JPH07122721A - Solid-state image pickup element and its manufacture - Google Patents

Abstract

PURPOSE:To suppress the occurrence of smears by making the clearance between a silicon substrate and light shielding film narrower. CONSTITUTION:An n-type area 105 which becomes a photoelectric conversion section and another n-type area 104 which becomes a charge transferring area are provided in the surface area of a first p-type well layer 102 on an n-type silicon substrate 101. Then a first charge transferring electrode 109 is provided on the substrate 101 with a gate insulating film composed of an oxide film 106, nitride film 107, and oxide film 108 in between and a second charge transferring electrode 113 is provided on the electrode 109 with an interlayer insulating film 112 in between. Thus only the gate insulating film can be interposed between the substrate 101 and a light shielding film 116 at the part where the substrate 101 and film 116 face the photoelectric conversion section.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charge-coupled device (C) for a charge transfer section for transferring signal charges generated by photoelectric conversion.
The present invention relates to a solid-state image sensor using a CD, and more particularly to a solid-state image sensor having a structure capable of reducing smear and a manufacturing method thereof.

[0002]

2. Description of the Related Art A solid-state image pickup device photoelectrically converts incident light in a photoelectric conversion part formed of a photodiode or the like, reads the generated signal charge to a charge transfer part and transfers the signal charge, and outputs the signal charge to a voltage. It is converted into a signal and output. A phenomenon peculiar to this solid-state image sensor is a false signal generating mechanism called smear. This is a phenomenon in which light that has entered the charge transfer unit and its periphery is photoelectrically converted, and the charges generated thereby are mixed with the signal charges and output as a false signal.

6 (a) to 6 (c) to 7 (a) to
(C) is a process sectional view for explaining a conventional method for manufacturing a solid-state imaging device. First, the n-type silicon substrate 201
Ion implantation of boron and high temperature heat treatment
The p-type well layer 202 of FIG. 6A is formed [FIG. 6A], and then the second p-type well layer 202 is formed in the surface region of the first p-type well layer 202.
Type well layer 203, n-type region 2 forming charge transfer region
04, the n-type area | region 205 which comprises a photoelectric conversion part is formed [FIG.6 (b)]. Here, the second p-type well layer 203
Is a semiconductor region provided to prevent punch-through between the n-type regions 204 and 205 and to control the channel potential of the n-type region 204. Next, thermal oxidation is performed to form a silicon oxide film 206 to be a gate oxide film, and then a polycrystalline silicon film is deposited and patterned to form a first charge transfer electrode 209. Subsequently, boron is ion-implanted using the photoresist and the first charge transfer electrode 209 as a mask to form a shallow p-type region 210 on the surface of the n-type region 205 of the photoelectric conversion unit, and then the first charge transfer electrode 209. Using the as a mask, etching is performed to remove the exposed thermal oxide film 206 [FIG. 6 (c)].

Next, thermal oxidation is performed to form a gate oxide film, and a second charge transfer electrode (not shown) is formed by depositing polycrystalline silicon and patterning the same. Then, thermal oxidation is performed to form a first interlayer insulating film 212 [FIG. 7 (a)]. In the thermal oxidation process and the previous gate oxide film formation process, an oxide film is formed below the first charge transfer electrode 209, so that the periphery of the first charge transfer electrode is warped. If this state is left as it is, the coverage is deteriorated in the next step of depositing the light-shielding film forming material, and there is a high possibility that an etching residue will occur when the light-shielding film is patterned.
To avoid this, a second interlayer insulating film 215 is formed as a step reducing layer [FIG. 7 (b)], and then the light shielding film 216 is formed.
Are formed [FIG. 7 (c)].

[0005]

In the above-mentioned conventional solid-state image pickup device, in order to secure the withstand voltage between the charge transfer electrode and the light shielding film, and to alleviate the step due to the warp around the charge transfer electrode. Further, an interlayer insulating film having a film thickness of 3000 to 4000 Å is formed on the charge transfer electrode.
Thus, in the conventional example, the same interlayer insulating film as that on the charge transfer electrode is formed on the silicon substrate, and this film thickness is added to the gate insulating film formed earlier, so that the silicon substrate and the light shielding film are not formed. There will be a large gap between them. The large distance between the silicon substrate and the light-shielding film increases the light component that is obliquely incident and leaks to the outside of the photoelectric conversion unit, resulting in an increase in smear. Therefore, it is an object of the present invention to improve the smear characteristic by minimizing the distance between the silicon substrate and the light shielding film.

