KR20070035243A - Image sensor and its manufacturing method - Google Patents

Abstract

The present invention discloses an image sensor and a method for manufacturing the same, including contact studs having different upper and lower widths. In detail, the present invention provides a floating diffusion region formed by implanting impurities into a predetermined region of a semiconductor substrate, a contact stud contacting the floating diffusion region, and having a structure having a different width between an upper portion and a lower portion, a metal wiring connected to the contact stud, And a transistor electrically connected to the floating diffusion region through the metal wire, and a method of manufacturing the same.

Contact Studs, Image Sensors, Floating Diffusion Areas, Metallization

Description

Image sensor and manufacturing method thereof

1 is an exemplary unit pixel equivalent circuit diagram of an image sensor in accordance with the present invention.

FIG. 2 is a layout corresponding to FIG. 1.

3 is a layout of an exemplary unit pixel of an image sensor in accordance with the present invention.

4 is a cross-sectional view taken along line IV-IV 'of FIG. 2.

5 to 8 are cross-sectional views illustrating the manufacturing method of the image sensor according to the process sequence.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device and a manufacturing method thereof, and more particularly, to an image sensor for converting an optical signal into an electrical signal and a manufacturing method thereof.

In general, an image sensor is a semiconductor device that converts an optical signal into an electrical signal. Examples of image sensors include complementary metal oxide semiconductor (CMOS) image sensors (CIS) and charge coupled device (CCD) image sensors. CIS and CCD image sensors have a similar principle and are very similar in structure in that light incident on two-dimensionally arranged photodiodes is converted into signal charges (electrons) and sequentially read out as signal voltages along the time axis. . However, CIS and CCD differ in the place where the signal charge is converted into a voltage and the method of transmitting the signal to the output terminal. That is, the CIS converts charges into voltages in a plurality of unit pixels and outputs signals by switching operations on signal lines. CCDs, on the other hand, transfer signal charges in the order of vertical registers and horizontal registers and convert them into voltage just before the output terminals.

The image sensor is divided into a pixel region including a photodiode for converting incident light into an electric charge capable of processing an image, and a peripheral circuit region for controlling the pixel. The pixel region has an active region defined by an isolation layer, and a photodiode and a plurality of gates are formed on the active region. The peripheral circuit region is also formed with elements for controlling the pixel on an active region defined by an element isolation film.

Elements formed in the pixel region, the peripheral circuit regions, for example, a photodiode, a floating junction region, a gate and a junction region of a transistor are connected to a metal wiring by a contact stud, and the metal wiring interconnects the elements. In the conventional image sensor, the contact stud is formed in a structure having a constant width of the upper and lower portions. The contact stud is widened for the wiring of the floating junction region, thereby increasing the width of the lower portion of the contact stud in contact with the floating junction region, thereby increasing the capacitance of the floating junction region. The floating junction region receives the charges received by the photodiode, and the larger the capacitance of the floating junction region is, the lower the voltage is, thereby reducing the recognizable dynamic range of the image sensor.

Accordingly, the present invention seeks to provide an image sensor having improved dynamic range by increasing its dynamic range.

In addition, the present invention seeks to provide a method of effectively manufacturing an image sensor having excellent function by increasing dynamic range.

In addition, the present invention is to provide a method that can effectively manufacture an image sensor while having an excellent function by increasing the dynamic range in the highly integrated image sensor.

The present invention provides a floating diffusion region formed by implanting impurities into a predetermined region of a semiconductor substrate on which a photodiode, a reset transistor, and a drive transistor are formed, and a contact stud contacting the floating diffusion region and having a structure having a different width between upper and lower portions ( contact stude), a metal wire connected to the contact stud, and an image sensor including a transistor electrically connected to the floating diffusion region through the metal wire.

Preferably, the contact stud is wider in width than an upper portion of the contact stud connected to the floating junction region. Therefore, the contact stud can reduce the contact area with the floating junction region, thereby reducing the capacitance of the floating junction region, thereby increasing the dynamic range of the image sensor.

In addition, the contact stud preferably consists of doped polysilicon, doped germanium, and mixtures thereof. Therefore, it is possible to prevent the dark current generated at the interface between the metal wiring and the contact stud to improve the image quality of the image sensor.

