JPS6335114B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an optical semiconductor device, and particularly to a method suitable for manufacturing an optical semiconductor device having a substantially spherical semiconductor crystal layer.

For example, in semiconductor light emitting diodes for optical communication,
The light extraction surface is formed into a substantially spherical shape to improve the light extraction efficiency and the coupling efficiency with the optical fiber.

Figure 1 shows the situation. 1 is the stem, 2 is the gold (Au) layer, 3 is the gold/zinc/gold (Au/Zn/Au) electrode, and 4 is the silicon dioxide (SiO ₂ ) insulation. film, 5 is p ⁺ -InGaAsP layer, 6 is p-
InP layer, 7 is InGaAsP layer, 8 is n-InP layer, 9 is
n ⁺ -InP layer, 9' is a light extraction part, 10 is a gold/germanium/nickel (Au/Ge/Ni) electrode, 1
1 is a fiber for optical communication, and 11' is a bulbous end.

By the way, in realizing such a device, the problem is how to form the substantially spherical light extraction portion 9'.

Conventionally, for example, a concave mirror-like recess is formed on a substrate for growing a semiconductor crystal for a light emitting device by chemical etching, a semiconductor crystal is grown thereon, and then only the substrate is selectively etched chemically. Alternatively, as shown in FIG. 2, a semiconductor crystal layer 21 of, for example, InP is covered with a mask 22 having a circular opening pattern 22A, and an etching solution is used to form a convex lens on the surface of a semiconductor crystal. For example, a method is known in which chemical etching is performed using bromine methanol to form a spherical shape as shown by the broken line in the figure.

However, since all of these methods utilize chemical etching, it is difficult to obtain a spherical shape without anisotropy due to the unique crystal plane orientation dependence. There are problems such as having to select an etching solution depending on the type.

The present invention employs a physical etching method that is less dependent on crystal plane orientation, and enables the formation of an isotropic, approximately spherical shape on the light extraction surface of a semiconductor light emitting device.This will be explained in detail below. do.

Now, in order to form an isotropic spherical shape on the light extraction surface of a semiconductor light emitting device, it is possible to apply the physical etching method described above, for example, the ion beam etching method using an inert gas such as argon. This is advantageous because there is no dependence, but in that case, the problem is what kind of mask to use to form a substantially spherical shape. Note that the spherical surface in the present invention includes curved surfaces such as an elliptical surface and a parapet surface.

In the present invention, photoresist, electron beam
A desired mask is obtained by using a normal resist, such as a resist or an X-ray resist, and performing a slightly special process during baking.

3 to 7 are sectional side views of essential parts of a semiconductor device in the middle of a process for explaining one embodiment of the present invention, and the following description will be made with reference to these figures.

See Figure 3 (1) Semiconductor crystal layer 31 to form the light extraction surface portion
A positive (or negative) type photoresist film 32 is formed on the entire surface.

Refer to FIG. 4 (2) The photoresist film is patterned by performing normal photomask contact exposure and development to form a substantially circular pattern mask 32'.

Refer to FIG. 5 (3) Baking is performed in a non-oxidizing atmosphere by applying high heat such that the approximately circular resist mask does not burn. As a result, the resist mask 32' is melted and softened and deformed into a stable spherical surface due to surface tension, resulting in a spherical resist mask 32''.
transformed into.

See Figure 6 (4) Ion beam of inert gas such as argon
Spherical resist mask 3 is created by etching.
The entire surface of the semiconductor crystal layer 31 on which the mask 32'' is formed is etched, and the etching is continued until the mask 32'' is completely removed. Ion beam etching using an inert gas has less material selectivity than chemical etching, so if etching is performed under the conditions shown in the figure, the resist mask 3
2" spherical shape is transferred onto the crystal layer 31. The ion beam is incident obliquely at an angle θ with respect to the axis 33 as necessary. Accordingly, by rotating the crystal layer 31 around the axis 33,
The etching rate ratio between the resist mask and the semiconductor crystal can be controlled, and the spherical shape of the resist mask can be transferred to the semiconductor crystal. According to the experimental results, the crystal layer 31
When it is GaAs, the angle θ is not a very important factor, but when it is InP, θ > 40°~
50°, and the rotation is θ≠
Required when 0.

See Figure 7 (5) When the etching is completed, the spherical light extraction part 3
1' is formed. In the figure, d is the etching depth, and L is the diameter of the light extraction portion 31'.

The light extraction portion 31' formed in this manner has an isotropic spherical shape and can achieve good focusing.

