TW201608711A - Image sensor and electronic device having the same - Google Patents

Abstract

An image sensor may include: a substrate including a substrate comprising a photoelectric conversion element; a pixel lens formed over the substrate and comprising a plurality of light condensing layers in which a lower layer has a larger area than an upper layer; a color filter layer covering the pixel lens; and an anti-reflection structure formed over the color filter layer.

Description

Image sensor and electronic device having the image sensor

Exemplary embodiments of the present invention relate to a semiconductor device fabrication technique, and more particularly to an image sensor including a concentrating element having a multi-layered stepped structure, and an electronic device having the image sensor.

The priority claimed by the present invention is an application filed with the Korean Intellectual Property Office on April 6, 2015. The Korean Patent Application No. 10-2015-0048436, the entire contents of which is incorporated herein by reference.

An image sensor refers to a device that converts an optical image into an electrical signal. Recently, due to the development of the computer industry and the communication industry, the demand for image sensors with improved performance is in various fields (such as digital cameras, cameras, personal communication systems (PCS), game consoles, security cameras, medical Both micro cameras and robots have increased.

Various embodiments are directed to an image sensor having improved performance, and an electronic device having the image sensor.

In an embodiment, an image sensor may include: a substrate including a photoelectric conversion element; a pixel lens formed on the substrate and including a plurality of light collecting layers, the lower layer having a lower layer than the upper layer a large area; a color filter layer covering the pixel lens; and an anti-reverse A shot structure formed over the color filter layer. The image sensor may further include a focusing layer provided between the photoelectric conversion element and the pixel lens. And the image sensor can further include an anti-reflection layer formed over the pixel lens.

The focusing layer can have a greater index of refraction than the pixel lens. The focusing layer can have the same area or larger area than the pixel lens. A focal length between the pixel lens and the photoelectric conversion element may be inversely proportional to a thickness of the focusing layer. The pixel lens can have a multi-layered stepped structure. The lower layer exposed by the upper layer may have a smaller width than the wavelength of the incident light. The lower layer exposed by the upper layer may have a smaller width than the wavelength of incident light whose color is separated by the color filter layer. The plurality of light collecting layers may have the same shape and be placed in parallel with each other. The upper layer may have the same thickness or a smaller thickness than the lower layer. The upper layer may have the same refractive index or less refractive index than the lower layer. The color filter layer covers the entire surface of the pixel lens and has a flat top surface. The color filter layer can have a smaller index of refraction than the pixel lens. The anti-reflective structure may comprise an anti-reflective layer or a hemispherical lens.

In an embodiment, an electronic device can include: an optical system; an image sensor adapted to receive light from the optical system and include an array of pixels, wherein the plurality of unit pixels are arranged in a matrix shape; and a signal A processing unit adapted to process a signal output from the image sensor. Each of the unit pixels may include: a substrate including a photoelectric conversion element; a pixel lens formed on the substrate and including a plurality of light collecting layers, wherein the lower layer has a larger area than the upper layer; a light layer covering the pixel lens; and an anti-reflection structure formed over the color filter layer. The electronic device may further include a focusing layer provided between the photoelectric conversion element and the pixel lens.

The focusing layer can have a greater index of refraction than the pixel lens. The color filter layer can be compared The pixel lens has a smaller refractive index. A focal length between the pixel lens and the photoelectric conversion element may be inversely proportional to a thickness of the focusing layer. The lower layer exposed by the upper layer may have a smaller width than the wavelength of the incident light.

100‧‧‧pixel array

110‧‧‧unit pixels

120‧‧‧Related Oversampling (CDS)

130‧‧‧ Analog-to-digital converter (ADC)

140‧‧‧buffer

150‧‧‧ column driver

160‧‧‧ Timing generator

170‧‧‧Control register

180‧‧‧Slope Signal Generator

210‧‧‧Substrate

220‧‧‧ photoelectric conversion components

230‧‧‧ Focusing layer

240‧‧‧pixel lens

241‧‧‧First concentrating layer

242‧‧‧Second concentrating layer

250‧‧‧Color filter layer

260‧‧‧Anti-reflective layer

270‧‧‧hemispherical lens

281‧‧‧First anti-reflective layer

282‧‧‧Second anti-reflective layer

283‧‧‧ Third anti-reflective layer

284‧‧‧fourth anti-reflection layer

285‧‧‧ fifth anti-reflective layer

300‧‧‧Image Sensor

310‧‧‧Optical system or optical lens

311‧‧‧Shutter unit

312‧‧‧Signal Processing Unit

313‧‧‧ drive unit

T‧‧‧ Thickness of the focusing layer

W1, W2‧‧‧ width

Thickness of the lower layer of t1‧‧

T2‧‧‧ thickness of the upper layer

D _out ‧‧‧ processed image signal

FIG. 1 is a block diagram schematically illustrating an image sensor according to an embodiment of the invention.