[0006]

In order to achieve the above object, according to the present invention, a photoelectric conversion section array comprising a plurality of photoelectric conversion sections (105) in a surface region of a semiconductor substrate, and the photoelectric conversion section. And a charge transfer region (104) of the charge transfer unit for transferring the signal charge of the photoelectric conversion unit column is formed in line,
A charge transfer electrode (10) of the photoelectric conversion unit is formed on a semiconductor substrate.
9, 113) and a light-shielding film (116) for covering the charge transfer electrode and a part of the photoelectric conversion part, and in the solid-state imaging device, the part of the light-shielding film for covering the photoelectric conversion part and the semiconductor substrate. And the gate insulating film (106, 10
(7, 108) and an insulating film (106, 107, 114) having a film thickness equal to or less than that of (7, 108) is only interposed.

Further, according to the present invention, a photoelectric conversion section array including a plurality of photoelectric conversion sections (105) in the surface region of the semiconductor substrate, and signals of the photoelectric conversion section array arranged in the photoelectric conversion section array. Charge transfer region (104) of the charge transfer unit for transferring charges
A step of forming a gate insulating film made of a silicon oxide film (106), a silicon nitride film (107) and a silicon oxide film (108) on the semiconductor substrate, and a step of covering the charge transfer region. Forming a first layer charge transfer electrode (109), forming a first interlayer insulating film (112) only on the first layer charge transfer electrode, and forming a second layer on the charge transfer region. Charge transfer electrode (11
3), a step of forming a second interlayer insulating film (115) only on the electrode transfer electrodes of the second layer, and a step of covering the charge transfer electrodes of the first and second layers, And a step of forming a light-shielding film (116) that covers a part of the photoelectric conversion unit, and a method for manufacturing a solid-state imaging device.

[0008]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1A is a plan view showing the configuration of one pixel of a solid-state image sensor according to one embodiment of the present invention, and FIG.
Is a sectional view taken along the line AA ′. In FIG. 1, 1
01 is an n-type silicon substrate, 102 is a first p-type well layer, 103 is a second p-type well layer, 104 is an n-type region forming a charge transfer region of a charge transfer unit (vertical CCD),
Reference numeral 105 denotes an n-type region of a photodiode that performs photoelectric conversion,
106 is a silicon oxide film formed by thermal oxidation, 10
7 is a silicon nitride film formed by a CVD method, 108 is a first CVD oxide film, 109 is a polycrystalline silicon film, and a first charge transfer electrode of a charge transfer portion, 110 is an n-type of a photoelectric conversion portion. A shallow p-type region for separating the surface of the region 105 from the interface between the silicon and the oxide film to reduce dark current, and 112 is a first interlayer formed by thermally oxidizing the surface of the first charge transfer electrode 109. An insulating film, 113 is a polycrystalline silicon film, a second charge transfer electrode of the charge transfer section, 114 is a third CVD oxide film, and 115 is a first charge transfer electrode formed by thermally oxidizing the surface of the second charge transfer electrode 113. The second interlayer insulating film 116 is a light shielding film made of tungsten.

A characteristic point of this embodiment is that an insulating film equivalent to a gate insulating film is interposed between the light shielding film 116 and the silicon substrate on the photoelectric conversion parts (105, 110). That is. The gate insulating film is 300
Since it is formed to about 1000 Å, the distance between the silicon substrate and the light-shielding film can be reduced by several thousand Å as compared with the conventional one. As shown in FIG. 2, smear changes almost linearly with respect to the distance X between the light-shielding film and the silicon substrate. Therefore, reducing the distance X is extremely effective in reducing smear. Yes, according to this embodiment, 10 to 15d
The smear of B was improved.

