JP4942283B2 - Solid-state imaging device and method for manufacturing solid-state imaging device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solid-state imaging device and a method for manufacturing the solid-state imaging device, and more particularly to a solid-state imaging device in which a channel stop portion between pixels (light receiving portions) is formed by impurity junction separation and a method for manufacturing the solid-state imaging device.
[0002]
[Prior art]
One of the disadvantages unique to solid-state imaging devices, for example, CCD (Charge Coupled Device) solid-state imaging devices, is smear. Smear is a phenomenon in which when there is a high-luminance subject in a captured image, bright striped stripes (vertical stripes) are formed in the vertical direction (vertical direction) due to light leakage. The main component of smear in the solid-state imaging device will be described below with reference to FIG. FIG. 7 is a cross-sectional view showing the configuration of the light receiving unit and the vertical charge transfer unit in the CCD solid-state imaging device.
[0003]
In FIG. 7, the light receiving portion (photoelectric conversion portion) 101 is configured by a photodiode having a pn junction between an n-type impurity diffusion region 103 and a p-type well region 104 formed in the surface layer portion of the silicon substrate 102. The vertical charge transfer portion 105 is formed on the silicon substrate 102 via the gate insulating film 108 and the n-type impurity transfer channel region 106 formed in the surface layer portion of the silicon substrate 102 and the p-type impurity region 107 therebelow. And the transfer electrode 109.
[0004]
The read gate portion 110 also uses a part of the transfer electrode 109 as a gate electrode, and is constituted by the gate electrode and a p-type impurity region 111 formed in the surface layer portion of the silicon substrate 102 therebelow. The surface layer portion of the silicon substrate 102 between the vertical charge transfer portion 105 of the light receiving portion of the next to the light receiving unit 101, a channel stop portion 112 of the p-type impurities is formed. A light shielding film 113 is formed so as to cover each of the vertical charge transfer portions 105.
[0005]
In the light receiving unit 101 and the vertical charge transfer unit 105 configured as described above, the general main component of smear is roughly divided into the following four components (1) to (4). Component {circle around (1)} is a smear component generated by electrons leaking into the transfer channel region 106 among the electrons-holes generated by photoelectric conversion in the deep part of the substrate due to obliquely incident light. Component (2) is caused by obliquely incident light being reflected between the silicon substrate 102 and the light shielding film 113 or the transfer electrode 109 and leaking into the transfer channel region 106 to generate electrons in the transfer channel region 106. It is a smear component.
[0006]
Component (3) is a smear component resulting from the generation of electrons in the transfer channel region 106 by the incident light component directly transmitted through the light shielding film 113 / transfer electrode 109. Component (4) is that electrons generated on the surface of the silicon substrate 102 by the incident light diffuse laterally along the substrate surface and pass through the p-type impurity region 111 or the channel stop portion 112 of the read gate portion 110 and transfer. This is a smear component generated by leaking into the channel region 106.
[0007]
Among these four components (1) to (4), in order to improve the component (4), which is dominant as a smear component, in the past, it has been conventionally positioned on the side of the n-type diffusion layer such as a transfer channel. By forming the impurity concentration of the control unit and isolation unit higher than that of the p-type well of the semiconductor substrate, the potential gradient near the n-type diffusion layer is almost eliminated, and the diffusion current along the surface of the semiconductor substrate is limited to a small level. Smear was reduced (see, for example, Patent Document 1).
[0008]
[Patent Document 1]
Japanese Patent Laid-Open No. 2000-77647
[Problems to be solved by the invention]
However, in the above-described prior art, it is difficult to eliminate the potential gradient in the vicinity of the n-type diffusion layer by setting the impurity concentration of the control unit and the separation unit, so that the diffusion current along the semiconductor substrate surface can be limited to a certain extent. However, since it is difficult to eliminate this completely, it is difficult to reliably suppress smear caused by the diffusion current.
[0010]
The present invention has been made in view of the above problems, and the object of the present invention is that among the smear components, electrons generated on the surface of the semiconductor substrate by incident light diffuse laterally along the substrate surface, An object of the present invention is to provide a solid-state imaging device capable of reliably suppressing a component that passes through a channel stop portion and leaks into a transfer channel region, and a method for manufacturing the solid-state imaging device.