2A is a cross-sectional view showing a unit pixel of the image sensor according to the embodiment of the present invention.

Fig. 2B is a cross-sectional view showing another embodiment of the present invention.

3A to 3C are perspective views illustrating a focusing layer and a pixel lens in accordance with an embodiment of the present invention.

4A to 4D are cross-sectional views of the antireflection layer in the focusing layer and the pixel lens in accordance with an embodiment of the present invention.

FIG. 5 is a diagram schematically illustrating an electronic device including an image sensor according to an embodiment of the present invention.

Various specific embodiments are described in more detail below with reference to the drawings. However, the invention may be embodied in different forms and should not be construed as limited to the specific embodiments set forth herein. Rather, these specific embodiments are provided so that this disclosure may be Throughout the disclosure, the same element symbols refer to like parts throughout the various figures and embodiments of the invention.

The figures are not necessarily drawn to scale, and in some instances, the scale may be enlarged The features of the specific embodiments are clearly illustrated. When the first layer is referred to as "on" or "on" the second layer, it is not only said that the first layer is directly formed on the second layer or the substrate. And refer to the case where the third layer exists between the first layer and the second layer or the substrate.

The specific embodiments of the present invention provide an image sensor with improved performance, and an electronic device having the image sensor. When the concentrating efficiency in the unit pixel is improved, the performance of the image sensor is correspondingly improved. In general, an image sensor can include a plurality of unit pixels. Each of the unit pixels may include a ML (Micro lens) mounted on a photoelectric conversion element. Through the microlens, incident light can be agglomerated and transmitted into the photoelectric conversion element. The concentrating efficiency of the unit pixel can be determined according to the quality of the microlens. The concentrating efficiency can be controlled according to a focal length between the microlens and the photoelectric conversion element.

In conventional microlenses, the focal length between the microlens and the photoelectric conversion element may be changed during a process of changing the curvature of the microlens. Therefore, it is not easy to control the focal length.

The microlens can be formed by a process of reflowing a lens forming material such as a resist. In such a process, it is difficult to form a hemisphere having a desired curvature. Moreover, since the microlens is formed over a color filter layer, the applicable material is limited. In addition, the reflow process may require high cost, may only be formed into a hemispherical shape, and may be difficult to form on a microlens having a symmetrical and uniform shape. This may increase crosstalk.

The following specific embodiments of the present invention provide an image sensor having improved concentrating efficiency in a unit pixel, and an electronic device having the image sensor. For the present structure, each of the unit pixels may include a pixel lens having a plurality of light collecting layers formed over a photoelectric conversion element. The lower layers of the plurality of concentrating layers have a larger area or critical dimension than the upper layers of the plurality of concentrating layers. Therefore, the pixel lens can have a multi-layered stepped structure. The pixel lens having a multi-layered stepped structure exhibits sub-wavelength optical or sub-wavelength effects and can condense incident light like a hemispherical microlens. The pixel lens effectively condenses light into a limited area. Therefore, the pixel lens according to the specific embodiment has an advantage in enhancing the integration of the image sensor and can easily change the focal length. According to the sub-wavelength optics, the optical effect can be obtained in a spatial scale smaller than one-half the wavelength of the incident light.

FIG. 1 is a block diagram schematically illustrating an image sensor according to an embodiment of the invention.

As illustrated in FIG. 1 , the image sensor according to an embodiment of the present invention may include a pixel array 100, a correlated double sampling (CDS) 120, and an analog-to-digital converter (ADC, analog-digital). A converter 130, a buffer 140, a column of drivers 150, a timing generator 160, a control register 170, and a ramp signal generator 180. The pixel array 100 can include a plurality of unit pixels 110 that are disposed in a matrix shape.

