JP2003313669A - Electroless plating process and semiconductor wafer wherein metal plating layer is formed through the process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electroless plating process for forming an electroless plating film with a mirror finish exerting high adhesion to a semiconductor wafer. <P>SOLUTION: The electroless nickel plating is performed after applying a palladium compound solution on the semiconductor wafer, using dimethylamine borane as a reducing agent and ammonia as a pH adjuster. Alternatively, the electroless copper plating is performed using an electroless copper plating solution containing copper nitrate. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for uniformly forming an electroless plating layer for forming a copper wiring on a surface to be plated with good adhesiveness, and particularly to a fine pattern formed on a semiconductor wafer. The present invention relates to a suitable electroless plating method capable of filling vias or trenches without causing defects such as voids and seams.

[0002]

2. Description of the Related Art In the processing of semiconductor wafers, aluminum has been mainly used as a wiring material. In recent years, since the degree of integration of wiring has increased, it has become possible to prevent an increase in signal delay time in place of copper having high electrical conductivity. A damascene method is used to form a copper wiring. After forming a wiring pattern on a silicon wafer, a barrier layer / seed layer is formed by a sputtering method or C
A general process is to form a film by the VD method, embed a wiring pattern by electroplating, and remove excess copper deposit by CMP. As the wiring pattern becomes finer and finer, the coverage of the copper seed layer on the inner walls of vias and trenches formed by the sputtering method becomes insufficient, causing defects during electroplating. There is. There was a need for a solution to this problem.

By the way, the electroless metal plating method is one of the methods for forming a metal film on an underlayer having no conductivity, and is used for a method for forming a printed wiring on a resin substrate. As a pretreatment for this electroless plating, a method called activation is generally used in which a noble metal such as palladium is used as a catalyst and is previously attached to the base. Until now, SnC
A method has been used in which Pd is adsorbed by dipping it in a PdCl ₂ aqueous solution after treating it with a hydrochloric acid aqueous solution of l ₂ or Pd is supported on the surface by a colloidal solution containing Sn and Pd.

[0004]

However, according to the conventional method, it was difficult to form electroless plating uniformly on a semiconductive mirror-finished object such as a semiconductor wafer with good adhesion.

Under the above circumstances, the present invention has good adhesion to semiconductor wafers such as Si wafers, which are difficult to apply by conventional electroless plating, and enables uniform electroless plating, and at the time of fine wiring described above. It is an object of the present invention to provide a novel metal plating method by electroless plating that can solve the problem of insufficient coverage of the seed layer on the inner wall of the via / trench.

[0006]

As a result of earnest studies, the present inventors have surprisingly found that dimethylamine borane is used as a reducing agent and ammonia is used as a pH adjusting agent in an electroless nickel plating solution, or By using a plating solution containing copper nitrate in the electrolytic copper plating solution, even for semiconductor wafer surfaces to which electroless plating is difficult to apply, it was found that the adhesion can form a good metal plating film, the present invention I arrived. That is, the present invention is characterized in that (1) when electroless nickel plating is performed on a surface to be plated, an electroless nickel plating solution containing dimethylamine borane as a reducing agent and ammonia as a pH adjusting agent is used. Electroless nickel plating method. (2) An electroless copper plating method characterized by using an electroless copper plating solution containing copper nitrate when performing electroless copper plating on a surface to be plated. (3) When electroless nickel plating is performed on the surface to be plated, electroless nickel plating is performed using an electroless nickel plating solution containing dimethylamine borane as a reducing agent and ammonia as a pH adjuster, and nitric acid is further added. An electroless plating method comprising performing electroless copper plating using an electroless copper plating solution containing copper. (4) A semiconductor wafer having a metal plating layer formed by the method according to any one of (1) to (3) above. (5) The present invention relates to a semiconductor device manufactured from the semiconductor wafer according to (4).

