JP2012060143A - Solid state imaging device and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid state imaging device in which a sufficient light-blocking effect is attained in a black reference pixel without increasing number of steps, and to provide its manufacturing method.SOLUTION: In a solid state imaging device having a wiring layer 60, the wiring layer 60 and a contact pad 30 are constituted of metal layers of different constitutive material. Since a light blocking layer 70 formed on a black reference pixel 2SB is constituted of a metal layer formed simultaneously with the metal layer of the contact pad 30, the number of manufacturing steps is not increased and since the light blocking layer is constituted of the metal layer, light can be blocked surely and a black level signal can be obtained correctly.

Description

  The present invention relates to a solid-state imaging device suitable for application to a CMOS sensor and a manufacturing method thereof.

The solid-state imaging device includes an imaging region portion in which imaging pixels having photoelectric conversion elements are arranged, a peripheral circuit portion, an external lead contact pad, a black reference pixel, and a wiring layer.
A light shielding layer is formed on at least the black reference pixel, and further on the peripheral circuit, for example.
In this solid-state imaging device, an electric signal is obtained by a signal charge generated in accordance with the amount of light received by the imaging pixel. For example, a thermal charge is generated and mixed with the signal charge.
Therefore, a black reference pixel that is shielded from light is provided in the imaging region or the periphery thereof, thereby obtaining a black reference level signal, and detecting the signal level due to thermal charge or the like to correct the received light signal. (For example, refer to Patent Document 1).

In the above-described configuration, various methods have been proposed and implemented as a light shielding method for the black reference pixel. For example, in the process of forming color filters for each color formed in the imaging region portion, the light-shielding layer is formed by laminating one or two color filters on the black reference pixel. In this case, there is an advantage that an extra process for forming the light shielding layer is avoided.
However, it is desirable that the black reference pixel be shielded as reliably as possible in order to obtain an accurate black reference level signal.
Therefore, in order to complete such light shielding, there is a case where, for example, an Al metal layer is specifically formed on the light shielding portion for the purpose of light shielding only. In this case, however, the number of processes increases.

  In addition, when the wiring layer described above has a multilayer wiring structure having a three-layer structure including, for example, first to third metal layers, for example, this is a first and second two-layer structure, and the third metal layer is It is conceivable to design the light-shielding layer. In this case, however, the wiring patterns of the first and second metal layers constituting the wiring layer are complicated, and the occupied area becomes large, and the occupied area of the pixel is increased. Increases, which hinders high density of pixel arrangement.

JP 2000-31450 A

The present invention provides a solid-state imaging device and a method for manufacturing the same that do not increase the number of steps as described above, and can sufficiently obtain a light shielding property in a black reference pixel.
That is, for example, a CMOS sensor in a solid-state imaging device has a high sensitivity because a CMOS circuit detects and amplifies a signal charge generated according to the amount of light received by a photodiode of a photoelectric conversion element for each pixel. In addition, the signal transmission circuit is less susceptible to noise.
In this CMOS solid-state imaging device, there is a high demand for reducing the width and thickness of the wiring layer as the pixels become finer and denser in line with higher image quality. A layer, generally composed of Cu.
However, since contact pads for external leads are not satisfactorily bonded to lead wires or the like, they are usually composed of a metal layer Al or an Al alloy layer different from the metal layer constituting the wiring layer.

  In the present invention, a solid-state imaging device and a method for manufacturing the same capable of reliably performing the light shielding without increasing the number of steps in forming the light shielding film or the like of the black reference pixel in view of this. Is to provide.

  That is, a solid-state imaging device according to the present invention includes an imaging region portion in which imaging pixels having photoelectric conversion elements are arranged, a peripheral circuit portion, an external lead contact pad, a black reference pixel, and a wiring layer, A fixed imaging device in which a wiring layer and the contact pad are formed of metal layers having different constituent materials, wherein a light shielding layer is formed at least on the peripheral circuit portion and the black reference pixel, and the light shielding The layer is constituted by a metal layer formed simultaneously with the metal layer of the contact pad.

In the method for manufacturing a semiconductor device according to the present invention, a step of forming at least an imaging region portion in which pixels having photoelectric conversion elements are arranged, a peripheral circuit portion, and a black reference pixel on a substrate;
A step of forming a wiring layer of the imaging region portion and the peripheral circuit portion; a step of forming a contact pad of an external lead; and a step of simultaneously forming a light shielding layer on at least the peripheral circuit portion and the black reference pixel by the same metal layer It is characterized by having.

