JP5248171B2 - Noble metal film forming apparatus and noble metal film forming method - Google Patents

Description

  The present invention relates to a noble metal film deposition apparatus and a noble metal film deposition method, and more particularly, to a nonvolatile semiconductor memory element such as a nonvolatile resistance change memory element such as a FeRAM (Ferroelectric Random Access Memory). The present invention relates to a noble metal film forming apparatus and a noble metal film forming method capable of forming a dense noble metal film having no defects such as voids and cracks inside.

  In recent years, in portable devices such as portable telephones and portable information terminals, there is an increasing need for handling a large amount of information such as image data, and the storage elements installed in these portable devices are also high-speed, low-power. There is an increasing demand for power consumption, a large capacity and a small nonvolatile semiconductor memory element (nonvolatile memory). Among them, a nonvolatile resistance change memory element (nonvolatile resistance change memory) whose resistance value changes depending on the crystal state of the chalcogen compound is attracting attention as a highly integrated and nonvolatile memory element (for example, a patent) Reference 1 etc.). This non-volatile resistance change type storage element has a simple structure in which a chalcogenide film as a recording layer is sandwiched between two electrodes, and can maintain the recording state stably even at room temperature. It is an excellent memory element that can be used.

FIG. 8 is a cross-sectional view showing an example of a conventional FeRAM electrode structure. In this figure, in order to make the electrode structure easy to understand, the ferroelectric layer and the upper electrode which are the upper structure of this electrode are omitted. is there. In the figure, 1 is a substrate such as a silicon wafer, 2 is a hole formed on the surface of the substrate 1, 3 is an insulating film made of an oxide film formed on the surface of the substrate 1 and the side and bottom surfaces of the hole 2, and 4 is an insulating film. This is an electrode made of a noble metal film formed on the film 3 by sputtering. This noble metal film is mainly made of Pt from the viewpoint of reliability.
When forming the electrode 4 using a normal sputtering apparatus, it is difficult to form the electrode 4 having a uniform thickness on the side wall and the bottom of the hole 3, and the electrode has a thickness of the hole 2. There is a problem that a so-called overhang is generated in which the vicinity of the opening is thicker than the inside. Therefore, as a film forming method for solving this problem, a long throw sputtering (LTS) apparatus (hereinafter abbreviated as an LTS apparatus). ) Is used.

FIG. 9 is a cross-sectional view showing a conventional LTS apparatus. In FIG. 9, 11 is a substantially cylindrical shield member provided in a vacuum chamber (not shown), and 12 is a static member provided below the shield member 11. A wafer stage with an electric chuck, 13 is a substrate such as a silicon wafer fixed to the wafer stage 12 by an electrostatic chuck, 14 is a target disposed above the shield member 11 and facing the substrate 13 on the wafer stage 12, 15 Is a magnet provided above the target 14 for fixing the target 14 by magnetic force, 16 is a power source for applying sputtering power P _t (W) to the target 14, 17 is plasma formed on the substrate 13, and 18 is sputtering. Particles.
This LTS apparatus can form a noble metal film having a uniform thickness even for holes having an aspect ratio of about 0.5 to 4.
JP 2004-348906 A

By the way, in the electrode formed by the conventional LTS apparatus, not only from the center part of the target, but also from both sides (target edges) of the target, the sputtered particles are obliquely incident on the hole. However, at both ends of the hole, the incidence is mainly from directly above (target edge) of the hole, and further, the film is formed by oblique incidence from the target center and the opposite target edge. Therefore, there is a problem in that the thickness of the electrode formed in the hole is different from each other on both sides of the hole.
As described above, when the thickness of the electrode becomes asymmetric, if the electrode is crystallized by heat treatment in a subsequent process, the electrode may be disconnected, and the reliability of the electrode, that is, the memory element may be reduced.

  The present invention has been made to solve the above-described problems, and the thickness of the noble metal film formed by sputtering inside the hole formed in the substrate is made symmetrical on both sides of the hole. Therefore, it is an object of the present invention to provide a noble metal film forming apparatus and a noble metal film forming method that can improve the reliability without causing a problem such as disconnection in the noble metal film.

