JP2009218438A - Solid-state imaging device, its manufacturing method, and electronic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid-state imaging device which can efficiently suppress a dark current, a method of manufacturing the solid-state imaging device, and an electronic device having the solid-state imaging device. <P>SOLUTION: The solid-state imaging device comprises a plurality of pixels having photoelectric conversion elements 24, a ferroelectric film 28 which is formed on the respective photoelectric conversion elements 24 of the pixels with an insulating film 25 disposed therebetween and which is polarized, and a transparent electrode film 29 formed on the ferroelectric film 28. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a solid-state imaging device, a manufacturing method thereof, and an electronic apparatus including the solid-state imaging device.

  Solid-state imaging devices are roughly classified into amplification type solid-state imaging devices represented by CMOS (Complementary Metal Oxide Semiconductor) image sensors and charge transfer type solid-state imaging devices represented by CCD (Charge Coupled Device) image sensors.

  A CMOS solid-state imaging device has a pixel (PD) as a photoelectric conversion element and a plurality of pixels made up of a plurality of pixel transistors (MOS transistors) arranged two-dimensionally, and arranged around the imaging region. And a peripheral circuit. The CCD solid-state imaging device has an imaging region including a photodiode (PD) serving as a plurality of photoelectric conversion elements arranged two-dimensionally and a vertical transfer register having a CCD structure arranged corresponding to each photodiode row. . The CCD solid-state imaging device further includes a horizontal transfer register having a CCD structure that transfers signal charges from the imaging region in the horizontal direction, an output unit, and peripheral circuits that constitute a signal processing circuit.

  The photodiode is usually configured by forming an n-type semiconductor region in a p-type semiconductor well region when signal charges are electrons. An insulating film made of, for example, silicon oxide is formed on the surface of each n-type semiconductor region constituting the photodiode. When light is incident on the n-type semiconductor region and photoelectrically converted to generate electron-hole pairs, electrons serving as signal charges are accumulated in the semiconductor region with n. Thereafter, this signal charge is read out.

  FIG. 9 shows a schematic configuration of a conventional solid-state imaging device. FIG. 9 is a cross-sectional view schematically showing the peripheral circuit unit 2 and the photodiode 3 in the imaging region in the solid-state imaging device 1. In the solid-state imaging device 1, a peripheral circuit unit 2 and an imaging region photodiode 3 are formed on a silicon substrate, and an insulating film 4 such as a silicon oxide film is formed thereon. Further, a light shielding film 5 made of aluminum or tungsten is formed on a region other than the photodiode 3 including the peripheral circuit portion 2, and a protective film 6 made of an insulating film such as a silicon oxide film is formed on the entire surface so as to cover the light shielding film 5. It is formed.

  In this configuration, the photodiode 3 is in a fully depleted state, and it is known that the interface state at the interface between the light receiving surface of the photodiode 3 and the insulating film 4 that is the upper layer film is a source of dark current. For example, a HAD (Hole Accumulation Diode) structure is used as a technique for suppressing the generation of dark current due to the interface state.

  As shown in FIG. 10, this HAD structure generally has a p + semiconductor on the surface of the n-type semiconductor region 12 constituting the photodiode 3 formed in the p-type semiconductor well region 11, that is, in the vicinity of the interface with the insulating film 14. The region 13 is formed and configured. This p + semiconductor region 13 is called a p + accumulation layer. In this HAD structure, electrons generated from the interface state are recombined in the p + semiconductor region 13 and disappear, thereby suppressing generation of dark current.

  As another method for suppressing the generation of dark current due to the interface state, a configuration shown in FIG. 11 is known. This solid-state imaging device 7 is configured by forming a bipolar electric polarization dielectric film 8 made of a phosphorus-doped silicon oxide film on the surface of a photodiode 3 with an insulating film 4 interposed therebetween. An insulating film 9 is formed on the bipolar electric polarization dielectric film 8 and the peripheral circuit portion 2, and a light shielding film 5 and a protective film 6 are formed on the insulating film 9. In this configuration, due to the remanent polarization of the bipolar electric polarization dielectric film 8, holes are induced near the interface of the n-type semiconductor region constituting the photodiode 3 to form a HAD structure, thereby suppressing dark current (patent) Reference 1).

  Furthermore, as another method, as shown in FIG. 12, a transparent electrode film 15 is formed on an n-type semiconductor region 3 constituting a photodiode via an insulating film 4, and a negative voltage ( A structure in which holes are induced near the interface of the n-type semiconductor region by applying -V) to form an HAD structure is also known (see Patent Document 1).

JP-A-4-343472

  By the way, in the configuration in which the bipolar electric polarization dielectric film 8 is formed on the photodiode shown in FIG. 11 described above, the polarization is generated during the manufacturing process, or the light shielding film 5 is used after the imaging element is formed. Need to be generated. However, when polarization is generated during the manufacturing process, the polarization disappears when a process higher than the Curie temperature Tc is applied in the subsequent steps. For example, even when lead zirconate titanate, which is a material having a high Curie temperature Tc, is used as the bipolar electric polarization dielectric film 8, since the Curie temperature Tc is about 350 ° C., it is difficult to form plasma SiO 2 in a later step. .

