JP2001291857A - Method for manufacturing slid-state image pickup element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of any white spot by suppressing any damage on a light receiving part 3 or the intrusion of any foreign matter into the lower part of the light receiving part 3, due to ashing for removing a photo- resist film 40 used as a mask at the time of impurity ion implantation for forming a source 32 and a drain 33 of a MOS transistor constituting an output part 30, in a CCD solid-state image pickup element in which a reflection preventing film 12 is formed on the light receiving part 3 so that sensitivity can be improved. SOLUTION: A process to form a reflection preventing film 12 on a semiconductor substrate 1 on which a silicon oxide film 7-1 covering the whole surface, a transfer electrode 8, and a silicon oxide film 7-2 coating the transfer electrode 8 are formed is operated prior to the process to form a source 32 and a drain 33 of an output transistor constituting an output part 30 by ion implantation. Also, after the whole surface formation of a reflection preventing member film 12a, the ion implantation can be performed before the formation of the reflection preventing film 12 by selective etching.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup area in which at least a plurality of photoelectric conversion units are arranged on a surface of a semiconductor substrate, and a plurality of MOS transistors, wherein the photoelectric conversion unit photoelectrically converts incident light. The present invention relates to a method for manufacturing a solid-state imaging device having at least an output unit for converting signal charges into a voltage, and including an antireflection film covering a light receiving unit on each of the photoelectric conversion units.

[0002]

2. Description of the Related Art Conventionally, a solid-state image pickup device such as a CCD generally has a photoelectric conversion unit for converting incident light into signal charges, a read gate for reading the converted signal charges, and a readout on a surface of a semiconductor substrate. A vertical transfer unit for transferring the transferred signal charges in the vertical direction, a horizontal transfer unit for transferring the signal charges transferred in the vertical direction in the horizontal direction, and converting the signal charges transferred in the horizontal direction to a voltage for output. And an output section composed of a MOS transistor. On the surface of the semiconductor substrate, a vertical transfer electrode for driving the vertical transfer section and a horizontal transfer electrode for driving the horizontal transfer section are formed. Above is formed a light-receiving part that allows light to enter there,
Other parts are shielded from light. As a specific light shielding means, a light shielding film made of a metal such as aluminum Al or tungsten W and selectively etched is provided.

Various proposals have been made for this type of solid-state imaging device in, for example, Japanese Patent Application Laid-Open No. Hei 10-256518 in order to improve sensitivity characteristics and maintain sensitivity characteristics accompanying a reduction in pixel size. For example, in the solid-state imaging device described in the publication, an antireflection film made of, for example, silicon nitride SiN is formed on the light receiving portion to suppress the reflection of light there, and more light is incident on the light receiving portion. The light is incident on the conversion unit.

In such a solid-state imaging device, the anti-reflection film is formed of, for example, silicon nitride (SiN) after the step of forming the source and drain of the MOS transistor forming the output section by the selective ion implantation step. The anti-reflective material film made of SiN) is formed entirely by selective etching for patterning the film.

[0005]

In the conventional method of manufacturing a solid-state imaging device, a mask is used for selectively implanting impurity ions for forming a source and a drain of a MOS transistor constituting an output section. Ashing for the removal of the resist film may damage the light-receiving part and the photoelectric conversion part under it, or the resist film may not be sufficiently stripped, and the material in the photoresist remaining on the light-receiving part may be subjected to a subsequent heat treatment. In some cases, it was diffused into the photoelectric conversion section below the light receiving section in the process.

That is, when forming the source and drain of a MOS transistor, the dose of impurities is usually 1E1.
Since it is as high as 4-1E15 cm ^-2 , the resist film to be selectively masked is hardened by receiving the impurity ions.
Therefore, in order to remove the resist, it is necessary to remove the resist by a chemical solution after a certain degree of removal by ashing.
The ashing causes damage to the light receiving portion and the photoelectric conversion portion thereunder, or foreign matter is mixed in. As a result, white spots are generated and the yield is reduced. .

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and a light reception by ashing of a photoresist used as a mask at the time of ion implantation of impurities forming a source and a drain of a MOS transistor forming an output portion. It is an object of the present invention to effectively prevent the occurrence of white spots by reducing damage to the photoelectric conversion unit below the unit and the light receiving unit and to reduce the intrusion of foreign matter, and to improve the yield of solid-state imaging devices.

