KR20110071712A - Image sensor having transparent interconnections - Google Patents

Abstract

PURPOSE: An image sensor having transparent interconnections is provided to increase the intensity of radiation on a photodiode area by using a transparent connection wire and a contact plug. CONSTITUTION: In an image sensor having transparent interconnections, an n-type well region(111) is formed in a p type silicon board(110). A p-type impurity region(112) is formed in the surface of the n-type well region. The n-type well region and p-type impurity region forms a photodiode(PD). A plurality of transistors forms a circuit outputting a signal measured from the photodiode. Transparent connection wirings(128,132) are connected to a plurality of transistors and the photodiode.

Description

Image sensor having transparent interconnections

An image sensor having a transparent connection line is provided.

The image sensor is a photoelectric conversion element that detects light and converts it into an electrical signal. The image sensor includes a plurality of unit pixels arranged in a matrix on a semiconductor substrate. Each unit pixel includes an optical sensor for sensing light and transistors for outputting an optical signal from the optical sensor.

Photoelectric sensors include photodiodes and oxide semiconductor transistors.

A CMOS (Complimentary Metal Oxide Semiconductor) image sensor including a photodiode includes a photodiode capable of receiving and storing an optical signal, and an image using a control element capable of controlling or processing the optical signal. Can be implemented. Since the control device can be manufactured using a CMOS fabrication technology, the CMOS image sensor has the advantage that the manufacturing process is simple, and furthermore, the control device can be manufactured in one chip together with several signal processing devices. .

On the other hand, since a CMOS image sensor integrates a photodiode and a plurality of transistors on one chip, the photodiode region is limited. If the photodiode area is reduced, the dynamic range is reduced, and therefore the sensitivity of the image sensor may be degraded. Even when the transistor is disposed on the photodiode with a transparent material, the connection wiring and the contact plug between the transistor and the transistors can reduce the amount of light incident on the photodiode.

When the oxide semiconductor transistor is used as an optical sensor, transistors constituting the peripheral circuit can be formed under the optical sensor, but the connection wiring and contact plug for signal transmission between the peripheral transistor and the optical sensor reduce the light incident to the optical sensor. You can.

One embodiment provides a CMOS image sensor that increases the amount of light incident to the photodiode region using transparent connection wiring and contact plugs.

Another embodiment provides an image sensor which increases the amount of light to an optical sensor which is an oxide semiconductor transistor by using a transparent connection wiring and a contact plug.

According to an embodiment, an image sensor having a transparent connection line may include:

An image sensor consisting of an array of pixels, each pixel

Photo diodes;

A plurality of transistors connected to the photodiode and constituting a circuit for outputting a signal measured from the photodiode; And

And contact plugs and connection wires connected to the plurality of transistors and the photodiode and formed of a transparent material formed on the photodiode.

At least one of the plurality of transistors is a transparent transistor formed on the photodiode, the transparent transistor,

A source electrode and a drain electrode on the first insulating layer covering the photodiode;

An oxide semiconductor layer covering the source electrode and the drain electrode on the first insulating layer;

A second insulating layer covering the oxide semiconductor layer; And

A gate electrode formed between the source electrode and the drain electrode on the second insulating layer, wherein the oxide semiconductor layer is formed of any one of an oxide including ZnO, SnO, and InO,

The source electrode, the drain electrode, and the gate electrode are each formed of a transparent material.

The connection wiring and the contact flag, and the electrodes are formed of a plurality of layers of a transparent conductive oxide layer and a transparent metal layer.

The connection wiring and the contact plug and the electrodes,

And at least one selected from the group consisting of a metal layer / transparent conductive oxide layer, a transparent conductive oxide layer / metal layer, a transparent conductive oxide layer / metal layer / transparent conductive oxide layer, and a metal layer / transparent conductive oxide layer / metal layer.

The metal layer may be any one material selected from Au, Ag, Cu, and Al.

The transparent conductive oxide layer may be any one material selected from transparent conductive oxides including InO, SnO, GaO, CdO, ZnO, CaO, ZnO, NiO, or alloys containing them.

In the connection wiring, the transparent conductive oxide layer and the metal dot layer may be alternately stacked.

