Light-receiving element, manufacturing method for the same, optical module, and optical transmitting device Number:7,520,680 from the United States Patent and Trademark Office (PTO) owispatent

Title: Light-receiving element, manufacturing method for the same, optical module, and optical transmitting device

Abstract: To provide a light-receiving element that is capable of high-speed operation and includes an optical element with controlled setting position, shape and size, a manufacturing method for the light-receiving element, and an optical module and an optical transmitting device including the light-receiving element, a light-receiving element includes a base member provided over a light-receiving surface, and an optical element provided on a top surface of the base member.

Patent Number: 7,520,680 Issued on 04/21/2009 to Kaneko,   et al.

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Inventors:	Kaneko; Tsuyoshi (Shimosuwa-machi, JP), Onishi; Hajime (Chino, JP)
Assignee:	Seiko Epson Corporation (Tokyo, JP)
Appl. No.:	11/593,487
Filed:	November 7, 2006

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Related U.S. Patent Documents

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	Application Number	Filing Date	Patent Number	Issue Date
	10761274	Dec., 2006	7150568

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Foreign Application Priority Data

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Feb 06, 2003 [JP]			2003-029655

Current U.S. Class:	385/88 ; 257/432; 359/665; 398/212; 438/64
Current International Class:	G02B 6/36 (20060101)
Field of Search:	385/88-94 438/48,64,65,492,493,497 359/642,665 398/212 257/E31.12,E31.128,E33.073,431-433

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References Cited [Referenced By]

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U.S. Patent Documents

4501637	February 1985	Mitchell et al.
4689291	August 1987	Popovic et al.
5269867	December 1993	Arai
5498684	March 1996	Bender
5707684	January 1998	Hayes et al.
5723264	March 1998	Robello et al.
6043481	March 2000	Tan et al.
6060113	May 2000	Banno et al.
6761925	July 2004	Banno et al.
6838361	January 2005	Takeo
6909554	June 2005	Liu et al.
7064907	June 2006	Kaneko
2001/0048968	December 2001	Cox et al.
2003/0076649	April 2003	Speakman
2005/0030399	February 2005	Suzuki et al.

Foreign Patent Documents

	336574		Oct., 1989		EP
	A 62-260104		Nov., 1987		JP
	A 63-124583		May., 1988		JP
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	A 01-120874		May., 1989		JP
	A 04-303801		Oct., 1992		JP
	A 5-102513		Apr., 1993		JP
	A 5-120722		May., 1993		JP
	A 05-129638		May., 1993		JP
	A 09-152503		Jun., 1997		JP
	A 2000-67449		Mar., 2000		JP
	A 2000-156485		Jun., 2000		JP
	A 2000-304906		Nov., 2000		JP
	A 2001-199644		Jul., 2001		JP
	A 2001-320081		Nov., 2001		JP
	2002-169004		Jun., 2002		JP
	A 2002-222962		Aug., 2002		JP
	A 2002-331532		Nov., 2002		JP
	2002-353511		Dec., 2002		JP
	A 2002-350606		Dec., 2002		JP
	A 2003-031785		Jan., 2003		JP
	A 2003-066299		Mar., 2003		JP
	A 2002-100758		Apr., 2005		JP

Primary Examiner: Pak; Sung H
Assistant Examiner: Petkovsek; Daniel
Attorney, Agent or Firm: Oliff & Berridge, PLC

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Parent Case Text

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This is a Division of application Ser. No. 10/761,274 filed Jan. 22, 2004, now issued as U.S. Pat. No. 7,150,568 B2 on Dec. 19, 2006. The disclosure of the prior application is hereby incorporated by reference herein in its entirety.

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Claims

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What is claimed is:

1. A light receiving element comprising: a substrate; a first conductive layer formed above the substrate; a light absorbing layer formed above the first conductive layer; a second conductive layer formed above the light absorbing layer, the first conductive layer, the light absorbing layer and the second conductive layer constituting a columnar section; a first electrode formed above the second conductive layer, the first electrode having an opening section forming a light-receiving surface; a base member formed above the light receiving surface, a top surface of the base member having a first shape; and an optical element formed above the base member, the optical element configured to have the first shape of the base member, and a diameter of the optical element being larger than a diameter of the base member.

2. The light receiving element according to claim 1, the first shape being a circular or elliptical shape.

3. The light receiving element according to claim 1, the base member being made of material that passes light of a predetermined wavelength.

4. The light receiving element according to claim 1, the optical element functioning as a lens.

5. The light receiving element according to claim 1, the optical element functioning as a polarizing element.

6. The light receiving element according to claim 1, further comprising: an anti-reflective layer formed on the light receiving surface; a sealing agent formed on a part of the optical element and on a part of the base member; an insulating layer formed surrounding a portion of the columnar section; and a second electrode formed on a side of the substrate where the optical element not being formed.

7. The light receiving element according to claim 1, the top surface of the base member further including a second shape, the second shape being a curve.

8. The light receiving element according to claim 1, an upper portion of the base member formed in a shape of an inverse taper.

9. The light receiving element according to claim 1, the light receiving element being a photodiode.

10. An optical module comprising: the light receiving element according to claim 1; and a light guide.

11. An optical transmitting device comprising the optical module according to claim 10.

12. A light receiving element comprising: a substrate having a first surface and a second surface; a first conductive layer; a light absorbing layer; a second conductive layer, the light absorbing layer formed between the first conductive layer and the second conductive layer, and the first conductive layer, the light absorbing layer, and the second conductive layer constituting a columnar section; a first electrode, the columnar section formed between the first electrode and the first surface of the substrate; a light receiving portion formed on the second surface of the substrate; a base member, a top surface of the base member having a first shape; and an optical element configured to have the first shape of the base member, a diameter of the optical element being larger than a diameter of the base member, and the base member formed between the light receiving portion and the optical element.

