JP2003086783A - Solid-state image pickup element and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve sensitivity by forming a longitudinal overflow barrier deep and to suppress color mixing due to interference between adjacent pixels accompanying reduction in cell size. SOLUTION: In order to optimize the impurity profile of a photodetection pixel of a solid-state image pickup element by colors that respective pixels take charge of, a sensor structure has a profile of multi-stage constitution increased in photoelectric conversion efficiency along the depth of a silicon substrate, by performing ion implantation of n+ impurities of a sensor divisionally a plurality of times while the energy and mask pattern are changed. So that photoelectric conversion is effectively performed corresponding to the incident wavelength filtered by a color filter on a photodetection pixel, part of the multi-stage constitution of n-type impurities of the sensor is expanded, the expanded area is formed to the best depth for each pixel to provide expanded parts at different positions by adjacent pixels, and interference between the adjacent pixels is avoided to actualize both sensitivity improvement and prevention against color mixing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device such as a two-dimensional image sensor or a line sensor for reading a color image, and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent solid-state image pickup devices, it is essential to increase the quantum efficiency per unit cell in order to compensate for the decrease in sensitivity due to the miniaturization of image pickup pixels (cells).
Therefore, conventionally, measures such as devising the shape of the on-chip microlens have been taken to effectively capture the amount of incident light into the sensor area. Unless photoelectrically converted in the (Si) substrate and effectively accumulated as a signal charge in the photodiode, it becomes a smear component or is discarded on the drain side of the silicon substrate, and as a result, it cannot contribute as sensitivity. .

In order to effectively store the photoelectrically converted charges in the sensor region, it is necessary to three-dimensionally expand the n region, which is the lower layer charge storage region of the photodiode. As the expansion method, (1) a method of expanding the n region in the depth direction of the silicon substrate and (2) a method of expanding the n region in the two-dimensional direction (substrate surface direction) of the silicon substrate can be considered.

[0004]

However, the method (1) for expanding the n region in the depth direction can be realized by forming the position of the overflow barrier deeply, but the depth relative to the cell size of the sensor region can be increased. Since the aspect ratio in the depth direction becomes large, it has become difficult to form a smooth profile so that three-dimensional tightening does not occur. FIG. 2 is an explanatory diagram showing an impurity profile in a sensor portion of a CCD solid-state imaging device having a general vertical overflow drain, and FIG.
Is a CCD with a deep overflow barrier
It is explanatory drawing which shows the impurity profile in the sensor part of a solid-state image sensor. In each figure, the vertical axis represents the potential level φ (V), and the horizontal axis represents the depth position from the surface of the silicon substrate.

As shown in the figure, in the sensor portion, after the incident light is photoelectrically converted, an n-type layer for accumulating charges, a p-type layer for forming an overflow barrier, and a charge outflow generated by an interface state. Of the p-type high concentration layer (p +) for pinning the silicon surface of the sensor portion so as to suppress the dark current (dark current). In the above-described configuration in which the sensor region (n region) is expanded in the depth direction, as shown in FIG. 3, the overflow barrier is formed at a deeper position from the silicon surface, and the gap between the overflow barriers is smoothly formed by the n-region. It can be achieved by taking a stretching profile.

FIGS. 5 and 6 are sectional views showing the structure of a CCD solid-state image pickup device in which the n region of the sensor is enlarged in the depth direction of the silicon substrate as described above. FIG. 6 shows the structure between adjacent pixels in the vertical direction. In FIG. 5, the sensor region 11 of each pixel corresponding to RGB is provided on the upper layer of the silicon substrate 10.
A and 11B are arranged, and a vertical transfer register 12 is formed between the sensor areas 11A and 11B. Then, the transfer electrodes 14 are arranged on the upper surface of the silicon substrate 10 so as to correspond to the vertical transfer registers 12 via the insulating film 13, and the light shielding film 16 is arranged on the upper surface thereof.

