JP2006319037A - Solid-state imaging element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve light collection efficiency by making an optical waveguide of metal oxides, and to prevent dark current generated by the waveguide made of the metal oxides. <P>SOLUTION: A solid-state imaging element has a photoelectric converter (31) for converting incident light into an electrical signal, according to its amount of light, the optical waveguide (38) formed of a metal oxide for leading the incident light to the photoelectric converter, and isolation layers (37 and 40) with translucent characteristics provided between the waveguide and the photoelectric conversion element. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a solid-state imaging device used for an imaging apparatus such as a digital still camera.

  In recent years, solid-state imaging devices used in imaging devices such as digital still cameras have improved the image quality by increasing the number of pixels, while reducing the cost by reducing the chip size. For this reason, the size of one pixel constituting the solid-state imaging element is decreasing year by year, and the area of the light receiving unit is also decreasing accordingly.

Since the light receiving sensitivity decreases as the area of the light receiving portion is reduced, a solid-state imaging device having an optical waveguide with a large incident aperture provided between the light incident surface and the light receiving portion to improve the light collecting characteristics has been proposed ( For example, see Patent Document 1). In this solid-state imaging device, an optical waveguide made of silicon oxide (SiO ₂ ), which is a high refractive index material, is provided on the light incident side of the photoelectric conversion unit, and magnesium oxide (MgO), which is a low refractive index material, is provided around it. ), And the incident light is totally reflected at the boundary surface, thereby improving the light collecting characteristics.

FIG. 5 is a cross-sectional view of a conventional CMOS solid-state imaging device having an optical waveguide. In the figure, reference numeral 43 denotes a microlens, which is disposed so as to efficiently collect light incident from a photographing lens (not shown) on the photoelectric conversion unit 31 formed on the silicon substrate 30. The light transmitted through the microlens 43 is transmitted through the transparent planarization layer 42 and is wavelength-selected by the color filter layer 41. The light having a predetermined wavelength that has passed through the color filter layer 41 is guided to the photoelectric conversion unit 31 through the planarization layer 39 by the optical waveguide 45 whose opening area on the incident side is larger than the area of the photoelectric conversion unit 31. The optical waveguide 45 is formed of silicon nitride (SiN) having a refractive index of about 2.0, and an interlayer insulating film 33 is formed around the optical waveguide 45 with silicon oxide (SiO ₂ ) having a refractive index of about 1.46. Therefore, for example, the light 50 about to escape from the optical waveguide 45 to the interlayer insulating film 33 is totally reflected at the refractive index interface due to the refractive index difference between the optical waveguide 45 and the interlayer insulating film 33 and is guided to the photoelectric conversion unit 31.

  In the figure, 32, 34, and 35 are electrodes for selectively reading out the charges generated in the photoelectric conversion unit 31, and the electrode 32 is usually polycrystalline silicon (Poly-Si) that transmits light in a part of the wavelength region. ), And the electrodes 34 and 35 are made of aluminum (Al).

JP-A-5-235313 (page 4, FIG. 1)

  In recent years, the angle range of light incident on a solid-state image sensor has become larger as the digital still camera is further zoomed. Therefore, as shown in the cross-sectional view of the solid-state imaging device in FIG. 5, the light 51 having a large incident angle is transmitted without being totally reflected at the refractive index interface between the optical waveguide 45 and the interlayer insulating film 33, and the photoelectric conversion unit 31. There was a problem that it was not led to.

In addition, in order for the light 51 having a large incident angle to be totally reflected at the refractive index interface between the optical waveguide 45 and the interlayer insulating film 33, it is effective to increase the difference in refractive index between the optical waveguide 45 and the interlayer insulating film 33. For example, it is conceivable that the optical waveguide 45 is made of titanium oxide (TiO ₂ ) having a refractive index of 2.3.

  However, metal of metal oxide such as titanium oxide acts as an impurity on silicon (Si) constituting the photoelectric conversion unit 31 and causes an increase in dark current and the like, so that it cannot be used practically. There were drawbacks.

  The present invention has been made in view of the above problems, and it is an object of the present invention to improve the light collection efficiency by configuring the optical waveguide with a metal oxide and to prevent dark current caused by the configuration with the metal oxide. And

  In order to achieve the above object, the solid-state imaging device of the present invention is formed of a photoelectric conversion unit that converts incident light into an electrical signal according to the amount of light, and a metal oxide for guiding the incident light to the photoelectric conversion unit. And a separation layer having a light transmission characteristic disposed between the optical waveguide and the photoelectric conversion element.

  ADVANTAGE OF THE INVENTION According to this invention, while comprising an optical waveguide with a metal oxide, while improving condensing efficiency, the dark current produced by comprising with a metal oxide can be prevented.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components exemplified in this embodiment should be changed as appropriate according to the configuration of the apparatus to which the present invention is applied and various conditions. However, the present invention is not limited to these examples.

<First Embodiment>
FIG. 1 is a cross-sectional view showing a schematic configuration of one pixel of a CMOS type solid-state image sensor according to the first embodiment of the present invention. Usually, a solid-state imaging device used in an imaging apparatus such as a digital still camera is composed of several million pixels. In addition, the same reference number is attached | subjected to the structure similar to FIG.

