KR20090022507A - Image sensor and method of fabricating the same - Google Patents

Abstract

An image sensor and a manufacturing method thereof are provided to transfer the electrons of photoelectric transforming portion to the charge-detecting portion by unifying the transition speed of the electrons. An image sensor comprises a semiconductor substrate(101), a photoelectron transform portion, a charge transport unit(130), and an electric charge detection part. The photoelectron transform portion, the charge transport unit and the electric charge detection part are arranged along the one-way of the semiconductor substrate. The charge transport unit has a gate insulating layer(134) and a gate electrode(136) which successively are integrated on the semiconductor substrate.

Description

Image sensor and method of manufacturing the same {Image sensor and method of fabricating the same}

The present invention relates to an image sensor and a method of manufacturing the same, and more particularly, to an image sensor and a method of manufacturing the improved reliability.

An image sensor is an element that converts an optical image into an electrical signal. Recently, with the development of the computer industry and the communication industry, the demand for improved image sensors in various fields such as digital cameras, camcorders, personal communication systems (PCS), gaming devices, security cameras, medical micro cameras, robots, etc. is increasing. have.

The unit pixel of the image sensor includes a photoelectric converter and a charge transfer unit configured to transfer charges generated by photoelectric conversion of incident light in the photoelectric converter to a charge detector.

In the image sensor, the charge generated in the photoelectric converter is transferred to the charge detector through the charge transmitter. At this time, when a voltage is applied to the gate electrode of the charge transfer unit, a channel region is formed in the lower substrate region of the charge transfer unit, and charge moves to the charge detection unit through the channel region. Here, the charge easily moves in the center region of the channel region in which the charge moves, but the charge does not move quickly in the edge region of the channel region, that is, the region adjacent to the device isolation region. Therefore, in the edge region of the channel region, the movement of charges is not smoother than that of the center region. As a result, some charges may remain in the photoelectric converter, thereby reducing the reliability of the image sensor.

An object of the present invention is to provide an image sensor with improved reliability.

Another object of the present invention is to provide a method of manufacturing an image sensor having improved reliability.

Problems to be solved by the present invention are not limited to the above-mentioned problems, and other problems not mentioned will be clearly understood by those skilled in the art from the following description.

An image sensor according to an embodiment of the present invention for achieving the above object includes a semiconductor substrate and a photoelectric conversion unit, a charge transfer unit and a charge detection unit formed in parallel in one direction on the semiconductor substrate, the charge transfer unit is a semiconductor substrate A gate insulating film formed on the gate insulating film and a gate insulating film formed on the gate insulating film, wherein the thickness of the center region of the gate insulating film in another direction perpendicular to the one direction is an edge region of the gate insulating film in the other direction. Thicker than

According to another aspect of the present invention, there is provided an image sensor including a semiconductor substrate, a photoelectric conversion unit formed in the semiconductor substrate, a gate insulating layer and a gate electrode stacked on the semiconductor substrate, and a charge detector in the photoelectric conversion unit. And a charge detector including a channel region to which charge is transferred, and a charge detector configured to detect charge by receiving charge from the charge transmitter, wherein a thickness of the gate insulating layer on the center region of the channel region is greater than that of the channel region. It is thicker than the thickness of the gate insulating film in the edge region.

According to one or more exemplary embodiments, a method of manufacturing an image sensor includes: forming a photoelectric conversion unit, a charge transfer unit, and a charge detection unit formed side by side in one direction on a semiconductor substrate; A gate insulating film formed on the gate insulating film and a gate insulating film formed on the gate insulating film, wherein the thickness of the center region of the gate insulating film in another direction perpendicular to the one direction is an edge region of the gate insulating film in the other direction. Make it thicker than.

Other specific details of the invention are included in the detailed description and drawings.

According to the image sensor and the manufacturing method as described above has the following effects.

According to the image sensor and the manufacturing method thereof according to an embodiment of the present invention, by forming a gate insulating film having a different thickness in the center region and the edge region, it is possible to more smoothly move the charge from the photoelectric conversion section to the charge detection section The reliability of the image sensor can be improved.

Advantages and features of the present invention, and methods of achieving the same will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various forms, and only the embodiments are to make the disclosure of the present invention complete, and the general knowledge in the technical field to which the present invention belongs. It is provided to fully convey the scope of the invention to those skilled in the art, and the present invention is defined only by the scope of the claims. Thus, well-known device structures and well-known techniques in some embodiments are not described in detail in order to avoid obscuring the present invention. Furthermore, n-type or p-type is exemplary, and each embodiment described and illustrated herein also includes its complementary embodiment. Like reference numerals refer to like elements throughout.

