JP2006210484A - Method of manufacturing solid state imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a low smear characteristic in a solid state imaging apparatus using tungsten in a shielding film. <P>SOLUTION: Tungsten is deposited on a semiconductor substrate 1 as the shielding film 14, and a silicon oxide film is deposited as a transparent protection film 16. Since a light reception opening on which light is made incident is formed in a photodiode 2, a resist pattern 15 is formed by a photo resist method (refer to Fig. (b)). The transparent protection film 16 and the shielding film 14 on the semiconductor substrate 1 are simultaneously etched with the resist pattern 15 as a mask as first etching. The resist pattern 15 is removed and a desired light reception opening is formed in an image pickup region (refer to Fig. (c)). A tungsten residue 17 which occurs in a peripheral region is removed by wet etching as a second etching processing (refer to Fig. (d)). The solid state image pickup device is manufactured where tungsten is used for the shielding film 14. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a solid-state imaging device that achieves low smear characteristics while using tungsten for a light shielding film.

  In recent years, with the increase in the number of pixels and the high integration of solid-state imaging devices, device structures using tungsten, which is a refractory metal from aluminum, have been proposed as a light shielding film.

  Hereinafter, a method for manufacturing a solid-state imaging device using tungsten disclosed in Patent Document 1 as a light shielding film will be described with reference to FIGS.

  First, as shown in FIG. 2A, a semiconductor substrate 1 is formed with a photodiode 2 composed of a combination of a shallow p-type and a deep n-type. A p-type readout layer 4 is formed on one side of the photodiode 2, and a p-type barrier layer 5 is formed on the other side. Further, on the side of the readout layer 4, there is a charge transfer unit 6 composed of a combination of n-type and p-type, and reads out the charges accumulated in the photodiode 2.

  In addition, a transfer electrode 8 is formed above the charge transfer portion 6 via a gate insulating film 7 in order to apply a voltage necessary to transfer this charge. The gate insulating film 7 uses a MONOS (Metal Oxide Nitride Oxide Semiconductor) structure composed of three layers of a first silicon oxide film 9, a silicon nitride film 10, and a second silicon oxide film 11.

  Further, a silicon oxide film as an interlayer insulating film 12 is formed on the transfer electrode 8, the readout layer 4, the photodiode 2, and the barrier layer 5.

  Next, as shown in FIG. 2B, after forming a light shielding film 14 on the semiconductor substrate 1, a resist pattern 15 is formed by a photoresist method in order to form a light receiving opening through which light enters the photodiode 2. Is formed. Further, as shown in FIG. 2C, the light shielding film 14 is etched using the resist pattern 15 as a mask.

As an apparatus for performing etching, a microwave ECR (Electron Cyclotron Resonance) etcher is used. The etching gas is a mixed gas having a ratio of SF ₆ (sulfur hexafluoride): Cl ₂ (chlorine): Ar (argon): N ₂ (nitrogen) = 2: 2: 14: 1, and the etching pressure is The power is 2.0 Pa, the microwave excitation power is 1100 W, the RF excitation power is 45 W, and the lower electrode temperature is 0 ° C.

Through the above steps, a solid-state imaging device using tungsten as a light shielding film is formed.
JP 2003-234467 A

  However, drive wiring is formed around the imaging region where the photodiode and the transfer electrode are formed in the solid-state imaging device formed as described above for controlling the input / output circuit and the transfer electrode. This peripheral region is removed after forming tungsten as a light shielding film once. Further, in order to remove tungsten on the peripheral region, a long-time etching process is required, and the interlayer insulating film on the photodiode is also etched by this process.

  For this reason, the interlayer insulating film needs to have a film thickness that is a sum of a thickness necessary for driving withstand voltage and a thickness removed by etching. However, increasing the thickness of the interlayer insulating film has a problem that light is likely to enter from the interlayer insulating film and smear characteristics are deteriorated.

  An object of the present invention is to provide a method for manufacturing a solid-state imaging device that achieves low smear characteristics in a solid-state imaging device using tungsten as a light-shielding film. To do.

  In order to achieve the above object, a method of manufacturing a solid-state imaging device according to the present invention includes a step of forming a plurality of photodiodes on a semiconductor substrate, a transfer electrode between the photodiodes, and a photodiode on the semiconductor substrate. A step of forming a drive wiring in a peripheral region around the imaging region where the transfer electrode is formed, a step of forming an insulating film on the photodiode, the transfer electrode, and the drive wiring; and a refractory metal on the insulating film. Forming a light shielding film, forming a transparent protective film on the light shielding film, forming a resist pattern on the transparent protective film in the imaging region, and using the resist pattern as a mask by the first etching process A step of removing the light shielding film and the transparent protective film on a part of the photodiode and on the drive wiring, and light shielding of the peripheral region by the second etching process And a step of removing the residue, the second etching process, and carrying out while protecting the transparent protective layer shielding film of the image area.

