CN110400815A - Image sensor and method of forming the same - Google Patents

Abstract

An image sensor and its forming method, the method includes: providing a semiconductor substrate; forming an initial photoelectric doped region in the semiconductor substrate; Doped with first ions and second ions, the conductivity type of the first ions is opposite to that of the initial photoelectric doping region, the conductivity type of the second ions is the same as that of the initial photoelectric doping region, and the second ion The diffusion rate is greater than the diffusion rate of the first ions; heat treatment is performed to diffuse the first ions and the second ions in the initial isolation region, and form the main photoelectric doping region, mutually separated isolation regions, and mutual isolation regions in the initial photoelectric doping region. A separate additional photoelectric doped region, the conductivity type of the additional photoelectric doped region is the same as that of the main photoelectric doped region, and the conductivity type of the isolation region is opposite to that of the main photoelectric doped region. The performance of the image sensor formed by the method is better.

Description

Image sensor and method of forming the same

technical field

The invention relates to the field of semiconductor manufacturing, in particular to an image sensor and a forming method thereof.

Background technique

With the continuous improvement of semiconductor technology, the image sensor (Image Sensor), as a basic device for information acquisition, has been more and more widely used in modern society. Complementary Metal Oxide Semiconductor (CMOS) image sensor is a fast-growing solid-state image sensor. Since the image sensor part and the control circuit part of the CMOS image sensor are integrated in the same chip, the volume of the CMOS image sensor Compared with the traditional charge-coupled device (CCD) image sensor, it has advantages of small size, low power consumption, and low price, and is also easier to popularize.

Existing CMOS image sensors include photosensors for converting optical signals into electrical signals. The photosensors are photodiodes formed in a silicon substrate, and there are isolation structures between adjacent photodiodes. In addition, a filter layer is formed on the surface of the silicon substrate on which the photodiode is formed. The filter layer filters the incident light to pass light of a specific wavelength; Grid structure that shields optical crosstalk.

However, as the size of the pixel unit continues to shrink, the full-well capacitance of the photodiode also decreases, resulting in poor performance of the image sensor.

Contents of the invention

The technical problem solved by the present invention is to provide an image sensor and its forming method to improve the performance of the image sensor.

In order to solve the above technical problems, an embodiment of the present invention provides a method for forming an image sensor, including: providing a semiconductor substrate; forming an initial photoelectric doped region in the semiconductor substrate; forming an initial photoelectric doped region in the initial photoelectric doped region Initial isolation regions separated from each other, and the initial isolation regions are respectively located on opposite sides of the initial photoelectric doping region, the initial isolation regions are doped with first ions and second ions, the conductivity type of the first ions and the initial The conductivity type of the photoelectric doped region is opposite, the conductivity type of the second ion is the same as that of the initial photoelectric doped region, and the diffusion rate of the second ion is greater than the diffusion rate of the first ion; heat treatment is carried out to make the initial isolation region Diffusion of the first ions and the second ions to form a main photoelectric doped region, mutually separated isolation regions and mutually separated additional photoelectric doped regions in the initial photoelectric doped region, and the conductivity of the additional photoelectric doped region The conductivity type is the same as that of the main photoelectric doped region, the conductivity type of the isolation region is opposite to that of the main photoelectric doped region, and the isolation regions are located on both sides of the main photoelectric doped region, and the additional photoelectric doped region The impurity region is located between the isolation region and the adjacent main photoelectric doped region, and the additional photoelectric doped region is adjacent to the isolation region and the main photoelectric doped region respectively.

Optionally, the method further includes: before forming the initial photoelectric doped region, forming a protective layer on the surface of the semiconductor substrate.

Optionally, the material of the protective layer includes: silicon oxide, silicon nitride, silicon carbide nitride, silicon boride nitride, silicon oxycarbide or silicon oxynitride.

Optionally, the method for forming the initial isolation region includes: forming a mask layer on the surface of the semiconductor substrate, the mask layer exposing a part of the surface of the initial photoelectric doped region; using the first ion implantation, with the The mask layer is a mask, and first ions are implanted into the initial photoelectric doping region; second ion implantation is used, and second ions are implanted into the initial photoelectric doping region by using the mask layer as a mask.

