KR100719344B1 - Image sensor and method of fabricating the same - Google Patents

Abstract

An image sensor and a method of manufacturing the same are provided. This image sensor includes an internal lens in the planarization layer formed on the photodiode region. The inner lens is formed at a predetermined position of the planarization layer in consideration of the wavelength of the transmitted light, and allows the focus of light to be formed at a predetermined position of the photodiode regardless of the wavelength of the light. Therefore, the light sensitivity and the photoelectric efficiency of the image sensor are improved.

Description

Image sensor and manufacturing method thereof {IMAGE SENSOR AND METHOD OF FABRICATING THE SAME}

1 is a cross-sectional view schematically showing a cell array portion of an image sensor according to the prior art;

2A to 2D are cross-sectional views illustrating a method of manufacturing an image sensor according to the present invention.

The present invention relates to a semiconductor device and a method for manufacturing the same, and more particularly, to an image sensor and a method for manufacturing the same.

An image sensor is a device that transforms an optical image into an electrical signal. The image sensor consists of a pixel array, ie, a plurality of pixels arranged in a two-dimensional matrix, each pixel comprising light sensing means and transmission and signal readout devices. Image sensors can be broadly divided into charge coupled device (CCD) image sensors and complementary metal oxide semiconductor (CMOS) image sensors, depending on the structure of the transmission and signal output devices. Among these, CMOS image sensors are used in various fields because they are advantageous in that low voltage, low power consumption, and peripheral circuits having various functions can be integrated into a single chip.

1 is a cross-sectional view schematically showing a cell array portion of an image sensor according to the prior art.

Referring to FIG. 1, a cell array region of an image sensor includes a light receiving region a in which a photodiode 11 for converting incident light into charges and a signal charge generated in the light receiving region a. It includes a charge transfer region (b) formed with a gate electrode 12 for transmitting.

The first planarization layer 14 is formed on the semiconductor substrate 10 on which the light receiving region a and the charge transfer region b are alternately arranged. Color filters 16r, 16g, and 16b are formed on the first planarization layer 14 to cover the upper portions of the light receiving regions a. The color filters include a first color filter 16r for selectively transmitting red light, a second color filter 16g for selectively transmitting green light, and a third color filter 16b for selectively transmitting blue light. The second planarization layer 18 is formed on the structure in which the color filters 16r, 16g, and 16b are formed. Microlenses 20 are formed on the second planarization layer 18 to cover each of the color filters 16r, 16g, and 16b.

As is well known, light constituting natural light has different wavelengths depending on its color. Therefore, as shown, the light passing through the same microlens has a different focal length depending on the wavelength of the light. For example, red light focuses on the lower portion of the light receiving region a while blue light focuses on the upper portion of the light receiving region a. As described above, as the portion of the focus in the light-receiving region a varies depending on the wavelength of light passing through each color filter, the light sensitivity is different. Therefore, a problem arises that it is difficult to obtain an accurate image because photoelectric conversion efficiency is different for each wavelength of light.

The present invention has been proposed to solve the above problems, and an object of the present invention is to provide an image sensor and a method of manufacturing the same with increased light collection efficiency and light sensitivity.

In order to achieve the above technical problem, the image sensor according to the present invention includes an internal lens in a flat layer formed on the light receiving unit. The inner lens is formed of a convex lens. A color filter and a micro lens are formed on the inner lens. The inner lens is formed at a predetermined position of the flat layer according to the wavelength of each light transmitted through the color filter. For example, the shorter the wavelength of transmitted light, the closer the inner lens is to the light receiving portion. The inner lens changes the refractive index of the light together with the microlens so that the focus of the light is formed on a portion of the light receiving unit regardless of the wavelength of the light transmitted through the color filter.

