JP2006108222A - Solid-state imaging device and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid-state imaging device which can suppress the generation of smear, without reducing the pixel opening size. <P>SOLUTION: The CCD solid-state imaging device is provided with a silicon substrate 1 where a light-receiving part 2, a reading gate 3, a vertical charge transmitter 4, a horizontal charge transmitter, and a channel stop region 5 are formed; a transfer electrode 6 formed on the upper layer of the vertical charge transmitter and the gate reading gate, and a light-shielding film 9 wherein an opening 8 is provided in a light-receiving region formed on the upper layer of the transfer electrode with an SiO<SB>2</SB>layer 7 in-between. In this case, grooves 10, arranged aside the vertical charge transmitter are formed on both sides of the vertical charge transmitter in the silicon substrate, and the groove region is covered entirely with the light-shielding film. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a solid-state imaging device and a method for manufacturing the solid-state imaging device. More specifically, the present invention relates to a solid-state image sensor that attempts to suppress the occurrence of smear by increasing the effective distance from the end of the light-shielding film to the charge transfer unit, and a method for manufacturing such a solid-state image sensor.

6 and 7 are a schematic plan view and a sectional view for explaining a conventional CCD (Charge Coupled Device) solid-state imaging device.
A conventional CCD solid-state imaging device includes a plurality of light receiving portions 101 arranged in a matrix in a silicon substrate 100, a read gate 102 that is provided adjacent to the light receiving portions, and that reads out electric charges taken in by the light receiving portions, and a read gate. , A vertical charge transfer unit 103 that transfers the charges read by the read gate in the vertical direction, a horizontal charge transfer unit 104 that transfers the charges transferred by the vertical charge transfer unit in the horizontal direction, and a light receiving unit A channel stop region 106 that is provided on the opposite side of the read gate and suppresses color mixing is formed.

  In addition, a transfer electrode 107 for applying a transfer pulse to the vertical charge transfer unit or applying a read pulse to the read gate is formed in the upper layer of the vertical charge transfer unit and the read gate. A light shielding film 109 in which an opening 108 is formed is formed (for example, see Patent Document 1).

JP-A-10-144907

  By the way, in a normal CCD solid-state image sensor, if there is something in the subject that emits very strong light such as the sun during continuous exposure operation, so-called smear occurs around the strong light in the imaging screen. To do.

Hereinafter, two smear generation mechanisms will be described with reference to FIG.
(1) One cause is that the charges photoelectrically converted deep in the silicon substrate 100 are not collected by the photodiode (light receiving unit) 101 but are absorbed by the vertical charge transfer unit 103 at a certain rate. For this reason, while the vertical charge transfer unit is transferring, such smear charges steadily leak into the vertical charge transfer unit. Then, a constant smear charge is always superimposed in addition to the signal charge from the nearby vertical charge transfer unit that is exposed to strong light, and as a result, smear is generated (see incident light indicated by symbol a in FIG. 8).
(2) Another cause is that incident light is irregularly reflected from between the silicon substrate and the light shielding film 109 that shields the vertical charge transfer portion and the transfer electrode 107, and jumps directly into the vertical charge transfer portion, where photoelectric conversion occurs. As a result, smear is generated (see incident light indicated by symbol b in FIG. 8).

  Although smear is generated by the mechanism as described above, the CCD solid-state imaging device for small digital still cameras, which is currently mainstream, has a small pixel pitch and is often disadvantageous for smear due to physical restrictions. In order to reduce smear, measures such as reducing the size of the pixel opening are taken. However, if the size of the pixel opening is reduced, there is a disadvantage that sensitivity is lowered.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a solid-state imaging device capable of suppressing the occurrence of smear and a method for manufacturing such a solid-state imaging device.

  In order to achieve the above object, a solid-state imaging device according to the present invention includes a light receiving unit, a charge transfer unit that is provided in the light receiving unit and transfers charges from the light receiving unit, the light receiving unit, and the charge transfer unit. A read gate portion provided between the transfer electrode, a transfer electrode that applies a clock signal to the charge transfer portion, and a light shielding film that is formed in an upper layer of the transfer electrode and has an opening formed in the light receiving portion region. In the solid-state imaging device provided, a groove is formed between the light receiving unit and the charge transfer unit.

