JP2000178753A - Electroless plating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent short circuit defect between wirings caused by the abnormal deposition generated after electroless plating by applying a surface modifying agent for decreasing the contact angle of the surface of an insulating body of a material to be plated before plating process. SOLUTION: In the case that the insulating body of a Cu wiring board or a Cu/Ni-wiring board is a polymer, the contact angle is about 65-67 deg. if the surface treatment is not applied and the abnormal deposition occurs after plating. When the board is treated with oxygen ashing as the surface modifying treatment, the contact angle is lowered to 7-11 deg. to exhibit hydrophilicity and the abnormal deposition does not occur on the board sent to the plating process. The contact angle is also lowered to 9-20 deg. by the irradiation with UV or the etching treatment with various kinds of polymers such as ethylene diamine/ hydrazine mixed solution and the abnormal deposition suppressing effect is exhibited by applying the surface treatment direct before the plating process. The contact angle is not changed, that is 65-69 deg., even by reduction annealing treatment in the surface treatments and the abnormal deposition occurs when the board is charged to the plating process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroless plating method for preventing a short circuit between wirings due to abnormal deposition occurring after electroless plating.

[0002]

2. Description of the Related Art As high-density mounting has progressed in recent years, electroless plating has attracted attention as a design constraint on a power supply lead wire for electrolytic plating and a method of plating an electrically isolated fine pattern. It is getting. A general electroless gold plating process when the metal to be plated is copper or nickel is shown in FIGS. 1 and 2, respectively. In displacement gold plating, gold ions in a plating solution displace the metal to be plated on the conductor. Therefore, when gold is deposited on the entire surface of the metal to be plated, the reaction stops, and a thick gold film cannot be obtained. On the other hand, in electroless gold plating, gold is deposited on a conductor to be plated by a reduction reaction of gold ions by a reducing agent, so that a thick gold film can be formed. However, when a thick gold film is required, it is used in combination with a replacement gold plating solution having better adhesion to the base metal to be plated.

[0003]

When electroless plating is performed, there is a problem that plating is deposited on an insulating portion, that is, abnormal deposition (also referred to as out-of-pattern deposition, plating spread, or extruded deposition) occurs.

As a cause of abnormal deposition, when the metal to be plated is copper, Pd colloids or Pd particles adhere to the surface of the insulator in the Pd activation treatment step, which is one of the plating pretreatment steps, and then nickel plating is performed. It is thought that it becomes the core of abnormal precipitation in the liquid. When the metal to be plated is nickel, the Pd treatment is not performed, but abnormal deposition may occur after gold plating. This is presumably because gold colloid or gold fine particles generated in the displacement gold plating solution or the electroless gold plating solution adhered to the insulator surface and became the core of abnormal deposition. The nuclei of these abnormal depositions grow with the progress of the plating reaction, and there is a problem that covering the insulator surface between the fine wiring patterns causes a short circuit failure or the like.

Therefore, in order to prevent abnormal deposition, a method of adding a component for suppressing abnormal deposition in advance to a Pd active solution or an electroless plating solution for plating pretreatment is generally used. For example, Japanese Patent Application Laid-Open No. 5-156457 discloses a nickel plating solution in which a Pd activating solution, which is a pretreatment solution for nickel plating, is added with a pH buffer agent that maintains the pH of the nickel plating solution at about 3.0 to 4.5. A method for suppressing nucleation of abnormal precipitation by suppressing a sudden pH change caused by bringing in a pretreatment liquid into the pit is disclosed.

[0006] A method of adding a nonionic surfactant and / or a nonionic polymer to a plating solution and adsorbing it on the surface of an insulator to be plated to prevent nucleus adsorption of abnormal precipitation is disclosed in Japanese Patent Application Laid-Open No. H06-26,004. -280039.

[0007]

[Means for Solving the Problems] The chemical solution in the pre-plating process is
When brought into the electroless plating solution, the metal complex in the plating solution is easily decomposed due to a sudden change in pH or the like. as a result,
Since it is fully conceivable that metal fine particles are generated and serve as nuclei for abnormal deposition, measures against such causes include:
The invention of JP-A-5-156457 is effective.
However, there is no effect when the disproportionation reaction that occurs irrespective of the pH fluctuation, for example, adhesion of gold fine particles generated by the disproportionation reaction during electroless gold plating (formula (1)) causes abnormal deposition. . 3Au ⁺ → 2Au ⁺ Au ³⁺ ...... formula (1) On the other hand, if the addition of surfactants and / or polymers are disclosed in JP-A-6-280039, adsorbed nuclei grow nucleus itself abnormal deposition Therefore, it is effective for suppressing abnormal precipitation. However, the surfactant and / or the polymer is easily adsorbed on the conductor surface, and there is a problem that the plating reaction itself is inhibited to cause a reduction in plating rate or cause non-precipitation. Therefore, these additives must be used at the lowest possible concentration, and because of their low concentrations, once added to the plating solution, they fall below the analytical detection limit, making it difficult to control the concentration of the additives. In addition, since the concentration of these additives decreases due to carry-out or consumption during continuous use of plating, there is a problem that the effect of suppressing abnormal precipitation is lost and abnormal precipitation occurs suddenly.

