JP2009088262A - Image sensor and method of manufacturing image sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image sensor capable of executing a self-align process and preventing a reduction in yield regardless of the structure of a charge transfer electrode, and to provide a method of manufacturing the image sensor. <P>SOLUTION: A method of manufacturing the image sensor 10 provided with a photoelectric conversion part PD formed on the semiconductor substrate 1 and charge transfer electrodes P1 and P2 for transferring the signal charge generated by the photoelectric conversion part PD onto the semiconductor substrate 1 includes: a step of forming an electrode layer P0 for forming the charge transfer electrodes P1 and P2 through an insulating film 2 on the semiconductor substrate 1; a step of forming an etch-stop layer 3 on the electrode layer P0; a step of forming a patterning layer M1 having the same pattern as the pattern of the charge transfer electrodes P1 and p2 at least in a part and formed of the same conductive material on the etch-stop layer 3; and a step of patterning the electrode layer P0 to form the charge transfer electrodes P1 and P2 by etching the electrode layer P0 and the patterning layers M1 and M2 and stopping at the etch-stop layer 3. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image pickup device and a method for manufacturing the image pickup device, and more particularly to an image pickup device manufactured by using a self-alignment process for transfer electrodes and the like and a method for manufacturing the image pickup device.

  The imaging device includes a photoelectric conversion unit such as a photodiode and a charge transfer unit including a charge transfer electrode for transferring a signal charge generated by the photoelectric conversion unit. A plurality of charge transfer electrodes are arranged adjacent to each other on a charge transfer path formed on the semiconductor substrate, and are sequentially driven by applying a predetermined drive pulse to each charge transfer electrode. As a manufacturing method of an image sensor, there is a method shown in the following patent document, for example.

JP-A-7-74337 JP 2003-209241 A JP 2004-356572 A JP 2006-1000036 A

  By the way, the structure of the charge transfer electrode includes a single layer structure in which the charge transfer electrodes are arranged in a single layer, and a multilayer structure in which a part of the charge transfer electrodes is stacked on another charge transfer electrode. is there. In the case of a multilayer electrode structure, ion implantation can be performed by self-alignment, so that a potential difference can be formed at the position of the transfer electrode. However, in the case of a single-layer electrode structure, since ion implantation cannot be performed by self-alignment, the characteristic yield is reduced. Will fall. For example, in a horizontal charge transfer unit of a solid-state imaging device, a potential gradient of potential is formed depending on the position of the charge transfer electrode, so that the requirements for ion implantation and transfer electrode position accuracy are severe. When self-alignment cannot be applied when forming such a portion, alignment is very difficult. In addition, in order to form a fine line / space electrode, it would be inevitable that the cost would increase if equipment and materials corresponding to fine processing were introduced.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to manufacture an image pickup device and an image pickup device that can execute a self-alignment process regardless of the structure of the charge transfer electrode and prevent a decrease in yield. It is to provide a method.

The above object of the present invention is achieved by the following configurations.
(1) A method of manufacturing an imaging device comprising a semiconductor substrate, a photoelectric conversion unit formed on the semiconductor substrate, and a charge transfer electrode that transfers a signal charge generated by the photoelectric conversion unit on the semiconductor substrate. There,
Forming an electrode layer on the semiconductor substrate for forming the charge transfer electrode via an insulating film;
Forming an etch stop layer on the electrode layer;
Forming a patterning layer on the etching stop layer, having a pattern that is at least partially the same as the pattern of the charge transfer electrode, and made of the same conductive material;
Etching the electrode layer and the patterning layer and stopping at the etching stop layer, thereby patterning the electrode layer to form the charge transfer electrode.
(2) The method for manufacturing an image pickup device according to (1), further comprising a step of performing ion implantation on the semiconductor substrate using the patterning layer as a mask.
(3) The charge transfer electrode has a first electrode and a second electrode formed in a predetermined pattern on the semiconductor substrate via the insulating film, and has the same pattern as the pattern of the first electrode. Forming a first patterning layer;
Performing ion implantation on the semiconductor substrate using the first patterning layer as a mask;
Forming an oxide film on the first patterning layer;
Forming a layer of the same conductive material as the first patterning layer on the oxide film, and then forming a second patterning layer for patterning the second electrode by planarization;
Etching the oxide film;
Or (1) or (2) including a step of patterning the electrode layer to form the charge transfer electrode by etching the first patterning layer, the second patterning layer, and the electrode layer. The manufacturing method of the image pick-up element as described in (2).
(4) The etching stop layer formed under the first patterning layer and the oxide film formed under the second patterning layer are made of the same material, and the oxide film and the etching stop layer And etching the electrode layer, the first patterning layer, and the second patterning layer so as to stop the etching, and patterning the electrode layer, The imaging device according to (3) above Manufacturing method.
(5) The imaging device according to any one of (1) to (4), wherein the charge transfer electrode is a horizontal charge transfer electrode in which two electrodes are alternately arranged in a straight line. Method.
(6) The method for manufacturing an imaging element according to any one of (1) to (5), wherein the electrode layer is made of a silicon-based conductive material.
(7) An image pickup device manufactured by the method for manufacturing an image pickup device according to any one of (1) to (6) above.

