JPS61183986A - Manufacture of semiconductor light emitting device - Google Patents

Abstract

PURPOSE:To obtain the title device of high output and high reliability which is easily produced, by a method wherein the first semiconductor substrate with a hetero junction structure and the second semiconductor substrate with a structure acting as current stricture or mode control are directly joined to each other. CONSTITUTION:A clad layer 12, an undoped active layer 13, and a clad layer 14 are successively grown above an N-GaAs substrate 11, thus forming a double hetero junction structure (first structure). Next, the surface of the clad layer 14 is polished into mirror. On the other hand, a P-SiC substrate 15 is provided with a metal mask in stripe form, and a high-resistant layer 16 is formed by front implantation, thus forming the second structure. The surface of the sub strate 15 is polished into mirror. The mirror-polished surfaces of the substrates 11, 15 are made opposed, brought into close contact, and adhered by heat treat ment. Next, the substrate 11 is removed, and the exposed surface of the clad layer 12 is polished into mirror; then, an N-SiC substrate (third semiconductor) 18 is adhered. A semiconductor laser chip is prepared by cutting this element for each stripe.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method of manufacturing a semiconductor light emitting device such as a semiconductor laser or a light emitting diode, and particularly to a method of manufacturing a semiconductor light emitting device using bonding of substrates.

[Technical background of the invention and its problems] In semiconductor lasers, heat generated from the active layer in the oscillation state saturates the current-optical output characteristics of the device, and in the case of constant output operation, the efficiency due to heat generation decreases. The reduction in the operating current reduces the operating current, which further increases heat. This kind of positive feedback eventually causes deterioration to the point where it stops firing. From these points of view, how quickly the heat generated in the active layer can be guided to the heat sink is an important issue, especially in high-power lasers and communication lasers that require long-term reliability.

In a laser having a conventional structure, semiconductor materials having poor thermal conductivity, called at least a cladding layer and a contact layer, are present between the active layer and the heat sink.

Furthermore, depending on the fusion metal, it is necessary to mount it with the junction facing upward, which requires a thick substrate, which results in poor heat dissipation.

Semiconductor lasers have various structures depending on their materials and applications, but in general, a heterojunction structure including an active layer and a cladding layer, and a structure having a current confinement effect or mode control effect are formed on a semiconductor substrate. Many are composed of bonds perpendicular to the surface. For example, Fig. 5(a)
As shown in m-EC0 (Modified, Enpepoid.

Confining Ray Two. optical guide)
The built-in structure, which is called the structure, is a waveguide laser (16th National Space Element Conference, Proceedings p153-1) 156.
(1984), an active layer 53 and cladding layers 52 and 54 forming a double heterojunction structure are formed on a semiconductor substrate 51, a current blocking layer 54 having a current confinement effect and a mode control effect due to an effective refractive index difference, and a high refractive index layer. The substrate 51 has a structure in which the index layer 55 is vertically bonded to the surface of the substrate 51. Figure 5(b) shows what is called a C3P (channeled, substrate, planar) laser (IEEE, Journal, Or2Quantum, Electronics).

(1978, QE-14, p.89), this laser consists of a semiconductor substrate 51 having a mode control effect and a heterojunction structure 52. . . , 54 are coupled to the substrate surface in the reverse order to that shown in FIG. In addition, Fig. 5 (C) shows N08 (native,
It is called a laser (oxide, stripe) (1
00C81 Proceedings MB-1), this is a heterojunction structure part 52. . . , 54 and current confinement portions 58 and 61 are sequentially coupled to form a gain waveguide laser.

A laser in which the heterojunction structure section and the current confinement or mode control section are vertically coupled in a direction perpendicular to the surface of the semiconductor substrate in this manner is manufactured as shown in FIGS. 6(a) to 6(C). Taking a GaAMAs laser as an example, first of all, Fig. 6 (a)
), N-QaAff is placed on the N-GaAS substrate 51.
iAS first cladding layer 52. GaAS active layer 53°P-
After growing the GaAnAS second cladding H54 and the N-GaAS current blocking layer 55, the current blocking layer 55 is etched into stripes as shown in FIG. P- to make a difference
GaAgAS high refractive index layer 56. A P-GaAs third cladding layer 57 and a P-GaAs contact layer 58 are grown.

