JP3292583B2 - Solid-state imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device, and more particularly to an improvement in an optical resonance structure of an infrared solid-state imaging device (IRCCD).

[0002]

2. Description of the Related Art FIG.
This will be described with reference to FIG. FIG. 6 is a diagram showing a cross section of an optical resonance structure of a conventional back-illuminated infrared solid-state imaging device.

In FIG. 6, reference numeral 1 denotes a p-type silicon substrate;
Is a silicon oxide film for pixel separation. Reference numeral 3 denotes a metal such as platinum (Pt) or iridium (Ir) for forming a Schottky junction for detecting light.
For example, a p-type dopant for forming a metal thin film such as a metal compound such as platinum silicide or iridium silicide or a heterojunction is 1 × 10 ¹⁹ to 1 × 1.
It is a photodetection unit such as a silicon-germanium mixed crystal (Si ₁ -xGex) which is p-doped at a high concentration of 0 ²¹ / cm ³ . Further, reference numeral 5 denotes an interlayer film such as a silicon oxide film or a silicon nitride film for filling the interlayer, and 6 denotes an infrared ray transmitted through the light detection unit 3 again to the light detection unit 3.
9 is an infrared ray incident from the back surface of the solid-state imaging device, and 10 is a reflected light of the infrared ray 9. Note that d is the thickness of the interlayer film 5.

Next, the operation of the optical resonance structure of the above-mentioned conventional solid-state imaging device will be described.

[0005] As shown in FIG. 6, infrared rays 9 incident from the back surface of the solid-state imaging device enter the light detecting section 3 without being absorbed by the p-type silicon substrate 1. Although the photoelectric conversion is performed by the light detection unit 3, the efficiency is not 100%, so that some infrared rays 9 pass through the light detection unit 3. In order to reuse the transmitted infrared light 9, the infrared light 9 is reflected by the aluminum reflective film 6 and returned to the light detection unit 3 as reflected light 10.

Important design parameters in the above operation are the refractive index “n” and the film thickness “d” of the interlayer film 5.

The incident light 9 and the reflected light 10 form a standing wave because the traveling directions thereof are opposite to each other. However, the incident light 9 and the reflected light 10 are designed so as to form antinodes of the standing wave at the location of the photodetector 3. By selecting the parameters, the infrared light can be most efficiently photoelectrically converted. The condition is represented by the following equation 1, assuming that the wavelength of infrared light in a vacuum is “λ ₀ ”.

D = (1/4) · (λ ₀ / n) Equation 1

At present, a Schottky junction type infrared solid-state image sensor which has been put to practical use has a photosensitivity in a band of 3 to 5 μm.
Is calculated as follows.

If a silicon oxide film is used as the material of the interlayer film 5, the refractive index n is 1.46, so that if the wavelength λ ₀ of the infrared ray is 4 μm, the following is obtained.

D = (1/4) · (4 / 1.46) ≒ 0.68 μm

If a silicon nitride film is used as the material of the interlayer film 5, the refractive index n is 2.05, so that the following is obtained.

D = (１ ／) · (4 / 2.05) ≒ 0.49 μm

The interlayer film 5 having such a thickness is used in various silicon semiconductor devices and does not cause any problem.

Next, another important function of the interlayer film 5 of the above-mentioned conventional solid-state imaging device will be described with reference to FIG. FIG. 7 is a diagram illustrating the energy potential near the light detection unit 3 in the light detection operation state of the conventional solid-state imaging device.

In FIG. 7, reference numeral 1 denotes a p-type silicon substrate;
Indicates the respective energy potentials of the photodetector (metal thin film) and 5 indicates the interlayer film (silicon oxide film or silicon nitride film). Reference numeral 7 denotes holes generated by absorbing infrared rays, and 8 denotes electrons excited by absorbing infrared rays. Incidentally, E _F represents the Fermi level, E _V is the level of the upper end of the valence band, respectively.

The holes 7 generated as "vacancies" of electrons excited by absorption of infrared rays in the metal thin film 3
Has kinetic energy, so it progresses in all directions. Of these, the holes 7 that have advanced in the direction of the p-type silicon substrate 1
Is injected into the p-type silicon substrate 1 over the Schottky barrier and detected as a photocurrent.

