JP4482253B2 - Photodiode array, solid-state imaging device, and radiation detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a photodiode array, a solid-state imaging device including the photodiode array, and a radiation detector.
[0002]
[Prior art]
A solid-state imaging device can be configured by arranging a plurality of photodiodes on a common substrate. The photodiode array can also be used as a radiation detector of an X-ray tomography apparatus (hereinafter referred to as “CT apparatus”). Here, when a photodiode array is used as a radiation detector for a CT apparatus, a scintillator is generally mounted on the light incident surface of the photodiode array in order to obtain a good detection result. As described above, when the scintillator is mounted on the light incident surface of the photodiode array, it is required to make the light incident surface side of the photodiode array as flat as possible in order to improve spatial resolution (resolution) and assembly efficiency.
[0003]
[Problems to be solved by the invention]
As a method for flattening the light incident surface side of the photodiode array, since the photodiode is usually provided with electrodes and wirings on the front surface side, the back surface may be configured as the light incident surface.
[0004]
However, in a so-called back-illuminated photodiode array in which electrodes and wiring are removed from the light incident surface side, carriers move by the thickness of the n− type substrate. In this case, when a bias is applied, the depletion layer is difficult to spread in the vertical direction, so that crosstalk is likely to occur between the photodiodes. Therefore, in order to apply a voltage to the n− type substrate via the n + type channel stopper layer, it is important to suppress the occurrence of crosstalk as much as possible.
[0005]
Therefore, the present invention can obtain a photodiode array, a solid-state imaging device having high imaging accuracy, and a high resolution that can satisfactorily suppress the occurrence of crosstalk even if electrodes and wirings are collected on one side. An object is to provide a radiation detector that can be used.
[0006]
[Means for Solving the Problems]
The photodiode array according to the present invention has a plurality of second conductivity type semiconductor layers on one surface side of the first conductivity type semiconductor substrate, a photodiode is formed by the semiconductor substrate and the second conductivity type semiconductor layer, and from the other surface side of the semiconductor substrate. In the photodiode array to which the light to be detected is incident, it is formed on the other surface side of the semiconductor substrate, and is provided on the one surface side of the first conductivity type accumulation layer having an impurity concentration higher than that of the semiconductor substrate. The first conductivity type channel stopper layer having an impurity concentration higher than that of the semiconductor substrate is provided on one surface side of the semiconductor substrate so as to substantially surround each photodiode, and extends to the other surface side of the channel stopper layer. A trench portion, and at least one portion around each photodiode does not have a trench portion. There are formed, through which each trench absence unit, site each other corresponding to the photodiodes adjacent to each other of the channel stopper layer is characterized by being continuous.
[0007]
This photodiode array is a so-called back-illuminated photodiode array in which electrodes and wiring are removed from the light incident surface side, and has a first conductivity type (n− type) semiconductor substrate. A plurality of second conductivity type (p-type) semiconductor layers (impurity diffusion layers) are disposed on one surface side (front surface side) of the semiconductor substrate. Further, a first conductivity type (n + type) channel stopper layer having an impurity concentration higher than that of the semiconductor substrate is provided on one surface side of the semiconductor substrate, and extends to the other surface side of the channel stopper layer. And a trench portion that roughly surrounds. A voltage is applied to the semiconductor substrate from the cathode through the n + type channel stopper layer.
[0008]
Here, the trench portion surrounds almost the entire periphery of each photodiode, but does not completely surround the periphery of each photodiode. That is, a trench non-existing portion where no trench portion exists is formed at least at one place around each photodiode. The portions corresponding to the photodiodes adjacent to each other in the channel stopper layer are (electrically) continuous through these trench non-existing portions. Thus, in this photodiode array, it is not necessary to provide an electrode for each photodiode, and the number of electrodes (cathodes) can be reduced. Accordingly, it is not necessary to route the wiring for the cathode on the semiconductor substrate, so that the aperture ratio can be increased and the assembling efficiency can be improved.
[0009]
Further, in this photodiode array, carriers generated by light incident from the other surface side (back surface side) of the semiconductor substrate are extended to the other surface side than the respective channel stopper layers, and are roughly surrounded by the trench portion. Movement between adjacent photodiodes is restricted. Therefore, in this photodiode array, it is possible to satisfactorily suppress the occurrence of crosstalk even if electrodes and wirings are gathered on one side.
[0010]
In this case, it is preferable that the trench non-existing portion is provided at one location for each of the two opposing edge portions of each photodiode.
[0011]
In addition, one trench non-existing portion may be provided for each photodiode.