Optionally, the process parameters of the first ion implantation include: a dose range of 1.0e12atm/cm2-2.0e12atm/cm2; the process parameters of the second ion implantation include: a dose range of 1.0e12atm/cm2-2.0e12atm/cm2 cm2.

Optionally, the concentration of the first ion in the isolation area is greater than the concentration of the second ion; the concentration of the first ion in the isolation area is 1.0e12atm/cm2～2.0e12atm/cm2, and the concentration of the second ion in the isolation area is 3.0 e11atm/cm2～8.0e11atm/cm2.

Optionally, the conductivity type of the initial photoelectric doped region is opposite to that of the semiconductor substrate; the method for forming the initial photoelectric doped region includes: using a third ion implantation process, implanting The third ions make the initial photoelectric doping region doped with third ions, and the conductivity type of the third ions is the same as that of the second ions.

Optionally, the first ions are indium ions, and the second ions are phosphorus ions.

Optionally, the heat treatment includes rapid annealing or spike annealing.

Correspondingly, an embodiment of the present invention also provides an image sensor formed by any one of the above methods, including: a semiconductor substrate; a main photoelectric doped region located in the semiconductor substrate, mutually separated isolation regions and mutually separated The additional photoelectric doped region, the conductivity type of the additional photoelectric doped region is the same as that of the main photoelectric doped region, the conductivity type of the isolation region is opposite to that of the main photoelectric doped region, and the isolation regions are respectively located on both sides of the main photoelectric doped region, the additional photoelectric doped region is located between the isolation region and the adjacent main photoelectric doped region, and the additional photoelectric doped region is adjacent to the isolation region and the main photoelectric doped region respectively .

Compared with the prior art, the technical solutions of the embodiments of the present invention have the following beneficial effects:

In the method for forming the image sensor provided by the technical solution of the present invention, since there are third ions in the initial photoelectric doping region, the conductivity type of the first ion in the initial isolation region is opposite to that of the initial photoelectric doping region, and the initial isolation region The conductivity type of the second ion in the region is the same as that of the initial photoelectric doping region. After the subsequent heat treatment, both the first ions and the second ions in the initial isolation region diffuse into the initial photoelectric doping region, and the rate at which the second ions diffuse into the initial photoelectric doping region is greater than that of the first ions diffusing into the initial photoelectric doping region. zone speed. On the one hand, the concentration of doped ions in the additional photoelectric doped region formed after diffusion can be higher than the concentration of doped ions in the main photoelectric doped region, thereby increasing the full-well capacitance of the formed photodiode. On the other hand, after the heat treatment, the net charge in the formed isolation region is the first ion, so the conductivity type of the isolation region is opposite to that of the main photoelectric doped region, and the conductivity type of the isolation region is the same as that of the additional The conductivity type of the photoelectric doped region is opposite. To sum up, the method can improve the full-well capacitance of the photodiode, so that the performance of the formed image sensor is better.

Further, the heat treatment includes annealing treatment. The annealing treatment includes rapid thermal treatment or spike annealing. The heat treatment adopts rapid heat treatment or spike annealing, the annealing time is short, and the thermal influence on other structures in the image sensor is small, so that the performance of the formed image sensor is better.

Description of drawings

FIG. 1 is a schematic cross-sectional structure diagram of an image sensor;

FIG. 2 to FIG. 6 are schematic cross-sectional structure diagrams of various steps in the forming process of the image sensor according to an embodiment of the present invention.

Detailed ways

As mentioned in the background, the performance of image sensors formed by existing methods is relatively poor.

FIG. 1 is a schematic cross-sectional structure diagram of an image sensor.

Please refer to FIG. 1, the image sensor includes: a semiconductor substrate 100; a photoelectric doped region 110 located in the semiconductor substrate 100, and the conductivity type of the photoelectric doped region 100 is opposite to that of the semiconductor substrate 100; The isolation region 120 on the sidewall of the photoelectric doped region 110 , and the conductivity type of the isolation region 120 is opposite to that of the photoelectric doped region 110 .

