JPH06252449A - Lens processing method - Google Patents

Abstract

PURPOSE:To realize a lens excellent in shape preventing its foot from sagging by a method wherein a substrate is etched as irradiated with light at an angle to a line perpendicular to its surface while the substrate is dipped into an etching liquid. CONSTITUTION:A gold layer 2 is evaporated on the surface of an InP substrate 1, a photoresist film is applied thereto and patterned into a disc shape, the metal layer 2 is etched using the disc-shaped photoresist film as a mask to form a disc-shaped gold layer 2, the photoresist film is removed off from the substrate 1, and the substrate 1 is directed an etching tank 20 filled with FeCl3 solution. Light is directed to the substrate 1 at an angle of 5 to 45 deg. to a line perpendicular to the surface of the substrate 1, and a photoetching operation is executed four times turning the etching tank 20 by an angle of 90 deg. each time, whereby an inverted quadrangular pyramid-shaped projection 3 is formed on the surface of the substrate 1, and then the gold layer 2 is removed by etching. Therefore, the substrate 1 is subjected to a rounding process by isotropic etching, whereby a lens excellent in shape can be obtained preventing its foot from sagging.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens processing method for an optical element, and more particularly to a technique effective when used to directly form a lens on a semiconductor substrate constituting an optical semiconductor device.

[0002]

2. Description of the Related Art Conventionally, various light emitting diodes using a direct transition type semiconductor have been put into practical use, and these are usually used in a structure having a lens attached. By the way, among light emitting diodes using a direct transition semiconductor, a semiconductor layer forming a light emitting layer, such as an InP-based light emitting diode, has a bandgap smaller than a bandgap of a semiconductor forming a substrate and light emitted from the substrate. In the case of a small absorption amount, a structure in which the light emitting layer is faced down and wire bonding is performed to emit light from the substrate side is effective. In this case, a technique for improving the light emission efficiency by directly processing the substrate into a lens shape has been proposed (FD King et. Al.
Journal of Electronic Mat
initials, VoL. 4, No. 2 1975 pp
243-253).

[0003]

Conventionally, the formation of a lens on the above-mentioned semiconductor substrate has been carried out by mechanical polishing or a wet etching technique which is one of semiconductor manufacturing techniques. However, each of the conventional lens processing methods for a substrate has problems that it requires manpower and the number of processing steps is extremely large and takes a long time. Further, the processing with a mechanical polishing apparatus could not be applied to brittle materials such as III-V group compound semiconductors.

Therefore, for example, there has been proposed a lens processing method utilizing photoetching, in which, when a substrate is etched while being irradiated with light, only a portion exposed to the light is etched. However, photo-etching is originally an etching method with a large aspect ratio and less over-etching of about several microns, and it has been found that the following disadvantages are encountered when processing a semiconductor substrate into a lens shape. That is, if a large amount of etching (20 μm or more) is attempted by photoetching, the side surface of the etched portion (column portion) 5 is also exposed to light during the etching, and the middle trunk portion is thinned. The resulting shape is as shown in FIG. As a result, when a rounding process is performed by isotropic etching after that, as shown in FIG. 6, the hem portion 4a of the lens is gently processed, and the performance as a lens is deteriorated. is there.

The present invention has been made by paying attention to the above problems, and an object thereof is to obtain a lens having an extremely good shape with no sagging at the hem portion in a few steps. To provide various processing technologies.

[0006]

According to the present invention, for example, a mask layer made of a light blocking material is formed on the surface of a substrate to be processed, and then the substrate is immersed in an etching solution suitable for photoetching. 5 to 4 from the vertical direction
The substrate is etched by irradiating light in a direction inclined by 5 °, and then the substrate is pulled up from the etching liquid to remove the mask layer, and isotropic etching is performed. In the above case, it is most preferable to irradiate the light from all directions around the substrate, but the light should be radiated twice by rotating at least 180 °, preferably by diverting the direction by 90 ° or 60 °. May be.

[0007]

According to the above-mentioned means, the photo-etched portion has an inverted cone shape, so that when rounded by isotropic etching after that, there is no sagging at the hem portion of the lens, which is a very good shape. Lens can be obtained, and the cost is not increased because only one mask is used in the photolithography process, and the number of processes is small because the number of times the mask formation process and etching process are repeated is small, and mechanical polishing is not required. Since it is unnecessary, lens processing can be extremely easily performed even on a fragile material.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A process of one embodiment in which the present invention is applied to lens processing for a substrate for an InP light emitting diode will be described below in order of steps with reference to the drawings. First, a gold layer is vapor-deposited on the surface of the InP substrate 1 as a non-light-transmitting film, a photoresist film is applied on the gold layer, and the photoresist film is patterned into a circular shape by a photolithography technique. . Next, using this photoresist film as a mask, the metal deposited by dry etching using Ar gas or the like was etched to form a circular gold layer 2 on the substrate 1, and then the resist film used as the mask was removed. (See Figure 1).

