JPH0644621B2 - Solid-state imaging device and driving method thereof - Google Patents

Description

The present invention relates to a solid-state imaging device and a driving method thereof.

[Prior art and its problems]

Infrared solid-state imaging devices have been rapidly developed by taking advantage of many advantages such as miniaturization, weight reduction, high reliability, and mass production. In particular, in a one-dimensional or two-dimensional infrared charge coupled device (CCD) type solid-state imaging device using a silicon Schottky barrier diode as a photoelectric conversion unit, a multi-element array having uniform characteristics can be relatively easily obtained. It is characterized by the fact that peripheral circuits can be integrated on the same chip by the silicon integrated circuit technology established in.

This infrared CCD type solid-state image pickup device (hereinafter simply referred to as SBCC) using a silicon Schottky barrier diode in a photoelectric conversion unit.
Abbreviated as D), International Electronic Device Meeting (International E Device Meeting) held in December 1981.
lectron Devices Meeting). F. “64 x 128” by Kosonky (WF Kosoncky)
Element High-Performance PtSi IR-CCD Image
Senser (64 x 128 element high performance platinum silicide infrared C
CD image sensor) ". Regarding one-dimensional SBCCD, FB Warren et al., RCA Engineer, 5/6 Issue, 1982 "Spa
ce Applications, for RCAInfrared Technology (R
One-dimensional CCD with palladium silicide Schottky barrier diode
An imaging device has been announced. However, these SBCCDs
Has the following drawbacks.

A solid-state image pickup device using a CCD has a small noise and can take an image with extremely low illuminance, but one-dimensional and two-dimensional C using a conventional Schottky barrier diode as a photoelectric conversion unit.
In a CD image pickup device, afterimages become more visible as the illuminance becomes lower,
This afterimage determines the low illuminance limit. Also, TD
The method of improving the sensitivity by the I (Time Delay and Integration) operation cannot be used due to the afterimage phenomenon. This afterimage phenomenon will be described using a conventional CCD sensor.

FIG. 4 shows a configuration diagram of a conventional one-dimensional imaging device using a Schottky barrier diode. Reference numeral 10 is a Schottky barrier diode, 11 is a transfer gate, and 12 is a CCD register for reading out signal charges accumulated in the Schottky barrier diode 10. The signal charge read out to the CCD register 12 is taken out from the output amplifier 13 as a time-series signal by the clock pulses φ ₁ and φ ₂ .

FIG. 5 is a block diagram of a conventional interline transfer SBCCD. The SBCCD includes a plurality of columns of CCD vertical shift registers 14 driven by the same charge transfer electrodes (not shown), and a Schottky barrier diode 10 adjacent to one side of each vertical shift register and electrically separated from each other. , A transfer gate 15 provided between the vertical shift register 14 and the Schottky barrier diode 10, which is a photoelectric conversion unit, and controls signal charge transfer between them.
And a charge transfer horizontal shift register 16 electrically coupled to one end of each vertical shift register, and an output amplifier 13 for detecting a signal charge at one end of the horizontal shift register.

FIG. 6 is a sectional view of a unit element taken along line VI-VI of the image pickup apparatus shown in FIG. This unit element is also made of the same constituent elements in the one-dimensional SBCCD shown in FIG.

A Schottky barrier diode is formed by depositing a metal layer 18 of platinum, palladium or the like on the main surface of the P-type silicon substrate 17. The periphery of the Schottky barrier diode is surrounded by N-type regions 19 and 20 in order to reduce dark current. In particular, the N-type region 20 adjacent to the transfer gate region below the transfer gate electrode 21 is in ohmic contact with the metal layer 18 forming the Schottky barrier diode with a high impurity concentration. The signal charge of the infrared image photoelectrically converted by the Schottky barrier diode is stored in the silicide side and the N-type regions 19 and 20. This signal charge is read out to the vertical shift register 22 via the transfer gate region. The signal charges read to the vertical shift register 22 are transferred to the output section by the pulse applied to the transfer electrode 23 that controls the transfer in the vertical shift register. The unit element is electrically separated from the adjacent element by the channel stopper region 24.