  As a result of intensive studies on the method of forming a noble metal film by sputtering in a hole formed in the substrate, the present inventors have determined that the diameter of a target having the same composition as that of the noble metal film is T, and between this target and the substrate. If the ratio L / T between the distance L and the target diameter T is 0.5 or more and 1.5 or less, the thickness of the noble metal film formed in the hole is Thus, the inventors have found that it is possible to improve the reliability by eliminating the possibility that the noble metal film has a problem such as disconnection and the like, thereby completing the present invention. It was.

The method for forming a noble metal film of the present invention is a method of forming a noble metal film by sputtering through an insulating film inside a hole formed in a substrate, wherein the diameter of a target having the same composition as the noble metal film is T When the distance between the target and the substrate is L, the ratio L / T between the distance L and the diameter T of the target is 0.5 or more and 1.5 or less, and the surface area of the substrate Is S _s (cm ² ), the bias power is P _s (W), the surface area of the target is S _t (cm ² ), and the sputtering power is P _t (W), the power density Ds of the substrate The ratio Ds / Dt with respect to the power density Dt of the target is expressed by the following formula (1).
0 ≦ Ds / Dt = (P _s × S _t ) / (P _t × S _s ) ≦ 0.3 (1)
It is characterized by satisfying .

Preferably, bias power is applied to the substrate and sputtering power is applied to the target .

It is preferable that the noble metal film is densely filled in the holes by optimizing the power density Ds of the substrate and the power density Dt of the target.
The noble metal film preferably contains one or more selected from the group of Ru, Rh, Pd, Os, Ir, Pt, Au, and Ag.
The noble metal film is preferably a conductive film of a nonvolatile semiconductor memory element.
The noble metal film forming apparatus of the present invention is an apparatus for forming a noble metal film by sputtering through an insulating film inside a hole formed in a substrate, and a target disposed in a vacuum chamber and the vacuum A stage for fixing the substrate disposed in the chamber and facing the target; and a power source for applying a sputtering power Pt (W) to the target. The diameter of the target is T, and the target and the stage are on the stage. When the distance between the substrate and L is L, the ratio L / T between the distance L and the diameter T of the target can be changed in a range of 0.5 or more and 1.5 or less, and the surface area of the substrate the _S s ^(cm 2), the bias power _P s (W), wherein the surface area of the target _S t ^(cm 2), when the sputtering power was set to _P t (W), wherein the group The ratio Ds / Dt for power density Dt of the target of the power density Ds, the following equation (1) 0 ≦ Ds / Dt = (P s × S t) / (P t × S s) ≦ 0.3 ... (1) It is used on the conditions which satisfy | fill.
The noble metal film forming apparatus is characterized in that a power source for applying bias power to the stage is provided.

  According to the noble metal film forming apparatus of the present invention, when the target diameter is T and the distance between the target and the substrate on the stage is L, the ratio L between the distance L and the target diameter T is L. / T can be changed in the range of 0.5 or more and 1.5 or less, so that the thickness of the noble metal film formed in the hole is symmetrical on both sides of the hole at both ends of the hole. The film can be formed as follows. Therefore, even when this noble metal film is crystallized by heat treatment, it is possible to form a noble metal film with no risk of causing cracks, fractures, etc. and having improved reliability.

According to the method for forming a noble metal film of the present invention, when the diameter of a target having the same composition as the noble metal film is T and the distance between the target and the substrate is L, the distance L and the target diameter T The ratio L / T to 0.5 and 1.5 or less is so that the thickness of the noble metal film formed in both ends of the hole is symmetrical on both sides of the hole. It can be. Therefore, even when this noble metal film is crystallized by heat treatment, there is no possibility that the noble metal film will be cracked or broken, and the reliability of this noble metal film can be improved.
Furthermore, if this noble metal film is applied to a nonvolatile semiconductor memory element such as a nonvolatile resistance change memory element such as FeRAM, the reliability of the memory element can be improved.

The best mode for carrying out the noble metal film forming apparatus and the noble metal film forming method of the present invention will be described.
This embodiment is specifically described for better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

“First Embodiment”
FIG. 1 is a schematic cross-sectional view showing a long throw sputtering (LTS) apparatus, which is a noble metal film forming apparatus according to a first embodiment of the present invention, and an insulating film is interposed inside a hole formed in a substrate. This is an apparatus for forming a noble metal film by sputtering.