In the above structure, generally there is a well region (not shown in the figure) in the semiconductor substrate 100, and there are first dopant ions in the well region; there are second dopant ions in the photoelectric doped region 110 , the conductivity types of the first dopant ions and the second dopant ions are opposite. Furthermore, the conductivity type of the photoelectric doped region 120 is opposite to that of the semiconductor substrate 100 , therefore, the photoelectric doped region 120 and the semiconductor substrate 100 form a photodiode. The photodiode is used to convert photons of incident light into electrons.

However, the distribution of the second doping ions in the photoelectric doping region 110 in the above structure is uniform, so that the full well capacitance of the formed photodiode is limited, and the performance of the image sensor is poor.

In order to solve the above technical problem, the present invention provides a method for forming an image sensor, including: performing heat treatment to diffuse the first ions and second ions in the initial isolation region, and form the main photoelectric doped region in the initial photoelectric doping region. Doped regions, mutually separated isolation regions, and mutually separated additional photoelectric doped regions, the conductivity type of the additional photoelectric doped regions is the same as that of the main photoelectric doped region, and the conductivity type of the isolated regions is the same as that of the main photoelectric doped region. The conductivity type of the doped region is opposite, and the isolation regions are respectively located on both sides of the main photoelectric doped region, the additional photoelectric doped region is located between the isolation region and the adjacent main photoelectric doped region, and the additional photoelectric doped region The region adjoins the isolation region and the main optoelectronic doping region respectively. The performance of the image sensor formed by the method is better.

In order to make the above objects, features and beneficial effects of the present invention more comprehensible, specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

FIG. 2 to FIG. 6 are schematic cross-sectional structure diagrams of various steps in the forming process of the image sensor according to an embodiment of the present invention.

Referring to FIG. 2 , a semiconductor substrate 200 is provided.

In this embodiment, the material of the semiconductor substrate 200 is single crystal silicon. The semiconductor substrate may also be polysilicon or amorphous silicon. The material of the semiconductor substrate may also be semiconductor materials such as germanium, silicon germanium, and gallium arsenide. The semiconductor substrate can also be a semiconductor-on-insulator structure, the semiconductor-on-insulator structure includes an insulator and a semiconductor material layer on the insulator, and the material of the semiconductor material layer includes silicon, germanium, silicon germanium, gallium arsenide or indium Semiconductor materials such as gallium arsenide.

In this embodiment, there are trap ions in the semiconductor substrate 200 , and the conductivity type of the trap ions is opposite to that of the subsequent initial photoelectric doping region.

In this embodiment, the conductivity type of the trap ions is P-type, for example: boron ions or BF ^2- ions.

In this embodiment, before forming the initial photoelectric doped region, it further includes: forming a protective layer 210 on the surface of the semiconductor substrate 200 .

The material of the protective layer 210 includes: silicon oxide, silicon nitride, silicon nitride carbide, silicon nitride boride, silicon oxycarbide or silicon oxynitride. The protection layer 210 is used to protect the semiconductor substrate 200 so that the surface of the semiconductor substrate 200 is not affected by the subsequent ion implantation process.

In this embodiment, the material of the protection layer 210 is silicon oxide; the formation process of the protection layer 210 includes: a thermal oxidation process.

In other embodiments, the protective layer is not formed.

Referring to FIG. 3 , an initial photoelectric doping region 220 is formed in the semiconductor substrate 200 .

In this embodiment, after the protective layer 210 is formed, the initial photoelectric doped region 220 is formed.

The conductivity type of the initial photoelectric doped region 220 is opposite to that of the semiconductor substrate 200 .

The method for forming the initial photoelectric doped region 220 includes: adopting a third ion implantation process, implanting third ions into the semiconductor substrate 200, so that the initial photoelectric doped region 220 is doped with third ions, the The conductivity type of the third ions is the same as the conductivity type of the subsequently implanted second ions.

