Palladium chloride 1.0 10 3mol/dm3 (as Pd) Disodium hydrogen phosphate (buffer) 0.1 mol/dm3 NH4Cl 1mol/dm3 Sodium dodecylsulfate 3 30 10 4mol/dm3

pH 2.5 (Adjusted by NaOH and HCl) Temperature R.T. (25

�

C)

Evaluation of Activating Process for Fine Pattern Deposition

Taiji Nishiwaki, Yozo Watanabe, Shingo Watanabe,

Katsuhiro Tashiro and Hideo Honma Faculty of Engineering, Kanto Gakuin University

1-50-1 Mutsuura-higashi, Kanazawa-ku, Yokohama-shi Kanagawa 236-0032, Japan

Abstract

In recent years, the electronic devices are becoming smaller and more complicated sharply, since many electronic instruments are downsized. As a result, L/S (lines and spaces) of circuit pattern and ULSI (ultra large scale integrated circuit) wiring formation progress toward minimal.

Accordingly, in order to correspond to LSI and CSP packaging with higher densities, PCBs (printed circuit boards) of 50 m L/S or less have been developed [1,2]. Electroless nickel and immersion gold plating for the high density PCBs, BGA (ball grid alley) and CSP (chip scale package) manufacturing process are the key technology to obtain the connection reliability. Moreover, in the semiconductor manufacturing technology, the wiring of ULSI shifts from aluminum to copper interconnection after damascene process using the copper electroplating is announced. In the manufacturing process, to improve electromigration of copper to the SiN film, it has been examined that electroless nickel plating is applied to establish the barrier metal layer in sub- m order[3]. In the case of electroless nickel plating using hypophosphite as a reducing agent, the palladium activation step is generally necessary for the initiation of electroless nickel deposition on copper, because metallic copper does not have a catalytic activity to the hypophosphite ions [4].

However, as the space between the patterns has become narrow, bridges and/or outgrowths between circuit patterns are critical issue and the palladium activation step in the pretreatment is considered to cause extraneous deposition on insulator. Accordingly, we investigated relationships between deposition of plating film to fine wiring and Pd activating process and developed the excellent bath composition with selectivity and proposed mechanism of the reaction [5].

On the other hand, we have previously reported on the alternative process using reducing agent to initiate the plating reaction without palladium activation step. [6,7,8].

In this examination, palladium activating process and initiation of the plating reaction by the alternative process without palladium activation were compared for the selective deposition of the electroless nickel plating to obtain fine patterns.

The composition and conditions of palladium activating solution were shown in Table 1 and an alternative process composition and conditions are shown in Table2.Epoxy resin PCB(L/S <100 m) and the silicon wafer treated CMP after electro copper deposition(trench of 0.25 1.0 m in width, and via hole of 0.35 1.0 m in diameter) were used as the test sample. After performing electroless nickel plating by using the experiment process as shown in Table 3, the substrate after treatment was observed by FE-SEM

(Field Emission scanning electron microscope) and SEM (scanning electron microscope) as shown in Fig.1. Selective deposition is evaluated as the above-method and the reaction mechanism of each process is discussed.

These results will be explained in detail. Table.1 Activating solution composition and operating condition Table.2 Alternative activating bath composition and conditions

Table3. Experimental procedure (a)Blank (b) Excellent selective deposition (c) Outgrowth deposition (extraneous deposition) Fig.1 FE-SEM images of surface morphology Reference 1) S.Hotta, H.Takahashi, Microelectronics symposium (Japan), 10, P27 2000 2) N.Shindo, K.Kikuchi, K.Matsui, Y.Shimada, Microelectronics symposium (Japan), 10, P31 (2000) 3) Y.Takada, K.Ishiwkawa, S.Miura, H.Honma, J.Jap.Inst.Electro.Pack. 4.4,318 (2001) 4) D.W.Baudand Plating and Surface Finishing, Vol.68, No.12, p.50 (1979) 5) T.Nishiwaki,Y.Watanabe,H.Honma, 2002 IEMT/IMC symposium,Procedings,161-164(2002) 6) H.Watanabe, Y.Igawashi, H.Honma, J.Jap.Inst.Intercon.Pack.Electro.Circ. 12,4,231-2351997 7) H.Watanabe, H.Honma, 1998 IEMT/IMC Symposium, Proceedings, 149(1998) 8)K.Tashiro,Y.Takada,H.Honma, 2001 IEMT/IMC symposium,Procedings,160-165(2001)

Nickel( )Chloride 0.05mol/dm3 Glycine 0.40mol/dm3 Boric acid 0.50mol/dm3 Hydrazine 0.40mol/dm3 Hypoposhite 0.00 1.00mol/dm3

Adjusted by KCl and HCl Temperature 80(

�

C)

a) Pd activation process b) Alternative process 1. Cleaning

2. Acid cleaning

3. Pd-activation step Alternative activation step (Table2) (Table3)

4. Electroless Ni plating

5. Evaluation

600nm

(a) (b) (c)