JPH0677461A - Solid state image pickup device - Google Patents

Abstract

PURPOSE:To provide a solid-state image pickup device for the detection of light incident on the rear which is composed of an FT-CCD or an FFT-CCD which facilitates a high speed operation. CONSTITUTION:The FT-CCD of the present invention is composed of a photoelectric conversion part 1, a storage part 2 and an output part 3. A vertical shift register(V) is composed of four electrodes which are arranged in parallel with each other for each unit picture element 11. The photoelectric conversion part 1 and the storage part 2 are composed of the vertical shift registers. A large number of the electrodes are provided in parallel with the longitudinal direction of the electrode and the longitudinal direction and the arrangement direction of the vertical shift registers are perpendicular to each other. Four-phase voltages (P1-P4) are applied to the respective electrodes to control the vertical shift registers. The output 3 is composed of horizontal shift registers and an amplifier part 31. An electrode composed of a double-layer structure of polycrystalline silicon and metal silicide is provided on the surface of the photoelectric conversion part 1 and light incident on the rear is detected by the photoelectric conversion part 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a frame transfer (FT) type CCD or a full frame transfer (FFT) type CC.
The present invention relates to a solid-state imaging device that includes D and that detects a subject image such as visible light incident from the back surface of the photoelectric conversion unit.

[0002]

2. Description of the Related Art Conventionally, polycrystalline silicon (polysilicon) having optical transparency is used as a MOS transfer electrode for forming a CCD shift register. There is also known a back-illuminated CCD in which a metal is used for a transfer electrode on the front surface and light is incident from the back surface.

Further, assuming that the electrode structure is similar,
In order to improve the transfer efficiency decrease and the transfer charge decrease due to the distortion of the clock pulse waveform due to the low resistance of the transfer electrode of the CCD, the transfer electrode of the interline transfer (IT) type CCD is made of metal (for example, Mo, Al). , W) or a polycrystalline silicon layer having metal silicide as an intermediate layer. The details of this technique are described in JP-A-63
-46763.

[0004]

Since the polycrystalline silicon of the vertical shift register has a size of several mm to several cm, it becomes a parasitic resistance having a larger specific resistance (Ωcm) than metal. Figure 5
Shows an equivalent circuit of a wiring of polycrystalline silicon of a vertical register. FIT (frame interline transfer), FT
Alternatively, when the vertical shift register is transferred at high speed like FFT, or when high speed transfer is desired, the operation speed is limited by the wiring resistance of the polycrystalline silicon.

Specifically, the clock applied from the outside becomes dull depending on the length of the wiring, the rise of the waveform varies depending on the location, and as a result, the transfer efficiency of the CCD (ratio of charge transfer between potential wells). Deteriorates. The cause of the blunted waveform is determined not only by the resistance but also by the combination with the capacitance, but the capacitance cannot be reduced unnecessarily because it determines the amount of charge that can be transferred by the CCD.

Although there has been a back-illuminated CCD in which a metal is used as a transfer electrode on the front surface, a backing structure of polycrystalline silicon and metal, or a backing structure of polycrystalline silicon and metal silicide, and a multilayer structure are transferred. There is nothing used for the electrodes. Furthermore, in Japanese Patent Laid-Open No. 63-46763, F
Although the use of metal or metal silicide for the transfer electrode of the charge storage unit of the T-type CCD is also described, the present invention is back-illuminated, and further, not only the charge storage unit but also the photoelectric conversion unit. A metal or a metal silicide is used for.

In view of the above problems, it is an object of the present invention to provide a backside illumination type FT-type CCD capable of high-speed operation using an opaque electrode such as a metal silicide, or a solid-state image pickup device using an FFT-type CCD. And

[0008]

In order to solve the above problems, a solid-state image pickup device having a CCD of either a frame transfer (FT) type or a full frame transfer (FFT) type, The transfer electrode on the front surface of the photoelectric conversion portion of the CCD is formed by a structure in which polycrystal silicon is lined with a metal or polycrystal silicon with metal silicide, and detects light incident from the back surface of the photoelectric conversion portion. And

Further, the transfer electrode may be formed of a multi-layer structure of polycrystalline silicon and metal, or polycrystalline silicon and metal silicide.

[0010]

According to the present invention, an electrically low-resistance metal or metal silicide is directly used as a transfer electrode, or a metal or metal silicide is superposed on polycrystalline silicon in a two-layer structure, or a multi-layer structure thereof is formed. By so doing, it is possible to reduce the conventionally existing parasitic resistance from several tenths to several hundreds.

