KR100754742B1 - Image sensor having wave guide and method for fabricating the same - Google Patents

Abstract

The present invention relates to an image sensor having an optical waveguide as a propagation path of incident light and a method of manufacturing the same. Minimize the pattern of neighboring color filters, and make the size of the color filter relatively small, thus minimizing the deterioration of light-receiving characteristics due to the overlap between the color filters and the generation of debris due to the formation of color filters. Also, in the design of micro lenses, the focal length can be shortened to stabilize the design characteristics.

Image sensor, light waveguide, return loss, color filter, superposition

Description

Image sensor having wave guide and method for manufacturing the same {Image sensor having wave guide and method for fabricating the same}             

1 is a circuit diagram schematically showing a unit pixel structure of a CMOS image sensor according to the prior art;

2 is a cross-sectional view schematically showing a structure of a conventional image sensor;

3 is a cross-sectional view schematically showing the structure of an optical waveguide;

4 is a cross-sectional view of an image sensor manufacturing process according to an embodiment of the present invention.

* Description of reference numerals for the main parts of the drawings *

41: semiconductor substrate 42: antireflection film

43: interlayer insulating film 44: passivation layer

45, 46: OCM planarization layer 47: microlens

R, G, B: Color filter W: Optical waveguide

TECHNICAL FIELD The present invention relates to the field of image sensor manufacturing, and more particularly, to an image sensor having a wave guide as a traveling path of incident light and a method of manufacturing the same.

An image sensor is an apparatus that converts optical information of one or two dimensions or more into an electrical signal. The types of image sensors are broadly classified into imaging tubes and solid-state imaging devices. Imaging tubes are widely used in measurement, control, and recognition using image processing technology centered on televisions, and applied technologies have been developed. There are two types of solid-state image sensors on the market: metal-oxide-semiconductor (MOS) type and charge coupled device (CCD) type.

CMOS image sensor is a device that converts an optical image into an electrical signal by using CMOS fabrication technology, and adopts a switching method in which MOS transistors are made by the number of pixels and the outputs are sequentially detected using the same. The CMOS image sensor is simpler to drive than the CCD image sensor, which is widely used as a conventional image sensor, and can realize various scanning methods, and can integrate a signal processing circuit into a single chip, thereby miniaturizing the product. The use of compatible CMOS technology reduces manufacturing costs and significantly lowers power consumption.

1 is a circuit diagram showing a unit pixel of a CMOS image sensor composed of four transistors and two capacitance structures, and a unit pixel of a CMOS image sensor composed of a photodiode (PD) as an optical sensing means and four NMOS transistors. . Of the four NMOS transistors, the transfer transistor Tx transmits a signal for transferring the photocharge generated in the photodiode PD to the floating diffusion region FD, and the reset transistor Rx supplies the floating diffusion region FD. The drive transistor Dx serves as a source follower, and the select transistor Sx receives a pixel data enable signal and receives a pixel to reset the voltage to the voltage V _DD level. It is responsible for transmitting the data signal to the output.

Operation of the image sensor unit pixel configured as described above is performed as follows. Initially, the unit pixel is reset by turning on the reset transistor Rx, the transfer transistor Tx, and the select transistor Sx. At this time, the photodiode PD starts to deplete, and carrier accumulation occurs, and the floating diffusion region is charged and stored up to the supply voltage VDD. The transfer transistor Tx is turned off, the select transistor Sx is turned on, and the reset transistor Rx is turned off. In this operation state, after reading the output voltage V1 from the unit pixel output terminal SO and storing it in the buffer, the transfer transistor Tx is turned on to move the carriers of the capacitance Cp changed according to the light intensity to the capacitance Cf. The output voltage (V2) is read from the output terminal (Out) again and the analog data for V1-V2 is converted into digital data, so one operation cycle for the unit pixel is completed.

FIG. 2 is a cross-sectional view schematically showing a structure of a conventional image sensor, on an interlayer insulating film 22 and an interlayer insulating film 22 covering a semiconductor substrate 21 on which a substructure including a photodiode (not shown) is completed. IMO (inter metal oxide) 23 covering the formed metal wiring (not shown), planarizing insulating film 24 covering the entire structure of the metal wiring forming process, color filters R, G, formed on the planarizing insulating film 24 B), a microlens formed on the over coating material (OCM) flattening layer 25 covering the color filters R, G, and B and the OCM flattening layer 25 and overlapping the color filters R, G, and B. An image sensor composed of (microlens) 26 is shown.