[0011]
[Means for Solving the Problems]
A solid-state imaging device according to the present invention includes a light receiving unit that photoelectrically converts incident light, a charge transfer unit that transfers signal charges read from the light receiving unit, and a charge transfer unit of an adjacent light receiving unit. In a state where the first channel stop portion provided, the second channel stop portion provided between the light receiving portions adjacent in the transfer direction of the charge transfer portion, and the periphery surrounded by the channel stop portion, The first channel stop portion and the getter portion for capturing electrons formed only in the second channel stop portion are formed on a semiconductor substrate having a carbon implantation region.
[0012]
In the solid-state imaging device having the above configuration, electrons generated on the surface of the semiconductor substrate by incident light diffuse in the horizontal and vertical directions along the substrate surface, and between the channel stop portion on the opposite side to the readout side and the pixels in the vertical direction. When entering the channel stop part, the getter part in the channel stop part captures it. Accordingly, it is possible to reliably suppress electrons caused by incident light dominant as a smear component from leaking into the transfer channel region through the channel stop portion. Further, since the getter portion is positioned in the vicinity of the light receiving portion, it is possible to suppress white defect and dark current component due to metal impurities mixed due to the process. Furthermore, since the impurities and crystal defects originally existing in the semiconductor substrate can be gettered by the carbon implantation region, white scratches and dark current components can be greatly reduced.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0016]
[First Embodiment]
FIG. 1 is a cross-sectional view showing a configuration of main parts (light receiving part and vertical charge transfer part) of a CCD solid-state imaging device according to the first embodiment of the present invention. In FIG. 1, an epitaxial substrate 10 is formed by forming an epitaxial layer 12 on an n-type CZ substrate 11 which is a silicon substrate grown by a CZ (Czochralski) method, and further forming a p-type well region 13 thereon. It has become the composition.
[0017]
In the p-type well region 13, a light receiving unit (photoelectric conversion unit) 20, a vertical charge transfer unit 40, a read gate unit 30, and a p-type channel stop unit 50 are formed. Specifically, the light receiving unit (pixel) 20 is configured by a photodiode having a pn junction between a p-type well region 13 and an n-type impurity diffusion region 21 formed in the well region 13 , and the n-type impurity diffusion region. 21, that is, a p-type positive charge (hole) accumulation region (p ⁺⁺ layer) 22 on the substrate surface side.
[0018]
The vertical charge transfer unit 30 includes an n-type transfer channel region (p ⁺ layer) 31 formed in the p-type well region 13 , and a second p-type well region 32 formed immediately below the transfer channel region 31. The transfer electrode 33 is composed of, for example, a two-layer structure made of polycrystalline silicon formed on the epitaxial substrate 10 via a gate insulating film 71 having an ONO film (SiO 2 / SiN / SiO 2) structure.
[0019]
The read gate unit 40 is configured by a part of the transfer electrode 33 of the vertical charge transfer unit 30 as a gate electrode, and the gate electrode and a channel region therebelow. The channel stop unit 50 is composed of a p-type impurity (p ⁺ layer). Further, a light shielding film 73 made of aluminum, tungsten or the like is formed through an interlayer insulating film 72 so as to cover each of the vertical charge transfer portions 30.
[0020]
FIG. 2 is a plan view of the CCD solid-state imaging device according to the first embodiment. In FIG. 2, in the vertical charge transfer section 30, the first-layer transfer electrode 33-1 and the second-layer transfer electrode 33-2 are alternately and repeatedly arranged in an overlapping state. The channel stop unit 50 is formed between the light receiving unit 20 and the vertical charge transfer unit 30 of the adjacent light receiving unit along the transfer direction of the vertical charge transfer unit 30.
[0021]
1 and 2, a getter portion 60 that is a gettering site is formed inside the channel stop portion 50. In the getter unit 60, electrons generated on the surface of the epitaxial substrate 10 by incident light diffuse laterally along the substrate surface, pass through the channel stop unit 50 on the side opposite to the reading side, and pass through the adjacent transfer channel region 31. It acts to capture the components that leak into.
[0022]
Here, various things can be considered as the getter portion 60, that is, the gettering site. As a gettering technique, generally, an IG (Intrinsic Gettering) method in which oxygen in a silicon substrate is deposited only inside the substrate and this is used as a gettering site, polysilicon or high-concentration phosphorus (Phos.) Is used on the back surface of the substrate. There is an EG (Extrinsic Gettering) method for forming a region or the like and forming a gettering site using strain stress with silicon.
