Explain the steps in standard RCA cycle, during wafer cleaning.
1 Answer
  • Contamination on a wafer consists of particles which must be removed by wafer cleaning In order to remove metallic impurities, organic contamination etc. wafers were subjected to standard RCA clearing procedure.

  • The purpose of RCA clean is to remove organic contaminants from the wafer surface, then remove any oxide layer that may have built ups, and finally remove any ionic or heavy metal contaminants.

  • First method uses an $H_2$ $S0_4$ and strong oxidants [ usually $H_2$ $O_2$ ] to decompose the resist into $CO_2$ and $H_2$O.

  • The second method uses oxygen plasma to convert resist to gaseous by products [again $CO_2$ and $H_2$O. ] This reduces pollution problems used in removal of photoresist in backend processes.

  • wafer clearing is usually accomplished either using immersion of cassettes of wafers into cleaning baths or through chemical sprays.

  • SC-1 [ standard cleaning 1 or APM ] and

SC - 2 [ standard cleaning 2 or HPM ] are used for the metal removal.

  • The SC-1 solution is high PH solution consisting of water, hydrogen peroxide and NH < OH [ in ratio 5:1: ], in which wafers are placed at 70 - $80^o$c for 10 minutes. then the water is rinsed under running DI water to remove the solution.

  • In this process it oxidizes the silicon and leaves a thin oxide on the surface of wafer, which should be removed if pure silicon is needed.

  • The SC - 2 solution is a low - PH solution consisting of water, hydrogen peroxide and HCL.

  • It is designed to dissolve and remove alkali residues from the si surface Also it removes and residual trace metals [such as Au And Ag] as well as metal hydroxides including

A1 $[OH]_3$ , Fe $[OH]_3$ , Mg $[OH]_2$ and Zn $[OH]_2$

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