Next, the manufacturing method of this embodiment will be described with reference to FIG.
(A)-(d), FIG. 4 (a)-(c) and FIG. 5 (a).
This will be described with reference to (c). First, as shown in FIG. 3A, boron is ion-implanted into the surface of the n-type silicon substrate 101, and then heat treatment at high temperature (about 1200 ° C.) is performed to form the first p-type well layer 102. Next, FIG.
As shown in (b), ions of p-type impurities and n-type impurities are implanted using a photoresist as a mask to form the second p-type well layer 103 and the n-type region 1 to be the charge transfer region of the charge transfer portion.
To form 04. Next, ion implantation of n-type impurities is performed using the photoresist as a mask to perform n-type region 10 of the photoelectric conversion portion.
5 is formed.

Subsequently, as shown in FIG. 3C, a silicon oxide film 106 is formed to a thickness of 200 to 700 Å by a thermal oxidation method, and a silicon nitride film 1 is formed thereon by a CVD method.
07 is grown to a film thickness of 50 to 300Å, and the first CVD oxide film 108 is grown to a film thickness of 50 to 300Å by the CVD method to form a first gate insulating film. Next, as shown in FIG. 3D, after forming a first polycrystalline silicon film by a CVD method, this is patterned into a predetermined shape by a dry method to form a first charge transfer electrode 109. After that, the photoresist and the first charge transfer electrode 109
P-type impurities are ion-implanted using the mask as a mask
A shallow p-type region 110 is formed on the surface of the mold region 105 to make this region an embedded type.

Next, the first CVD oxide film 108 is removed by a wet method using the first charge transfer electrode 109 as a mask. Thereafter, as shown in FIG. 4A, a second CVD oxide film 111 is formed to a thickness of 50 to 300 Å by the CVD method, and the silicon oxide film 106, the silicon nitride film 107, and the second CVD oxide film are formed. A second gate insulating film is formed with a stacked body of 111. Next, as shown in FIG. 4B, thermal oxidation is performed using the silicon nitride film 107 as a mask to form a first film having a film thickness of 2000 to 4000 Å on the surface of the first charge transfer electrode 109.
The interlayer insulating film 112 is formed. Subsequently, as shown in FIG. 4C, a second polycrystalline silicon film is deposited by a CVD method and patterned into a predetermined shape by a photolithography method to form a second charge transfer electrode 113.

Next, the second CVD oxide film 111 is removed by a wet method using the second charge transfer electrode 113 as a mask. Then, as shown in FIG. 5A, a third CVD oxide film 114 is formed to a thickness of 50 to 300 Å by a CVD method, and the third CVD oxide film 114 is formed on the silicon substrate not covered with the first and second charge transfer electrodes. Silicon oxide film 106 and silicon nitride film 107
Then, an insulating film made of a laminated body of the third CVD oxide film 114 is formed. Next, as shown in FIG. 5B, thermal oxidation is performed using the silicon nitride film 107 as a mask to form a second interlayer insulating film 115 having a film thickness of 2000 to 4000 Å on the surface of the second charge transfer electrode 113. . Subsequently, as shown in FIG. 5C, a light-shielding film 116 is formed by depositing tungsten by a sputtering method and patterning it into a predetermined shape. At this time, the exposed third CVD oxide film 114 and silicon nitride film 107 are removed if necessary.

The preferred embodiment has been described above.
The present invention is not limited to the above-mentioned embodiments, and various modifications can be made within the scope of the present invention described in the claims. For example, in the embodiment, the silicon nitride film is used as the gate insulating film, but it is not always necessary to use the nitride film, as long as the insulating film is selective to the silicon oxide film and has an etching selectivity and a masking property against thermal oxidation. It can be replaced with a nitride film. Further, the formation of the third CVD oxide film 114 can be omitted. Thereby, the distance between the silicon substrate and the light shielding film can be further shortened. Further, in the embodiment, the charge transfer electrode is formed by the two-layer polycrystalline silicon film, but the present invention is also applied to the case where the charge transfer electrode is formed by using the one-layer or three-layer polycrystalline silicon film. It is possible. Further, the light shielding film can be formed using another metal material such as aluminum.

[0015]

As described above, in the solid-state image pickup device of the present invention, the interlayer insulating film is not formed under the light shielding film that covers the partial area of the photoelectric conversion portion, and the solid-state image sensor does not interfere with the silicon substrate. Since the distance between the films is at most about that of the gate insulating film, according to the present invention, it is possible to sufficiently suppress the light component that enters obliquely from the end of the light shielding film and enters the charge transfer region and its vicinity. You can Therefore, according to the present invention, smear caused by photoelectric conversion charges generated outside the photoelectric conversion unit can be suppressed to a low level.

