JP2795241B2 - Solid-state imaging device and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a solid-state imaging device and a method of manufacturing the same.

[0002]

2. Description of the Related Art FIG. 10 is a view for explaining the configuration of a conventional solid-state imaging device, and is a plan view showing the configuration of an interline transfer type CCD imaging device. The solid-state imaging device includes a photodiode 101 that performs photoelectric conversion, a vertical CCD register 102 that receives signal charges accumulated in the photodiode 101 and transfers the signal charges in a vertical direction, and receives charges from the vertical CCD registers 102 and transfers the signals in a horizontal direction. A horizontal CCD register 103, a charge detection unit 104 for detecting transferred charges, and an amplifier 105. The portion surrounded by the dashed line is the unit pixel 106.

FIG. 11 is a cross-sectional view when the unit pixel 106 is cut in the horizontal direction. P-type impurity well layer 112 is formed on one main surface of N-type semiconductor substrate 111. An N-type impurity layer 113 constituting the photodiode 101 and a P + -type impurity layer 114 for suppressing current generated at the Si / SiO ₂ interface are formed therein. Further, an N-type impurity layer 115 constituting the vertical CCD register 102 and a P-type impurity layer 116 are formed below the N-type impurity layer 115. Between the photodiode 101 and the vertical CCD register 102, a P + type element isolation layer 117 and a vertical CCD
A read gate region 118 for transferring charges to the register 102 is provided. On one main surface of the semiconductor substrate 111, an insulating film 119 made of a silicon oxide film, a silicon nitride film or the like is formed, and a vertical transfer electrode 120 made of a polysilicon film or the like is formed thereon. Further, an insulating film 121 made of a silicon oxide film or the like is formed thereon, and a light shielding film 122 is provided thereon. The light-shielding film 122 has an opening 123 above the photodiode 101 so that light can enter the N-type impurity layer 113 serving as the photodiode.

[0004] The operating principle of the imaging apparatus is as follows. From the opening 123 of the light shielding film 122, the photodiode 1
Light enters the N-type impurity layer 113 constituting the first semiconductor layer 01, and electrons generated by photoelectric conversion are accumulated in the N-type impurity layer 113. Next, by applying a positive pulse voltage to the vertical transfer electrode 120, the signal electrons in the N-type impurity layer 113 pass through the readout gate region 118 and the vertical CCD register 1
02 is transferred to the N-type impurity layer 115. Next, the signal electrons are transferred through the vertical CCD register 102, further transferred through the horizontal CCD register 103, and output via the charge detection unit 104 and the amplifier 105.

In a CCD image pickup device, silicon is generally used as a substrate, and therefore, a photodiode portion for performing photoelectric conversion is constituted by a Pn junction of silicon. As shown in FIG. 12, in the spectral sensitivity characteristic of an imaging device using a Pn junction of silicon, the sensitivity is reduced to 1/5 to 1/10 in a long wavelength region of 800 to 1000 nm. Infrared rays are used for medical treatment and plant observation, etc.
It is also used as a surveillance camera using infrared strobe light. For such applications, a solid-state imaging device having high sensitivity to infrared light is required.

As a method of increasing the sensitivity to infrared light,
As described in JP-A-63-122285, there is a method of forming a photodiode in a silicon-germanium mixed crystal layer. FIG. 13 is a view for explaining this, and shows the structure of an element cell in which a photodiode and a MOS transistor are combined, and shows a silicon or germanium substrate 201, a stepwise composition change layer 202, and an n-type silicon-germanium mixed layer. Crystal layer 203, drain electrode 204, gate electrode 205, SiO ₂ film 206,
It comprises a drain 207 made of P + impurities and a source 208 made of P + impurities and functioning as a photodiode.

In this conventional example, since the light receiving portion is formed of the silicon-germanium mixed crystal layer 2, the band gap is as small as about 0.8 eV with respect to 1.1 eV of silicon.
For this reason, it has a feature that the sensitivity to infrared light is high.

[0008]

A first problem of a conventional imaging device using an n-type silicon-germanium mixed crystal layer is that noise generated in a charge transfer section is large. That is, the charge transfer portion is formed in a silicon-germanium mixed crystal layer having a narrow band gap,
_It has a drawback that a large current is generated at the interface of ₂ / semiconductor layer.