  In the configuration of FIG. 11, when polarization is generated using the light-shielding film 5 after the imaging element is formed, an electric field cannot be applied perpendicularly to the photodiode 3, and the polarization direction is perpendicular to the substrate. It cannot be generated. For this reason, efficient electric field application is impossible. Processes such as biased etching, plasma, and electroplating on as-deposited bipolar or polarized bipolar dielectric films may cause random polarization. There is.

  In the configuration in which the transparent electrode film is formed on the photodiode of FIG. 12 via the insulating film, the electric potential is continuously supplied during the operation of the solid-state imaging device, resulting in an increase in power consumption.

  In view of the above points, the present invention provides a solid-state imaging device capable of efficiently suppressing dark current, a manufacturing method thereof, and an electronic apparatus including the solid-state imaging device.

  A solid-state imaging device according to the present invention includes a plurality of pixels each having a photoelectric conversion element, a polarization-processed ferroelectric film formed on the photoelectric conversion element of each pixel via an insulating film, and a ferroelectric film A transparent electrode film formed thereon.

  In the solid-state imaging device of the present invention, a ferroelectric film polarized through an insulating film is formed on the photoelectric conversion element, so that the signal charge and signal charges are generated in the vicinity of the interface with the insulating film of the photodiode by this dielectric film. A charge accumulation region in which opposite charges are accumulated is induced. By this charge accumulation region, dark current due to the interface state is suppressed. The transparent electrode film becomes one voltage application electrode during the polarization treatment by voltage application. Since the transparent electrode film is formed on the ferroelectric film, polarization in the direction perpendicular to the substrate can be obtained.

  A method of manufacturing a solid-state imaging device according to the present invention includes a step of forming a plurality of pixels having photoelectric conversion elements on a semiconductor substrate, and a ferroelectric film and a transparent electrode film are stacked on the photoelectric conversion elements via an insulating film. And a step of performing a depolarization process on the ferroelectric film by performing a heat treatment and then performing a polarization process, and the transparent electrode film remains after the polarization.

  According to the method for manufacturing a solid-state imaging device of the present invention, the method includes the step of laminating the ferroelectric film and the transparent electrode film on the photoelectric conversion element via the insulating film, so that a voltage is generated between the transparent electrode film and the substrate. Can be applied in a direction perpendicular to the substrate. Since the transparent electrode film remains after the polarization, even if the polarization state is changed due to any cause, the voltage can be applied again, so that the normal state can be restored.

  An electronic apparatus according to the present invention includes a solid-state imaging device, an optical system that guides incident light to a photoelectric conversion element of the solid-state imaging device, and a signal processing circuit that processes an output signal of the solid-state imaging device. A solid-state imaging device is formed on a plurality of pixels having photoelectric conversion elements, a ferroelectric film that has been subjected to polarization treatment formed on an insulating film on the photoelectric conversion elements of each pixel, and a ferroelectric film. A transparent electrode film.

  In the electronic apparatus of the present invention, dark current due to the interface state is suppressed in the solid-state imaging device having the above configuration.

According to the solid-state imaging device according to the present invention, it is possible to provide a solid-state imaging device capable of efficiently suppressing dark current.
According to the method for manufacturing a solid-state imaging device according to the present invention, it is possible to manufacture a solid-state imaging device capable of efficiently suppressing dark current.
According to the electronic apparatus according to the present invention, since the solid-state imaging device capable of efficiently suppressing dark current is provided, it is possible to provide an electronic apparatus with high image quality and high performance.

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

  The solid-state imaging device according to the embodiment of the present invention is characterized by the configuration of the photoelectric conversion element section. The configuration of the photoelectric conversion element portion of the solid-state imaging device according to the present embodiment can be applied to both a CMOS solid-state imaging device and a CCD solid-state imaging device, but is not limited thereto.

  A schematic configuration of a CMOS solid-state imaging device applied to the present embodiment will be described. Although not shown, the CMOS solid-state imaging device includes an imaging region in which pixels including a plurality of photoelectric conversion elements are regularly arranged in a two-dimensional manner on a semiconductor substrate such as a silicon substrate, and a peripheral circuit unit. The The pixel includes, for example, a photodiode serving as a photoelectric conversion element and a plurality of pixel transistors (so-called MOS transistors). The plurality of pixel transistors can be configured by four transistors, for example, a transfer transistor, a reset transistor, an amplification transistor, and a selection transistor. In addition, for example, the selection transistor can also be configured by three transistors by winning the selection transistor. The peripheral circuit section includes a vertical drive circuit, a column signal processing circuit, a horizontal drive circuit, an output circuit, a control circuit, and the like.

