JP2009124053A - Photoelectric converter and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain process works for efficiently collecting light incident on an optical waveguide, according to the position of pixels, at low cost. <P>SOLUTION: The photoelectric converter includes an imaging surface constituted of a plurality of pixels. Each of the plurality of pixels includes a photoelectric conversion part 6 and an optical waveguide, arranged on the light-incident side of the photoelectric conversion part 6 for guiding the incident light to the photoelectric conversion part 6. The optical waveguide includes a plurality of layers 3, 4, and 5 (31, 41, and 51 or 32, 42, and 52). The plurality of layers 3, 4, and 5 (31, 41, and 51 or 32, 42, and 52) in the optical waveguide are disposed more eccentric with the center of the imaging surface, the farther away the distance from the center of the imaging surface to the layers is. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a photoelectric conversion device used for a digital still camera or the like and a manufacturing method thereof.

  In recent years, a photoelectric conversion device used in a digital still camera or the like has been improved in price by increasing the number of pixels and improving the image quality, while reducing the chip size. For this reason, the size of one pixel constituting the photoelectric conversion device is decreasing year by year, and the area of the photoelectric conversion unit in the pixel is also decreasing accordingly. When the area of the photoelectric conversion unit is reduced, the light receiving sensitivity is lowered.

  On the other hand, Patent Document 1 discloses a photoelectric conversion device in which an optical waveguide is provided between a light incident surface and a photoelectric conversion unit to improve light collection characteristics. In this photoelectric conversion device, a symmetrical optical waveguide composed of a high refractive index material is provided on the light incident side of the photoelectric conversion unit, and a low refractive index material is provided around the optical waveguide, and all incident light is transmitted at the boundary surface. The light collecting characteristic is improved by reflecting the light. In addition, the optical axis of the microlens (on-chip lens) formed on each photoelectric conversion unit is shifted from the optical axis of the photoelectric conversion unit toward the center in the peripheral portion of the photoelectric conversion device. As a result, light incident obliquely is efficiently collected on the photoelectric conversion unit.

Patent Document 2 discloses a method of forming a well-shaped optical waveguide. The light incident on the micro lens on the surface enters the optical waveguide with a high refractive index through the protective layer disposed below the micro lens, and is condensed on the pixel.
JP-A-2005-259824 JP 2003-224249 A

  However, in the method of Patent Document 1, since a fine pattern less than the resolution of the exposure apparatus is formed on the photomask, it is very difficult to form an optical waveguide, and a desired structure cannot be formed, or the cost is high. End up.

  Further, the method of Patent Document 2 requires a step of forming holes in multiple stages, and depending on the depth of focus of the optical system, the patterning accuracy is lowered and the yield is lowered.

  The present invention has been made in view of the above problems, and an object thereof is to realize a process of efficiently condensing light incident on an optical waveguide at a low cost in accordance with the position of a pixel.

  A first aspect of the present invention relates to a photoelectric conversion device having an imaging surface composed of a plurality of pixels, wherein each of the plurality of pixels is disposed on a photoelectric conversion unit and an incident light side of the photoelectric conversion unit, An optical waveguide for guiding the incident light to the photoelectric conversion unit, the optical waveguide has a plurality of layers, and the plurality of layers of the optical waveguide have a large distance from the center of the imaging surface It is characterized by being arranged at a position eccentric to the center direction of the imaging surface.

  A second aspect of the present invention relates to a method for manufacturing a photoelectric conversion device, the step of forming a photoelectric conversion unit for photoelectric conversion of incident light, and the incident light side of the photoelectric conversion unit from the center of the imaging surface. A step of forming an optical waveguide composed of a plurality of layers arranged at a position decentered in the center direction of the imaging surface as the distance is larger, using a photomask corresponding to each of the plurality of layers. It is characterized by including.

  According to the present invention, a process of efficiently condensing light incident on an optical waveguide can be realized at low cost according to the position of a pixel.

  A preferred embodiment of the present invention will be specifically described below. Note that the configuration, arrangement, impurity type, and the like of each part described in the following description are not intended to limit the scope of the present invention only to them.

(First embodiment)
FIG. 1 is a schematic view of a photoelectric conversion device according to a preferred first embodiment of the present invention. FIG. 1 exemplarily shows an optical system having a short pupil distance.

