JP2004363473A - Solid imaging device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid imaging device that can suppress the generation of white blemish and is superior in reliability. <P>SOLUTION: The solid imaging device is provided with a photoelectric conversion part, a charge transmission part that has a charge transmission part to transmit charges generated by the photoelectric conversion part, and a peripheral circuit connected with the charge transmission part. The surface of the photoelectric conversion part is covered with a reflection prevention film formed of a silicon nitride film. A hydrogen permeable spacer film is interposed between the side wall of a gate oxide film below a charge transmission electrode and the reflection prevention film. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solid-state imaging device and a manufacturing method thereof.
[0002]
[Prior art]
A solid-state imaging device using a CCD (charge coupled device) used for an area sensor or the like is a charge transfer device including a photoelectric conversion unit such as a photodiode and a charge transfer electrode for transferring a signal charge from the photoelectric conversion unit. Part. A plurality of charge transfer electrodes are arranged on the charge transfer path formed on the semiconductor substrate and are sequentially driven.
[0003]
In recent years, in a solid-state imaging device, pixel miniaturization has progressed due to an increase in the number of imaging pixels. Along with this, miniaturization of the photoelectric conversion part has progressed and it has become difficult to maintain high sensitivity.
[0004]
Under such circumstances, as shown in FIG. 7, a solid-state imaging element in which a film having a refractive index higher than that of a silicon oxide film such as a silicon nitride film serving as an antireflection film is formed in a pixel portion has been proposed. .
[0005]
Then, by supplying hydrogen to the pixel portion, the substrate interface potential can be reduced, and generation of dark current and white scratches can be suppressed. This is known as the hydrogen annealing effect.
[0006]
By the way, as shown in a cross-sectional view in FIG. 7, the surface of the charge transfer electrode 3 is oxidized and covered with a silicon oxide film 6a, and a silicon nitride film 6b is formed as a spacer film. A structure in which a film 62 is formed and a metal light-shielding film 71 is formed thereon has been proposed (Reference Document 1).
[0007]
However, in this structure, the gate oxide film is a single silicon oxide film layer in order to reduce noise in the amplifier transistors in the peripheral circuit section. This is for amplifier noise reduction (thermal noise & 1 / f noise component). That is, to reduce the thermal noise, it is necessary to increase the mutual conductance (gm) of the driver, but this gm can be increased by increasing Cox (thinning the gate oxide film). Since the 1 / f noise component is inversely proportional to Cox (Cox = εox / tox is more proportional to tox), gate thinning is effective.
[0008]
For this reason, the gate oxide film is not patterned all at once, but is patterned leaving the silicon nitride film. That is, in the patterning process of the gate electrode, the silicon oxide film in the other region is left so that the gate oxide film of the amplifier part which is a silicon oxide single layer is not damaged, and the silicon nitride film is used as an etching stopper in the gate electrode. A certain silicon type conductive film is patterned.
Then, the electrode surface is oxidized to form a silicon oxide film, and then the silicon nitride film in the photoelectric conversion portion (pixel portion) is removed by etching.
[0009]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-324899
[Problems to be solved by the invention]
In this state, the side wall of the gate oxide film, particularly the side wall of the silicon nitride film 2b is exposed, and when silicon nitride is formed as the antireflection film 62, the silicon nitride film of the gate oxide film and the silicon nitride film of the antireflection film are formed. Are connected by the side wall of the gate oxide film, and there is a problem that the hydrogen supply path is cut off.
This causes white scratches in the dark. Here, the white scratch means that a signal charge is generated regardless of the level of incident light, and the screen looks like a white scratch.
[0011]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a solid-state imaging device that suppresses the occurrence of white scratches and has high reliability.
[0012]
[Means for Solving the Problems]
Therefore, the present invention includes a photoelectric conversion unit, a charge transfer unit including a charge transfer electrode that transfers charges generated in the photoelectric conversion unit, and a peripheral circuit unit connected to the charge transfer unit, A solid-state imaging device in which a surface of the photoelectric conversion unit is covered with an antireflection film made of a silicon nitride film, and a hydrogen permeable film is interposed between the side wall of the gate oxide film under the charge transfer electrode and the antireflection film. A spacer film is interposed.
[0013]
According to this configuration, since the hydrogen permeable spacer film is interposed between the side wall of the gate oxide film and the antireflection film, the side wall of the silicon nitride film of the gate oxide film and the antireflection film are interposed. The spacer film is interposed, and the hydrogen annealing effect can be successfully achieved.
Here, the spacer film is preferably a silicon oxide film. Thereby, it can be formed efficiently by a normal process.