When using the method shown in FIG. 6 for the m-EC0 laser,
This causes some problems. First, the high refractive index layer 56. Since the cladding layer 57 and the contact layer 58 are grown on GaAaAS in the stripe portion, they cannot be formed by the LPE method, and cannot be formed by the MOCVD method or M B'
The E method must be used. Second, even when using the vapor phase growth method, the growth of the groove tends to cause crystal defects, which causes a decrease in laser performance and reliability. Third, since the double heterojunction itself undergoes an etching process and a growth process, it is exposed to etching solutions and exposed to high temperatures during the growth process, which tends to cause changes in structure and doping level and the introduction of crystal defects.

Further, the C8P laser shown in FIG. 5(b) is manufactured by forming a channel in the substrate and then forming a double heterojunction, but problems arise in this case as well. For example, since a heterojunction is grown on the groove, the quality of the active layer may deteriorate depending on the growth conditions. In particular, when vapor phase growth is used, the groove shape is reflected in the grown layer, which tends to bend the active layer and cause a decrease in reliability.

In addition to the problems mentioned above, in the case of vertically bonded structures, the structure is generally formed using a crystal growth method, so the material and composition of each layer has to be lattice-matched with the underlying material. It must be able to be removed and crystal grown, and there are restrictions in that the plane orientation of the crystal is determined by the plane orientation of the substrate, the processed shape of the base, the crystal growth conditions, etc. These constraints severely limit the possibilities of device construction and performance.

On the other hand, in communication diodes, when coupling with a fiber is considered, it is necessary to reduce the spread angle and spot size, and to increase the brightness.

Since the spot size is controlled by the spread of the current, it is necessary that the active layer and the constriction layer be sufficiently close to each other, and in order to avoid absorption by the contact layer, etc., the constriction layer is buried by epitaxial growth twice. There is a need.

Therefore, the process is complicated and there is a problem in mass production.

[Purpose of the invention]

The present invention has been made in consideration of the above-mentioned circumstances, and its purpose is to be able to manufacture a semiconductor light emitting device that is easy to manufacture, has high output, and has high reliability, and that also has a material and a surface that can be improved by crystal growth. It is an object of the present invention to provide a method for manufacturing a semiconductor light emitting device that can significantly alleviate restrictions on orientation.

[Summary of the invention]

The gist of the present invention is to directly bond a first semiconductor substrate on which a heterojunction structure is formed and a second semiconductor substrate on which a structure functioning as current confinement or mode control is formed, thereby producing a semiconductor light emitting device. The purpose is to manufacture.

That is, the present invention provides a method for manufacturing a semiconductor light emitting device, in which a first structure section consisting of a heterojunction in which an active layer and a cladding layer are stacked is formed on the surface of a first semiconductor substrate, and then the surface of the structure section is mirror-finished. After polishing and further forming a second structure on the surface of the second semiconductor substrate that exerts at least one of a current confinement effect and a mode control effect with respect to the first structure, the structure is mirror-polished. Then, in a clean atmosphere, the mirror-polished surfaces of the first and second structural parts were brought into close contact with each other facing each other, and in this state, 200 ["0
In this method, each of the substrates is bonded by heat treatment at one or more temperatures.

〔Effect of the invention〕

According to the present invention, the first structure consisting of a heterojunction and the second structure functioning as a current confinement or mode control section can be manufactured separately, so that the first structure can be formed by vapor phase growth on the first structure. Compared to the conventional method of forming the second structure, the structure of the second structure and its formation method are influenced by the first structure and its material, or conversely, the second structure is formed. Problems such as exposure of the heterojunction structure to etching solutions, changes in structure and doping due to high temperatures, and introduction of crystal defects are all solved. Furthermore, since there is no need to perform processes that take mutual structures into consideration, process procedures and conditions are simplified, which is effective in improving device yield and mass productivity. Furthermore, there is no need to consider restrictions on mutual structures, materials, and crystal growth methods. For example, the second structure in which the current confinement effect or mode control effect occurs does not necessarily need to be manufactured by crystal growth. This greatly alleviates the constraints on conventional semiconductor lasers, and allows more complete current confinement effects and more complex mode control effects to be realized.