Although the first, second, etc. are used to describe various elements, components and / or sections, these elements, components and / or sections are of course not limited by these terms. These terms are only used to distinguish one element, component or section from another element, component or section. Therefore, the first device, the first component, or the first section mentioned below may be a second device, a second component, or a second section within the technical spirit of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In this specification, the singular also includes the plural unless specifically stated otherwise in the phrase. As used herein, “comprises” and / or “comprising” refers to the presence of one or more other components, steps, operations and / or elements. Or does not exclude additions.

An image sensor according to an embodiment of the present invention includes a charge coupled device (CCD) and a CMOS image sensor. Here, the CCD has less noise and better image quality than the CMOS image sensor, but requires a high voltage and a high process cost. CMOS image sensors are simple to drive and can be implemented in a variety of scanning methods. In addition, since the signal processing circuit can be integrated on a single chip, the product can be miniaturized, and the CMOS process technology can be used interchangeably to reduce the manufacturing cost. Its low power consumption makes it easy to apply to products with limited battery capacity. Therefore, hereinafter, a CMOS image sensor will be described as an image sensor of the present invention. However, the technical idea of the present invention can be applied to the CCD as it is.

Hereinafter, an image sensor according to embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram of an image sensor according to an exemplary embodiment.

Referring to FIG. 1, an image sensor according to an exemplary embodiment of the present invention may include an active pixel sensor array (APS arrray) 10, a timing generator 20, and a row decoder. 30, a row driver 40, a correlated double sampler (CDS) 50, an analog to digital converter (ADC) 60, a latch (70) ) And a column decoder 80 and the like.

The active pixel sensor array 10 includes a plurality of unit pixels arranged in two dimensions. A plurality of unit pixels serve to convert an optical image into an electrical signal. The active pixel sensor array 10 is driven by receiving a plurality of driving signals such as a pixel selection signal ROW, a reset signal RST, a charge transfer signal TG, and the like from the row driver 40. The converted electrical signal is also provided to the correlated double sampler 50 via a vertical signal line.

The timing generator 20 provides a timing signal and a control signal to the row decoder 30 and the column decoder 80.

The row driver 40 provides a plurality of driving signals to the active pixel sensor array 10 for driving the plurality of unit pixels according to a result decoded by the row decoder 30. In general, when unit pixels are arranged in a matrix form, a driving signal is provided for each row.

The correlated double sampler 50 receives, holds, and samples electrical signals formed in the active pixel sensor array 10 through vertical signal lines. That is, a specific reference voltage level (hereinafter referred to as "noise level") and a voltage level (hereinafter referred to as "signal level") by the formed electrical signal are sampled twice, corresponding to the difference between the noise level and the signal level. Output the difference level.

The analog-to-digital converter 60 converts an analog signal corresponding to the difference level into a digital signal and outputs the digital signal.

The latch unit 70 latches the digital signal, and the latched signal is sequentially output from the column decoder 80 to the image signal processor (not shown) according to the decoding result.

2 is a circuit diagram of a unit pixel of an image sensor according to an exemplary embodiment. 3 is a schematic plan view of an active pixel sensor array of an image sensor according to an embodiment of the present invention.

2 and 3, the unit pixel 100 of the image sensor according to the exemplary embodiment may include a photoelectric converter 110, a charge detector 120, a charge transmitter 130, and a reset unit 140. ), An amplifier 150 and a selector 160. In the exemplary embodiment of the present invention, the unit pixel 100 has a four transistor structure as shown in FIG. 2, but may have a five transistor structure.

The photoelectric converter 110 absorbs incident light and accumulates charges corresponding to the amount of light. The photoelectric converter 110 may be a photo diode, a photo transistor, a photo gate, a pinned photo diode (PPD), and a combination thereof.

As the charge detector 120, a floating diffusion region (FD) is mainly used, and the charge accumulated in the photoelectric converter 110 is received. Since the charge detector 120 has a parasitic capacitance, charges are accumulated cumulatively. The charge detector 120 is electrically connected to the gate of the amplifier 150 to control the amplifier 150.

The charge transfer unit 130 transfers charges from the photoelectric conversion unit 110 to the charge detection unit 120. The charge transfer unit 130 generally includes one transistor and is controlled by a charge transfer signal TG.

