JP4752193B2 - Solid-state image sensor - Google Patents

Description

  The present invention relates to a solid-state imaging device such as a CCD image sensor or a CMOS image sensor in which a plurality of photoelectric conversion elements are formed on a semiconductor substrate.

Recently, image input cameras used with personal computers and the like have been actively developed. A solid-state imaging device mounted on these cameras uses a CCD image sensor using a charge coupled device (CCD) or a CMOS image sensor compatible with a CMOS manufacturing process.
In the CCD image sensor, photoelectric conversion elements (photodiodes) corresponding to pixels are two-dimensionally arranged, and signals of each pixel converted into electric charges by the photoelectric conversion elements are sequentially used using a vertical transfer CCD and a horizontal transfer CCD. This is a type of image sensor that reads out.
On the other hand, a CMOS image sensor is similar to a CCD image sensor in that photoelectric conversion elements corresponding to pixels are two-dimensionally arranged. However, vertical and horizontal transfer CCDs are not used for signal readout, and As described above, a signal stored for each pixel is read out from the selected pixel by a selection line made of aluminum, copper wire, or the like.
As described above, the CCD image sensor and the CMOS image sensor have many different elements such as a readout method, but the photodiodes have a common structure in both.

Next, the structure of the photodiode portion will be described with reference to FIG.
The illustrated example shows a state in which the photodiode portion 30 is formed in the middle of the element isolation portion 20 formed on the surface layer portion of the silicon substrate 10, and the photodiode portion 30 has a depth from the upper surface of the silicon substrate 10. Each of the impurity regions of the P + region 31, the N + region 32, the N− region 33, and the P− region 34 is formed in order in the direction (Note that, here, + and − are impurity concentrations different from those of other regions. Compared to dark and light)
With such a structure, dark current generated from the surface of the silicon substrate of the photodiode portion 30 can be reduced (see, for example, Patent Document 1).
When this region is irradiated with light, electron-hole pairs are generated, and signal charges (electrons) are accumulated at the junction between the P region and the N region.
The maximum value of the signal charge that can be accumulated is called the saturation signal charge (Qs). An image sensor having a high Qs has an improved dynamic range and SN ratio.
Therefore, an increase in Qs is a very important factor for improving the characteristics of the image sensor.
JP 2002-170945 A

By the way, as a method of increasing the saturation signal charge amount (Qs), it is conceivable to increase the area of the photodiode portion or increase the PN junction capacitance C1 of the photodiode portion.
However, when the area of the photodiode portion is increased, the total number of pixels of the image sensor decreases as the area of the photodiode portion increases as compared with the same angle of view (for example, 2/3 inch).
Further, if the concentration of the P region and the N region is increased in order to increase the PN junction capacitance of the photodiode portion, the dark current also increases, so there is a limit to increasing the PN junction capacitance.

  Accordingly, an object of the present invention is to provide a solid-state imaging device capable of increasing the saturation signal charge amount (Qs) and obtaining high sensitivity without increasing the area or impurity concentration of the photoelectric conversion device. .

In order to achieve the above object, a solid-state imaging device of the present invention includes a photoelectric conversion element in which a P-type impurity region and an N-type impurity region are provided in order from a top surface of a substrate to a semiconductor substrate. The conversion element includes a capacitance expansion portion in which a P-type impurity region protrudes toward the N-type impurity region and forms a three-dimensional PN junction surface in a substrate surface direction and a depth direction. A plurality of photoelectric conversion elements are arranged corresponding to a plurality of color components, and P-type impurity regions of the photoelectric conversion elements are different corresponding to the characteristics of the color components. The protrusions having a shape and formed for each color component are formed at different positions in the semiconductor substrate depth direction, and the protrusions of the photoelectric conversion elements corresponding to the red pixels are the protrusions of the photoelectric conversion elements corresponding to the blue pixels. Japanese to be formed at a position deeper than the projecting portion To.

  According to the solid-state imaging device of the present invention, a P-type impurity region formed on the surface of the photoelectric conversion device protrudes toward the N-type impurity region to form a three-dimensional PN junction surface in the substrate surface direction and the depth direction. Since the capacitance expanding portion is provided, there is an effect that the saturation signal charge amount (Qs) can be increased and high sensitivity can be obtained without increasing the area of the photoelectric conversion element or increasing the impurity concentration.

In the embodiment of the present invention, not only the PN junction photodiode capacitance forming region of the image sensor is formed in the substrate surface direction with respect to the silicon substrate, but also in the depth direction of the substrate, thereby forming the signal charge storage portion. Expanded to increase the effective area of the signal charge storage section. In order to enlarge the signal charge storage portion of the photodiode portion, a portion protruding in the depth direction is referred to as a capacitance enlargement portion here.
Then, in order to make it easy to read the signal charge from the capacitance expansion portion expanded in the depth direction of the substrate, the capacitance expansion portion formed linearly around the transfer gate is laid out radially or near the transfer gate. The capacity expansion section is laid out, and further, the potential of the capacity expansion section is inclined.
Further, the color sensitivity for each pixel is changed by changing the depth of the P region on the outermost surface for each pixel in accordance with the purpose of improving sensitivity.

