JPH08316446A - Infrared solid-state image sensing element - Google Patents

Abstract

PURPOSE: To provide an infrared image sensing element of a rear irradiation type which is cooled and driven, wherein characteristic variation due to swirl caused by the pulling-up of silicon ingot is reduced, and it is prevented that the lower layer of a function element group constituting an infrared image sensing element turns to high resistance and has a potential distribution and therefore the performance commensurate with a driving signal is not obtained. CONSTITUTION: On a P-type silicon substrate 1 as a first conductivity type bulk silicon substrate, an epitaxial growth silicon layer of two-layered structure composed of a same conductivity P<+> type high concentration epitaxial growth silicon layer 2 and a P-type low concentration epitaxial growth silicon layer 3 is formed. A function element group 4 constituting an infrared solid-state image sensing element is formed on the epitaxial growth silicon layer of the two-layered structure.

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 image sensor driven by being cooled by cooling means, and more particularly to a backside illuminated infrared solid-state image sensor.

[0002]

2. Description of the Related Art Conventionally, in a backside illumination type infrared solid-state image pickup device which is driven by being cooled by a cooling means, a functional element group such as a light-receiving part and an electronic scanning part forming the infrared solid-state image pickup device is formed on a bulk silicon substrate. The configuration is known.

[0003]

In the infrared solid-state image pickup device having such a structure, the swirl caused by the unevenness of impurities during the pulling up of the silicon ingot causes characteristic variations among the pixels, resulting in a large amount of noise. There is.

Generally, in order to reduce the characteristic variation due to the swirl, a device is formed on an epitaxially grown silicon layer formed on a first conductivity type bulk silicon substrate, which is a method used in other semiconductor devices. It is known how to do it. An example in which this method is applied to an infrared solid-state image sensor is shown in FIG. That is, a light receiving portion or an electron constituting an infrared solid-state imaging device is formed on an epitaxially grown silicon layer of the same conductivity type (P type low concentration epitaxially grown silicon layer 3) formed on a first conductivity type bulk silicon substrate (P type silicon substrate 1). This is an infrared solid-state image sensor in which a functional element group 4 such as a scanning unit is formed.

However, in the structure shown in FIG. 2, after the semiconductor manufacturing process, a difference in oxygen content (a bulk silicon substrate usually contains oxygen near the solid solubility limit) near the interface between the bulk silicon substrate and the epitaxially grown silicon layer. However, the epitaxially grown silicon layer contains almost no oxygen) and a residual stress due to the residual stress and a defect layer accompanying it are introduced, and a potential barrier of about 0.1 to 0.2 eV is formed. At room temperature, this potential barrier is not a problem because it is a level at which electrons and holes can easily jump by obtaining thermal energy, but at a cooling temperature at which the back-illuminated infrared solid-state imaging device operates, for example, near liquid nitrogen temperature. However, since the thermal energy is small and electrons and holes cannot easily cross the potential barrier, there is a problem that the epitaxially grown silicon layer is electrically insulated from the bulk silicon substrate. In this state, since the lower layer of the functional element group such as the light receiving section and the electronic scanning section that configures the infrared solid-state image sensor, which should maintain the reference potential, has a high resistance, the lower layer of the functional element group is affected by various drive signals. A potential distribution is generated, and the performance commensurate with the applied drive signal cannot be obtained.

An object of the present invention is to reduce variations in characteristics between pixels due to swirl caused by pulling up of a silicon ingot, and to provide a lower resistance layer of a functional element group forming an infrared solid-state image pickup element with a high potential distribution. By
It is an object of the present invention to provide a backside illumination type infrared imaging device which is driven by being cooled by a cooling means, which prevents a phenomenon in which performance commensurate with an applied drive signal cannot be obtained.

[0007]

In order to solve the above-mentioned problems, an infrared solid-state imaging device according to the present invention comprises a high-concentration epitaxially grown silicon layer of the same conductivity type and a high-concentration epitaxially grown silicon layer of the same conductivity type on a first conductivity type bulk silicon substrate. It has an epitaxially grown silicon layer having a two-layer structure composed of a conductive type low concentration epitaxially grown silicon layer, and a functional element group is formed thereon.