On the other hand, the holes 7 traveling in the opposite direction to the p-type silicon substrate 1 are not originally detected as a photocurrent, but the interlayer film 5 using an insulator such as a silicon oxide film or a silicon nitride film is As shown in FIG. 7, it becomes a high potential barrier for the holes 7 and quantum mechanical reflection occurs. Therefore, the traveling direction of the holes 7 is reversed, and the holes 7 are injected into the p-type silicon substrate 1 and detected as photocurrent. That is, the light detection sensitivity is increased.

The injection process by the reflection of the holes 7 must be performed within the mean free path of the holes 7. This is because if the motion of the hole 7 exceeds the mean free path, the hole 7
This is because they experience collisions with phonons and lose kinetic energy, so that they cannot cross the Schottky barrier.

[0020]

In the conventional back-illuminated infrared solid-state imaging device as described above, when the detection wavelength is increased as shown in Equation 1, the thickness d of the interlayer film 5 increases. Therefore, various problems occur. The problem will be described below.

When the detection wavelength is in the 10 μm band, for example, when the peak of the optical resonance is set to 12 μm, according to Equation 1, when the silicon oxide film is used as the interlayer film 5, the thickness of the interlayer film 5 is about When the silicon nitride film is used, the thickness is about 1.5 μm. As described above, when the thickness d of the interlayer film 5 is large, the following problems occur.

The silicon oxide film and the silicon nitride film, which are the materials of the interlayer film used in the manufacture of a normal silicon semiconductor device, have different thermal expansion coefficients from the silicon substrate.
These interlayer films are formed at a temperature of several hundred degrees centigrade by a method such as CVD.
Done at high temperatures. Therefore, when the temperature is lowered to room temperature after the film is formed, the wafer is warped due to a difference in thermal expansion coefficient. This phenomenon becomes more significant as the thickness of the interlayer film increases. Further, the occurrence of the warpage of the wafer means that a great deal of stress is applied to each circuit element formed on the wafer, which is a very serious problem from the viewpoint of the reliability of each circuit element. The operation of the infrared detecting element is usually 80K
This effect is particularly remarkable because the operation is performed at the following extremely low temperature.

Next, since silicon oxide and silicon nitride used as the material of the interlayer film are materials that absorb infrared rays well, the absorption of infrared rays by the interlayer film increases as the film thickness increases, The intensity of the reflected light decreases, and the detection sensitivity of infrared rays decreases.

Further, there is a problem of optical signal crosstalk. The infrared light transmitted through the light detection unit 3 is reflected by the aluminum reflective film 6, but not all of the infrared light is reflected vertically. Some of the infrared light is reflected obliquely by scattering or diffraction. . The infrared rays are reflected several times in the interlayer film 5 and are incident on adjacent pixels, causing crosstalk. The crosstalk of this optical signal is
It increases as the thickness of the interlayer film increases.

As described above, when the thickness d of the interlayer film is large, there is a problem that the wafer is warped, the detection sensitivity of infrared rays is reduced, and crosstalk occurs.

The present invention has been made in order to solve the above-mentioned problems, and can reduce the thickness of an interlayer film.
An object of the present invention is to provide a solid-state imaging device having an optical resonance structure that does not reduce the collection efficiency of holes generated by infrared rays.

[0027]

[0028]

[0029]

According to a first aspect of the present invention, there is provided a solid-state image pickup device provided on a semiconductor substrate for converting incident light into light.
A photodetector for electrical conversion, provided on the photodetector;
A barrier film that reflects carriers generated by the emitted light.
An interlayer film provided on the wall film, and an interlayer film provided on the interlayer film.
A reflecting film for reflecting incident light transmitted through the light detecting section.
The barrier film is made of silicon oxide or silicon nitride, and the interlayer film is made of silicon, germanium, or a silicon-germanium mixed crystal.

According to a second aspect of the present invention, there is provided a solid-state image pickup device provided on a semiconductor substrate for photoelectrically converting incident light.
Outgoing part, generated by the incident light provided on this light detecting part
Barrier film that reflects the trapped carriers.
Interlayer film, and the photodetector provided on the interlayer film
And a reflection film for reflecting incident light transmitted through the semiconductor device, and the barrier film is made of a doped semiconductor.

According to a third aspect of the present invention, there is provided a solid-state image pickup device provided on a semiconductor substrate for photoelectrically converting incident light.
Outgoing part, generated by the incident light provided on this light detecting part
Barrier film that reflects the trapped carriers.
Interlayer film, and the photodetector provided on the interlayer film
A reflecting film that reflects incident light transmitted through the barrier film , wherein the barrier film is made of doped silicon, germanium, or silicon-germanium mixed crystal, and the interlayer film is silicon, germanium, or silicon-germanium mixed crystal. It consists of.

