JP2006147657A - Solid-state imaging apparatus and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid-state imaging apparatus having a high sensitivity and little after-image, and to provide its manufacturing method. <P>SOLUTION: When light is incident into a photoelectric conversion film 21, paired electron-holes are created and the holes move to the side of a transparent electrode 22 while the electrons are accumulated in an accumulation diode 13 via a pixel electrode 20. At this point, since there is no recombination center nor a trap level inside the crystalline photoelectric conversion film 21, the reduction in photoelectric current due to the absorption of the electrons created by photoelectric conversion by a recombination center or a trap level and the occurrence of after-image due to the emission of the carrier from the trap level can be suppressed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a solid-state imaging device, in particular, a stacked solid-state imaging device and a method for manufacturing the same.

Conventionally, CCD (Charge-Coupled Device) type and MOS (Metal Oxide)
2. Description of the Related Art Solid-state imaging devices that use a semiconductor imaging device such as a (Semiconductor) type are widely used. In these semiconductor imaging devices for solid-state imaging devices, a signal charge accumulation region, a signal charge readout region, and a signal charge transfer region are formed in a planar manner on a semiconductor substrate.

  In recent years, a semiconductor having a structure in which a photoelectric conversion film is formed on a charge transfer element instead of a semiconductor image pickup element in which a signal charge accumulation region, a signal charge readout region, and a signal charge transfer region are formed in a plane on a semiconductor substrate. A solid-state imaging device using an imaging element has been developed (see, for example, Patent Document 1).

  FIG. 6 shows the structure of this solid-state imaging device disclosed in Patent Document 1 as the prior art. An element isolation layer 62, a storage diode 63 that is a signal charge storage region, and a vertical CCD channel 64 that is a signal charge transfer region are formed on the silicon substrate 61 that is a semiconductor substrate. A space between the storage diode 63 and the vertical CCD channel 64 corresponds to a signal readout region.

  In addition, transfer electrodes 66 and 67 are formed on the silicon substrate 61 via a first insulating layer 65. A lead electrode 68 is formed along the first insulating layer 65 and is electrically connected to the storage diode 63. A second insulating layer 69 and a pixel electrode 70 are formed on the extraction electrode 68, and the extraction electrode 68 and the pixel electrode 70 are electrically connected. Further, a photoelectric conversion film 71 formed by laminating a plurality of layers is provided on a semiconductor imaging element serving as the solid-state imaging device, and a transparent electrode 72 is formed thereon.

  The solid-state imaging device according to the invention disclosed in Patent Document 1 basically has the same configuration as that of the solid-state imaging device of FIG. 5, and is formed with a groove portion that partitions the pixel electrode for each pixel. The difference is that a void is formed in the photoelectric conversion film in the region to be processed. Therefore, the materials used for the photoelectric conversion film should be equivalent, and it is described that amorphous silicon (a-Si) is used.

  The solid-state imaging device having the above-described configuration has an excellent characteristic that it has high sensitivity and low smear because the opening area of the photosensitive portion can be widened. For this reason, this solid-state imaging device is expected to be applied to cameras such as various monitoring televisions and HDTV (High Definition TeleVision).

  A technique for crystallizing an amorphous semiconductor film by heat treatment, laser light irradiation, or the like is also known (see, for example, Patent Document 2).

JP-A-7-86546 JP 2002-50575 A

  However, in the conventional solid-state imaging device, since amorphous silicon (amorphous silicon) is used for the photoelectric conversion film, there are many defects that become recombination centers and trap levels in the photoelectric conversion film. For this reason, there are problems such that carriers generated by photoelectric conversion are absorbed by recombination centers and trap levels to reduce the photocurrent, and afterimages are generated due to carrier emission from the trap levels.

  An object of the present invention is to provide a solid-state imaging device with high sensitivity and low afterimage and a method for manufacturing the same.

The present invention relates to a stacked solid-state imaging device including a transfer electrode, a photoelectric conversion film, and an electrode on a semiconductor substrate having a signal charge transfer region.
The photoelectric conversion film is a solid-state imaging device characterized in that it is a recrystallized semiconductor film.

  According to the present invention, a semiconductor substrate having a signal charge transfer region, a transfer electrode for transferring a signal charge to the signal charge transfer region, a photoelectric conversion film formed on the semiconductor substrate and the transfer electrode, and a semiconductor substrate And a solid-state imaging device using a stacked type semiconductor imaging device is formed. Since a recrystallized semiconductor film is used for the photoelectric conversion film, there are no recombination centers and trap levels in the photoelectric conversion film, and electrons generated by photoelectric conversion are absorbed by the recombination centers and trap levels. Accordingly, it is possible to suppress the reduction of the photocurrent due to the above and the generation of an afterimage due to the carrier emission from the trap level.

  In the present invention, the photoelectric conversion film has a recrystallized crystal grain size larger than one pixel.

  According to the present invention, since the size of the recrystallized crystal grains in the photoelectric conversion film is larger than the size of one pixel, the crystal grain boundary density in the pixel region is lowered and the photocurrent is reduced. Can be taken out with loss.