A second problem is that after forming a mixed crystal of silicon and germanium, the temperature cannot be raised to about 900 ° C. or more, and the process conditions are limited. this is,
In this mixed crystal, the germanium in the silicon crystal dissociates from the lattice with the silicon crystal in a short time at about 900 ° C. or more, even at 800 ° C. or more. This causes the deterioration of. For this reason, it is necessary that the temperature after the step of forming the mixed crystal layer of silicon and germanium be equal to or lower than the above temperature.
Therefore, it is necessary to perform all the steps at low temperature, such as the diffusion region under the transfer electrode after the formation of the photodiode for photoelectric conversion, the gate film under the transfer electrode, and the formation of the transfer electrode. For this reason, there is a restriction in the manufacturing process such that thermal oxidation of silicon cannot be performed and thermal diffusion of impurities cannot be performed, and productivity has decreased and cost has increased.

An object of the present invention is to provide a solid-state imaging device which has high sensitivity to infrared light and low noise, and a method of manufacturing the same.

[0011]

According to the present invention, there is provided a solid-state imaging device which forms a part of a photoelectric conversion region on a surface of a silicon semiconductor substrate.
A first region , a charge transfer region, a first insulating film on the charge transfer region, and a charge transfer electrode on the first insulating film. A second insulating film on the electrode and the silicon semiconductor substrate, a light-shielding film on the second insulating film, and an opening in a portion above the first region of the light-shielding film and the second insulating film; A third insulating film on the inner wall of the opening; and a second region which is a part of the photoelectric conversion region in a portion surrounded by the third insulating film.

According to an embodiment of the present invention, the second region is a silicon-germanium mixed crystal.

According to another embodiment of the present invention, a second region is provided.
Between the second region and the third insulating film, the second region and the first conductive type
And a second region on the upper surface of the second region .
Region and a second semiconductor region of the opposite conductivity type.

According to another embodiment of the present invention, the second region
The region is between the silicon-germanium mixed crystal layer and the silicon layer .
Ru laminated der.

According to another embodiment of the present invention, the second region
The surface of the region is germanium-free silicon or a germanium-silicon mixed crystal containing 5% or less of germanium.

In the method of manufacturing a solid-state imaging device according to the present invention, an impurity of a second conductivity type is selectively introduced into a silicon semiconductor substrate of a first conductivity type to form a charge transfer region of a second conductivity type. Forming a first insulating film on the silicon semiconductor substrate and the charge transfer region; forming a charge transfer electrode on the charge transfer region; and forming a second conductivity type near the surface of the silicon semiconductor substrate. Selectively introduce impurities,
Forming a first region that is to be a part of the photoelectric conversion region , forming a second insulating film over the entire surface of the wafer,
Forming a light-shielding film on the first insulating film, forming a fourth insulating film on the light-shielding film, forming a fourth region on the first region of the fourth insulating film, the light-shielding film and the second insulating film . forming an opening, and forming a third insulating film along the inner wall of the opening, a part of the photoelectric conversion region portion surrounded by the third insulating film
And forming a second insulating film. The step of forming the second insulating film may be performed before the step of forming the first region .

According to another embodiment of the present invention, the second region
The region is formed by an epitaxial growth method.

According to another embodiment of the present invention, the second region
A silicon-germanium mixed crystal is used in the region .

According to another embodiment of the present invention , the second region
The step of forming a region forms a stack of a silicon-germanium mixed crystal layer and a silicon layer.

According to the present invention, the photoelectric conversion portion is provided in a silicon-germanium mixed crystal layer (which may be another semiconductor such as silicon) having a high photoelectric conversion efficiency with respect to infrared light, and the charge transfer portion is provided with crystal defects. It is formed in a small amount of single crystal silicon. This enables a solid-state imaging device having particularly high infrared light sensitivity and low noise.

[0021]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a plan view of a solid-state imaging device according to a first embodiment of the present invention, FIG. 2 is a sectional view taken along a line AA 'in FIG. 1, and FIG. 3 is a line BB' in FIG. Sectional view along FIG. 4,
FIGS. 5A to 5C, FIGS. 5A and 5B are cross-sectional views of the solid-state imaging device according to the present embodiment in the order of steps along the line AA ′ in FIG. 1, and FIG. It is sectional drawing along BB '. The solid-state imaging device according to the first embodiment includes a second photodiode N-type region 20 made of a silicon-germanium mixed crystal embedded in an opening 18 provided in a light-shielding film 16 and a second photodiode N-type region 20 provided in a silicon substrate. One photodiode N-type region 4 constitutes a photoelectric conversion unit. On the other hand, the charge transfer N-type region 6 as a charge transfer portion is formed in single crystal silicon.