  1 is an exit pupil. Reference numerals 2, 21, and 22 denote microlenses (on-chip lenses), which are located at the center, the left corner, and the right corner, respectively, of an imaging surface formed of a plurality of pixels. Reference numeral 9 denotes a high refractive index layer formed when the microlenses 2, 21, and 22 are formed, and has a refractive index equivalent to that of the microlenses 2, 21, and 22. 3, 4, 5 and 31, 41, 51 and 32, 42, 52 are optical waveguides, and are formed using a material (for example, SiN) having a higher refractive index than the surrounding material. Reference numeral 6 denotes a photoelectric conversion unit such as a photodiode formed on the substrate 7. The optical waveguides 3, 4, and 5 formed in the pixels near the center of the imaging surface are arranged on the incident light side of the photoelectric conversion unit 6 so that the centroid of the photoelectric conversion unit and the centroid of each layer coincide.

  The optical waveguides 31, 41, 51 formed in the pixel located on the left side of the imaging surface have a plurality of layers arranged at positions eccentric to the right with respect to the photoelectric conversion unit 6 according to incident light. Here, decentering means that the center of gravity of each layer is not on the normal line from the center of gravity of the photoelectric conversion unit. In addition, the optical waveguides 32, 42, and 52 formed in the pixels located on the right side of the imaging surface have a plurality of layers that are arranged at positions decentered in the left direction with respect to the photoelectric conversion unit 6. Similarly, the microlens 21 disposed above the pixel located on the left side of the imaging surface is disposed at a position eccentric to the right with respect to the photoelectric conversion unit 6. The micro lens 22 disposed above the pixel located on the right side of the imaging surface is disposed at a position eccentric to the left with respect to the photoelectric conversion unit 6.

  Note that the above-described eccentric amounts of the optical waveguide and the microlens are preferably increased as the distance from the center of the imaging surface is increased. For example, there are cases where it increases in proportion or increases exponentially. Furthermore, it is desirable that the centroids of the microlens and the optical waveguide coincide with a straight line connecting the incident light and the centroid of the photoelectric conversion unit 6. Moreover, it is preferable that the above-described eccentric amounts of the optical waveguide and the microlens increase as the distance from the photoelectric conversion unit 6 (the distance from the substrate surface on which the photoelectric conversion unit 6 is formed) increases. For example, there are cases where it increases in proportion or increases exponentially. Furthermore, it is preferable that the planar dimensions of the plurality of layers of each optical waveguide increase as the distance from the photoelectric conversion unit 6 increases. For example, there are cases where it increases in proportion or increases exponentially. In addition, when a color filter is disposed corresponding to each photoelectric conversion element, the plane size and the rate of change according to the distance from the surface of the photoelectric conversion unit may be changed according to the color (wavelength). .

Reference numeral 8 denotes a low refractive index layer, which is formed using a material (for example, SiO ₂ ) having a refractive index lower than those of the optical waveguides 3, 4, 5 and 31, 41, 51 and 32, 42, 52. The low refractive index layer 8 is in contact with each optical waveguide and guides light by utilizing the difference in refractive index between the two. If the difference between the positions of the end portions of the optical waveguide 42 and the optical waveguide 52 is d, the difference d is formed to be equal to or less than the incident wavelength (λ / n ₁ or less). Here, λ is a wavelength incident on the optical waveguide (incident wavelength), and n ₁ is a refractive index of the optical waveguide. In FIG. 1, this condition between the optical waveguide 42 and the optical waveguide 52 is shown. However, it is preferable that the above condition is satisfied between all two adjacent layers constituting the optical waveguide. Reference numeral 61 denotes a gate electrode formed of polysilicon or the like. Reference numerals 62 and 64 denote contacts formed of tungsten (W) or the like. Reference numerals 63 and 65 denote wirings formed of a wiring material such as aluminum (AL) or copper (Cu).

  As shown in FIG. 1, the bottoms of the wiring 63 and the optical waveguides 4, 41, 42 have the same height from the surface of the substrate 7. This is because the optical waveguide and the contact are formed at the same level in each contact forming step, and it is possible to cope with a fine pattern. Further, the important point in this embodiment is that the direction of the optical waveguide can be changed stepwise as in the optical waveguides 31, 41, 51, and any position can be obtained by using a photomask in the manufacturing process. It is possible to create it.

