JP2010045235A - Method for manufacturing charge coupled device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that a foundation insulating film is scraped away when removing by dry etching a barrier metal adhered to the side wall portion of a level difference by a transfer electrode. <P>SOLUTION: A method for manufacturing a CCD includes a process to form a first metal film 7 while covering an insulating film 6, after forming the insulating film 6 on a semiconductor substrate 1 while covering a transfer electrode 4, a process to form a barrier metal film 11 and a second metal film 12 by laminating in this sequence on the first metal film 7 while embedding a connection hole formed on the transfer electrode 4, a process to process the second metal film 12 by dry etching making a resist pattern 14 formed on the second metal film 12 as a mask, a process to process the barrier metal film 11 by dry etching making a resist pattern 14 as the mask and making the first metal film 7 as an etching stopper, and a process to process the first metal film 7 by dry etching making the resist pattern 14 as the mask. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a charge coupled device. Specifically, the present invention relates to a method of manufacturing a charge coupled device having a shunt wiring.

  In the field of charge-coupled devices (CCDs) and solid-state imaging devices using the same, in order to transfer signal charges generated by photoelectric conversion at high speed, transfer electrodes that transfer signal charges are transferred from the transfer electrodes. Also, a structure for connecting a shunt wiring having a low sheet resistance has been proposed (see Patent Document 1). For example, in the 1.55 μm CCD and 1.43 μm CCD currently being developed, the metal wiring is applied to the shunt wiring, thereby realizing a low resistance of the wiring and a low layer of the device.

  Tungsten is a promising material for shunt wiring in terms of ease of manufacture. However, when the transfer electrode is formed of polysilicon, a barrier metal film for preventing diffusion under the shunt wiring made of tungsten is used so that tungsten is not diffused into silicon when crystallizing by annealing. Need to form.

  4 and 5 are diagrams for explaining a conventional method of manufacturing a charge coupled device. First, as shown in FIG. 4A, after forming a gate insulating film 52 on a semiconductor substrate 51, a transfer electrode 54 is formed on the gate insulating film 52 using a hard mask 53. A portion of the semiconductor substrate 51 covered with the gate insulating film 52 between two adjacent transfer electrodes 54 becomes a sensor region S that performs photoelectric conversion in the configuration of the solid-state imaging device including the charge coupled device. Next, an oxide film 55 is formed on the entire surface (one surface) of the semiconductor substrate 51 so as to cover the hard mask 53 on the transfer electrode 54 and the gate insulating film 52 between the transfer electrodes 54.

  Next, as shown in FIG. 4B, after the oxide film 55 is etched by anisotropic dry etching, the gate insulating film 52 is thinned.

Next, as illustrated in FIG. 4C, an insulating film 56 is formed over the entire surface of the semiconductor substrate 51. The insulating film 56 is formed of a laminated film having an LP (Low Pressure) -SiN film as a lower layer film and an LP (Low Pressure) -TEOS film as an upper layer film. TEOS is an abbreviation for Si (OC ₂ H ₅ ) ₄ . Next, a resist pattern 58 having an opening 57 is formed by a photolithography technique, and then a connection hole 59 is formed by dry etching using the resist pattern 58 as a mask. At the site where the connection hole 59 is formed, the surface (upper surface) of the transfer electrode 54 is exposed. After the connection hole 59 is formed, the resist pattern 58 is removed.

  Next, as shown in FIG. 5A, a barrier metal film 61 and a metal film 62 are sequentially stacked on the insulating film 56 by a CVD method. As the barrier metal film 61, a laminated film of a titanium (Ti) film and a titanium nitride (TiN) film is formed. As the metal film 62, a tungsten film is formed.

  Next, as shown in FIG. 5B, a resist pattern 63 is formed on the metal film 62 by photolithography, and then the metal film 62 is processed by dry etching using the resist pattern 63 as a mask. Etching is performed under the following conditions using, for example, an ECR (Electron Cyclotron Resonance) etching apparatus.

