Session: 03-16-01: Manufacturing: General

Paper Number: 112938

112938 - Error Budget of Wafer Bonding Alignment System Based on Machine Vision 

As one of the ways to transcend Moore's Law, 3D stacking technology is a hot research direction of microsystem integration. Wafer bonding is one of the key technologies of 3D stacking. Alignment is a critical component of wafer bonding, and the accuracy of the alignment determines the yield and performance of the bonding process.

To ensure the accuracy of wafer alignment during high-precision wafer bonding, the Marks on two quasi-wafers to be aligned are precisely positioned by machine vision. The method of machine vision measurement brings new challenges to the error budget of such high-precision systems. At the same time, as a kind of complex precision system, the wafer bonding alignment system completes the complex motion through the complex mechanism to realize the function, involving the multi-degree of freedom motion components that drive the wafers to be aligned respectively, introducing the influence of multiple sources of error. Moreover, there are many links in the alignment process, which makes the coupling effect of multiple errors more complex, and brings difficulties to the error budget of the alignment system.

This research is aimed at the error budget of a wafer bonding alignment system based on machine vision. First of all, considering that the alignment system has the characteristics of a shorter alignment process time and is dominated by static links, ignoring the impact of large inertia changes such as temperature, mainly focusing on the impact of static errors, the system is modeled with the Homogeneous Transformation Matrix (HTM) method as the core, and four error transfer chains are established. Then the possible error sources in the system are sorted out, the error types and action modes are defined, and the parameter modeling of a single error is carried out based on the actual test results. Combined with the process flow, the error model of each link is customized. Finally, the Monte Carlo simulation process is established to quantitatively simulate the error impact of the alignment system.

According to the simulation results, it can be determined that the main error influencing items of the alignment system include the position error of the alignment Marks on the wafer, the Z-direction positioning error of the wafer carrier platform, and the motion error of the wafer micro-motion platform. Combined with the alignment accuracy requirements of ± 100nm, the accuracy requirements of Marks’ position error within ± 100nm and wafer carrier Z’s position error within ± 100nm are proposed. At the same time, it guides the strategy design of improving the accuracy of the alignment system. The calibration scheme of the micro-motion table is proposed to reduce the motion error. Two horizontal position measurement schemes of wafer carriers are compared, and the advantages of two-point vision measurement over three-point capacitance sensor measurement are verified. The rationality of the error budget conclusion in this study is verified by the experiments in the construction machine platform, and the final accuracy of wafer alignment is effectively improved.

In summary, the main contributions of this paper are in the following three aspects: (a)an error budget method for complex precision systems is proposed, which can quantify the impact of various errors on multiple components and multiple process links; (b) the main error influencing items in wafer bonding alignment are determined, which provides optimized directions for improving the alignment accuracy; (c) the strategy design to effectively improve the alignment accuracy is given, which improves the accuracy of wafer deviation detection and motion compensation.

Presenting Author: Rui Wang Tsinghua University

Presenting Author Biography: Rui Wang received the B.S. degree in Mechanical Engineering from Tsinghua University, Beijing, China, in 2019. He is currently pursuing the Ph.D. degree in Mechanical Engineering at Tsinghua University, Beijing, China.
His research interests include precision assurance strategy of wafer bonding system and measurement accuracy of machine vision.

Authors:

Rui Wang Tsinghua University
Sen Lu Beijing Key Laboratory of Precision/Ultra-Precision Manufacturing Equipments and Control
Kaiming Yang Beijing Key Laboratory of Precision/Ultra-Precision Manufacturing Equipments and Control
Yu Zhu Department of Mechanical Engineering, Tsinghua University