JP2004204265A - Plating method and plating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To selectively and economically form a plating film such as a wiring protection film on the surface of metallic wires, without eroding the wires. <P>SOLUTION: This plating method is characterized by forming an oxidized-metal thin film 50 having a photo-electrochemical reactivity on the exposed surface of the wires 8 of a substrate W that has embedded wires 8 formed on the surface, and while contacting a plating solution 34 with the surface of the substrate W, irradiating the surface of the substrate W with light.The oxidized-metal thin film having the photo-electrochemical reactivity includes, for instance, a crystalline copper oxide film (a Cu<SB>2</SB>O film). <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a plating method and a plating apparatus, and particularly, to protect a surface of an embedded wiring formed by embedding a conductor such as copper or silver in a fine recess for wiring provided on the surface of a substrate such as a semiconductor wafer. The present invention relates to a plating method and a plating apparatus used for forming a wiring protection film.
[0002]
[Prior art]
As a wiring forming process of a semiconductor device, a process (so-called damascene process) in which a metal (conductor) is embedded in a wiring groove and a contact hole is being used. This is a process of embedding a metal such as aluminum, recently copper or silver in a wiring groove or a contact hole previously formed in an interlayer insulating film, and then removing and flattening excess metal by chemical mechanical polishing (CMP). Technology.
[0003]
In the case of this type of wiring, for example, copper wiring using copper as a wiring material, after flattening, the surface of the wiring made of copper is exposed to the outside to prevent thermal diffusion of the wiring (copper), For example, when an insulating film (oxide film) in an oxidizing atmosphere is subsequently laminated to form a semiconductor device having a multilayer wiring structure, the wiring (copper) is made of a Co alloy, a Ni alloy, or the like in order to prevent oxidation of the wiring (copper). It has been studied to selectively cover the surface of the exposed wiring with a wiring protective film (cover material) to prevent thermal diffusion and oxidation of the wiring. The wiring protection film made of a Co alloy, a Ni alloy, or the like is obtained by, for example, electroless plating.
[0004]
Here, for example, as shown in FIG. 7, a fine concave portion 4 for wiring is formed inside an insulating film 2 made of SiO ₂ or the like deposited on the surface of a substrate W such as a semiconductor wafer, and the surface is made of TaN or the like. After the barrier layer 6 and the Cu seed layer are formed, for example, copper plating is performed to form a copper film on the surface of the substrate W and bury the copper film in the concave portion 4. By performing (chemical mechanical polishing) and flattening, a wiring 8 made of a copper film is formed inside the insulating film 2, and the exposed surface of the wiring (copper film) 8 is obtained by, for example, electroless plating. A case is considered in which a wiring protection film (cover material) 9 made of a Co-WP alloy film is selectively formed to protect the wiring 8.
[0005]
The step of selectively forming the wiring protection film (cover material) 9 made of such a Co-WP alloy film on the surface of the wiring 8 by general electroless plating will be described. First, a CMP treatment is performed. The substrate W such as a semiconductor wafer is immersed, for example, in a diluted acid solution such as H ₂ SO ₄ at a liquid temperature of 25 ° C. for, for example, about 1 minute, and CMP of copper or the like remaining on the surface of the insulating film 2 Remove residue etc. Then, after cleaning the surface of the substrate W with a cleaning liquid such as ultrapure water, for example, the substrate is placed in a mixed solution of 0.005 g / L PdCl ₂ and 0.2 ml / L HCl at a liquid temperature of 25 ° C. W is immersed, for example, for one minute, thereby causing Pd as a catalyst to adhere to the surface of the wiring 8 to activate the exposed surface of the wiring 8.
[0006]
Next, after washing the surface of the substrate W with ultrapure water, the substrate W is immersed in, for example, a Co-WP plating solution having a solution temperature of 80 ° C. for, for example, about 120 seconds to activate the activated wiring 8. Is subjected to selective electroless plating (electroless Co-WP lid plating), and then the surface of the substrate W is washed with a cleaning solution such as ultrapure water. Thus, the wiring protection film 9 made of a Co-WP alloy film is selectively formed on the surface of the wiring 8 to protect the wiring 8.
