KR20020045864A - Photodiode in image sensor and method for fabricating the same - Google Patents

Abstract

PURPOSE: A photodiode of an image sensor is provided to improve light sensitivity regarding light of a short wavelength, by overcoming a decrease of the light sensitivity and charge capacitance and by preventing the characteristic of the image sensor from being deteriorated by interference of adjacent pixels. CONSTITUTION: The photodiode of the image sensor has a field oxide layer(4) and a gate electrode(7) of a transfer transistor. An impurity layer of the second conductivity type is formed under a semiconductor substrate(1) of the first conductivity type. A partial region of the impurity layer is separated at the edge of the field oxide layer, and the impurity layer is aligned with an edge of the gate electrode. An epi layer(12) of the first conductivity type is formed on the impurity layer including the partial region, separated at the edge of the gate electrode. The impurity layer of the second conductivity type is completely depleted when a reverse bias is applied, and a depletion region extends to the semiconductor substrate and the epi layer.

Description

Photodiode of image sensor and method of manufacturing the same {Photodiode in image sensor and method for fabricating the same}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of manufacturing semiconductor devices, and more particularly, to a photodiode of an image sensor device and a method for manufacturing the same.

A photodiode is used as part of its component inside a unit pixel of an image sensor used as an image recognition device. The photodiode converts light incident on the unit pixel into electrons, which is a major factor in determining the characteristics of the sensor. Usually, the photodiode is composed of an impurity bonding layer formed on a silicon substrate through an impurity ion implantation process.

A depletion layer is formed by applying a bias to the impurity bonding layer configured as described above, and an image signal is realized by collecting electrons generated in the silicon substrate in the depletion layer by the incident light for a predetermined time and reading them in a circuit.

Therefore, it is important to increase the photosensitive efficiency of the photodiode. In order to increase the photosensitive efficiency of the photodiode, not only the area of the photodiode but also the width of the depletion layer generated in the junction layer of impurities is increased. The size of the dimensional depletion layer should be increased.

1 is a cross-sectional view illustrating a partial structure of a unit pixel of a conventional image sensor. In the related art, an impurity bonding layer is formed inside a silicon substrate in a photodiode region through an ion implantation process to manufacture a photodiode. Let's look at this in detail.

Referring to FIG. 1, a gate 7 of a transfer transistor is formed on a P-type silicon substrate 1 on which a field oxide film 4 is formed, and spacers 8 are formed on sidewalls of the gate 7. An N-type impurity layer 3 and a P-type impurity layer 2 are laminated and formed under the surface of the silicon substrate 1 on one side of the gate 7, and below the surface of the silicon substrate 1 on the other side of the gate 7. In the sensing region 6, which is a high concentration N-type impurity layer, is formed.

The photodiode forms a PNP junction structure by the P-type impurity layer 2, the N-type impurity layer 3, and the P-type silicon substrate 1, and the photodiode has a high energy N on the P-type silicon substrate 1 The type impurity ion implantation and the low energy P-type impurity ion implantation process are continuously performed to form the N-type impurity layer 3 and the P-type impurity layer 2.

At this time, if the N-type impurity layer 3 is completely depleted by applying a bias to the N-type impurity layer 3, not only the N-type impurity layer 3 but also the P-type impurity layer 2 and the silicon substrate 1 The depletion layer is formed. In particular, since the concentration of the silicon substrate 1 is lower than that of the N-type impurity layer 3, the depletion width is large.

Meanwhile, in order to manufacture a miniaturized and high resolution image sensor device, a small unit pixel design and an advanced semiconductor manufacturing technology are required. Since the unit pixel contains not only a photodiode but also a circuit for signal detection, there is a limit in increasing the area of the photodiode through the design of chip miniaturization.

In addition, since the distance for device isolation is reduced in the advanced semiconductor manufacturing process, the depth of the impurity layer formation through the ion implantation process is reduced, thereby reducing the width of the depletion layer generated in the impurity junction layer.

As a result, the photosensitive efficiency and accumulating charge capacity of the photodiode are reduced to deteriorate the characteristics of the sensor.

