Method of fabricating a semiconductor device

A method of fabricating a semiconductor device includes steps of forming at least one shallow-trench isolation region in a semiconductor substrate; forming a photoresist pattern for blocking a photodiode region; sequentially implanting dopant ions and boron ions into the at least one shallow-trench isolation region; and activating the implanted ions. Since germanium ions are implanted before implanting P-type ions in a channel-stop ion implantation process, the lattice structure of the surface of a shallow-trench isolation region is maintained, to thereby allow a deeper penetration of the implanted P-type ions (boron ions), and to prevent the P-type ions from being outwardly diffused according to an increased lattice scattering phenomenon generated upon a thermal process.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No. 10-2004-0118442, filed on Dec. 31, 2004, which is hereby incorporated by reference as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of fabricating a semiconductor device, and more particularly, to a method of fabricating a semiconductor device in which germanium ions are implanted before implanting P-type ions in a channel-stop ion implantation process, such that the lattice structure of the surface of a shallow-trench isolation region is maintained to thereby allow a deeper penetration of the implanted P-type ions (boron ions), and to prevent the P-type ions from being outwardly diffused according to an increased lattice scattering phenomenon generated upon thermal processing.

2. Discussion of the Related Art

An imaging device for converting an optical image into an electrical signal may be realized by a charge-coupled device or a CMOS image sensor. A CMOS image sensor uses CMOS fabricating technology.

CMOS image sensors include a photosensitive portion for sensing light and a logic circuit for processing the sensed light into an electrical signal. The unit pixel of the CMOS image sensor may be composed of one photodiode and four NMOS transistors. Typically, the four transistors are a transfer transistor, for transferring an optical charges collected in the photodiode to a floating node, a reset transistor, for setting the potential of the node to a desired value, discharging charges, and resetting the floating node, a drive transistor, functioning as a source follower buffer amplifier, and a select transistor, functioning as a switch for addressing. Among these transistors, the transfer transistor and the reset transistor are formed of native NMOS transistors having depletion modes or low threshold voltages, to improve charge transfer efficiency and reduce a charge loss (voltage drop) in the output signal. In the unit pixel of the CMOS image sensor, the potential barriers of the transfer transistor and the reset transistor are controlled such that the reset of the floating node is performed through the transfer transistor and the reset transistor, and excessive charges in a saturation region flow into a power line through the transfer transistor and the reset transistor.

FIGS. 1A-1Cillustrate a method of fabricating a CMOS image sensor according to the related art.

Referring toFIG. 1A, a trench is formed in a silicon substrate101to form a shallow-trench isolation region102.

Referring toFIG. 1B, P-type ions, such as BF2or boron, are implanted into the shallow-trench isolation region102of the silicon substrate101while covering the photodiodes103with a photoresist104. The N-type photodiode and the shallow-trench isolation region102are separated from each other, and thus leakage in the interface of the shallow-trench isolation region102is removed and isolation is improved.

Referring toFIG. 1C, because the boron is light in weight it is outwardly diffused upon a post-thermal process. Thus, the boron cannot perform its function well because upon thermal processing the P-type region105becomes wider, and the photodiode103becomes narrower.

SUMMARY OF THE INVENTION

An advantage of the present invention is that it can provide a method of fabricating a semiconductor device, in which germanium ions are implanted before implanting P-type ions in a channel-stop ion implantation process, to maintain the lattice structure of the surface of a shallow-trench isolation region and thereby allow a deeper penetration of the P-type ions (boron ions) and to prevent the implanted P-type ions from being outwardly diffused according to an increased lattice scattering phenomenon generated upon thermal processing.

To achieve these and other advantages in accordance with the purpose of the invention, as embodied and broadly described herein, a method of fabricating a semiconductor device comprises forming at least one shallow-trench isolation region in a semiconductor substrate; forming a photoresist pattern for blocking a photodiode region; sequentially implanting dopant ions and boron ions into the at least one shallow-trench isolation region; and activating the implanted ions.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, like reference designations will be used throughout the drawings to refer to the same or similar parts.

Developed in the 1960s, the CMOS image sensor has a lower image quality, a more complex circuitry, a lower packing density, and a larger chip size than a charge-coupled device (CCD) and offers no cost benefits. In the late 1990s, however, these disadvantages began to disappear with the development of CMOS fabricating technology and improvements in signal processing algorithms. By selectively applying CCD fabrication processing to CMOS image sensor technology, the quality of a CMOS image sensor can be significantly improved.

FIGS. 2A-2Eillustrate a method of fabricating a CMOS image sensor according to the present invention.

Referring toFIG. 2A, a semiconductor substrate201is etched to form shallow-trench isolation regions202. Photodiode regions203are formed between the shallow-trench isolation regions202.

Referring toFIG. 2B, photoresist204is formed and patterned to block the photodiode regions203.

Referring toFIGS. 2C and 2D, dopant ions, such as germanium (Ge), are implanted into the shallow-trench isolation regions202to form a germanium region205before implanting boron (B) ions. Then, P-type ions such as boron ions are implanted into the shallow-trench isolation regions202. In this manner, it may be possible to prevent the outward diffusion of the implanted boron ions during a post-thermal process.

Referring toFIG. 2E, by forming the germanium region205, the boron ions are not spread to a region other than a boron region206and are collected in the vicinity of the shallow-trench isolation regions202.

According to an exemplary embodiment of the present invention, since germanium ions are implanted before implanting P-type ions in a channel-stop ion implantation process, the lattice structure of the surface of a shallow-trench isolation region may be maintained to thereby allow a deeper penetration of the P-type ions (boron ions), and to prevent the implanted P-type ions from being outwardly diffused according to an increased lattice scattering phenomenon generated upon a thermal process.