Structure and method for improving noise of CMOS image sensor

Abstract

The present invention discloses a structure for improving the noise of a CMOS image sensor. A grating structure is formed on a semiconductor substrate. The grating structure is composed of a grating dielectric layer filled in a groove. The grating dielectric layer includes at least a first grating dielectric layer and a second grating dielectric layer according to the different light transmittance of the material, and respectively constitutes a first grating structure and a second grating structure. The first grating structure covers each pixel unit in a first partial area, and the material of the first grating dielectric layer has a first light transmittance. The second grating structure covers each pixel unit in a second partial area, and the material of the second grating dielectric layer has a second light transmittance. The CMOS image sensor uses the first light transmittance, the second light transmittance, the incident light signal and the collected electrical signal to calculate the noise of the CMOS image sensor and eliminate the noise in the electrical signal of each pixel unit. The present invention also discloses a method for improving the noise of a CMOS image sensor.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor integrated circuit manufacturing, and in particular to a structure for improving the noise of a CMOS image sensor (CIS); the present invention also relates to a method for improving the noise of a CMOS image sensor. Background Art

[0002] CIS is composed of pixel unit circuits located in the pixel area and CMOS circuits in the logic area. Compared with CCD image sensors, CMOS image sensors have better integration because they use CMOS standard manufacturing processes. They can be integrated with other digital-analog operations and control circuits on the same chip, making them more adaptable to future development. According to the number of transistors contained in the pixel unit circuit of existing CMOS image sensors, they are mainly divided into 3T-type structure and 4T-type structure.

[0003] CIS uses photoelectric conversion devices to convert light signals into electrical signals. Ideally, the number of signal charges increases with the increase of light intensity until the number of charges reaches saturation, thereby obtaining an image.

[0004] However, the signal charge always contains a part caused by noise. In order to obtain higher quality images, it is important to reduce the noise level. Generally speaking, the noise of image sensors can be divided into fixed pattern noise, thermal noise, scattering noise, flicker noise, etc. These noises are usually related to hot electrons, dark current, and semiconductor manufacturing processes (such as interface charge, doping concentration, and contamination during the manufacturing process).

[0005] Currently, reducing the noise of image sensors has become an important aspect of improving the performance of image sensors, and how to reduce the noise of image sensors as much as possible has also become an important topic. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a structure for improving the noise of a CMOS image sensor, which can reduce the noise of the image sensor and thus improve the performance of the image sensor. To this end, the present invention also provides a method for improving the noise of a CMOS image sensor.

[0007] In order to solve the above technical problem, in the structure for improving the noise of a CMOS image sensor provided by the present invention, a pixel area of ​​the CMOS image sensor includes a plurality of pixel units, and each of the pixel units includes a photodiode.

[0008] Each of the photodiodes is formed in a semiconductor substrate.

[0009] A grating structure is formed on the semiconductor substrate, and the grating structure is used to provide a channel for light to be incident on the photodiode.

[0010] The grating structure is composed of a grating medium layer filled in the groove. According to the different light transmittances of the materials, the grating medium layer includes at least a first grating medium layer and a second grating medium layer. According to the different materials of the grating medium layer, the grating structure includes at least a first grating structure and a second grating structure, and the groove includes at least a first groove and a second groove. The first grating structure is composed of the first grating medium layer filled in the first groove, and the second grating structure is composed of the second grating medium layer filled in the second groove.

[0011] The first grating structure covers each of the pixel units in the first partial area, and the material of the first grating medium layer has a first light transmittance.

[0012] The second grating structure covers each of the pixel units in the second partial area, and the material of the second grating medium layer has a second light transmittance.

[0013] The CMOS image sensor uses the first light transmittance, the second light transmittance, an incident light signal, and a received electrical signal to calculate the noise of the CMOS image sensor and eliminate the noise in the electrical signal of each pixel unit.

[0014] A further improvement is that the CMOS image sensor calculates the noise of the CMOS image sensor through a logic circuit arranged in a logic area and eliminates the noise in the electrical signal of each pixel unit.

