JPS6351546B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an infrared photoelectric conversion section (hereinafter referred to as a "Schottkey type infrared detection section") consisting of a Schottky junction.
The present invention relates to an infrared solid-state image pickup device constructed with an infrared ray sensor (referred to as .

FIG. 1 is a diagram schematically showing the basic configuration of an example of an infrared solid-state imaging device.

In the figure, reference numeral 100 denotes a shot key-type infrared detection unit that is arranged in multiple rows in the horizontal direction and in multiple columns in the vertical direction at intervals between each other and accumulates charges corresponding to the amount of infrared rays irradiated, and 200 in the vertical direction. A plurality of infrared detection units 1 arranged in each row of
A transfer MOS transistor 300 is formed in common contact with the transfer MOS transistor 200 and transfers the accumulated charge of these infrared detection sections 100 to a vertical register to be described later. A vertical register 400 formed of a charge coupled device (CCD) is commonly connected to the output end of each vertical register 300 so as to sequentially transfer the accumulated charge of each infrared detection section 100 to the output end. Horizontal registers 50 configured with CCDs so as to sequentially transfer charges formed and transferred by these vertical registers 300 to output terminals.
0 is an output section connected to the output end of the horizontal register 400, which converts the charge transferred by the horizontal register 400 into, for example, a voltage and outputs it to the outside. transfer
MOS transistor 200, vertical register 300,
The horizontal register 400 and the output section 500 constitute a readout mechanism that sequentially reads out the accumulated charges of the plurality of infrared detection sections 100 arranged two-dimensionally and outputs them as electrical signals.

FIG. 2 is a cross-sectional view of an example of a conventional infrared solid-state imaging device taken along a line corresponding to the - line shown in FIG.

In the figure, 1 is a p-type silicon substrate with an impurity concentration of 10 ¹⁴ to 10 ¹⁵ atoms/cm ³ , and 2 is an oxidized silicon substrate formed on the main surface of the p-type silicon substrate 1 other than the part where the Schottky junction is to be formed. Silicon film, 3
is a p-type silicon substrate consisting of a vapor-deposited layer of metal such as gold (Au) or palladium (Pd) or metal silicide such as platinum silicide (Pt/Si), palladium silicide (Pd/Si), or iridium silicide (Ir/Si). The metal side electrode of the Schottky junction is formed by adhering to the part separated by the silicon oxide film 2 on the main surface of the p-type silicon substrate 1, and the metal side electrode 4 contacts the peripheral edge of the metal side electrode 3 on the main surface of the p-type silicon substrate 1. A guard ring 5, which is an n-type region formed in a portion, is an electrode lead made of an aluminum layer and connected to the surface peripheral part of the metal side electrode 3. p-type silicon substrate 1,
The metal side electrode 3, guard ring 4, and electrode lead 5 constitute an infrared detection section 100 shown in FIG. Reference numeral 6 indicates an n ⁺ type region formed in a portion of the main surface of the p-type silicon substrate 1 near the outer periphery of the guard ring 4, and an electrode lead 5 is connected to a part of the surface by penetrating the silicon oxide film 2; A first layer is buried parallel to the main surface of the p-type silicon substrate 1 in a portion of the silicon oxide film 2 corresponding to a portion extending from the n ⁺ type region 6 to the n-type buried channel region described below.
Transfer MOS transistor 20 shown in the figure
0 (hereinafter referred to as "transfer gate electrode"), 8 includes the lower part of the end of the transagate electrode 7 on the main surface of the p-type silicon substrate 1 on the side opposite to the n ⁺ type region 6 side. An n-type buried channel region 9 is formed in the outer part of the transfer gate electrode 7 in the silicon oxide film 2.
a gate electrode extending from an upper portion of the end opposite to the infrared detection unit 100 side and buried so as to be parallel to the surface of the n-type buried channel region 8;
301 is a vertical register 30 shown in FIG.
0 constitutes a CCD, 10 constitutes an infrared detection section 100
and a silicon nitride film for device protection formed on the entire upper surface of the silicon oxide film 2.

Next, the operation of this conventional element will be explained.

Normally, this element is used by applying a reverse bias voltage to the Schottky junction of the infrared detecting section 100 at the temperature of liquid nitrogen (77°).
In this state, when infrared light is irradiated to either the p-type silicon substrate 1 side or the metal side electrode 3 side, pairs of electrons and holes are positively formed in the metal side electrode 3. do. Of the generated holes, those with kinetic energy exceeding the Schottky barrier are injected into the p-type silicon substrate 1, and charges corresponding to the amount of light irradiated are accumulated in the metal side electrode 3. This accumulated charge on the metal side electrode 3 passes through the electrode lead 5.
The CCD 3 forming the vertical register 300 is passed from the n ⁺ type region 6 through the portion between the n ⁺ type region 6 and the n type buried channel region 8 on the main surface of the p type silicon substrate 1 by means of the transfer gate electrode 7.
01 into the n-type buried channel region 8. As shown in FIG.
00 as an electrical signal. In this way, the accumulated charge corresponding to the amount of light irradiated by each of the plurality of infrared detecting sections 100 arranged two-dimensionally is transferred to the transfer MOS transistor 200,
A reading mechanism composed of a vertical register 300, a horizontal register 400, and an output section 500 can sequentially read out the data.

