JP2011066097A - Rear incidence type photo-detector and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rear incidence type photo-detector sufficiently securing a coupling tolerance to the positional displacement of incident light when light is received to a light reception integrated in an array shape in a semiconductor substrate by a microlens, and also to provide a method for manufacturing the rear incidence type photo-detector. <P>SOLUTION: The photo-detectors 11 having the longitudinal direction in the specific direction are arranged in an internal space brought into contact with the first surface of the plate-shaped semiconductor substrate at intervals. The microlens 12 as a partial cylinder using the specific direction as the axial direction and cutting a cylinder forming a specified curved surface by a surface parallel with the axial direction is formed to a second surface opposed to the first surface so that the photo-detectors 11 are used as the positions of focuses. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a back-illuminated light receiving element that receives light from the back side of a substrate and receives the light, and a method of manufacturing the back-illuminated light receiving element.

  As a related technique of the present invention, there has been proposed a back-illuminated type light receiving element in which microlenses are integrated on the back surface of a substrate and light is received from the back surface side to receive light (see, for example, Non-Patent Document 1). This back-illuminated light receiving element is used as an optical receiver in optical communication, for example.

  FIG. 12 shows an example of a back-illuminated light receiving element using this related technology. On the back surface of the semiconductor substrate 101, there is formed a microlens 102 in which the central part of the circle forms a part of a spherical surface and the peripheral part becomes an aspherical surface. Yes. A light receiving portion 103 is formed at the focal position when light incident in the vertical direction with respect to the semiconductor substrate 101 passes through the microlens 102. Here, the light receiving unit 103 is a position that takes into account the shift of the focal position due to the aspherical surface to the focal position due to the spherical surface.

  FIG. 13 shows a state in which the microlens shown in FIG. 12 is cut in the AA direction shown in FIG. 12 at a position perpendicular to the back surface of the semiconductor substrate and including the light receiving portion. A convex microlens 102 is formed on the back surface of the semiconductor substrate 101 so that the position directly above the light receiving portion 103 is a vertex.

  In such a back-illuminated light receiving element 104, the microlens 102 can be integrated by etching the semiconductor substrate 101. As a result, in the back-illuminated light receiving element 104, the coupling tolerance with the incident light can be increased while the area of the pn junction that is the light receiving unit 103 is kept small. Therefore, a light receiving element having a small element capacity and a high response speed can be manufactured with high yield.

Japan Society for Invention and Innovation Open Technical Bulletin No. 93-606

  However, in the related art, when a plurality of back-illuminated light receiving elements 104 are integrated in an array on the same semiconductor substrate 101, the interval between adjacent microlenses 102 is shortened. Here, the array form means a state in which objects are arranged at equal intervals. For this reason, when the related technique is used, distortion occurs in the etching shape when a part of the spherical surface is formed as a lens in the manufacturing process of the microlens 102. As a result, a normal spherical microlens surface cannot be produced, and the optical image cannot be favorably converged on the light receiving unit 103. As a result, there arises a problem that the coupling tolerance against the positional deviation of the incident light cannot be kept large.

  Accordingly, an object of the present invention is to provide a back-illuminated light-receiving element and a back-surface incident light source that can ensure a sufficient coupling tolerance against a positional deviation of incident light when light is received by a microlens in a light-receiving unit integrated in an array of semiconductor substrates An object of the present invention is to provide a method for manufacturing a mold type light receiving element.

  In the present invention, (a) the internal space in contact with the front surface as the first surface of the flat semiconductor substrate has a longitudinal direction in the specific direction of the first surface described above, and a constant interval in the specific direction. And (b) a light receiving element having a partial cylinder obtained by cutting a cylinder having a predetermined curved surface with the specific direction as an axial direction and a plane parallel to the axial direction. The back-illuminated light-receiving element includes a cylindrical microlens formed on the back surface as the second surface facing the first surface so that is at the focal position.

