JP2005109021A - Solid state imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid state imaging device which features excellent antiblooming characteristics and can reduce readout voltage, and which has low smear even if it is shrunk in size. <P>SOLUTION: The solid state imaging device 1 has such a structure that an optical sensor 2 and a vertical transfer register 3 are formed, and a readout gate 18 is formed between the optical sensor 2 and the vertical transfer register 3 to form an imaging region. In the imaging region, the other region than the optical sensor 2 is covered by a lightproof film 22. The lightproof film 22 also serves as a readout electrode for reading out signal charges accumulated in the optical sensor 2 to the vertical transfer register 3. Except when reading out the signal charges, such voltage as to form an inverse layer 28 on the surface of the readout gate is applied to the lightproof film 22. When reading out the signal charges, such voltage as to remove the inverse layer 28 is applied to the lightproof film. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a solid-state imaging device.

FIG. 6 shows a configuration of a conventional solid-state imaging device, for example, an interline transfer (IT) type solid-state imaging device (for example, a CCD type solid-state imaging device).
In this solid-state imaging device 41, a large number of light receiving sensor portions 42 made of, for example, photodiodes constituting pixels are arranged in a matrix, and a vertical transfer register 43 extending in the vertical direction is formed on one side of each column of the light receiving sensor portions 42. Thus, the imaging region 44 is configured. Further, a horizontal transfer register 45 is disposed at the vertical end of the imaging region 44, and an output unit 46 is connected to the horizontal transfer register 45 via charge-voltage conversion means (not shown).

  In the solid-state imaging device 41 having such a configuration, for example, the signal charges photoelectrically converted according to the amount of received light in each light receiving sensor unit 42 are read to the vertical transfer register 43 and read to the vertical transfer register 43. The signal charges are transferred to the horizontal transfer register 45 for each horizontal line, sequentially transferred through the horizontal transfer unit register 45, and output through the output unit 46.

Next, FIG. 7 shows a cross-sectional view of the imaging region 44 in FIG. 6 on the line AA.
In the imaging region 44, a first semiconductor well region 51 of a second conductivity type, for example, P type, is formed in a first conductivity type, for example, an N type silicon semiconductor substrate 50, and on the surface side of the semiconductor substrate 50, A photodiode including an N ⁺ semiconductor region (so-called charge storage region) 52 constituting the light receiving sensor unit 42 and a P ⁺⁺ semiconductor region (positive charge storage region) 53 on the surface thereof is formed. An N ⁺ transfer channel region 55 constituting the vertical transfer register 43 is formed on one side of the light receiving sensor section 42 row, and a P ⁺ second semiconductor well is formed below the N ⁺ transfer channel region 55. Region 56 is formed. On the other side of the light receiving sensor section 42 row, a pixel separation region for separating pixels adjacent in the horizontal direction, that is, a high-concentration P-type channel stop region 57 is formed. Between the light receiving sensor unit 42 and the vertical transfer register 43, a read gate unit 58 for reading the signal charges accumulated in the light receiving sensor unit 42 to the vertical transfer register 43 is formed.

An insulating film 59 is formed on the surface of the semiconductor substrate 50, and a transfer electrode 60 made of, for example, a polycrystalline silicon layer is formed on the read gate portion 58, the N ⁺ transfer channel region 55 and the channel stop region 57. Yes. The transfer channel region 55 and the transfer electrode 60 constitute a vertical transfer register 43. A light shielding film 62 made of, for example, Al is formed on the transfer electrode 60 with an interlayer insulating film 61 interposed therebetween.

  A plasma SiN film 63 is formed on the light shielding film 62 so as to cover the entire surface, and a planarizing film 64 is formed on the plasma SiN film 63 so as to cover the entire surface. A color filter 65 is formed on the planarizing film 64. Is formed. An on-chip lens 66 is formed at a position corresponding to the light receiving sensor portion 42 on the color filter 65.

  Here, in the solid-state imaging device 41 having such a configuration, an impurity region (potential barrier) 67 made of, for example, a P-type impurity is provided on the surface portion of the read gate portion 58 in order to suppress, for example, blooming. (See Patent Document 1).

