JPH0567798A - Photo detector and manufacture of photo detector - Google Patents

Abstract

PURPOSE:To reduce a resistance at a photo detecting part diffusion part as a whole while having a part wherein light of short wavelength is also absorbed in a depletion layer by thinning the photo detecting part diffusion part. CONSTITUTION:A second conductivity type impurity diffusion layer 20 is formed near a surface of a high resistance layer 12 of a first conductivity type semiconductor substrate 10. The second conductivity type impurity diffusion layer 20 is formed of a relatively thick layer 21 and a relatively thin layer 22 having a periodic structure which form a photo detecting part. According to such an arrangement, it is possible to transmit carrier generated by light of short wavelength absorbed by the relatively thin layer 22 through a low resistance part of the relatively thick layer 21; therefore, light of short wavelength can also have sensitivity and a photo detector which enables rapid response can be acquired.

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 used for optical communication, optical recording, optical information processing, etc., and a method for manufacturing the light receiving element.

[0002]

2. Description of the Related Art Conventionally, as a light receiving element in the above technical field, a photodiode using a semiconductor PN junction or a Schottky junction is often used. Among them, PIN photodiodes are widely used because of their high quantum efficiency, small dark current, small operating voltage and high-speed response (see "Optical Communication Device Engineering" written by Hiroo Yonezu, Engineering Book Co., Ltd. edition).

As an example of the structure, a vertical sectional view of a silicon PIN photodiode is shown in FIG. In this silicon PIN photodiode, a silicon substrate of the first conductivity type is used as the substrate 100. The substrate 100 is the low resistance layer 11
0 is formed with a high resistance layer 120. A second conductive type impurity diffusion layer 120 is formed near a part of the surface of the substrate 100 to form a light receiving portion. The surface of the substrate 100 is covered with an insulating film 130, and the impurity diffusion layer 120 is electrically connected to the electrode 140 through the connection portion 90 from which a part of the insulating film 130 is removed. Further, two terminals of the light receiving element are formed by pairing with an electrode (not shown) provided by being connected to the back surface of the substrate 100 or the like. Note that FIG. 8 shows the relationship between the wavelength of the silicon PIN photodiode and the quantum efficiency (sensitivity).

[0004]

However, in the PIN photodiode described above, it is mainly the depletion layer 108 that contributes to the photocurrent output of the incident light.
It is an electron-hole pair generated by the light absorbed in (shown by the broken line). On both the upper and lower sides of the depletion layer 108, minority carriers generated by light absorbed within the diffusion length of minority carriers from the end of each depletion layer 108 may reach the depletion layer 108 by diffusion and become a photocurrent. Since the diffusion speed is slow, the effective photocurrent output cannot be achieved at high speed operation.

On the other hand, recently, development of green and blue light emitting sources by various blue light emitting elements and second harmonic generating elements has been actively made, and in order to use them for optical recording and optical information processing, the light receiving elements are Will be needed. When silicon is used for such a light receiving element due to the requirements of manufacturing process, product stability, integration with other electronic elements, etc., there are the following problems.

That is, the absorption length of light of silicon has a wavelength of 0.
Since it is about 1 μm at 5 μm and 0.2 μm or less at the wavelength of 0.4 μm, the sensitivity on the short wavelength side is remarkably lowered in the conventional photodiode structure due to the above relationship.
This is because, in the above-described structure, the second conductivity type impurity diffusion layer 120 has a thickness of about 1 μm according to a normal manufacturing process, and thus light is absorbed before reaching the depletion layer 108. Therefore, in order to improve the sensitivity on the short wavelength side, the second conductivity type impurity diffusion layer 1 of the light receiving portion is required.
It is necessary to make 20 as thin as possible.

As an approach to this, there is a method disclosed in Japanese Patent Laid-Open No. 200733. According to this method, a flat pn junction is formed by implanting B + ions into an n-conducting oriented silicon single crystal, and an upper layer having a relatively low p-type doping generated at that time is replaced with a relatively high p +. This is a method of forming an extremely thin pn junction by shaving off a region of a layer existing at a deeper portion having type doping by anisotropic etching.

