Lecture_8_2_Dry_Etching

Lecture_8_2_Dry_Etching - Lecture 8.2 Dry Etching IH2655...

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Dry Etching Lecture 8.2
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IH2655 Spring 2009 Mikael Östling KTH ETCHING Introduction : • Etching of thin films and sometimes the silicon substrate are very common process steps. • Usually selectivity, and directionality are the first order issues.
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IH2655 Spring 2009 Mikael Östling KTH Drawbacks of Wet Etching In the manufacture of large-scale ICs, wet etching is being replaced by dry etching. (1) Wet etching is isotropic while dry etching can be anisotropic. (2) Dry etching can achieve high resolution. Wet etching has poor resolution. (3) Wet etching depends on a lot of corrosive chemicals, which are harmful to human bodies and environments. (4) Wet etching needs a large number of chemical reagents to wash away the residues. Non-economical!!
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IH2655 Spring 2009 Mikael Östling KTH In practice, BOE buffered oxide etching or BHF: buffered HF NH 4 F buffer: Help to prevent depletion of F - and decrease etch rate of photoresist Example 1: Etch SiO 2 using HF Example 2: Ecth Si using HNO 3 and HF (HNA) Example 3: Ecth Si 3 N 4 using hot phosphoric acid Isotropic
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IH2655 Spring 2009 Mikael Östling KTH Example 4: Etch Si using KOH Anisotropic Si + 2OH - + 4H 2 O Si(OH) 2 ++ + 2H 2 + 4OH - Anisotropic wet etching results from surface orientation
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IH2655 Spring 2009 Mikael Östling KTH Atomic density: <111> > <110> > <100> Etch rate: R (100) 100 R (111)
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IH2655 Spring 2009 Mikael Östling KTH HNA isotropic etching Self-Limited
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IH2655 Spring 2009 Mikael Östling KTH MEMS ( M icro E lectro M echanical S ystems) Made from Si Anisotropic Wet Etching
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IH2655 Spring 2009 Mikael Östling KTH Two Critical Issues: ¾ Selectivity ¾ Directionality: isotropic/anisotropic 2 1 r r S = Etching rate of material being etched Etching rate of masking material or the material below the film vert lat r r A = 1 Lateral etch rate Vertical etch rate Pattern Transfer Demo Pattern Transfer =Lithography + Etching
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IH2655 Spring 2009 Mikael Östling KTH Gate Source Drain silicide metal metal channel gate oxide poly-Si NiSi 50nm 150nm KTH, Stockholm NiSi NiSi
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Mikael Östling KTH Unilateral overetching Undercut Etching directionality A =0, isotropic; A =1, anisotropic Anisotropy A The ratio of the etch rates between two different materials Selectivity S Variation of etch rate throughout one wafer, multiple wafers or multiple batches of wafers Etch Uniformity The film thickness being etched per unit time. R has significant effects on throughput. Etch Rate
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This note was uploaded on 03/09/2009 for the course EE 300 taught by Professor Y during the Spring '09 term at CUNY City.

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Lecture_8_2_Dry_Etching - Lecture 8.2 Dry Etching IH2655...

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