The light-receiving structure of the conventional image sensor described above is configured in such a way that the light incident on the microlens 26 is focused onto the photodiode by the snell's law shown in Equation 1 below.

However, in this structure, the incident light has a large reflection loss at the interface of various material layers from the microlens 26 to the photodiode, and the area where the incident light travels is relatively large, so that it is not suitable for the amount or sensitivity of light received depending on the state of the surface. It may not affect. In particular, the edge of the color filter may be affected by the scum, and the overlapping part of the color filter may have a curved shape, which affects the light sensitivity of the sensor and maintains uniform and stable characteristics. Difficult to do

The present invention for solving the above problems, to improve the light sensitivity and to prevent the neighboring color filter pattern is overlapped, to provide an image sensor having an optical waveguide as a traveling path of the incident light and a manufacturing method thereof. The purpose is to.

The present invention for achieving the above object, the semiconductor substrate is completed the formation of a lower structure including a light receiving area; At least one interlayer insulating film stacked over the semiconductor substrate; An optical waveguide formed in the interlayer insulating film and connected to the light receiving region by using the interlayer insulating film as a cladding layer; A core layer filling the optical waveguide of the clad layer formed of the interlayer insulating film; And condensing means formed on the core layer to focus incident light onto the entrance of the optical waveguide.

In addition, the present invention for achieving the above object, the step of forming an anti-reflection film on the semiconductor substrate is completed, the lower structure including a light receiving region; Forming an interlayer insulating film on the anti-reflection film; Selectively etching the interlayer insulating film to form openings exposing a portion of the anti-reflection film in the light receiving region; Embedding a core layer in the opening to form an optical waveguide comprising the core layer and the interlayer insulating film on the sidewalls of the core layer; And a light collecting means for focusing the light incident on the core layer to the entrance of the optical waveguide.

The present invention minimizes the loss of incident light due to a multi-layer interface by allowing the incident path of the light incident to the photodiode, which is a light receiving region, to pass through a circular wave guide, and the patterns of neighboring color filters are separated from each other. The size of the color filter can be made relatively small, thereby minimizing the deterioration of light receiving characteristics due to the overlap between the color filters and the occurrence of debris due to the formation of the color filter, and the shortening of the focal length even in the design of the micro lens. Can be expected to stabilize.

The optical waveguide is a waveguide in which light can be transmitted without loss in a zigzag form as shown in FIG. 3, and its structure is composed of a relatively high refractive index core layer 31 and a cladding layer 32 surrounding the core layer 31. It is actually configured to transmit light through the core layer 31.

The optical waveguide has a constant cut off frequency, which is determined by the difference in the refractive indices of the materials constituting the clad layer 32 and the core layer 31 and the width of the core layer 31, respectively.

In the present invention, the cladding layer 32 of the optical waveguide provided inside the image sensor is formed of a material having a refractive index of 1.32 to 1.61, and the core layer 31 is formed of a cladding layer 32 of the material having a refractive index of 1.44 to 1.76. Determined in consideration of the relationship, the diameter of the core is to be 0.9 ㎛ to 1.1 ㎛. Under these conditions, it is possible to satisfy the cut-off wavelength of more than the visible light wavelength, that is, 1 m. Therefore, it is possible to form a waveguide capable of transmitting the light in the visible light region without loss. In addition, since the diameter of the core layer 31 is about 0.9 μm to 1.1 μm, the size of the color filter covering the core layer may be reduced. That is, the color filter of the conventional 0.5 ㎛ CMOS image sensor is 7.5 ㎛ × 7.5 ㎛, whereas the color filter of the CMOS image sensor according to the present invention, since one side thereof should have a size of about the diameter of the core layer 31, The size of the filter can be reduced by about 1/7. In addition, it is possible to minimize generation of debris due to overlapping of adjacent color filter patterns and to ensure uniformity of color filter characteristics.

Hereinafter, an image sensor structure and a manufacturing method thereof according to an embodiment of the present invention will be described in detail with reference to FIG. 4.

