JP2005340338A - Solid-stage imaging device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To output an image based on a proper black reference level by removing a difference in characteristics between an effective pixel and an OPB without complicating a manufacturing process and increasing a manufacturing cost. <P>SOLUTION: When forming the effective pixel 10 and photo diodes PD1 and PD2 of the OPB 20 in a semiconductor substrate 30, the profile of a mask, etc. is common, but additional impurity ions are implanted into the photo diode PD2 of the OPB 20 to remove a difference in characteristics which is caused by the existence of a light shielding film 43 (opening 43A) produced in a subsequent process. The additional impurity ion implantation may be performed over the whole region of the photo diode PD2 of the OPB 20, or it could be performed partially. An optimal region is properly selected for the additional impurity ion implantation depending on the dopant profile, etc. of the photo diode PD2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a solid-state imaging device having an OPB (optical black) unit for generating a black reference signal and a method for manufacturing the same.

Conventionally, in a solid-state imaging device such as a CCD image sensor or a CMOS image sensor, a light shielding film is disposed on a semiconductor substrate provided with a number of pixels in a two-dimensional array via an upper layer film. By making light incident on the photodiode (photoelectric conversion element) of each pixel from the corresponding opening, a signal charge corresponding to the amount of incident light is generated in each photodiode, and an image signal is obtained by reading this signal charge. (For example, refer to Patent Document 1).
In such an image sensor, in general, in order to obtain a black reference level that is a reference for determining the luminance level of the image signal, a photodiode is provided in a region shielded by a light-shielding film, and is obtained from this photodiode. An OPB (optical black) portion that uses the signal level as a black reference is provided.
JP 2001-8113 A

By the way, the OPB part provided in the conventional image sensor basically forms a photodiode by the same process as that of the photodiode of the effective pixel, and shields the light receiving part of the photodiode by the light shielding film common to the effective pixel. It arrange | positions in the state which cannot open an opening part.
However, when the OPB portion is formed by such a method, the effect on the photodiode due to the presence / absence of the light shielding film (that is, presence / absence of the opening) in the process after the light shielding by the light shielding film is caused in the effective pixel and the OPB portion Unlikely, there may be a difference in characteristics between the photodiode of the effective pixel and the photodiode of the OPB portion.
For this reason, an error occurs in the black reference level that is actually required, and when the error becomes large, for example, when the signal level of the effective pixel is larger than the signal level of the OPB part in the dark, the place that should become black does not become black. The image becomes unnatural.
On the contrary, when the signal level of the effective pixel is lower than the signal level of the OPB portion in the dark, the effective pixel having the signal level lower than the OPB portion is recognized as black and ignored, and the image to be displayed disappears, which is unnatural. It becomes an image.
In addition, as a method of removing the step difference in characteristics between the effective pixel and the OPB portion, a method of changing the shape of both is also possible. However, in this case, the OPB portion is changed using a mask different from the effective pixel. There is a problem that it is necessary to create the manufacturing process, and the manufacturing process becomes complicated and the manufacturing cost increases.

  Accordingly, the present invention provides a solid-state imaging device capable of removing the step difference in characteristics between the effective pixel and the OPB portion without complicating the manufacturing process and increasing the manufacturing cost, and realizing image output with an appropriate black reference level. It aims at providing the manufacturing method.

In order to achieve the above-described object, a method for manufacturing a solid-state imaging device of the present invention includes a semiconductor substrate on which a semiconductor element including a photoelectric conversion element is formed, and a light-shielding film disposed on the semiconductor substrate via an upper layer film. A plurality of effective pixels having photoelectric conversion elements that perform photoelectric conversion by receiving light incident from an opening formed in the light shielding film, and a signal that becomes a black reference in a dark state shielded by the light shielding film. A method of manufacturing a solid-state imaging device in which an OPB part having a photoelectric conversion element to be formed is formed on the semiconductor substrate, and when the impurity implantation of the photoelectric conversion element is performed, the photoelectric conversion element of the OPB part is It is characterized in that a step of performing additional impurity implantation that is not implanted into the photoelectric conversion element of the effective pixel is provided.
The solid-state imaging device of the present invention includes a semiconductor substrate on which a semiconductor element including a photoelectric conversion element is formed, and a light-shielding film disposed on the semiconductor substrate via an upper layer film. A plurality of effective pixels having a photoelectric conversion element that receives light incident from an opening formed in the light shielding film and performs photoelectric conversion, and a photoelectric that generates a black reference signal in a dark state shielded by the light shielding film. And an OPB portion having a conversion element, wherein the photoelectric conversion element of the OPB portion is injected with an additional impurity that is not injected into the photoelectric conversion element of the effective pixel.

  According to the solid-state imaging device and the method of manufacturing the same of the present invention, by introducing additional impurities that are not injected into the photoelectric conversion element of the effective pixel into the photoelectric conversion element of the OPB unit, the characteristics of the effective pixel and the OPB unit are improved. Since the step is removed, the characteristics of the effective pixel and the OPB portion can be matched without adding a significant process, and the proper black reference can be achieved without complicating the manufacturing process and increasing the manufacturing cost. There is an effect that image output by level can be realized.