In this embodiment, the conductivity type of the third ions is N type, including: arsenic ions or phosphorus ions.

Next, separate initial isolation regions are formed in the initial photoelectric doping region 220, and the initial isolation regions are respectively located on opposite sides of the initial photoelectric doping region. For the specific process of forming the initial isolation regions, please refer to FIG. 4 to 5.

Referring to FIG. 4 , a mask layer 230 is formed on the surface of the semiconductor substrate 200 , and the mask layer 230 exposes part of the surface of the initial photoelectric doped region 220 .

In this embodiment, a mask layer 230 is formed on the surface of the protection layer 210 .

The material of the mask layer 230 includes: silicon oxide, silicon nitride, silicon carbide nitride, silicon nitride boride, silicon oxycarbide, silicon oxynitride, amorphous carbon or photoresist material.

In this embodiment, the material of the mask layer 230 is a photoresist material, and the process of forming the mask layer 230 is a spin coating process.

The mask layer 230 is used as a mask for subsequent first ion implantation and second ion implantation.

Please refer to FIG. 5, using the first ion implantation, using the mask layer 230 as a mask, implanting first ions into the initial photoelectric doped region 220; using the second ion implantation, using the mask layer 230 as a mask mask, implanting second ions into the initial photoelectric doped region 220 .

In this embodiment, the first ion implantation process and the second ion implantation process are performed simultaneously. In other embodiments, the first ion implantation process and the second ion implantation process are performed successively.

By using the mask layer 230 as a mask, the initial photoelectric doped region 220 is subjected to the first ion implantation process and the second ion implantation process to form mutually separate initial isolations in the initial photoelectric doped region 220 region 240, the initial isolation region 240 is doped with first ions and second ions, the conductivity type of the first ions is opposite to that of the initial photoelectric doping region 220, and the conductivity type of the second ions is the same as that of the initial photoelectric doping region 240. The conductivity types of the impurity regions 220 are the same, and the diffusion rate of the second ions is greater than that of the first ions.

The parameters of the first ion implantation process include: a dose range of 1.0e12atm/cm ² -2.0e12atm/cm ² .

In this embodiment, the first ions are indium ions.

The parameters of the second ion implantation process include: a dose range of 1.0e12atm/cm ² -2.0e12atm/cm ² .

In this embodiment, the second ions are phosphorus ions.

In this embodiment, the conductivity type of the third ions in the initial photoelectric doping region 220 is N type, and there are first ions and second ions in the initial isolation region 240, and the conductivity type of the first ions is P Type, the conductivity type of the first ion is opposite to the conductivity type of the initial photoelectric doping region 220, the conductivity type of the second ion is N type, and the conductivity type of the second ion is the same as that of the initial photoelectric doping region 220, And the diffusion rate of the second ion is greater than the diffusion rate of the first ion, which is beneficial to make the second ion of the same conductivity type as the third ion be more efficient than the first ion of the conductivity type opposite to the third ion after subsequent heat treatment. Diffusion into the initial photoelectric doped region 220, so that the concentration of N-type ions doped in the subsequently formed main photoelectric doped region can be greater than the concentration of N-type ions doped in the additional photoelectric doped region, and the subsequently formed The net charge in the isolation region is the first ion, that is, the conductivity type of the subsequent isolation region is P type.

In this embodiment, after the initial isolation region 240 is formed, the mask layer 230 is removed.

The process of removing the mask layer 230 includes: an ashing process.

Please refer to FIG. 6, heat treatment is performed to diffuse the first ions and the second ions in the initial isolation region 240, and form the main photoelectric doped region 250 in the initial photoelectric doped region 220 (shown in FIG. 5 ). Separate isolation regions 260 and additional photoelectric doped regions 270 separated from each other. The conductivity type of the additional photoelectric doped regions 270 is the same as that of the main photoelectric doped region 250. The conductivity type of the isolation regions 260 is the same as that of the main photoelectric doped regions. The conductivity type of the doped region 250 is opposite, and the isolation regions 260 are respectively located on both sides of the main photoelectric doped region 250, and the additional photoelectric doped region 270 is located between the isolation region 260 and the adjacent main photoelectric doped region 250, The additional photoelectric doped region 270 is adjacent to the isolation region 260 and the main photoelectric doped region 250 respectively.