In addition, when the junction layer is formed inside the photodiode through a conventional ion implantation process in a miniaturized image sensor having a shorter distance between devices, interference with adjacent pixels occurs due to diffusion of an impurity layer and expansion of a depletion layer. There is a problem of deteriorating characteristics.

The present invention can increase the depletion layer of the three-dimensional photodiode even if the unit pixel is small and the area of the photodiode is small, so that the photosensitive efficiency caused by the reduction in the size of the unit pixel as the chip has a small size and high resolution And a photodiode of an image sensor capable of overcoming a decrease in charge capacity and a method of manufacturing the same.

It is also an object of the present invention to provide a photodiode of an image sensor and a method of manufacturing the same that can prevent deterioration of characteristics of an image sensor due to interference with adjacent pixels.

1 is a cross-sectional view showing a photodiode structure of an image sensor according to the prior art,

2A to 2D are cross-sectional views illustrating a photodiode manufacturing process according to an embodiment of the present invention;

3 is a cross-sectional view showing a photodiode structure according to another embodiment of the present invention.

* Explanation of symbols for main parts of the drawings

1: silicon substrate 4: field oxide film

5: photodiode area 6: sensing area

7 gate electrode 8 spacer

9: interlayer insulating film 10: N-type impurity layer

12 epitaxial layer 13 p-type impurity layer

The photodiode of the present invention for achieving the above object is formed under the surface of the first conductive type (P type) semiconductor substrate in a photodiode in an image sensor having a field oxide film and a gate electrode of a transfer transistor. A second conductive type (N-type) impurity layer formed at a portion of the field oxide film spaced apart from each other and aligned at one edge of the gate electrode; And an epitaxial layer of a first conductivity type (P type) formed on an impurity layer of the second conductivity type (N type) including the partial region and spaced apart from one edge of the gate electrode. When the reverse bias is applied, the second conductive type (N-type) impurity layer is completely depleted, and the depletion region extends to the semiconductor substrate and the epi layer.

In addition, the present invention further includes a first conductive type (P type) impurity layer formed in the semiconductor substrate under the semiconductor substrate surface of the partial region and under the impurity layer of the second conductive type (N type). Characterized in that made.

Since the photodiode of the present invention having the above structure grows and forms the epitaxial layer on the semiconductor substrate, the depletion layer can be induced into the epitaxial layer on the upper side of the semiconductor substrate rather than inside the semiconductor substrate. Therefore, even if the unit pixel becomes smaller and the area of the photodiode becomes smaller, the depletion layer of the three-dimensional photodiode can be increased. That is, as the chip becomes smaller and has a higher resolution, it is possible to overcome a decrease in photosensitive efficiency and charge capacity caused by the reduction in the size of the unit pixel.

In addition, since the main depletion layer in the photodiode region that converts light into electrons can be formed in the epi layer, the diffusion of the impurity layer and the depletion layer It is possible to suppress or prevent deterioration of the characteristics of the image sensor due to interference with adjacent pixels due to expansion.

In addition, since the photodiode region is raised above the semiconductor substrate by the thickness of the epi layer, it is also possible to obtain an effect of shortening the distance that the incident light passes to reach the photodiode region than before. Therefore, an advantageous effect can be obtained in terms of the transmittance of the incident light reaching the photodiode, which results in better photosensitive efficiency. In particular, it is possible to improve the photosensitivity of the blue light having low transmittance.

In addition, in the case of the photodiode formed by the prior art, the charge is transferred from the N-type impurity layer (3 in FIG. 1) to the sensing region (6 in FIG. 1) due to the diffusion of the P-type impurity layer (2 in FIG. 1) on the surface of the semiconductor substrate. It forms a barrier potential that interferes with transmission.

However, since the photodiode formed in the present invention is directly connected to the gate electrode of the transfer transistor, the impurity layer of the second conductive type (N type), which is completely depleted, can be obtained in terms of charge transport efficiency.

