KR20080014301A - Back illuminated cmos image sensors with deep trench isolation and method for producing the same - Google Patents

Abstract

A back illuminated CMOS image sensor having a deep trench device isolating film and a method for producing the same are provided to prevent an electrical crosstalk and an optical crosstalk between pixels by isolating a photo diode of a pixel array using a device isolating film with a deep trench structure. A back illuminated CMOS image sensor comprises a device isolating film with a deep trench structure(13), a photo diode(11), a pixel circuit(20), and a lens(30). The device isolating film with the deep trench structure is formed by extending from a first side to a second side of a semiconductor substrate(10). The photo diode is defined by the device isolating film with the deep trench structure, and is formed by extending from a first side to a second side of the semiconductor substrate. The pixel circuit adjacent to the first side of the semiconductor substrate is formed. The lens adjacent to the second side of the semiconductor substrate is formed.

Description

Back illuminated CMOS image sensors with deep trench isolation and method for producing the same

1 is a schematic cross-sectional view of a pixel array region of a conventional backside-illumination type CMOS sensor.

2 is a schematic cross-sectional view of a pixel array region of a chip edge portion of a conventional backside-illumination type CMOS sensor.

3 is a schematic cross-sectional view of a pixel array region of a backside-illuminated CMOS image sensor according to an embodiment of the present invention.

4 is a schematic flowchart for sequentially explaining a method of manufacturing a backside-illumination type CMOS image sensor according to the present invention.

* Explanation of symbols for the main parts of the drawings

10: semiconductor substrate 11: photodiode

13: deep trench device isolation layer 20: pixel circuit portion

30: lens unit 31: color filter

33: microlens 40: support substrate

The present invention relates to a CMOS image device, and more particularly, to a back illuminated CMOS image sensor capable of preventing cross talk and a method of manufacturing the same.

A general image sensor refers to a semiconductor device that converts an optical image into an electrical signal. Such an image sensor may be classified into a charge coupled device (CCD) and a CMOS image sensor (CIS). Image sensors are based on a two-dimensional array of pixels. Each pixel includes a sensing element capable of converting a portion of the optical image into an electrical signal. Electrical signals are used, for example, to recreate the optical image on the display.

CMOS image sensor is a device having a photodiode that receives an optical signal in a unit pixel and a MOS transistor that can control the optical signal. The CMOS image sensor is simpler in manufacturing process than a CCD and uses a well-established CMOS technology. In addition to the signal processing device, there is an advantage that can be manufactured in a single chip.

As CMOS technology evolves toward shrinking photolithography, the size of pixels and circuits in CMOS image sensors is also decreasing. As the size of the pixel is reduced, there is an advantage in that a pixel array made up of a large number of pixels can be manufactured at a low cost. In particular, in a front illuminated CMOS image sensor using an active pixel sensor (APS), metal lines associated with the active circuit reduce the fill factor of the pixel array. This occurs even when the line width of the metal line is reduced, because the presence of the metal line obscures the photodiode diffusion region, which is the light sensing unit, or the distance that the light reaches the photodiode diffusion region is reduced, thereby reducing the amount of light reaching the diffusion region.

Back illuminated CMOS sensors are image sensors in which circuits are present on the front of the substrate and lenses are present on the back of the substrate. Since light enters the impurity region of the photodiode directly through the lens without passing through the circuit region, the problem of reducing the filling rate of the front-illumination CMOS image sensor can be solved.

1 is a schematic cross-sectional view of a conventional back-illumination CMOS sensor. The pixel circuit portion 1 of the CMOS sensor is laminated in contact with one surface 7 of the substrate 2. An impurity region 9 of a photodiode is formed above the pixel circuit portion 1 and extends to the other surface 8 of the substrate 2, and a color filter 3 and a microlens 4 are formed thereon. The substrate 2 of the CMOS image sensor is very thin and is supported by the supporting substrate 6 in contact with the pixel circuit portion 1.

The manufacturing method of such a conventional backside-illumination type CMOS sensor is as follows. First, the impurity region 2 of the photodiode is formed at a predetermined depth from the entire surface of the substrate by ion implantation, and then circuit pattern layers constituting the pixel circuit unit 1 are formed. The support substrate 6 is attached to the front surface of the substrate in contact with the pixel circuit portion 1, and the back surface of the substrate is polished to expose the impurity region 2 of the photodiode from the rear surface of the substrate. A lens unit 5 including a color filter 3 and a micro lens 4 is formed on the exposed photodiode 2.

The area immediately below the color filter 3 in the photodiode 2 area corresponds to the farthest part from the front surface of the substrate, thereby increasing the probability that the concentration of the ion-implanted impurities is not uniform. In the back-illumination type CMOS sensor, device separation between the photodiodes 2 is performed by a doping profile. The area under the color filter 3 is a region where a large amount of light is received, but the doping profile is not clear due to uneven impurities. Electrical crosstalk may not be completely eliminated.