[0023]
On the other hand, as a getter portion 60, a gettering site that can be locally formed in the region of the channel stop portion 50 between pixels, is electrically neutral, and has low diffusion, can be a group 4 impurity element. The gettering technique in which ions are formed by ion implantation is most desirable. Specifically, as a Group 4 impurity element, for example, carbon ions are implanted at a dose of 5 × 10 ¹³ cm ⁻² or more, preferably 5 × 10 ^{13 to} 5 × 10 ¹⁵ cm ⁻² to form a gettering site. . However, the Group 4 impurity element to be ion-implanted is not limited to carbon, but may be germanium, tin, lead, or the like.
[0024]
When carbon is ion-implanted, the carbon dose is set to 5 × 10 ¹³ cm ⁻² or more, so that the formation of high-density crystal defects and the generation of stress can be sufficiently performed by the ion implantation of carbon. Therefore, the gettering ability for capturing electrons can be enhanced. In addition, when the carbon dose is set to 5 × 10 ¹⁵ cm ⁻² or less, deterioration of crystallinity on the surface of the epitaxial substrate 10 can be suppressed to a minimum.
[0025]
In forming the getter portion 60, it is necessary to form the getter portion 60 inside the channel stop portion 50 so as not to protrude from the region of the channel stop portion 50. This is because when the getter unit 60 protrudes from the region of the channel stop unit 50, electrons are generated due to defects or levels of the getter unit 60, which may cause white defects or dark current components. . In order to form the getter portion 60 so as not to protrude from the region of the channel stop portion 50, a dose amount, energy, angle or the like at the time of ion implantation may be appropriately selected.
[0026]
Thus, by forming the getter portion 60 so as not to protrude from the region of the channel stop portion 50, a region of only the P ⁺ layer remains between the channel stop portion 50 and the getter portion 60. Electrons generated on the surface of the substrate can be diffused by incident light, but since the mean free path is longer than that of the conventional structure, the probability of electron / hole recombination increases. Thereby, the number of electrons leaking into the transfer channel region 31 can be reduced, and as a result, smear characteristics can be improved.
[0027]
As described above, in the CCD solid-state imaging device in which the channel stop unit 50 is formed between the light receiving unit 20 and the vertical charge transfer unit 30 of the adjacent light receiving unit along the transfer direction of the vertical charge transfer unit 30. By forming the getter portion 60 inside the channel stop portion 50, electrons generated on the surface of the epitaxial substrate 10 by incident light diffuse in the lateral direction (horizontal direction) along the substrate surface, and are opposite to the readout side. Since the getter unit 60 captures the smear component that passes through the channel stop unit 50 and leaks into the transfer channel region 31, it can be reliably suppressed.
[0028]
Since electrons captured by the getter unit 60 are dominant components as smear components, the formation of the getter unit 60 in the channel stop unit 50 can greatly improve smear characteristics. In addition, since the getter unit 60 is located in the vicinity of the light receiving unit 20, it is possible to suppress white defects and dark current components due to metal impurities mixed due to the process.
[0029]
In this embodiment, in the CCD solid-state imaging device in which the channel stop unit 50 is formed between the light receiving unit 20 and the vertical charge transfer unit 30 of the adjacent light receiving unit, that is, between the pixels in the horizontal direction, the channel stop unit Although the getter portion 60 is formed inside 50, the present invention is not limited to this. That is, as shown in FIG. 3, in a CCD solid-state imaging device in which a channel stop 50 'is also formed between vertical pixels for the purpose of preventing color mixing, only the channel stop 50 between horizontal pixels is used. In addition, it is possible to form the getter portion 60 'between the pixels in the vertical direction and inside the channel stop portion 50'. As a result, it is possible to capture even the electrons that are generated by the incident light on the surface of the epitaxial substrate 10 and diffuse in the vertical direction (vertical direction) along the substrate surface, so that the smear characteristic can be further improved.
[0030]
[Second Embodiment]
FIG. 4 is a cross-sectional view showing a configuration of a main part of a CCD solid-state imaging device according to the second embodiment of the present invention. In FIG. 4, the same parts as those in FIG.
[0031]
The CCD solid-state imaging device according to this embodiment includes silicon before forming the epitaxial layer 12 as a semiconductor substrate on which the light receiving unit 20, the vertical charge transfer unit 30, the readout gate unit 40, the channel stop unit 50, and the getter unit 60 are formed. Epitaxial substrate 10 formed by forming carbon implantation region 14 by implanting carbon ions at a dose of 1 × 10 ¹⁵ cm ^{−2 on} the surface of n-type CZ substrate 11, which is a substrate, and then forming epitaxial layer 12. The other configuration is basically the same as the configuration of the solid-state imaging device according to the first embodiment.