The operation principle will be described. The incident light is photoelectrically converted by the photoelectric conversion unit, and charges are accumulated. next,
By applying a positive pulse to the first single-crystal silicon layer 9 or the second single-crystal silicon layer 11, the charge in the photoelectric conversion portion passes through the readout gate region and is a charge transfer N-type region which is a vertical CCD register. 6 is transferred. Thereafter, a signal is output to the outside similarly to the conventional example.

Next, the manufacturing method will be described.

First, a P-type impurity is introduced on an N-type semiconductor substrate 1 to form a P-well 2 which is a silicon semiconductor substrate. Next, the surface of the P well 2 is oxidized to form a first silicon oxide film 3. Next, using a photoresist (not shown) patterned by photolithography as a mask, a P-type impurity and an N-type impurity are
Is implanted into the P well 2 and then the photoresist is removed, followed by thermal diffusion to form a P-type region 5 and a charge transfer N-type region 6 as a charge transfer portion. The cross section at this time is shown in FIG.

Next, a channel stop P + region 7 is formed on the surface of the P well 2 in the same manner as the formation of the charge transfer N-type region 6. Next, the first silicon oxide film 3 is removed with hydrofluoric acid, and a first gate oxide film 8 as a first insulating film is formed by thermal oxidation. Next, a polycrystalline silicon layer 9 is deposited to a thickness of about 0.2 to 0.4 μm by a low pressure CVD method. Next, a photoresist 12 is formed. The cross section at this time is shown in FIG.

Next, the first polycrystalline silicon layer 9 serving as a charge transfer electrode is patterned using the photoresist 12 as a mask. Next, etching is performed with dilute hydrofluoric acid using the first polycrystalline silicon layer 9 as a mask, the first gate oxide film 7 is removed by etching, and the P well 2 is exposed. Next, a second gate oxide film 10 having the same thickness as the first gate oxide film 7 as a second insulating film is formed on the entire surface of the wafer by the CVD method. Next, a polycrystalline silicon film having a thickness of 0.2 to 0.4 μm is deposited on the entire surface of the wafer. The photoresist 13 is patterned by a lithography technique. FIG. 4C shows a cross section taken along a line AA ′ in FIG. 1, and FIG. 6 shows a cross section taken along a line BB ′.

Next, the second polycrystalline silicon layer 11 is etched by a dry etching method using the photoresist 13 as a mask. Next, phosphorus is ion-implanted into a portion surrounded by the first polysilicon electrode 8 and the second polysilicon layer 11, and the first photodiode N-type region 4 serving as a first photoelectric conversion region is formed. To form Next, boron is ion-implanted using a photoresist as a mask, and a shallow first P
+ Region 14 is formed. The first P + region 14 is formed along the periphery of the first photodiode N-type region 4. The cross section at this time is shown in FIG.

Next, the first interlayer insulating film 15 is
Then, the light shielding film 16 is deposited to a thickness of, for example, 400 nm. Subsequently, the second interlayer insulating film 1
7 is formed to a thickness of, for example, 100 to 500 nm. Next, the second interlayer insulating film 17 as a fourth insulating film and the light shielding film 16 are anisotropically etched using a photoresist as a mask. Next, anisotropic etching is performed while leaving the first interlayer insulating film 15 at, for example, about 30 nm. Thus, an opening 18 which is an opening is formed. Next, an insulating film 19 as a third insulating film is deposited to a thickness of, for example, 100 to 200 nm, and the insulating film 19 is removed by anisotropic etching except for the side wall of the opening 18. The cross section at this time is shown in FIG.
Shown in Next, the first interlayer insulating film 15 remaining at the bottom of the opening 18 is removed with dilute hydrofluoric acid, and the photodiode N
The mold region 4 is exposed. FIG. 5B shows a cross section at this time.

Next, a silicon-germanium mixed crystal is selectively epitaxially grown on the bottom of the opening 18 to form the opening 1.
8 is buried in a second photodiode N-type region 20 which is a second photoelectric conversion region. In this growth, for example, Si ₂ H ₆ and GeH ₄ are used as source gases, PH ₃ is used as a doping gas, and the temperature is 560 ° C. and the pressure is 2 × 10 6.
^-5 Torr. Thereby, the solid-state imaging device shown in FIGS. 1 to 3 is completed.

The light-shielding film 16 may be any material that can withstand later silicon-germanium epitaxial growth and short-time heat treatment and has a light-shielding property. Examples thereof include tungsten, molybdenum, and tantalum.

