JP2007305690A - Element for solid-state image sensing device and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an element for solid-state image sensing device and a method for manufacturing the same for eliminating damage of a waveguide due to plasma and generation of particle during dry etching in the step of forming a waveguide, reducing the steps of photolithography, etching, embedding, and flattening, and simultaneously achieving simplification of element manufacturing step and shortening of manufacturing period. <P>SOLUTION: The element for solid-state image sensing device is provided with a light sensor that is formed on the principal surface of a semiconductor substrate to execute photoelectric conversion by receiving the light at the front surface thereof, and an insulating film provided on the principal surface of the semiconductor substrate. A part of the insulating film is defined as a waveguide region for guiding an incident light from the external side to the light sensor for the entire part in the thickness of the insulating film. In the insulating film explained above, the waveguide region has a refractive index higher than that of the non-waveguide region, and the waveguide region has a distribution of refractive index that gradually becomes high toward the center axis from the circumferential edge in the principal surface direction of the substrate. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an element for a solid-state imaging device and a method for manufacturing the same, and more specifically to an element for a solid-state imaging device including an insulating film in which a waveguide region is formed at a portion facing a light receiving portion and a method for manufacturing the same. It is.

  In recent years, some solid-state imaging device elements use a waveguide as means for increasing the light collection efficiency (see, for example, Patent Document 1). The waveguide is formed for each element for a solid-state imaging device, that is, for each pixel cell. The waveguide is provided on a light receiving portion that receives light and performs photoelectric conversion, and is formed of an insulating film. An on-chip lens is provided on this waveguide. By adopting the waveguide structure, the light condensed by the on-chip lens can be efficiently incident on the light receiving unit.

  FIG. 3 is a cross-sectional view showing a conventional example of a solid-state imaging device element having a waveguide. As illustrated in FIG. 3, the solid-state imaging device element 200 including a waveguide includes a semiconductor substrate 115, and a light receiving unit 101 that functions as a photodiode is formed on a main surface portion 114 thereof. On the main surface portion 114, a gate insulating film 102, an element isolation insulating film 103, and a stopper SiN film 104 are provided. An insulating film 105 is provided on the gate insulating film 102, the element isolation insulating film 103, and the stopper SiN film 104. The stopper SiN film 104 functions as an etching stopper when the insulating film 105 provided on the film 104 is etched. A transfer gate 106, a multilayer wiring 107, and a conductive plug 108 are embedded in the insulating film 105. The transfer gate 106 is for reading signal charges from the light receiving unit 101 and transferring the read charges. The conductive plug 108 electrically connects the wirings 107 arranged in multiple layers. A waveguide 109 made of a light transmissive material is formed over the entire thickness direction of the insulating film 105 at a portion of the insulating film 105 facing the light receiving portion 101. A passivation film 110, a planarization film 111, and a color filter 112 are sequentially stacked on the insulating film 105 and the waveguide 109, and an on-chip lens 113 is provided on the color filter 112.

  In such an element 200 for a solid-state imaging device, the waveguide 109 has an order in which the size in plan view seen from the light incident direction (upward in FIG. 3) gradually decreases from the light incident side toward the light receiving unit 101 side. Tapered shape.

  In the method for manufacturing the element 200 for the solid-state imaging device, the step of providing the insulating film 105 on the main surface portion 114 on which the light receiving portion 101 is formed, and the thickness of the insulating film 105 at the portion facing the light receiving portion 101 in the insulating film 105. A step of forming a hole over the entire direction, and a step of forming a waveguide 109 by embedding a light-transmitting material in the hole. The waveguide 109 can guide incident light from the outside to the light receiving unit 101. Note that, in the step of forming the hole, the resist opening of the photoresist patterning provided on the insulating film 105 is formed in a forward tapered shape. Thus, when the insulating film 105 is etched to form a hole, the forward tapered shape of the resist opening is transferred to the insulating film 105.

  In the step of forming the hole, anisotropic etching is performed. That is, the etching is performed under the condition that the forward tapered shape can be formed while suppressing the isotropic etching. As a result, a forward tapered hole is formed in which the size in plan view as viewed from the light incident direction gradually decreases from the light incident side toward the light receiving unit 101.

