JPH04293264A - Infrared ray solid-state image sensing element - Google Patents

Abstract

PURPOSE:To provide the structure for improving crosstalk properties between the infrared ray detection elements arranged in a one-dimensional or two-dimensional manner in one semiconductor substrate of the title infrared ray solid-state image sensing element. CONSTITUTION:An impurity layer with high precision as a photoabsorption layer 5 absorbing the incident infrared rays 12 is provided in a semiconductor substrate 1 so that the layer 5 may absorb the infrared rays 1 coming-in from the surface of a detector and reflecting the rays 12 on the rear surface thereof.

Description

[Detailed description of the invention]

0001

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 infrared solid-state imaging device having a structure capable of improving crosstalk between infrared detecting devices arranged one-dimensionally or two-dimensionally within a single semiconductor substrate.

0002

2. Description of the Related Art FIG. 5 is a plan view schematically showing the layout of a conventional infrared solid-state imaging device using a Schottky barrier diode as an infrared detector.
FIG. 6 shows VI-VI of the infrared solid-state image sensor 5 in FIG.
FIG. 3 is a cross-sectional structural diagram of a portion corresponding to the line.

In the configuration of the conventional example shown in FIG. 5, numeral 2 is an infrared light detection section arranged in a vertical and horizontal two-dimensional array using Schottky junctions, and numeral 6 is an infrared light detecting section that transfers charges in the vertical direction. 7 is a vertical shift register using a sweep method (hereinafter referred to as CSD method); 7 is a horizontal shift register using a CCD method that transfers charges in the horizontal direction; and 8 is an output section for reading out charges to the outside.

Further, 9 is a transfer gate (hereinafter referred to as T
10 is a CSD scanner,
A gate electrode (component of the vertical shift register 6) 11 on a horizontal line is electrically connected to each of these scanners 9 and 10 via a scanning line wiring 3, and a read pulse from the TG scanner 9 and a CSD scanner are connected to each other. Transfer pulses from 10 can be applied to each.

Next, in the cross section shown in FIG. 6, 1 is a P-type silicon semiconductor substrate, and 2 is a Schottky junction photoelectric conversion layer formed by a metal electrode and the substrate 1. This photoelectric conversion layer is made of a metal such as platinum palladium or iridium, or a metal silicide such as platinum silicide, palladium Δ silicide, or iridium silicide. Further, numeral 3 is a scanning line wiring made of aluminum wiring, and numeral 4 is a field insulating film made of a silicon oxide film for isolation and insulation between elements. Reference numeral 12 indicates incident infrared rays, which are incident from the surface side of the detector, and whose path is bent by an imaging lens provided in front of the surface of the detector. 12a is reflected light from the back surface of the substrate. 13 is also incident infrared rays. 13a is the scattered light scattered by the scanning line wiring 3, field insulating film 4, etc., and 13b is the scattered light 13a reflected by the back surface of the substrate.

Next, the operation of this Schottky type infrared detection element will be explained. The Schottky junction between the platinum silicide electrode 2 and the P-type silicon substrate 1 has a barrier height of about 0.22 eV, but when infrared rays are incident on this Schottky junction, electron-hole pairs are generated, and energy exceeding the barrier is generated. The holes held therein are injected into the P-type silicon substrate 1 over the barrier. As a result, electrons are accumulated in the platinum silicide electrode 2 of the Schottky junction. This optical signal charge is accumulated in the Schottky junction. The accumulated signal charge is vertical C
It is read out to SD6 and then transferred in the vertical direction. Next, this optical signal charge is transferred in the horizontal direction by the horizontal CCD 7 and read out from the output section 8 as a video signal.

[0007]

By the way, the thinner the platinum silicide electrode 2 is, the higher the detection sensitivity is, and it is usually formed of a thin film of 100 angstroms or less. Furthermore, the silicon of the substrate 1 has a band gap of 1.1 eV,
It is transparent to infrared rays longer than 1.2 μm. Therefore, a portion of the infrared rays 12 incident from the front surface of the detector is transmitted obliquely through the thin platinum silicide electrode 2 and reflected by the back surface of the silicon substrate 1. Here, a lens attached to the front of the detector to focus an image on the infrared detection element
When using optical system 1, the maximum angle of incidence is approximately 26.6°
become. Considering that the pitch between the detection elements is several tens of μm and the silicon substrate is 400 to 500 μm thick, the incident light is reflected on the back surface of the substrate, and the reflected light 12a enters the adjacent detection element and causes crosstalk. will occur. To avoid this, the spacing between the detection elements should be set at 400 to 50
It must be 0 μm, and if this is done, it cannot be used as an image sensor. It is also possible to make the silicon substrate thinner, but the mechanical strength of the substrate will be reduced, so even if this method is used, it cannot be used as an image sensor.

Furthermore, as shown in FIG. 6, the incident infrared rays 13 are scattered by the scanning line wiring 3, the field insulating film 4, etc., producing scattered light 13a, and the light that exceeds the total reflection condition for the back surface becomes reflected light. Crosstalk occurs as in the conventional example. When such crosstalk exists, there is a problem that a clear imaging signal cannot be obtained.