The reset unit 140 periodically resets the charge detector 120. The source of the reset unit 140 is connected to the charge detector 120 and the drain is connected to Vdd. It is also driven in response to the reset signal RST.

The amplifier 150 serves as a source follower buffer amplifier in combination with a constant current source (not shown) located outside the unit pixel 100, and changes in response to the voltage of the charge detector 120. The voltage is output to the vertical signal line 162. The source is connected to the drain of the selector 160 and the drain is connected to Vdd.

The selector 160 selects the unit pixel 100 to be read in units of rows. Driven in response to the select signal ROW, the source is coupled to a vertical signal line 162.

In addition, the driving signal lines 131, 141, and 161 of the charge transfer unit 130, the reset unit 140, and the selector 160 may be driven in the row direction (horizontal direction) so that the unit pixels included in the same row are simultaneously driven. Is extended.

4A is a cross-sectional view of a unit pixel of an image sensor according to an exemplary embodiment, and is taken along line AA ′ of FIG. 3. FIG. 4B is a cross-sectional view of the unit pixel of the image sensor according to the exemplary embodiment, taken along the line BB ′ of FIG. 3.

4A and 4B, an image sensor according to an exemplary embodiment may include a semiconductor substrate 101, a deep well 107, an isolation well 108, and an isolation region 109. , A photoelectric converter 110, a charge detector 120, and a charge transfer unit 130. In an embodiment of the present invention, a pinned photo diode (PPD) is used as the photoelectric conversion unit 110.

The semiconductor substrate 101 is of a first conductivity type (eg, N-type), and the deep well 107 of the second conductivity type (eg, P-type) formed at a predetermined depth in the semiconductor substrate 101. By the lower and upper substrate regions 101a and 101b. Here, the semiconductor substrate 101 has been described using an N type as an example, but is not limited thereto.

The deep well 107 forms a potential barrier to prevent charges generated in the deep portion of the lower substrate region 101a from flowing into the photoelectric converter 110, and increases the recombination of charges and holes. It plays a role. Therefore, crosstalk between pixels due to random drift of charges can be reduced.

Deep well 107 may be formed to have a highest concentration at a depth of 3-12 μm from the surface of semiconductor substrate 101, for example, and to form a layer thickness of 1-5 μm. Here, 3 to 12 μm is substantially the same as the absorption length of red or near infrared region light in silicon. Here, as the depth of the deep well 107 is shallower from the surface of the semiconductor substrate 101, the diffusion prevention effect is larger, so that the crosstalk becomes smaller, but the area of the photoelectric conversion unit 110 is also shallower, so the photoelectric conversion ratio is deeper. Sensitivity to incident light having this relatively large long wavelength (eg, red wavelength) can be lowered. Therefore, the formation position of the deep well 107 can be adjusted according to the wavelength region of the incident light.

An isolation region 109 is formed in the upper substrate region 101b to define the active region. The device isolation region 109 may be, for example, Field Oxide (FOX) or Shallow Trench Isolation (STI) using a LOCOS (LOCal Oxidation of Silicon) method.

In addition, a separation well 108 of a second conductivity type (eg, P-type) may be formed under the device isolation region 109. The separation well 108 serves to separate the plurality of photodiodes 112 from each other. In order to reduce the crosstalk in the horizontal direction between the photodiodes 112, the separation well 108 may be formed deeper than the formation depth of the photodiode 112 and may be connected to the deep well 107 as shown in FIG. 4. Can be formed.

The photoelectric conversion unit 110 is formed in the semiconductor substrate 101 to form an N-type photodiode 112, a P ⁺ -type pinning layer 114, and an upper substrate region 101b below the photodiode 112. It includes.

Charges generated in response to incident light are accumulated in the photodiode 112, and the pinning layer 114 serves to reduce dark current by reducing an electro-hole pair (EHP) generated thermally in the upper substrate region 101b. .

In addition, since the photodiode 112 is formed to be spaced apart from the deep well 107 by a predetermined distance, the photodiode 112 may be used as a region for photoelectric conversion of the upper substrate region 101b under the photodiode 112. Thus, color sensitivity for long wavelengths (eg, red wavelengths) having a large penetration depth in silicon can be improved.