[0014]
The spacer film is desirably 10 nm or less in thickness. More preferably, it is 5 nm or less. As a result, it is possible to suppress a decrease in sensitivity and to suppress light that causes a smear reflected from the projecting portion of the light shielding film, thereby forming a highly reliable solid-state imaging device.
[0015]
In the solid-state imaging device, the peripheral circuit portion includes a transistor having a single-layer gate oxide film. In this case, the side walls of the silicon nitride film are particularly easily exposed, but the hydrogen can be transmitted through the spacers, and the occurrence of white scratches is suppressed.
[0016]
Further, the present invention comprises a photoelectric conversion unit, a charge transfer unit including a charge transfer electrode for transferring charges generated in the photoelectric conversion unit, and a peripheral circuit unit connected to the charge transfer unit, A method of manufacturing a solid-state imaging device in which a surface of the photoelectric conversion portion is covered with an antireflection film made of a silicon nitride film, and a three-layer structure film of silicon oxide film-silicon nitride film-silicon oxide film (on a semiconductor substrate surface) A step of forming a gate oxide film made of an ONO film), a step of forming a silicon-based conductive film on the gate oxide film, and patterning the silicon-based conductive film using a silicon nitride film as an etching stopper to form a charge transfer electrode A step of oxidizing the surface of the charge transfer electrode, a step of etching away the silicon nitride film of at least the pixel portion of the photoelectric conversion portion, Forming a hydrogen-permeable spacer so as to cover the sidewall of the silicon nitride under the transfer electrodes, characterized in that it comprises a step of forming an anti-reflection film.
[0017]
Preferably, the method includes a step of etching the surface of the substrate to form a silicon oxide film prior to the formation of the spacer film.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is an explanatory view showing a cross section of a main part of a solid-state image sensor according to an embodiment of the present invention, and FIGS. 2 and 3 are plan views showing the solid-state image sensor according to the embodiment of the present invention and its AA cross section. FIG. 4 to 6 are manufacturing process diagrams.
[0019]
As shown in FIGS. 1 and 3, the solid-state imaging device includes a photoelectric conversion unit 30 and a charge transfer unit 40 including a single-layer structure charge transfer electrode that transfers charges generated in the photoelectric conversion unit. The solid-state imaging device includes a hydrogen permeable spacer film interposed between a side wall of the gate oxide film under the charge transfer electrode and the antireflection film.
[0020]
In this configuration, the silicon oxide film 6b, which is a hydrogen permeable spacer film, is interposed between the side wall of the gate oxide film and the antireflection film while avoiding a decrease in sensitivity and optical characteristics. A spacer film is interposed between the side wall of the silicon nitride 2b of the gate oxide film and the antireflection film, so that the hydrogen annealing effect can be satisfactorily achieved.
[0021]
Here, an n-type silicon substrate having a low efficiency of 5.0 to 9.5 Ωcm is used as the semiconductor substrate 1, and the gate oxide film 2 is composed of three layers of a silicon oxide film 2a, a silicon nitride film 2b, and a silicon oxide film 2c. Consists of a structural film.
[0022]
As shown in a plan view in FIG. 2 and an overall cross-sectional schematic diagram in FIG. 3, a plurality of photodiodes 30 are formed on the silicon substrate 1, and a charge transfer unit for transferring signal charges detected by the photodiodes. 40 is formed between the photodiodes 30.
[0023]
Although not shown in FIG. 1, the charge transfer channel 31 through which the signal charge transferred by the charge transfer electrode moves is formed in a direction crossing the direction in which the charge transfer unit 40 extends.
[0024]
In FIG. 2, the description of the interelectrode insulating film 3 formed near the boundary between the photodiode region and the charge transfer portion 40 is omitted.
[0025]
As shown in FIG. 3, a photodiode 30, a charge transfer channel 31, a channel stop region 32, and a charge readout region 33 are formed in the silicon substrate 1, and a gate oxide film 2 is formed on the surface of the silicon substrate 1. The On the surface of the gate oxide film 2, an interelectrode insulating film 6a made of a silicon oxide film and a charge transfer electrode (electrode 3) are formed.
[0026]
Although the charge transfer unit 40 is as described above, an interlayer insulating film 70 is formed on the upper surface of the charge transfer electrode of the charge transfer unit 40 as shown in FIG. Reference numeral 71 denotes a light shielding film, 72 denotes an insulating film made of P-TEOS, and 74 denotes a planarizing layer made of a BPSG film.