However, in this method, B + ions are
Problems of ion implantation at a relatively low acceleration voltage of about 0 keV, problems of residual thickness of the B + implantation layer on the deep side, and surface condition caused by etching off the silicon surface of the light receiving part. There is a problem that deterioration of (interface state) increases surface recombination and lowers sensitivity. Further, As + as the N-type impurity, or when it is also conceivable to use a technique of forming a shallow junction by implanting BF ₂ + as a P-type impurity, an attempt to form a thin diffusion layer as described above However, the amount of implanted ions cannot be increased, and the sheet resistance of the diffusion layer cannot be reduced. This problem also occurs when using a shallow junction forming method other than ion implantation, and the increase in sheet resistance of the light receiving portion is
It adversely affects the operation of the light receiving element.

The object of the present invention is to solve the above problems and to thin the light receiving portion diffusion portion so that the light receiving portion diffuses as a whole while having a portion where short wavelength light is also absorbed by the depletion layer. It is to propose a light receiving element that can reduce the resistance of a part and a manufacturing method thereof.

[0010]

The invention according to claim 1 is
The second conductivity type impurity diffusion layer formed in the vicinity of the surface of the first conductivity type substrate has a structure in which relatively thick layers and relatively thin layers are periodically arranged. According to a second aspect of the present invention, the direction in which the period of the periodic structure is formed is substantially perpendicular to the direction in which the second conductivity type impurity diffusion layer and the electrode to the outside are connected. It is what

According to a third aspect of the invention, there is provided the above-mentioned second aspect.
In the portion where the conductivity type impurity diffusion layer and the electrode to the outside are connected, the second conductivity type impurity diffusion layer is made a relatively thick layer. According to a fourth aspect of the present invention, there is provided a method of manufacturing a light receiving element, wherein a portion corresponding to a relatively thick layer of a second conductivity type impurity diffusion layer is formed in a plane shape defined by a first shape mask layer formed on a surface of a substrate. After that, it is a method of forming a relatively thin layer and a relatively thick layer of the second-conductivity-type impurity diffusion layer having a planar shape defined by the newly formed second-shaped mask layer.

According to a fifth aspect of the present invention, there is provided a method for manufacturing a light receiving element, wherein after forming a portion corresponding to a relatively thick layer of the second-conductivity-type impurity diffusion layer having a planar shape defined by a mask layer formed on the substrate surface. In this method, a relatively thin layer and a relatively thick layer of the second conductivity type impurity diffusion layer are formed by performing heat treatment. According to a sixth aspect of the present invention, there is provided a method of manufacturing a light receiving element, wherein a mask layer having a relatively thin portion having a first shape and a relatively thick portion having a second shape is formed on a surface of a substrate to remove impurities of a second conductivity type. This is a method of forming a second conductivity type impurity diffusion layer having a relatively thin layer and a comparatively thick layer by diffusion.

[0013]

According to the invention described in claim 1, by making the thickness of the relatively thin layer thinner than the absorption length of a desired light receiving wavelength, light is absorbed at that portion after reaching the depletion layer. The ratio becomes large, and the generated electron-hole pairs move at high speed due to drift in the depletion layer, and the electrons move to the N-type region,
The holes reach the P-type region. On the other hand, the relatively thick layer has a large amount of impurities and is deeply diffused, so that the resistance of that portion can be made sufficiently small. Therefore, by periodically arranging the relatively thin layer and the relatively thick layer as described above, the carriers generated by the light of the short wavelength absorbed in the thin portion are passed through the low resistance portion of the thick portion in the vicinity. Since the light can be transmitted, it is possible to obtain a light receiving element which is sensitive to light having a short wavelength and can respond at high speed.

According to the second aspect of the present invention, the area (light receiving area) of the relatively thin layer that absorbs light of a short wavelength is maximized, and at the same time, it is low for extracting the photocurrent to the outside. The area of the relatively thick layer forming the resistive layer can be minimized. According to the third aspect of the invention, since the portion to which the electrode is connected is a low-resistance semiconductor layer, ohmic contact is easily obtained, and a PN junction is formed by alloying the metal of the electrode and a semiconductor such as silicon. You can prevent the destruction of. Of course, for this problem, it is effective to provide a barrier layer between the semiconductor layer and the metal layer of the electrode, but according to this configuration, there is no increase in the number of manufacturing steps and it is simple.