Further, in FIG. 6, transfer electrodes 14 and 15 for each vertical transfer register 12 are arranged, and a light shielding film 16 is arranged on the upper surface thereof. As illustrated, when the n regions of the sensor regions 11A and 11B are enlarged in the depth direction of the silicon substrate 10, adjacent n regions are too close to each other in the deep portion of the silicon substrate 10, and the vertical transfer register 12 is not particularly interposed. There is a concern about color mixing between adjacent pixels in the vertical direction.

On the other hand, in the method of simply enlarging the n region in the two-dimensional direction of the profile of (2), the handling charge is reduced by reducing the vertical transfer electrode region and the blooming margin is reduced by reducing the read gate. Causes deterioration of basic characteristics such as color mixing in adjacent cells.

Therefore, an object of the present invention is to provide a solid-state image sensor capable of suppressing a decrease in sensitivity and color mixture due to a reduction in cell size, and a method for manufacturing the same.

[0010]

In order to achieve the above-mentioned object, the present invention provides a semiconductor substrate with a sensor portion constituting a plurality of image pickup pixels and a transfer register for transferring the signal charge accumulated in each sensor portion. In the solid-state imaging device, in which the signal charge storage region of the sensor unit is enlarged in the depth direction of the semiconductor substrate, the signal charge storage regions of the image pickup pixels adjacent to each other are provided.
It is characterized in that it is enlarged in the surface direction of the semiconductor substrate at different depth positions of the semiconductor substrate which are determined corresponding to the wavelength of the incident light which each imaging pixel is responsible for.

Further, according to the present invention, a semiconductor substrate is provided with a sensor section which constitutes a plurality of image pickup pixels, and a transfer register which transfers the signal charge accumulated in each sensor section. In a method of manufacturing a solid-state imaging device enlarged in a depth direction of a semiconductor substrate, impurity ion implantation for forming a signal charge storage region of the sensor unit is performed in plural times, and the ion implantation amount of each time is adjacent. By changing between the image pickup pixels, the signal charge storage areas of the image pickup pixels adjacent to each other are determined at the different depth positions of the semiconductor substrate determined according to the wavelength of the incident light which each image pickup pixel covers. It is characterized in that it is designed to expand.

In the solid-state image pickup device of the present invention, the signal charge storage regions of the image pickup pixels adjacent to each other are formed at different depth positions of the semiconductor substrate which are determined corresponding to the wavelength of incident light which each image pickup pixel covers. Since it is enlarged in the plane direction, while preventing the adjacent signal charge storage regions from approaching,
The signal charge storage region can be expanded at a depth position that is optimum for the wavelength of incident light. Therefore, it is possible to realize both the sensitivity improvement effect by expanding the signal charge storage area and the color mixing suppression effect by separating the adjacent signal charge storage areas, and it is possible to prevent the deterioration of the image quality due to the reduction of the cell size. It is possible to obtain a solid-state image sensor of high quality.

In the method for manufacturing a solid-state image pickup device of the present invention, the signal charge storage regions of the image pickup pixels adjacent to each other of the solid-state image pickup device are adjusted to the wavelength of the incident light which each image pickup pixel takes charge of, by implanting impurity ions a plurality of times. Since the semiconductor substrate is expanded in the plane direction of the semiconductor substrate at different depth positions corresponding to each other, it is possible to prevent the adjacent signal charge storage regions from approaching each other by an easy manufacturing process and optimize the wavelength of the incident light. The signal charge storage region can be expanded at the depth position. Therefore, it is possible to realize both the sensitivity improvement effect by expanding the signal charge storage area and the color mixing suppression effect by separating the adjacent signal charge storage areas, and it is possible to prevent the deterioration of the image quality due to the reduction of the cell size. It is possible to manufacture a solid-state image sensor of high quality.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a solid-state image sensor and a method of manufacturing the same according to the present invention will be described below. The embodiments described below are preferred specific examples of the present invention, and various technically preferable limitations are given. However, the scope of the present invention is not limited to the present invention in the following description. Unless otherwise stated, the present invention is not limited to these embodiments. In the present embodiment, in order to optimize the impurity profile of the light-receiving pixel portion in the solid-state image sensor for each color that each pixel is responsible for, ion implantation is performed by dividing the n + impurity in the sensor portion into a plurality of times and changing the energy or mask pattern. In a sensor structure having a multi-stage profile with improved photoelectric conversion efficiency in the depth direction, the sensor is configured so that photoelectric conversion is effectively performed according to the incident wavelength filtered by the color filter on the light receiving pixel. A part of the multi-stage structure of n + impurities in the part, and
By forming the enlarged region at an optimum depth for each pixel, both sensitivity improvement and color mixture prevention are achieved.

