Au-Sn 공정 접합을 이용한 RF MEMS 소자의 Hermetic 웨이퍼 레벨 패키징
Application of Au-Sn eutectic bondingin hermetic RF MEMS wafer level packaging
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초록
RF MEMS 기술에서 패키지의 개발은 매우 중요하다. RF MEMS 패키지는 소형화, hermetic 특성, 높은 RF 성능 및 신뢰성을 갖도록 설계되어야 한다. 또한 가능한 저온의 패키징 공정이 가능해야 한다. 본 연구에서는 저온 공정을 이용한 RF MEMS 소자의 hermetic 웨이퍼 레벨 패키징을 제안하였다. Hermetic sealing을 위하여 약 300C의 Au-Sn 공정 접합 (eutectic bonding) 기술을 사용하였으며, Au-Sn의 조합으로 형성된 sealing부의 폭은 70 µm이었다. 소자의 전기적 연결을 위하여 기판에 수직 via hole을 형성하고 전기도금 (electroplating) 방법을 이용하여 Cu로 채웠다. 완성된 RF MEMS 패키지의 최종 크기는 1mm 1mm 700 µm이었다. 패키징 공정의 최적화 및 O2 플라즈마 애싱 공정을 통하여 접합 계면 및 via hole의 void들을 제거할 수 있었다. 또한 패키지의 전단 강도 및 hermeticity는 MIL-STD-883F의 규격을 만족하였으며, 패키지 내부에서 오염 및 기타 유기 물질은 발생하지 않았다. 패키지의 삽입 손실은 2 GHz에서 0.075 dB로 매우 작았으며, 여러 종류의 신뢰성 시험 결과 패키지의 파손 및 성능의 감소는 발견되지 않았다.
Abstract
Development of the packaging is one of the critical issues for commercialization of the RF-MEMS devices. RF MEMS package should be designed to have small size, hermetic protection, good RF performance and high reliability. In addition, packaging should be conducted at sufficiently low temperature. In this paper, a low temperature hermetic wafer level packaging scheme for the RF-MEMS devices is presented. For hermetic sealing, Au-Sn eutectic bonding technology at the temperature below 300C is used. Au-Sn multilayer metallization with a square loop of 70 m in width is performed. The electrical feed-through is achieved by the vertical through-hole via filled with electroplated Cu. The size of the MEMS package is 1mm1mm700 m. By applying O2 plasma ashing and fabrication process optimization, we can achieve the void-free structure within the bonding interface as well as via hole. The shear strength and hermeticity of the package satisfy the requirements of MIL-STD-883F. Any organic gases or contamination are not observed inside the package. The total insertion loss for the packaging is 0.075 dB at 2 GHz. Furthermore, the robustness of the package is demonstrated by observing no performance degradation and physical damage of the package after several reliability tests.
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