JPH10135441A - Method of manufacturing solid-state imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a crystal defect-contg. photodiode from being formed by executing an ion implanting step separated in sub-steps for forming n-layers for photodiodes and N-annealing after each ion implanting sub-step. SOLUTION: In an ion implanting step, a first ion implanting is performed to form an n<+> -layer 10, then it is N-annealed, a second ion implanting is performed to form an n<+> -layer 10, then it is N-annealed, a second ion, another implanting is performed to form an p<+> -layer 11 and then it is N-annealed. Thus the ion implanting step is divided in several sub-steps to make point defects/ inter-lattice atom pairs caused at a high energy ion implanting step disappear by the N-anneal after each ion implanting sub-step before the point defects/inter- lattice atom pairs mutually combine into stable crystal defects.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solid-state imaging device, and more particularly, to a method for manufacturing an embedded photodiode constituting a solid-state imaging device.

[0002]

2. Description of the Related Art FIG. 2 is a sectional structural view of a CCD type solid-state imaging device.

The structure of a CCD type solid-state imaging device is roughly p
A p-type substrate on which a mold well layer 13 is formed, a buried photodiode including an n ⁺ layer 10 and a p ⁺ layer 11 formed near the surface of the p-type substrate, an n layer 16 and a read transfer electrode 15. CCD analog shift register and p ⁺
An element isolation region composed of a layer 12 and a light shielding layer 1 formed so as to cover the CCD analog shift register and the element isolation region.
And 4.

The charge generated by the light incident on the embedded photodiode is sequentially transferred by applying a predetermined drive signal to the transfer electrode 15 and driven, and output as an image signal from an output unit.

FIG. 3 is a flowchart of an ion implantation process for forming a buried photodiode of a CCD type solid-state imaging device.

A CCD is formed on a p-type substrate on which a p-type well layer 13 is formed while repeating formation and peeling of a resist.
After forming an n-layer 16 forming an analog shift register and a p ⁺ layer 12 forming an element isolation region, and further forming a transfer electrode 15 via an insulating film, the transfer electrode 15 is used to make self-alignment. Next, an ion implantation step for forming a buried photodiode is performed. In addition, the light shielding layer 14
Is formed after the ion implantation step.

In the ion implantation step, first, after ion implantation for forming the n ⁺ layer 10 is performed (S31), nitrogen annealing is performed (S32), and then, the p ⁺ layer 11 is formed. After performing ion implantation (S33), nitrogen annealing is performed (S34).

Normally, in a high energy ion implantation step for forming a photodiode, atoms constituting a crystal are repelled by the kinetic energy of the implanted ions, and many point defects and interstitial atom pairs are generated. Is known.

In the above-described ion implantation step, the reason why the nitrogen annealing is performed after each ion implantation is to eliminate generated point defects and interstitial atom pairs.

[0010]

However, when the concentration of the point defect / interstitial atom pair generated in the high energy ion implantation step exceeds a certain value, these point defects and
It has been found that some of the pairs of interstitial atoms are bonded to each other, resulting in stable crystal defects that do not disappear by annealing.

In particular, a CC having a depletion region in the p ⁺ layer 11 and a photodiode having a crystal defect in the n ⁺ layer 10
Since the D-type solid-state imaging device causes an image defect, the crystal defect causes a decrease in yield.

The present invention has been made in view of the above problems, and has as its object to manufacture a solid-state imaging device capable of preventing the formation of a photodiode containing crystal defects and improving the yield. Is to provide a way.

[0013]

According to a method of manufacturing a solid-state imaging device according to the present invention, a photodiode constituting a photodiode is formed.
^The feature is that the ion implantation process for forming the ⁺ layer is divided into a plurality of times, and nitrogen annealing is performed after each ion implantation process, whereby a photodiode including a crystal defect is formed by this configuration. Can be prevented, and the yield can be improved.

More specifically, a first ion implantation step of performing ion implantation to form an n ⁺ layer constituting a photodiode to be formed near the surface of the substrate on which the p-type well layer is formed; After the first ion implantation step, a first annealing step of performing nitrogen annealing on the substrate, a second ion implantation step of performing ion implantation to form an n ⁺ layer, and after the second ion implantation step, A second annealing step of performing nitrogen annealing on the substrate, a third ion implantation step of performing ion implantation to form ap ⁺ layer constituting a charge neutral region of the photodiode, and a third ion implantation And a third annealing step of performing nitrogen annealing on the substrate after the step.
The formation of a photodiode including crystal defects can be prevented, and the yield can be improved.

Further, it is preferable that the respective ion implantation amounts in the respective ion implantation steps for forming the n ⁺ layer are the same.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a method for manufacturing a solid-state imaging device according to the present invention will be described below with reference to the drawings.

FIG. 1 is a flowchart of a method for manufacturing a solid-state imaging device according to the present invention, specifically, a flowchart of an ion implantation step for forming an embedded photodiode of a CCD solid-state imaging device. The CCD to be manufactured
The structure of the solid-state imaging device is the same as that shown in FIG.

