JP2720566B2 - Infrared solid-state imaging device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared solid-state imaging device, and more particularly, to an improvement in an infrared solid-state imaging device using a Schottky barrier diode as an infrared photodetector. is there.

[Conventional technology]

In recent years, as an infrared solid-state imaging device, a device using a silicon Schottky barrier diode as an infrared light detector and having a resolution sufficient to withstand practical use has been developed.

As a general infrared solid-state imaging device using this type of Schottky barrier diode as an infrared photodetector, here, a so-called charge sweeping method (CSD: Charge Sweep
A conventional example in which (Device) is employed will be described with reference to FIGS. 3 (a) and 3 (b). FIG. 3A is a plan view showing the outline of the arrangement of the photodetector unit in the infrared solid-state imaging device, and FIG. 3B is a line IIIb-IIIb in FIG. 3A. FIG. 2 is a cross-sectional view schematically showing the configuration of FIG.

In addition, for the infrared solid-state imaging device using the CSD method, for example, a known document (“ISSCC: IEEE Internati
onal Solid-State Circuits Conference.Digest of Tec
hnical Paper, February 1987, p. 110 ”).

That is, in the configuration of the conventional infrared solid-state imaging device shown in FIGS. 3 (a) and 3 (b), reference numeral 1 denotes a p-type silicon substrate, and 2 denotes a platinum silicide or the like on the main surface of the substrate 1. A metal-side electrode of a photodetector formed by selectively depositing a metal silicide or a metal by a Schottky barrier diode; 3 is an n ^- type guard ring formed around the metal-side electrode 2; Reference numeral 4 denotes a silicon oxide film provided for element isolation and insulation, and reference numeral 5 denotes an insulating film such as phosphorus glass formed on the silicon oxide film 4.

Reference numeral 6 denotes a transfer gate unit for reading out optical signal charges stored in the metal-side electrode 2 of the photodetector into a vertical transfer channel 7 formed by an n-type buried channel. And transfer electrodes 10 and 11 respectively connected to these transfer electrodes 8 and 9 for transferring the optical signal charges in the vertical direction. First to apply vertical transfer pulse
Scanning lines each formed by Al film layer 12 be on the photodetector, SiO, was formed by Al film of SiO _2, Si _x N _y second layer so as to sandwich an interlayer insulation film 13 such as It is a reflective film.

Subsequently, the operation of the element configuration according to this conventional example will be described.

As is well known, first, an infrared ray to be detected is incident from the back side of the silicon substrate 1 to form an electron-hole pair in the metal-side electrode 2 of the Schottky barrier diode. When the infrared energy is higher than the barrier height of the Schottky barrier diode,
Holes are generated across the barrier, and electrons are accumulated in the metal electrode 2 and the guard ring 3 as optical signal charges. At this time, the reflection film 12 reflects the infrared light that is not absorbed by the metal-side electrode 2 out of the infrared light incident from the back surface side of the silicon substrate 1, and again reflects the reflected light.
Incident on the device improves the light receiving sensitivity of the element.

Next, by sequentially applying vertical transfer pulses to the scanning lines 10 and 11, the accumulated optical signal charges are read out to the vertical transfer channel 7 via the transfer gate 6, and are passed through the vertical transfer channel 7. It is sequentially transferred in the vertical direction (downward in the figure), and the horizontal CC (not shown)
After reaching D (Charge Coupled Device), it is transferred again inside the horizontal CCD and output to the outside.

Further, in the infrared solid-state imaging device based on the CSD method, the optical signal charges stored in one photodetector are transferred to one vertical transfer channel 7 and the light spread over the entire vertical transfer channel 7. The signal charges are swept and transferred to the horizontal CCD. Therefore, the charge transfer capability of the vertical transfer channel 7 is extremely large. For example, even if the width of the vertical transfer channel 7 is designed to be 2 μm, it is normal. Size of the infrared solid-state imaging device photodetector
Since it is about 100 × 100 μm ² or less, the maximum charge transfer amount in the vertical transfer channel 7 is much larger than the signal charge amount that can be stored in the capacitance of the Schottky barrier diode constituting the photodetector. As a result, the amount of saturation signal when strong infrared rays are incident is determined by the capacity of the photodetector.