  Further, the present invention is the above-described solid-state imaging device according to the present invention and the manufacturing method thereof, wherein the wiring layer is formed of copper (Cu), and the contact pad and the light shielding layer are formed of aluminum (Al) or aluminum. It is characterized by being formed of a Cu alloy (Al—Cu).

  In the solid-state imaging device and the manufacturing method thereof according to the present invention, as in the above-described CMOS, the wiring layer is configured by a metal layer having high conductivity, and the contact pad is formed by a metal layer different from this. Since the light shielding layer is formed simultaneously with the formation of the contact pad with the metal layer that forms the contact pad, the number of steps for forming the light shielding layer is not increased. Further, since the light shielding layer is made of a metal layer, in particular, the same light shielding layer as the relatively thick metal layer constituting the contact pad, it has a sufficient function as the light shielding layer and can be formed as a complete light shielding layer. it can. Therefore, accurate black level signals can be detected, and high-quality imaging can be performed.

It is a block diagram which shows the structure of an example of the imaging device by this invention. It is a circuit diagram of an imaging pixel of an example of an imaging device by the present invention. It is a mechanical sectional view of an example of an embodiment of a solid-state imaging device according to the present invention. It is a schematic sectional drawing of the principal part of an example of this invention apparatus. It is a schematic sectional drawing in one process of an example of this invention manufacturing method. It is a schematic sectional drawing in one process of an example of this invention manufacturing method. It is a schematic sectional drawing in one process of an example of this invention manufacturing method. It is a schematic sectional drawing in one process of an example of this invention manufacturing method. It is a schematic sectional drawing in one process of an example of this invention manufacturing method. It is a schematic sectional drawing in one process of an example of this invention manufacturing method.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to these embodiments.
First, a solid-state imaging device according to the present invention will be described.
FIG. 1 is a block diagram showing a configuration of a solid-state imaging device according to the present invention, in this example, a CMOS solid-state imaging device (image sensor).
In this CMOS solid-state imaging device 1, an imaging pixel region 3 in which a plurality of (many) imaging pixels 2 including photoelectric conversion elements are two-dimensionally arranged in a matrix on a substrate 100 such as a silicon substrate, and its peripheral circuit unit 40 includes a vertical driving circuit 4, a column signal processing circuit 5, a horizontal driving circuit 6, an output circuit 7, a control circuit 8, and the like.
Further, contact pads 30 are arranged on the outside of the peripheral circuit portion 40 to contact external leads (not shown).

FIG. 2 is a circuit diagram of an example of the imaging pixel 2. The imaging pixel 2 includes, for example, a photodiode 21 constituting a photoelectric conversion element and a transfer transistor 22, a reset transistor 23, an MOS transistor, for example, an n-channel MOS transistor, An amplification transistor 24 and a selection transistor 25 are provided.

  On the other hand, as shown in FIG. 1, the black reference pixel 2SB is formed in or near the imaging pixel region 3. The black reference pixel 2SB has a configuration similar to that of the imaging pixel 2, but a light shielding layer is formed thereon so that external light is not incident as much as possible.

  The control circuit 8 generates a clock signal, a control signal, and the like that serve as a reference for operations of the vertical drive circuit 4, the column signal processing circuit 5, and the horizontal drive circuit 6 based on the vertical synchronization signal, the horizontal synchronization signal, and the master clock. Are input to the vertical drive circuit 4, the column signal processing circuit 5, the horizontal drive circuit 6, and the like.

The vertical drive circuit 4 is configured by, for example, a shift register, and selectively scans each pixel 2 in the imaging pixel region unit 3 sequentially in the vertical direction in units of rows, and the photoelectric conversion element (photodiode) of each pixel 2 through the vertical signal line 9. In 21, the signal charge generated according to the amount of received light is supplied to the column signal processing circuit 5.
The column signal processing circuit 5 is arranged, for example, for each column of the pixels 2, and the signal output from the pixels 2 for one row is subjected to noise removal or signal amplification by a signal from the black reference pixel for each pixel column. Perform signal processing.
At the output stage of the column signal processing circuit 5, a horizontal selection switch (not shown) is provided connected to the horizontal signal line 10.