  In the present invention, (a) the internal space in contact with the front surface as the first surface of the flat semiconductor substrate has a longitudinal direction in a specific direction of the first surface, and a constant interval in the specific direction. A light-receiving element forming step for forming a plurality of light-receiving elements, and (b) a position facing the position where the plurality of light-receiving elements are formed on the back surface as the second surface facing the first surface. A mesa forming step for forming a stripe-shaped forward mesa along the specific direction, and (c) the surface is curved so as to take an angle of the forward mesa formed in the mesa forming step, and the light receiving element is focused on. The manufacturing method of the back-illuminated light receiving element includes a lens forming step of forming a cylindrical lens having a cylindrical shape at a position.

  As described above, according to the present invention, one cylindrical microlens is formed in common to a plurality of light receiving elements arranged in a row. Therefore, in the case of forming a normal circular microlens, it is necessary to align the individual microlenses in the column direction of the light receiving elements, but this labor is not required, which not only simplifies the manufacturing process but also improves the yield. Has the advantage of improving.

It is a claim corresponding | compatible figure of the back incidence type light receiving element of this invention. It is a claim corresponding | compatible figure of the manufacturing method of the back incidence type light receiving element of this invention. It is a principal part top view showing the principal part of the planar structure of the back-illuminated type light receiving element by embodiment of this invention. It is sectional drawing of the AA direction of the back-illuminated type light receiving element shown in FIG. It is sectional drawing of the BB direction of the back-illuminated type light receiving element shown in FIG. It is the principal part top view which showed the state which formed the etching mask in the semiconductor substrate side of the back-illuminated type light receiving element in the Example of this invention. It is sectional drawing of the AA direction of the back-illuminated type light receiving element shown in FIG. It is sectional drawing of the BB direction of the back incidence type light receiving element shown in FIG. It is the principal part top view which showed the state which formed the striped mesa after the wet etching in a present Example. It is sectional drawing of the AA direction of the back-illuminated type light receiving element shown in FIG. It is sectional drawing of the BB direction of the back-illuminated type light receiving element shown in FIG. It is a principal part top view of the back incidence type light receiving element using the related technology of this invention. It is sectional drawing of the AA direction of the back-illuminated type light receiving element shown in FIG.

  FIG. 1 is a diagram corresponding to the claims of the back-illuminated light receiving element of the present invention. The back-illuminated light receiving element 10 of the present invention includes a plurality of light receiving elements 11 and microlenses 12. Here, the plurality of light receiving elements 11 have a longitudinal direction in the specific direction of the first surface described above in the internal space that is in contact with the front surface as the first surface of the flat semiconductor substrate. They are arranged at regular intervals. The microlens 12 is the first surface described above so that the light receiving element 11 becomes a focal position in a partial cylinder obtained by cutting a cylinder having a predetermined curved surface with the specific direction as an axial direction and a plane parallel to the axial direction. Is a cylindrical lens formed on the back surface as the second surface opposite to the lens.

  FIG. 2 is a view corresponding to claims of the method for manufacturing the back-illuminated light receiving element of the present invention. The back-illuminated light receiving element manufacturing method 20 of the present invention includes a light receiving element forming step 21, a mesa forming step 22, and a lens forming step 23. Here, in the light receiving element formation step 21, the internal space in contact with the front surface as the first surface of the flat semiconductor substrate has a longitudinal direction in the specific direction of the first surface, and is constant in the specific direction. A plurality of light receiving elements are formed at intervals. In the mesa formation step 22, a stripe-shaped forward mesa is formed along the specific direction described above at a position facing the position where the plurality of light receiving elements are formed on the back side surface as the second surface facing the first surface. Form. In the lens forming step 23, the surface is curved so as to take the corner of the forward mesa formed in the mesa forming step 22, and is formed into a cylindrical microlens having the light receiving element as a focal position.

  <Embodiment of the Invention>

  Next, an embodiment of the present invention will be described.

  FIG. 3 shows the main part of the planar structure of the back-illuminated light receiving element according to the embodiment of the present invention. In the back-illuminated light receiving element 200, a microlens 202 having a cylindrical lens shape is formed on the back surface of the semiconductor substrate 201. The cylindrical lens has a shape obtained by dividing a cylinder in the axial direction, and has no refractive power in the axial direction, but has a refractive power in a direction orthogonal to the cylindrical direction.