According to the method of the fourth aspect of the present invention, since the relatively thick layer and the relatively thin layer of the impurity diffusion layer can be formed under substantially independent diffusion conditions, the range of manufacturing conditions is widened. According to the method of the invention described in claim 5, the above-mentioned light receiving element can be manufactured with a mask having one shape. Also, an extremely thin impurity diffusion layer can be formed. According to the method of the sixth aspect of the present invention, the light receiving element can be manufactured by a single impurity introduction step.

[0016]

EXAMPLES Examples of the present invention will be described below. Figure 1
FIG. 3 is a vertical cross-sectional view showing the configuration of the light receiving element according to the first embodiment of the present invention. The light receiving element of this embodiment has the first substrate 10
A conductive silicon substrate is used. Substrate 10 is low resistance layer 1
1 on which a high resistance layer 12 is formed. Further, the second conductivity type impurity diffusion layer 20 is formed in the vicinity of the surface of the high resistance layer 12 of the first conductivity type semiconductor substrate 10. The second conductivity type impurity diffusion layer 20 is formed of a relatively thick layer 21 and a relatively thin layer 22 and has a periodic structure, and they form a light receiving portion. The surface of the substrate 10 is covered with an insulating film 30, and the impurity diffusion layer 20
Are electrically connected to the electrodes through the connection part obtained by removing a part of the insulating film 30. Further, two terminals of the light receiving element are formed by pairing with an electrode (not shown) connected to the back surface of the substrate 10 or the like.

The periodic structure of the light receiving portion is striped, grid-shaped,
Radial, concentric, or a combination thereof can be arbitrarily configured. Also, a relatively thick layer 21 and a relatively thin layer 2
It is not necessary to be binary-differentiated from 2, and the thickness may be continuously changed. Further, the area ratio of each of them can be arbitrarily set in consideration of the light receiving surface effective for short wavelength light and the low resistance portion. However, the electrons or holes (depending on the conductivity type) that are incident on the relatively thin layer 22 and are mostly absorbed in the depletion layer 2 are relatively thick.
The principle of the invention, which is transmitted as photocurrent by the low resistance part of 1, remains unchanged.

FIG. 2 is a plan view of a light receiving element according to the second embodiment of the present invention. In the figure, the impurity diffusion layer 20 is
Through the opening portion 33 provided in the insulating film 30, the connection portion 92 is connected to the electrode 40 such as a metal which is drawn out to the outside. Therefore, the relatively thick layer 21 and the relatively thin layer 22 have a striped periodic structure, and the direction of the period is substantially perpendicular to the direction toward the connecting portion 92, that is, each striped portion is substantially toward the connecting portion 92. As a result, the efficiency of photocurrent transmission to the connection portion 92 of the relatively thick layer 21 is increased while ensuring the area of the relatively thin layer 22. In FIG. 2, an example is shown in which the connection is made on one side of the rectangular light receiving area, but in the case where the connection is made at the outer peripheral portion of the circular light receiving area, for example, a relatively thick layer 21,
The relatively thin layer 22 can be optimized according to the form, such as a radial or fan-shaped periodic structure.

3A and 3B are views for explaining the structure of a light receiving element according to the third embodiment of the present invention. FIG. 3A is its plan view and FIG. 3B is its longitudinal sectional view. .. In this embodiment, the portion of the impurity diffusion layer 20 including at least the connecting portion 93 between the impurity diffusion layer 20 and the electrode 40 is a relatively thick layer 2.
It is 1. In this case, the impurity diffusion layer 2 in the other portion
The structure of 0 is arbitrary, but the portion of the relatively thick layer 21 among them includes the above-mentioned connecting portion 93.
It is more advantageous in connection with the part of (1) to transfer photocurrent. As described above, for the first to third embodiments, the silicon PI
Although the example of the N photodiode is shown, the configuration of the present invention is also effective for other photodiodes.