By the way, in this Schottky-type infrared detection section 100 of this conventional example, normally 10 ¹⁴ to 10 ¹⁵ atoms/cm ³
A p-type silicon substrate 1 having a relatively low impurity concentration is used, and a metal side electrode 3 made of a deposited layer of Pt.Si is used. In this case, p-type silicon substrate 1
Since the height _B of the Schottky barrier between the metal side electrode 3 made of Pt and Si is 0.27 eV, the maximum wavelength of detectable light that is quantum determined from this barrier height of 0.27 eV is 4.60 μm. Become.

In general, the quantum efficiency Y of a Schottky photodetector is expressed as Y=C ₁ ·(hν− _B ) ² /hν (electrons/photon). Here, h is Planck's constant, ν is the frequency of the irradiated light, and C ₁ is the quantum efficiency coefficient.

As can be seen from the above equation, in the Schottky type light detector, in order to obtain high detection sensitivity in the 3 to 5 μm light wavelength region called the atmospheric window, the height _B of the Schottky barrier can be reduced. In order to lower the height _B of this barrier, the p-type silicon substrate 1
If the impurity concentration of is increased, the height _B of the Schottky barrier will effectively decrease due to the Schottky effect. However, in the n-type buried channel region 8 of the CCD 301, in order to increase the charge transfer efficiency at the temperature of liquid nitrogen (77〓), the density of donors, which act as a trap that lowers the transfer efficiency, must be made as low as possible. In order to lower the donor density, the impurity concentration of the p-type silicon substrate 1 must be as low as about 10 ¹⁴ to 10 ¹⁵ atoms/cm ³ .

In this way, in the conventional element, the infrared detecting section 1
There was a problem in that aiming to improve the detection sensitivity in the 3-5 μm wavelength range of light of 0.00 and improving the transfer efficiency of the CCD 301 contradicted each other.

This invention has been made in view of the above-mentioned problems, and it is possible to form a Schottky junction on the main surface of a semiconductor substrate by introducing impurities of the same conductivity type as the semiconductor substrate into a region where a Schottky junction is to be formed on the main surface of the semiconductor substrate. By making the impurity concentration in the formation region higher than the impurity concentration in other regions, the height _B of the Schottky barrier of the infrared detection section can be effectively lowered and detectable irradiation can be achieved while using a semiconductor substrate with a low impurity concentration. Extend the maximum wavelength of light to the long wavelength side, and
The purpose of the present invention is to provide an infrared solid-state image sensor with improved detection sensitivity in the 5 μm wavelength range of light.

FIG. 3 is a sectional view showing an infrared detection section of an infrared solid-state image sensor according to an embodiment of the present invention.

In the figure, the same reference numerals as those in the conventional example shown in FIG. 2 indicate equivalent parts. 11 is formed by ion implantation or diffusion of p-type impurities such as boron or gallium into the main surface of the p-type silicon substrate 1 surrounded by the guard ring 5, and has an impurity concentration higher than that of the p-type silicon substrate 1. This is the p ⁺ type region of concentration. A Schottky junction is formed between this p ⁺ type region 11 and the metal side electrode 3. 100a is
p ⁺ type region 11, metal side electrode 3, guard ring 4
The infrared detecting section of this embodiment is composed of an electrode lead 5 and an electrode lead 5.

The structure of the infrared solid-state imaging device of this embodiment is the same as that of the conventional example shown in FIG. 2, except for the infrared detecting section 100a.

Generally, it is known that the height _B of the Schottky barrier is effectively reduced by Δφ due to the Schottky effect. Here, Δφ is the barrier lowering energy due to the interfacial electric field of the Schottky junction. The magnitude of this Δφ increases as the strength E of the interfacial electric field of the Schottky junction increases. Therefore, in the infrared detecting section 100a of this embodiment, by forming the p ⁺ type region 11 with a high impurity concentration at the interface of the Schottky junction, the strength E of the interfacial electric field of this junction is increased and the effective It becomes possible to increase the above-mentioned Δφ, which reduces the height _B of the Schottky barrier, and the height _B of the Schottky barrier can be controlled by the impurity concentration of the p ⁺ type region 11. For example, the infrared detection section 1 of this embodiment
In 00a, a Pt/Si vapor deposited layer is used for the metal side electrode 3, and the impurity of the p ^{+ type} region 11 formed on the main surface of the p type silicon substrate 1 with a low impurity concentration of about 10 ¹⁴ to 10 15 atoms/cm ³ is used. The concentration is set to about ¹⁰¹⁶ atoms/ ^cm3 ,
When a reverse bias voltage of about 5 V is applied to the Schottky junction and the Schottky junction is used at the temperature of liquid nitrogen (77〓), the Schottky barrier height _B is 0.23 eV.
The maximum wavelength of detectable light is 5.4 μm. Furthermore, when the impurity concentration of the p ⁺ type region 11 is set to about 10 ¹⁷ atoms/cm ³ , the height _B of the Schottky barrier further decreases to 0.20 eV, and the maximum wavelength of detectable light becomes 6.2 μm. . As a result, the maximum wavelength of light that can be detected by the infrared detecting section 100a of this embodiment is 4.6 μm, which is the maximum wavelength of light that can be detected by the infrared detecting section 100 of the conventional example shown in FIG. It can be seen that it extends toward longer wavelengths compared to .