[0027]
Above the solid-state imaging device, a light shielding film 71 is provided except for the photodiode 30, and a color filter 50 and a microlens 60 are further provided. Further, a flattening layer 61 made of an insulating transparent resin or the like is filled between the color filter 50 and the microlens 60. Except for the charge transfer portion 40 and the interelectrode insulating film 6, the description is omitted because it is the same as the usual one. Further, FIG. 2 shows a so-called honeycomb-structured solid-state imaging device, but it goes without saying that the present invention can also be applied to a square lattice type solid-state imaging device.
[0028]
Next, the manufacturing process of this solid-state image sensor will be described in detail.
First, as shown in FIG. 4A, a silicon oxide film 2a having a thickness of 35 nm, a silicon nitride film 2b having a thickness of 50 nm, and a silicon oxide film 2c having a thickness of 5 nm are formed on the surface of the n-type silicon substrate 1. Then, a gate oxide film 2 having a three-layer structure is formed.
[0029]
Subsequently, as shown in FIG. 4B, the silicon oxide film 2c and the silicon nitride film 2b corresponding to the transistor region of the amplifier section in the peripheral circuit section 40S are selectively removed to form a single layer.
[0030]
Thereafter, a polycrystalline silicon film having a thickness of 0.4 μm is formed on the gate oxide film 2 by a low pressure CVD method using SiH ₄ as a reactive gas. The substrate temperature at this time shall be 600-700 degreeC. Thereafter, heat treatment is performed at 900 ° C. in a mixed gas atmosphere of POCl ₃ , N _2, and O ₂ to dope the polycrystalline silicon film 3 (phosphoric acid treatment).
Subsequently, the gate oxide film 2 is formed by reactive ion etching using a mixed gas of HBr and O ₂ (HBr / O ₂ : 60/2 (ml / min)) using a resist pattern formed by photolithography as a mask. The polycrystalline silicon film 3 is selectively removed by etching using the silicon nitride film 2b as an etching stopper to form an electrode. Here, it is desirable to use a high-density plasma etching apparatus.
[0031]
Subsequently, ion implantation for compensating transfer efficiency is performed using this resist pattern as a mask as necessary. Here, boron is ion-implanted at ²⁰ to 100 KeV and 1 × 10 ¹⁰ to 1 × 10 ¹³ / cm ² .
Then, the resist pattern is removed by ashing (FIG. 4C).
[0032]
Thereafter, an interelectrode insulating film 6 made of a silicon oxide film having a thickness of 80 nm is formed on the surface of the electrode pattern by thermal oxidation (FIG. 5A).
[0033]
Next, the silicon nitride in the pixel portion is removed by etching with a high selectivity between the silicon oxide film and the silicon nitride film (FIG. 5B).
[0034]
Next, as shown in FIG. 5C, the silicon oxide film is lightly etched in order to clean the silicon oxide film in the pixel portion and expose a clean silicon oxide film.
[0035]
Thereafter, as shown in FIG. 6A, a silicon oxide film 6b as a 5 nm-thickness spacer is formed on the entire surface by low pressure CVD. Then, ion implantation is performed through a mask formed using photolithography to form a pn junction (not shown) of the photoelectric conversion portion.
[0036]
Then, as shown in FIG. 6B, an antireflection film 62 made of a silicon nitride film with a film thickness of 30 nm is deposited by low pressure CVD, and an antireflection film is formed so as to cover the pixel portion by photolithography. (In addition, an opening is formed in an unnecessary part such as an electrode for hydrogen permeation.)
[0037]
Then, as shown in FIG. 6C, a light shielding film 17 made of a tungsten thin film or the like is formed, and a window is formed in the photoelectric conversion portion by photolithography.
[0038]
In this method, since a silicon oxide film as a spacer is interposed between the antireflection film 62 and the sidewall of the gate oxide film having the ONO film structure, a hydrogen permeation path is formed by the spacer even during hydrogen annealing. , Generation of white scratches can be suppressed.
Since the silicon oxide film as the spacer is formed by the low pressure CVD method, the coverage is good, and even if it is thin, it can sufficiently serve as the spacer.
[0039]
Then, after forming a light shielding film 71 and a 100 nm thick P-TEOS film 72 on the upper layer, a 700 nm thick BPSG film 73 is formed and reflowed at 850 ° C. to be flattened. In this way, the insulating film 70 is obtained.
[0040]
Thereafter, sintering including a hydrogen annealing step is performed to stabilize the substrate. The conditions for the hydrogen annealing step at this time are as follows.
Temperature 380 ° C
Time 30 minutes Gas H ₂ + N ₂
Thereafter, the color filter 50, the planarization layer 61, the microlens 60, and the like are formed to obtain the solid-state imaging device as shown in FIG.
