JPH0322755B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid-state imaging device using a charge transfer device.

Imaging devices using charge transfer devices can be broadly divided into frame transfer methods and interline transfer methods, and these methods take advantage of the characteristics of solid-state imaging devices, such as small size, light weight, low power consumption, high reliability, and ease of use. It is rapidly developing based on its strengths. In terms of characteristics, imaging devices using charge transfer devices are superior to currently used image pickup tubes and other solid-state imaging devices in terms of noise, afterimages, and burn-in, but they have the major drawback of large blooming smear. . Another drawback is that because the electrode wiring is fine and complicated, disconnections and shorts occur between the wirings, resulting in poor yield.

As shown in FIG. 1, a conventional charge transfer imaging device using an interline transfer method has multiple columns of vertical shift registers 1 driven by the same charge transfer electrode group.
00, a photoelectric conversion unit 101 adjacent to one side of each vertical register and electrically isolated from each other, a transfer electrode 102 that controls the transfer of signal charges between the vertical shift register and the photoelectric conversion unit, and It consists of a horizontal shift register 103 provided at one end of the vertical shift register and a device 104 for detecting signal charges provided at one end of the horizontal register. The vertical shift register is connected to terminals 106 and 107.
The transfer gate is driven by pulses φ ₁ and φ ₂ from terminal 105, and the transfer gate is driven by pulse φ _T from terminal 105.

In an imaging device using such an interline transfer method, signal charges accumulated in the photoelectric conversion unit 101 according to the amount of incident light are transferred to the transfer gate 102.
respectively corresponding shift registers 10 through
Transferred to 0. After the signal charges are transferred to the vertical shift register, the transfer gate is closed and the photoelectric conversion unit 101 accumulates the signal charges for the next period (field or frame). On the other hand, the signal charges transferred to the vertical registers 100 are transferred in parallel in the vertical direction, and are transferred to the horizontal registers 103 for each horizontal line of each vertical register. The charge sent to the horizontal register is transferred in the horizontal direction until the next signal charge is transferred from the vertical shift register, and is taken out from the charge detection section 104 as a time-series video signal.

A top view of a typical unit cell of such an interline transfer method is shown in FIG.
Cross-sectional views taken along the lines ', -' and -' are shown in Figures 2b, c and d, respectively. In the following description, parts denoted by the same numbers have the same structure and function the same. In FIG. 2, the unit cell includes charge transfer electrodes 203 and 204 formed on the main surface of a P-type semiconductor substrate 201 through a thin insulating film 202 on an accumulation region 215 of a two-phase drive vertical register, a barrier region 214, and a photovoltaic electrode. Transfer gate electrode 102 that controls the transfer of signal charges from the conversion unit 101 to the vertical register
and a photoelectric conversion section 101 made of a P-N junction composed of a substrate semiconductor 201 and an N-type conductivity type layer 205 having a conductivity type different from that of the substrate semiconductor, and each photoelectric conversion section is connected to an adjacent vertical shift register or other It is electrically separated from the photoelectric conversion section by a double layer of a high concentration impurity region 207 and a thick insulating film 211 that has the same conductivity type as the substrate.

Further, the two transfer electrodes 203 and 204 are separated from each other by an insulating film 208. Further, the transfer electrode and the transfer gate electrode are separated by an insulating film 213. In addition, for example, the metal layer 2 other than the photoelectric conversion part
It is illuminated at 12. Note that in FIG. 2a, the light-resistant layer is not illustrated. Furthermore, the insulating film 209 prevents the transfer electrodes 203 and 204 from being shortened when the metal layer shields the light. Further, 210 is a layer having a conductivity type different from that of the substrate for forming a buried channel charge transfer path, and 212 is a layer having the same conductivity type as the substrate formed in this layer to realize two-phase drive. Transfer electrodes 203 and 20 constituting another transfer stage
4 are connected by a wiring 216, and when using two-phase drive for the vertical register as in this example, separate transfer pulses φ ₁ and φ ₂ are applied to every other pair of transfer electrodes 203 and 204. be done.

In such a conventional charge transfer device, the transfer electrodes 203, 204 and the transfer gate electrode 102 are wired on an uneven surface, so that wire breakage is likely to occur. Furthermore, since the transfer electrodes 203 and 204 become thinner in a region A indicated by an arrow in FIG. 2a, wire breakage occurs or wiring resistance increases, making it difficult to transfer charges at high frequencies. Furthermore, since there is a large overlap between the electrodes and between the electrodes and the photoresist layer, short circuits often occur between them. Furthermore, since three layers of electrode wiring and one layer of light-shielding layer are required, the number of manufacturing steps is increased, resulting in poor yield. Furthermore, the structure is complex and various margins (meeting, overlap, etc.) are required during manufacturing.
The disadvantages are that it is difficult to miniaturize and increase the number of elements, and the aperture ratio of the light-receiving area is small.

