KR20110072516A - Method of fabricating image sensor - Google Patents

Abstract

In another aspect, a method of manufacturing an image sensor includes forming a gate on a semiconductor substrate; Forming a photodiode on the semiconductor substrate on one side of the gate; Stacking a first oxide film, a nitride film, and a second oxide film on an entire surface of the semiconductor substrate on which the photodiode and the gate are formed; Performing a first etching process on the first oxide film and the nitride film to form a first spacer on the sidewall of the gate on the second oxide film; Forming a mask pattern over the first spacer and the gate to cover the first spacer; And etching the second oxide film by performing a second etching process on the semiconductor substrate on which the mask pattern is formed, to form a second spacer including a first spacer and a second oxide film.

Mask Patterns, Photoresists, Spacers

Description

Manufacturing method of an image sensor {Method of Fabricating Image Sensor}

Embodiments relate to a method of manufacturing an image sensor.

An image sensor is a semiconductor device that converts an optical image into an electrical signal, and is classified into a charge coupled device (CCD) image sensor and a CMOS image sensor (CIS). .

The CMOS image sensor is a structure in which a photo diode area for receiving a light signal and converting it into an electric signal and a transistor area for processing the electric signal are horizontally disposed.

At this time, after forming a photodiode in the CMOS image sensor, a transistor is formed. When forming a spacer of the ONO structure of the transistor, dry etching is performed on a portion of the transistor, and the remaining oxide film is a plasma of the photodiode as a light receiving unit. In order to reduce damage, it is formed by performing wet etching.

However, due to the loss of the spacer due to isotropic etching during wet etching, dark current of the image sensor is generated.

The embodiment may improve the performance of the image sensor by preventing the loss of the spacer when forming the gate spacer.

In another aspect, a method of manufacturing an image sensor includes forming a gate on a semiconductor substrate; Forming a photodiode on the semiconductor substrate on one side of the gate; Stacking a first oxide film, a nitride film, and a second oxide film on an entire surface of the semiconductor substrate on which the photodiode and the gate are formed; Performing a first etching process on the first oxide film and the nitride film to form a first spacer on the sidewall of the gate on the second oxide film; Forming a mask pattern over the first spacer and the gate to cover the first spacer; And etching the second oxide film by performing a second etching process on the semiconductor substrate on which the mask pattern is formed, to form a second spacer including a first spacer and a second oxide film.

In the method of manufacturing the image sensor according to the embodiment, when the spacer is formed, a mask pattern is formed on the gate, the nitride layer pattern, and the second oxide layer, and the wet etching process is performed on the first oxide layer, thereby preventing the loss of the spacer.

Therefore, the loss of the spacer can be effectively reduced, so that the generation of dark current of the image sensor can be minimized.

An image sensor and a method of manufacturing the same according to an embodiment will be described in detail with reference to the accompanying drawings.

In the description of the embodiments, where described as being formed "on / over" of each layer, the on / over may be directly or through another layer ( indirectly) includes everything formed.

In the drawings, the thickness or size of each layer is exaggerated, omitted, or schematically illustrated for convenience and clarity of description. In addition, the size of each component does not necessarily reflect the actual size.

The embodiment is not limited to the CMOS image sensor, and may be applied to all image sensors requiring a photodiode such as a CCD image sensor.

1 to 7 are side cross-sectional views illustrating a method of manufacturing an image sensor according to an embodiment.

As shown in FIG. 1, the gate 270 is formed on the semiconductor substrate 100 on which the device isolation layer 110 is formed, and the photodiode 200 is formed on the semiconductor substrate 100.

The semiconductor substrate 100 may have a low concentration p-type epi layer (not shown) on a high concentration p ++ type silicon substrate. This may increase the depth of the depletion region of the photodiode due to the low concentration of p epitaxial layer, thereby increasing the photodiode's ability to collect photocharges.

In addition, having a high concentration of p ++ type substrate under the p-type epi layer reduces the random diffusion of photocharges because the charge is recombined before the charge is diffused to neighboring pixel units. This is because the change in the transfer function of the photocharge can be reduced.

The isolation layer 110 may be formed by forming a trench in the semiconductor substrate 100 and then filling an insulating material.

The gate 270 may be formed by stacking the gate insulating layer 250 and the polysilicon pattern 260 by forming and patterning an oxide film and polysilicon on the semiconductor substrate 100.

In this case, the gate 270 may be a transfer transistor.

In the present embodiment, the gate 270 is formed of polysilicon, but is not limited thereto, and may include a metal silicide layer.

Subsequently, as shown in FIG. 2, a photodiode 200 is formed on the semiconductor substrate 100.

The photodiode 200 includes a first impurity region 210 and a second impurity region 220, and may be formed by performing an ion implantation process on the semiconductor substrate 100 after forming the gate 270. Can be.

The first impurity region 210 is formed by performing the first ion implantation process on the semiconductor substrate 100 with n-type impurities.

The second impurity region 220 is formed by performing a second ion implantation process on the semiconductor substrate 100 with p-type impurities.