[0015] A further improvement is that the formula for calculating the noise of the CMOS image sensor is:

[0016] I1=λ1P+φ (1);

[0017] I2=λ2P+φ (2);

[0018]

[0019] Wherein, I1 represents the electrical signal received by each of the pixel units in the first partial area;

[0020] I2 represents the electrical signal received by each of the pixel units in the second part area;

[0021] P represents the incident light signal of each pixel unit;

[0022] φ represents the noise of the CMOS image sensor;

[0023] λ1 represents a coefficient between P and I1, and λ1 is related to the first light transmittance of the material of the first grating medium layer;

[0024] λ2 represents a coefficient between P and I2, and λ2 is related to the second light transmittance of the material of the second grating medium layer.

[0025] A further improvement is that the material of the first grating dielectric layer includes silicon nitride;

[0026] The material of the second grating medium layer includes silicon oxide.

[0027] A further improvement is that the CMOS image sensor is a back-illuminated CMOS image sensor.

[0028] A further improvement is that the grooves of the grating structure pass through a second light-proof material layer, and the second light-proof material layer can block the propagation of incident light signals.

[0029] A further improvement is that the grating structure consists of the first grating structure and the second grating structure, and the first grating structure and the second grating structure cover all the pixel units in the pixel area.

[0030] In order to solve the above technical problem, in the method for improving the noise of a CMOS image sensor provided by the present invention, a pixel area of ​​the CMOS image sensor includes a plurality of pixel units, each of the pixel units includes a photodiode;

[0031] Each of the photodiodes is formed in a semiconductor substrate;

[0032] A grating structure is formed on the semiconductor substrate, and the grating structure is used to provide a channel for light to be incident on the photodiode; the steps of forming the grating structure at least include:

[0033] Step 1: forming a first groove on the top of each pixel unit in the first part area by using a photolithography definition and etching process.

[0034] Step 2: Filling the first groove with a first grating dielectric layer, wherein the material of the first grating dielectric layer has a first light transmittance; and forming a first grating structure with the first grating dielectric layer filled in the first groove.

[0035] Step three: using a photolithography definition and etching process to form a second groove on the top of each pixel unit in the second part area.

[0036] Step 4: filling the second groove with a second grating dielectric layer, wherein the material of the second grating dielectric layer has a second light transmittance; and forming a second grating structure with the second grating dielectric layer filled in the second groove.

[0037] The CMOS image sensor uses the first light transmittance, the second light transmittance, an incident light signal, and a received electrical signal to calculate the noise of the CMOS image sensor and eliminate the noise in the electrical signal of each pixel unit.

[0038] A further improvement is that the CMOS image sensor calculates the noise of the CMOS image sensor through a logic circuit arranged in a logic area and eliminates the noise in the electrical signal of each pixel unit.

[0039] A further improvement is that the formula for calculating the noise of the CMOS image sensor is:

[0040] I1=λ1P+φ (1);

[0041] I2=λ2P+φ (2);

[0042]

[0043] Wherein, I1 represents the electrical signal received by each of the pixel units in the first partial area;

[0044] I2 represents the electrical signal received by each of the pixel units in the second part area;

[0045] P represents the incident light signal of each pixel unit;

[0046] φ represents the noise of the CMOS image sensor.

[0047] λ1 represents a coefficient between P and I1, and λ1 is related to the first light transmittance of the material of the first grating medium layer;

[0048] λ2 represents a coefficient between P and I2, and λ2 is related to the second light transmittance of the material of the second grating medium layer.

[0049] A further improvement is that the material of the first grating dielectric layer includes silicon nitride;

[0050] The material of the second grating medium layer includes silicon oxide.

[0051] A further improvement is that the CMOS image sensor is a back-illuminated CMOS image sensor.

[0052] A further improvement is that both the first groove and the second groove pass through a second light-proof material layer, and the second light-proof material layer can block the propagation of incident light signals.

[0053] A further improvement is that the grating structure consists of the first grating structure and the second grating structure, and the first grating structure and the second grating structure cover all the pixel units in the pixel area.