A waveguide 109 is formed in this hole by depositing a light transmitting material (typically a silicon oxide film) using a CVD method using high density plasma or the like. When the hole has a forward tapered shape, the front end of the hole (that is, the uppermost part of the hole) is widened. For this reason, even if the light-transmitting material for constituting the waveguide 109 tends to be deposited near the opening, the opening is not blocked when the light-transmitting material is embedded in the hole. Further, even if the size of the light receiving portion 101 per pixel is reduced by increasing the number of pixels, that is, by increasing the pixel density, it is possible to increase the light collection area. Even when the wiring 107 or the like is disposed near the light receiving unit 101 in the vicinity of the light receiving unit 101, incident light is transmitted to the wiring 107 or the like because the light receiving unit 101 side of the waveguide 109 is constricted. It becomes difficult to interfere with. Thereby, it is possible to prevent the wiring 107 from obstructing the light collection of the light receiving unit 101.
JP 2004-221532 A

  A method of manufacturing the waveguide 109 in the above-described conventional solid-state imaging device element 200 will be described in more detail. After the wiring 107 is formed inside the insulating film 105, a resist pattern is formed on the insulating film 105 by photolithography. Next, using the resist pattern as a mask, the insulating film 105 is etched to the front of the light receiving portion 101 by anisotropic dry etching to form a truncated cone-shaped hole as shown in FIG. Next, after providing a highly reflective material film made of a metal such as aluminum on the inner wall of the hole, a silicon oxide film is laminated and filled as a waveguide material in the hole, or directly without providing a highly reflective material film. The high refractive material is laminated and filled. Thereby, the waveguide 109 is formed.

  After stacking and filling a silicon oxide film as a waveguide material, an excess silicon oxide film on the surface of the waveguide is removed by a CMP (Chemical Mechanical Polish) method or an etch back method to planarize the surface.

  Therefore, conventionally, the process of forming the hole and the waveguide 109 and the process of flattening the surface are necessary, and it is difficult to shorten the manufacturing time and simplify the manufacturing process, which results in a problem that the wafer cost increases. Further, when the waveguide 109 is formed, a hole is formed by dry-etching the section from the surface of the insulating film 105 to the surface of the light receiving unit 101, so that the surface of the hole is roughened and incident on the rough surface. When the light is reflected, the light collection efficiency may decrease due to light scattering. Further, when the hole portion is filled, if the aspect ratio of the hole portion is high, voids may be generated in the filling material, resulting in variation in light collection. In addition, since the plasma CVD method is used for filling the holes, the plasma may induce crystal defects or the like of the light receiving unit 101, and white scratches or dark current may occur. Further, in the mask formation process for forming the hole, it is necessary to reduce a margin for misalignment in mask positioning in order not to cut the lower layer wiring 107. If a mask is disposed at a position exceeding the allowable margin for misalignment and etching is performed, the wiring layer 107 may be scraped, and as a result, particles may be generated. Wiring layer scraping and particle generation increase wiring resistance and cause image defects.

  In view of the above circumstances, the present invention reduces the number of steps such as photolithography, etching, embedding, planarization, etc. without incurring image defects caused by damage to the light receiving part due to plasma and generation of particles during etching, An object of the present invention is to provide an element for a solid-state imaging device that can improve the light collection efficiency by forming a waveguide without voids in an insulating film, and can ensure the reliability of the element, and a method for manufacturing the same. To do.

  In order to achieve the above object, an element for a solid-state imaging device according to the present invention is provided on a main surface portion of a semiconductor substrate and is provided on a main surface portion of the semiconductor substrate, and a light receiving portion that receives light on the surface and performs photoelectric conversion. And a part of the insulating film serves as a waveguide region for guiding incident light from the outside to the light receiving portion over the entire thickness direction of the insulating film, and the waveguide is included in the insulating film. The region has a refractive index higher than that of the non-waveguide region, and the waveguide region has a refractive index distribution in which the refractive index gradually increases from the peripheral portion toward the central axis portion in the main surface direction of the substrate.

  According to the present invention, the refractive index of the waveguide region gradually decreases from the central axis portion to the peripheral portion. Accordingly, the waveguide region has a refractive index distribution similar to that of the core of the graded index optical fiber. Therefore, the light incident obliquely into the waveguide region travels while repeating total reflection on the wave-like path toward the light receiving portion in the waveguide region. Further, the light incident in the axial direction of the waveguide region travels straight toward the light receiving unit. Therefore, incident light is efficiently condensed on the light receiving part without causing energy loss. Therefore, a highly sensitive solid-state imaging device element can be provided.

