JP2009239493A - Solid-state imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a single chip color imaging apparatus with high blue sensitivity. <P>SOLUTION: The solid-state imaging apparatus includes: a plurality of photoelectric conversion areas on a semiconductor substrate; a reading circuit for reading a signal charge generated in the photoelectric conversion area; and an on-chip color filter formed in the upper part of the plurality of photoelectric conversion areas for dividing incident light. The on-chip color filter includes at least two or more color filter layers among a first color filter layer 510R for transmitting read light, a second color filter layer 510G for transmitting green light, and a third color filter layer 510B for transmitting blue light, and also includes a transparent filter layer 510W with transparency in the whole wavelength areas of a visible light area. The transmittance of the transparent filter layer is ≥98% in the wavelength area of wavelength from 400 mm to 700 mm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a solid-state imaging device, and more particularly to a single-chip color imaging device.

  In recent years, based on the demand for downsizing and multiple pixels in solid-state image sensors, the pixel size has been rapidly miniaturized, and a sample shipment plan for CMOS sensor elements consisting of 1.4 μm-sized fine pixels has been reported. Yes.

  In the trend toward finer pixel sizes, the amount of incident light decreases rapidly, and there is a concern about characteristic deterioration such as a decrease in SN ratio accompanying a decrease in the number of signal electrons generated in the photoelectric conversion unit inside the pixel.

  As one approach for dealing with such characteristic deterioration, a method for increasing the sensitivity of an on-chip color filter formed in a single-chip color image sensor has been attracting attention.

  Conventionally, as an on-chip color filter formed in a single-chip color image pickup device, a Bayer array proposed more than 30 years ago is generally used. The Bayer array is a so-called primary color filter, and is characterized by good color reproducibility (see, for example, Patent Document 1).

  The present inventors have proposed a new color filter that is highly sensitive by introducing transparent filter pixels in addition to the RGB primary color filters as a primary color filter having higher sensitivity than the Bayer arrangement. A high-sensitivity color CMOS sensor into which a new color filter is introduced has been prototyped and the evaluation results have been reported (for example, see Non-Patent Documents 1 and 2).

  The RGB primary color filter absorbs up to 1/3 of the incident light energy, whereas the transparent filter pixel does not absorb the incident light energy and efficiently converts the incident light into signal electrons. Therefore, high sensitivity is realized.

  Regarding the high-sensitivity color filter in which the transparent filter pixel is introduced, in addition to the present inventors, Dr. Luo and Eastman Kodak Company have proposed (for example, see Non-Patent Documents 3 and 4).

The color filter having the transparent filter pixel is proposed for the so-called complementary color filter. However, the problem of color reproducibility, which is a weak point of the complementary color system, the SN ratio deterioration due to the subtraction process essential in the complementary color signal processing, etc. There was a problem, and it did not come to spread.
US Pat. No. 3,971,065 H. Honda, et al., “A novel Bayer-like WRGB color filter array for CMOS image sensors”, SPIE6492-57, 2007 H. Honda, et al., “High Sensitivity Color CMOS Image Sensor with WRGB Color Filter Array and Color Separation Process Using Edge Detection”, Proceedings of International Image Sensor Workshop 2007, p.263, 2007 G.Luo, “A novel color filter array with 75% transparent elements”, SPIE6502-28, 2007 G.Luo, “Color filter array with sparse color sampling crosses for mobile phone image sensors”, Proceedings of International Image Sensor Workshop 2007, p.162, 2007

  In the above-described high-sensitivity color filter technology having transparent filter pixels, it is important for increasing the sensitivity to increase the transparency, that is, the transmittance of the transparent filter pixels.

  Conventional complementary color filters are generally of the so-called dyeing type. After forming a transparent dyed layer, a color filter is formed by sequentially dyeing in accordance with each color filter region. . The dyed layer uses a casein / gelatin-based material, but contains a photosensitive agent that absorbs i-line light (wavelength 365 nm) for the purpose of enabling processing by lithography. The blue sensitivity at will decrease.

  On the other hand, in a primary color filter, a single color filter layer is generally formed sequentially for each color. In this case as well, i-line light (wavelength 365 nm) is used for the purpose of enabling processing by lithography. It contains a photosensitive agent that absorbs, and the blue sensitivity in the vicinity of a wavelength of 400 nm decreases due to the influence.

  Therefore, it cannot be said that the high sensitivity to blue light is still sufficient.