SUMMARY OF THE INVENTION An object of the present invention is to provide a charge transfer device with a new structure that eliminates the above-mentioned drawbacks and a method for driving the same.

According to the present invention, a layer having a conductivity type opposite to that of the semiconductor substrate is provided on the main surface of the semiconductor substrate, and a photoelectric conversion storage region and a plurality of charge transfer register regions arranged two-dimensionally on the layer, the same as the substrate. This vertical electrode consists of a conductivity type region and a conductivity type region opposite to that of the substrate above it, a transfer gate region for controlling charge transfer between the two regions, a horizontal register region, and a charge detection region. Storage regions and barrier regions of the same conductivity type as the substrate are provided below, which are arranged alternately in the transfer direction, and the impurity concentration of the storage regions is higher than that of the barrier regions. One storage region corresponds to the conversion storage region, and every other storage region and barrier region have a layer on the surface of the conductivity type opposite to that of the substrate, and the direction is from the storage region without this layer to the storage region with this layer. A solid-state imaging device in which charge is transferred in the past is characterized in that the drive electrode in the vertical register region is composed of one vertical electrode.

Furthermore, according to the present invention, a layer of conductivity type opposite to that of the semiconductor is provided on the main surface of the semiconductor substrate, and a photoelectric conversion storage region is arranged two-dimensionally on the layer, and a photoelectric conversion storage region is driven by a single vertical electrode, and Under the electrodes, storage regions and barrier regions of the same conductivity type as the substrate are provided alternately in the transfer direction, and the impurity concentration of the storage regions is higher than that of the barrier regions. One storage region corresponds to the photoelectric conversion storage region, and every other storage region and barrier region has a charge transfer vertical register having a layer of conductivity type opposite to that of the substrate on its surface, and a region of the same conductivity type as the substrate and a layer above it. A large reverse bias voltage is applied between the semiconductor substrate and the opposite conductivity type layer during photoelectric conversion in a solid-state imaging device including a transfer gate region consisting of a substrate and a region of opposite conductivity type, a horizontal register, and a charge detection region. A method for driving a solid-state imaging device is obtained, characterized in that the signal charge stored in the photoelectric conversion storage region is transferred to the vertical register by applying the reverse bias voltage and reducing the reverse bias voltage.

In the present invention, since the vertical register and transfer gate region, which had a very complicated structure in the conventional structure, can be formed by a single vertical electrode, the above-mentioned drawbacks can be overcome. Furthermore, as will be described later, the present invention can be driven in field accumulation mode with less afterimage.

Next, embodiments of the present invention will be specifically described using the drawings. The following description of the embodiments of the present invention is provided by N.
Although the present invention will be described with reference to a P-channel semiconductor device, it goes without saying that the present invention can also be applied to a P-channel semiconductor device.

3 and 4 show an embodiment of the structure of the present invention, FIG. 3 shows the overall view, and FIG. 4 shows the structure of a unit cell thereof. In Figure 4, a is a top view of the unit cell, figures b and c are the -' line of figure a, -
A cross-sectional view taken along the line ′ is shown. The major difference from the conventional structure is that, as can be seen from FIGS. 3 and 4, there is no transfer gate in the conventional structure, and the vertical register electrode is replaced with a single layer of vertical electrodes 301 formed on a thin oxide film 202. It is that you are.

Another major difference is that the active region is an N substrate 41
This is created in the P well 413 on the top of the second well. Next, the structure and operation of these parts will be explained. First, the vertical register section has four areas 40.
1,402, 403, and 404, each having a different impurity distribution. i.e. 401,4
In the part corresponding to 02, N regions 407 (donor concentration N ₄ ) and 40
6 (donor concentration N ₃ ), and a P ⁺ region 405 is further formed thereon. Also 4
In the portions corresponding to 03 and 404, N regions 409 (donor concentration N ₂ ) and 408 (donor concentration N ₁ ) are formed on the P well 413, respectively.