  That is, the optical waveguides 5, 51 and 52 are formed in the same process. The mask pattern for creating the optical waveguides 5, 51, 52 is located immediately above the mask pattern for creating the photoelectric conversion unit 6. The mask pattern for creating the next optical waveguides 4, 41, 42 is arranged at a position decentered in the center direction of the imaging surface with respect to the mask pattern for creating the optical waveguides 5, 51, 52. Similarly, the mask pattern for creating the optical waveguides 3, 21, and 22 is further arranged at a position decentered in the center direction of the imaging surface. With such an arrangement, each pixel can be formed to have a different shape depending on incident light.

  6A to 6K are cross-sectional views of the photoelectric conversion device according to the preferred first embodiment of the present invention. A first manufacturing method of the photoelectric conversion device will be described with reference to FIG. 6A to 6K, the optical waveguide is formed in substantially the same process as the wiring layer.

6A, reference numeral 501 denotes an N-type semiconductor substrate, 502 denotes a P well (PWL) constituting a photoelectric conversion unit, and 503 denotes an insulating film for element isolation, which can be formed by LOCOS, for example. Reference numeral 504 denotes an N-type region constituting the photoelectric conversion unit, and reference numeral 505 denotes a P-type surface passivation layer for suppressing dark current of the photoelectric conversion unit. Reference numeral 506 denotes a MOSFET gate oxide film, and reference numeral 507 denotes a gate electrode formed of polysilicon or the like. Actually, the periphery of the gate electrode 507 can be variously processed to have a structure corresponding to miniaturization, but the description thereof is omitted in FIG. 6A. Note that a CCD image sensor or the like is configured to transfer charges under the gate electrode 507 and sequentially transfer the charges. In a CMOS image sensor or the like, an N-type region is provided on the counter electrode side of the N-type region 504, and charges are transferred to the N-type region by controlling the polysilicon voltage of the gate electrode 507 (not shown). . Reference numeral 508 denotes an interlayer insulating film, which is formed of SiO ₂ or the like. Reference numeral 509 denotes an optical waveguide, which is formed of a material such as SiN having a refractive index higher than that of the interlayer insulating film 508.

  First, in the process shown in FIG. 6A, the interlayer insulating film 508 is patterned by a known photolithography process or the like to form a hole for the optical waveguide 509. Next, a material such as SiN having a higher refractive index than the interlayer insulating film 508 is embedded in the hole for the optical waveguide 509. Further, an insulating layer 510 such as SiN is deposited above the optical waveguide 509.

  In the step shown in FIG. 6B, a contact hole 511 is formed.

  In the step shown in FIG. 6C, the plug 512 is formed by filling the contact hole 511 with tungsten or the like. Next, a wiring layer 513 made of tungsten is formed on the surface by CVD or the like. At this time, in order to improve the contact with the semiconductor substrate 501, Ti / TiN (titanium / titanium nitride) may be deposited before tungsten deposition.

  In the step shown in FIG. 6D, the wiring layer 513 and the insulating layer 510 formed on the surface are removed by etch back, CMP, or the like.

  In the step shown in FIG. 6E, a wiring material is deposited and patterned by a known photolithography process or the like to form the wiring 514.

In the step shown in FIG. 6F, an interlayer insulating film 516 is formed. Next, an optical waveguide 515 made of a high refractive index material such as SiN is formed, and a via hole 517 is formed by patterning. At this time, if the difference between the positions of the end portions of the first-layer optical waveguide 509 and the second-layer optical waveguide 515 is d, d ≦ λ / n ₁ is satisfied.

  In the step shown in FIG. 6G, a plug 518 is formed by filling tungsten or the like in the contact hole. Next, a wiring layer 519 made of tungsten is formed on the surface by CVD or the like.

  In the step shown in FIG. 6H, the wiring layer 519 and the optical waveguide 515 formed on the surface are removed by etch back, CMP, or the like. As a result, the contact of the second layer via hole and the optical waveguide 515 are formed.

  In the step shown in FIG. 6I, a wiring material is deposited and patterned by a known photolithography process or the like to form the wiring 520. Next, an interlayer insulating film 521 is deposited, and a microlens 522 made of a high refractive index material is formed on the surface thereof. As shown in FIG. 6J, an optical waveguide 523 may be provided below the microlens 522. In addition, as illustrated in FIG. 6K, color filters 524 and 525 may be provided below the microlens 522. If an antireflection film is provided between the color filter 524 and the optical waveguide, the light collection efficiency can be further improved.