In the solid-state imaging device and the manufacturing method thereof according to the embodiment of the present invention, when the effective pixel and the OPB portion photodiode are formed on the semiconductor substrate, the mask and the like are formed in common, but the OPB portion photodiode is Then, additional impurity ion implantation is performed to remove a characteristic step caused by the presence or absence of a light-shielding film (opening) generated in the subsequent process.
The additional impurity ion implantation may be performed on the entire photodiode of the OPB portion, but may be performed partially, and an optimum region is appropriately selected according to the impurity profile of the photodiode. If done, it is possible to further improve the characteristics.

1 to 3 are diagrams showing a structure of a solid-state imaging device according to an embodiment of the present invention. FIG. 1 is a plan view showing an element arrangement of effective pixels, and FIG. 2 is a plan view showing an element arrangement of an OPB portion. . FIG. 3 is a cross-sectional view showing the laminated structure of the effective pixel and the OPB portion, and shows the α-α ′ cross section and the β-β ′ cross section of FIG.
In this embodiment, the effective pixel and the OPB portion basically have a common structure, and the only difference is the state of impurity implantation into the photodiode portion.

First, in FIG. 1, the effective pixel 10 is provided with a photodiode PD1 as a photoelectric conversion element, a transfer gate 11 for transferring a signal charge from the photodiode PD1 to the floating diffusion portion FD1, and a floating diffusion portion FD1. An amplifying gate 12 that converts the potential of the amplifying gate into a voltage signal or a current signal, a reset gate 13 that resets the potential of the floating diffusion portion FD1 to the power supply potential VDD, and a selection gate 14 that connects the output signal of the amplifying gate to the output signal line. Each MOS transistor is provided.
On the other hand, as shown in FIG. 2, the OPB unit 20 is also provided with a photodiode PD2 as a photoelectric conversion element, a transfer gate 21 for transferring signal charges from the photodiode PD2 to the floating diffusion unit FD2, and a floating device. An amplification gate 22 that converts the potential of the fusion portion FD2 into a voltage signal or a current signal, a reset gate 23 that resets the potential of the floating diffusion portion FD2 to the power supply potential VDD, and an output signal of the amplification gate are connected to an output signal line. Each MOS transistor of the selection gate 24 is provided. The effective pixel 10 and the OPB portion 20 are separated from adjacent pixels by the element isolation region 1.

In FIG. 3, the photodiode PD <b> 1 of the effective pixel 10 and the photodiode PD <b> 2 of the OPB portion 20 are formed in the P-type region 31 provided in the upper layer of the semiconductor substrate 30. The photodiode PD1 of the effective pixel 10 includes an upper P + layer 32 and a lower N layer 33, and the photodiode PD2 of the OPB portion 20 includes an upper P + layer 34 and a lower N− layer 35. That is, the impurity concentration of the photodiode PD1 of the effective pixel 10 is different from that of the photodiode PD2 of the OPB unit 20, and additional P-type ion implantation is performed on the photodiode PD2 of the OPB unit 20, thereby reducing the N-type impurity concentration of the lower layer. N-. Further, the effective pixel 10 and the OPB unit 20 perform the N-type ion implantation process separately.
Further, the transfer gates 11 and 21 described above are disposed on the side portions of the photodiodes PD1 and PD2, and the transfer gate electrodes 36 and 37 are provided on the upper surface of the semiconductor substrate 30 via the insulating film 40. N + layers 38 and 39 to be floating diffusion portions FD1 and FD2 are formed on the outside thereof.
In addition, a plurality of wiring layers 42 are provided on the semiconductor substrate 30 above the insulating film 40 and the transfer gate electrodes 36 and 37 via an interlayer insulating film 41, and a light shielding film 43 is provided on the upper surface of the interlayer insulating film 41. Is arranged. The light shielding film 43 is made of an aluminum film or the like, and has an opening 43A corresponding to the light receiving region of the photodiode PD1 of the effective pixel 10, but the photodiode PD2 of the OPB portion 20 does not have an opening. It has a complete shielding structure.
Note that a color filter and an on-chip lens are further disposed on the light shielding film via an upper layer film, but are omitted here because they are not directly related to the configuration of the present invention.

Next, the ion implantation process of the photodiode, which is a feature of this embodiment, will be described.
In this embodiment, in order to remove the step difference in characteristics between the photodiode PD1 of the effective pixel 10 and the photodiode PD2 of the OPB portion 20, the photodiode PD2 of the OPB portion 20 is introduced into the photodiode PD1 of the effective pixel 10. Do not perform additional ion implantation.
This additional ion implantation can be realized at low cost without a significant addition of the process by repeating the existing ion implantation process once or a plurality of times instead of using a new ion implantation process.
Further, the ion implantation to be added is performed by optimizing the generation amount of the dark current in the OPB unit 20 in order to remove the step difference in the characteristics of the photodiode PD2 in the OPB unit 20, and the ion species, the dose amount, and the implantation energy. Shall be determined. Note that the final condition can be determined in detail by a prototype experiment or the like.