  According to the method for manufacturing an image pickup device of the present invention, an electrode layer for forming a charge transfer electrode is formed, an etching stop layer is formed on the electrode layer, and then the charge transfer electrode is formed on the etching stop layer. A patterning layer having the same pattern as the pattern and made of the same conductive material is formed. Thereafter, the electrode layer and the patterning layer are etched. Since the electrode layer and the patterning layer are made of the same material, the same amount is removed by etching under the same conditions during etching. Since the electrode layer below the patterning layer remains without being removed by the etching stop layer, only the electrode layer in the region where the patterning layer is not formed above is etched away. Then, the electrode layer remaining in the same pattern as the pattern of the patterning layer becomes a charge transfer electrode having a target pattern. Ion implantation into the semiconductor substrate is performed using the patterning layer on the electrode layer as a mask, and by etching the electrode layer and the patterning layer, charge transfer is accurately performed according to the position of the region where ions are implanted by self-alignment. An electrode can be formed. In this way, when manufacturing an imaging device having a single-layer electrode structure, it is possible to perform ion implantation by a self-alignment process as in the case of the multilayer electrode structure, and to prevent a decrease in yield. In particular, a part where the position of the transfer electrode needs to be formed with high accuracy, such as a horizontal charge transfer electrode of a solid-state image sensor, is formed with high accuracy without reducing the yield by a self-alignment process regardless of the electrode structure. can do.

  According to the present invention, a self-alignment process can be performed regardless of the structure of the charge transfer electrode, and an image pickup device and a method for manufacturing the image pickup device that can prevent a decrease in yield can be provided.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing a schematic configuration of an image sensor according to the present invention. 2A is an enlarged view showing a part indicated by a broken line A of the image sensor in FIG. 1, and FIG. 2B is an enlarged view showing a part indicated by a broken line B of the image sensor in FIG. In FIG. 2, other layers and films are not shown and are omitted in order to explain the shape of the transfer electrode.

  The imaging element 10 has a configuration of a solid-state imaging element, that is, a plurality of photoelectric conversion units PD such as photodiodes arranged in the imaging region 12 on the semiconductor substrate, and signal charges generated by each photoelectric conversion unit PD. A vertical charge transfer unit that transfers the signal charge in the vertical direction and a horizontal charge transfer unit 14 that is connected to the vertical end of the vertical charge transfer unit and transfers the signal charge in the horizontal direction.

  Each of the vertical charge transfer unit and the horizontal charge transfer unit 14 includes a plurality of charge transfer electrodes P1 and P2. The charge transfer electrodes P1 and P2 are formed of the same material as the first electrode P1 and the first electrode P1 formed in a predetermined pattern using a silicon-based conductive material such as polysilicon, and are different from the first electrode. The second electrode (P2) is formed in the pattern.

  In the imaging device of this embodiment, the charge transfer electrodes P1 and P2 are formed in the same layer (single layer) on the semiconductor substrate. As shown in FIG. 2A, the charge transfer electrodes P1 and P2 of the vertical charge transfer portion are formed in a meandering pattern in the horizontal direction (left and right direction in FIG. 2A), and P1 and P charge transfer are performed. The electrodes 2 are alternately formed in the vertical direction (vertical direction in FIG. 2A).

