JPS61182280A - Manufacture of blue light-emitting element - Google Patents

Abstract

PURPOSE:To form a p-n junction, and to obtain a blue LED by a method wherein each surface of p-type and n-type predetermined compound semiconductors having forbidden band width of 2.6eV or more is flattened, brought to a hydrophilic state, dried, bonded directly and joined at 200 deg.C or higher. CONSTITUTION:SiC, ZnSSe and CuAlGa(SSe)2 are used as a p-type compound semiconductor 11 and ZnSSe and GaN as an n-type compound semiconductor 13. The surfaces of both semiconductors are processed to a mirror surface, thinned to 500Angstrom or less, washed by pure water, brought to a hydrophilic state and dried by Freon. When the surfaces of both semiconductors are bonded mutually in a clean atmosphere in the quantity of floating of dust of 20pcs/m<3> or less and treated at 200 deg.C or higher, adhesive strength is increased remarkably, and a p-n junction not lattice-joined is formed. According to the method, the two compound semiconductors having wide forbidden band width are bonded directly, and the p-n junction is shaped, thus mass-producing blue LEDs.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for manufacturing a semiconductor light emitting device, and particularly relates to a method for manufacturing a semiconductor light emitting device.
The present invention relates to a method of manufacturing a blue light emitting device in which two wide bandgap compound semiconductors are directly bonded to form a PN junction.

[Technical background of the invention and its problems]

2) Red to green light emitting devices using group V compound semiconductors have entered the era of mass production and are now widely used as discless devices.

Under these circumstances, there are growing expectations for light-emitting elements that provide blue light, the only luminescent color lacking in the visible range. However, the reality is that no technology for producing blue light-emitting devices that can compete with the conventional 1-2 group light-emitting devices has yet been found.

The first condition for obtaining a blue semiconductor light emitting device is that the forbidden band width Ea of the semiconductor used exceeds 2.6 [eV]. A semiconductor crystal satisfying this condition is I
In the I-Vl group compound semiconductor, Zn5 (Eo=3.5eV
), znse (Ea-2,6eV), I[[-V group compound semiconductors include GaN (Ea-3,5eV), and TV group compound semiconductors include 5iC (Ea-3eV). However, each of these materials has its own material disadvantages.

For example, SIC is the only material that can form a PN junction using the same material, but since it is a high melting point material, the temperature at the time of forming the bonding surface is high, making it difficult to form a bond with fewer non-luminous centers. Furthermore, since it is an indirect transition type semiconductor, its luminous efficiency is low.

In addition, ZnS, Zn8e, GaN or chalcopyrite type CuAlS2. Semiconductor single crystals such as CuAlS2 can be obtained on ■-V group semiconductor substrates or sapphire substrates by metal organic chemical vapor deposition (MOCVD), molecular beam epitaxial growth (MBE), etc. It has not yet been possible to form PN junctions continuously. In particular, it is difficult to obtain P-type crystals for ZnS, Zn5e, and GaN, and CuAlS2゜CuAβ8132 has N-type crystals.
It is difficult to obtain type crystals.

As described above, although research on blue light emitting devices is being conducted, the process and device characteristics are not yet suitable for mass production.

[Purpose of the invention]

The present invention has been made in consideration of the above circumstances, and its purpose is to easily form good PN junctions of compound semiconductors of different conductivity types and different materials, and to emit blue light. It is an object of the present invention to provide a method for manufacturing a blue light emitting device that allows the device to be realized and mass-produced.

[Summary of the invention]

The gist of the present invention is to realize a blue light emitting device by directly bonding a P-type wide forbidden band compound semiconductor and an N-type wide forbidden band compound semiconductor.

The present inventors mirror-polished each bonding surface of two wide bandgap semiconductor crystals to a surface roughness of 500 [mm] or less, washed and dried the polished surfaces, and then polished them to a surface roughness of, for example, 20 [pieces/m3] or less in a clean room, under conditions that substantially no foreign matter intervenes between the respective polished joint surfaces, and by heating them at a temperature of 200 [''C] or more. We have discovered that forbidden band semiconductor crystals are strongly bonded.

Conventionally, when mirror-polished semiconductor wafers are brought into contact with each other while wet with water, alcohol, etc., it has often been observed that the two adhere to each other.

However, this is due to the surface tension of liquids such as water, and has not been observed in dried wafers. In contrast, the present inventors have found that by sufficiently cleaning the surface of a mirror-polished compound semiconductor and bringing two surfaces of the same or different types into contact in a highly clean atmosphere, a strong bonded body can be obtained. I discovered that. Roughly speaking, in order to sufficiently increase the adhesive strength of the bonded body obtained in this way, 200
It was also found that heat treatment at a temperature of [°C] or higher is essential.

As a result of further detailed investigation of this adhesion phenomenon, it was found that the formation of a natural oxide film on the surface of these crystals is a necessary condition for adhesion. The presence of this natural oxide film can be confirmed, for example, by a method such as ellipsometry, but more easily can be determined by placing a water droplet on the cleaned surface and allowing it to spread. That is, the change of the surface from hydrophilic to hydrophilic is evidence of the presence of a natural oxide film.