Furthermore, since adhesion does not depend on the surface orientation, a new semiconductor laser, which is a laser in which structures with different surface orientations are combined in the vertical direction, can be realized without changing other characteristics.

Furthermore, for the above reasons, a semiconductor material with high thermal conductivity, such as SiC, 0.degree.

Therefore, it is possible to increase the light emission output.

[Embodiments of the invention]

First, before explaining embodiments, the basic principle of the present invention will be explained.

Conventionally, it has been known that when two such glass plates are directly brought into close contact with each other by keeping the smooth surfaces of the glass plates extremely normal, the coefficient of friction between them increases and a bonded state is obtained. It is also known that if the surfaces of the glass plates slide against each other, cracks will occur due to the peeling off of the bonded surfaces. On the other hand, the reason why there is no known bonding method for semiconductor crystals like the one described above for glass is that it is difficult to strictly maintain the smoothness and cleanliness of the surfaces of semiconductor crystals to be bonded. It can be said that this was the biggest cause.

The inventors of the present invention have therefore discovered that it is possible to bond semiconductor crystal bodies together, similar to the bonding of glasses together, by performing the following treatment. That is, the surfaces of two semiconductor crystal bodies to be joined are smoothed to a surface roughness of 5 o○ [person] or less, and
Washed with water for a minute.

The smoothing method is performed by forming an epitaxial growth layer on the mirror-polished surface by a method that does not impair the flatness of the surface, such as MOCVD or MBE. The surface of the obtained semiconductor was well wetted with water, and it was assumed that a layer of natural oxide was formed. Then replace with methanol.

Freon drying was carried out, and the semiconductor crystal thus obtained was brought into direct contact with the bonding surfaces in a substantially dust-free clean room with a dust floating amount of 20 [pieces/7FL3] at 200 [°C]. When heat treated at the above temperature, both were bonded extremely firmly. The adhesive strength of this bonded body increases particularly when the heat treatment temperature is 200[° C.] or higher.

From the above, the surface of a polished clean semiconductor becomes hydrophilic simply by washing with water, and even in a clean environment and at a temperature of 200 [
A strong bond can be obtained by bonding at a temperature of 0.01 or higher.

On the other hand, it is well known that at a heating temperature of about 200 [° C.], the diffusion rate in the semiconductor crystal is usually negligible, not only for semiconductor constituent atoms but also for monovalent ions, which are the most easily diffused.

It is also known that at a temperature around 200 [° C.], most of the water molecules adsorbed on the surface of the oxide film are desorbed, and dehydration bonding of 10H groups formed by chemical adsorption begins to occur. Taking these things into consideration, the bonding between the semiconductor crystals is not due to interdiffusion, which is known as metal-to-metal bonding, but is due to interaction between hydrated layers of the surface oxide film of the semiconductor crystals, or - It is thought that a strong bonding structure of semiconductor-〇-semiconductor is formed by dehydration polymerization of OH groups.

This fact makes the surface of the semiconductor crystal hydrophilic,
This means that high adhesive strength can be obtained if heat treatment is performed at 200[° C.] or higher after the close bonding.

Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIGS. 1(a) to 1(d) are cross-sectional views showing the manufacturing process of a GaAlAs semiconductor laser according to a first embodiment of the present invention.

First, as shown in FIG. 1(a),
N with a thickness of 1.51μTrL] on the semiconductor substrate) 11
G ao-s5A Qo, 4y A S cladding layer 1
2<n=1x10 cm”), thickness 0308[, cz
ml undoped Qao, o AρO, IAS active layer 13 and 1.5 [μm] thick P Gao, 55 Aρo, 4s As cladding layer 14
(n=1×10 cm3) are sequentially grown and formed by MOCVD method. Here, a double heterojunction structure (first structure) is formed from the active layer 13 and the cladding layer 12.14. Then P-GaAffi
The surface of the AS cladding layer 14 is mirror-polished to a thickness of 500 mm or less and degreased.

