JP2006344654A - Solid-state imaging device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a highly reliable solid-state imaging device at a low cost. <P>SOLUTION: A gate electrode 6 is formed on a silicon substrate with a gate insulating film 5 in-between, and then an opening is made in the gate insulating film 5 on the silicon substrate 1 so as to expose an FD 4. Next, a conductive film 7 is formed on the silicon substrate 1, and it is selectively etched and removed so that a range from a portion in contact with the FD 4 to a portion in contact with the gate electrode 6 may be left (Fig. 3(d)). Then, a film is formed on the silicon substrate 1 using a metallic material, and the metallic material film is selectively etched and removed so that it may be left on the conductive film 7 (Fig. 3(e)). In the processing step, the metallic material film left on the conductive film 7 functions as a wiring 8 for connecting electrically the gate electrode 6 and the FD 4. Furthermore, an insulating film 9 made of a BPSG film or the like is formed on the silicon substrate 1 (Fig. 3(f)), and subjected to reflow treatment. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention includes a floating diffusion portion that accumulates signal charges, and an output circuit that includes a transistor having a gate electrode electrically connected to the floating diffusion portion, and outputs a signal corresponding to a potential change in the floating diffusion portion. The present invention relates to a method for manufacturing a solid-state imaging device.

  A CCD type solid-state imaging device includes a plurality of photoelectric conversion elements composed of photodiodes arranged vertically and horizontally on a light receiving surface, a vertical transfer register arranged corresponding to the vertical direction of each photoelectric conversion element, and a termination of the vertical transfer register. And a signal output unit that is arranged at the end of the horizontal transfer register, converts the transfer charge from the horizontal transfer register into a voltage signal, and outputs the voltage signal.

  As the configuration of the signal output unit, for example, an FDA (Floating Diffusion Amplifier) type as described in Patent Document 1 is widely adopted. This is a floating diffusion (FD) section that accumulates signal charges from the horizontal transfer register and has a potential corresponding thereto, and then resets to a predetermined reset potential at a predetermined cycle, and a reset that performs the reset. Usually, it comprises a transistor and an output circuit that amplifies and outputs a signal corresponding to the potential change of the FD portion. The output circuit is generally composed of a plurality of stages (two or three stages) of source follower circuits.

FIG. 4 is a partial cross-sectional schematic diagram illustrating an example of a manufacturing process of the signal output unit described in Patent Document 1.
First, a p-well layer 2 is formed on the surface of an n-type silicon substrate 1, a field oxide film 3 such as a LOCOS film is formed thereon, an n + region 4 serving as an FD portion, a photodiode (not shown), a vertical transfer register, Then, after forming a horizontal transfer register or the like by ion implantation or the like, a gate insulating film 5 made of an ONO film or the like is formed on the p well layer 2 (FIG. 4A).

  Next, although not shown, a driving electrode made of polysilicon or the like for driving the vertical transfer register or the horizontal transfer register formed on the surface of the p-well layer 2 (when reading the charge from the photodiode) (Also serving as a readout electrode) is formed through the gate insulating film 5. Simultaneously with the formation of the drive electrode, the gate electrode of the reset transistor and the gate electrode 6 of the transistor included in the output circuit electrically connected to the FD portion 4 are formed on the silicon substrate 1 using the same material as the drive electrode. After that, the gate insulating film 5 on the FD portion 4 is removed in order to expose the FD portion 4 (FIG. 4B).

  Next, an insulating film 19 made of a BPSG film or the like covering the silicon substrate 1 on which the gate insulating film 5, the gate electrode 6, and the drive electrode are formed is formed (FIG. 4C), and this is subjected to a reflow process.

  Next, a contact hole is formed in the insulating film 19 by a reactive ion etching (RIE) method or the like, and a metal material 18 such as tungsten is formed so as to fill the contact hole (FIG. 4D).

  Finally, an excess portion of the deposited metal material 18 is removed by performing etch back, thereby forming a wiring 18 ′ that electrically connects the gate electrode 6 and the FD portion 4.

  According to the method described above, since the wiring is formed of a metal material, the capacity of the wiring can be reduced. Even if the aspect ratio of the contact hole is increased by miniaturization of the FD portion 4, the wiring can be formed with high reliability.

JP 2002-368203 A

  However, in the above-described method, it is necessary to take steps such as forming a contact hole in the insulating film, embedding a metal material therein, and further removing excess metal material, which increases the number of steps. In addition, there is a risk of damaging the silicon substrate by etching during contact hole formation.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to make it possible to manufacture a highly reliable solid-state imaging device at low cost.