  Based on the vertical synchronization signal, horizontal synchronization signal, and master clock, the control circuit generates a clock signal and a control signal that serve as a reference for operations of the vertical drive circuit, the column signal processing circuit, the horizontal drive circuit, and the like. Input to the vertical drive circuit, column signal processing circuit, horizontal drive circuit, and the like.

  The vertical drive circuit is configured by, for example, a shift register, and sequentially selects and scans each pixel in the imaging region in the vertical direction in units of rows, and is generated according to the amount of light received by the photoelectric conversion element (photodiode) of each pixel through the vertical signal line The pixel signal based on the signal charge is supplied to the column signal processing circuit.

  The column signal processing circuit is arranged, for example, for each column of pixels, and a signal output from the pixels for one row is generated by a signal from a black reference pixel (formed around the effective pixel region) for each pixel column. Performs signal processing such as noise removal and signal amplification. At the output stage of the column signal processing circuit, a horizontal selection switch is provided connected to the horizontal signal line.

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

  A multilayer wiring layer is formed above the substrate on which the pixels are formed via an interlayer insulating film, an on-chip color filter is formed thereon via a planarizing film, and an on-chip microlens is further formed thereon. . A light-shielding film is formed in a region other than the pixel portion in the imaging region, more specifically, in the peripheral circuit portion and other region other than the photodiode (so-called light receiving portion) in the imaging region. This light shielding film can be formed by, for example, the uppermost wiring layer of the multilayer wiring layer.

  Next, a schematic configuration of the CCD solid-state imaging device applied to this embodiment will be described. Although not shown, the CCD solid-state imaging device includes a plurality of photoelectric conversion elements formed on a semiconductor substrate such as a silicon substrate, a vertical transfer register having a CCD structure corresponding to each photoelectric conversion element array, a horizontal transfer register, and an output unit. And a peripheral circuit portion constituting a signal processing circuit. The photoelectric conversion elements are formed of, for example, photodiodes, and are regularly arranged two-dimensionally. The vertical transfer register is configured by forming a transfer electrode on a transfer channel region formed by a diffusion layer via a gate insulating film. A unit pixel is formed by each photodiode and a vertical transfer register corresponding to the photodiode. An imaging region is configured by the photodiode and the vertical transfer register. The horizontal transfer register is arranged at the end of the vertical transfer register, and is similarly configured by forming a transfer electrode on a transfer channel region formed by a diffusion layer via a gate insulating film. The output unit is connected to the last stage of the horizontal transfer register. A light shielding film is formed in a region other than the pixel portion in the imaging region, more specifically, in the region portion excluding the peripheral circuit and the photodiode in the imaging region, the horizontal transfer register, and the output portion. The light shielding film is formed so as to cover the transfer electrode.

  In the CCD solid-state imaging device, signal charges generated by photoelectric conversion by a photodiode are read out to a vertical transfer register, transferred in the vertical direction, and signal charges for each line are transferred to a horizontal transfer register. In the horizontal transfer register, signal charges are transferred in the horizontal direction, converted into pixel signals via an output unit, and output. The output pixel signal is taken out as an image signal through a signal processing circuit of a peripheral circuit. The CCD solid-state image pickup device in the above example is an interline transfer (IT) type solid-state image pickup device, and further includes an accumulation region formed only by a vertical transfer register between the image pickup region and the horizontal transfer register. The present invention is also applied to a frame interline transfer (FIT) type solid-state imaging device.

  The configuration of the solid-state imaging device according to the present embodiment, particularly its photoelectric conversion element, is applied to both the above-described CMOS solid-state imaging device and CCD solid-state imaging device.

  FIG. 1 shows a solid-state imaging device according to the first embodiment of the present invention. This figure is a cross-sectional view schematically showing a peripheral circuit portion 23 formed on a semiconductor substrate, for example, a silicon substrate 22, and a photodiode portion 24 which is a photoelectric conversion element in an imaging region. In the solid-state imaging device 21 according to the present embodiment, as shown in FIG. 1, a peripheral circuit portion 23 and a photodiode portion (hereinafter referred to as a photodiode) 24 in an imaging region are formed on a silicon substrate 22. Although not shown on the silicon substrate, a pixel transistor is formed in the case of a CMOS solid-state imaging device, and a vertical transfer register and a horizontal transfer register are formed in the case of a CCD solid-state imaging device. An insulating film 25 having a required film thickness is formed on the entire surface of the substrate including the peripheral circuit portion 23 and the photodiode 24. The insulating film 25 is formed of, for example, a silicon oxide film after the pixels including the peripheral circuit portion 23 and the photodiode 24 are formed. For example, as shown in FIG. 2, in the photodiode 24, an n-type semiconductor region 27N is formed in a second conductivity type, for example, a p-type semiconductor well region 26P in an n-type silicon substrate 22N in the first conductivity type. Configured.