[0054] A further improvement is that the semiconductor substrate comprises a silicon substrate.

[0055] The present invention forms a grating structure in a pixel area and divides the grating structure into at least a first grating structure and a second grating structure. The grating medium layers in the first grating structure and the second grating structure, i.e., the first grating medium layer and the second grating medium layer, have different light transmittances. By utilizing the characteristics that, in the process of each pixel unit receiving a light signal and forming an electric signal, the electric signal of each pixel unit is affected by the same noise and the influence caused by the light signal is proportional to the light transmittance of the corresponding grating medium layer, the noise of each pixel unit can be calculated through two groups of grating structures, and thus the noise of each pixel unit can be eliminated. Therefore, the present invention can reduce the noise of the image sensor, thereby improving the performance of the image sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0057] Figure 1 is a flow chart of a method for improving noise of a CMOS image sensor according to an embodiment of the present invention;

[0058] Figure 2A is a cross-sectional view of a method for improving noise of a CMOS image sensor according to an embodiment of the present invention after a first groove is formed in a first partial region;

[0059] Figure 2B is a cross-sectional view of a method for improving noise of a CMOS image sensor according to an embodiment of the present invention after a first grating dielectric layer is formed in a first partial region;

[0060] Figure 2C yes Figure 2B The corresponding top view;

[0061] Figure 3A is a cross-sectional view of a method for improving noise of a CMOS image sensor according to an embodiment of the present invention after a second groove is formed in a second portion of the area;

[0062] Figure 3B is a cross-sectional view of a method for improving noise of a CMOS image sensor according to an embodiment of the present invention after a second grating dielectric layer is formed in a second part of the region;

[0063] Figure 3C yes Figure 3B The corresponding top view. DETAILED DESCRIPTION

[0064] Combination Figure 3B and Figure 3C As shown, in the structure for improving the noise of a CMOS image sensor according to an embodiment of the present invention, the pixel area of ​​the CMOS image sensor includes a plurality of pixel units, and each of the pixel units includes a photodiode.

[0065] Each of the photodiodes is formed in a semiconductor substrate.

[0066] A grating structure is formed on the semiconductor substrate, and the grating structure is used to provide a channel for light to be incident on the photodiode.

[0067] The grating structure is composed of a grating dielectric layer filled in the groove. According to the different light transmittance of the material, the grating dielectric layer at least includes a first grating dielectric layer 103a and a second grating dielectric layer 103b. According to the different materials of the grating dielectric layer, the grating structure at least includes a first grating structure and a second grating structure, and the grooves at least include a first groove 102a and a second groove 102b. The first grating structure is composed of the first grating dielectric layer 103a filled in the first groove 102a, and the second grating structure is composed of the second grating dielectric layer 103b filled in the second groove 102b.

[0068] The first grating structure covers each of the pixel units in the first partial area, and the material of the first grating medium layer 103a has a first light transmittance.

[0069] The second grating structure covers each of the pixel units in the second partial area, and the material of the second grating medium layer 103 b has a second light transmittance.

[0070] The CMOS image sensor uses the first light transmittance, the second light transmittance, an incident light signal, and a received electrical signal to calculate the noise of the CMOS image sensor and eliminate the noise in the electrical signal of each pixel unit.

[0071] The CMOS image sensor calculates the noise of the CMOS image sensor through a logic circuit arranged in a logic area and eliminates the noise in the electrical signal of each pixel unit.

[0072] The formula for calculating the noise of the CMOS image sensor is:

[0073] I1=λ1P+φ (1);

[0074] I2=λ2P+φ (2);

[0075]

[0076] Wherein, I1 represents the electrical signal received by each of the pixel units in the first partial area;

[0077] I2 represents the electrical signal received by each of the pixel units in the second part area;

[0078] P represents the incident light signal of each pixel unit.

[0079] φ represents the noise of the CMOS image sensor.

[0080] λ1 represents a coefficient between P and I1, and λ1 is related to the first light transmittance of the material of the first grating medium layer;

[0081] λ2 represents a coefficient between P and I2, and λ2 is related to the second light transmittance of the material of the second grating medium layer.

