Physical-Chemical Etching

Plasma etching. (PE) Physical-chemical etching with free radicals, supported by ions. Etching profile anisotropic-isotropic, good selectivity. 

Physical-chemical etching Perfect pattern transfer... 

Bosch process Deep reactive-ion etching (DRIE) Etching single crystalline materials Physical-chemical etching Potassium hydroxide (KOH) etching Silicon etching... 

Limitations of Plasma CVD. With plasma CVD, it is difficult to obtain a deposit of pure material. In most cases, desorption of by-products and other gases is incomplete because of the low temperature and these gases, particularly hydrogen, remain as inclusions in the deposit. Moreover, in the case of compounds, such as nitrides, oxides, carbides, or silicides, stoichiometry is rarely achieved. This is generally detrimental since it alters the physical properties and reduces the resistance to chemical etching and radiation attack. However in some cases, it is advantageous for instance, amorphous silicon used in solar cells has improved optoelectronic properties if hydrogen is present (see Ch. 15). 

Likewise, when Ar impinged on the surface, pure sputtering ( 2 A/min) was noted. However, when the beams were simultaneously directed at the silicon surface, a relatively large (--SS A/min.) etch rate was observed the measured rate was approximately an order of magnitude greater than the sum of the chemical and physical components. Obviously, synergistic effects due to ion bombardment are crucial to this chemical etch process. Unfortunately, the exact nature of these effects is at present undefined. 

It is necessary to prebake the PI film to 200°C to improve its resistance towards negative photoresist with a commercial stripper. After baking, remove the photoresist with a commercial stripper which is usually composed of phenol, strong mineral acids and solvents. 11) Neutralization and rinse. 12) final cure. Typical schedules are 30 min. at 350°C or 15 min. at 400°C. 10)PIasma,chemically etching) or physically (roughening) treat the polyimide surface to improve adhesion for next level metal. 

MEMS (microelectromechanical systems) are systems with small device sizes of 1-100 pm. They are typically driven by electrical signals. To fabricate such systems materials like semiconductors, metals, and polymers are commonly used. MEMS technology fabrication is very cost-efficient. The structures are transferred by processes, which are applied to many systems on one substrate or even many of them simultaneously. The most important fabrication processes are physical vapor deposition (PVD), chemical vapor deposition (CVD), lithography, wet chemical etching, and dry etching. Typical examples for MEMS are pressure, acceleration, and gyro sensors [28,29], DLPs [30], ink jets [31], compasses [32], and also (bio)medical devices. 

Figure 2.14 Isotropic wet chemical etching of silicon glass (with friendly permission of the Institute of Physical High Technology).

A technique that combines both physical and chemical etching mechanisms is chemically assisted ion beam etching (CAIBE). In CAIBE, an inert gas ion beam is directed at a sample which is situated in a... 

Nanostracturing processes for silicon Photolithographic fabrication X-ray lithography [130] Electron beam lithography [139] Chemical etching [140] Physical and chemical vapor deposition [141]... 

The positive ions arrive at the cathode with increased kinetic energy, and the target material (used as the cathode) is removed from its surface by cumulative physical and chemical etching, the magnitude of which is dependent on the nature of the plasma gas. The substrate is placed on the surface of the anode (electrically insulated). Perfluoropropane was used as the plasma gas, and silicon, germanium, molybdenum, tungsten, and copper were employed as the cathode (target materials to be sputtered). 

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