CMOS image sensor and method for manufacturing the same

A CMOS image sensor is provided. The CMOS image sensor can include: a plurality of photodiodes formed on a semiconductor substrate; an interlayer dielectric layer formed on an entire surface of the semiconductor substrate having the plurality of photodiodes; color filter layers including multi-layered blue color filter layers formed on the interlayer dielectric layer corresponding to respective photodiodes of the plurality of photodiodes; a planarization layer formed on the semiconductor substrate having the color filter layers; and microlenses formed on the planarization layer.

This application claims priority under 35 U.S.C. §119(e) of Korean Patent Application No. 10-2005-0132608 filed Dec. 28, 2005, which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a CMOS image sensor and a method for manufacturing the same.

BACKGROUND OF THE INVENTION

In general, an image sensor is a semiconductor device for converting an optical image into an electric signal, and is mainly classified as a Charge Coupled Device (CCD) image sensor or a Complementary Metal Oxide Semiconductor (CMOS) image sensor.

The CMOS image sensor includes a photodiode for detecting light and a CMOS logic circuit for converting detected light into electric signals to form image data. As the quantity of light received in the photodiode increases, the photosensitivity of the image sensor is improved.

To improve the photosensitivity, either a fill factor, which is a ratio of a photodiode area to the whole area of the image sensor, must be increased, or a photo-gathering technology is used to change the path of light incident onto an unintended area such that the light can be gathered in the photodiode.

A representative example of the photo-gathering technology is to make a microlens. That is, a convex microlens is formed on a top surface of the photodiode using a material having superior light transmittance, thereby refracting the incident light in such a manner that a greater amount of light can be transmitted into the photodiode area.

In this case, light parallel with an optical axis of the microlens is refracted by the microlens so that the light is focused on a certain position of the optical axis.

Hereinafter, a conventional CMOS image sensor is described with reference to the accompanying drawing.

FIGS. 1ato1dare cross-sectional views illustrating the procedure of manufacturing a conventional CMOS image sensor.

Referring toFIG. 1a, an interlayer dielectric layer13is formed on a semiconductor substrate having a plurality of light sensing elements, e.g., photodiodes12.

Here, the interlayer dielectric layer13may be formed as multiple layers. Although not shown in the figure, after one interlayer dielectric layer is formed, a light shielding layer is formed to prevent light from being incident onto a portion other than the photodiode region, and then another interlayer dielectric layer is formed thereupon.

Then, a dyeable resist is applied on the interlayer dielectric layer13, and color filter layers14for filtering light for each wavelength band are then formed by performing an exposure and development process.

Subsequently, a planarization layer15is formed on the color filter layers in order to adjust a focus distance and secure a planarity for forming a microlens layer.

As shown inFIG. 1b, a resist layer16afor microlenses is applied on the planarization layer15, and a reticle17with openings is aligned above the resist layer16a.

Subsequently, the resist layer16ais selectively exposed to correspond to the openings of the reticle17by radiating light such as laser onto the semiconductor substrate11through the reticle17.

Referring toFIG. 1c, the exposed resist layer16ais developed to form microlens patterns16b.

Referring toFIG. 1d, convex shaped microlenses16are formed by reflowing the microlens patterns16bat a temperature of 150 to 200° C.

The micro lenses16allow a larger amount of light to be focused onto the photodiodes12by passing the light through the color filter layers14according to the wavelengths thereof, when a natural light is incident into the micro lenses16.

The light incident into the image sensor is focused by the micro lenses16and filtered through the color filter layers14, and then the filtered light is incident onto each photodiode12which is correspondingly located below each color filter layer14.

In a case where such a conventional CMOS image sensor is used for a Digital Still Camera (DSC) in which a thin color pixel is required, a process of forming a color filter layer with a high thickness is performed in order to implement color reproduction.

Accordingly, since all color filter layers for DSC CMOS image sensors have been currently formed in a range of 0.7 to 1.0 μm, color reproduction of colors is low, and sensitivity is the chief consideration. If a color pixel with a high thickness is formed by a one-time process when performing a process of forming a thin color filter layer described above, in particular a blue color filter layer, transmittance for an in-line exposure wavelength (when coating a color photoresist in 0.9 μm or more) is 0.5% or less, and reactivity for light is almost close to zero at a portion contacted with the interlayer dielectric layer13. For this reason, there is a problem in that the peeling of a color pixel occurs.

BRIEF SUMMARY

Accordingly, it is an object of embodiments of the present invention to provide a CMOS image sensor and a method for manufacturing the same, wherein a thin color pixel can be formed using a double exposure process.

According to one aspect of the present invention, there is provided a CMOS image sensor, which includes: a plurality of photodiodes formed on a semiconductor substrate at a predetermined interval; an interlayer dielectric layer formed on an entire surface of the semiconductor substrate having the photodiodes; color filter layers including multi-layered blue color filter layers formed to correspond to respective photodiodes on the interlayer dielectric layer; a planarization layer formed on the entire surface of the semiconductor substrate having the color filter layers; and microlenses formed on the planarization layer.

A CMOS image sensor and a method for manufacturing the same according to embodiments of the present invention have advantages as follows.

That is, in the CMOS image sensor used for a DSC in which a thin color pixel is required, a blue color filter layer can be formed as multiple layers in order to implement color reproduction, so that a thin color pixel can be formed. Thus, the implementation of uniform color reproduction and the peeling of the color filter layer can be prevented, so that stable colors can be implemented.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2is a cross-sectional view illustrating a structure of a CMOS image sensor according to an embodiment of the present invention.

