JPH0864855A - Semiconductor photodetector and manufacture thereof - Google Patents

Abstract

PURPOSE: To lessen the transmission coefficient of the incident light for a light shielding film laminate by forming on a window layer the light shielding film laminate which includes a light shielding metal film as an intermediate layer. CONSTITUTION: A shielding film laminate 30 is made by depositing a shielding metal film 32 and an Si N insulating film 34. The insulating film 34 is constituted of an upper insulating film 34a and a lower insulating film 34b. The light shielding metal film 32, being put between the upper and the lower insulating film 34a, 34b as an intermediate layer, is so formed as to be included inside the shielding film laminate 30 without being exposed on the surface. Under these conditions, the reflection coefficient and the transmission coefficient of the incident light for the shielding film laminate 30 are about 40-50% and 1% or smaller respectively. Due to this structure, therefore, the transmission coefficient of the incident light for the shielding film laminate 30 can be lessened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light receiving element for photoelectrically converting light at high speed in optical communication.

[0002]

2. Description of the Related Art An example of a conventional semiconductor light receiving element (hereinafter, also referred to as "photodiode" or "element") is described in the literature: "Optical communication element optics, -light emitting / light receiving element-", pp. 3
71-373, pp. 347-350, Optical Book ". This semiconductor light receiving element is basically a pn
This is because the photovoltaic effect in the junction diode is utilized, and light is incident on the depletion layer of the light absorption layer directly below the diffusion region of the semiconductor light receiving element from the light receiving surface to perform photoelectric conversion. The cutoff frequency that limits the frequency band, which is the frequency response characteristic of the photodiode, is limited by the CR time constant of the device and the carrier transit time. This CR time constant is
It is determined by the pn junction capacitance of the element, electrode capacitance and other stray capacitance, load resistance and the like. The frequency response characteristics of the device can be improved by reducing these capacitances and reducing the CR time constant.

[0003]

By the way, in the conventional semiconductor light receiving element, light is transmitted through the insulating film and enters the window layer covered with the insulating film around the light receiving surface of the element. The incident light may become stray light and may enter the region of the light absorption layer where the depletion layer is not formed to generate a small number of carriers. The generated carriers diffuse into the depletion layer immediately below the diffusion region, but the diffusion speed is so slow that the response speed of the device may deteriorate.

Therefore, conventionally, there has been proposed an element in which a light-shielding metal film is formed on the insulating film around the light-receiving surface to shield light. However, when the light-shielding metal film is formed on the surface, the reflected light reflected by the light-shielding metal film becomes stray light, which may adversely affect the entire device equipped with the element. on the other hand,
In order to block light, a structure in which a light-shielding metal film is directly formed on the window layer and an insulating film is formed on the light-shielding metal film is also conceivable. However, in order to prevent a short circuit between the light-shielding metal film and the diffusion region, it is necessary to provide a gap larger than the width of the depletion layer between the light-shielding metal film and the end of the diffusion region. As a result, light enters from the gap to the light absorption layer in which the depletion layer formed by applying the reverse bias voltage is not formed. For this reason, the generation of minority carriers in the light absorption layer cannot be controlled, resulting in deterioration of high-speed response.

Therefore, in order to solve these problems,
The inventor of this application proposes a semiconductor light receiving element having a shielding film laminate in Japanese Patent Application No. 5-262806. In this shield film laminated body, the insulating film and the light shielding metal film (metal film) are laminated so that the light shielding metal film is contained inside without being exposed. Stray light can be prevented by this shielding film laminate, and as a result, deterioration of response characteristics of the element due to stray light can be suppressed.

However, in this shielding film laminated body, the light shielding metal film is provided without being exposed on the surface, and is electrically insulated from the window layer in order to prevent a short circuit with the diffusion region. Therefore, stray capacitance is generated between the light shielding metal film and the element. When stray capacitance occurs, the element capacitance of the entire element increases. An increase in element capacitance causes deterioration in element response speed.

Therefore, the inventor of the present application further proposes, in Japanese Patent Application No. 6-144162, a semiconductor light receiving element in which this light shielding metal film is electrically connected to a window layer via an ohmic electrode. There is.

However, even through the ohmic electrode, a slight stray capacitance is generated between the light shielding metal film and the window layer. On the other hand, since the response speed of the device is required to be further improved, it is desirable to suppress the stray capacitance as much as possible.

Further, in manufacturing the semiconductor light receiving element, it is desirable that the steps are not complicated.

Therefore, it has been desired to realize a semiconductor light receiving element in which the stray capacitance is reduced and the response speed of the element is further improved.

