Patent ID: 12261182

DETAILED DESCRIPTION

This patent document provides implementations and examples of an image sensing device that may be used in specific ways to substantially address one or more technical or engineering issues and mitigate limitations or disadvantages encountered in some other image sensing devices. Some implementations of the disclosed technology suggest examples of an image sensing device for more effectively blocking an optical black pixel (OBP) region. The disclosed technology provides various implementations of an image sensing device which can improve the structure of the microlens material layer formed in the optical black pixel (OBP) region to more effectively block light incident upon the optical black pixel (OBP) region.

Reference will now be made in detail to certain embodiments, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or similar parts. In the following description, a detailed description of related known configurations or functions incorporated herein will be omitted to avoid obscuring the subject matter.

Hereafter, various embodiments will be described with reference to the accompanying drawings. However, it should be understood that the disclosed technology is not limited to specific embodiments, but includes various modifications, equivalents and/or alternatives of the embodiments. The embodiments of the disclosed technology may provide a variety of effects capable of being directly or indirectly recognized through the disclosed technology.

FIG.1is a block diagram illustrating an image sensing device based on some implementations of the disclosed technology.

Referring toFIG.1, the image sensing device may include a pixel array100, a row driver200, a correlated double sampler (CDS)300, an analog-digital converter (ADC)400, an output buffer500, a column driver600, and a timing controller700. The components of the image sensing device illustrated inFIG.1are discussed by way of example only, and this patent document encompasses numerous other changes, substitutions, variations, alterations, and modifications.

The pixel array100may include a plurality of unit pixels (PXs) arranged in rows and columns. A plurality of unit pixels (PXs) may include red color filters (Rs), green color filters (Gs), and blue color filters (Bs), and these color filters may be arranged in a Bayer pattern. The pixel array100may include an image pixel region for generating an image corresponding to incident light, an optical black pixel (OBP) region for correcting a black level or a dark level for the image pixel region, and a dummy pixel region disposed between the image pixel region and the optical black pixel (OBP) region.

The pixel array100may include a lens layer formed over the color filters. The lens layer may be formed to have different shapes in the image pixel region, the dummy pixel region, and the optical black pixel (OBP) region. Specifically, in some implementations, the lens layer may be formed in a shape of dispersing light incident upon the optical black pixel (OBP) region. Detailed formats of the lens layer will be described later.

The pixel array100may receive driving signals (for example, a row selection signal, a reset signal, a transmission (or transfer) signal, etc.) from the row driver200. Upon receiving the driving signal, the unit pixels (PXs) may be activated to perform the operations corresponding to the row selection signal, the reset signal, and the transfer signal.

The row driver200may activate the pixel array100to perform certain operations on the unit pixels in the corresponding row based on control signals provided by controller circuitry such as the timing controller700. In some implementations, the row driver200may select one or more pixel groups arranged in one or more rows of the pixel array100. The row driver200may generate a row selection signal to select one or more rows from among the plurality of rows. The row driver200may sequentially enable the reset signal and the transfer signal for the unit pixels arranged in the selected row. The pixel signals generated by the unit pixels arranged in the selected row may be output to the correlated double sampler (CDS)300.

The correlated double sampler (CDS)300may remove undesired offset values of the unit pixels using correlated double sampling. In one example, the correlated double sampler (CDS)300may remove the undesired offset values of the unit pixels by comparing output voltages of pixel signals (of the unit pixels) obtained before and after photocharges generated by incident light are accumulated in the sensing node (i.e., a floating diffusion (FD) node). As a result, the CDS300may obtain a pixel signal generated only by the incident light without causing noise. In some implementations, upon receiving a clock signal from the timing controller700, the CDS300may sequentially sample and hold voltage levels of the reference signal and the pixel signal, which are provided to each of a plurality of column lines from the pixel array100. That is, the CDS300may sample and hold the voltage levels of the reference signal and the pixel signal which correspond to each of the columns of the pixel array100. In some implementations, the CDS300may transfer the reference signal and the pixel signal of each of the columns as a correlate double sampling (CDS) signal to the ADC400based on control signals from the timing controller700.