In the present invention, when nickel plating is performed in electroless plating, it is important to use dimethylamine borane as a reducing agent and ammonia as a pH adjusting agent in the nickel plating solution, and copper plating. In doing so, it is important that the copper plating solution contains copper nitrate. The same applies when copper plating is performed subsequently to nickel plating. Other electroless plating conditions are not particularly limited.

When performing electroless plating, a silane coupling agent is preferably applied as a treatment of the surface to be plated. As the silane coupling agent useful in the present invention, a silane coupling agent having a functional group having a metal capturing ability is more preferable. As the functional group having the metal capturing ability,
Although not limited thereto, examples thereof include an amino group, a carboxyl group, an azole group, a hydroxyl group, and a mercapto group. Of these, an azole group is preferable. As the azole group, imidazole, oxazole, thiazole, selenazole, pyrazole, isoxazole,
Examples thereof include isothiazole, triazole, oxadiazole, thiadiazole, tetrazole, oxatriazole, thiatriazole, bendazole, indazole, benzimidazole and benzotriazole.
Among them, an imidazole group is particularly preferable.

The silane coupling agent is a compound having a -SiX ₁ X ₂ X ₃ group in addition to the noble metal ion trapping group, wherein X _1, X ₂ and X ₃ are alkyl groups, halogens and halogens. It means an alkoxy group or the like and may be any functional group that can be fixed to an object to be plated. X ₁ , X ₂ and X ₃ may be the same or different. For example, a silane coupling agent obtained by the reaction of an azole compound and an epoxysilane compound can be exemplified (JP-A-6-2.
56358).

Further, as the epoxy group-containing silane compound to be reacted with such a nitrogen-containing heterocyclic azole compound,

[0011]

[Chemical 1]

(In the formula, R ¹ and R ² are hydrogen or have 1 carbon atoms.
It is preferable to use an epoxy silane coupling agent represented by alkyl groups of 3 to 3 and n of 1 to 3).

The reaction between the azole compound and the epoxy group-containing silane compound can be carried out under the conditions described in JP-A-6-256358. For example,
0.1 to 1 mol of azole compound at 80 to 200 ° C
-10 mol of epoxy group-containing silane compound is added dropwise and 5
Allow to react for minutes to 2 hours. At that time, a solvent is not particularly necessary, but an organic solvent such as chloroform, dioxane methanol, ethanol or the like may be used.

Other examples of the silane coupling agent having a metal capturing ability used in the present invention include γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane and N-β (aminoethyl) γ-aminopropyl. Examples thereof include trimethoxysilane, N-β (aminoethyl) γ-aminopropyltriethoxysilane, and γ-mercaptopropyltrimethoxysilane.

In the present invention, after the above-mentioned pretreatment, a noble metal compound having catalytic activity for depositing copper, nickel, cobalt or the like from the electroless plating solution on the surface of the object to be plated is applied. A palladium compound is particularly preferable as such a noble metal compound. Specific examples thereof include palladium chlorides, hydroxides, oxides, sulfates, ammonium salts, and other ammine complexes that exhibit a catalytic effect. Palladium chloride is particularly preferable. The palladium compound is used as an aqueous solution or an organic solvent solution, but it is preferably used as an organic solvent solution. As the organic solvent, for example, methyl alcohol, ethyl alcohol, isopropanol, acetone, methyl ethyl ketone, toluene, ethylene glycol, polyethylene glycol, dimethylformamide, dimethyl sulfoxide, dioxane, or the like, or a mixture thereof can be used. Moreover, the concentration in the solution is 20 to 300 mg.
/ L is preferred.

The semiconductor wafer in the present invention includes not only silicon-based wafers but also compound semiconductor-based wafers such as gallium / arsenic, gallium / phosphorus and indium / phosphorus. According to the metal plating method of the present invention, the material of the plated surface of the semiconductor wafer is not limited. For example, when forming an LSI wiring, a barrier metal having a low conductivity selected from titanium, tantalum, tungsten, or their nitrides (nitrides) formed by vapor deposition, sputtering, CVD, etc., is the surface to be plated. However, in any case, the method of the present invention can be preferably applied. The method of the present invention can be preferably applied to the case where the surface to be plated is silicon or its oxide film.