FIG. 1 is a cross-sectional view showing a structure of a photodiode portion of a solid-state imaging device according to an embodiment of the present invention.
As shown in the figure, an element isolation portion 120 is formed in the surface layer portion of the silicon substrate 110, and a photodiode portion 130 that is a feature of the present embodiment is formed in the middle.
As in the conventional example shown in FIG. 8, the photodiode portion 130 is formed by forming impurity regions of a P + region 131, an N + region 132, an N− region 133, and a P− region 134 on the silicon substrate 110. The shape of each impurity region is different from the conventional example of FIG.
That is, basically, the P + region 131, the N + region 132, the N− region 133, and the P− region 134 are arranged in order from the upper surface of the silicon substrate 110 to the depth direction. The central portion protrudes in the depth direction of the silicon substrate 110 and is formed so as to bite into the central portion of the N + region 132. Note that the portion biting below the P + region 131 functions as a capacitance expanding portion for expanding the PN junction capacitance in the photodiode portion, but in the following description, it will be described as the protruding portion 131A for convenience.
By providing such a protruding portion 131A of the P + region 131, the underlying N + region 132 is formed in an annular shape on the outer periphery of the protruding portion 131A. In addition, the lower end of the protruding portion 131 </ b> A reaches a position in contact with the upper portion of the N− region 133.

  In the photodiode portion 130 having the impurity distribution as described above, the area of the PN junction surface formed by the P + region 131 and the N + region 132 extends not only in the substrate surface direction but also in the substrate depth direction. Since the effective area of the PN junction is increased, the PN junction capacitances C1 to C3 are increased correspondingly, and the saturation signal charge amount (Qs) can be increased without increasing the impurity concentration.

FIG. 2 is a cross-sectional view showing a modification of the first embodiment shown in FIG. 2 that are the same as those in FIG. 1 are denoted by the same reference numerals and description thereof is omitted.
As illustrated, in this example, a plurality of (three in the illustrated example) hemispherical protrusions 131B are provided in the P + region 131. Each protrusion 131B protrudes toward the N + region 132, and, like the protrusion 131A, contributes to the expansion of the PN junction surface, thereby increasing the PN junction capacitance and increasing the saturation signal charge amount (Qs). It is something to be made.

FIG. 3 is a sectional view showing another modification of the first embodiment shown in FIG. 2 that are the same as those in FIG. 1 are denoted by the same reference numerals and description thereof is omitted.
As illustrated, in this example, a plurality of (three in the illustrated example) bar-shaped protrusions 131 </ b> C are provided in the P + region 131. Each protrusion 131C is arranged in a state of protruding and penetrating to the N + region 132 side. Like the protrusion 131A, the protrusion 131C contributes to the expansion of the PN junction surface, thereby increasing the PN junction capacitance and increasing the saturation signal. The charge amount (Qs) is increased.
The examples shown in FIGS. 1 to 3 may be used by appropriately selecting the most convenient one according to the structure of each element in the image sensor actually created and the actual state of processing technology such as ion implantation. It is also possible to form in shapes other than the illustrated example.

FIG. 4 is a plan view showing an arrangement example of the protrusion 131B and the protrusion 131C of the P + region 131 in one photodiode portion 130. FIG. As shown in the figure, a plurality of protrusions 141 can be arranged on a two-dimensional array in one pixel 140, the PN junction capacitance can be increased, and the saturation signal charge amount (Qs) can be increased.
FIG. 5 is a plan view showing the positional relationship between the photodiode section 130 and the transfer gate (TG) 150 in the example shown in FIG. In general, in a CMOS image sensor, a transfer gate 150 is arranged for each pixel 140 as shown in the figure, and signal charges accumulated in the photodiode unit 130 are transferred to a floating diffusion (FD) unit (not shown).
In the photodiode portion 130 of this example, since the protruding portions 131A, 131B, and 131C having the above-described shapes are provided in the P + region 131, the signal charge storage portion is formed in the deep portion of the substrate. It is preferable that the signal charges can be transferred by the transfer gate 150 well.
Therefore, for example, it is effective to form a plurality of protrusions in a line along the substrate surface and lay them out radially around the transfer gate, or to lay out the protrusions near the transfer gate. It is. It is also effective to incline the potential of the protruding portion.
FIG. 6 shows an example in which a plurality of protrusions 161 are formed in a line shape along the substrate surface and arranged such that the longitudinal direction thereof faces the transfer gate 150, and the potential of each protrusion 161 is indicated by an arrow a. By inclining so as to gradually increase in the direction shown, signal charges (electrons) generated in the photodiode portion easily flow to the transfer gate.

