JP2798006B2 - Infrared solid-state imaging device and manufacturing method thereof - Google Patents

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 driven by cooling by cooling means, and more particularly to a back-illuminated infrared solid-state imaging device.

[0002]

2. Description of the Related Art Conventionally, in a back-illuminated infrared solid-state imaging device driven by being cooled by a cooling means, a functional element group such as a light receiving portion and an electronic scanning portion constituting the infrared solid-state imaging device is formed on a bulk silicon substrate. A known configuration is known.

[0003]

The infrared solid-state image pickup device having such a structure has a problem that characteristics are varied among pixels due to swirl due to impurity unevenness when pulling up a silicon ingot, and noise is increased. There is.

In general, in order to reduce the variation in characteristics due to swirl, a method used in other semiconductor devices is to form an element on an epitaxially grown silicon layer formed on a first conductivity type bulk silicon substrate. There are known ways to do this. FIG. 2 shows an example in which this method is applied to an infrared solid-state imaging device. That is, a light-receiving portion and an electron constituting an infrared solid-state imaging device are formed on an epitaxially grown silicon layer (P-type low-concentration epitaxially grown silicon layer 3) of the same conductivity type formed on a first-conductivity-type bulk silicon substrate (P-type silicon substrate 1). This is an infrared solid-state imaging device on which a functional element group 4 such as a scanning unit is formed.

However, in the structure shown in FIG. 2, after a semiconductor manufacturing process, a difference in oxygen content (the 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, a residual stress based on the epitaxially grown silicon layer containing almost no oxygen and a defect layer accompanying the residual stress are introduced, and a potential barrier of about 0.1 to 0.2 eV is formed. At room temperature, this potential barrier is at a level at which electrons and holes can easily jump over by obtaining thermal energy, but this is not a problem.However, at a cooling temperature at which the back-illuminated infrared solid-state imaging device operates, for example, near the temperature of liquid nitrogen, 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 constituting the infrared solid-state imaging element to maintain the reference potential has high resistance, the lower layer of the functional element group is affected by various drive signals. A potential distribution occurs, and the performance corresponding to the applied drive signal cannot be obtained.

SUMMARY OF THE INVENTION It is an object of the present invention to reduce variation in characteristics between pixels due to swirl caused by pulling up a silicon ingot, and to have a potential distribution due to a high resistance in a lower layer of a functional element group constituting an infrared solid-state imaging device. By
It is an object of the present invention to provide a back-illuminated infrared imaging device driven by cooling by cooling means, which prevents a phenomenon in which performance corresponding to 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 on a bulk silicon substrate of a first conductivity type. 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 subsequently a low-concentration epitaxially grown silicon layer of the same conductivity type is formed thereon, the high-concentration silicon layer of the first conductivity type is formed. Since there is no difference in oxygen content 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, defects are present 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 near 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 first conductivity type bulk silicon substrate side interface. Therefore, the potential barrier near the interface is formed in the silicon containing the impurity at a high concentration. It is buried. Under such circumstances, the thickness of the region where the potential barrier is formed becomes extremely thin, and the probability of tunneling of electrons and holes passing through the potential barrier becomes extremely large. In addition, the potential barrier does not hinder the flow of electrons and holes. Therefore, the above-mentioned problem is solved.

If the bulk silicon substrate contains a high concentration of impurities, the absorption of infrared rays by majority carriers is not negligible. However, in the present invention, the high-concentration epitaxially grown silicon layer is at most about 10 μm thick, Even if the layer and the low-concentration epitaxially grown silicon layer are combined, it is an extremely thin epitaxially grown silicon layer of about several tens of μm, so that the sensitivity does not decrease due to infrared absorption.

[0011]

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

FIG. 1 is a schematic structural view of an embodiment of an infrared solid-state image sensor according to the present invention. P ⁺ type high concentration epitaxially grown silicon layer 2 formed on P type silicon substrate 1
A functional element group 4 such as a light receiving unit and an electronic scanning unit that constitutes an infrared solid-state imaging device is provided on an epitaxially grown silicon layer having a two-layer structure including a P-type low-concentration epitaxially grown silicon layer 3.