Further, the use of metal or metal silicide makes the photoelectric conversion part opaque to visible light, but by etching the back surface to make it sufficiently thin, the light incident from the back surface can be detected. can do.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an FT type C which is a first embodiment of the present invention.
The schematic block diagram seen from the surface in the solid-state imaging device of CD is shown.

This FT type CCD comprises a photoelectric conversion unit 1, a storage unit 2 and an output unit 3. A shaded portion 11 of the photoelectric conversion unit 1 indicates a unit pixel, and a vertical shift register is formed by four electrodes arranged in parallel per unit pixel. This vertical shift register constitutes the photoelectric conversion unit 1 and the storage unit 2. A large number of electrodes are arranged in parallel with the longitudinal direction of the electrodes, and the longitudinal direction and the configuration direction of the vertical shift register are orthogonal to each other. 4 for each electrode
Phase voltages (P1-P4) are applied to control the vertical shift register. The output section 3 is composed of a horizontal shift register and an amplifier section 31. An electrode having a two-layer structure of polycrystalline silicon and metal silicide is arranged on the front surface of the photoelectric conversion unit 1, and the photoelectric conversion unit 1 detects light incident from the back surface.

The metal used in the electrode of the present invention includes
Ti, W, Mo, Ta, etc. are used, and as the metal silicide, TiSi ₂ , WSi ₂ , MoSi ₂ , T is used.
aSi ₂ , NbSi ₂ or the like is used.

FIG. 3 shows an electrode structure of the photoelectric conversion section in the embodiment of the present invention. As the electrode of the conventional photoelectric conversion unit,
Generally, a transparent electrode made of polycrystalline silicon or the like is used, but in the above-described embodiments, an electrode having a structure in which polycrystalline silicon is lined with metal silicide (or metal) is used. That is, polycrystalline silicon 7 is formed on semiconductor substrate 5 having a pn junction with oxide film 6 interposed. Furthermore, on this polycrystalline silicon 7,
The metal silicide 8 is lined to reduce the resistance. The polycrystalline silicon 7 is formed in order to improve conformity with the semiconductor substrate 5 (oxide film 6) and workability, and to prevent diffusion of metal atoms of the metal silicide 8 into the semiconductor layer. Further, the light receiving region of the p layer 51 in the semiconductor substrate 5 is sufficiently thinly etched, and charges are excited by the light incident from the back surface side.

FIG. 4A shows a view of one pixel of the photoelectric conversion section 1 in the first and second embodiments as seen from the surface.
Four electrodes 10 to 1 arranged in parallel per pixel
A vertical shift register is formed by 5. A large number of electrodes 10 to 15 are arranged parallel to the left-right direction of the paper, that is, parallel to the longitudinal direction of the electrodes 10 to 15, and adjacent electrodes 10 to 15 are electrically insulated by the insulating film 9. ing. The longitudinal direction and the configuration direction of the vertical shift register are orthogonal to each other.

Four-phase voltages (P1 to P1) are applied to the electrodes 10 to 15, respectively.
P4) is added to control the vertical shift register by changing the potential level in the semiconductor. By controlling these voltages, a potential well is formed in the semiconductor and the charge collected in this potential well is transferred. In this embodiment, the charges are transferred from P1 to P4, that is, from the top to the bottom of the paper.
Further, the pixels adjacent to each other in the left-right direction on the paper surface are separated from each other by providing an isolation region in the semiconductor in the vertical direction.

FIG. 4B is a sectional view taken along line AA 'of FIG. In addition, in order to make it easier to see in this figure, the scale is different from that of FIG. The electrodes 10 to 15 overlapping each other are electrically insulated by the oxide film 9, and thus the entire surface of the photoelectric conversion unit 1 is covered by the electrodes 10 to 15. In this figure, the charge is transferred from left to right on the page. The light enters from the back surface, that is, from the lower side of the paper surface.

The principle of detection will be described below. C from the back
When light enters the semiconductor of CD, photoelectric conversion is performed and signal charges are generated. This signal charge is collected in a potential well below an electrode for a certain period of time. The positions for forming the potential wells for a certain period of time are determined by the four-phase voltages (P1 to P4) applied to the electrodes. Then, this signal charge is transferred to the storage unit at high speed for each frame by utilizing the vertical blanking period. Thus, in the FT CCD, the vertical shift register of the photoelectric conversion unit 1 functions as a photoelectric conversion device during the signal storage period,
Also, it functions as a charge transfer device during the vertical blanking period.

In the storage unit 2, the horizontal blanking period, that is,
While the photoelectric conversion unit 1 is performing photoelectric conversion and the accumulation of signal charges, the charges are transferred to the horizontal shift register of the output unit 3 for each line (one row in the lateral direction of the drawing). Further, the transferred charges are output to the outside via the amplifier 31. In the FT type CCD, the back surface portion other than the photoelectric conversion portion is covered with a light shielding material such as metal so that light does not enter.