Therefore, the present inventors focused on the surface of the object to be plated and, using a Cu wiring substrate or a Cu / Ni-W wiring substrate, performed surface modification treatment of the object to be plated immediately before the electroless plating step by various methods. , And then passed through an electroless plating process to evaluate the occurrence of abnormal precipitation. As a result, they found that abnormal plating deposition did not occur if the contact angle of the insulator surface was reduced by modifying the substrate surface. FIGS. 3 and 4 show a series of plating steps including the substrate surface modification treatment of the present invention.
It was shown to.

When the insulator of the Cu wiring substrate or the Cu / Ni-W wiring substrate is a polymer, the contact angle is about 65 ° to 67 ° without the substrate surface modification treatment. When this surface condition was applied to the plating step shown in FIG. 1 or FIG. 2, abnormal deposition was observed after plating. On the other hand, immediately before the plating step, when the substrate was subjected to oxygen ashing as a surface modification treatment, the contact angle was reduced to 7 ° to 11 °, indicating hydrophilicity. When this substrate was put into the plating step shown in FIG. 1 or FIG. 2, no abnormal precipitation was observed after plating. In other words, this suggests that nuclei of abnormal precipitation are unlikely to be adsorbed on the surface of the insulator subjected to the hydrophilic treatment. It was found that the contact angle of the insulator polymer was reduced to 9 ° to 20 ° in the UV irradiation treatment and various polymer etching treatments such as a mixed solution of ethylenediamine / hydrazine, similarly to the oxygen ashing treatment. Even when these surface modification treatments were used alone or in combination freely just before the plating step, an effect of suppressing abnormal precipitation was observed.

On the other hand, even when the surface modification treatment was carried out in the plating step with the contact angle of the insulator surface being 65 ° to 69 ° after the reduction annealing treatment, which was unchanged from that before the treatment, abnormal deposition was observed after plating. . That is, in the surface modification treatment, the effect of suppressing abnormal precipitation can be obtained only when the contact angle of the insulator surface is significantly reduced. The insulator surface modification treatment that exhibits the effect of suppressing abnormal precipitation is not limited to the insulator surface modification treatment method described above as long as the contact angle after treatment is 20 ° or less.

[0011] The effect of the insulator surface modification treatment step for reducing the contact angle cannot be expected unless it is always performed immediately before the plating step. For example, the substrate after the reduction annealing treatment was subjected to oxygen ashing, and when put into the plating process, abnormal precipitation was not recognized, but after the oxygen ashing treatment,
When the substrate subjected to the reduction annealing treatment was put into the plating step, abnormal deposition was observed.

Although the mechanism of suppressing abnormal precipitation due to a decrease in the contact angle of the insulator surface is unknown, carboxyl groups were detected by ESCA analysis of the surface of the insulator polymer subjected to oxygen ashing. That is, it is considered that the formation of the hydrophilic group is the cause of the decrease in the contact angle. Since the polymer surface which originally has no hydrophilic group has poor wettability to water or plating solution, the nuclei of abnormal deposition adsorbed on the polymer surface will not be detached by the washing process or the self-cleaning effect of the plating solution itself. It seems to grow to abnormal precipitation. Therefore, it can be presumed that the nucleus adsorption of abnormal precipitation is suppressed on the hydrophilic polymer surface.

As described above, the present invention effectively suppresses abnormal deposition by modifying the surface of the insulator to be plated without adding an abnormal deposition suppressing component to the electroless plating solution as in the prior art. An electroless plating process is provided.

[0014]

(Embodiment 1) The contact angle of the insulator polymer surface of a sputtered Cu (2.0 μm thick) / sputtered Ni-W (2.0 μm thick) wiring board was measured (contact angle). Total: CA-A type: manufactured by Kyowa Interface Science Co., Ltd.)
This substrate was first subjected to a surface modification treatment according to the process shown in FIG. After measuring the insulator surface contact angle again, it was immersed in an acidic degreasing solution for 1 minute as a degreasing treatment. Next, it was immersed in 10% hydrochloric acid for one minute as an acid treatment. Further, it was poured into a displacement gold plating solution to form a gold film of about 0.05 μm. Finally, plating was carried out to a thickness of about 0.2 micron with an electroless gold plating solution, washed with running water for 1 minute, washed for 1 minute, dried for 1 minute, and checked for abnormal precipitation with a metallographic microscope. Table 1 shows the results.
(Nos. 1 to 16). In addition, between each process, washing with running water (1 minute for primary washing, 1 to 3 minutes for secondary washing) was always performed.