  In FIG. 3, the portion (the portion corresponding to the ridge line of the mountain) 203 where the thickness of the microlens 202 is the thickest coincides with the cut surface in the BB direction and is linear in the axial direction of the cylinder. . A portion where the thickness of the micro lens 202 is the thinnest and the portion where the lens is in contact with the substrate plane is indicated by a solid line 204. The light receiving unit 205 is placed at a predetermined interval on a line intersecting a vertical line from a portion 203 where the thickness of the microlens 202 is thickest at a position on the substrate surface side inside the semiconductor substrate 201. Are arranged.

  4 shows a cross-sectional view of the back-illuminated light receiving element taken along the line AA shown in FIG. 3, and FIG. 5 shows the back-illuminated light receiving element shown in FIG. The cross-sectional view cut | disconnected in the B direction is represented.

  As shown in these drawings, a microlens 202 is formed in a convex shape on the upper surface (back surface side) of the semiconductor substrate 201. The light receiving unit 205 is integrated in an array at a predetermined interval at a focal position formed on the line of the microlens 202. As shown in FIG. 3 or FIG. 5, the respective light receiving portions 205 are arranged in an array, that is, the length of the cylinder in the axial direction is longer than the length in the direction perpendicular to the axial direction on the plane parallel to the back surface. Is also getting longer.

  According to the back-illuminated light receiving element 200 of this embodiment, the direction in which the light receiving portions 205 are integrated in an array is the axial direction of the cylinder of the microlens 202, and in this direction, the thickness of the lens is It does not change and has no refractive power. Therefore, even if the intervals between the light receiving portions 205 are close to each other, unlike a normal microlens having a curved surface in this direction, the lens is not distorted in this direction.

  Thus, the microlens 202 of the present embodiment does not have refractive power in the axial direction of the cylinder. However, as shown in FIGS. 3 to 5, the shape of the light receiving portion 205 is elongated in the axial direction of the cylinder. For this reason, the microlens 202 has an effect that the coupling tolerance against the positional deviation of the incident light in the axial direction of the cylinder can be kept large.

  Further, the microlens 202 of the present embodiment has a refractive power with respect to the direction perpendicular to the axis of the cylinder, similar to a normal spherical microlens. For this reason, it has the effect of expanding the coupling tolerance in the same way as a normal spherical microlens, and the coupling tolerance with the incident light is expanded while the width of the light receiving unit 205 in this direction is narrowed to keep the element capacitance small. There is an effect that can be done.

  Next, as an example of the present embodiment described above, a manufacturing process of a back-illuminated light receiving element will be described.

  FIG. 6 shows a state in which a stripe-like etching mask is formed on the semiconductor substrate side of the back-illuminated light receiving element. In this embodiment, first, an etching mask 302 having a predetermined width made of a SiO film is formed on the back surface of the semiconductor substrate 301 constituting the back-illuminated light receiving element 200. On the surface side inside the semiconductor substrate 301 on which the etching mask 302 is formed, the light receiving portions 303 are formed at predetermined intervals on the center line of the stripe. In the light receiving unit 303, the direction of the center line is a longitudinal direction, and the length in the direction of the center line is 2 to 4 times the length in the direction parallel to the back surface and perpendicular to the axial direction. It has become. Of course, the length ratio may be smaller or larger.

  FIG. 7 shows a cross section in the AA direction shown in FIG. 6 of the back-illuminated light receiving element in this manufacturing stage. FIG. 8 shows a cross section in the BB direction shown in FIG. 6 of the back-illuminated light receiving element in this manufacturing stage. On the upper side (rear surface side) of the semiconductor substrate 301, an etching mask 302 made of an SiO film is formed with a predetermined thickness. The etching mask 302 is formed by patterning by a normal photolithography process after a SiO film is formed on the semiconductor substrate 301 by a CVD (Chemical Vapor Deposition) method. Here, the longitudinal direction of the stripe of the SiO film constituting the etching mask 302 is made to coincide with the direction in which the light receiving portions 303 are integrated in an array.