In this way, in the device of this example, the p-type silicon substrate 1 with a low impurity concentration is used as shown in FIG.
While improving the transfer efficiency of the CCD 301, the height of the shot key barrier of the infrared detection unit 100a is
By lowering _B and extending the maximum wavelength of detectable irradiation light to the longer wavelength side, it is possible to improve detection sensitivity in the wavelength range of light from 3 to 5 μm.

In this embodiment, a case is described in which Pt/Si is used for the metal side electrode 3, but the invention is not limited to this.
Metals such as PD, Ir, or Pd/Si, Ir/Si, Pt/Si
Even if metal silicides such as silicides are used, the same effect as in this example can be obtained. Further, although the case where the p-type silicon substrate 1 is used has been described, an n-type silicon substrate may also be used. In this case, p ⁺ type region 11
If it is made into an n ⁺ type region, the same effect as this embodiment can be obtained.

Although the case of a readout mechanism using a CCD as a component has been described as an example, the present invention is not limited to this, and is applicable to MOS devices that require a semiconductor substrate with a low impurity concentration to suppress an increase in junction capacitance. The present invention can also be applied to readout mechanisms that include other semiconductor elements such as transistors. Further, although the case where the infrared detection sections are arranged two-dimensionally has been described as an example, the present invention can also be applied to the case where the infrared detection sections are arranged one-dimensionally.

As described above, in the infrared solid-state imaging device of the present invention, an impurity having the same conductivity type as the semiconductor substrate is introduced into the portion of the main surface of the semiconductor substrate where the Schottky junction is to be formed. Since the impurity concentration in the formation region is higher than the impurity concentration in other regions of the semiconductor substrate,
While using a semiconductor substrate with a low impurity concentration, the height _B of the Schottky barrier in the infrared detection section is effectively lowered to extend the maximum wavelength of detectable irradiation light to the long wavelength side, and it is possible to increase the wavelength range of light in the range of 3 to 5 μm. Detection sensitivity can be improved.

[Brief explanation of drawings]

Fig. 1 is a diagram schematically showing the basic configuration of an example of an infrared solid-state image sensor, and Fig. 2 is a cross-sectional view of an example of a conventional infrared solid-state image sensor taken along a line corresponding to the - line shown in Fig. 1. , FIG. 3 is a sectional view showing an infrared detection section of an infrared solid-state imaging device according to an embodiment of the present invention. In the figure, 1 is a p-type silicon substrate (semiconductor substrate), 3 is a metal side electrode, 11 is a p ⁺ type region (region with high impurity concentration), 100a is an infrared detection section (infrared photoelectric conversion section), 200, 300, Reference numerals 400 and 500 represent a transfer MOS transistor, a vertical register, a horizontal register, and an output section, respectively, which constitute a readout mechanism. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A semiconductor substrate, and a metal side electrode made of metal or metal silicide and bonded to a required portion of the main surface of the semiconductor substrate to form a Schottky junction, and having a metal side electrode that is attached to the main surface of the semiconductor substrate to form a Schottky junction. a plurality of infrared photoelectric conversion units arranged one-dimensionally or two-dimensionally with intervals between them and accumulating charges corresponding to the amount of irradiated infrared rays on the metal side electrode; and the infrared photoelectric conversion unit on the main surface of the semiconductor substrate. and a readout mechanism that is formed in a portion other than the formation region and sequentially reads out the accumulated charge of each of the infrared photoelectric conversion sections, wherein the Schottky junction formation region of the main surface of the semiconductor substrate has the same conductivity type as the semiconductor substrate. An infrared solid-state imaging device characterized in that an infrared solid-state imaging device is provided with a region having a higher impurity concentration than other regions of the semiconductor substrate by introducing an impurity. 2. The infrared solid-state imaging device according to claim 1, characterized in that a charge-coupled device is used for the register of the readout mechanism. 3. The infrared solid-state imaging device according to claim 1, characterized in that a switching MOS transistor is used in the readout mechanism.