JPH11330534A - Mesa type photodiode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To contrive simply the reduction in the stray capacity of a mesa type photodiode, by a method wherein the mesa type photodiode is formed on a semiinsulative substrate and the surface of a pad, which is connected with the p-type electrode of this photodiode, has a prescribed angle to connect the pad with the p-type substrate. SOLUTION: An n-type InP layer 21, an undoped InGaAs layer 22 and a p-type InP layer 23 are laminated in order on a semiinsulative substrate 201, then, the layers 23 and 22 other than the parts, which are formed with a mesa type photodiode, of the layers 23 and 22 are removed to form an insulating film 24 on the substrate 20 including the layer 23. After the parts, which correspond to a pad connection part of a p-type electrode and a pad connection part of an n-type electrode, of the film 24 are removed, the p-type electrode 23a and the n-type electrode 21a are respectively formed. Subsequently, a polyimide 25 is formed on the substrate 20 including a light-receiving part 26 in an almost same thickness as that of the layer 21, and the p-type electrode part 23a exposed on the polyimide 25 is connected with a pad 27 having a prescribed angle via a lead-out wire 27a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mesa photodiode having reduced stray capacitance between extraction electrodes.

[0002]

2. Description of the Related Art In recent years, high-speed information has been demanded, and the transmission speed of a photodiode has been realized, for example, from about 2.5 Gb / s (gigabit / second) to about 10 Gb / s. FIG. 3 shows a cross-sectional configuration of a conventional mesa photodiode which achieves such high speed. In FIG. 3, n
A contact layer 2 is formed on one surface of a mold substrate (InP) 1, and a P layer (InP) 4 and a top contact layer 5 are formed on the other surface via an undoped layer (InGaAs) 3.

[0003] An insulator (polyimide) layer 6 is formed on the top contact layer 5, and the periphery of the mesa portion A indicated by a dashed line is removed to form a light receiving portion 6 and a pad 7 including a portion for extracting an electric signal. Have been. An electric signal C related to the intensity of the light B is generated between the pad 7 and the contact layer 2.

FIGS. 4A and 4B show another embodiment of a mesa photodiode, in which FIG. 4A is a sectional view, and FIG.
Is a perspective view. In this conventional example, an n-type layer 11 made of InP is formed on a semiconductive InP substrate 10, and an undoped layer (InGaAs) 12 and an n-type layer 13 made of InP are formed thereon. An insulating film 14 is formed on the n-type layer 13. This insulating film 14
A is partially removed to show the photodiode A
Is formed in the Zn diffusion portion 15 of the p-type layer.

A pad 16 serving as a line for taking out an electric signal is formed on the insulating film 14 and connected to the Zn diffusion portion 15. A pad 17 serving as a part for taking out an electric signal is formed on the n-type layer 11. Are formed. A cavity 18 is formed in the lower part of the pad 16 near the photodiode A by a method such as under-etching to remove the influence of the stray capacitance.

[0006]

In order to reduce the stray capacitance in the conventional example shown in FIG. 3, it is necessary to increase the thickness of the polyimide 6 or reduce the area of the pad 7. Even if the thickness of layer 6 is increased, the limit is about 10 μm, which is not an effective means for reducing the stray capacitance. Further, the method of reducing the area of the pad 7 has a problem that the mounting margin is reduced.

Although the structure in which the cavity 18 is formed and a cavity is provided in a part of the wiring as shown in FIG. 4 is effective, the formation of the cavity requires a complicated process, and a portion located in the air is required. There is a problem that it is weak against vibration and the like. The present invention has been made to solve such a problem, and an object of the present invention is to provide a mesa photodiode in which stray capacitance can be easily reduced by devising a shape of a pad connected to a photodiode portion. .

[0008]

According to the present invention, there is provided a mesa-type photodiode formed on a semi-insulating substrate, which is connected to a P-type electrode of the photodiode. The pad surface is connected at a predetermined angle.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a plan view showing an embodiment of the present invention. In the figure, the light receiving section (mesa photodiode) 26
Is formed, for example, to have a diameter of about 20 to 30 μm. It is connected to the p-type electrode 23a on the upper part of
A lead line 27 a having a width of about 0 to 40 μm and a width of about 8 μm is formed, and a pad 27 is formed following the lead line 21.

