KR100667499B1 - Method for fabricating cmos image sensor - Google Patents

Abstract

The present invention is to provide a manufacturing process that does not change the characteristics of the logic transistor in the process of self-aligning for manufacturing the photodiode of the CMOS image sensor, the present invention for this purpose is the first gate for the gate of the transfer transistor on the substrate Forming a conductive film pattern; Forming a hard mask pattern on the first conductive layer pattern; Forming a second conductive film pattern for a gate of a transistor other than a transfer transistor on the substrate; Forming a photoresist pattern for the photodiode to be formed in a region in contact with the first conductive layer pattern; And performing an implant process for the photodiode using the photoresist pattern as a mask, wherein the hard mask pattern serves as a barrier film of the lower portion of the implant during the implant process.

CMOS image sensor, hard mask, photodiode, deep implant process.

Description

Manufacturing method of CMOS image sensor {METHOD FOR FABRICATING CMOS IMAGE SENSOR}

1 is a layout showing unit pixels of a conventional CMOS image sensor.

2A to 2D are cross-sectional views illustrating a method of manufacturing a CMOS image sensor according to the prior art.

3A to 3H are cross-sectional views illustrating a method of manufacturing a CMOS image sensor according to a preferred embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

20: substrate 21: polysilicon film

22: buffer film 23: hard mask film

24a, 24b: Photosensitive film 25: Photosensitive film for deep implants

The present invention relates to a CMOS image sensor, and more particularly to a process for forming a photodiode.

In general, an image sensor of a semiconductor device is a semiconductor device that converts an optical image into an electrical signal. Representative image sensor devices include a charge coupled device (CCD) and a CMOS image sensor.

Among them, the charge-coupled device is a device in which charge carriers are stored and transported in the capacitor while individual metal-oxide-silicon (MOS) capacitors are located very close to each other, and the CMOS image sensor is a control circuit and a signal processing circuit. It is a device that adopts a switching method of making MOS transistors by the number of pixels by using CMOS technology using a signal processing circuit as a peripheral circuit and sequentially detecting the output using the MOS transistors.

A typical CMOS image sensor includes a pixel array in which a plurality of unit pixels are arrayed, an ADC block for converting an analog signal output from the pixel array into a digital signal, a line buffer for storing digital values output from the ADC block, and an input. And a control register and logic for controlling the decoder / pixel driver and the decoder / pixel driver to decode the address and select the unit pixel of the pixel array.

A circuit diagram showing a unit pixel composed of one photodiode (PD) and four MOS transistors in a conventional CMOS image sensor. A photodiode that receives light to generate photocharges and a photocharge collected from the photodiode A transfer transistor for transporting to the floating diffusion region, a reset transistor for setting the potential of the floating diffusion region to a desired value and discharging the charge to reset the floating diffusion region, and a voltage of the floating diffusion region is applied to the source follower buffer A drive transistor serves as an amplifier (Source Follower Buffer Amplifier) and a select transistor serving as an addressing role as a switching role. Outside the unit pixel, a load transistor for reading an output signal is formed.

1 is a layout showing unit pixels of a conventional CMOS image sensor.

Referring to FIG. 1, in the unit pixel of the CMOS image sensor, a photodiode PD is largely disposed, and a transfer transistor Tx and a gate of the driver transistor Dx cross the active region Active.

Since the photodiode is formed vertically based on the region shown in FIG. 1, a P region is formed at an upper portion and an N region is formed at a lower portion.

Therefore, since the N region is formed in the deep region of the substrate, it is formed by the implant process with high energy.

However, since the N region of the photodiode should not be formed at the lower end of the gate pattern of the transfer transistor Tx, an implant process for the N region of the photodiode is performed using the gate pattern of the transfer transistor Tx as a mask. .

2A to 2D are cross-sectional views illustrating a method of manufacturing a CMOS image sensor according to the prior art.

As shown in FIG. 2A, a polysilicon film 11 for forming a gate is formed on the substrate 10, and a hard mask film 12 is formed thereon.

Subsequently, photosensitive film patterns 13a and 13b for forming a gate pattern are formed.

Here, the photoresist pattern 13a is for forming the gate pattern of the transfer transistor Tx, and the photoresist pattern 13b is for forming the gate pattern of the remaining transistor Tx.

Subsequently, as shown in FIG. 2B, the hard mask film 12 and the polysilicon film 10 are patterned using the photoresist patterns 13a and 13b as etch masks.

Subsequently, as shown in FIG. 2C, a photosensitive film pattern 15 for forming an N region of the photodiode is formed and an implant process is performed.

Subsequently, as shown in FIG. 2D, the photosensitive film pattern and the hard mask film patterns 14a and 14b are removed.

Next, although not shown, the remaining process of forming the gate pattern is performed.

In manufacturing the CMOS image sensor, a photodiode must be formed, and a transfer transistor for transmitting the photoelectrons formed in the photodiode to an external circuit is required.

