Fabrication of three-dimensional parylene HT diaphragms using D-RIE with a Si substrate

• Published in: Sensors and actuators. A. Physical. Vol. 253; pp. 146 - 155
• Main Author: Imai, Satomitsu
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01.01.2017; Elsevier BV
• Subjects: Aluminum; Corners; D-RIE; Defects; Diaphragm; Diaphragm (anatomy); Dimensional analysis; Fabrication characteristics; Grooves; Heat resistance; Ion etching; Mechanical properties; MEMS; Microelectromechanical systems; Modulus of elasticity; Parylene; Plasma etching; Reactive ion etching; Scanning electron microscopy; Silicon substrates; Surface roughness; Thermal resistance; Three-dimensional shape; Yield stress; Fabrication characteristics; MEMS; Diaphragm; Parylene; D-RIE; Three-dimensional shape
• ISSN: 0924-4247; 1873-3069
• DOI: 10.1016/j.sna.2016.11.021

•A method to fabricate a parylene HT diaphragm by using D-RIE was developed.•This method can fabricate an arbitrary outline of a diaphragm easily.•Diaphragms with concentric grooves up to 50μm deep were successfully fabricated.•The presented measures were effective to prevent thermal damage of the diaphragm. This work demonstrates the fabrication of parylene diaphragms with three-dimensional configurations using deep-reactive ion etching (D-RIE, or ion-coupled plasma etching using the Bosch process) and assessed the characteristics of the resulting products. Parylene HT, which has superior temperature resistance up to 350°C, was used due to the significant heat generated in the D-RIE process. Parylene was first deposited on a silicon substrate and a diaphragm configuration was etched on the backside of this substrate. In contrast to wet etching, D-RIE was able to fabricate any outline of diaphragms with fine projections, such that could be employed in a microelectromechanical system (MEMS). Planar diaphragms were produced to ascertain the heat resistance of the parylene, and diaphragms (5mm in diameter, 10μm thick) with corrugated rectangular grooves (30–50μm deep) were also fabricated. Scanning electron microscopy (SEM) identified some defects in the corners of grooves when employing a depth of 50μm. Such grooves were eventually fabricated without defects by converting the rectangular corners to rounded shapes and by depositing aluminum on the parylene layer. It was found to be necessary to carefully assess the thermal stress in the vicinities of corners, and that this stress was primarily affected by the groove depth. Surface roughness and mechanical properties of the parylene layers, including Young’s modulus and yield stress, were assessed after the D-RIE process.