US4208240A
Expired / Lapsed
US
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Method and apparatus for controlling plasma etching
Assignee: Gould Electronics Inc
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Filing: 1979-01-26
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Granted: 1980-06-17
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Expires: 1999-01-26
Abstract
Abstract A method and apparatus are disclosed for controlling plasma etching processes in which a thin layer is etched away to expose a substrate. Coherent light is directed onto the surface being etched, so that the change in reflectivity of the surface upon exposure of the underlying substrate produces a detectable change in the characteristics of the light reflected. A derivative detector having a variable timer is provided to sample continuously the reflected light and provide a control signal in response to a predetermined change in the characteristics of the light reflected, which is used to terminate the plasma etch process before an overetch condition occurs. The method and apparatus of the invention will detect a desired end point of etching through insulation to an underlying metal substrate, through metal to an underlying insulation substrate, through one insulation type to an underlying substrate of another insulation type and through one metal to an underlying substrate of another metal.
Inventors
- 👤 Thomas S. Latos
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 17:42
CPC Classifications
H; H01; H01J; H01J37/00; H01J37/32; H01J37/32917; H01J37/32935; C; C23; C23F; C23F4/00; G; G01; G01N; G01N21/00; G01N21/17; G01N21/25; G01N21/27; G01N21/272
Claims Analysis
Total Claims: 6
Claim 1
Independent Claim
144 words
A method for etching a first layer of material to expose an underlying layer of a second material, comprising the steps of: exposing said first layer to an etching medium; projecting a beam of coherent radiation onto the surface of said first layer, and in sequence said second layer, during etching; detecting radiation reflected from said first or second layer and producing a first analog signal in response thereto; determining the time derivative of said analog signal during successive intervals, each interval being of a length in time selectably chosen to ensure a maximum acceptable overetch beyond said first layer into said second layer; comparing the derivative determined for each successive interval to predetermined criteria indicative of the end-point of etching between said layers and providing a control signal upon achievement of end-point; and terminating said exposing step in response to said control signal.
Claim 2
Independent Claim
144 words
A method for etching a first layer of material to expose an underlying layer of a second material, comprising the steps of: exposing said first layer to an etching medium; projecting a beam of coherent radiation onto the surface of said first layer, and in sequence said second layer, during etching; detecting radiation reflected from said first or second layer and producing a first analog signal in response thereto; determining the time derivative of said analog signal during successive intervals, each interval being of a length in time selectably chosen to ensure a maximum acceptable overetch beyond said first layer into said second layer; comparing the derivative determined for each successive interval to predetermined criteria indicative of the end-point of etching between said layers and providing a control signal upon achievement of end-point; and terminating said exposing step in response to said control signal.
Claim 3
Dependent Claim
86 words
A method according to claim 1, wherein said determining step comprises the steps of: converting said analog signal to a train of pulses occuring at a frequency proportional to said analog signal; counting said pulses during successive intervals, each interval being of a length in time selectably chosen to ensure a maximum acceptable overetch beyond said first layer into said second layer; and comparing the count of pulses in successive intervals to provide a train of signals proportional to the time derivative of said analog signal.
Claim 4
Dependent Claim
190 words
Apparatus for etching a first layer of material to expose an underlying second layer, comprising: means for exposing said first layer to an etching medium; means for projecting a beam of coherent radiation onto the surface of said first or second layer during etching; means for detecting radiation reflected from said first layer or said second layer during etching and for producing a first analog signal in response thereto; means for converting said signal to a train of pulses occuring at a frequency proportional to said first signal; means for counting said pulses during successive intervals, each interval being of a length in time selectably chosen to ensure a maximum acceptable overetch beyond said first layer into said second layer; means for comparing the count of pulses in successive intervals to provide a train of signals porportional to the slope of said analog signal; means for storing criteria indicative of the end-point of etching between said layers; means for comparing said train of signals to said criteria to provide a control signal upon achievment of end point; and means responsive to said control signal for inactivating said means for exposing.
Claim 5
Dependent Claim
190 words
Apparatus for etching a first layer of material to expose an underlying second layer, comprising: means for exposing said first layer to an etching medium; means for projecting a beam of coherent radiation onto the surface of said first or second layer during etching; means for detecting radiation reflected from said first layer or said second layer during etching and for producing a first analog signal in response thereto; means for converting said signal to a train of pulses occuring at a frequency proportional to said first signal; means for counting said pulses during successive intervals, each interval being of a length in time selectably chosen to ensure a maximum acceptable overetch beyond said first layer into said second layer; means for comparing the count of pulses in successive intervals to provide a train of signals porportional to the slope of said analog signal; means for storing criteria indicative of the end-point of etching between said layers; means for comparing said train of signals to said criteria to provide a control signal upon achievment of end point; and means responsive to said control signal for inactivating said means for exposing.
Claim 6
Dependent Claim
18 words
Apparatus according to claim 3, wherein said means for counting comprises adjustable timer means for selecting said interval.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1983-06-17 | 1983-12-17 | 1984-06-17 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1987-06-17 | 1987-12-17 | 1988-06-17 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1991-06-17 | 1991-12-17 | 1992-06-17 | $7700.00 | Window Closed / Lapsed |