  A method of manufacturing a solid-state imaging device according to the present invention includes a floating diffusion portion that accumulates signal charges and a transistor having a gate electrode electrically connected to the floating diffusion portion, and a signal corresponding to a potential change in the floating diffusion portion. A solid-state imaging device having an output circuit that outputs an opening forming step of forming an opening in a gate insulating film formed on a semiconductor substrate and exposing at least a part of the floating diffusion portion; Forming a gate electrode on the semiconductor substrate through the gate insulating film; and forming a wiring material on the semiconductor substrate after the opening forming step and the gate electrode forming step. A film process; and selectively removing a film of the wiring material to form the gate electrode Wherein including a wiring forming step of forming a wiring for electrically connecting the floating diffusion portion, after the wiring formation, and an insulating film forming step of forming an insulating film covering the wiring and the gate electrode.

  According to this method, since the wiring is formed before forming the insulating film, the number of steps can be reduced and a fine wiring can be easily formed. Further, since the step of forming a contact hole in the insulating film is not performed, damage to the silicon substrate can be reduced. As a result, a highly reliable solid-state imaging device can be manufactured at low cost.

  The method for manufacturing a solid-state imaging device of the present invention includes an electrode forming step of forming an electrode for charge transfer via the gate insulating film on a charge transfer portion formed in the semiconductor substrate for transferring the signal charge. The wiring material is the same as the material constituting the light shielding film that shields the electrode, and the wiring material film forming step is performed after the opening forming step, the gate electrode forming step, and the electrode forming step, In the wiring formation step, the light shielding film is formed simultaneously with the wiring by removing the film so as to leave the film of the wiring material on the electrode.

  According to this method, since the light shielding film and the wiring can be formed at the same time, the number of steps can be further reduced.

  The method for manufacturing a solid-state imaging device of the present invention includes a conductive film forming step of forming a conductive film between the wiring and the gate electrode.

  According to this method, the adhesion between the wiring and the gate electrode can be ensured.

  In the method for manufacturing a solid-state imaging device according to the present invention, the conductive film is TiN.

  In the method for manufacturing a solid-state imaging device of the present invention, the wiring material is made of a metal material.

  In the method for manufacturing a solid-state imaging device according to the present invention, the metal material is tungsten.

  The solid-state imaging device of the present invention includes a floating diffusion portion that accumulates signal charges and a transistor having a gate electrode electrically connected to the floating diffusion portion, and outputs a signal corresponding to a potential change in the floating diffusion portion. A solid-state imaging device having an output circuit, comprising: a wiring that electrically connects the gate electrode and the floating diffusion portion; and an insulating film that covers the gate electrode and the wiring.

  The solid-state imaging device of the present invention includes a conductive film between the wiring and the gate electrode.

  In the solid-state imaging device of the present invention, the conductive film is TiN.

  In the solid-state imaging device of the present invention, the wiring material is made of a metal material.

  In the solid-state imaging device of the present invention, the metal material is tungsten.

  According to the present invention, a highly reliable solid-state imaging device can be manufactured at low cost.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a partial cross-sectional schematic view of a signal output unit of a solid-state imaging device for explaining an embodiment of the present invention. The signal output unit of the solid-state imaging device according to the present embodiment stores the signal charge from the horizontal transfer register and becomes a potential corresponding to the signal charge from the horizontal transfer register as in the configuration described in Patent Document 1, and then reset to a predetermined reset potential. Is configured to include an FD portion that repeats the above in a constant cycle, a reset transistor that resets the FD portion, and an output circuit that outputs a signal corresponding to a potential change in the FD portion. The output circuit includes a source follower circuit connected in two or three stages, and each source follower circuit includes a drive transistor and a load transistor. FIG. 1 illustrates a connection portion between the FD portion and the gate electrode of the driving transistor of the first-stage source follower circuit included in the output circuit.

  As shown in FIG. 1, an FD portion 4 made of an n + region is formed in a p-well layer 2 formed on an n-type silicon substrate 1 and is formed on a field oxide film 3 made of a LOCOS film or the like in the vicinity of the FD portion 4. A gate electrode 6 made of polysilicon or the like is formed through a gate insulating film 5 made of an ONO film or the like formed on the p well layer 2. This gate electrode 6 corresponds to the gate electrode of the driving transistor of the first-stage source follower circuit described above. An opening is formed in the gate insulating film 5 above the FD portion 4.