[0008]

According to the present invention, there is provided a method for manufacturing a solid-state imaging device, which comprises the steps of: forming an anti-reflection material film for forming an anti-reflection film covering each light receiving portion; It is characterized in that the step of forming the anti-reflection film by the later selective etching is performed before the step of forming the source and drain of the MOS transistor constituting the output section.

Therefore, according to the method of manufacturing the solid-state imaging device of the present invention, the source and the drain of the MOS transistor forming the output section are formed by the anti-reflection film or the anti-reflection material film (which is selectively etched) covering at least each light receiving section. Ashing to remove the resist film used as a mask for selective ion implantation of impurities for forming the source and drain, and removal by a chemical solution. In this case, the anti-reflection film or the anti-reflection material film functions to protect the light receiving portion.
Accordingly, it is possible to effectively prevent the generation of white spots by reducing the damage to the light receiving unit and the photoelectric conversion unit below the light receiving unit due to the ashing, and to reduce the intrusion of foreign substances below the light receiving unit and the light receiving unit.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, basically, M
Before forming the source and drain of the OS transistor, an anti-reflection film or an anti-reflection material film is formed. After forming the anti-reflection material film over the entire surface, patterning of the anti-reflection material film is performed. To form an anti-reflection film and then implanting impurity ions to form the source and drain of the MOS transistor, and forming an anti-reflection material film over the entire surface and then implanting impurity ions to form M
There is a mode in which a source and a drain of an OS transistor are formed, and thereafter, an anti-reflection material film is patterned to form an anti-reflection film.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for manufacturing a solid-state imaging device according to the present invention will be described in detail with reference to the illustrated embodiments. Prior to description of the present embodiment, a solid-state imaging device manufactured according to the present embodiment will be described. FIG. 5 shows a CCD manufactured according to an embodiment of the present invention.
FIG. 6 is a schematic plan view of the solid-state imaging device, FIG. 6 is an enlarged plan view near the light receiving unit in FIG. 5, and FIG. 7 is a sectional view taken along line XX of FIG.

In FIG. 1, reference numeral 1 denotes a semiconductor substrate, 2 denotes a photoelectric conversion unit of each pixel, and a light receiving unit 3 which is an opening located thereon.
Photoelectrically converts the light incident through the light source. The photoelectric conversion unit 2
Are arranged vertically and horizontally in a matrix,
A vertical transfer unit 6 is provided corresponding to each of the vertical columns. Reference numeral 4 denotes a reading unit (read gate) provided between each photoelectric conversion unit 2 and the vertical transfer unit 6, and signal charges generated by photoelectric conversion in the photoelectric conversion unit 2 are vertically transferred via the reading unit 4. The data is read out to the unit 6 and is transferred by the vertical transfer unit 6 in the vertical direction. Reference numeral 5 denotes a channel stop unit.

Reference numeral 20 denotes each of the light receiving units 3 and each of the vertical transfer units 6.
A horizontal transfer unit provided on the vertical transfer destination side of the rectangular area (imaging area) provided with receives the signal charge vertically transferred from each vertical transfer unit 6 and transfers it in the horizontal direction. 30
Is an output unit provided on the output end side of the horizontal transfer unit 20,
The signal charges horizontally transferred by the horizontal transfer unit 20 are converted into voltages and output.

Reference numeral 7-1 denotes a silicon oxide film made of SiO ₂ , which is formed entirely on the surface of the semiconductor substrate 1. Reference numeral 8 denotes a vertical transfer electrode formed of, for example, polysilicon on the silicon oxide film 7-1 and drives each of the vertical transfer units 6 to transfer. Although the vertical transfer electrodes 8 have two layers (or three layers), only one transfer electrode 8 is shown in the drawing. The vertical transfer electrodes 8 are formed so as to avoid over the respective photoelectric conversion units 2, and reference numeral 9 denotes the avoided portions, that is, transfer electrode openings.

Reference numeral 7-2 denotes a silicon oxide film formed on the silicon oxide film 7-1 made of SiO ₂ and the transfer electrode 8. The silicon oxide film 7-1 is integrated with the silicon oxide film 7-1 on the light receiving section 3. Make Reference numeral 10 denotes a light-shielding film formed on the silicon oxide film 7-2, for example, made of tungsten such as aluminum Al or W.
The opening formed in the light-receiving unit 3 forms the light receiving unit 3, and light from the subject enters the photoelectric conversion unit 2 through the light receiving unit 3.

Reference numeral 12 denotes an antireflection film made of, for example, silicon nitride (SiN), which is formed along the vertical transfer direction so as to cover each light receiving section 3. Reference numeral 13 denotes a protective film made of a BPSG film or the like formed over the entire surface of the antireflection film 12 and the light-shielding film 10, and 14 denotes a flattening film made of, for example, SiN.
Reference numeral 5 denotes a color filter formed on the flattening film 14;
Reference numeral 6 denotes an on-chip lens 16 formed on the color filter 15.

1 (A) to 1 (D) and 2 (E) to 2 (E).
(H) is a cross-sectional view showing a first example of the method of manufacturing the solid-state imaging device shown in FIGS. 5 to 7, that is, the first embodiment of the method of manufacturing the solid-state imaging device of the present invention in the order of steps. The part indicates the state near the light receiving unit 3, and the left part indicates the state of the output unit 30. When forming the light receiving unit 3 and the output unit 30 including the MOS transistor of the solid-state imaging device of the present embodiment, the prerequisite is that the impurity is diffused into the semiconductor substrate 1 first.
A p-type read gate 4, a p-type channel stop unit 5, an n-type vertical transfer unit 6, and the like are formed in advance.

(A) Next, as shown in FIG. 1A, the entire surface of the semiconductor substrate 1 is made of SiO
₂ is formed, an electrode material made of, for example, polysilicon is deposited on the silicon oxide film 7-1, and the electrode material is patterned to form the transfer electrode 8 and the gate electrode 31 of the MOS transistor. At the same time, the electrode material in a region other than the gate 31 of the output unit 30 is removed. Then, after forming an interlayer insulating film by thermal oxidation, a second-layer transfer electrode 8 not appearing in the drawing is formed,
Further, the entire surface including the gate 31 is coated with Si
An insulating film 7-2 such as an O ₂ film is formed.

(B) Next, as shown in FIG.
An anti-reflection material film 12a made of iN or the like is deposited on the entire surface. (C) Next, as shown in FIG.
A photoresist film 40 is selectively formed on 2a. Specifically, the resist film 40 is formed in the same pattern as the pattern in which the antireflection film 12 covering each light receiving section 3 is to be formed.

(D) Next, as shown in FIG. 1 (D), the anti-reflection film 12 is formed by etching the anti-reflection material film 12a using the photoresist film 40 as a mask. This antireflection film 12 covers each light receiving unit 3,
It plays a role of suppressing the reflection of light passing therethrough, thereby increasing the light receiving sensitivity, and serves as a protective film for preventing the generation of white spots below the light receiving portion 3 as described later.

(E) Next, as shown in FIG. 2E, the resist film 40 is removed by wet etching using a chemical solution or the like. Incidentally, since the resist film 40 is not hardened because the impurities are not ion-implanted, it is not necessary to remove the resist film 40 by ashing. Therefore, it can be sufficiently removed only by wet etching using a chemical solution. (F) Next, a resist film 41 is entirely formed, and thereafter, as shown in FIG.
Patterning is performed by photolithography so as to cover regions other than the region where the OS transistor is to be formed (that is, the gate, source and drain regions).

(G) Next, as shown in FIG. 2G, using the resist film 41 and the gate electrode 31 as a mask,
By implanting impurity ions 41 into the surface of the semiconductor substrate 1, the source 32 and the drain 33 are formed. In this case, the dose of the impurity ions is 1E14 to 1E1.
It needs to be as large as 5cm ^{- 2} .

(H) Next, as shown in FIG. 2H, the resist film 41 used as a mask in the previous step is unnecessary and is removed. This removal is performed because the resist film 41 is hardened by implanting a high dose of impurity ions 42 in the step (G).
After removing the resist pattern 41 to some extent, it is necessary to peel off the resist pattern 41 by wet etching using a chemical solution.

Incidentally, damage to the light receiving portion 3 of the semiconductor substrate 1 due to the ashing of the resist film 41 can be prevented by the antireflection film 12. Therefore, it is possible to prevent the antireflection film 12 from deteriorating characteristics such as generation of a white spot due to damage in the light receiving unit 3. Note that various processes continue thereafter, as described later. However, the intrusion of foreign matter into the light receiving unit 3 in each of these processes can be prevented by the antireflection film 12.

Thereafter, a light-shielding film 10 made of aluminum Al or tungsten W is deposited on the entire surface and selectively etched to form a light-shielding film opening. That is the light receiving unit 3. Next, a protective film 13 such as a BPSG film is deposited on the entire surface, the surface thereof is flattened by a flattening film 14 such as a SiN film, a color filter 15 is deposited, and an on-chip lens 16 is formed. The device manufacturing process ends.

According to the first embodiment, as described above, before forming the source 32 and the drain 33 in the ion implantation step (G), the antireflection film 12 is formed in the steps (B) to (F). Since the light receiving portion 3 is formed, damage to the light receiving portion 3 due to ashing and the semiconductor substrate 1 of the light receiving portion 3
Intrusion of foreign matter into the inside can be suppressed by the antireflection film 12. As a result, generation of white spots can be effectively prevented.

FIGS. 3A to 3D and FIGS. 4E to 4H.
9 is a sectional view showing another example of the method for manufacturing the solid-state imaging device shown in FIGS. 5 to 7, that is, a second embodiment of the method for manufacturing a solid-state imaging device of the present invention in the order of steps. The state in the vicinity is shown, and the right part shows the state of the output unit 30, respectively.
(A), (B) Steps (A), (B) of the second embodiment
Are the same as steps (A) and (B) in FIG.
An anti-reflective material film 12a is formed on the entire surface by the steps (A) and (B) of FIG. 3 similar to (A) and (B).

(C) Next, as shown in FIG. 3 (C), regions where the MOS transistors of the output section 30 are to be formed on the antireflection film 12a (specifically, the gate electrode 31 and the gate electrode 31).
A photoresist film 40 for masking a region other than the region where the source / drain is to be formed) is formed. (D) Next, as shown in FIG. 3 (D), impurities 42 are formed using the photorest film 40 and the gate electrode 31 as a mask.
Is implanted into the surface of the semiconductor substrate 1 so that the source 32 and the drain 33 of each MOS transistor are
To form

In the ion implantation of the impurity,
Since it is necessary to form the source and the drain, the dose of the impurity to be implanted needs to be as large as 1E14 to 1E15 cm ^{− 2} , so that a large amount of impurities are added to the resist film 40 serving as a mask.

(E) Next, as shown in FIG. 4E, the resist film 40 is peeled off. Since the resist film 40 to be stripped is hardened by the implantation of a high dose of impurity ions 42 in the step (D) shown in FIG. 1D, the resist film 40 is hardened to some extent by ashing, for example. After the removal, the resist film 40 is peeled off by wet etching using a chemical solution.

(F) Next, as shown in FIG. 4 (F), the antireflection film (1) of the light receiving section 3 is formed on the antireflection material film 12a.
A resist film 41 having a pattern covering only a portion where 2) is to be formed is formed. (G) Next, as shown in FIG. 4 (G), the antireflection film 12a covering the light receiving section 3 is formed by etching the antireflection material film 12a using the resist film 41 as a mask.

(H) Next, as shown in FIG. 4H, the resist film 41 is peeled off by wet etching using a chemical solution or the like. Thereafter, as in the case of the first embodiment, the light shielding film 10, the opening 2, the protective film 13, and the planarizing film 1 are formed.
4. If the color filter 15 and the on-chip lens 16 are sequentially formed, the manufacturing process of the solid-state imaging device is completed.

In the second embodiment, step (B)
After forming the anti-reflective material film 12a over the entire surface, the source 32 and the drain 33 forming each MOS transistor of the output unit 30 are formed in steps (C) to (D).
Thereafter, in steps (E) to (H), the anti-reflection material film 12 is formed.
a, and the source 32 and the drain 33 are formed in a state where the surface of the substrate 1 is entirely covered with the anti-reflection material film 12a, so that the impurities forming the source 32 and the drain 33 are formed. The light receiving portion 3 is prevented from being damaged by ashing for removing the photoresist film 40 used as a mask at the time of ion implantation by the anti-reflective material film 12a, and furthermore, the intrusion of foreign matter into the semiconductor substrate 1 is prevented. This can be prevented by the anti-reflection material film 12a, and the generation of white spots can be effectively prevented.

[0034]

According to the method of manufacturing a solid-state imaging device according to the first aspect, the source of the MOS transistor constituting the output section,
Since the drain can be formed in a state where the antireflection film covering each light receiving portion is formed, ion implantation of impurities using the patterned resist film for forming the source and the drain as a mask and the formation of the resist film are performed. The anti-reflection film functions to protect the light receiving portion during ashing and removal with a chemical solution.

Therefore, it is possible to effectively prevent the occurrence of white spots by reducing the damage to the light receiving portion due to the ashing and to reduce the intrusion of foreign matter into the light receiving portion, thereby improving the yield of the solid-state imaging device. Can be planned.

According to the method of manufacturing a solid-state image pickup device of the present invention, after forming an anti-reflection material film over the entire surface and performing selective etching to form an anti-reflection film covering the light-receiving portion, the output transistor of the output transistor is subjected to ion implantation. Since the source and the drain are formed, ashing for removing the resist film forming the mask for forming the source and the drain can be performed in a state protected by the antireflection film. Therefore, it is possible to prevent the light receiving portion from being damaged by the ashing and to prevent foreign matter from entering under the light receiving portion, and to effectively prevent the generation of white spots.

According to the method of manufacturing a solid-state imaging device of the third aspect, after the antireflection material film is deposited on the entire surface, the source and drain of the MOS transistor forming the output section are formed by ion implantation. Ashing for removing the resist film serving as the source and drain forming mask can be performed while the surface of the semiconductor substrate is protected by the prevention material film. Therefore, it is possible to prevent the light receiving portion from being damaged by the ashing and to prevent foreign matter from entering under the light receiving portion, and to effectively prevent the generation of white spots.

[Brief description of the drawings]

FIGS. 1A to 1D are cross-sectional views sequentially showing steps (A) to (D) of a first embodiment of a method for manufacturing a solid-state imaging device according to the present invention, and the right part shows the vicinity of a light receiving unit. , The left part indicates an output unit.

FIGS. 2 (E) to 2 (H) are cross-sectional views sequentially showing steps (E) to (H) of a first embodiment of a method for manufacturing a solid-state imaging device according to the present invention, and the right part shows the vicinity of a light receiving unit. , The left part indicates an output unit.

FIGS. 3A to 3D are cross-sectional views sequentially showing steps (A) to (D) of a second embodiment of the method for manufacturing a solid-state imaging device according to the present invention, and the right part shows the vicinity of a light receiving unit. , The left part indicates an output unit.

4 (E) to 4 (H) are cross-sectional views sequentially showing steps (E) to (H) of a second embodiment of the method for manufacturing a solid-state imaging device according to the present invention, and the right part shows the vicinity of a light receiving unit. , The left part indicates an output unit.

FIG. 5 is a schematic plan view of a solid-state imaging device manufactured in an example of the present invention.

FIG. 6 is an enlarged plan view showing the vicinity of a light receiving unit in FIG. 5;

FIG. 7 is a sectional view taken along line XX of FIG. 6;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor substrate, 2 ... Photoelectric conversion part, 3 ... Light receiving part, 4 ... Read-out part (read-out gate), 6 ...
・ Vertical transfer section, 7-1, 7-2 ... insulating film, 8 ...
Transfer electrode, 10: light shielding film, 12: anti-reflection film,
12a: anti-reflection material film, 30: output unit.

Claims (3)

[Claims] 1. An image pickup area having at least a plurality of photoelectric conversion units disposed on a surface of a semiconductor substrate, and a plurality of MOS transistors, wherein the photoelectric conversion unit converts signal charges photoelectrically converted from incident light into a voltage into a voltage. A method of manufacturing a solid-state imaging device having an antireflection film that covers at least a light-receiving unit on each of the photoelectric conversion units, wherein an entire surface of the antireflection material film is formed to form the antireflection film. The source or drain of the MOS transistor is formed by ion-implanting impurities using the selectively formed resist film as a mask in a formation step or a selective etching step for the antireflection material film after the entire formation step. A method of manufacturing a solid-state imaging device, which is performed prior to the step of performing the following. 2. A step of forming an anti-reflective material film on the surface of the semiconductor substrate on which the light-receiving portion is formed, and reflecting the anti-reflective material film by etching the anti-reflective material film while leaving a portion covering the light-receiving portion. Forming an anti-reflection film; and ion-implanting impurities into the surface of the semiconductor substrate using a resist film selectively formed on the surface of the semiconductor substrate on which the anti-reflection film is formed as a mask.
2. The method according to claim 1, wherein the steps of: forming a source and a drain of the S transistor; 3. A step of forming an anti-reflective material film on the surface of the semiconductor substrate on which the light-receiving portion is formed, and masking the resist film with a resist film selectively formed on the anti-reflective material film. Forming a source and a drain of the MOS transistor by ion-implanting an impurity into the surface of the semiconductor substrate through the anti-reflection film, and leaving the portion of the anti-reflection material film covering the light-receiving portion. 2. The method according to claim 1, wherein the steps of: forming the antireflection film by etching are sequentially performed.