  In the present invention, the waveguide region can be formed by irradiating the insulating film with laser light. Since it is not necessary to use plasma in forming the waveguide region, there is no damage to the light receiving portion due to the plasma. In addition, since it is not necessary to perform etching for forming the waveguide region, image defects due to generation of particles during etching are not caused, and light collection efficiency is not reduced due to roughness of the reflection surface due to etching. In addition, since the waveguide region can be formed by irradiating the insulating film with laser light, the number of steps such as photolithography, etching, embedding, and planarization can be reduced, and a waveguide region without voids can be formed. Can do.

  In the present invention, the insulating film is preferably made of an undoped silicon oxide film. In the present invention, the insulating film is preferably made of a silicon oxide film doped with at least one of phosphorus, fluorine, and boron.

  With such an insulating film, it is possible to more reliably form a high-quality waveguide region that can guide incident light to the light receiving portion without loss by irradiating the insulating film with laser light. .

  The method for manufacturing an element for a solid-state imaging device according to the present invention includes a step of forming a light receiving portion for performing photoelectric conversion by receiving light on a main surface portion of a semiconductor substrate, and an insulating film on the main surface portion of the semiconductor substrate. And a step of condensing and irradiating a portion of the insulating film facing the light receiving portion with a laser beam. In the condensing irradiation step, the condensing position extends over the entire thickness direction of the insulating film. Is continuously changed in the thickness direction, the refractive index inside the insulating film is increased, and a waveguide region is formed in a part of the insulating film.

  According to the present invention, the waveguide region is formed by irradiating the insulating film with laser light. Since it is not necessary to use plasma in forming the waveguide region, there is no damage to the light receiving portion due to the plasma. In addition, since it is not necessary to perform etching for forming the waveguide region, image defects due to generation of particles during etching are not caused, and light collection efficiency is not reduced due to roughness of the reflection surface due to etching. In addition, since the waveguide region is formed by irradiating the insulating film with laser light, the number of steps such as photolithography, etching, embedding, and planarization can be reduced, and a waveguide region without voids can be formed.

  The refractive index of the waveguide region formed according to the present invention gradually decreases from the central axis portion to the peripheral portion. Accordingly, the waveguide region has a refractive index distribution similar to that of the core of the graded index optical fiber. Therefore, the light incident obliquely on the waveguide region travels while repeating total reflection on the wave-like path toward the light receiving portion in the waveguide region. Further, the light incident in the axial direction of the waveguide region travels straight toward the light receiving unit. Therefore, incident light is efficiently condensed on the light receiving part without causing energy loss. Therefore, a highly sensitive solid-state imaging device element can be obtained.

In the present invention, the peak power of the laser beam at the condensing position is preferably 105 W / cm ² or more, and the laser beam is preferably a femtosecond pulse laser beam having a repetition frequency of 100 kHz or more.

  By using such laser light, it is possible to more reliably form a high-quality waveguide region that can guide incident light to the light receiving unit without loss.

  In the present invention, the insulating film is preferably made of an undoped silicon oxide film. In the present invention, the insulating film is preferably made of a silicon oxide film doped with at least one of phosphorus, fluorine, and boron.

  By using such a material, a waveguide with small optical loss can be formed more reliably.

  According to the element for a solid-state imaging device according to the present invention, the light incident obliquely into the waveguide region through the on-chip lens travels while repeating total reflection along the wave path toward the light receiving unit. Therefore, incident light is efficiently condensed on the light receiving part without causing energy loss. Therefore, a highly sensitive solid-state imaging device element can be provided. In addition, according to the method for manufacturing a solid-state imaging device element according to the present invention, the solid-state imaging device element can be obtained with certainty. In addition, the number of processes such as photolithography, etching, embedding, and planarization is reduced without causing damage to the light receiving portion due to plasma and image defects due to generation of particles during etching, and a waveguide region without voids. It can be formed to improve the light collection efficiency. Further, the reliability of the element can be ensured by suppressing the occurrence of wiring scraping.