[0032]

In the solid-state imaging device according to the first aspect of the present invention, incident light is photoelectrically converted by a photodetector provided on a semiconductor substrate. Further, the carrier generated by the incident light is reflected by the barrier film provided on the light detecting section. Further, the film thickness is reduced by the interlayer film provided on the barrier film. Then, the incident light transmitted through the photodetector is reflected by the reflective film provided on the interlayer film.

In the solid-state imaging device according to a second aspect of the present invention, the carrier generated by the incident light is reflected by the barrier film made of an insulator.

In the solid-state imaging device according to a third aspect of the present invention, the carriers generated by the incident light are reflected by the barrier film made of silicon oxide or silicon nitride. Further, the thickness is reduced by an interlayer film formed of silicon, germanium, or a silicon-germanium mixed crystal.

In the solid-state imaging device according to a fourth aspect of the present invention, carriers generated by the incident light are reflected by the barrier film made of a doped semiconductor.

In the solid-state imaging device according to claim 5 of the present invention, doped silicon, germanium,
Alternatively, carriers generated by the incident light are reflected by a barrier film made of a silicon-germanium mixed crystal. In addition, silicon, germanium, or by an interlayer film composed of silicon-germanium mixed crystal,
The film thickness is reduced.

[0037]

【Example】

Embodiment 1 FIG. The configuration of Embodiment 1 of the present invention will be described with reference to FIG. FIG. 1 is a diagram showing a cross section of an optical resonance structure of an infrared solid-state imaging device according to Embodiment 1 of the present invention, wherein a p-type silicon substrate 1, a silicon oxide film 2, a light detection unit 3, and an aluminum reflection film 6 This is the same as that of the above-described conventional device. In the drawings, the same reference numerals indicate the same or corresponding parts.

In FIG. 1, reference numeral 4 denotes an extremely thin first insulating film of, for example, about several hundreds of degrees (0.02 to 0.06 μm), which is formed on the photodetecting section 3 by a silicon oxide film or a silicon nitride film. It is an interlayer film. 5A is formed on the first interlayer film 4 and is a material having a large refractive index and a small infrared absorption, for example, not doped with impurities, or having a low p-type or n-type dopant of 1 × 10 17 / cm 3 or less. This is a second interlayer film of silicon, germanium, or a silicon-germanium mixed crystal doped at a high concentration.
The refractive index of these materials is 1.46 for the silicon oxide film,
While the silicon nitride film is 2.05, the silicon is 3.5, the germanium is 4.1, and the silicon-germanium mixed crystal is 3.5 to 4.1. This second interlayer film 5
A is formed with a film thickness that satisfies the condition of optical resonance. The light detector according to claim 1 of the present invention corresponds to the light detector 3 In Example 1, claim of the present invention
The barrier film according to the first embodiment corresponds to the first interlayer film 4 in the first embodiment, and the interlayer film according to claim 1 of the present invention corresponds to the second interlayer film 5A in the first embodiment. Claims of the invention
The reflecting film according to No. 1 corresponds to the aluminum reflecting film 6 in the first embodiment.

Next, the operation of the optical resonance structure of the first embodiment will be described. As shown in FIG. 1, infrared light 9 incident from the back surface of the solid-state imaging device is incident on the light detection unit 3 without being substantially absorbed by the p-type silicon substrate 1. The photoelectric conversion is performed by the light detection unit 3, but the efficiency is 1
Since it is not 00%, some infrared rays pass through the light detection unit 3. In order to reuse the transmitted infrared light, the infrared light is reflected by the aluminum reflection film 6 and returned to the light detection unit 3.

Important design parameters in the above operation are the refractive index “n” and the film thickness “d” of the first interlayer film 4 and the second interlayer film 5A.

The incident light 9 and the reflected light 10 form a standing wave because the traveling directions thereof are opposite to each other. However, the incident light 9 and the reflected light 10 are designed so as to form antinodes of the standing wave at the location of the photodetector 3. By selecting the parameters, the infrared light can be most efficiently photoelectrically converted.

