of the active layer inside the semiconductor layer to facilitate laser oscillation. The reflection mirror can be formed by using a commonly used thin film growth apparatus such as sputtering, vapor deposition, and plasma CVD.

[0012]

[Function] Since sapphire has a rhombohedral structure, it basically does not have cleavage. However, we have found that it is only slightly cleavable in a particular direction of the A-plane. Therefore, with respect to the direction perpendicular to the C axis of the A surface,
By splitting the substrate in the direction of 58 ± 5 ° or 40 ± 5 ° using, for example, a scribe, a dicer, or the like, the nitride semiconductor grown on the A-plane can be accurately separated. In particular, 58 ± 5 ° is a plane substantially corresponding to the R plane, and a cleavage plane of the nitride semiconductor layer can be obtained as a flat plane close to a mirror surface and a plane almost perpendicular to the substrate is formed. This is the most suitable surface for the resonance surface. That is,
In order to form a laser device, it is possible to form a resonance surface which is most preferably grown on the A-plane of sapphire and cleaved on the R-plane.

[0013]

FIG. 1 is a plan view of a sapphire substrate, and a plane perpendicular to the C axis, that is, the C plane is an orientation flat surface. Hereinafter, a method of growing a nitride semiconductor on the substrate by using the MOVPE method to form a light emitting element will be described in detail. FIG. 3 is a schematic cross-sectional view showing the structure of the laser device according to one embodiment of the present invention, and shows a view from the resonance surface. FIG. 4 is a perspective view showing the shape of the laser device of FIG.

[Example 1] 2 inches φ, thickness 500 μm
After thoroughly cleaning the sapphire substrate having the surface A (Formula 1) as the main surface and the surface C as the orientation flat surface, the substrate is placed in a reaction vessel of a MOVPE apparatus, and TMG (trimethylgallium) and ammonia are added to the raw material gas. A GaN buffer layer 2 was formed on the surface of a sapphire substrate 1 at a temperature of 500 ° C.
It was grown to a thickness of Å. The buffer layer 2 may be made of GaAlN, AlN, or the like.

Next, the temperature is raised to 1050 ° C., and a first n-type layer 3 made of Si-doped GaN is grown to a thickness of 4 μm using TMG, ammonia as a source gas and SiH 4 (silane) gas as a donor impurity. I let it. The first n-type layer 3 functions as a contact layer. Particularly, by using n-type GaN, a high carrier concentration can be obtained, and a favorable ohmic contact with the negative electrode material can be obtained.

Next, the temperature is lowered to 750 ° C., and TEG, TMI (trimethylindium) and ammonia are used as source gases, silane gas is used as impurity gas, and Si-doped In0.
A second n-type layer 4 of 1Ga0.9N was grown to a thickness of 200 Å. The second n-type layer 4 is a nitride semiconductor containing at least indium, preferably InYG
A ternary mixed crystal or a binary mixed crystal of a1-YN (0 <Y ≦ 1) gives a better crystallinity. More preferably, 10
This layer acts as a second buffer layer by growing with a film thickness of not less than 0 Å and not more than 0.5 μm, and when growing a third n-type layer 5 containing Al, a thick film is formed. You can grow well. This layer can be omitted.

Next, the temperature is set to 1050 ° C., and a third n-type layer made of Si-doped n-type Al0.3Ga0.7N is formed by using TEG, TMA (trimethylaluminum), ammonia as a source gas and silane gas as an impurity gas. 5 to 0.5 μm
The thickness was grown. The third n-type layer 5 functions as an optical confinement layer in the case of LD, and is preferably grown to a thickness of 0.1 μm to 1 μm, and is preferably grown to a nitride semiconductor containing Al.

Subsequently, TMG, ammonia,
Si-doped n-type GaN using silane gas as impurity gas
A fourth n-type layer 6 was grown to a thickness of 500 Å. The fourth n-type layer 6 functions as a light guide layer in the case of LD, and usually has a thickness of 100 Å to
It is desirable to grow with a film thickness of 1 μm, and it is also possible to grow with an n-type nitride semiconductor containing In such as InGaN other than GaN. In particular, by using InGaN or GaN, the next active layer has a quantum well structure. It becomes possible to do.