According to another embodiment of the present invention, an image sensor having a transparent connection line is provided.

An image sensor consisting of an array of pixels, each pixel

An optical sensor for changing a voltage-current characteristic according to energy of incident light and generating a sensing current determined by the energy of the incident light;

A plurality of transistors connected to the optical sensor to configure a circuit for outputting the sensing current from the optical sensor; And

And a plurality of contact plugs and connection wires connected to the plurality of transistors and the optical sensor, the contact plugs being made of a transparent material.

The optical sensor may include an oxide transistor or an oxide diode whose voltage-current characteristics change according to the amount or wavelength of the incident light.

The oxide transistor or the oxide diode may be made of ZnO or TiO ₂ metal oxide.

The oxide transistor,

A gate electrode on the substrate and an active layer above the gate electrode; And

Source and drain electrodes formed on both ends of the active layer; Equipped with

The source electrode and the drain electrode may be formed of a transparent conductive oxide layer and a transparent metal layer.

In the image sensor according to the exemplary embodiment of the present invention, transparency of the electrode, the connection wiring, and the contact plug on the light receiving area is improved, and the light receiving area is increased to improve the sensitivity of the image sensor.

In addition, the resistance of the connection wiring and the contact plug reduces the power consumption of the image sensor.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this process, the thicknesses of layers or regions illustrated in the drawings are exaggerated for clarity.

1 is a plan view of a CMOS image sensor 100 having a transparent connection line according to an embodiment.

The CMOS image sensor has a two dimensional array of pixels. Each pixel (or unit pixel) is provided with a condenser lens for transmitting a lot of light to the lower photodiode, and a color filter which transmits light of a predetermined wavelength to each photodiode and blocks light of another wavelength. Hereinafter, the unit pixel will be described, and the configuration of the condenser lens and the color filter is omitted in the drawing.

Referring to FIG. 1, the image sensor 100 of the present invention includes a photodiode PD and four gates. The four gate electrodes are a transfer gate (TG), a reset gate (RG), a drive gate (DG), and a selection gate (SG), each of which is a transfer transistor (Tx), a reset transistor (Reset transistor, Rx), Drive transistor Dx, and selection transistor Sx.

The transfer transistor Tx and the reset transistor are formed on the side of the photodiode PD. An oxide semiconductor layer OS is formed on a portion of the photodiode PD, and the drive transistor Dx and the selection transistor Sx are formed on the oxide semiconductor layer OS.

The photodiode PD is an area that receives light and generates electrons and holes. The photodiode PD in the present invention is also formed in the drive transistor Dx and the select transistor Sx, and its area is extended.

The first contact plug CT1 and the second contact plug CT2 are electrically connected to each other by a conductor not shown.

FIG. 2 is a cross-sectional view taken along the line II-II of FIG. 1.

Referring to FIG. 2, an n type well region (N-well) 111 is formed in a semiconductor substrate, for example, a p type Si substrate 110, and a p type impurity region is formed on a surface of the n type well region 111. 112 is formed. The p-type impurity region 112 is formed to be surrounded by the n-type well region 111. The n-type well region 111 and the p-type impurity region 112 constitute a photodiode PD.

A floating diffusion region 113 and a reset diffusion region 114 doped with n-type impurities are formed at one side of the photodiode PD. The floating diffusion region 113 and the reset diffusion region 114 may be doped to have a lower potential than the photodiode PD region.

The first insulating layer 120 is formed on the substrate 110. The transfer gate 121 is formed between the n-type well region 111 and the floating diffusion region 113 in the first insulating layer 120, and is reset between the floating diffusion region 113 and the reset diffusion region 114. The gate 122 is formed. The transfer gate 121 may be connected to the row driver by the contact plug 123 and the connection wiring 124. The row driver inputs a control signal to the transfer gate 121 and the reset transistor 122 described later.

The n-type well region 111, the floating diffusion region 113, and the transfer gate 121 of the photodiode PD form a transfer transistor. The floating diffusion region 113, the reset diffusion region 114, and the reset gate 122 form a reset transistor. The reset gate 122 may be connected to the row driver by the contact plugs 125 and 127 and the connection wirings 125 and 128.