Timing generator 160 may generate one or more control signals for controlling column driver 150, CDS 120, ADC 130, and ramp signal generator 180. Control register 170 may generate one or more control signals for controlling ramp signal generator 180, timing generator 160, and buffer 140.

Column driver 150 can drive pixel array 100 based on the column lines. For example, column driver 150 can generate a selection signal for selecting any of the plurality of column lines. Each unit pixel 110 can sense incident light and output image reset signals and image signals to the CDS 120 through the line. The CDS 120 can sample the image reset signal and the image signal.

The ADC 130 compares the ramp signal output from the ramp signal generator 180 with the sample signal output from the CDS 120 and outputs a comparison signal. According to the clock provided from the timing generator 160 The signal, ADC 130 can count the level transition time of the comparison signal and output the count value to the buffer 140. The ramp signal generator 180 is operable under the control of the timing generator 160.

The buffer 140 can store the complex digital signals output from the ADC 130, and then sense and amplify the digital signals. Therefore, the buffer 140 can include a memory (not shown) and a sense amplifier (not shown). This memory can be used to store the count value. These count values are related to the signals output from the complex unit pixels 110. The sense amplifier can be used to sense and amplify the count values output from the memory.

In the above image sensor, each of the unit pixels may include a pixel lens, which can improve the light collecting efficiency. Hereinafter, a unit pixel including a pixel lens will be described in detail with reference to the accompanying drawings.

2A is a cross-sectional view showing a unit pixel of an image sensor according to the embodiment of the present invention, and FIG. 2B is a cross-sectional view illustrating another embodiment of the present invention. 3A through 3C are perspective views illustrating an example of a focusing layer and a pixel lens in accordance with this embodiment of the present invention.

2A, 2B, and 3A to 3C, each unit pixel 110 can include a substrate 210, a focusing layer 230, a pixel lens 240, a color filter layer 250, and an anti-reflection structure. The substrate 210 may include a photoelectric conversion element 220. The focusing layer 230 may be formed over the substrate 210. The pixel lens 240 may be formed over the focusing layer 230 and include a plurality of light collecting layers. The lower layer has a larger area or critical dimension (CD) than the upper layer in the plurality of concentrating layers. A color filter layer 250 may be formed over the focusing layer 230 to cover the pixel lens 240. An anti-reflective structure can be formed over the color filter layer 250.

In this embodiment, the pixel lens 240 may include a first light collecting layer 241 formed on the focusing layer 230 and a second light collecting layer 242 formed on the first light collecting layer 241. And having a smaller area than the first light collecting layer 241. The first light collecting layer 241 may form the lower layer, and the second light collecting layer 242 may form the upper layer. Accordingly, the first concentrating layer and the lower layer may be represented by the same component symbol 241, and the second concentrating layer and the upper layer may be represented by the same component symbol 242.

The substrate 210 may include a semiconductor substrate. The semiconductor substrate can have a single crystal state and include a germanium-containing material. That is, the substrate 210 may include a single crystal germanium-containing material.

The photoelectric conversion element 220 may include a photodiode. For example, the photoelectric conversion element 220 formed over the substrate 210 may include a plurality of photoelectric conversion layers (not shown) stacked vertically. Each of the photoelectric conversion layers can be used as a photodiode including an N-type impurity region and a P-type impurity region.

The focusing layer 230 can be used to adjust the distance that the incident light condensed by the pixel lens 240 reaches the photoelectric conversion element 220, that is, the focal length. Due to the focusing layer 230, the focal length can be adjusted without a varying curvature, unlike conventional devices that use a hemispherical microlens with a given curvature to adjust. Furthermore, a shorter focal length can be set in a limited space. This focal length can be inversely proportional to the thickness T of the focusing layer 230. For example, the focal length may be shortened as the thickness T of the focusing layer 230 increases, and may increase as the thickness T of the focusing layer 230 decreases.

In order to efficiently transmit the incident light condensed by the pixel lens 240 to the photoelectric conversion element 220, the focusing layer 230 may have the same area or larger area than the pixel lens 240. The focusing layer 230 may have a shape corresponding to each unit pixel 110. Therefore, between adjacent unit pixels 110, the focusing layers 230 may be in contact with each other. For example, the focusing layer 230 can have a rectangular shape.

