US20100044820A1

US20100044820A1 - Cmos image sensor and method of fabricating the same

Info

Publication number: US20100044820A1
Application number: US12/607,896
Authority: US
Inventors: Jun Woo Song
Original assignee: Dongbu HitekCo Ltd
Current assignee: DB HiTek Co Ltd
Priority date: 2006-12-22
Filing date: 2009-10-28
Publication date: 2010-02-25
Also published as: US7622320B2; US20080149974A1; KR100788381B1; CN101207081A; CN101207081B

Abstract

A CMOS image sensor is disclosed. The image sensor includes a plurality of polysilicon patterns provided on a silicon epitaxial layer which correspond to the location of a plurality of photodiodes provided in a dummy pixel area, a silicide layer of metal with a high melting point provided on the plurality of the polysilicon patterns, a device protecting layer and a planarization layer provided on the silicon epitaxial layer and silicide layer, and a plurality of microlenses on the planarization layer which correspond to the location of the silicide layer.

Description

CROSS-REFERENCES AND RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser. No. 11/926,028, filed on Oct. 28, 2007, which claims the benefit of the Korean Patent Application No. P2006-0133128, filed on Dec. 22, 2006. Each of the foregoing applications is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention
Embodiments of the present invention relate to CMOS image sensors.
2. Discussion of the Related Art
Image sensors are typically used for converting an optical image to an electric signal. The image sensors currently used in the art are generally categorized as either CMOS (complementary metal-oxide-silicon) image sensors or CCS (charge coupled device) image sensors. The CCD image sensor has superior photosensitivity and noise characteristics compared to the CMOS image sensor, but is difficult to incorporate in highly integrated systems has a comparatively high power consumption.
On the contrary, the CMOS image sensor uses simpler processes than the CCD image sensor, making it more suitable for the density of highly integrated systems. Additionally, the CMOS image sensor has comparatively low power consumption.
As the technology of manufacturing semiconductor devices has become more highly developed, many efforts have been made to research and develop the photosensitivity and noise characteristics of the CMOS image sensor.
Generally, each pixel of a CMOS image sensor consists of photodiodes capable of receiving light and CMOS devices capable of controlling the received light. Within the photodiodes, electron-hole pairs are generated which correspond to the wavelength and intensity of red, green and blue rays detected using a color filter. The out signals vary according to the quantity of the generated electrons, making it possible to capture an image.
A CMOS image sensor is shown in FIGS. 1A and 1B, and consists of a main pixel area 1 comprising a photocharge converting unit such as a photodiode 21, a dummy pixel area 2 provided outside the main pixel area 1, and a peripheral circuit area 3 for detecting signals detected by the pixel area 1 and the dummy pixel area 2. The peripheral circuit area 3 is formed so as to surround the main pixel area 1 and the dummy pixel area 2.
In a CMOS image sensor manufacturing process of the current art, an oxide layer is coated on the surface of the sensor in order to form a device protecting layer 22 in order to protect a device from moisture or external physical shock. Additionally, a dark shield layer 23 is formed on the device protecting layer 22 corresponding to the photodiode 21 in order to shield the dummy pixel area 2 from light.
Subsequently, a planarization layer 24 is formed with its surface being planarized. Then, a microlens 25 is formed on the planarization layer 24.
Thus, in a typical manufacturing processes currently used for forming the dummy pixel area 2 and main pixel area 1, the dummy pixel area 2 forming process requires an additional process step in order to form the dark shield layer 23 to shield the area from light.

SUMMARY

Accordingly, embodiments of the present invention are directed to a CMOS image sensor that substantially obviates one or more problems, limitations, or disadvantages of the related art.
In an example embodiment, a CMOS image sensor is provided wherein the light-shielding function is carried out using a polysilicon pattern and a silicide layer in a main pixel area, without requiring a dark shield layer in the dummy pixel area. For example, an embodiment of a CMOS image sensor includes a plurality of polysilicon patterns on a silicon epitaxial layer which correspond to the locations of a plurality of photodiodes in a dummy pixel area. A silicide layer of a metal with a high melting point is provided on each of the polysilicon patterns. A device protecting layer and a planarization layer is sequentially provided on the silicon epitaxial layer and silicide layer, and a plurality of microlenses on the planarization layer which correspond to the location of the silicide layer.
It is to be understood that both the foregoing Summary and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included in order to provide a further understanding of the invention and are incorporated in and constitute a part of this application. The drawings illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:

FIG. 1A is a diagram of a CMOS image sensor known in the art;

FIG. 1B is a cross-sectional diagram of a dummy pixel area of a CMOS image sensor of the art; and