In addition, the maximum impurity concentration of the photodiode 112 may be 1 × 10 ¹⁵ to 1 × 10 ¹⁸ atoms / cm ³ , and the impurity concentration of the pinning layer 114 may be 1 × 10 ¹⁷ to 1 × 10 ²⁰ atoms / cm. ³ Can be. However, the concentration and the location to be doped may vary depending on the manufacturing process and design is not limited thereto.

The charge detector 120 is formed in the semiconductor substrate 101 to receive charges accumulated in the photoelectric converter 110 through the charge transfer unit 130. The charge transfer unit 130 includes an impurity region 132, a gate insulating layer 134, a gate electrode 136, and a spacer 138.

The impurity region 132 prevents dark current generated regardless of an image sensed by the charge transfer unit 130 in a turn-off state. The impurity region 132 may be formed to be close to the surface of the upper substrate region 101b to prevent dark current, and may be formed at a depth within 2000 mA, for example.

The gate insulating film 134 and the gate electrode 136 are formed by being stacked on a semiconductor substrate. In addition, a channel region C through which charge moves may be formed in the semiconductor substrate 101b under the gate insulating layer 134. The charge moves to the charge detector 120 through the channel region C formed in the semiconductor substrate of the charge transmitter 130 in the photoelectric converter 110. In this case, the thickness h1 of the center region of the gate insulating layer 134 over the center region of the channel region C may be the thickness h2 of the edge region of the gate insulating layer 134 over the edge region of the channel region C. Thicker than That is, when the photoelectric conversion unit 110, the charge transfer unit 130, and the charge detection unit 120 are formed side by side in one direction, the center region of the gate insulating layer 134 in the other direction perpendicular to the one direction is formed. The thickness h1 is thicker than the thickness h2 of the edge region of the gate insulating film 134 in the other direction. Here, the thickness of the gate insulating film 134 in one direction is uniform. The gate insulating layer 134 is formed of SiO ₂ , SiON, SiN, Al ₂ O 3, Si ₃ N ₄ , Ge _x O _y N _z , Ge _x Si _y O _z Or high dielectric constant materials may be used. Here, the high dielectric constant material may form HfO ₂ , ZrO ₂ , Al ₂ O ₃ , Ta ₂ O ₅ , hafnium silicate, zirconium silicate, or a combination thereof, by atomic layer deposition. In addition, the gate insulating layer 134 may be formed by stacking two or more selected materials from a plurality of layers. The gate insulating film 134 may be formed to have a thickness of 5 to 100 microseconds.

The gate insulating film 134 forms an insulating film of a first thickness only in the center region, and then deposits an insulating film of a second thickness in the center region and the edge region, and insulates the first thickness and the second thickness in the central region. Can be formed. Alternatively, an insulating film having a third thickness may be deposited in the center region, and an insulating film having a fourth thickness thinner than the third thickness may be formed in the edge region. However, the present invention is not limited thereto, and the gate insulating layer 134 having different thicknesses of the center region and the edge region may be formed through various conventional methods that can be performed by those skilled in the art.

When the thickness h1 of the center region of the gate insulating layer 134 is formed to be thicker than the thickness h2 of the edge region, the threshold voltage of the edge region of the gate insulating layer 134 is greater than the threshold voltage of the center region of the gate insulating layer 134. As it becomes smaller, the charge can move to the charge detector 120 more easily in the edge region. Therefore, the charges move more easily in the edge region as well as in the center region of the channel region C, whereby the reliability of the image sensor can be improved.

That is, according to the image sensor according to the present invention, by forming the gate insulating film 134 having a different thickness in the center region and the edge region, the movement of the charge from the photoelectric converter 110 to the charge detector 120 more smoothly This can improve the reliability of the image sensor.

The gate electrode 136 is a conductive polysilicon film, a metal film such as W, Pt, or Al, a metal nitride film such as TiN, or a metal obtained from a refractory metal such as Co, Ni, Ti, Hf, or Pt. It may consist of a silicide film or a combination film thereof. Alternatively, the gate electrode 136 may be formed by stacking the conductive polysilicon film and the metal silicide film in order, or may be formed by stacking the conductive polysilicon film and the metal film in order, but is not limited thereto.

The spacer 138 may be formed on both sidewalls of the gate electrode 136 and may be formed of a nitride film SiN.

5 is a schematic diagram illustrating a processor-based system including an image sensor according to an embodiment of the present invention.