  In the present embodiment, a ferroelectric film 28 and a transparent electrode film 29 thereon are formed on the insulating film 25 of the photodiode 24. An insulating layer 31 is formed on the entire surface including the peripheral circuit portion 23 so as to cover the transparent electrode film 29, and a light shielding film 32 is formed on the insulating layer 31 in the region including the peripheral circuit portion 23 other than the photodiode portion 24. Is done. Further, a protective film 33 made of an insulating film is formed on the entire surface so as to cover the light shielding film 32.

  The ferroelectric film 28 is polarized by a voltage applied between the transparent electrode film 29 and the silicon substrate 22. In this example, as shown in FIG. 2, the ferroelectric film 28 is polarized such that the photodiode 24 side is minus (−) and the transparent electrode film 29 side is plus (+). Due to the polarized ferroelectric film 28, holes 35 that are opposite to the signal charges (electrons in this example) are formed in the vicinity of the interface with the insulating film 25 of the n-type semiconductor region 27N constituting the photodiode 24. The hole accumulation region 36 is induced near the interface. After the polarization treatment, the switch element 37 is turned off to turn off the power source 38 and no voltage is applied to the transparent electrode film 29.

  As the ferroelectric film 28, it is preferable to use a material having a high Curie temperature Tc. Examples of the ferroelectric film 28 include lead zirconate titanate (PZT: Curie temperature 350 ° C.), bismuth strontium tantalate (SBT: Curie temperature 300 ° C.), lead titanate (PTO: Curie temperature 490 ° C.), and titanium. Barium oxide (BTO: Curie temperature 130 ° C), lead zirconate titanate mixed with metal such as lanthanum (PLZT), strontium bismuth titanium oxide (Curie temperature 550 ° C), yttrium manganese oxide (Curie) All ferroelectric films such as 640 ° C.) and others can be used. In the polarization process, the ferroelectric film 28 is heat-treated at a temperature equal to or higher than the Curie temperature (Tc) to once disappear the polarization state, and then polarized by applying a voltage while lowering the temperature.

  As the insulating film 25, a silicon oxide film, a metal oxide film such as Hf, Zr, Pr, Al, Ta, Ti, or a laminated structure film of this metal oxide film and a silicon oxide film or a silicon nitride film is used. You can also.

Next, an embodiment of the method for manufacturing the solid-state imaging device according to the first embodiment will be described with reference to FIG. The example of FIG. 3 is a case where it is applied to the manufacture of a CCD solid-state imaging device.
First, as shown in FIG. 3A, a pixel part including a peripheral circuit part 23 and a photodiode 24 in an imaging region, and a horizontal transfer register and an output part (not shown) having a CCD structure are formed on a silicon substrate 22. The formation of the pixel portion includes a photodiode 24 and a vertical transfer register having a CCD structure (not shown) having a transfer electrode. After that, for example, a silicon oxide film to be the insulating film 25 is deposited on the entire surface of the substrate to produce a structure similar to the conventional one.

  Next, as shown in FIG. 3B, a ferroelectric film 28 is selectively formed on a portion of the insulating film 25 corresponding to the photodiode 24. For example, a ferroelectric film having a required film thickness, for example, 2 nm to 20 nm is formed by sputtering a ferroelectric material such as lead zirconate titanate. The ferroelectric film is heat-treated at a temperature higher than the Curie temperature, for example, 500 ° C. to 700 ° C. Thereafter, the ferroelectric film 28 is left only in the region of the photodiode 24 by patterning.

  The ferroelectric film 28 can be formed by any method other than the sputtering method, such as a sol-gel method, a laser deposition method, an electron beam evaporation method, and an aerosol deposition method. The heat treatment may be performed by any method regardless of the furnace and the lamp, and an appropriate temperature and time conditions for allowing the applied ferroelectric material to be transferred to the perovskite structure may be selected.

  The film type and film thickness of the ferroelectric film 28 are not limited to the above and can be selected and determined as appropriate. As the ferroelectric film 28, in addition to lead zirconate titanate, for example, a film in which a metal such as lanthanum is mixed in lead zirconate titanate, a barium titanate film, a strontium / bismuth oxide film, an yttrium / manganese oxide film All ferroelectric films such as can be used.

  The ferroelectric film 28 has visible light transmission characteristics. For example, it is known that a lead zirconate titanate film can be formed with a visible light transmittance of 70 to 80% (Jpn. J. Appl. Phys. Vol. 40 (2001) pp. 5528-5532). reference).

  Next, as shown in FIG. 3C, a transparent electrode film 29 is formed on the entire surface including the peripheral circuit portion so as to be in contact with the surface of the ferroelectric film 28. As the transparent electrode film 29, for example, an ITO (indium tin oxide) film, a ZnO (zinc oxide) film, another transparent conductive film, or the like can be used. As a method for forming the transparent electrode film, any method such as a sputtering method, a vacuum deposition method, or a sol-gel method can be used. The material of the transparent electrode film 29 is not limited.