  In FIG. 1, a solid-state imaging device includes a microlens 43 for condensing incident light, a microlens flattening layer 42, a color filter layer 41 for selecting the wavelength of incident light, a color filter flattening layer 39, and a silicon substrate. 30 includes a photoelectric conversion unit 31 formed in the electrode 30, electrodes 32, 34, and 35 for reading out photoelectric charges generated in the photoelectric conversion unit 31. An optical waveguide 38 is formed between the electrode 32 and the color filter planarizing layer 39. Reference numeral 40 denotes an etching stopper film made of silicon nitride (SiN) necessary for forming the optical waveguide 38 by etching.

The optical waveguide 38 is formed of a material having a relatively high refractive index with respect to the interlayer insulating film 33. In the first embodiment, the optical waveguide 38 is made of titanium oxide (TiO ₂ ) having a refractive index of about 2.3. Is formed. The interlayer insulating film 33 is made of silicon oxide (SiO ₂ ) having a refractive index of 1.46. As described above, since the refractive index difference between the optical waveguide 38 and the interlayer insulating film 33 is large, the light 51 having a large incident angle as well as the light 50 having a small incident angle is reflected at the boundary surface between the optical waveguide 38 and the interlayer insulating film 33. Totally reflected and efficiently guided to the photoelectric conversion unit 31. In this way, light having a large incident angle can be totally reflected between the optical waveguide 38 and the interlayer insulating film 33 and guided to the photoelectric conversion unit, and the light use efficiency of the solid-state imaging device can be improved. .

Further, since titanium oxide (TiO ₂ ) constituting the optical waveguide 38 is a metal oxide, titanium (Ti), which is a metal, is deposited on the silicon of the photoelectric conversion unit 31 (when the titanium oxide film is formed by the CVD method). A transparent protective layer 37 having a thickness of 3000 mm or more is formed between the optical waveguide 38 and the photoelectric conversion unit 31 so as not to diffuse into Si) as an impurity. In the first embodiment, the transparent protective layer 37 is made of silicon nitride (SiN) having a refractive index of about 2.0 and has a thickness of about 3500 mm. Further, due to the difference in refractive index between the transparent protective layer 37 (refractive index of about 2.0) and the interlayer insulating film 33 (refractive index 1.46), total reflection occurs at the refractive index interface between the transparent protective layer 37 and the interlayer insulating film 33, and light It contributes to the improvement of the utilization rate. The transparent protective layer 37 and the etching stopper film 40 form a separation layer that separates the optical waveguide 38 and the photoelectric conversion unit 31.

  FIG. 2 is a spectral reflection characteristic diagram between the optical waveguide 38 and the photoelectric conversion unit 31. In the first embodiment, the transparent protective layer 37 prevents the metal component constituting the optical waveguide 38 from diffusing into the photoelectric conversion unit 31, and the blue and red wavelengths with relatively low sensitivity of the solid-state imaging device. The region is configured to have antireflection characteristics.

  Next, with reference to FIG. 3, an optical waveguide forming process for manufacturing the solid-state imaging device according to the first embodiment of the present invention will be described.

  In addition, the pre-process which manufactures CMOS type solid-state image sensor 3 uses the method currently disclosed by Unexamined-Japanese-Patent No. 2000-85659, for example.

FIG. 3A shows the structure of the solid-state imaging device 3 after the completion of the previous process. An electrode 35 made of aluminum (Al) is formed on an interlayer insulating film 33 made of silicon oxide (SiO ₂ ). Furthermore, in the solid-state imaging device of the present invention, an etching stopper film 40 made of silicon nitride (SiN) is formed on the photoelectric conversion unit 31.

  First, a hole 36 for forming the optical waveguide 38 is formed on the photoelectric conversion unit 31. The hole 36 is formed by applying a photoresist on the interlayer insulating film 33, providing an opening corresponding to the incident opening of the optical waveguide 38 by resist patterning, and further performing dry etching. At this time, since the etching stopper film 40 (not shown) is formed between the interlayer insulating film 33 and the photoelectric conversion unit 31, the photoelectric conversion unit 31 itself is not etched (FIG. 3B).

  Next, a silicon nitride (SiN) film is formed on the entire surface of the solid-state imaging device by a CVD method, and a transparent protective layer 37 is formed in the hole 36 (FIG. 3C). The thickness of the silicon nitride (SiN) is about 3500 mm, and the metal component of the optical waveguide 38 formed in the region of the hole 36 in the next step is prevented from diffusing into the photoelectric conversion unit 31, and the solid-state imaging device The thickness is controlled so as to have antireflection characteristics for light in the blue and red wavelength regions where the sensitivity is relatively low. Moreover, since the area | region of the optical waveguide 38 by a metal oxide will become narrow when the thickness of the transparent protective layer 37 is thick, the thickness of the transparent protective layer 37 is restrict | limited to about 7000 mm or less.