[0008]

When a high-concentration epitaxially grown silicon layer of the same conductivity type is formed on a bulk silicon substrate of the first conductivity type, and a low-concentration epitaxial growth silicon layer of the same conductivity type is subsequently formed thereon, the first layer of Since there is no oxygen content difference between the high-concentration epitaxially grown silicon layer and the second low-concentration epitaxially grown silicon layer, which causes a stress difference during the heat treatment, even if a defect occurs at the interface even after the semiconductor manufacturing process. No layers or potential barriers are introduced.

On the other hand, since there is a large difference in oxygen content between the first conductivity type bulk silicon substrate and the first high-concentration epitaxially grown silicon layer, a potential barrier is formed in the vicinity of the interface as in the conventional case. However, when the first and second epitaxial growth silicon layers are formed on the first conductivity type bulk silicon substrate, or by heat treatment during the semiconductor manufacturing process, the first high concentration epitaxial growth silicon layer is removed. Impurities are diffused into the first conductivity type bulk silicon substrate, and a high-concentration impurity layer is formed near the interface of the first conductivity type bulk silicon substrate side. Therefore, the potential barrier near the interface is in the silicon containing high concentration of impurities. It will be buried. In such a situation, the region where the potential barrier is formed becomes extremely thin, and the tunneling probability that electrons and holes penetrate through the potential barrier becomes very large. Therefore, even if the region is cooled near the liquid nitrogen temperature. , The potential barrier does not obstruct the movement of electrons and holes. Therefore, the above problem is solved.

When the bulk silicon substrate as a whole contains impurities at a high concentration, infrared absorption due to majority carriers becomes non-negligible. However, in the present invention, the high concentration epitaxially grown silicon layer has a thickness of about a few tens of μm. Even if the layer and the low-concentration epitaxially grown silicon layer are combined, it is an ultrathin epitaxially grown silicon layer with a thickness of about several tens of μm, so sensitivity deterioration due to infrared absorption does not occur.

[0011]

Next, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a structural schematic view of an embodiment of an infrared solid-state image pickup device of the present invention. P ⁺ -type high-concentration epitaxial growth silicon layer 2 formed on P-type silicon substrate 1
A functional element group 4 such as a light receiving portion and an electronic scanning portion forming an infrared solid-state image pickup device is provided on the epitaxially grown silicon layer having a two-layer structure composed of the P-type low concentration epitaxially grown silicon layer 3.

The P ⁺ type high-concentration epitaxially grown silicon layer 2 of the first layer and the P-type low-concentration epitaxially grown silicon layer 3 of the second layer are continuously formed without being taken out into the air from the epitaxial growth apparatus between them. Then do it. The impurities to be added are, for example, P of the first layer.
^{The +} type high concentration epitaxially grown silicon layer 2 has 10 ¹⁶
Boron of about 10 ¹⁹ cm ^-3 was added to make the film thickness 5 μm. Further, boron of about 10 ¹⁴ to 10 ¹⁵ cm ⁻³ was added to the P-type low-concentration epitaxially grown silicon layer 3 of the second layer to have a film thickness of 25 μm. There is no difference in oxygen content between the P ⁺ -type high-concentration epitaxially grown silicon layer 2 of the first layer and the P-type low-concentration epitaxially-grown silicon layer 3 of the second layer thus formed, and there is no contaminant on the interface. Since there is no risk of contamination by the impurities, high crystallinity is maintained and no defect layer or potential barrier is introduced at the interface even after the semiconductor manufacturing process.