On the other hand, in the present invention, when the impurity layer of the first conductivity type (P type) is further included, the depletion layer is excessively expanded inside the semiconductor substrate to effectively prevent interference with adjacent pixels, in addition to the above-described effects. More effect can be obtained.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings so that those skilled in the art may easily implement the technical idea of the present invention. do.

2a to 2d show a photodiode manufacturing process according to a preferred embodiment of the present invention. Description of the process for the completion of the present invention will be described with the main portion of the photodiode region, the transfer transistor and the sensing region of the elements constituting the unit pixel.

FIG. 2A shows a field oxide film 4 for isolation between devices on a P-type silicon substrate 1 in a conventional manner, and is used as a gate for transferring charge from the photodiode region 5 to the sensing region 6. The gate electrode 7 of the transfer transistor is formed.

Next, FIG. 2B is a step of forming a junction of an impurity layer on the photodiode through an ion implantation process. Unlike the prior art, in the present invention, low energy N-type impurity ions are implanted into the photodiode region 5 through a mask and an ion implantation process to form an N-type impurity layer 10 under the surface of the silicon substrate 1. Let's do it.

Then, the spacer 8 is formed on the sidewalls of the gate electrode, and the sensing region 6 is formed through the mask and ion implantation process, and then the interlayer insulating material 9 is deposited.

The N-type impurity layer 10 uses energy enough to be doped near the surface of the silicon substrate 1. The reason for doing this is to prevent the depletion layer of the P-type silicon substrate 1, which is depleted by the bias applied to the N-type impurity layer 10 during the operation of the image sensor element, to be widely expanded to cause interference with adjacent pixels. . In addition, the concentration of the N-type impurity layer 10 selects an appropriate amount that can be completely depleted by the P-type epitaxial layer or the substrate.

In addition, the N-type impurity layer 10 is electrically aligned by being formed in alignment with one edge of a gate of the transfer transistor. The reason is that the electrons collected in the N-type impurity layer 10 can be easily transferred to the sensing region 6.

In addition, the other side of the N-type impurity layer 10 is to be spaced apart from the field oxide film 4 and a partial region (planarly) as indicated by a dotted line in FIG. 2B because the photodiode region 5 is formed in a subsequent process. This is to connect the P-type epilayer and silicon substrate to be grown electrically. Only then can the N-type impurity layer 10 be completely depleted at low operating voltage.

Subsequently, as illustrated in FIG. 2C, the photoresist film 11 is applied to selectively etch the interlayer insulating material 9 on the photodiode region 5, and then a mask process is performed, followed by an etching process of the interlayer insulating material. Are continuously performed to form holes in which the surface of the silicon substrate 1 of the photodiode region 5 is exposed.

At this time, the hole formed by etching is spaced apart from the spacer 8 of the gate electrode 7 of the transfer transistor. The reason is to reliably connect the N-type impurity layer 10 with the channel of the transfer transistor.

Next, as shown in FIG. 2D, the silicon epitaxial layer 12 is selectively grown on the portion where the silicon substrate 1 is exposed.

At this time, the silicon epitaxial layer is grown in an atmosphere that can be doped with a P-type, the concentration is selected so that the N-type impurity layer 10 on the surface of the silicon substrate 1 can be completely depleted. In this way, the P-type silicon epitaxial layer 12 electrically connected to the P-type silicon substrate 1 can be formed.

In addition, the thickness of the epi layer 12 may be selected to an appropriate thickness in consideration of the photosensitive efficiency and the charge capacity of the image sensor. Even if the thickness of the grown epitaxial layer is thicker than the interlayer insulating material 9, causing a large step, there is no problem because a contact for connecting the metal wires or the metal wires is not formed on the upper portion of the photodiode region 5. Do not.

3 shows a photodiode structure according to another embodiment of the present invention. Like reference numerals refer to like elements as in the exemplary embodiment of FIG. 2, and descriptions thereof will be omitted.