  The refractory metal is tungsten, the transparent protective film is an oxide film, the second etching process is wet etching, and hydrogen peroxide is used as an etching solution.

  According to the above manufacturing method, the second etching process can suppress the tungsten residue in the peripheral region while maintaining the uniformity of the shape of the light receiving opening in the imaging region, and can obtain the driving breakdown voltage for the interlayer insulating film. It can be thinned to a thickness.

  According to the present invention, it is possible to obtain low smear characteristics by suppressing tungsten residues while maintaining the uniformity of the shape of the light receiving opening and reducing the thickness of the interlayer insulating film to the minimum film thickness that can provide a driving breakdown voltage. There is an effect.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  1A to 1D show steps of a method for manufacturing a solid-state imaging device according to an embodiment of the present invention. Here, components having substantially the same functions corresponding to the components described in FIGS. 2A to 2C showing the conventional example are denoted by the same reference numerals.

  Embodiments of the present invention will be described below with reference to FIGS. 1 (a) to 1 (d). First, as shown in FIG. 1A, a photodiode 2 composed of a combination of a shallow p-type and a deep n-type is formed in the imaging region of the semiconductor substrate 1. A p-type readout layer 4 is formed on one side of the photodiode 2 and a p-type barrier layer 5 is formed on the other side. Further, a charge transfer unit 6 composed of a combination of n-type and p-type is formed on the side of the readout layer 4 to read out the charge accumulated in the photodiode 2.

  In addition, a transfer electrode 8 is formed on the charge transfer portion 6 via a gate insulating film 7 in order to apply a voltage necessary for transferring the charge. The gate insulating film 7 uses a MONOS (Metal Oxide Nitride Oxide Semiconductor) structure composed of three layers of a first silicon oxide film 9, a silicon nitride film 10, and a second silicon oxide film 11.

  Further, a silicon oxide film as an interlayer insulating film 12 is formed on the transfer electrode 8, the readout layer 4, the photodiode 2, and the barrier layer 5 to a thickness of 30 nm.

  Note that the film thickness of the interlayer insulating film 12 is thinner than that of the conventional structure, and is thinned to such a film thickness that a breakdown voltage can be obtained with respect to the drive voltage.

  On the other hand, in the peripheral region of the semiconductor substrate 1, the second silicon oxide film 11, the first polycrystalline silicon 13 a and the second polycrystalline silicon 13 b that are drive wirings, and the interlayer insulating film 12 are formed on the semiconductor substrate 1. Form.

  Next, as shown in FIG. 1B, after a tungsten film is formed as a light shielding film 14 on the semiconductor substrate 1 to a thickness of about 40 nm, a silicon oxide film is formed as a transparent protective film 16 to a thickness of about 20 nm. Form a film. Tungsten can be formed as a thin film because it has better light shielding properties than aluminum.

  Thereafter, a resist pattern 15 is formed by a photoresist method in order to form a light receiving opening through which light enters the photodiode 2 in the imaging region. At this time, the light shielding film 14 and the transparent protective film 16 are formed in the peripheral region, and the resist pattern 15 is not formed.

  Next, as a first etching process, the transparent protective film 16 and the light shielding film 14 are etched using the resist pattern 15 as a mask. Thereafter, the resist pattern 15 is removed to form a desired light receiving opening in the imaging region. Further, the transparent protective film 16 and the light shielding film 14 are etched also in the peripheral region.

Etching is performed by a microwave ECR (Electron Cyclotron Resonance) etcher, and an etching gas is a mixed gas having a ratio of SF ₆ : Cl ₂ : Ar: N ₂ = 2: 2: 14: 1.

  Further, as specific etching conditions, the etching pressure is 2.0 Pa, the microwave excitation power is 1100 W, the RF excitation power is 45 W, and the lower electrode temperature is 0 ° C. However, if the over-etching is increased to remove the light shielding film 14 in the peripheral region, the interlayer insulating film 12 above the photodiode 2 is etched to damage the photodiode 2. Therefore, it is preferable that overetching be as short as possible, and overetching is not performed in this embodiment.

  Next, as shown in FIG. 1C, wet etching is performed as a second etching process in order to remove the tungsten residue 17 of the light shielding film 14 formed in the peripheral region after the first etching process.

As specific etching conditions, hydrogen peroxide (H ₂ O ₂ ) is used as an etchant, the temperature of the etchant is 50 to 80 ° C., and the treatment time is 10 to 20 seconds. Further, the etching rate to the transparent protective film 16 and the interlayer insulating film 12 is 1/10 or less of the etching rate of tungsten. In the case of the wet etching of the present embodiment, the transparent protective film 16 and the interlayer insulating film 12 are Not etched. Thereby, side etching to tungsten can be prevented, and the uniformity of the light receiving opening can be maintained (see FIG. 1D).

