Deep trenches, as essential elements of silicon chips used in electronic high-power and high-frequency devices, are known as starting points for dislocation generation under the influence of internal mechanical stresses resulting mainly from the difference in the thermal expansion coefficients between silicon and silicon dioxide. Since the electrical insulation of the devices requires a sequence of mechanical, chemical, and high-temperature processes during the preparation of the deep trenches, including the formation of an amorphous SiO2 edge layer, the emergence of the internal stresses is hardly avoidable. The method of cross correlation backscattered electron diffraction in the scanning electron microscope is used here to quantitatively determine the magnitude and local distribution of internal stresses in silicon around the deep trenches after four different process steps. For this purpose, Kikuchi diffraction images are recorded of the wafer cross section areas along lines perpendicular and parallel to the deep trenches. After Fourier transformation, these images are cross correlated with the Fourier transform of the diffraction image from a stressfree reference sample site. The well-established numerical evaluation of cross correlation functions provides the complete distortion tensor for each measuring point of the line scan, from which the stress tensor can be calculated using Hooke's law. It is found that the in-plane normal stress component σ11 perpendicular to the long edges of the deep trench is larger than the other stress components. That means it essentially determines the magnitude of the von-Mises stress, which was determined as a general stress indicator for all measuring points, too. A characteristic feature is the local distribution of the stress component σ11 with maximum tensile stresses of some hundred megapascals at transition between Si and amorphous SiO2 on the long edges of the deep trench, and with even higher maximum compressive stresses immediately below the bottom of the deep trench. At a distance of about 2 μm from the edges of a single deep trench, all stress components decrease to negligibly small values so that steep stress gradients occur. The range and distribution of tensile and compressive stresses are in accordance with finite element simulations; however, the measured stresses are higher than expected for all investigated states so that dislocation formation seems to be possible. The influence of the electron acceleration voltage on the determination of the internal stresses is discussed as well.

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深沟槽高压器件内应力的研究

深沟槽作为电子大功率和高频器件中硅芯片的基本要素，被认为是在主要由硅和硅之间的热膨胀系数差异引起的内部机械应力影响下产生位错的起点。二氧化氮。由于在制备深沟槽期间，器件的电绝缘需要一系列机械、化学和高温工艺，包括形成非晶 SiO2 边缘层，因此很难避免内应力的出现。此处使用扫描电子显微镜中的交叉相关背散射电子衍射方法来定量确定经过四个不同工艺步骤后深沟槽周围硅中内应力的大小和局部分布。为此，沿垂直和平行于深沟槽的线记录晶片横截面区域的菊池衍射图像。傅里叶变换后，这些图像与来自无应力参考样本点的衍射图像的傅里叶变换相互关联。互相关函数的完善的数值评估为线扫描的每个测量点提供了完整的畸变张量，从中可以使用虎克定律计算应力张量。发现垂直于深沟槽长边的面内法向应力分量σ11大于其他应力分量。这意味着它本质上决定了 von-Mises 应力的大小，它也被确定为所有测量点的一般应力指标。一个特征是应力分量 σ11 的局部分布，在深沟槽长边上的 Si 和非晶 SiO2 之间的过渡处具有数百兆帕的最大拉应力，并且在深沟槽底部的正下方具有更高的最大压应力。沟。在距单个深沟槽边缘约 2 μm 的距离处，所有应力分量都减小到可以忽略不计的小值，从而出现陡峭的应力梯度。拉压应力的范围和分布符合有限元模拟；然而，对于所有研究状态，测得的应力都高于预期，因此位错的形成似乎是可能的。还讨论了电子加速电压对内应力确定的影响。