The ADC400is used to convert analog CDS signals received from the CDS300into digital signals. In some implementations, the ADC400may be implemented as a ramp-compare type ADC. The analog-to-digital converter (ADC)400may compare a ramp signal received from the timing controller700with the CDS signal received from the CDS300, and may thus output a comparison signal indicating the result of comparison between the ramp signal and the CDS signal. The analog-to-digital converter (ADC)400may count a level transition time of the comparison signal in response to the ramp signal received from the timing controller700, and may output a count value indicating the counted level transition time to the output buffer500.

The output buffer500may temporarily store column-based image data provided from the ADC400based on control signals of the timing controller700. The image data received from the ADC400may be temporarily stored in the output buffer500based on control signals of the timing controller700. The output buffer500may provide an interface to compensate for data rate differences or transmission rate differences between the image sensing device and other devices.

The column driver600may select a column of the output buffer500upon receiving a control signal from the timing controller700, and sequentially output the image data, which are temporarily stored in the selected column of the output buffer500. In some implementations, upon receiving an address signal from the timing controller700, the column driver600may generate a column selection signal based on the address signal, may select a column of the output buffer500using the column selection signal, and may control the image data received from the selected column of the output buffer500to be output as an output signal.

The timing controller700may generate signals for controlling operations of the row driver200, the ADC400, the output buffer500and the column driver600. The timing controller700may provide the row driver200, the column driver600, the ADC400, and the output buffer500with a clock signal required for the operations of the respective components of the image sensing device, a control signal for timing control, and address signals for selecting a row or column. In some implementations, the timing controller700may include a logic control circuit, a phase lock loop (PLL) circuit, a timing control circuit, a communication interface circuit and others.

The image sensing device may include a three-dimensional (3D) stack structure in which a first semiconductor layer in which the pixel array100is formed and a second semiconductor layer in which the CDS300, the ADC400, the output buffer500, the column driver600, and the timing controller700are formed are stacked. Alternatively, the row driver200, the CDS300, the ADC400, the output buffer500, the column driver600, and the timing controller700may be disposed outside the pixel array100within the same semiconductor layer as that of the pixel array100.

FIG.2is a schematic plan view illustrating an example of a pixel array shown inFIG.1based on some implementations of the disclosed technology.

Referring toFIG.2, the pixel array100may include an image pixel region110, a dummy pixel region120, and an optical black pixel (OBP) region130. The image pixel region110, the dummy pixel region120, and the optical black pixel (OBP) region130are arranged relative to one another.

The image pixel region110may be formed in a rectangular shape near or at the center of the pixel array100, and may include a plurality of active pixels arranged in each of the row and column directions. The active pixels are utilized to capture an image projected onto the image sensing device, for example, by sensing and converting light into electrical signals. The plurality of active pixels may convert incident light into an electrical signal corresponding to the incident light so as to generate imaging pixel signals, thereby forming an image. For example, the plurality of active pixels may include a plurality of red pixels (Rs), a plurality of green pixels (Gs), and a plurality of blue pixels (Bs). The red pixels (Rs) may generate photocharges corresponding to incident light of a red spectrum region. The green pixels (Gs) may generate photocharges corresponding to incident light of a green spectrum region. The blue pixels (Bs) may generate photocharges corresponding to incident light of a blue spectrum region. In addition, each of the active pixels may include a photoelectric conversion element, a transfer transistor, a reset transistor, a source follower transistor, and a selection transistor.

The dummy pixel region120may be located outside the image pixel region110adjacent to the image pixel region110. The dummy pixel region120may include a plurality of dummy pixels having the same structure as the active pixels, and the dummy pixels may be consecutively arranged in the row and column directions. The dummy pixels included in the dummy pixel region120may be distinguished from the active pixels in the image pixel region110in terms of the operations as not sensing and converting light into the electrical signals. The dummy pixel region120is disposed between the image pixel region110and the optical black pixel (OBP) region130to compensate for undesired characteristics of the image sensing device100. For example, by forming the dummy pixel region120between the image pixel region110and the optical black pixel (OBP) region130, the area having the pixels with the same structure as the active pixels in the image pixel region110can be extended to a region outside of the image pixel region110, which can help to solve the problems caused by a step difference that is generated between the image pixel region110and the optical black pixel (OBP) region130by a light blocking layer160formed in the optical black pixel (OBP) region130.