13. The light receiving element according to claim 12, further comprising: a recessed portion formed in the substrate between the light receiving portion and the first conductive layer.

14. The light receiving element according to claim 13, the recessed portion including a light propagating layer.

15. The light receiving element according to claim 12, further comprising: an insulating layer formed between the first surface of the substrate and the first electrode, and surrounding the columnar section.

16. The light receiving element according to claim 12, further comprising: a second electrode formed on the second surface of the substrate, the second electrode having an opening section corresponding to the light receiving portion.

17. The light receiving element according to claim 12, further comprising: an anti-reflective layer formed between the light receiving portion and the base member.

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Description

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BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a light-receiving element and its manufacturing method, and an optical module and an optical transmitting device including the light-receiving element.

2. Description of Related Art

A light-receiving element is an element to receive light and converting the light into electricity, which is used for optical communication and optical operation, for example. In some of these applications, the need to control optical properties, such as radiation angle and wavelength of light, arises. In addition, in recent years, when a light-receiving element is applied to optical communication, higher-speed operation has been required for the light-receiving element.

SUMMARY OF THE INVENTION

The present invention provides a light-receiving element capable of high-speed operation including an optical element whose setting position, shape, and size are controlled, and its manufacturing method.

The present invention also provides an optical module and an optical transmitting device including the light-receiving element

A first light-receiving element according to the present invention includes: a base member provided over a light-receiving surface; and an optical element provided on the top surface of the base member.

The "optical element" refers to a member having a function of changing optical properties and a traveling direction of light entering the light-receiving surface of the light-receiving element. The "optical properties" include wavelength, polarization, and radiation angle, for example. As such an optical element, a lens or polarizing element is an example.

The "base member" refers to a member having a top surface on which the optical element is set. Hence, the "top surface of the base member" refers to the surface on which the optical element is set. The top surface of the base member may be either plane or curved, provided that the optical element is set thereon.

The base member may be set directly on the light-receiving surface of the light-receiving element, or may be set over the light-receiving surface with another layer interposed. In the latter case, the another layer can, for example, be an anti-reflective layer, which has the function of reducing or preventing reflection of light on the light-receiving surface.

According to the first light-receiving element of an aspect of the present invention, by having the above-described structure, the light-receiving element capable of high-speed operation including the optical element whose setting position, shape, and size are advantageously controlled can be obtained.

According to one aspect of the present invention, the base member is composed of a material that allows light of a predetermined wavelength to pass. The "pass" refers to the light that enters the base member and subsequently emerging from the base member, and includes not only the case where all of the light entering the base member emerges from the base member, but also the case where only a part of the light entering the base member emerges from the base member.

According to an aspect of the present invention, the optical element can function as a lens or polarizing element.

According to an aspect of the present invention, the optical element can have a spherical shape or elliptical spherical shape.

According to an aspect of the present invention, the optical element can have a cut spherical shape or cut elliptical spherical shape. The "cut spherical shape" refers to a shape obtained by cutting a sphere in a plane, and the spherical shape includes not only a complete sphere but also an approximate sphere. In addition, the "cut elliptical spherical shape" refers to a shape obtained by cutting an elliptical sphere in a plane, and the elliptical spherical shape includes not only a complete elliptical sphere but also an approximate elliptical sphere.

In this case, a cross section of the optical element is circular or elliptical. Furthermore, in this case, a function as a lens or polarizing element is applied to the optical element.

According to an aspect of the present invention, the top surface of the columnar part is circular or elliptical.

According to an aspect of the present invention, a sealing agent can be formed so as to, at least, partially cover the optical element.

According to an aspect of the present invention, the top surface of the base member is curved.

According to an aspect of the present invention, the angle, formed between the top surface of the base member and the surface of side wall of the base member that contact the top surface, can be acute. Such a structure can reduce or prevent the side wall of the base member from getting wet by droplets during the step of discharging droplets to form the optical element precursor and the subsequent curing of the optical element precursor to form the optical element. As a result, an optical element of the preferred shape and size can be obtained reliably.

According to an aspect of the present invention, the upper portion of the base member can be formed into an inverse taper. The "upper portion of the base member" refers to the region of the base member that is close to the its top surface. Such a structure can preserve the stability of the base member during the step of discharging droplets to form the optical element precursor and the subsequent curing of the optical element precursor to form the optical element, and at the same time allows the angle formed, between the top surface of the base member and the side wall the of the base member, to be made even smaller. This will reduce or prevent the side wall of the base member from getting wet by the droplet. As a result, an optical element of the preferred shape and size can be obtained.

According to an aspect of the present invention, the light-receiving element is a photodiode.

According to an aspect of the present invention, the columnar part can include a first conductive type layer, a light-absorbing layer, and a second conductive type layer, and the light-absorbing layer being formed between the first conductive type layer and the second conductive type layer.

According to an aspect of the present invention, the base member can function as an anti-reflective layer.

According to an aspect of the present invention, the base member is composed of a semiconductor layer.

According to an aspect of the present invention, the base member is composed of an insulating material, which is silicon oxide or silicon nitride.

