CN106409854B - Method and structure for improving red light quantum efficiency of front-illuminated CMOS image sensor - Google Patents

Abstract

The invention provides a method and a structure for improving red light quantum efficiency of a front-illuminated CMOS image sensor. The method for improving the red light quantum efficiency of the front-illuminated CMOS image sensor comprises the following steps: the first step is as follows: etching the silicon dioxide layer of the barrier layer of the metal silicide by using a mask plate for defining the red light sensitive area as an open mask plate before the etching barrier layer of the contact hole is grown, completely etching and removing the barrier layer of the metal silicide of the red light sensitive area, and exposing the silicon substrate of the red light sensitive area; the second step is as follows: and growing a contact hole etching barrier layer.

Description

Method and structure for improving red light quantum efficiency of front-illuminated CMOS image sensor

technical field

The invention relates to the field of semiconductor manufacturing, in particular to the improvement of photosensitive efficiency of a CMOS image sensor; more specifically, the invention relates to a method for improving the red light quantum efficiency of a front-illuminated CMOS image sensor and a corresponding CMOS image sensor structure.

Background technique

At present, the mainstream front-illuminated CMOS image sensor has a traditional CMOS logic circuit manufacturing process because the manufacturing technology applicable to its peripheral circuit, so its thin film layer above the silicon substrate in the photodiode photosensitive area is typically SAB (silicide barrier layer). ) silicon dioxide (for barrier layer of metal silicide)/CESL (contact hole etch barrier layer) silicon nitride (for contact hole etch barrier layer, silicon oxynitride is also used here/ILD (interlayer Dielectric) silicon dioxide (used to isolate the active area from the metal layer), before the light is transmitted to the photodiode area on the surface of the silicon substrate, it needs to penetrate these layers, and part of the light intensity will be lost due to the refraction and reflection of the interface layer. The amount of loss is determined by the thickness and refractive index of these thin film layers. The film thickness and refractive index of these three layers are usually determined by the standard process of logic circuits, that is, the process of different logic circuits determines the loss of incident light.

Therefore, it is desirable to provide a method for improving the red light quantum efficiency of the front-illuminated CMOS image sensor.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method capable of improving the red light quantum efficiency of a front-illuminated CMOS image sensor in view of the above-mentioned defects in the prior art.

In order to achieve the above technical purpose, according to the present invention, a method for improving the red light quantum efficiency of a front-illuminated CMOS image sensor is provided, including:

The first step: before growing the contact hole etching barrier layer, use a mask plate to define the red light sensitive area as an open mask, etch the silicon dioxide layer of the barrier layer of the metal silicide, and completely remove the red light sensitive area. The barrier layer of metal silicide in the red light sensitive area exposes the silicon substrate;

The second step: growing a contact hole etch barrier layer.

Preferably, in the first step, the green photosensitive area and the blue photosensitive area are defined as not opened in the mask, that is, when the silicon dioxide layer of the barrier layer of the metal silicide is etched, it will not be etched and removed. The blocking layer of the metal silicide in the green light sensitive area and the blue light sensitive area will not expose the silicon substrate in the green light sensitive area and the blue light sensitive area.

Preferably, in the second step, the parameters of the thin film growth process are adjusted so that the refractive index of the contact hole etching barrier layer in the red light sensitive region is between 2.24±3%.

Preferably, in the second step, the film thickness of the contact hole etch barrier layer in the red photosensitive region is between between.

Preferably, in the second step, the etch barrier layer of the contact hole of the red photosensitive region is directly formed on the silicon substrate.

Preferably, in the second step, the etching stopper layer for the contact hole of the green photosensitive region and the blue photosensitive region is formed on the metal silicide stopper layer.

In order to achieve the above technical purpose, according to the present invention, a front-illuminated CMOS image sensor structure is also provided, including: a red light sensitive area, a green light sensitive area and a blue light sensitive area; The contact hole etching barrier layer on the substrate, the green photosensitive area and the blue photosensitive area include a metal silicide barrier layer directly formed on the silicon substrate, and a contact hole etched directly on the metal silicide barrier layer. etch barrier.

Preferably, the refractive index of the contact hole etch barrier layer in the red photosensitive region is between 2.24±3%.

Preferably, the film thickness of the contact hole etch barrier layer in the red photosensitive area is between between.

The invention improves the red light quantum efficiency of the front-illuminated CMOS image sensor by improving the film structure, refractive index and thickness above the red light photodiode.

Description of drawings

A more complete understanding of the invention, and its accompanying advantages and features, will be more readily understood by reference to the following detailed description, taken in conjunction with the accompanying drawings, in which:

Fig. 1 schematically shows a flowchart of a method for improving the quantum efficiency of red light of a front-illuminated CMOS image sensor according to a preferred embodiment of the present invention.