In order to transmit the incident light condensed by the pixel lens 240 to the photoelectric conversion element 220 more efficiently, the focusing layer 230 may have a larger refractive index than the pixel lens 240. As for the focusing layer 230, any material having a larger refractive index than the pixel lens 240 can be applied.

Since the focusing layer 230 is positioned at the bottom of the color filter layer 250, it is generally half Various materials used in the process can be applied. For example, a transparent material that can be applied as the focusing layer 230 may include inorganic materials such as hafnium oxide, tantalum nitride, and titanium nitride. The focusing layer 230 may have a single layer structure or a multilayer structure in which transparent materials having different refractive indices are stacked. When the focusing layer 230 has a multilayer structure, the refractive index of the focusing layer 230 may vary depending on the position. The layer located at the lower level may have a higher refractive index than the layer at the higher level.

The pixel lens 240 can be used as a light collecting element to agglomerate incident light. In order to improve the light collecting efficiency, the pixel lens 240 may have a multilayer structure in which two or more light collecting layers 241 and 242 are stacked. The upper layer 242 can have a smaller area or critical dimension (CD) than the lower layer 241. Therefore, the pixel lens 240 can have a multi-layered stepped structure. When the pixel lens 240 has a multi-layered stepped structure, the difference in width, that is, the widths W1 and W2 may be smaller than the wavelength of the incident light. That is, in the pixel lens, the lower layer exposed by the upper layer has a smaller width than the wavelength of the incident light. More specifically, the difference in width, that is, the widths W1 and W2 between the upper layer 242 and the lower layer 241 may be smaller than the wavelength of the incident light whose color is transmitted through the color filter layer 250. Through this structure, the pixel lens 240 having a multi-layered stepped structure can condense light like a conventional hemispherical lens. This is based on this sub-wavelength optics. The widths W1 and W2 form a step width between the upper layer 242 and the lower layer 241 at both ends, respectively, and may be equal to each other (W1 = W2) or different from each other (W1 ≠ W2).

The plurality of light collecting layers 241 and 242 may have the same shape and be disposed in parallel with each other. Specifically, the plurality of light collecting layers 241 and 242 may have a circular shape, a polygonal shape including a quadrangle, or the like.

To further improve the concentrating efficiency, the thickness t2 of the upper layer 242 may be equal to the thickness t1 of the lower layer 241 (t1 = t2) or less than the thickness t1 of the lower layer 241 (t1 > t2). Furthermore, to further improve the light collecting efficiency, the upper layer 242 may have the same refractive index or smaller refractive index than the lower layer 241. plural The light collecting layers 241 and 242 may include a transparent material. When the upper layer 242 and the lower layer 241 have the same refractive index, the upper layer 242 and the lower layer 241 may be formed of the same material.

Since the plurality of light collecting layers 241 and 242, that is, the pixel lens 240 are positioned at the bottom of the color filter layer 250, various materials used in a general semiconductor process can be applied. For example, transparent materials that are applicable as the plurality of light collecting layers 241 and 242 may include inorganic materials such as hafnium oxide, tantalum nitride, and titanium nitride. The light collecting layers 241 and 242 may have a single layer structure or a multilayer structure in which transparent materials having different refractive indices are stacked. When such complex concentrating layers are provided, the refractive indices of the concentrating layers may vary depending on the location. The concentrating layer at the higher level may have a lower refractive index than the concentrating layer at the lower level. That is, the refractive indices of the concentrating layers may increase as the concentrating layers are adjacent to the photoelectric conversion element 220 or the focusing layer 230.

A color filter layer 250 for color separation may be formed over the focusing layer 230 to cover the pixel lens 240 and have a flat surface. Since the color filter layer 250 is in contact with the pixel lens 240 and covers the pixel lens 240, light transmission between the color filter layer 250 and the pixel lens 240 can be improved. That is, the concentrating efficiency can be improved. The color filter layer 250 may include a red filter, a green filter, a blue filter, a cyan filter, a yellow filter, a magenta filter, and an infrared filter. (infrared pass filter), an infrared cutoff filter, a white filter, or a combination thereof. To further improve the concentrating efficiency, the color filter layer 250 may have a smaller refractive index than the pixel lens 240.