[0082] Usually P is expressed by the intensity of the light signal, and the unit is: μW / cm 2 The electrical signals corresponding to I1 and I2 are both expressed in terms of charge quantity, such as the number of electrons. That is, before the charge quantity reaches saturation, the greater the light intensity, the greater the number of photogenerated charges generated, and the two are linearly related, and the linear correlation coefficients are λ1 and λ2.

[0083] In some preferred embodiments, the material of the first grating dielectric layer 103a includes silicon nitride;

[0084] The material of the second grating medium layer 103 b includes silicon oxide.

[0085] The CMOS image sensor is a back-illuminated CMOS image sensor.

[0086] The grooves of the grating structure pass through the second light-proof material layer 101, and the second light-proof material layer 101 can block the propagation of incident light signals. Figure 3B As shown, the second light-impermeable material layer 101 is formed by stacking material layers 101a and 101b, wherein the material layer 101a is light-impermeable and the material layer 101b is also made of silicon oxide.

[0087] In an embodiment of the present invention, the grating structure is composed of the first grating structure and the second grating structure, and the first grating structure and the second grating structure cover all the pixel units in the pixel area. In other embodiments, the grating structure can also include more grating structures in addition to the first grating structure and the second grating structure, which can be achieved by making corresponding settings as needed.

[0088] In the embodiment of the present invention, a grating structure is formed in a pixel area and the grating structure is divided into at least a first grating structure and a second grating structure. The grating dielectric layers in the first grating structure and the second grating structure, i.e., the first grating dielectric layer 103a and the second grating dielectric layer 103b, have different light transmittances. By utilizing the characteristics that, in the process of each pixel unit receiving a light signal and forming an electric signal, the electric signal of each pixel unit is affected by the same noise and the influence caused by the light signal is proportional to the light transmittance of the corresponding grating dielectric layer, the noise of each pixel unit can be calculated through two groups of grating structures, and the noise of each pixel unit can be eliminated. Therefore, the embodiment of the present invention can reduce the noise of the image sensor, thereby improving the performance of the image sensor.

[0089] like Figure 1 , which is a flow chart of a method for improving noise of a CMOS image sensor according to an embodiment of the present invention; in the method for improving noise of a CMOS image sensor according to an embodiment of the present invention, a pixel area of ​​the CMOS image sensor includes a plurality of pixel units, and each of the pixel units includes a photodiode.

[0090] Each of the photodiodes is formed in a semiconductor substrate.

[0091] In the method of the embodiment of the present invention, the semiconductor substrate includes a silicon substrate.

[0092] The CMOS image sensor is a back-illuminated CMOS image sensor.

[0093] A grating structure is formed on the semiconductor substrate, and the grating structure is used to provide a channel for light to be incident on the photodiode; the steps of forming the grating structure at least include:

[0094] Step 1: Figure 2A As shown, a first groove 102a is formed on the top of each pixel unit in the first part area by using a photolithography definition and etching process.

[0095] In the method of the embodiment of the present invention, the first groove 102a and the subsequent second groove 102b both pass through the second light-impermeable material layer 101, and the second light-impermeable material layer 101 can block the propagation of incident optical signals. Figure 2A In the embodiment, the second light-impermeable material layer 101 is formed by stacking material layers 101a and 101b, wherein the material layer 101a is light-impermeable and the material layer 101b is also made of silicon oxide.

[0096] Step 2: Figure 2B As shown, a first grating dielectric layer 103a is filled in the first groove 102a, and a material of the first grating dielectric layer 103a has a first light transmittance; the first grating dielectric layer 103a filled in the first groove 102a forms a first grating structure.

[0097] Figure 2C A top view after forming the first grating structure is shown.

[0098] In the method of the embodiment of the present invention, the material of the first grating dielectric layer 103a includes silicon nitride;

[0099] Step 3: Figure 3A As shown, a second groove 102b is formed on the top of each pixel unit in the second part area by using a photolithography definition and etching process.