FIG. 2 schematically shows a schematic view of the structure of a front-illuminated CMOS image sensor according to a preferred embodiment of the present invention.

It should be noted that the accompanying drawings are used to illustrate the present invention, but not to limit the present invention. Note that drawings showing structures may not be drawn to scale. And, in the drawings, the same or similar elements are marked with the same or similar symbols.

Detailed ways

In order to make the content of the present invention clearer and easier to understand, the content of the present invention will be described in detail below in conjunction with specific embodiments and accompanying drawings.

The invention improves the red light quantum efficiency of the front-illuminated CMOS image sensor by improving the film structure, refractive index and thickness above the red light photodiode.

Specifically, FIG. 1 schematically shows a flow chart of a method for improving the red light quantum efficiency of a front-illuminated CMOS image sensor according to a preferred embodiment of the present invention.

As shown in Figure 1, the method for improving the red light quantum efficiency of a front-illuminated CMOS image sensor according to a preferred embodiment of the present invention includes:

The first step S1: Before growing the contact hole etching barrier layer, use a layer of mask plate to define the red light sensitive area as an open mask to etch the silicon dioxide layer of the metal silicide barrier layer to completely remove the red light The barrier layer of metal silicide in the photosensitive area exposes the silicon substrate in the red photosensitive area;

Wherein, in the first step S1, the green photosensitive region and the blue photosensitive region are defined as not opened in the mask, that is, when the silicon dioxide layer of the barrier layer of the metal silicide is etched, it will not be etched and removed. The blocking layer of the metal silicide in the green light sensitive area and the blue light sensitive area will not expose the silicon substrate in the green light sensitive area and the blue light sensitive area.

Second step S2: growing a contact hole etching stopper layer.

Preferably, in the second step S2, the parameters of the thin film growth process are adjusted so that the refractive index of the contact hole etching barrier layer in the red light sensitive area is between 2.24±3%.

And preferably, in the second step S2, the film thickness of the contact hole etching barrier layer in the red light sensitive area is between between.

In the second step S2 , the etching stopper layer 300 for the contact hole of the red photosensitive region is directly formed on the silicon substrate 100 . Moreover, in the second step S2 , an etch barrier layer for the contact holes of the green light sensitive area and the blue light sensitive area is formed on the metal silicide barrier layer 200 , as shown in FIG. 2 .

The parameters of the solution proposed by the present invention are the best results of theoretical derivation, and its theoretical model is that light passes through two dielectric layers and enters the silicon substrate. Assuming that the first dielectric layer has a refractive index of N1 and a film thickness of T1, the second The refractive index of the second dielectric layer is N2, the film thickness is T2, and the refractive index of the silicon substrate is 3.44 (considered known). Considering a beam of incident light with a wavelength of λ, its horizontal component is not helpful for photosensitivity, so the model only considers the ideal situation where the incident light is perpendicular to the thin film layer and enters the photodiode, that is, the incident angle is 0°C, then the light can be obtained from medium one to the medium The reflectivity of two is expressed as

The reflectivity from medium two to the silicon substrate is expressed as

Then the total reflectivity of the two interfaces can be expressed as

Substituting (1), (2) into (3), it is appropriate

When R obtains the minimum value, the expression is

It can be seen from (5) that when The reflectance is 0, that is, there is no reflection loss.

For the traditional "silicide barrier silicon dioxide layer/contact hole etching barrier layer/silicon dioxide layer" structure, its N ₂ = 1.46, to meet this condition N ₁ needs to be 0.61, and there is no known such material exists; but if it is the structure of "contact hole etch barrier layer/silicon dioxide layer", then, N ₁ =1.46, to satisfy (6) formula, N ₂ =2.24, the traditional contact hole etch barrier layer can By adjusting the process parameters to meet this requirement, and then substituting N ₂ into (4), the value of T ₂ is obtained, that is, the film thickness value of the contact hole etching barrier layer when there is no reflection, considering that the peak wavelength of red light is 650nm, thus _T2 can be calculated as

For example, for a certain CIS (CMOS Image Sensor) process, the silicon dioxide thickness of the barrier layer of the metal silicide is X, and after the silicide is deposited and cleaned, a light is added before the growth of the contact hole etching barrier layer. In this process, the area sensitive to red light is defined as the open area after the photoresist is developed, and the photoresist in other areas is the reserved area after development. After that, an etching process is performed to completely etch the silicon dioxide film above the red light sensor to expose the silicon substrate. After the photoresist is removed, the pre-cleaning process before the growth of the contact hole etching barrier layer is mainly to remove the natural oxide layer above the red light sensor, and then grow a film thickness of A contact hole with a refractive index of 2.24±3% is etched into a barrier layer; and then the active region and the metal isolation layer are grown silicon dioxide.