  Further, as shown in FIG. 2B, the charge transfer electrodes P1 and P2 of the horizontal charge transfer unit 14 are alternately arranged linearly along the horizontal direction. The charge transfer electrodes P1 and P2 of the horizontal charge transfer unit form one transfer stage in two sets, and a horizontal drive signal is applied to each transfer stage, whereby the charge transfer electrodes P1 and P2 of each transfer stage are applied. The level of the potential potential changes, and signal charges are sequentially transferred to transfer stages adjacent in the horizontal direction. Since the potential gradient is determined based on the positions of the charge transfer electrodes P1 and P2 of the horizontal charge transfer unit, high positional accuracy is required.

  As will be described later, the charge transfer electrodes P1 and P2 of the vertical charge transfer unit and the horizontal charge transfer unit are simultaneously formed in the same process during manufacturing.

  Next, a manufacturing procedure of the image sensor according to this embodiment will be described with reference to the drawings. 3 to 9 are simplified cross-sectional views showing the manufacturing procedure of the image sensor. 3A to 9A are cross-sectional views of the vertical charge transfer portion shown in FIG. 2A viewed in the direction of the arrow CC, and FIG. 3B to FIG. FIG. 2 shows a cross-sectional view of the horizontal charge transfer portion 14 shown in FIG. 2B as seen in the direction of arrow DD.

As shown in FIGS. 3A and 3B, a gate insulating film 2 is formed on the upper surface of a semiconductor substrate 1 made of silicon or the like. The gate insulating film 2 is formed by laminating a silicon oxide (SiO ₂ ) film 2a with a thickness of about 250 mm on the semiconductor substrate 1, and a silicon nitride (SiN) film 2b with a thickness of about 500 mm on the silicon oxide film 2a. The silicon oxide film 2c is stacked on the silicon nitride film 2b so as to have a thickness of about 50 mm. Each of the silicon oxide film 2c and the silicon nitride film 2b is formed by a CVD method. The silicon oxide film 2a is formed by thermal oxidation. Note that the gate insulating film 2 is not limited to the above configuration, and may be a two-layer structure including one silicon oxide film and one silicon nitride film, or may be a structure including only a silicon oxide film.

  An electrode layer P0 made of a silicon-based conductive material such as polysilicon is formed on the gate insulating film 2 by a CVD method. Here, the thickness of the electrode layer P0 was about 2000 mm.

  On the electrode layer P0, the silicon oxide film 3 is formed with a thickness of about 400 mm by CVD. The silicon oxide film 3 functions as an etching stop layer that stops etching in an etching process described later. The etching stop layer is not limited to the silicon oxide film 3, and other layers may be used.

  A polysilicon layer which is the same material as the electrode layer P0 is formed on the silicon oxide film 3 by CVD, and a patterning layer M2 is formed by a photolithography process using a mask. In the present embodiment, the pattern of the patterning layer M2 corresponds to the pattern of the second electrode P2 formed by a subsequent process. However, it is also possible to form the pattern of the patterning layer M2 so as to correspond to the pattern of the first electrode P1 formed in a subsequent process.

  After the patterning layer M2 is formed, as shown in FIG. 4B, impurity ions are implanted into the semiconductor substrate 1 on the horizontal charge transfer unit 14 side using the patterning layer M2 as a mask. Then, an impurity diffusion region 1a such as a charge accumulation region at the time of horizontal charge transfer is formed below the region where the patterning layer M2 is not formed on the upper surface of the semiconductor substrate 1. On the other hand, since the resist (not shown) is applied and covered on the vertical charge transfer portion side shown in FIG. 4A, impurity ions are not implanted.

  As shown in FIGS. 5A and 5B, after the impurity diffusion region 1a is formed on the horizontal charge transfer portion side, the patterning layer M2 on the silicon oxide layer 3 on the horizontal charge transfer portion side and the vertical charge transfer portion side is formed. A film made of the same silicon oxide is formed to a thickness of about 800 mm on the entire surface including the film by CVD. Thus, the silicon oxide layer 4 that covers the entire patterning layer M2 is formed on the electrode layer P0. The silicon oxide layer 4 can also be formed by thermally oxidizing the surface of the patterning layer M2.