Further, an optical waveguide 38 is formed by depositing titanium oxide (TiO ₂ ) by a CVD method (FIG. 3D). At this time, a part of titanium (Ti) as a metal component diffuses into the transparent protective layer 37 formed of silicon nitride (SiN). However, since the transparent protective layer 37 is 3000 mm or more, the silicon of the photoelectric conversion unit 31 ( Si) is not reached. When the titanium oxide (TiO ₂ ) is formed, a planarization process using CMP or the like is performed.

  When the optical waveguide 38 is formed, the color filter layer 41 is formed after the color filter flattening layer 39 for forming the color filter layer 41 is formed. Further, the microlens 43 is formed after the microlens flattening layer 42 for forming the microlens 43 is formed. The microlens is formed by a known registry flow method, and finally a solid-state imaging device 3 structure as shown in FIG. 1 is manufactured.

  In the description of the first embodiment described above, only the portion 38 formed of titanium oxide is referred to as an optical waveguide. However, the transparent protective layer 37 and the optical waveguide 38 formed in the hole 36 are referred to as the optical waveguide. Needless to say, they can be combined as an optical waveguide.

<Second Embodiment>
FIG. 4 is a cross-sectional view showing a schematic configuration of one pixel of a CMOS solid-state imaging device according to the second embodiment of the present invention. The same members as those in the schematic cross-sectional view of the CMOS solid-state imaging device in FIG. In the second embodiment, an interlayer insulating film 33 having a thickness of 3000 mm or more is disposed as a transparent protective layer between the optical waveguide 38 formed of titanium oxide (TiO ₂ ) and the photoelectric conversion unit 31. . The interlayer insulating film 33 is made of silicon oxide (SiO ₂ ). A hole for forming the optical waveguide 38 is manufactured by dry etching the interlayer insulating film 33. The depth of the hole is controlled by the etching time.

  As a result, since the refractive index difference between the optical waveguide 38 (refractive index of about 2.3) and the interlayer insulating film 33 (refractive index 1.46) is large, the light 51 having a large incident angle is also a boundary surface between the optical waveguide 38 and the interlayer insulating film 33. And are efficiently guided to the photoelectric conversion unit 31.

Further, when the optical waveguide 38 is formed of titanium oxide (TiO ₂ ), the interlayer insulating film 33 functions as a transparent protective layer, and prevents titanium (Ti), which is a metal, from diffusing to the photoelectric conversion portion 33. ing.

In the first and second embodiments, an example in which titanium oxide (TiO ₂ ) is used as the metal oxide constituting the optical waveguide 38 has been shown, but niobium oxide (Nb ₂ ) having a refractive index of about 2.3 respectively. It is also effective to use a metal oxide such as O ₅ ) or tantalum oxide (Ta ₂ O ₅ ).

It is sectional drawing which shows schematic structure of 1 pixel of the CMOS type | mold solid-state image sensor in the 1st Embodiment of this invention. It is a spectral reflection characteristic view between the optical waveguide of the CMOS type individual image sensor and the photoelectric conversion unit in the first embodiment of the present invention. It is explanatory drawing of the manufacturing process of the CMOS type solid-state image sensor in the 1st Embodiment of this invention. It is sectional drawing which shows schematic structure of 1 pixel of the CMOS type solid-state image sensor in the 2nd Embodiment of this invention. It is sectional drawing which shows schematic structure of 1 pixel of the conventional CMOS type | mold solid-state image sensor.

Explanation of symbols

30 Silicon substrate 31 Photoelectric conversion parts 32, 34, 35 Electrode 33 Interlayer insulating film 37 Transparent protective layers 38, 45 Optical waveguide 40 Etching stopper film 41 Color filter layers 39, 42 Flattening layer 43 Micro lens

Claims (10)

A photoelectric conversion unit that converts incident light into an electrical signal according to the amount of light;
An optical waveguide formed of a metal oxide for guiding incident light to the photoelectric conversion unit;
A solid-state imaging device, comprising: a separation layer having a light transmission characteristic disposed between the optical waveguide and the photoelectric conversion device.   The solid-state imaging device according to claim 1, wherein the metal oxide includes titanium oxide, niobium oxide, or tantalum oxide.   3. The solid-state imaging device according to claim 1, wherein the separation layer has a thickness capable of preventing a metal oxide constituting the optical waveguide from diffusing into the photoelectric conversion unit.   The solid-state imaging device according to claim 3, wherein the separation layer further has a thickness for preventing reflection of light in a wavelength region in which the sensitivity of the photoelectric conversion unit is relatively low.   5. The solid-state imaging device according to claim 3, wherein a thickness of the separation layer is between about 3000 mm and about 7000 mm. Further comprising an interlayer insulating film disposed around the optical waveguide,
The solid-state imaging device according to claim 1, wherein the separation layer is made of a material having a refractive index higher than that of the interlayer insulating film.   The solid-state imaging device according to claim 6, wherein the separation layer is made of silicon nitride.   The individual imaging element according to claim 1, wherein the separation layer constitutes an optical waveguide that follows the optical waveguide. Further comprising an interlayer insulating film disposed around the optical waveguide,
The solid-state imaging device according to claim 1, wherein the separation layer is formed of the same material as the interlayer insulating film.   The solid-state imaging device according to claim 8, wherein the separation layer is made of silicon oxide.

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