  An object of the present invention is to obtain a single-chip color imaging device with high sensitivity to blue light.

  A solid-state imaging device according to one embodiment of the present invention is formed on a semiconductor substrate over a plurality of photoelectric conversion regions, a readout circuit for reading signal charges generated in the photoelectric conversion regions, and the plurality of photoelectric conversion regions. An on-chip color filter for splitting incident light, wherein the on-chip color filter includes at least a first color filter layer that transmits red light and a second color filter layer that transmits green light. And a third filter layer that transmits blue light, and a transparent filter layer having transparency in the entire wavelength region of the visible light region. The rate is characterized by being 98% or more in the wavelength region from 400 nm to 700 nm.

  According to the present invention, a single chip color imaging device with high blue sensitivity can be obtained.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 schematically shows a color filter array of a single chip color imaging device according to an embodiment of the present invention. The color filter 510 includes a color filter layer 510B that transmits only blue light, a color filter layer 510G that is arranged on the right side of the color filter layer 510B and transmits only green light, and an array below the color filter layer 510G. And a color filter layer 510R that transmits only red light, and a transparent filter layer 510W that is arranged on the left side of the color filter layer 510R and has a high transmittance over a visible light region of 400 nm to 700 nm. These filter layers are provided so as to cover the corresponding pixels, and a 2 × 2 pixel block is formed by four pixels corresponding to the filter layer.

  A method of manufacturing a color filter of the single chip color imaging apparatus according to the present embodiment will be described with reference to FIGS. 2 (a) to 2 (f). FIG. 2A to FIG. 2F are cross-sectional views along the line ABCD of the one pixel portion shown in FIG.

  First, for example, a color filter layer 510R that transmits only red light is formed so as to cover the pixel 502R of the monochrome imaging device 500 before the color filter is formed (FIGS. 2A and 2B). The color filter layer 510R is formed, for example, by applying an acrylic polymer material containing an organic pigment and patterning it into a desired shape by performing lithography using i-line. For this reason, the color filter layer 510R also contains a photosensitive agent having absorption characteristics for i-line.

  Next, similarly, a color filter layer 510G that transmits only green light is formed so as to cover the pixel 502G (FIG. 2C). The color filter layer 510G is, for example, an acrylic polymer material containing an organic pigment, and also contains a photosensitive agent having absorption characteristics for i-line for the purpose of lithography using i-line.

  Further, similarly, a color filter layer 510B that transmits only blue light is formed so as to cover the pixel 502B (FIG. 2D). The color filter layer 510B is, for example, an acrylic polymer material containing an organic pigment, and also contains a photosensitive agent having absorption characteristics for i-line for the purpose of lithography using i-line.

  Finally, a transparent filter layer 510W having a high transmittance over the entire visible light region from 400 nm to 700 nm is formed on the entire surface of the element. That is, the filter 510W is formed so as to cover the pixel 502W and cover the color filter layers 510R, 510B, and 510G (FIG. 2E).

  Thereafter, as shown in FIG. 2F, microlenses 512 are respectively formed on the transparent filter layer 510W immediately above the sub-pixels 502R, 502G, 502B, and 502W.

  In the present embodiment, unlike the above-described color filter layers 510R, 510G, and 510B, the transparent filter layer 510W is not premised on processing by lithography, and therefore it is not necessary to add a photosensitive agent that absorbs i-line. Therefore, the absorption characteristic in the vicinity of 400 nm generated with the i-line absorption characteristic at a wavelength of 365 nm does not appear, and a single-chip color imaging device having high blue sensitivity can be obtained.

  In general, after forming color filters for each color, it is common to form an optically transparent flattening layer in order to absorb the thickness variation of multiple color filters and flatten the surface. However, according to this embodiment, since the transparent filter layer 510W is already formed on the entire pixel region, the surface structure is flat. Therefore, the microlens structure for each pixel can be formed immediately after the formation of the transparent filter layer, and the process before forming the microlens for high sensitivity in the fine pixel can be omitted.

  At this time, by setting the thickness of the transparent filter layer 510W formed on the color filter layers 510R, 510B, and 510G to ½ or more of the thickness of the color filter layers 510R, 510B, and 510G, the transparent filter layer 510W. It is possible to keep the flatness of the surface shape favorable, and it is more preferable.