[Main etching conditions]
Cl ₂ / SF ₆ / N ₂ / Ar = 100/20/20/100 sccm
Microwave power: 400W
Bias power: 30W
Processing pressure: 0.7Pa
Substrate temperature: 20 ° C

[Over-etching conditions]
SF ₆ = 100 sccm
Microwave power: 1000W
Bias power: 0W
Processing pressure: 1.0 Pa
Substrate temperature: 20 ° C

  In this case, in dry etching, main etching is performed first, and then over etching is performed. Since the bias power is applied under the main etching conditions, the metal film 62 is etched with anisotropy. Therefore, the metal film 62 adhering to the portion parallel to the substrate surface of the semiconductor substrate 51 and the shoulder portion of the step due to the transfer electrode 54 is mainly removed by main etching. On the other hand, since the bias power is not applied under the overetching condition, the metal film 62 is etched with isotropic properties. Therefore, the metal film 62 adhering to the side wall portion of the step due to the transfer electrode 54 is mainly removed by overetching.

  Next, as shown in FIG. 5C, the barrier metal film 61 is processed by anisotropic dry etching using the resist pattern 63 as a mask. Etching is performed under the following conditions using, for example, an ECR etching apparatus.

[Barrier metal (Ti / TiN) processing conditions]
Cl ₂ = 100 sccm
Microwave power: 800W
Bias power: 40W
Processing pressure: 0.5Pa
Substrate temperature: 20 ° C

  Thereafter, the resist pattern 63 is removed. As a result, a shunt wiring having a laminated structure of the barrier metal film 61 and the metal film 62 is formed on the transfer electrode 54 following the pattern shape of the resist pattern 63.

JP 2006-140411 A (paragraph 0006)

  In the method for manufacturing the charge coupled device described above, when the barrier metal film 61 is etched, it is necessary to remove the barrier metal film 61 attached to the side wall portion of the step due to the transfer electrode 54. In order to remove the barrier metal film 61 adhering to the side wall portion by anisotropic dry etching with bias power applied, it is necessary to perform over-etching for the film thickness corresponding to the step. For example, when the thickness of the transfer electrode 54 is 200 nm, a step is formed with a dimension larger than that, and it is necessary to perform overetching of about 300 nm. In such a case, the surface of the LP-TEOS film, which is the upper layer film of the underlying insulating film 56, and the SiN film, which is the lower layer film, are scraped off by over-etching particularly in a portion parallel to the substrate surface of the semiconductor substrate 51. There was a problem. The SiN film functions as an antireflection film for the sensor region S between the transfer electrodes 54. For this reason, when the SiN film is thinned, the function as an antireflection film is lowered. Further, when the SiN film is formed again in order to restore the function as the antireflection film, the SiN film is also formed on the side wall of the step portion. For this reason, the effective aperture size of the sensor region S is reduced (the aperture ratio is reduced), and another problem that the sensor sensitivity is deteriorated occurs.

  In the present invention, after removing the barrier metal film adhering to the side wall portion of the step due to the transfer electrode by dry etching, a sufficient film thickness of the insulating film can be left without forming the insulating film again. An object of the present invention is to provide a method for manufacturing a charge coupled device.

  The method of manufacturing a charge coupled device according to the present invention includes a step of forming a transfer electrode on a semiconductor substrate, a step of forming an insulating film on the semiconductor substrate so as to cover the transfer electrode, Forming a first metal film in a state of covering the insulating film; forming a connection hole on the transfer electrode in a state of penetrating the first metal film and the insulating film; and embedding the connection hole. A step of sequentially stacking and forming a barrier metal film and a second metal film on the first metal film in a state; a step of forming a resist pattern on the second metal film; and the resist pattern A step of processing the second metal film by dry etching using the mask as a mask, and dry etching the barrier metal film using the resist pattern as a mask and the first metal film as an etching stopper A step of further processing, the first metal film using the resist pattern as a mask is intended to include a step of processing by dry etching.

  In the method for manufacturing a charge coupled device according to the present invention, the first metal film is formed on the semiconductor substrate so as to cover the insulating film. Then, when the barrier metal film is processed by dry etching using the resist pattern formed on the second metal film as a mask, the first metal film functions as an etching stopper. Therefore, even when the barrier metal film adhering to the side wall portion of the step due to the transfer electrode is processed by anisotropic dry etching, the barrier metal film is securely protected while protecting the insulating film with the first metal film. It can be removed.

