A single-mask substrate transfer technique for the fabrication of high-aspect-ratio micromachined structures

In this paper, a single-mask substrate transfer process for the fabrication of high-aspect-ratio (HAR) suspended structures is presented. The HAR silicon structures are fabricated using a deep reactive ion etching (DRIE) technique and then transferred to a glass wafer using silicon/thin film/glass anodic bonding and silicon thinning techniques. The HAR structures are released using self-aligned wet etching of the glass. Two key processes are discussed. One is the silicon/thin film/glass anodic bonding, with special emphasis on the effect of the bonding material on the bonding shear strength. The other is the silicon backside thinning via aqueous solution of potassium hydroxide (KOH). A lateral RF MEMS switch has been fabricated and demonstrates low loss up to 25 GHz. This substrate transfer process has the advantages of high-aspect ratio, low loss and high flexibility.