In the structure of the first embodiment, the first interlayer film 4 has a thickness of several hundred Å (0.02 to 0.06
μm), the contribution to the optical distance to transmitted incident infrared radiation can be neglected.
Further, since it is extremely thin, the amount of absorption can be ignored even if the material of the first interlayer film 4 has a high infrared absorptance. Further, the first interlayer film 4 and the photodetector 3
Light reflected at the boundary between the first interlayer film 4 and the second interlayer film 5
The reflected light at the boundary of A cancels out if the first interlayer film 4 is thin, since it has almost the opposite phase.

That is, if the first interlayer film 4 is extremely thin, its existence can be ignored optically. This is because, as described above, the infrared absorption is small, and the reflected light at the boundary between the first interlayer film 4 and the photodetector 3 and the reflected light at the boundary between the first interlayer film 4 and the second interlayer film 5A. This is because the influence of the interference of the reflected light is small. The optically negligible thickness is smaller than the wavelength of incident infrared rays, for example, 1000 °.
(0.1 μm) or less.

Therefore, ignoring the existence of the first interlayer film 4,
If the refractive index of the second interlayer film 5A is “n ₂ ”, its thickness is “d ₂ ”, and the wavelength of infrared light in vacuum is “λ ₀ ”,
The condition giving the highest photoelectric conversion efficiency is expressed by the following equation 2.

D ₂ = (1/4) · (λ ₀ / n ₂ ) Equation 2

For example, when the peak of the optical resonance is set to 12 μm, if silicon is used as the material of the second interlayer film 5A, the refractive index n ₂ is 3.5, so that the film thickness d ₂ is become that way. That is, d ₂ = (１ ／) · (1
2 / 3.5) ≒ 0.86 μm. Further, the use of germanium as the material of the second interlayer film 5A, the thickness thereof d ₂ the refractive index n ₂ is 4.1 as follows.
That is, d ₂ = (1/4) · (12 / 4.1) ≒ 0.7
3 μm. Furthermore, if a silicon-germanium mixed crystal is used as the material of the second interlayer film 5A, the refractive index n ₂
Its thickness d ₂ because it is from 3.5 to 4.1 takes an intermediate value of the binary. Accordingly, an optical resonance structure having a smaller interlayer thickness and a smaller infrared absorption amount in the interlayer film than the conventional structure can be obtained. Further, since a material having the same or similar thermal expansion coefficient as that of the silicon substrate is used as the material of the thick second interlayer film 5A, stress and strain are eliminated or significantly reduced.

As described above, the first interlayer film 4 of the first embodiment can be almost ignored optically because it is extremely thin, but plays an important role. Therefore, in order to explain the important function, a case where the first interlayer film 4 is not provided will be described with reference to FIG. FIG. 5 is a diagram showing the energy potential in the vicinity of the light detection unit 3 when the first interlayer film 4 is not provided. In the figure, 1 is a p-type silicon substrate, 3 is a photodetector (silicon-germanium mixed crystal), 5
A indicates the energy potential of each of the second interlayer film (silicon), 7 indicates holes generated by absorbing infrared rays, 8 indicates electrons excited by absorbing infrared rays, and E
_F represents the Fermi level, E _V is the level of the upper end of the valence band, respectively. For example, when a silicon-germanium mixed crystal is used as the light detection unit 3, the depletion layer hardly extends because the silicon-germanium mixed crystal 3 is heavily p-doped. On the other hand, the second interlayer film 5A
Since the impurity is not doped (or is doped at a low concentration), a thick depletion layer extends.
This means that the potential in the depletion layer is gently inclined. When the holes 7 generated by the incident light proceed to the second interlayer film 5A side (X), the potential barrier does not exist at the interface, so that the second layer 7A does not exist.
Into the interlayer film 5A. The holes 7 that have penetrated collide with a potential barrier formed inside the second interlayer film 5A and are reflected if there is no scattering due to collision. However, since the mean free path of the holes 7 is at most about 100 ° in silicon, the holes 7 are scattered by phonons or the like before colliding with the potential barrier and lose kinetic energy. In order to eliminate this inconvenience, a high potential barrier for the holes 7 may be provided at the interface.

An important function of the first interlayer film 4 of the first embodiment will be described with reference to FIG. FIG. 2 is a diagram illustrating an energy potential near the light detection unit 3 in the light detection operation state according to the first embodiment of the present invention. In the figure, 1 is a p-type silicon substrate, 3 is a photodetector (silicon-
Germanium mixed crystal), 4 denotes the first interlayer film, 5A denotes the energy potential of the second interlayer film, and 7 denotes the energy potential of the second interlayer film.
Holes generated by absorbing infrared rays, 8 is an electron excited by absorbing infrared, E _F is the Fermi level, E _V
Indicates the level at the upper end of the valence band.