FIG. 1 shows a CCD according to an embodiment of the present invention.
It is sectional drawing which shows the structure of a solid-state image sensor, and has shown the structure between the pixels which adjoin a vertical direction. In this example, sensor regions 111A, 111B, 111C of pixels corresponding to RGB are arranged on the upper layer of the silicon substrate 110. Although omitted in FIG. 1, each sensor region 11
1A, 111B, and 111C are shown in FIG.
A vertical transfer register is formed similarly to the structure shown in FIG. The insulating film 11 is formed on the upper surface of the silicon substrate 110.
Upper and lower two-phase transfer electrodes 114 and 115 are arranged corresponding to each vertical transfer register via the light-shielding film 3, and the light-shielding film 1 is provided on the upper surface thereof.
16 are arranged.

On the upper surface of the silicon substrate 110, a color filter 120 for separating the three color lights of R, G, and B into the respective image pickup pixels and providing them is provided.
The color filter 120 causes blue (Blue) light to enter the sensor region 111A, green (Green) light to enter the sensor region 111B, and red (Red) light to enter the sensor region 111C. In each of the sensor regions 111A, 111B, and 111C, a depletion layer formed of an n − -type impurity region is formed below the photoelectric conversion layer formed of the n + -type impurity region in the upper layer in the depth direction of the silicon substrate 110 to form a signal charge storage region. With such an impurity profile structure, the position of the overflow barrier is formed deeply to improve the sensitivity.

The sensor regions 111A, 111B, 111C having such an impurity profile structure are formed by ion implantation divided into a plurality of times (7 steps in the illustrated example), and the ion implantation energy and mask pattern of each time. Is changed to have an impurity region enlarged in the substrate surface direction at a different depth position for each of the sensor regions 111A, 111B, and 111C of pixels that are in charge of each color. That is, for the Blue pixel with the shortest wavelength (sensor region 111A), the shallowest n-type impurity region is enlarged, and for the Green pixel with the next shortest wavelength (sensor region 111B), the third row from the top. The red pixel (sensor region 111C) having the longest wavelength is enlarged by expanding the n-type impurity region, and the n pixels in the first stage and the second stage from the bottom.
Enlarge the − type impurity region. As a result, the n-type impurity region at the depth position optimum for the wavelength of the incident light is expanded in the substrate surface direction, the sensitivity in each pixel is improved, and the n-type impurity region at the depth position different between adjacent pixels is n-type. By enlarging the type impurity region, mutual separation is ensured and color mixture is suppressed.

FIG. 4 is an explanatory diagram showing the relationship between the formation position of the overflow barrier and the sensitivity for each incident wavelength on the silicon substrate, where the vertical axis is the spectral sensitivity and the horizontal axis is the incident wavelength (μ
m), and each polygonal line shows a spectral characteristic curve (calculated value) at each position from 0.3 μm to 12 μm. Here, the blue light (light that has passed through the blue filter) has a spectral curve having a sensitivity peak at a wavelength of about 450 nm (0.45 μm), so that it is 3
If there is an overflow barrier at a depth of about μm, photoelectric conversion is efficiently performed in the sensor area, but green light (light transmitted through the green filter) is 500 to 550.
Since it has a sensitivity peak in the vicinity of nm, it is necessary to form an overflow barrier at a depth of about 5 μm in order to obtain effective photoelectric conversion.