FIG. 7 schematically shows a lateral potential distribution of the unit element shown in FIG. The vertical axis represents voltage and the horizontal axis represents distance. 25 is a Schottky barrier diode region, 26
Is a transfer gate area and 27 is a voltage distribution in the vertical shift register area. When the transfer gate is in the off state, the voltage distribution is as shown by the broken line 28, and a potential barrier is formed between the Schottky barrier diode region 25 and the vertical shift register region 27. Therefore, the Schottky barrier diode is in a floating state, and signal accumulation starts. The voltage of the Schottky barrier diode decreases as the signal charge increases, and becomes a voltage indicated by 29, for example. Next, when the transfer gate is turned on, the voltage immediately below the transfer gate becomes the voltage shown by the solid line 30. At the same time, the signal charges accumulated in the Schottky barrier diode start to move to the vertical shift register area. The voltage 29 of the Schottky barrier diode increases with the read amount of the signal charge. However, when the voltage 29 of the Schottky barrier diode becomes large and the potential difference from the voltage 30 in the transfer gate region becomes small, the channel in the transfer gate region is in a weak inversion state, and the signal charge reading speed becomes slow. Therefore, the voltage of the Schottky barrier diode does not easily reach the voltage 30 of the transfer gate region, which is the final reached value. For example, the channel length of the transfer gate region 26 is 5 μm, the channel width is 5 μm, and the capacitance of the Schottky barrier diode is 0.
Assuming that the voltage of the Schottky barrier diode reaches 03 pF, it takes several 1
It is 0 msec. However, the on-state period of the transfer gate in the standard television system is usually 1 μsec to 500 μsec. Therefore, the signal charges cannot be completely read from the Schottky barrier diode to the vertical shift register during the normal transfer gate on-time, and some charges are left behind in the Schottky barrier diode. This residual charge is read out after the transfer gate is turned on, and there is a drawback that it appears as an afterimage in a reproduced image.

[Object of the Invention]

An object of the present invention is to provide a solid-state imaging device that eliminates the above-mentioned drawbacks.

Another object of the present invention is to provide a method for driving a solid-state imaging device according to the present invention.

[Structure of Invention]

The present invention provides a photoelectric conversion element column, a shift register provided along the photoelectric conversion element column, a signal provided between the photoelectric conversion element column and the shift register, and accumulated in the photoelectric conversion element. In a solid-state imaging device including a transfer gate that transfers charges to the shift register, the photoelectric conversion element is formed of a P-type region formed on an N-type semiconductor substrate and a metal layer provided on the P-type region. A Schottky barrier diode is provided, and a means for connecting at least a part of the metal-side periphery of the Schottky barrier diode to the N-type semiconductor substrate is provided.

Another aspect of the present invention is to provide a row of photoelectric conversion elements, a shift register provided along the row of photoelectric conversion elements, a row of the photoelectric conversion elements and the shift register, and store the photoelectric conversion elements in the row. And a transfer gate for transferring the signal charge to the shift register, the photoelectric conversion element,
A Schottky barrier diode formed by a P-type region formed on an N-type semiconductor substrate and a metal layer provided on the P-type region is formed, and at least a part of the periphery of the metal side of the Schottky barrier diode is formed by the N-type semiconductor region. Means for connecting to the P-type semiconductor substrate, the impurity concentration of the P-type region is adjusted so that the P-type region is completely depleted after the signal charges accumulated in the photoelectric conversion element are read out. In the solid-state imaging device, the transfer gate region has a voltage higher than a voltage that completely depletes the P-type region, and a voltage is applied to the transfer gate to transfer charges from the P-type region to the shift register. It has a feature.

〔Example〕

 Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing a unit element constituting an embodiment of the present invention and corresponds to FIG. 6 of a conventional example. Unlike the prior art, the silicon substrate 31 is made of an N-type conductor. P is formed on the main surface of the N-type silicon substrate to form an infrared light detecting portion.
A mold region 32 is formed. A metal layer 33 of platinum, palladium, indium, nickel, tungsten, titanium or the like forming a Schottky barrier diode is deposited on the main surface of the P type region 32, and then a Schottky barrier diode is formed by heat treatment. . At least a part of the metal-side periphery of the Schottky barrier diode is ohmically connected to the high-concentration N-type region (channel stop region) 34 adjacent to the P-type region 32. Reference numeral 35 is a transfer gate electrode, and 36 is a transfer electrode of a vertical CCD register. The CCD may be a surface channel type, but in this example, it is a buried channel type having a P-type region 37.

FIG. 2 is an energy band diagram on the line II-II of FIG.

FIG. 3 schematically shows the lateral potential distribution of the unit element shown in FIG. 1 and corresponds to FIG. 7 of the conventional example. The difference from FIG. 7 is that the polarities of the voltage axes are opposite because the signal charges change from electrons to holes.

Next, the operation of this embodiment will be described with reference to FIGS.

When a pulse is supplied to the transfer gate electrode 35 and the transfer gate is turned on, holes which are electric charges in the P-type region 32 are read out to the vertical CCD register.
The solid line in FIG. 2 is an energy band diagram immediately after the holes are read from the P-type region 32. Here, 38 indicates the potential of the valence band of the shift register, and 39 indicates the potential of the conduction band. The right side of FIG. 2 is the Schottky barrier diode portion, and the contact portion between the metal and the P-type region 32 is V
It has a barrier potential of s. Moreover, 40 has shown the felt level. As is clear from the figure, the P-type region 32 is
Reverse biased to the Schottky barrier diode and the substrate. An important point of the present invention is that the P-type region 3 is completely depleted after the signal is read out.
2 is to adjust the impurity concentration to a low concentration. Specifically, the impurity concentration of the N-type substrate 31 is set to 10 ^{14 to} 5 × 10.
¹⁶ / cm ³ , the surface density of the P-type region 32 is 10 ¹¹
It is formed in the range of up to 5 × 10 ¹² / cm ² . In this concentration range, the P-type region 32 can be depleted with a reverse bias voltage of 30 V or less. The barrier potential Vs of the Schottky barrier diode is preferably in the range of 0.15 to 0.4 eV.

