JP2003078126A - Solid-state imaging element and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve light reception sensitivity and image quality in an imaging part, as well as transfer efficiency in a horizontal transmission register and make a unit cell finer. SOLUTION: A vertical transfer register 120 is provided with a transfer electrode 122 formed of metal electrode with a single-layer structure, and a horizontal transfer register 130 is provided with a lower-layer transfer electrode 132 made of polysilicon film and an upper-layer transfer electrode 133 formed of metal electrode made of tungsten or the like. In addition, the barier layer 134 in a transfer part is formed through ion implantation by which the polysilicon film of the lower-layer transfer electrode 132 is self-aligned, in the horizontal transfer register 130. The metal electrode films as the transfer electrode 122 of the vertical transfer register 120, and the upper-layer transfer electrode 133 of the horizontal transfer register 130, are manufactured through a simultaneous step.

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 sensor used as a two-dimensional image sensor or the like and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, in this type of solid-state image sensor,
An image of a subject is picked up by a large number of photosensors arranged in a two-dimensional matrix, and signal charges accumulated in each photosensor are sequentially transferred in the vertical direction by a vertical transfer register provided for each photosensor column. Then, the signal charges transferred from the vertical transfer register are sequentially read out to the horizontal transfer register, sequentially transferred in the horizontal direction and sent to the output section, and the output section converts the signal charge into a voltage signal and outputs it. Each transfer register is provided with a channel layer for transferring signal charges in a semiconductor substrate, and two superposed transfer electrodes are sequentially arranged on the channel layer along the transfer direction, and each transfer electrode has two phases or four phases. By applying a phase transfer clock, the signal charges read from the read gate into the channel layer are sequentially transferred.

[0003]

By the way, in the solid-state image pickup device having the above-mentioned structure, when the number of pixels for obtaining a high-definition image is increased, high-speed driving becomes necessary, and a unit pixel (unit It is also necessary to miniaturize the cell. However, when the transfer electrode is formed of a polysilicon film, if the unit cell is miniaturized, the transfer electrode needs to be thinned due to processing restrictions, and it is also necessary to reduce the width of the transfer electrode between each pixel. Therefore, it becomes necessary to form the transfer electrode with a thin polysilicon film having a small width, which increases the resistance in the polysilicon film and causes a problem that the amount of charge Qv handled by the register decreases due to propagation delay. . On the other hand, when a metal electrode such as tungsten having a low resistance is used instead of the polysilicon film, the occurrence rate of the white spot phenomenon increases due to the heat treatment such as oxidation, which causes a problem that the image quality deteriorates.
Further, since the metal electrode cannot be oxidized, there arises a problem that it is difficult to form the upper interlayer insulating film (even if it can be formed, the interlayer withstand voltage is low).

Therefore, as a method for solving such a problem, a single-layer electrode CCD has been proposed (Japanese Patent Laid-Open No. 5-3).
155). However, in this case, there is a drawback that the barrier layer of the horizontal transfer register cannot be formed by self-alignment. As a method of constructing the horizontal transfer register with a single-layer electrode, an attempt has been made to change the gate oxide film thickness of the storage section and the transfer section for transferring the signal charge (Technical Report of the Institute of Image Information and Television Engineers, "Single Layer"). p
Structure and Features of FT-CCD Image Sensor Formed by PolySi Electrode "ITE Technical Report Vol.23, No.49, P
P.31-36 IPU'99-50 (Jul, 1999)), a crystal defect occurs at the edge of the LOCOS portion, and there is a problem that the horizontal transfer efficiency decreases.

Therefore, an object of the present invention is to provide a solid-state image pickup device capable of miniaturizing a unit cell while improving the light receiving sensitivity and image quality in the image pickup section and the transfer efficiency in the horizontal transfer register, and a manufacturing method thereof. To do.

[0006]

In order to achieve the above-mentioned object, the present invention comprises photosensors arranged in a two-dimensional matrix, and a plurality of vertical transfer registers for vertically transferring the signal charges of the photosensors. In a solid-state imaging device including a horizontal transfer register that transfers the signal charge transferred from the vertical transfer register to an output unit, the vertical transfer register has a transfer electrode having a single-layer structure, and the horizontal transfer register has a lower layer. It has a two-layer structure transfer electrode composed of a transfer electrode and an upper transfer electrode, and at least the lower transfer electrode of the horizontal transfer register is formed of a polysilicon electrode or a silicide electrode.

According to the present invention, the photosensors are arranged in a two-dimensional matrix in the vertical and horizontal directions, a plurality of vertical transfer registers for transferring the signal charges of the photosensors in the vertical direction, and the vertical transfer registers. In a method of manufacturing a solid-state imaging device including a horizontal transfer register that transfers transferred signal charges to an output section, a lower transfer electrode that constitutes a transfer electrode having a two-layer structure of the horizontal transfer register is made of polysilicon or silicide. Forming process,
Forming a single-layered transfer electrode of the vertical transfer register and an upper-layered transfer electrode constituting the two-layered transfer electrode of the horizontal transfer register.