A second light-receiving element of an aspect of the present invention include a columnar part provided on a semiconductor substrate; a light-receiving surface provided on the top surface of the columnar part; a base member provided over the light-receiving surface; and an optical element provided on the top surface of the base member.

According to the second light-receiving element of an aspect of the present invention, the same actions and effects can be performed as in the first light-receiving element.

A third light-receiving element of an aspect of the present invention includes a columnar part provided on a semiconductor substrate; a light-receiving surface provided on the back surface of the semiconductor substrate; a base member provided over the light-receiving surface; and an optical element provided on the top surface of the base member.

According to the third light-receiving element of an aspect of the present invention, the same actions and effects can be performed as in the first light-receiving element.

A light-receiving element manufacturing method of an aspect of the present invention includes: a) forming a base member over a light-receiving surface; (b) forming an optical element precursor by discharging droplet onto the top surface of the base member; and (c) forming an optical element by curing the optical element precursor.

According to the manufacturing method of the light receiving element of an aspect of the present invention, in the step (a), the base member is formed with the shape of its top surface, its height and its setting position adjusted, while in the step (b), by adjusting the discharging amount of droplet, the light-receiving element, which is capable of high-speed operation including the optical element whose setting position, shape and size are advantageously controlled, can be provided.

According to an aspect of the present invention, in the step (a), the base member is formed from a material that allows light of a predetermined wavelength to pass. The "pass" means that after light enters the base member, the light exits the base member, and includes not only the case where all of the light entering the base member exits from the base member, but also the case where only a part of the light entering the base member exits from the base member.

According to an aspect of the present invention, in the step (a), the base member is formed so that the angle, formed between the top surface of the base member and the surface of the side wall of the base member that contacts the top surface of the base member, is acute. This will reduce or prevent the side wall of the base member from getting wet by droplets during the step (b). As a result, an optical element with the preferred shape and size is formed reliably.

According to an aspect of the present invention, in the step (a), the upper portion of the base member is formed into an inverse taper. This will preserve the stability of the base member and at the same time permit the angle, formed between the top surface and the side wall of the base member, to be made even smaller, which will reduce or prevent the side wall of the base member from getting wet by the droplets during the step (b). As a result, an optical element with the preferred shape and size can be formed more reliably.

According to an aspect of the present invention, the method can further include a step (d) adjusting the wettability of the top surface of the base member with respect to the droplet, prior to the step (b). This will allow the formation of an optical element with the preferred shape and size. In the step (d), the wettability of the top surface of the base member with respect to the droplet can be controlled, for example, by forming a lyophilic or liquid-repellent film with respect to the droplet on the top surface of the base member.

According to an aspect of the present invention, the method can further include a step (e) covering, at least, a part of the optical element with a sealing agent.

An aspect of the present invention can be applied to an optical module including the light-receiving element according to an aspect of the present invention and a light guide. Furthermore, an aspect of the present invention can be applied to an optical transmitting device including the optical module.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross sectional view of the light-receiving element in a first exemplary embodiment of the present invention;

FIG. 2 is a schematic plan view of the light-receiving element in the first exemplary embodiment of the present invention;

FIG. 3 is a schematic cross sectional view of a step in the manufacturing of the light-receiving element shown in FIGS. 1 and 2;

FIG. 4 is a schematic cross sectional view of a step in the manufacturing of the light-receiving element shown in FIGS. 1 and 2;

FIG. 5 is a schematic cross sectional view of a step in the manufacturing of the light-receiving element shown in FIGS. 1 and 2;

FIG. 6 is a schematic cross sectional view of a step in the manufacturing of the light-receiving element shown in FIGS. 1 and 2;

FIG. 7 is a schematic cross sectional view of a step in the manufacturing of the light-receiving element shown in FIGS. 1 and 2;

FIG. 8 is a schematic cross sectional view of a step in the manufacturing of the light-receiving element shown in FIGS. 1 and 2;

FIG. 9 is a schematic cross sectional view of a step in the manufacturing of the light-receiving element shown in FIGS. 1 and 2;

FIG. 10 is a schematic cross sectional view of a step in the manufacturing of the light-receiving element shown in FIGS. 1 and 2;

FIG. 11 is a schematic cross sectional view of a modification of the light-receiving element shown in FIGS. 1 and 2;

FIG. 12 is a schematic cross sectional view of another modification of the light-receiving element shown in FIGS. 1 and 2;

FIG. 13 is a schematic cross sectional view of the light-receiving element in a second exemplary embodiment of the present invention;

FIG. 14 is a schematic cross sectional view of the light-receiving element in a third exemplary embodiment of the present invention;

FIG. 15 is a schematic cross sectional view of the light-receiving element in a fourth exemplary embodiment of the present invention;

FIG. 16 is a schematic cross sectional view of a step in the manufacturing of the light-receiving element shown in FIG. 15;

FIG. 17 is a schematic cross sectional view of a step in the manufacturing of the light-receiving element shown in FIG. 15;

FIG. 18 is a schematic cross sectional view of a step in the manufacturing of the light-receiving element shown in FIG. 15;

FIG. 19 is a schematic cross sectional view of a step in the manufacturing of the light-receiving element shown in FIG. 15;

FIG. 20 is a schematic cross sectional view of a step in the manufacturing of the light-receiving element shown in FIG. 15;

FIG. 21 is a schematic cross sectional view of the light-receiving element in a fifth exemplary embodiment of the present invention;

FIG. 22 is a schematic cross sectional view of the light-receiving element in a sixth exemplary embodiment of the present invention;

FIG. 23 is a schematic cross sectional view of the light-receiving element in a seventh exemplary embodiment of the present invention;

FIG. 24 is a schematic plan view of the light-receiving element in the seventh exemplary embodiment of the present invention;

FIG. 25 is a schematic view of the optical module relating to a eighth exemplary embodiment of the present invention;

FIG. 26 is a schematic illustration of the optical transmitting device relating to the eighth exemplary embodiment of the present invention;

FIG. 27 is an another schematic illustration of the optical transmitting device relating to the eighth exemplary embodiment of the present invention;

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, the preferred exemplary embodiments of the present invention will be described referring to the accompanying figures.