  According to the present invention, since the recrystallized semiconductor film is used for the photoelectric conversion film, the photoelectric conversion film has no recombination center or trap level contained in the amorphous film, and is generated by photoelectric conversion. It is possible to suppress a decrease in photocurrent due to absorption of electrons by recombination centers and trap levels and generation of an afterimage due to carrier emission from the trap levels.

  Further, according to the present invention, since the size of the recrystallized crystal grains in the photoelectric conversion film is larger than the size of one pixel, the crystal grain boundary density in the pixel region is lowered, and the photocurrent is reduced. Can be taken out with low loss.

  FIG. 1 shows a schematic configuration of a solid-state imaging device 10 as an embodiment of the present invention. On top of a p-type silicon substrate 11 which is a semiconductor substrate, a p + type element isolation layer 12, an n− type storage diode 13 which is a signal charge storage region, and an n− type vertical CCD channel 14 which is a signal charge transfer region. Is formed. A portion between the storage diode 13 and the vertical CCD channel 14 functions as a signal charge reading unit. In addition, transfer electrodes 16 and 17 are formed in the vertical CCD channel 14 and the signal charge readout region on the p-type silicon substrate 11 via the first insulating layer 15. The transfer electrodes 16 and 17 transfer charges from the signal charge storage region in which charges generated in the photoelectric conversion film are stored to the signal charge transfer region.

  The first insulating layer 15 is formed so as to cover up to the vertical CCD channel 14, the signal charge reading region and a part of the storage diode 13. A lead electrode 18 is formed along the first insulating layer 15. The extraction electrode 18 is substantially V-shaped and is electrically connected to the storage diode 13. A second insulating layer 19 is formed on the extraction electrode 18. Further, a pixel electrode 20 is formed on the extraction electrode 18 and the second insulating layer 19, and the extraction electrode 18 and the pixel electrode 20 are electrically connected.

This includes a p-type silicon substrate 11, an element isolation layer 12, a storage diode 13, a vertical CCD channel 14, a first insulating layer 15, transfer electrodes 16 and 17, an extraction electrode 18, a second insulating layer 19 and a pixel electrode 20. The charge transfer element 111 is configured as described above. A photoelectric conversion film 21 to be described later is deposited and formed on a semiconductor chip as the charge transfer element 111. Then, ITO (Indium Tin) is formed on the photoelectric conversion film 21 by a reactive sputtering method or the like.
A transparent electrode 22 made of Oxide) or tin oxide is formed.

  The photoelectric conversion film 21 is made of a crystalline silicon film, and the crystal grain size is grown larger than the size of one pixel. The size of one pixel of the solid-state imaging device 10 is 1/2 type and 2 million pixels, and is about 4 μm.

  FIG. 2 shows an enlarged view of the photoelectric conversion film 21 of the solid-state imaging device 10 of FIG. Compared to the area of one pixel of the solid-state imaging device 10, the crystal grain is larger than that, so that the density of crystal grain boundaries existing in one pixel 112 can be lowered. Therefore, the photocurrent can be taken out with low loss, and a highly sensitive solid-state imaging device 10 can be created. That is, when the crystal grain size is 0.3 μm, as will be described later, the total extension of the grain boundary 113 in the 4 μm square pixel is 107 μm on average, but when the crystal grain size becomes 4 μm, the length is increased. Is 8 μm and is reduced to 1/14.

3 and 4 show schematic steps for manufacturing the solid-state imaging device 10 of FIG.
FIG. 3A shows a state in which an N-type amorphous silicon film 32 is first formed on the charge transfer element 111 by a plasma CVD method in order to form the photoelectric conversion film 21. FIG. 3B shows a state in which hydrofluoric acid treatment is performed to remove dirt and a natural oxide film, and then an oxide film 33 is formed. If the contamination can be ignored, the natural oxide film may be used as it is instead of the oxide film 33. Here, the oxide film 33 is formed by irradiation with ultraviolet (UV) light in an oxygen atmosphere. As a method for forming the oxide film 33, a thermal oxidation method may be used. Alternatively, treatment with hydrogen peroxide may be used.

  This oxide film 33 is used for spreading the acetate solution over the entire surface of the amorphous silicon film 32 in the subsequent step of applying an acetate solution containing nickel, that is, for improving the wettability. is there. For example, when an acetate solution is applied directly to the surface of the amorphous silicon film 32, amorphous silicon repels the acetate solution, so nickel may be introduced to the entire surface of the amorphous silicon film 32. Can not. That is, uniform crystallization cannot be performed.

  FIG. 3C shows a state in which an acetate solution 34 in which nickel is added to an acetate solution is made and this acetate solution 34 is dropped on the surface of the oxide film 33 on the amorphous silicon film 32. FIG. 3D shows a state where spin drying is performed using the spinner 35. If the concentration of nickel in the acetate solution 34 is 1 ppm or more, preferably 10 ppm or more, it is practical. Further, when a nonpolar solvent such as a toluene solution of nickel 2-ethylhexanoate is used as the solution, the oxide film 33 is unnecessary, and the catalytic element can be directly introduced onto the amorphous silicon film 32.