  Next, as shown in FIG. 3D, the transparent electrode film 29 is patterned, and the other transparent electrode film 29 is removed leaving the wiring 24 on the photodiode 24. The lead wiring portion can be formed so as to pass between pixels.

  Next, as shown in FIG. 3E, a planarized insulating film 31 is formed on the entire surface including the peripheral circuit portion 23, the imaging region including the photodiode 24, the horizontal transfer register, and the output portion. As the insulating film 31, for example, a silicon oxide film, a silicon nitride film, or the like can be used.

  Next, as shown in FIG. 3F, a light shielding film 32 is formed on the region other than the photodiode 24. As the light shielding film 32, for example, an aluminum film, a tungsten film, or the like can be used.

  Next, as shown in FIG. 3G, a protective film 33 made of an insulating film that also serves as a planarizing film is formed on the entire surface. On-chip color filters and on-chip microlenses are formed on the protective film 33. After the formation of the protective film 33, an electrode pad for wire bonding is formed. In this way, an image sensor is manufactured.

  Then, a polarization process is performed on the ferroelectric film 28 during the manufacturing process. The polarization treatment is required to be a temperature that does not affect the element produced in the step prior to the polarization treatment, and to use a ferroelectric film having a Curie temperature higher than the temperature of the subsequent step. It is necessary to select an appropriate ferroelectric film according to the process temperature.

  That is, as long as the conditions are satisfied, after the ferroelectric film 28 and the transparent electrode film 29 are formed, the polarization process may be performed at any time, such as an intermediate process or a final process.

  In the process after forming the transparent electrode film 29, a heat treatment at a temperature equal to or higher than the Curie temperature Tc of the ferroelectric film 28, for example, 380 ° C. in the case of a PZT film, is performed, and the ferroelectric film generated during the manufacturing process. The polarization in 28 is extinguished. After the polarization is extinguished, the ferroelectric film 28 is polarized by applying a required voltage between the lead wiring portion connected to the transparent electrode film 29 and the substrate 22. The heat treatment temperature and time may be selected appropriately depending on the type of the ferroelectric film 28 to be applied and the manufacturing process temperature. For example, in the case of a barium titanate film, the temperature is about 150 ° C.

  When the voltage is applied, for example, in the case of the n-type photodiode shown in FIG. 2 as the photodiode 24, the transparent electrode film 29 side is minus (−) and the substrate 22 side is plus (+) as shown in FIG. For example, an electric field of about 4 MV / CM is applied. By applying this voltage, the ferroelectric film 28 is polarized so that the photodiode 24 side becomes negative (−) and the transparent electrode film 29 side becomes positive (+). After the polarization, voltage application to the transparent electrode film 28 is released. As a result, holes are induced near the interface between the n-type photodiode, that is, the insulating film 25 of the n-type semiconductor region 27N shown in FIG. 2, and the hole accumulation region 36 is induced.

  A depolarization / polarization treatment method in which the temperature is lowered while applying an electric field after applying heat is also effective. That is, the polarization process for the ferroelectric film 28 is performed by applying a voltage between the semiconductor substrate 22 and the transparent electrode film 29 while lowering the temperature after performing a depolarization process by a heat treatment. Although polarization can be obtained even if the heat treatment is omitted, the characteristics are inferior to those obtained when the heat treatment is applied.

  Thus, the target CCD solid-state imaging device is obtained.

  As a manufacturing method of the solid-state imaging device according to the first embodiment, a case where it is applied to the manufacture of a CMOS solid-state imaging device will be described. In the manufacture of a CMOS solid-state imaging device using Cu wiring as the multilayer wiring, it is desirable to terminate the polarization process for the ferroelectric film 28 before the Cu wiring manufacturing process. In this manufacturing method, the structure is produced with the same contents up to FIGS. 3A to 3E. Thereafter, as shown in FIG. 4, an electrode pad 41 is formed on the routing wiring portion of the transparent electrode film 29 drawn out of the photodiode 24 through the through hole of the insulating film 31. The electrode pad 41 can be formed of a conductive film such as tungsten. Next, the same voltage as in the above example is applied between the electrode pad 41 and the substrate 22 to perform polarization processing on the ferroelectric film 28. After the polarization treatment, the voltage application to the transparent electrode film 29 is released.

  In addition, after forming the transparent electrode film 29 as described above, a multilayer wiring layer, an on-chip color filter, and an on-chip microlens are formed. The polarization treatment may be performed in any process as long as the above-described conditions are satisfied as long as the process is after the formation of the ferroelectric film 28 and the transparent electrode film 29.

  By the polarization process on the ferroelectric film 28, the ferroelectric film 28 is polarized so that the photodiode 24 side becomes minus (−) and the transparent electrode film 29 side becomes plus (+), as in the above example. . After the polarization, voltage application to the transparent electrode film 28 is released. Thereby, holes 35 are induced near the interface between the n-type photodiode, that is, the insulating film 25 of the n-type semiconductor region 27N shown in FIG. 2, and the hole accumulation region 36 is formed.