Next, an active layer 7 was grown using TMG, TMI, and ammonia as source gases. The active layer 7 has a temperature of 7
While maintaining the temperature at 50 ° C., first, a well layer made of non-doped In0.2Ga0.8N is grown to a thickness of 25 Å. Next, by changing the molar ratio of TMI, the non-doped In
A barrier layer of 0.01 Ga 0.95 N is grown to a thickness of 50 Å. This operation was repeated 13 times, and finally, a well layer was grown to grow an active layer 7 having a multiple quantum well structure with a total thickness of 0.1 μm. The preferred thickness of the well layer is 100 Å or less, and the thickness of the barrier layer is 15 Å.
By growing with a film thickness of 0 Å or less,
Since the well layer and the barrier layer are elastically deformed and crystal defects are reduced, and the output of the element is dramatically improved, laser oscillation becomes possible. Further, the well layer is made of InGaN such as InGaN.
It is desirable that the nitride semiconductor and the barrier layer are composed of GaN, InGaN, or the like.
GaN is very preferable in terms of production technology because the growth temperature can be kept constant.

After the growth of the active layer 7, the temperature is raised to 1050 ° C., and TMG, TMA, ammonia and Cp 2 Mg (cyclopentadienyl magnesium) are used as acceptor impurity sources.
Was used to grow a first p-type layer 8 made of Mg-doped p-type Al0.2 Ga0.8 N to a thickness of 100 Å. By growing this first p-type layer 8 to a thickness of 0.1 μm or less, the first p-type layer 8 acts as a cap layer for preventing the active layer made of InGaN from being decomposed. By growing the first p-type layer made of a p-type nitride semiconductor containing the compound, the light emission output is improved.
The p-type nitride semiconductor layer is made of Zn, Mg, Cd, Ca, B
can be obtained by doping an acceptor impurity such as e or C during the growth. Among them, Mg is the most preferable p.
Shows type characteristics. Further, after doping with an acceptor impurity, annealing at 400 ° C. or higher in an inert gas atmosphere provides a more preferable p-type. This layer may be omitted.

Next, while maintaining the temperature at 1050 ° C., T
Mg-doped p-type G using MG, ammonia, Cp2Mg
A second p-type layer 9 of aN was grown to a thickness of 500 Å. In the case of LD, the second p-type layer 9 functions as a light guide layer, and it is preferable that the second p-type layer 9 is grown to a thickness of 100 Å to 1 μm.
In addition to N, it can be grown by a p-type nitride semiconductor containing In such as InGaN. In particular, by using InGaN or GaN, the following third p-type layer 10 containing Al can be grown with good crystallinity.

Subsequently, TMG, TMA, ammonia, C
Using p2Mg, a third p-type layer 10 of Mg-doped Al0.3Ga0.7N was grown to a thickness of 0.5 .mu.m. In the case of LD, the third p-type layer 10 functions as a light confinement layer, and is preferably grown to a thickness of 0.1 μm to 1 μm, and is preferably a p-type nitride semiconductor containing Al such as AlGaN. Thereby, it preferably functions as a light confinement layer.

Subsequently, TMG, ammonia, Cp2Mg
The p-type contact layer 11 made of Mg-doped p-type GaN was grown to a thickness of 0.5 μm. If the p-type contact layer is made of GaN containing Mg, a p-type layer having the highest carrier concentration is obtained, and good ohmic contact with the material of the positive electrode is obtained.

The wafer on which the nitride semiconductor has been laminated as described above is taken out of the reaction vessel and selectively etched from the uppermost p-type contact layer 11 to expose the surface of the n-type contact layer 3 as shown in FIG. Let and exposed n
Stripe-shaped electrodes were formed on the surfaces of the mold contact layer 3 and the p-type contact layer 11, respectively. When the electrodes are formed, the stripe width is formed so as to be orthogonal to the angle θ at which the wafer is divided in consideration of the division of the wafer.

Next, after the sapphire substrate side of the wafer is polished to 80 μm using a polishing machine, the wafer is set on a table of a scriber, and θ = θ as shown in FIG. A scribe line was made parallel at 58 °. After the formation of the scribe line, the wafer was pressed with a roller to obtain a bar having a division surface orthogonal to the scribe-like electrodes. The split surface of this bar was very flat and a surface close to a mirror surface was obtained, and the opposing split surfaces were almost parallel surfaces. There was no defective bar in the bar state. This 58 ° substantially corresponds to the R plane.

Next, a reflector made of a dielectric multilayer film was formed on the divided surface of the bar using a CVD apparatus to form a resonance surface. Next, after scribing the substrate side of the bar at a position parallel to the electrode, the bar was split to obtain a laser element having a resonator length of 1 mm and a width of 500 μm and having the shape shown in FIG. When this laser element was placed on a heat sink and made into an LD, the threshold current density was 4.0 kA / cm 2 and the emission wavelength was 410 nm.
Laser oscillation having a half value width of 2 nm was shown.