The second insulating layer 130 is formed on the first insulating layer 120. Each of the first insulating layer 120 and the second insulating layer 130 may be formed of silicon oxide. In the floating diffusion region 113, a first contact plug 131 penetrating the first insulating layer 120 and the second insulating layer 130 is formed. The wiring 132 connected to the first contact plug 131 is for connection with the second contact plug 133 connected to the selection gate of the selection transistor, which will be described later.

In FIG. 2, the connection wires 128 and 132 are shown in the same plane for convenience, but are actually disposed so as not to overlap each other by further forming an intermediate insulating layer, which is not shown.

3 is a cross-sectional view taken along line III-III of FIG. 1.

Referring to FIG. 3, a source electrode 141, a common electrode 142, and a drain electrode 143 are formed on the first insulating layer 120. The oxide semiconductor layer 140 and the third insulating layer 150 covering the electrodes 141 to 143 are formed on the first insulating layer 120. The third insulating layer 150 may be formed of the same material as the first insulating layer 120 and the second insulating layer 130. In addition, a drive gate 144 is formed on the third insulating layer 150 between the drain electrode 141 and the common electrode 142, and a third insulating layer between the common electrode 142 and the source electrode 143. The select gate 145 is formed on the 150. The drain electrode 141, the common electrode 142, and the drive gate 144 form a drive transistor. The drive gate 144 may be connected to the input voltage (Vdd of FIG. 9) by the contact plug 146 and the connection wiring 147.

 The common electrode 142, the drain electrode 143, and the selection gate 145 form a selection transistor. The selection gate 143 outputs the measurement current by the contact plug 148 and the connection wiring 149.

The second contact plug 133 and the wiring 134 connected to the wiring 132 are formed on the drive gate 144.

In FIG. 3, the connection wires 147, 134, and 149 are shown in the same plane for convenience, but in reality, they are not overlapped with each other by forming an intermediate insulating layer, which is not shown.

The oxide semiconductor layer 140 forms a charge transfer channel between the electrodes of the transistor, and is preferably formed of a transparent material. The oxide semiconductor layer 140 may be formed of ZnO, SnO, InO, and oxides including Ta, Hf, In, Ga, and Sr in these oxides.

The electrodes 141 to 145, the contact plugs 146, 133, and 148, and the connection wires 147, 134, and 149 may include a transparent conducting oxide (TCO) and a transparent metal layer (TM). It is a plurality of layers consisting of). Specifically, transparent metal layer / transparent conductive oxide layer (TM / TCO), transparent conductive oxide layer / transparent metal layer (TCO / TM), transparent conductive oxide layer / transparent metal layer / transparent conductive oxide layer (TCO / TM / TCO), transparent Metal layer / transparent conductive oxide layer / transparent metal layer (TM / TCO / TM), or a combination thereof. The transparent metal layer / transparent conductive oxide layer (TM / TCO) means that the transparent metal layer TM is formed on the transparent conductive oxide layer TCO.

The transparent metal layer may be formed of any one material selected from Au, Ag, Cu, and Al.

The transparent conductive oxide layer may be formed of a transparent conductive oxide including InO, SnO, GaO, CdO, ZnO, CaO, ZnO, NiO, or an alloy containing them.

4A is an exemplary diagram illustrating an example of a connection wiring and a contact plug. Referring to FIG. 4A, a contact plug 20 is formed on the first connection wire 10, and a second connection wire 30 is connected to the contact plug 20. The first connection wiring 10, the second connection wiring 30, and the contact plug 20 each have a two-layer structure of a transparent metal layer and a transparent conductive oxide layer. For example, the lower layers 11, 21, 31 are formed of a transparent metal layer, and the upper layers 12, 22, 32 are formed of a transparent conductive oxide layer.

4B is a cross-sectional view illustrating a structure of a connection line and a transparent electrode. Referring to FIG. 4B,

As shown in FIG. 4B, the connection wires 147, 134, and 149 and the electrodes 141 to 145 may be formed by alternately stacking the transparent conductive oxide layer 41 and the metal dot layer 42. Can be. The metal dot layer 42 is a layer formed by gathering nano-size metal dots, and may be formed of the same material as the transparent metal layer TM, and the transparent conductive oxide layer 41 may include the transparent conductive oxide layer ( TCO), and a detailed description thereof will be omitted.