The anti-reflective structure may be formed over the color filter layer 250 and include an anti-reflective layer 260 or a half-spherical lens 270. The anti-reflective layer 260 can include two or more layers of material having different indices of refraction and alternately stacked one or more times. The hemispherical lens 270 not only prevents reflection of incident light but also condenses light incident on the pixel lens 240.

As the image sensor having the above structure includes the pixel lens 240 having a plurality of stepped structures, the light collecting efficiency in the unit pixel 110 can be improved. Furthermore, as the color filter layer 250 has a shape that can cover the pixel lens 240, the light collecting efficiency in the unit pixel 110 can be further improved. As the concentrating efficiency in the unit pixel 110 is improved, the quantum efficiency in the photoelectric conversion element 220 can also be improved. As a result, the performance of the image sensor can be improved.

In the image sensor according to an embodiment of the present invention, the focusing layer and the pixel lens may have a structure in which a plurality of material layers are stacked. Therefore, the anti-reflection layer can be easily mounted between the layers. The anti-reflection layer prevents incident light from being reflected from the surface, thereby preventing a decrease in the light collecting efficiency due to a decrease in light intensity. However, in the image sensor including the semi-spherical microlens, the formation positions of the anti-reflection layers can be restricted. Hereinafter, the anti-reflection layers will be described in detail with reference to FIGS. 4A to 4D. The first to fifth anti-reflection layers illustrated in FIGS. 4A to 4D may respectively indicate that two or more material layers having different refractive indexes are alternately stacked one or more times.

4A-4D are cross-sectional views illustrating the anti-reflective layers in accordance with an embodiment of the present invention.

First, as illustrated in FIG. 4A, the first anti-reflection layer 281 may be formed under the focusing layer 230. Specifically, the first anti-reflection layer 281 may be formed between the focusing layer 230 and the substrate including the photoelectric conversion element. Furthermore, the second anti-reflective layer 282 can be formed between the focusing layer 230 and the pixel lens 240. The first anti-reflective layer 281 and the second anti-reflective layer 282 may be formed through a deposition process before and after the formation of the focusing layer 230.

As illustrated in FIG. 4B, a third anti-reflective layer 283 may be formed over the pixel lens 240. Specifically, a third anti-reflective layer 283 may be formed between the pixel lens 240 and the color filter layer. The third anti-reflective layer 283 may be formed through a deposition process after the pixel lens 240 is formed. The deposition process The third anti-reflective layer 283 can be performed in such a manner that the surface of the structure has a constant thickness.

As illustrated in FIG. 4C, a fourth anti-reflective layer 284 may be formed over the first light collecting layer 241. The fifth anti-reflective layer 285 may be formed over the second light collecting layer 242. The fourth anti-reflection layer 284 and the fifth anti-reflection layer 285 may be simultaneously formed as the first light-concentrating layer 241 and the second light-concentrating layer 242 are respectively formed. When the first concentrating layer 241 and the second concentrating layer 242 have different refractive indices from each other, the fourth anti-reflective layer 284 may be at the boundary surface between the first concentrating layer 241 and the second concentrating layer 242 Prevent surface reflections.

As illustrated in FIG. 4D, all of the first anti-reflection layer 281 to the fifth anti-reflection layer 285 may be formed. In the image sensor according to an embodiment of the present invention, the focusing layer 230 and the pixel lens 240 may have a structure in which a plurality of material layers are stacked. Therefore, the anti-reflection layer can be easily mounted between the layers. This structure can further improve the light collecting efficiency.

The image sensor can be used in various electronic devices or systems in accordance with an embodiment of the present invention. Hereinafter, the image sensor according to a specific embodiment of the present invention applicable to a camera will be explained with reference to FIG.

FIG. 5 is a diagram schematically illustrating an electronic device including an image sensor according to an embodiment of the invention. Referring to FIG. 5, the electronic device including the image sensor according to an embodiment of the present invention may include a camera capable of capturing still images or moving images. The electronic device may include an optical system or optical lens 310, a shutter unit 311, a driving unit 313 for controlling/driving the image sensor 300 and the shutter unit 311, and a signal processing unit 312.