According to the method of manufacturing an image sensor according to the present invention, a flat layer is formed on a substrate including a light receiving unit. A mask is formed on the flat layer to expose a portion of the flat layer. Isotropic etching through the exposed portion forms concave grooves in the flat layer. The isotropic etching may be dry etching or wet etching. The concave groove is filled with a material having a refractive index higher than that of the flat layer to form an internal lens. A color filter and a micro lens are formed on the inner lens. The inner lens changes the refractive index of the light passing through the color filter so that the focus of the light is formed on a portion of the light receiver.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings so that those skilled in the art may easily implement the technical idea of the present invention. do. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosed subject matter is thorough and complete, and that the spirit of the present invention to those skilled in the art will fully convey. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. In addition, where a layer is said to be "on" another layer or semiconductor substrate, it may be formed directly on the other layer or semiconductor substrate, or a third layer may be interposed therebetween. Portions denoted by like reference numerals denote like elements throughout the specification.

2A to 2D are cross-sectional views illustrating a method of manufacturing an image sensor according to the present invention. Here, reference numeral a denotes a light receiving region, and reference numeral b denotes a charge transfer region.

Referring to FIG. 2A, the semiconductor substrate 100 includes a light receiving region a for converting light from the outside into signal charge and a charge transfer region b for transferring the signal charge. The light receiving region a and the charge transfer region b are alternately formed on the semiconductor substrate 100. Although not shown in the light-receiving region a, a photodiode having a structure in which an N-type impurity layer formed by implanting N-type impurities and a P-type impurity layer formed by injecting P-type impurities on the N-type impurity layer are bonded ( 115 may be formed. An impurity layer (not shown) for charge transfer is formed in the charge transfer region b. In addition, since the gate electrode 110 for transmitting the signal charges generated in the light receiving region a to the outside is formed in the charge transfer region b, it protrudes from the semiconductor substrate 100.

The first planarization layer 120 is formed on the structure. The first planarization layer 120 is formed to planarize the step between the light receiving region a and the charge transfer region b, and serves to protect the photodiode 115 and the gate electrode 110. The first planarization layer 120 may be formed using a material film having excellent visible light transmittance, for example, a polyimide-based thermosetting resin.

The mask layer 130 is formed on the first planarization layer 120. The mask layer may be formed by depositing a photoresist pattern. The mask layer 130 is patterned to expose a portion of the first planarization layer 120. In this case, the exposed portion 133 is positioned on at least one light receiving area a. In order for the internal lens 140 (see FIG. 2C) to be formed later to be positioned on the light receiving area a, the exposed portion 133 is preferably formed at the center of the light receiving area a.

Referring to FIG. 2B, when the first planarization layer 120 is isotropically etched using the mask layer 130, a concave groove 135 is formed on the first planarization layer 120. In this case, the etching process may be performed through wet etching or dry etching. In the case of dry etching, when the reactive ionized gas and the radical are used, the first planarization layer may have a concave shape as illustrated by the isotropic etching of radicals in addition to the anisotropic etching by the ionized gas. 120 may be etched. Thereafter, the mask layer 130 is removed.

Referring to FIG. 2C, an internal lens 140 is deposited on the first planarization layer 120 to fill the concave groove 133 through a chemical mechanical polishing process. Form. The inner lens 140 adjusts the refractive index of light selectively transmitted through the color filters 150r, 150g, and 150b of FIG. 2D. In addition, the internal lens 140 adjusts the focus of the light transmitted together with the microlens (170 in FIG. 2D) to be at a predetermined position on the light receiving area a. Therefore, the material constituting the inner lens 140 is preferably a material having a larger refractive index than the material constituting the first planarization layer 120. For example, the inner lens 140 may be formed using silicon nitride (SiN) or silicon oxynitride (SiON).