  Thus, the target CMOS solid-state imaging device is obtained.

  According to the solid-state imaging device 21 according to the first embodiment, the ferroelectric film 28 that is polarized through the insulating film 25 is formed on the photodiode 24, whereby the n-type semiconductor of the photodiode 24 is formed. A hole accumulation region 36 is induced in the vicinity of the interface between the region 27N and the insulating film 25. The hole accumulating region 36 can recombine electrons generated from the interface state and annihilate them, so that dark current due to the interface state can be suppressed.

  In the present embodiment, a transparent electrode film 29 is formed on the ferroelectric film 28, and the ferroelectric film 28 is polarized in the subsequent steps. For example, in the final step of the manufacturing process, a voltage is applied between the transparent electrode film 29 and the substrate 22 to polarize the ferroelectric film 28. For this reason, polarization in the direction perpendicular to the substrate 22 can be generated without being affected by the disappearance of polarization due to the thermal process during the manufacturing process, and efficient dark current suppression can be achieved.

  In the present embodiment, it is not necessary to always apply a voltage to the transparent electrode film 29 during use of the solid-state imaging device 21, so that power consumption is suppressed and a leak current that causes white spots does not occur. In the solid-state imaging device 21 of the present embodiment, the transparent electrode film 29 remains even after the manufacturing is completed. Therefore, even when the polarization of the ferroelectric film 28 is reduced, disappears, or reverses for some reason, a voltage is applied between the transparent electrode film 29 and the substrate 22 to normalize the polarization of the ferroelectric film 28. It can be returned to the state.

In this embodiment, the voltage stored by the charge by the polarization treatment of the ferroelectric film 28 is larger than the voltage by the fixed charge of the conventional HfO ₂ film. For this reason, the effect of dark current suppression is greater than when the HfO 2 film is used. Further, since the p + accumulation layer of the HAD sensor is formed by ion implantation, it is difficult to know how much hole accumulation amount is obtained when ions are implanted. This embodiment has a greater effect of suppressing dark current than the HAD sensor.

  FIG. 5 shows a solid-state imaging device according to the second embodiment of the present invention. This figure is a cross-sectional view schematically showing a peripheral circuit section 23 and a photodiode 24 which is a photoelectric conversion element in the imaging region, as in FIG. In the solid-state imaging device 43 according to the present embodiment, an insulating film 25 having a required film thickness is formed on the entire surface of the substrate including the peripheral circuit unit 23 and the photodiode 24 as in the first embodiment. A ferroelectric film 28 and a transparent electrode film 29 are formed on a portion corresponding to the photodiode 24.

In this embodiment, in particular, the barrier film 44 is formed between the ferroelectric film 28 and the transparent electrode film 29. The barrier film 44 can be formed of an insulating film such as a silicon oxide film or a silicon nitride film.
Since other configurations are the same as those described in FIG. 1 and the first embodiment, the same reference numerals are given to portions corresponding to FIG. 1 in FIG.

  According to the solid-state imaging device 43 according to the second embodiment, since the barrier film 44 is interposed between the ferroelectric film 28 and the transparent electrode film 29, the transparent electrode film is provided on the ferroelectric film 28. Unnecessary interference between the two films 28 and 29 that occurs when 29 is directly attached can be suppressed. That is, even if there is a possibility that a reaction occurs between the ferroelectric film 28 and the transparent electrode film 29 depending on the film type of the ferroelectric film 28, the reaction is blocked by the barrier film 44, and both maintain good film characteristics. can do. In addition, the same effects as described in the first embodiment can be obtained.

  Next, FIGS. 6 and 7 show a solid-state imaging device according to a third embodiment of the present invention. The solid-state imaging device according to the present embodiment uses a signal charge as a hole, and the conductivity type of each semiconductor region is a conductivity type opposite to that of the solid-state imaging device 21 in which the signal charge of the first embodiment is an electron. It is constituted by replacing with. In this case, the first conductivity type is p-type and the second conductivity type is n-type. The solid-state imaging device of the present embodiment basically has the same configuration as that shown in FIG. 1 except that the conductivity types are different.

  As shown in FIG. 6, in the solid-state imaging device 51 according to the present embodiment, the peripheral circuit unit 23 and the photodiode 24 in the imaging region are formed on the silicon substrate 22 as in the first embodiment. An insulating film 25 having a required film thickness is formed on the entire surface of the substrate including the peripheral circuit portion 23 and the photodiode 24. The insulating film 25 is formed of, for example, a silicon oxide film after the pixels including the peripheral circuit portion 23 and the photodiode 24 are formed. For example, as shown in FIG. 7, the photodiode 24 is configured by forming a p-type semiconductor region 27P in an n-type semiconductor well region 26N on a p-type silicon substrate 22P.