  Here, since the groove is formed between the light receiving portion and the charge transfer portion, an effective distance from the light shielding film end to the charge transfer portion can be increased.

  In order to achieve the above object, a method of manufacturing a solid-state imaging device according to the present invention includes a light receiving unit, a charge transfer unit that is attached to the light receiving unit, and charges are transferred from the light receiving unit, and the light receiving unit. And a read gate portion provided between the charge transfer portion and a transfer electrode for applying a clock signal to the charge transfer portion. A step of forming a groove portion with the formation region, a step of forming the light receiving portion, the charge transfer portion, the readout gate portion, and the transfer electrode, and at least a part of the groove in the upper layer of the transfer electrode. And a step of forming a light shielding film having an opening in the light receiving area.

  Here, a groove portion is formed between the formation region of the readout gate portion and the formation region of the light receiving portion, and at least a part is embedded in the groove portion on the upper layer of the transfer electrode, and an opening portion is provided in the light receiving portion region. By forming the light shielding film, the effective distance from the edge of the light shielding film to the charge transfer portion can be increased.

  In the above-described solid-state imaging device to which the present invention is applied and the solid-state imaging device obtained by the method for manufacturing the solid-state imaging device to which the present invention is applied, the effective distance from the light shielding film edge to the charge transfer portion is long. The probability that electrons absorbed inside and generated by photoelectric conversion will reach the charge transfer unit can be reduced, and incident light from between the light shielding film and the semiconductor substrate can also be incident on the end region of the groove. Therefore, the probability that the reflected light travels to the charge transfer portion can be reduced, and smear can be suppressed without changing the opening width of the light shielding film.

  In addition, since the protruding portion of the light shielding film with respect to the transfer electrode can be dropped into the groove portion, the sensitivity of the oblique light component can be improved through the improvement of the light collection rate of the oblique light.

Hereinafter, embodiments of the present invention will be described with reference to the drawings to facilitate understanding of the present invention.
FIG. 1 is a schematic cross-sectional view for explaining an example of a CCD solid-state imaging device to which the present invention is applied. The CCD solid-state imaging device shown here is similar to a conventional CCD solid-state imaging device in the silicon substrate 1. In addition, a plurality of light receiving portions 2 arranged in a matrix, provided adjacent to the light receiving portions, a read gate 3 for reading charges taken in by the light receiving portions, provided adjacent to the read gates, The vertical charge transfer unit 4 that transfers the read charges in the vertical direction, the horizontal charge transfer unit (not shown) that transfers the charges transferred by the vertical charge transfer unit in the horizontal direction, and the readout gate of the light receiving unit are opposite. A channel stop region 5 that is provided on the side and suppresses color mixing is formed.

Further, a transfer electrode 6 for applying a transfer pulse to the vertical charge transfer unit or applying a read pulse to the read gate is formed on the vertical charge transfer unit and the read gate, and an SiO ₂ layer is formed on the transfer electrode. A light shielding film 9 in which an opening 8 is formed in the light receiving portion region is formed through 7.

  Further, grooves 10 are provided on both sides of the vertical charge transfer portion on the surface of the silicon substrate, and the light shielding film covers the entire region where the groove is formed (hereinafter referred to as the groove region). Is formed.

  Here, in this embodiment, a groove is formed on both sides of the vertical charge transfer unit, that is, on both the read gate side and the channel stop region side of the vertical charge transfer unit, and smear charges caused by light incident from the light receiving unit are formed. By moving in the readout gate direction (indicated by reference symbol A in FIG. 1) and flowing into the vertical charge transfer unit 4A and by moving smear charges in the channel stop region direction (indicated by reference symbol B in FIG. 1). Both the flow into the vertical charge transfer unit 4B is reduced, and the irregular reflection component of the light incident from the light receiving unit enters the read gate direction, so that the jump into the vertical charge transfer unit 4A and the irregular reflection component in the channel stop region direction. The occurrence of smear is suppressed by reducing both jumping into the vertical charge transfer unit 4B due to the entry, If the smear can be sufficiently suppressed by forming the groove on one side of the transfer unit, that is, on the read gate side or the channel stop region side of the vertical charge transfer unit, the groove is not necessarily provided on both sides of the vertical charge transfer unit. There is no need to form. However, in order to more sufficiently suppress the occurrence of smear, it is preferable to form groove portions on both sides of the vertical charge transfer portion.