In the same manner as in the conventional example, an n-layer 1 forming a CCD analog shift register is formed on a p-type substrate on which a p-type well layer 13 is formed by repeatedly forming and peeling a resist.
6. After each of the p ⁺ layers 12 constituting the element isolation region are formed, and further, the transfer electrode 15 is formed via the insulating film,
An ion implantation process for forming a buried photodiode is performed in a self-aligned manner using the transfer electrode 15.
Note that the light shielding layer 14 is formed after the ion implantation step.

The feature of the method of manufacturing the solid-state imaging device according to the present invention is that the ion implantation, in particular, the ion implantation for forming the depletion layer, that is, the n ⁺ layer 10 is divided into a plurality of times, and after each ion implantation. The point is that nitrogen annealing is performed.
In the present embodiment, the ion implantation for forming the n ⁺ layer 10 is performed in two steps.

In the ion implantation step, first, after the first ion implantation for forming the n ⁺ layer 10 is performed (S1
1) Then, nitrogen annealing is performed (S12), and then the n ⁺ layer 1
After performing the second ion implantation for forming 0 (S13), nitrogen annealing is performed (S14).
After ion implantation for forming the p ⁺ layer 11 (S
15) Perform nitrogen annealing (S16).

Here, since the ion implantation for forming the n ⁺ layer 10 is performed in two divided times, the ion implantation amount in each time is about the same as the ion implantation amount in the case of performing the ion implantation in one time. 1/2.

As described above, by performing ion implantation in a plurality of times, a point defect / interstitial atom pair generated in the high-energy ion implantation step is bonded to each other to form a stable crystal defect. A point defect / interstitial atom pair can be eliminated by nitrogen annealing performed after each ion implantation.

Therefore, according to the method of manufacturing a solid-state imaging device according to the present invention, it is possible to prevent a photodiode including a crystal defect from being formed and to improve the yield.

The number of times of ion implantation for forming the n ⁺ layer 10 is not limited to two, but may be three or more.

It is not necessary to make the amount of ion implantation in each time equal to the amount of ion implantation performed in one time, and the point defect / interstitial atom pair is eliminated by annealing each time. The adjustment may be performed so that the n ⁺ layer 10 having the finally required depth and concentration is formed within a range where the operation can be performed.

Further, the acceleration energy of the ion implantation in each time is appropriately set according to the readout voltage, drive voltage, and the like of the resulting CCD solid-state imaging device. Therefore, the acceleration energy of the ion implantation in each time may be the same or different.

Here, in particular, the reason why the ion implantation for forming the n ⁺ layer 10 is divided into plural times is usually p
^This is because an image defect of the solid-state imaging device occurs when a photodiode including a crystal defect is formed in the depletion region in the ⁺ layer 11 and the n ⁺ layer 10. Therefore, the n ⁺ layer 10
By performing ion implantation for forming a plurality of times in a plurality of times, image defects of the solid-state imaging device can be effectively prevented.

Crystal defects in the charge neutral region in the p ⁺ layer 11 usually do not adversely affect image defects and the like, but if any adverse effects are observed, the p ⁺ layer 11 May be divided into a plurality of times, and nitrogen annealing may be performed after each ion implantation.

[0029]

As described above, according to the method of manufacturing a solid-state imaging device according to the present invention, ion implantation, in particular, ion implantation for forming an n ⁺ layer serving as a depletion layer is divided into a plurality of times. Since nitrogen annealing is performed after each ion implantation, the formation of a photodiode containing crystal defects can be prevented, and the yield can be improved.

[Brief description of the drawings]

FIG. 1 is a flowchart of a method for manufacturing a solid-state imaging device according to the present invention.

FIG. 2 is a sectional structural view of a CCD solid-state imaging device.

FIG. 3 is a flowchart of an ion implantation process for forming a buried photodiode of a CCD solid-state imaging device.

DESCRIPTION OF SYMBOLS 10 n ⁺ layer constituting photodiode 11 p ⁺ layer constituting photodiode 12 p ⁺ layer 13 constituting element isolation region 13 p-type well layer 14 light shielding layer 15 readout transfer electrode 16 CCD analog shift register N layer constituting

Claims (3)

[Claims] In a method of manufacturing a solid-state imaging device having a photodiode, an ion implantation step for forming an n ⁺ layer constituting the photodiode is performed in a plurality of times, and after each ion implantation step, nitrogen is added. A method for manufacturing a solid-state imaging device, wherein annealing is performed. 2. A first ion implantation step of performing ion implantation to form an n ⁺ layer constituting a photodiode to be formed near a surface of a substrate on which a p-type well layer is formed; After the ion implantation step, a first annealing step of performing nitrogen annealing on the substrate, a second ion implantation step of performing ion implantation to form the n ⁺ layer, and after the second ion implantation step A second annealing step of performing nitrogen annealing on the substrate; a third ion implantation step of performing ion implantation to form ap ⁺ layer forming a charge neutral region of the photodiode; A third annealing step of performing nitrogen annealing on the substrate after the third ion implantation step. 3. The method of manufacturing a solid-state imaging device according to claim 1, wherein the ion implantation amounts in the ion implantation steps for forming the n ⁺ layer are the same. A method for manufacturing a solid-state imaging device, comprising: