JP4496753B2 - Solid-state imaging device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a solid-state imaging device and a method for manufacturing the same, and more particularly, a solid-state imaging device in which a photosensor portion is formed in a semiconductor substrate, that is, charge transfer by a so-called HAD (Hole Accumulated Diode) structure in which a charge storage layer is formed on the surface. The present invention is intended to improve smear on a solid-state imaging device of a type (CCD: Charge Coupled Device type) and a manufacturing method thereof.

  In the CCD type solid-state imaging device, as shown in FIG. 1, a basic photo sensor unit 1, a photo sensor unit 1 serving as a pixel, a read unit 2 for reading signal charges from the photo sensor unit 1, and the read unit 2 A vertical charge transfer unit 3 having a CCD configuration for transferring the read signal charges, a horizontal charge transfer unit 4 for sequentially transferring the charges transferred by the vertical charge transfer unit 3 to the output circuit for each horizontal line, And an element isolation portion 5.

  As shown in the schematic cross-sectional view of the main part in FIG. 9, a CCD solid-state imaging device having a normal HAD structure photosensor unit 1 has a semiconductor substrate 20 made of, for example, Si on the n-type substrate 6. 1 p-type well region 7 is formed, n-type low impurity concentration region 13 is formed on first well region 7, and charge storage region 8 is formed on the surface thereof. As shown in FIG. 1, the photodiodes 9 are arranged vertically and horizontally, and each pixel of the photosensor unit 1 is formed.

Further, the second p-type well region 10 is formed on the low impurity concentration region 13 along the arrangement direction of the photosensors 1, that is, the photodiodes 9 arranged on the common vertical line in FIG. The n-type charge transfer region 11 is formed on the second well 10 and is formed at a required distance from the diode 9 to form the vertical charge transfer unit 3.
In addition, a p-type signal charge readout region 32 is formed between the charge transfer unit 3 and the corresponding photodiode 9 to constitute the readout unit 2.
In addition, an element isolation portion 5 including a p-type element isolation region 35 is formed between adjacent different vertical transfer portions.

Then, a light-transmitting insulating layer 14 made of, for example, SiO 2 is deposited on the surface of the semiconductor substrate 20, and a heat-resistant polycrystal is formed on the charge transfer region 11 and the readout region 32. A vertical transfer electrode 15 made of silicon is deposited.
Further, a light shielding film 17 is formed on the entire surface including the transfer electrode 15 via an interlayer insulating film 16 such as SiO 2.
An opening 18 is formed in the light-shielding film 17 on the photosensor unit 1 so that light is received by the photosensor unit 1 through the opening 18, and signal charges corresponding to the received light amount are generated by the photodiode. Made.

  In the case of this configuration, light enters the transfer unit as shown by the arrow a in FIG. 9 and generates smear.

On the other hand, in such a CCD type solid-state imaging device, when the pixel size is made finer in order to reduce the size and increase the resolution, the gate length in the readout unit 2 becomes short, and the readout is affected by the short channel effect. There arises a problem that variations in voltage become large.
On the other hand, there has been proposed a technique for suppressing the lateral diffusion of boron (B) and selectively increasing the width of the effective vertical CCD by selectively etching the element isolation region and the optical signal readout region. (For example, refer to Patent Document 1).
However, in this case, the interlayer insulating film is transparent in the element isolation region, and the polycrystalline silicon electrode is transparent to visible light in the signal charge readout region, so that obliquely incident light leaks into the vertical transfer portion. The problem of generating smears arises.

In addition, in the CCD solid-state imaging device having the HAD structure which is currently mainstream shown in FIG. 9, the lateral diffusion of the high-concentration charge storage region 8 of the photosensor is large, so that the two-dimensional effect is obtained. There has been a problem in that the charge signal reading path from the photosensor to the vertical charge transfer unit 3 is tightened, and as a result, the reading voltage increases.
Furthermore, since the distance between the vertical charge transfer unit 3 and the photosensor unit 1 is shortened, there has been a problem that smear components increase.
In FIG. 9, the main smear generation path is indicated by an arrow a.
JP-A-2-183564

  The present invention provides a solid-state imaging device and a method for manufacturing the same that can more effectively block the occurrence of smear as described above.

A solid-state imaging device according to the present invention includes a photosensor unit formed in a substrate, a readout unit that is formed in the substrate and reads a signal charge from the photosensor unit, and a signal formed from the photosensor unit. An element separation unit that prevents charge leakage and a charge transfer unit that transfers the signal charge read by the reading unit are provided. A groove is formed along the charge transfer direction of the charge transfer unit in the substrate portion provided with the read unit and the element isolation unit, and a one-conductivity-type read is performed at the bottom of the groove in the read unit. A region is formed, and an element isolation region of one conductivity type is formed at the bottom of the groove in the element isolation portion. The both grooves are filled with a light-shielding electrode integrally with a transfer electrode formed on the surface of the substrate in the charge transfer portion .

A method for manufacturing a solid-state imaging device according to the present invention includes a step of forming a charge transfer region on a semiconductor substrate on which a solid-state image sensor is formed, and continuous or intermittent along the charge transfer direction on both sides of the charge transfer region. Forming a groove on the substrate. Next, a step of forming a readout region at the bottom of the groove on one side of the charge transfer region and forming an element isolation region at the bottom of the groove on the other side of the charge transfer region is filled in the groove and the groove A light-shielding electrode is formed across the charge transfer region between them, and a process of using the electrode portion on the charge transfer region as a transfer electrode is performed to form a photosensor portion at a position adjacent to the readout region It is characterized by performing the process to do .

  According to the above-described solid-state imaging device according to the present invention, the charge reading portion and the element separation portion formed in the substrate are formed by the light-shielding electrode, so that a light-shielding effect is effectively produced and smear is effectively improved. Is planned.

  In addition to the transfer unit electrode and element isolation unit electrode, a signal charge readout electrode is formed in the substrate as a light-shielding electrode, so that the readout path from the photosensor unit to the vertical charge transfer is higher than that of the conventional structure. Also gets longer. Accordingly, the short channel effect is thereby suppressed, and variations in read voltage can be reduced.

  Since the lateral diffusion of the charge accumulation region of the photosensor portion does not occur in principle, the two-dimensional effect avoids tightening of the read path from the photosensor to the vertical charge transfer region, and reduces the signal charge read voltage. be able to.

  Furthermore, in a pixel of a miniaturized CCD type solid-state imaging device, electrons photoelectrically converted by a photosensor formed in the substrate diffuse on the device isolation region or the surface of the optical signal readout region and reach the vertical CCD. This smear component is not generated in principle because the smear component generated in the above is blocked by the electrode between the photosensor and the vertical charge transfer unit.

Embodiments of a solid-state imaging device according to the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments.
As described above, the solid-state imaging device according to the present invention can be based on the configuration of the solid-state imaging device having a CCD configuration schematically shown in FIG.
That is, the photo sensor unit 1 serving as a pixel, the read unit 2 that reads out signal charges corresponding to the amount of light received from the photo sensor unit 1, and the charge transfer by a CCD configuration that transfers the signal charges read out by the read unit 2 Unit, that is, the vertical charge transfer unit 3, the horizontal charge transfer unit 4 for sequentially transferring the charges transferred by the vertical charge transfer unit 3 to an output circuit (not shown) for each horizontal line, and the photosensor unit 1 And an element isolation portion 5 for preventing leakage of signal charges from the device.

In the present invention, as shown in a schematic cross-sectional view of the main part in FIG. 2 and a schematic plan view in FIG. 3, a photosensor part is formed in the semiconductor substrate, that is, a charge accumulation region on the surface. According to the HAD structure in which 8 is formed.
In this case as well, as described with reference to FIG. 9, the basic configuration is that, for example, a semiconductor substrate 20 made of Si is formed on the n-type substrate 6 and the first p-type well region 7 is formed. A photodiode 9 having a structure in which an n-type low impurity concentration region 13 is formed and a p-type high impurity concentration charge storage region 8 is formed on the surface of the region 13 is shown in FIG. As shown in FIG. 1, the pixels of the photosensor unit 1 are formed in a vertical and horizontal arrangement.

  Further, a p-type second well region 12 is formed on the region 13 along the arrangement direction of the photosensors 1 arranged on the common vertical line in FIG. The n-type charge transfer region 11 is formed on the second well region 12 to form the vertical charge transfer unit 3.