[0012]
By disposing a plurality of photodiodes as described above on a common substrate, it is possible to easily realize a solid-state imaging device having high imaging accuracy.
[0013]
Further, a substrate for fixing each photodiode as described above is prepared, and each second conductivity type semiconductor layer is bump-connected to a predetermined wiring of the substrate via an anode, and each channel stopper layer is connected via a cathode. A bump detector connected to a predetermined wiring on the substrate and a scintillator attached to the other side of the photodiode array makes it possible to easily realize a radiation detector capable of obtaining high resolution.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of a photodiode array, a solid-state imaging device, and a radiation detector according to the present invention will be described in detail with reference to the drawings.
[0015]
FIG. 1 is a cross-sectional view showing a first embodiment of a photodiode array according to the present invention. FIG. 2 is a plan view of the photodiode array of FIG. 1 as viewed from the light incident side, with electrodes and surface insulating films omitted. A photodiode array 1 shown in these drawings is a so-called back-illuminated photodiode array in which electrodes and wiring are removed from the light incident surface side, and includes a semiconductor substrate 2 made of n-type (first conductivity type) Si or the like. . The semiconductor substrate 2 has an impurity concentration of about 1.0 × 10 ¹² / cm ³ , for example, and its thickness is about 270 μm, for example. On one side of the semiconductor substrate 2, that is, on the surface 2s of the semiconductor substrate 2, a plurality of second conductive semiconductor layers (p-type impurity diffusion layers) 3 made of p-type (second conductive type) Si or the like are formed in a matrix ( In the present embodiment, 2 × 2 = 4) are arranged to constitute a photodiode array. Each second conductivity type semiconductor layer 3 has an impurity concentration of about 1.0 × 10 ¹⁹ / cm ³ , and a depth (thickness) from the surface 2 s is, for example, about 0.5 μm.
[0016]
Further, on the surface 2s side (one surface side) of the semiconductor substrate 2, an n + type (first conductivity type) having an impurity concentration higher than that of the semiconductor substrate 2 so as to be located in the vicinity of each of the second conductivity type semiconductor layers 3. ) A channel stopper layer 4 made of Si or the like is provided. As shown in FIG. 2, in this embodiment, the channel stopper layer 4 is formed in a lattice shape so as to surround the periphery of each second conductivity type semiconductor layer 3. The channel stopper layer 4 has an impurity concentration of about 1.0 × 10 ¹⁸ / cm ³ , and the depth (thickness) from the surface 2s is, for example, about 1.5 μm.
[0017]
Further, an insulating layer 5 is laminated on the surface 2s of the semiconductor substrate 2, and a pattern wiring made of polysilicon, Au, Al or the like is applied. Each second conductive type semiconductor layer 3 is connected to an electrode Ea serving as an anode in the pattern wiring, and each channel stopper layer 4 is connected to an electrode Ec serving as a cathode in the pattern wiring (see FIG. 2). Is done. As a result, a voltage is applied to the semiconductor substrate 2 from an electrode pad and an electrode Ec (not shown) through the n + type channel stopper layer 4. As a material for forming the insulating layer 5, SiO ₂ or SiN _x can be used.
[0018]
On the other hand, an accumulation layer 6 for preventing carriers generated in the semiconductor substrate 2 from recombining at the back surface 2u is formed on the back surface 2u of the semiconductor substrate 2 serving as a light incident surface. The accumulation layer 6 is made of n-type Si or the like, and has an impurity concentration of, for example, about 5.0 × 10 ¹⁸ / cm ³ . The thickness of the accumulation layer 6 is, for example, about 0.2 μm. A protective layer 7 is further laminated on the accumulation layer 6, and a light shielding film 8 having a plurality of openings 8 a corresponding to the PD junction region is laminated on the protective layer 7. Thereby, crosstalk between PDs can be improved. As a material for forming the light shielding film 8, for example, a black photoresist in which a black dye or an insulating pigment such as carbon black is mixed in a photoresist, a light shielding metal, or the like can be used.
[0019]
As described above, the photodiode array 1 is configured as a so-called back-illuminated type. In this case, if no countermeasure is taken, crosstalk is likely to occur between the photodiodes. In view of this point, a trench portion 10 is formed on the surface 2s side (one surface side) of the semiconductor substrate 2 of the photodiode array 1 as shown in FIGS.
