Possibility of silicon-on-insulator (SOI) structure production using wet surface treatment and smart technique

Full text: he proposed methods of silicon surface formation using heat treatment in wet environment (including chemical surface assembling by the molecular deposition method) and the smart technique allow to produce high-quality SOI-structures suitable for using in special ICs, semiconductor devices, micromechanical systems and sensors. We have carried out experiments of SOI-structures production using the smart technology (the radiation-induced gas-stimulated splitting) and surface treatment in wet environment. Preparation of wafers consisted of super-finished polishing and chemical treatment to obtain maximum clean and smooth surface. The hydrogen atom implantation was carried out in equipment with the ion current density on wafer surface of about 0.5 μA/cm2 and 5 μA/cm2. Ion energy was 40 and 150 keV. The samples have been obtained with the following implantation dozes: 3·1016; 4·1016, 5·1016; 7·1016, 1017 cm-2. Before joining, the samples were treated in 40 % solution of ammonia fluoride - 2 seconds, D.I. water - 10 minutes and 100 % nitric acid - 10 minutes, and after that - in D.I. water. Along with it special chemical treatment methods were investigated. The splitting was carried out by heat treatment in the diffusion furnace at 450-600 deg. C during 10-20 min in nitrogen or oxygen atmosphere. The device layer have completely splitted from device wafers with H+ implantation doze of 3·1016 cm-2. For H+ implantation dozes of 5·1016 cm-2, 7·1016 cm-2. 1017 cm-2 the device layer was splitted as small islands. This effect is explained by the absence of a continuous contact of wafers due to appearance of a micro relief of 40-450 nm height caused by growing blisters. This circumstance makes to search for special methods of joining and preliminary bonding of wafers before splitting (heat treatment at 120-300 deg. C), by selection of pressure of environment where the operation is carried out, by fine adjustment of H+ implantation doze. The structures obtained in described experiments had device layers of 0.3-0.8 microns thickness, roughness of outer surface of this layer was 20-30 nm. The following conclusions can be made basing on conducted experiments: 1) Formation of SOI-structures with thick device layers is feasible to carry out by the wafer bonding method and subsequent thinning of the device wafer; 2) The most prospective method of SOI-structures formation with thin device layers (less than 1 micron) is the method of splitting of the device layer from the structure obtained by the wafer bonding method; 3) To obtain SOI-structures with thicker device layers, the chemical-mechanical thinning and plasma etching methods are acceptable