JP5035452B2 - Solid-state imaging device - Google Patents

Description

The present invention provides a semiconductor device for forming a variety of elements into a plurality of layers of the semiconductor substrate, it relates to a solid-state imaging equipment in which a separation layer capable of effectively insulating isolation between the plurality of layers, in particular back-illuminated solid-state those related to the imaging equipment.

Conventionally, in a solid-state imaging device such as a CCD image sensor or a CMOS image sensor, a photoelectric conversion element such as a photodiode on one side of a semiconductor substrate, a CCD register or a transistor circuit for reading a signal charge generated by the photoelectric conversion element, etc. Various elements are integrated, and the light received by the light receiving portion of the photoelectric conversion element is converted into a pixel signal and output.
However, in such a solid-state imaging device, since the elements are concentrated on one side of the semiconductor substrate, the light receiving area of the photoelectric conversion element in each pixel is restricted by the arrangement space of other elements, and the light receiving sensitivity is hindered. This may be a factor or an obstacle to downsizing and increasing the number of pixels of the solid-state imaging device.
Therefore, as a configuration for solving such a problem, a structure in which a light receiving portion of a photoelectric conversion element is provided on one surface (back surface) of a semiconductor substrate and an element such as a transistor or its wiring is disposed on the opposite surface is proposed. Yes. Such a solid-state imaging device is called a so-called back-illuminated solid-state imaging device (see, for example, Patent Document 1).

JP 2003-31785 A

However, in the backside illumination type solid-state imaging device as described above, it is difficult to electrically separate the photoelectric conversion element formed on the back surface side of the semiconductor substrate and the transistor formed on the front surface side.
For this reason, electrons generated in the transistor wrap around to the photoelectric conversion element side to become a false signal, or conversely, electrons converted photoelectrically on the photoelectric conversion element side will affect the operating characteristics of the transistor, It was causing characteristic problems.
Such a problem is not limited to a back-illuminated solid-state imaging device, and is also necessary for insulating and separating each element layer in a semiconductor device in which a plurality of element layers are formed in a semiconductor substrate. is there.

The present invention aims to provide a solid-state imaging equipment capable of effectively insulating isolation between the plurality of layers in a semiconductor device for forming a variety of elements into a plurality of layers of the semiconductor substrate.

To achieve the above object, a first element layer including a photoelectric conversion element formed on the first surface side of the semiconductor substrate and a second element including a pixel transistor formed on the second surface side of the semiconductor substrate. An isolation layer formed by ion implantation of impurity ions between the photoelectric conversion element and the pixel transistor at a boundary portion between the first element layer and the second element layer of the semiconductor substrate, and the semiconductor A wiring layer that constitutes various signal lines formed on the second surface of the substrate, the element isolation layer is formed of an oxide film, and the element isolation layer has a missing portion for passing electric charge. Features.

According to the solid-state imaging device of the present invention, the boundary between the first element layer on the first surface side where the photoelectric conversion element of the semiconductor substrate is formed and the second element layer on the second surface side where various circuit elements are formed. Since the element isolation layer is formed by ion implantation of impurity ions, the two element layers provided on both sides of the substrate can be effectively and easily separated and signal charges between the photoelectric conversion element and various circuit elements are improper. It is possible to prevent solid leakage and to provide a solid-state imaging device with good characteristics.

It is sectional drawing which shows the manufacturing process of the solid-state imaging device by the Example of this invention. It is sectional drawing which shows the manufacturing process of the solid-state imaging device by the Example of this invention. It is sectional drawing which shows the manufacturing process of the solid-state imaging device by the Example of this invention. It is sectional drawing which shows the manufacturing process of the solid-state imaging device by the Example of this invention.

In the embodiment of the present invention, a light receiving portion of a photoelectric conversion element (photodiode) is intensively arranged on one surface (back surface) of a semiconductor substrate, and a circuit such as a pixel transistor is formed on the opposite surface (front surface). In a back-illuminated solid-state imaging device having a wiring layer disposed thereon, the element isolation layers on the light receiving unit side and the circuit side are implanted into the semiconductor substrate by oxygen ion implantation through a predetermined mask pattern and subsequent heat treatment. This is realized by forming an oxide film.
Specifically, for example, an oxygen as a photoelectric conversion element layer and an element separation layer from a silicon substrate (surface) side with respect to a semiconductor substrate in which a silicon layer is provided on a support substrate portion (insulator layer) such as an SOI substrate. Circuit layers such as an ion implantation layer and a pixel transistor are sequentially formed, and then a wiring layer is formed on the silicon layer. Then, by removing the insulator layer on the back surface side, the light receiving portion of the silicon layer is exposed, and a solid-state imaging device made of a thin silicon substrate can be formed. The heat treatment for oxygen ions can be performed by thermal oxidation with oxygen ions without providing a new heat treatment step by using, for example, a heat diffusion step in another ion implantation region or a heat treatment necessary for sintering an aluminum wiring. Heat treatment can be performed.
The semiconductor substrate used in the present invention is an SOI substrate as described above, a thin silicon substrate formed by removing the support substrate portion from the SOI substrate, and various types used for various semiconductor manufacturing. It means that a substrate having a semiconductor layer is widely included, and can be widely applied as a structure for separating a plurality of element layers formed in the thickness direction on the semiconductor layer of such a substrate.