[0011]

According to the semiconductor light receiving element of the first invention of this application, the first substrate of the first conductivity type is provided.
A first-conductivity-type light absorption layer and a first-conductivity-type window layer are sequentially formed on the main surface, and the second-conductivity that reaches a boundary between the window layer and the light-absorption layer in a partial region of the window layer. A light receiving / diffusing region of a mold, a shield film laminate on a window layer around the light receiving / diffusing region, a first main electrode electrically connected to the light receiving / diffusing region, and a second main surface of the substrate. In a semiconductor light receiving element including a second main electrode, the light receiving region is a partial region of the window layer and is separated from the light receiving diffusion region with respect to a width of a depletion layer formed around the light receiving diffusion region. The shielding film laminate includes a peripheral diffusion region made of the same material as the diffusion region, and the shielding film laminate is formed by laminating a light shielding metal film and an insulating film, and the light shielding metal film is included in the inside of the shielding film laminate. , And electrically via the peripheral diffusion region and ohmic electrode And characterized by being connected.

Further, according to the method of manufacturing the semiconductor light receiving element of the second invention of the present application, the first conductivity type substrate
A step of sequentially laminating a first conductive type light absorbing layer and a first conductive type window layer on the main surface, and reaching a boundary between the window layer and the light absorbing layer in a partial region of the window layer. A step of forming a peripheral diffusion region in a partial region of the window layer separated from the light receiving diffusion region at the same time as forming the second conductivity type light receiving diffusion region of depth, and a step of forming the peripheral diffusion region in the partial region of the light receiving diffusion region. Forming an ohmic electrode made of the same material as the first main electrode in at least a part of the peripheral diffusion region at the same time as forming the first main electrode; In a region where the ohmic electrode is not formed, a step of forming a lower insulating film forming the shielding film laminate, and on a part of the ohmic electrode and the lower insulating film,
A step of forming a light-shielding metal film that constitutes the shield film laminate,
And a step of forming an upper insulating film forming a shielding film laminated body in a peripheral region on the light receiving diffusion region and including at least the light shielding metal film.

[0013]

According to the semiconductor light receiving element of the present invention, since the light-shielding film laminated body including the light-shielding metal film as the intermediate layer is provided on the window layer, the transmittance of light incident on the light-shielding film laminated body is reduced. can do. As a result, the deterioration of the response characteristics of the element due to stray light can be suppressed. further,
In the device of the present invention, since the light-shielding metal film is electrically joined to the window layer via the ohmic electrode, no stray capacitance is generated between the light-shielding metal film and the device. As a result, an increase in element capacitance can be suppressed, so that the response speed of the element can be improved.

By the way, when the light shielding metal film and the window layer are directly joined, the light shielding metal film becomes a Schottky electrode.
For this reason, a Schottky barrier is formed at this junction and junction capacitance is generated. If the element capacitance increases due to the junction capacitance, the response characteristics of the element deteriorate. Therefore,
In this invention, the generation of the junction capacitance can be reduced by electrically connecting the light shielding metal film and the window layer via the ohmic electrode.

Further, according to the semiconductor light receiving element of the present invention, by providing the peripheral diffusion region in the window layer and providing the ohmic electrode in the peripheral diffusion region, the light shielding metal film, the peripheral diffusion region and the ohmic electrode are interposed. It is electrically connected. Therefore, it is possible to further suppress the generation of stray capacitance due to the junction capacitance. As a result, it is possible to improve the response speed of the element by further suppressing the generation of the element capacitance.

Further, since the peripheral diffusion region and the ohmic electrode are provided at a position farther from the diffusion region than the width of the depletion layer, there is no possibility of short circuit with the light receiving diffusion region. Further, even if the ohmic electrode is farther from the light receiving diffusion region than the width of the depletion layer, there is no possibility that light will enter through the gap and the response characteristics will be deteriorated because of the light shielding metal film.

Further, according to the method of manufacturing a semiconductor light receiving element of the present invention, the peripheral diffusion region is formed simultaneously with the light receiving diffusion region. Further, at the same time as forming the first main electrode on the light receiving diffusion, the ohmic electrode on the peripheral diffusion region is formed. For this reason, it is possible to easily manufacture the semiconductor light receiving element in which the stray capacitance is suppressed and the response speed is improved without increasing the number of steps as compared with the conventional manufacturing method of the related art.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of the structure of the semiconductor light receiving element of the present invention will be described below with reference to the drawings. It should be noted that the drawings are only schematically shown so that the present invention can be understood. Therefore, it is obvious that the present invention is not limited to the illustrated examples. In the drawing, hatching showing a cross section is partially omitted.