  From the above steps, the solid-state imaging device is manufactured by the manufacturing method according to the present embodiment.

  In the prior art, the etching to the light shielding film 14 simultaneously forms the light receiving opening in the imaging region and prevents the generation of the tungsten residue 17 in the peripheral region. For this reason, in order to prevent the generation of the tungsten residue 17, it is necessary to perform overetching for a long time in addition to the main etching for forming the light receiving opening as the etching time.

  However, if overetching is performed for a long time, the interlayer insulating film 12 on the photodiode 2 is also etched, resulting in a thin film thickness and surface roughness. Therefore, the interlayer insulating film 12 used in the conventional technique needs to have a film thickness that is the sum of the thickness necessary for the driving breakdown voltage and the thickness removed by etching. Further, since the thick interlayer insulating film 12 is formed on the photodiode 2, there is a problem that the smear characteristic is deteriorated due to the incident light from the interlayer insulating film 12 and the stray light reaching the charge transfer unit 6. It occurred.

  However, in this embodiment, since the interlayer insulating film 12 can be thinned to the minimum film thickness that can provide a driving breakdown voltage, low smear characteristics can be obtained.

  Further, in the prior art, over-etching is performed at the time of etching to tungsten in order to remove residues in the peripheral region. At this time, the tungsten formed in the imaging region is a resist pattern, and since this pattern is an organic material, a shape change is inevitable.

  Therefore, side etching occurs in tungsten forming the light receiving opening, and there is a problem that the shape uniformity of the light receiving opening is deteriorated.

  However, in this embodiment, in the second etching process for removing the residue, the tungsten formed in the imaging region is the transparent protective film 16 made of the same material as that of the interlayer insulating film 12. The shape of the film 16 does not change.

Therefore, the transparent protective film 16 protects the light shielding film 14 in the imaging region,
In order to prevent side etching to tungsten, the uniformity of the light receiving opening can be maintained.

  Therefore, as compared with the prior art, by reducing the tungsten residue 17 while maintaining the shape uniformity of the light receiving opening, and by reducing the thickness of the interlayer insulating film 12 to the minimum film thickness that can obtain the driving breakdown voltage, the low smear characteristic is achieved. Obtainable.

  According to the present embodiment, the interlayer insulating film 12 has a thickness approximately half that of the conventional structure, and a low smear characteristic of −4 db can be obtained as compared with the conventional structure.

  In the present embodiment, the wet etching solution may be another solution that can obtain a selection ratio between the light shielding film 14 and the transparent protective film 16 and the interlayer insulating film 12. The transparent protective film 16 may be a film that transmits light and has a selectivity with respect to the wet etching solution, such as a silicon nitride film.

  The method for manufacturing a solid-state imaging device according to the present invention suppresses tungsten residues while maintaining the shape uniformity of the light receiving opening, and reduces the thickness of the interlayer insulating film to a minimum film thickness that can obtain a driving breakdown voltage, thereby providing low smear characteristics. This is useful for manufacturing a solid-state imaging device using tungsten as a light shielding film.

(A)-(d) is a fragmentary sectional view which shows the process of the manufacturing method of the solid-state imaging device in embodiment of this invention (A)-(c) is a fragmentary sectional view which shows the process of the manufacturing method of the conventional solid-state imaging device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Photodiode 4 Read-out layer 5 Barrier layer 6 Charge transfer part 7 Gate insulating film 8 Transfer electrode 9 First silicon oxide film 10 Silicon nitride film 11 Second silicon oxide film 12 Interlayer insulating film 13a Crystalline silicon 13b Second polycrystalline silicon 14 Light shielding film 15 Resist pattern 16 Transparent protective film 17 Tungsten residue

Claims (3)

Forming a plurality of photodiodes on a semiconductor substrate;
On the semiconductor substrate, a transfer electrode is formed between the photodiodes, and a drive wiring is formed in a peripheral region around the imaging region where the photodiode and the transfer electrode are formed;
Forming an insulating film on the photodiode, the transfer electrode, and the drive wiring; and
Forming a light-shielding film made of a refractory metal on the insulating film;
Forming a transparent protective film on the light shielding film;
Forming a resist pattern on the transparent protective film in the imaging region;
Removing a part of the photodiode and the light-shielding film and the transparent protective film on the drive wiring by using the resist pattern as a mask by a first etching process;
Removing the residue of the light shielding film in the peripheral region by a second etching process,
A method of manufacturing a solid-state imaging device, wherein the second etching process is performed while protecting the light-shielding film in the imaging region with the transparent protective film.   2. The method of manufacturing a solid-state imaging device according to claim 1, wherein the refractory metal is tungsten, and the transparent protective film is an oxide film.   3. The method for manufacturing a solid-state imaging device according to claim 1, wherein the second etching process is wet etching, and hydrogen peroxide is used as an etching solution.

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