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

We describe the patterning of multiple 10 mu m wide conductive tracks down the vertical sidewall of a 500 mu m 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.