[0100] Step 4: Figure 3B As shown, a second grating dielectric layer 103b is filled in the second groove 102b, and the material of the second grating dielectric layer 103b has a second light transmittance; the second grating dielectric layer 103b filled in the second groove 102b forms a second grating structure.

[0101] Figure 3C A top view after forming the second grating structure is shown.

[0102] In the method of the embodiment of the present invention, the material of the second grating dielectric layer 103 b includes silicon oxide.

[0103] The grating structure is composed of the first grating structure and the second grating structure, the first grating structure and the second grating structure cover all the pixel units in the pixel area, and the grooves of the grating structure only include the first groove 102a and the second groove 102b. In other embodiments, the grating structure can also include more grating structures other than the first grating structure and the second grating structure, and more grating structures can be realized by simply repeating the groove etching and filling processes, and only need to be set according to needs.

[0104] The CMOS image sensor uses the first light transmittance, the second light transmittance, an incident light signal, and a received electrical signal to calculate the noise of the CMOS image sensor and eliminate the noise in the electrical signal of each pixel unit.

[0105] In the method of the embodiment of the present invention, the CMOS image sensor calculates the noise of the CMOS image sensor through a logic circuit arranged in a logic area and eliminates the noise in the electrical signal of each pixel unit.

[0106] The formula for calculating the noise of the CMOS image sensor is:

[0107] I1=λ1P+φ (1);

[0108] I2=λ2P+φ (2);

[0109]

[0110] Wherein, I1 represents the electrical signal received by each of the pixel units in the first partial area;

[0111] I2 represents the electrical signal received by each of the pixel units in the second part area;

[0112] P represents the incident light signal of each pixel unit;

[0113] φ represents the noise of the CMOS image sensor.

[0114] λ1 represents a coefficient between P and I1, and λ1 is related to the first light transmittance of the material of the first grating medium layer;

[0115] λ2 represents a coefficient between P and I2, and λ2 is related to the second light transmittance of the material of the second grating medium layer.

[0116] Usually P is expressed by the intensity of the light signal, and the unit is: μW / cm 2 The electrical signals corresponding to I1 and I2 are both expressed in terms of charge quantity, such as the number of electrons. That is, before the charge quantity reaches saturation, the greater the light intensity, the greater the number of photogenerated charges generated, and the two are linearly related, and the linear correlation coefficients are λ1 and λ2.

[0117] The present invention has been described in detail above through specific embodiments, but these do not constitute limitations of the present invention. Without departing from the principle of the present invention, those skilled in the art may also make many variations and improvements, which should also be considered as the protection scope of the present invention.

Claims

1. A structure for improving noise of a CMOS image sensor, characterized in that: The pixel area of ​​the CMOS image sensor includes a plurality of pixel units, each of which includes a photodiode; Each of the photodiodes is formed in a semiconductor substrate; A grating structure is formed on the semiconductor substrate, and the grating structure is used to provide a channel for light to be incident on the photodiode; The grating structure is composed of a grating medium layer filled in the groove, and the grating medium layer includes at least a first grating medium layer and a second grating medium layer according to different light transmittance of the material, and the grating structure includes at least a first grating structure and a second grating structure according to different materials of the grating medium layer, and the groove includes at least a first groove and a second groove; the first grating structure is composed of the first grating medium layer filled in the first groove, and the second grating structure is composed of the second grating medium layer filled in the second groove; The first grating structure covers each of the pixel units in the first partial area, and the material of the first grating medium layer has a first light transmittance; The second grating structure covers each of the pixel units in the second partial area, and the material of the second grating medium layer has a second light transmittance; The CMOS image sensor uses the first light transmittance, the second light transmittance, the incident light signal and the received electrical signal to calculate the noise of the CMOS image sensor and eliminate the noise in the electrical signal of each pixel unit; The CMOS image sensor calculates the noise of the CMOS image sensor through a logic circuit arranged in a logic area and eliminates the noise in the electrical signal of each pixel unit; The formula for calculating the noise of the CMOS image sensor is: I1=λ1P+φ; I2=λ2P+φ; Wherein, I1 represents the electrical signal received by each of the pixel units in the first partial area; I2 represents the electrical signal received by each of the pixel units in the second part area; P represents the incident light signal of each pixel unit; φ represents the noise of the CMOS image sensor; λ1 represents a coefficient between P and I1, and λ1 is related to the first light transmittance of the material of the first grating medium layer; λ2 represents a coefficient between P and I2, and λ2 is related to the second light transmittance of the material of the second grating medium layer.

