KR100776148B1 - Method of manufacturing cmos image sensor - Google Patents

Abstract

The present invention provides a method of manufacturing a CMOS image sensor that can implement a deep N-region profile of a photodiode capable of securing dead zone and chroma signal characteristics while shortening processing time. A method of manufacturing a CMOS image sensor according to the present invention includes the steps of sequentially forming a gate insulating film and a polysilicon film on a first conductivity-type semiconductor substrate in which a transfer transistor and a photodiode region are defined; Forming a convex mask on the polysilicon layer; Etching the polysilicon film using the mask to form a gate of the transfer transistor; Forming a photoresist film on the substrate on which the gate is formed to expose the photodiode region; And deeply injecting low-concentration impurity ions of the second conductivity type in the ion implantation process using the photoresist film as a mask to form a low-concentration deep impurity region of the second conductivity type having a profile partially overlapping the lower portion of the gate. Here, the convex mask is formed of a hard mask or a photoresist film. In addition, ion implantation for forming a deep impurity region is performed with energy suitable for selective gate channeling of ions by a convex mask.

Dead Zone, Saturation Signal, Channeling

Description

Manufacturing method of CMOS image sensor {METHOD OF MANUFACTURING CMOS IMAGE SENSOR}             

1A to 1E are cross-sectional views illustrating a method of manufacturing a CMOS image sensor according to a first embodiment of the present invention.

2A to 2C are cross-sectional views illustrating a method of manufacturing a CMOS image sensor according to a second embodiment of the present invention.

※ Explanation of code for main part of drawing

10, 20: semiconductor substrate 11, 21: field insulating film

12, 22: gate insulating film 13, 23: polysilicon film

13A, 23A: Gate 14: insulating film

14A, 14B: hard mask 15, 17, 24, 24A, 25: photoresist film

16: oxide film 18, 26 deep N-region

The present invention relates to a complementary metal oxide semiconductor (CMOS) image sensor technology, and more particularly, to a method of manufacturing a CMOS image sensor capable of improving deadzone characteristics.

In general, a CMOS image sensor is a semiconductor device that converts an optical image into an electrical signal, and is composed of a light sensing part that senses light and a logic circuit part that processes the sensed light into an electrical signal to make data. It uses CMOS technology to make MOS transistors by the number of pixels and employs a switching method that uses them to detect the output in turn. In addition, the unit pixel of the CMOS image sensor is composed of one photodiode and four MOS transistors, that is, a transfer transistor, a reset transistor, a drive transistor, and a select transistor.

As a factor for determining the characteristics of the CMOS image sensor, there are a dead zone, a dark current and a saturation signal. In order to improve the dead zone characteristics, the deep N- region of the photodiode has a profile partially overlapping with the gate lower portion of the transfer transistor. In contrast, conventionally, a deep N-region having such a profile is formed by tilt and rotation ion implantation or twist ion implantation.

However, when rotating ion implantation is performed, the process time is long depending on the number of rotations. If ion implantation is performed only by tilt or twist without rotation, the process time can be shortened, but the chroma signal margin is reduced due to the decrease of Rp. There was a downside to this decline.

In order to solve this problem, the deep N- region of the photodiode was formed by performing ion implantation twice without tilt or twist, but in this case, the chroma signal margin is improved because a separate ion implantation has to be performed once more. Even if it can be done, the process time could not be significantly reduced.

Disclosure of Invention The present invention is to solve the conventional problems as described above, and provides a method of manufacturing a CMOS image sensor that can implement a deep N-region profile of a photodiode capable of securing dead zone and chroma signal characteristics while reducing process time. The purpose is to provide.

In order to achieve the object of the present invention, a method of manufacturing a CMOS image sensor according to the present invention comprises the steps of sequentially forming a gate insulating film and a polysilicon film on a first conductive type semiconductor substrate having a transfer transistor and a photodiode region defined; Forming a convex mask on the polysilicon layer; Etching the polysilicon film using the mask to form a gate of the transfer transistor; Forming a photoresist film on the substrate on which the gate is formed to expose the photodiode region; And deeply implanting low-concentration impurity ions of the second conductivity type in the ion implantation process using the photoresist film as a mask to form a low-concentration deep impurity region of the second conductivity type having a profile partially overlapping the lower portion of the gate.

Here, the convex mask is formed of a hard mask or a photoresist film. In addition, ion implantation for forming a deep impurity region is performed with energy suitable for selective gate channeling of ions by a convex mask.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

1A to 1E are cross-sectional views illustrating a method of manufacturing a CMOS image sensor according to a first embodiment of the present invention.

Referring to FIG. 1A, a field insulating film 11 for inter-element insulation is formed on a P-type semiconductor substrate 10 to define a transfer transistor and a photodiode region, and the front surface of the substrate 10 on which the field insulating film 11 is formed. The gate insulating film 12 is formed in this. Next, a polysilicon film 13 is formed on the gate insulating film 12 as a gate material, and an insulating film 14 is formed thereon. At this time, the gate material is formed of only the polysilicon layer 13 without applying tungsten silicide (WSix) to obtain a gate thickness suitable for channeling during ion implantation for forming a deep N- region. Therefore, in the present embodiment, after forming the transistor of the unit pixel, titanium silicide (TiSi2) is applied to the polysilicon film 13 instead of tungsten silicide, and the description of the formation of the titanium silicide is omitted.