1 to 4 are cross-sectional views showing a manufacturing process of a solid-state imaging device according to an embodiment of the present invention.
First, in FIG. 1, a plurality of photodiodes 11 are formed as photoelectric conversion element layers in a predetermined depth region of the silicon layer 10 </ b> A of the SOI substrate 10. Note that the solid-state imaging device of this embodiment is an area sensor, and the photodiodes 11 are formed in a two-dimensional array with a predetermined pattern. The formation process of this photodiode is the same as that of the conventional solid-state imaging device.
Next, in FIG. 2, oxygen ion implantation is performed on the upper layer of the photoelectric conversion element layer of the silicon layer 10 </ b> A to form an element isolation layer 12 that separates a plurality of element layers formed side by side in the thickness direction of the substrate. To do. In this ion implantation, by using photolithography and etching techniques using a predetermined mask pattern such as a photoresist, a portion necessary for conduction between the photodiode and the pixel transistor circuit is partially implanted without implanting ions. The missing element isolation layer 12 is formed. As ions to be implanted, for example, O + ions can be used, and further compound ions containing oxygen may be used.

Next, in FIG. 3, the pixel transistor circuit 14 and the like are formed as circuit element layers on the uppermost layer of the silicon layer 10A. As the pixel transistor, a transfer transistor that transfers signal charges generated by the photodiode to the floating diffusion portion, an amplification transistor that converts the potential of the floating diffusion portion into a pixel signal, and an output timing of the pixel signal are selected. Each of the MOS transistors such as a selection transistor and a reset transistor that resets the potential of the floating diffusion portion is formed in the same manner as a conventional solid-state imaging device.
Next, an upper layer film such as the gate insulating film 16, the gate electrode 18, the interlayer insulating film 20, and the wiring film 22 is patterned on the silicon layer 10A. This formation process is the same as that of the conventional solid-state imaging device.

Then, in FIG. 4, the front and back of the semiconductor substrate 10 are reversed, and the insulator layer 10B is removed by CMP or the like, thereby exposing the light receiving portion of the photodiode 11.
Note that a color filter, an on-chip lens, and the like are further mounted on the light receiving portion of the photodiode 11 via a protective film or the like, but these are the same as those of the conventional solid-state imaging device. The description is omitted.
Further, in the process after the oxygen ion implantation described above, various heat treatments necessary for film formation and the like are performed. The ion implantation region is heat-treated by this heat treatment, recovery of crystal defects caused by the oxygen ion implantation, and more. A high-quality oxide film can be formed. Note that the heat treatment in this case may be performed not only by using a heat treatment necessary for other film formation, but also by adding a dedicated heat treatment step for the oxygen ion implantation region and under optimum conditions.

In the above embodiment, the element isolation layer is formed using oxygen ions. However, the element isolation layer may be formed using impurity ions other than oxide ions as long as the layer can prevent charge leakage. .
In the embodiment, the example using the SOI substrate has been described, but another semiconductor substrate may be used. That is, the semiconductor substrate used in the present invention is an SOI substrate as described above, a thin silicon substrate formed by removing the support substrate portion from the SOI substrate, and various types used for various semiconductor manufacturing. A substrate having a semiconductor layer is widely included.
The present invention can be applied not only to a CMOS solid-state image pickup device having a pixel transistor as described above but also to a CCD solid-state image pickup device, and further to a method for manufacturing a semiconductor device other than a solid-state image pickup device. Is also widely applicable.

DESCRIPTION OF SYMBOLS 10 ... SOI substrate, 11 ... Photodiode, 12 ... Element isolation layer, 14 ... Pixel transistor circuit, 16 ... Gate insulating film, 18 ... Gate electrode, 20 ... Interlayer insulating film, 22 ... Wiring film

Claims (1)

A first element layer including a photoelectric conversion element formed on the first surface side of the semiconductor substrate;
A second element layer including a pixel transistor formed on the second surface side of the semiconductor substrate;
An element isolation layer formed by ion implantation of impurity ions between the photoelectric conversion element and the pixel transistor at a boundary between the first element layer and the second element layer of the semiconductor substrate;
Wiring layers constituting various signal lines formed on the second surface of the semiconductor substrate;
Have
The solid-state imaging device , wherein the element isolation layer is formed of an oxide film, and the element isolation layer has a missing portion for allowing electric charges to pass therethrough.

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