Next, when the transfer gate is turned off, the P-type region 32 becomes in a floating state. When infrared light enters in this state, infrared light having an energy larger than the barrier potential Vs is absorbed by the metal side of the Schottky barrier diode and holes are emitted from the metal side to the semiconductor. This hole is a P-type region 32
Stored in. The potential of the P-type region 32 becomes shallow depending on the amount of holes that are signal charges, and the energy band of the valence band is as shown by the broken line 41.

When the transfer gate is turned on again, the P-type region 3
The signal charge stored in 2 is completely read out to the vertical CCD register, and the P-type region 32 is completely depleted. To transfer charges from the P-type region to the vertical CCD register, a voltage is applied to the transfer gate electrode such that the voltage of the transfer gate region is higher than the voltage that completely depletes the P-type region by 300 mV or more.
As a result, the channel in the transfer gate region can always be in the strong inversion state. That is, by adjusting the peak value of the transfer gate pulse, the signal generated by the infrared light can be completely transferred to the vertical CCD register.

Although one embodiment of the present invention has been described above, it is needless to say that the present invention is not limited to the above-described example and many modifications can be made. For example, although the embodiment of the present invention has been described with respect to the CCD type sensor, the present invention can be applied to a MOS type sensor.

〔The invention's effect〕

As described above, the low concentration of P on the N-type silicon substrate as in the present invention.
In an infrared solid-state imaging device having a structure in which a mold region is formed, a Schottky barrier diode is formed on the P-type region, and the metal side of the Schottky barrier diode is in ohmic contact with a substrate surface exposed on the surface. , P is set so that the P-type region is completely depleted after the transfer gate is turned on and the signal charge is read out to the CCD.
Of the Schottky barrier infrared imaging device, which has been a problem in the past, by reducing the type impurity concentration and selecting the peak value of the transfer gate pulse so that the voltage of the transfer gate region becomes larger than the voltage of the depleted P type region. Afterimages can be reduced.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a solid-state image pickup device according to the present invention, FIG. 2 is an explanatory view showing an energy band on a line II-II of FIG. 1, and FIG. 3 is a solid-state image pickup of FIG. 4 and 5 are configuration diagrams showing a conventional one-dimensional and two-dimensional solid-state imaging device, respectively. FIG. 6 is a sectional view taken along line VI-VI in FIG. FIG. 7 is a sectional view showing the unit element, and FIG. 7 is a diagram showing the potential distribution of the unit element of FIG. 10, 18 ...... Schottky barrier diode 11, 15, 21 ...... Transfer gate 12 ...... CCD register 13 ...... Output amplifier 14, 22 ...... Vertical shift register 16 ...... Horizontal shift register 17 ...... P-type silicon substrate 19, 20 ... N-type region 23, 36 ... Transfer electrode 24 ... Channel stop region 25 ... Schottky barrier diode region 26 ... Transfer gate region 27 ... Vertical shift register region 31 ... N-type silicon substrate 32, 37 ... ... P-type region 33 ... metal layer 34 ... high-concentration N-type region (channel stop region) 35 ... transfer gate electrode

Claims (3)

[Claims] 1. A row of photoelectric conversion elements, a shift register provided along the row of photoelectric conversion elements, and a row of the photoelectric conversion elements and the shift register, and accumulated in the photoelectric conversion elements. In a solid-state imaging device comprising a transfer gate that transfers signal charges to the shift register,
The photoelectric conversion element is composed of a Schottky barrier diode formed of a P-type region formed on an N-type semiconductor substrate and a metal layer provided on the P-type region, and a metal-side periphery of the Schottky barrier diode is formed. A solid-state imaging device comprising means for connecting at least a part to the N-type semiconductor substrate. 2. The solid-state image pickup device according to claim 1, wherein the P-type region is completely depleted after the signal charge accumulated in the photoelectric conversion element is read out. A solid-state imaging device, wherein the impurity concentration of the P-type region is adjusted. 3. A row of photoelectric conversion elements, a shift register provided along the row of photoelectric conversion elements, and a row of the photoelectric conversion elements and the shift register, and accumulated in the photoelectric conversion elements. A transfer gate for transferring signal charges to the shift register,
A Schottky barrier diode formed by a P-type region formed on a P-type semiconductor substrate and a metal layer provided on the P-type region, and at least a part of the metal-side periphery of the Schottky barrier diode is formed by the N-type region. A means for connecting to the semiconductor substrate is provided, and after the signal charge accumulated in the photoelectric conversion element is read out, the impurity concentration of the P-type region is adjusted so that the P-type region is completely depleted. In the solid-state imaging device, the voltage of the transfer gate region is higher than the voltage that completely depletes the P-type region, and the charge is transferred from the P-type region to the shift register by applying the voltage to the transfer gate. Driving method for solid-state imaging device.