The holes 7 generated as “vacancies” of electrons excited by absorbing infrared rays and being photoexcited inside the silicon-germanium mixed crystal 3 have kinetic energy and thus travel in all directions. Of these, the holes 7 traveling in the direction of the p-type silicon substrate 1 are injected into the p-type silicon substrate 1 across the hetero barrier and detected as photocurrent.

The holes 7 traveling in the direction opposite to that of the p-type silicon substrate 1 are not normally detected as a photocurrent. However, since the first interlayer film 4 uses an insulator, the holes 7
, And a quantum mechanical reflection occurs as shown by the arrow in FIG. Therefore, the traveling direction of the holes 7 is reversed, is injected into the p-type silicon substrate 1, and is detected as a photocurrent.

If the first interlayer film 4 does not exist,
It goes without saying that the holes 7 are injected into the second interlayer film 5A without being reflected, and are not detected as a photocurrent. That is, even in the first embodiment, the effect of improving the light detection sensitivity due to the reflection of the holes of the conventional structure is not lost at all.

As described above, the peak of the optical resonance is 1
When the thickness is set to 2 μm, in the conventional optical resonance structure, according to Equation 1, when a silicon oxide film is used as the interlayer film 5, the thickness d of the interlayer film 5 is 2.0 μm and a silicon nitride film is used. Sometimes it is 1.5 μm. On the other hand, in the optical resonance structure of the first embodiment, the second interlayer film 5A
When silicon is used, the thickness d ₂ of the second interlayer film 5A is 0.86 μm according to Equation 2, when germanium is used, 0.73 μm, and when silicon-germanium mixed crystal is used, the above two values are obtained. Take an intermediate value of. That is,
It is less than half compared to the conventional structure.

Therefore, when the thickness of the interlayer film is reduced, the problem of mechanical stress and distortion caused by the difference in the coefficient of thermal expansion between the silicon substrate and the interlayer film is reduced, and the scattering and diffraction in the interlayer film is reduced. Crosstalk of optical signals due to multiple reflection is reduced. Further, since a material having a small infrared absorptivity is used as the material of the interlayer film, the loss of the infrared intensity in the interlayer film can be suppressed.

Embodiment 1 of the present invention, as described above,
A light detection unit 3 for performing photoelectric conversion of incident infrared light; a first interlayer film 4 formed on the surface of the light detection unit 3 with an insulator thinner than the wavelength of the incident infrared light; and a first interlayer film 4, a second interlayer film 5A having a thickness satisfying the optical resonance condition and having a high refractive index and a low infrared absorptivity, and a second interlayer film 5A And an aluminum reflective film 6 having high reflectivity.

That is, as the photodetecting section 3, for example, platinum (P) for forming a Schottky junction is used.
t), a metal thin film such as a metal such as iridium (Ir), a metal compound such as platinum silicide or iridium silicide, or a heterojunction for forming a heterojunction.
As the first interlayer film 4, a silicon-germanium mixed crystal (Si ₁ -xGex) in which a p-type dopant is p-doped at a high concentration of 1 × 10 ¹⁹ to 1 × 10 ²¹ / cm ³ is used. Using silicon oxide or silicon nitride, the second interlayer film 5A is not doped with impurities, or contains 1 × 10 ¹⁷ p-type or n-type dopants.
It uses silicon, germanium, or a silicon-germanium mixed crystal doped with p-type or n-type at a low concentration of not more than the number of pieces / cm ³ .

That is, the first embodiment aims at providing an optical resonance structure capable of reducing stress / distortion of an element, reducing optical signal crosstalk, and improving photodetection sensitivity in an infrared solid-state imaging device. I have. for that reason,
Hundreds of よ り thinner than the wavelength of the incident infrared light
The first interlayer film 4 is formed of a thin insulating film (about 0.02 to 0.06 μm), has a thickness on the surface of the first interlayer film 4 that satisfies the optical resonance condition, and has a refractive index. The second interlayer film 5A having a high infrared absorption rate is low, and the aluminum reflection film 6 having a high infrared reflectance is formed on the surface of the second interlayer film 5A. As a result, the first
The interlayer film 4 reflects the photocarriers generated by the photodetecting unit 3, increases the efficiency of photocarrier injection into the semiconductor, and maintains high photosensitivity. In addition, since the second interlayer film 5A has a large refractive index and a small infrared absorptance, it is possible to reduce the thickness of the interlayer film and the amount of infrared absorption, thereby reducing stress / strain of the element and reducing the optical signal. Crosstalk can be reduced and photodetection sensitivity can be improved.

