Chemical mechanical planarization (CMP) is an integral process in the semiconductor industry that enables the fabrication of advanced integrated circuit (IC) components. It is the method of choice for obtaining both local and global planarization of IC thin films, including metals, such as copper, aluminum and tungsten, and dielectrics such as silicon dioxide. An emerging area for application of CMP is in Micro-Electro-Mechanical Systems (MEMS). Fabricated from a variety of materials, including polymers, metals and ceramics, MEMS devices present new opportunities and new challenges for CMP. This paper describes the planarization and fabrication requirements of MEMS CMP, from both a materials and a processing perspective, with a comparison to IC CMP. Examples using popular MEMS fabrication materials, such as standard and photosensitive polyimides, alumina and copper, will demonstrate the efffectiveness of CMP for microfabrication and micromachining applications. Additional results will illustrate the use of CMP as a means to selectively and controllably effect a high degree of planarization efficiency on a variety of microelectronics substrates. Finally, the role of CMP in meeting future MEMS/MOEMS-related applications will be addressed.
MEMS and other emerging applications such as planar photonic devices, display devices and advanced chip and wafer level packaging, require superior planarity of thin films in order to enable greater functionality. The only process technology shown to consistently deliver both global and local planarity is Chemical Mechanical Planarization (CMP). CMP was initially developed to meet the increasingly stringent planarity requirements of the integrated circuit (IC) industry and has since become the standard planarization process within the semiconductor industry. However, emerging applications share film characteristics that present planarization challenges quite different from the traditional IC applications, including: 1) much larger step heights and wider feature sizes, 2) thicker films, 3) multiple materials present within the same layer, and 4) large discrepancies in pattern densities and feature sizes. Due to these challenges, standard CMP process steps, alone, may not deliver the desired planarity. In this paper, other techniques in combination with standard CMP will be investigated as a means to meet stringent planarity requirements of MOEMS. These techniques include: (a) optimizing CMP slurry formulation for both material removal rate and material selectivity, (b) integrating various technologies such as additional etch steps, protective masks and lift-off processes to deliver a surface that is more complementary to CMP, and (c) developing a two-step CMP process with a bulk removal step followed by a soft landing step. A working example will also be presented to demonstrate the feasibility of the proposed methodology.