[0041]
According to such a configuration, it is possible to provide a solid-state imaging device that suppresses white scratches and is highly sensitive and highly reliable.
[0042]
In the solid-state imaging device, it is preferable that the inter-electrode region G as the inter-electrode separation region has a width of 0.2 μm or less.
[0043]
In the above-described embodiment, the gate oxide film is composed of a three-layer film having an ONO film structure. Absent.
[0044]
Moreover, in the said embodiment, although the silicon oxide film was used as a spacer film, it is not limited to a silicon oxide film, What is necessary is just a hydrogen permeable film | membrane, such as a titanium oxide porous by anodic oxidation.
[0045]
In the above-described embodiment, the solid-state imaging device having a single-layer electrode structure has been described. However, it is needless to say that the present invention can be applied to a solid-state imaging device having a multilayer electrode structure.
[0046]
In the above embodiment, a polycrystalline silicon film is used as the silicon-based conductive film for forming the electrode. However, the present invention is not limited to the polycrystalline silicon film, and other silicon-based conductive films such as amorphous silicon and microcrystalline silicon are used. A conductive film may be used.
[0047]
In addition, by forming a metal film on the electrode, the resistance of the electrode can be reduced, and high-speed driving is possible.
[0048]
【The invention's effect】
As described above, according to the solid-state imaging device of the present invention, a hydrogen permeable film such as a silicon oxide film is formed prior to the formation of silicon nitride as an antireflection film, so that the hydrogen annealing process is good. Thus, it is possible to provide a highly reliable solid-state imaging device free from white scratches.
[Brief description of the drawings]
FIG. 1 is an explanatory cross-sectional view of a main part of a solid-state imaging device according to an embodiment of the present invention.
FIG. 2 is a plan view of the solid-state imaging device according to the embodiment of the present invention.
FIG. 3 is a cross-sectional view of a solid-state image sensor according to an embodiment of the present invention.
FIG. 4 is a diagram showing a manufacturing process of the solid-state imaging device according to the embodiment of the present invention.
FIG. 5 is a diagram showing a manufacturing process of the solid-state imaging device according to the embodiment of the present invention.
FIG. 6 is a diagram showing a manufacturing process of the solid-state imaging device according to the embodiment of the present invention.
FIG. 7 is a cross-sectional view showing a conventional solid-state imaging device.
[Explanation of symbols]
1 Silicon substrate 2 Gate oxide film 3 Charge transfer electrode (polycrystalline silicon film)
6a Interelectrode insulating film 6b Spacer film (silicon oxide film)
62 Antireflection film 71 Light shielding film 30 Photodiode part 40 Charge transfer part 50 Color filter 60 Micro lens 70 Insulating film

Claims (6)

A photoelectric transfer unit, a charge transfer unit including a charge transfer electrode that transfers charges generated in the photoelectric conversion unit, and a peripheral circuit unit connected to the charge transfer unit, A solid-state imaging device having a surface coated with an antireflection film made of a silicon nitride film,
A solid-state imaging device, wherein a hydrogen permeable spacer film is interposed between a side wall of a gate oxide film under the charge transfer electrode and the antireflection film. The solid-state imaging device according to claim 1, wherein the spacer film is a silicon oxide film. The solid-state imaging device according to claim 1, wherein the spacer film has a thickness of 10 nm or less. 4. The solid-state imaging device according to claim 1, wherein the peripheral circuit portion includes a transistor having a gate oxide film having a single layer structure. A photoelectric transfer unit, a charge transfer unit including a charge transfer electrode that transfers charges generated in the photoelectric conversion unit, and a peripheral circuit unit connected to the charge transfer unit, A method for manufacturing a solid-state imaging device having a surface coated with an antireflection film made of a silicon nitride film,
Forming a gate oxide film composed of a three-layer structure film (ONO film) of silicon oxide film-silicon nitride film-silicon oxide film on a semiconductor substrate surface;
Forming a silicon-based conductive film on the gate oxide film;
Patterning the silicon-based conductive film using a silicon nitride film as an etching stopper to form a charge transfer electrode; and
Oxidizing the charge transfer electrode surface;
Etching the silicon nitride film of at least the pixel portion of the photoelectric conversion portion; and
Forming a hydrogen permeable spacer so as to cover a side wall of silicon nitride under the charge transfer electrode;
Forming an antireflection film;
The manufacturing method of the solid-state image sensor characterized by including. 6. The method of manufacturing a solid-state imaging device according to claim 5, further comprising a step of etching the substrate surface to form a silicon oxide film prior to forming the spacer film.

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