Vertical tracks on the sidewall of a silicon die using 3D holographic photolithography

Abstract

We describe the patterning of multiple 10 µm wide conductive tracks down the vertical sidewall of a 500 µm thick silicon die. A novel photolithographic technique is used, which utilizes a computer-generated hologram mask in conjunction with a diffraction grating. 3D holographic photolithography is a powerful method for eliminating the troublesome diffractive line broadening that is usually encountered when patterning non-planar substrates. When used in conjunction with a diffraction grating, it creates the possibility to pattern fine features onto vertical surfaces—an achievement outside the normal realm of photolithography. The technique has many potential applications in MEMS, microsystem integration and packaging.