Referring to FIG. 2D, the processes of FIGS. 2A to 2C are repeated to form the second planarization layer 122 and the third planarization layer 124 including the internal lenses 142 and 144, respectively. The inner lens may be formed in plural instead of only one in each planarization layer. In addition, a plurality of planarization layers including an internal lens may be further formed on the third planarization layer. Although the inner lenses 140, 142, and 144 are shown as being positioned in different planarization layers 120, 122, and 124, the wavelengths of the inner lenses 140, 142, and 144 are different from each other by using a material having a different refractive index. If different light focal points can come to a certain position of the photodiode, they may be located on the same planarization layer. In addition, the formation of an internal lens may be omitted below the color filter that transmits light having a wavelength in which the focus of the light may be formed at an appropriate position on the photodiode using only the microlens 170.

Color filters 150r, 150g, and 150b are formed on the third planarization layer 124. The color filters 150r, 150g, and 150b are materials that transmit light of a specific color in order to obtain a high quality image. For example, pigment dispersion photos may selectively transmit any one of red, green, and blue, respectively. It can be formed using a resist. In this case, the color filter may further include a color filter for selectively transmitting other colors in addition to the color.

A fourth planarization layer 160 is formed on the structure to planarize the step between the color filters 150r, 150g, and 150b and the third planarization layer 124. The fourth planarization layer 160 is a material film having excellent visible light transmittance, and may be formed using, for example, a polyimide-based thermosetting resin. The microlens 170 is formed on the fourth planarization layer 160 to cover the color filters 150r, 150g, and 150b, respectively. The microlens 170 forms a photoresist pattern (not shown) covering the tops of the color filters 150r, 150g, and 150b on the fourth planarization layer 160, and uses a thermal process to form a flow pattern. flow).

In the present invention, by including an internal lens in the flat layer formed on the light receiving area (a) by varying the refractive index of the light together with the micro lens, the focus of light having different wavelengths is formed at a constant position of the light receiving area (a). . At this time, the inner lens is formed to be located far from the micro lens under a color filter that transmits light having a short wavelength, and the inner lens is formed to be located close to the micro lens under a color filter which transmits light having a long wavelength. . Therefore, the light sensitivity can be maintained constant regardless of the wavelength of light, and the photoelectric efficiency can be increased.

On the other hand, in the detailed description of the present invention has been described with respect to specific embodiments, various modifications are of course possible without departing from the scope of the invention. Therefore, the scope of the present invention should not be limited to the above-described embodiments, but should be defined by the equivalents of the claims of the present invention as well as the following claims.

As described above, according to the present invention, the focus of light having different wavelengths may be formed at a constant position of the light receiving unit by changing the refractive index of light using the internal lens. Therefore, it is possible to prevent the light sensitivity from changing depending on the wavelength of light. In addition, since the focus of light is formed at a certain position, the photoelectric change efficiency is increased.

Claims (8)

delete delete A flat layer formed on the light receiving portion; A plurality of color filters formed on the flat layer; A plurality of microlenses formed to correspond to the plurality of color filters, respectively; And At least one inner lens for adjusting the refractive index of the light together with the micro lenses so that the focus of the light passing through the color filters located on the flat layer is formed at a predetermined position of the light receiving unit, The inner lens is provided closer to the light receiving portion as the wavelength of light passing through the color filters is shorter. delete The method of claim 3, wherein And the inner lens is formed of a material having a higher refractive index than the flat layer. Forming a light receiving unit on the semiconductor substrate; Forming a first flat layer on the semiconductor substrate; Forming a concave first groove on the first flat layer; Forming a first internal lens in the first groove; Forming a second flat layer on the first flat layer; Forming a concave second groove on the second flat layer; Forming a second internal lens in the second groove; And Forming color filters and micro lenses on the first inner lens and the second inner lens, And a wavelength of light passing through the first internal lens is shorter than a wavelength of light passing through the second internal lens. The method of claim 6, Forming the first groove may include: Forming a mask on the first flat layer to expose a portion of the first flat layer; And And etching the first flat layer through the exposed portion to form a concave first groove. The method of claim 6, And each of the first internal lens and the second internal lens is formed of a material having a higher refractive index than the first flat layer and the second flat layer.

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