5 is a graph measuring light transmittance and resistance when the connection wiring is an ITO / Ag / ITO layer. The ITO thicknesses on both sides of Ag are 40 nm each. Referring to FIG. 5, it can be seen that light transmittance and resistance change according to the thickness of Ag. The light transmission of FIG. 5 is for light with a wavelength of 550 nm.

6 is a light transmittance according to a wavelength when the connection wiring is formed to an ITO 80 nm thickness.

Referring to FIG. 6, the light transmittance of the ITO monolayer is approximately 78% for light of wavelength 550 nm. This is the light transmittance as in Fig. 5 when the thickness of Ag is "0". It is shown that the light transmittance increases as the connection wiring is formed into a plurality of layers.

Transparent conductive oxides are approximately one to two orders of magnitude larger than transparent metals. It can be seen that the resistance is reduced by one to two orders by laminating the transparent conductive oxide together with the transparent metal layer as shown in FIG. 5.

7 is an I-V characteristic curve when the source electrode and the drain electrode are made of the ITO / Ag / ITO layer, and FIG. 8 is an I-V characteristic curve when the source electrode and the drain electrode are formed only of ITO.

For the experiments of FIGS. 7 and 8, GIZO was used as the active layer, and SiO 2 having a thickness of 1000 mW was used as the gate oxide.

Referring to FIGS. 7 and 8, it can be seen that the current between the source electrode and the drain is about 1 order higher when the electrode and the drain electrode are made of the ITO / Ag / ITO layer. This shows that the dynamic range of the optical sensor employing such an electrode material is increased.

The image sensor 100 utilizes an area under which the selection transistor and the drive transistor are formed as a photodiode (PD) region, thereby increasing the area approximately 40% than those formed on one side of the photodiode (PD) region. do. This area increase increases the ability to accept electrons formed in the photodiode PD and thus the dynamic range is improved.

In addition, by forming the selection transistor and the drive transistor as a transparent material, an area to which light is irradiated may be increased, thereby improving sensitivity of the image sensor.

In addition, since the resistance of the connection wiring and the contact plug is reduced, the power consumption can be reduced.

9 is an equivalent circuit diagram of the image sensor 100 shown in FIGS. 1 to 3. Referring to FIG. 9, a CMOS image sensor may include a photo diode (PD), a transfer transistor (Tx), a reset transistor (Rx), a drive transistor (Dx), and a selection transistor. Sx).

Photodiode PD receives light energy and generates charge accordingly. The transfer transistor Tx may control the transfer of the generated charges to the floating diffusion region FD by the transfer gate line TG. The reset transistor Rx may control the input power supply Vdd by the reset gate line RG to reset the potential of the floating diffusion region FD. The drive transistor Dx may serve as a source follower amplifier. The selection transistor Sx is a switching element capable of selecting a unit pixel by the selection gate line SG. The input power source Vdd may be output to the output line OUT through the drive transistor Dx and the selection transistor Sx. The control signals of the transfer transistor Tx, the reset transistor Rx, and the selection transistor Sx are output from the row driver.

In the above embodiment, a pixel having four transistors has been described, but the present invention is not limited thereto. For example, a pixel having three transistors (reset transistor (Rx), drive transistor (Dx), and selection transistor (Sx)) in one photodiode may be implemented. Since the structure is well known in the detailed description is omitted.

10 is a partial cross-sectional view of an image sensor 200 having a transparent connection line according to another embodiment.

Referring to FIG. 10, the image sensor 200 forms a peripheral connection circuit with an optical sensor 210 that changes a voltage-current characteristic according to the energy of incident light and generates a sensing current determined by the energy of the incident light. A plurality of transistors 241-244, a contact plug, a connection wiring, and the like connected to the photosensor 210 and the electrodes (not shown) of the transistors 241-244 are provided. Reference numerals 251 and 252 are intermediate insulation layers, respectively.