Then, the substrate 1 is immersed in an etching bath 20 containing a FeCl ₃ solution, and the light of a white lamp is irradiated from a direction inclined by 20 ° with respect to the vertical direction of the substrate to advance photoetching. (See FIG. 2). Then, the etching bath 20 is rotated by 90 ° in a horizontal plane to obtain a total of 4
Diffractive etching was performed. As a result, as shown in FIG. 3, the inverted quadrangular pyramidal projection 3 was formed on the surface of the substrate 1.
Next, the substrate 1 is taken out from the etching bath 20 containing the FeCl ₃ solution, the gold layer 2 is removed by etching, and then the substrate 1 is treated with a bromic acid-based etchant (Br ₂ : HBr:
It was immersed in an etching bath 20 containing H ₂ O = 2: 8: 100) for 30 minutes. As a result, the corners of the convex portion 3 are removed,
As shown in FIG. 4, the lens portion 4 having a good shape with the skirt rising sharply was formed.

For comparison, in the same process as described above, light irradiation was performed in the direction perpendicular to the substrate to perform lens processing by photoetching. Then, when a light emitting element was created using those substrates and the light emission outputs were compared,
It was found that the device using the substrate obtained in the above example has an output increased by 20% as compared with the device using the substrate obtained in the comparative example. In the above embodiment, the substrate is 9
Although the light was irradiated while irradiating the light while rotating it by 0 °, the substrate may be rotated by 60 ° in the circumferential direction so that the light is irradiated, or the light is obliquely fed from all directions around the substrate. You may make it perform photoetching, irradiating to. Further, even if the substrate is rotated 180 ° on the way and the light is irradiated twice in total, a lens having a good shape with a steeply rising skirt can be obtained as compared with the comparative example.

Further, in the above-mentioned embodiment, the light of the white lamp is irradiated from the direction inclined by 20 ° from the vertical direction to the substrate to advance the photoetching, but the irradiation angle of the light is not limited to 20 °. , In the range of 5 to 45 °. When the angle is less than 5 °, there is no difference from the conventional method, and when the angle exceeds 45 °, the region to be etched becomes too large to be practical. Further, in the above-described embodiment, the etching tank 20, that is, the substrate 2 was rotated. However, it goes without saying that the lamp may be rotated. Further, although the gold layer 2 serving as an etching mask for lens processing is left in a circular shape, it may be left in an elliptical shape, an oval shape, or another shape. In addition, in the above embodiment, In
Although the lens processing on the P light emitting diode substrate has been described as an example, the present invention can be generally applied to the lens processing on the GaAs light emitting diode, the light receiving diode and other optical semiconductor device substrates.

[0012]

As described above, according to the present invention, a mask layer made of a light blocking material is formed on the surface of a substrate to be processed, and then the substrate is immersed in an etching solution suitable for photoetching. 5 to 45 from the vertical direction
° After the substrate is etched by irradiating light from the tilted direction, the substrate is pulled up from the etching solution to remove the mask layer, and isotropic etching is performed. Therefore, when a rounding process is performed by isotropic etching after that, there is no sagging at the hem of the lens and a lens with an extremely good shape can be obtained, and only one mask is used in the photolithography process. The cost is not high because the number of mask formation steps and etching steps is small, and the number of steps is small, and mechanical polishing is not required, so lens processing is extremely easy even for fragile materials. The effect is that it can be done.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a first step of a process of an example when the present invention is applied to lens processing for a substrate for InP light emitting diode.

FIG. 2 is a cross-sectional view showing a second step of the process of one example in the case where the present invention is applied to lens processing for a substrate for InP light emitting diode.

FIG. 3 is a cross-sectional view showing a final step of a process of an example when the present invention is applied to lens processing for a substrate for InP light emitting diode.

FIG. 4 is a sectional view showing the shape of a lens on the surface of a substrate obtained by applying the method of the present invention.

FIG. 5 is a cross-sectional view showing a substrate cross-sectional shape in the middle of a process in a lens processing method by photoetching of a comparative example.

FIG. 6 is a cross-sectional view showing a shape of a lens on a surface of a substrate obtained by a lens processing method by photoetching of a comparative example.

[Explanation of symbols]

 1 substrate 2 light blocking mask layer (gold layer) 4 lens section 20 etching bath

Claims (2)

[Claims] 1. A mask layer made of a light blocking material is formed on the surface of a substrate to be processed, and then the substrate is immersed in an etching solution suitable for photoetching while the substrate is dipped in a direction of 5 to 45 from the vertical direction. A method for processing a lens, characterized in that after the substrate is etched by irradiating light from a tilted direction, the substrate is pulled up from an etching solution to remove the mask layer and isotropic etching is performed. 2. The lens processing method according to claim 1, wherein the substrate is an InP substrate, and the etching solution used for the photo-etching is a FeCl ₃ solution.