Abstract
We propose and demonstrate a drop-in test structure to visualize and measure the residual stress in the conformally deposited film. For reliable device process of microsystems (such as 3-D MEMS), the residual stress must be controlled through quantitative evaluation at each deposition step. A small drop-in test structure placed near the main sample is suitable for monitoring film characteristics. We developed a free-standing rotating beam stress sensor as the drop-in test structure to visualize and measure the residual stress in conformally deposited films with no additional processes. The dimensions of the developed drop-in test structure chips were 5 mm ×10 mm. For a demonstration, supercritical fluid deposition (SCFD) was performed over the test structure chips under a couple of conditions. The residual stresses in SCFD films were successfully extracted by equation-based analysis.
Highlights
M ETALIZATION and/or insulation on high aspect ratio microstructures (HARMS [1]) and suspended structures is a major concern in the research of the micro electromechanical system (MEMS) technology
The Cu film was clearly deposited through our supercritical fluid deposition (SCFD) process
The fabricated drop-in test structure chip was small enough to be placed with the main sample in the chamber
Summary
M ETALIZATION and/or insulation on high aspect ratio microstructures (HARMS [1]) and suspended structures is a major concern in the research of the micro electromechanical system (MEMS) technology. Its applicable thickness is limited to several hundreds of nanometers [12] Another method is surface micromachining, in which strain gauges [15] and rotating strain sensors [16] are used to evaluate the stress of a film under test (FUT). The value is typically in hundreds of nanometers, and it does not necessarily match the request from the process engineers (e.g., they may want to characterize the stress of a < 50-nm-thick film). USAMI et al.: DROP-IN TEST STRUCTURE TO EVALUATE RESIDUAL STRESS IN CONFORMALLY GROWN FILMS
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