First Exemplary Embodiment

1. Structure of the Light-Receiving Element

FIG. 1 is a schematic cross sectional view showing a light-receiving element 100 according to a first exemplary embodiment of the present invention. FIG. 2 is a schematic plan view showing the light-receiving element 100 according to the first exemplary embodiment of the present invention. FIG. 1 shows a cross section taken along the plane A-A of FIG. 2. As for the exemplary embodiment, the case where the light-receiving element 100 is a photodiode will be described.

As shown in FIG. 1, the light-receiving element 100 includes a light-receiving surface 108, a base member 110 provided over the light-receiving surface 108, and an optical element 111 provided on a top surface 110a of the base member 110.

As for the light-receiving element 100 of the present exemplary embodiment, light enters through the light-receiving surface 108, which is provided on a top surface 130a of a columnar part 130 formed on a semiconductor substrate 101. Thus, the top surface 130a of the columnar part 130 includes the light-receiving surface 108. More specifically, on the top surface 130a of the columnar part 130, a portion (opening 114), which is not covered by a first electrode 107 (described below), is provided, and the light-receiving surface 108 is provided within the opening 114.

Furthermore, as for the exemplary embodiment, the case where the optical element 111 functions as a lens will be described. That is, as shown in FIGS. 1 and 2, the light converged by the optical element 111 enters the light-receiving surface 108 through the base member 110.

Base Member

As for the present exemplary embodiment, the base member 110 is made of a material that can transmit light of a predetermined wavelength. More specifically, the base member 110 is made of a material that can transmit the light that is converged by the optical element 111. For example, the base member 110 is formed from polyimide resin, acrylic resin, epoxy resin or fluorocarbon resin. Alternatively, the base member is formed from a semiconductor layer, as in a light-receiving element 400 (refer to FIG. 15) of a fourth exemplary embodiment described below.

As for the present exemplary embodiment, FIG. 1 shows the case where the base member 110 and an anti-reflective layer 105 are separate layers, but alternatively, the base member 110 itself is rendered to function as an anti-reflective layer, instead of providing the separated anti-reflective layer 105. In this case, the base member 110 is made of a material that can effect a reduction of the reflection of the incident light, as well as transmit the incident light. More specifically, in this case, the base member 110 is made of an insulator such as silicon oxide and silicon nitride.

There is no particular restriction on the three-dimensional shape of the base member 110, but the base member should, at least, have a structure that the optical element can be set on its top surface. The same requirement is applied to base members of light-receiving elements in the other exemplary embodiments to be described below.

The height and shape of the base member 110 are determined by the function, application, shape and size of the optical element 111 that is formed on the top surface 110a of the base member 110. Accordingly, by controlling the shape of the top surface 110a of the base member 110, the shape of the optical element 111 can be controlled.

For example, as for the light-receiving element 100 (refer to FIGS. 1 and 2), the shape of the top surface 110a of the base member 110 is circular. The other exemplary embodiments, which are described below, also show cases that the shapes of the top surface of the base members are circular.

When the optical element is used, for example, as a lens or polarizing element, the shape of the top surface of the base member is circular. This allows the three-dimensional shape of the optical element to be a spherical shape or cut spherical shape, thereby the resultant optical element is used as a lens or polarizing element.

Although a figure is not shown here, when the optical element is used as an anisotropic lens or polarizing element, the shape of the top surface of the base member can be elliptical. This allows the three-dimensional shape of the optical element to be formed as an elliptical spherical shape or cut elliptical spherical shape, thereby the resultant optical element 111 is used as a lens or polarizing element.

Optical Element

Because the three-dimensional shape of the optical element 111 is described above, a detailed description will be omitted.

The optical element 111 is formed by curing a curable liquid material (e.g. a precursor of UV-cured resin or thermosetting resin) with applying energy, such as heat and light. As for the UV-cured resin, UV-curable acrylic resin and epoxy resin are exemplified. As for the thermosetting resin, thermosetting polyimide resin or the like are exemplified.

The precursor of UV-cured resin is cured by a short-time ultraviolet irradiation. Accordingly, the UV-cured resin can be cured without going through the step such as heating in which the element is apt to be damaged. Thus, when the optical element 111 is formed using the precursor of UV-cured resin, influence on the element can be reduced.

As for the present exemplary embodiment, specifically, the optical element 111 is formed by discharging a droplet 111a made of the liquid material on the top surface 110a of the base member 110 to form an optical element precursor 111b and curing the optical element precursor 111b (refer to FIGS. 9 and 10). A method to form the optical element 111 will be described below.

FIG. 1 shows the case where the maximum width "d" of the optical element 111 at its maximum cross section "S" is larger than the diameter of the base member 110. This allows a large distance between the upper portion of the curved surface of the optical element 111 (surface of the optical element 111) and the light-receiving surface 108. As a result, the lens effect of the optical element can be enhanced. The shape and size of the optical element 111 are not limited to those shown in FIG. 1; the maximum width d of the optical element 111 at its maximum cross section "S" is equal to or smaller than the diameter of the base member 110. This is similarly applied to optical elements in other exemplary embodiments described below.

