10 - Dry Etching Himanshu J. Sant Fundamentals of...

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Unformatted text preview: Dry Etching Himanshu J. Sant Fundamentals of Microfabrication Etching Issues - Anisotropy Isotropic etchants etch at the same rate in every direction Isotropic An-isotropic mask Etching Issues - Selectivity Selectivity is the ratio of the etch rate of the target material being etched to the etch rate of other materials Chemical etches are generally more selective than plasma etches Selectivity to masking material and to etch- stop is important Mask target Etch stop Dry Etching Overview What is dry etching? Material removal reactions occur in the gas phase. Types of dry etching Non-plasma based dry etching Plasma based dry etching Why dry etching? Development of dry etching Plasma parameters/influences Dry Etching Advantages Eliminates handling of dangerous acids and solvents Uses small amounts of chemicals Isotropic or anisotropic etch profiles Directional etching without using the crystal orientation of Si Faithfully transfer lithographically defined photoresist patterns into underlying layers High resolution and cleanliness Less undercutting No unintentional prolongation of etching Better process control Ease of automation (e.g., cassette loading) Dry Etching Disadvantages: Some gases are quite toxic and corrosive Re-deposition of non-volatile compounds Need for specialized (expensive) equipment Types: Non-plasma based = uses spontaneous reaction of appropriate reactive gas mixture Plasma based = uses radio frequency (RF) power to drive chemical reaction Non-plasma Based Dry Etching Isotropic etching of Si Similar to wet HF etching of Si Typically fluorine-containing gases (fluorides or interhalogens) that readily etch Si High selectivity to masking layers No need for plasma processing equipment Highly controllable via temperature and partial pressure of reactants Xenon Difluoride (XeF 2 ) Etching Isotropic etching of Si High selectivity for Al, SiO 2 , Si 3 N 4 , PR, PSG 2XeF 2 + Si b 2Xe + SiF 4 Typical etch rates of 1 to 3 m/min Heat is generated during exothermic reaction XeF 2 reacts with water (or vapor) to form HF Used as a release step in many fab processes Interhalogen (BrF 3 & ClF 3 ) Etching Nearly isotropic profile Gases react with Si to form SiF...
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10 - Dry Etching Himanshu J. Sant Fundamentals of...

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