JP3584629B2 - Solid-state imaging device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a solid-state imaging device, and more particularly, to a vertical overflow drain type solid-state imaging device having an epitaxial barrier layer which forms an overflow barrier and has a conductivity type opposite to that of a semiconductor substrate and a photoelectric conversion unit.
[0002]
[Background Art]
As a solid-state imaging device, a so-called vertical overflow drain type solid-state imaging device in which excess charge in a light receiving unit is discharged to a substrate side is known, and a barrier to charge flow to the substrate side is known. Conventionally, the overflow barrier is formed deep from the substrate surface by high-energy ion implantation.
[0003]
However, according to the ion implantation, the overflow barrier can be formed only at a depth of about 5 μm at the maximum, and there is a limit in increasing the depth of the overflow barrier formation position.
[0004]
On the other hand, there is a demand for a solid-state imaging device that has sensitivity not only to visible light but also to near-infrared light. However, such a solid-state imaging device requires a deeper overflow barrier, and is formed by ion implantation. Depending on the method, it is impossible or difficult to achieve the required depth. Therefore, attempts have been made to make the depth of the barrier arbitrary by forming an overflow barrier using an epitaxial layer.
[0005]
[Problems to be solved by the invention]
However, in such a solid-state imaging device, as shown in FIG. 3, when a wafer is chipped by scribing, a PN junction by an epitaxial layer is exposed on a scribe surface, and a leak current is generated between a semiconductor substrate and ground. A new problem has arisen.
[0006]
In FIG. 3, 1 is an N-type semiconductor substrate, 2 is a P-type overflow barrier made of an epitaxial layer, 3 is a P ⁺ type channel stopper, 4 is a peripheral portion of an N-type semiconductor region, 5 is a scribe surface, and A leakage current due to the substrate bias voltage Vsub flows through the PN junction between the overflow barrier 2 and the PN junction. Since the scribe surface 5 is a rough surface, the magnitude of the leak current is large enough to prevent normal operation.
[0007]
Such a problem occurs for the following reason. That is, when the overflow barrier is formed by ion implantation as in the related art, an ion implantation site is selected by ion implantation through a mask, and the PN junction between the overflow barrier and the substrate is not exposed on the scribe surface. However, when formed by an epitaxial layer, an overflow barrier is formed over the entire surface, and the PN junction between the barrier and the substrate is prevented from being exposed on the scribe surface. It is impossible.
[0008]
The inventor of the present application has sought to prevent leakage current from flowing even when the epitaxial layer forming the overflow barrier (in other words, the PN junction between the epitaxial layer and the substrate or the like) is exposed on the scribe surface. The inventors have obtained the idea that this can be achieved by completely depleting the portion exposed to the scribe surface of the barrier, and have further studied to arrive at the present invention.
[0009]
In other words, the present invention provides a vertical overflow drain type solid-state imaging device having an epitaxial layer of a conductivity type opposite to that of a semiconductor substrate and a photoelectric conversion portion, forming an overflow barrier, and exposing an epitaxial layer forming an overflow barrier to a scribe surface. To eliminate the leak current in
[0010]
[Means for Solving the Problems]
The solid-state imaging device according to claim 1, wherein a ring-shaped region of the same conductivity type as the semiconductor substrate and the photoelectric conversion unit is formed on a peripheral surface portion of the device inside a predetermined distance from a scribe surface, A voltage for completely depleting the semiconductor substrate and the ring-shaped region is applied between the epitaxial layer forming the overflow barrier and the epitaxial layer.
[0011]
Therefore, according to the solid-state imaging device of the first aspect, the voltage applied between the ring-shaped region and the semiconductor substrate and the epitaxial layer forming the overflow barrier causes the ring-shaped region provided in the vicinity of the device to be between the substrate and the substrate. Is completely depleted, so that there is no potential difference at the PN junction between the epitaxial layer and the semiconductor substrate, etc., which is exposed on the scribe surface, and thus no leak current flows.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.