When the surface of the substrate for electroless plating is surface-treated with a silane coupling agent having a functional group having a metal-capturing ability as described above, this solution is a suitable solvent such as water,
It can be used as a solution obtained by dissolving methyl alcohol, ethyl alcohol, 2-propanol, acetone, toluene, ethylene glycol, polyethylene glycol, dimethylformamide, dimethylsulfoxide, dioxane, or the like, or a mixed solution thereof. When using water,
In particular, it is necessary to optimize the pH of the solution depending on the surface to be plated and the plating conditions. However, it is more preferable to use the solution of the silane coupling agent as an organic solvent solution as well as the palladium compound. For semiconductor wafers,
Although the method of volatilizing the solvent after the surface coating by the dipping treatment is general, in the present invention, it is preferable to apply the solvent by a spin coater. The concentration of the silane coupling agent having a functional group having a metal capturing ability in the solution is not limited to this, but 0.001 to 10% by weight is easy to use. If it is less than 0.001% by weight, the amount of the compound attached to the surface of the base material tends to be low, and the effect is difficult to obtain. On the other hand, if the amount exceeds 10% by weight, the amount of adhesion is too large and it is difficult to dry, or the powder easily aggregates. To evaporate the solvent used after the surface treatment, it is sufficient to heat the solvent to a temperature above the volatilization temperature and dry the surface.
It is preferable to heat at 0 to 150 ° C. for 3 to 10 minutes.
When water is used as the solvent, it is possible to omit the drying step and perform the plating simply by washing with water after the surface treatment. However, at this time, it is necessary to sufficiently wash with water in order to prevent the catalyst from being brought into the plating solution. Room temperature is sufficient for the pretreatment, but heating can increase the deposition rate and deposition amount of the catalyst. The temperature for heating is preferably 30 to 80 ° C. As a matter of course, the surface to be plated may be washed before the pretreatment for plating. In some cases, it may be effective to treat with a solution containing a reducing agent before plating. In particular, in the case of copper plating, it may be treated with a dimethylamine-borane solution as a reducing agent.

According to the present invention, copper, nickel, or nickel and copper can be plated on a semiconductor wafer by electroless plating. When forming an LSI wiring, a via trench for embedding a copper wiring in the surface of a semiconductor (such as silicon) wafer is formed, and titanium, tantalum, or tantalum is formed on the surface to prevent copper from diffusing into silicon. A barrier metal selected from tungsten or nitrides thereof (nitride) is coated to a thickness of about 0.01 to 0.1 μm by sputtering, CVD, or the like.

Then, conventionally, a thin copper layer (seed layer) is coated on this barrier metal layer by the sputtering, CVD method or the like as described above. The barrier metal generally has a large electric resistance, and in the electrolytic copper plating to be coated later, the difference in the current density between the periphery and the central portion of the contact provided on the peripheral portion of the wafer becomes large. Is applied (thinly coated). However, as the wiring becomes finer and the diameter of the via / trench becomes smaller, the coverage of the inner sidewall of the via / torrent cannot be sufficiently obtained by the conventional sputtering method, and defects (voids) during the subsequent electroplating (void).・ It may cause seams. Further, although the CVD method improves the coverage, there is a problem that the cost is very high.