On the other hand, when a CCD is used for vertical transfer, the CCD method transfers signal charges of one photodetector to a transfer channel below one electrode, so that the saturation signal amount is generally small.
The maximum charge transfer amount of the CCD is limited so as not to exceed the maximum charge transfer amount. Therefore, in the CSD method, the saturation signal amount can be increased to increase the dynamic range as compared with the CCD method.

[Problems to be solved by the invention]

However, in the conventional infrared solid-state imaging device configured as described above, the amount of the saturation signal is determined by the capacitance of the Schottky barrier diode serving as the photodetector. There is a problem that is limited by.

The present invention has been made in order to solve such a conventional problem, and an object of the present invention is to increase the capacity of a Schottky barrier diode as a photodetector to increase a saturation signal amount. Accordingly, it is an object of the present invention to provide an infrared solid-state imaging device of this kind which can increase the dynamic range.

[Means for solving the problem]

In order to achieve the above object, an infrared solid-state imaging device according to the present invention is a conductive film which forms a capacitor between a substrate and a metal side electrode in a photodetector using a Schottky barrier diode. And the conductive film is electrically connected only to the metal-side electrode, and is insulated and separated from the others.

That is, the present invention provides an infrared photodetector comprising at least an infrared photodetector composed of a Schottky barrier diode disposed continuously on a semiconductor substrate, and means for reading out signal charges accumulated in the photodetector to the outside. In the solid-state imaging device, around the metal-side electrode of the photodetector by the Schottky barrier diode, the capacitor is electrically connected to the metal-side electrode, and forms a capacitance with the substrate. An infrared solid-state imaging device comprising a conductive film that is insulated and separated.

[Action]

Therefore, in the infrared solid-state imaging device of the present invention, a conductive film electrically connected to the metal-side electrode is provided around the metal-side electrode in the photodetector using the Schottky barrier diode. A capacitance can be formed between the film and the substrate, and the capacitance of the photodetector itself can be increased to further increase the saturation signal amount.

〔Example〕

Hereinafter, an embodiment of an infrared solid-state imaging device according to the present invention will be described in detail with reference to FIGS. 1 (a) and 1 (b) and FIGS. 2 (a) to 2 (e).

FIGS. 1 (a) and 1 (b) are plan pattern diagrams showing an outline of the arrangement of photodetectors in an infrared solid-state imaging device to which an embodiment of the present invention is applied, and FIGS. It is a cross-sectional view schematically showing the configuration of the Ib-Ib line portion,
In the configuration of the embodiment shown in FIGS. 1 (a) and 1 (b), the same reference numerals as those of the conventional configuration shown in FIGS. 3 (a) and 3 (b) denote the same or corresponding parts.

That is, in the configuration of the infrared solid-state imaging device of the embodiment shown in FIGS.
Reference numeral 2 denotes a metal electrode of a photodetector formed by a Schottky barrier diode formed by selectively depositing a metal silicide such as platinum silicide or a metal on the main surface of the p-type silicon substrate 1. 3 is the metal-side electrode 2
N ^- type guard ring formed around substrate side of silicon oxide film 4 provided for element isolation and insulation;
Is an insulating film such as phosphorus glass formed on the silicon oxide film 4.

Reference numeral 6 denotes a transfer gate unit for reading out optical signal charges stored in the metal-side electrode 2 of the photodetector comprising the Schottky barrier diode into a vertical transfer channel 7 formed by an n-type buried channel. Denotes transfer electrodes made of first and second layers of polysilicon films for transferring the optical signal charges accumulated in the metal-side electrode 2 in the vertical direction. Reference numerals 10 and 11 denote these transfer electrodes, respectively. electrode
Al of the first layer connected to 8 and 9 to apply a vertical transfer pulse
Scanning lines each formed by film, 12 be on the each _{photodetector, SiO, SiO 2, Si x} N y reflective film formed by Al film of the interlayer insulating film 13 to sandwich manner the second layer, such as It is.