  In the back-illuminated light receiving element 200, the light receiving portion 303 can be manufactured in the same manner as a conventional semiconductor light receiving element. Therefore, the description of the manufacture of the light receiving portion 303 prior to the formation of the etching mask 302 is omitted.

  FIG. 9 shows a state in which striped mesas are formed after wet etching. Here, Mesa is a term that means a table-like plateau formed by erosion. When etching is performed with an etching solution (not shown) in a state where the anticorrosion etching mask 302 is formed on the semiconductor substrate 301 as shown in FIGS. 6 to 8, stripe-like mesas are formed. Thereafter, when the SiO film as the etching mask 302 is removed, the state shown in FIG. 9 is obtained. That is, the portion where the etching mask 302 was present in FIG. 6 is a flat surface 311 without being etched, and slopes (forward mesa surfaces) 312 and 312 forming obtuse angles with this surface 311 are formed on both sides thereof. As a whole, the forward mesa is configured.

  FIG. 10 shows a cross section of the back-illuminated light receiving element in the AA direction shown in FIG. FIG. 11 shows a cross-section in the BB direction shown in FIG. 9 of the back-illuminated light receiving element in this manufacturing stage. As a first step for obtaining the cross-sectional shape of the microlens as shown in FIG. 4, slopes 312 and 312 are formed so as to spread on both sides of the flat surface 311. For this reason, the etching solution for etching the semiconductor substrate 301 is adjusted to a relatively low concentration so that a good forward mesa surface is easily formed.

  When the forward mesa shown in FIGS. 9 to 11 is configured, the back side of the back-illuminated light receiving element is etched again. At this time, the etching solution is higher than the etching solution when the mesa is formed in the previous step so that the crystal plane bent in a flat shape such as a forward mesa surface is smoothed into one curved surface and etched. Adjust to density. As a result, the corner of the forward mesa surface having a trapezoidal cross section is taken, and a cylindrical microlens as shown in FIG. 4 is formed. As a result, the light receiving unit 303 is disposed at the focal position of the cylindrical lens.

  As described above, according to the back-illuminated type light receiving element of this embodiment, the forward mesa surface is first formed as shown in FIG. 10, and the microlens is manufactured by etching based on the forward mesa surface. . For this reason, there is an effect that it is possible to satisfactorily obtain an ideal cylindrical surface shape in which the lens thickness does not change in the axial direction of the cylinder as the direction in which the light receiving portions 303 are integrated in an array.

  <Possibility of modification of embodiment>

  In the embodiment described above, the etching mask 302 is formed once on the semiconductor substrate 301 to form the forward mesa, and the microlens is formed based on this. In addition to this, a method of performing etching a plurality of times using etching masks having different widths is also effective. For example, a first etching mask having a relatively wide width is used for the first etching, and a second etching mask having a relatively narrow width is formed on the upper surface of a forward mesa surface having a trapezoidal cross section. The second etching may be performed after use. A cylindrical microlens can be manufactured by smoothing the stepwise forward mesa surface thus formed with an etching solution having a relatively high concentration.

  In addition, a resist pattern having a relatively low viscosity is formed on, for example, three rows in the axial direction of a cylinder as a direction in which the light receiving portions are integrated in an array, and a resist pattern having a relatively high viscosity is formed on a semiconductor substrate on a plane. Etching may be performed after being formed so as to overlap each row. In the initial stage of etching by this, a highly viscous resist pattern functions as a mask. As a result, etching with small side etching is performed. When the etching progresses and the highly viscous resist pattern is removed by side etching, the less viscous resist pattern now functions as a mask. As a result, a large amount of side etching is performed, and a cylindrical microlens can be manufactured.

  In addition to the above-described embodiments and modifications, it is natural that microlenses having a cylindrical shape can be manufactured by various methods.

  In the embodiments and the modifications, the microlens is described as a lens having a shape cut in the axial direction of the cylinder, but the cylinder here does not need to be a perfect circle. Although it is ideal to form a curved surface as a lens, even if the curved surface is partially distorted during the etching process, it may be any shape that contributes to the convergence of light. The focal position of the microlens may be a position that functions as a focal point as pointed out in the related art.