The germanium composition ratio of the silicon-germanium mixed crystal layer of the second photodiode N-type region 20 is preferably about 30% or less. Of course, silicon containing no germanium may be formed.

According to this embodiment, since the charge transfer portion is formed in single crystal silicon, noise generation due to crystal defects such as a silicon-germanium mixed crystal is small.

The first photodiode N-type region 4 may be formed before the second gate oxide film 10.

FIG. 7 is a sectional view of a solid-state imaging device according to a second embodiment of the present invention. In the solid-state imaging device according to the second embodiment, the second P + region 21 (second semiconductor region) and the third P + region 22 that are P-type are formed around and around the second photodiode N-type region 20. (A first semiconductor region).

The manufacturing method is as follows.
The structure up to the mold region 20 is the same as in the first embodiment. next,
Boron is implanted into the surface of the second photodiode N-type region 20 to form a second P + region 21. Then, using a photoresist as a mask, boron is implanted into a portion of the second photodiode N-type region 20 which is in contact with the insulating film 19, and a third P +
A region 22 is formed. This third P + region is the first P +
It is connected to the area 14. FIG. 7 shows a cross-sectional view at this time. Thus, the solid-state imaging device according to the second embodiment is completed.

In the second embodiment, since the periphery of the second photodiode N-type region 20 is surrounded by the P-type semiconductor, noise such as dark current generation on the semiconductor surface is reduced.

Next, a third embodiment of the present invention (Claim 4)
Will be described with reference to FIG.

In the solid-state imaging device according to the third embodiment, the second
The photodiode N-type region 20 is made of germanium-
Silicon mixed crystals 23 and silicon layers 24 are alternately deposited in layers.

The manufacturing method is the same as that of the first embodiment up to the step of removing the first interlayer insulating film 15 remaining at the bottom of the opening 18 with dilute hydrofluoric acid and exposing the N-type region 4 for the photodiode. .

Next, a silicon-germanium mixed crystal is selectively epitaxially grown on the bottom of the opening 18 to form the opening 1.
8 is buried. At this time, germanium-silicon mixed crystal 2
3 and the silicon layer 24 are alternately deposited in layers. Subsequent steps are the same as in the first embodiment.

As a result, the stress generated in the germanium-silicon mixed crystal can be alleviated, and crystal defects can be reduced and noise can be further reduced. Of course, the P-type second P region 21 and the third P + region 22 may be formed as in the second embodiment.

Next, a fourth embodiment of the present invention will be described.
Will be described with reference to FIG.

In the fourth embodiment, the third P + region 22 is formed of a silicon layer containing no germanium or a low germanium silicon-germanium mixed crystal layer.

The manufacturing method is the same as that of the first embodiment up to the step of removing the first interlayer insulating film 15 remaining at the bottom of the opening 18 with dilute hydrofluoric acid and exposing the photodiode N-type region 4. . Next, a silicon-germanium mixed crystal is selectively epitaxially grown at the bottom of the opening 18 to bury the opening 18. At this time, the surface 24 of the germanium-silicon mixed crystal 23 is a silicon layer containing no germanium or a silicon-germanium mixed crystal layer of low germanium. As a result, the third P + region 22 has a very low or no germanium concentration. Then the second
This is the same as the embodiment.

By forming the third P + region 22 from a silicon layer not containing germanium having a small light absorption coefficient or a silicon-germanium mixed crystal layer made of low germanium, visible light having a short wavelength is absorbed in this portion. And the sensitivity is improved. Thereby, a solid-state imaging device having high sensitivity for both infrared light and visible light can be manufactured.

[0047]

As described above, the present invention has the following effects.

(1) Since the steps of the charge transfer portion, the transfer electrode, and the like are performed before the formation of the silicon-germanium mixed crystal layer, the process conditions are not limited as in the second conventional example, and ordinary This can be performed under the same conditions as those of a solid-state imaging device on silicon, so that the manufacturing cost can be significantly reduced.

(2) Since the charge transfer portions are formed in single crystal silicon, noise generation due to crystal defects such as silicon-germanium mixed crystal is small.

(3) Since the light-shielding film is formed at a position lower than the N-type region for the second photodiode, it is difficult for light to directly enter the N-type region for charge transfer. Smear generation can be greatly reduced as compared with the conventional technology.

[Brief description of the drawings]

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

FIG. 2 is a sectional view taken along a line A-A 'in FIG.

FIG. 3 is a cross-sectional view along a line B-B 'in FIG.

