JP2596190B2 - Schottky barrier type infrared image sensor and method of manufacturing the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Schottky barrier-type infrared image sensor that converts information of an infrared image into a time-series electric signal and a method of manufacturing the same.

[Conventional technology]

FIG. 3 shows a conventional Schottky barrier type infrared image sensor unit pixel vertical sectional structure. This is an interline transfer CCD type Schottky barrier type infrared image sensor. Further, it is of a backside illumination type in which infrared rays 15 are incident from the backside of a semiconductor substrate constituting the infrared image sensor.

The unit pixel includes a Schottky barrier infrared sensor, a transfer gate 2, and a vertical CCD3. The Schottky barrier type infrared sensor 1 is made of a metal such as PdSi, PiSi,
Schottky electrode 4 composed of a thin film of IrSi or the like and p-type single crystal
A potential barrier is formed by contact with the Si substrate 5, and around the Schottky electrode 4 n
A mold guard ring 6 is provided. On the transfer gate 2 side of the Schottky electrode 4, an n ⁺ -type region 7 which is in ohmic contact with a part of the Schottky electrode 4 and serves as a source region when reading an optical signal charge is formed. The structure of the vertical CCD 3 is a buried channel type. A polycrystalline Si electrode 8 serving as a transfer electrode is provided from above the Si substrate of the transfer gate 2 to above the n-type channel region 9 via a thermal oxide film 10. The channel width in the horizontal direction with respect to the charge transfer direction is limited, and p ⁺ -type separation regions 11 for separating each unit pixel are formed on both sides of the vertical CCD 3 and around the guard ring 6 of the Schottky barrier type infrared sensor 1. Is provided. FIG. 3 shows the transfer gate 2
Is shown, so that the p ⁺ isolation region is not drawn at the end of the vertical CCD channel on the Schottky barrier type infrared sensor 1 side, but the p ⁺
There is an isolation region.

The entire surface of the infrared image sensor is covered with an insulating film 32 made of silicon oxide (SiO, SiO ₂ ) or silicon nitride (SiN, Si ₃ N ₄ ) formed by a CVD method or the like. A metal reflection film 13 made of aluminum or the like is provided on a portion facing the Schottky electrode 4 with the insulating film 12 interposed therebetween. This is for reusing the infrared light coming from the back surface of the single-crystal Si substrate 5 and passing through the Schottky electrode 4, and the single-crystal Si substrate 5 / Schottky electrode 4 / insulating film 12 / metal reflective film 13 Produces an optical resonance state with a multilayer structure.

In addition, their entire surface is again an insulating film as a protective film.
An anti-reflection film 14 is provided on the entire back surface of the substrate.

The Schottky barrier type infrared image sensor has
There is also a MOS type scanning circuit type.

[Problems to be solved by the invention]

The following phenomenon occurs in the above-described conventional Schottky barrier type infrared image sensor. The incident infrared ray 15 is partially absorbed by the Schottky electrode, but the infrared light that has not been completely absorbed is returned to the back surface of the substrate. There is an anti-reflection film on the back surface of the substrate, which has good transparency but not 100% transmission, and is partially reflected and goes to the pixels again. The reflection of infrared light between the front and rear surfaces of the substrate does not affect the imaging state when the intensity of infrared light is weak, but when the intensity is strong, it becomes multiple reflection, and it is not reflected on pixels formed by the optical system. This also causes a phenomenon that infrared light enters. That is, the conventional Schottky barrier-type infrared image sensor has a disadvantage that flare occurs when a high-temperature object is imaged, and the image expands.

[Means for solving the problem]

In order to solve the above-described problem, the Schottky barrier type infrared image sensor of the present invention is configured such that an isolation region containing a high concentration of impurities for electrically separating each unit pixel is formed from a front surface to a back surface of a semiconductor substrate constituting the infrared image sensor. It has a structure that penetrates up to.

Further, in order to realize the above-described structure, the method of manufacturing the Schottky barrier type infrared image sensor of the present invention is the method of manufacturing the Schottky barrier type infrared image sensor, wherein the unit pixel is deepest from the surface of the semiconductor substrate in the impurity-added region in the image region where one-dimensional or two-dimensional arrangement is provided. An impurity is added to the isolation region, and the image region portion of the semiconductor substrate is etched from the back surface to reduce the thickness of the image region portion of the semiconductor substrate until the isolation region appears on the back surface.

[Action]

In the Schottky barrier type infrared image sensor of the present invention, since the separation region containing impurities at a high concentration electrically separating each unit pixel penetrates from the front surface to the back surface of the semiconductor substrate constituting the infrared image sensor, When infrared light enters a pixel other than a pixel which is imaged by the optical system due to multiple reflection of infrared light between the front and back surfaces of the substrate, the infrared light always passes through the separation region. A region containing a high concentration of impurities has abundant free carriers, and therefore has infrared absorption due to free carrier absorption. Accordingly, since the infrared rays are attenuated when passing through the separation region, the above-mentioned disadvantages are reduced in the Schottky barrier type infrared image sensor of the present invention.