The optical black pixel (OBP) region130may be located outside the dummy pixel region120. The optical black pixel (OBP) region130may include a plurality of unit pixels (hereinafter referred to as black pixels). The black pixels refer to pixels that are shielded from light that is incident upon a surface of the image sensing device and can be used, for example, for noise correction, and so on. The black pixels may be configured to generate black pixel signals without any incident light for correcting a black level or a dark level for the image pixel region110. The image sensing device100may correct a dark current for the active pixels of the image pixel region110based on black pixel signals (i.e., dark current) output from black pixels of the optical black pixel (OBP) region130when incident light is blocked. The optical black pixel (OBP) region130may include a light blocking layer160for blocking light from being introduced into the black pixels. In this case, the light blocking layer160may be formed under the color filters, and may include metal such as tungsten (W) or copper (Cu).

The lens layer may be formed in each of the image pixel region110, the dummy pixel region120, and the optical black pixel (OBP) region130. The structure of the surface (light incidence surface) upon which light is incident in the lens layer may be different depending on the location of the light incident surface. Thus, the light incidence surface has different shapes in the image pixel region110, the dummy pixel region120, and the optical black pixel (OBP) region130. Detailed shapes of the lens layers will be described later.

AlthoughFIG.2shows an embodiment in which the dummy pixel region120and the optical black pixel (OBP) region130are formed to surround the image pixel region110in a frame shape, other implementations are also possible. For example, the dummy pixel region120and the optical black pixel (OBP) region130may be formed at one side of the image pixel region110in a horizontal or vertical direction. In addition, the sizes of the dummy pixel region120and the optical black pixel (OBP) region130may be determined based on process parameters.

FIG.3is a cross-sectional view illustrating an example of the pixel array taken along the line A-A′ shown inFIG.2based on some implementations of the disclosed technology.

Referring toFIG.3, the image sensing device100may include a substrate layer140, an interconnect layer150, a light blocking layer160, a color filter layer170, an over-coating layer180, and a lens layer190.

The substrate layer140may include a semiconductor substrate142having a first surface and a second surface opposite to the first surface. The semiconductor substrate142may be formed of or include a silicon bulk wafer or an epitaxial wafer. The epitaxial wafer may include a crystalline material layer grown by an epitaxial process on a bulk substrate. The semiconductor substrate142is not limited to the bulk wafer or the epitaxial wafer, and may be formed using a variety of wafers, such as a polished wafer, an annealed wafer, a silicon-on-insulator (SOI) wafer, or others. The substrate layer140may include photoelectric conversion elements144formed in the semiconductor substrate142to correspond to the active pixels, the dummy pixels, and the black pixels. In addition, the substrate layer140may include device isolation layers146disposed between the photoelectric conversion elements144in the semiconductor substrate142.

Each of the photoelectric conversion elements144may include a photodiode, a phototransistor, a photogate, or a pinned photodiode. The photoelectric conversion elements144may be formed in the semiconductor substrate142through an ion implantation process. For example, when the semiconductor substrate142is based on a P-type epitaxial wafer, the photoelectric conversion elements144may be doped with N-type impurities. The device isolation layer146may include a structure in which an insulation material is buried in a trench, or may include a structure in which high-density insulation impurities are implanted into the semiconductor substrate142.

The substrate layer140may be divided into an image pixel region110, a dummy pixel region120, and an optical black pixel (OBP) region130. The photoelectric conversion elements144of the image pixel region110may generate imaging pixel signals by converting incident light into an electrical signal, and the photoelectric conversion elements144of the optical black pixel (OBP) region130may generate a black pixel signal (i.e., dark current) caused by internal factors of the substrate layer140in a state in which incident light is blocked by the light blocking layer160.