Further, reference numeral 14 denotes a conductive film formed around the metal-side electrode 2 of the photodetector made of the Schottky barrier diode on the side of the interlayer insulating film and electrically connected to the metal-side electrode 2. It consists of three polysilicon films. In the drawing, reference numeral 15 denotes ap ⁺ layer formed under the silicon oxide film 4 for element isolation and insulation.

Next, the operation of the element configuration according to this embodiment will be described.

Also in this embodiment, first, the infrared light to be detected enters from the back side of the p-type silicon substrate 1,
Electrons in the metal side electrode 2 of the Schottky barrier diode
A pair of holes is formed, but when the energy of the incident infrared ray is higher than the barrier height of the Schottky barrier diode, holes are generated that exceed the barrier, and electrons are generated by the metal-side electrode 2.
Is stored in the guard ring 3 as an optical signal charge. At this time, the reflection film 12 reflects the infrared light that is not absorbed by the metal-side electrode 2 out of the infrared light incident from the back side of the silicon substrate 1, and returns the reflected light to the metal-side electrode 2 again. By making the light incident, the light receiving sensitivity of the element is improved.

Next, by sequentially applying vertical transfer pulses to the scanning lines 10 and 11, the accumulated optical signal charges are read out to the vertical transfer channel 7 via the transfer gate 6, and are passed through the vertical transfer channel 7. After being sequentially transferred in the vertical direction (downward in the figure) and reaching the horizontal CCD, it is transferred again in the horizontal CCD and output to the outside.

In the case of this embodiment, the conductive film 14 formed around the metal-side electrode 2 of the Schottky barrier diode on the side of the interlayer insulating film forms a capacitance between the conductive film 14 and the p-type silicon substrate 1. Since the conductive film 14 is electrically connected to the metal electrode 2, the capacity of the photodetector including the Schottky barrier diode can be increased as expected.

2 (a) to 2 (e) are the parts corresponding to the arrow II in the embodiment of FIG. 1, that is, in other words,
Each configuration example of a corresponding portion of the conductive film 14 for increasing the capacity of the photodetector is shown.

That is, FIG. 2 (a) shows the metal side electrode 2 and the conductive film.
14 is a case where a metal film such as Pt is formed by vapor deposition using an apparatus having relatively good coverage such as sputtering. In this case, a conductive film made of a metal side electrode 2 and a polysilicon film is used. Connection film 16 of PtSi etc. between film 14
Are formed, and the electrical connection between them is made good.

FIG. 3B shows a case where the metal-side electrode 2 and the conductive film 14 are formed by depositing a metal film such as Pt using an evaporation apparatus having relatively poor coverage. In addition, simultaneously with the Al film of the first layer as the scanning lines 10 and 11, a connection film 17 made of a similar Al film connecting the metal-side electrode 2 and the conductive film 14 is provided at least at one place around the metal film. A good electrical connection can be made in this case as well.

FIG. 4C shows a case where the conductive film 14 is formed of polysilicon doped with an n-type impurity such as P or As at a high concentration. In this case, the polysilicon film is formed on the metal side electrode 2. Is directly in contact with the p-type silicon substrate 1 around the substrate, the n-type impurity is diffused into the substrate, and the metal-side electrode 2 and the conductive film are formed together with the n-type guard ring 3. 14 can be connected.

FIG. 2D shows a case where the silicon oxide film 4 for element isolation and insulation is formed relatively thin, and then the embodiment shown in FIG. 2C is employed. The capacity of the photodetector can be further increased.

FIG. 2E shows a second conductive film made of another polysilicon film with a thin insulating film 18 interposed on the conductive film 14 after adopting the form of FIG. 2C. 19 is formed so that a voltage can be applied to the second conductive film 19 as well. In this case, the former conductive film 14
The capacity between the second conductive film 19 and the capacity between the second conductive film 19 can be used in addition to the capacity between the second conductive film 19 and the substrate 1 to further increase the capacity of the photodetector.
It can be bigger.