[0007]
[Problems to be solved by the invention]
However, in the conventional example, when a wiring protection film (cover material) made of a Co-WP alloy film is formed by electroless plating, a catalyst such as Pd is applied to the surface of the metal wiring. Since this catalyst is applied, for example, by displacement plating represented by the following chemical formula, the underlying wiring (copper film) is eroded (etched) in principle, and as a result, voids are generated inside the wiring. As a result, the wiring characteristics are degraded, and the anisotropic growth of the plating film causes a problem in the operation of the semiconductor device, leading to a reduction in yield.
_{Cu + PdSO 4 → CuSO 4 +} Pd
Moreover, since Pd is a diffusion element for copper, it not only impairs the low resistance of the copper wiring, but also has a problem in economy because it is generally expensive.
[0008]
The present invention has been made in view of the above circumstances, and is a plating method capable of forming a plating film such as a wiring protective film on a surface of a wiring with good selectivity and economically without eroding a metal wiring. And a plating apparatus.
[0009]
[Means for Solving the Problems]
According to the first aspect of the present invention, a metal oxide thin film having photoelectrochemical reactivity is formed on an exposed surface of a wiring having a buried wiring formed on the surface thereof, and a plating solution is brought into contact with the surface of the substrate. A plating method characterized by irradiating light to a surface of a substrate.
[0010]
In this way, instead of applying a catalyst such as Pd to the surface of the substrate (the surface to be treated), a metal oxide thin film having photoelectrochemical reactivity is formed, so that the metal plating is not performed by displacement plating. The metal oxide thin film can be formed on the surface of the substrate without erosion (etching) of the wiring or the like. In addition, for example, by irradiating the metal copper oxide film of Cu ₂ O with light, as shown in the following chemical formula, the activation of the exposed surface of the wiring is promoted, and the metal M such as Co is deposited and grown. be able to. Here, e indicates a free electron, and H indicates a hole.
Cu ₂ O + hν → Cu ₂ O (e + H)
M ²⁺ + 2e → M
[0011]
The invention according to claim 2 is the plating method according to claim 1, wherein the metal oxide thin film is an oxide film obtained by forcibly oxidizing an exposed surface of a wiring. This forced oxidation can be performed by bringing the surface of the substrate into contact with an oxidant solution such as H ₂ O ₂ .
[0012]
The invention according to claim 3 is characterized in that the wiring is copper, the metal oxide thin film is a crystalline copper oxide film, and light having a wavelength of 560 nm or less is directed toward the surface of the substrate. This is a plating method.
[0013]
The surface of copper can be changed into crystalline copper oxide (Cu ₂ O), which is a p-type semiconductor, by being brought into contact with an aqueous solution of ammonia water, hydrogen peroxide, or the like whose pH or potential is controlled, or a mixture thereof. it can. That is, copper takes various forms under specific pH and potential conditions, as shown in its pH-potential diagram in FIG. 1, in which Cu ₂ O has stable pH and oxidation-reduction potential. When a region is present and copper is immersed in an oxidizing agent solution having a pH-potential region, a Cu ₂ O film is formed on the surface. For example, when the substrate on which the copper wiring is formed is immersed in an aqueous solution having a pH of 10 and an oxidation-reduction potential of 0.1 V (standard hydrogen electrode potential), a Cu ₂ O film is formed on the surface of the copper serving as the wiring.
[0014]
Here, since Cu ₂ O is a p-type semiconductor having a band gap of about 2.2 eV, when light having a wavelength of about 560 nm or less corresponding to the band gap is irradiated, free electrons and holes are formed inside the Cu ₂ O film. Since the generated electrons are p-type semiconductors, the generated electrons are localized on the surface and have a property of easily transferring electrons as shown in FIG. Therefore, when metal ions in the solution reach the surface of the Cu ₂ O film in such a state, the metal ions receive electrons from Cu ₂ O and precipitate as metals.
[0015]
The invention according to claim 4 is the plating method according to claim 1 or 2, wherein the wiring is made of copper, a copper alloy, silver, or a silver alloy.