  Next, as shown in FIGS. 6A and 6B, a layer made of the same material as the patterning layer M2 is formed on the silicon oxide layer 4 on the horizontal charge transfer portion side and the vertical charge transfer portion side by the CVD method. Then, a patterning layer M1 is formed by performing a planarization process by CMP (Chemical Mechanical Polishing). At this time, the surface of the silicon oxide layer 4 formed on the upper surface of the patterning layer M2 and the upper surface of the patterning layer M1 are formed to be the same surface. Here, the pattern of the patterning layer M1 corresponds to the pattern of the first electrode P1 formed in a subsequent process. In the present embodiment, of the patterning layers M1 and M2, the patterning layer formed in the same pattern as the pattern of the first electrode P1 is defined as the first patterning layer M1, and is formed in the same pattern as the pattern of the second electrode P2. The patterning layer is referred to as a second patterning layer M2, and the first patterning layer M1 and the second patterning layer M2 are collectively referred to as patterning layers M1 and M2.

  7A and 7B, a resist layer R is formed on the upper surface of the patterning layer M1 and the silicon oxide layer 4 using a mask in which an area including the photoelectric conversion portion PD in the imaging area 12 is opened. Then, the patterning layer M1 in the region where the resist layer R is opened is removed by a photolithography process, an opening of the photoelectric conversion unit PD is formed, and then the resist layer R is removed.

  Next, as shown in FIGS. 8A and 8B, the silicon oxide layer 4 on the horizontal charge transfer portion side and the vertical charge transfer portion side is etched. By doing so, the silicon oxide layer 4 on the upper and side surfaces of the patterning layers M1 and M2 is removed, and the silicon oxide layer 3 remains only between the patterning layers M1 and M2 and the electrode layer P0.

  With the patterning layers M1 and M2 exposed on the electrode layer P0, the electrode layer P0, the patterning layer M1, and the patterning layer M2 are etched. At this time, the patterning layer M1 and the patterning layer M2 are removed by etching, and the etching is stopped at the silicon oxide layer 3 formed thereunder. In addition, in the electrode layer P0, both the patterning layer M1 and the patterning layer M2 are formed thereabove, the region is removed by etching, and the gate insulating film 2 stops the etching.

  After the etching, as shown in FIGS. 9A and 9B, the first electrode P1 and the second electrode P2 are formed in a predetermined pattern on the gate insulating film 2, respectively.

  The manufacturing method of the imaging device 10 of the present invention includes a step of forming an electrode layer P0 for forming charge transfer electrodes P1 and P2 on an insulating film such as a gate insulating film 2 on a semiconductor substrate 1, and an electrode layer P0. A step of forming an etching stop layer thereon, and a pattern (at least in this embodiment, a pattern of the charge transfer electrode P2) having the same pattern as the charge transfer electrodes P1 and P2 on the etch stop layer; In addition, the patterning layer M2 made of the same conductive material is formed, and the electrode layer P0 and the patterning layers M1 and M2 are etched and stopped at the etching stop layer, thereby patterning the electrode layer P0 and transferring charges. Forming the electrodes P1 and P2. Further, in a state where only the patterning layer M2 of the charge transfer electrode P2 is formed, alignment by self-alignment can be performed by performing an ion implantation process on the semiconductor substrate 1 using the patterning layer M2 as a mask.

  According to the imaging device manufacturing method described above, the electrode layer P0 for forming the charge transfer electrodes P1 and P2 is formed, and the silicon oxide layer 3 functioning as an etching stop layer is formed on the electrode layer P0. After that, the silicon oxide layer 3 has a pattern (P2 pattern in the above embodiment) that is at least partly the same as the pattern of the charge transfer electrodes P1 and P2, and is made of the same conductive material. A patterning layer (second patterning layer M2 in the above embodiment) is formed. Thereafter, the electrode layer P0 and the patterning layer are etched. Since the electrode layer P0 and the patterning layer are made of the same material, during etching, the same amount is removed by etching under the same conditions. Since the electrode layer P0 below the patterning layer remains without being removed by the silicon oxide layer 3, only the electrode layer P0 in the region where the patterning layer is not formed above is removed by etching. Then, the electrode layer P0 remaining in the same pattern as the pattern of the patterning layer becomes the charge transfer electrodes P1 and P2 having the target pattern. Here, when the same patterning layer as the charge transfer electrode P2 is formed and ions are implanted into the semiconductor substrate 1 using the patterning layer as a mask, the electrode layer P0 and the patterning layer are etched, so that the ion-implanted region can be obtained. The charge transfer electrode P2 can be formed by self-alignment according to the position. In this way, when manufacturing an imaging device having no single-layer electrode structure, ion implantation can be performed by a self-alignment process, as in the case of the multilayer electrode structure, and a decrease in yield can be prevented. In particular, a portion where the position of the transfer electrode needs to be formed with high accuracy like the horizontal charge transfer electrode of the solid-state imaging device as in the above embodiment is reduced by a self-alignment process regardless of the electrode structure. And can be formed with high accuracy.