FIG. 2 is a cross-sectional diagram of a dummy pixel area of a CMOS image sensor according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Reference will now be made in detail to preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
Methods of fabricating a CMOS image sensor include the steps of forming a polysilicon pattern of a gate electrode in a main pixel area, replacing of the process of forming a dark shield layer for shielding incoming light from a dummy pixel area of the CMOS image sensor that is currently used in the current art. Thus, embodiments of the present invention provide a CMOS image sensor wherein a gate electrode is formed in the main pixel area while the polysilicon pattern and silicide layer are formed in a dummy area.
In a method of fabricating a CMOS image sensor, a polysilicon pattern 221 is used in order to form a gate electrode in the main pixel area. At the same time, the polysilicon pattern 221 is formed on a silicon epitaxial layer 200 in a dummy pixel area. The dummy pixel area includes a photodiode 210, such as a red, green, or blue sensing photodiode, and the polysilicon pattern 221 is formed so as to cover the photodiodes 210.
In particular, the process of forming a polysilicon pattern in the dummy pixel area using a process that is similar to the process of forming a gate electrode in a main pixel area. More specifically, the polysilicon is deposited in a prescribed CVD chamber at a low temperature using silane gas and then forming into a polysilicon layer using a chemical mechanical polishing or “CMP” process.
Then, a first photoresist pattern is formed on the polysilicon layer, with an opening over each photodiode 210. An etching process is then carried out using the first photoresist pattern in order to form the polysilicon pattern 221 shown in FIG. 2.
Alternatively, the polysilicon pattern 221 can be formed in various ways using the process used to form the gate electrode in the main pixel area.
Subsequently, the spaces between the respective polysilicon patterns 221 are filled with a second photoresist pattern. Then a metal having a high melting point, such as Co, Ti and the like, is deposited on the silicon epitaxial layer 200 and polysilicon patterns 221 at a substrate temperature of 200° C. with a vacuum degree of 10 Torr.
In one embodiment, the dummy pixel area 2 acts as a reference area for enhancing the image characteristics during image signal processing. Thus, the dummy pixel area 2 is formed so as not to be affected by light. The low reflectivity and low transmissivity of cobalt (Co) is desirable, so cobalt may be used as the high melting point metal. In one example embodiment, cobalt is deposited on the polysilicon pattern 221.
After the cobalt has been deposited on the polysilicon pattern 221, the second photoresist pattern is removed using an ashing process. The cobalt silicide layer 222 is then formed by a rapid annealing process being carried out at between 800 and 1,000° C. in an Ar gas ambience environment for 20 seconds.
Advantageously, the cobalt silicide layer 222 plays the same light shielding role as the dark shield layer, preventing light from being transmitted to the photodiode 210.
After the Co silicide layer 222 has been formed, a device protecting layer 2220 formed of USG (undoped silicate glass) is formed on the silicon epitaxial layer 200 and cobalt silicide layer 222.
If the device protecting layer 220 is formed by coating USG (undoped silicate glass), the device protecting layer 220 in the dummy pixel area has different height than the neighbor areas.
To prevent the difference in heights, a liquid SOG (spin on glass) phase is formed in a planarization process. Then the planarization layer 230 is formed by hardening the coated SOG in an annealing process.
Subsequently, a CMP process is performed on the surface of the semiconductor so as to planarize the surface. A nitride layer (not shown in the drawing) formed of silicon nitride such a SiN is selectively formed on the planarization layer 230. Than, a plurality of microlenses 240 are formed on the nitride layer over the photodiodes 210.
As mentioned in the foregoing description, in the example image sensor fabricating method, the polysilicon patterns 221 and the cobalt silicide layer 222 are formed while the gate electrode in the main pixel area is formed without requiring a dark shield layer in the dummy area 2, thus reducing the number of processes required to produce the sensor. Because the polysilicon pattern and the silicide are able to cut off light, it is unnecessary to form the dark shield layer. Therefore, the disclosed embodiments enhance the performance of image TOPS.
It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention covers any modifications or variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims

1. A CMOS image sensor comprising:

a plurality of polysilicon patterns provided on a silicon epitaxial layer which correspond to the location of a plurality of photodiodes provided in a dummy pixel area;

a silicide layer of metal with a high melting point provided on the plurality of the polysilicon patterns;

a device protecting layer and a planarization layer which are sequentially provided on the silicon epitaxial layer and silicide layer; and

a plurality of microlenses on the planarization layer which correspond to the location of the silicide layer.

2. The CMOS image sensor of claim 1, wherein the silicide layer of the high melting point metal comprises a cobalt silicide layer.

3. The CMOS image sensor of claim 1, wherein the device protecting layer is provided using undoped silicate glass.

4. The CMOS image sensor of claim 1, wherein the planarization layer is provided using spin on glass.