Next, a method of manufacturing the light-receiving element having the above structure will be described. FIG. 4 is a diagram for explaining the method of manufacturing the light receiving element according to the fourth embodiment of the present invention.
8A and 8B are vertical sectional views showing a part of the manufacturing process. In the method of this embodiment, first, the mask layer 81 is formed on the surface of the substrate 10, and the second conductivity type impurity diffusion layer 211 corresponding to the later relatively thick layer 21 due to its shape is formed (FIG. 4 ( a)). Next, after removing a part or all of the mask layer 81, a new mask layer 82 is formed and is used to form a relatively thin layer 22 and a relatively thick layer 21 (FIG. 4B). .. After forming the deep junction as described above, the shallow junction is formed, so that both can be formed in a mixed manner.

In order to form the impurity diffusion layer as described above, it is possible to use an annealing process after ion implantation, a two-step diffusion method or a semiconductor process technique such as diffusion from doped polysilicon, and the mask layer is also diffused. Depending on the method, a resist, an oxide film, a nitride film, an amorphous silicon film or the like can be used. At this time, when a dielectric film is used, a part thereof may be left as the insulating film 30 of the photodiode. Further, the mask shape is not limited to the presence or absence of the mask layer, and may be the difference in the mask layer thickness. Further, the insulating film may be formed on the light receiving portion simultaneously in the diffusion process.

FIG. 5 is a diagram for explaining a method of manufacturing a light receiving element according to the fifth embodiment of the present invention.
(B) Both are longitudinal sectional views showing a part of the manufacturing process.
In the method of this embodiment, first, a second conductivity type impurity diffusion layer 212 similar to the second conductivity type impurity diffusion layer 211 is formed by using the mask layer 83 similar to the mask layer 81 of the fourth embodiment ( FIG. 5A). Then, heat treatment is performed in an inert or oxidizing gas. As a result, the diffusion of impurities from the portion of the second-conductivity-type impurity diffusion layer 212 is continued, and the diffusion proceeds in the lateral direction along with the depth direction, and the intermediate surface of the adjacent second-conductivity-type impurity diffusion layer 212. A relatively thick layer 21 and a relatively thin layer 22 are formed by performing the process until the diffusion layers from both sides come into contact with each other in the vicinity (FIG.
(B)).

It is also possible to form an extremely thin diffusion layer in the portion of the relatively thin layer 22. In this embodiment, only one mask is required for manufacturing. In this case, it is preferable that the second conductivity type impurity diffusion layer 212 has a narrower width and a higher concentration on the surface side in advance, and the distance between them is about twice the spread of the diffusion in the lateral direction.

FIG. 6 is a view for explaining a method of manufacturing a light receiving element according to the sixth embodiment of the present invention, and is a vertical sectional view showing a part of the manufacturing process. In the method of this embodiment, the relatively thick layer 21 and the relatively thin layer 22 are simultaneously formed by utilizing the difference in the film thickness of the mask layer 84. That is, the mask layer 84 is formed of a silicon oxide film or the like, and the impurity diffusion layer 20 is formed by ion implantation or thermal diffusion through the silicon oxide film. At this time, the impurity diffusion layer 20 is not formed under the thick portion of the mask layer 84, and the mask layer 8 is formed.
Below the thin portion of 4, a relatively thin layer 22 is formed,
Moreover, a desired structure can be obtained by selecting the mask layer 84 thickness difference and diffusion conditions so that a relatively thick layer 21 is formed in a portion having no mask layer or a thinner layer. The mask such as the mask layer 84 may be formed of one material, or an oxide film and a resist, etc. may be formed depending on the difference in thickness.
It may be a laminate of the above materials.

[0025]

According to the first aspect of the present invention, short wavelength light also passes through a relatively thin impurity diffusion layer and is absorbed by the depletion layer below it, generating carriers that can move at high speed and contributing to photocurrent. However, since the photocurrent can be transmitted through the low resistance portion of the relatively thick impurity diffusion layer, it is possible to obtain a light receiving element which is highly sensitive and can respond at high speed to light on the short wavelength side. In addition to the above, the light receiving element having a sensitivity to short-wavelength light, the low resistance portion, and the light receiving element having a structure in which the efficiency of the other side is optimized can be obtained. In addition to the above, the structure of the third aspect of the present invention can provide a light-receiving element having a low resistance and reliable contact of the electrode lead-out portion from the light-receiving portion and improved reliability.

