JP2004031438A - Semiconductor device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device which includes a solid-state image pickup device which is easily made fine with high dimensional accuracy. <P>SOLUTION: In the semiconductor device in which the solid-state image pickup device is formed in a region surrounded with a field oxide film 11, the field oxide film 11 is formed on a gate oxide film 12. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device and a manufacturing method thereof, and more particularly to a miniaturized structure of a solid-state imaging device and a manufacturing method thereof.
[0002]
[Prior art]
With the high integration and high density of semiconductor devices, the number of imaging pixels is also increasing in solid-state imaging devices, but due to the demand for high-speed signal charge transfer, that is, high-speed driving with the increase in the number of pixels, Device miniaturization is progressing.
[0003]
In a semiconductor device including a solid-state imaging element, a field oxide film 11 made of a thick CVD oxide film is formed in the peripheral portion as shown in a plan view of an example in FIG. 1, and the element surrounded by the field oxide film 11 A photoelectric conversion element and a charge transfer element are arranged in the region. The channel 13 of each solid-state imaging device is separated by an impurity region called CS (Channel Stopper).
[0004]
Under such circumstances, the demand for miniaturization of the channel stopper 14 is increasing. Conventionally, when manufacturing a solid-state imaging device, as shown in FIGS. 5A to 5C, after forming a channel stopper 14 made of a p-type impurity region, a field oxide film 11 made of a CVD oxide film. After this, a gate oxide film 12 is formed, and a channel composed of an n-type impurity region is formed.
[0005]
That is, as shown in FIG. 5A, ion implantation is performed using a resist pattern formed by photolithography in a p-well 10 formed on the surface of an n-type silicon substrate 1 as a mask, and the p-type impurity region is removed. A channel stopper 14 is formed.
[0006]
Thereafter, as shown in FIG. 5B, a silicon oxide film having a thickness of about 400 nm is formed by a CVD method, and etching is performed so that the edge is tapered using a resist pattern formed by photolithography as a mask. A field oxide film 11 is formed.
[0007]
Then, as shown in FIG. 5C, a gate oxide film 12 composed of a two-layer structure film of a silicon oxide film 12a and a silicon nitride film 12b is formed, a channel 13 composed of an n-type impurity region is formed, and a gate is formed. An electrode is formed.
[0008]
[Problems to be solved by the invention]
In this method, the channel stopper 14 is formed after the field oxide film is formed. Therefore, when the mask pattern for ion implantation for forming the channel stopper is formed, the field stopper film 14 is caused by a step due to the pattern of the field oxide film 11. There is a problem that it is impossible to form a fine channel stopper 14 in the vicinity of the oxide film. This has become a very serious problem with the miniaturization of elements.
[0009]
Further, since the gate oxide film is formed after the channel stopper is formed, the impurity diffusion proceeds in the thermal oxidation process for forming the gate oxide film, and the lateral diffusion of the channel stopper 14 which is a high concentration impurity region is ignored. It will not be obtained. For this reason, the p-type impurity in the channel stopper 14 diffuses into the channel 13 and the effective channel width is reduced.
[0010]
Further, since the surface of the semiconductor substrate 1 is in direct contact with the CVD film 11 with poor purity, there is a diffusion of impurities mixed in the CVD film 11 during a thermal process such as the formation of a gate oxide film, resulting in characteristic fluctuations. There was a cause. In addition, heavy metals may be contained, which may increase dark current.
[0011]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a semiconductor device including a solid-state imaging device that can be easily miniaturized and has high dimensional accuracy.
[0012]
[Means for Solving the Problems]
The semiconductor device of the present invention is a semiconductor device in which a semiconductor element is formed in a region surrounded by a field oxide film on the surface of the semiconductor substrate, and the gate oxide film of the semiconductor element is formed on almost the entire surface of the semiconductor substrate. The field oxide film is formed on the gate oxide film.
[0013]
According to this configuration, the gate oxide film including the non-oxygen permeable film and the non-heavy metal permeable film silicon nitride film is interposed between the semiconductor substrate and the field oxide film. Diffusion and heavy metal diffusion are prevented, and manufacturing is easy and reliable.
Here, the field oxide film is preferably formed by a chemical vapor deposition (CVD) method. Further, a silicon oxide film doped with impurities, such as a BPSG film or a PSG film, or a film formed by a coating method is also applicable.