FIG. 6 shows a schematic principle diagram of charge transfer, and the principle of charge transfer will be briefly described with reference to this figure. For ease of explanation, the CCD is a three-phase clock type, (a) is the structure, (b) is the drive clock waveform that is the voltage applied to each electrode, and (c) is the potential due to the voltage applied to the electrodes. The operation principle will be explained by showing changes in shape with time. Three types of electrodes to which a voltage of φ _{1 to} φ ₃ is applied are formed close to each other on a thin oxide film on a semiconductor substrate. For example, at time t ₀ , a potential is provided immediately below the electrode driven by φ _1. A well is formed in which a charge can be stored. Then from time t ₁ to t
Over ₂ , the charge is transferred below the electrode driven by φ ₂ . In this way, charges are sequentially transferred.

As a second embodiment, an FFT type CC
A schematic configuration diagram of the solid-state imaging device D is shown in FIG. The FFT CCD is a CCD having a photoelectric conversion unit 1 and an output unit 3, and basically has no FT CCD storage unit. The other parts are the same as those in the above-described embodiment. Further, since there is no storage unit, it is usually used in combination with some external shutter mechanism.

The principle of operation is almost the same as that of the FT type CCD. In the signal accumulating period, electric charges are collected in the potential well of the light receiving portion, and the electric charges are transferred to the horizontal shift register in a closing period such as a shutter. Further, the transferred charges are output to the outside via the amplifier 31. Since there is no storage unit, the same size can be used for multiple pixels, and the size of the light receiving unit can be increased.

The present invention is not limited to the above-mentioned embodiment, but various modifications can be made. The electrode structure is also different from that shown in FIG. 3, and the structure is a direct metal electrode or a metal silicide electrode, a structure in which a metal silicide (or a metal) is sandwiched by polycrystalline silicon, and a metal silicide (or a metal) and a polycrystalline silicon. A structure in which several layers are stacked may be considered.
In FIG. 3, only one electrode is shown, but the actual CCD
Then, the method of forming the electrodes varies depending on the two-phase, three-phase, four-phase, and the like.

[0025]

As described above, according to the present invention, as a transfer electrode, a metal or metal silicide having an electrically low resistance is superposed on polycrystalline silicon in a two-layer structure, or these are formed in a multi-layer structure. As a result, the conventionally existing parasitic resistance can be reduced from several tenths to several hundreds. Therefore, in the conventional technique, the transfer speed of the vertical shift register is limited due to a large wiring resistance, but the present invention enables high-speed transfer of charges in the vertical shift register.

The metal or metal silicide is not used directly as an electrode, but is provided with a backing / multi-layer structure with polycrystalline silicon to improve the compatibility with the semiconductor substrate. Furthermore, since it is possible to prevent the metal atoms used for the electrodes from diffusing into the semiconductor, an electrically extremely stable CCD can be manufactured.

Therefore, a back-illuminated type F that can operate at high speed is used.
It is possible to provide a solid-state imaging device using a T-type CCD or an FFT-type CCD.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an FT CCD according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of an FFT type CCD according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a structure of an electrode.

4A and 4B are a top view and a cross-sectional view showing an arrangement of electrodes for one pixel.

FIG. 5 is a diagram illustrating a problem in the conventional technique.

FIG. 6 is a schematic diagram illustrating charge transfer of a CCD.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photoelectric conversion part, 11 ... Unit pixel of a photoelectric conversion part, 2 ... Storage part, 3 ... Output part, 31 ... Amplifier, 5 ... Semiconductor substrate, 5
DESCRIPTION OF SYMBOLS 1 ... P layer, 52 ... N layer, 6 ... Oxide film, 7 ... Polycrystalline silicon, 8 ... Metal silicide (metal), 9 ... Oxide film for electrode insulation, 10-15 ... Electrodes.

Claims (2)

[Claims] 1. A solid-state imaging device comprising a CCD of either a frame transfer type or a full frame transfer type, wherein a transfer electrode on a surface of a photoelectric conversion portion of the CCD is made of polycrystalline silicon or metal. Or a structure in which polycrystal silicon is lined with a metal silicide, and the light incident from the back surface of the photoelectric conversion unit is detected. 2. A solid-state image pickup device comprising either a frame transfer type CCD or a full frame transfer type CCD, wherein a transfer electrode on the surface of the photoelectric conversion part of the CCD is made of polycrystalline silicon or metal. Alternatively, the solid-state imaging device is formed of a multilayer structure of polycrystalline silicon and metal silicide, and detects light incident from the back surface of the photoelectric conversion unit.