In addition, as shown in FIG. 2, in the case of the pixel at the edge of the chip, the microlens 3 and the color filter 4 are not aligned with the photodiode 2, and the photodiode is used to increase the amount of light received. It is formed by shifting constantly with respect to 2). Therefore, in the case of the pixel at the chip edge, there is a high possibility of optical crosstalk.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a backside-illuminated CMOS image sensor capable of blocking electrical crosstalk and optical crosstalk between pixels.

Another object of the present invention is to provide a method of manufacturing a backside-illumination type CMOS image sensor capable of blocking electrical crosstalk and optical crosstalk between pixels.

In order to achieve the above object, a backside-illumination type CMOS image sensor extends from the first surface to the second surface in a semiconductor substrate having a first surface and a second surface, and has a deep trench structure. ; A photodiode defined by the deep trench isolation layer and extending from the first surface toward the second surface; A pixel circuit portion formed adjacent to the first surface of the semiconductor substrate; And a lens unit formed adjacent to the second surface of the semiconductor substrate.

The substrate may further include a support substrate on the pixel circuit unit.

The depth of the device isolation layer of the deep trench structure is preferably 3 ~ 10㎛.

The device of the deep trench structure may be formed of an insulating film having a refractive index lower than that of the semiconductor substrate so that the light incident through the photodiode and totally reflected at the boundary of the device isolation film may be silicon oxide.

A glass substrate may be further included between the second surface of the semiconductor substrate and the lens unit.

The pixel circuit unit may include a transfer transistor, a reset transistor, a driving transistor, a selection transistor, and a wiring.

The lens unit may include a color filter adjacent to the second surface of the semiconductor substrate and a micro lens on the color filter.

According to another aspect of the present invention, there is provided a method of manufacturing a backside-illumination type CMOS image sensor, the method including: forming an isolation layer of a deep trench structure from a first surface of a semiconductor substrate; Forming a photodiode region by ion implantation from the first surface in the semiconductor substrate defined by the device isolation film; Forming a pixel circuit portion on the first surface of the semiconductor substrate over the photodiode region; Polishing the second surface of the semiconductor substrate on which the pixel circuit portion is formed; And forming a lens unit on the second surface of the polished semiconductor substrate by aligning the photodiode.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided so that the disclosure may be made thorough and complete, and to fully convey the spirit of the present invention to those skilled in the art. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. Like numbers refer to like elements throughout.

3 is a cross-sectional view schematically illustrating a portion of a backside-illuminated CMOS image sensor according to an embodiment of the present invention. 3 shows a pixel array portion including a photodiode 11, a pixel circuit portion 20, and a lens portion 30. In FIG. 3, the front side 13 of the semiconductor substrate 10 on which the photodiode 11 is formed is faced downward, and the back side 15 of the semiconductor substrate 10 faces upward. In the backside-illumination type CMOS image sensor, since the light is incident from the backside 15 of the semiconductor substrate 10, the thickness of the substrate should be thin enough to allow the incident light to reach the photodiode 11.

The photodiode 11 in the semiconductor substrate 10 may be formed by a p-type impurity region in the n-type impurity or an n-type impurity region in the p-type impurity region. On the front surface 13 of the semiconductor substrate 10 under the photodiode 11, a pixel circuit unit 20 including transistors and wirings constituting a unit pixel together with the photodiode 11 is stacked. The support substrate 40 may be attached under the pixel circuit unit 20, and a passivation layer (not shown) and an adhesive layer (not shown) may be further formed between the pixel circuit unit 20 and the support substrate 40. On the back surface of the semiconductor substrate 10 on the photodiode 11, a lens portion 30 including a color filter 31 and a micro lens 33 is formed. A transparent substrate such as glass (not shown) may be further formed between the photodiode 11 and the lens unit 30.

In the present invention, adjacent photodiodes 11 are separated from each other by the deep trench device isolation layer 13. The deep trench device isolation layer 13 may be formed as deep as the photodiode 11 or slightly shallower. The deep trench device isolation layer 13 is formed directly below the lens unit 30, so that electrons or holes generated by light in the photodiode 11 do not move vertically but move to adjacent pixel regions. Electrical crosstalk can be prevented. In the backside-illumination type CMOS image sensor, the impurity region of the photodiode 11 is generated by deep ion implantation from the front surface of the semiconductor substrate 10, so that the impurity region in contact with the backside of the semiconductor substrate 10 under the lens portion 30 is Electrical crosstalk may occur due to scattering of the doping profile, and electrical crosstalk may be prevented by the deep trench device isolation layer 13, which is an insulating layer.

