Direct Electroless Deposition of Nickel onto Silicon Nitride Ceramic: A Novel Approach for Copper Metallization of Micro‐/Nano‐fabricated Devices

Abstract

Current surface modification chemistry of silicon nitride (Si3N4) in the fabrication of micro/nano systems (MEMS/NEMS) mainly relies on multistep chemical processes, essentially consisting of a surface pretreatment and a challenging silanization procedure. Although direct modification of Si3N4 surface has rarely been reported in the literature, here a simple surface functionalization strategy using diazonium chemistry in open air and at room temperature, which provides a practical solution to directly attach aminophenyl groups to pristine silicon nitride without altering its intrinsic properties, is described. These strongly grafted amine‐terminated groups are easily activated to become nuclei for initializing electroless nickel plating (autocatalytic nickel deposition). This electroless nickel plating of silicon nitride while avoiding the multiplicity and complexity of the process steps is ideal for its integration into a typical MEMS/NEMS process flow. In a possible integration scheme, due to its suitable properties, this nickel film serves as a conducting seed layer for the electrolytic deposition of copper to fill the microdevices, thereby avoids the use of typically employed expensive vacuum processes.

Electrochemical Grafting of an Aminated Poly(methyl methacrylate) (PMMA)-like Liner onto a Silicon Surface for the Metallization of Microfeatures

“…Besides the step-coverage, continuity, and uniformity of the electrolessly plated Ni, the chemical composition of Ni film is another crucial factor that determines its conductivity and diffusion barrier properties and hence its suitability as a seed layer. ,, Figure presents the EDX spectrum of the Ni/polymer composite, which confirms the presence of Ni peaks (at 0.742/0.762 and 0.851 keV) in addition to the elements from the underlying polymer layer (C at 0.277 keV, N at 0.392 keV, and O at 0.525 keV). A small peak of boron positioned at 0.183 keV cannot be undervalued as it is a light element ( Z = 5) and often undetectable on EDX measurements because of various inherent physical problems for the analysis of light elements with EDX (low fluorescence yield, absorption and peak overlapping with L, M, and N lines of the heavier elements.…”

“…The metallic Ni formed around the palladium nuclei autocatalyzes further reduction of Ni cations, for which reason the electroless plating can be regarded as “autocatalytic deposition”. With the passage of time, three-dimentional nucleation and growth of a Ni alloy via catalytic action occurs. , Under our working condition, an immersion duration of 5–6 min in a plating bath was sufficient to reach a point where a continuous compact film with strong adhesion entirely covers the top surface, scallop sidewall, and bottom of the microstructure as shown in Figure . The efficiency of the grafted PMMA-like liner in capturing Pd catalysts can explain the thickness uniformity from top to bottom of the microstructures, and a uniform film thickness of about 60 nm is found for all the areas exposed to the plating solution.…”

“…Here, the weight percentage of boron is quantified to be 6.0% from XPS elemental analysis, which is within the range of 5 to 7% as reported to be suitable for direct electrolytic plating of copper. 5,10,33 After obtaining the boron percentage within the target limits, we tested the applicability of the Ni−B seed/polymer liner. Figure 10 presents the cross-sectional SEM images exhibiting the metallic liner on the top surface and inside the microstructure after electroplating of copper.…”

“…Autocatalytic deposition, also known as electroless plating, onto dielectric films (SiO 2 , Si 3 N 4 ) is a key metallization technique in the fabrication of Si-based microelectromechanic systems (MEMS) in industry. − Current electroless plating processes rely on surface modification for grafting amine-terminated groups onto these dielectric substrates, allowing an activation to form nuclei for initiating the plating process. , These dielectric films are conventionally deposited on a Si substrate through different physical techniques, e.g., thermal oxidation, physical vapor deposition, and plasma-enhanced chemical vapor deposition. Various applications requiring these processes mainly face the following challenges: complex and high-maintenance-requiring process equipment, only operative at high temperature, resultant poor film uniformity in high-aspect-ratio features.…”

Study of Electroless Nickel Plating on Rapid Prototyping Model Using Acrylonitrile Butadiene Styrene

“…Copper [11], zinc [12], nickel [13], and chromium [14] are metals that can be metallized using various processes such as metal spray [15][16], metal paint [17][18], and electroless plating [19][20][21]. Because of the ease of the procedure, electroless plating is the most extensively utilized method among the previously stated ways in industry.…”