The present invention also provides a method of forming a floating diffusion region in a semiconductor substrate, forming an interlayer insulating film in the resultant, forming an etch mask for forming a contact stud in contact with the floating diffusion region on the interlayer insulating film, Isotropically etching the interlayer insulating film using the etching mask, anisotropically etching the interlayer insulating film using the etching mask, and removing the etching mask and using the opening formed by the etching steps as a conductive material. It comprises a method of manufacturing an image sensor comprising the step of completing the contact stud.

In the manufacturing method of the image sensor, anisotropic etching may be performed after isotropic etching, or isotropic etching may be performed after anisotropic etching.

The present invention also provides a method of forming a floating diffusion region, a gate pattern and a junction region of a transfer transistor, and a gate pattern and a junction region of a reset transistor on a semiconductor substrate, forming an interlayer insulating layer on the resultant, and forming the interlayer insulating layer on the interlayer insulating layer. Forming an etching mask exposing a floating junction region, a gate pattern of the transfer transistor, and a predetermined region of an interlayer insulating layer on the gate pattern of the reset transistor; etching the interlayer insulating layer using the etching mask to etch the floating junction region; Forming an opening that exposes the gate pattern of the transfer transistor and the gate pattern of the reset transistor, and removing the etch mask and filling the opening with a conductive material to complete the contact stud.It includes a method.

Accordingly, in the method of manufacturing the image sensor, in the highly integrated image sensor, a contact stud having a structure having an upper width greater than that of a lower width may be formed by a self-aligning method using transfer transistors and reset transistors. This may not take into consideration the problems caused when using the photo process, for example, misalignment of the photoresist pattern or CD (critical dimension) deviation according to each position on the semiconductor substrate. In addition, it may not be considered that it is difficult to form a photoresist pattern having a vertical profile.

Next, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. The following exemplary embodiments can be modified in many different forms, and the scope of the present invention is not limited to the following exemplary embodiments. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art. In the accompanying drawings, the size or thickness of the films or regions is exaggerated for clarity.

1 is an exemplary unit pixel equivalent circuit diagram of an image sensor in accordance with the present invention.

Referring to FIG. 1, two photodiodes PD ₁ and PD ₂ and transfer transistors Tx ₁ and Tx ₂ have a common reset transistor Rx, select transistor Sx, and drive transistor Dx. An equivalent circuit diagram of CIS unit pixels sharing an equivalent is illustrated. This is to reduce the size of the image sensor and to be highly integrated, and may include two or more photodiodes in a unit pixel as necessary. Therefore, it is possible to manufacture an image sensor that can sense a wide range of light at the same time. The unit pixel is, respectively, which transport the signal charges generated at the photodiodes to receive applying a light generating a photo-charges (PD _1, PD _2), the photodiode (PD _1, PD ₂₎ to the floating diffusion region (FD) Transfer transistors Tx ₁ and Tx ₂ , a reset transistor Rx that periodically resets the charge stored in the floating diffusion region FD, and act as a source follower buffer amplifier. A drive transistor Dx for buffering a signal according to the charge charged in the diffusion region FD, and a select transistor Sx for switching and addressing to select the unit pixel. Include.

FIG. 2 includes two photodiodes in a layout corresponding to FIG. 1. 3 includes four photodiodes in a layout of another exemplary unit pixel of an image sensor in accordance with the present invention.

Referring to FIG. 2, two photodiodes 20a and 20b are provided in a unit pixel and transfer transistors 30a and 30b respectively connected thereto. Two transfer transistors 30a and 30b are connected to a common floating junction region 40. The reset transistor 50 is formed in the active region 60 in which the floating junction region 40 is formed. The drive transistor 70 and the select transistor may be formed on an extension line of the active region 60, and are formed on another active region 65 as shown in FIG. 2 to reset the reset transistor 60 and floating through the wiring. It may also be connected to the junction region 40. The contact stud 110 formed in the floating junction region 40 for the wiring has a width W1 of an upper portion contacting the wiring, and a width of W2 smaller than W1 of a lower portion of the contact stud 110 contacting the wiring. Therefore, the capacitance of the floating junction region 40 is reduced to increase the dynamic range of the image sensor.