  According to the method of manufacturing a charge coupled device according to the present invention, the insulating film can be formed without removing the barrier metal film attached to the side wall portion of the step due to the transfer electrode by dry etching and then forming the insulating film again. A sufficient film thickness can be left. For this reason, even when the insulating film includes a film that functions as an antireflection film in the sensor region, the film thickness of the antireflection film can be maintained at a desired thickness without narrowing the sensor region.

  Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the technical scope of the present invention is not limited to the embodiments described below, and various modifications and improvements have been made within the scope of deriving specific effects obtained by the constituent requirements of the invention and combinations thereof. Including form.

1 to 3 are diagrams for explaining a method of manufacturing a charge coupled device according to an embodiment of the present invention. First, as shown in FIG. 1A, after forming a gate insulating film 2 on a semiconductor substrate 1, a transfer electrode 4 is formed on the gate insulating film 2 using a hard mask 3. The semiconductor substrate 1 is made of, for example, a silicon substrate. The gate insulating film 2 is made of, for example, a thermal oxide film (Th—SiO ₂ film) having a thickness of 40 nm. The hard mask 3 is made of LP-TEOS, for example. The transfer electrode 3 is made of, for example, polysilicon having a thickness of 200 nm. Next, an oxide film 5 is formed on the entire surface (one surface) of the semiconductor substrate 1 so as to cover the hard mask 3 on the transfer electrode 4 and the gate insulating film 2 between the transfer electrodes 4. The oxide film 5 is made of, for example, an LP-TEOS film having a thickness of 50 nm.

  Next, as shown in FIG. 1B, the gate insulating film 2 is thinned by anisotropic dry etching. In this thinning process, the gate insulating film 2 is thinned to about 15 nm, for example. At this time, by applying anisotropic dry etching, the hard mask 3 remains on the upper surface of the transfer electrode 4 without being completely etched, and the oxide film 5 remains on the side surface of the transfer electrode 4 without being etched. .

  Next, as shown in FIG. 1C, an insulating film is formed on the entire surface of the semiconductor substrate 51 so as to cover the hard mask 3 and the oxide film 5 around the transfer electrode 4 and the gate insulating film 2 between the transfer electrodes 4. 6 is formed. For example, the insulating film 6 is formed of a laminated film in which an LP-SiN film having a thickness of 60 nm is a lower layer film and an LP-TEOS film having a thickness of 50 nm is an upper layer film. Next, a first metal film 7 is formed on the entire surface of the semiconductor substrate 1 by sputtering, for example, so as to cover the insulating film 6. The first metal film 7 is made of a metal material having a high etching selectivity (preferably a metal material having an etching selectivity of 4 or more) with respect to both the insulating film 6 and the barrier metal film 11 described later. Form. Here, as an example, a tungsten film having a thickness of 50 nm is formed as the first metal film 7.

  Next, as shown in FIG. 2A, a resist pattern 9 having an opening 8 is formed on the first metal film 7 by photolithography, and then dry etching using the resist pattern 9 as a mask. Thus, the connection hole 10 is formed. The connection hole 10 is formed in a state of penetrating the first metal film 7, the insulating film 6 and the hard mask 3. For this reason, in the formation part of the connection hole 10, the surface (upper surface) of the transfer electrode 4 will be in the exposed state. After the connection hole 10 is formed, the resist pattern 9 is removed.

  Next, as shown in FIG. 2B, a barrier metal film 11 and a second metal film 12 are formed on the first metal film 7 in a state of being sequentially laminated by the CVD method. The barrier metal film 11 and the second metal film 12 are respectively formed on the entire surface of the semiconductor substrate 1. As the barrier metal film 11, a titanium film, a titanium nitride film, or a laminated film thereof is formed. However, the barrier metal film 11 may be formed of ruthenium (Ru), ruthenium oxide (RuO), ruthenium nitride (RuN), or a laminated film thereof. Further, as the second metal film 12, a tungsten film that is the same kind of metal film as the first metal film 7 is formed. The connection hole 10 connected to the transfer electrode 4 is filled with the barrier metal film 11 and the second metal film 12.