(First embodiment)
Hereinafter, embodiments of the element for a solid-state imaging device of the present invention will be described. FIG. 1 is a cross-sectional view showing an element for a solid-state imaging device according to the first embodiment of the present invention. As shown in FIG. 1, the solid-state imaging device element 100 includes a light receiving unit 1 and an insulating film 5 as main components. The light receiving portion 1 is formed in the main surface portion 18 of the semiconductor substrate 17 and receives light on the surface to perform photoelectric conversion. The insulating film 5 is provided on the main surface portion 18 of the semiconductor substrate 17. A part of the insulating film 5 extends over the entire thickness direction of the insulating film 5 and a waveguide region 9 (region sandwiched between two broken lines in FIG. 1) for guiding incident light from the outside to the light receiving unit 1. Has been. In the insulating film 5, the waveguide region 9 has a higher refractive index than the non-waveguide region. The waveguide region 9 has a refractive index distribution in which the refractive index gradually increases from the peripheral portion toward the central axis portion in the main surface direction of the substrate 17. This refractive index distribution is the same as the refractive index distribution of the core of the graded index optical fiber.

  The light receiving unit 1 is, for example, a photodiode. A gate insulating film 2 and an element isolation insulating film 3 are provided on the main surface portion 18. An antireflection film 4 (SiN film) is provided on the gate insulating film 2. The antireflection film 4 covers the surface of the light receiving unit 1 through the surface P-type layer 14 and the gate insulating film 2. The antireflection film 4 is provided at a position facing the surface P-type layer 14 on the light receiving unit 1. The insulating film 5 is provided on the gate insulating film 2, the element isolation insulating film 3, and the antireflection film 4. In the insulating film 5, a transfer gate 6, multilayer wirings 7a to 7d, and a conductive plug 8 are provided. The transfer gate 6 is necessary for reading signal charges from the light receiving unit 1 and transferring the read signals. The conductive plug 8 connects the wirings 7a to 7d arranged in multiple layers.

The insulating film 5 is made of a light transmissive material having insulating properties. A silicon oxide film can be mainly applied to the light transmissive material. A waveguide region 9 is formed at a portion of the insulating film 5 facing the light receiving portion 1. The shape of the waveguide region 9 is not particularly limited. For example, the waveguide region 9 may have a column shape extending in the thickness direction over the entire thickness direction of the insulating film 5, and preferably a columnar shape or a quadrangular column shape. be able to. In the main surface direction of the semiconductor substrate 17, the waveguide region 9 has a light refractive index that gradually increases from the peripheral edge toward the central axis. Although the optical refractive index of the waveguide region 9 is not particularly limited, for example, when the refractive index of the non-waveguide region of the insulating film 5 is about 1.450, the refractive index near the central axis of the waveguide region 9 The rate can be set about 1 × 10 ⁻³ higher than this value. The optical refractive index of the waveguide region 9 decreases as the distance from the central axis portion increases, and becomes closer to the refractive index of the non-waveguide region of the insulating film 5. The peripheral portion of the waveguide region 9 has the same refractive index as that of the non-waveguide region. This means that there is no clear interface between the waveguide region 9 and the non-waveguide region. A method for manufacturing the waveguide region 9 will be described later. An on-chip lens 13 is provided on the upper surface of the insulating film 5 via a passivation film 10, a planarizing film 11, and a color filter 12.

  By adopting such a structure for the waveguide region 9, the core-like portion (that is, the waveguide region 9) which is a region having a high refractive index and transmits light and a region having a low refractive index other than the core-like portion are used. As described above, there is no clear interface between certain clad portions (that is, non-waveguide regions). The core-like portion and the clad-like portion correspond to the core and the clad of the graded index optical fiber, respectively. Therefore, the light incident on the waveguide region 9 from the outside via the on-chip lens 13 enters the light receiving unit 1 as it goes straight in the central axis direction of the waveguide region 9. On the other hand, light incident obliquely with respect to the central axis of the waveguide region 9 proceeds through a wave-like path while repeating total reflection inside the waveguide region 9 as in the case of the graded index optical fiber, and receives the light receiving unit 1. (See FIG. 1). Total reflection has zero energy loss, so no loss due to reflection occurs. Further, as will be described later, the waveguide region 9 is formed by irradiating the insulating film 5 with laser light, and it is not necessary to use etching and plasma CVD methods for the formation. Therefore, in this embodiment, energy loss does not occur when incident light is reflected in the waveguide region 9 and when photoelectric conversion is performed in the light receiving unit 1, and the light collection efficiency is improved as compared with the buried waveguide of the conventional example.