Referring to FIG. 5, the processor-based system 300 is a system that processes an output image of the CMOS image sensor 310. The system 300 may illustrate a computer system, a camera system, a scanner, a mechanized clock system, a navigation system, a videophone, a supervision system, an auto focus system, a tracking system, a motion monitoring system, an image stabilization system, etc., but is not limited thereto. It doesn't happen.

Processor-based system 300, such as a computer system, includes a central information processing unit (CPU) 320, such as a microprocessor, that can communicate with input / output (I / O) device 330 via bus 305. CMOS image sensor 310 may communicate with the system via a bus 305 or other communication link. In addition, processor-based system 300 may include RAM 340, floppy disk drive 350 and / or CD ROM drive 355, and port 360, which may communicate with CPU 320 via bus 305. It may further include. The port 360 may be a port for coupling a video card, a sound card, a memory card, a USB device, or the like, or for communicating data with another system. The CMOS image sensor 310 may be integrated with a CPU, a digital signal processing device (DSP), a microprocessor, or the like. In addition, the memories may be integrated together. In some cases, of course, it may be integrated into a separate chip from the processor.

Although embodiments of the present invention have been described above with reference to the accompanying drawings, those skilled in the art to which the present invention pertains may implement the present invention in other specific forms without changing the technical spirit or essential features thereof. I can understand that. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

1 is a block diagram of an image sensor according to an exemplary embodiment.

2 is a circuit diagram of a unit pixel of an image sensor according to an exemplary embodiment.

3 is a schematic plan view of an active pixel sensor array of an image sensor according to an embodiment of the present invention.

4A is a cross-sectional view of a unit pixel of an image sensor according to an exemplary embodiment, and is taken along line AA ′ of FIG. 3.

FIG. 4B is a cross-sectional view of the unit pixel of the image sensor according to the exemplary embodiment, taken along the line BB ′ of FIG. 3.

5 is a schematic diagram illustrating a processor-based system including an image sensor according to an embodiment of the present invention.

(Explanation of symbols for the main parts of the drawing)

10: active pixel sensor array 20: timing generator

30: low decoder 40: low driver

50: correlated double sampler 60: analog-to-digital converter

70: latch portion 80: column decoder

100: unit pixel 101: semiconductor substrate

101a: lower substrate region 101b: upper substrate region

107: deep well 108: separation well

109: device isolation region 110: photoelectric conversion section

112: photodiode 114: pinning layer

120: charge detector 130: charge transfer unit

132: impurity region 134: gate insulating film

136: gate electrode 138: spacer

140: reset unit 150: amplification unit

160: selection unit 600: processor-based system

605: bus 610: CMOS image sensor

620: central information processing unit 630: I / O element

640: RAM 650: floppy disk drive

655: CD ROM drive 660: port

Claims (7)

Semiconductor substrates; And It includes a photoelectric conversion unit, a charge transfer unit and a charge detection unit formed side by side in one direction on the semiconductor substrate, The charge transfer unit includes a gate insulating layer formed on the semiconductor substrate and a gate electrode formed on the gate insulating layer, And a thickness of a center region of the gate insulating layer in another direction perpendicular to the one direction is thicker than a thickness of an edge region of the gate insulating layer in the other direction. The method of claim 1, And the photoelectric converter and the charge transfer part partially overlap each other. The method of claim 1, The thickness of the gate insulating film in the one direction is uniform image sensor. The method of claim 1, The thickness of the pair of edge regions of the gate insulating film in the other direction are all thinner than the thickness of the center region of the gate insulating film. Semiconductor substrates; A photoelectric conversion unit formed in the semiconductor substrate; A charge transfer unit including a gate insulating layer and a gate electrode stacked on the semiconductor substrate, and a channel region in which charge is transferred from the photoelectric conversion unit to a charge detection unit; And And a charge detector configured to detect charge by receiving charge from the charge transfer unit, wherein the thickness of the gate insulating layer on the center region of the channel region is thicker than the thickness of the gate insulating layer on the edge region of the channel region. The method of claim 5, The thickness of the pair of edge regions of the gate insulating film are all thinner than the thickness of the center region of the gate insulating film. On the semiconductor substrate to form a photoelectric conversion unit, a charge transfer unit and a charge detection unit formed side by side in one direction, The charge transfer part may include a gate insulating film formed on the semiconductor substrate and a gate electrode formed on the gate insulating film, and the thickness of the center region of the gate insulating film in another direction perpendicular to the one direction may be equal to the other direction. And a thickness greater than a thickness of an edge region of the gate insulating film.

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