In the solid-state imaging device of the present invention, the transfer electrode of the vertical transfer register has a single-layer structure, and the transfer electrode of the horizontal transfer register has a two-layer structure composed of a lower transfer electrode and an upper transfer electrode, and at least the horizontal transfer register. Since the lower transfer electrode is formed of a polysilicon electrode or a silicide electrode, the vertical transfer register arranged in the imaging unit can be thinned and miniaturized by a single-layer thin transfer electrode, and the horizontal transfer register In this case, the transfer electrode having the two-layer structure can ensure high transfer efficiency, and high-speed driving becomes possible. Further, since the lower transfer electrode of the horizontal transfer register is a polysilicon electrode or a silicide electrode, the lower transfer electrode can be used to form a barrier layer by adding impurities by self-alignment. It can contribute to the improvement of transfer efficiency.

Further, according to the manufacturing method of the present invention, when the transfer electrode having the single-layer structure of the vertical transfer register and the transfer electrode having the two-layer structure of the horizontal transfer register are manufactured, the transfer electrode in the lower layer of the horizontal transfer register is It is made of silicon or silicide, and the transfer electrode of the vertical transfer register and the transfer electrode of the upper layer of the horizontal transfer register are formed on the upper layer, so that the self-alignment is performed by using the transfer electrode of the lower layer of polysilicon or the silicide of the horizontal transfer register. It is possible to form the barrier layer of the horizontal transfer register by the above, and it is possible to easily improve the transfer efficiency of the horizontal transfer register.

[0010]

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.

FIG. 1 is a schematic plan view showing an example of a solid-state image pickup device according to an embodiment of the present invention. The solid-state image sensor is configured as a two-dimensional image sensor, and has an image pickup unit 100 that picks up an image of a subject and an output unit 200 that outputs an image pickup signal from the image pickup unit 100 to the outside.
The image pickup unit 100 has a vertical (V) direction and a horizontal (H) direction.
Photosensors 110 that form a large number of unit pixels (unit cells) arranged in a three-dimensional matrix, and are arranged for each photosensor column in the vertical direction.
And a plurality of vertical transfer registers 120 for vertically transferring the signal charges of. In addition, a horizontal transfer register 130 that horizontally transfers the signal charges transferred from each vertical transfer register 120 is arranged on the side of the imaging unit 100, and the output unit 200 is provided at the end of the horizontal transfer register 130. It is provided. Further, an on-chip lens (OCL), a color filter, etc., which are not shown, are arranged on the upper surface of the image pickup unit 100, and control the incidence of light on the light receiving unit of each photosensor 110.

In such a solid-state image pickup device, the signal charges accumulated by the photosensor 110 are read out to the vertical transfer register 120 via a read gate (not shown), and the signal charges are sequentially transferred in the vertical direction. And
The signal charges transferred from the vertical transfer register 120 are sequentially read out to the horizontal transfer register 130, which are sequentially transferred in the horizontal direction and sent to the output unit 200. The output unit 200 converts the signal charge transferred by the horizontal transfer register 130 into a voltage signal and outputs the voltage signal.

FIG. 2 shows the vertical transfer register 1 in this example.
It is sectional drawing which shows the structure of 20, and has shown the AA line cross section of FIG. Further, FIG. 3 is a plan view showing the shape of the transfer electrode 122 of the vertical transfer register 120. The vertical transfer register 120 has an embedded CCD structure, and has an n-type S
The p-type well region 20 is formed in the i-substrate 10, and the n-type layer 30 is provided on the p-type well region 20 as a channel layer for transferring signal charges. Then, a transfer electrode 122 made of a metal electrode having a single-layer structure is provided on the upper surface of the channel layer via an insulating film 40, and a vertical transfer clock is supplied to the transfer electrode 122 to control the gate voltage of the channel layer. , Transfer signal charges. The transfer electrode 122 of this example is
For example, it is formed of tungsten (W), is formed in a pattern that avoids the light receiving portion 110A of the photosensor as shown in FIG. 3, and is provided so as not to overlap in the signal charge transfer direction (V). . It should be noted that each of the transfer electrodes 12 is formed on the n-type layer 30 of the vertical transfer register 120.
The p- region 3 in which impurities such as boron are ion-implanted for potential adjustment for canceling charge accumulation (so-called dip) due to the absence of transfer electrodes in the gap portion 2
Two are provided.

