Study On Technique And Mechanism Of Electrochemical Etching For 3D Structure On Silicon

Porous silicon as sacrified layer is an important technology, which is based on the development of porous silicon photoluminescence property. Electrochemical etching is low-cost and simpe processing comparised with dry etching.Howevver, this technology is based on holes exhausted in the sidewalls of microstructrures which space is below 20μm. No circular recesses and microstructures with convex corner and space at 300μm are not studied and investigated till now. In this paper, the etching morphorlogy and mechanism of etching were analysied for the microtructures with large space, and microstructures on silion substrate were etched by electrochemical etching with magnetic field assitted.The etching property of KOH solution was studied with additional direct electric field, isotropic etching property of KOH was changed as the additional electric field and circular recess array were fabricated used KOH+IPA solution with direct electric field. This technology comes over the crystallygrapic limitation of isotropic etching. Mictrostructures were fabricated by single-step electrochemical etching with various masks on P(100) Si substrate in mixture of HF and DMF. Then square and trapiza 3D microstructures with perfect convex corner were fabricated, the experimental results show that the technology of single-step electrochemical etching for mictrostructures with convex corner fabricated is no need any compenstated structures and no crystallygraphic limitation.Effect of Hall voltage on the etching morphology of microstructures on N(100),P(100),N-type layer on P(111) substrate was respectively studied based on Hall-effect when the maginetic field is vertical to the etching electric current. Some rules are obtained during investaged the optimal etching processing:the vertical degree microstructues increases as the magnetic field intensity increases on N(100) substrate; the vertical etching rate is enhanced and undercutting rate is low for P(100) substrate compared with N(100) substrate.The circular and square microstructures with vertical sidewalls were obtained on P(111) substrate with N-type epitaxial layer as mask materials. In order to obtain microstructures with vertical sidewall, N-type epitaxial layer was chosen as mask materials for electrochemical etching, the microstructures with circular and square mask mask were fabricated by electrochemical etching with vertical magnetic field assited. Experimental results show the microstructures with large space at 300μm can be fabricated.In addition, we studied the morphology of micristructures with large space by electrochemical etching. Microstructures was electrochemically etched after it was isotropically etched in KOH solution for 7min, the edge of microstructure was presented collapse; the experimental result shows that edge effect can be alleviated at some extent by double sides with mask which limits the trail of electrons and holes flowing through, but it cann't completely stop the edge effect due to dispersion of electrions and holes moving from back side of silicon to front side but not along line. Space charge distributed model was built to explain edge effect due to not exhausted holes between space of microstructures deflexed.In order to confirmate the limitation of electrochemical etching for microstructures with large space, reversed pyramids with space at 300μm was electrochemically etched, holes energy distribution sphere model and trails of holes deflexion model were built based on experimental results. Maginetic field was added to the etching system which parallel to electric current for confirmation this model, etched trace was obviously developed in the middle of sidewalls when the periodic reversed pyramids were electrochemically etched.