<First Embodiment> FIG. 1 is a diagram for explaining an embodiment of a semiconductor light receiving element of the present invention. The figure is a perspective view of a cross-section of a main part of a planar photodiode having a window layer. In FIG. 1, the detailed structure of the shield laminate is omitted.

In the semiconductor light receiving element of this embodiment, an n ^-- InP layer having a thickness of 1.5 to 2.0 .mu.m is formed on the first main surface 10a of the n.sup. ⁺ -InP substrate 10 as the first conductivity type substrate. Buffer layer 12, n ^--In having a thickness of 1.5 to 2.2 μm
The GaAs light absorption layer 14 and a thickness of 1.5 μm n ⁻ −
InP window layers 16 are sequentially laminated by a normal crystal growth method. A partial region of the window layer 16 is provided with a p ⁺ light receiving diffusion region as a light receiving diffusion region of the second conductivity type which reaches the interface between the window layer 16 and the light absorbing layer 14. The p ⁺ light receiving diffusion region 18 is formed by selectively diffusing zinc (Zn) or cadmium (Cd) in the window layer.

A partial area on the p ⁺ light receiving diffusion area 18 is a light receiving surface 22 on which an antireflection film 20 is formed in a circular shape when seen in a plane pattern. Further, a p-side electrode 26 as a first main electrode is formed in a region of the non-light receiving surface on the p ⁺ light receiving diffusion region 18. On the other hand, the n-side electrode 28 is formed on the second main surface 10b of the substrate 10.

In the semiconductor light receiving element of the present invention,
The light receiving diffusion region 18 is located in a part of the window layer, which is farther from the light receiving diffusion region 18 than the width of a depletion layer (not shown) formed around the light receiving diffusion region 18.
And a peripheral diffusion region 38 made of the same material as the above.

A shielding film laminate 30 is provided on the window layer 16 around the p ⁺ light receiving diffusion region 18.

Next, the shielding film laminate 30 will be described. FIG. 2 is an enlarged cross-sectional view of the main part (near the shielding film laminate 30) of the semiconductor light receiving element shown in FIG.

The shielding film laminate 30 is made of titanium (Ti).
The light-shielding metal film 32 and the insulating film 34 of Si ₃ N ₄ are laminated. This insulating film 34 is the upper insulating film 3
4a and the lower insulating film 34b. The light-shielding metal film 32 is sandwiched between the upper insulating film 34a and the lower insulating film 34b as an intermediate layer, and is contained inside the shielding film laminated body 30 without being exposed on the surface.

Further, the light shielding metal film 32 is electrically connected (contacted) with the peripheral diffusion region 38 provided in the window layer 16 via the ohmic electrode 36.

[0027] The ohmic electrode 36, the p ⁺ light diffusion area 18, a peripheral diffused region 38 at a position apart than the width of the depletion layer formed around the p ⁺ light diffusion region 18 (not shown) It is electrically connected.

The reflectance and the transmittance with respect to the incident light obtained by the shielding film laminate 30 of this embodiment are about 40 to 50% and 1% or less, respectively. Therefore, it is possible to prevent stray light from entering the light absorption layer 14 in which the depletion layer is not formed, which is generated by applying the reverse bias voltage between the p-side electrode 26 and the n-side electrode 28. As a result, generation of minority carriers due to stray light can be suppressed.
Therefore, the delay of the waveform at the time of high-speed response due to the minority carriers does not occur, and the high-speed response of the element becomes possible, and the frequency response characteristic can be improved as compared with the conventional element in which the light shielding metal film is provided on the surface of the insulating film. it can.

Further, in this shielding film laminated body 30,
Since the light shielding metal film 32 is in contact with the window layer 16 via the ohmic electrode 36, no stray capacitance is formed between the light shielding metal film 32 and the light receiving element. For this reason,
Since the element capacitance does not increase due to the stray capacitance, the response speed does not deteriorate.

In the semiconductor light receiving element of the present invention, the thickness of the insulating film (for example, the thickness of the insulating film on the light shielding metal film and the thickness of the insulating film between the light shielding metal film and the window layer) is set. , Λ / (4n) (where λ represents the wavelength of incident light and the refractive index of the n insulating film), the light transmittance of the shielding film laminate can be further reduced.

If a Si ₃ N ₄ film is used as the insulating film and titanium (Ti) or molybdenum (Mo) is used as the light shielding metal film, the adhesion between the light shielding metal film and the Si ₃ N ₄ film is good. It is possible to reduce the risk that the light-shielding metal film will peel off.