According to the method of the fourth aspect of the present invention, since the thick portion and the thin portion of the impurity diffusion layer can be formed under substantially independent diffusion conditions, the range of manufacturing conditions can be wide and stable, and the light receiving element can be manufactured. .. According to the method of the invention described in claim 5, the above-mentioned light receiving element can be manufactured with a mask having one shape. Further, since an extremely thin impurity diffusion layer can be formed, a light receiving element with improved sensitivity on the shorter wavelength side can be manufactured.
According to the method of the invention as set forth in claim 6, the light-receiving element can be manufactured by a single impurity introduction step, so that mass productivity is good.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a configuration of a light receiving element according to a first embodiment of the present invention.

FIG. 2 is a plan view of a light receiving element according to a second embodiment of the present invention.

3A and 3B are views for explaining the configuration of a light receiving element according to a third embodiment of the present invention, FIG. 3A being a plan view thereof and FIG.
(B) is the longitudinal cross-sectional view.

FIG. 4 is a view for explaining the manufacturing method of the light receiving element of the fourth embodiment of the present invention, and both (a) and (b) are vertical cross-sectional views showing a part of the manufacturing process.

FIG. 5 is a view for explaining the manufacturing method of the light receiving element of the fifth embodiment of the present invention, and both (a) and (b) are vertical sectional views showing a part of the manufacturing process.

FIG. 6 is a view for explaining the method of manufacturing the light receiving element of the sixth embodiment of the present invention, which is a vertical cross-sectional view showing a part of the manufacturing process.

FIG. 7 is a vertical sectional view of a conventional silicon PIN photodiode.

FIG. 8 is a diagram showing the relationship between the wavelength and quantum efficiency (sensitivity) of a silicon PIN photodiode.

[Explanation of symbols]

 10 semiconductor substrate 11 low resistance layer 12 high resistance layer 20 impurity diffusion layer 21 relatively thick layer 22 relatively thin layer 30 insulating film 40 electrode 81, 82, 83, 84 mask layer 92, 93 connection part

Claims (6)

[Claims] 1. A second conductivity type is provided near a surface of a semiconductor substrate of a first conductivity type.
In a light receiving element formed by forming a conductivity type impurity diffusion layer, the second conductivity type impurity diffusion layer is formed of a relatively thick layer and a relatively thin layer which are periodically arranged. Light receiving element. 2. The impurity diffusion layer of the second conductivity type is electrically connected to the electrode in a cycle direction in which a relatively thick layer and a relatively thin layer of the second conductivity type impurity diffusion layer are arranged. The light-receiving element according to claim 1, wherein the light-receiving element is substantially perpendicular to the direction toward the connected portion. 3. The impurity diffusion layer of the second conductivity type, wherein at least a portion electrically connected to the electrode is a relatively thick layer. Light receiving element. 4. A portion newly formed after forming a portion corresponding to a relatively thick layer of an impurity diffusion layer of the second conductivity type in a plane shape defined by a mask layer having a first shape formed on the surface of a substrate. The light receiving according to claim 1, 2, or 3, wherein a relatively thin layer and a relatively thick layer of the second-conductivity-type impurity diffusion layer are formed in a planar shape defined by the two-shaped mask layer. Manufacturing method of device. 5. The second conductive material is formed by forming a portion corresponding to a relatively thick layer of the second conductive type impurity diffusion layer in a planar shape defined by the mask layer formed on the surface of the substrate and then performing a heat treatment. The method for manufacturing a light-receiving element according to claim 1, claim 2, or claim 3, wherein a relatively thin layer and a relatively thick layer of the type impurity diffusion layer are formed. 6. A mask layer having a relatively thin portion of the first shape and a relatively thick portion of the second shape formed on the surface of the substrate is used to diffuse impurities of the second conductivity type, thereby relatively The method of manufacturing a light-receiving element according to claim 1, claim 2, or claim 3, wherein a second-conductivity-type impurity diffusion layer having a thin layer and a comparatively thick layer is formed.