The acceptor concentration in P-well 413 is 1×
The donor concentration in the N regions ⁴⁰⁷ and 409 is about 1×10 ¹⁵ /cm ³ , and the donor concentration in the N regions 408 and ⁴ is about 1×10 15 /cm 3 .
The donor concentration of 06 is about 5×10 ¹⁴ /cm ³ , P ⁺ region 4
The acceptor concentration of 05 is about 5×10 ¹⁵ /cm ³ . In addition, the donor concentration of the photoelectric conversion region 414 is 1×
The depth is about 10 ¹⁵ cm ^-3 and about 3 μm. In addition, the transfer gate portion is formed by forming an n region 41 on a thin island-like region.
1 is provided, and furthermore, a P region 410 is provided thereon. The thickness of the n region 411 is about 1.5 μm and the impurity concentration is about 1×10 ¹⁵ /cm ³ .
The thickness of the layer 0 is about 2 μm, and the impurity concentration is about 5×10 ¹⁵ /cm ³ .

If the donor concentrations N ₁ to N ₄ are appropriately selected, the maximum potential _nax and vertical electrode voltage φ _P when these N regions are in depletion are
The relationships can be made as shown in FIG. 5, 501 to 504. In other words, _nax in area 401 and area 402
_nax is unrelated to φ _P due to the existence of P ⁺ region 405, and _nax in region 401 is
It's getting bigger than _nax . Also area 403 _nax
Since there is no P region, _nax in region 404 is a function of φ _P , and when φ _P is high (when φ _P = φ ^H _P ), both are higher than _nax in regions 401 and 402, and φ _P is low (φ _P = φ ^L _P ) Sometimes both are low.
Also, regardless of φ _{P, the nax} of area 403 is the same as that of 404.
It is higher than _nax . Areas 401 and 403 are storage areas of the shift register, and areas 402 and 404 are barrier areas. The region corresponding to the transfer gate is an N region 411 on the P well.
is formed, and a P region 410 is formed thereon. The operation of this part is the same in principle as areas 401 and 402, but will be explained in detail since it is important for the operation of the device.

Figure 6a shows the structure in the thickness direction of the region corresponding to the transfer gate, and Figure 6b shows the relationship between the potential V _TG on the surface of the SiO ₂ film in the region corresponding to the transfer gate and the potential distribution in the depth direction. There is. Although there is no electrode on this SiO ₂ surface, the potential on its surface may change within the range of the amplitude of φ _P. When V _TG is negative or positive and small, the P region 410 is not depleted, so the maximum potential _TG in the N region 411

Claims (1)

[Scope of Claims] 1. A layer having a conductivity type opposite to that of the semiconductor substrate is provided on the main surface of the semiconductor substrate, and a photoelectric conversion storage region and a plurality of charge transfer vertical register regions are arranged two-dimensionally on the layer; A solid comprising a region of the same conductivity type as the substrate and a region thereon of the conductivity type opposite to that of the substrate, and provided with a transfer gate region, a horizontal register region, and a charge detection region for controlling charge transfer between the two regions. In the imaging device, the driving electrode of the charge transfer vertical register region is composed of a single vertical electrode, and storage regions and barrier regions of the same conductivity type as the substrate are provided below the vertical electrode and arranged alternately in the transfer direction. , the impurity concentration in the storage region is higher than that in the barrier region, one storage region corresponds to one photoelectric conversion storage region with a transfer gate region in between, and every other storage region and barrier region are separated by a substrate. 1. A solid-state imaging device having a layer of opposite conductivity type on its surface, in which charge is transferred from an accumulation region without this layer to an accumulation region with this layer. 2. A layer of conductivity type opposite to that of the semiconductor substrate is provided on the main surface of the semiconductor substrate, and a photoelectric conversion and storage region is arranged two-dimensionally on the layer, and a photoelectric conversion storage region is driven by one vertical electrode and transferred under this vertical electrode. Storage regions and barrier regions of the same conductivity type as the substrate are arranged alternately in the direction, the impurity concentration of the storage region is higher than that of the barrier region, and a transfer gate region is sandwiched between them to form one photoelectric conversion storage region. One storage region corresponds to the other, and every other storage region and barrier region are charge transfer vertical registers having a layer on the surface of a conductivity type opposite to that of the substrate, and a region having the same conductivity type as the substrate and an overlying region having a conductivity opposite to that of the substrate. A driving method of a solid-state imaging device comprising a transfer gate region consisting of a mold region, a horizontal register and a charge detection region, wherein a large reverse bias is applied between the semiconductor substrate and the opposite conductivity type layer during photoelectric conversion. Apply voltage,
A method for driving a solid-state imaging device, characterized in that the signal charge stored in the photoelectric conversion storage region is transferred to the charge transfer vertical register by reducing the reverse bias voltage.