JPH07183568A - Photodetector - Google Patents

Abstract

(57) [Abstract] [Purpose] It is possible to prevent electric field concentration at the junction end of the light receiving part to eliminate edge breakdown, improve the electrical reliability of the device, and perform high integration using a simplified process. A light receiving element is provided. In a light-receiving element having at least a light-receiving portion 7 functioning as an avalanche photodiode on a single-crystal silicon substrate 5, the single-crystal silicon substrate 5 is etched in the peripheral portion of the light-receiving portion 7 so that an inclination of a light-receiving portion end face A A gentle groove 10 was formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light receiving element manufactured by a process technique used in the fields of optical communication, optical pickup and the like.

[0002]

2. Description of the Related Art Conventionally, as a structure of a light receiving element manufactured by using a process technique, a planar structure by selective diffusion of a pn junction is most often used as shown in FIG. In this case, the breakdown (avalanche breakdown) in the light receiving portion 1 formed of the pn junction is surrounded by the broken line at the end before the flat central flat portion 2 by applying a small voltage. It occurs in the diffusion peripheral portion 3. The avalanche breakdown phenomenon that occurs in the diffusion peripheral portion 3 in this way is called edge breakdown, and even if the voltage is increased, only a current flows, and the pn junction of the central flat portion 2 The reverse voltage hardly increases, so that it cannot function as an avalanche photodiode.

Therefore, in order to cause avalanche breakdown in the pn junction region of the central flat portion 2 at the center of the light receiving portion 1, the breakdown voltage of the diffusion peripheral portion 3 is set to be lower than the breakdown voltage of the central flat portion 2. Must also be set high. Because of this, the diffusion peripheral part 3
As shown in FIG. 7, a guard ring of an inclined junction having a small impurity concentration gradient and a large radius of curvature is formed.
It is necessary to form the structure so that the breakdown voltage of the diffusion peripheral portion 3 is set high.

[0004]

As described above, the avalanche photodiode generally has a guard ring structure in order to prevent avalanche breakdown at the edge of the light receiving portion 1 (diffusion peripheral portion 3). is there. In particular, in a III-V group avalanche photodiode, it is possible in the laboratory to form a so-called mesa structure in which the pn junction is formed obliquely to reduce the electric field strength, but when using silicon as the substrate Since such a mesa structure cannot be formed, it is indispensable to devise a diffusion condition such as a guard ring structure. By using a guard ring structure in this way, it is possible to prevent electric field concentration on the edges of the junction,
A manufacturing method is adopted in which the breakdown voltage of the diffusion peripheral portion 3 is set high. However, the method of devising the diffusion conditions such as reducing the impurity concentration at the edge of the junction of the light receiving section 1 or setting the concentration gradient gently complicates the manufacturing process, and as a practical matter, the avalanche photodiode is There is a problem that it cannot be integrated on the substrate.

[0005]

According to a first aspect of the present invention, in a light receiving element having a light receiving portion functioning as at least an avalanche photodiode on a single crystal silicon substrate, the single crystal silicon is provided around the light receiving portion. The substrate was etched to form a groove having a gentle slope on the end surface of the light receiving portion.

According to a second aspect of the present invention, in the first aspect of the present invention, the light receiving portions of at least two avalanche photodiodes are formed adjacent to each other on the same substrate, and at least a pair of the light receiving portions adjacent to each other are formed. A groove was formed by etching the single crystal silicon substrate between the light receiving portions.

According to a third aspect of the invention, in the first aspect of the invention, the groove is formed by using anisotropic etching with an alkaline etchant.

According to the invention of claim 4, in the invention of claim 3, the single crystal silicon substrate is (100)
A substrate having a plane orientation was used.

According to a fifth aspect of the invention, in the third aspect of the invention, a solution containing no alkali metal such as hydrazine or ethylenediaminepyrocatechol is used as an etchant for etching the single crystal silicon substrate.

[0010]

According to the present invention, the electric field to the junction end surface of the light receiving portion is formed by etching the peripheral portion of the light receiving portion of the avalanche photodiode made of a silicon substrate to form a groove having a gentle slope. It is possible to prevent concentration and eliminate edge breakdown, and it is possible to manufacture a substrate having a mesa structure with a simple manufacturing process.