The optical system 310 can direct image light, that is, incident light, from the object to the pixel array 100 (see FIG. 1) of the image sensor 300. Optical system 310 can include a plurality of optical lenses. The shutter unit 311 can control the light irradiation period and the light shielding period for the image sensor 300. The driving unit 313 can control the transmission operation of the image sensor 300 and the shutter operation of the shutter unit 311. The signal processing unit 312 can process the signals output from the image sensor 300 in various ways. The processed image signals _Dout can be stored in a storage medium (such as a memory or output to a monitor or the like).

In accordance with an embodiment of the present invention, an image sensor can include a pixel lens to improve the efficiency of concentrating in the unit pixel. Furthermore, as the color filter layer has a shape that can cover the pixel lens, the light collecting efficiency in the unit pixel can be further improved.

According to a specific embodiment, the light collecting efficiency in the unit pixel is improved and the quantum efficiency in the photoelectric conversion element is improved. As a result, the performance of the image sensor can be improved.

While the invention has been described with respect to the specific embodiments, the various embodiments and modifications of the embodiments of the invention may be made without departing from the spirit and scope of the invention as defined in the following claims .

110‧‧‧unit pixels

210‧‧‧Substrate

220‧‧‧ photoelectric conversion components

230‧‧‧ Focusing layer

240‧‧‧pixel lens

241‧‧‧First concentrating layer

242‧‧‧Second concentrating layer

250‧‧‧Color filter layer

260‧‧‧Anti-reflective layer

W1, W2‧‧‧ width

T‧‧‧ Thickness of the focusing layer

Thickness of the lower layer of t1‧‧

T2‧‧‧ thickness of the upper layer

Claims (20)

An image sensor comprising: a substrate comprising a photoelectric conversion element; a pixel lens formed on the substrate and comprising a plurality of light collecting layers, wherein a lower layer has a larger area than an upper layer; a color filter layer covering the pixel lens; and an anti-reflection structure formed over the color filter layer. The image sensor of claim 1, further comprising: a focusing layer provided between the photoelectric conversion element and the pixel lens. The image sensor of claim 2, wherein the focusing layer has a larger refractive index than the pixel lens. The image sensor of claim 2, wherein the focusing layer has the same area or a larger area than the pixel lens. The image sensor of claim 2, wherein a focal length between the pixel lens and the photoelectric conversion element is inversely proportional to a thickness of the focusing layer. The image sensor of claim 1, wherein the pixel lens has a multi-layered stepped structure. The image sensor of claim 1, wherein the lower layer exposed by the upper layer has a smaller width than the wavelength of the incident light. The image sensor of claim 1, wherein the lower layer exposed by the upper layer has a smaller width than the wavelength of incident light whose color is separated by the color filter layer. The image sensor of claim 1, wherein the plurality of light collecting layers have the same shape and are disposed in parallel with each other. The image sensor of claim 1, wherein the upper layer has the same thickness or a smaller thickness than the lower layer. The image sensor of claim 1, wherein the upper layer has the same refractive index or a smaller refractive index than the lower layer. The image sensor of claim 1, further comprising: an anti-reflection layer formed over the pixel lens. The image sensor of claim 1, wherein the color filter layer covers the entire surface of the pixel lens and has a flat top surface. The image sensor of claim 1, wherein the color filter layer has a smaller refractive index than the pixel lens. The image sensor of claim 1, wherein the anti-reflection structure comprises an anti-reflection layer or a hemispherical lens. An electronic device comprising: an optical system; an image sensor adapted to receive light from the optical system and comprising an array of pixels, wherein the plurality of unit pixels are arranged in a matrix shape; and a signal processing unit is adapted Processing a signal output from the image sensor, wherein each of the unit pixels comprises: a substrate comprising a photoelectric conversion element; a pixel lens formed on the substrate and comprising a plurality of light collecting layers, wherein a lower layer has a larger area than an upper layer; a color filter layer covering the pixel lens; and an anti-reflection structure, It is formed over the color filter layer. The electronic device of claim 16, further comprising: a focusing layer provided between the photoelectric conversion element and the pixel lens. The electronic device of claim 17, wherein the focusing layer has a larger refractive index than the pixel lens, and wherein the color filter layer has a smaller refractive index than the pixel lens. The electronic device of claim 17, wherein a focal length between the pixel lens and the photoelectric conversion element is inversely proportional to a thickness of the focusing layer. The electronic device of claim 16, wherein the lower layer exposed by the upper layer has a smaller width than the wavelength of the incident light.