Embodiment 2 FIG. In the first embodiment, the light detection unit 3
After the first interlayer film 4 made of an insulator is once formed thereon, the second interlayer film 5A having a large refractive index and a small infrared absorption is formed. The second embodiment provides an optical resonance structure that reduces the number of manufacturing process steps of the first embodiment and simplifies the element manufacturing process.

The configuration of the second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a view showing a cross section of the structure of the second embodiment of the present invention. The p-type silicon substrate 1, the silicon oxide film 2, the photodetector 3, the second interlayer film 5A and the aluminum reflection film 6 are the same as those described above. Same as in Example 1.

In FIG. 3, reference numeral 4A denotes a silicon, germanium, or silicon-germanium layer formed on the photodetecting section 3 and having an n-type dopant doped at a high concentration of 1 × 10 19 to 1 × 10 21 / cm 3. The first interlayer film is formed of a mixed crystal and has an extremely small thickness of, for example, about several hundreds of Å (0.02 to 0.06 μ). It should be noted that the present invention
The light detector according to the second and third aspects corresponds to the light detector 3 in the second embodiment, and the barrier film according to the second and third aspects of the present invention is the first interlayer film 4A in the second embodiment. Is equivalent to
The interlayer film according to claim 2 and 3 of the invention corresponds to In the second embodiment the second interlayer film 5A, a second aspect of the present invention
The reflecting films according to the first and second embodiments correspond to the aluminum reflecting film 6 in the second embodiment.

In the manufacturing process of the optical resonance structure according to the second embodiment, since the first interlayer film 4A on the photodetecting section 3 uses silicon or germanium, the insulating film and the semiconductor film as in the first embodiment are used. Thus, it is not necessary to provide two types of deposition apparatus and etching apparatus, so that the manufacturing process can be simplified and the apparatus can be saved.

Next, the operation of the optical resonance structure of the second embodiment will be described. The optical function is almost the same as that of the first embodiment. First
As a material of the interlayer film 4A, the n-type dopant is 1 × 10 ¹⁹ to 1 × 10 ²¹ / c instead of the insulator as described above.
Silicon, germanium, or a silicon-germanium mixed crystal with n-type doping at a high concentration of m ³ is used. These highly doped semiconductor materials absorb infrared light well, but have a thickness of several hundred Å (0.02 to 0.0
The absorption amount is kept low by making it as thin as about 6 μ).

Next, another operation other than the optical resonance structure of the second embodiment, that is, the operation of improving the optical carrier collection efficiency, will be described with reference to FIG. FIG.
Light detection unit 3 in the light detection operation state according to the second embodiment of the present invention
It is a figure which shows the energy potential of the vicinity.

In FIG. 4, 1 is a p-type silicon substrate, 3
Indicates a photodetector (silicon-germanium mixed crystal), 4A indicates the energy potential of the first interlayer film, 5A indicates the energy potential of the second interlayer film, 7 indicates holes generated by absorbing infrared rays, and 8 indicates holes. Electrons excited by absorbing infrared light,
E _F represents the Fermi level, E _V is the level of the upper end of the valence band, respectively.

First, the potential shape created by the photodetector section 3, the first interlayer film 4A and the second interlayer film 5A will be described.

[0065] The first interlayer film 4A is the Fermi level E _F is the charge neutral condition since the n-type doping,
It is near the upper end in the band gap. Second interlayer film 5A
It is not subjected to impurity doping (or low concentration is performed doped) Fermi level E _F in the charge neutrality condition is near the middle of the band gap. Silicon-germanium mixed crystal (photodetector) 3
Since doing a p-type doped at a high concentration impurity levels are degenerate, the Fermi level E _F is in a valence band. The first interlayer film 4A, the second interlayer film 5A and the silicon
When the germanium mixed crystal 3 is brought into contact, carriers move so as to match the Fermi level which differs depending on each semiconductor.

