TAILIEUCHUNG - Semiconductor Technologies Part 4

Tham khảo tài liệu 'semiconductor technologies part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Advanced Plasma Processing Etching Deposition and Wafer Bonding Techniques for Semiconductor Applications 83 and IEDF include the bias voltage Vb the ion density the gas composition and the mean free path which also depends on the aforementioned parameters . Glow Discharge Region Dark Space IADF IEDF Fig. 2. Illustration of the ion angular and ion energy distribution functions with hypothetical resultant etched profile distortion. Points in IEDF correspond to different ion kinetic energies while points in the IADF correspond to different angles of incidence Etch Reaction Dynamics In wet chemical processes etching is accomplished through physical dissolution or reactionspecific dissolution Reinhardt Kern 2008 . This takes place at any exposed surface and thus results in isotropic etching although the etch rate can vary along different crystalline orientations due to the bonding state variation of the surfaces. A good example of crystalline anisotropy in Si wet processing is potassium hydroxide KOH etching which is widely used for making MEMS structures that capitalize on the direction-dependent etch rate of KOH Wolf Tauber 2000 . However in a myriad of planar processes that are utilized in the semiconductor industry an anisotropic etching profile with sidewalls perpendicular to the wafer surface is frequently required for effective pattern transfer. In order to prevent the isotropic or crystalline anisotropic behavior of our processing gases the sidewalls must be protected from further etching. This is accomplished by forming a passivating or inhibiting layer on the sidewall in one of the following ways - Surface passivation o inserting gases in the plasma which react with wafer materials and forming involatile compounds Legtenberg et al. 1995 o freezing volatile reaction products at the structure s walls using . cryogenic wafer cooling Aachboun et al. 2000 - Inhibitor deposition o using polymer precursor gases to form physical barrier layers . C4F8 .

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