使用气动翘曲晶圆的低失真融合键合
Low Distortion Fusion Bonding using Pneumatically Warped Wafers
AI总结：
本文评估了SUSS XBA工具中的低失真键合方法，通过无局部外力启动键合和保持晶圆柔顺对称，利用气动翘曲实现亚10纳米网格失真。
摘要：
背面供电网络（BSPDN）方案需要晶圆到晶圆的键合步骤，这些步骤不会在键合堆叠中留下高阶形状变化或局部应力，以确保这些不会转移到减薄晶圆以进行进一步的光刻曝光。然而，键合力学涉及强大的粘附力，这本质上会产生局部失真，最终需要光刻工具进行补偿。目标晶圆网格失真的一些贡献因素包括：键合启动方法、键合前沿速度变化以及晶圆之间缺乏对称性。在这项工作中，我们评估了SUSS XBA工具中的低失真键合方法，其中一些贡献因素在源头得到解决，即通过在没有局部外力的情况下启动键合，并在键合过程中保持晶圆的柔顺性和对称性。晶圆在键合过程中由于施加在整个晶圆背面的受控气压而带有轻微的预应力。使用键合堆叠的晶圆形状测量进行基于梯度的面内位移（IPD）建模，以估计键合引起的网格失真。使用密集扫描仪计量学对图案化键合晶圆进行测量，以确认来自图案化晶圆几何（PWG）测量的失真预测的位置和严重程度。在PWG失真图和扫描仪网格读数上，我们使用不同的场布局进行对准和CPE建模。使用相对低阶的校正模型可以实现亚10纳米的残余网格失真水平，而使用高级CPE模型则可达到小于或等于3纳米。这些结果表明，气动翘曲键合可产生低失真的键合堆叠，并且简单的工艺调整可以将主要失真源与边缘相关变异性解耦。
英文摘要：
Backside power-delivery-network (BSPDN) schemes require wafer-to-wafer bonding steps that do not leave high order shape changes or localized stresses in the bonded stack to ensure that these don't get transferred to the thinned wafer for further lithographic exposure. However, bonding mechanics involve strong adhesive forces which can inherently create localized distortions that lithography tools must eventually compensate. Some contributors to grid distortion of the target wafer are, method of bond initiation, bond front velocity variations, and lack of symmetry between the wafers. In this work, we evaluate a low-distortion bonding approach in the SUSS XBA tool, where some of these contributors are tackled at the source, namely by initiating the bond without a localized external force, and keeping the wafers compliant & symmetric during bonding. Wafers are bonded with a slight pre-stress due to controlled gas pressure applied over the whole backside of the wafers throughout bonding. Wafer-shape measurements of the bonded stacks are used to perform gradient-based in-plane-displacements (IPD) modelling to estimate bonding-induced grid distortion. Dense scanner metrology is used on patterned-bonded wafers to confirm the location and severity of distortion predictions from patterned wafer geometry (PWG) measurements. On the PWG distortion maps and scanner grid readouts, we perform alignment and CPE modelling with different field layouts. Sub-10 nm levels of residual grid distortion are achievable with relatively low-order correction models, and less than or equal to 3 nm by using advanced CPE models. These results demonstrate that pneumatically warped bonding yields low-distortion bonded stacks, and that simple process tuning can decouple the dominant distortion source from edge-related variability.
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