2. The structure for improving noise of a CMOS image sensor according to claim 1, wherein: The material of the first grating dielectric layer includes silicon nitride; The material of the second grating medium layer includes silicon oxide.

3. The structure for improving noise of a CMOS image sensor according to claim 1, wherein: The CMOS image sensor is a back-illuminated CMOS image sensor.

4. The structure for improving noise of a CMOS image sensor according to claim 1, wherein: The grooves of the grating structure pass through the second light-proof material layer, and the second light-proof material layer can block the propagation of incident light signals.

5. The structure for improving noise of a CMOS image sensor according to claim 1, wherein: The grating structure consists of the first grating structure and the second grating structure, and the first grating structure and the second grating structure cover all the pixel units in the pixel area.

6. A method for improving the noise of a CMOS image sensor, characterized in that: The pixel area of ​​the CMOS image sensor includes a plurality of pixel units, each of which includes a photodiode; Each of the photodiodes is formed in a semiconductor substrate; A grating structure is formed on the semiconductor substrate, and the grating structure is used to provide a channel for light to be incident on the photodiode; The step of forming the grating structure at least comprises: Step 1: forming a first groove on the top of each pixel unit in the first part area by using a photolithography and etching process; Step 2: filling a first grating dielectric layer in the first groove, wherein the material of the first grating dielectric layer has a first light transmittance; and forming a first grating structure by the first grating dielectric layer filled in the first groove; Step 3: forming a second groove on the top of each pixel unit in the second part area by using a photolithography and etching process; Step 4: filling a second grating dielectric layer in the second groove, wherein the material of the second grating dielectric layer has a second light transmittance; and forming a second grating structure by the second grating dielectric layer filled in the second groove; The CMOS image sensor uses the first light transmittance, the second light transmittance, the incident light signal and the received electrical signal to calculate the noise of the CMOS image sensor and eliminate the noise in the electrical signal of each pixel unit; The CMOS image sensor calculates the noise of the CMOS image sensor through a logic circuit arranged in a logic area and eliminates the noise in the electrical signal of each pixel unit; The formula for calculating the noise of the CMOS image sensor is: I1=λ1P+φ; I2=λ2P+φ; Wherein, I1 represents the electrical signal received by each of the pixel units in the first partial area; I2 represents the electrical signal received by each of the pixel units in the second part area; P represents the incident light signal of each pixel unit; φ represents the noise of the CMOS image sensor; λ1 represents a coefficient between P and I1, and λ1 is related to the first light transmittance of the material of the first grating medium layer; λ2 represents a coefficient between P and I2, and λ2 is related to the second light transmittance of the material of the second grating medium layer.

7. The method for improving noise of a CMOS image sensor according to claim 6, wherein: The material of the first grating dielectric layer includes silicon nitride; The material of the second grating medium layer includes silicon oxide.

8. The method for improving noise of a CMOS image sensor according to claim 6, wherein: The CMOS image sensor is a back-illuminated CMOS image sensor.

9. The method for improving noise of a CMOS image sensor according to claim 6, wherein: Both the first groove and the second groove pass through a second light-proof material layer, and the second light-proof material layer can block the propagation of incident optical signals.

10. The method for improving noise of a CMOS image sensor according to claim 9, wherein: The grating structure consists of the first grating structure and the second grating structure, and the first grating structure and the second grating structure cover all the pixel units in the pixel area.

11. The method for improving noise of a CMOS image sensor according to claim 6, wherein: The semiconductor substrate includes a silicon substrate.

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