〔Example〕

FIG. 1 shows an embodiment of a Schottky barrier type infrared image sensor according to the present invention, and is a longitudinal sectional view of a unit pixel. This is an interline transfer CCD type Schottky barrier type infrared image sensor similar to the conventional example. The vertical cross-sectional structure is almost the same as that of FIG. 3 except that the p ⁺ -type isolation region 11 extends from under the thermal oxide film 10 on the surface of the p-type single-crystal Si substrate 5 to under the antireflection film 14 on the back surface of the substrate 5. The place where you go is different. Therefore, each pixel is partitioned by the wall of the separation region 11.

As an example, the impurity concentration (carrier concentration) is ~ 10 ¹⁹ cm ^-3
The attenuation that occurs when infrared light having a wavelength of 4 μm passes through the p ⁺ -type separation region having a width of 5 μm is shown below.

The intensity I of the electromagnetic wave at the point x when the electromagnetic wave of the intensity I ₀ propagates the distance x is represented by the following expression: I = I ₀ exp (−αx) (1) Here, α is an absorption coefficient, and the free carrier absorption (hole) has the relationship of the following equation (2).

Where e: elementary charge λ: wavelength of electromagnetic wave p: hole concentration
c: Speed of light n: Refractive index ε ₀ : Vacuum permittivity m _h ^* : Effective mass of hole μ _h : Hole mobility As a typical value, n = 3.4, m _h ^* = (9.1 × 10 ⁻³¹⁾ )
× 0.37 kg, μ _h = 80 cm ² / Vsec, and the p ⁺ type separation region (p = 10 ¹⁹ c
When the free carrier absorption coefficient of m ⁻³ ) is calculated, approximately α = 2
26 cm ^-1 . If the infrared ray is incident on the p ⁺ -type separation region at 45 degrees, the above α and x = 5 / sin45 ゜ = 7.1 μm are substituted into the equation (1), and (I / I ₀ ) becomes about 85%. , For a shallower angle of incidence, eg 10 degrees, x = 5 / sin10 ゜ = 28.8μ
Substituting m into equation (1) gives (I / I ₀ ) about 52%.

FIG. 2 shows an embodiment of a method for manufacturing a Schottky barrier type infrared image sensor according to the present invention. FIG.
(C) shows a method for forming the p ⁺ -type isolation region. First, the oxide film 17 formed on the p-type single-crystal Si substrate 5 is cut in a pattern of an isolation region, and the p-type single-crystal
A groove 18 is formed in the Si substrate 5. The dimensions of the groove 18 are, for example, 3 μm in width and 30 μm in depth. Next, boron is added into the groove 18 by a diffusion method or the like. Thereafter, polycrystalline Si20 containing boron in a high concentration is grown and filled in the trench 18. This forms ap ⁺ -type isolation region. As shown in FIG. 2 (d), after all the components necessary for the Schottky barrier type infrared image sensor on the substrate front side are completed, the surface is protected, and then the potassium hydroxide solution is applied from the rear surface of the substrate. The thickness of the image region from the back surface of the substrate is reduced by anisotropic etching using the method described above, and the thickness of the substrate at that portion is reduced to about 30 μm in accordance with the depth of the groove 18 or the depth of the boron-added region 19. Thus, a structure in which the p ⁺ -type isolation region penetrates from the front surface to the back surface of the substrate can be realized.

The present invention can be realized even when the above-mentioned pn is exchanged, and can be applied to a MOS scanning circuit type.

〔The invention's effect〕

As described above, the Schottky barrier type infrared image sensor of the present invention has the effects of suppressing the occurrence of flare when capturing an image of a high-temperature object and reducing the phenomenon of image swelling.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a unit image of one embodiment of a Schottky barrier type infrared image sensor according to the present invention. FIG. 2 is an explanatory view of one embodiment of a method for manufacturing a Schottky barrier type infrared image sensor according to the present invention. FIG. 3 is a longitudinal sectional view of a unit pixel of a conventional Schottky barrier type infrared image sensor. 1. Schottky barrier infrared sensor 2. Transfer gate 3. Vertical CCD 4. Schottky electrode
5 ...... p-type single crystal silicon substrate, 6 ...... n-type guard ring, 7 ...... n ⁺ -type region, 8 ...... polycrystalline silicon electrode, 9 ...
... n-type channel region, 10 ... thermal oxide film, 11 ... p ⁺ type isolation region, 12 ... insulating film, 13 ... metal reflective film, 14 ... anti-reflective film, 15 ... infrared, 17 ... Oxide film, 18 …… groove, 19 ……
Boron-doped region, 20: Boron-containing polycrystalline silicon.

Claims (2)

(57) [Claims] A Schottky barrier type infrared sensor array arranged one-dimensionally or two-dimensionally, and an electronic scanning circuit for reading out a signal charge generated by photoelectric conversion in the Schottky barrier type infrared sensor array as a time-series signal to the outside. In the Schottky barrier type infrared image sensor provided, a separation region containing a high concentration of impurities for electrically separating each unit pixel penetrates from a front surface to a back surface of a semiconductor substrate constituting the infrared image sensor. Schottky barrier type infrared image sensor. 2. A step of adding an impurity to an isolation region deepest from a surface side of a semiconductor substrate in an impurity added region in an image region in which unit pixels are arranged one-dimensionally or two-dimensionally. Forming an electronic scanning circuit for reading out the sensor array and signal charges to the outside; and etching the semiconductor substrate from the back surface to reduce the thickness of the semiconductor substrate until the isolation region appears on the back surface. Of manufacturing a Schottky barrier type infrared image sensor.