  This impurity region (in the case of FIG. 7, a high-concentration P-type impurity region) 67 is from the light receiving sensor unit 42 to the vertical transfer register 43 except during reading, that is, while signal charges are accumulated in the light receiving sensor unit 42. When reading, that is, when reading the signal charge accumulated in the light receiving sensor unit 42 to the vertical transfer register 43, a voltage (reading) that causes the impurity region 67 to be crushed in the transfer electrode 60 is read. Voltage) is applied, the flow of signal charges from the light receiving sensor unit 42 to the vertical transfer register 43 is allowed.

  Further, in the solid-state imaging device 41 having such a configuration, for example, in order to prevent smear from occurring in the vertical transfer register 43 due to light incident from the end of the light shielding film 62, the light receiving sensor unit is included in the light shielding film 62. An overhanging portion 621 that partially spans 42 is provided (see Patent Document 2).

That is, for example, when light incident obliquely on the light receiving sensor portion 42 enters the insulating film 59 between the surface of the semiconductor substrate 50 and the light shielding film 62, the light is multiplexed between the surface of the semiconductor substrate 50 and the overhang portion 621. For example, light is attenuated before it reaches the vertical transfer register 43 by reflection, so that light incident on the vertical transfer register 43 that causes smear is reduced.
JP-A-11-54739 Japanese Patent Laid-Open No. 2002-164522

By the way, in the solid-state imaging device 41 having such a configuration, the blooming characteristic and the readout voltage are affected by the amount of P-type impurity implanted.
That is, for example, when the injection amount of the P-type impurity is increased, the impurity concentration is increased and the potential barrier 67 is deepened. Therefore, the signal charge from the light receiving sensor unit 42 to the vertical transfer register 43 is not used during reading. The blooming characteristic can be advantageously improved by increasing the effect of suppressing the outflow of light, but at the time of reading, it is necessary to apply a high read voltage that can collapse the deep potential barrier 67 to the transfer electrode 60, and the read voltage becomes high. End up.

  On the other hand, for example, when the implantation amount of the P-type impurity is reduced, the impurity concentration becomes low and the potential barrier 67 becomes shallow. Therefore, at the time of reading, the potential barrier 67 can be crushed with a low voltage, and the reading voltage is reduced. Although it can be lowered, the effect of suppressing the outflow of signal charges from the light receiving sensor unit 42 to the vertical transfer register 43 is reduced except at the time of reading, and the blooming characteristic is deteriorated.

  That is, in the conventional solid-state imaging device 41 described above, the relationship between the blooming characteristic and the readout voltage is a so-called trade-off relationship.

Further, when the solid-state imaging device 41 is manufactured, if the impurity concentration of the impurity region 67 varies, the blooming characteristics also vary.
In order to obtain sufficient blooming characteristics even if the impurity concentration of the impurity region 67 varies, the impurity concentration is set higher.
For this reason, in consideration of the production margin and securing sufficient blooming characteristics, the impurity concentration of the impurity region 67 increases and a high read voltage is required.

  In recent years, demands for miniaturization of solid-state imaging devices have increased. However, in the above-described solid-state imaging device 41, if further miniaturization is attempted, smear characteristics are deteriorated.

  That is, for example, when trying to miniaturize while maintaining a certain degree of sensitivity, the opening area of the light receiving sensor unit 42 cannot be reduced so much, for example, the overhanging portion 621 of the light shielding film 62 straddling the light receiving sensor unit 42, for example. The length D must be shortened.

  However, when the length D of the overhang portion 621 is shortened, the light entering the insulating film 59 between the surface of the semiconductor substrate 50 and the light shielding film 62 is multiplexed as compared with the case where the length D of the overhang portion 621 is long. There is little reflection, for example, it becomes difficult to attenuate light before reaching the vertical transfer register 43.

As a result, the light incident on the vertical transfer register 43 that causes smear cannot be reduced,
Smear characteristics deteriorate.

  In view of the above points, the present invention provides a solid-state imaging device having a configuration capable of ensuring blooming characteristics, reducing read voltage, and ensuring smear characteristics even when miniaturized. is there.