The thickness of the light-shielding metal film is 500 to 10
It is desirable to set it to 00Å (50 to 100 nm). This is because if the film thickness is 500 Å or more, the light transmittance can be sufficiently lowered, and if the film thickness is 1000 Å or less, the light-shielding metal film is less likely to peel off.

Further, as a result of providing the peripheral diffusion region 38, p
It is conceivable that a pn junction is formed between the peripheral diffusion region of the n-type and the n-type buffer layer or the substrate. But,
During manufacturing of the device, the pn junction is destroyed in the dicing process. Therefore, it is possible to prevent the generation of the stray capacitance due to the pn junction. Therefore, even if the peripheral diffusion region 38 is provided, the capacitance of the element does not increase, and it is possible to obtain a semiconductor light receiving element having an excellent frequency response characteristic and a wide bandwidth.

<Second Embodiment> Next, an embodiment of a method for manufacturing a semiconductor light receiving element of the second invention will be described. FIGS. 3A to 3C and FIGS. 4A to 4C are process drawings used to describe the second embodiment. 3 and 4
Then, the principal part of the element is shown enlarged.

In this embodiment, first, an n ⁻ -InP buffer layer having a thickness of 1.5 to 2.0 μm is formed on the first main surface 10a of the n ⁺ -InP substrate 10 as the first conductivity type substrate. 12, n ^-- InGaAs having a thickness of 1.5 to 2.2 μm
The light absorption layer 14 and the n ⁻ -InP window layer 16 having a thickness of 1.5 μm are sequentially laminated by a normal crystal growth method ((A) of FIG. 3).

Next, in a partial region of the window layer 16,
The p ⁺ light receiving diffusion region 18 as the second conductivity type light receiving diffusion region reaching the interface between the window layer 16 and the light absorbing layer 14.
At the same time, the peripheral diffusion region 38 is formed in a partial region of the window layer 16 separated from the light receiving region. This p
^{The +} light receiving diffusion region 18 and the peripheral diffusion region 38 are formed by selectively diffusing zinc (Zn) or cadmium (Cd) in the window layer 16 ((B) of FIG. 3).

Next, at the same time as forming the p-side electrode 26 as the first main electrode in the non-light-receiving surface area on the p ⁺ light-receiving diffusion area 18, at least a part of the peripheral diffusion area 38 is formed. An ohmic electrode 36 made of the same material as the p-side electrode 26 is formed. In addition, the second main surface 10b of the substrate 10
Then, an n-side electrode (not shown) is formed (FIG. 3C).

Next, a circular antireflection film 20 is formed in a partial area on the p ⁺ light receiving diffusion area 18 as seen in a plane pattern to form a light receiving surface 22.

Next, the formation of the shielding film laminate 30 will be described.

In forming the shield film laminate 30, first, the Si ₃ N ₄ film forming the shield film laminate 30 is formed in the peripheral region on the light receiving diffusion region 18 where the ohmic electrode 36 is not formed. The lower insulating film 34b is formed ((A) of FIG. 4).

Next, a light shielding metal film 32 of titanium (Ti) forming the shielding film stack 30 is formed on a part of the ohmic electrode 36 and the lower insulating film 34b ((B) of FIG. 4).

Next, in the peripheral region on the p ⁺ light receiving diffusion region 18 and including at least the light shielding metal film 32,
The upper insulating film 34a of the Si ₃ N ₄ film forming the shielding film stack 30 is formed ((C) of FIG. 4).

As a result, the light-shielding metal film 32 serves as an intermediate layer, which is the upper insulating film 34a and the lower insulating film 34 of the insulating film 34.
and the shielding film laminated body 3 without being exposed on the surface.
It will be included inside 0. In addition, the light shielding metal film 32 is provided in the peripheral diffusion region 38 provided in the window layer 16.
And is electrically connected (contacted) via the ohmic electrode 36.

In each of the above-described embodiments, the invention is described as an example in which a specific material is used and is configured under specific conditions, but the present invention can be modified and modified in many ways. For example, although titanium (Ti) is used as the light shielding metal film in each of the above-described embodiments, for example, tungsten (W) or molybdenum (Mo) may be used in the present invention. Further, in the above-described embodiment, S is used as the insulating film.
Although an i ₃ N ₄ film is used, in the present invention, for example, Al ₂ O is used.
_You may use ₃ membranes. Further, in the above-described embodiment, the first
Although the conductivity type is n-type and the second conductivity type is p-type, in the present invention, the first conductivity type may be p-type and the second conductivity type may be n-type.