  In this embodiment, the light shielding film is formed so as to cover the entire region of the groove region arranged in parallel with the vertical charge transfer portion. However, as shown in FIG. 2, a part of the groove region is covered. Even if the light shielding film is formed in this manner, the effective distance from the edge of the light shielding film to the vertical charge transfer portion can be increased, and the reflection direction of incident light can be changed by covering the edge of the groove with the light shielding film. Since it can be changed, it is not always necessary to form the light shielding film so as to cover the entire region of the groove region. However, it is preferable that the light shielding film is formed so as to cover the entire region of the groove region so as to further increase the effective distance from the edge of the light shielding film to the vertical charge transfer portion and change the reflection direction of incident light. .

  When a groove is formed on the silicon substrate, lattice defects or the like are likely to be formed on the surface or inside of the groove, and there is a concern that dark current may be generated from an oblique portion at the end of the groove indicated by C in FIG. However, it is possible to suppress the generation of dark current by strengthening pinning by applying a voltage to the light shielding film by covering the oblique part of the end of the groove with a light shielding film. Therefore, it is preferable that the light shielding film is formed so as to cover the entire region of the groove region from the viewpoint of suppressing dark current.

  Hereinafter, a manufacturing method of the CCD solid-state imaging device configured as described above will be described. That is, an example of a method for manufacturing a solid-state imaging device to which the present invention is applied will be described.

In the manufacturing method of the CCD solid-state imaging device described above, first, as shown in FIG. 3A, the surface of the silicon substrate 1 is thermally oxidized to grow a pad oxide film 11 (SiO ₂ film), and the upper layer of the pad oxide film. Then, ammonia (NH ₃ ) and silane (SiH ₄ ) are reacted with each other to deposit a silicon nitride film 12 (Si ₃ N ₄ ).

  Next, as shown in FIG. 3B, a region 14 (hereinafter referred to as a vertical charge transfer portion forming region) in which a vertical charge transfer portion is formed by a general-purpose photolithography technique and an etching technique by an impurity implantation process described later. The silicon nitride film and the pad oxide film on both sides are removed.

Subsequently, as shown in FIG. 3C, with a silicon nitride film having oxidation resistance as a mask, a thick SiO ₂ film 13 is formed on the silicon substrate surface in a region not covered with the silicon nitride film by a thermal oxidation method. After the growth, as shown in FIG. 4D, the silicon nitride film is removed with hot phosphoric acid and the pad oxide film is removed with hydrofluoric acid.

  Next, as shown in FIG. 4E, impurities are implanted into the vertical charge transfer portion forming region to form the vertical charge transfer portion 4, and further impurity implantation is performed to form the matrix-shaped light receiving portion 2. Further, impurity implantation is performed in a region adjacent to the light receiving portion to form the read gate 3, and a channel stop region 5 and a horizontal charge transfer portion (not shown) are also formed.

Thereafter, the transfer electrode 6 is formed so as to cover the vertical charge transfer portion and the readout gate, and the transfer electrode and the entire groove region are covered over the transfer electrode via the SiO ₂ layer 7, and an opening is formed in the light receiving portion region. By forming the light shielding film 9 having 8, a CCD solid-state imaging device as shown in FIG. 4F can be obtained.

  In this embodiment, the method of forming the groove using LOCOS oxidation has been described as an example. However, the method of forming the groove is not limited to LOCOS oxidation, and the groove is formed by any method. It may be formed.