FIGS. 7A and 7B are cross-sectional views showing the structure of the photodiode portion of the solid-state imaging device according to the second embodiment of the present invention. FIG. 7A shows the photodiode portion of the blue pixel, and FIG. The diode part is shown.
In the second embodiment, the depth of the P + region at the top of the photodiode portion is changed in accordance with the color sensitivity. In FIG. 7, a color filter and a condensing microlens are provided on each photodiode portion through, for example, a multilayer wiring layer, and incident light is converted into blue, red, and green color components by the color filter. The light is split and incident on the photodiode portion of each pixel.
The photodiode portions 230 and 240 are formed by forming impurity regions of P + regions 231 and 241, N + regions 232 and 242, N− regions 233 and 243, and P− regions 234 and 244 in the silicon substrate 210, respectively. However, both P + regions 231 and 241 have different depths. For example, since red light is absorbed most in a region near 3 μm deep in the silicon substrate 210, the color sensitivity characteristic can be improved by forming the P + region 241 at a deep position so as to form a charge storage portion in this vicinity. Can be improved.
Also in this embodiment, the protruding portions 231A and 241A are formed in the P + regions 231 and 241 of the photodiode portions 230 and 240, respectively, to increase the PN junction capacitance.

It is sectional drawing which shows the structure of the photodiode part of the solid-state image sensor by the Example of this invention. It is sectional drawing which shows the structure of the photodiode part of the solid-state image sensor by the modification of the Example shown in FIG. It is sectional drawing which shows the structure of the photodiode part of the solid-state image sensor by the other modification of the Example shown in FIG. It is a top view which shows the example of arrangement | positioning of the protrusion part of the photodiode part in the Example shown in FIG. FIG. 2 is a plan view showing an arrangement example of photodiode portions and transfer gates in the embodiment shown in FIG. 1. It is a top view which shows the other example of arrangement | positioning of the protrusion part of the photodiode part in the Example shown in FIG. It is sectional drawing which shows the structure of the photodiode part of the solid-state image sensor by Example 2 of this invention. It is sectional drawing which shows the structure of the photodiode part of the conventional solid-state image sensor.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 110 ... Silicon substrate, 120 ... Element isolation part, 130 ... Photodiode part, 131 ... P + area | region, 131A, 131B, 131C ... Protruding part, 132 ... N + area | region, 133 ... N- area | region, 134 ... P-region.

Claims (10)

A semiconductor substrate having a photoelectric conversion element provided with a P-type impurity region and an N-type impurity region in the depth direction from the top surface of the substrate;
The photoelectric conversion element includes a capacitance expansion portion in which a P-type impurity region protrudes toward the N-type impurity region and forms a PN junction surface in a substrate surface direction and a depth direction, and the capacitance expansion portion includes: It is configured to include a protruding portion protruding in the depth direction of the semiconductor substrate,
A plurality of the photoelectric conversion elements are arranged corresponding to a plurality of color components, and the P-type impurity regions of the photoelectric conversion elements have different shapes corresponding to the characteristics of the color components,
The protrusions formed for each color component are formed at different positions in the semiconductor substrate depth direction ,
The solid-state imaging device , wherein the protruding portion of the photoelectric conversion element corresponding to the red pixel is formed at a deeper position than the protruding portion of the photoelectric conversion element corresponding to the blue pixel . And the N + -type impurity region where the N-type impurity region is formed in the upper layer, is formed on the lower layer, than the N + form impurity regions in claim 1, characterized in that it comprises a lower concentration of N- type impurity regions The solid-state imaging device described. 3. The solid-state imaging device according to claim 1, wherein a P − type impurity region having a lower concentration than the P type impurity region constituting the PN junction is further provided below the N type impurity region. The protrusion, the solid-state imaging device according to any one of claims 1 to 3, characterized in that it is formed to protrude in a substantially spherical shape in the depth direction of the semiconductor substrate. The protrusion, the solid-state imaging device according to any one of claims 1 to 3, characterized in that it is formed to protrude substantially rod shape in the depth direction of the semiconductor substrate. The capacity expansion portion protrudes in the depth direction of the semiconductor substrate, and protrusions described it to any one of claims 1 to 3, characterized in that is formed in a linear shape along the semiconductor substrate surface Solid-state image sensor. The solid-state imaging device according to any one of claims 1 to 6, characterized in that a plurality of capacity expansion portion for one of said photoelectric conversion elements. The solid-state image pickup device according to claim 7, wherein the plurality of capacitance expansion units are arranged radially with respect to a transfer gate for reading signal charges of the photoelectric conversion unit. 9. The solid-state imaging device according to claim 1, wherein the potential of the capacity expanding portion is inclined toward a transfer gate for reading a signal charge of the photoelectric conversion unit. 10. The solid-state imaging device according to claim 1, wherein the capacitance expansion unit is disposed in proximity to a transfer gate for reading signal charges of the photoelectric conversion unit.

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