The interconnect layer150may be disposed over the second surface of the substrate layer140. The interconnect layer150may include a plurality of stacked interlayer insulation layers152, and a plurality of interconnects (such as metal interconnects)154stacked in the interlayer insulation layers152. The interlayer insulation layers152may include at least one of an oxide layer and a nitride layer. Each interconnect154may include at least one of aluminum (Al), copper (Cu), and tungsten (W). The plurality of interconnects154may be electrically coupled to each other through contacts (not shown), and may be electrically coupled to logic elements.

A support substrate (not shown) for preventing the substrate layer140from being bent by thinning of the substrate layer140may be formed under the interconnect layer150. The support substrate may be adhered to the interconnect layer150by an adhesive layer. The support substrate may include a semiconductor substrate, a glass substrate, and a plastic substrate. Alternatively, a lower substrate layer (not shown) including logic circuits such as the row driver200, the CDS300, the ADC400, the output buffer500, the column driver600, and the timing controller700may be stacked under the interconnect layer150.

The light blocking layer160may be disposed in the optical black pixel (OBP) region130on the substrate layer140such that the light blocking layer160is in contact with the first surface of the substrate layer140. The light blocking layer160may block light from being incident upon the photoelectric conversion element144of the optical black pixel (OBP) region130. The light blocking layer162may include, in some implementations, metal such as tungsten (W) or copper (Cu).

The color filter layer170may be disposed over the substrate layer140in the image pixel region110and the dummy pixel region120. For example, the color filter layer170may be disposed over the first surface of the substrate layer140in each of the image pixel region110and the dummy pixel region120, and may be disposed over the light blocking layer160in the optical black pixel (OBP) region130. The color filter layer170may include a plurality of red color filters (Rs), a plurality of green color filters (Gs), and a plurality of blue color filters (Bs). Each red color filter (R) may transmit only red light from among RGB lights of visible light while blocking light in other colors. Each green color filter (G) may transmit only green light from among RGB lights of visible light while blocking light in other colors. Each blue color filter (B) may transmit only blue light from among RGB lights of visible light while blocking light in other colors. A grid structure (not shown) for preventing crosstalk of incident light may be formed between adjacent color filters. The grid structure may be formed simultaneously with formation of the light blocking layer160.

In the image pixel region110and the dummy pixel region120, the color filters may be arranged in a Bayer pattern and may be arranged as a single layer having the same thickness (height).

In the optical black pixel (OBP) region130, the color filters may be configured in different ways. In some implementations, the color filters in the OPB region130may be different from the color filter layers in the image pixel region110and the dummy pixel region120and may be formed in a structure in which two filter layers are stacked. For example, as shown in the example inFIG.3, in the optical black pixel (OBP) region130, a lower filter layer may be formed to have a pattern in which the red color filter (R) and the green color filter (G) are alternately arranged, and an upper filter layer may be formed in a shape in which the blue color filter (B) covers the lower red and green filter layer. Alternatively, the lower filter layer may be arranged in a Bayer pattern with red, green and blue filters as in color filters in the image pixel region110and the dummy pixel region120, and the upper filter layer may be formed such that the blue color filter (B) covers the lower filter layer with red, green and blue filters in the Bayer pattern.

The over-coating layer180may be disposed over the color filter layer180in the image pixel region110and the dummy pixel region120. The over-coating layer180may prevent irregular or diffused reflection of incident light to suppress flare characteristics. In addition, the over-coating layer180may compensate for a step difference between the color filters, so that the over-coating layer180may allow a plurality of condensing lens layers192ato have a constant height in each of the image pixel region110and the dummy pixel region120. The over-coating layer180may be formed of or include a light transmissive material as in the microlens layer192.

The lens layer190may be disposed over the over-coating layer180and the color filter layer170. For example, the lens layer190may be disposed over the over-coating layer140in the image pixel region110and the dummy pixel region120, and may be disposed over the color filter layer170in the optical black pixel (OBP) region130.

The lens layer190may include a microlens layer192and an anti-reflection layer194. The microlens layer192may be formed in a manner that the surface (light incidence surface) upon which light is incident is formed to have different structures according to where the microlenses are located in the microlens layer192. For example, the microlens layer192may include a condensing lens layer192aformed in the image pixel region110, a planarization lens layer192bformed in the dummy pixel region120, and a dispersion lens layer192cformed in the optical black pixel (OBP) region130.