  Next, as shown in FIG. 3A, a resist pattern 14 is formed on the second metal film 12 by photolithography. The resist pattern 14 is formed corresponding to a desired shunt wiring pattern. Next, the second metal film 12 is processed by dry etching using the resist pattern 14 as a mask. Etching is performed under the following conditions using, for example, an ECR etching apparatus. As the etching gas, a fluorine-based gas is used.

[Main etching conditions]
Cl ₂ / SF ₆ / N ₂ / Ar = 100/20/20/100 sccm
Microwave power: 400W
Bias power: 30W
Processing pressure: 0.7Pa
Substrate temperature: 20 ° C

[Over-etching conditions]
SF ₆ = 100 sccm
Microwave power: 1000W
Bias power: 0W
Processing pressure: 1.0 Pa
Substrate temperature: 20 ° C

  In this case, in dry etching, main etching is performed first, and then over etching is performed. Since the bias power is applied under the main etching conditions, the second metal film 12 is etched with anisotropy. For this reason, the second metal film 12 adhering to the portion parallel to the substrate surface of the semiconductor substrate 1 or the shoulder portion of the step due to the transfer electrode 4 is mainly removed by main etching. In contrast, since the bias power is not applied under the overetching condition, the second metal film 12 is etched with isotropic properties. Therefore, the second metal film 12 adhering to the side wall portion of the step due to the transfer electrode 4 is mainly removed by overetching.

  Next, as shown in FIG. 3B, the barrier metal film 11 is processed by anisotropic dry etching using the resist pattern 14 as a mask. Etching is performed under the following conditions using, for example, an ECR etching apparatus. As the etching gas, a chlorine-based gas is used.

[Barrier metal (Ti / TiN) processing conditions]
Cl ₂ = 100 sccm
Microwave power: 800W
Bias power: 40W
Processing pressure: 0.5Pa
Substrate temperature: 20 ° C

  Here, a chlorine-based gas is used as an etching gas. For this reason, in the etching of the barrier metal film 11, tungsten constituting the underlying first metal film 7 generates WClx by a chemical reaction with the etching gas, so that the etching does not proceed from there. Accordingly, the progress of etching stops on the surface of the first metal film 7. That is, when the barrier metal film 11 is etched, the first metal film 7 functions as an etching stopper. Note that in the case where ruthenium (Ru), ruthenium oxide (RuO), ruthenium nitride (RuN), or a stacked film thereof is formed as the barrier metal film 11, a chlorine-oxygen-based gas is used as an etching gas.

  Next, as shown in FIG. 3C, the first metal film 7 is processed by dry etching using the resist pattern 14 as a mask. Etching is performed under the following conditions using, for example, an ECR etching apparatus. As the etching gas, a fluorine-based gas is used.

[Main etching conditions]
Cl ₂ / SF ₆ / N ₂ / Ar = 100/20/20/100 sccm
Microwave power: 400W
Bias power: 30W
Processing pressure: 0.7Pa
Substrate temperature: 20 ° C

[Over-etching conditions]
SF ₆ = 100 sccm
Microwave power: 1000W
Bias power: 0W
Processing pressure: 1.0 Pa
Substrate temperature: 20 ° C

  In this case, in dry etching, main etching is performed first, and then over etching is performed. Since the bias power is applied under the main etching conditions, the first metal film 7 is etched with anisotropy. Therefore, the first metal film 7 adhering to the portion parallel to the substrate surface of the semiconductor substrate 1 and the shoulder portion of the step due to the transfer electrode 4 is mainly removed by main etching. On the other hand, since the bias power is not applied under the overetching condition, the first metal film 7 is etched with isotropic properties. Therefore, the first metal film 7 adhering to the side wall portion of the step due to the transfer electrode 4 is mainly removed by overetching. Further, since the underlying insulating film 6 is not biased under overetching conditions, its surface (upper layer film) can be cut only about several nm. Therefore, the thickness of the SiN film constituting the lower layer film of the insulating film 6 is maintained as it is.