Example 2 When a wafer was scribed and divided, an LD was obtained in the same manner as in Example 1 except that the scribe angle θ shown in FIG. 1 was set to 40 °. There were almost no defects, and similarly, laser oscillation having a light emission wavelength of 410 nm and a half value width of 2 nm was shown at a threshold current density of 4.0 kA / cm2. Since the scribe angle is changed, it is needless to say that the stripe-shaped electrodes are similarly formed in a direction orthogonal to the scribe angle.

Example 3 When a wafer was scribed and divided, bars were obtained in the same manner except that θ = 34 °, and almost no divided planes were obtained. The half-cut divided face at an angle perpendicular to
Since the angle with respect to the C-axis was equal to 56 °, a very smooth divided surface was obtained. For this reason, this element could be sufficiently used as an LED element, not as a laser element.

[Embodiment 4] Next, an LED element will be described. As in Example 1, a buffer layer made of GaN was grown to a thickness of 200 Å on a sapphire substrate having the A surface as the main surface and the C surface as the orientation flat surface.

An n-type contact layer made of Si-doped n-type GaN having a thickness of 4 μm and a non-doped In0.
An active layer having a single quantum well structure made of 2Ga0.8N is 40 angstroms, a p-type cladding layer made of Mg-doped p-type Al0.2Ga0.8N is 0.2 μm, and a p-type contact layer made of Mg-doped p-type GaN. Was grown to a thickness of 0.5 μm.

Selective etching was performed from the p-type contact layer of the wafer to expose the surface of the n-type contact layer, and electrodes were formed on the exposed n-type contact layer and the surface of the p-type contact layer, respectively. In this case, unlike the above-described laser element, it has a normal LED electrode shape.

Next, after the sapphire substrate side of the wafer is polished to 80 μm using a polishing machine, the wafer is set on a table of a scriber, and θ = 62 ° at a pitch of 350 μm with respect to the orientation flat surface of the substrate. A scribe line was inserted in parallel, and a scribe line was inserted at a pitch of 350 μm in a direction perpendicular to the scribe line in the same manner. After the formation of the scribe line, the wafer was pressed with a roller to form LED chips of 350 μm square. From the LED chip obtained in this way, a chip having a cross section crack, chipping or the like was removed, and the yield was 95%.
% Or more.

Fifth Embodiment In the fourth embodiment, θ = 54.
A 350 μm-square LED element was obtained in the same manner except that Δ was given, and the yield was also 95% or more.

[Embodiment 6] In Embodiment 4, θ = 44
The yield was 90% or more when the LED element was made in the same manner except that the symbol “゜” was used.

[0035]

As described above, according to the method of the present invention, a nitride semiconductor grown on a sapphire substrate can be divided into chips with a high yield. In addition, the angle shown in the present invention makes it possible to obtain a very preferable divided surface for forming a resonance surface as a laser element, and thus enables laser oscillation with a nitride semiconductor. The fact that the LD is realized by the method of the present invention has a great value in practical use of a short-wavelength semiconductor laser.

[Brief description of the drawings]

FIG. 1 is a plan view of a sapphire substrate illustrating a method of the present invention.

FIG. 2 is a unit cell diagram showing a plane orientation of a sapphire single crystal.

FIG. 3 is a schematic sectional view showing a structure of an LD according to one embodiment of the present invention.

FIG. 4 is a perspective view showing the shape of the LD in FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Sapphire substrate 2 ... Buffer layer 3 ... 1st n-type layer 4 ... 2nd n-type layer 5 ... 3rd n-type layer 6 ... 4th n Mold layer 7 Active layer 8 First p-type layer 9 Second p-type layer 10 Third p-type layer 11 P-type contact layer

Claims (2)

[Claims] After a nitride semiconductor including a light emitting active layer is grown on a surface A of a sapphire substrate, the surface of the sapphire substrate A is 58 ± 5 ° or 40 ± 5 ° from a direction perpendicular to the C axis. A method for manufacturing a nitride semiconductor light emitting device, characterized by dividing by an angle. 2. The method for manufacturing a nitride semiconductor light emitting device according to claim 1, wherein after the substrate is split, a reflection mirror is formed on the split surface to form an optical resonance surface.