JPH073866B2 - Back-thinned infrared detector - Google Patents

Description

TECHNICAL FIELD The present invention relates to an infrared detector using a Schottky barrier diode.

[Conventional technology]

Infrared CCD using conventional Schottky barrier diode
Image sensor (SB-IRCCD), WFKosonocky
(Kosonocky) etc. SPIE (the Society of Photo-Op
tical Instrumentation Engineers), 443, 167 pages,
I will explain based on a 1983 paper.

FIG. 2 is a schematic plan view of SB-IR CCD. Light receiving part 1
A reverse-biased Schottky barrier diode is used for and is regularly arranged in the horizontal and vertical directions. A vertical CCD register 2 is provided near one side of the column of the light receiving units 1, and a transfer gate unit 3 is provided between the vertical CCD register 2 and the light receiving unit 1. The horizontal CCD is at the end of the vertical CCD register 2 in the charge transfer direction.
A CD register 4 is provided, and an output section 5 is provided at the end of the horizontal CCD register 4 in the charge transfer direction.

FIG. 3 is a schematic sectional view in the horizontal direction of the unit cell of the SB-IR CCD shown in FIG. A platinum silicide layer 7 is formed on one main surface of the p-type silicon substrate 6. An n-type guard ring portion 8 is formed in a region in contact with the edge portion of the platinum silicide layer 7 in order to increase the reverse bias breakdown voltage. An aluminum reflection film 9 is formed above the platinum silicide layer 7.
Are provided through the oxide film 10. An n ⁺ region 12 is formed for the purpose of electrically connecting the platinum silicide layer 7 and the transfer gate 11. Platinum silicide layer 7
And n ⁺ region 12 are in ohmic contact. The channel below the transfer gate 11 is surface type. Driving gate 13 for vertical CCD register adjacent to transfer gate 11
And an n-type buried layer 14 are formed.

In the SB-IR CCD shown in FIG. 2 and FIG. 3, infrared rays are incident from the back surface, the infrared rays are absorbed by the platinum silicide layer 7, and electrons and holes with large energy are generated. The Schottky barrier height of the Schottky barrier diode formed by the p-type silicon substrate 6 and the platinum silicide layer 7 is 0.2 to 0.27 eV. The hot holes excited by infrared rays exceed this Schottky barrier height, and the Schottky barrier diode is injected into the p-type silicon substrate 6. , Electrons and holes are separated,
The electrons remaining in the platinum silicide layer 7 become signal charges. The signal charge is accumulated in the platinum silicide layer 7 and the n ⁺ region 12 in ohmic contact therewith. The transfer gate portion 3 is turned on every field period or frame period, the signal charges are transferred to the vertical CCD register 2 by the platinum silicide layer 7 and the n ⁺ region 12, and the vertical C
The CD register 2 and the horizontal CCD register 4 work to transfer the data to the output unit 5 and output it to the outside of the fixed image sensor.

[Problems to be solved by the invention]

Consider the process by which hot holes cross Schottky barriers. The distribution of the directions of movement of holes excited by infrared rays is spherically symmetric, and the probability is equal in all directions. The hot holes traveling in the direction opposite to the direction of the p-type silicon substrate 6 are the platinum silicide layer 7 and the oxide film 10.
It is reflected at the interface with and advances toward the p-type silicon substrate 6 this time. Among the hot holes reaching the interface between the p-type silicon substrate 6 and the platinum silicide layer 7, those having an energy larger than the Schottky barrier height have a certain probability p.
It is injected into the mold type silicon substrate 6. The holes that have not been injected are reflected and travel toward the oxide film 10. It may be directly injected into the p-type silicon substrate 6 or may be injected into the p-type silicon substrate 6 after being reflected at the interface several times. The hot holes lose energy due to scattering in the grain boundary, electron / electron scattering, and the like while moving in the platinum silicide layer 7. For this reason, a considerable proportion of the hot holes excited by infrared rays are not injected into the p-type silicon substrate 6, resulting in deterioration of quantum efficiency.

An object of the present invention is to eliminate such a conventional defect and provide an infrared detection element having high quantum efficiency.

[Means for solving problems]

In order to achieve the above object, the present invention forms a metal layer forming a Schottky barrier diode with the semiconductor substrate on one main surface of the semiconductor substrate, and forming the metal layer and the Schottky barrier diode on the metal layer. A semiconductor layer having the same conductivity type as that of the semiconductor substrate and having an optical thickness of a quarter of the wavelength of infrared rays to be detected, and a metal reflection film provided on the semiconductor layer.