In the present invention, a seed layer is formed by electroless plating with copper or nickel after applying a catalyst on the barrier layer by the above-mentioned pretreatment method instead of the conventional seed layer forming method. By this method, the problem of insufficient coverage of the inner sidewall of the via / trench in the case of fine wiring is solved by CVD.
It can be solved at a lower cost than the law. When copper is electrolessly plated, it is possible not only as a seed layer but also as it is, to continuously embed wiring by electroless plating. In electroless plating, when the catalyst is evenly attached to the surface to be plated, the film grows evenly on the surface to be plated, so that seams are likely to occur in the case of fine wiring. However, when the catalyst is applied by the pretreatment method, the catalyst tends to adhere to the inner wall of the fine wiring. Since the metal tends to deposit more easily in a place where the amount of catalyst deposited is larger, in this case, bottom-up type deposition such as the electrolytic copper plating solution used for embedding fine wiring occurs, and it does not generate seams. Wiring can be embedded. Of course, it is also possible to embed the wiring by electrolytic copper plating after forming the seed layer by electroless copper plating. Generally, the electroless copper plating solution contains formalin as a reducing agent. However, the use of formalin has tended to be avoided in recent years due to the growing problem of environmental impact. Therefore, this problem can be solved by using an electroless nickel plating solution. In the case of electroless nickel plating, the coating generally contains a few% of phosphorus or boron, so that the electrical resistance is high. Therefore, when the seed layer is formed by electroless nickel plating, it is necessary to suppress the film thickness to the minimum thickness at which conduction can be obtained. In general, the electroless copper plating solution and the electroless nickel plating solution often contain an alkaline component as a raw material. Alkaline components are the most disliked impurities in wiring materials. Further, by using the electroless plating method of the present invention, it is possible to form a barrier metal on an insulating film when forming an LSI wiring. As an example of the barrier metal in that case, nickel, cobalt, or an alloy of these metals and another metal (such as tungsten) can be considered. As a matter of course, after forming a barrier metal film by the electroless plating method of the present invention, it is possible to further form a copper wiring film by electroless plating. In the electroless nickel plating of the present invention, it is important to use dimethylamine-borane as a reducing agent for the nickel plating solution and ammonia for pH adjustment. By using dimethylamine-borane as a reducing agent and ammonia for pH adjustment, the stress of the nickel plating film is relieved, and the plating film becomes difficult to peel off. For example, even if hypophosphite is used as a reducing agent, the intended effect of the present invention cannot be exhibited. Also, if dimethylamine-borane is used as a reducing agent and sodium hydroxide is used for pH adjustment,
The desired effect of the present invention cannot be expressed. Also,
In the electroless copper plating of the present invention, it is important to use a copper nitrate system for the copper plating solution, and when a copper sulfate system is used, the intended effect of the present invention cannot be exhibited. By using the plating solution of the present invention, the present invention can form an electroless nickel plating film and / or an electroless copper plating film with good adhesion.

[0021]

Example 1 A 0.02% isopropyl alcohol solution of a silane coupling agent, which is a reaction product of equimolar amounts of imidazole and γ-glycidoxypropyltrimethoxysilane, is applied to a silicon wafer whose surface is made SiO 2 by thermal diffusion. Was applied by a spin coater at 1000 rpm for 1 minute. Then, an isopropyl alcohol solution of palladium chloride (Pd concentration 60 mg / L) was applied by a spin coater under the conditions of 1000 rpm and 1 minute. Electroless plating was performed using an electroless nickel plating solution using dimethylamine borane as a reducing agent and ammonia as a pH adjusting agent. The obtained nickel-plated film was subjected to a tape peeling test on a mirror surface, and as a result, the adhesion was good.
As a result of measuring the film thickness by Auger analysis, the nickel film thickness was estimated to be 1000Å.

Comparative Example 1 A 0.02% isopropyl alcohol solution of a silane coupling agent, which is an equimolar reaction product of imidazole and γ-glycidoxypropyltrimethoxysilane, is applied to a silicone wafer whose surface is made SiO 2 by thermal diffusion. It was applied by a spin coater at 1000 rpm for 1 minute. Then, an isopropyl alcohol solution of palladium chloride (Pd concentration 60 mg / L) was applied by a spin coater under the conditions of 1000 rpm and 1 minute. Electroless nickel plating was performed using an electroless nickel plating solution using sodium hypophosphite as a reducing agent. The obtained nickel-plated film had a mirror surface, but the tape peeling test revealed that the adhesion was poor. As a result of measuring the film thickness by Auger analysis, the nickel film thickness is 100.
It was estimated to be 0Å.

