Image sensor having inner lens
An image sensor includes an inner lens to enable incident light to reach a condensing lens, so that the incident light may further reach photodiodes. Light loss can be reduced and photosensitivity can be improved. The image sensor includes at least one microlens that focuses incident light onto at least one photosensor that receives a light signal transmitted from the at least one microlens. The image sensor also includes at least one inner lens, disposed between the at least one microlens and the at least one photosensor, having an upper surface of a predetermined curvature to compensate photosensitivity of light received from the at least one microlens.
This application claims the benefit of Korean Patent Application No. 10-2004-0116512, filed on Dec. 30, 2004, which is hereby incorporated by reference for all purposes as if fully set forth herein.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention relates to an image sensor. More particularly, the present invention relates to an image sensor having an inner lens formed in a color filter portion to enable incident light to reach a condensing lens, so that the incident light may further reach photodiodes. Thus, light loss can be reduced and photosensitivity can be improved.
2. Discussion of the Related Art
An image sensor is a semiconductor module that converts optical images to electrical signals. Image sensors may be charge-coupled devices (CCD) or complementary-metal-oxide-semiconductor (CMOS) image sensors. Such image sensors employ photodiodes to detect a light signal, and resolution is determined by the number of photodiodes existing in an image plane. The photodiodes receive images. Each photodiode represents a key element of one pixel unit, which includes a corresponding color filter of a color filter array and a corresponding microlens, all of which may be integrated on a single chip. With the demand for increased resolution along with greater miniaturization, more pixels are needed per unit area, which requires a decrease in pixel size. As a result, a photodiode area is reduced accordingly, thereby reducing photosensitivity.
To compensate photosensitivity, an inner lens may be additionally formed. The inner lens enables incident light to adapt to variations of a condensing angle due to an F-number. The inner lens also compensates for stray light that occurs due to the long travel distance to the photodiode area. The inner lens may be formed of an organic material or an inorganic material. If the inner lens is formed of an organic material, a positive photoresist having fluidity is used. Therefore, the process of forming the inner lens of an organic material is the same as the process of forming a condensing lens formed on a color filter portion. That is, the inner lens may be also formed by coating, exposure, development, bleaching, curing, and planarizing the color filter portion.
If a photoresist having fluidity is used, a problem in controlling critical dimension due to notching occurs. The notching occurs as the photoresist is affected by a light-shielding metal layer to be coated with the photoresist. For this reason, problems occur in that the process of forming the inner lens is complicated and an additional interlayer process is required.
SUMMARY OF THE INVENTIONAccordingly, the present invention is directed to an image sensor having an inner lens that substantially obviates one or more problems due to limitations and disadvantages of the related art.
An advantage of the present invention is to provide an image sensor having an inner lens, in which the inner lens is formed in a color filter portion to enable incident light to reach a condensing lens, so that the incident light may further reach photodiodes. Thus, light loss can be reduced and photosensitivity can be improved.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure and method particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an image sensor includes at least one microlens that focuses incident light onto at least one photosensor that receives a light signal transmitted from the at least one microlens, and at least one inner lens, disposed between the at least one microlens and the at least one photosensor, having an upper surface of a predetermined curvature to compensate photosensitivity of light received from the at least one microlens.
According to another aspect of the present invention, a method for fabricating an image sensor includes forming a photoresist layer on a planarization layer, performing an alignment exposure with respect to the photoresist layer, performing a dry etching process with respect to the exposed photoresist layer, and forming an oxide layer on the etched photoresist layer by silation using a silane gas.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:
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.
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After the color filter portion is formed, an overcoating layer serving as another planarization layer is formed to protect the color filter portion, to control focal length, and to provide a surface for the microlenses, which are disposed to correspond to each pixel. Thus, the image sensor according to the present invention is completed. The color filter portion is formed on the oxide layer when the inner lens is formed to compensate received light. Thus, the process steps are simplified.
In fabricating the color filter portion and the lens for the image sensor, photosensitivity is increased and a phase signal is reduced so as to obtain an image sensor having high resolution and high photosensitivity. Also, the complicated process can be shortened when the inner lens is formed. The planarization layer for the color filter portion may be omitted, facilitating production and enabling reduced costs.
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 cover the modifications and variations provided they come within the scope of the appended claims and their equivalents.
Claims
1. An image sensor, comprising:
- at least one microlens that focuses incident light onto at least one photosensor that receives a light signal transmitted from said at least one microlens; and
- at least one inner lens, disposed between said at least one microlens and said at least one photosensor, having an upper surface of a predetermined curvature to increase photosensitivity to light received from said at least one microlens.
2. The image sensor of claim 1, further comprising:
- a protective oxide layer formed on said at least one inner lens.
3. The image sensor of claim 1, further comprising:
- a color filter portion, disposed between said at least one microlens and said at least one inner lens, that enables a color separation in the transmitted light signal.
4. The image sensor of claim 3, further comprising:
- a protective oxide layer formed between said at least one inner lens and said color filter portion.
5. The image sensor of claim 3, wherein said at least one inner lens is disposed between said color filter portion and the at least one photosensor.
6. The image sensor of claim 3, wherein said color filter portion is part of a color filter array including different color filters that filters transmitted light according to wavelength.
7-18. (canceled)
Type: Application
Filed: Feb 28, 2008
Publication Date: Oct 9, 2008
Inventor: Sang Sik Kim (Suwon-city)
Application Number: 12/073,043
International Classification: G02B 3/00 (20060101); H01L 31/0232 (20060101);