Method and apparatus for controlling plasma etching

• US 4,208,240 A
• Filed: 01/26/1979
• Issued: 06/17/1980
• Est. Priority Date: 01/26/1979
• Status: Expired due to Term

• Current Assignee: Gould Electronics Incorporated (Eternal Materials Co., Ltd.)
• Original Assignee: Gould, Inc. (Transdigm Group Incorporated)
• Inventors: Latos, Thomas S.
• Primary Examiner(s): Massie, Jerome W.
• Application Number:
  US06/006,627
• Time in Patent Office: 508 Days
• Field of Search: 156/345, 156/626, 156/627, 156/643, 356/381, 356/445, 356/448, 328/114, 328/132, 328/150
• US Class Current: 216/60
• CPC Class Codes: C23F 4/00 Processes for removing metallic material from surfaces, not provided for in group C23F1/00 or C23F3/00
• CPC Class Codes: G01N 21/272 for following a reaction, e.g. for determining photometrically a reaction rate (photometric cinetic analysis)
• CPC Class Codes: H01J 37/32935 Monitoring and controlling tubes by information coming from the object and/or discharge

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.

Claims

1. 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.

2. 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.

3. 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.

4. Apparatus according to claim 3, wherein said means for counting comprises adjustable timer means for selecting said interval.