The "maximum cross section S" means a cross section that has the largest area among cross sections that can be obtained by cutting the optical element 111 in planes parallel to the light-receiving surface 108. The "maximum width d at maximum cross section S" refers to the maximum width of the optical element at its maximum cross section S as defined above. When the maximum cross section S is, for example, circular, d is the diameter of the circle defined by the maximum cross section S, while when the maximum cross section S is elliptical, d is the major axis of the ellipse defined by the maximum cross section S.

Other Components

As above described, the light-receiving element 100 includes a semiconductor substrate 101, and a columnar part 130 that is formed over the semiconductor substrate 101. The semiconductor substrate 101 is composed of n-type GaAs substrate.

The columnar part 130 is a columnar semiconductor deposition structure that is formed on the semiconductor substrate 101. More specifically, the columnar part 130 is formed by etching a portion in the light-receiving element 100 from the light-receiving surface 108 side to the middle of the substrate 101 so as to form a circular shape as viewed from the light-receiving surface 108 side. As for the present exemplary embodiment, although the plane shape of the columnar part 130 is circular, the shape may take any other shape.

The columnar 130 includes a first conductive type layer 102, a light-absorbing layer 103, and a second conductive type layer 104. As for the light-receiving element 100 according to the exemplary embodiment, the light-receiving surface 108 is provided on the second conductive type layer 104. Accordingly, light entering the second conductive type layer 104 through the light-receiving surface 108 propagates in the second conductive type layer 104 and then enters the light-absorbing layer 103. In this case, the columnar part 130 can be formed by depositing, for example, the first conductive type layer 102 made of an n-type GaAs layer, the light-absorbing layer 103 made of a GaAs layer with no impurities doped, and the second conductive type layer 104 made of a p-type GaAs layer on the substrate 101 made of an n-type GaAs layer, in the order described as above. In this case, for example, the first conductive type layer 102 can have a film thickness of 0.5 .mu.m, the light-absorbing layer 103 can have a film thickness of 3.5 .mu.m, and the second conductive type layer 104 can have a film thickness of 0.1 .mu.m. However, the compositions and thickness of respective layers composing the first conductive type layer 102, the light-absorbing layer 103, and the second conductive type layer 104 are not limited to the above-described example.

The second conductive type layer 104 is made into the p-type, for example, by doping C (carbon), and the first conductive type layer 102 is made into the n-type, for example, by doping Si (silicone). Thus, a pin diode is composed of the second conductive type layer 104, the light-absorbing layer 103 in which impurities are not doped, and the first conductive type layer 102.

The second conductive type layer 104 has a carrier density so that it can take an ohmic contact with an electrode (the first electrode 107 described below).

Furthermore, the columnar part 130 is embedded with an insulating layer 106. That is, a side wall 130b of the columnar part 130 is encompassed with the insulating layer 106. As for the light-receiving element 100 according to the exemplary embodiment, the insulating layer 106 covers the side wall 130b of the columnar part 130 and the top surface of the substrate 101.

In the manufacturing steps of the light-receiving element 100, after the insulating layer 106 covering the side wall 130b of the columnar part 130 is formed, the first electrode 107 is formed on the top surface 130a of the columnar part 130 and the top surface of the insulating layer 106, and a second electrode 109 is formed on the back surface of the semiconductor substrate 101 (the surface opposite to the surface of the semiconductor substrate 101, on which the columnar part 130 is set). When forming these electrodes, an annealing treatment is generally carried out at about 400.degree. C. (refer to the manufacturing step described below). Accordingly, in the case where the insulating layer 106 is formed using resin, the resin composing the insulating layer 106 needs to be excellent in heat resistance so as to withstand the annealing treatment. In order to satisfy this requirement, the resin composing the insulating layer 106 is preferably polyimide resin, fluorocarbon resin, acrylic resin, or epoxy resin, more preferably polyimide resin or fluorocarbon resin from the viewpoint of easiness in processing and insulation performance. Furthermore, in the case where the optical element (e.g. lens) is formed on the insulating layer 106 using resin as a raw material, the insulating layer 106 is preferably made of polyimide resin or fluorocarbon resin from the viewpoint of large contact angle with the lens material (resin) and easiness in controlling the lens shape. In this case, the insulating layer 106 is formed by curing a resin precursor with energy irradiation, such as heat and light, or by chemical reaction.

The first electrode 107 is composed of a multi-layered film of an alloy of Au and Zn, and Au, for example.

Furthermore, the second electrode 109 is formed on the back surface 101b of the semiconductor substrate 101. That is, as for the light-receiving element 100, the top surface 130a of the columnar part 130 contacts the first electrode 107, and the back surface 101b of the semiconductor substrate 101 contacts the second electrode 109. The second electrode 109 is composed of a multi-layered film of an alloy of Au and Ge, and Au, for example.

The materials to form the first electrode 107 and the second electrode 109 are not limited to the above-described examples. For example, metals of Ti, Pt or the like, or alloys of these metals are applicable.

Furthermore, as shown in FIG. 1, the anti-reflective layer 105 is formed on the light-receiving surface 108, as required. Thus, as for the light-receiving element 100 of the present exemplary embodiment, the base member 110 is set on the light-receiving surface 108 with the anti-reflective layer 105 interposed. Because this can reduce the reflection of the incident light on the light-receiving surface 108, the injection efficiency of the light entering the light-receiving surface 108 can be increased.