[0015]

[Table 1]

Example 2 The contact angle of the insulator polymer surface of a sputtered Cu (film thickness: 2.0 μm) wiring board was measured (contact angle meter: CA-A type: manufactured by Kyowa Interface Science Co., Ltd.).
Thereafter, the substrate was first subjected to a surface modification treatment according to the process shown in FIG. After measuring the insulator surface contact angle again, it was immersed in an acidic degreasing solution for 1 minute as a degreasing treatment. Then C
As a u-light etching treatment, the substrate was immersed in an aqueous solution of sodium persulfate for 30 seconds. Next, it was immersed in a 10% aqueous sulfuric acid solution for one minute as an acid treatment. Next, after being immersed in a Pd activation treatment solution for one minute, electroless nickel plating was performed. After a nickel film having a thickness of about 2 μm was formed, the resultant was poured into a displacement gold plating solution to form a gold film having a thickness of about 0.05 μm. And finally plating with electroless gold plating solution to about 0.2 micron thickness,
After washing with running water, drying was performed, and the presence or absence of abnormal precipitation was confirmed by a metallographic microscope. The results are shown in Table 2 (Nos. 17 to 32). In addition, between each process, running water washing (primary washing 1 minute, secondary washing 1 minute)
３3 minutes).

[0017]

[Table 2]

Comparative Example 1 The contact angle of the insulator polymer surface of a sputtered Cu (2.0 μm thick) / sputtered Ni—W (2.0 μm thick) wiring board was measured (contact angle meter: CA−). After type A: manufactured by Kyowa Interface Science Co., Ltd.), the substrate was first immersed in an acidic degreasing solution for 1 minute as a degreasing treatment according to the process shown in FIG. Next, as an acid treatment, add 1%
After immersion, it was poured into a displacement gold plating solution to form a gold film of about 0.05 μm. Finally, it was plated to a thickness of about 0.2 micron with an electroless gold plating solution, washed with running water, dried, and checked for abnormal deposition with a metallographic microscope. The results are shown in Table 3 (Nos. 1 to 3). In addition, between each process, washing with running water (1 minute for primary washing, 1 to 3 minutes for secondary washing) was always performed.

[0019]

[Table 3]

(Comparative Example 2) The contact angle of the insulator polymer surface of a sputtered Cu (film thickness: 2.0 μm) wiring substrate was measured (contact angle meter: CA-A type: manufactured by Kyowa Interface Science Co., Ltd.).
Thereafter, the substrate was immersed in an acidic degreasing solution for one minute as a degreasing treatment in accordance with the process shown in FIG. Next, as a Cu light etching treatment, the substrate was immersed in an aqueous solution of sodium persulfate for 30 seconds. Next, it was immersed in a 10% aqueous sulfuric acid solution for one minute as an acid treatment. Next, after being immersed in a Pd activation treatment solution for 1 minute, electroless nickel plating was performed. After forming a nickel film having a thickness of about 2 μm, the nickel film was introduced into a displacement gold plating solution to form a gold film having a thickness of about 0.05 μm. And finally, it was plated with an electroless gold plating solution to a thickness of about 0.2 μm, washed with running water and dried, and the presence or absence of abnormal deposition was confirmed by a metallographic microscope. The results are shown in Table 4 (Nos. 3 to 6). In addition, between each process, washing with running water (1 minute for primary washing, 1 to 3 minutes for secondary washing) was always performed.

[0021]

[Table 4]

[0022]

As described above in detail, according to the present invention, since abnormal deposition can be suppressed, there is no fear of short-circuit failure between wirings caused by abnormal deposition. Therefore, electroless plating on a high-density fine wiring pattern is possible. Further, since it is not necessary to add an abnormal precipitation suppressing component to the electroless plating solution, it is not necessary to control the concentration of the trace suppressing component, so that the plating workability is improved and the method can be sufficiently applied to mass production.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a conventional electroless Au plating process.

FIG. 2 is a flowchart showing a conventional electroless Ni / Au plating process.

FIG. 3 is a flowchart showing an electroless Au plating process according to one embodiment of the present invention.

FIG. 4 is a flowchart showing an electroless Ni / Au plating process according to another embodiment of the present invention.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yuko Takehara 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside of Hitachi, Ltd. (72) Inventor Toshihiko Ota 1 Horiyamashita, Hadano-shi, Kanagawa F-term (reference) 4G022 AA13 AA42 BA03 BA08 CA03 CA05 CA06 CA07 CA12 CA21 CA22 CA28 CA29 DA01 DA03 5E343 AA12 BB23 BB24 BB55 CC46 DD25 DD33 EE32 EE36 EE37 GG08 GG20

Claims (4)

[Claims] 1. An electroless plating method, comprising: performing a surface modification treatment to reduce a contact angle of an insulator surface of an object to be plated before a plating step. 2. The electroless plating method according to claim 1, wherein said surface modification treatment is an insulator surface modification step. 3. The electroless plating method according to claim 2, wherein said insulator surface modifying step comprises at least one of an oxygen ashing step, a UV irradiation step and a wet etching step. 4. The electroless plating method according to claim 2, wherein said insulator is made of a polymer.