  In the solid-state imaging device according to the present invention, a light receiving sensor unit and a vertical transfer register are formed, and a reading gate unit is formed between the light receiving sensor unit and the vertical transfer register to form an imaging region. The area excluding the light receiving sensor part is covered with a light shielding film, and the light shielding film also serves as a readout electrode for reading the signal charges accumulated in the light receiving sensor part to the vertical transfer register. In addition, a voltage is applied so that an inversion layer is formed on the surface of the read gate portion, and a voltage that erases the inversion layer is applied to the light-shielding film when reading signal charges.

  According to the solid-state imaging device of the present invention, in the imaging region, the region excluding the light receiving sensor unit is covered with the light shielding film, and the light shielding film reads out the signal charges accumulated in the light receiving sensor unit to read out to the vertical transfer register. Also serves as an electrode, except when reading out signal charges, a voltage is applied to the light shielding film so that an inversion layer is formed on the surface of the readout gate. When reading out signal charges, the inversion layer is erased from the light shielding film. Therefore, when the signal charge is read, the inversion layer can suppress the outflow of the signal charge from the light receiving sensor unit to the vertical transfer register except when reading the signal charge. Then, the inversion layer is erased, and the signal charge can be read out with a low voltage. As a result, the read voltage can be reduced.

  Further, according to the solid-state imaging device of the present invention, since the light shielding film also serves as the readout electrode, the light shielding film is formed on the readout gate portion. Therefore, compared with the solid-state image sensor in which the light-shielding film is formed so as to straddle a part on the light-receiving sensor unit, it is possible to obtain a highly sensitive solid-state image sensor by increasing the opening area on the light-receiving sensor unit.

According to the present invention, it is possible to provide a solid-state imaging device that can ensure blooming characteristics and has a low readout voltage.
This eliminates the need to increase the read voltage even when considering the production margin and securing blooming characteristics. In this case, the yield can be improved.

In addition, according to the present invention, a solid-state imaging device having a large opening area on the light-receiving sensor portion and a high sensitivity can be obtained. Therefore, it is possible to provide a solid-state imaging device that can ensure smear characteristics even when miniaturized. .
In addition, since a solid-state imaging device having a large opening area on the light-receiving sensor portion and a high sensitivity can be obtained, a solid-state imaging device capable of coping with further miniaturization can be provided.

Embodiments of the present invention will be described below with reference to the drawings.
First, FIG. 1 shows a case where the solid-state imaging device according to the present invention is applied to, for example, an interline transfer (IT) type solid-state imaging device (for example, a CCD type solid-state imaging device).
In the solid-state imaging device 1 according to the present embodiment, a plurality of light receiving sensor units 2 made of, for example, photodiodes constituting pixels are arranged in a matrix, and vertical transfer extends in the vertical direction to one side of each column of the light receiving sensor units 2 The register 3 is formed, and the imaging region 4 is configured. Further, a horizontal transfer register 5 is disposed at the vertical end of the imaging region 4, and an output unit 6 is connected to the horizontal transfer register 5 via charge voltage conversion means (not shown).

  In the solid-state imaging device 1 having such a configuration, for example, the signal charges photoelectrically converted according to the amount of received light in each light receiving sensor unit 2 are read to the vertical transfer register 3 and read to the vertical transfer register 3. The signal charges are transferred to the register 5 by horizontal transfer for each horizontal line, sequentially transferred through the horizontal transfer unit register 5 and output through the output unit 6.