As shown in FIGS. 2 and 3, between the photodiodes 9 corresponding to the vertical charge transfer units 3 and between different vertical lines adjacent to each other, that is, the signal charge readout unit 2, the element isolation unit 5, Then, the grooves 32G and 35G are formed continuously or intermittently along the charge transfer direction of the vertical charge transfer unit 3.
In addition, a region of one conductivity type, that is, in this example, a p-type readout region 32 and an element isolation region 35 are formed at the bottoms of the trenches 32G and 35G, respectively, and thus in each trench 32G and 35G. The read electrode 32E and the element isolation electrode 35E are filled on the region 32 and the element isolation region 35, respectively, and constitute the read unit 2 and the element isolation unit 5, respectively.
In this example, both electrodes 32E and 35E and each transfer electrode 15 are integrally formed of, for example, the same conductive layer. In this manner, the readout electrode 32E and the element isolation electrode 35E are formed so as to enter the semiconductor substrate 20.
In this case, when the grooves 32G and 35G are formed as continuous grooves, as shown in FIGS. 3 and 7A, discontinuous portions 32f and 35f that electrically separate the transfer electrodes 15 are formed.

Then, on the surface of the semiconductor substrate 20 on which the photosensor unit 1, the readout unit 2, the vertical charge transfer unit 3 and the like are formed, an insulating layer 14 made of, for example, SiO 2 having light transmittance is deposited and further formed. A light shielding film 17 is formed on the entire surface.
An opening 18 is formed in the light-shielding film 17 on the photosensor unit 1 so that light is received by the photosensor unit 1 through the opening 18, and signal charges corresponding to the received light amount are generated by the photodiode. Made.

Next, an example of a method for manufacturing the solid-state imaging device 2 shown in FIGS. 2 and 3 will be schematically described with reference to the process diagrams of FIGS.
As shown in FIG. 4A, the p-type and the n-type are respectively formed in the region 13 of the Si semiconductor substrate 20 on which the n-type substrate 6, the first p-type well region 7, and the n-type low impurity concentration region 13 are formed. The second p-type well region 12 and the n-type charge transfer region 11 are formed in a normal predetermined pattern in the vertical charge transfer direction by ion implantation of impurities.
As shown in FIG. 4B, grooves 32G and 35G are formed in the region 13 on both sides of the regions 11 and 12, for example, continuously along the charge transfer direction.
On the bottom surface of the groove 32G and the bottom surface of the groove 35G, a p-type read region 32 and a high impurity concentration element isolation region 35, so-called isolation regions, are formed by ion implantation, respectively, with a required impurity concentration.
As shown in FIG. 4C, a metal electrode material having a light-shielding property is formed on the semiconductor substrate 20 by vapor deposition, sputtering, etc. over the entire surface (not shown) including the inside of each of the grooves 32G and 35G. Thus, in each of the grooves 32G and 35G, the readout electrode 32E and the element isolation electrode 35E, and further, each transfer electrode 15 is formed simultaneously and continuously.
In this case, when the grooves 32G and 35G are continuous grooves between the transfer electrodes 15, as shown in FIG. Then, the grooves 32G and 35G are divided, or the grooves 32G and 35G are used as the dividing grooves, and the discontinuous portions 32f and 35f that divide the electrodes 32E and 35E are formed.
The transfer electrode 15 is composed of a light-shielding metal electrode made of, for example, Ti, Mo, W, silicide thereof, or a combination thereof.

Next, as shown in FIG. 5, using the transfer electrode 15 as a mask, the photodiode 9 and the charge storage region 8 constituting the photosensor unit 1 are formed by, for example, ion implantation of impurities.
Thereafter, as shown in FIG. 2, an insulating layer 14 and a light shielding film 17 are formed.

In the example described above, the transfer electrode 15, the readout electrode 32 </ b> E, and the element isolation electrode 35 </ b> E are integrally formed. However, as illustrated in a schematic cross-sectional view in FIG. 6, the transfer electrode 15 is interposed between the insulating layers 14. Therefore, the read electrode 32E and the element isolation electrode 35E can be separated from each other electrically or structurally.
In the configuration of FIG. 6, the transfer electrode 15 can be made of a metal electrode material having the same light shielding property as the readout electrode 32E and the element isolation electrode 35E, or the readout electrode made of a metal electrode material. For example, it may be made of polycrystalline Si different from 32E and the element isolation electrode 35E.
Then, the interlayer insulating layer 16 is formed to cover the transfer electrode 15 formed separately from the readout electrode 32E and the element isolation electrode 35E, and the light shielding film 17 is formed.
In FIG. 6, parts corresponding to those in FIG.

As described above, according to the configuration of the present invention, the grooves 32G and 35G are formed in the semiconductor substrate 20, and the electrodes 32E and 35E are formed thereon. 2 and 6, the generation of smear can be effectively improved as indicated by the arrow a in FIG. 2 and FIG.
The arrangement pattern of the grooves 32G and 35G, that is, the light shielding, is basically as shown in FIG. 2 and FIG. 6, with the photosensor unit 1 relating to each vertical line and the photosensor unit 1 relating to the vertical line adjacent thereto. Place between. Then, between the adjacent transfer electrodes 15, the grooves 32G and 35G are divided, and the electrodes 32E and 35E are divided, or only the electrodes 32E and 35E are divided. 7A to 7E are plan views schematically showing examples of arrangement patterns of the grooves 32G and 35G.