The photosensor 210 may be an oxide semiconductor transistor. The photosensor 210 includes a gate electrode 212 formed on the substrate 202, a gate oxide 213 on the gate electrode 212, an active layer 214 on the gate oxide 213, and a source electrode on both ends of the active layer 214. 215 and the drain electrode 216 are provided. The optical sensor 210 may be implemented with an oxide diode.

When a threshold voltage is applied to the gate electrode 212, a current flows in the active layer 214 between the source electrode 215 and the drain electrode 216.

The optical sensor 210 may vary in voltage-current characteristics according to energy of incident light. For example, the active layer 214 includes a material whose voltage-current characteristics change according to the energy of incident light. Such materials may be, for example, metal oxides such as ZnO, TiO _2, and the like. In the active layer 214, the voltage-current characteristics change according to the energy and the light wavelength of the incident light. By measuring the change, the wavelength and the amount of light incident on the active layer can be known. Therefore, the optical sensor 210 can operate even without including the color filter as a component.

The source electrode 215 of the optical sensor 210 is connected to a power supply voltage not shown by the contact plug 261 and the connection wiring 262. The drain 216 is connected to the transistor 243 by the connection wiring 264. The transistor 243 may be a transfer transistor. The gate electrode 212 may be connected to a row driver (not shown) by contact plugs and connection wirings 271-274.

The transistors 241-244 are connected to an external power source and other transistors by contact plugs 263, 265, and 267 and connection wirings 264, 266, and 268. In FIG. 10, some of the connection wires are overlapped for convenience, but are not disposed to overlap each other using an intermediate insulating layer, which is not shown.

The transistors may be four transistors described in the above embodiments, and the connection structure thereof may be known from the structure in which the photodiode is replaced with the optical sensor 210 in FIG.

The transistors 241-244 may be disposed under the photosensor 210 to increase the area of the active layer 214. The source electrode 215 and the drain electrode 216 and the connection wires and the contact plugs of the optical sensor 210 may block the light incident to the active layer 214. In order to prevent this, the connection wiring and the contact plug, The source electrode 215 and the drain electrode 216 of the photosensor 210 are formed of a transparent material.

The electrodes 215 and 216, the contact plugs, and the connection wirings are a plurality of layers including a transparent conducting oxide (TCO) and a transparent metal (TM). Specifically, transparent metal layer / transparent conductive oxide layer (TM / TCO), transparent conductive oxide layer / transparent metal layer (TCO / TM), transparent conductive oxide layer / transparent metal layer / transparent conductive oxide layer (TCO / TM / TCO), transparent Metal layer / transparent conductive oxide layer / transparent metal layer (TM / TCO / TM), or a combination thereof. The transparent metal layer / transparent conductive oxide layer (TM / TCO) means that the transparent metal layer TM is formed on the transparent conductive oxide layer TCO.

The transparent metal layer may be formed of any one material selected from Au, Ag, Cu, and Al.

The transparent conductive oxide layer may be formed of a transparent conductive oxide including InO, SnO, GaO, CdO, ZnO, CaO, ZnO, NiO, or an alloy containing them.

The transistors 241-244 are disposed below the photosensor 210 in FIG. 10, but embodiments of the present invention are not limited thereto. For example, only some transistors may be formed below the photosensor, and others may be formed on the side of or above the photosensor 210.

The image sensor 200 improves the light transmittance of the electrode, the connection wiring, and the contact plug on the active layer of the optical sensor, and thus, the light receiving area is increased, thereby improving the sensitivity. In addition, the power consumption is reduced because the resistance of the connection end and the contact plug is reduced.

While the foregoing has been described with reference to preferred embodiments of the present invention, those skilled in the art will be able to variously modify and change the present invention without departing from the spirit and scope of the invention as set forth in the claims below. It will be appreciated.

1 is a plan view of a CMOS image sensor 100 having a transparent connection line according to an embodiment.

FIG. 2 is a cross-sectional view taken along the line II-II of FIG. 1.

3 is a cross-sectional view taken along line III-III of FIG. 1.

4A and 4B are cross-sectional views illustrating a structure of a connection line and a transparent electrode.

5 is a graph measuring light transmittance and resistance when the connection wiring is an ITO / Ag / ITO layer.

6 is a light transmittance according to a wavelength when the connection wiring is formed to an ITO 80 nm thickness.