[0020]
As shown in FIGS. 1 and 2, the trench portion 10 is formed in a lattice-shaped groove (concave portion) 11 formed so as to penetrate the central portion of the channel stopper layer 4 formed in a lattice shape, and on the surface of the groove 11. It consists of the laminated insulating layer 12 and the insulator 14 embedded in the groove 11. As shown in FIG. 1, the trench portion 10 extends to the back surface 2 u side from the channel stopper layer 4. That is, the depth from the surface 2 s of the trench portion 10 is larger than the depth from the surface 2 s of each channel stopper layer 4.
[0021]
As a material for forming the insulating layer 12, SiO ₂ or SiN _x can be used. As the insulator 14, as in the light shielding film 8, for example, a black photoresist in which a black dye or an insulating pigment such as carbon black is mixed in the photoresist can be used. Furthermore, as the insulator 14, a resin such as polyimide, a non-doped insulating silica solution, or the like can be used. In this case, the insulator 14 may be embedded in the groove 11 by introducing a resin such as polyimide or a non-doped insulating silica solution into the groove 11 by spin coating and baking. Further, the pattern wiring may be arranged (turned) along the trench portion 10 (insulator 14).
[0022]
Here, as shown in FIG. 2, the trench portion 10 surrounds almost the entire periphery of each second conductivity type semiconductor layer 3 and the portion 4 c surrounding each second conductivity type semiconductor layer 3 of the channel stopper layer 4. However, it does not completely surround the second conductive semiconductor layer 3 and the portion 4c. That is, as shown in FIG. 2, a trench non-existing portion 9 in which the trench portion 10 does not exist is formed at each of the two opposite edge portions of each second conductivity type semiconductor layer 3 at one location. Yes. The portions 4 c corresponding to the second conductive semiconductor layers 3 adjacent to each other of the channel stopper layer 4 are electrically continuous with each other through the trench non-existing portions 9.
[0023]
As described above, when the trench non-existing portion 9 is provided in at least one place around each of the second conductive type semiconductor layers 3, the portions 4 c corresponding to the second conductive type semiconductor layers 3 adjacent to each other of the channel stopper layer 4. Can be made continuous. Therefore, it is not necessary to provide an electrode (cathode) Ec for each second conductivity type semiconductor layer 3, and the number of electrodes Ec can be reduced as shown in FIG. 2 (one in this embodiment). As a result, it is not necessary to route the cathode wiring on the semiconductor substrate 2, so that the aperture ratio can be increased and the assembly efficiency can be improved.
[0024]
In the photodiode array 1 configured as described above, when light is incident from the back surface 2u side of the semiconductor substrate 2, carriers (electrons / holes) are generated in response to the incident light. The generated carriers move according to the electric field in the semiconductor substrate 2, one of which is connected to the second conductive semiconductor layer 3 from the electrode Ec serving as a cathode through the n + -type channel stopper layer 4. It is taken out from the electrode Ea serving as the anode and output to the outside through the electrode pad.
[0025]
Here, as described above, in the photodiode array 1, the trench portion 10 extends to the other side of the channel stopper layer 4, and the periphery of each photodiode is the trench portion except for the trench non-existing portion 9. 10 is outlined. Therefore, the movement of the carriers generated by the light incident from the back surface 2 u of the semiconductor substrate 2 between the adjacent photodiodes is restricted by the trench portion 10. As a result, in the photodiode array 1, it is possible to satisfactorily suppress the occurrence of crosstalk even if the pattern wirings including the electrode Ea serving as the anode and the electrode Ec serving as the cathode are collected on the surface 2s side.
[0026]
By using the photodiode array 1 described above, a solid-state imaging device having high imaging accuracy and a radiation detector capable of obtaining high resolution can be easily configured. For example, when configuring a radiation detector, a wiring board 15 is prepared as shown in FIG. The wiring substrate 15 is obtained by applying a wiring pattern on a glass epoxy substrate or a flexible substrate. On this wiring board 15, as shown in FIG. 4, a plurality (in this case, four) of photodiode arrays 1 are arranged. That is, the wiring pattern provided on the surface 2s side of the photodiode array 1 is electrically connected to the wiring pattern of the wiring board 15 via the bumps 16 (see FIG. 5). Furthermore, if the gap between the wiring board 15 and each photodiode array 1 is filled with an insulating resin or the like, the mechanical strength of the entire radiation detector can be improved.
[0027]
When each photodiode array 1 is mounted on the wiring board 15, as shown in FIG. 5, the scintillator 17 is fixed to the back surface 2u side of each photodiode array 1, whereby the radiation detector 20 is completed. As described above, in the photodiode array 1, since the wiring patterns (electrodes) are collected on the front surface 2s side, the back surface 2u side of the photodiode array 1 is in a flat state where no protrusions such as electrodes exist. . Accordingly, it is possible to attach the scintillator 17 to the back surface 2u side of the photodiode array 1 very easily and reliably. Further, since the photodiode array 1 and the scintillator 17 can be maintained in an extremely close state, the radiation detector 20 has a high spatial resolution (resolution). As the scintillator 17, as shown in FIG. 5, one that covers the entire photodiode array 1 may be used, or a plurality that covers only one photodiode array 1 may be used.
