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Control of etch selectivity

  • US 5,770,097 A
  • Filed: 06/11/1997
  • Issued: 06/23/1998
  • Est. Priority Date: 12/23/1994
  • Status: Expired due to Fees
First Claim
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1. A method for selectively etching a plurality of materials of a workpiece comprising steps of:

  • enveloping the workpiece with a plasma having first and second species of a reactant which are operative to etch said plurality of materials, said plasma being provided by interacting an RF electromagnetic field with said first and said second species;

    modulating said field by pulse-width modulation to provide a sequence of field energization intervals interspersed among intervals of field deenergization, said first and said second species of reactant being characterized respectively by first and second rates of decay during one of said deenergization intervals, said first rate of decay being different from said second rate of decay resulting in an etchant concentration ratio of average values of concentrations of said first and said second species of reactant which varies in dependency on a duration of said one deenergization interval, and wherein an etching of said materials results in an etch selectivity ratio of a first etching rate of a first of said materials relative to a second etching rate of a second of said materials, the etch selectivity ratio depending on said etchant concentration ratio and on the duration of said one deenergization interval;

    measuring concentrations of said first and said second species of said reactant in said plasma for providing said etchant concentration ratio;

    based on said etchant concentration ratio, determining said etch selectivity ratio; and

    wherein, in said modulating step, the durations of said deenergization intervals are adjusted to obtain a desired value of the etch selectivity ratio.

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