As a result, the Fermi level has a constant value in the equilibrium state. With respect to this potential formation, the n-type doped first interlayer film 4A plays an important role. In order to explain the function, a case where the first interlayer film 4A is not provided will be described.

FIG. 5 is a diagram showing the energy potential when the first interlayer film 4A is not provided. Since the silicon-germanium mixed crystal 3 is highly p-doped, the depletion layer hardly extends. On the other hand, the second interlayer film 5
Since A is not doped with an impurity (or is doped at a low concentration), a thick depletion layer extends. This means that the potential in the depletion layer is gently inclined.

When the holes 7 generated by the incident light travel toward the second interlayer film 5A, they penetrate into the second interlayer film 5A as they are because there is no potential barrier at the interface. The holes 7 that have penetrated collide with a potential barrier formed inside the second interlayer film 5A and are reflected if there is no scattering due to collision. However, the mean free path of the holes 7 is
Since it is at most about 100 ° in silicon, it is scattered by phonons or the like before colliding with a potential barrier and loses kinetic energy.

In order to solve this inconvenience, the potential of the second interlayer film 5A may be rapidly raised at a distance shorter than the mean free path of the holes 7. In order to increase the potential, a high density of positive space charges is required. To form a high density of positive space charges, a semiconductor layer heavily doped with n-type is provided at the interface. I just need.

Therefore, when a heavily doped n-type semiconductor layer is provided as the first interlayer film 4A, a potential which rises sharply at the interface as shown in FIG. 4 is formed. In such a potential shape, the holes 7 generated by the incident light and traveling to the first interlayer film 4A side
After invading the interlayer film 4A, it immediately collides with the potential barrier without passing through the parallel free path and is reflected. However, since the first interlayer film 4A is highly doped with impurities and has a high infrared absorptance, it must be made as thin as possible.

Further, the structure of the second embodiment has the following excellent effects in addition to the effects described above.

When the photodetecting section 3 is formed of a silicon-germanium mixed crystal, the difference in lattice constant between the p-type silicon substrate 1 and the silicon-germanium mixed crystal 3 causes the inside of the silicon-germanium mixed crystal 3 to be inside. , Strong stress is occurring. Since this stress affects the photodetection cutoff wavelength, it is necessary that the stress be stable.However, the stress is alleviated after a process such as heat treatment, and the photodetection cutoff wavelength changes. Would.

When the first interlayer film 4A and the second interlayer film 5A are formed of silicon, the p-type silicon substrate 1,
Mechanically stable because it has a sandwich structure with a silicon-germanium mixed crystal in the middle and a silicon layer on both sides, such as silicon-germanium mixed crystal 3, silicon first and second interlayer films 4A and 5A. It becomes extremely strong against stress relaxation such as heat treatment. Therefore, it also has an excellent effect of stabilizing the light detection characteristics.

The second embodiment of the present invention, as described above,
A photodetector 3 for performing photoelectric conversion of incident infrared light; a first interlayer film 4A formed on the surface of the photodetector 3 so as to be thinner than the wavelength of the incident infrared light; and a surface of the first interlayer film 4A. A second interlayer film 5A having a thickness satisfying the optical resonance condition and having a high refractive index and a low infrared absorptivity; and a second interlayer film 5A formed on the surface of the second interlayer film 5A and having a high infrared reflectance. And a high aluminum reflective film 6.

That is, as the light detecting section 3, for example,
A metal thin film such as a metal such as platinum (Pt) or iridium (Ir), a metal compound such as platinum silicide or iridium silicide, or a p-type dopant for forming a heterojunction is 1 × 10 ¹⁹ to 1 ×. 10 ²¹
A silicon-germanium mixed crystal (Si ₁ -xGex) which has been p-doped at a high concentration of 1 / cm ³ is used, and an n-type dopant of 1 × 10
^Using silicon, germanium, or a silicon-germanium mixed crystal which is n-doped at a high concentration of ¹⁹ to 1 × 10 ²¹ / cm ³ , the second interlayer film 5A is not doped with impurities or is p-type. Alternatively, silicon, germanium, or a silicon-germanium mixed crystal doped with an n-type dopant at a low concentration of 1 × 10 ¹⁷ / cm ³ or less at a low concentration is used.

