JPH06283811A - Semiconductor laser manufacturing method - Google Patents

Abstract

PURPOSE:To realize a semiconductor laser in which the thickness of protective film can be formed with high controllability by forming the protective film for the emission edge by Langmuir-Blodgett method. CONSTITUTION:An n-type current block layer 2, a lower clad layer 3 of P-type AlGaAs, a P-type active layer 4, an upper clad layer 5 of n-type AlGaAs, an n-type contact layer 6, and an electrode 7 are deposited sequentially on a P-type GaAs wafer 1 to obtain a desired semiconductor laminate structure. Subsequently, the wafer is cleaved to obtain a semiconductor chip bar 15. In order to form a dielectric protective film only on the emission edge 8, the electrode 7 forming face and the like are previously covered and the semiconductor chip bar 15 is shifted up and down with respect to the interface of an aqueous liquid medium, on which a single molecular film of an amphiliphic organic substance 12 is formed, while keeping the axis thereof normal to the interface. This method allows thickness control of the dielectric protective film in the molecular order thus realizing a high quality, low noise semiconductor laser.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor laser, and more particularly to forming a protective film on a light emitting end face of a semiconductor laser chip.

[0002]

2. Description of the Related Art A semiconductor laser according to the present invention is used as a light source or the like in the field of communication such as optical fiber communication or in the field of information recording such as optical disk files, digital audio disks, video disks, laser beam printers and the like.

By the way, in a semiconductor laser device used as a light source for such optical communication and information reading, a protective film made of a dielectric material is coated on a light emitting end face which is a cleavage face. The reason for coating the protective film in this manner is to prevent the end face deterioration from occurring on the cleaved face and to set the reflectance of the light emitting end face to a predetermined value.

In the production of a semiconductor laser device, a protective film coating is performed on a semiconductor chip bar after cleaving a wafer on which electrodes have been attached and polished. Conventionally, such protective film coating is performed by EB. It is performed by the vapor deposition method, the plasma CVD method, the MOCVD method, or the like. However, with such a conventional method, it is difficult to control the film thickness, and there is considerable variation in the film thickness distribution.

The film thickness of the protective film influences the reflectance of the light emitting end face, and the variation in the film thickness distribution is due to the generation of noise due to the returning light reflected by the external optical system and returning. Since it has a great influence, stricter control of the film thickness when forming the protective film has been desired.

[0006]

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a method for forming a protective film for the emission surface of a semiconductor laser device with good controllability of the film thickness in the manufacture of a semiconductor laser. .

[0007]

The present invention, which achieves the above object, is a method for manufacturing a semiconductor laser device, which is developed on an aqueous liquid medium in forming a protective film for the light emitting end face of the device. A dielectric protective film is formed on the end surface by a Langmuir-Brodget method (hereinafter abbreviated as LB method) in which a monomolecular film of the amphiphilic organic substance is transferred to the end surface. It is what

[0008]

[Function] The semiconductor chip bar obtained by cleaving a substrate on which electrodes have been attached or polished in the manufacture of a semiconductor laser device passes through an interface of an aqueous liquid medium on which a monomolecular film of an amphipathic organic substance is formed. Then, the monomolecular film is transferred to the cleaved surface of the tip bar. The number of monomolecular layers transferred to the cleavage plane by one vertical movement is one, and by repeating this, the monomolecular layers can be accumulated one by one. Therefore, it is possible to control the film thickness on the molecular order by the number of times the semiconductor chip bar is moved up and down, and it is possible to form a protective film having good film thickness uniformity.

The present invention will be described in detail below based on embodiments. In the method for manufacturing a semiconductor laser of the present invention,
First, a desired laminated structure is formed on a substrate based on a conventional method. For example, when an AlGaAs semiconductor laser is to be obtained, as shown in FIG. 3, an n-type current blocking layer 2, a lower clad layer 3 made of p-type AlGaAs, and a p-type active layer 4 are formed on a p-type GaAs wafer 1. , N-type AlGaAs upper clad layer 5, n-type contact layer 6, electrode 7
Are sequentially deposited by a known thin film forming technique and photolithography technique. When the desired semiconductor laminated structure is obtained, the wafer is cleaved to obtain semiconductor chip bars. In the semiconductor chip bar, the cleavage surface is the light emitting end surface 8, and the surface intersecting this is the surface on which the electrode 7 is formed as described above.

On the other hand, a monomolecular film of an amphipathic organic substance is formed on the interface of an aqueous liquid medium such as water. The monolayer is formed as is well known in the LB method. That is, as schematically shown in FIG. 2, an amphipathic organic substance 12 having a hydrophilic head portion 13 and a hydrophobic chain portion 14 is spread on the interface of the aqueous liquid medium 11 and surface pressure is applied to this interface. The hydrophilic head portion 13 is oriented on the interface side of the aqueous liquid medium 11 and the hydrophobic chain portion 14 is oriented on the gas side.