The condensing lens layer192amay include a plurality of planoconvex lenses, each of which has a convex light incidence surface and a flat light emission surface. The planarization lens layer192bmay include a lens in which both the light incidence surface and the light emission surface are flat. The dispersion lens layer192cmay include a plurality of planoconcave lenses, each of which has a concave light incidence surface and a flat light emission surface. Each of the planoconvex lenses of the condensing lens layer192amay be formed for each active pixel, and each of the planoconcave lens of the dispersion lens layer192cmay be formed to correspond to at least one black pixel. The condensing lens layer192amay be formed to extend from the image pixel region110to a partial region of the dummy pixel region120.

FIG.4Ais a view illustrating an example of a state in which light is collected through the planoconvex lens based on some implementations of the disclosed technology.FIG.4Bis a view illustrating an example of a state in which light is dispersed through the planoconcave lens based on some implementations of the disclosed technology.

In the image pixel region110, as shown inFIG.4A, the planoconvex lenses of the condensing lens layer192amay converge incident light onto the photoelectric conversion elements of the corresponding active pixels, thereby improving photoelectric efficiency of the active pixels. In the optical black pixel (OBP) region130, as shown inFIG.4B, the planoconcave lenses of the dispersion lens layer192cmay disperse the incident light to prevent light from being concentrated. Thus, in some implementations, light rays incident upon the optical black pixel (OBP) region130may be primarily dispersed by the planoconcave lenses, and light rays scattered by the planoconcave lenses may be secondarily absorbed by the light blocking layer160. Accordingly, the image sensing device based on some implementations of the disclosed technology can more effectively block incident light from flowing into the photoelectric conversion elements of the black pixels.

The degree or ratio of the dispersed incident light dispersed by the dispersion lens layer192cto the incident light introduced to the dispersion lens layer192cmay be adjusted by adjusting a curvature, a refractive index, etc. of the planoconcave lens. For example, as shown inFIG.4B, when a refractive index of a material included in the planoconcave lens material is set to ‘n2’, a refractive index of a material disposed on the light incidence surface of the planoconcave lens is set to ‘n1’, and a refractive index of a material disposed below the light incidence surface of the planoconcave lens is set to ‘n3’, the refractive index of n2 is adjusted to be higher or lower than the refractive index of n3 while being adjusted to be higher than the refractive index of n1, so that the degree or ratio of light dispersion in the planoconcave lenses can be adjusted.

The anti-reflection layer194may be disposed over the microlens layer192to protect the microlens layer192, and may prevent incident light from being reflected by the microlens layer192. The anti-reflection layer194may be formed of or include a light transmissive material having a refractive index smaller than that of the microlens layer192.

A planarization layer (not shown) may be further formed not only between the substrate layer140and the color filter layer170, but also between the light blocking layer160and the color filter layer170.

FIG.5is a cross-sectional view illustrating another example of the pixel array taken along the line A-A′ shown inFIG.2based on some implementations of the disclosed technology.

Although the embodiment ofFIG.3shows an exemplary case in which one planoconcave lens is formed for each black pixel for convenience of description, the planoconcave lenses of the dispersion lens layer192dmay be formed to be sufficiently large to cover the plurality of black pixels as shown inFIG.5. For example, one planoconcave lens may be formed to cover two adjacent black pixels or four adjacent black pixels.

FIGS.6to10are cross-sectional views illustrating examples of a method for forming the structure ofFIG.3based on some implementations of the disclosed technology.

Referring toFIG.6, impurities may be implanted into the semiconductor substrate142to form a well region (not shown) and photoelectric conversion elements144, and device isolation layers146by which the photoelectric conversion elements144are separated from each other for each unit pixel may be formed.

In a process for forming the device isolation layers146, the device isolation layers defining an active region may be formed at the second surface of the semiconductor substrate142, and pixel transistors (e.g., a transfer transistor, a reset transistor, a source follower transistor, and a selection transistor) may be formed in the active region.

Subsequently, the interconnect layer150including the interlayer insulation layers152and the interconnects154may be formed over the second surface of the substrate layer140.