  That is, the conventional waveguide 109 shown in FIG. 3 is formed by forming a hole in the insulating film 105 and embedding a high refractive index material in the hole, and the high refractive index material and the low refractive index outside the high refractive index material. It was the structure which reflected in the interface with material. For this reason, when the aspect ratio of the hole portion becomes high, voids are generated in the material when the high refractive index material is embedded in the hole portion, and light scattering occurs in interface reflection, which often reduces the light collection efficiency. . Further, the etching at the time of forming the hole portion causes roughness on the inner surface of the hole portion, and this roughness causes light scattering. Further, plasma in the plasma CVD method has damaged the light receiving portion 101. On the other hand, this embodiment does not cause such inconvenience.

The impurity concentration of the light receiving unit 1 may be in a range where photoelectric conversion can be performed, but the impurity concentration of the light receiving unit 1 is preferably about 10 ¹⁵ to 10 ¹⁶ cm ⁻³ . Moreover, it is preferable that the thickness of the light-receiving part 1 is about 0.5-2.0 micrometers. In the present embodiment, in order to reduce the dark output of the light receiving unit 1, a surface P-type layer 14 which is a shallow P ⁺⁺ type semiconductor region is formed on the surface of the light receiving unit 1. The impurity concentration of the surface P-type layer 14 is preferably 10 ¹⁸ to 10 ¹⁹ cm ⁻³ . Thus, the light receiving unit 1 is configured as an embedded photodiode. The surface P-type layer 14 may not be provided.

  The antireflection film 4 is provided at a position facing the light receiving unit 1 on the surface of the gate insulating film 2 provided so as to cover the light receiving unit 1. The thickness of the antireflection film 4 is not particularly limited, but the wavelength of light that can prevent reflection differs depending on the thickness. For example, an SiN film (refractive index is about 2.000) can be used as the antireflection film 4, and the antireflection film 4 can be provided on the surface of the gate insulating film 2. In this case, if the thickness of the antireflection film 4 is 40 to 60 nm, reflection of light having a wavelength of 550 nm can be most effectively suppressed.

  The insulating film 5 can be composed of, for example, an undoped silicon oxide film. As a specific example, an NSG (NonDoped Silicate Glass) film can be used. In addition, the insulating film 5 can also be composed of, for example, a silicon oxide film doped with at least one of phosphorus, fluorine, and boron. As a specific example, it can be composed of any one of a BPSG (Boron Phosphorous Silicate Glass) film, an FSG (Fluorine Silicate Glass) film, and a PSG (Phosphorous Silicate Glass) film. The insulating film 5 can be formed by depositing a film by, for example, an atmospheric pressure CVD method. Inside the insulating film 5, first-layer wirings 7a and 7b made of a metal material such as aluminum are provided. Second-layer wirings 7c and 7d are provided above the first-layer wirings 7a and 7b. The second-layer wirings 7 c and 7 d also function as a light shielding film for preventing light from entering a region other than the region where the light receiving unit 1 is formed in the semiconductor substrate 17.

  Further, a passivation film 10 is provided as a protective film that covers the surface of the insulating film 5. The passivation film 10 can be composed of, for example, a silicon nitride film. A planarizing film 11 is provided on the surface of the passivation film 10. The planarization film 11 can be composed of, for example, an acrylic transparent film. A color filter 12 is provided on the surface of the planarizing film 11. For the color filter 12, for example, primary (red), green (G), and blue (B) filters are used to obtain a color imaging signal.

  Furthermore, an on-chip lens 13 is provided on the surface of the color filter 12 as a condensing optical element. The curvature of the on-chip lens 13 is set so that light transmitted through the on-chip lens 13 is condensed into the waveguide region 9. The surface of the on-chip lens 13 is formed in, for example, a spherical shape or a bowl shape.

  As will be described later, since the waveguide region 9 is formed by irradiating the insulating film 5 with laser light, the waveguide region 9 is not formed in a range not affected by the laser light. Therefore, if the wirings 7a to 7d are provided in a range not affected by the laser light, the wirings 7a to 7d are necessarily located in the non-waveguide region. In this case, there is no light shielding object inside the waveguide region 9. Therefore, the light incident on the waveguide region 9 is not reflected by the wirings 7a to 7d inside the non-waveguide region, or is not likely to go around to the adjacent pixels. Also in this point, this embodiment can improve the sensitivity characteristic of the element for solid-state imaging devices.