According to the second aspect of the present invention, when the light receiving portions of a plurality of avalanche photodiodes are formed adjacent to each other on one substrate, a groove formed by etching the division between the light receiving portions on the substrate. By doing
It is possible to shorten the distance between the light receiving parts.

According to the third aspect of the present invention, by forming the groove by anisotropic etching using an alkaline etchant, the inclination of the end face of the light receiving portion becomes much gentler, and the electrical stability of the device is further enhanced. It is possible to raise it.

According to the fourth aspect of the present invention, by setting the plane orientation of the silicon substrate to be the (100) plane, when the entire periphery of the light receiving portion is surrounded by the groove, all four sides thereof can be surrounded by oblique surfaces. If a plurality of avalanche photodiodes are integrated on one substrate and the light receiving parts are divided by grooves, the angle formed by the bottom surface of the grooves will be smaller, and the distance between the light receiving parts will be further shortened. It becomes possible.

According to the invention of claim 5, the solution used as the etchant is a solution containing no alkali metal to reduce the uptake of mobile ions as a contamination source into the oxide film, thereby electrically insulating the patterns. It becomes possible to raise.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described with reference to FIG. In this embodiment, in a light-receiving element having at least a light-receiving portion functioning as an avalanche photodiode on a single-crystal silicon substrate, the single-crystal silicon substrate is etched in the peripheral portion of the light-receiving portion to form a groove with a gentle slope on the end surface of the light-receiving portion. Is formed. Hereinafter, as a specific example, a manufacturing process in the case where the light receiving portion 7 is completely surrounded by the groove 10 will be described with reference to FIGS.

First, in (a), a P + layer 4a and a π layer 4b are provided.
A p layer 6 having an impurity concentration of about 10 ¹⁵ / cm ³ is formed on the entire surface of a silicon epitaxial substrate 5 (hereinafter referred to as a silicon substrate) having a P + / π structure composed of N + layer 7 (hereinafter referred to as light-receiving portion 7) on the upper part of the p-channel stopper layer 8 on the outer region thereof.
To form. Next, in (b), after covering the entire surface of the substrate with an oxide film 9 (SiO ₂ ) by thermal oxidation, the central light receiving portion 7
The oxide film 9 between the p + channel stopper layer 8 and the outside thereof is covered with a buffered hydrofluoric acid solution (HF: NHF ₄ F = 1 :).
It is selectively removed in 6), thereby forming a mask pattern made of the oxide film 9. Next, in (c), the surface of the p layer 6 is etched through the formed mask pattern using hydrofluoric nitric acid (HF: HNO ₃ = 1: 3). This makes it possible to form the groove 10 having a gentle slope on the light-receiving-portion end surface A of the light-receiving portion 7 (hereinafter referred to as the end surface A). Finally, in (d), the mask pattern is removed,
The upper surface of the silicon substrate 5 is again thermally oxidized, and the entire surface of the substrate is covered with an oxide film 11 (SiO ₂ ). Then, an electrode 12 made of Al or the like is wired and a connection wire 13 (for example, a bonding wire) is used. By making electrical connection, a desired avalanche photodiode can be manufactured.

As described above, the upper surface (p layer 6) of the silicon substrate 5 located in the peripheral portion of the light receiving portion 7 is isotropically etched, so that the end face A of the light receiving portion 7 has a much simpler structure. It is possible to form the groove 10 having a mesa structure with a gradual inclination, and by doing so, it is possible to prevent electric field concentration on the junction end face and prevent breakdown at the end face A. Moreover, the groove 10 having such a gentle slope is used.
By forming, the complicated manufacturing process for devising the diffusion conditions, such as the conventional guard ring structure, becomes unnecessary, and the process can be simplified.

Next, a second embodiment of the present invention will be described with reference to FIG. The description of the same parts as those in the first embodiment described above will be omitted, and the same reference numerals will be used for the same parts. In the above-described first embodiment, the upper surface of the silicon substrate 5 is isotropically etched by using hydrofluoric nitric acid, so that the light receiving portion 7 of the avalanche photodiode is obtained.
The groove 10 was formed on the end face of the. On the other hand, in the present embodiment, the V groove 14 is formed by performing anisotropic etching using an alkaline etchant. Specifically, using hydrazine-hydrate,
Etching was performed while maintaining the temperature at 80 ° C. Therefore,
As described above, anisotropic etching is performed using hydrazine to form the V-shaped groove 14, whereby the inclination of the end face A of the light receiving portion 7 can be made more gradual, and the stability of the electrical characteristics of the avalanche photodiode can be improved. Can be further improved.