  A wiring 8 made of a high melting point metal material such as tungsten is formed on the gate electrode 6 and the FD portion 4, and the gate electrode 6 and the FD portion 4 are electrically connected by the wiring 8. A conductive film 7 made of TiN or the like is formed under the gate electrode 8, and the adhesion between the wiring 8 and the gate electrode 6 is sufficiently secured by the conductive film 7. An insulating film 9 made of a BPSG film or the like is formed on the silicon substrate 1 on which the gate electrode 6 and the wiring 8 are formed. By this insulating film 9, the gate electrode 6, the conductive film 7, and the wiring 8 are thereby formed. It is completely insulated from the upper layer.

  In the signal output unit configured as described above, the signal charge transferred from a horizontal transfer register (not shown) is temporarily stored in the FD unit 4. Then, the potential of the FD section 4 changes according to the accumulated signal charge, and this change in potential is applied as an output signal to the gate electrode 6 via the wiring 8, and this output signal is amplified by the output circuit to the outside. Is output. Note that the conductive film 7 may not be provided.

Hereinafter, a method for manufacturing the solid-state imaging device shown in FIG. 1 will be described.
2 and 3 are process diagrams for explaining a method of manufacturing the solid-state imaging device shown in FIG.
First, a p-well layer 2 is formed on the surface of an n-type silicon substrate 1, and a field oxide film 3 such as a LOCOS film is formed thereon. Further, after forming an n + region 4 serving as an FD portion, a photodiode (not shown), a vertical transfer register, a horizontal transfer register, and the like in the p well layer 2 by ion implantation or the like, an ONO film or the like is formed on the p well layer 2. A gate insulating film 5 is formed (FIG. 2A).

  Next, although not shown in the drawing, on a vertical transfer register or a horizontal transfer register formed on the surface of the p-well layer 2, a drive electrode made of polysilicon or the like for driving them (when reading charge from a photodiode) Is also formed through the gate insulating film 5. Simultaneously with the formation of the drive electrode, a gate electrode 6 made of the same material as the drive electrode is formed on the field oxide film 3 in the vicinity of the FD portion 4 via the gate insulating film 5. Thereafter, in order to expose at least part of the FD part 4, at least part of the gate insulating film 5 on the FD part 4 is removed to form an opening (FIG. 2B). Note that the gate electrode 6 or the like may be formed after the opening is formed in the gate insulating film 5. The steps so far are known.

  Next, a conductive film 7 made of TiN or the like is formed on the silicon substrate 1 by, for example, a sputtering method (FIG. 2C), and the conductive film 7 is formed from the portion in contact with the FD portion 4 to the gate electrode. Etching is selectively removed so that the portion in contact with 6 remains (FIG. 3D).

  Next, a high melting point metal material made of tungsten or the like is formed on the silicon substrate 1 by, for example, a CVD method, and the formed metal material film is selectively left on the conductive film 7 and the drive electrode. Etching is removed (FIG. 3E). By this step, the metal material film remaining on the conductive film 7 functions as a wiring 8 that electrically connects the gate electrode 6 and the FD portion 4, and the metal material film remaining on the drive electrode Functions as a light-shielding film. The wiring 8 only needs to have one end electrically connected to at least a part of the FD portion 4 and the other end electrically connected to at least a part of the gate electrode 6.

  Next, an insulating film 9 made of a BPSG film or the like is formed on the silicon substrate 1 (FIG. 3F), and this is subjected to a reflow process. Since the wiring 8 and the light shielding film are made of a metal material having a high melting point, the wiring 8 and the light shielding film can sufficiently withstand the reflow process. Thereafter, a flattening film made of a transparent resin or the like is formed on the insulating film 9, a color filter is formed thereon, and a microlens is formed thereon via the flattening film. Finalize.

  As described above, according to the manufacturing method of the present embodiment, since the wiring 8 is formed before the insulating film 9 is formed, a step of forming a contact hole in the insulating film 9 becomes unnecessary. The number of processes can be reduced as compared with the above, and the solid-state imaging device can be manufactured at low cost. Further, since the light shielding film of the drive electrode and the wiring 8 can be formed in the same process, the number of processes can be further reduced.

  Moreover, according to the manufacturing method of this embodiment, since the damage to the silicon substrate 1 can be reduced as compared with the case where the contact hole is formed, the reliability of the element can be improved.

  Further, according to the manufacturing method of the present embodiment, the wiring 8 can be formed by a normal patterning technique. Therefore, even when the FD portion 4 is miniaturized, the fine wiring 8 can be formed very easily. Therefore, the wiring capacity can be reduced.