In the figure, 21 is a substantially cylindrical shield member provided in a vacuum chamber (not shown) and constituted by two cylindrical members 21a and 21b, and 22 is a stage with an electrostatic chuck provided below the shield member 21. , 23 is a substrate fixed to the stage 22 by an electrostatic chuck, 24 is a target disposed above the shield member 21 and facing the substrate 23 on the stage 22, and 25 is provided above the target 24 and has the target 24 mounted thereon. A magnet for fixing by magnetic force, 26 a power source for applying sputtering power P _t (W) to the target 24, 27 a plasma formed on the substrate 23, 28 a noble metal ion struck out from the target 24, 29 Neutral particles such as argon.

  When the distance between the target 24 and the substrate 23 is L (m) and the diameter of the target 24 is T (m), the ratio L / T between the distance L and the diameter T of the target 24 is 0.5. It can be changed in the range of 1.5 to 1.5, preferably 0.7 to 1.3.

  The target 24 is preferably a target material made of a material having the same composition as the noble metal film to be formed. For example, one type selected from the group of Ru, Rh, Pd, Os, Ir, Pt, Au, and Ag. Or the target material containing 2 or more types is used suitably. More specifically, a Pt target composed of Pt and inevitable impurities, a Pt—Rh target composed of a Pt—Rh alloy, a Pt—Ru target composed of a Pt—Ru alloy, an Ag—Pd target composed of an Ag—Pd alloy, and the like. It is done.

The substrate 23 only needs to have a hole for forming a noble metal film. For example, a silicon wafer used in manufacturing a FeRAM (Ferroelectric Random Access Memory) is mentioned. It is done.
FIG. 2 is a cross-sectional view showing a FeRAM silicon wafer. A plurality of holes 32 are formed in parallel on the surface 31a of the silicon wafer 31, and on the surface 31a and on the inner surfaces of the holes 32 and 32, respectively. An insulating film 33 made of silicon oxide generated by the oxidation treatment is formed. The shape of the hole 32 is, for example, a width (W) of 0.05 to 1 μm and a depth (D) of 0.05 to 4 μm.

Next, a noble metal film is formed in the hole 32 of the silicon wafer 31 shown in FIG. 2 using the above LTS apparatus.
In this film formation, a sputtering power P _t (W) is applied to the target 24 using the power source 26 to generate plasma on the substrate 23, and noble metal ions 28 struck out from the target 24 are deposited on the substrate 23. Let

In this sputtering, by optimizing the ratio L / T between the distance L and the diameter T of the target 24 and the sputtering power P _t (W), as shown in FIG. The deposition pressure in the incident direction of the ions 28 is increased, the noble metal ions 28 are scattered in the holes 32, and the noble metal film 34 is formed on the insulating film 33 in the holes 32.
While the noble metal ions 28 are scattered in the holes 32, the traveling directions thereof are random, and the traveling directions of the noble metal ions 28 are uniformed as a whole. As a result, the noble metal film 34 in the holes 32 is formed. The thicknesses are substantially equal to each other on both sides of the hole 32, and the symmetry of the noble metal film 34 is improved.
As described above, as shown in FIG. 4, the noble metal film 34 having excellent symmetry can be formed on the insulating film 33 in the hole 32 of the silicon wafer 31.

Next, a description will be given of the results of experiments conducted by the present inventors on the noble metal film sputtering method of the present embodiment.
FIG. 5 shows the ratio L / T between the distance L (m) between the target and the silicon wafer and the diameter T (m) of the target when the Pt film is formed on the insulating film in the hole of the silicon wafer. is a diagram showing a relationship between coverage ratio _(t B / _{t i)} and the sputtering rate. Here, the coverage ratio (t _B / t _i ) is the film thickness (t _B ) of the Pt film formed on the bottom surface of the hole when the Pt film is formed on the insulating film of the hole, and the outside of the hole It is a ratio with the film thickness (t _i ) of the Pt film formed on the insulating film.
Here, the diameter of the Pt target was 300 mm, the DC power of the power source 26 was 1.0 kW, and the temperature of the silicon wafer was 300 ° C.

According to FIG. 5, when the coverage (t _B / t _i ) is 0.57 or more in order to ensure in-plane uniformity of the Pt film, L / T is 0.5 or more. In addition, when the sputtering rate is 1.0 considering the productivity of the Pt film, L / T is 1.4 or less. Therefore, the range of L / T that satisfies both the coverage (t _B / t _i ) and the sputtering rate is 0.5 or more and 1.4 or less, preferably 0.6 or more and 1.2 or less.