Next, a third embodiment of the present invention will be described with reference to FIG. The description of the same parts as those of the first and second embodiments described above is omitted, and the same reference numerals are used for the same parts. In this embodiment, in a light receiving element having a light receiving portion that functions as an avalanche photodiode, at least two light receiving portions are formed adjacently on the same substrate, and the silicon substrate 5 is provided between at least a pair of light receiving portions among these light receiving portions. The upper surface of is etched to form the V groove 14. The specific manufacturing process will be described below. First, as in the first embodiment, the silicon substrate 5
After forming the p-layer 6 on top of it by using the
Nb layers 7b are formed adjacent to each other with a distance of about 10 μm. Next, the two light receiving portions 7 formed in this way
The p + channel stopper layer 8 and the guard ring 15 were formed except for the portion between a and 7b. Next, the entire surface of the substrate is covered with an oxide film 11 (SiO ₂ , see FIG. 2) by thermal oxidation, and then only the portion between the two light receiving portions 7a and 7b is opened and removed by using a buffered hydrofluoric acid solution. Anisotropic etching is performed using hydrazine hydrate in the same manner as in the second embodiment, whereby the V groove 14 having a gentle slope is formed between the two light receiving portions 7a and 7b. Finally, the applied oxide film 1
After removing 1, the whole surface of the substrate is again covered with a similar oxide film 11 by thermal oxidation, and then an electrode 12 is formed to thereby manufacture an avalanche photodiode having light receiving portions 7a and 7b divided into two. You can

As described above, the light receiving portions 7a and 7b of the two avalanche photodiodes are formed adjacent to each other on the same substrate, and the V groove 14 is formed only between the light receiving portions by anisotropic etching. Therefore, it is possible to avoid the formation of the p + channel stopper layer 8 and the guard ring 15 between the light receiving portions, and thus the light receiving portions 7a, 7a,
Since the distance of 7b can be shortened, high-density arrangement can be performed. Further, by using the same manufacturing method as this, the light receiving portions 7a to 7d are divided into four as shown in FIG.
It is possible to manufacture an avalanche photodiode having In this case, the light receiving portions 7a to 7d are arranged close to each other, and the V groove 14 is formed vertically and horizontally between the light receiving portions. Further, FIG. 5 shows an example of a case where five light receiving portions 7a to 7e are arranged in an array, and in this case also, the V groove 14 is formed between the light receiving portions arranged in proximity to each other. Has been done. Even when a plurality of light receiving portions 7a to 7e are formed close to each other as described above, the V groove 1 can be formed without any problem.
4 can be formed, and the degree of integration of elements can be further increased.

In the second and third embodiments described above, hydrazine hydrate was used as an etchant for anisotropic etching, but an etchant capable of anisotropically etching a single crystal silicon substrate is used. If there is, it is not particularly limited. For example, ethylenediamine pyrocatechol, sodium hydroxide, potassium hydroxide and the like can be used. However, among these etchants, an etchant containing an alkali metal such as sodium (Na) or potassium (K) becomes a contamination source of mobile ions and is not so preferable in terms of reliability such as electrical insulation. Therefore, if possible, it is better to use a solution containing no alkali metal such as hydrazine or ethylenediaminepyrocatechol as an etchant for etching the single crystal silicon substrate.

Further, in all the above-mentioned embodiments, the (100) plane is used as the plane orientation of the silicon substrate 5, but other than this, for example, the V groove 14 such as the (110) plane can be formed. The orientation of the plane is not particularly limited. In this case, comparing the (100) plane with the (110) plane, the V groove 14 formed on the (100) plane is (1
Since the angle formed by the bottom surface of the V groove 14 is smaller than that formed on the 10) surface, it is suitable in terms of integration. Moreover, as described in the first embodiment, in the case where the light receiving portion 7 is completely surrounded by the groove 10, the groove 10 formed in two directions orthogonal to each other when the (110) plane is used. Since it is not possible to form both V-grooves, it is better to use the (100) plane also in this respect.