[0032]
In the CCD solid-state imaging device having such a configuration, the carbon in the carbon implantation region 14 accelerates the precipitation of oxygen to form high-density crystal defects on the CZ substrate 11, and these crystal defects serve as gettering sites. . Further, stress is generated by the difference in covalent bond radius between the element (silicon) forming the CZ substrate 11 and the carbon in the carbon implantation region 14, and this stress itself is also a gettering site. For this reason, the impurities and crystal defects originally present in the CZ substrate 11 and the impurities and crystal defects introduced when forming the epitaxial layer 12 and subsequently forming the solid-state imaging device are strongly gettered. The
[0033]
As described above, the epitaxial substrate 10 ′ having the carbon implantation region 14 is used as the semiconductor substrate, and the vertical charge transfer unit 30, the read gate unit 40, the channel stop unit 50, and the getter unit 60 are formed on the epitaxial substrate 10 ′. By adopting the configuration, in addition to the effect similar to that of the first embodiment, that is, the effect of improving the smear characteristic by the getter unit 60, impurities and crystal defects can be strongly gettered by the carbon implantation region 14, so that the CCD solid-state imaging device It is possible to obtain the effect of greatly reducing white defect and dark current component.
[0034]
[Production method]
Next, a manufacturing method of the CCD solid-state imaging device according to the second embodiment will be described with reference to manufacturing process diagrams of FIGS. 5 and 6, the same parts as those in FIG. 4 are denoted by the same reference numerals.
[0035]
First, as shown in FIG. 5A, an n-type CZ substrate 11 which is a silicon substrate grown by the CZ method is prepared. The CZ substrate 11 is a substrate having a main surface of (100) plane and having a specific resistance of 10 Ωcm and a diameter of 200 mm. A carbon implanted region 14 is formed on the surface of the CZ substrate 11 by implanting a Group 4 impurity element such as carbon at a dose of 1 × 10 ¹⁵ cm ⁻² through a thermal oxide film 81. Annealing is performed after carbon ion implantation, and then the thermal oxide film 81 is removed.
[0036]
Next, as shown in FIG. 5B, an n-type silicon epitaxial layer 2 of, for example, 8 μm is formed on one main surface of the CZ substrate 11 by using a hydrogen reduction method with SiHC13 source gas, for example, at an epitaxial growth temperature of, for example, 1110 ° C. Grow. Next, as shown in FIG. 5C, a first p-type well region 13 is formed in the n-type silicon epitaxial layer 12.
[0037]
Next, as shown in FIG. 5D, a gate insulating film 71 having an ONO film (SiO 2 / SiN / SiO 2) structure is formed on the surface of the p-type well region 13, and the inside of the first p-type well region 13 is formed. N-type and p-type impurities are selectively ion-implanted into the n-type transfer channel region 31 and the p-type channel stop unit 50 constituting the vertical charge transfer unit 30, and the second p-type well region 32. Form each one. Further, carbon ions are selectively implanted into the channel stop portion 50 at a dose of 5 × 10 ¹³ cm ⁻² or more, preferably 5 × 10 ^{13 to} 5 × 10 ¹⁵ cm ⁻² , thereby obtaining the getter portion 60. Form.
[0038]
Next, as shown in FIG. 6A, the transfer electrode 33 having the two-layer structure of the vertical charge transfer unit 30 (the first and second transfer electrodes 33-1 and 33-2 in FIG. 2). Is formed of polycrystalline silicon. Next, as shown in FIG. 6B, n-type and p-type impurities are selectively ion-implanted into the first p-type well region 13 using the transfer electrode 33 as a mask to form the light-receiving unit 20. An n-type impurity diffusion region 21 and a p-type positive charge accumulation region 17 are formed.
[0039]
Next, after forming an interlayer insulating film 72 over the entire surface of the device, a light shielding film 73 covering the vertical charge transfer portion 30 is formed of aluminum or tungsten. Thereafter, a well-known color filter and an on-chip lens are sequentially formed to obtain a target CCD solid-state imaging device. In the case of manufacturing the CCD solid-state imaging device according to the first embodiment, the step of forming the carbon implantation region 14 is omitted in FIG.