The heat treatment includes annealing treatment. The annealing treatment includes rapid thermal treatment or spike annealing. The advantages of adopting rapid heat treatment or spike annealing for the heat treatment include: the annealing time is short, and the thermal influence on other structures in the image sensor is small, so that the performance of the formed image sensor is better.

In this embodiment, the temperature of the heat treatment is 700-800 degrees Celsius.

The significance of selecting this range for the temperature of the heat treatment is: if the temperature of the heat treatment is less than 700 degrees Celsius, the driving ability to the first ions and the second ions is insufficient, which is not conducive to the diffusion of the first ions and the second ions into the initial photoelectric doping. In the impurity area 220 ; if the temperature of the heat treatment is greater than 800 degrees Celsius, it is easy to cause some damage to other structures in the image sensor, resulting in poor performance of the formed image sensor.

After the heat treatment, the concentration of the first ions in the isolation region 260 is 1.0e12atm/cm ² -2.0e12atm/cm ² ; the concentration of the second ions in the isolation region 260 is 3.0e11atm/cm ² -8.0e11atm/cm ² .

The concentration of the first ion in the isolation region 260 is greater than the concentration of the second ion, that is, the net charge of the isolation region 260 is the first ion.

In this embodiment, the conductivity type of the isolation region 260 is P type.

The conductivity type of the main photoelectric doped region 250 is opposite to that of the semiconductor substrate 200, and the conductivity type of the additional main photoelectric doped region 270 is opposite to that of the semiconductor substrate 200. Therefore, the main photoelectric doped region 250 , the additional photoelectric doped regions 270 located on both sides of the main photoelectric doped region 250 and the semiconductor substrate 200 together constitute a photodiode. The photodiode is used to convert photons of incident light into electrons.

In this embodiment, since there are third ions in the initial photoelectric doping region 220, there are first ions and second ions in the initial isolation region 240, and the conductivity type of the first ions is the same as the conductivity type of the initial photoelectric doping region 220. On the contrary, the conductivity type of the second ions is the same as that of the initial photoelectric doping region 220 . Through the heat treatment, both the first ions and the second ions in the initial isolation region 240 diffuse into the initial photoelectric doped region 220, and the diffusion rate of the second ions into the initial photoelectric doped region 220 is greater than that of the first ions diffused into the initial The speed of the photoelectric doped region 220 . On the one hand, the concentration of N-type ions doped in the additional photoelectric doped region 270 formed after diffusion can be greater than the concentration of N-type ions doped in the main photoelectric doped region 250, thereby increasing the full well of the formed photodiode capacitance. On the other hand, after the heat treatment, the net charge in the formed isolation region 260 is the first ion, that is, the conductivity type of the isolation region 260 is P-type, so the conductivity type of the isolation region 260 and the main photoelectric The conductivity type of the doped region 250 is opposite, and the conductivity type of the isolation region 260 is opposite to that of the additional optoelectronic doped region 270 . To sum up, the method can improve the full-well capacitance of the photodiode, so that the performance of the formed image sensor is better.

Correspondingly, the present invention also provides an image sensor formed by the above method, please refer to FIG. 6 , including: a semiconductor substrate 200; a main photoelectric doped region 250 located in the semiconductor substrate 200, and mutually separated isolation regions 260 and separate additional photoelectric doped regions 270, the conductivity type of the additional photoelectric doped regions 270 is the same as that of the main photoelectric doped region 240, the conductivity type of the isolation region 260 is the same as that of the main photoelectric doped region 250 The conductivity type is opposite, and the isolation region 260 is located on both sides of the main photoelectric doped region 250, and the additional photoelectric doped region 270 is located between the isolation region 260 and the adjacent main photoelectric doped region 250. The doped region 270 is adjacent to the isolation region 260 and the main optoelectronic doped region 250 respectively.