  As described above, according to the LTS apparatus of this embodiment, when the distance between the target 24 and the silicon wafer 31 is L (m) and the diameter of the target 24 is T (m), the distance L Since the ratio L / T of the target 24 and the diameter T of the target 24 can be changed in the range of 0.5 or more and 1.5 or less, the insulation of the hole 32 of the silicon wafer 31 is maintained while maintaining the sputtering rate at the optimum condition. A noble metal film 34 having excellent symmetry can be formed on the film 33.

According to the method for forming a noble metal film of the present embodiment, when the diameter of a target having the same composition as the noble metal film 34 is T and the distance between the target and the silicon wafer 31 is L, the distance L and the target Since the ratio L / T with respect to the diameter T of the hole 32 is 0.5 or more and 1.5 or less, the thickness of the noble metal film 34 formed in the hole 32 is also reduced at both ends of the hole 32. It can be symmetrical on both sides. Therefore, even when the noble metal film 34 is crystallized by heat treatment, there is no possibility that the noble metal film 34 will be cracked or broken, and the reliability of the noble metal film 34 can be improved.
Furthermore, if this noble metal film 34 is applied to a nonvolatile semiconductor memory element such as a nonvolatile resistance change memory element such as FeRAM, the reliability of the memory element can be improved.

“Second Embodiment”
FIG. 6 is a schematic cross-sectional view showing a bias-long throw sputtering (B-LTS) apparatus which is a noble metal film forming apparatus according to the second embodiment of the present invention. The difference from the LTS device of the first embodiment is that a power supply 41 for applying high-frequency bias power to the stage 22 is provided, and other components are exactly the same as those of the LTS device of the first embodiment. The description will be omitted.

Next, a noble metal film is formed in the hole 32 of the silicon wafer 31 shown in FIG. 2 using the B-LTS apparatus.
In this film formation, in order to form a dense noble metal film excellent in symmetry, a bias power P _s (W) is applied to the substrate 23 using the power supply 41, and the target 24 is applied using the power supply 26. A sputtering power P _t (W) is applied to generate plasma on the substrate 23, and noble metal ions 28 struck out from the target 24 are deposited on the substrate 23.

In order to optimize the bias power P _s (W) and the sputtering power P _t (W), the surface area of the substrate 23 is S _s (cm ² ), the bias power is P _s (W), and the surface area of the target 24 is Is S _t (cm ² ) and the sputtering power is P _t (W), the ratio Ds / Dt of the power density Ds of the substrate 23 to the power density Dt of the target 24 is expressed by the following formula (1).
0 ≦ Ds / Dt = (P _s × S _t ) / (P _t × S _s ) ≦ 0.3 (1)
It is necessary to satisfy.

By optimizing the bias power P _s (W) and sputtering power P _t (W), noble metal ions are drawn into the hole during sputtering, and the bottom of the hole is re-sputtered. Thereby, the coverage of the noble metal film in the film forming process is improved.
As described above, a noble metal film having excellent symmetry and high density can be formed.

Next, a description will be given of the results of experiments conducted by the present inventors on the noble metal film sputtering method of the present embodiment.
FIG. 7 shows the ratio Ds / Dt of the power density Ds of the silicon wafer to the power density Dt of the target when the Pt film is formed on the insulating film in the hole of the silicon wafer, and the covering ratio (t _B / t _i ). It is a figure which shows the relationship.
Here, the diameter of the Pt target was 300 mm, the DC power of the power source 26 was 1.0 kW, the high frequency power of the power source 41 was 0.1 kW, and the temperature of the silicon wafer was 300 ° C.

According to FIG. 7, when the coverage (t _B / t _i ) is 0.7 or more in order to ensure in-plane uniformity of the Pt film, (P _s × S _t ) / (P _t × S _s ) Is 0.3 or less. Therefore, it can be seen that the ratio Ds / Dt of the power density Ds of the substrate 23 to the power density Dt of the target 24 satisfies the above equation (1).

Also in the B-LTS device of the present embodiment, the same effects as those of the LTS device of the first embodiment can be obtained.
In particular, since the power supply 41 for applying bias power to the stage 22 is provided, the coverage of the noble metal film during the film formation process can be improved, and a dense noble metal film with further excellent symmetry can be formed.