Further, the red light (light transmitted through the red filter) has a sensitivity peak in the vicinity of 600 to 650 nm, so the required depth position of the overflow barrier is 10 μm or more. In other words, if the position of the overflow barrier is formed deep in advance, and the wavelength is assigned to each pixel, and only the sensor region at the photoelectric conversion depth different for each color is enlarged, It is possible to efficiently perform photoelectric conversion without invading the sensor regions of adjacent pixels.

Therefore, as an example of the method of creating such a profile structure, the following procedure can be adopted. First, high-energy ion implantation of an overflow barrier (Boron: 8
(10 MeV) or a two-layer Epi method or the like, and then an area corresponding to the n + area shown in FIG. This n + region determines the minimum potential of the sensor portion, and is formed with As or Phos to a depth of about 0.5 μm. After that, ion implantation is performed in multiple steps with different energies so that the depletion region spreads smoothly to the n + region and the overflow barrier in a potential manner to form the n- region. The n-region is formed with higher energy and lower concentration than the n + region.

Then, for each multi-stage ion implantation (implantation) operation of the n-region, the above-mentioned Blue, Red,
A mask pattern of energy corresponding to the depth at which each wavelength of Green is photoelectrically converted in Si is optimized for each pixel. That is, as shown in FIG. 1, in the multi-stage implantation work for forming the n − region, in the implantation that is driven to a depth of 3 μm or less, the mask pattern at that time is
Only the opening of the pixel (sensor area 111A) that handles the blue light is made larger than the other pixels. Also, 3 to 5 μm
The mask pattern at the time of implanting work to the depth of
Only the opening of the pixel (sensor region 111B) that handles the green light is made larger than the other pixels. Similarly, the opening of the mask pattern of the pixel (sensor region 111C) that handles the red light is made larger than the other pixels during the implantation work for implanting to a depth of 5 μm or more.

Then, after forming the transfer electrode by a normal method, the P + region on the outermost surface is formed by an implantation work by self-alignment with the transfer electrode, and a normal light-shielding film or the like is formed. In the manufacturing method of the present example as described above, since the n − region forming the signal charge storage region of each sensor is formed by the multi-stage implanter, the pattern can be easily optimized for each implanter, as shown in FIG. It is possible to easily realize such a sensor profile. Note that the number of ion implantation steps in the multi-step n region is shown as an example of seven steps in the example of FIG. 1, but it is optimal depending on the position of the overflow barrier and the two-dimensional tightening effect of impurities surrounding the sensor. The number of stages can be changed as appropriate.

[0023]

As described above, in the solid-state image pickup device of the present invention, the signal charge storage regions of the image pickup pixels adjacent to each other are different from each other in the semiconductor substrate determined according to the wavelength of the incident light which each image pickup pixel covers. Since the semiconductor substrate is expanded at the depth position in the surface direction, it is possible to expand the signal charge storage region at the optimum depth position for the wavelength of the incident light while preventing the adjacent signal charge storage regions from approaching each other. Therefore, the sensor regions do not interfere with each other between adjacent pixels, and a structure in which charge color mixing does not occur particularly between pixels that are adjacent to each other in the vertical direction, and the sensitivity improvement effect due to the expansion of the signal charge storage region and the adjacent signal charge storage region It is possible to realize both the effect of suppressing the color mixture by separating the. As a result, it is possible to prevent the deterioration of the image quality due to the reduction of the cell size, and it is possible to obtain a high quality solid-state imaging device.