FIG. 4 is a cross-sectional view illustrating a method of manufacturing the solid-state imaging device shown in FIGS.

FIG. 5 shows a method of manufacturing the solid-state imaging device of FIGS. 1 to 3;
FIG. 5 is a step-by-step cross-sectional view following FIG. 4.

FIG. 6 shows a method for manufacturing the solid-state imaging device of FIGS. 1 to 3;
It is sectional drawing of an intermediate process.

FIG. 7 is a sectional view of a solid-state imaging device according to a second embodiment of the present invention.

FIG. 8 is a sectional view of a solid-state imaging device according to a third embodiment of the present invention.

FIG. 9 is a sectional view of a solid-state imaging device according to a fourth embodiment of the present invention.

FIG. 10 is a configuration diagram of a first conventional example of a solid-state imaging device.

11 is a cross-sectional view of the solid-state imaging device of FIG.

FIG. 12 is a graph showing a relationship between light wavelength and sensitivity.

FIG. 13 is a sectional view of a second conventional example of a solid-state imaging device.

[Explanation of symbols]

 Reference Signs List 1 N-type semiconductor substrate 2 P well 3 First silicon oxide film 4 First N-type region for photodiode 5 P-type region 6 N-type region for charge transfer 7 P + region for channel stop 8 First gate oxide film 9 1 polycrystalline silicon layer 10 second gate oxide film 11 second polycrystalline silicon layer 12, 13 photoresist 14 first P + region 15 interlayer insulating film 16 light shielding film 17 second interlayer insulating film 18 opening 19 insulating film Reference Signs List 20 second N-type region for photodiode 21 second P + region 22 third P + region 23 silicon-germanium mixed crystal layer 24 silicon layer 25 silicon substrate 26 stepwise texture change layer 27 n-type silicon-germanium mixed crystal layer 28 p-type silicon-germanium mixed crystal layer 29 n-type silicon-germanium mixed crystal layer 30 silicon oxide film 31 electrode

Claims (9)

(57) [Claims] 1. A photoelectric conversion region on a surface of a silicon semiconductor substrate.
Having a first region and a charge transfer region that are a part of a charge transfer region, having a first insulating film on the charge transfer region, and having a charge transfer electrode on the first insulating film; A second insulating film on the first region, the charge transfer electrode and the silicon semiconductor substrate, a light-shielding film on the second insulating film, and a light-shielding film and the second insulating film; has an opening in a portion corresponding to on the first region, a third insulating film on an inner wall of the opening, a part of the photoelectric conversion region surrounded portion in said third insulating film A solid-state imaging device having a second region . Between wherein said said second region third insulating film, having a first semiconductor region of the second region and Hanshirube conductivity type, also on the surface of the second region The semiconductor device according to claim 1, further comprising the second region and a second semiconductor region of an opposite conductivity type. Wherein the second region is silicon - solid-state imaging device according to claim 1 or 2, wherein the germanium alloy. Wherein said second region is silicon - Ru laminated der of germanium mixed crystal layer and the silicon layer according to claim 1 or 2
20. The solid-state imaging device according to claim 20. Wherein said second surface region does not include germanium silicon or germanium 5% or less of germanium - any of claims 1 to 4, a silicon alloy
2. The solid-state imaging device according to claim 1. 6. A step of selectively introducing an impurity of a second conductivity type into an upper portion of a silicon semiconductor substrate of a first conductivity type to form a charge transfer region of a second conductivity type; Forming a first insulating film on the region, forming a charge transfer electrode on the charge transfer region, and selectively introducing a second conductivity type impurity near a surface of the silicon semiconductor substrate. And become part of the photoelectric conversion region
Forming a first region , forming a second insulating film over the entire surface of the wafer, forming a light-shielding film on the second insulating film, and forming a fourth light-shielding film on the light-shielding film. Forming an insulating film; forming an opening in the first region of the fourth insulating film, the light shielding film and the second insulating film; and forming a third insulating film along an inner wall of the opening. Forming a film, and forming a photoelectric conversion region in a portion surrounded by the third insulating film.
And forming a portion to become the second region of the step of forming the second insulating film may be performed before the step of forming the first realm, the solid-state imaging Device manufacturing method. 7. The method according to claim 6, wherein the second region is formed by an epitaxial growth method. 8. The method according to claim 6, wherein a silicon-germanium mixed crystal is used for the second region . 9. A process of forming the second region is silicon - method for manufacturing a solid-state imaging device according to claim 6 or 7, wherein a step of forming a laminate of germanium mixed crystal layer and the silicon layer.