Next, FIG. 2 shows an enlarged cross-sectional view of the imaging region 4 in FIG. 1 on the line AA.
In the imaging region 4, a first semiconductor well region 11 of a second conductivity type, eg, P type, is formed in a first conductivity type, eg, N type silicon semiconductor substrate 10, and is formed on the surface side of the silicon semiconductor substrate 10. A photodiode comprising an N ⁺ semiconductor region (so-called charge storage region) 12 constituting the light receiving sensor section 2 and a P ⁺⁺ semiconductor region (positive charge storage region) 13 on the surface thereof is formed. An N ⁺ transfer channel region 15 constituting the vertical transfer register 3 is formed on one side of the light receiving sensor section 12 row, and a P ⁺ second semiconductor well is formed below the N ⁺ transfer channel region 15. Region 16 is formed. On the other side of the 12 rows of light receiving sensor sections, a pixel separation region for separating pixels adjacent in the horizontal direction, that is, a high-concentration P-type channel stop region 17 is formed. On the N-type semiconductor substrate 10 between the light receiving sensor unit 12 and the vertical transfer register 13, a read gate unit 18 for reading the signal charges accumulated in the light receiving sensor unit 12 to the vertical transfer register 13 is formed. ing.
The P-type first semiconductor well region 11 is formed, for example, by implanting a P-type impurity into a predetermined region of the N-type silicon substrate 10 later.

An insulating film 19 is formed on the surface of the semiconductor substrate 10, and a transfer electrode 20 made of, for example, a polycrystalline silicon layer is formed on the read gate portion 18, the N ⁺ transfer channel region 15 and the channel stop region 17. Yes. The transfer electrode 20 has a three-layer structure.
The N ⁺ transfer channel region 15 and the transfer electrode 20 constitute the vertical transfer register 3. A light shielding film 22 made of, for example, Al is formed on the transfer electrode 20 via an interlayer insulating film 21.
As described above, the light shielding film 22 is provided with the overhanging portion 221 in order to prevent smear from occurring in the vertical transfer register 3 due to, for example, light incident from the end of the light shielding film 22.

  A plasma SiN film 23 is formed on the light shielding film 22 so as to cover the entire surface, and a planarizing film 24 is formed on the plasma SiN film 23 so as to cover the entire surface. A color filter is formed on the planarizing film 24. 25 is formed. An on-chip lens 26 is formed at a position corresponding to the light receiving sensor unit 2 on the color filter 25.

In the solid-state imaging device 1 according to the present embodiment, in particular, the light shielding film 22 is formed above the readout gate unit 18, and the readout electrode for reading out the signal charges accumulated in the light receiving sensor unit 2 to the vertical transfer register 3. It is comprised so that it may serve as.
That is, in the conventional solid-state imaging device, the readout gate portion has a configuration in which the transfer electrode is formed on the substrate via the gate insulating film (see FIG. 7), but in the solid-state imaging device 1 of the present embodiment, The readout gate portion 18 has a configuration in which an overhang portion 221 of the light shielding film 22 is formed on the substrate via the gate insulating film 19, and the light shielding film 22 also serves as a readout electrode. A wiring 27 for applying a read voltage is connected to the light shielding film 22.

  Further, in the solid-state imaging device 1 of the present embodiment, a voltage that causes an inversion layer (barrier) to be formed in the readout gate portion is applied to the light shielding film 22 except when signal charges are read out. During reading, a voltage is applied to the light shielding film 22 so that the inversion layer is erased.

Hereinafter, the reading operation in the solid-state imaging device 1 of the present embodiment will be specifically described with reference to FIGS.
FIGS. 2 and 3 show the signal charges other than when reading, and FIGS. 4 and 5 show the signal charges when read.

  First, at a time other than reading signal charges, a voltage φV that forms an inversion layer is applied to the light shielding film 22 via the wiring 27 as shown in FIG. Here, in the solid-state imaging device 1 of the present embodiment, since the read gate portion 18 is formed of N-type impurities, a negative voltage is applied as the voltage φV at which the inversion layer is formed.

  At this time, in the read gate unit 18, as shown in FIG. 3A, electrons having negative charges are moved away from the interface of the semiconductor substrate 10 to the bottom of the semiconductor substrate 10, so that the vicinity of the interface of the semiconductor substrate 10 becomes a hole. Only the depleted region 29 is formed. Further, the conductivity type is inverted, and positively charged holes are induced on the surface portion of the read gate portion 18. In this way, the inversion layer 28 as shown in FIGS. 2 and 3B is formed.