As the amphipathic organic substance 12, various compounds having an insulating property can be used. For example, a long chain carboxylic acid such as stearic acid or palmitic acid can be used. The single molecule length of the organic substance 12 is about 5 to 30 angstroms.

Then, as shown in FIG. 1, the semiconductor chip bar 15 obtained as described above is attached to the interface of the aqueous liquid medium on which the monomolecular film of the amphipathic organic substance 12 is formed as described above. Up and down while keeping so that it is perpendicular to the interface. Since one monolayer is transferred to the surface of the semiconductor chip bar by one vertical movement, the vertical movement is repeated until the desired thickness is obtained.

Prior to this operation, in order to form the dielectric protective film only on the light emitting end face 8 of the semiconductor chip bar 15, the electrode 7 forming face of the semiconductor chip bar 15 is previously covered with an appropriate covering means. It is desirable to keep.

After the dielectric protective film having a desired film thickness is formed on the light emitting end surface 8 of the semiconductor chip bar 15 in this manner, the semiconductor chip bar 15 is cleaved according to a conventional method.
A semiconductor chip is obtained, and thereafter, steps such as die bonding and wire bonding are performed to obtain a predetermined semiconductor laser element.

In the above description, the semiconductor chip bar 15 is subjected to the dielectric protective film forming process, but this process can also be performed after forming the semiconductor chip.

[0016]

EXAMPLES Next, a more specific example will be given to describe the step of forming the dielectric protective film.

Example 1 CH ₃ (C) stearate prepared by dissolving chloroform in an aqueous solution containing 1 × 10 ⁻⁴ mol / dm ^{3 of} BaCl ₂
H ₂ ) ₁₆ COOH is developed on the water surface and oriented to form a monomolecular film, and the chip bar of the AlGaAs semiconductor laser is moved vertically to the water surface to transfer the film. The thickness of one layer of stearic acid is 2.45 nm, and the refractive index in the film thickness direction is 1.54 ± 0.01. When the chip bar is moved up and down 51 times, the film thickness is 126.6 nm.
Since the refractive index is 1.54, the oscillation wavelength is approximately 1/4 of 780 nm, and a low reflection film can be formed.

Example 2 CH ₃ (C) palmitate prepared by dissolving chloroform in an aqueous solution containing 1 × 10 ⁻⁴ mol / dm ^{3 of} BaCl _2.
H ₂ ) ₁₄ COOH is developed on the water surface and oriented to form a monomolecular film, and the film is transferred by moving the chip bar of the AlGaAs semiconductor laser vertically to the water surface. The thickness of one layer of stearic acid is 2.30 nm, and the refractive index in the film thickness direction is 1.60 ± 0.01. When the chip bar is moved up and down 53 times, the film thickness becomes 121.9 nm.
Since the refractive index is 1.60, the oscillation wavelength is approximately 1/4 of 780 nm, and a low reflection film can be formed.

[0019]

As described above, according to the present invention, in the method of manufacturing a semiconductor laser, the step of forming the dielectric protective film on the light emitting surface of the laser element is performed by applying the LB method. The thickness of the dielectric protective film can be controlled on the molecular order by the number of times the monomolecular film of the amphipathic organic substance spread on the liquid medium is passed through the light emitting surface of the laser element. Since the uniformity is enhanced, it can be expected to obtain a semiconductor laser with high quality and low noise.

[Brief description of drawings]

FIG. 1 is a schematic view showing a process for forming a light emitting surface protective film according to a method for manufacturing a semiconductor laser of the present invention,

FIG. 2 is a schematic diagram showing formation of a monomolecular film at an interface of an aqueous liquid medium,

FIG. 3 is a schematic cross-sectional view showing an example of a semiconductor laminated structure of a semiconductor laser device.

[Explanation of symbols]

1 ... p-type GaAs wafer, 2 ... n-type current blocking layer, 3 ... p-type AlGaAs lower cladding layer,
4 ... p-type active layer, 5 ... n-type AlGaAs upper cladding layer, 6 ... n-type contact layer, 7 ... electrode,
8 ... Light emitting end face, 11 ... Water-soluble liquid medium, 12 ... Amphiphilic organic substance,
13 ... Hydrophilic head portion, 14 ... Hydrophobic chain portion, 15 ... Semiconductor chip bar.

Claims (1)

[Claims] 1. A method for manufacturing a semiconductor laser device, wherein a monomolecular film of an amphipathic organic substance developed on an aqueous liquid medium is transferred to the end face when forming a protective film for the light emitting end face of the device. A method for manufacturing a semiconductor laser, characterized in that a dielectric protective film is formed on the end face by a Langmuir-Blodgett method.