KR20030037883A - Method of forming microlens for image sensor - Google Patents

Abstract

PURPOSE: A method for forming a microlens in an image sensor is provided to improve photo sensitivity by minimizing the difference of focusing point between major axis and minor axis of a microlens. CONSTITUTION: In an image sensor having a non-square pixel, the first planarization layer(20) is formed on a semiconductor substrate(10). The first microlens(M1) of square shape having convex sphere is formed on the first planarization layer except for edge portions of a major axis of the pixel. A capping layer(21) is covered on the first microlens(M1). The second planarization layer(22) is formed on the capping layer to expose the convex sphere of the first microlens. The second microlens(M2) is formed to overlap partially the first microlens at the edge portions of the major axis.

Description

Micro lens formation method of image sensor {METHOD OF FORMING MICROLENS FOR IMAGE SENSOR}

The present invention relates to image sensor technology, and more particularly to a method for forming a micro lens of the image sensor.

The image sensor is composed of a light sensing part that detects light and a logic circuit part that processes the detected light into an electrical signal to make data. In addition, although efforts are made to increase the fill factor of the area of the light sensing portion of the entire image sensor element in order to increase the light sensitivity, this effort is limited under a limited area since the logic circuit portion cannot be removed. There is.

Therefore, in order to increase the light sensitivity, a microlens is applied to change the path of light incident to a region other than the light sensing portion and collect the light path.

However, when the pixels of the image sensor are non-square rather than square, a focal difference occurs because the focusing point distances of light incident on the short axis of the microlens and light incident on the long axis are different from each other. That is, since the focus of light incident on the long axis is deeper than the focus of light incident on the short axis, when the short axis is focused, the long axis is not in focus, and when the long axis is focused, the short axis is not in focus. Occurs. As a result, the amount of charge generation to light is reduced, thereby reducing the light sensitivity characteristic of the image sensor.

The present invention is to solve the conventional problems as described above, in the image sensor having a non-square pixel of the image sensor that can improve the light sensitivity by minimizing the focus difference of the light incident on the long axis and short axis of the micro lens It is an object of the present invention to provide a microlens forming method.

1 to 3 are cross-sectional views illustrating a method for forming a micro lens of an image sensor according to an exemplary embodiment of the present invention.

(a) is a cross sectional view taken along the short axis (x) direction of the pixel,

(b) is each sectional drawing along the major axis y direction of a pixel.

4 and 5 are plan views of first and second masks for a microlens according to an embodiment of the present invention;

※ Explanation of code for main part of drawing

10 semiconductor substrate 11: light receiving element

20 first planarization film 21 capping oxide film

22: second planarization film M1: first micro lens

M2: second microlens 100: first photomask

200: second photomask

In order to achieve the object of the present invention, a method of forming a micro lens of the image sensor according to the present invention comprises the steps of forming a first planarization film on a substrate having a predetermined process; Forming a square first micro lens having a convex spherical surface in a region excluding an edge portion in the major axis direction of the pixel on the first planarization film; Forming a capping layer on the substrate to cover the first micro lens; Forming a second planarization film to expose the convex portion of the first micro lens on the capping layer; And forming a second micro lens overlapping the first micro lens by a predetermined portion at the edge portion in the long axis direction.

The forming of the first microlens may include applying a first photoresist film on the first planarization film; Exposing and developing the first photoresist film using a square first photomask covering a central region of the pixel except the edge in the long axis direction of the pixel; And heat treating and flowing the first photoresist film, wherein forming the second micro lens comprises applying a second photoresist film on the entire surface of the substrate; Etching back the second photoresist film to remain only around the convex portion; Exposing and developing a second photoresist film using a second photomask that covers only the edge portion in the major axis direction; And heat treating and flowing the second photoresist film.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

1 to 3 are cross-sectional views illustrating a method of forming a microlens of an image sensor according to an exemplary embodiment of the present invention, and FIGS. 1 to 3 (a) illustrate a direction along a short axis (x; see FIG. 4) of a pixel. (B) is sectional drawing along the major axis y (refer FIG. 4) direction of a pixel.

Referring to FIG. 1, a surface is formed by forming a first planarization layer 20 on a semiconductor substrate 10 having a non-square pixel including a light receiving element 11 such as a photodiode and performing a predetermined process. Smooth. Next, a first photoresist film for microlenses is coated on the first planarization film 20, and as shown in FIG. After exposing and developing the first photoresist film using the photomask 100, a first micro-lens having a convex spherical surface is formed by flowing the first poresist film by performing a heat treatment process such as curing. M1) is formed. Thereafter, a capping oxide film 21 is formed on the substrate to cover the first micro lens M1, and a second planarization film 22 is formed on the capping oxide film 21. Then, the second planarization film 22 is etched by the etch back process to expose the convex portion of the first micro lens M1.

Referring to FIG. 2, a second photoresist film 23 for microlenses is coated on a substrate so as to cover the exposed convex portions of the first microlens M1, and a second etchback process is performed so as to remain only around the convex portions. The photoresist film 23 is etched.

Referring to FIG. 3, as shown in FIG. 5, the second photoresist film 23 is exposed and developed using a second photomask 200 covering only the edge portion in the y-direction, which is a long axis, and then cured. A heat treatment process such as a ring is performed to flow to form a second micro lens M2 overlapping a predetermined portion with the first micro lens M1 only at an edge portion in the long axis direction as shown in (b). Here, the second micro lens M2 is formed to have a larger radius of curvature than the first micro lens M2. Then, the exposed second planarization film 22 is removed.

That is, as shown in FIG. 3, the radius of curvature of the edge portion in the long axis direction of the microlens is larger than the radius of curvature in the minor axis direction, but the distance from the light receiving element 11 is increased by the planarization film and the capping oxide film. The focal difference between the long axis and the short axis direction is minimized and the focal point is almost coincident.

The present invention is not limited to the above embodiments, and various modifications can be made without departing from the technical spirit of the present invention.

As described above, according to the present invention, in the image sensor having non-square pixels, the microlenses in the long axis direction are formed in two stacked structures with the planarization film and the capping oxide film interposed therebetween, Since the focal point is almost coincident with the amount of charge generated to the light, the effect of improving the light sensitivity of the image sensor can be obtained.

Claims (3)

A method of forming a micro lens of an image sensor having non-square pixels, Forming a first planarization film on the substrate on which the predetermined process is completed; Forming a square first micro lens having a convex spherical surface in a region excluding an edge portion in the long axis direction of the pixel on the first planarization film; Forming a capping layer on the substrate to cover the first micro lens; Forming a second planarization layer on the capping layer to expose the convex portion of the first micro lens; And And forming a second micro lens overlapping the first micro lens by a predetermined portion at an edge portion of the long axis direction. The method of claim 1, Forming the first micro lens Applying a first photoresist film on the first planarization film; Exposing and developing the first photoresist film using a square first photomask covering a central region of the pixel except an edge in the long axis direction of the pixel; And And heat treating and flowing the first photoresist film. The method according to claim 1 or 2, Forming the second micro lens Applying a second photoresist film on the entire surface of the substrate; Etching the second photoresist film so as to remain only around the convex portion; Exposing and developing the second photoresist film using a second photomask covering only the edge portion of the long axis direction; And And heat treating and flowing the second photoresist film.