An optical film thickness of the anti-reflective layer 105 is expressed in (2 m-1) .lamda./4 (.lamda. represents a wavelength of light entering the light-receiving surface 108 (incident light) and m represents a natural number). The "optical film thickness" refers to a value obtained by multiplying an actual film thickness of the layer by a refraction factor thereof. For example, when the wavelength of incident light is .lamda. and a layer has an optical film thickness of .lamda./4 and a refraction factor n of 2.0, the actual film thickness of this layer is expressed in .lamda./4/2=0.125.lamda. by the fact that the actual film thickness is equal to optical film thickness/refraction factor n. "Film thickness" in the invention refers to an actual film thickness of a layer.

Materials of the anti-reflective layer 105 are not specifically limited, however, they may be materials that have an effect of reducing the reflection factor of the incident light and allow the incident light to pass therethrough. For example, the anti-reflective layer 105 is made of a silicon oxide or silicon nitride.

Furthermore, in the light-receiving element 100, a reflective layer (not shown) is formed between the first conductive type layer 102 and the light-absorbing layer 103, as required. By forming the reflective layer, light which passed through the light-absorbing layer 103 can be reintroduced to the light-absorbing layer 103. This can increase the light utilizing efficiency. In particular, when the film thickness of the light-absorbing layer 103 is reduced, a part of incident light passes through the light-absorbing layer 103, thereby decreasing the light utilizing efficiency in the light-absorbing layer 103. In this case, forming the reflective layer is effective from the viewpoint of increasing the light utilizing efficiency.

2. Operation of the Light-Receiving Element

General operation of the light-receiving element 100 according to the exemplary embodiment is described below. The case where the first conductive type is of n-type and the second conductive type is of p-type is described. The method to drive the light-receiving element described below is only an example, and various modifications can be made without departing from the intent of the present invention.

First, light having a predetermined wavelength enters the optical element 111. The incident light is converged by the optical element 111 and enters the light-receiving surface 108. The incident light through the light-receiving surface 108 generates the light excitation in respective layers constituting the columnar part 130 (semiconductor layer) to generate electrons and positive holes. At this time, in the light-absorbing layer 103, the electrons are accumulated in the vicinity of an interface with the first conductive type layer 102, and the positive holes are accumulated in the vicinity of an interface with the second conductive type layer 104. When more than a predetermined amount of electrons and positive holes are accumulated in the light-absorbing layer 103, the electrons move to the first conductive type layer 102, and the positive holes move to the second conductive type layer 104. As a result, a current flows in the direction from the first conductive type layer 102 to the second conductive type layer 104 (a direction Z in FIG. 1). At this time, if an electric field is impressed to the light-absorbing layer 103 so that a potential on the side of the first conductive type layer 102 becomes high, the separation of generated electrons and positive holes becomes easy and the probability of recombination is reduced, thereby increasing the photoelectric conversion efficiency.

3. Manufacturing Method of Light-Receiving Element

Next, an example of the manufacturing method of the light-receiving element 100 according to the first exemplary embodiment of the present invention will be described referring to FIGS. 3 through 10. FIGS. 3 through 10 are schematic cross sectional views, each showing a manufacturing step of the light-receiving element 100 according to the exemplary embodiment as shown in FIGS. 1 and 2, and corresponding to the cross section shown in FIG. 1.

(1) First, on the surface of the semiconductor substrate 101 made of n-type GaAs, a semiconductor multilayer film 150 is formed by generating epitaxial growth while modulating the composition (refer to FIG. 3).

As shown in FIG. 3, the semiconductor multilayer film 150 is composed by depositing the first conductive type layer 102, the light-absorbing layer 103, and the second conductive type layer 104 in the order described as above. Furthermore, each of the layers is made of GaAs. In this case, the first conductive type layer 102 is doped with Si (silicone) so as to be of n-type and the second conductive type layer 104 is doped with C (carbon) so as to be of p-type. Furthermore, the reflective layer (not shown) is made to grow in a predetermined position, as required.

Although the temperature for the epitaxial growth is determined in each case in accordance with growth method, raw material, type of the semiconductor substrate 101, or type, thickness, and carrier density of the semiconductor multilayer film 150 to be formed, in general, the temperature is in the range of 450 to 800.degree. C., preferably. The time required for the epitaxial growth is also determined in each case as in the temperature. Furthermore, as a method of epitaxial growth, MOVPE (Metal-Organic Vapor Phase Epitaxy) method, MBE (Molecular Beam Epitaxy) method, or LPE (Liquid Phase Epitaxy) method can be used.

Subsequently, after applying photoresist (not shown) on the semiconductor multilayer film 150, a resist layer R100 of a predetermined pattern is formed by patterning the photoresist using a photolithography method (refer to FIG. 3).

(2) Thereafter, by partially etching (e.g. dry etching method) the second conductive type layer 104, the light-absorbing layer 103, the first conductive type layer 102, and the semiconductor substrate 101 using the resist layer R100 as a mask, the columnar semiconductor deposition structure (columnar part) 130 is formed (refer to FIG. 4). Thereafter, the resist layer R100 is removed.

(3) Subsequently, the insulating layer 106 encompassing the columnar part 130 is formed (refer to FIGS. 5 and 6). The case where polyimide resin is used as a material for forming the insulating layer 106 will be described.