In addition, since the light incident with the inclination through the lens unit 30 is totally reflected at the boundary between the photodiode 11 and the device isolation layer 13 and cannot pass through the photodiode 11 of the adjacent pixel, optical crosstalk is performed. ) Can be prevented. The pixels of the edge portion of the chip of the conventional CMOS image sensor are formed such that the lens unit 30 and the corresponding photodiode 11 corresponding to each other do not overlap vertically but obliquely with each other in order to increase the light receiving efficiency of light coming in at an angle. There was a high possibility of optical crosstalk between adjacent pixels. However, in the present invention, as shown in FIG. 4, the deep trench device isolation layer 13 between the photodiodes 11 is obliquely introduced into the deep trench device isolation layer 13 using a material having a lower refractive index than the silicon of the photodiode 11. By total reflection of light it is possible to prevent optical crosstalk.

5 is a schematic flowchart for sequentially explaining a method of manufacturing a backside-illumination type CMOS image sensor according to the present invention.

Referring to FIG. 5, first, a deep trench device isolation layer is formed on a semiconductor substrate (S10). The deep trench device isolation layer is formed by etching a semiconductor substrate using a hard mask pattern such as a silicon nitride film as a mask to form a deep trench, and then filling an insulating film such as a silicon oxide film. The insulating film is filled by forming and planarizing the insulating film so as to fill the deep trench, and then removing the hard mask pattern.

Subsequently, a photodiode region is formed by implanting impurities into the semiconductor substrate on which the deep trench device isolation layer is formed (S20). The photodiode region can be made by forming a p-type impurity region in the n-type impurity or by forming an n-type impurity region in the p-type impurity region.

After the photodiode region is formed in the semiconductor substrate, a pixel circuit portion including transistors and wirings forming unit pixels, such as a transfer transistor, a reset transistor, a driving transistor, and a selection transistor, is formed on the substrate (S30).

The support substrate is attached to the entire surface of the semiconductor substrate on which the pixel circuit portion is formed (S40). A passivation layer may be formed to protect the pixel circuit portion before attachment of the support substrate.

After attaching the support substrate, the back surface of the semiconductor substrate is ground and chemical mechanical polishing is performed so that light may be incident from the back surface of the semiconductor substrate to the photodiode region (S50).

A lens unit including a color filter and a micro lens is formed on the photodiode on the rear surface of the semiconductor substrate (S60). In this case, a glass substrate may be further formed between the rear surface of the semiconductor substrate and the lens unit.

Although the embodiments of the present invention have been described in detail above, the present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes without departing from the technical spirit of the present invention are made. It will be apparent to one of ordinary skill in the art that this is possible.

According to the present invention, the electrical crosstalk and the optical crosstalk between pixels can be blocked by isolating the photodiode of the pixel array with the device isolation layer having the deep trench structure in the backside-illumination type CMOS image sensor.

Claims (9)

A device isolation layer having a deep trench structure extending from the first surface toward the second surface in a semiconductor substrate having a first surface and a second surface; A photodiode defined by the deep trench isolation layer and extending from the first surface toward the second surface; A pixel circuit portion formed adjacent to the first surface of the semiconductor substrate; And And a lens unit formed adjacent to the second surface of the semiconductor substrate. The back-illuminated CMOS image sensor of claim 1, further comprising a support substrate on the pixel circuit portion. The backside-illumination type CMOS image sensor of claim 1, wherein a depth of the device isolation layer having the deep trench structure is 3 to 10 μm. The backside type CMOS image sensor of claim 1, wherein the device isolation film having the deep trench structure is formed of an insulating film having a refractive index lower than that of the semiconductor substrate so that the light incident obliquely through the photodiode is totally reflected at the boundary of the device isolation film. The backside irradiation CMOS image sensor of claim 4, wherein the device isolation layer of the deep trench structure is a silicon oxide layer. The back-illumination type CMOS image sensor of claim 1, further comprising a glass substrate between the second surface of the semiconductor substrate and the lens unit. The back-illumination CMOS image sensor of claim 1, wherein the pixel circuit unit comprises a transfer transistor, a reset transistor, a driving transistor, a selection transistor, and a wiring. The back-illumination CMOS image sensor of claim 1, wherein the lens unit comprises a color filter adjacent to the second surface of the semiconductor substrate and a micro lens on the color filter. Forming a device isolation film having a deep trench structure from a first surface of the semiconductor substrate; Forming a photodiode region by ion implantation from the first surface in the semiconductor substrate defined by the device isolation film; Forming a pixel circuit portion on the first surface of the semiconductor substrate over the photodiode region; Polishing the second surface of the semiconductor substrate on which the pixel circuit portion is formed; And forming a lens unit on the second surface of the semiconductor substrate to be aligned with the photodiode.

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