  Further, in the present embodiment, a ferroelectric film 28 and a transparent electrode film 29 thereon are laminated on the insulating film 25 of the photodiode 24. An insulating layer 31 is formed on the entire surface including the peripheral circuit portion 23 so as to cover the transparent electrode film 29, and a light shielding film 32 is formed on the insulating layer 31 in the region including the peripheral circuit portion 23 other than the photodiode portion 24. Is done. Further, a protective film 33 made of an insulating film is formed on the entire surface so as to cover the light shielding film 32.

The ferroelectric film 28 is polarized by a voltage applied between the transparent electrode film 29 and the silicon substrate 22. In the present embodiment, as shown in FIG. 7, the ferroelectric film 28 is polarized with a plus (+) on the photodiode 24 side and a minus (−) on the transparent electrode film 29 side. The polarized ferroelectric film 28 induces electrons 52 in the vicinity of the interface between the p-type semiconductor region 27P constituting the photodiode 24 and the insulating film 25, and induces an electron storage region 53 in the vicinity of the interface. After the polarization treatment, the switch element 37 is turned off to turn off the power source 38 and no voltage is applied to the transparent electrode film 29.
Since other configurations are the same as those described in the first embodiment, detailed description thereof is omitted.

  The manufacturing method of the solid-state imaging device 51 according to the third embodiment can be manufactured by the same process as described in FIG. 3 with the conductivity type of the semiconductor region reversed.

  According to the solid-state imaging device 51 according to the third embodiment, the ferroelectric film 28 that is polarized through the insulating film 25 is formed on the photodiode 24, whereby the p-type semiconductor of the photodiode 24 is formed. Electrons that are charges opposite to the signal charges (holes in this example) are induced near the interface of the region 27P with the insulating film 25, and the electron accumulation region 53 is induced near the interface. Since holes generated from the interface state can be eliminated by the electron accumulation region 53, dark current due to the interface state can be suppressed. Although the redundant description is omitted, the same effects as described in the first embodiment can be obtained.

  Also in the third embodiment, a barrier film 44 is formed between the ferroelectric film 28 and the transparent electrode film 29 in the same manner as described with reference to FIG. Unnecessary interference can be suppressed.

  As another embodiment of the present invention, the polarization process may be performed after the transparent electrode film 29 of FIG. 3C is formed, for example, without performing the polarization process in the final step. This embodiment can be applied when using the ferroelectric film 28 having a Curie temperature Tc higher than the temperature in the subsequent process of the manufacturing process. As the ferroelectric film 28, for example, strontium / bismuth oxide, lead titanate, magnesium / lead niobate, or the like can be used.

The present invention is not limited to a CCD solid-state imaging device and a CMOS solid-state imaging device, but can be applied to any solid-state imaging device as long as it has a depleted photodiode structure.
The present invention can be applied to both a front-illuminated solid-state imaging device and a back-illuminated solid-state imaging device. For example, in the case of a CMOS solid-state imaging device, it can be applied to a front side irradiation type in which light is incident from the multilayer wiring layer side and a back side irradiation type in which light is incident from the back surface of the substrate opposite to the multilayer wiring layer.
The solid-state imaging device according to the present invention can be applied to a linear image sensor or the like in addition to the above-described area image sensor.

The solid-state imaging device according to the present invention can be applied to electronic devices such as a camera equipped with a solid-state imaging device, a portable device with a camera, and other devices equipped with a solid-state imaging device.
FIG. 8 shows an embodiment applied to a camera as an example of the electronic apparatus of the present invention. The camera 60 according to the present embodiment includes an optical system (optical lens) 61, a solid-state imaging device 62, and a signal processing circuit 63. Any one of the above-described first to third embodiments is applied to the solid-state imaging device 62. The optical system 61 forms image light (incident light) from the subject on the imaging surface of the solid-state imaging device. As a result, signal charges are accumulated in the photoelectric conversion element of the solid-state imaging device 63 for a certain period. The signal processing circuit 63 performs various signal processing on the output signal of the solid-state imaging device 62 and outputs the processed signal. The camera 60 according to the present embodiment includes a camera module in which an optical system 61, a solid-state imaging device 62, and a signal processing circuit 63 are modularized.

The present invention can constitute a camera-equipped portable device such as a mobile phone provided with the camera of FIG. 8 or a camera module.
Furthermore, the configuration of FIG. 8 can be configured as a module having an imaging function in which the optical system 61, the solid-state imaging device 62, and the signal processing circuit 63 are modularized, a so-called imaging function module. The present invention can constitute an electronic apparatus provided with such an imaging function module.

According to the electronic device according to the present embodiment, it is possible to efficiently suppress dark current in the solid-state imaging device, obtain high image quality, and provide a high-performance electronic device.
Compared to a conventional structure in which a hole (or electron) accumulation region is formed by ion implantation, the present embodiment is superior in the ability to bond interface charges that cause random noise. In this embodiment, if the ferroelectric film is left in the solid-state imaging device (imager element), it becomes easy to repolarize after a long period of use.