Here, the pad 27 extends in two directions at a predetermined angle (90 degrees in the embodiment) from the point S connected to the lead line 27a, and is formed in parallel when the width becomes 100 μm. The length from the beginning T is about 10
It is formed at 0 μm. A pad 28 (having a width of 50 μm in the figure) that is different from the p-type electrode 23a only in the shape of the tip is formed on the n-type electrode 21a.

FIG. 2 shows the outline of the manufacturing process of the mesa photodiode shown in FIG.
'To f' are plan views. A description will be given according to the steps. Step (a) An n-type InP layer 21 is formed on a semi-insulating substrate (InP) 20.
An undoped InGaAs layer 22 and a p-type InP layer 23 are sequentially stacked.

Step (b) p-type In other than the portion where the mesa photodiode is formed
The P layer 23 and the undoped InGaAs layer 22 are removed. Step (c) An insulating film (SiN) is formed on the substrate 20 including the p-type InP layer 23.
x) p-type electrode and n forming 24 and forming a light receiving portion
The insulating film in other portions is removed except for a portion for forming a pad on the mold electrode 21a.
The P layer 21 is also removed.

Step (d) The p-type electrode 23a and the n-type electrode 21a are formed after removing the insulating film corresponding to the pad connection of the p-type electrode and the pad connection of the n-type electrode. Step (e) A polyimide resin (insulator) 25 is formed on the substrate including the light receiving portion to a thickness substantially equal to that of the n-type InP layer 21, and corresponds to a pad connection portion of a p-type electrode and a pad connection portion of an n-type electrode. The portions of the polyimide resin 25 to be removed are removed and the electrode portions 21a, 2
Expose 3a.

Step (f) A lead 27a (width 8 × length 20 μm) is formed on the p-type electrode portion 23a exposed on the polyimide resin 25, and a pad 27 is formed. The shape of the pad 27 is formed so as to spread out in a fan shape at θ ° (about 90 ° in the embodiment) from the end of the lead wire 27a, and the width of the end of the fan is 100 μm.
At the width of, it is horizontally extended by 100 μm.

Here, the shape of the pad 28 formed on the n-type electrode is a rectangle having a side of about 50 μm on the side facing the pad 27 of the p-type electrode, and subsequently has the same shape as the pad of the p-type electrode. . The effect of the present invention is approximately 49 fF in a shape that is not tapered by calculation by the finite element method.
(Femtofarad), about 32fF when tapered
It was estimated to be about 30 fF in the actual measurement. As a result, the effect of the stray capacitance was reduced to about 60%.

Also, the foregoing description of the invention merely illustrates certain preferred embodiments for purposes of explanation and illustration. Thus, it will be apparent to one skilled in the art that the present invention may be modified or modified in many ways without departing from its essentials. For example, in the present embodiment, the angle spreading in a fan shape from the lead line 27a is set to 90 °, but the angle may be increased or decreased to such an extent that the influence of the stray capacitance does not matter.

Also, In as the material of the photodiode
Although P and InGaAs were used, other materials may be used as long as they function similarly. The scope of the present invention defined by the description in the claims section is intended to cover alterations and modifications within the scope.

[0018]

As described above, according to the present invention, in a mesa photodiode formed on a semi-insulating substrate, a pad surface connected to a P-type electrode of the photodiode has a predetermined angle. Connection, a mesa photodiode having a reduced stray capacitance can be realized.

[Brief description of the drawings]

FIG. 1 is a plan view of a mesa photodiode according to the present invention.

FIGS. 2A and 2B are a cross-sectional view and a plan view schematically showing a manufacturing process of a mesa photodiode according to the present invention.

FIG. 3 is a cross-sectional view illustrating an example of a conventional mesa photodiode.

FIG. 4 is a cross-sectional view showing another example of a conventional mesa photodiode.

[Explanation of symbols]

 Reference Signs List 20 semi-insulating substrate 21 n-type layer 21a n-type electrode 22 insulating layer 23 p-type layer 23a p-type electrode 24 insulating film (SiNx) 25 insulator (polyimide resin) 26 light-receiving unit 27 pad 27a lead-out line 28 pad

Claims (2)

[Claims] 1. A mesa photodiode formed on a semi-insulating substrate, wherein a pad surface connected to a P-type electrode of the photodiode is connected at a predetermined angle. Type photodiode. 2. The angle of a pad surface connected to a P-type electrode is set to 1
2. The mesa photodiode according to claim 1, wherein the angle is not more than 00 degrees.