Referring to FIG. 3, four photodiodes 20a, 20b, 20c, and 20d are provided in a unit pixel, and transfer transistors 30a, 30b, 30c, and 30d respectively connected to the unit pixel. The transfer transistors 30a, 30b, 30c, 30d include a common floating junction region 40, a reset transistor 60, a drive transistor 70, and a select transistor 80. The transistors may be formed on an active region connected to one, or may be formed on another active region and interconnected through metal lines 146, 147, and 148 as shown in FIG. 3. In particular, the contact stud 110 formed in the floating junction region 40 for wiring has a structure in which upper and lower widths are formed differently as described with reference to FIG. 2.

4 is a cross-sectional view taken along line IV-IV 'of FIG. 2.

Referring to FIG. 4, an isolation region 15 having a shallow trench isolation (STI) structure is formed on a semiconductor substrate 10 to define an active region. A photodiode 20, a gate conductive film 32 of the transfer transistor, a gate insulating film 34, and a floating junction region 40 are formed in the active region. After forming the other transistors, the interlayer insulating film 100 having the contact stud 110 is formed on the entire surface of the resultant. The contact stud 110 has a width different from a bottom contacting the floating junction region 40 and a top contacting the metal wiring 140. That is, the upper width W1 is made wider than the lower width W2, thereby reducing the capacitance of the floating junction region 40 while increasing the dynamic range of the image sensor while reducing the resistance between the metal wires. In addition, the contact stud 110 may be made of doped polysilicon, doped germanium, or a mixture thereof to prevent dark current generation.

The contact stud 110 may be connected to the metal wire 140 and may further form a barrier layer 115 therebetween. Aluminum, copper, polysilicon, or the like may be used as the metal wire 140.

5 to 8 are cross-sectional views illustrating the manufacturing method of the image sensor according to the process sequence.

Referring to FIG. 5, a photodiode 20, a hole accumulation region 25, a transfer transistor, a floating junction region 40, and a reset transistor are formed in an active region of the semiconductor substrate 10 defined by the device isolation layer 15. Is provided. The transfer transistor includes a gate conductive film 32, a gate insulating film 34, a gate sidewall spacer 36, and a junction region (not shown). The reset transistor also includes a gate conductive film 52, a gate insulating film 54, Spacer 56 and junction region 60. An etch stop layer 102 may be further formed on the elements to facilitate an etching process to be performed later. An interlayer insulating layer 100 is formed on the etch stop layer 102. An etching mask 105 is formed to expose a predetermined region of the interlayer insulating film 100 on which contact studs 110, 111, 112, and 113 of FIG. 8 are to be formed. The contact studs 110 (in FIG. 8) contacting the floating junction region may be formed differently from the contact studs (111, 112, 113 in FIG. 8) contacting other devices, and may be simultaneously formed on the process margin.

Referring to FIG. 6, the interlayer insulating layer 110 is isotropically etched 120 using the etch mask 105. Isotropic etching 120 is preferably wet etching. The contact stud to be formed in the present invention has a structure in which the upper width and the lower width are different so that the etching amount is adjusted so that the floating junction region 40 and other devices are not exposed by the isotropic etching 120. The wide first opening 125 is formed by the isotropic etching.

Referring to FIG. 7, the interlayer insulating film 100 having the first opening 125 is anisotropically etched by using the etching mask 105. Anisotropic etching 130 is preferably dry etching. The second opening 135 is formed to expose the floating junction region 40 and the devices to be contacted by the anisotropic etching 130. Therefore, an opening in which the upper width is wider than the lower width is formed in the interlayer insulating film 100. In this embodiment, anisotropic etching is performed after isotropic etching, but is not limited thereto, and anisotropic etching may be performed after isotropic etching.

Referring to FIG. 8, the openings are filled with a conductive material and planarized to expose the interlayer insulating layer 100 to form contact studs 110, 111, 112, and 113. The conductive material can prevent leakage current generation by using doped polysilicon, doped germanium, or a mixture thereof. When the leakage current flows into the photodiode, it causes a dark current phenomenon in which the current is generated even in the absence of light, thereby preventing it from being implemented, thereby improving image quality of the image sensor. The contact studs 110, 111, 112, and 113 are connected to the metal wires 140, 141, 142, and 143, respectively, so as to interconnect each other with desired elements.

