10.1.2023 – Miller Paper

12.8 Final.2025

Abstract
Silicon nitride (SiNx) is an important and widely used material in many applications due to its intermediate (7 ~ 10) dielectric constant, ultrawide band gap, high strength, and other properties [1]. Patterning thin films of SiNx typically involves the use of plasma etching with fluorocarbons such as CF4, CHF3, and others [2]. While these gases are highly effective for silicon nitride (and many other) etches, they have an unfortunately high global warming potential. As a result, Skyworks Solutions has taken the initiative to substantially reduce the use of fluorocarbons and other greenhouse gases [3, 4]. In the current study, a legacy fluorocarbon-based SiNx etch for the resistor layer is investigated. This plasma etch is somewhat unique in that undercutting the dielectric beneath the photoresist mask is the desired result, and therefore little to no sidewall passivation should be required. Suitable undercut facilitates a successful liftoff of the reactively-sputtered tantalum nitride thin film. The results show that well-targeted critical dimensions and device performance can be achieved for a resistor layer etch without the use of a polymerizing gas (i.e. CHF3). Moreover, by eliminating CHF3, a higher etch rate is achieved and the process time can be halved without negatively impacting the device. This study demonstrates that manufacturing processes can be designed to meet or exceed both sustainability and productivity goals simultaneously.

12.14 Final.2025

Abstract
Defects known as “craters” because of their resemblance to actual craters (Fig. 1) can cause scrap events, lower die yields, and increased cycle time due to the necessary process reworks to remove the defect source. Affected wafers exhibit a delaminated metal seed layer along the defect site, resulting in inconsistent gold plating atop the seed layer (Fig. 2). Without a uniform plated-gold layer, wafers must either be scrapped or reworked due to increased risk of copper migration through the collector layer [1].
Crater defect formation has been revealed with the help of cross-sectional SEM (Scanning Electron Microscope) using FIB (Focused Ion Beam). A pinhole is created through the seed layer being deposited atop a particle. The pinhole enables NH4OH to galvanically corrode the underlying metal within the multi-metallic seed layer during the pre-plating clean. This galvanic corrosion of the seed layer then causes nonuniform gold plating. Leveraging this finding, it is explored how modifying this pre-clean step can significantly reduce crater defect prevalence, as with the seed layer more intact, gold plating remains uniform.
Through this multi-faceted approach, both the prevalence and impact of crater defects is reduced through halting the frequency of initial pinhole formation and mitigating the impact of the subsequent galvanic corrosion.