One of the important processes for forming a photodiode is a deep n implant process, in which n + ions are implanted with high energy into the photodiode region.

At this time, n + ions must penetrate only the region where the photodiode is to be formed and must not penetrate the region where the gate pattern of the transfer transistor in contact with the photodiode is to be formed.

Therefore, in order to solve this problem, polysilicon, which will be a gate pattern of the transfer transistor, is used as a mask, that is, a process of injecting n + ions for photodiodes in a self-aligned process. This is shown in Figure 2c.

As a method for self-alignment at this time, after polysilicon is patterned for the gate pattern of the transfer transistor, the photoresist film is used as a blocking layer without removing the photoresist film, or a hard mask film such as a silicon nitride film or a silicon oxide film is used. There is a way to form.

However, the method of using the blocking layer without removing the photoresist layer is difficult to apply due to particle problems. At present, as described above, a hard mask layer is formed on the polysilicon pattern, and n + ions are applied to the photodiode region with high energy. After the injection process, a method of removing the hard mask layer is used.

In general, however, a wet etching method is used to remove the hard mask layer. At this time, an attack is applied to a portion of the polysilicon pattern remaining in the process and a portion to be an active region later, thereby changing the characteristics of the transistor. Occurs.

Because the transfer transistor only functions to transfer charges, the attack received when removing the hard mask layer is not very important. However, since the remaining transistors are logic parts related to the operation of the CMOS image sensor, such a change in the characteristics of the transistors has a serious adverse effect. do.

An object of the present invention is to provide a manufacturing process that does not change the characteristics of the logic transistor in the process of self-aligning for the production of the photodiode of the CMOS image sensor.

According to an aspect of the present invention, there is provided a method of forming a first conductive film pattern for a gate of a transfer transistor on a substrate, and forming a hard mask pattern on the first conductive film pattern. Forming a second conductive film pattern for a gate of a transistor other than the transfer transistor on the substrate, forming a photosensitive film pattern for a photodiode to be formed in a region in contact with the first conductive film pattern, and Performing an implant process for the photodiode using a photoresist pattern as a mask, wherein the hard mask pattern serves as a barrier film of the lower water during the implant process, and removes the hard mask pattern exposed through the photoresist pattern And a method of manufacturing the CMOS image sensor, the method including removing the photoresist pattern. The.
According to another aspect of the present invention, there is provided a method of forming a first conductive film pattern for a gate of a transfer transistor on a substrate, and forming a hard mask pattern on the first conductive film pattern. Forming a second conductive film pattern for a gate of a transistor other than the transfer transistor on the substrate, forming a photosensitive film pattern for a photodiode to be formed in a region in contact with the first conductive film pattern; And performing an implant process for the photodiode using the photoresist pattern as a mask, wherein the hard mask pattern serves as a barrier film of the lower water during the implant process, and removing the photoresist pattern. Forming a photoresist film so that the mask pattern is exposed and the remaining area is covered; It provides a method of manufacturing a CMOS image sensor comprising the step of removing the hard mask pattern exposed through the photosensitive film is formed, and removing the additionally formed photosensitive film.

Hereinafter, the preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the technical idea of the present invention. .

3A to 3H are cross-sectional views illustrating a method of manufacturing a CMOS image sensor according to a preferred embodiment of the present invention.

Referring to FIG. 3A, in the method of manufacturing the CMOS image sensor according to the present embodiment, a polysilicon film 21 for a gate pattern is first formed on a substrate 20, and a buffer layer 22 is formed thereon. The hard mask 23 is formed.

Subsequently, a photoresist pattern 24a for the gate pattern of the transfer transistor Tx is formed thereon.

The buffer layer 22 is used to reduce the damage that the polysilicon film 21 receives at the lower end thereof when the hard mask film 23 is formed and removed.

3B, the hard mask film 23 and the buffer layer 22 are patterned using the photoresist pattern 24a as an etch mask. The buffer layer 22 uses a silicon nitride film, a silicon oxide film, a silicon carbide alloy, and the like, and has a thickness in the range of 200 to 4000 microseconds.

The hard mask film 23 uses a silicon nitride film, a silicon oxide film, a silicon carbide alloy, and the like, and has a thickness in the range of 200 to 4000 microseconds.

Subsequently, as shown in FIG. 3C, a photosensitive film pattern 24b of organic barc or inorganic is formed. The photoresist pattern 24b is for gate patterning of the remaining transistors other than the transfer transistor.

3D, the polysilicon film 21 is patterned using the photoresist pattern 24b and the hard mask pattern 23a as etch masks.

Subsequently, as shown in FIG. 3E, the photosensitive film pattern 25 for forming the photodiode is formed, and an implant process is performed at high energy to form an N region of the photodiode.

Subsequently, as shown in FIG. 3F, the photosensitive film pattern 25 is removed, the hard mask film 25 is removed, and the buffer layer is removed.