[0023]

According to the invention described in claim 1, in a light receiving element having a light receiving portion functioning as at least an avalanche photodiode on a single crystal silicon substrate, the single crystal silicon substrate is etched in the peripheral portion of the light receiving portion. Since the groove having a gentle slope is formed on the end surface of the light receiving portion, it is possible to prevent electric field concentration on the end surface of the junction of the light receiving portion, eliminate edge breakdown, and improve the electrical reliability of the device. In addition, since it is possible to fabricate a substrate having a mesa structure with a simple manufacturing process, it is possible to simplify the process without making a complicated manufacturing process such as a conventional guard ring structure that devises diffusion conditions into essential conditions. it can.

According to a second aspect of the invention, in the first aspect of the invention, the light receiving portions of at least two avalanche photodiodes are formed adjacent to each other on the same substrate, and at least a pair of light receiving portions among these light receiving portions are provided. Since the groove is formed by etching the single crystal silicon substrate, the distance between the light receiving portions can be shortened and the degree of integration in the same substrate can be increased.

According to a third aspect of the present invention, in the first aspect of the invention, the groove is formed by using anisotropic etching with an alkaline etchant, so that the end face of the light-receiving portion has a more gradual inclination. The electrical stability of can be further enhanced.

According to a fourth aspect of the invention, in the third aspect of the invention, since a substrate having a plane orientation of (100) plane is used as the single crystal silicon substrate, the entire periphery of the light receiving portion is surrounded by a groove. In this case, all four sides can be surrounded by diagonal surfaces, and in the case where multiple light receiving parts are integrated on one substrate and the light receiving parts are divided by grooves, the bottom surface of the groove forms Since the angle can be made smaller, the distance between the light receiving portions can be further shortened, which can further increase the degree of integration of the device.

According to a fifth aspect of the invention, in the third aspect of the invention, the etchant for etching the single crystal silicon substrate is a solution containing no alkali metal such as hydrazine or ethylenediaminepyrocatechol. It is possible to reduce the uptake of mobile ions, which are the source of contamination, and to improve the electrical insulation between the patterns, thereby further improving the reliability of the device.

[Brief description of drawings]

FIG. 1 shows a first embodiment of the present invention and is a process drawing in the case of forming a groove around a light receiving portion of a light receiving element.

FIG. 2 shows a second embodiment of the present invention and is a cross-sectional view showing a state where a V groove is formed by anisotropic etching using hydrazine.

FIG. 3 shows a third embodiment of the present invention and is a perspective view showing a state where a V groove is formed between two light receiving portions.

FIG. 4 is a plan view showing a shape of a light receiving portion formed by dividing it into four parts.

FIG. 5 is a plan view showing the shape of the light receiving parts arranged in an array.

FIG. 6 is a cross-sectional view showing the shape of a conventional light receiving element having a planar structure.

FIG. 7 is a cross-sectional view showing a state in which a guard ring is formed on an edge.

[Explanation of symbols]

 5 Single crystal silicon substrate 7, 7a to 7d Light receiving part 10, 14 Groove A Light receiving part end face

Claims (5)

[Claims] 1. A light-receiving element having a light-receiving portion functioning as at least an avalanche photodiode on a single-crystal silicon substrate, wherein the peripheral portion of the light-receiving portion is etched with the single-crystal silicon substrate so that the end face of the light-receiving portion has a gentle inclination. A light-receiving element characterized in that a transparent groove is formed. 2. A light receiving portion of at least two avalanche photodiodes is formed adjacent to each other on the same substrate, and a groove is formed by etching a single crystal silicon substrate between at least a pair of light receiving portions of these adjacent light receiving portions. The light receiving element according to claim 1, which is formed. 3. The light receiving element according to claim 1, wherein the groove is formed by anisotropic etching using an alkaline etchant. 4. A (100) single crystal silicon substrate
The light receiving element according to claim 3, wherein a substrate having a plane orientation of a plane is used. 5. The light receiving element according to claim 3, wherein a solution containing no alkali metal such as hydrazine or ethylenediaminepyrocatechol is used as an etchant for etching the single crystal silicon substrate.