Further, in the method for manufacturing a solid-state image pickup device of the present invention, the signal charge accumulation regions of the image pickup pixels adjacent to each other of the solid-state image pickup device are adjusted to the wavelength of the incident light which each image pickup pixel takes charge of by implanting impurity ions a plurality of times. Since the semiconductor substrate is expanded in the plane direction of the semiconductor substrate at different depth positions corresponding to each other, it is possible to prevent the adjacent signal charge storage regions from approaching each other by an easy manufacturing process and optimize the wavelength of the incident light. The signal charge storage region can be expanded at the depth position. Therefore, it is possible to easily manufacture the solid-state imaging device having a structure in which the sensor regions do not interfere with each other between adjacent pixels and charge mixing especially between pixels adjacent in the vertical direction is difficult to occur, and the effect of improving the sensitivity by enlarging the signal charge storage region is achieved. In addition, it is possible to realize both the effect of suppressing color mixture by separating the adjacent signal charge storage regions. As a result, it is possible to prevent the deterioration of image quality due to the reduction of the cell size, and it is possible to manufacture a high-quality solid-state imaging device.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a CCD solid-state image sensor according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an impurity profile in a sensor portion of a CCD solid-state imaging device having a general vertical overflow drain.

FIG. 3 C in which the position of the overflow barrier is deeply formed
It is explanatory drawing which shows the impurity profile in the sensor part of a CD solid-state image sensor.

FIG. 4 is an explanatory diagram showing the relationship between the formation position of the overflow barrier and the sensitivity for each incident wavelength on the silicon substrate.

FIG. 5 is a cross-sectional view showing a structure between horizontally adjacent pixels in a conventional CCD solid-state imaging device.

FIG. 6 is a sectional view showing a structure between vertically adjacent pixels in a conventional CCD solid-state imaging device.

[Explanation of symbols]

110 ... Silicon substrate, 111A, 111B, 111
C ... Sensor area, 113 ... Insulating film, 114, 115
...... Transfer electrode, 116 …… Light-shielding film, 120 …… Color filter.

Claims (6)

[Claims] 1. A semiconductor substrate is provided with a sensor section that constitutes a plurality of image pickup pixels and a transfer register that transfers the signal charge accumulated in each sensor section, and the signal charge storage region of the sensor section is provided in the semiconductor substrate. In the solid-state imaging device expanded in the depth direction, the signal charge storage regions of the imaging pixels adjacent to each other are determined according to the wavelength of the incident light that each imaging pixel covers A solid-state image sensor characterized by being enlarged in the plane direction. 2. The solid-state image pickup device according to claim 1, wherein the image pickup pixels adjacent to each other are pixels which are in charge of image pickup of different colors. 3. A signal charge storage region of a blue pixel among the image pickup pixels for three colors of red, blue, and green is enlarged at a shallowest depth position, and a signal charge storage region of a green pixel is located at a second shallowest depth position. 3. The solid-state imaging device according to claim 2, wherein the signal charge storage region of the red pixel is enlarged at the deepest position. 4. A semiconductor substrate is provided with a sensor portion that constitutes a plurality of image pickup pixels and a transfer register that transfers the signal charge accumulated in each sensor portion, and the signal charge accumulation region of the sensor portion is formed in the semiconductor substrate. In a method of manufacturing a solid-state image pickup device enlarged in a depth direction, impurity ion implantation for forming a signal charge storage region of the sensor unit is performed in plural times, and the ion implantation amount of each time is set between adjacent image pickup pixels. The signal charge storage regions of the image pickup pixels adjacent to each other are expanded in the plane direction of the semiconductor substrate at different depth positions determined according to the wavelength of the incident light which each image pickup pixel covers by A method of manufacturing a solid-state image sensor, comprising: 5. The method of manufacturing a solid-state image pickup device according to claim 4, wherein the image pickup pixels adjacent to each other are pixels which are responsible for image pickup of different colors. 6. A signal charge storage region of a blue pixel among the image pickup pixels for three colors of red, blue, and green is enlarged at a shallowest depth position, and a signal charge storage region of a green pixel is located at a second shallowest depth position. 6. The method for manufacturing a solid-state imaging device according to claim 5, wherein the signal charge storage region of the red pixel is enlarged at the deepest position.