[0045]

According to the semiconductor light receiving element of the present invention, since the light-shielding film laminate including the light-shielding metal film as an intermediate layer is provided on the window layer, the transmittance of light incident on the light-shielding film laminate is provided. Can be made smaller. As a result, the deterioration of the response characteristics of the element due to stray light can be suppressed.

Further, according to the semiconductor light receiving element of the present invention, by providing the peripheral diffusion region in the window layer and providing the ohmic electrode in the peripheral diffusion region, the light shielding metal film, the peripheral diffusion region and the ohmic electrode are interposed. It is electrically connected. Therefore, it is possible to further suppress the generation of stray capacitance due to the junction capacitance. As a result, it is possible to improve the response speed of the element by further suppressing the generation of the element capacitance.

Further, since the peripheral diffusion region and the ohmic electrode are provided at a position farther from the diffusion region than the width of the depletion layer, there is no possibility of short circuit with the light receiving diffusion region. Further, even if the ohmic electrode is farther from the light receiving diffusion region than the width of the depletion layer, there is no possibility that light will enter through the gap and the response characteristics will be deteriorated because of the light shielding metal film.

Further, according to the method of manufacturing the semiconductor light receiving element of the present invention, the peripheral diffusion region is formed simultaneously with the light receiving diffusion region. Further, at the same time as forming the first main electrode on the light receiving diffusion, the ohmic electrode on the peripheral diffusion region is formed. For this reason, it is possible to easily manufacture the semiconductor light receiving element in which the stray capacitance is suppressed and the response speed is improved without increasing the number of steps as compared with the conventional manufacturing method of the related art.

Further, the semiconductor light receiving element of the present invention is suitable for optical communication, particularly for high-speed photoelectric conversion of light in the wavelength range of 1 μm band.

[Brief description of drawings]

FIG. 1 is a perspective cross-sectional view of a main part for explaining an embodiment of a semiconductor light receiving element of the present invention.

FIG. 2 is a cross-sectional view showing an enlarged main part of FIG.

3 (A) to 3 (C) are process diagrams of the first half used to describe an embodiment of a method for manufacturing a semiconductor light receiving element of the present invention.

FIG. 4A to FIG. 4C are process diagrams of the latter half of FIG.

[Explanation of symbols]

10: substrate 12: buffer layer 14: light absorption layer 16: window layer 18: p ⁺ light receiving diffusion region 20: antireflection film 22: light receiving surface 26: p-side electrode 28: n-side electrode 30: shielding film laminate 32: Light-shielding metal film 34: insulating film 34a: upper insulating film 34b: lower insulating film 36: ohmic electrode 38: peripheral diffusion region

Claims (2)

[Claims] 1. A light-absorbing layer of the first conductivity type and a window layer of the first conductivity type are sequentially laminated on a first main surface of a substrate of the first conductivity type, and a partial region of the window layer. A light-receiving diffusion region of the second conductivity type having a depth reaching the boundary between the window layer and the light-absorbing layer, and a shielding film laminated body on the window layer around the light-receiving diffusion region. A semiconductor light-receiving element comprising a first main electrode electrically connected to a diffusion region and comprising a second main electrode on a second main surface of the substrate, wherein the light-receiving diffusion is a partial region of the window layer. A peripheral diffusion region made of the same material as the light receiving diffusion region is provided in a region farther from the light receiving diffusion region than the width of the depletion layer formed around the region, and the shielding film laminate is insulated from the light shielding metal film. And a light-shielding metal film, A semiconductor light receiving element, which is included in the shielding film laminate and is electrically connected to the peripheral diffusion region via an ohmic electrode. 2. A step of sequentially laminating a first-conductivity-type light absorption layer and a first-conductivity-type window layer on a first main surface of a first-conductivity-type substrate, and forming the window layer. At the same time as forming a light receiving diffusion region of the second conductivity type having a depth reaching the boundary between the window layer and the light absorbing layer in a partial region, at the same time, in a partial region of the window layer separated from the light receiving diffusion region. Forming a peripheral diffusion region; and forming a first main electrode on a partial region of the light receiving diffusion region, and at the same time, forming at least a partial region of the peripheral diffusion region from the same material as the first main electrode. A step of forming a lower insulating film that constitutes a shielding film laminate in a peripheral region on the light receiving diffusion region in which the ohmic electrode is not formed, and the ohmic electrode And a part of the lower insulating film And a step of forming a light-shielding metal film that constitutes the shielding film laminate, and an upper insulating layer that constitutes the shielding film laminate in a peripheral region on the light receiving diffusion region, the region including at least the light-shielding metal film. And a step of forming a film.