JPS6085586A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To improve productivity by a method wherein an insulating film with a low light-absorbing effect is formed to cover an upper electrode and a beam-emitting plane constituting a laser main body and is then subjected to anisotropic etching. CONSTITUTION:An SiN film 16 is formed from the direction of an upper electrode 12 on a laser bae 11 so that the film 16 satisfies an equation d1=0.80Xd0 where d0 is the thickness of the film covering the electrode 12 and d1 the thickness of the film covering the activation layer portion. Next, the film 16 is subjected to anisotropic dry etching. The film 16 covering the electrode 12 is removed in the dry etching process while thickness d3 on the activation layer portion is thinned out to satisfy an equation 2nd3=lambda (n: refraction constant of the film 16, lambda: laser oscillation wavelength). This technique reduces into half the need for film-forming and etching.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a method for manufacturing a semiconductor laser.

Background technology and its problems FIG. 1 shows an example of a semiconductor laser body.

In the figure, fil is a substrate made of n-type GaAs, (
2) is a cladding layer made of n-type AQGaAs, (31 is an active layer made of AgGaAs, and (41 is a p-type AQGaA
(5) is a cap layer made of n-type GaAs, (6) is a current limiting region, (7) and (8)
are insulating films, and (9) and QO) are electrodes, respectively. The surface perpendicular to the drawing is a mirror surface.

In such a semiconductor laser, a protective film is formed on the active layer portion to protect the active layer. Conventionally, this protective film has been processed as follows.

First, a bar-shaped object α11 (hereinafter referred to as a laser bar) is formed by interlacing GaAs. In this case, the interfold surface is a mirror surface. Incidentally, this laser beam <-(ill) is cut to obtain a plurality of semiconductor laser bodies.

Next, as shown in FIG. 2A, a SiN film (silicon Na 1 dry film) (141) is formed by plasma CVD from the upper electrode (13 side).
It shows a cross section of a laser bar (111), and the left and right surfaces are mirror surfaces.

Next, as shown in Figure B, a SiOz film (silicon oxide film) (
151 is formed.

Next, as shown in Figure C, the SiN film I is etched by isotropic dry etching using, for example, CF4) plasma.

Next, as shown in the figure, the Sr02 film a is etched by wet etching using a hydrofluoric acid system, and the processing is completed while leaving the SiN film α in the active layer portion.

According to such a conventional method, it is necessary to form the SiN film I and the 5i02 film on two opposing sides of the laser bar (Ill), which increases the time required for plasma CVD.
Manufacturing efficiency is poor. Further, the etching requires both wet etching using carbon citric acid and dry etching (isotropic) using CF4 plasma, which takes a lot of time.

In addition, a large number of laser bars (111
In order to process these laser bars all at once, these laser bars are fixed on a Si wafer using resin, but at this time, the etching surface must be facing upward, and the etching surface must be etched twice, for the SiN film I and the 5i02 film. It is necessary to perform this fixing work for each etching. In addition, hydrofluoric acid is used for etching the 5i02 film, but at this time the 8iN film α(a) attached on the opposite side has already been etched, and the electrode fiz is exposed. This hydrofluoric acid etching is carried out for 3 to 4 minutes, during which time the Ti, which is one of the electrode materials exposed on the opposite side, is attacked by the heptanoic acid. Since this Ti is in direct contact with the laser crystal body, the electrode area becomes unstable, which has an extremely large effect on the laser. Also,
On the active layer of the laser, a SiN film I is formed to a thickness of approximately 20,000 mm, and a Si02 film Q5+ is further formed to a thickness of approximately 1,000 mm.
It is formed to a thickness of
Since the process is carried out at high temperatures, the SiN film circle and the 5i02 film (1
51, and the effect of stress is thought to be on the active layer.

OBJECTS OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a method for manufacturing a semiconductor laser in which a protective film is formed without the above-mentioned disadvantages.

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the present invention forms an insulating film with a low light absorption effect on the upper electrode constituting the main body of a semiconductor laser and a light emitting surface, and then anisotropically etches the upper electrode side. The insulating film is removed, and the insulating film corresponding to the light exit surface remains with a thickness that satisfies predetermined optical conditions.