FIG. 4 shows the horizontal transfer register 1 in this example.
It is sectional drawing which shows the laminated structure in each electrode manufacturing process of 30, and has shown the BB sectional view of FIG. Like the vertical transfer register 120, the horizontal transfer register 130 also has a buried CCD structure, forms the p-type well region 20 in the n-type Si substrate 10, and has an n-type layer as a channel layer for transferring signal charges thereabove. 30 is provided. In addition,
The p-type well region 20 and the n-type layer 30 may be common to the vertical transfer register 120 and the horizontal transfer register 130, or may be common. The horizontal transfer register 130 has a transfer electrode having a two-layer structure provided on the channel layer with the insulating film 40 interposed therebetween. The lower transfer electrode 132 is made of a polysilicon electrode and the upper layer transfer is made of a metal electrode. An electrode 133 is provided, and these transfer electrodes 13
A signal charge is transferred by supplying a horizontal transfer clock to 2 and 133 to control the gate voltage of the channel layer.

The lower transfer electrode 132 is made of a polysilicon film, and the upper transfer electrode 133 is formed of tungsten (W) common to the transfer electrode 122 of the vertical transfer register 120 described above, and is formed in a common process. Also,
The lower layer transfer electrode 132 of the horizontal transfer register 130 is arranged corresponding to each storage unit that stores the signal charge of the channel layer, and the upper layer transfer electrode 133 transfers the signal charge stored in each storage unit to the next storage unit. It is arranged corresponding to the transfer part to be transferred. A barrier layer 134 is formed of p-type impurities in the upper layer of the transfer portion. The barrier layer 134 is one in which impurities such as boron are ion-implanted by self-alignment using the polysilicon film of the lower layer transfer electrode 132 as a mask.

Next, the vertical transfer register 12 as described above
The manufacturing process of 0 and the horizontal transfer register 130 will be described. First, after forming the photosensor 110 and the channel layers of the respective resistors 120 and 130 on the Si substrate 10, the insulating film 40 is formed, and as shown in FIG.
A lower transfer electrode 132 of the horizontal transfer register 130 is formed of a polysilicon film. Next, this lower layer transfer electrode 13
Boron etc. are ion-implanted by 2 self-alignment,
The barrier layer 134 is formed. Next, as shown in FIG. 4B, a polysilicon oxide film 140 is provided on the upper layer of the lower layer transfer electrode 132 by thermal oxidation or the like.
As shown in (C), the transfer electrode 122 of the vertical transfer register 120 and the upper layer transfer electrode 13 of the horizontal transfer register 130.
3 is formed by a simultaneous process. The upper layer transfer electrode 133 of the horizontal transfer register 130 is the lower layer transfer electrode 132.
Are formed so as to partially overlap with each other, and improve the transfer efficiency of the horizontal transfer register 130.

In the solid-state image pickup device of the present example as described above, the following effects can be obtained. (1) Since the resistivity of tungsten is smaller than that of polysilicon by one digit or more, sufficient transfer characteristics can be obtained even if the transfer electrode of the vertical transfer register has a single layer structure.
It is possible to suppress the width between pixels in the imaging unit to be equal to or smaller than the conventional one. (2) Since it is not necessary to perform heat treatment such as oxidation after forming the metal electrode of tungsten, it is possible to suppress deterioration of image quality such as a white spot phenomenon. (3) Since the height of the transfer electrode of the vertical transfer register in the image pickup section can be reduced, the light collection efficiency of the on-chip lens provided in the upper layer can be improved and the light receiving sensitivity can be improved. (4) In the horizontal transfer register, the ion implantation of the barrier layer can be formed by self-alignment, and a decrease in horizontal transfer efficiency can be prevented. (5) Since the transfer electrode of the transfer unit has a lower resistance than the transfer electrode of the storage unit of the horizontal transfer register, the transfer unit rises earlier than the storage unit,
Further, the transfer efficiency can be improved.

Although polysilicon is used as the lower layer transfer electrode of the horizontal transfer register in the above example, silicide such as tungsten may be used instead. Further, although the metal electrode of tungsten is used as the transfer electrode of the vertical transfer register and the upper transfer electrode of the horizontal transfer register, a metal electrode such as Mo may be used, and polysilicon or silicide may be used. Is also possible.

[0019]

As described above, in the solid-state image pickup device of the present invention, the transfer electrode of the vertical transfer register has a single layer structure,
The transfer electrode of the horizontal transfer register has a two-layer structure including a lower transfer electrode and an upper transfer electrode, and at least the lower transfer electrode of the horizontal transfer register is formed of a polysilicon electrode or a silicide electrode. Therefore, in the vertical transfer register arranged in the image pickup unit, thinning and miniaturization can be performed by the single-layer thin transfer electrode, and in the horizontal transfer register, the high transfer efficiency can be ensured by the transfer electrode having the two-layer structure and the high speed. It becomes possible to drive. Further, since the lower transfer electrode of the horizontal transfer register is a polysilicon electrode or a silicide electrode, the lower transfer electrode can be used to form a barrier layer by adding impurities by self-alignment. It can contribute to the improvement of transfer efficiency.