On the other hand, as shown in FIG. 1(b), a metal mask (not shown) is placed on a P-8t C substrate (second semiconductor substrate) 15, which is a material with high thermal conductivity, with a width of 3 [μTrL].

The high resistance layer 16 is formed by forming stripes in the <110> direction with a period of 300 [μm] and performing proton implantation. Then, the surface of the substrate 15 is mirror-polished to a surface roughness of 500 [mm] or less, and then degreased. In addition, the above P
A second structural portion that acts as a current confinement portion is formed from the −8i C substrate 15 and the high-resistance layer 16. Further, on the back surface of the P-8i C substrate 15, a P-side metal electrode 17 is formed in advance.

Next, the surface layer of the N-GaAS substrate 11 is P-
Surface and layer surface 48 i of GaAffiAS cladding layer 14
Wash the surface of the C substrate 15 with clean water for several minutes. Next, this is dehydrated using a spinner. Next, in a clean atmosphere of class 1 or below, the mirror-polished surfaces of the substrates 11 and 15 are placed facing each other as shown in FIG.
aAffiAs cladding layer 14 and P-8i C substrate 15
and bring them into close contact.

In this state, heat treatment is performed at a temperature of 200[° C.] or higher to bond the substrates 11.15.

Next, as shown in FIG. 1 (CI), the N-Ga'As
The substrate 11 is etched with a PA etchant until the N-GaAnAs cladding layer 12 is exposed, and the etched surface is mirror polished and then dehydrated and washed with water. Then, another N-8iC substrate (third semiconductor substrate) 18 is pretreated in the same way, and it is brought into close contact with the polished surface of the N-GaAgAS cladding layer 12, and the same procedure as before is carried out. Glue. Note that the back surface of the N-8iC substrate 18 is coated with N in advance.
AuGe/Au is first applied as the side electrode 19.

Similarly, a P-side electrode 1 is provided on the back surface of the P-8i substrate 15.
7, T r PtAu is attached first.

Next, the sample shown in FIG. 1(d) above was opened so that a cleavage plane was exposed perpendicular to the stripe, and the length in the stripe direction, that is, the resonator length was 250 [μm]. was cut into strips for each strip, and one semiconductor laser chip was fabricated as shown in Fig. 2.This chip was made with the AU on the Cu base with the N-side electrode 19 facing down.
It is mounted using Sn as a fusion metal.

Compared to conventional NOS lasers, the semiconductor laser thus manufactured has a firing threshold of 50 [
mA], CW optical output saturates at 120 [mW] < lasing threshold is 46 rmA],
The optical output saturation under CW was 170 [mW] or more, which was a significant improvement. In addition, 50%
[℃].

Even in a constant output operation test of 5 [mW], the average operating current was 10 [mA], lower than any other NOS laser, and almost no deterioration was observed.

In addition, compared to the conventional method in which a current confinement structure is formed by epitaxial growth on a heterojunction structure, the heterojunction structure is exposed to an etching solution, and the structure and doping change due to high temperature and crystal defects are introduced. There are no such inconveniences. Furthermore, since there is no need to perform a process that takes mutual structures into consideration, the process procedure and conditions become simpler.

Therefore, manufacturing yield and productivity can be improved, and reliability can also be improved.

FIG. 3 is a sectional view showing a schematic structure of a ballast type light emitting diode (LED) according to the second embodiment. The manufacturing process is basically the same as that shown in FIGS. 1(a) to (d). In the case of a rosette type LED, the shape of the mask when forming the current confinement layer is not a stripe but a circle with a diameter of 50 [μm1]. However, the cross section after proton implantation is shown in Figure 1(b).
It is the same as. Figure 1 (C)
After forming a cross section like this, N-GaAS
A photoresist is applied to the substrate 11, and the photoresist is removed leaving a 150 [μm] diameter portion on the substrate where a current is injected and emits light.
e/Au) is deposited, the resist is peeled off, and lift-off is performed. Next, using this metal electrode as a mask, etching is performed using a PA etchant to a depth that reaches the N-GaAλAS cladding layer 12. Thereafter, by cutting each chip by dicing, an LED as shown in FIG. 3 is completed.