Although the present invention is disclosed above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, so the protection scope of the present invention should be based on the scope defined in the claims.

Claims (10)

1. A method for forming an image sensor, comprising: Provide semiconductor substrates; forming an initial photoelectric doping region in the semiconductor substrate; Initial isolation regions separated from each other are formed in the initial photoelectric doping region, and the initial isolation regions are respectively located on opposite sides of the initial photoelectric doping region, and the initial isolation regions are doped with first ions and second Ions, the conductivity type of the first ion is opposite to that of the initial photoelectric doping region, the conductivity type of the second ion is the same as that of the initial photoelectric doping region, and the diffusion rate of the second ion is greater than that of the first ion rate; performing heat treatment to diffuse the first ions and the second ions in the initial isolation region, forming a main photoelectric doping region, mutually separated isolation regions and mutually separated additional photoelectric doped regions in the initial photoelectric doped region, so The conductivity type of the additional photoelectric doped region is the same as that of the main photoelectric doped region, the conductivity type of the isolation region is opposite to that of the main photoelectric doped region, and the isolation regions are respectively located in the main photoelectric doped region On both sides, the additional photoelectric doped region is located between the isolation region and the adjacent main photoelectric doped region, and the additional photoelectric doped region is adjacent to the isolation region and the main photoelectric doped region respectively. 2 . The method for forming an image sensor according to claim 1 , further comprising: before forming the initial photoelectric doped region, forming a protective layer on the surface of the semiconductor substrate. 3 . 3. The method for forming an image sensor according to claim 2, wherein the material of the protective layer comprises: silicon oxide, silicon nitride, silicon carbide nitride, silicon boride nitride, silicon oxycarbide, or oxynitride silicon. 4. The method for forming an image sensor according to claim 1, wherein the method for forming the initial isolation region comprises: forming a mask layer on the surface of the semiconductor substrate, and the mask layer exposes a part of the initial region. The surface of the photoelectric doping region; using the first ion implantation, using the mask layer as a mask, implanting first ions into the initial photoelectric doping region; using the second ion implantation, using the mask layer as a mask , implanting second ions into the initial photoelectric doped region. 5. The method for forming an image sensor according to claim 4, wherein the process parameters of the first ion implantation include: a dose range of 1.0e12atm/cm ² to 2.0e12atm/cm ² ; the second ion implantation The implantation process parameters include: the dose range is 1.0e12atm/cm ² -2.0e12atm/cm ² . 6. The method for forming an image sensor according to claim 1, wherein the concentration of the first ion in the isolation region is greater than the concentration of the second ion; the concentration of the first ion in the isolation region is 1.0e12atm/cm ² ~2.0e12atm/cm ² , the concentration of the second ion in the isolation area is 3.0e11atm/cm ² ~8.0e11atm/cm ² . 7. The method for forming an image sensor according to claim 1, wherein the conductivity type of the initial photoelectric doped region is opposite to that of the semiconductor substrate; the method for forming the initial photoelectric doped region comprises: The third ion implantation process is used to implant third ions into the semiconductor substrate, so that the initial photoelectric doping region is doped with third ions, and the conductivity type of the third ions is the same as that of the second ions. 8. The method for forming an image sensor according to claim 1, wherein the first ions are indium ions, and the second ions are phosphorus ions. 9. The method for forming an image sensor according to claim 1, wherein the heat treatment comprises rapid annealing or spike annealing. 10. An image sensor formed by the method according to any one of claims 1 to 9, characterized in that it comprises: semiconductor substrate; The main photoelectric doped region, the isolated isolation regions and the additional photoelectric doped regions separated from each other in the semiconductor substrate, the conductivity type of the additional photoelectric doped region is the same as that of the main photoelectric doped region, The conductivity type of the isolation region is opposite to that of the main photoelectric doped region, and the isolation regions are respectively located on both sides of the main photoelectric doped region, and the additional photoelectric doped region is located between the isolation region and the adjacent main photoelectric doped region. Between regions, the additional photoelectric doped region is adjacent to the isolation region and the main photoelectric doped region respectively.