  Further, in the conventional structure, as described above, the transparent flattening layer is often formed after the transparent filter layer is formed. In this case, a dissimilar material interface between the transparent filter layer and the transparent flattening layer is formed, and path modulation of incident light may occur due to light reflection, refraction, etc. at the interface. Optical crosstalk, that is, so-called color mixing due to incidence on a different pixel from that of the other pixel occurs.

  On the other hand, in the present embodiment, since the transparent filter layer 510W is formed on the entire surface, it is not necessary to form the transparent flattening layer. There is also an effect that does not occur.

  In the present embodiment, transparent acrylic can be used as the material for the transparent filter layer 510W, which is preferable. In addition, as the spectral transmission characteristics of the transparent filter layer 510W, it is important to have a transmittance of 98% or more in a wavelength range of 400 nm to 700 nm that is a visible light region.

  The comparison result of the transmittance | permeability with the transparent filter layer 510W used for the imaging device of this embodiment and the transparent filter layer of a prior art example is shown in FIG. Note that, unlike the transparent filter layer 510W according to the present embodiment, a photosensitive agent that absorbs i-line is added to the conventional transparent filter layer in order to assume processing by lithography. As can be seen from FIG. 3, the transparent filter layer 510W according to the present embodiment exhibits high spectral transmittance characteristics over the entire visible light region. In particular, the transmittance in the short wavelength region near 400 nm is higher than in the conventional case. The transmittance at 400 nm is only 90% in the conventional case, whereas 98% or more can be obtained in the present embodiment.

  In the present embodiment, the distance between the bottom surface of the microlens 12 and the color filter layers 510R, 510B, and 510G can be shortened by etching the transparent filter layer 510W after forming the transparent filter layer 510W. As a result, the height of the pixel portion can be reduced, and the sensitivity and shading characteristics can be improved by improving the optical aspect ratio of the fine pixel, which is more preferable.

  Next, a solid-state imaging device according to an embodiment of the present invention will be described with reference to FIGS. The solid-state imaging device of this embodiment includes a solid-state imaging device, and this solid-state imaging device is shown in FIG. The solid-state image sensor 10 is formed on a solid-state image sensor chip 100.

  The solid-state imaging device chip 100 includes an imaging region 101 in which photoelectric conversion pixels that convert incident light signals into electrical signals by photoelectric conversion are arranged in a two-dimensional array, and a peripheral circuit disposed around the imaging region 101. It has. This peripheral circuit includes a load transistor unit 102, a CDS circuit (correlated double sampling circuit) 103, a V selection circuit 104, an H selection circuit 105, an AGC (automatic gain control circuit) 106, and an ADC (A / D). Converter) 107, digital amplifier 108, and TG (timing generator) circuit 109 that generates timing pulses. Note that the ADC 107 can also be configured as a column-type CDS-ADC circuit configured integrally with the CDS circuit 103 (see, for example, T. Sugiki et al., ISSCC2000 Thecnical Digest, p. 108, 2000). . Further, the TG 109, the AGC 106, the ADC 107, the digital amplifier 108, etc. may be provided as separate chips, or a signal processing circuit not shown in FIG. 4 may be mounted.

  In the pixel region 101, pixels having photoelectric conversion elements that convert an incident signal into an electric signal by photoelectric conversion are arranged in a two-dimensional matrix. An equivalent circuit of each pixel is shown in FIG. FIG. 5 is an equivalent circuit diagram of the pixel 2 and the load transistor unit 102 of the solid-state imaging device 10 according to the present embodiment. The pixel 2 includes a photodiode 201 that is a photoelectric conversion element, a capacitor 202, a transfer transistor (read transistor) 203, and a read circuit 210. The read circuit 210 has a three-transistor structure composed of n-channel MOS transistors, and includes an amplification transistor 212, a selection transistor 214, and a reset transistor 216. The photodiode 201 has an anode connected to the potential control line VP and a cathode connected to one of the source and drain of the transfer transistor 203. The transfer transistor 203 has a gate to which a timing pulse from the TG circuit 109 is applied, and the other of the source and the drain serving as the detection node 204 is connected to one electrode of the capacitor 202. The other electrode of the capacitor 202 is connected to the potential control line VP. Therefore, in this embodiment, the pixel potential can be controlled from the outside. The transfer transistor 203 operates based on the timing pulse from the TG circuit 109 and transfers the signal charge accumulated in the photodiode 201 to the detection node 204.