The invention according to claim 5 is to form a Co, Co alloy, Ni or Ni alloy film by electroless plating by irradiating light to the surface of the substrate while bringing the plating solution into contact with the surface of the substrate. The plating method according to any one of claims 1 to 4, wherein:
[0016]
7. A substrate holder for holding a substrate on which a buried wiring is formed on a surface and a metal oxide thin film having photoelectrochemical reactivity is formed on an exposed surface of the wiring, and a substrate held by the substrate holder. Means for bringing a plating solution into contact with the surface of the substrate, and a light source for irradiating light having a wavelength equal to or less than the wavelength corresponding to the band gap of the metal oxide thin film toward the surface of the substrate held by the substrate holder and brought into contact with the plating solution. And a plating apparatus comprising:
[0017]
The invention according to claim 7 is the plating apparatus according to claim 6, wherein the metal oxide thin film is a crystalline copper oxide film, and the light source emits light having a wavelength of 560 nm or less.
[0018]
The invention according to claim 8 is directed to an oxide thin film forming apparatus for forming a metal oxide thin film on an exposed surface of an embedded wiring formed on a surface of a substrate, and a plating solution is brought into contact with the surface of the substrate while the plating solution is in contact with the surface. A substrate processing apparatus comprising: a plating apparatus that irradiates light.
According to a ninth aspect of the present invention, there is provided the substrate processing apparatus according to the eighth aspect, further comprising a post-cleaning device for post-cleaning the plated surface of the substrate after plating.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
FIG. 3 is a plan layout view of a substrate processing apparatus provided with a plating apparatus according to an embodiment of the present invention. As shown in FIG. 1, the substrate processing apparatus includes a load / unloader for loading and storing a substrate cassette accommodating a substrate W (see FIG. 7) having a wiring 8 formed in a wiring recess 4 formed on the surface. A load unit 10 is provided. Then, an oxide thin film forming apparatus 12 for forming a metal oxide thin film having photoelectrochemical reactivity on the exposed surface of the embedded wiring 8 formed on the surface (processed surface) of the substrate W, and a surface of the substrate after forming the metal oxide thin film And a post-cleaning device 20 for post-cleaning the surface of the substrate after plating are provided in series. Further, a substrate transfer section 22 composed of a transfer robot for transferring the substrate W is disposed at a side of each of these devices so as to be able to travel in parallel with each of these devices. In this example, an example in which the oxide thin film forming device 12, the plating device 18, and the post-cleaning device 20 are arranged in series is shown, but it is a matter of course that the present invention is not limited to this.
[0020]
FIG. 4 shows a plating apparatus 18 according to the embodiment of the present invention. The plating apparatus 18 has a substrate holder 30 for holding a substrate W detachably with its surface facing upward. The substrate holder 30 is configured to be movable up and down, and is located above the substrate holder 30 and is in a ring shape and pressed against the peripheral portion of the substrate W held by the substrate holder 30 as the substrate holder 30 is raised. A seal ring 32 for sealing the front and rear ends is arranged. In this manner, by sealing the peripheral portion of the substrate W with the seal ring 32, a plating chamber 36 for holding the plating solution 34 is defined by the surface (upper surface) of the substrate W and the seal ring 32. The substrate holder 30 and the seal ring 32 are configured to be able to rotate integrally. Note that the substrate holder 30 may be fixed, and the seal ring 32 may be configured to be vertically movable.
[0021]
A processing head 38 is disposed above the seal ring 32. Inside the processing head 38, light is emitted toward the substrate W held by the substrate holder 30, such as a fluorescent lamp, an incandescent lamp, or a halogen lamp. The light source 40 is stored. The light source 40 can irradiate the entire surface of the substrate W held by the substrate holder 30 with light with uniform light intensity. The light intensity may be changed or may be adjusted locally. Further, the processing head 38 is provided with a plating solution inlet 42 for supplying the plating solution 34 to the plating chamber 36.
[0022]
In this example, when the light source 40 uses a crystalline copper oxide film (Cu ₂ O film) as a metal oxide thin film having photoelectrochemical reactivity as described below, Cu ₂ O has a band gap of about 2.2 eV. Irradiation of light having a wavelength of about 560 nm or less corresponding to the band gap generates free electrons and holes inside Cu ₂ O, so that light of a wavelength of 560 nm or less is irradiated. I have.