This natural oxide film is formed under various conditions, but according to experiments by the present inventors, a normal water washing process of several minutes at most was sufficient.

Wafers with hydrophilic and clean surfaces obtained in this way can be easily bonded to each other, but the natural oxidation layer must be removed and the wafers must be carefully handled to prevent the formation of a natural oxide film again to prevent the surface from becoming water-repellent. Attempts were made to bond the retained surfaces, but it was found that a sufficient bond could not be obtained. Furthermore, the reason why heat treatment at 200 [℃] or higher is necessary to obtain sufficient adhesive strength is that at around this temperature the active groups present on the surface of the natural oxide film react with each other to form strong bonds. Conceivable. It was also confirmed that the semiconductors bonded in this manner were electrically connected to each other.

The present invention has been made with attention to such points, and in the manufacturing method of a blue light emitting element, the forbidden band width is 2.
The surfaces of the P-type compound semiconductor and the N-type compound semiconductor with a voltage of 6 [8V] or more are formed flat, and then each of the flat surfaces is made hydrophilic by washing with water, etc., and then dried, and then substantially free of dust. In this method, the respective flat surfaces are directly brought into close contact with each other in a clean atmosphere without intervention, and in this state, a heat treatment is performed at 200 [° C.] or higher to bond the semiconductors.

〔Effect of the invention〕

According to the present invention, it is possible to firmly bond P-type and N-type semiconductor crystals to such an extent that it is difficult to separate them without causing deterioration of the crystal properties of the wide bandgap semiconductor that is the material for forming the blue light emitting device. In addition, a good PN junction can be formed. Therefore, selection and combination of materials for the P-type semiconductor and the N-type semiconductor becomes easy. For example, N-type znss
When forming PfJICuAj2Ga (SSe)2 on e, it is possible to prevent the N layer from becoming high in resistance due to diffusion of Cu or the like. In addition, P-type ZnSSe on N-type ZnSSe
When forming the layer, it is possible to prevent the resistance of each layer from increasing due to the influence of each other's dopants. Therefore, the blue light emitting device can be easily manufactured, and its mass productivity can be improved.

[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 fact that there is no known method for bonding compound semiconductor crystals (for example, Zn, 5Se) together with glass, as described above, is due to the fact that the smoothness and cleanliness of the surfaces of the semiconductor crystals to be bonded must be strictly controlled. It can be said that the biggest reason was that it was difficult to maintain.

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 500 [in] or less, and
Washed with water for a minute.

The smoothing method is performed by forming one bitaxial growth layer on a mirror-polished surface or a mirror-polished surface by a method that does not impair the flatness, such as MOCVD or MBEa. The surface of the obtained semiconductor was well wetted with water, and it was assumed that a layer of natural oxide was formed. Thereafter, methanol substitution and Freon drying were performed, and the semiconductor crystals obtained in this way were brought into close contact with each other with the bonding surfaces described above in a substantially dust-free clean room with a dust floating amount of 20 [pieces/77L3]. When heat treated at a temperature of 200 [°C] or more, the two were extremely firmly bonded. 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 higher than [°C].

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 of active 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 interactions between hydrated layers of the surface oxide film of the semiconductor crystals. It is thought that a strong bonding structure is formed by dehydration polymerization of active 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. 1A to 1C are cross-sectional views showing the manufacturing process of a blue light emitting diode according to an embodiment of the present invention. first,
P-ZnS with plane orientation (100) as shown in Figure 1(a)
xSet-x (0≦X≦1) The lower surface of the crystal body 11 is mirror-polished to a surface roughness of 500
An ohmic electrode 12 was formed on the upper surface side of 1.

On the other hand, as shown in Fig. 1(b), the N-
A Zn5xSt-X crystal body 13 is prepared, and this crystal body 13
The upper surface side has a surface roughness of 5 similar to the lower surface side of the crystal body 11.
00 [people] or less, and further, an ohmic electrode 14 was formed on the lower surface side of the crystal body 13.

Next, each polished surface of the crystal bodies 11 and 13 is subjected to an oxidation treatment (for example, water washing treatment) to the extent that the flatness is not lost, and in an atmosphere in which no dust is substantially involved (the amount of floating dust is 20 particles/m3). As shown in FIG. 1(C), these polished surfaces were brought into contact and in close contact with each other, and then placed in a heating furnace and heat-treated at a temperature of 200 [° C.] for about 1 hour.

The light emitting device thus obtained was one in which a good PN junction of 11°13 crystals was formed and emitted blue light.

Furthermore, when a current is passed in the forward direction, it emits light showing the current-voltage characteristics of a PN junction, and at 10 [mA], 5[, mcd]
brightness could be obtained.

As described above, according to the method of this embodiment, this was previously impossible. A good PN junction of ZnSSe+ can be easily formed. Therefore, it becomes extremely easy to realize a blue light emitting device, and its mass productivity can also be improved.