Compared with the traditional front-illuminated CMOS sensor, which has the same thin film structure above the red, green and blue light, the present invention uses an additional layer of mask plate and etching process to define the thin film structure above the red light separately. The order of the film layer structure above the red light sensor is adjusted to "contact hole etching barrier layer/silicon dioxide layer", and the green and blue light areas keep the traditional structure unchanged, that is, "silicide blocking silicon dioxide layer/contact hole etching barrier layer". layer/silicon dioxide layer". The refractive index requirement of the contact hole etching barrier layer is 2.24±3%, and its film thickness requirement is

In addition, it should be noted that, unless otherwise specified or pointed out, the terms “first”, “second”, “third” and other descriptions in the specification are only used to distinguish each component, element, step, etc. in the specification, and It is not used to represent the logical relationship or sequential relationship between various components, elements, and steps.

It can be understood that although the present invention has been disclosed above with preferred embodiments, the above embodiments are not intended to limit the present invention. For any person skilled in the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or be modified to be equivalent to equivalent changes. Example. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention, which do not deviate from the technical solution of the present invention, still fall within the protection scope of the technical solution of the present invention.

Furthermore, it is to be understood that this invention is not limited to the particular methods, compounds, materials, fabrication techniques, usages and applications described herein, which may vary. It should also be understood that the terminology described herein is used to describe particular embodiments only and is not intended to limit the scope of the present invention. It must be noted that as used herein and in the appended claims, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, a reference to "an element" means a reference to one or more elements and includes equivalents thereof known to those skilled in the art. Similarly, as another example, a reference to "a step" or "a means" means a reference to one or more steps or means, and may include sub-steps as well as sub-means. All conjunctions used should be understood in their broadest sense. Therefore, the word "or" should be understood as having a logical "or" definition rather than a logical "exclusive or", unless the context clearly indicates the contrary meaning. Structures described herein are to be understood as also referring to functional equivalents of the structures. Language that may be construed as approximation should be construed as such, unless the context clearly dictates otherwise.

Moreover, implementation of the method and/or system of embodiments of the present invention may include performing selected tasks manually, automatically, or in combination. Moreover, according to actual instruments and equipment of embodiments of the method and/or system of the present invention, several selected tasks may be implemented by hardware, software, or a combination thereof using an operating system.

Claims (3)

1. A method for improving the red light quantum efficiency of a front-illuminated CMOS image sensor is characterized by comprising the following steps:

the first step is as follows: etching the silicon dioxide layer of the barrier layer of the metal silicide by using a mask plate for defining the red light sensitive area as an open mask plate before the etching barrier layer of the contact hole is grown, completely etching and removing the barrier layer of the metal silicide of the red light sensitive area, and exposing the silicon substrate of the red light sensitive area;

in the first step, the green light sensitive area and the blue light sensitive area are defined as not opened in the mask plate, namely when the barrier layer silicon dioxide layer of the metal silicide is etched, the barrier layers of the metal silicide of the green light sensitive area and the blue light sensitive area are not etched and removed, and the silicon substrates of the green light sensitive area and the blue light sensitive area are not exposed;

the second step is as follows: growing a contact hole etching barrier layer;

in the second step, parameters of a film growth process are adjusted to enable the refractive index of the etching barrier layer of the contact hole of the red light sensitive area to be between 2.24 +/-3%;

in the second step, the thickness of the etching barrier layer of the contact hole of the red light sensitive area is betweenTo (c) to (d);

in the second step, the etching barrier layer of the contact hole of the red light sensitive area is directly formed on the silicon substrate.

2. The method of improving red quantum efficiency of a front-illuminated CMOS image sensor as claimed in claim 1, wherein in the second step, the contact hole etch barrier layer of the green light-sensitive area and the blue light-sensitive area is formed on the barrier layer of the metal silicide.

3. A front-illuminated CMOS image sensor structure, comprising: a red light sensitive area, a green light sensitive area and a blue light sensitive area; the red light sensitive area comprises a contact hole etching barrier layer directly formed on a silicon substrate, and the green light sensitive area and the blue light sensitive area comprise a metal silicide barrier layer directly formed on the silicon substrate and a contact hole etching barrier layer directly formed on the metal silicide barrier layer; the refractive index of the etching barrier layer of the contact hole of the red light sensitive area is between 2.24 +/-3%; the thickness of the contact hole etching barrier layer of the red light sensitive area is betweenIn the meantime.