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Tetramethylammonium hydroxide (TMAH) presents a safer alternative than EDP, with a 37X selectivity between {100} and {111} planes in silicon. Etching a (100) silicon surface through a rectangular hole in a masking material, like a hole in a layer of silicon nitride, creates a pit with flat sloping {111}-oriented sidewalls and a flat (100 ...
Typical etching temperatures are between 70 and 90 °C and typical concentrations are 5–25 wt.% TMAH in water. In case of (100) silicon etching rates generally increase with temperature and decrease with TMAH concentration.
Bulk micromachining starts with a silicon wafer or other substrates which is selectively etched, using photolithography to transfer a pattern from a mask to the surface. Like surface micromachining, bulk micromachining can be performed with wet or dry etches, although the most common etch in silicon is the anisotropic wet etch.
To etch through a 0.5 mm silicon wafer, for example, 100–1000 etch/deposit steps are needed. The two-phase process causes the sidewalls to undulate with an amplitude of about 100–500 nm . The cycle time can be adjusted: short cycles yield smoother walls, and long cycles yield a higher etch rate.
Micro-machining starts with a silicon wafer or other substrate upon which new layers are grown. These layers are selectively etched by photo-lithography; either a wet etch involving an acid, or a dry etch involving an ionized gas (or plasma). Dry etching can combine chemical etching with physical etching or ion bombardment. Surface micro ...
Briefly, the etching of silicon is a two-step process. First, the top surface of the silicon is converted into a soluble oxide by a suitable oxidizing agent(s). Then the resulting oxide layer is removed from the surface by dissolution in a suitable solvent, usually HF. This is a continuous process during the etch cycle.
Use of a hardmask involves an additional deposition process, and hence additional cost. First, the hardmask material is deposited and etched into the required pattern using a standard photoresist process. Following that the underlying material can be etched through the hardmask. Finally the hardmask is removed with a further etching process. [2]
STI is created early during the semiconductor device fabrication process, before transistors are formed. The key steps of the STI process involve etching a pattern of trenches in the silicon, depositing one or more dielectric materials (such as silicon dioxide ) to fill the trenches, and removing the excess dielectric using a technique such as ...