[0040]
As described above, by forming the getter portion 60 in the region of the channel stop portion 50, the getter portion 60 diffuses electrons generated on the surface of the semiconductor substrate by incident light in the lateral direction along the substrate surface, When entering the channel stop portion 50 on the opposite side to the reading side, an action is taken to capture this. Therefore, it is possible to reliably suppress electrons caused by incident light that is dominant as a smear component from leaking into the transfer channel region 31 through the channel stop unit 50, and the getter unit 60 in the vicinity of the light receiving unit 20. By being positioned, white scratch defects and dark current components due to metal impurities mixed due to the process can be suppressed, so that a CCD solid-state imaging device having excellent smear characteristics and few white scratch defects can be manufactured.
[0041]
In FIG. 6, the gate insulating film 71 below the transfer electrode 33 has an ONO film structure, but the gate insulating film only in the region of the light receiving portion 20 is reattached to form an SiO 2 film. However, the present invention is not limited to the structure of the gate insulating film.
[0042]
Further, here, an n-type diffusion region 21 is formed on the surface of the p-type well region 13 formed on the n-type Si epitaxial substrate, and photon is formed by a pn junction between the p-type well 13 and the n-type diffusion region 21. The case of manufacturing a CCD solid-state image pickup device of a type that forms a diode has been described as an example. However, for a CCD solid-state image pickup device of a type that forms a photodiode by forming an n-type impurity region on a p-type Si epitaxial substrate. Can be applied similarly.
[0043]
In addition, a CCD solid-state image pickup device of a type having a plurality of intra-layer lenses, a CCD solid-state image pickup device of a type having an epitaxial layer after forming a vertical overflow barrier and having sensitivity to near infrared rays, and further being transparent to ultraviolet rays. Of course, the present invention can also be applied to a CCD solid-state imaging device in which a light receiving portion is formed only by a film having the same.
[0044]
【Effect of the invention】
As described above, according to the solid-state imaging device according to the present invention, by providing the getter portion inside the channel stop portion, the getter portion is generated by the incident light on the surface of the semiconductor substrate and laterally extends along the substrate surface. Since the electrons that enter the channel stop between the pixels on the opposite side of the readout side and between the pixels in the vertical direction after being diffused in the vertical and vertical directions can be reliably captured, smear characteristics can be improved, and the getter unit receives light. By being located in the vicinity of the portion, it is possible to suppress white defect and dark current component due to metal impurities mixed due to the process. Furthermore, since the semiconductor substrate has a carbon implanted region, impurities and crystal defects originally present in the semiconductor substrate can be gettered by the carbon implanted region, so that white scratches and dark current components can be greatly reduced.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a configuration of a main part of a CCD solid-state imaging device according to a first embodiment of the present invention.
FIG. 2 is a plan view showing an example of a configuration of a channel stop unit.
FIG. 3 is a plan view showing another example of the configuration of the channel stop unit.
FIG. 4 is a cross-sectional view showing a configuration of a main part of a CCD solid-state imaging device according to a second embodiment of the present invention.
FIG. 5 is a process diagram (part 1) illustrating a procedure of a manufacturing method of the CCD solid-state imaging device according to the second embodiment;
FIG. 6 is a process diagram (part 2) illustrating the procedure of the method of manufacturing the CCD solid-state imaging device according to the second embodiment.
FIG. 7 is a cross-sectional view showing a configuration of a main part of a CCD solid-state imaging device according to a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Epitaxial substrate, 11 ... CZ substrate, 12 ... N-type epitaxial layer, 13 ... First p-type well region, 14 ... Carbon implantation region, 20 ... Light receiving portion, 21 ... N-type diffusion region, 22 ... Positive charge accumulation Region 30... Vertical charge transfer portion 31... Transfer channel region 32 second p-type well region 33 33 1 33-2 transfer electrode 40 read gate portion 50 channel stop portion 60 ... Getter

Claims (3)

A light receiving unit for photoelectrically converting incident light;
A charge transfer unit for transferring a signal charge read from the light receiving unit;
A first channel stop portion provided between the light receiving portion and a charge transfer portion of an adjacent light receiving portion;
A second channel stop portion provided between adjacent light receiving portions in the transfer direction of the charge transfer portion;
A getter portion for capturing electrons formed only in the first channel stop portion and the second channel stop portion in a state surrounded by the channel stop portion, and having a carbon injection region A solid-state image sensor formed on a semiconductor substrate. The getter unit, the solid-state imaging device according to claim 1, wherein is formed by impurity element group 4. The solid-state imaging device according to claim 2 , wherein the Group 4 impurity element is carbon.

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