As described above, the present invention has a structure in which a contact stud in contact with the floating junction region is in contact with the metal wiring, and a width thereof is relatively wide, and a lower portion in contact with the floating junction region is relatively narrow in width. Thus, the image sensor of the present invention increases the dynamic range of the image sensor by narrowing the area where the contact stud contacts the floating junction area, thereby reducing capacitance. In addition, the contact studs may be formed of doped polysilicon, doped germanium, or a mixture thereof to prevent dark currents, thereby improving image quality of the image sensor.

In addition, according to the method of manufacturing an image sensor of the present invention, an anisotropic etching and an isotropic etching may be used to effectively manufacture an image sensor including contact studs having different upper and lower widths.

In addition, according to another method of manufacturing an image sensor, according to the integration of an image sensor, contact studs having different upper and lower widths may be formed by a self-aligning method using transistors. Therefore, an image sensor including the contact stud can be easily manufactured without considering a misalignment or CD deviation problem due to a photo process.

In the above, the present invention has been described in detail with reference to preferred embodiments, but the present invention is not limited to the above embodiments, and various modifications and changes by those skilled in the art within the spirit and scope of the present invention. This is possible.

Claims (12)

A semiconductor substrate on which a photodiode, a reset transistor, and a drive transistor are formed; A floating diffusion region formed by implanting impurities into a predetermined region of the semiconductor substrate, A first contact stud in contact with the floating diffusion region, the first contact stud having a structure having a different width between an upper part and a lower part, A metal wire connected to the first contact stud, and And a transistor electrically connected to the floating diffusion region through the metal wire. The image sensor of claim 1, wherein the first contact stud is any one selected from the group consisting of doped polysilicon, doped germanium, and mixtures thereof. The image sensor of claim 1, wherein the first contact stud has a structure in which an upper width thereof is wider than a lower width. The image sensor according to claim 1, further comprising a long wall on the first contact stud in contact with the metal wiring. The image sensor of claim 1, further comprising a second contact stud connected to the gate conductive layer of the transistor, the second contact stud having a structure having an upper width wider than a lower width. The image sensor of claim 1, further comprising a third contact stud connected to the junction region of the transistor, the third contact stud having a structure having an upper width wider than a lower width. A semiconductor substrate on which a photodiode, a reset transistor, and a drive transistor are formed; Forming a floating diffusion region in the semiconductor substrate, Forming an interlayer insulating film on the resultant, Forming an etching mask on the interlayer insulating layer to form a contact stud in contact with the floating diffusion region; Isotropically etching the interlayer insulating layer using the etching mask; Anisotropically etching the interlayer insulating layer using the etching mask, and Removing the etch mask and filling the opening formed by the etching steps with a conductive material to complete the contact stud. The method of claim 7, wherein the etching steps areotropically etch the interlayer insulating layer using the etch mask, and then anisotropically etch the interlayer insulating layer using the etch mask to expose the floating junction region and to form an upper width. A method of manufacturing an image sensor characterized by forming an opening having a structure wider than the width of the lower portion. The method of claim 7, wherein the etching steps are performed by anisotropically etching the interlayer insulating layer using the etching mask, and then isotropically etching the interlayer insulating layer using the etching mask to expose the floating junction region and to have an upper width. A method of manufacturing an image sensor, characterized in that to form an opening having a structure wider than the width of the lower portion. 8. The method of claim 7, wherein removing the etch mask and filling the opening formed by the etching steps with any one selected from the group consisting of doped polysilicon, doped germanium, and mixtures thereof to complete the contact stud. The manufacturing method of the image sensor characterized by the above-mentioned. Forming a floating diffusion region, a gate pattern and a junction region of a transfer transistor, and a gate pattern and a junction region of a reset transistor in a semiconductor substrate, Forming an interlayer insulating film on the resultant, Forming an etch mask on the interlayer insulating layer to expose the floating junction region, the gate pattern of the transfer transistor, and a predetermined region of the interlayer insulating layer on the gate pattern of the reset transistor; Etching the interlayer insulating layer using the etching mask to form an opening exposing the floating junction region, the gate pattern of the transfer transistor, and the gate pattern of the reset transistor; Removing the etch mask and filling the opening with a conductive material to complete a contact stud. 12. The method of claim 11, wherein the opening is filled with one selected from the group consisting of doped polysilicon, doped germanium, and mixtures thereof to complete the contact stud.

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