  The reset transistor 216 in the read circuit 210 resets the signal charge transferred by the transfer transistor 203 based on the reset signal RST. The amplification transistor 214 generates a signal voltage corresponding to the signal charge on the signal line SL, and the selection transistor 214 activates the readout circuit 210 in the pixel in the row selected by the row selection pulse ADR. The amplification transistor 212 inside the readout circuit 210 constitutes a source follower circuit in combination with the load transistor 220 of the load transistor unit 102 arranged outside the imaging region 101, and is not selected by the selection transistor 214. Are separated from the power supply voltage Vdd by the source follower circuit and deactivated.

  In this embodiment, as shown in FIG. 5, the photodiode 201 that is a photoelectric conversion element and the readout circuit 210 are provided in the pixel 2, but one readout circuit is provided by the plurality of photodiodes 201. Can be shared. In this case, the average number of transistors per pixel can be suppressed, which is advantageous in reducing the pixel size.

  Returning to FIG. 4 again, signals generated in the pixels arranged in a matrix are output in time series by the V selection circuit 104 and the H selection circuit 105 as follows. The signal photoelectrically converted in the pixel arranged in the row selected by the V selection circuit 104 is sent to the CDS circuit 103 via the signal line SL by the readout circuit 210 in the pixel, and the inherent noise is removed. The signal from which the inherent noise has been removed is sent to the ADC 107 controlled by the AGC 106 and converted into digital data. The converted digital data is sequentially selected and read by the H selection circuit 105, amplified by the digital amplifier 108, and output to the outside. The operations of the V selection circuit 104, the H selection circuit 105, and the CDS circuit 103 are controlled by timing pulses output from the TG circuit 109.

  Next, a solid-state imaging device having the solid-state imaging element 100 of the present embodiment is shown in FIG. The solid-state imaging device 400 includes a solid-state imaging device 100, an optical system 410 that supplies incident light to the solid-state imaging device 100, and a signal processing device 430 that processes an electrical signal output from the solid-state imaging device 100. .

  According to the solid-state imaging device of the present embodiment, it is possible to improve the blue sensitivity, and thus it is possible to obtain a highly sensitive solid-state imaging device.

  Further, in the camera module and the solid-state imaging device using the solid-state imaging device of the present embodiment, the blue sensitivity can be improved, so that a highly sensitive camera module and solid-state imaging device can be obtained.

  In addition, various modifications can be made without departing from the scope of the present invention.

1 is a diagram illustrating a color filter array of a single chip color imaging device according to an embodiment of the present invention. Sectional drawing explaining the manufacturing method of the color filter of the single-chip color imaging device of one Embodiment. The figure which compared the spectral transmission factor of the transparent filter layer of the single-chip color imaging device of one Embodiment, and the transparent filter of the conventional imaging device. 1 is a block diagram of a solid-state image sensor according to an embodiment of the present invention. The equivalent circuit schematic of the pixel of the solid-state image sensor of one Embodiment. 1 is a block diagram of a solid-state imaging device having a solid-state imaging element according to an embodiment.

Explanation of symbols

500 monochrome imaging device 502R sub-pixel 502G sub-pixel 502B sub-pixel 510 color filter 510R color filter layer 510B color filter layer 510G color filter layer 510W transparent filter layer 512 microlens

Claims (4)

A plurality of photoelectric conversion regions on a semiconductor substrate;
A readout circuit for reading out signal charges generated in the photoelectric conversion region;
An on-chip color filter for dispersing incident light formed above the plurality of photoelectric conversion regions;
The on-chip color filter includes at least a first color filter layer that transmits red light, a second color filter layer that transmits green light, and a third color filter layer that transmits blue light It includes two or more color filter layers and a transparent filter layer having transparency in the entire wavelength region of the visible light region, and the transmittance of the transparent filter layer is 98% or more in the wavelength region of wavelengths from 400 nm to 700 nm. A solid-state imaging device characterized by the above.   A transparent flattening layer made of the same material as the transparent filter layer is formed on the on-chip color filter, and a microlens is formed for each pixel on the flattening layer. Item 2. The solid-state imaging device according to Item 1.   The solid-state imaging device according to claim 2, wherein a thickness of the planarizing layer is not less than ½ of a thickness of the on-chip color filter.   The solid-state imaging device according to claim 1, wherein the colorless filter is made of a transparent acrylic polymer material.

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