In the above-described embodiment, the case where the photodetector using the Schottky barrier diode forming one pixel is two-dimensionally arranged and the reading in the vertical direction is the CSD method has been described. May be one-dimensional, and may be read out by CCD method or MOS method (a method of attaching a MOPS-Tr to the output of a photodetector and reading signals by ON / OFF). You may. For example, if the CCD system is a one-dimensional pixel array and the reading is performed by the CCD system, the maximum charge transfer amount in the CCD system can be increased as long as the width of the CCD itself is increased, and the saturation level is detected by light detection. The same effect can be obtained because it is determined by the capacity of the
In the system, the same effect can be obtained because the saturation level is determined only by the capacity of the photodetector.

Further, in the above embodiment, regarding the conductive film 14,
The figure shows a case in which this does not overlap with each of the transfer electrodes 8, 9 or each of the scanning lines 10, 11, but even if they are electrically separated and insulated, even if they overlap. Although it does not matter, the case where each of the conductive films 14 and 19 is formed by a polysilicon film is described. However, other conductive films other than polysilicon, such as W, WSi, and MoSi, are used. Of course, it may be a metal or metal silicide, or a conductive film having a two-layer structure of these metals or metal silicide and polysilicon, or a conductive film such as α-Si.
If it can be an electrode of the capacitance in the photodetector,
Regardless of its type.

〔The invention's effect〕

As described above in detail, according to the present invention, an infrared photodetector composed of a Schottky barrier diode connected to a semiconductor substrate and a signal charge stored in the photodetector are read out to the outside. In the infrared solid-state imaging device comprising at least the means, around the metal-side electrode of the photodetector by the Schottky barrier diode, electrically connected to the metal-side electrode, and forming a capacitance between the substrate,
Since a conductive film that is insulated and separated from other than the metal side electrode is provided, a capacitance can be formed between the conductive film and the substrate, and the capacity of the photodetector itself can be easily increased, and the photodetection can be performed. The detector has a higher saturation level, and even if stronger infrared light is incident, it can be detected without being saturated.The dynamic range of an infrared solid-state imaging device using a Schottky barrier diode for this type of photodetector It can be large, and
It has excellent features such as relatively simple structure and easy implementation.

[Brief description of the drawings]

FIGS. 1 (a) and 1 (b) are plan pattern diagrams showing an outline of the arrangement of photodetectors in an infrared solid-state imaging device to which an embodiment of the present invention is applied, and FIGS.
2 (a) to 2 (e) are cross-sectional views schematically showing the configuration of the Ib-Ib line portion, and FIG. 2 (a) to FIG. 2 (e) each show a portion corresponding to the conductive film corresponding to the arrow II in the configuration of FIG. FIGS. 3 (a) and 3 (b) are cross-sectional views schematically showing an example of the configuration of FIG. 1; FIG. 3 is a cross-sectional view schematically illustrating a configuration of a line IIIb-IIIb in FIG. 3 and FIG. 1 .... p-type silicon substrate (semiconductor substrate), 2 .... metal side electrode of photodetector composed of Schottky barrier diode,
3 ... guard ring, 4 ... isolation between elements, silicon oxide film for insulation, 5, 18 ... insulation film, 6 ... transfer gate part,
7 ... vertical transfer channel, 8,9 ... transfer electrode, 10,11 ...
Scanning line, 12 ... reflective film, 13 ... interlayer insulating film, 14,19 ...
Conductive film, 15 ... p ⁺ layer, 16,17 ... connection film.

Claims (1)

(57) [Claims] 1. An infrared solid-state device comprising at least an infrared photodetector composed of a Schottky barrier diode disposed continuously on a semiconductor substrate, and means for reading out signal charges stored in the photodetector to the outside. In the imaging device, around the metal-side electrode of the photodetector by the Schottky barrier diode, a capacitor is electrically connected to the metal-side electrode, and forms a capacitance with the substrate, and is insulated from other than the metal-side electrode. An infrared solid-state imaging device having a separated conductive film.