  In the solid-state imaging device according to the present invention described above, the transfer of the signal charge generated in the photosensor unit 1 from the photosensor unit 1 to the vertical charge transfer unit 3 is performed as shown in FIG. Is generated through a path indicated by an arrow b in FIGS. 2 and 6.

The above-described solid-state imaging device according to the present invention can be configured as various devices such as an electric device having a camera and a monitor, for example.
In the above-described example, the case where the signal charge, that is, the transfer charge is an electron is illustrated, but the present invention can also be applied to the case where the signal charge is a hole.

  As described above, according to the configuration of the present invention, smear is effectively improved, and in addition to the transfer unit electrode and the element isolation unit electrode, the signal charge readout electrode is used as a light shielding electrode in the substrate. By forming it, the read path from the photo sensor portion to the vertical charge transfer becomes longer than that of the conventional structure. Accordingly, the short channel effect is thereby suppressed, and variations in read voltage can be reduced.

It is a schematic block diagram of the solid-state image sensor to which this invention is applied. It is a schematic sectional drawing of the principal part of the solid-state image sensor by this invention. It is a schematic plan view of the principal part of the solid-state image sensor by this invention. FIGS. 4A to 4C are manufacturing process diagrams (part 1) of an example of a solid-state imaging device according to the present invention. It is a manufacturing-process figure (2) of an example of the solid-state image sensor by this invention. It is a schematic sectional drawing of the principal part of the other example of the solid-state image sensor by this invention. AE is a schematic plan view which shows the example of the groove pattern of this invention apparatus, respectively. It is a potential diagram for explaining transfer of signal charges from a photo sensor unit to a vertical charge transfer unit. It is a schematic sectional drawing of the principal part of the conventional solid-state image sensor.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Photo sensor part, 2 ... Reading part, 3 ... Charge transfer part (vertical charge transfer part), 4 ... Horizontal charge transfer part, 5 ... Element isolation part, 7 ... 1st well region, 8 ... charge storage region, 9 ... photodiode, 11 ... charge transfer region, 12 ... second well region, 13 ... low impurity concentration region, 14 · .... Insulating layer, 15 ... Transfer electrode, 16 ... Interlayer insulating layer, 17 ... Light shielding film, 18 ... Opening, 20 ... Semiconductor substrate, 32 ... Reading region, 35 ... Element isolation region, 32G, 35G ... groove, 32E ... readout electrode, 35E ... element isolation electrode, 32f, 35f ... discontinuous part

Claims (5)

A photosensor portion formed in the substrate;
A readout unit that is formed in the substrate and reads out signal charges from the photosensor unit;
An element isolation unit formed in the substrate and preventing leakage of signal charges from the photosensor unit ;
A charge transfer unit that transfers the signal charge read by the reading unit ;
A groove is formed along the charge transfer direction of the charge transfer unit in the substrate portion provided with the readout unit and the element isolation unit,
A one-conductivity type readout region is formed at the bottom of the groove in the readout unit, and a one-conductivity type element isolation region is formed at the bottom of the trench in the element isolation unit,
Both the grooves are filled with an electrode having a light shielding property integrally with a transfer electrode formed on the surface of the substrate in the charge transfer portion.
Solid-state image sensor. Electrode having a light shielding property, it is a metal electrode
The solid-state imaging device according to claim 1 . A light shielding film is provided on the substrate to cover the light-shielding electrode and to have an opening on the photosensor portion.
The solid-state imaging device according to claim 1 or 2. The groove is disposed continuously or intermittently along the charge transfer direction of the charge transfer unit.
The solid-state image sensor of any one of Claims 1-3. Forming a charge transfer region on a semiconductor substrate on which a solid-state imaging element is formed;
Forming grooves on both sides of the charge transfer region continuously or intermittently along the charge transfer direction ;
Forming a readout region at the bottom of the groove on one side of the charge transfer region and forming an element isolation region at the bottom of the groove on the other side of the charge transfer region;
Filling the groove and forming an electrode having a light shielding property across the charge transfer region between the grooves, and using the electrode part on the charge transfer region as a transfer electrode ;
And a step of forming a photosensor in a position adjacent to the reading area
Manufacturing method of solid-state image sensor .

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