[0076]

[0077]

[0078]

As described above, the solid-state imaging device according to the first aspect of the present invention is provided on a semiconductor substrate and is provided with an incident light.
A photodetector for photoelectrically converting light, provided on the photodetector
A barrier film that reflects carriers generated by the incident light;
An interlayer film provided on the barrier film, and
A reflection provided to reflect incident light transmitted through the photodetector;
Comprising a film , the barrier film is made of silicon oxide or silicon nitride, and the interlayer film is made of silicon, germanium, or silicon-germanium mixed crystal, without reducing the carrier collection efficiency ,
There is an effect that the thickness of the interlayer film can be reduced for detecting light of the same wavelength.

The solid-state imaging device according to the second aspect of the present invention is provided on a semiconductor substrate and
A photodetector for photoelectrically converting light, provided on the photodetector
A barrier film that reflects carriers generated by the incident light;
An interlayer film provided on the barrier film, and
A reflection provided to reflect incident light transmitted through the photodetector;
Since the barrier film is made of a doped semiconductor, the thickness of the interlayer film can be reduced by a simple manufacturing process for detecting light of the same wavelength without reducing the carrier collection efficiency. This has the effect that it can be performed.

As described above, the solid-state image pickup device according to the third aspect of the present invention is provided on
A photodetector for photoelectrically converting light, provided on the photodetector
A barrier film that reflects carriers generated by the incident light;
An interlayer film provided on the barrier film, and
A reflection provided to reflect incident light transmitted through the photodetector;
Comprising a film , wherein the barrier film is doped silicon,
Germanium, or silicon-germanium mixed crystal, and the interlayer film is silicon, germanium, or silicon-germanium mixed crystal,
There is an effect that the thickness of the interlayer film can be reduced by a simple manufacturing process for detecting light of the same wavelength without reducing the carrier collection efficiency.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross section of an optical resonance structure according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an energy potential in the vicinity of a light detection unit according to the first embodiment of the present invention.

FIG. 3 is a diagram illustrating a cross section of an optical resonance structure according to a second embodiment of the present invention.

FIG. 4 is a diagram illustrating an energy potential in the vicinity of a light detection unit according to a second embodiment of the present invention.

FIG. 5 is a diagram for explaining an energy potential in the vicinity of a light detection unit when there is no first interlayer film according to a second embodiment of the present invention.

FIG. 6 is a diagram illustrating a cross section of an optical resonance structure of a conventional solid-state imaging device.

FIG. 7 is a diagram illustrating an energy potential in the vicinity of a light detection unit of a conventional solid-state imaging device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 P-type silicon substrate 2 Silicon oxide film 3 Photodetection part 4 1st interlayer film 4A 1st interlayer film 5A 2nd interlayer film 6 Aluminum reflective film

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-260468 (JP, A) JP-A-3-156969 (JP, A) JP-A-2-268465 (JP, A) JP-A-4- 111467 (JP, A) JP-A-3-296280 (JP, A) Cosmic ray symposium, Vol. 1989 (1990), p. 118-126 (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 27/14 H01L 31/00 H01L 31/10 JICST file (JOIS)

Claims (3)

(57) [Claims] 1. A photoelectric conversion device provided on a semiconductor substrate for photoelectrically converting incident light.
A light detection unit which is provided on the light detection unit and which is generated by the incident light.
A barrier film that reflects the carrier, an interlayer film provided on the barrier film, and an input film that is provided on the interlayer film and that has passed through the photodetector.
Equipped with a reflective film that reflects light, The barrier film is made of silicon oxide or silicon nitride.
Composed of The interlayer film is made of silicon, germanium, or silicon
-Composed of germanium mixed crystals Characterized by
Solid-state imaging device. (2)Photoelectric conversion of incident light provided on a semiconductor substrate
Replacing light detector, A key provided on the light detection unit and generated by the incident light.
Barrier film that reflects the carrier An interlayer film provided on the barrier film, as well as The light transmitted through the photodetector provided on the interlayer film
Reflective film that reflects light With The barrier film is composed of a doped semiconductor
Characterized by Solid-state imaging device. (3)Photoelectric conversion of incident light provided on a semiconductor substrate
Replacing light detector, A key provided on the light detection unit and generated by the incident light.
Barrier film that reflects the carrier An interlayer film provided on the barrier film, as well as The light transmitted through the photodetector provided on the interlayer film
Reflective film that reflects light With The barrier film is made of doped silicon or germanium.
Or silicon It is composed of rumanium mixed crystal, The interlayer film is made of silicon, germanium, or silicon
-Composed of germanium mixed crystals Characterized by
 Solid-state imaging device.