  In the present embodiment, the material of the wiring 8 and the material of the light shielding film are the same metal material, but different metal materials may be used. In this case, the formation of the light shielding film and the formation of the wiring 8 need to be performed in separate steps, but still the number of steps can be reduced as compared with the conventional method. In this case, the light shielding film is formed between the step of FIG. 2B and the step of FIG. 2C, between the step of FIG. 3D and the step of FIG. 3E, or FIG. ) And the step shown in FIG. Further, when the wiring material is removed by etching, the etching may be performed so that the wiring material remains only on the conductive film 7.

  In this embodiment, the drive electrode and the gate electrode 6 are formed in the same process, but, of course, they may be formed in different processes.

  In the present embodiment, the conductive film 7 is sandwiched between the wiring 8 and the gate electrode 6 in order to ensure the adhesion between the wiring 8 and the gate electrode 6. 6 or a combination of materials of the wiring 8 or a method for forming the same), the formation of the conductive film 7 can be omitted. In this case, a wiring material is formed instead of the conductive film 7 in FIG. 2C, and this is selectively removed by etching so as to have the same shape as the conductive film 7, thereby forming the wiring 8. Thereafter, a process of forming the insulating film 9 may be taken. In this embodiment, the conductive film 7 is formed under the wiring 8, but the conductive film 7 only needs to exist at least between the wiring 8 and the gate electrode 6.

1 is a partial cross-sectional schematic diagram of a signal output unit of a solid-state imaging device for explaining an embodiment of the present invention Process drawing for demonstrating the manufacturing method of the solid-state image sensor shown in FIG. Process drawing for demonstrating the manufacturing method of the solid-state image sensor shown in FIG. Partial cross-sectional schematic diagram showing an example of the manufacturing process of the signal output unit described in Patent Document 1

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 P well layer 3 Field oxide film 4 Floating diffusion part 5 Gate insulating film 6 Gate electrode 7 Conductive film 8 Wiring 9 Insulating film

Claims (11)

A solid-state imaging device having a floating diffusion part that accumulates signal charges, and an output circuit that includes a transistor having a gate electrode electrically connected to the floating diffusion part, and that outputs a signal corresponding to a potential change of the floating diffusion part A manufacturing method of
Forming an opening in a gate insulating film formed on a semiconductor substrate to expose at least a part of the floating diffusion portion; and
Forming a gate electrode on the semiconductor substrate via the gate insulating film; and
A wiring material film forming step of forming a wiring material on the semiconductor substrate after the opening forming step and the gate electrode forming step;
A wiring forming step of selectively removing a film of the wiring material to form a wiring for electrically connecting the gate electrode and the floating diffusion portion;
A method for manufacturing a solid-state imaging device, comprising: forming an insulating film that covers the gate electrode and the wiring after forming the wiring. It is a manufacturing method of the solid-state image sensing device according to claim 1,
Including an electrode forming step of forming an electrode for charge transfer via the gate insulating film on a charge transfer portion formed in the semiconductor substrate for transferring the signal charge,
The wiring material is the same as the material constituting the light shielding film that shields the electrode,
The wiring material film forming step is performed after the opening forming step, the gate electrode forming step, and the electrode forming step,
A method of manufacturing a solid-state imaging device, wherein the light shielding film is formed simultaneously with the wiring by removing the film so as to leave a film of the wiring material on the electrode in the wiring forming step. It is a manufacturing method of the solid-state image sensing device according to claim 1 or 2,
A method for manufacturing a solid-state imaging device, including a conductive film forming step of forming a conductive film between the wiring and the gate electrode. It is a manufacturing method of the solid-state image sensing device according to claim 3,
The method for manufacturing a solid-state imaging device, wherein the conductive film is TiN. It is a manufacturing method of the solid-state image sensing device according to any one of claims 1 to 4,
A method for manufacturing a solid-state imaging device, wherein the wiring material is made of a metal material. It is a manufacturing method of the solid-state image sensing device according to claim 5,
The manufacturing method of the solid-state image sensor whose said metal material is tungsten. A solid-state imaging device having a floating diffusion part that accumulates signal charges, and an output circuit that includes a transistor having a gate electrode electrically connected to the floating diffusion part, and that outputs a signal corresponding to a potential change of the floating diffusion part Because
Wiring for electrically connecting the gate electrode and the floating diffusion portion;
A solid-state imaging device comprising an insulating film covering the gate electrode and the wiring. The solid-state imaging device according to claim 7,
A solid-state imaging device comprising a conductive film between the wiring and the gate electrode. The solid-state imaging device according to claim 8,
The solid-state imaging device, wherein the conductive film is TiN. A solid-state imaging device according to any one of claims 7 to 9,
The wiring material is a solid-state imaging device made of a metal material. The solid-state imaging device according to claim 10,
The solid-state image sensor whose said metal material is tungsten.

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