The present invention was made to solve the above-mentioned problems, and aims to provide an infrared solid-state imaging device that can eliminate crosstalk between adjacent detection elements and provide clear image signals. The purpose is

0010

[Means for Solving the Problems] An infrared solid-state imaging device according to the present invention has photodetectors arranged one-dimensionally or two-dimensionally on the surface of a semiconductor substrate, and in which a highly concentrated impurity layer is formed on the back surface of the semiconductor substrate. A highly concentrated impurity layer is provided in the semiconductor substrate, such as by adding a layer of impurity or forming an impurity layer inside the semiconductor substrate, and it becomes a light absorption layer that absorbs infrared rays. It is designed to absorb.

[0011]

[Operation] The infrared solid-state imaging device of the present invention can absorb infrared rays incident from the front surface and reaching the back surface of the semiconductor substrate by the light absorption layer formed by the highly concentrated impurity layer provided on the semiconductor substrate. Reflected light on the back surface can be eliminated, and crosstalk with adjacent elements can be eliminated.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view schematically showing the structure of an infrared solid-state imaging device according to a first embodiment of the present invention. In the figure, 1
4 and 12 are the same as the conventional ones, and 5 is a light absorption layer formed on the back surface of the semiconductor substrate 1. This light absorption layer is formed by low energy ion implantation from the back side. It can also be formed by covering the surface with an oxide film and diffusing it.

FIG. 2 is a sectional view schematically showing the structure of an infrared solid-state imaging device according to a second embodiment of the present invention. 5a is a light absorption layer, which is formed by implanting high energy ions from the surface.

FIG. 3 is a sectional view schematically showing the structure of a third embodiment of the present invention. In this method, a silicon epitaxial layer 15 is formed on an impurity semiconductor substrate 14, and elements 2 and 3 similar to those in the above two embodiments are formed on the epitaxial layer 15.
, 4, etc.

FIG. 4 is a sectional view schematically showing the structure of a fourth embodiment of the present invention. In the figure, 1 to 4 and 7 are the same as the conventional one, and 5b is a light absorption layer selectively formed on the back surface of the portion of the semiconductor substrate 1 where the detector is formed.

Although the above-mentioned embodiments can be considered as a method for forming the light absorption layer, the same impurity layer can be obtained by using any method for forming an impurity layer on a semiconductor substrate.

The impurities can be n-type P, As, Sb or P-type B, Al, Ga, but similar effects can be obtained by using other impurities. The concentration is 1×10
It is 18 pieces/cm3 or more.

The operating principle of this embodiment device is the same as that of the conventional device, but infrared rays transmitted through the platinum silicide electrode and the silicon substrate are absorbed by the light absorption layer provided on the back surface or inside the silicon substrate. Reflected infrared radiation is eliminated and crosstalk between adjacent elements is prevented.

In the above embodiment, platinum silicide (PtSi) was used as the platinum silicide electrode, but palladium silicide (PdSi), iridium silicide (
IrSi) may also be used, and metals such as gold (Au) may also be used. Further, the substrate is not limited to the P type, and may be of the N type.

Further, in the above embodiment, the CSD method is used in the vertical direction and the CCD method is used in the horizontal direction as the signal charge readout method, but any other readout method may be used, and the same method as in the above embodiment may be used. The effect of this can be obtained.

[0021]

As described above, according to the infrared solid-state image sensor of the present invention, a light absorption layer for absorbing infrared rays is provided on the back surface or inside of the silicon substrate, so that the infrared rays on the back surface of the silicon substrate can be absorbed. Reflection can be prevented and crosstalk with adjacent detection elements can be eliminated. Therefore, there is an effect that a clear image can be obtained without image blurring.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an infrared solid-state imaging device according to a first embodiment of the present invention.

FIG. 2 is a sectional view of an infrared solid-state imaging device according to a second embodiment of the invention.

FIG. 3 is a sectional view of an infrared solid-state imaging device according to a third embodiment of the invention.

FIG. 4 is a sectional view of an infrared solid-state imaging device according to a fourth embodiment of the invention.

FIG. 5 is an arrangement diagram of a conventional infrared solid-state imaging device.

6 is a sectional view taken along the line VI-VI in FIG. 5. FIG.

[Explanation of symbols]

1 P-type silicon substrate 2 Platinum silicide electrode 3 Scanning line wiring 4 Interelement isolation 5, 5a, 5b Light absorption layer 6 Vertical shift register 7 Horizontal shift register 8 Output section 9 Transfer gate scanner 10 CSD
Scanner 11 Gate electrode 12 Incident infrared rays (oblique direction) 13 Incident infrared rays (vertical direction) 14 Impurity semiconductor substrate

Claims (1)

[Claims] [Claim 1] A front-illuminated infrared solid-state imaging device in which photodetectors are arranged one-dimensionally or two-dimensionally on the surface of a semiconductor substrate, excluding the detector, signal readout mechanism, etc. formed on the surface of the semiconductor substrate. An infrared solid-state imaging device characterized by having a high-precision impurity layer provided within a semiconductor substrate.