[0014]
Desirably, a plurality of solid-state imaging devices are formed in a region surrounded by a field oxide film, and a channel stopper made of an impurity region having a conductivity type opposite to that of the channel is provided between the channels of the charge transfer device. It is characterized by. In such a case, lateral diffusion from the channel stopper to the channel is prevented, and a reduction in effective channel length can be prevented.
[0015]
Desirably, the gate oxide film is composed of a silicon oxide film formed on the surface of the semiconductor substrate by thermal oxidation and a silicon nitride film formed on the silicon oxide film. Thus, the substrate surface is covered with a silicon oxide film formed by thermal oxidation with good film quality, and the upper layer is covered with a denser silicon nitride film, so that a solid-state imaging device with high withstand voltage and high reliability is obtained. It becomes possible.
[0016]
In the method of the present invention, a gate oxide film is formed at least on the surface of the semiconductor substrate and in the vicinity thereof, and after the gate oxide film is formed, the oxide is oxidized by chemical vapor deposition (CVD). Forming a silicon film and selectively removing the silicon oxide film by photolithography to form a field oxide film; and forming a solid-state imaging device in an element region surrounded by the field oxide film It is characterized by including.
[0017]
According to this method, since the field oxide film is formed by the CVD method after the gate oxide film is formed, the diffusion of impurities from the CVD film into the semiconductor substrate can be prevented even when the CVD film is formed. In addition, it is possible to prevent the substrate from being contaminated by heavy metal even when heavy metal is contained in the CVD film forming process or the like.
[0018]
Desirably, the step of forming the solid-state imaging device includes an impurity having a conductivity type opposite to that of the channel in a region surrounded by the field oxide film in order to form a channel stopper prior to the step of forming the field oxide film. The method includes a step of forming a region.
[0019]
According to this configuration, since the field oxide film is not formed when the channel stopper is formed, the focus margin is increased, the fine pattern can be easily processed, and there is no pattern misalignment due to the step.
[0020]
Further, if an insulating film including a thermal oxide film is formed on the entire surface of the semiconductor substrate, contamination of the semiconductor substrate due to impurities contained in a field oxide film such as a CVD film can be reliably prevented. .
[0021]
The step of forming the gate oxide film includes a step of forming a thermal oxide film on the surface of the semiconductor substrate and a step of forming a silicon nitride film on the thermal oxide film.
According to such a configuration, the surface of the substrate is covered with the thermal oxide film when the silicon nitride film is formed, and it is possible to prevent damage to the substrate surface during the film formation and to form a highly reliable gate oxide film. Become.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
(First embodiment)
[0023]
As shown in FIGS. 1 to 3, the semiconductor device of this embodiment includes a photodiode, a charge transfer element, and a p-type well 10 formed on the surface of an n-type silicon substrate 1 so as to form an interline type. A field imaging film 11 made of a silicon oxide film having a thickness of about 500 nm is formed by a CVD method, and a gate made of a two-layer film of a silicon oxide film 12a and a silicon nitride film 12b. It is formed on the oxide film 12. Here, FIG. 1 is an explanatory diagram of a plan configuration of the semiconductor device, FIG. 2 is a cross-sectional view taken along the line AA of FIG. 1, and FIG.
[0024]
In this structure, the gate oxide film is formed on the entire substrate surface as thick as a total film thickness of about 800 nm of the silicon oxide film 12a and the silicon nitride film 12b.
Except that the field oxide film is formed on the gate oxide film 12, it is formed in the same manner as the conventional solid-state imaging device shown in FIGS. FIG. 3 is an overall schematic diagram.
[0025]
That is, as shown in FIGS. 2 and 3, a field oxide film 11 for element isolation is formed through a gate oxide film 12 on the periphery of an n-type silicon substrate 1 having a p-well 10 formed on the surface. The vertical channel stopper LCS 14 is arranged in the element formation region surrounded by the field oxide film 11 (in this case, parallel to each other), and the charge transfer in which the channel region 13 is formed between the channel stoppers 14. A solid-state imaging device composed of an element and a photodiode is arranged. The charge transfer element includes the channel region 13 and a gate electrode 15 as a charge transfer electrode made of a polycrystalline silicon film formed on the surface with a gate oxide film 12 interposed therebetween.
[0026]
Although detailed description is omitted in this figure, a plurality of photodiodes are formed in the p-well 10 on the surface of the silicon substrate 1, and charge transfer electrodes (gate electrodes) for transferring signal charges detected by the photodiodes are provided. An array is formed.