First, a resin precursor layer (polyimide precursor) is applied on the semiconductor substrate 101, for example, using a spin coat method, to effect imidization. Thereby, the insulating layer 106 is formed around the columnar part 130 as shown in FIG. 5. As for the forming method of the insulating layer 106, for example, the method given in Japanese laid-open patent publication No. 13-066299 can be used. As for the forming method of the resin precursor layer, in addition to the above-described spin coat method, suitable techniques, such as dipping method, spray coat method, and an ink jet method, can be used.

(4) Next, the first electrode 107 and the second electrode 109, and the light-receiving surface 108 are formed (refer to FIG. 6).

First, before the first electrode 107 and the second electrode 109 are formed, the top surface 130a of the columnar 130 is cleaned using a plasma treatment method or the like, as required. This enables an element having more stable properties to be formed. Subsequently, after a multi-layered film (not shown) made of an alloy of Au and Zn, and Au, for example, is formed on the top surface of the insulating layer 106 and the top surface 130a of the columnar part 130 using the vacuum deposition method, for example, a portion (opening 114), which does not have the multi-layered film formed thereon, is formed on the top surface 130a of the columnar part 130 using the lift off method. This allows the region inside of the opening 114 to function as the light-receiving surface 108. Incidentally, in the above-described step, the dry etching method can be used instead of the lift off method.

Furthermore, a multi-layered film (not shown) made of, for example, an alloy of Au and Ge, and Au, is formed on the back surface of the semiconductor substrate 101 using the vacuum deposition method, for example, and then is subjected to an annealing treatment, thereby forming ohmic contact. The temperature of the annealing treatment depends on the electrode material. Typically, the electrode material used in the exemplary embodiment is treated at about 400.degree. C. Through the above-described steps, the first electrode 107 and the second electrode 109 are formed (refer to FIG. 6).

Subsequently, the anti-reflective layer 105 is formed on the light-receiving surface 108, as required (refer to FIG. 7).

Specifically, an insulating layer (not shown in the figures) to form the anti-reflective layer 105 is multi-layered by a method, such as plasma CVD, so that a layer of a predetermined thickness is produced. The description is given to the insulating layers composed of silicon nitride, but the insulating layers may be made of silicon oxide. Then the resist patterning is conducted by the photolithographic process so as to leave only resist over the light-receiving surface 108. Following that, portions of the insulating layers that are not covered by the resist are removed by the wet etching, for example, using buffered hydrofluoric acid solution as the etchant. The dry etching using fluorine plasma can be employed instead of the wet etching. Finally the resist is removed. The anti-reflective layer 105 can be obtained through the above-described steps.

(5) Next, the base member 110, on which the optical element 111 (refer to FIG. 1) will be set, is formed over the light-receiving surface 108 (refer to FIGS. 7 and 8).

To form the base member 110, a method (e.g. the selective growth method, the dry etching, the wet etching, the lift-off method and the transfer method) can be selected that is appropriate for material, shape and size of the base member 110. As for the present exemplary embodiments, the case where the base member 110 is formed by patterning with the wet etching will be described.

First a resin layer 110x is formed over, at least, the light-receiving surface 108, as shown in FIG. 7. As for the present exemplary embodiment, the case where the resin layer 110x is formed over the light-receiving surface 108 and over the entire top surface of the first electrode 107 using the spin coat method, for example, is shown.

Subsequently, a resist layer R200 of a predetermined pattern is formed over the resin layer 110x. The resist layer R200 is used to form the base member 110, which is accomplished by patterning the resin layer 110x. Specifically, the resin layer 110x is patterned by the lithographic process employing the wet etching that uses the resist layer R200 as mask and, for example, an alkaline solution as the etchant. As a result, the base member 110 is formed over the light-receiving surface 108 as shown in FIG. 8. Afterwards, the resist layer R200 is removed.

(6) Next, the optical element 111 is formed on the top surface 130a of the columnar part 130 (refer to FIGS. 9 and 10). As for the present exemplary embodiments, the case where the optical element 111 is formed on the top surface 110a of the base member 110 via the first electrode 107 is shown.

First, a treatment to adjust a wet angle of the optical element 111 is conducted to the top surface 110a of the base member 110, as required. The treatment enables the optical element precursor 111b with a preferable shape to be obtained when the liquid material 111a is introduced on the top surface 110a of the base member 110 in the step described below. As a result, the optical element 111 having a preferable shape can be obtained (refer to FIGS. 9 and 10).

Subsequently, a droplet of the liquid material 111a is discharged onto the top surface 110a of the base member 110 using the ink jet method, for example. As for discharging methods of the ink jet, (i) a method of generating pressure by changing the sizes of bubbles in the liquid (lens material in the invention) with heat so as to discharge the liquid, and (ii) a method of generating pressure with a piezoelectric element so as to discharge the liquid, are exemplified. The method (ii) is preferable from the viewpoint of pressure controllability.

The alignment of the nozzle position of an ink jet head and the discharging position of the droplet is performed using suitable image recognition techniques used in an exposure process or inspection process in a general manufacturing process of semiconductor integrated circuit. For example, as shown in FIG. 9, the position of a nozzle 112 of an ink jet head 120 and the position of the columnar part 130 are aligned. After the alignment, the voltage applied to the ink jet head 120 is controlled and then the droplet of the liquid material 111a is discharged. Thereby, as shown in FIG. 10, the optical element precursor 111b is formed on the top surface 110a of the base member 110.

In this case, as shown in FIG. 9, the liquid material 111a is deformed due to surface tension when the droplet, discharged from the nozzle 112, lands on the top surface 110a of the base member 10, and the liquid material 111a comes to the center of the top surface 110a of the base member 110. Thereby, the position is automatically corrected.