As shown in FIG. 4, the image sensor according to the present invention includes an anti-reflection film 42 covering a semiconductor substrate 41 on which a substructure including a photodiode is completed, as an light receiving region. 43, a core layer 45 and a core layer formed in the passivation layer 44 covering the interlayer insulating layer 43, the passivation layer 44, and the interlayer insulating layer 43 and connected to the photodiode. (45) an optical waveguide (W) having a cladding layer composed of the interlayer insulating film (43) and a passivation layer (44) of sidewalls, and color filters (R, G,) covering an inlet of the core layer (45) of the waveguide; B), an OCM planarization layer 46 covering the entire structure including the color filters R, G, and B, and a condensing light formed on the OCM planarization layer 46 and overlapping the color filters R, G, and B. An example of the means includes a micro lens 47. The microlens 47 is formed so that incident light is focused at the inlet of the optical waveguide W through the color filters R, G, and B.

The method of manufacturing such an image sensor includes the following process.

First, as a light receiving region, a tetraethyl ortho silicate (TEOS) film (not shown) having a thickness of 135 GPa to 165 GPa is formed on a semiconductor substrate 41 on which a substructure including a photodiode is completed, and a refractive index of 1.67 to An oxynitride film 42 of 2.05 is formed to have a thickness of 400 kPa to 500 kPa. The oxynitride layer 42 serves as an antireflection layer and an etch stop layer.

Next, the interlayer insulating layer 43 and the passivation layer 44 are stacked, and the passivation layer 44 and the interlayer insulating layer 43 are selectively etched to expose a portion of the anti-reflection layer 42 covering the photodiode. The core region exposing the passivation layer 44 and the interlayer insulating film 43 is formed on the sidewalls thereof, and the OCM planarization layer 46 is formed on the entire structure to fill the core region. Accordingly, the OCM planarization layer 46 in the core region forms an optical waveguide W including the passivation layer 44 and the interlayer insulating film 43 as the cladding layer.

Subsequently, the OCM planarization layer 46 and the microlens 47 are formed on the OCM planarization layer 46 to cover the entire structure including the color filters R, G and B and the color filters R, G and B. do. In this case, the microlens 47 is formed so that the incident light is focused at the inlet of the optical waveguide W through the color filters R, G, and B. As a result, the focusing distance is relatively short, thereby improving condensing effect, facilitating design, and improving process uniformity. On the other hand, the deviation of light can be made almost " 0 " by widening the core region. As the diameter of the core increases, the cut-off extends into the longer wavelength region. Therefore, a desired wavelength band such as infrared rays can be used.

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes can be made in the art without departing from the technical spirit of the present invention. It will be clear to those of ordinary knowledge.

According to the present invention, the waveguide is provided in the interlayer insulating film covering the light receiving region, thereby suppressing the reflection loss caused by the interlayer interface and minimizing the effects of debris and cross-section bending that may be generated in the color filter manufacturing process. As a result, the quality and stability of the product can be improved by improving light sensitivity, uniformity of process, and stable implementation of device characteristics.

Claims (13)

delete delete In the image sensor, A semiconductor substrate on which a lower structure including a light receiving region is completed; At least one interlayer insulating film stacked over the semiconductor substrate; An optical waveguide formed in the interlayer insulating film and connected to the light receiving region by using the interlayer insulating film as a cladding layer; A core layer filling the optical waveguide of the clad layer formed of the interlayer insulating film; Condensing means formed on the core layer to focus incident light onto an entrance of the optical waveguide; A color filter covering an inlet of the core layer of the optical waveguide; And Including a planarization layer covering the entire structure including the color filter, The interlayer dielectric layer may be formed of a material having a refractive index of 1.32 to 1.61, and the core layer may be formed of a material having a refractive index of 1.44 to 1.76. The method of claim 3, wherein The core layer has a diameter of 0.9 μm to 1.1 μm. The method of claim 3, wherein And an anti-reflection film between the core layer and the semiconductor substrate. The method of claim 5, The anti-reflection film has an index of refraction of 1.67 to 2.05 characterized in that the image sensor. The method of claim 6, The anti-reflection film is an image sensor, characterized in that the oxynitride film. delete delete delete delete delete delete

Images