电镀温度对硅晶片上化学镀非晶 Ni-P 膜的影响

Abstract 

Nickel-phosphorus(NiP) film was depositedby electroless process on the surface of p-type polycrys-talline silicon at the temperature of 60 80 C and pH valueof 10.0. The effect of plating temperature on morphologycrystallographic structure, chemical composition anddeposition rate of Ni-P film was studied. Microstructureand morphology of surface and cross section of the filmwere examined by a scanning electron microscopy andoptical microscopy. The crystallographic structure andchemical composition of the film were determined byX-ray diffraction and energy dispersive spectroscopy.respectively. The results show that electroless Ni-P filmswere composed of the amorphous phase. The stable valueP-content of the film was maintained at about 12 wt% withincreasing bath temperature. The film surface was denseand no cracking was found at 60 and 80 °C.However, thefilm deposited at 70 and 80 °C had a poor adherence to thesubstrate with evidence of delamination. The depositionrate of the film was increased with increasing platingtemperature. At the same time, the deposition mechanismof the film on silicon substrate in the alkaline bath solutionwas addressed.

Introduction

Silicon (Si) wafer is a thin slice of semiconductor materialwhich could be used for many areas, such as solar cell.integrated circuits, sensors and optical devices, electronicdevices and so on. However, the construction of thesedevices is dependent on quality and purity of silicon wafer(Shacham-Diamand et al. 2015). Metallization of Si waferis a vital step on device fabrication, which could affect thefunctional performance of the device (Sudagar et al. 2013;Furukawa and Mehregany 1996). Electroless metal deposition was a more attractive process for metallization inmany applications of nanotechnology. Electroless processis a fast, low cost and low energy process without voltageor vacuum condition (Andersson et al. 2008: Zhou et al.2009: Chen et al. 2001). Uniform and adherent metallicfilms by electroless could be produced on the surface of Siwafer. This process could be occurred by the complexedredox reactions of a reductant and an oxidizer in an electrolyte solution.

Nickel-phosphorus (Ni P) alloy has excellent mechan-ical, electrical, magnetic and anticorrosive propertieswhich could be synthesized by electroless process. Forelectroless process, the deposition conditions, such as bathcomposition, plating temperature, pH, stirring, platingperiod, stabilizer and additives, could have a significantinfluence on the deposition rate, structure an chemicalcomposition and the quality of film (Xie and Zhang 2002:Liu et al. 2006; Singh et al. 2014; Moniruzzaman and Roy2011; Liu et al. 2015, Rahman and Jayaganthan 2015; Huaet al. 2013). The stability of the electrolyte bath was relatedwith bath chemistry and stabilizer (Osifuye et al. 2014:Bulasara et al. 201 1). Therefore, it is necessary to optimizethe deposition conditions to obtain a good quality film. Xieand Zhang (Xie and Zhang 2002) studied the effects of bath chemistry and pH value on the structure and amorphous forming region for electroless Ni–P alloys with 9–10 at % P-content in the alkaline bath solution at plating temperature of 90  C and found that deposition rates had a maximum value with increase in the concentration of Ni2?, H2PO2 and pH value, respectively. However, the deposition rates decreased with the increase in the concentration of citrate ions. The pH value is a signifificant factor on the complex ions between the Ni2? ions and complex agent, and the P-content in the deposit depends on the solution pH value (Lobanova et al. 2011). Liu et al. (Liu et al. 2006) studied the deposition rate of electroless Ni–P fifilms on Si substrates with prior to sensitization and activation treatment in an acid plating bath increased with increase of the pH and the plating temperature. Plating temperature is also a signifificant parameter in determining deposition rate, which is related with the nature of the plated material (Cheong et al. 2007). Until now, few reports studied the effect of plating temperature on electroless Ni–P fifilm on Si substrates in an alkaline bath solution. In this work, the electroless Ni–P fifilm was plated in an alkaline bath solution on the surface of p-type polycrystalline Si substrates. The effect of plating temperature on the morphology, crystallographic structure, chemical composition and deposition rate of Ni–P fifilm was studied. At the same time, the deposition mechanism of electroless Ni–P fifilm on Si wafers in the alkaline bath solution was addressed.

Experimental 

The p-type polycrystalline Si wafers were used as the substrates (size: 15 9 15 9 0.2 mm). One surface of the substrate was etched by reactive ion etching process, which was described in detail in reference (Yoo et al. 2011). Prior to plating, the substrates were cleaned with acetone in an ultrasonic bath for 5 min. A small deposition cell was used for the deposition of the fifilm on the substrates. The bath chemistry and operation conditions are listed in Table 1. No additives and stabilizers were used. The deposition times corresponded at plating temperatures of 60, 70 and 80  C were set for 40, 45 and 40 min, respectively. The volume of bath solutions was 50 mL. All solutions were dissolved in deionized water (Simplicity, Millipore) on a magnetic stirring apparatus with a magnetic stir bar. The pH of the solution was measured by pH meter (PHS-3C) under magnetic stirring, and was adjusted to a desired value by adding 5.0 M sodium hydroxide (NaOH) solution at room temperature. A HH-S thermostatic bath was used to control the plating temperature. During plating process, the substrate was put into the electrolyte through a plastic clip without magnetic stirring.