In CMOS image sensors, the transfer transistor is larger than the rest of the transistor, so CD is less important than the rest.

Therefore, as described above, only the gate pattern portion of the transfer transistor forms a hard mask, and as a barrier, the photodiode is formed, and the hard mask is removed to form a hard mask film, thereby removing other transistors. Will not adversely affect the characteristics of the.

In the present invention, two methods for producing a hard mask are presented, which are shown in FIGS. 3G and 3H, respectively.

First, referring to FIG. 3G, the first method of removing the hard mask is a method of removing the hard mask without performing the n-implant process of the photodiode and removing the photoresist pattern 25.

Since the n-implant process of the photodiode is applied only to the region where the photodiode is to be formed, only the photodiode portion has no photoresist pattern, and the rest of the photodiode is covered with the photoresist pattern.

Therefore, when the wet etching process is performed in this state, only a hard mask layer on the gate pattern of the transfer transistor is partially removed.

In general, the mask for the n-implant process of the photodiode has some overlap with the transfer transistor region in order to prevent the formation of the photodiode in the portion other than the photodiode region. If this value is set to about 50 nm to 150 nm, the wet etching process Due to the isotropic properties of the hard mask underneath the photoresist film is removed to some extent.

Referring to FIG. 3H, the second method of removing the hard mask is to remove the photoresist pattern 25 after the n implant process of the photodiode, and then expose the gate portion of the transfer transistor through a new photo process. Then, the hard mask and the buffer layer are removed, and the entire photoresist film including the added photoresist film is removed.

In the above-described embodiment, the hard mask and the buffer layer may be removed using only a wet etching process, or a wet etching process and a dry etching process may be used together. In the removal process, the process is performed using phosphoric acid.

As described above, the present invention is not limited to the above-described embodiments and the accompanying drawings, and the present invention may be variously substituted, modified, and changed without departing from the spirit of the present invention. It will be apparent to those of ordinary skill in Esau.

In manufacturing the photodiode of the CMOS image sensor according to the present invention, since the hard mask formed for self-alignment is formed and removed, the change of the characteristics of the transistors other than the transfer transistor is not affected. It is possible to manufacture reliable CMOS image sensor.

Claims (12)

Forming a first conductive film pattern for a gate of the transfer transistor on the substrate; Forming a hard mask pattern on the first conductive layer pattern; Forming a second conductive film pattern for gates of transistors other than the transfer transistor on the substrate; Forming a photoresist pattern for the photodiode to be formed in a region in contact with the first conductive layer pattern; Performing an implant process for the photodiode using the photoresist pattern as a mask, wherein the hard mask pattern serves as a barrier film of the lower water during the implant process; Removing the hard mask pattern exposed through the photoresist pattern; And Removing the photoresist pattern Method for manufacturing a CMOS image sensor comprising a. The method of claim 1, The method of claim 1, further comprising forming a buffer layer between the first conductive layer and the hard mask layer pattern. The method of claim 2, The hard mask pattern is a method of manufacturing a CMOS image sensor, characterized in that using any one selected from silicon nitride film, silicon oxide film or silicon carbide alloy. The method of claim 2, The buffer layer is a method of manufacturing a CMOS image sensor, characterized in that using any one selected from silicon nitride film, silicon oxide film or silicon carbide alloy. The method of claim 4, wherein The hard mask pattern is The manufacturing method of the CMOS image sensor characterized in that the thickness is formed in the range of 200 ~ 4000Å. The method of claim 1, Removing the hard mask pattern is a method of manufacturing a CMOS image sensor, characterized in that using a wet etching process. The method of claim 6, The wet etching process is a method of manufacturing a CMOS image sensor, characterized in that using phosphoric acid. Forming a first conductive film pattern for a gate of the transfer transistor on the substrate; Forming a hard mask pattern on the first conductive layer pattern; Forming a second conductive film pattern for gates of transistors other than the transfer transistor on the substrate; Forming a photoresist pattern for the photodiode to be formed in a region in contact with the first conductive layer pattern; Performing an implant process for the photodiode using the photoresist pattern as a mask, wherein the hard mask pattern serves as a barrier film of the lower water during the implant process; Removing the photoresist pattern; Forming a photoresist film so that the hard mask pattern is exposed and the remaining area is covered; Removing the hard mask pattern exposed through the photosensitive film further formed; And Removing the additionally formed photosensitive film Method of manufacturing a CMOS image sensor comprising. The method of claim 8, Removing the hard mask pattern is a method of manufacturing a CMOS image sensor, characterized in that the wet etching process. The method of claim 8, The wet etching process is a method of manufacturing a CMOS image sensor, characterized in that using phosphoric acid. The method of claim 1, The photosensitive film pattern is a method of manufacturing a CMOS image sensor, characterized in that formed to overlap a predetermined portion with the first conductive film. The method of claim 11, The overlapping region is a method of manufacturing a CMOS image sensor, characterized in that the range of 50nm ~ 150nm.

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