FIGS. 2(a) to 2(C) are cross-sectional views showing the manufacturing process of a blue light emitting device according to another embodiment. In this example, first, as shown in FIG. 2(a), P-8i with plane orientation (100)
The lower surface of the C crystal body 21 is mirror-polished to a surface roughness of 500 mm or less, and an ohmic electrode 1 is placed on the upper surface of the crystal body 21.
2 was formed.

On the other hand, as shown in Fig. 2(b), the N-
N-Zn5xSt-x crystal 23 on GaAS substrate 25
was epitaxially grown, and the upper surface side of this crystal body 23 was mirror-polished to a surface roughness of 500 mm or less in the same manner as the lower surface side of the crystal body 21, and an ohmic electrode 14 was further formed on the lower surface side of the substrate 25. . Here, the mixed crystal ratio X of the Zn5xSt-x crystal body 23 is O≦X≦0.5 when using a GaAS substrate, and 0.5 when using a GaP substrate.
It may be selected within the range of 5≦X≦1.

Next, the polished surfaces of the crystals 21' and 23 are subjected to oxidation treatment to the extent that the flatness is not lost, and the crystals are oxidized to the extent that the flatness is not lost. As shown in FIG. 2(C), these polished surfaces were brought into contact and in close contact with each other, and then placed in a heating furnace and heat-treated at a temperature of 200 [° C.] for about 1 hour.

The light emitting device thus obtained also had a good PN junction like the previously described example, emitted blue light, and was able to obtain the same brightness as the previous example.

Note that the present invention is not limited to the methods of each embodiment described above. The semiconductor material used may be a wide forbidden band compound semiconductor having a forbidden band width of 2.6 [eV] or more necessary for emitting blue light. Furthermore, it is also possible to reverse the conductivity type of each semiconductor material. For example, as shown in FIG. 3, P-CUAffy Gat-y (Sz 5ei
-z) 2 crystal body 33 and N-ZnSxSe1-x31
A PN junction may be formed by bonding the two.

Here, CuAfly Gat-y (Sz 5et-
Regarding the mixed crystal ratio y and Z of z ) 2 lunch break 33, the range of 0.5≦y≦1 was selected in order to obtain an appropriate forbidden band width for blue light emission, and the range of 0.5≦y≦1 was selected to eliminate the deviation of the lattice constant. .3≦7≦0
．． It is desirable to choose a range of 7.

Further, even if the substrate 35 is removed after forming the PN junction, the same device characteristics can be obtained.

Moreover, from N-GaN and P-8iC, P-znsse or P-CuAj2Ga (SSe)2, furthermore, from N-8iC and P-ZnSSe or P-C
A similar light emitting element can also be obtained from LIAj2Ga (SSe)2. In addition, various modifications can be made without departing from the gist of the present invention.

[Brief explanation of drawings]

FIGS. 1(a) to (C) are cross-sectional views showing the manufacturing process of a blue light emitting device according to an embodiment of the present invention, and FIGS. 2(a) to (C)
) is a cross-sectional view showing the manufacturing process of another embodiment. FIG. 3 is a cross-sectional view showing a modified example. 1l-P-ZnSSe crystal, 12.14--ohmic electrode, 13,23.31-N-ZnSSe crystal, 2
1...P-8iC crystal, 25 ・N-G a A
s substrate, 33-P-CuAffiGa (SSe) 2 crystal, 3
5-PGaAs substrate. Applicant's agent Patent attorney Takehiko Suzue F 0 sun -'s

Claims (6)

[Claims] (1) A step of forming flat surfaces of a P-type compound semiconductor and an N-type compound semiconductor each having a forbidden band width of 2.6 [eV] or more, and after making each of the above-mentioned flat surfaces hydrophilic by a predetermined treatment. A blue light emitting device characterized by comprising a step of drying, and then a step of directly contacting each of the flat surfaces in a clean atmosphere, and performing heat treatment at 200[° C.] or more in this state to bond the semiconductors. Method of manufacturing elements. (2) SiC, ZnSSe as the P-type compound semiconductor
Alternatively, a chalcopyrite semiconductor of CuAlGa(SSe)_2 is used, and ZnSS is used as the N-type compound semiconductor.
2. The method for manufacturing a blue light emitting device according to claim 1, characterized in that e or GaN is used. (3) The method for manufacturing a blue light emitting device according to claim 1, wherein the step of forming the semiconductor surface flatly is mirror polishing the semiconductor surface to a surface roughness of 500 [Å] or less. (4) The method for manufacturing a blue light emitting element according to claim 1, wherein the treatment for making the flat surface hydrophilic is a water washing treatment. (5) The above-mentioned clean atmosphere means that the amount of floating debris is 20 [pieces/
The method for manufacturing a blue light emitting device according to claim 1, characterized in that the atmosphere is less than or equal to m^3]. (6) A method for manufacturing a blue light emitting device according to claim 1, characterized in that a PN junction that is not lattice matched is formed at the junction surface of the P-type compound semiconductor and the N-type compound semiconductor. .