What is important in the above steps is the baking of the photoresist mask described as step (3).
That is, the baking must be carried out at a temperature that sufficiently reduces the viscosity of the heat-softening organic film such as photoresist, but does not cause combustion. The optimum temperature differs depending on the chemical composition of the resist, but in general, positive resists are lower than negative resists (for example, 120 to 200 [° C.]) and can be obtained with better controllability. Factors that influence the shape of the light extraction portion 31' include, in addition to the baking of the resist, the etching rate ratio of the resist to the semiconductor at the inclination angle θ in step (4).

Next, specific data when forming a spherical shape in the InP semiconductor crystal layer will be illustrated.

Resist type: Positive UV resist AZ-
1350J (Shipley) Resist thickness: Approximately 2 [μm] Baking temperature: Approximately 200 [℃] Baking time: 5 [minutes] Ion beam Argon ion beam inclination angle θ 50° Current density 0.57 [A/cm ² ] Etching time 45 [minutes] d (see Figure 7) 4 [μm] L (see Figure 7) 80 to 150 [μm] The light extraction section thus realized has a nearly spherical surface with low anisotropy, that is, with little aberration. It was hot.

FIG. 8 shows the magnification β due to the spherical light extraction portion of the InP semiconductor light emitting device formed according to the present invention.
As shown in FIG. 9, this shows the results obtained from the ratio of the light emission pattern measured through the spherical light extraction part to the gold electrode pattern provided on the p-electrode surface. In Figure 9, s
is the distance between the p-electrode 3 and the surface of the light extraction part, r _p
indicates the radius of curvature of the spherical surface of the light extraction portion. The refractive index n p is calculated by applying the equation ( ) that expresses the relationship between the magnification _β of a lens whose curvature is constant over the entire spherical surface and the parameters s and r _p to the measurement results shown in Figure 8. As a result, n _p =3.5 was obtained.

1/β=1−n _p −1/n _p s/r _p () Since this matches the known refractive index of InP of 3.5, the light extraction portion formed by the present invention extends over the entire spherical surface. It can be seen that the curvature is constant.

The semiconductor light emitting device produced in this way is
By a suitable combination of the thickness and spherical shape of the n ⁺ -InP layer, it can be coupled with optical fibers with good efficiency.

FIG. 10 shows a sample manufactured according to the invention described above.
This shows the current/coupled light power characteristics of an InP semiconductor light emitting device. In FIG. 10, the horizontal axis shows current [mA] and the vertical axis shows coupled light power [μW]. The fiber used in the measurements shown in Figure 10 has a core diameter of
85 [μm], numerical aperture 0.16, and radius of curvature of the tip of the fiber 75 [μm].

According to the present invention, the emission diameter is 30 [μm] and the current is 100 [μm].
[mA], the combined optical power is approximately 200 [μW]
A large combined optical power can be obtained.

In the above embodiment, the InP-InGaAsP type was explained, but the present invention is also applicable to other types, for example,
It is also useful for Ga _1-x Al _x As systems. Further, when a thick mask film is required, it is preferable to use a resist for electron beams or X-rays.
Furthermore, the mask film is not limited to the above-mentioned photoresist film, but may also be a heat-softening organic material film such as acrylic resin.

As can be seen from the above description, according to the present invention, a spherical light extraction portion can be formed on the light extraction surface of a semiconductor light emitting device without relying on chemical etching, and the spherical shape has no aberration. Since the number is small, the light extraction efficiency or the coupling efficiency with the optical fiber can be improved.

[Brief explanation of the drawing]

Figure 1 is a side sectional view of the main part of a semiconductor light emitting device, Figure 2
The figure is a sectional side view of a main part of a semiconductor light emitting device for explaining a conventional technique for forming a spherical light extraction part, and FIGS. 3 to 7 are main parts of a semiconductor light emitting device for explaining an embodiment of the present invention. FIG. FIG. 8 is a diagram showing the measurement results of lens magnification β, FIG. 9 is a schematic diagram of the light emitting device used for the measurement in FIG. 8, and FIG. 10 is a diagram showing the current and combined optical power of the light emitting device according to the present invention. It is. In the figure, 31 is a crystal layer, 31' is a light extraction part, 32 is a resist film, 32', 32'' are resist masks, 33 is an axis, θ is an inclination angle, d is an etching depth, and L is a light extraction part. This is the diameter of the part.

Claims (1)

[Claims] 1. Forming a heat-softening organic material film on the entire surface of the semiconductor crystal layer, then selectively removing the heat-softening organic material film to pattern it into a substantially circular shape, and then removing the heat-softening organic material film. is baked to form a mask whose surface forms a part of a substantially spherical surface and protrudes, and then the entire surface is etched by an etching method using physical impact of particles until the heat-softening organic material film is completely removed. 1. A method for manufacturing an optical semiconductor device, comprising the step of processing a part of the surface of a semiconductor crystal layer into a protruding shape that forms part of a substantially spherical surface.