On the other hand, at the time of reading the signal charge, as shown in FIG. 4, a read voltage φVR that erases the inversion layer 28 is applied to the light shielding film 22 via the wiring 27. Here, in the solid-state imaging device 1 of the present embodiment, since the inversion layer 28 is formed by applying the negative voltage φV, the read voltage φVR that erases the inversion layer 28 is a positive voltage. Is applied.
Note that the inversion layer 28 can be erased if the positive voltage is 0 V or higher. This eliminates the need to apply a high read voltage.

  At this time, in the read gate unit 18, as shown in FIG. 5A, the holes are moved away from the interface of the semiconductor substrate 10 to the bottom of the semiconductor substrate 10, whereby electrons near the interface of the semiconductor substrate 10 have negative charges. It becomes only. As a result, the above-described depletion region 29 disappears, and the inversion layer 28 is erased from the surface portion of the read gate portion 18 as shown in FIGS. 4 and 5B.

  As described above, according to the solid-state imaging device 1 of the present embodiment, the light shielding film 22 also serves as the readout electrode, and the inversion layer 28 is formed in the readout gate portion 18 in the light shielding film 22 except during reading. By applying such a voltage φV (negative voltage), the inversion layer 28 is formed on the surface portion of the read gate portion 18, and the voltage at which the inversion layer 28 is erased from the light shielding film 22 at the time of reading. By applying φVR (positive voltage), the inversion layer 28 is erased from the surface portion of the read gate unit 18. Therefore, the light receiving sensor unit 2 is used by the inversion layer 28 except when reading the signal charge. Can be suppressed from flowing out to the vertical transfer register 3 and the reading voltage φVR applied to the light-shielding film 22 can be prevented from increasing during the reading of the signal charges.

Further, according to the solid-state imaging device 1 of the present embodiment, the readout gate portion 18 is provided with the protruding portion 221 of the light shielding film 22 via the insulating film 19 on the substrate 10, and the light shielding film 22 serves as the readout electrode. Since it is configured so that it also serves as a conventional structure, the light-shielding film has no overhanging portion on the light-receiving sensor unit as compared to the conventional structure in which the light-shielding film overhangs the light-receiving sensor unit. In addition, it is possible to obtain a configuration with a large opening area and high sensitivity.
As a result, it is possible to reduce the size without affecting the smear characteristics without shortening the protruding portion of the light shielding film 221 on the light receiving sensor portion 22 as in the prior art.

  In the solid-state imaging device 1 according to the above-described embodiment, when the readout gate unit 18 is formed of an N-type impurity, a negative voltage is applied to the light shielding film 22 via the wiring 27 except during readout. In FIG. 1, the inversion layer 28 is formed on the surface of the read gate unit 18, and at the time of reading, the inversion layer 28 is erased by applying a positive voltage to the light shielding film 22. However, when formed from P-type impurities, the polarity of the voltage applied to the light shielding film 22 at the time of reading is opposite to that at the time of reading.

That is, in the case of the solid-state imaging device having such a configuration, since the readout gate portion 18 is formed of P-type impurities, a positive voltage is used as the voltage φV at which the inversion layer is formed except during readout. Applied.
On the other hand, at the time of reading, since the inversion layer 28 is formed by applying a positive voltage, a negative voltage is applied as the read voltage φVR at which the inversion layer 28 is erased.

Also in the solid-state imaging device having such a configuration, as in the case of the above-described embodiment, the signal charge flows from the light receiving sensor unit 2 to the vertical transfer register 3 by the inversion layer 28 except during reading. It is possible to suppress the reading voltage φVR applied to the light shielding film 22 at the time of reading.
Further, as in the case of the above-described embodiment, in the read gate portion 18, an overhang portion 221 of the light shielding film 22 is provided on the substrate 10 via the insulating film 19, so that the light shielding film 22 also serves as a read electrode. Therefore, the aperture area is wide and the sensitivity is high. Thereby, even if it does not shorten the overhang | projection part 221 of the light shielding film 22 on the light-receiving sensor part 2, it can refine | miniaturize, without affecting a smear characteristic.