[0023]
As a result, the substrate W is held by the substrate holder 30, the substrate holder 30 is raised, and the peripheral portion of the substrate W is pressed against the seal ring 32 to form the plating chamber 36 by the upper surface of the substrate W and the seal ring 32. . Then, after supplying the plating solution 34 into the plating chamber 36, the substrate W is rotated and irradiated with light from the light source 40 toward the substrate W, so that plating is performed on the surface of the substrate W. Have been.
[0024]
Next, a series of substrate processing (cover plating processing) by this substrate processing apparatus will be further described with reference to FIGS. In this example, as shown in FIG. 7, a case is described in which a wiring protection film (cover material) 9 made of a Co-WP alloy film is selectively formed to protect the wiring 8 made of copper. .
[0025]
First, as shown in FIG. 6A, a substrate W in which a wiring 8 made of copper is buried and formed is stored inside the insulating film 2 with the surface (the surface to be processed) of the substrate W facing upward (face-up). Then, one substrate W is taken out from the substrate cassette mounted on the loading / unloading section 10 by the substrate transport section 22 and transported to the oxide thin film forming apparatus 12 (see FIG. 3).
[0026]
In the oxide thin film forming apparatus 12, for example, the substrate W is immersed in a mixed aqueous solution of ammonia water and hydrogen peroxide having a pH of 10 and an oxidation-reduction potential of 0.1 V (standard hydrogen electrode potential), or the surface of the substrate W As shown in FIG. 6B, the exposed surface of the wiring 8 of the substrate W has a photoelectrochemical reactivity composed of a crystalline copper oxide film (Cu ₂ O film) 50 in this example, as shown in FIG. Forming a metal oxide thin film having the same. That is, copper takes various forms under specific pH and potential conditions, as shown in its pH-potential diagram in FIG. 1, in which Cu ₂ O has stable pH and oxidation-reduction potential. When a region exists and is immersed in, for example, an aqueous solution having a pH of 10 and an oxidation-reduction potential of 0.1 V (standard hydrogen electrode potential), a Cu ₂ O film is formed on the surface.
[0027]
The crystalline copper oxide film (Cu ₂ O film) 50 serves as a substitute for a conventional catalyst such as Pd. Thus, the crystalline copper oxide film (Cu ₂ O film) 50 Is formed on the surface of the wiring 8 in place of the above catalyst, the crystalline copper oxide film (Cu ₂ O film) 50 is formed without displacement plating, that is, without erosion (etching) of the underlying wiring 8. It can be formed on the surface of the wiring 8.
[0028]
Next, the substrate W after the formation of the metal oxide thin film is transported to the plating apparatus 18 by the substrate transport unit 22. In the plating apparatus 18, as described above, the substrate W is held face up by the substrate holder 30, the substrate holder 30 is raised, and the periphery of the substrate W is pressed against the seal ring 32 to form a plating chamber 36. For example, a Co-WP plating solution having a solution temperature of 80 ° C. is supplied into the plating chamber 36, and light is emitted from the light source 40 toward the substrate W while rotating the substrate W, so that wiring is performed. 8 is subjected to selective plating (Co-WP lid plating), and then the surface of the substrate W is cleaned with a cleaning liquid such as ultrapure water. As a result, a wiring protection film 9 (see FIG. 7, the same applies hereinafter) made of a Co-WP alloy film is selectively formed on the surface of the wiring 8 to protect the wiring 8.
[0029]
At this time, as shown in FIG. 6C, by irradiating the crystalline copper oxide film (Cu ₂ O film) 50 with light, the activation of the surface of the wiring 8 is promoted as shown by the following chemical formula. Thus, a plating film made of a metal M such as Co can be deposited and grown. Here, e indicates a free electron, and H indicates a hole.