(Modification)
FIG. 7A to FIG. 7E are views showing a second manufacturing method of the photoelectric conversion device according to the first embodiment of the present invention. The final configuration is as shown in FIGS. 7I, 7J, and 7K, and thus the basic configuration is the same as in FIGS. 6A to 6K. Hereinafter, the steps different from the first manufacturing method described above will be mainly described.

  As shown in FIG. 7A, the basic structure is the same as FIG. 6A. In the step shown in FIG. 7A, a plug 609 is formed by embedding tungsten or the like in a contact hole in which an interlayer insulating film 508 is formed by a known photolithography process or the like. Next, a wiring layer 610 made of TiN, tungsten, or the like is formed on the surface by CVD or the like.

  In the step shown in FIG. 7B, the interlayer insulating film 508 and the wiring layer 610 are patterned by a known photolithography process or the like to form an opening 611 for embedding a high refractive material.

  In the step illustrated in FIG. 7C, the high refractive material 612 is embedded in the opening 611. Next, a highly refractive material 613 is deposited on the surface by CVD or the like.

  In the step shown in FIG. 7D, the high refractive material 613 and the wiring layer 610 formed on the surface are removed by etching back, CMP (Chemical Mechanical Polishing), or the like. As a result, the same configuration as in FIG. 7D is obtained.

  In the process shown in FIG. 7E, a wiring material is deposited and patterned by a well-known lithography process to form a wiring 514.

As described above, the second manufacturing method is different from the first manufacturing method in that the step of forming a contact such as W in the contact hole is performed first. Subsequent steps are the same as the steps shown in FIGS. 6F to 6K described above, and a description thereof will be omitted. Similarly to the first manufacturing method, it is preferable that the difference between the positions of the end portions of two adjacent optical waveguides is λ / n ₁ or less.

(Second Embodiment)
FIG. 2 is a plan view of the photoelectric conversion device according to the second preferred embodiment of the present invention. The optical waveguides 202, 203, 204, and 205 are arranged so as to be point symmetric with respect to the optical pupil position 201. Reference numeral 206 denotes an optical axis. The optical waveguides 202, 203, 204, and 205 have asymmetric shapes, but by arranging them so as to be point-symmetric with respect to the optical pupil position 201, uniform light can be obtained within the imaging surface.

  FIG. 3 is a plan view (FIG. 3A) and a cross-sectional view (FIG. 3B) of a photoelectric conversion device according to a preferred second embodiment of the present invention. FIG. 3A is a plan view of one pixel corresponding to the optical waveguide 202 of FIG. FIG. 3B is a cross-sectional view of the optical waveguide 200 of FIG. FIG. 4 shows each layer of FIG. 3B individually.

FIG. 3B shows the difference d between the positions of the end portions of the optical waveguides 302 and 303. By setting the difference d to be λ / n ₁ or less (λ: wavelength incident on the optical waveguide, n ₁ : refractive index of the optical waveguide), loss of the optical waveguides 302 and 303 can be suppressed.

  As shown in FIG. 4, the photoelectric conversion unit 6 has an asymmetric shape, and an optical waveguide 305 similar to the shape of the photoelectric conversion unit 6 is formed. That is, it is formed so as to gradually approach a substantially square shape with 304, 303, 302. That is, the incident light capturing portion in the uppermost layer of the optical waveguide can be made substantially rectangular. Thereby, the condition of total reflection can be satisfied. As a result, the light incident from the microlens 2 reaches the asymmetrical photoelectric conversion unit 6 without leaking from the optical waveguide.

  Thus, in this embodiment, even if it is a complicated-shaped photoelectric conversion part, the light taking-in part of an optical waveguide can be asymptotically approximated to a square or a rectangle.

  FIG. 5 is a diagram illustrating a state in which the optical waveguide 200 of FIG. 3 is arranged in the photoelectric conversion unit 6. FIG. 3 is a cross-sectional view of the optical waveguides 203 and 202 of FIG. 2 and the optical waveguides further disposed on the right side.

  The optical waveguide 203 disposed on the left side of the imaging surface has a structure displaced to the left in accordance with incident light. Conversely, the optical waveguide 202 disposed on the right side of the imaging surface has a structure that is displaced to the right according to incident light. Thus, the present embodiment is extremely effective in adapting an optical system having a short pupil distance in a sensor having a complicated shape.