Further, the ion implantation may be performed on the entire photodiode PD2, or may be performed partially. FIG. 2 shows an example in which additional ion implantation is performed on a partial region of the photodiode PD2, and a region 51 indicated by hatching is an additional ion implantation region.
For example, when P-type ions are additionally implanted in order to obtain the impurity profile shown in FIG. 3, the photoelectric conversion region of the photodiode becomes shallow due to the P-type ion implantation. Specifically, ion implantation is performed on a region along three sides excluding the side adjacent to the transfer gate so as not to affect the signal charge reading characteristics.
FIG. 4 shows an example in which an ion implantation region different from that in FIG. 2 is selected. In this example, N-type ions are additionally implanted to obtain the impurity profile shown in FIG. In this case, the additional ion implantation is performed in the vicinity of the transfer gate 21 as indicated by the hatched area 52. That is, since the photoelectric conversion region of the photodiode is deepened by the N-type ion implantation, ion implantation is performed in the region near the transfer gate 21 so that the signal charge read characteristics are not affected.

As described above, in this embodiment, in order to remove the step in the characteristics of the photodiode PD2 of the OPB portion 20, additional ion implantation using an existing ion implantation process is performed. It is only necessary to change the ion species, energy, and dose without changing the structure of the photodiode itself, and a trial production or the like is easy. In particular, if a test mask for ion implantation can be determined, the prototype can be repeated after changing the energy and dose, and the characteristics can be easily optimized without increasing the number of facilities.
Therefore, the optimum characteristics can be realized without significantly increasing the number of trials and the working time for reducing the characteristic step of the OPB section 20.

It is a top view which shows element arrangement | positioning of the effective pixel of the solid-state image sensor which concerns on Example 1 of this invention. It is a top view which shows the 1st example of the element arrangement | positioning of the OPB part of the solid-state image sensor shown in FIG. It is sectional drawing which shows the element structure of the solid-state image sensor shown in FIG. It is a top view which shows the 2nd example of element arrangement | positioning of the OPB part of the solid-state image sensor shown in FIG.

Explanation of symbols

  PD1, PD2 ... Photodiode, 10 ... Effective pixel, 11, 21 ... Transfer gate, 12, 22 ... Amplification gate, 13, 23 ... Reset gate, 14, 24 ... Select gate, 20 ... OPB , 30... Semiconductor substrate, 31... P-type region, 32 and 34... P + layer, 33... N layer, 35... N-layer, 36 and 37. N + layer, 40 ... insulating film, 41 ... interlayer insulating film, 42 ... wiring layer, 43 ... light shielding film, 43A ... opening.

Claims (7)

A semiconductor substrate on which a semiconductor element including a photoelectric conversion element is formed, and a light shielding film disposed on the semiconductor substrate via an upper layer film, and receives light incident from an opening formed in the light shielding film. Solid-state imaging in which a plurality of effective pixels having photoelectric conversion elements for performing photoelectric conversion and an OPB portion having a photoelectric conversion element for generating a black reference signal in the dark state shielded by the light-shielding film are formed on the semiconductor substrate A method for manufacturing an element, comprising:
In the case of performing the impurity implantation of the photoelectric conversion element, a step of performing an additional impurity implantation that is not implanted into the photoelectric conversion element of the effective pixel is provided for the photoelectric conversion element of the OPB portion.
A method for manufacturing a solid-state imaging device.   2. The method of manufacturing a solid-state imaging device according to claim 1, wherein the additional impurity implantation is performed by adding an impurity implantation step common to the effective pixel and the OPB portion to the OPB portion only once or a plurality of times.   2. The method of manufacturing a solid-state imaging device according to claim 1, wherein the additional impurity implantation is performed on a part of the photoelectric conversion element of the OPB portion.   4. The method of manufacturing a solid-state imaging device according to claim 3, wherein the additional impurity implantation is performed at a position near a readout gate in the photoelectric conversion element of the OPB portion.   4. The method of manufacturing a solid-state imaging device according to claim 3, wherein the additional impurity implantation is performed at a position near a readout gate in the photoelectric conversion element of the OPB portion. Provided with a semiconductor substrate on which a semiconductor element including a photoelectric conversion element is formed and a light shielding film disposed on the semiconductor substrate via an upper layer film, and is incident on the semiconductor substrate from an opening formed in the light shielding film A plurality of effective pixels having a photoelectric conversion element that receives photoelectrically converted light and performs photoelectric conversion, and an OPB unit having a photoelectric conversion element that generates a black reference signal in a dark state shielded by the light shielding film,
In the photoelectric conversion element of the OPB portion, an additional impurity that is not injected into the photoelectric conversion element of the effective pixel is implanted.
A solid-state imaging device.   The solid-state imaging device according to claim 6, wherein the additional impurity is implanted in a part of the photoelectric conversion element of the OPB portion.

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