According to the film formation method of the noble metal film of the present embodiment, the surface area of the substrate 23 is S _s (cm ² ), the bias power is P _s (W), the surface area of the target 24 is S _t (cm ² ), and the sputtering is performed. When the power is P _t (W), the ratio Ds / Dt of the power density Ds of the substrate 23 to the power density Dt of the target 24 is expressed by the following formula (1).
0 ≦ Ds / Dt = (P _s × S _t ) / (P _t × S _s ) ≦ 0.3 (1)
Therefore, the coverage of the noble metal film in the film formation process can be improved, and a dense noble metal film having excellent symmetry can be formed.

It is a schematic sectional drawing which shows the LTS apparatus of the 1st Embodiment of this invention. It is sectional drawing which shows the silicon wafer for FeRAM. It is sectional drawing which shows the film-forming process of the noble metal film of the 1st Embodiment of this invention. It is sectional drawing which shows the film-forming process of the noble metal film of the 1st Embodiment of this invention. The ratio L / T, which is a diagram showing a relationship between coverage ratio _(t B / _{t i)} and the sputtering rate. It is a schematic sectional drawing which shows the B-LTS apparatus of the 2nd Embodiment of this invention. And the ratio _{(P s × S t) /} (P t × S s), a diagram showing a relationship between coverage ratio _(t B / t _i). It is sectional drawing which shows an example of the electrode structure of the conventional FeRAM. It is sectional drawing which shows the conventional LTS apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 21 Shield member 21a, 21b Cylindrical member 22 Stage 23 Substrate 24 Target 25 Magnet 26 Power supply 27 Plasma 28 Precious metal ion 29 Neutral particle 31 Silicon wafer 31a Surface 32 Hole 33 Insulating film 41 Power supply

Claims (7)

A method of forming a noble metal film by sputtering through an insulating film inside a hole formed in a substrate,
When the diameter of the target having the same composition as the noble metal film is T and the distance between the target and the substrate is L, the ratio L / T between the distance L and the target diameter T is 0.5. or more and is 1.5 or less,
When the surface area of the substrate is S _s (cm ² ), the bias power is P _s (W), the surface area of the target is S _t (cm ² ), and the sputtering power is P _t (W), The ratio Ds / Dt of the power density Ds to the power density Dt of the target is expressed by the following formula (1).
0 ≦ Ds / Dt = (P _s × S _t ) / (P _t × S _s ) ≦ 0.3 (1)
A method for forming a noble metal film, wherein: The substrate bias power is applied to the method of forming the noble metal film according to claim 1, wherein applying a sputtering power to the target. By optimizing the power density Dt of the power density Ds and the target of the substrate, method of forming the noble metal film according to claim 1, wherein the densely packed the noble metal layer in said hole. The noble metal film, Ru, Rh, Pd, Os , Ir, Pt, Au, any one of claims 1, characterized by containing one or two or more selected from the group of Ag 3 2. A method for forming a noble metal film according to item 1. The noble metal film, according to claim 1 to the film forming method of the noble metal film according to any one of 4, characterized in that a conductive film of the nonvolatile semiconductor memory device. An apparatus for depositing a noble metal film by sputtering through an insulating film inside a hole formed in a substrate,
A target disposed in the vacuum chamber, a stage for fixing the substrate disposed in the vacuum chamber and facing the target, and a power source for applying a sputtering power Pt (W) to the target,
When the diameter of the target is T and the distance between the target and the substrate on the stage is L, the ratio L / T between the distance L and the target diameter T is 0.5 or more and 1 It can be changed within the range of 5 or less,
The surface area of the substrate is S _s (Cm ² ), The bias power is P _s (W), the surface area of the target is S _t (Cm ² ), The sputtering power is P _t (W), the ratio Ds / Dt of the power density Ds of the substrate to the power density Dt of the target is expressed by the following formula (1).
0 ≦ Ds / Dt = (P _s × S _t ) / (P _t × S _s ) ≦ 0.3 (1)
A film forming apparatus for a noble metal film, which is used under a condition satisfying 7. The noble metal film forming apparatus according to claim 6, wherein a power source for applying bias power to the stage is provided.

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