Note that in the case of an LED, the parameters (particularly the thickness) of the double heterojunction structure are different from those of the semiconductor laser.

That is, the thickness of the cladding layer 12.14 is 2.5 [μm]
, the thickness of the active layer 13 is 1. ○ [μm].

FIGS. 4(a) to 4(f) show GaAf according to the third embodiment.
FIG. 3 is a cross-sectional view showing the manufacturing process of a fiAS-based semiconductor laser. Note that this figure only shows a portion corresponding to one chip.

First, as shown in Fig. 4(a), N-
N-G with a thickness of 1.5 μm on a GaAS substrate 41 (Si doped 1×10 cm”)
a n, as A Qo, ss A S cladding layer 4
2 (Se doped 1 x 1017cm”), thickness 0
．． 08 [μ711L] undoped G ao,ot
A Qo, os A S active layer 43 and thickness 1.5 [μ
771] P-Gao,,, Affi,,,,
A S cladding layer 44 (Zn doped 7 x 101!
1 cm") are sequentially grown. Here, a double heterojunction structure (first structure portion) is formed from the active layer 43 and the cladding layers 42 and 44.

On the other hand, as shown in Fig. 4(b), P-
PG with a thickness of 0.05 rμm on the GaAs substrate 45
ao, s Ano, , As high refractive index R46 is grown. Next, as shown in FIG. 4(C), a high refractive index layer 46 is formed.
An etching mask (not shown) is formed in the form of a stripe on the etching mask.
rL] to form a mesa stripe. Next, Figure 4 (
As shown in d), N- is applied to the part removed by etching.
GaAs current element layer 47 (Se doped 5X10 cI
l-') is grown and formed. Here, the high refractive index layer 46 and the current element layer 47 form a second structure that acts as a current confinement and mode control section.

Next, the sample in the state shown in FIG. 4(a) and the same figure (
Each surface of the sample in the state shown in d) has a surface roughness of 500 [large]
Mirror polish the following. At this time, the P-GaAs substrate 45
During polishing, it is assumed that the P-GaAgAS high refractive index layer 46 and the N-GaAs current element layer 47 are exposed on the polished surface.

Next, each polished surface is washed with clean water and subjected to dehydration treatment such as spinner treatment at the lowest temperature. Each mirror-polished surface subjected to these treatments is placed in a clean atmosphere of, for example, 1 class or less, and the mirror-polished surface is exposed to substantially no foreign matter as shown in FIG. 4(e). be closely attached to each other.

After that, the bonded wafers are heat-treated at 200 [° C.] or higher to increase the bonding strength.

Next, the P-GaAs substrate 45 and the N-GaAs substrate 41 are separated by a number [μm] and a number 10, respectively.
It is polished to a thickness of [μm], and ohmic electrodes 48 and 49 are formed on both surfaces as shown in FIG. 4(f).

In the semiconductor laser manufactured in this way, the first structure section consisting of a double heterojunction structure and the second structure section functioning as a current confinement and mode control section are manufactured separately. Therefore, effects similar to those of the first embodiment described above can be obtained.

Further, in the structure shown in FIG. 5(a), the high refractive index layer 56 is P
Since the high refractive index layer 56 covers the entire surface of the mold cladding layer 54 and the current element layer 55 and rises at both side portions of the stripe groove, the effective refractive index difference in this portion is larger than that in the center of the groove. Although there is a problem that the mode is biased, the above problem does not occur in the structure of this embodiment.

