3D Etching

We report realization of highly featured three-dimensional micro- and nano-structures on silicon substrates with a single masking layer using a hydrogen-assisted deep reactive ion etching process. Three gases of oxygen, hydrogen and SF6 are used in a sequential passivation and etching process to achieve high aspect ratio features. By controlling the flows of these gases and the power and timing of each subsequence, it is possible to achieve desired deep vertical etching with controlled underetching and recovery, yielding three-dimensionalfeatures directly on silicon substrates. Etch rates up to 0.75 μmmin−1 have been obtained with a low plasma power density of 1 W cm−2. Also features with a controllable underetchingwith more than 8 μm in sidewall recession have been achieved. The three-dimensional structures can be used as a mold for polymers as well as a holding substrate for projection display applications where an electro-chromic material (WO3) has been used.

Light Emitting Diodes

A low-temperature hydrogenation-assisted sequential deposition and crystallization technique is reported for the preparation of nano-scale silicon quantum dots suitable for light-emitting applications. Radio-frequency plasma-enhanced deposition was used to realize multiple layers of nano-crystalline silicon while reactive ion etching was employed to create nano-scale features. The physical characteristics of the films prepared using different plasma conditions were investigated using scanning electron microscopy, transmission electron microscopy, room temperature photoluminescence and infrared spectroscopy. The formation of multilayered structures improved the photon-emission properties as observed by photoluminescence and a thin layer of silicon oxy-nitride was then used for electrical isolation between adjacent silicon layers. The preparation of light-emitting diodes directly on glass substrates has been demonstrated and the electroluminescence spectrum has been measured.