Method and apparatus for detecting imminent end-point when etching dielectric layers in a plasma etch system
First Claim
1. A method for detecting imminent end-point of a dielectric etching process in a plasma etch system comprising the steps of:
- placing a substrate having a dielectric layer to be etched within a plasma etch chamber proximate a cathode;
etching said dielectric layer,detecting the direct current (D.C.) bias voltage on said cathode; and
determining imminent end-point of said etching of said dielectric layer by comparing a change in said D.C. bias voltage, caused by a change in the impedance of said substrate as said dielectric layer thins, against a predetermined criteria.
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Abstract
A method for detecting imminent end-point when plasma etching a dielectric layer of a substrate by monitoring the D.C. bias voltage of the cathode during the etching process. The D.C. bias voltage gives an indirect reading of the impedance of the substrate which changes appreciably just prior to etch-through of the dielectric layer. The plasma etching process is then terminated and a less damaging etch process is used to complete the etch-through of the dielectric layer. The apparatus of the present invention includes an A.C. blocking network coupled to the cathode, an A/D converter coupled to the blocking network and a digital signal analyzer coupled to the A/D converter. Plasma etching can be automatically terminated by the signal analyzer upon the detection of imminent end-point.
52 Citations
20 Claims
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1. A method for detecting imminent end-point of a dielectric etching process in a plasma etch system comprising the steps of:
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placing a substrate having a dielectric layer to be etched within a plasma etch chamber proximate a cathode; etching said dielectric layer, detecting the direct current (D.C.) bias voltage on said cathode; and determining imminent end-point of said etching of said dielectric layer by comparing a change in said D.C. bias voltage, caused by a change in the impedance of said substrate as said dielectric layer thins, against a predetermined criteria. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method for detecting imminent end-point in a dielectric etching process in a plasma etch system comprising the steps of:
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placing a substrate having a dielectric layer to be etched within a chamber of a plasma etch system between a cathode and anode provided within said chamber; applying radio frequency (R.F.) power to at least one of said cathode and said anode and releasing reactant gas into said chamber to initiate the etching of said dielectric layer; monitoring the direct current (D.C.) bias voltage of said cathode over time; and determining imminent end-point by comparing a change in said D.C. bias voltage, caused by a change in the impedance of said substrate as said dielectric layer thins, against a predetermined criteria. - View Dependent Claims (10, 11, 12)
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13. A dielectric etching apparatus comprising:
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a chamber; cathode means for supporting a substrate within said chamber, said substrate having a dielectric layer to be etched; anode means separated from said cathode means such that said substrate is between said anode means and said cathode means; radio frequency (RF) power means coupled to at least one of said cathode means and said anode means; reactant gas release means for releasing dielectric etching gas into said chamber; voltage monitoring means coupled to said cathode means and operative to produce a direct current (D.C.) bias signal which varies with the thickness of said dielectric layer; and voltage comparison means coupled to said voltage monitoring means for forming a first time derivative of said D.C. bias signal and for producing an imminent end-point signal prior to actual end-point of the dielectric etching process if this time derivative satisfies a predetermined criterion. - View Dependent Claims (14, 15, 16, 17, 20)
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18. A method for controlling an etching process when plasma etching a dielectric layer comprising the steps of:
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placing a substrate having a dielectric layer to be etched within a plasma etch chamber; etching said dielectric layer; monitoring a change in impedance of said substrate as said dielectric layer is etched; and terminating said etching process prior to the etch-through of said dielectric layer by comparing said change in impedance of said substrate against a predetermined criteria.
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19. An apparatus for determining imminent end-point when etching a dielectric layer in a plasma etching system comprising:
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monitoring means for monitoring the change in impedance of a substrate having a dielectric layer as said dielectric layer is being etched; and comparison means for comparing said change in impedance against a predetermined criteria to determine imminent end-point.
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Specification