The horizontal drive circuit 6 is constituted by, for example, a shift register, and sequentially outputs horizontal scanning pulses to select each of the column signal processing circuits 5 in order, and the pixel signal is output from each of the column signal processing circuits 5 to the horizontal signal line. 10 to output.
The output circuit 7 performs signal processing and outputs the signals sequentially supplied from each of the column signal processing circuits 5 through the horizontal signal line 10.

FIG. 3 is a schematic cross-sectional view of a main part of an example of an embodiment of the solid-state imaging device according to the present invention. In FIG. 3, for example, on a silicon substrate 100, an imaging region portion 3 in which an imaging pixel 2 and a black reference pixel 2 BS are formed, a peripheral circuit portion 40, and a pad portion 31 in which contact pads 30 are arrayed are schematically illustrated. Has been shown.
The imaging region section 3 and the peripheral circuit section 40 formed on the substrate 100 have the configuration described with reference to FIGS. 1 and 2. In FIG. 3, some of the photodiodes 21 and MOS transistors are shown. .

On the substrate 100, wiring layers made of first, second and third metal layers M1 to M3 made of, for example, Cu each having excellent conductivity are respectively provided in a required pattern via an interlayer insulating layer 50 in the drawing. For example, a damascene wiring layer 60 connected to each other through a via hole at a predetermined position is formed.
In addition, a predetermined portion of the wiring layer 60 is extended and formed on the pad portion 31.
The surface of the upper interlayer insulating layer 50 is formed as a flat surface, and the pad portion 31 is formed with a contact pad 30 that contacts an extended portion from the wiring layer 60 and contacts an external lead. The contact pad 30 is made of, for example, an Al alloy layer such as Al or Al—Cu that can be satisfactorily contacted with an external lead wire having a thickness of 0.4 to 2 μm.

In the configuration of the present invention, the light shielding layer 70 made of the same metal layer as the contact pad 30 is formed on the black reference image 2BS to be shielded from light, the peripheral circuit section 40, and the like. The contact pad 30 and the light shielding layer 70 are simultaneously formed in the same process as described later.

  For example, red R, green G, and blue B color filters are formed on the image pickup pixels 2 of the image pickup area unit 3, and further, a minute lens so-called on-chip lens OCL is formed thereon.

Next, an embodiment of the method for manufacturing the solid-state imaging device according to the present invention will be described.
4 to 10 are schematic cross-sectional views of the main part in the main process of this manufacturing method, and the same reference numerals are given to the parts corresponding to those in FIG.
As shown in FIG. 4, on the silicon semiconductor substrate 100, as described above, the black reference pixel 2SB, the imaging region 3 having the imaging pixel 2, the peripheral circuit unit 40, the pad layer 31 having the contact pad 30, the interlayer insulating layer 50, A wiring layer 60 is formed, and the surface of the interlayer insulating layer 50 is flattened.

As shown in FIG. 5, a photoresist layer 80 is formed on the planarized surface, and an opening 80a is formed on the wiring layer 60 with which the contact pad 30 of the pad portion 31 described in FIG. Form.
Then, an opening 50 a is formed in the interlayer insulating layer 50 on the contact pad 30 through the opening 80 a.
As shown in FIG. 6, the photoresist layer 80 is removed, and the entire surface is made of Al or Al alloy having a thickness of 0.4 μm to 2 μm, for example, so as to contact the contact pad 30 through the opening 50a of the interlayer insulating layer 50. The metal layer 32 is formed by sputtering, for example.

As shown in FIG. 7, a photoresist layer 80 is once formed on the entire surface of the metal layer 32, and finally the contact pad 30 and the light shielding layer 70 shown in FIG. The other imaging region portion 3 photoresist layer 80 is removed.
As shown in FIG. 8, using the photoresist layer 80 as a mask, the exposed metal layer 32 is etched by removing the photoresist 80, the photoresist layer 80 is removed, and the contact pad 30 and the light shielding layer are removed by the metal layer 32. 70.