Next, the first photoresist film 15 is formed on the insulating film 14 in the form of a gate, and the insulating film 14 is etched using the first photoresist film 15 as a mask, as shown in FIG. 1B. As described above, after the hard mask 14A is formed on the polysilicon film 13, the first photoresist film 15 is removed by a known method. Then, the hard mask 14A is etched by a blanking etching process to form a convex hard mask 14B, as shown in FIG. 1C.

Referring to FIG. 1D, the polysilicon layer 13 is etched using the hard mask 14B as an etch mask to form the gate 13A of the transfer transistor. Thereafter, a selective oxidation process is performed to form an oxide film 16 on the sidewall of the gate 13A.

Referring to FIG. 1E, a second photoresist film 17 is formed on the structure of FIG. 1D so that the photodiode region is exposed, and the second photoresist film 17 is used as a mask in an ion implantation process. Deeply implanted to form the deep N-region 18 of the photodiode. At this time, ion implantation is performed without tilt or twist and rotation. In addition, ion implantation is performed with energy suitable to cause selective gate channeling of ions by the convex hard mask 14B, such that the deep N-region 18 has a profile overlapping with a portion of the bottom of the gate 13A. .

Then, although not shown, the second photoresist film 17 is removed and a subsequent process is performed.

According to the first embodiment, by forming the hard mask 14B on the gate 13A in a convex shape, the deep N-region 18 of the photodiode can be formed by only one ion implantation process without tilting, twisting or rotating. It can be formed to have a profile overlapping with a portion of the lower portion of the gate (13A). As a result, the dead zone characteristics can be improved while reducing the process time, and stable saturation signal margin can be secured.

On the other hand, in the first embodiment, a convex hard mask is applied on the gate for selective gate channeling of ions, but a photoresist film may be applied instead of the hard mask.

2A to 2C show a photoresist film instead of a hard mask, and a method of manufacturing a CMOS image sensor according to a second exemplary embodiment of the present invention will be described with reference to FIGS. 2A to 2C.

First, referring to FIG. 2A, a field insulating film 21 for inter-element insulation is formed on a P-type semiconductor substrate 20 to define a transfer transistor and a photodiode region, and the substrate 20 having the field insulating film 21 formed thereon. The gate insulating film 22 and the polysilicon film 23 are formed on the front surface. Next, a first photoresist film 24 is formed on the polysilicon film 23 in the form of a gate.

Then, the first photoresist film 24 is etched by the blanking etching process to form a convex first photoresist film 24A, as shown in FIG. 2B. Next, the polysilicon film 23 is etched using this convex first photoresist film 24A as an etching mask to form the gate transistor 23A of the transfer transistor.

Referring to FIG. 2C, a second photoresist film 25 is formed on the structure of FIG. 2B to expose the photodiode region, and the second photoresist film 25 is used as a mask for the N-ion. Deeply implanted to form the deep N-region 26 of the photodiode. At this time, ion implantation is performed without tilt or twist and rotation. In addition, ion implantation is performed with energy suitable for selective gate channeling of ions by the convex first photoresist film 24A, so that the deep N-region 26 overlaps a part of the lower portion of the gate 23A. Have a profile

Then, although not shown, the second photoresist film 25 is removed and a subsequent process is performed.

As described above, according to the present invention, by applying a convex mask to the top of the gate as a hard mask or a photoresist film, the deep N-region of the photodiode can be formed by only one ion implantation process without tilting, twisting or rotating. It can be formed to have a profile overlapping a portion of the gate lower portion.

On the other hand, in the above embodiment, the case where the PNP type photodiode is formed on the P-type substrate has been described, but it can be applied to the case where the NPN type photodiode is formed on the N-type substrate.

The present invention is not limited to the above embodiments, and various modifications can be made without departing from the technical spirit of the present invention.

The present invention described above can achieve the effect of improving the dead zone characteristics while securing a stable chroma signal margin while reducing the process time.

Claims (6)

In the method of manufacturing a CMOS image sensor having a transfer transistor and a photodiode, Sequentially forming a gate insulating film and a polysilicon film on the first conductivity type semiconductor substrate; Forming a convex mask on the polysilicon layer; Etching the polysilicon layer using the mask to form a gate of the transfer transistor; Forming a photoresist film on which the region of the photodiode is opened on the substrate on which the gate is formed; And Implanting impurity ions of the second conductivity type by an ion implantation process using the photoresist film as a mask to form a second conductivity type impurity region having a profile partially overlapping the lower portion of the gate; CMOS image sensor manufacturing method. The method of claim 1, And said convex mask is formed as a hard mask. The method of claim 1, And the convex mask is formed of a photoresist film. delete The method of claim 1, And the first conductivity type is P type and the second conductivity type is N type. The method of claim 1, Wherein the first conductivity type is N-type and the second conductivity type is P-type.

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