Embodiment Hereinafter, an embodiment of the present invention will be described with reference to FIG. In FIG. 3, parts corresponding to those in FIG. 2 are designated with the same reference numerals.

To form the protective film in this example, first, as shown in FIG. 1A, a SiN film Q61 is formed by plasma CVD from the upper electrode (12+ side) of the laser bar (111).

In this case, the film thickness d1 of the active layer portion (approximately 2 μm from the top) is d1=0.80 with respect to the film thickness dO on the upper electrode a2 side.
Xdo”...(The film grows according to the relationship shown in 11.

Next, as shown in Figure B, this SiN film is subjected to anisotropic dry etching using, for example, CHF3 + c2F'. In this case, when etching the upper surface dO, the etching amount d2 of the active layer portion is -1...
......(2) The relationship is d2-1dO.

In this case, the film thickness d3 of the active layer portion after processing is S
When the refractive index of iN is n and the oscillation wavelength of the laser is λ, 2nd3=λ (3) is satisfied.

Here, d3 = dl - d2 = (0,8--'-) dO = 0.62do...
...(415,5, so substitute this into equation 31 and get 2n Xo,
62d6=λ.

Therefore, if the thickness dO of the upper surface of the SiN film Q6 is selected as shown in equation (5), the film thickness d3 of the active layer portion after etching satisfies equation (3).

For example, when λ=7800X and n=2.05, do+3070X.

In this way, according to this example, Si is used to form the protective film.
N H (161 wo formations ffl K, Kono S t N
MA Q61) Only anisotropic etching is required, film formation and etching are halved compared to the conventional method (see Figure 2), improving manufacturing efficiency. Further, according to this example, before forming the SiN film αe, that is, immediately between the folds, and
After processing the film, there was almost no increase in the threshold current. In other words, there is almost no deterioration in characteristics due to the provision of the protective film. This is considered to be because (1) in this example, the end face film thickness can be accurately controlled and a predetermined film thickness can always be obtained, and (2) there are fewer steps and less contamination and damage. Furthermore, according to this example, the aging yield was significantly improved. This is thought to be because the number of steps is reduced and there is no need for wet etching, which destabilizes the electrodes as in the conventional method.

Incidentally, according to the above embodiment, when anisotropically etching the SiN film (L61), it is performed in plasma mode, but R
It may also be performed in IE (reactive ion etching) mode. In this RIE mode, the selection ratio between the top surface and the active layer surface (corresponding to 15.57 in Equation 21) can be improved, and more stable processing can be performed.In other words, the film thickness dO is small. get well.

Further, although not mentioned in the above embodiments, cleaning with an organic solvent or acid or light etching may be added depending on the case where a polymer film or the like is formed during etching.

Further, in the above embodiment, the protective film is a SiN film (I6
), but is not limited to this, and may be formed of a material that blocks oxygen and moisture, such as a 5i02 film or an AQ203 film.

Effects of the Invention According to the present invention described above, the amount of film formation and etching for forming a protective film is halved compared to the conventional method, and manufacturing efficiency is improved. Further, according to the present invention, there is almost no increase in the threshold value 'K 51t before and after forming the protective film, and there is almost no deterioration of the characteristics. Furthermore, according to the present invention, the aging yield is significantly improved.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing an example of a semiconductor laser main body;
The figure is a diagram for explaining the conventional method, and FIG. 3 is a diagram for explaining the method of the present invention. αB is a laser bar, az is an upper electrode, (131 is a lower electrode, (16) is a SiN film.

Claims (1)

[Claims] An insulating film with a low light absorption effect is formed on the upper electrode and at least the light exit surface that constitute the main body of the semiconductor laser, and the insulating film on the upper electrode side is removed by anisotropic etching, and an insulating film corresponding to the light exit surface is formed. A method for manufacturing a semiconductor laser, characterized in that the film remains at a thickness that satisfies predetermined optical conditions.