Referring toFIG. 2, the CMOS image sensor according to an embodiment of the present invention can include photodiodes32, at least one of which is formed on a semiconductor substrate31to generate electric charges according to an amount of incident light; an interlayer dielectric layer33formed on an entire surface of the semiconductor substrate31including the photodiodes32; color filter layers including a red color filter layer34R, a multi-layered blue color filter layer34B and a green color filter layer34G formed on the interlayer dielectric layer33corresponding to the photodiodes32so as to allow light having specific wavelength bands to be irradiated onto the photodiodes32; a planarization layer35formed on the entire surface of the semiconductor substrate31having the color filter layers; and microlenses36formed on the planarization layer35corresponding to the photodiodes32so as to guide light onto the photodiodes32.

The microlens36can be formed in a convex hemispherical shape.

The color filter layer can include red and green color filter layers34R and34G formed as a single layer and a blue color filter layer34B formed as double layers34B1and34B2on the interlayer insulating layer33.

In the double blue color filter layer34B, a first blue color filter layer34B1can be formed to a thickness of 0.8 to 0.9 μm on a blue color filter layer area of the interlayer dielectric layer33by a dyeable resist coating/exposure/development process.

In addition, in the blue color filter layer34B, a second blue color filter layer34B2can be formed having the same thickness as the first blue color filter layer34B1on the first blue color filter layer34B1by a dyeable resist coating/exposure/development process.

To increase the overlay degree of the first and second blue color filter layers34B1and34B2, the size (width and length) of the second blue color filter layer34B2can be formed to be smaller than that of the first blue color filter layer34B1. In a specific embodiment, when forming the second blue color filter layer34B2, misalignment can be prevented by allowing exposure energy to be smaller by about 5 to 10% than when forming the first blue color filter layer34B1. Here, the overlay degree of the first and second blue color filter layers34B1and34B2can be set to be about ±5% of the size of a pixel.

That is, in a CMOS image sensor according to a preferred embodiment of the present invention used for a DSC in which a thin color pixel is required, the blue color filter layer is formed as multiple layers in order to implement color reproduction, so that a thin color pixel can be formed. Thus, the implementation of uniform color reproduction and the peeling of the color filter layer can be prevented, so that stable colors can be implemented.

FIGS. 3ato3gare cross-sectional views illustrating a procedure for manufacturing a CMOS image sensor according to an embodiment of the present invention.

Referring toFIG. 3a, an interlayer dielectric layer33can be formed on a semiconductor substrate31having a plurality of light sensing elements, e.g., photodiodes32.

In an embodiment, the interlayer dielectric layer33may be formed as multiple layers. Although not shown in the figure, after one interlayer dielectric layer is formed, a light shielding layer is formed to prevent light from being incident onto unintended regions not having the photodiodes32, and then another interlayer dielectric layer is formed thereupon.

Referring toFIG. 3b, a dyeable resist can be applied on a blue color filter layer area of the interlayer dielectric layer33, and a first blue color filter layer34B1for filtering light in a blue wavelength band can then be formed by performing an exposure and development process.

Subsequently, referring toFIG. 3c, a dyeable resist can be applied on the first blue color filter layer34B1, and a second blue color filter layer34B2for filtering light in a blue wavelength band can then be formed by performing an exposure and development process. To increase an overlay degree of the first and second blue color filter layers34B1and34B2, the size of the second blue color filter layer34B2is formed to be smaller than that of the first blue color filter layer34B1. To this end, when forming the second blue color filter layer34B2, misalignment can be prevented by allowing exposure energy to be smaller by about 5 to 10% or so than when forming the first blue color filter layer34B1. In a specific embodiment, the overlay degree of the first and second blue color filter layers34B1and34B2can be set to be about ±5% of the size of a pixel.

Subsequently, referring toFIG. 3d, a dyeable resist can be applied on a red color filter layer area of the interlayer dielectric layer33, and a red color filter layer34R for filtering light in a red wavelength band can then be formed by performing an exposure and development process.

A dyeable resist can be applied on a green color filter layer area of the interlayer dielectric layer33, and a green color filter layer34G for filtering light in a green wavelength band can then be formed by performing an exposure and development process.

Subsequently, referring toFIG. 3e, a planarization layer15can be formed on the entire surface of the semiconductor substrate31having the color filter layers in order to adjust a focus distance and secure a planarity for forming a lens layer.

Meanwhile, since optical transmission is very important in an image sensor, the planarization layer35can be formed to have a thickness of 1000 to 6000 Å so as to eliminate an interference phenomenon of thin films due to the thickness thereof.

Subsequently, referring toFIG. 3f, a photoresist for microlenses can be coated on the entire surface of the semiconductor substrate31having the planarization layer35, and the photoresist for microlenses can be selectively patterned by an exposure and development process, to form microlens patterns36a.

Then, referring toFIG. 3g, convex shaped microlenses36can be formed by reflowing the microlens patterns37at a temperature of 150 to 200° C. In one embodiment, the microtenses36can have a hemispherical shape.

The micro lenses36allow a larger amount of light to be focused onto the photodiodes32through the respective color filter layers according to the wavelengths thereof, when a natural light is incident into the micro lenses36.

A CMOS image sensor and a method for manufacturing the same according to embodiments of the present invention have advantages as follows.

That is, in the CMOS image sensor used for a DSC in which a thin color pixel is required, a blue color filter layer can be formed as multiple layers in order to implement color reproduction, so that a thin color pixel can be formed. Thus, the implementation of uniform color reproduction and the peeling of the color filter layer can be prevented, so that stable colors can be implemented.

The embodiment and the accompanying drawings illustrated and described therein are intended to not limit the present invention, and it will be obvious to those skilled in the art that various changes, variations and modifications can be made to the present invention without departing from the technical spirit of the invention.