  Next, a method for manufacturing the element for solid-state imaging device according to the present embodiment will be described with reference to FIGS. 2A to 2D.

  2A to 2D are views showing a method of manufacturing the element for the solid-state imaging device shown in FIG. 1 in the order of steps. FIG. 2A is a cross-sectional view showing a first step of the manufacturing method.

  In the first step, as shown in FIG. 2A, first, the light receiving portion 1 is formed in the main surface portion 18 of the P-type semiconductor substrate 17. The light receiving unit 1 is formed as an N-type impurity diffusion region. The light receiving unit 1 is formed by injecting N-type impurities into a predetermined range from the surface of the P-type semiconductor substrate 17 and thermally diffusing the injected impurities. Thereafter, a P-type impurity is implanted into the surface portion of the formed N-type impurity diffusion region and thermally diffused to form a surface P-type layer 14 that is a P-type impurity diffusion region. As a result, a photodiode having a PNP junction structure is formed from the surface P-type layer 14, the N-type light receiving unit 1, and the P-type semiconductor substrate 17.

  Next, the gate insulating film 2 is provided on the main surface portion 18 of the P-type semiconductor substrate 17. A transfer gate 6 is provided on the gate insulating film 2. The transfer gate 6 is formed by depositing a polycrystalline silicon film on the entire surface of the gate insulating film 2 to a predetermined thickness and then selectively patterning the polycrystalline silicon film.

  Next, an antireflection film 4 is provided on the gate insulating film 2 at a position facing the light receiving portion 1. In the present embodiment, a silicon nitride film is provided as an example of the antireflection film 4. When silicon nitride is used as the antireflection film 4, light reflection can be effectively suppressed. In particular, when the thickness of the antireflection film 4 is set to 40 to 60 nm and the thickness of the gate insulating film 2 is set to 10 to 30 nm, reflection of light having a wavelength of 550 nm can be most effectively suppressed. When the thickness of the gate insulating film 2 is smaller than 10 nm, a silicon oxide film may be further provided between the antireflection film 4 and the gate insulating film 2.

The antireflection film 4 can be formed by depositing silicon nitride with a predetermined thickness on the entire surface of the gate insulating film 2 at a reaction temperature of 700 to 800 ° C. according to a hot wall low pressure CVD method. The chemical reaction in this case is as shown in the following reaction formula (1).
3SiH ₂ Cl ₂ + 4NH ₃ → Si ₃ N ₄ + 6HCl + 6H ₂ (1)

Next, a part of the silicon nitride is removed by photolithography and a wet etching method using H ₃ PO ₄ or a dry etching method using a fluorine-based gas such as CF ₄ or C ₂ F ₆ , so that FIG. The pattern of the antireflection film 4 as shown in FIG.

  FIG. 2B is a cross-sectional view showing a second step following FIG. 2A. As shown in FIG. 2B, a first insulating film 5a is provided on the gate insulating film 2 by, for example, atmospheric pressure thermal CVD. The material of the first insulating film 5a is not particularly limited. For example, a BPSG (Boron Phosphorous Silicate Glass) film can be used. Thereafter, the insulating film 5a is annealed at 650 ° C. to remove impurities such as moisture in the insulating film 5a.

  The surface of the first insulating film 5a is planarized by the CMP method. Thereafter, a contact hole is formed in the first insulating film 5a by anisotropic dry etching. Thereafter, a contact hole is filled with W (Tungsden), and the surface is planarized by an etch back method or a CMP (Chemical mechanical polish) method, thereby forming the conductive plug 8. Next, first-layer wirings 7a and 7b made of aluminum are provided by a method similar to a normal CMOS manufacturing process. Next, a second insulating film 5b is provided on the first insulating film 5a by a plasma CVD method. Thereafter, the surface of the second insulating film 5b is planarized. Second-layer wirings 7c and 7d made of aluminum are provided on the second-layer insulating film 5b. If the plasma CVD method is used for the second or more layers, the plasma does not affect the light receiving unit 1. Next, a third-layer insulating film 5c is provided on the second-layer insulating film 5b by, for example, plasma CVD. Thereafter, the surface of the third insulating film 5c is planarized.