Further, according to the present invention, the end portion of the charge transfer charge does not warp during the thermal oxidation of the charge transfer electrode (polycrystalline silicon film), and the unevenness of the substrate surface is alleviated.
Inconveniences such as generation of etching residue are avoided. Further, since the first interlayer insulating film on the first charge transfer electrode is a film formed independently of the step of forming the second gate insulating film, it becomes possible to form the first interlayer insulating film with a sufficient film thickness. ,
The breakdown voltage between the first and second charge transfer electrodes can be improved.

[Brief description of drawings]

FIG. 1 is a plan view and a sectional view of an embodiment of the present invention.

FIG. 2 is a characteristic diagram for explaining the effect of one embodiment of the present invention.

FIG. 3 is a part of a process cross-sectional view for explaining the manufacturing method according to the embodiment of the present invention.

FIG. 4 is a part of a process cross-sectional view for explaining the manufacturing method according to the embodiment of the present invention.

FIG. 5 is a part of a process cross-sectional view for explaining the manufacturing method according to the embodiment of the present invention.

FIG. 6 is a part of a process cross-sectional view for explaining a conventional manufacturing method.

FIG. 7 is a part of a process cross-sectional view for explaining a manufacturing method of a conventional example.

[Explanation of symbols]

 101, 201 n-type silicon substrate 102, 202 first p-type well layer 103, 203 second p-type well layer 104, 204 n-type region 105, 205 forming a charge transfer region n-type forming a photoelectric conversion unit Regions 106 and 206 Silicon oxide film 107 Silicon nitride film 108 First CVD oxide film 109 and 209 First charge transfer electrode 110 and 210 p-type region 111 Second CVD oxide film 112 and 212 First interlayer insulating film 113 2 charge transfer electrode 114 third CVD oxide film 115, 215 second interlayer insulating film 116, 216 light shielding film

Claims (5)

[Claims] 1. A semiconductor substrate is provided with a photoelectric conversion part array including a plurality of photoelectric conversion parts and a charge transfer region of a charge transfer part for transferring signal charges of the photoelectric conversion part array in a surface region of a semiconductor substrate. In a solid-state imaging device in which a charge transfer electrode of the photoelectric conversion unit and a light shielding film that covers the charge transfer electrode and a portion of the photoelectric conversion unit are formed on a substrate, the light shielding of the portion that covers the photoelectric conversion unit. A solid-state imaging device, wherein an insulating film having a film thickness equal to or less than that of a gate insulating film is interposed between the film and the semiconductor substrate. 2. The gate insulating film and the insulating film interposed between the light shielding film and the semiconductor substrate are a silicon oxide film and an insulating film having a different etching property from the silicon oxide film and having a masking action against thermal oxidation. The solid-state imaging device according to claim 1, wherein the solid-state imaging device is a laminated body including. 3. The gate insulating film and the insulating film interposed between the light shielding film and the semiconductor substrate are a laminate of a silicon oxide film, a silicon nitride film and a silicon oxide film. Solid-state image sensor. 4. A photoelectric conversion section array comprising a plurality of photoelectric conversion sections in a surface region of a semiconductor substrate, and a charge of a charge transfer section arranged in the photoelectric conversion section array for transferring signal charges of the photoelectric conversion section array. A step of forming a transfer region, a step of forming a gate insulating film made of a silicon oxide film, an oxidation resistant film and a silicon oxide film on a semiconductor substrate, and a first layer charge transfer electrode covering the charge transfer region. And a step of forming
Forming the first interlayer insulating film only on the charge transfer electrode of the layer, forming the second charge transfer electrode on the charge transfer region, and only forming the electrode transfer electrode of the second layer A step of forming a second interlayer insulating film, and a step of forming a light shielding film that covers the charge transfer electrodes of the first layer and the second layer and partially covers the photoelectric conversion unit. And a method for manufacturing a solid-state image sensor. 5. The charge transfer electrodes of the first layer and the second layer are formed of a polycrystalline silicon film, and the first and second charge transfer electrodes are formed.
5. The method for manufacturing a solid-state image sensor according to claim 4, wherein the step of forming the interlayer insulating film is the step of thermally oxidizing the charge transfer electrodes of the first layer and the second layer.