KR20020017747A - Method for forming image sensor capable of improving characteristics of photodiode - Google Patents

Abstract

PURPOSE: A method for fabricating an image sensor capable of improving a surface characteristic of a photodiode is provided to effectively prevent a defect or contaminant on the surface of the photodiode in a subsequent process, by forming an insulation layer pattern for protecting a photodiode region in forming an insulation layer spacer on the sidewall of a gate. CONSTITUTION: The first region includes the photodiode, and the second region includes a transistor. The gate(42) is formed on a semiconductor substrate in the second region. Impurity ions of the first conductivity type are implanted into the semiconductor substrate in the first region to form the first impurity ion implantation region(43) of the photodiode. An insulation layer is formed on the resultant structure. An etch mask covering the first region is formed. The insulation layer not covered with the etch mask is etched to form an insulation layer spacer(45A) on the sidewall of the gate while an insulation layer pattern(45B) covering the first region is formed. The etch mask is eliminated. Impurity ions of the second conductivity type are implanted into the semiconductor substrate in the first region covered with the insulation layer pattern to form the second impurity ion implantation region(47) of which the bottom surface is in contact with the first impurity ion implantation region of the photodiode.

Description

Method for forming image sensor capable of improving characteristics of photodiode

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of image sensor fabrication, and more particularly, to an image sensor fabrication method capable of shallowly forming a surface damage of a photodiode and an impurity ion implantation region of the photodiode surface.

An image sensor is an apparatus that converts optical information of one or two dimensions or more into an electrical signal. The types of image sensors are broadly classified into imaging tubes and solid-state imaging devices. Imaging tubes are widely used in measurement, control, and recognition using image processing technology centered on televisions, and applied technologies have been developed. There are two types of solid-state image sensors on the market: metal-oxide-semiconductor (MOS) type and charge coupled device (CCD) type.

CMOS image sensor is a device that converts an optical image into an electrical signal by using CMOS fabrication technology, and adopts a switching method in which MOS transistors are made by the number of pixels and the outputs are sequentially detected using the same. The CMOS image sensor has a simpler driving method than the CCD image sensor which is widely used as a conventional image sensor, and can implement various scanning methods, and can integrate a signal processing circuit into a single chip, thereby miniaturizing the product. The use of compatible CMOS technology reduces manufacturing costs and significantly lowers power consumption.

FIG. 1 is a circuit diagram showing a unit pixel of a CMOS image sensor having four transistors and two capacitance structures, and a unit pixel of a CMOS image sensor including a photodiode (PD) and four NMOS transistors for optical sensing. . Of the four NMOS transistors, the transfer transistor Tx serves to transport the photocharge generated in the photodiode PD to the floating diffusion region, and the reset transistor Rx is stored in the floating diffusion region for signal detection. It serves to discharge the charge, the drive transistor (Dx) serves as a source follower (Source Follower), the select transistor (Sx) is for switching (Switching) and addressing (Addressing). In the drawing, "Cf" represents capacitance of the floating diffusion region, and "Cp" represents capacitance of the photodiode, respectively.

Operation of the image sensor unit pixel configured as described above is performed as follows. Initially, the unit pixel is reset by turning on the reset transistor Rx, the transfer transistor Tx, and the select transistor Sx. At this time, the photodiode PD starts to deplete, the capacitance Cp occurs in the carrier change, and the capacitance Cf of the floating diffusion region is charged up to the supply voltage VDD. The transfer transistor Tx is turned off, the select transistor Sx is turned on, and the reset transistor Rx is turned off. In this operation state, after reading the output voltage V1 from the unit pixel output terminal Out and storing it in the buffer, the transfer transistor Tx is turned on to move the carriers of the capacitance Cp changed according to the light intensity to the capacitance Cf. The output voltage (V2) is read from the output terminal (Out) again and the analog data for V1-V2 is converted into digital data, so one operation cycle for the unit pixel is completed.

2 is a cross-sectional view showing the formation of a photodiode region for photodetection and a transfer transistor for photocharge transfer, wherein a field oxide film 21 is formed on a semiconductor substrate 20, and a photodiode 22 is formed. A state in which a region B other than the light sensing including the region A, the transfer transistor 23, the insulating film spacer 24, the active region 25, and the like is formed is schematically shown.

Hereinafter, a problem of the conventional CMOS image sensor manufacturing method will be described with reference to FIGS. 3A to 3C. In the drawing, 'A' shows a light sensing area, and 'B' shows a region other than the light sensing area.

3A illustrates forming a field oxide film 31 on a p-type silicon substrate 30 and then forming a gate 32 by performing a polyside forming process, a mask process, an etching process, and the like, and then n-type impurities of the photodiode. The ion implantation process for forming the ion implantation region 33 is carried out, and the ion implantation process for forming the n- and p- source and drain 34 in the region B other than the photodiode is shown.

3B illustrates that an insulating film spacer 35 is formed on the sidewall of the gate 32 by forming an insulating film over the entire structure and etching the entire surface thereof.

FIG. 3C shows that an ion implantation process for forming n + and p + source and drain 36 in a region B other than the photodiode and an ion implantation process for forming a p-type impurity doped region 37 of the photodiode are performed. have.

As described above, although the photosensitive region A is a region irrelevant to a process other than an ion implantation process for forming a photodiode, the etching process for forming the insulating film spacer 35, an ion implantation mask formation, and a removal process may be performed. Even during a process that does not contribute to the formation of the photo-sensing area, the photo-sensing area (A) is open, which is very likely to cause defects and contamination on the surface of the photodiode. Improving the characteristics of the sensing area is essential, in particular, it should not be overlooked that the degradation of the surface state of the photosensitive region, which has a great influence on the dark current characteristics.