It is a figure which shows schematic structure of an image pick-up element. It is an enlarged view which shows the site | part of the image pick-up element shown in FIG. FIG. 11 is a cross-sectional view showing a manufacturing procedure on each of the vertical charge transfer unit side and the horizontal charge transfer unit side in the imaging device. FIG. 11 is a cross-sectional view showing a manufacturing procedure on each of the vertical charge transfer unit side and the horizontal charge transfer unit side in the imaging device. FIG. 11 is a cross-sectional view showing a manufacturing procedure on each of the vertical charge transfer unit side and the horizontal charge transfer unit side in the imaging device. FIG. 11 is a cross-sectional view showing a manufacturing procedure on each of the vertical charge transfer unit side and the horizontal charge transfer unit side in the imaging device. FIG. 11 is a cross-sectional view showing a manufacturing procedure on each of the vertical charge transfer unit side and the horizontal charge transfer unit side in the imaging device. FIG. 11 is a cross-sectional view showing a manufacturing procedure on each of the vertical charge transfer unit side and the horizontal charge transfer unit side in the imaging device. FIG. 11 is a cross-sectional view showing a manufacturing procedure on each of the vertical charge transfer unit side and the horizontal charge transfer unit side in the imaging device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Gate insulating film 3 Silicon oxide layer (etching stop layer)
10 Image sensor M1 1st patterning layer (patterning layer)
M2 Second patterning layer (patterning layer)
P0 electrode layer P1 first electrode (charge transfer electrode)
P2 Second electrode (charge transfer electrode)

Claims (7)

A method for manufacturing an imaging device, comprising: a semiconductor substrate; a photoelectric conversion unit formed on the semiconductor substrate; and a charge transfer electrode that transfers a signal charge generated by the photoelectric conversion unit on the semiconductor substrate,
Forming an electrode layer on the semiconductor substrate for forming the charge transfer electrode via an insulating film;
Forming an etch stop layer on the electrode layer;
Forming a patterning layer on the etching stop layer, having a pattern that is at least partially the same as the pattern of the charge transfer electrode, and made of the same conductive material;
Etching the electrode layer and the patterning layer and stopping at the etching stop layer, thereby patterning the electrode layer to form the charge transfer electrode.   The method for manufacturing an image pickup device according to claim 1, further comprising a step of performing ion implantation on the semiconductor substrate using the patterning layer as a mask. The charge transfer electrode has a first electrode and a second electrode formed in a predetermined pattern on the semiconductor substrate via the insulating film, and has the same pattern as the pattern of the first electrode. Forming a layer;
Performing ion implantation on the semiconductor substrate using the first patterning layer as a mask;
Forming an oxide film on the first patterning layer;
Forming a layer of the same conductive material as the first patterning layer on the oxide film, and then forming a second patterning layer for patterning the second electrode by planarization;
Etching the oxide film;
3. The method includes: patterning the electrode layer to form the charge transfer electrode by etching the first patterning layer, the second patterning layer, and the electrode layer. The manufacturing method of the image pick-up element of description.   The etching stop layer formed under the first patterning layer and the oxide film formed under the second patterning layer are made of the same material, and etching is stopped at the oxide film and the etching stop layer. The method for manufacturing an imaging device according to claim 3, further comprising: etching the electrode layer, the first patterning layer, and the second patterning layer to pattern the electrode layer.   5. The method of manufacturing an image pickup device according to claim 1, wherein the charge transfer electrode is a horizontal charge transfer electrode in which two electrodes are alternately arranged in a straight line.   6. The method for manufacturing an image pickup device according to claim 1, wherein the electrode layer is made of a silicon-based conductive material.   An image pickup device manufactured by the method for manufacturing an image pickup device according to any one of claims 1 to 6.

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