  In addition, the semiconductor substrate may be made of any material as long as it transmits the wavelength of incident light.

  By the way, in the embodiment and the modification, the case where a plurality of light receiving elements are integrated in a line in an array has been described. Such a back-illuminated light receiving element 200 can be used, for example, for a purpose of simultaneously receiving a plurality of light beams emitted from a planar quartz waveguide having a plurality of light emitting ends arranged in a line at a relatively narrow fixed interval. it can. In such an application, since the coupling tolerance can be kept large when connecting with the optical component, the adjustment can be easily realized.

  For example, when receiving optical signals from a group of optical fibers arranged in multiple layers to the corresponding light receiving elements, use a back-illuminated light receiving element in which a plurality of light receiving elements are arranged in a matrix. Is also possible. In such a case, the arrangement of the array of light receiving elements described in the embodiments and modifications may be a back-illuminated light receiving element in a form in which the light receiving elements are arranged in a plurality of rows at intervals.

DESCRIPTION OF SYMBOLS 10,200 Back-illuminated type light receiving element 11 Light receiving element 12, 202 Micro lens 20 Manufacturing method of back-illuminated type light receiving element 21 Light receiving element formation step 22 Mesa formation step 23 Lens shaping step 201, 301 Semiconductor substrate 205, 303 Light receiving part 302 Etching Mask 311 Flat surface 312 Slope (forward mesa surface)

Claims (10)

A plurality of semiconductor plates each having a longitudinal direction in a specific direction of the first surface in an internal space in contact with the surface on the front side as the first surface of the flat semiconductor substrate, and arranged at a certain interval in the specific direction A light receiving element,
A partial cylinder obtained by cutting a cylinder having a predetermined curved surface with the specific direction as an axial direction and a plane parallel to the axial direction as a second surface facing the first surface so that the light receiving element is in a focal position. A back-illuminated light receiving element comprising: a cylindrical microlens formed on a back surface.   The back-illuminated light receiving element according to claim 1, wherein the microlens is formed integrally with the semiconductor substrate by etching.   The back-illuminated light receiving element according to claim 1, wherein the plurality of light receiving elements are arranged in a line in the specific direction.   2. The back-illuminated type according to claim 1, wherein the plurality of light receiving elements form a row in the specific direction and are arranged in a plurality of rows in a direction orthogonal to the specific direction in the first plane. Light receiving element.   The length in the longitudinal direction of the light receiving surface of the light receiving element is 2 to 4 times the length in the short direction perpendicular to the first surface. The back-illuminated light receiving element according to 1. A plurality of light receiving elements having a longitudinal direction in a specific direction of the first surface and having a certain interval in the specific direction in an internal space in contact with the surface on the front side as the first surface of the flat semiconductor substrate. A light receiving element forming step to be formed;
A mesa forming step of forming a stripe-shaped forward mesa along the specific direction at a position facing the position where the plurality of light receiving elements are formed on the back surface as the second surface facing the first surface;
And a lens forming step for forming a cylindrical surface into a cylindrical microlens having the light receiving element as a focal position, with the surface curved so as to take the corner of the forward mesa formed in the mesa forming step. Manufacturing method of incident type light receiving element.   7. The method of manufacturing a back-illuminated light receiving element according to claim 6, wherein in the lens forming step, the surface is curved so as to take a corner of the forward mesa by wet etching.   The mesa forming step includes a mask forming step of forming a striped etching mask along the specific direction at a position facing the position where the plurality of light receiving elements are formed, and an upper surface of the etching mask formed in the mask forming step. The method of manufacturing a back-illuminated light receiving element according to claim 6, further comprising:   7. The method of manufacturing a back-illuminated light receiving element according to claim 6, wherein the mesa forming step is a step of forming one or more mesa molds.   7. The method of manufacturing a back-illuminated light receiving element according to claim 6, wherein an etching rate of the etching solution in the mesa forming step is adjusted to be slower than an etching rate of the etching solution in the lens forming step. .

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