[0028]
FIG. 6 shows a modification of the first embodiment of the photodiode array according to the present invention. The photodiode array 1A shown in FIG. 1 is obtained by increasing the number of pixels of the photodiode array 1 shown in FIGS. 1 and 2 while maintaining the basic configuration. In this example, the photodiode array 1A includes 4 × 4 = 16 photodiodes. Even in the case where the number of pixels is increased as in this photodiode array 1A, if the trench non-existing portion 9 is provided in at least one place around each photodiode, the portions corresponding to the photodiodes adjacent to each other in the channel stopper layer 4 4c can be made continuous. Accordingly, it is not necessary to provide an electrode (cathode) Ec for each photodiode, and the number of electrodes Ec can be reduced as shown in FIG. 6 (four in this example). As a result, the aperture ratio can be increased and the assembly efficiency can be improved.
[0029]
7 and 8 show a second embodiment of the photodiode array according to the present invention. In addition, the same code | symbol is attached | subjected about the element same as the element demonstrated regarding 1st Embodiment mentioned above, and the overlapping description is abbreviate | omitted. In the photodiode array 1B shown in these drawings, a plurality of trench portions 10 are provided for each photodiode with respect to the semiconductor substrate 2, and each trench portion 10 is formed so as to substantially surround only the periphery of each photodiode. Yes. Then, as shown in FIG. 7, a trench non-existing portion 9 in which the trench portion 10 does not exist is formed for each one edge portion (one side of the outer periphery) of each photodiode. Through the non-existing portion 9, the portions 4c corresponding to the photodiodes adjacent to each other of the channel stopper layer 4 are (electrically) continuous.
[0030]
Even if such a configuration is adopted, the portions 4c corresponding to the photodiodes adjacent to each other of the channel stopper layer 4 can be electrically connected to each other. Therefore, it is not necessary to provide an electrode (cathode) Ec for each photodiode, and the number of electrodes Ec can be reduced as shown in FIG. 7 (one in this embodiment). As a result, it is not necessary to route the cathode wiring on the semiconductor substrate 2, so that the aperture ratio can be increased and the assembly efficiency can be improved.
[0031]
Also in the photodiode array 1B, as shown in FIG. 8, each trench portion 10 extends to the other surface side from the channel stopper layer 4, and the periphery of each photodiode except for the trench non-existing portion 9, It is substantially surrounded by the trench portion 10. Therefore, the movement of the carriers generated by the light incident from the back surface 2 u of the semiconductor substrate 2 between the adjacent photodiodes is restricted by the trench portion 10. As a result, in the photodiode array 1B, it is possible to satisfactorily suppress the occurrence of crosstalk even if the pattern wirings including the electrode Ea serving as the anode and the electrode Ec serving as the cathode are collected on the surface 2s side.
[0032]
FIG. 11 shows a third embodiment of the photodiode array according to the present invention. In addition, the same code | symbol is attached | subjected about the element same as the element demonstrated regarding 1st Embodiment etc. mentioned above, and the overlapping description is abbreviate | omitted. In the photodiode array 1D shown in FIG. 11, as in the photodiode array 1B according to the second embodiment described above, a plurality of trench portions 10 are provided for each photodiode on the semiconductor substrate 2, and each trench portion 10 is These are formed so as to roughly surround only the periphery of each photodiode. On the other hand, the photodiode array 1D has a trench non-existing portion 9 provided so as to correspond to any one corner portion (in this embodiment, the upper left corner portion in the figure) of each photodiode. Different from the photodiode array 1B according to the second embodiment. Also in this case, the portions 4c corresponding to the photodiodes adjacent to each other in the channel stopper layer 4 are electrically continuous with each other through the trench non-existing portions 9.
[0033]
Even if such a configuration is adopted, the portions 4c corresponding to the photodiodes adjacent to each other of the channel stopper layer 4 can be electrically connected to each other. Therefore, it is not necessary to provide an electrode (cathode) Ec for each photodiode, and the number of electrodes Ec can be reduced as shown in FIG. 11 (one in this embodiment). As a result, it is not necessary to route the cathode wiring on the semiconductor substrate 2, so that the aperture ratio can be increased and the assembly efficiency can be improved.