As shown in FIG. 9, the planarizing film 51 is formed, and the color filter RGB is formed in parallel in a predetermined pattern in the imaging region portion 3 that needs to receive light, and at the same time, other peripheral circuit portions, etc. For example, two layers of color filters are formed so as to cover the light shielding layer 70.
As shown in FIG. 10, the on-chip lens material 101 is formed so as to form a formed flat surface on at least an imaging region having imaging pixels.
Then, a photoresist layer 80 is formed on the on-chip lens material 101, and a photoresist layer is formed and reflowed on a portion where the on-chip lens OCL is finally formed by photolithography, so that an OCL forming portion is formed. An etching mask is formed with an OCL-shaped photoresist layer.
Thereafter, etch back is performed to remove the photoresist layer, and etching is performed in accordance with this pattern to form an on-chip lens OCL as shown in FIG. 3, thereby obtaining the target solid-state imaging device 1 according to the present invention.

As described above, since the light shielding layer 70 is formed of the same metal layer as the contact pad 30 in the manufacturing method of the present invention, this metal layer has a sufficient thickness required as a contact pad, For this reason, the light shielding layer which has a complete shielding effect is comprised.
That is, for example, excellent light shielding is achieved as compared with the case where the light shielding layer is formed by a color filter, and at the same time, since the light shielding layer 70 is formed at the same time as the contact pad 30, the number of processes is not increased. It is.

  Note that the present invention is not limited to the above-described embodiments, and in the configuration of the present invention, modifications and changes can be made according to the usage mode, purpose, and the like.

  DESCRIPTION OF SYMBOLS 1 ... CMOS solid-state imaging device, 2 ... Imaging pixel, 3 ... Imaging pixel area, 4 ... Vertical drive circuit, 5 ... Column signal processing circuit, 6 ... Horizontal drive circuit, 7 ... Output circuit, 8 ... Control circuit, 9 ... Vertical signal line, 10 ... Horizontal signal line, 2SB ... Black reference pixel, 21 ... Photo diode, 22 ... Transfer transistor, 23 ... Reset transistor, 2 parts ... Amplification transistor 25 …… Select transistor, 30 …… Contact pad, 31 …… Pad portion, 32 …… Metal layer, 40 …… Peripheral circuit portion, 50 …… Interlayer insulating layer, 51 …… Planarization film, 60 …… Wiring Layer 70 .. light-shielding layer 80... Photoresist layer 50 a .. opening 80 a .. opening 80... Silicon substrate 101 .. on-chip lens material OCL .. on-chip lens

That is, the solid-state imaging device according to the present invention is a solid-state imaging device having an imaging unit having a photoelectric conversion element on a substrate, and a peripheral circuit portion which processes the signals obtained by the imaging section, the peripheral circuit section on Further, a light shielding layer is provided, and a contact pad for outputting the signal processed data to the outside is provided in the same layer as the light shielding layer .

In the semiconductor device manufacturing method according to the present invention, the substrate, an imaging unit having a photoelectric conversion element, and forming a peripheral circuit portion which processes a signal obtained by the imaging unit, the light shielding on the peripheral circuit portion and having a layer, and a step that form simultaneously in the same layer and a contact pad for outputting a signal processed data.

Claims (4)

An imaging region portion in which imaging pixels having photoelectric conversion elements are arranged, a peripheral circuit portion, a contact pad of an external lead, a black reference pixel, and a wiring layer;
The wiring layer and the contact pad are fixed imaging devices configured by metal layers having different constituent materials,
A solid-state imaging device, wherein a light shielding layer is formed at least on the peripheral circuit portion and the black reference pixel, and the light shielding layer is constituted by a metal layer formed simultaneously with the metal layer of the contact pad. . 2. The wiring layer according to claim 1, wherein the wiring layer is made of copper (Cu), and the metal layer of the contact pad and the light shielding layer is made of aluminum (Al) or an alloy of aluminum and Cu (Al—Cu). Solid-state imaging device. Forming at least an imaging region portion in which pixels having photoelectric conversion elements are arranged on a substrate, a peripheral circuit portion, and a black reference pixel;
Forming a wiring layer of the imaging region portion and the peripheral circuit portion;
A method of manufacturing a solid-state imaging device, comprising: forming contact pads for external leads; and simultaneously forming a light shielding layer on at least the peripheral circuit portion and the black reference pixel by the same metal layer. 4. The wiring layer according to claim 3, wherein the wiring layer is formed of copper (Cu), and the contact pad and the light shielding layer are formed of aluminum (Al) or an alloy of aluminum and Cu (Al—Cu). Manufacturing method of solid-state imaging device.

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