FIG. 2C is a cross-sectional view showing a third step following FIG. 2B. As shown in FIG. 2C, in the insulating films 5a-5c facing the light receiving portion 1, there is no waveguide forming portion 15 other than the insulating films 5a-5c (no wiring or the like). is doing. The passivation film 10 (see FIG. 2D) is not yet provided. In this state, laser light is irradiated into the portion 15 from the surface of the waveguide forming portion 15. Specifically, the laser light is condensed and applied to the portion between the surface of the waveguide forming portion 15 and the surface of the light receiving portion 1 through a lens or the like. During the focused irradiation, the focused position is continuously changed in the thickness direction of the insulating films 5a to 5c (vertical direction in FIG. 2C). As a result, a light-induced refractive index change is caused in the waveguide forming portion 15 and the refractive index of the portion 15 is increased by about 10 ⁻³ . This increased refractive index portion becomes the waveguide region 9. The laser used here is a pulse laser.

  The phenomenon in which the refractive index changes due to irradiation with a pulsed laser is called photoinduced refractive index change. Silica glass to which P (phosphorus) or the like is added is known as a material that causes a photoinduced refractive index change. This phenomenon is caused by the existence of oxygen defects having an intrinsic absorption wavelength region in the ultraviolet region in the glass, and a partial change in the structure of oxygen defects by irradiating the glass with an absorption wavelength laser beam. The result is believed to be due to the glass becoming dense and the refractive index increasing. In order to appropriately collect and irradiate laser light, when the original beam diameter is 50 to 500 μm, it is usually preferable to change the spot diameter from several μm to several tens of μm using a condensing lens. The spot diameter can be appropriately changed according to the type of laser used.

When the insulating films 5a to 5c are focused and irradiated with laser light, the peak power at the focused position is preferably 105 W / cm ² or more. It is desirable to use femtosecond pulsed laser light having a repetition frequency of 100 kHz or more. The laser beam irradiation time (pulse width) in one pulse is preferably about 150 femtoseconds.

The peak power of the laser beam is a value obtained by converting a peak output (W) expressed by a ratio of output energy per pulse (J) / pulse width (seconds) per irradiation unit area. If the peak power is less than 105 W / cm ² , the light-induced refractive index change does not occur and the waveguide region 9 is not formed. The higher the peak power intensity, the more the light-induced refractive index change is promoted, and the waveguide region 9 is easily formed. However, it is difficult to practically obtain an excessively large amount of laser light. Therefore, it is preferable to use a pulse laser whose peak output is increased by narrowing the pulse width. The wavelength of the laser beam is not particularly limited as long as the above peak power is satisfied.

  When the condensing diameter (diameter) of the laser light is smaller than the diameter of the waveguide forming portion 15 at the time of laser light irradiation, the condensing position on the central axis of the waveguide forming portion 15 is set to the thickness of the insulating films 5a to 5c. Irradiation may be performed while moving in the direction. Alternatively, it is also possible to irradiate while changing the condensing position in the surface direction of the waveguide forming portion 15 while changing the condensing position in the thickness direction of the insulating films 5a to 5c. However, if the condensing diameter of the laser light is larger than the diameter of the waveguide forming portion 15, only the waveguide forming portion 15 may be irradiated with the laser light through the light shielding mask.

  FIG. 2D is a cross-sectional view showing a fourth step following FIG. 2C. As shown in FIG. 2D, the passivation film 10, the planarization film 11, the color filter 12, and the on-chip lens 13 are sequentially provided on the insulating film 5c, whereby the solid-state imaging device element 100 is completed.