It is a schematic block diagram of the principal part of the solid-state imaging device which concerns on 1st Embodiment of this invention. It is a block diagram of the photoelectric conversion element part of 1st Embodiment. A to F are manufacturing process diagrams illustrating a manufacturing method of the solid-state imaging device according to the first embodiment. It is sectional drawing of the principal part which shows the other manufacturing method of the solid-state imaging device of this invention. It is a schematic block diagram of the principal part of the solid-state imaging device which concerns on 2nd Embodiment of this invention. It is a schematic block diagram of the principal part of the solid-state imaging device which concerns on 3rd Embodiment of this invention. It is a block diagram of the photoelectric conversion element part of 3rd Embodiment. It is a schematic block diagram at the time of applying the electronic device which concerns on this invention to a camera. It is a schematic sectional drawing of the principal part which shows an example of the conventional solid-state imaging device. It is a schematic sectional drawing which shows an example of the HAD sensor part of the conventional solid-state imaging device. It is a schematic sectional drawing of the principal part which shows the other example of the conventional solid-state imaging device. It is a schematic sectional drawing of the photoelectric conversion element part which shows the other example of the conventional solid-state imaging device.

Explanation of symbols

  21 ..Solid-state imaging device 22 ..Semiconductor substrate 23 ..Peripheral circuit part 24 ..Photoelectric conversion element 25 ..Insulating film 28 ..Ferroelectric film 29 ..Transparent electrode film 31. ..Insulating film 32..Light-shielding film 33..Protective film 36, 53..Charge storage region 44..Barrier film

Claims (13)

A plurality of pixels having photoelectric conversion elements;
A polarized ferroelectric film formed on the photoelectric conversion element of each pixel via an insulating film,
A solid-state imaging device comprising: a transparent electrode film formed on the ferroelectric film. A photodiode serving as the photoelectric conversion element;
2. The solid according to claim 1, further comprising a charge accumulation region in the vicinity of an interface between the first conductivity type semiconductor region constituting the photodiode and the insulating film and a charge opposite to the signal charge induced by the ferroelectric film. Imaging device. The solid-state imaging device according to claim 1, further comprising: a barrier film formed between the ferroelectric film and the transparent electrode film. The insulating film is formed of a silicon oxide film, a metal oxide film selected from Hf, Zr, Pr, Al, Ta, and Ti, or a laminated film of the metal oxide film and a silicon oxide film or a silicon nitride film. The solid-state imaging device according to claim 1. Forming a plurality of pixels having photoelectric conversion elements on a semiconductor substrate;
A step of laminating a ferroelectric film and a transparent electrode film on the photoelectric conversion element via an insulating film;
Performing a depolarization process on the ferroelectric film by performing a heat treatment, and then performing a polarization process;
A method for manufacturing a solid-state imaging device, wherein the transparent electrode film remains after polarization. The solid-state imaging device according to claim 5, wherein after the depolarization process is performed by the heat treatment, the polarization process is performed on the ferroelectric film by applying a voltage between the semiconductor substrate and the transparent electrode film while lowering the temperature. Manufacturing method. After forming the transparent electrode film,
Depositing an insulating film and forming a contact hole in the insulating film;
Forming a connection wiring connected to an extension of the transparent electrode film facing the contact hole;
6. The solid-state imaging device according to claim 5, wherein after the depolarization process is performed on the ferroelectric film, a voltage is applied between the connection wiring and the semiconductor substrate to perform the polar process on the ferroelectric film. Production method. The method for manufacturing a solid-state imaging device according to claim 5, wherein a barrier film is formed between the ferroelectric film and the transparent electrode film. The silicon oxide film, a metal oxide film selected from Hf, Zr, Pr, Al, Ta, and Ti, or a stacked film of the metal oxide film and a silicon oxide film or a silicon nitride film is used as the insulating film. 6. A method for producing a solid-state imaging device according to 5. A solid-state imaging device;
An optical system for guiding incident light to the photoelectric conversion element of the solid-state imaging device;
A signal processing circuit for processing an output signal of the solid-state imaging device;
The solid-state imaging device
A plurality of pixels having the photoelectric conversion element;
A polarized ferroelectric film formed on the photoelectric conversion element of each pixel via an insulating film,
An electronic device comprising: a transparent electrode film formed on the ferroelectric film. A photodiode serving as the photoelectric conversion element;
11. The electron according to claim 10, further comprising: a charge accumulation region due to a charge opposite to a signal charge induced by the ferroelectric film, in a vicinity of an interface between the first conductivity type semiconductor region constituting the photodiode and the insulating film. machine. The electronic device according to claim 10, further comprising: a barrier film formed between the ferroelectric film and the transparent electrode film. The insulating film is formed of a silicon oxide film, a metal oxide film selected from Hf, Zr, Pr, Al, Ta, and Ti, or a laminated film of the metal oxide film and a silicon oxide film or a silicon nitride film. The electronic device according to claim 10.

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