[0013]
1A and 1B show a first embodiment of a solid-state imaging device according to the present invention, wherein FIG. 1A is a plan view, and FIG. 1B is an enlarged cross-sectional view taken along line BB ′ of FIG. FIG. 2 is a sectional view showing potential contour lines during operation.
[0014]
In the figure, 1 is an N-type semiconductor substrate, 2 is a P-type overflow barrier composed of an epitaxial layer, formed at a depth of, for example, about 2 to 5 μm or more from the semiconductor surface, and has a thickness of, for example, 1 μm or less. It is. The impurity concentration of the barrier 2 is, for example, about 10 ¹⁵ / cm ³ . Reference numeral 3 denotes a P ⁺ type channel stopper, 4 denotes a peripheral portion of the N-type semiconductor region, and 5 denotes a scribe surface.
[0015]
Reference numeral 6 denotes a ring-shaped N ⁺ formed near the periphery of the surface of the peripheral portion 4 of the N-type semiconductor region of the element, specifically, for example, about 10 μm inward from the element side surface (scribed surface) 5. It is a type area. As described above, the solid-state imaging device has a ring-shaped N ⁺ -type region 6. In use, the substrate bias voltage Vsub applied to the semiconductor substrate 1 is applied to the N ⁺ -type region 6. Is applied. In other respects, there is no particular difference from the solid-state imaging device shown in FIG. Of course, the application of the ground potential (0 V) to the overflow barrier 2 is performed through the channel stopper 3.
[0016]
Therefore, the potential contours at the peripheral portion of the device during use are as shown in FIG. 2 [V1 = Vsub.multidot.1 / 5 (for example, 3 V when Vsub is 15 V), V2 = Vsub.multidot.2 / 5 (eg. When Vsub is 15 V, the contour line is 6 V),...], The space between the ring-shaped N ⁺ type region 6 and the substrate 1 is completely depleted, the overflow barrier 2 composed of the epitaxial layer 2, the substrate 1, No potential difference occurs at the PN junction with the N-type semiconductor region 4. Therefore, even if the exposed portion of the PN junction on the scribe surface 5 is rough, no leak current flows because no potential difference occurs between the exposed portions.
[0017]
Thus, according to the present solid-state imaging device, it is possible to form the overflow barrier 2 from an epitaxial layer that cannot be selectively formed without causing a risk of generating a leak current.
[0018]
Therefore, the degree of freedom in designing the profile in the depth direction of the impurity concentration such as the depth and spread of the overflow barrier 2 is remarkably increased. It can be easily realized.
[0019]
【The invention's effect】
According to the solid-state imaging device of the first aspect, the voltage applied to the epitaxial layer forming the overflow barrier completely depletes the substrate between the ring-shaped region provided in the vicinity of the device and the substrate. The exposed PN junction between the epitaxial layer and the substrate or the like has no potential difference, so that no leak current flows.
[Brief description of the drawings]
FIGS. 1A and 1B show a first embodiment of a solid-state imaging device according to the present invention, wherein FIG. 1A is a plan view and FIG. 1B is a view taken along line BB ′ of FIG. It is an expanded sectional view.
FIG. 2 is a cross-sectional view showing potential contour lines in a peripheral portion during use.
FIG. 3 is a cross-sectional view showing a problem of the background art.
[Explanation of symbols]
1 ... substrate, 2 ... overflow barrier, 5 ... scribe surface, Vsub ... substrate bias voltage.

Claims (2)

A semiconductor substrate and a photoelectric conversion portion and a vertical overflow drain type solid-state imaging device having an epitaxial layer of the opposite conductivity type to form an overflow barrier,
Forming a ring-shaped region of the same conductivity type as the semiconductor substrate and the photoelectric conversion portion on the element peripheral surface inside a predetermined distance from the scribe surface ,
A voltage that completely depletes the space between the semiconductor substrate and the ring-shaped region between the ring-shaped region and the semiconductor substrate and the epitaxial layer that forms the overflow barrier. Solid-state imaging device 2. The semiconductor device according to claim 1, wherein a substrate bias potential is applied to the ring-shaped region and the semiconductor substrate, and a ground potential is applied to the epitaxial layer forming the overflow barrier through a channel stopper of the same conductivity type. Solid-state imaging device

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