  In the solid-state imaging device 1 of the present embodiment, since the light shielding film 22 covers the area other than the light receiving sensor unit 2 in the imaging area 4, for example, wiring to the light shielding film 22 at the time of reading signal charges. When a read voltage is applied through the signal line 27, signal charges accumulated in all the light receiving sensor units 2 are read. That is, in the solid-state imaging device 1 of the present embodiment, a signal charge reading operation is performed by all-pixel reading.

  However, for example, by changing the shape of the light-shielding film 22, the solid-state imaging device 1 according to the present embodiment can perform a signal charge reading operation by field reading or frame reading.

In such a case, first, in the solid-state imaging device 1 of the present embodiment, for example, the light shielding film 22 is divided for each row of the light receiving sensor unit 2, and the readout voltage is set for each row of the light receiving sensor unit. It is set as the structure applied. In the solid-state imaging device 1 having such a configuration, the configuration of the transfer electrode can be changed, and the timing for applying the read voltage can be changed in each of the odd and even rows.
The light shielding film 22 divided for each row of the light receiving sensor unit is formed, for example, by making the shape of the mask pattern divided for each row of the light receiving sensor unit in the formation process of the light shielding film 22. be able to.

  In the above-described embodiments, the present invention is applied to the IT solid-state image sensor. However, the present invention is not limited to the IT solid-state image sensor. For example, the present invention is applied to a frame interline transfer (FIT) solid-state image sensor. Can be applied.

  The present invention is not limited to the above-described embodiment, and various other configurations can be taken without departing from the gist of the present invention.

1 is a schematic plan view showing an embodiment of a solid-state imaging device according to the present invention. It is an expanded sectional view on the AA line of the imaging region shown in FIG. A and B are enlarged cross-sectional views in the vicinity of the read gate portion in FIG. FIG. 2 is an enlarged cross-sectional view (when reading) of the imaging region shown in FIG. FIGS. 5A and 5B are enlarged sectional views in the vicinity of a read gate portion in FIG. It is a schematic plan view of the conventional solid-state image sensor. It is an expanded sectional view on the AA line of the imaging area | region of the solid-state image sensor shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Solid-state image sensor, 2 ... Light-receiving sensor part, 3 ... Vertical transfer register, 4 ... Imaging area, 5 ... Horizontal transfer register part, 6 ... Output part, 7 ... 8 ... 10 ... N-type silicon semiconductor substrate, 11 ... P-type first semiconductor well region, 12 ... N ⁺ semiconductor region, 13 ... P ⁺⁺ readout Gate portion, 15... N ⁺ transfer channel region, 16... P ⁺ second semiconductor well region, 17... P ⁺ channel stop region, 18. Insulating film, 20 ... transfer electrode, 21 ... interlayer insulating film, 22 ... light shielding film, 221 ... overhang, 23 ... plasma SiN film, 24 ... flattening film, 25 ... Color filters, 26 ... On-chip lenses, 27 ... Wiring, 28 ... Rolling layer

Claims (3)

A light receiving sensor unit and a vertical transfer register are formed, and a reading gate unit is formed between the light receiving sensor unit and the vertical transfer register to form an imaging region,
In the imaging region, the region excluding the light receiving sensor portion is covered with a light shielding film,
The light shielding film also serves as a readout electrode for reading the signal charge accumulated in the light receiving sensor unit to the vertical transfer register,
Except at the time of reading out the signal charge, a voltage is applied to the light shielding film so that an inversion layer is formed on the surface of the readout gate portion.
At the time of reading out the signal charge, a voltage that erases the inversion layer is applied to the light shielding film.   The read gate portion is formed of an N-type semiconductor region, and a negative voltage is applied to the light shielding film so that an inversion layer is formed on the surface of the read gate portion, except when reading the signal charge, 2. The solid-state imaging device according to claim 1, wherein a positive voltage that erases the inversion layer is applied when signal charges are read. The read gate portion is formed of a P-type semiconductor region, and a positive voltage is applied to the light shielding film so that an inversion layer is formed on the surface of the read gate portion except when the signal charge is read. The solid-state imaging device according to claim 1, wherein a negative voltage is applied so that the inversion layer is erased when reading out the electric charge.

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