Cu ₂ O + hν → Cu ₂ O (e + H)
M ²⁺ + 2e → M
[0030]
That is, since the Cu ₂ O film is a p-type semiconductor having a band gap of about 2.2 eV, irradiation with light having a wavelength of about 560 nm or less corresponding to this band gap causes free electrons e and holes H inside Cu ₂ O. Is generated and, since it is a p-type semiconductor, the generated electron e is localized on the surface, and has a property of easily transferring the electron e as shown in FIG. When the metal ions M ⁺ in the solution reach the surface of the Cu ₂ O film in such a state, the electrons e are received from the Cu ₂ O film, and the metal M is deposited. When the deposition of the metal M proceeds, light does not reach the Cu ₂ O film due to the deposited metal M, and the deposition stops due to the effect of the light. Then, once the deposition of the metal M occurs by light irradiation, the deposition of the metal proceeds in the same state as in the conventional electroless plating.
[0031]
In addition, since there is nothing on the surface of the insulating film 2 that plays a role as a catalyst, it is possible to reliably prevent a plating film from being formed on the surface of the insulating film 2, and thereby, Can be improved when plating is selectively performed on the substrate.
[0032]
Next, the substrate W after the plating process is transported to the post-cleaning device 20 by the substrate transport unit 22, and the particles and unnecessary substances attached to the surface of the substrate W are removed by the cleaning device 20 with a roll-shaped brush or the like. Thereafter, the surface of the substrate W is subjected to chemical cleaning and pure water cleaning and spin-dried.
Then, the substrate W after the spin drying is returned to the substrate cassette mounted on the loading / unloading unit 10 by the substrate transport unit 22.
[0033]
Here, in this example, a Co-WP alloy film is used as the wiring protection film 9. That is, an electroless plating solution containing a compound containing Co ions, a complexing agent, a pH buffering agent, a pH adjusting agent, sodium hypophosphite as a reducing agent, and W is used. By immersing the surface, a wiring protection film 9 made of a Co-WP alloy is formed.
[0034]
If necessary, one or more of a heavy metal compound or a sulfur compound as a stabilizer or at least one of a surfactant is added to the plating solution, and tetramethylammonium hydroxide, sodium hydroxide or The pH is adjusted to preferably 5 to 14, more preferably 6 to 10, using a pH adjuster such as aqueous ammonia. The temperature of the plating solution is, for example, 30 to 90 ° C, preferably 40 to 80 ° C.
[0035]
Examples of the supply source of the cobalt ions in the plating solution include cobalt salts such as cobalt sulfate, cobalt chloride, and cobalt acetate. The addition amount of the cobalt ion is, for example, about 0.001 to 1.0 mol / L, and preferably about 0.01 to 0.3 mol / L.
[0036]
Examples of the complexing agent include carboxylic acids such as acetic acid and salts thereof, oxycarboxylic acids such as tartaric acid and citric acid and salts thereof, aminocarboxylic acids such as glycine and salts thereof. They may be used alone or in combination of two or more. The total addition amount of the complexing agent is, for example, about 0.001 to 1.5 mol / L, and preferably about 0.01 to 1.0 mol / L. Examples of the pH buffer include ammonium sulfate, ammonium chloride, boric acid and the like. The amount of the pH buffer added is, for example, about 0.01 to 1.5 mol / L, preferably about 0.1 to 1.0 mol / L.
[0037]
Examples of the pH adjuster include ammonia water, sodium hydroxide, tetramethylammonium hydroxide (TMAH) and the like, and the pH is adjusted to 5 to 14, preferably 6 to 10. Examples of the reducing agent include sodium hypophosphite. The addition amount of the reducing agent is, for example, about 0.01 to 1.0 mol / L, preferably about 0.01 to 0.5 mol / L. As described above, even when a reducing agent such as dimethylamine borane (DMAB) is used, the selectivity when selectively performing electroless plating on the wiring surface can be improved. This reducing agent can be omitted.
[0038]
Examples of the compound containing tungsten include, for example, tungstic acid and a salt thereof, or a heteropolyacid such as tungstophosphoric acid (eg, H ₃ (PW ₁₂ P ₄₀ ) · nH ₂ O) and a salt thereof. . The addition amount of the compound containing tungsten is, for example, about 0.001 to 1.0 mol / L, and preferably about 0.01 to 0.1 mol / L.
[0039]
Known additives other than the above components can be added to the plating solution. Examples of the additive include one or more of a metal salt such as a heavy metal compound such as a lead compound and a sulfur compound such as a thiocyan compound as a bath stabilizer, and an anionic, cationic or nonionic surfactant. Can be.