In another embodiment of the present invention, in order to effectively prevent the depletion layer generated in the low concentration P-type silicon substrate 1 from being extended by the N-type impurity layer 10 in the photodiode region and contacting adjacent pixels, the low-energy N The ion implantation process for forming the high energy P-type impurity layer 13 is performed before the ion implantation process for forming the impurity layer 10. The concentration of the high energy P-type impurity is appropriately selected in consideration of the degree of expansion of the depletion layer. This makes it easier to control the width of the P-type depletion layer generated inside the silicon substrate 1, and the width of the N-type impurity layer 10 on the surface of the silicon substrate can be widened.

In addition, the P-type impurity layer 13 may be formed over the entire photodiode region 5 to help the silicon substrate 1 and the silicon epitaxial layer 12 to be electrically connected through the dotted inner region of FIG. 3. Make sure

Although the technical idea of the present invention has been described in detail according to the above preferred embodiment, it should be noted that the above-described embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.

The photodiode of the image sensor of the present invention can overcome the miniaturization of the chip, the decrease in the photosensitive efficiency corresponding to the high resolution, and the decrease in the charge capacity, and suppress the deterioration of the characteristics of the image sensor due to interference with adjacent pixels or It can be prevented, and an advantageous effect can be obtained in terms of the transmittance of the incident light to the photodiode, thereby improving the photosensitivity efficiency, especially for short wavelength light having low transmittance. In addition, since the fully depleted N-type impurity layer is directly connected to the channel of the transfer transistor, the effect of charge transport efficiency can be obtained.

Claims (4)

A photodiode in an image sensor having a field oxide film and a gate electrode of a transfer transistor, An impurity layer of a second conductive type formed under the surface of the first conductive type semiconductor substrate and formed to be spaced apart from the edge of the field oxide layer and aligned with one edge of the gate electrode; And An epitaxial layer of a first conductivity type formed on the impurity layer of the second conductivity type including the partial region and spaced apart from one edge of the gate electrode; And a depletion region extends to the semiconductor substrate and the epi layer as the impurity layer of the second conductive type is completely depleted upon application of reverse bias. The method of claim 1, And a first conductive type impurity layer formed inside the semiconductor substrate under the semiconductor substrate surface of the partial region and under the impurity layer of the second conductive type. In the image sensor manufacturing method having a photodiode, Forming a gate electrode of a field oxide film and a transfer transistor on a first conductive semiconductor substrate; The impurity layer of the second conductivity type is formed to be formed near the surface of the semiconductor substrate through a mask and ion implantation process, and a partial region is spaced apart from the edge of the field oxide layer, and is aligned with one edge of the gate electrode. step; Forming a spacer on a sidewall of the gate electrode and forming a sensing region as a second concentration impurity layer formed on the semiconductor substrate on the other side of the gate electrode through a mask and an ion implantation process; Forming an interlayer insulating film on the entire structure; Etching the interlayer insulating layer through a mask and an etching process to form a hole including the partial region and spaced apart from the gate electrode; And Forming an epitaxial layer in the hole by the epitaxial growth Image sensor manufacturing method characterized in that it comprises a. In the image sensor manufacturing method having a photodiode, Forming a gate electrode of a field oxide film and a transfer transistor on a first conductive semiconductor substrate; Forming an impurity layer of a first conductivity type to be formed under the surface of the semiconductor substrate through a mask and an ion implantation process and aligned with an edge of the field oxide film and one edge of the gate electrode; The impurity layer of the second conductivity type is formed to be formed near the surface of the semiconductor substrate through a mask and ion implantation process, and a partial region is spaced apart from the edge of the field oxide layer, and is aligned with one edge of the gate electrode. step; Forming a spacer on a sidewall of the gate electrode and forming a sensing region as a second concentration impurity layer formed on the semiconductor substrate on the other side of the gate electrode through a mask and an ion implantation process; Forming an interlayer insulating film on the entire structure; Etching the interlayer insulating layer through a mask and an etching process to form a hole including the partial region and spaced apart from the gate electrode; And Forming an epitaxial layer in the hole by the epitaxial growth Image sensor manufacturing method characterized in that it comprises a.