Recently, the circuit under pad (CUP) designs are getting very popular because they could save lots of silicon especially for high-density and high-complexity applications. Polysilicon is a material widely used in many electronic device components. When such devices are placed underneath the bond pads, it is highly expected not to show any change in the electrical behavior due to any kind of thermo-mechanical stresses such as probing or wire bonding mainly during the process of packaging. This article presents a detailed investigation of such impacts on a polysilicon resistor placed underneath the bond pads. The standard meander-shaped polysilicon resistor was used as a test vehicle. In this article, different stress-causing factors such as probing insertions, probing temperature, and wire bond materials were investigated in detail. The impact of such thermo-mechanical stresses is simulated using Comsol to understand the stress phenomenon and for qualitative analysis. Then, the wafer-level silicon testing was carried out to quantify the impact of such thermo-mechanical stresses using a standard design of experiments (DOEs). The impact in terms of change in resistance of the polysilicon resistor of two different widths (5 and 0.42 $\mu \text{m}$ ) for two different bond pad metal options viz. Middle thickness metal (METMID) (thickness of 880 nm) and thick metal (METTHK) (thickness of 3000 nm) was investigated. The percent change in resistance was observed to be very negligible after multiple probing attempts and probe temperatures. However, after wire bonding, up to ~14% change in resistance was observed when copper was used as the wire bonding material. Nevertheless, this percent change was still well within the reliability specification limit set by Joint Electron Device Engineering Council (JEDEC), which is widely used in the industry. This detailed investigation will help CUP designers choose the correct back end of line (BEOL) metal options and also wire bonding material upfront and accordingly plan their design margins.

中文翻译：

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由于探测和引线键合对 CUP 器件的热机械应力的影响

最近，焊盘下电路（CUP）设计变得非常流行，因为它们可以节省大量硅，特别是对于高密度和高复杂性的应用。多晶硅是一种广泛用于许多电子设备组件的材料。当此类器件放置在焊盘下方时，非常希望不会由于任何类型的热机械应力（例如主要在封装过程中的探测或引线键合）而导致电气行为发生任何变化。本文详细研究了这种对放置在焊盘下方的多晶硅电阻器的影响。标准的曲折形多晶硅电阻器用作测试载体。在本文中，详细研究了不同的应力引起因素，例如探测插入、探测温度和引线键合材料。使用 Comsol 模拟此类热机械应力的影响，以了解应力现象并进行定性分析。然后，使用标准实验设计 (DOE) 进行晶圆级硅测试以量化此类热机械应力的影响。两种不同宽度（5 和 0.42 $\mu \text{m}$ ) 用于两种不同的焊盘金属选项，即。研究了中等厚度金属（METMID）（880nm的厚度）和厚金属（METTHK）（3000nm的厚度）。在多次探测尝试和探测温度后，观察到电阻的百分比变化可以忽略不计。然而，在引线键合之后，当使用铜作为引线键合材料时，观察到高达约 14% 的电阻变化。尽管如此，这个百分比变化仍然完全在联合电子设备工程委员会 (JEDEC) 设定的可靠性规范限制内，该委员会在行业中广泛使用。这项详细的调查将帮助 CUP 设计人员选择正确的后端 (BEOL) 金属选项，并预先选择引线键合材料，并相应地规划他们的设计余量。