[0040]
In this example, a Co-WP alloy is used as the wiring protection film 9, but a wiring protection film made of Co-P, Ni-P or Ni-WP is formed as the wiring protection film 9. You may make it. Although an example in which copper is used as a wiring material is shown, a copper alloy, silver, a silver alloy, gold, a gold alloy, or the like may be used in addition to copper.
[0041]
【The invention's effect】
As described above, according to the present invention, a metal oxide thin film serving as a substitute for a catalyst such as Pd can be formed without replacement plating, that is, without erosion (etching) of an underlying metal wiring or the like. It can be formed on the exposed surface of the wiring, thereby improving the yield and eliminating the need to use expensive Pd, thereby improving the economic efficiency. Further, since light in the visible light range can be used, not only does not adversely affect the plating solution, but also the intensity of the light can be adjusted to locally control the film formation rate, thereby achieving high in-plane uniformity. Can be ensured.
[Brief description of the drawings]
FIG. 1 is a diagram showing the relationship between the pH and the potential of a Cu—H ₂ O system.
FIG. 2 is a diagram showing an energy band at a semiconductor-solution interface.
FIG. 3 is a plan layout view of a substrate processing apparatus provided with a plating apparatus according to an embodiment of the present invention.
FIG. 4 is a sectional view showing an outline of a plating apparatus according to an embodiment of the present invention.
5 is a view showing a flow when a series of substrate processing (cover plating processing) is performed by the substrate processing apparatus shown in FIG. 3;
FIG. 6 is a view showing a state in which a wiring protective film is formed on the surface of the embedded wiring in the order of steps.
FIG. 7 is a cross-sectional view showing a state where a wiring protection film is formed by electroless copper plating.
[Explanation of symbols]
2 Insulating film 8 Wiring 9 Wiring protection film 10 Load / unload unit 12 Oxide thin film forming device 18 Plating device 20 Post-cleaning device 22 Substrate transporting unit 30 Substrate holder 32 Seal ring 34 Plating solution 36 Plating chamber 38 Processing head 40 Light source 42 Plating Liquid inlet 50 Crystalline copper oxide film (Cu ₂ O film)

Claims (9)

A metal oxide thin film having photoelectrochemical reactivity is formed on the exposed surface of the wiring having a buried wiring on the surface, and light is irradiated toward the surface of the substrate while the plating solution is in contact with the surface of the substrate. Plating method. The plating method according to claim 1, wherein the metal oxide thin film is an oxide film obtained by forcibly oxidizing an exposed surface of a wiring. The plating method according to claim 2, wherein the wiring is copper, and the metal oxide thin film is a crystalline copper oxide film, and light having a wavelength of 560 nm or less is irradiated toward the surface of the substrate. 3. The plating method according to claim 1, wherein the wiring is made of a copper alloy, silver, or a silver alloy. 4. A method of forming a Co, Co alloy, Ni or Ni alloy film by electroless plating by irradiating light onto the surface of the substrate while bringing the plating solution into contact with the surface of the substrate. 5. The plating method according to any one of 4. A substrate holder that holds a substrate on which a buried wiring is formed on the surface and a metal oxide thin film having photoelectrochemical reactivity is formed on an exposed surface of the wiring;
Means for bringing a plating solution into contact with the surface of the substrate held by the substrate holder,
A plating apparatus, comprising: a light source for irradiating light having a wavelength equal to or less than a wavelength corresponding to a band gap of the metal oxide thin film toward a surface of a substrate held by the substrate holder and brought into contact with a plating solution. The plating apparatus according to claim 6, wherein the metal oxide thin film is a crystalline copper oxide film, and the light source irradiates light having a wavelength of 560 nm or less. An oxide thin film forming apparatus for forming a metal oxide thin film on the exposed surface of the embedded wiring formed on the surface of the substrate;
A plating apparatus for irradiating light to the surface of the substrate while bringing a plating solution into contact with the surface of the substrate. 9. The substrate processing apparatus according to claim 8, further comprising a post-cleaning device for post-cleaning a plated surface of the substrate after plating.

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