  FIG. 4A shows an average film of several to hundreds of gallium on the oxide film 33 on the surface of the amorphous silicon film 32 after the spin-drying of the nickel acetate solution 34 is applied several times. The state where the layer 34a containing nickel having a thickness is formed is shown. In this case, nickel in the layer 34a diffuses into the amorphous silicon film 32 in the subsequent heating step, and acts as a catalyst for promoting crystallization.

  In FIG. 4B, the heat treatment at 550 ° C. for 4 hours is performed in a nitrogen atmosphere, whereby the amorphous silicon film 32 shown in FIG. Indicates the state. The crystal grows in the vertical direction in the figure, that is, in the thickness direction of the semiconductor chip as the charge transfer element 111. Then, as shown in FIG. 4C, a laser annealing process for crystal growth that further promotes the crystallinity of the crystalline silicon film 36 is performed, for example, by irradiation with KrF excimer laser light.

  FIG. 4D shows a state where an impurity (boron) is implanted on the N-type crystalline silicon film 36 by plasma doping to form a P-type crystalline silicon film 37 thereafter. Subsequently, as shown in FIG. 4E, laser light is irradiated from the upper surface, laser annealing treatment is performed, and the doped impurities are activated. Then, a transparent electrode 22 to be the pixel electrode 20 is formed. The solid-state imaging device 10 shown in FIG. 1 is completed through the above steps.

  Next, the operation of the solid-state imaging device 10 of FIG. 1 having such a configuration will be described. When light enters the photoelectric conversion film 21, an electron / hole pair is generated, the hole moves to the transparent electrode 22 side, and the electron is stored in the storage diode 13 through the pixel electrode 20. At this time, since there is no recombination center or trap level in the photoelectric conversion film 21, the photocurrent is reduced due to absorption of electrons generated by photoelectric conversion in the recombination center or trap level, or the trap level. It is possible to suppress the occurrence of an afterimage due to carrier emission from the.

  The p-type surface layer of the photoelectric conversion film 21 is set to the same potential as that of the silicon substrate 11 and is maintained in a non-depleted state except for the pn junction portion. Then, when a high voltage pulse is applied to the transfer electrodes 16 and 17 according to a known interline transfer method, the signal charge reading unit becomes conductive, and the signal charge stored in the storage diode 13 is transferred to the vertical CCD channel 14. Is done.

  FIG. 5 is an enlarged view of a case where a polycrystalline silicon film is used for the photoelectric conversion film 21 in the solid-state imaging device 10 of FIG. Since the crystal grain size of the polycrystalline silicon film is relatively small, such as about 0.3 μm, the density of crystal grain boundaries existing in one pixel 112 is large. Since electrons are scattered at the crystal grain boundary 113, a loss of photocurrent occurs when the frequency of passing through the crystal grain boundary 113 increases, resulting in a decrease in sensitivity of the solid-state imaging device. Therefore, it is preferable to increase the crystal grain size. However, the sensitivity reduction can be improved as compared with the conventional case where an amorphous silicon film is used.

  As described above, since the solid-state imaging device 10 of the present embodiment uses a recrystallized semiconductor having a crystal grain boundary larger than that of the pixel 112 as the photoelectric conversion film 21, the recombination center and the trap level are compared with amorphous silicon. There are few defects. For this reason, it is possible to solve the problem that the sensitivity is reduced due to the decrease in photocurrent and the afterimage due to the trap level is generated, and the solid-state imaging device 10 having high sensitivity and low afterimage can be provided. Play.

1 is a cross-sectional view illustrating a schematic configuration of a solid-state imaging device 10 as an embodiment of the present invention. It is a figure which expands and shows the photoelectric converting film 21 of the solid-state imaging device 10 of FIG. It is sectional drawing which shows the state in the schematic process of manufacturing the solid-state imaging device 10 of FIG. It is sectional drawing which shows the state in the schematic process of manufacturing the solid-state imaging device 10 of FIG. It is a figure which expands and shows the case where a polycrystalline film is used for the photoelectric converting film 21 of the solid-state imaging device 10 of FIG. It is sectional drawing which shows the schematic structure of the conventional laminated | stacked solid-state imaging storage.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Solid-state imaging device 11 P-type silicon substrate 12 Element isolation layer 13 Storage diode 14 Vertical CCD channel 15 1st insulating layer 16, 17 Transfer electrode 18 Extraction electrode 19 2nd insulating layer 20 Pixel electrode 21 Photoelectric conversion film 22 Transparent electrode 32 Amorphous silicon film 33 Oxide film 34 Acetate solution 35 Spinner 36 N-type crystalline silicon film 37 P-type crystalline silicon film 111 Charge transfer element 112 Pixel 113 Grain boundary

Claims (2)

In a stacked solid-state imaging device including a transfer electrode, a photoelectric conversion film, and an electrode on a semiconductor substrate having a signal charge transfer region,
A solid-state imaging device, wherein the photoelectric conversion film is a recrystallized semiconductor film.   The solid-state imaging device according to claim 1, wherein the photoelectric conversion film has a recrystallized crystal grain size larger than one pixel.

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