7 is an I-V characteristic curve when the source electrode and the drain electrode are made of the ITO / Ag / ITO layer, and FIG. 8 is an I-V characteristic curve when the source electrode and the drain electrode are formed only of ITO.

9 is an equivalent circuit diagram of the image sensor 100 shown in FIG. 1.

10 is a partial cross-sectional view of an image sensor 200 having a transparent connection line according to another embodiment.

Claims (14)

In an image sensor consisting of an array of pixels, each pixel is Photo diodes; A plurality of transistors connected to the photodiode and configured to output a signal measured from the photodiode; And And connection wires connected to the plurality of transistors and the photodiode and formed of a transparent material formed on the photodiode. The transparent connection line is an image sensor having a transparent connection line is a plurality of layers consisting of a transparent conductive oxide layer and a transparent metal layer. The method of claim 1, At least one of the plurality of transistors is a transparent transistor formed on the photodiode, the transparent transistor, A source electrode and a drain electrode on the first insulating layer covering the photodiode; An oxide semiconductor layer covering the source electrode and the drain electrode on the first insulating layer; A second insulating layer covering the oxide semiconductor layer; And A gate electrode formed between the source electrode and the drain electrode on the second insulating layer, wherein the oxide semiconductor layer is formed of any one of an oxide including ZnO, SnO, and InO, And the source electrode, the drain electrode, and the gate electrode are each formed of a transparent material. The method of claim 1, The connection wiring, An image sensor comprising at least one selected from the group consisting of a metal layer / transparent conductive oxide layer, a transparent conductive oxide layer / metal layer, a transparent conductive oxide layer / metal layer / transparent conductive oxide layer, and a metal layer / transparent conductive oxide layer / metal layer. The method of claim 1, The metal layer is an image sensor of any one selected from Au, Ag, Cu, Al. The method of claim 1, The transparent conductive oxide layer is an image sensor made of any one material selected from transparent conductive oxides including InO, SnO, GaO, CdO, ZnO, CaO, ZnO, NiO or alloys containing them. The method of claim 1, The transparent metal layer is a metal dot layer, The connection wiring is an image sensor in which the transparent transparent conductive oxide layer and the metal dot layer are alternately stacked. In an image sensor consisting of an array of pixels, each pixel is An optical sensor for changing a voltage-current characteristic according to energy of incident light and generating a sensing current determined by the energy of the incident light; A plurality of transistors connected to the optical sensor to configure a circuit for outputting the sensing current from the optical sensor; And connection wires connected to the plurality of transistors and the optical sensor and made of a transparent material.  The connection wiring is an image sensor having a transparent connection wiring is a plurality of layers consisting of a transparent conductive oxide layer and a transparent metal layer. The method of claim 7, wherein The connection wiring, An image sensor comprising at least one selected from the group consisting of a metal layer / transparent conductive oxide layer, a transparent conductive oxide layer / metal layer, a transparent conductive oxide layer / metal layer / transparent conductive oxide layer, and a metal layer / transparent conductive oxide layer / metal layer. The method of claim 7, wherein The metal layer is an image sensor of any one selected from Au, Ag, Cu, Al. The method of claim 7, wherein The transparent conductive oxide layer is an image sensor made of any one material selected from transparent conductive oxides including InO, SnO, GaO, CdO, ZnO, CaO, ZnO, NiO or alloys containing them. The method of claim 7, wherein The transparent metal layer is a metal dot layer, The connection wiring is an image sensor in which the transparent transparent conductive oxide layer and the metal dot layer are alternately stacked. The method of claim 7, wherein The optical sensor may include an oxide transistor or an oxide diode whose voltage-current characteristics change according to the amount or wavelength of the incident light. 13. The method of claim 12, The oxide transistor or the oxide diode is an image sensor consisting of ZnO or TiO ₂ metal oxide. 13. The method of claim 12, The oxide transistor, A gate electrode on the substrate and an active layer above the gate electrode; And Source and drain electrodes formed on both ends of the active layer; Equipped with The source electrode and the drain electrode are a plurality of layers consisting of a transparent conductive oxide layer and a transparent metal layer.

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