[0034]
【The invention's effect】
Since the photodiode array according to the present invention is configured as described above, the following effects are obtained. That is, the photodiode array according to the present invention has a plurality of second conductive semiconductor layers on one surface side of the first conductive semiconductor substrate, the photodiode is formed by the semiconductor substrate and the second conductive semiconductor layer, and the other surface of the semiconductor substrate. Detected light is incident from the side, and is provided on one side of the semiconductor substrate so as to roughly surround the periphery of each photodiode and the first conductivity type channel stopper layer having a higher impurity concentration than the semiconductor substrate. Provided on one side of the semiconductor substrate and extending to the other side of the channel stopper layer, and at least one portion around each photodiode is formed with a trench non-existing portion where no trench portion exists. The portions corresponding to the photodiodes adjacent to each other in the channel stopper layer through each trench non-existing portion Judges are continuous. Therefore, in this photodiode, the occurrence of crosstalk can be satisfactorily suppressed even if the electrodes and wirings are gathered on one side. If such a photodiode array according to the present invention is used, a solid-state imaging device having high imaging accuracy and a radiation detector capable of obtaining high resolution can be realized.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a photodiode array according to the present invention.
FIG. 2 is a plan view of the photodiode array of FIG. 1 as viewed from the light incident side.
FIG. 3 is a plan view showing an example of a wiring board on which a photodiode array according to the present invention can be mounted.
FIG. 4 is a plan view showing a state in which a photodiode array according to the present invention is mounted on a substrate.
FIG. 5 is a cross-sectional view illustrating an example of use of a photodiode array according to the present invention.
FIG. 6 is a cross-sectional view showing a modification of the first embodiment of the photodiode array according to the present invention.
FIG. 7 is a cross-sectional view showing a second embodiment of the photodiode array according to the present invention.
8 is a plan view of the photodiode array of FIG. 7 as viewed from the light incident side.
FIG. 9 is a sectional view showing a modification of the photodiode array according to the second embodiment of the present invention.
10 is a plan view of the photodiode array of FIG. 9 as viewed from the light incident side.
FIG. 11 is a sectional view showing a third embodiment of the photodiode array according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1,1A, 1B, 1C ... Photodiode array, 2 ... Semiconductor substrate, 2s ... Front surface, 2u ... Back surface, 3 ... 2nd conductivity type semiconductor layer, 4 ... Channel stopper layer, 5 ... Insulating layer, 6 ... Accumulation layer, 7 DESCRIPTION OF SYMBOLS ... Protective layer, 8 ... Light shielding film, 9 ... Trench non-existing part, 10 ... Trench part, 11 ... Groove, 12 ... Insulating layer, 14 ... Insulator, 15 ... Wiring board, 16 ... Bump, 17 ... Scintillator, 20 ... Radiation detector, Ea, Ec ... electrodes.

Claims (5)

A plurality of second conductivity type semiconductor layers are provided on one surface side of the first conductivity type semiconductor substrate, a photodiode is formed by the semiconductor substrate and the second conductivity type semiconductor layer, and light to be detected is transmitted from the other surface side of the semiconductor substrate. In the incident photodiode array,
An accumulation layer of a first conductivity type formed on the other surface side of the semiconductor substrate and having a higher impurity concentration than the semiconductor substrate;
A channel stopper layer of a first conductivity type provided on the one surface side of the semiconductor substrate and having a higher impurity concentration than the semiconductor substrate;
A trench portion that is provided on the one surface side of the semiconductor substrate so as to substantially surround the periphery of each photodiode, and extends to the other surface side than the channel stopper layer;
At least one portion around each photodiode is formed with a trench non-existing portion where the trench portion does not exist, and corresponds to the photodiodes adjacent to each other in the channel stopper layer via each trench non-existing portion. A photodiode array characterized in that the parts are continuous. 2. The photodiode array according to claim 1, wherein the trench non-existing portion is provided for each of two opposing edge portions of the photodiodes. 2. The photodiode array according to claim 1, wherein the trench non-existing portion is provided for each of the photodiodes. 4. A solid-state imaging device comprising a plurality of the photodiode arrays according to claim 1, wherein a plurality of the photodiode arrays are arranged on a common substrate. A radiation detector comprising the photodiode array according to any one of claims 1 to 3,
A substrate for fixing the photodiode array; each photodiode is bump-connected to a predetermined wiring of the substrate via an anode; and each channel stopper layer is bumped to a predetermined wiring of the substrate via a cathode A scintillator is attached to the other surface side of the photodiode array connected to the radiation detector.

Images