  As described above, according to the method for manufacturing the element 100 for the solid-state imaging device according to the first embodiment, compared with the conventional method of forming the hole by etching and embedding the light transmissive material in the hole. Thus, it is possible to omit the steps of photolithography, anisotropic dry etching, silicon oxide film (light transmissive material) deposition and planarization. Therefore, it is possible to reduce the manufacturing process, the manufacturing time, and the associated wafer cost. Further, since the waveguide region 9 having the same refractive index distribution as that of the graded index optical fiber can be formed, incident light can be guided to the light receiving unit 1 without energy loss by total reflection. Further, unlike the conventional case, when forming the optical waveguide region, it is not necessary to dry-etch the section from the surface of the insulating film to the surface of the light receiving portion to form the hole, and it is not necessary to fill the hole by the plasma CVD method. Therefore, void generation in the waveguide, crystal defects in the light receiving portion, and the like are not induced, and it is possible to suppress reduction in light collection efficiency, generation of white flaws and dark current. Further, since anisotropic dry etching is not performed, it is possible to eliminate the wiring layer scraping and the generation of particles associated therewith. Therefore, the cause of the increase in wiring resistance and the occurrence of image defects is eliminated. Furthermore, since the process of anisotropic dry etching the section to the light receiving portion and then embedding the high refractive index material film is not performed, no void is generated even when the aspect ratio of the waveguide region 9 is increased. Therefore, it is possible to prevent variations in light collection due to voids. Furthermore, since it is not necessary to use a highly reflective material such as a metal in constructing the waveguide region 9, the material restrictions on the waveguide region are eliminated. In addition, since the waveguide region is formed through a relatively simple process of simply irradiating laser light, a high-performance solid-state imaging device element can be manufactured with high reproducibility.

  In the present embodiment, various film forming methods can be used for forming the insulating film 5. When using the CVD method, it is also possible to use a plasma CVD method in addition to the thermal CVD method. However, the film formation by plasma CVD is preferably used in the second and higher layers as in the above embodiment. This is because the plasma does not affect the light receiving unit 1 by being used in the second and higher layers.

  As described above, the present invention is useful for an element for a solid-state imaging device in which a waveguide region is formed on a light receiving portion, a manufacturing method thereof, and the like.

Sectional drawing of the element for solid-state imaging devices which concerns on the 1st Embodiment of this invention Sectional drawing which shows the manufacturing process (1st process) of the element for solid-state imaging devices shown by FIG. Sectional drawing which shows the manufacturing process (2nd process) following FIG. 2A. Sectional drawing which shows the manufacturing process (3rd process) following FIG. 2B. Sectional drawing which shows the manufacturing process (4th process) following FIG. 2C. Sectional drawing which shows an example of the element for conventional solid-state imaging devices

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light-receiving part 2 Gate insulating film 3 Element isolation insulating film 4 Antireflection film (SiN film)
5a to 5c insulating film 6 transfer gate 7a to 7d wiring 8 conductive plug 9 waveguide region 10 passivation film 11 planarizing film 12 color filter 13 on-chip lens 14 surface P-type layer 15 waveguide forming portion 16 incident optical path

Claims (7)

A light receiving portion that is formed in the main surface portion of the semiconductor substrate and receives light on the surface to perform photoelectric conversion;
An insulating film provided on a main surface portion of the semiconductor substrate,
A part of the insulating film serves as a waveguide region that guides incident light from the outside to the light receiving unit over the entire thickness direction of the insulating film,
In the insulating film, the waveguide region has a refractive index higher than that of the non-waveguide region, and has a refractive index distribution in which the refractive index gradually increases from the peripheral portion toward the central axis portion in the main surface direction of the substrate. Imaging device element.   2. The element for a solid-state imaging device according to claim 1, wherein the insulating film is made of an undoped silicon oxide film.   2. The element for a solid-state imaging device according to claim 1, wherein the insulating film is made of a silicon oxide film doped with at least one of phosphorus, fluorine, and boron. Forming a light receiving portion for performing photoelectric conversion by receiving light on the surface in the main surface portion of the semiconductor substrate;
Forming an insulating film on a main surface portion of the semiconductor substrate;
A step of condensing and irradiating a laser beam on a portion of the insulating film facing the light receiving portion,
In the condensing irradiation step, the refractive index inside the insulating film is increased by continuously changing the condensing position in the thickness direction over the entire thickness direction of the insulating film, and a part of the insulating film A method for manufacturing an element for a solid-state imaging device, in which a waveguide region is formed on the substrate. 5. The solid-state imaging according to claim 4, wherein a peak power of the laser beam at the condensing position is 105 W / cm ² or more, and the laser beam is a femtosecond pulse laser beam having a repetition frequency of 100 kHz or more. A method for manufacturing a device element.   5. The method of manufacturing an element for a solid-state imaging device according to claim 4, wherein the insulating film is made of an undoped silicon oxide film. 5. The method for manufacturing an element for a solid-state imaging device according to claim 4, wherein the insulating film is made of a silicon oxide film doped with at least one of phosphorus, fluorine, and boron.

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