  Thereafter, the resist pattern 14 is removed. As a result, a shunt wiring having a laminated structure of the barrier metal film 11 and the second metal film 12 is formed on the transfer electrode 4 following the pattern shape of the resist pattern 14. This shunt wiring also includes a part of the first metal film 7 protected by the resist pattern 14.

  In such a method of manufacturing a charge coupled device, a first metal film 7 is formed on the semiconductor substrate 1 so as to cover the insulating film 6, and a barrier metal film is formed using the first metal film 7 as an etching stopper. 11 is processed by dry etching. Therefore, when the barrier metal film 11 adhering to the side wall portion of the step due to the transfer electrode 4 is removed by overetching, the progress of etching stops at the position where the first metal film 7 is formed, and the insulating film 6 Will not be scraped. Therefore, even if the insulating film 6 includes a SiN film that functions as an antireflection film in the sensor region S, the SiN film is not etched by the etching of the barrier metal film 11. As a result, it is possible to form the shunt wiring on the transfer electrode 4 while leaving the SiN film sufficiently thick without forming the SiN film again.

  In the above embodiment, the case where the shunt wiring is formed of tungsten has been described. However, the present invention is not limited to this, and the present invention can also be applied to the case where the shunt wiring is formed of a metal material other than tungsten, for example, aluminum. is there. When the shunt wiring is formed of aluminum, the first metal film 7 is formed of W, WN or the like, the barrier metal film 11 is formed of Ti, TiN, TiON, Ru, RuO or the like, and the second The metal film 12 may be formed of aluminum. The dry etching of the first metal film 12 is performed by using a chlorine-based etching gas for the dry etching of the second metal film 12 and the chlorine-based etching gas for the dry etching of the barrier metal film 11. Then, it is preferable to use a fluorine-based etching gas.

It is FIG. (1) explaining the manufacturing method of the charge coupled device which concerns on embodiment of this invention. It is FIG. (2) explaining the manufacturing method of the charge coupled device which concerns on embodiment of this invention. It is FIG. (3) explaining the manufacturing method of the charge coupled device which concerns on embodiment of this invention. It is FIG. (1) explaining the manufacturing method of the conventional charge coupled device. It is FIG. (2) explaining the manufacturing method of the conventional charge coupled device.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor substrate, 4 ... Transfer electrode, 6 ... Insulating film, 7 ... 1st metal film, 10 ... Connection hole, 11 ... Barrier metal film, 12 ... 2nd metal film, 14 ... Resist pattern

Claims (5)

Forming a transfer electrode on a semiconductor substrate;
Forming an insulating film on the semiconductor substrate so as to cover the transfer electrode;
Forming a first metal film on the semiconductor substrate so as to cover the insulating film;
Forming a connection hole on the transfer electrode in a state of penetrating the first metal film and the insulating film;
Forming a barrier metal film and a second metal film in order on the first metal film in a state of embedding the connection holes;
Forming a resist pattern on the second metal film;
Processing the second metal film by dry etching using the resist pattern as a mask;
Processing the barrier metal film by dry etching using the resist pattern as a mask and the first metal film as an etching stopper;
And a step of processing the first metal film by dry etching using the resist pattern as a mask. Each of the first metal film and the second metal film is made of a tungsten film,
The method for manufacturing a charge coupled device according to claim 1, wherein the barrier metal film is made of a titanium film, a titanium nitride film, or a laminated film thereof. In the dry etching of the first metal film and the second metal film, a fluorine-based etching gas is used,
The charge-coupled device manufacturing method according to claim 2, wherein a chlorine-based etching gas is used in the dry etching of the barrier metal film. Each of the first metal film and the second metal film is made of a tungsten film,
The method for manufacturing a charge coupled device according to claim 1, wherein the barrier metal film is made of ruthenium, ruthenium oxide, ruthenium nitride, or a laminated film thereof. In the dry etching of the first metal film and the second metal film, a fluorine-based etching gas is used,
The method for manufacturing a charge coupled device according to claim 4, wherein a chlorine-oxygen-based etching gas is used in the dry etching of the barrier metal film.

Images