As shown in FIG. 3, an oxide-nitride-oxide (ONO) film is formed on the semiconductor substrate 100 on which the photodiode 200 is formed.

The ONO film is formed by sequentially stacking a first oxide film 301, a nitride film 302, and a second oxide film 303.

Subsequently, as illustrated in FIG. 4, a first etching process is performed on the nitride layer 302 and the second oxide layer 303 to form a nitride layer pattern 320 on sidewalls of the gate 270 on the first oxide layer 301. And a second oxide film pattern 330.

In this case, the first etching process is a dry etching process.

An anisotropic dry etching process may be performed on the semiconductor substrate 100 to form the spacer layer-shaped nitride layer pattern 320 and the second oxide layer pattern 330 on sidewalls of the gate 270.

In this case, the first oxide film 301 formed on the gate 270 may be removed or left.

The first oxide film 301 left on the photodiode 200 and on the semiconductor substrate 100 may be left at about 100 kV.

That is, during the first etching process, part of the first oxide layer 301 may be etched.

As shown in FIG. 5, a photoresist pattern 400 is formed on the gate 270.

The photoresist pattern 400 may be formed only on the gate 270, and a part of the photoresist pattern 400 may be formed on the nitride layer pattern 320 and the second oxide layer pattern 330.

Subsequently, as illustrated in FIG. 6, a reflow process is performed on the photoresist pattern 400 to form a mask pattern 500 on the gate 270.

The mask pattern 500 may be formed on the gate 270, the nitride layer pattern 320, and the second oxide layer pattern 330.

In addition, the mask pattern 500 may be formed to have a rounded upper portion through the reflow process to cover the nitride layer pattern 320 and the second oxide layer pattern 330.

That is, the mask pattern 500 covers the nitride layer pattern 320 and the second oxide layer pattern 330 so as not to be etched into the nitride layer pattern 320 and the second oxide layer pattern 330 in the subsequent etching process. It is formed to.

As shown in FIG. 7, a second etching process is performed on the semiconductor substrate 100 on which the mask pattern 500 is formed to form spacers 300 on sidewalls of the gate 270.

The spacer 300 is formed of a first oxide layer pattern 310, a nitride layer pattern 320, and a second oxide layer pattern 330.

The second etching process is a wet etching process.

The first oxide layer 301 is etched by the second etching process to form the spacer 300.

In this case, the second etching process proceeds to a wet etching process, so that plasma damage is not applied to the photodiode 200.

In addition, the mask pattern 500 is formed to cover the nitride layer pattern 320 and the second oxide layer pattern 330, so that the second oxide layer pattern 330 is not etched by the second etching process.

In addition, due to the mask pattern 500, etching is not performed on the first oxide layer 301 which is in contact with the upper portion of the gate 270.

In addition, the first oxide layer 301 disposed under the nitride layer pattern 320 and the second oxide layer pattern 330 may be etched stably.

Accordingly, the first oxide film 301 in the region where the mask pattern 500 is in contact with the gate 270 may be prevented from being etched to prevent loss of the spacer 300, thereby preventing a dark current of the image sensor. It is possible to minimize the occurrence of (dark current).

As described above, in the method of manufacturing the image sensor according to the embodiment, when the spacer is formed, a mask pattern is formed on the gate, the nitride layer pattern, and the second oxide layer, and the wet etching process is performed on the first oxide layer, thereby losing the spacer. Can be prevented.

Therefore, the loss of the spacer can be effectively reduced, so that the generation of dark current of the image sensor can be minimized.

The above-described embodiments are not limited to the above-described embodiments and drawings, and it can be variously substituted, modified, and changed without departing from the technical spirit of the embodiments. It will be clear to those who have it.

1 to 7 are side cross-sectional views illustrating a method of manufacturing an image sensor according to an embodiment.

Claims (6)

Forming a gate on the semiconductor substrate; Forming a photodiode on the semiconductor substrate on one side of the gate; Stacking a first oxide film, a nitride film, and a second oxide film on an entire surface of the semiconductor substrate on which the photodiode and the gate are formed; Performing a first etching process on the first oxide film and the nitride film to form a first spacer on the sidewall of the gate on the second oxide film; Forming a mask pattern over the first spacer and the gate to cover the first spacer; And Performing a second etching process on the semiconductor substrate on which the mask pattern is formed to etch the second oxide layer to form a second spacer including a first spacer and a second oxide layer. The method of claim 1, The first etching process is a method of manufacturing an image sensor comprising a dry etching process. The method of claim 1, The second etching process is a manufacturing method of the image sensor comprising a wet etching (wet etching) process. The method of claim 1, And the mask pattern is formed of photoresist. The method of claim 4, wherein Forming the mask pattern, Forming a photoresist pattern on the gate; And And performing a reflow process on the semiconductor substrate on which the photoresist pattern is formed to form a mask pattern covering the first spacer and the gate. The method of claim 5, The mask pattern manufacturing method of the image sensor comprising a rounded top.

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