On the other hand, the depth of the p-type impurity doped region 37 of the photodiode should be formed as shallow as possible, the minimum energy of the ion implantation equipment currently used has a problem that the depth control is not easy at 30 KeV.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of manufacturing an image sensor capable of shallowly forming a surface damage of a photodiode and an impurity ion implantation region of the photodiode surface.

1 is a cross-sectional view schematically showing a unit pixel structure of a conventional CMOS image sensor;

2 is a cross-sectional view showing that a photodiode region for photodetection and a transfer transistor for photocharge transfer are formed;

3A to 3C are cross-sectional views of a CMOS image sensor fabrication process according to the prior art;

4A-4C are cross-sectional views of a CMOS image sensor fabrication process in accordance with an embodiment of the present invention.

* Description of reference numerals for the main parts of the drawings *

42: gate 43: n-type impurity ion implantation region

44: n- and p- source drain 45A: insulating film spacer

45B: insulating film pattern 47: p-type impurity doped region

According to an aspect of the present invention, there is provided a method of manufacturing an image sensor including a first region including a photodiode and a second region including a transistor, the method including forming a gate on a semiconductor substrate of the second region. First step; A second step of forming a first impurity ion implantation region of a photodiode by implanting a first conductivity type impurity into the semiconductor substrate of the first region; A third step of forming an insulating film on the entire structure; A fourth step of forming an etching mask covering the first region; A fifth step of forming an insulating film pattern covering the first region by etching the insulating film not covered with the etching mask to form an insulating film spacer on the sidewall of the gate; A sixth step of removing the etching mask; And a seventh impurity ion implantation region in which a second conductivity type impurity is implanted into the semiconductor substrate of the first region covered with the insulating film pattern, the bottom surface of which is in contact with the first impurity ion implantation region of the photodiode. It provides an image sensor manufacturing method comprising the step.

According to the present invention, by forming an etching mask covering the photodiode region on the insulating layer in the process of forming the insulating layer spacer on the sidewall of the gate and etching the entire surface of the insulating layer, the insulating layer pattern is formed so that the surface of the photodiode region is not exposed in the entire etching process. In addition, the ion implantation is performed while the photodiode region is covered with the insulating film pattern, so that the impurity ion implantation region on the surface of the photodiode is formed to be shallow.

Hereinafter, a method of manufacturing an image sensor according to an exemplary embodiment of the present invention will be described with reference to FIGS. 4A to 4C. In the drawing, 'A' shows a light sensing area, and 'B' shows a region other than the light sensing area. Areas other than the photodetection are areas in which native transistors, floating diffusion regions, drive transistors, reset transistors, and the like are formed.

First, as shown in FIG. 4A, the field oxide film 41 is formed on the p-type silicon substrate 40, and then the gate 42 is formed by performing a polyside forming process, a mask process, an etching process, and the like. An ion implantation process is performed to form the n-type impurity ion implantation region 43 of the diode, and an ion implantation process is performed to form the n- and p- source and drain 44 in regions B other than the photodiode. .

Next, as shown in FIG. 4B, an insulating film is formed over the entire structure, an etching mask (not shown) covering the photodiode region is formed on the insulating film, and an etching process is performed to form an insulating film on the sidewall of the gate 42. The insulating film pattern 45B covering the photodiode region is formed while forming the spacer 45A.

Subsequently, as illustrated in FIG. 4C, an ion implantation process for forming n + and p + source and drain 46 is performed in regions B other than the photodiode, and an ion implantation process is performed while the insulating film pattern 45B is covered. Thus, the p-type impurity doped region 47 of the photodiode is formed.

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes can be made in the art without departing from the technical spirit of the present invention. It will be apparent to those of ordinary knowledge.

According to the present invention as described above, by forming an insulating film pattern for protecting the photodiode region in the process of forming the insulating film spacer on the gate sidewall, it is possible to effectively prevent the occurrence of defects or contamination on the surface of the photodiode in a subsequent process. Further, by performing the ion implantation process in a state where the insulating film pattern is covered, the impurity implantation region on the surface of the photodiode can be formed to a shallow depth. Accordingly, the yield of the product can be improved by improving the characteristics of the light sensing region, and the competitiveness of the product can be strengthened by improving the optical characteristics.

Claims (3)

In the image sensor manufacturing method comprising a first region having a photodiode and a second region having a transistor, Forming a gate on the semiconductor substrate in the second region; A second step of forming a first impurity ion implantation region of a photodiode by implanting a first conductivity type impurity into the semiconductor substrate of the first region; A third step of forming an insulating film on the entire structure; A fourth step of forming an etching mask covering the first region; A fifth step of forming an insulating film pattern covering the first region by etching the insulating film not covered with the etching mask to form an insulating film spacer on the sidewall of the gate; A sixth step of removing the etching mask; And A seventh step of forming a second impurity ion implantation region in which a second conductivity type impurity is implanted into the semiconductor substrate of the first region covered with the insulating layer pattern, the bottom surface of which is in contact with the first impurity ion implantation region of the photodiode Image sensor manufacturing method comprising a. The method of claim 1, After the second step, Performing an ion implantation process for forming a low concentration source / drain in the semiconductor substrate of the second region, After the seventh step, And performing an ion implantation process for forming a high concentration source and drain in the semiconductor substrate of the second region. The method according to claim 1 or 2, And the first conductivity type is n-type and the second conductivity type is p-type.