[0027]
In FIG. 1 to FIG. 4, descriptions of the configuration of the element formation region inside the silicon substrate 1, the configuration of the light shielding film above the silicon substrate, the color filter, the microlens, and the like are omitted. In addition to the interline type solid-state image sensor, it is needless to say that the present invention can be applied to a so-called honeycomb structure solid-state image sensor.
[0028]
Next, the manufacturing process of this solid-state imaging device will be described with reference to FIGS.
First, as shown in FIG. 4A, a silicon oxide film 12a having a thickness of 30 nm is formed on the surface of the n-type silicon substrate 1 by thermal oxidation in an oxygen atmosphere to 800 to 900 ° C. Subsequently, a 50 nm-thickness silicon nitride film 12b is formed by chemical vapor deposition (CVD), and a two-layer gate insulating film 12 is formed.
[0029]
Next, a resist is applied so as to have a thickness of 0.8 to 1.4 μm. Then, exposure is performed by photolithography using a desired mask, development, and water washing are performed to form a resist pattern having desired openings at pixel intervals.
[0030]
Then, using this resist pattern as a mask, boron ions are implanted at a dose of 1 × 10 ^{12 to} 9 × 10 ¹² / cm ² and an acceleration voltage of 50 to 100 eV to form a channel stopper 14 having a desired depth. Thereafter, in the same manner, exposure is performed by photolithography using a desired mask, development, and water washing are performed to form a resist pattern having openings of 0.5 μm width on both sides of the channel stopper 14.
[0031]
Then, using this resist pattern as a mask, arsenic ions are implanted at a dose of 1 × 10 ^{12 to} 9 × 10 ¹² / cm ² and an acceleration voltage of 50 to 100 eV to form a channel 13. (Fig. 4 (b))
[0032]
Next, as shown in FIG. 4C, a silicon oxide film 11s having a thickness of 500 nm is formed by a low pressure CVD method using a mixed gas of TEOS and O ₂ . Thereafter, a resist is applied so as to have a thickness of 0.8 to 1.4 μm. Then, exposure is performed using a desired mask by photolithography, development and washing with water are performed, and a resist pattern R is formed.
[0033]
Then, as shown in FIG. 4D, the field oxide film 11 having a gentle edge is formed by causing the etching to proceed in the horizontal direction by isotropic etching.
[0034]
According to this solid-state imaging device, since the channel stopper can be formed prior to the formation of the field oxide film, the focus margin in photolithography is widened, and a fine pattern can be processed.
[0035]
In addition, since the channel stopper is formed after the gate oxide film is formed, it is possible to suppress an increase in diffusion due to thermal oxidation when the gate oxide film is formed. In particular, lateral diffusion from the channel stopper to the channel is prevented, and a reduction in effective channel length can be prevented. In this way, it is possible to form a highly accurate and fine channel stopper and channel, and miniaturization of the element can be achieved.
[0036]
Further, ion implantation for channel stopper or channel formation can be performed through the gate oxide film, so that damage to the substrate surface can be prevented.
[0037]
Furthermore, a gate oxide film including a silicon oxide film 12a formed by dense thermal oxidation and a silicon nitride film 12b formed thereon is formed between the semiconductor substrate 1 (p well 10) and the field oxide film 11. Since 12 is interposed, diffusion of impurities from the field oxide film 11 and diffusion of heavy metal are prevented, characteristic variation is suppressed, and dark current is also suppressed.
[0038]
The gate oxide film is composed of a silicon oxide film 12a formed by thermal oxidation on the silicon substrate surface and a silicon nitride film 12b formed on the silicon oxide film 12a. Since it is covered with a good silicon oxide film 12a and the upper layer is covered with a denser silicon nitride film 12b, it is possible to obtain a solid-state imaging device with high breakdown voltage and high reliability.
[0039]
Note that, in the case of a high breakdown voltage device configured with a gate insulating film as thick as 80 nm as in the first embodiment, the time required for thermal oxidation is particularly long. Since the diffusion of impurities from the field oxide film to the substrate becomes a problem, the configuration of the present invention is particularly effective. However, it goes without saying that this is also effective when a gate oxide film having a normal thickness is used.
Further, as the gate electrode, other conductive materials such as a metal silicide in addition to the polycrystalline silicon film may be used.