  In the CCD solid-state imaging device to which the present invention described above is applied, the occurrence of smear can be suppressed as compared with the conventional CCD solid-state imaging device. That is, the present invention indicated by symbol d in FIG. 5B is compared with the effective distance from the light shielding film end to the vertical charge transfer portion in the conventional CCD solid-state imaging device indicated by symbol d ′ in FIG. The effective distance from the light-shielding film edge to the vertical charge transfer section in the CCD solid-state imaging device to which is applied is long, the probability that electrons generated by photoelectric conversion inside the silicon substrate reach the vertical charge transfer section is reduced, and the groove edge The incidence direction of the incident light is changed in the oblique portion of the portion and the probability that the reflected light travels in the direction of the vertical charge transfer portion is reduced, so that it is possible to suppress the occurrence of smear as compared with a CCD solid-state imaging device having a conventional structure.

Further, in the CCD solid-state imaging device to which the present invention is applied, an increase in sensitivity of the oblique light component can be expected. That is, in the conventional CCD solid-state imaging device, since the cross section of the transfer electrode has a horizontally long square shape, the shape of the light-shielding film laminated via the SiO ₂ layer also reflects the shape of the transfer electrode, and its side wall The elevation angle viewed from an arbitrary point of the light receiving portion indicated by symbol φ1 in FIG. 7 is determined by the top portion of the side wall of the light shielding film, and the amount of light incident obliquely on the light receiving portion is limited. It was a thing. On the other hand, in the CCD solid-state imaging device to which the present invention is applied, the protruding portion of the light-shielding film with respect to the transfer electrode can be dropped into the groove portion. However, the amount of light incident obliquely on the light receiving portion is increased by that amount, and the light collection rate of oblique light is improved, and the improvement of sensitivity of oblique light components can be expected.

It is typical sectional drawing for demonstrating an example of the CCD solid-state image sensor to which this invention is applied. It is typical sectional drawing for demonstrating the modification of the CCD solid-state image sensor to which this invention is applied. It is typical sectional drawing (1) for demonstrating the manufacturing method of the CCD solid-state image sensor to which this invention is applied. It is typical sectional drawing (2) for demonstrating the manufacturing method of the CCD solid-state image sensor to which this invention is applied. FIG. 6 is a schematic cross-sectional view for explaining an effective distance from a light shielding film end to a vertical charge transfer portion. It is a typical top view for demonstrating the conventional CCD solid-state image sensor. It is typical sectional drawing for demonstrating the conventional CCD solid-state image sensor. It is typical sectional drawing for demonstrating the generation | occurrence | production mechanism of a smear.

Explanation of symbols

1 silicon substrate 2 light receiving unit 3 read gate 4 vertical charge transfer section 5 the channel stop region 6 transfer electrodes 7 SiO ₂ layer 8 opening 9 the light shielding film 10 groove 11 the pad oxide film 12 a silicon nitride film 13 SiO ₂ film 14 vertical charge transfer section Formation area

Claims (5)

A light receiver;
A charge transfer unit that is provided in the light receiving unit and transfers charges from the light receiving unit;
A readout gate unit provided between the light receiving unit and the charge transfer unit;
A transfer electrode for applying a clock signal to the charge transfer unit;
In a solid-state imaging device, which is formed in an upper layer of the transfer electrode and includes a light-shielding film in which an opening is formed in the light-receiving region.
A solid-state imaging device, wherein a groove is formed between the light receiving unit and the charge transfer unit. The solid-state imaging device according to claim 1, wherein at least a part of the light shielding film is embedded in the groove. The solid-state imaging device according to claim 1, wherein the groove portion is provided between the readout gate portion and the light receiving portion. The solid-state imaging device according to claim 1, wherein the groove is provided on both sides of the charge transfer unit. A light-receiving unit, a charge transfer unit that is provided in the light-receiving unit and transfers charges from the light-receiving unit, a readout gate unit provided between the light-receiving unit and the charge transfer unit, and a clock signal to the charge transfer unit In a method for manufacturing a solid-state imaging device comprising a transfer electrode to be applied,
Forming a groove between a formation region of the read gate portion and a formation region of the light receiving portion;
Forming the light receiving portion, the charge transfer portion, the read gate portion, and the transfer electrode;
And a step of forming a light-shielding film having at least a portion embedded in the groove and provided with an opening in the light-receiving portion region above the transfer electrode.

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