Furthermore, in this case, the optical element precursor 111b (refer to FIG. 9) obtains a shape and size in accordance with the shape and size of the top surface 110a of the base member part 110, the discharging amount of the liquid material 111a, the surface tension of the liquid material 111a, and the interfacial tension between the top surface 130a of the columnar part 130 and the liquid material 111a. For example, the method of dispensing the droplet is repeated as many times as needed, to form the optical element 111 of the required shape and size. Accordingly, by controlling these factors, the shape and size of the optical element 111 obtained finally (refer to FIG. 1) can be controlled, thereby enhancing the flexibility in lens design.

After conducting the above-described steps, as shown in FIG. 10, the optical element precursor 111b is cured by irradiation of energy beam 113 (e.g. ultraviolet rays) to form the optical element 111 on the top surface 110a of the base member 110 (refer to FIG. 1). At this time, an optimal wavelength and amount of the ultraviolet rays depend on the material of the optical element precursor 111b. For example, in the case where the optical element precursor 111b is formed using a precursor of acrylic UV-cured resin, it is irradiated for five minutes by ultraviolet rays having a wavelength of about 350 nm and an intensity of 10 mW to be cured. Through the above-described steps, the light-receiving element 100 according to the exemplary embodiment can be obtained as shown in FIG. 1.

4. Actions and Effects

The light-receiving element 100 according to the exemplary embodiment has actions and effects described below.

(A) First, because the optical element 111 is formed on the top surface 110a of the base member 110, a amount of light per unit cross section area, which is introduced to the light-absorbing layer 103, can be increased. This allows the film thickness of the light-absorbing layer 103 to be thinner, thereby decreasing the distance that the electrons and the positive holes moves to the electrodes (the first electrode 107 and the second electrode 109). As a result, a high-speed operation becomes possible while maintaining the light-receiving sensitivity.

Furthermore, because the light-absorbing layer 103 has a high insulation performance in general, the capacitance of the light receiving element 100 is increased in proportional to the cross section area of the light-absorbing layer 103. The increase of capacitance is a factor preventing the high-speed operation of the element. By contrast, in the light receiving element 100 according to the exemplary embodiment, because the amount of light per unit cross section area, which is introduced to the light-absorbing layer 103, can be increased as above described, the cross section area of the light-absorbing layer 103 can be decreased. Because this can reduce the capacitance, higher-speed operation becomes possible while maintaining the light utilizing efficiency.

(B) Second, because the optical element 111 is provided on the top surface 110a of the base member 110, an appropriate path length can be secured for the light that enters through the light-receiving surface 108. That is, by adjusting the height of the base member 110, the path length for the light that enters through the light-receiving surface 108 (the incident light) can be adjusted. Thus, the curvature of the optical element 111 and the path length for the incident light can be controlled independently. Therefore, an optical design that will bring the incident light into the light-absorbing layer 103 with good efficiency can be conducted with ease.

(C) Third, the size and shape of the optical element 111 can be strictly controlled. In order to form the optical element 111, as described in the step (6), the optical element precursor 111b is formed on the top surface 110a of the base member 110 in the step of forming the optical element 111 (refer to FIGS. 9 and 10). At this time, as long as the side wall 110b of the base member 110 is not wetted with the liquid material composing the optical element precursor 110a, the surface tension of the top surface 110a of the base member 110 does not act on the optical element precursor 111b, but the surface tension of the liquid material mainly acts on the optical element precursor 111b. Therefore, the shape of the optical element precursor 111b can be controlled by controlling the amount of the liquid material (droplet 111a) used to form the optical element 111. Thereby, the optical element 111 whose shape is more strictly controlled can be formed. As a result, the optical element 111 having a preferred shape and size can be obtained.

(D) Fourth, the setting position of the optical element 111 can be strictly controlled. As above described, the optical element 111 is formed by discharging the droplet of the liquid material 111a onto the top surface 110a of the base member 110 to form the optical element precursor 111b and curing the optical element precursor 111b (refer to FIG. 10). In general, a strict control of the landing position of the discharged droplet is difficult. This method, however, allows the optical element 111 to be formed on the top surface 110a of the base member 110 without performing special alignment. That is, by only discharging the droplet 111a on the top surface 110a of the base member 110, the optical element precursor 111b can be formed without alignment. To put it differently, the optical element 111 can be formed with the alignment accuracy, which is applied when the base member 110 is formed. Thereby, the optical element 111 whose setting position is controlled can be formed with ease and with good yield.

In particular, in the case where the droplet 111a is discharged using the ink jet method, the droplet 111a can be discharged in a more precise position, so that the optical element 111 whose setting position is controlled more strictly can be formed with ease and with good yield. Furthermore, by discharging the droplet 111a using the ink jet method, the amount of the discharged droplet 111a can be controlled in units of pico-liter order, thereby a fine structure can be produced precisely.

(E) Fifth, by setting the shape and area of the top surface 110a of the base member 110, the shape and size of the optical element 111 can be set. In particular, by selecting the shape of the top surface 110a of the base member 110 in each case, the optical element 111 having a predetermined function can be formed. Moreover, by forming a plurality of base members having different shapes of top surface thereof, and forming each optical elements on the top surface of each of the base members, optical elements having different functions can be integrated on the same substrate.

5. Modification

Next, a modification of the light-receiving element 100 of the present exemplary embodiment will be described with reference to FIG. 11. FIG. 11 is a schematic cross sectional view of a modification (light-receiving element 190) of the light-receiving element 100