Example 2 A 0.02% isopropyl alcohol solution of a silane coupling agent, which is an equimolar reaction product of imidazole and γ-glycidoxypropyltrimethoxysilane, is applied to a silicone wafer whose surface is made SiO 2 by thermal diffusion. It was applied by a spin coater at 1000 rpm for 1 minute. Then, an isopropyl alcohol solution of palladium chloride (Pd concentration 60 mg / L) was applied by a spin coater under the conditions of 1000 rpm and 1 minute. It was immersed in the same electroless nickel plating solution as in Example 1 to perform electroless nickel plating, and then electroless plating was performed using an electroless copper plating solution using copper nitrate. The obtained copper plating film is a result of tape peeling test on the mirror surface,
Adhesion was good. As a result of measuring the film thickness by Auger analysis, the nickel film thickness is 700Å and the copper film thickness is 20.
It was estimated to be 00Å.

Comparative Example 2 A silicone wafer having a surface made of SiO 2 by thermal diffusion was applied with a 0.02% isopropyl alcohol solution of a silane coupling agent which is a reaction product of equimolar amounts of imidazole and γ-glycidoxypropyltrimethoxysilane. It was applied by a spin coater at 1000 rpm for 1 minute. Then, an isopropyl alcohol solution of palladium chloride (Pd concentration 60 mg / L) was applied by a spin coater under the conditions of 1000 rpm and 1 minute. It was immersed in the same electroless nickel plating solution as in Example 1 to carry out electroless nickel plating, and subsequently, electroless copper plating using copper sulfate instead of copper nitrate. The obtained copper plating film was cloudy. As a result of a tape peeling test, the adhesion was good. As a result of measuring the film thickness by Auger analysis, it was estimated that the nickel film thickness was 700Å and the copper film thickness was 2000Å.

EXAMPLE 3 A 0.022% methyl ethyl ketone solution of a silane coupling agent, which is an equimolar reaction product of imidazole and γ-glycidoxypropyltrimethoxysilane, is spin-coated on a silicon wafer whose surface is made SiO 2 by CVD. Was applied at 1000 rpm for 1 minute. After drying at 100 ° C. for 5 minutes in a dryer, the mixture was cooled to room temperature and palladium chloride in methyl ethyl ketone (Pd
Concentration 60 mg / L) was measured by a spin coater to 1000
It was applied under the conditions of rpm and 1 minute. 100 by dryer
After drying at 5 ° C. for 5 minutes, it was cooled to room temperature, immersed in the same electroless nickel plating solution as in Example 1 to carry out electroless nickel plating, and subsequently, as in Example 2, electroless copper plating using copper nitrate. went. The copper plating film obtained was subjected to a tape peeling test on a mirror surface, and as a result, the adhesion was good. As a result of measuring the film thickness by Auger analysis, it was estimated that the nickel film thickness was 1200Å and the copper film thickness was 600Å.

[0026]

As described above, according to the plating method of the present invention, the electroless plating method can be easily performed even on a semiconductive mirror-finished object such as a semiconductor wafer, which has been difficult in the past. And good adhesion on the wafer,
A mirror-like metal film layer can be formed.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] December 3, 2002 (2002.12.
3)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction content]