Note that the present invention is not limited to the embodiments described above. For example, in the first embodiment, the GaAs substrate 11 at the beginning of growth is an N-type substrate, and as shown in FIG.
), the N-GaAs substrate 11 is left without etching, and an ohmic contact is made by attaching A, uGe/Au as an electrode 19 to the bottom surface of this substrate 11. In addition, in this embodiment, when the PN is reversed, the substrate 15 is N-
This will be an 8i C board. In this case, striped 3i3
After applying a mask such as N4, Zn is diffused and the high resistance layer 16 is made of P type, so that current confinement can be performed in the form of NPN. Furthermore, the material of the heat sink is not limited to SiC, but also C1Si, GaP, InP, GaA
s etc. may also be used.

Further, the current element layer and the high refractive index layer may be made of a material that has a current element effect and a material that has a high effective refractive index and can inject current into the active layer, such as GaAS or G.
It does not have to be aAQAs. For example, undoped Zn5e may be used for the current element layer, or Ga1nP grown on a GaASP base may be used instead of GaAs. Although Ga1nP and GaAl AS cannot have lattice matching except for one composition, there is no problem if the bonding technique of the present invention is used. Further, the crystal growth method is not limited to the MOCVD method, and it is also possible to use the MBE method or the LPE method. In general, the structure, material, conductivity type, etc. of the first and second structural parts can be changed as appropriate according to specifications. In addition, various modifications can be made without departing from the gist of the present invention.

[Brief explanation of the drawing]

1(a) to (d) are cross-sectional views showing the manufacturing process of a semiconductor laser according to the first embodiment of the present invention, and FIG. 2 is a cross-sectional view showing the schematic structure of the semiconductor laser manufactured by the above steps. , FIG. 3 is a cross-sectional view showing a schematic structure of a ballast type LED according to the second embodiment, and FIGS. 4(a) to (f) are cross-sectional views showing the manufacturing process of a semiconductor laser according to the third example. , FIGS. 5(a) to 5(C) are sectional views showing the schematic structure of a conventional semiconductor laser, and FIGS. 6(a) to 6(C) are sectional views showing the manufacturing process of the conventional semiconductor laser. 11, 41-N-GaAS substrate (first semiconductor substrate)
, 12.42-N-GaA/lAs cladding layer, 13
．． 43...Undoped GaAj2AS active layer, 14.
44-P-GaA QAs cladding layer, 15...P-
8iC substrate (second semiconductor substrate), 16... High resistance layer, 17.48... P side electrode, 18... N-8iC substrate (third semiconductor substrate), 19.49-N side electrode, 45
-P-GaAs substrate (second semiconductor substrate),
46-P-GaAffiAs high refractive index layer, 47...N
-GaAS current element layer. Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 Figure 2 Figure 3 Figure 4 Figure 4 Figure 5

Claims (4)

[Claims] (1) After forming a first structural part consisting of a heterojunction in which an active layer and a cladding layer are laminated on the surface of a first semiconductor substrate, mirror polishing the surface of the structural part; A second structure that exerts at least one of a current confinement effect and a mode control effect on the first structure on the surface of the structure.
After forming the structural part, the structural part is mirror-polished, and then the mirror-polished surfaces of the first and second structural parts are brought into close contact with each other facing each other in a clean atmosphere, and in this state, A method for manufacturing a semiconductor light emitting device, comprising the step of bonding each of the substrates by heat treatment at a temperature of 200[° C.] or higher. (2) The mirror polishing step has a surface roughness of 500 [Å]
2. A method for manufacturing a semiconductor light emitting device according to claim 1, which comprises polishing. (3) The above-mentioned clean atmosphere means that the amount of floating debris is 20 [pieces/
The method for manufacturing a semiconductor light emitting device according to claim 1, characterized in that the atmosphere is less than or equal to m^3]. (4) etching the back side of the first semiconductor substrate until it reaches the first structural portion or near the structural portion, and having this etched surface have the same conductivity type as the first semiconductor substrate; 2. The method of manufacturing a semiconductor light emitting device according to claim 1, further comprising bonding a third semiconductor substrate having better thermal conductivity than the first semiconductor substrate.