On the other hand, the P-type silicon substrate 1 and the first
As described above, there is a large difference in oxygen content between the P ⁺ -type high-concentration epitaxially grown silicon layer 2 of the layer,
There is a difference in coefficient of thermal expansion. Therefore, there is a residual stress after the epitaxial growth, and like the conventional case, a defect due to the stress due to the difference between expansion and contraction is introduced in the vicinity of the interface between the two, every time the heat treatment is performed during the semiconductor manufacturing process. As a result, a potential barrier is formed at the interface, but in the structure of the present invention, the P ⁺ -type high-concentration epitaxially grown silicon layer 2 of the first layer is formed.
In forming the Pd or by heat treatment during the semiconductor manufacturing process, boron as an impurity diffuses from the P ⁺ type high concentration epitaxial growth silicon layer 2 of the first layer to the P type silicon substrate 1, state since the vicinity of the interface to the P ⁺ -type high concentration impurity layer of the P ⁺ -type highly-doped epitaxial silicon layer 2 of is formed, a potential barrier near the interface which is buried in the P ⁺ -type silicon containing boron at a high concentration become.

FIG. 3 (a) is an energy band diagram of the structure of the P type low concentration epitaxial growth silicon layer / P ⁺ type high concentration epitaxial growth silicon layer / P type silicon substrate of the present invention, and FIG. 3 (b) is shown in FIG. Energy band diagrams in the structure of the P-type low-concentration epitaxially grown silicon layer / P-type silicon substrate shown in FIG. In the structure of FIG. 2, since the region in which the potential barrier is formed is thick, as shown in (b), the holes 6 are generated in the P-type low-concentration epitaxial growth silicon layer 3 and the P-type silicon substrate 1 at low temperature.
It cannot be easily passed through the interface with and, but (a)
In the above structure, the potential barrier is sandwiched between the P ⁺ -type high-concentration epitaxially grown silicon layer 2 and the P ⁺ -type high-concentration impurity layer 5 formed in the P-type silicon substrate 1, and as a result, the region where the potential barrier is formed is extremely large. The holes 6 become thin and can freely move back and forth between the P ⁺ -type high-concentration epitaxially grown silicon layer 2 and the P-type silicon substrate 1 by tunneling.

As described above, in the structure of the infrared solid-state image pickup device of the present invention, the lower layer of the functional element group such as the light receiving part and the electronic scanning part forming the infrared solid-state image pickup device does not have a high resistance and is suitable for the applied drive signal. High performance can be obtained.

Although the first conductivity type is the P type in the present embodiment, the present invention is also effective if the first conductivity type is the N type.

[0018]

As described above, according to the infrared solid-state image pickup device of the present invention, there is a functional element group such as a light receiving portion and an electronic scanning portion on the epitaxially grown silicon layer in which the characteristic variation between pixels can be suppressed. Moreover, since the lower layer of the functional element group does not have high resistance, there is an effect that a high-performance infrared solid-state imaging element can be obtained.

[Brief description of drawings]

FIG. 1 is a structural schematic view of an embodiment of an infrared solid-state image pickup device of the present invention.

FIG. 2 is a structural schematic diagram of an example of an infrared solid-state image sensor to which a general method of reducing characteristic variation due to swirl is applied.

FIG. 3 is a diagram showing a structure of an embodiment of the present invention and an energy band diagram in the structure shown in FIG.

[Explanation of symbols]

1 P-type silicon substrate 2 P ⁺ type high-concentration epitaxial growth silicon layer 3 P-type low-concentration epitaxial growth silicon layer 4 Functional element group that constitutes an infrared solid-state imaging device 5 P ⁺ type high-concentration impurity layer 6 hole 7 valence in silicon substrate Electronic band 8 Forbidden band 9 Conduction band 10 Fermi level

Claims (1)

[Claims] 1. A back-illuminated infrared solid-state imaging device, which is driven by being cooled by a cooling means and is incident from the back surface opposite to the surface on which the functional element group is formed, on a first conductivity type bulk silicon substrate. , Having a two-layer structure epitaxial growth silicon layer composed of a high-concentration epitaxial growth silicon layer of the same conductivity type and a low-concentration epitaxial growth silicon layer of the same conductivity type on which a functional element group is formed. Characteristic infrared solid-state image sensor.