[Action]

In the conventional structure, the metal layer forms the Schottky barrier diode only with the semiconductor substrate, but in the structure of the present invention, the metal layer forms the Schottky barrier diode not only with the semiconductor substrate but also with the semiconductor element provided thereon. Reverse the two Schottky barrier diodes. Then, since hot carriers excited by infrared rays are injected into the semiconductor substrate or the semiconductor layer over one of the two Schottky barriers, the probability of crossing the Schottky barrier is significantly increased as compared with the conventional structure.
As a result, the quantum efficiency of the infrared detector increases.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic horizontal sectional view of a unit cell of an SB-IR CCD of an embodiment of the present invention. A schematic plan view of this SB-IR CCD is the same as FIG. Note that, in FIG. 1, the same reference numerals as those in FIG. 3 indicate the same components.

In this SB-IR CCD, a p-type silicon layer 15 is formed on a platinum silicide layer 7 formed on one main surface of a p-type silicon substrate 6. An aluminum reflection film 9 and an oxide film 10 for protection are formed on the silicon layer 15. The thickness of the silicon layer 15 is determined so that the effect of the aluminum reflection film 9 is most effective. That is, it is preferable to set the optical thickness in consideration of the refractive index to ¼ of the wavelength of infrared rays.

Next, a method of manufacturing the SB-IR CCD of this embodiment will be described with reference to FIG. An n-type guard ring portion 8 and an n-type buried layer 14 for a vertical CCD register are formed on one main surface of the p-type silicon substrate 6. Next, vertical with the transfer gate 11
And a drive gate 13 for the CCD register. Further n ⁺
FIG. 4A is a schematic sectional view when the region 12 is formed and the oxide film 10 is formed on the surface.

Next, the oxide film 10 in the region where the platinum silicide layer 7 is formed is removed, and platinum is deposited. Heat treatment is performed to form the platinum silicide layer 7. Depending on the formation conditions of platinum silicide, it grows epitaxially on the p-type silicon substrate 6. The characteristics are better when grown epitaxially. The platinum on the oxide film 10 does not become a silicide and is removed by aqua regia etching. A schematic sectional view at this time is shown in FIG.

Next, the p-type silicon layer 15 is formed by a vapor deposition method, a sputtering method, a CVD method or the like. It is preferable that the platinum silicide layer 7 is epitaxially grown, but the effect of the present invention can be obtained even if it is a non-epitaxial polycrystalline or amorphous material. The unnecessary p-type silicon layer 15 is removed by lithography and etching. Next, the aluminum reflection film 9 is formed together with the wiring. The p-type silicon layer 15 and the aluminum reflection film 9 are in ohmic contact so that the potential of the p-type silicon layer 15 can be set through the reflection film 9. A schematic sectional view at this time is shown in FIG. Further, a protective oxide film 10 is formed and the process is completed.

In the SB-IR CCD of the embodiment of the present invention described above, the Schottky barrier diode is formed on both surfaces of the platinum silicide layer 7. The potential of the semiconductor layer 15 may be at the same ground level as the p-type silicon substrate 6 or may be set at another potential. When the two Schottky barrier diodes are in a reverse bias state, a hot hole excited by infrared rays becomes a signal regardless of which Schottky barrier is injected into the p-type silicon substrate 6 or the p-type silicon layer 15. Therefore, the quantum efficiency is significantly improved as compared with the case where there is only one Schottky barrier diode as in the conventional structure.

Although the example of the two-dimensional image sensor using the CCD is shown in the above embodiments, the present invention can be applied to a single type or one-dimensional image sensor. The scanning method is not limited to CCD, and any method such as MOS type is possible. Although the n-channel type has been described, the p-channel type is also possible. Further, materials other than silicon can be used as the semiconductor, and metals other than silicide can be widely used as the metal layer.

〔The invention's effect〕

As described above, in the Schottky barrier diode type infrared detection device according to the present invention, the quantum efficiency is significantly improved by forming the Schottky barrier diodes on both sides of the metal layer.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an infrared detecting device according to an embodiment of the present invention, FIG. 2 is a plan view of the infrared detecting device, FIG. 3 is a schematic sectional view of a conventional infrared detecting device, and FIG. FIG. 6 is a schematic cross-sectional view showing the manufacturing process of the infrared detection device according to the embodiment of the present invention. 6 ... p-type silicon substrate 7 ... platinum silicide layer 9 ... reflective film 10 ... oxide film 15 ... silicon layer

Claims (1)

[Claims] 1. A metal layer forming a Schottky barrier diode with the semiconductor substrate is formed on one main surface of a semiconductor substrate, and the same conductivity type as the semiconductor substrate forming the Schottky barrier diode with the metal layer is formed on the metal layer. A back-illuminated infrared detection device comprising a semiconductor layer whose optical thickness is 1/4 of the wavelength of infrared light to be detected, and a metal reflection film provided on the semiconductor layer.