Further, according to the manufacturing method of the present invention, when the transfer electrode having a single-layer structure of the vertical transfer register and the transfer electrode having a two-layer structure of the horizontal transfer register are manufactured, the transfer electrode in the lower layer of the horizontal transfer register is made of poly. It is formed of silicon or silicide, and the transfer electrode of the vertical transfer register and the transfer electrode of the upper layer of the horizontal transfer register are formed on the upper layer. Therefore, it is possible to form the barrier layer of the horizontal transfer register by self-alignment by using the polysilicon or silicide transfer electrode below the horizontal transfer register, and it is possible to easily improve the transfer efficiency of the horizontal transfer register. Become.

[Brief description of drawings]

FIG. 1 is a schematic plan view showing an example of a solid-state image sensor according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the structure of a vertical transfer register of the solid-state image sensor shown in FIG.

3 is a plan view showing a shape of a transfer electrode of the vertical transfer register shown in FIG.

FIG. 4 is a cross-sectional view showing a laminated structure in each electrode manufacturing process of the horizontal transfer register of the solid-state imaging device shown in FIG.

[Explanation of symbols]

10 ... n-type Si substrate, 20 ... p-type well region, 30
... n-type layer, 40 ... insulating film, 100 ... imaging section, 11
0 ... Photo sensor, 110A ... Light receiving part, 120 ...
Vertical transfer register, 122 ... Transfer electrode, 130 ... Horizontal transfer register, 132 ... Lower layer transfer electrode, 133 ...
Upper transfer electrode, 134 ... Barrier layer, 140 ... Polysilicon oxide film, 200 ... Output section.

Claims (11)

[Claims] 1. Photosensors arranged in a two-dimensional matrix, a plurality of vertical transfer registers for vertically transferring signal charges of the photosensors, and signal charges transferred from the vertical transfer registers to an output section. In a solid-state imaging device having a horizontal transfer register for transferring, the vertical transfer register has a transfer electrode having a single-layer structure, and the horizontal transfer register has a transfer structure having a two-layer structure including a lower-layer transfer electrode and an upper-layer transfer electrode. A solid-state imaging device having an electrode, wherein at least a transfer electrode in a lower layer of the horizontal transfer register is formed of a polysilicon electrode or a silicide electrode. 2. The solid-state image pickup device according to claim 1, wherein a transfer electrode of the vertical transfer register is made of a metal electrode. 3. The solid-state imaging device according to claim 1, wherein the transfer electrode of the vertical transfer register is made of a polysilicon electrode or a silicide electrode. 4. The solid-state imaging device according to claim 1, wherein the transfer electrode in the upper layer of the horizontal transfer register is made of a metal electrode. 5. The solid-state imaging device according to claim 1, wherein the transfer electrode in the upper layer of the horizontal transfer register is made of a polysilicon electrode or a silicide electrode. 6. The solid-state image sensor according to claim 1, wherein the transfer electrode of the vertical transfer register and the transfer electrode of the upper layer of the horizontal transfer register are formed of metal electrodes in the same layer. 7. The solid-state image sensor according to claim 1, wherein the horizontal transfer register has a barrier layer of a transfer portion formed by self-alignment of a lower transfer electrode. 8. Photosensors arranged in a two-dimensional matrix in the vertical and horizontal directions, a plurality of vertical transfer registers for transferring signal charges of the photosensors in the vertical direction, and a plurality of vertical transfer registers transferred from the vertical transfer registers. A method of manufacturing a solid-state imaging device, comprising: a horizontal transfer register that transfers signal charges to an output section, wherein a lower transfer electrode that constitutes a transfer electrode having a two-layer structure of the horizontal transfer register is formed of polysilicon or silicide. And a step of forming a single-layered transfer electrode of the vertical transfer register and an upper-layered transfer electrode that constitutes a two-layered transfer electrode of the horizontal transfer register. Production method. 9. A transfer electrode having a single-layer structure of the vertical transfer register and an upper-layer transfer electrode forming a transfer electrode having a two-layer structure of the horizontal transfer register are formed by metal electrodes. A method for manufacturing the solid-state imaging device according to claim 1. 10. The method according to claim 8, further comprising a step of forming a barrier layer of a transfer portion of the horizontal transfer register by self-alignment of the transfer electrode of the lower layer.
A method for manufacturing the solid-state imaging device according to claim 1. 11. The method of manufacturing a solid-state image sensor according to claim 8, wherein an insulating film between the lower transfer electrode of the horizontal transfer register and the upper transfer electrode is formed by thermal oxidation.