[0040]
(Second Embodiment)
Next, a second embodiment of the present invention will be described. In the first embodiment, the solid-state imaging device has been described. However, the present invention can also be applied when using other semiconductor devices such as transistors.
Also in this case, impurity contamination from the CVD film is suppressed, characteristic fluctuations such as potential fluctuations of the transistor are suppressed, and a highly reliable semiconductor device can be obtained.
[0041]
The present invention is particularly effective for a CCD area sensor, but can also be applied to other semiconductor devices such as line sensors, CMOS sensors, logic elements, analog elements, and bipolar elements.
[0042]
Here, the field oxide film is a silicon oxide film formed by a CVD method. However, even if it is formed by a coating method such as an impurity doped film such as a BPSG film or a PSG film, the substrate is contaminated by impurities when formed directly. However, the structure of the present invention makes it possible to form a highly reliable semiconductor device without fear of contamination.
[0043]
Further, as the gate oxide film, a two-layer film of a silicon oxide film and a silicon nitride film is used. However, the present invention is not limited to this, and non-oxygen permeable films such as silicon carbide, iridium, iridium oxide, osmium, and neodymium are used. Further, a heavy metal non-permeable film or a laminated film thereof can also be applied.
[0044]
【The invention's effect】
As described above, according to the semiconductor device of the present invention, the focus margin at the time of photolithography for forming the channel stopper is widened, and the element can be miniaturized.
In addition, during device formation and use, contamination due to diffusion of impurities from the field oxide film to the substrate can be suppressed, characteristic variation can be prevented, and a highly reliable semiconductor device can be provided. .
[Brief description of the drawings]
FIG. 1 is a diagram showing a semiconductor device according to a first embodiment of the present invention.
FIG. 2 is a diagram illustrating a semiconductor device according to a first embodiment of the present invention.
FIG. 3 is a diagram showing a semiconductor device according to the first embodiment of the present invention.
FIG. 4 is a diagram showing a manufacturing process of the semiconductor device of the first embodiment of the present invention.
FIG. 5 is a diagram showing a manufacturing process of a conventional semiconductor device.
[Explanation of symbols]
10 Silicon substrate 11 Field oxide film 12 Gate oxide film 13 Channel 14 Channel stopper 15 Gate electrode

Claims (7)

In a semiconductor device formed by forming a semiconductor element in a region surrounded by a field oxide film on the surface of a semiconductor substrate,
A gate oxide film of the semiconductor element is formed on substantially the entire surface of the semiconductor substrate;
The semiconductor device according to claim 1, wherein the field oxide film is formed on a gate oxide film. A solid-state imaging device including a plurality of photoelectric conversion elements and charge transfer elements is formed in a region surrounded by the field oxide film. Between the channels of each charge transfer element, the channel has a reverse conductivity type. 2. The semiconductor device according to claim 1, further comprising a channel stopper made of a plurality of impurity regions. 3. The gate oxide film according to claim 1, wherein the gate oxide film comprises a silicon oxide film formed on the surface of the semiconductor substrate by thermal oxidation and a silicon nitride film formed on the silicon oxide film. The semiconductor device described. A method of forming a semiconductor device including a solid-state imaging element on a surface of a semiconductor substrate,
Forming a gate oxide film at least in the vicinity of the solid-state imaging device forming region on the surface of the semiconductor substrate; and
Forming a field oxide film by forming a silicon oxide film by a chemical vapor deposition (CVD) method after the gate oxide film is formed, and selectively removing the silicon oxide film by photolithography; ,
Forming a solid-state imaging element in an element region surrounded by the field oxide film. Prior to the step of forming the field oxide film, the step of forming the solid-state imaging device includes an impurity region having a conductivity type opposite to that of the channel in a region surrounded by the field oxide film in order to form a channel stopper. The method of manufacturing a semiconductor device according to claim 4, comprising a step of forming the semiconductor device. 6. The method of manufacturing a solid-state imaging device according to claim 4, wherein the step of forming the gate oxide film is a process of forming an insulating film including a thermal oxide film on the entire surface of the semiconductor substrate. The step of forming the gate oxide film includes a step of forming a thermal oxide film on the surface of the semiconductor substrate,
The method for manufacturing a solid-state imaging device according to claim 4, further comprising: forming a silicon nitride film on the thermal oxide film.

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