The formation of the first P ⁺ -type high-concentration epitaxially grown silicon layer 2 and the second P-type low-concentration epitaxially grown silicon layer 3 is carried out continuously without taking out the air from the inside of the epitaxial growth apparatus. And do it. As an impurity to be added, for example, P
10 ^{16 for the +} type high concentration epitaxial growth silicon layer 2
Boron of about 10 ¹⁹ cm ^-3 was added to make the film thickness 5 μm. Further, about 10 ¹⁴ to 10 ¹⁵ cm ⁻³ of boron was added to the second P-type low-concentration epitaxially grown silicon layer 3 to have a thickness of 25 μm. There is no difference in oxygen content between the first P ⁺ -type high-concentration epitaxially grown silicon layer 2 and the second P-type low-concentration epitaxially grown silicon layer 3. Since there is no danger of contamination, 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 layer and the P ⁺ -type high-concentration epitaxially grown silicon layer 2.
There is a difference in thermal expansion coefficient. For this reason, there is a residual stress after the epitaxial growth, and as in the conventional case, every time heat treatment is performed during the semiconductor manufacturing process, a defect caused by the stress due to the difference in expansion and contraction is introduced near the interface between the two. As a result, a potential barrier is formed at the interface. In the structure of the present invention, the first P ⁺ -type high-concentration epitaxially grown silicon layer 2 is formed.
Is formed, or by heat treatment during the semiconductor manufacturing process, boron as an impurity diffuses from the first P ⁺ -type high-concentration epitaxially grown silicon layer 2 into the P-type silicon substrate 1, and 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. 3A shows an energy band diagram in the structure of the P-type low-concentration epitaxially grown silicon layer / P ⁺ -type high-concentration epitaxially grown silicon layer / P-type silicon substrate of the present invention, and FIG. 2 shows energy band diagrams in the structure of the P-type low-concentration epitaxial growth silicon layer / P-type silicon substrate shown in FIG. In the structure of FIG. 2, as shown in FIG. 2B, since the region where the potential barrier is formed is thick, the holes 6 are formed at low temperature by the P-type low-concentration epitaxial growth silicon layer 3 and the P-type silicon substrate 1.
(A) cannot easily pass through the interface with
In the structure (1), 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, so that the region where the potential barrier is formed is extremely large. The holes 6 become thin, and the holes 6 can freely move 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 imaging device of the present invention, the lower layer of the functional element group such as the light receiving section and the electronic scanning section constituting the infrared solid-state imaging element does not have a high resistance and corresponds to the applied drive signal. High performance can be obtained.

In the present embodiment, the first conductivity type is a P-type, but the present invention is also effective when the first conductivity type is an N-type.

[0018]

As described above, according to the infrared solid-state imaging device of the present invention, a functional device group such as a light receiving portion and an electronic scanning portion is provided on an epitaxially grown silicon layer capable of suppressing variation in characteristics between pixels. In addition, 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 the drawings]

FIG. 1 is a schematic structural diagram of an embodiment of an infrared solid-state imaging device according to the present invention.

FIG. 2 is a schematic structural diagram of an example of an infrared solid-state imaging device to which a general method of reducing variation in characteristics due to swirl is applied.

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. 2;

[Explanation of symbols]

REFERENCE SIGNS LIST 1 P-type silicon substrate 2 P ⁺ -type high-concentration epitaxially grown silicon layer 3 P-type low-concentration epitaxially grown silicon layer 4 Functional element group constituting infrared solid-state imaging device 5 P ⁺ -type high-concentration impurity layer in silicon substrate 6 Hole 7 valence Electronic band 8 Forbidden band 9 Conduction band 10 Fermi level

Claims (5)

(57) [Claims] 1. A back-illuminated infrared solid-state imaging device driven by being cooled by a cooling means and receiving light from a back surface opposite to a surface on which a functional element group is formed, wherein the first conductivity type bulk silicon substrate is A two-layer epitaxially grown silicon layer composed of a high-concentration epitaxially grown silicon layer of the same conductivity type and a low-concentration epitaxially grown silicon layer of the same conductivity type thereon, on which a functional element group is formed. Characteristic infrared solid-state imaging device. 2. A cooling device driven by cooling means,
Back side where light enters from the back side opposite to the side on which the element group was formed
In the irradiation type infrared solid-state imaging device, the first conductivity type
High-concentration epitaxy of the same conductivity type on a silicon substrate
-Grown silicon layer and overlying low-concentration epitaxial film of the same conductivity type
Epitaxy of a two-layer structure consisting of an axially grown silicon layer
It has a char-grown silicon layer on which functional element groups are formed.
And a high-concentration epitaxial growth system of the same conductivity type.
Impurities from the recon layer to the first conductivity type bulk silicon substrate
The first conductivity type bulk silicon is diffused by
High-concentration impurity layer is formed near the interface on the substrate side
And the potential barrier near the interface contains a high concentration of impurities.
High-concentration epitaxy of the same conductivity type which is silicon having
In the silicon film grown in the first conductivity type and the first conductivity type bulk silicon
Buried in the high-concentration impurity layer of the substrate
An infrared solid-state imaging device, characterized in that: 3. The infrared solid-state imaging device according to claim 1, wherein the high-concentration epitaxially grown silicon layer of the same conductivity type has a thickness of 5 μm to 10s μm. 4. The same conductive type bulk silicon substrate on a first conductive type.
Formed high-concentration epitaxially grown silicon layer
Later, without removing from the epitaxial growth equipment
Continuously low-concentration epitaxially grown silicon of the same conductivity type
-Layer epitaxially grown silicon with a two-layer structure
Forming a layer and providing a functional element section thereon.
Of manufacturing an infrared solid-state imaging device. 5. A high-concentration epitaxial growth of the same conductivity type.
Long silicon layer is 10 ¹⁶ -10 ¹⁹ cm ^-3 , The same conductivity type
Of the low-concentration epitaxially grown silicon layer is 10 ¹⁴ -10
^Fifteen cm ^-3 5. The method according to claim 4, wherein boron is added.
A method for manufacturing the infrared solid-state imaging device according to the above.