  As described above, the optical waveguide is formed using a photomask, but the photomask may be a normal one and does not require an expensive photomask. In addition, even a photoelectric converter having a complicated shape can be asymptotically approximated to a square or rectangle, and even in an optical system having a short pupil, an optical waveguide corresponding to incident light at a steep angle is provided. Can be formed. Therefore, it is possible to prevent light loss between steps of the multi-stage optical waveguide, and an optical waveguide with less loss can be formed regardless of the position of the imaging surface of the photoelectric conversion device. Further, the yield in forming the optical waveguide can be improved by improving the forming method.

  As described above, according to a preferred embodiment of the present invention, a sensor having a complicated shape can be manufactured with good and low cost in an optical system having a short pupil distance. Note that the photoelectric conversion device according to the second embodiment can also be manufactured by the first manufacturing method or the second manufacturing method described above.

1 is a schematic diagram of a photoelectric conversion device according to a preferred first embodiment of the present invention. It is a top view of the photoelectric conversion apparatus which concerns on suitable 2nd Embodiment of this invention. It is a top view of the photoelectric conversion apparatus which concerns on suitable 2nd Embodiment of this invention. It is the figure which represented each layer of FIG. 3 separately. It is a figure showing the state which has arrange | positioned the optical waveguide of FIG. 3 above the photoelectric conversion part. It is a figure which shows the 1st manufacturing method of the photoelectric conversion apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the 1st manufacturing method of the photoelectric conversion apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the 1st manufacturing method of the photoelectric conversion apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the 1st manufacturing method of the photoelectric conversion apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the 1st manufacturing method of the photoelectric conversion apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the 1st manufacturing method of the photoelectric conversion apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the 1st manufacturing method of the photoelectric conversion apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the 1st manufacturing method of the photoelectric conversion apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the 1st manufacturing method of the photoelectric conversion apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the 1st manufacturing method of the photoelectric conversion apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the 1st manufacturing method of the photoelectric conversion apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the 2nd manufacturing method of the photoelectric conversion apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the 2nd manufacturing method of the photoelectric conversion apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the 2nd manufacturing method of the photoelectric conversion apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the 2nd manufacturing method of the photoelectric conversion apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the 2nd manufacturing method of the photoelectric conversion apparatus which concerns on the 1st Embodiment of this invention.

Explanation of symbols

2, 21, 22 Microlens 6 Photoelectric conversion unit 3, 4, 5 Multiple layers 31, 41, 51 of optical waveguide Multiple layers 32, 42, 52 of optical waveguide Multiple layers of optical waveguide

Claims (6)

A photoelectric conversion device having an imaging surface composed of a plurality of pixels,
Each of the plurality of pixels is
A photoelectric conversion unit;
An optical waveguide disposed on the incident light side of the photoelectric conversion unit and guiding the incident light to the photoelectric conversion unit;
With
The optical waveguide has a plurality of layers,
The photoelectric conversion device, wherein the plurality of layers of the optical waveguide are arranged at positions decentered toward the center of the imaging surface as the distance from the center of the imaging surface increases.   2. The photoelectric conversion device according to claim 1, wherein the planar dimensions of the plurality of layers increase as the distance from the photoelectric conversion unit increases.   3. The photoelectric conversion device according to claim 2, wherein a difference between positions of end portions of two adjacent layers of the plurality of layers is equal to or less than a wavelength of the incident light. The shape of the photoelectric conversion unit is asymmetric,
The said several layer has a shape similar to the shape of the said photoelectric conversion part, so that the distance with the said photoelectric conversion part is near, The any one of Claim 1 thru | or 3 characterized by the above-mentioned. The photoelectric conversion device described.   5. The photoelectric conversion device according to claim 1, wherein a microlens is disposed on an incident light side of the photoelectric conversion unit. A method for manufacturing a photoelectric conversion device, comprising:
Forming a photoelectric conversion unit that photoelectrically converts incident light;
On the incident light side of the photoelectric conversion unit, an optical waveguide composed of a plurality of layers arranged at positions decentered in the center direction of the imaging surface as the distance from the center of the imaging surface of the photoelectric conversion device increases. Forming using a photomask corresponding to each of the plurality of layers;
A process for producing a photoelectric conversion device comprising:

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