In recent years, the semiconductor industry has witnessed an increasingly fast rate of the adoption of Cu pillar bumps for a variety of devices including memory, logic, processors, FPGA, etc. Cu pillar bumping technology is a critical and important part of today’s Advanced Packaging for 2D flip chip devices, 2.5D interposers and 3D packages. They provide several advantages over their counterparts, among which are tighter pitch, larger number of I/Os as well as better heat dissipation. In today's semiconductor process the predominant source of defects lie within the process tool itself. Defects introduced during an individual processes step are either caused by the particles generated by the tool or the defects generated by the process itself. Bumping process tools are no exception and therefore monitoring their particle generation is very important to determine the right time for tool maintenance. Additionally, due to the constant drive to miniaturization, the size and pitch of these bumps are getting smaller and making the need for process tool monitoring stronger. Typical particle sizes need to be detected in back-end equipment with ranges anywhere from 0.1μm to 10μm and even more. The purpose of this article is to examine how a unique darkfield laser technique can be used to monitor process tools for the amount of particles they generate. Figure 1 shows the working principal of this sensor and an example of maps generated by the inspection tool. Particle and haze data generated using this technology on a monitor wafer allows engineers to maintain process tools at optimal cleaning levels.
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