In the present invention, a seed layer is formed by electroless plating with copper or nickel after applying a catalyst on the barrier layer by the above-mentioned pretreatment method instead of the conventional seed layer forming method. By this method, the problem of insufficient coverage of the inner sidewall of the via / trench in the case of fine wiring is solved by CVD.
It can be solved at a lower cost than the law. When copper is electrolessly plated, it is possible not only as a seed layer but also as it is, to continuously embed wiring by electroless plating. In electroless plating, when the catalyst is evenly attached to the surface to be plated, the film grows evenly on the surface to be plated, so that seams are likely to occur in the case of fine wiring. However, when the catalyst is applied by the pretreatment method, the catalyst tends to adhere to the inner wall of the fine wiring. Since the metal tends to deposit more easily in a place where the amount of catalyst deposited is larger, in this case, bottom-up type deposition such as the electrolytic copper plating solution used for embedding fine wiring occurs, and it does not generate seams. Wiring can be embedded. Of course, it is also possible to embed the wiring by electrolytic copper plating after forming the seed layer by electroless copper plating. Generally, the electroless copper plating solution contains formalin as a reducing agent. However, the use of formalin has tended to be avoided in recent years due to the growing problem of environmental impact. Therefore, this problem can be solved by using an electroless nickel plating solution. In the case of electroless nickel plating, the coating generally contains a few% of phosphorus or boron, so that the electrical resistance is high. Therefore, when the seed layer is formed by electroless nickel plating, it is necessary to suppress the film thickness to the minimum thickness at which conduction can be obtained. Further, by using the electroless plating method of the present invention, it is possible to form a barrier metal on an insulating film when forming an LSI wiring. As an example of the barrier metal in that case, nickel, cobalt, or an alloy of these metals and another metal (such as tungsten) can be considered. As a matter of course, after forming a barrier metal film by the electroless plating method of the present invention, it is possible to further form a copper wiring film by electroless plating. In the electroless nickel plating of the present invention, it is important to use dimethylamine-borane as a reducing agent for the nickel plating solution and ammonia for pH adjustment. By using dimethylamine-borane as a reducing agent and ammonia for pH adjustment, the stress of the nickel plating film is relieved, and the plating film becomes difficult to peel off. For example, even if hypophosphite is used as a reducing agent, the intended effect of the present invention cannot be exhibited. Further, even if dimethylamine-borane is used as a reducing agent and sodium hydroxide is used for pH adjustment, the intended effect of the present invention cannot be exhibited. Further, in the electroless copper plating of the present invention, it is important to use a copper nitrate system in the copper plating solution, and when a copper sulfate system is used, the desired effect of the present invention is not exhibited. Can not.
By using the plating solution of the present invention, the present invention,
The electroless nickel plating film and / or the electroless copper plating film can be formed with good adhesion.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Junji Yabe             187, Hwagawa-cho, Kitaibaraki City, Ibaraki Prefecture 4 Stock Association             Inside the company's Isohara factory (72) Inventor Takashi Kinase             1-6-8 Akasaka, Minato-ku, Tokyo Nikko Meta             Within Ruplating Co., Ltd. F-term (reference) 4K022 AA05 BA08 BA31 BA36 CA03                       CA05 DA03 DB01 DB02 DB03                 4M104 BB04 BB05 DD53

Claims (5)

[Claims] 1. When performing electroless nickel plating on the surface to be plated, dimethylamine borane is used as a reducing agent and pH is adjusted.
A method for electroless nickel plating, which comprises using an electroless nickel plating solution containing ammonia as a modifier. 2. An electroless copper plating method, which comprises using an electroless copper plating solution containing copper nitrate when performing electroless copper plating on a surface to be plated. 3. When performing electroless nickel plating on the surface to be plated, electroless nickel plating is performed using an electroless nickel plating solution containing dimethylamine borane as a reducing agent and ammonia as a pH adjuster, Furthermore, the electroless plating method is characterized in that electroless copper plating is performed using an electroless copper plating solution containing copper nitrate. 4. A semiconductor wafer having a metal plating layer formed by the method according to claim 1. 5. A semiconductor device manufactured from the semiconductor wafer according to claim 4.