Referring toFIG.7, the light blocking layer160and the color filter layer170may be formed over the first surface of the substrate layer140. For example, after the light blocking layer160is formed in the optical black pixel (OBP) region130, the color filter layer170may be formed to cover the substrate layer140of each of the image pixel region110and the dummy pixel region120while covering the light blocking layer160.

The color filters R, G, and B of the color filter layer170may be formed to have a single layer structure in each of the image pixel region110and the dummy pixel region120. In the single layer structure, the color filters R, G, and B of the color filter layer170may be arranged in a Bayer pattern. In the optical black pixel (OBP) region130, the color filters R, G, and B of the color filter layer170may be formed in a stacked structure of two filter layers. For example, in the optical black pixel (OBP) region130, the lower filter layer may be formed to have a pattern in which the red color filter (R) and the green color filter (G) are alternately arranged, and the upper filter layer may be formed in a shape in which the blue color filter (B) covers the lower filter layer. Alternatively, the lower filter layer may be arranged in a Bayer pattern, and the upper filter layer may be formed such that the blue color filter (B) covers the lower filter layer.

Subsequently, the over-coating layer180may be formed over the color filter layer170of each of the image pixel region110and the dummy pixel region120. Referring toFIG.8, a microlens material layer191may be formed over the over-coating layer180and the color filter layer170to cover the image pixel region110, the dummy pixel region120, and the optical black pixel (OBP) region130.

Subsequently, first to third mask patterns193ato193cmay be formed over the microlens material layer191. For example, after a photoresist layer is formed over the microlens material layer191, the first to third mask patterns193ato193cmay be formed through exposure and development processes.

In this case, the first mask pattern193aserving as a mask pattern for forming planoconvex lenses of the condensing lens layer192amay include a plurality of island patterns disposed to overlap the active pixels and the center portion of some dummy pixels. The second mask pattern193bserving as a mask pattern for forming the planarization lens layer192bformed in the dummy pixel region120may be formed in a frame shape covering a partial region of the dummy pixel region120. The third mask pattern193cserving as a mask pattern for forming planoconcave lenses of the dispersion lens layer192cmay be formed in a grid shape that overlaps the device isolation layer146in the optical black pixel (OBP) region130. The third mask pattern193cmay be formed to have a smaller width than the first mask pattern193a.

Referring toFIG.9, a reflow process may be performed on the first to third mask patterns193ato193cso as to form first to third reflow patterns195ato195c.

The reflow process may be performed based on, for example, blank exposure using a stepper. When the mask patterns193ato193care irradiated with light having a predetermined wavelength through the stepper, PAC (Photo Active Compound) components present in the mask patterns193ato193cmay be decomposed. Thereafter, the resultant mask patterns may be annealed such that the reflow process can be smoothly performed.

Referring toFIG.10, an etchback process may be performed using the first to third reflow patterns195ato195cas masks, so that the microlens layer192including the condensing lens layer192a, the planarization lens layer192b, and the dispersion lens layer192ccan be formed. In this case, the etchback process may be performed until all of the first to third reflow patterns195ato195care removed.

Alternatively, when the microlens material layer191is formed of or include a photoresist material, a thermal reflow process is also performed on the microlens material layer191using the first to third reflow patterns195ato195cas masks, resulting in formation of the microlens layer192.

Alternatively, the reflow process may be performed using the first and second reflow patterns195aand195bas masks in the image pixel region110and the dummy pixel region120, and a plasma etching process may be performed using the third reflow pattern195cas a mask in the optical black pixel (OBP) region130, resulting in formation of the microlens layer192.

After the microlens layer192is formed, the anti-reflection layer194may be formed over the microlens layer192.

As is apparent from the above description, the image sensing device based on some implementations of the disclosed technology may improve the structure of the microlens material layer formed in the optical black pixel (OBP) region to more effectively block light incident upon the optical black pixel (OBP) region.

The embodiments of the disclosed technology may provide a variety of effects capable of being directly or indirectly recognized through the above-mentioned patent document.

Although a number of illustrative embodiments have been described, it should be understood that various modifications or enhancements of the disclosed embodiments and other embodiments can be devised based on what is described and/or illustrated in this patent document.