Method and apparatus for automatically measuring semiconductor etching process parameters
First Claim
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1. A method for automatically measuring the depth and rate of etching of an article, comprising the steps of:
- (a) directing light towards the article, formed of a substrate having an overlying light transmissive layer, to cause a first beam of light to be reflected from the substrate and a second, conincident beam to be reflected from the light transmidsive layer, the coincident, reflected beams interfering because of a path length difference therebetween, causing the composite intensity of the beams to exhibit periodic maxima and minima as the path length difference changes during etching of said light transmissive layer;
(b) detecting the composite intensity of the beams during etching;
(c) generating a first electrical signal, which changes in state in response to a minima or maxima of the composite intensity, and generating a second electrical signal which is phase shifted from the first electrical signal by 90°
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(d) processing said first and second electrical signals to obtain a count of the number of maxima or minima of the composite intensity;
(e) timing the period between successive changes in the count of minima or maxima and inverting the value of the period to establish the frequency of the maxima or minima; and
(f) computing the etch depth and the etch rate in accordance with the number of maxima or minima, and the frequency, respectively, of the composite intensity.
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Abstract
An apparatus for automatically measuring the depth and rate of etching of a semiconductor body (10) comprises an interferometer (18) and a counter circuit (28). The interferometer (18) directs light towards the semiconductor body (10) and detects the intensity of the light reflected therefrom which varies periodically during etching. The counter circuit (28) is responsive to the periodically varying intensity of the reflected light and automatically determines the number of cycles and the frequency thereof to compute the etch depth and etch rate therefrom.
24 Citations
14 Claims
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1. A method for automatically measuring the depth and rate of etching of an article, comprising the steps of:
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(a) directing light towards the article, formed of a substrate having an overlying light transmissive layer, to cause a first beam of light to be reflected from the substrate and a second, conincident beam to be reflected from the light transmidsive layer, the coincident, reflected beams interfering because of a path length difference therebetween, causing the composite intensity of the beams to exhibit periodic maxima and minima as the path length difference changes during etching of said light transmissive layer; (b) detecting the composite intensity of the beams during etching; (c) generating a first electrical signal, which changes in state in response to a minima or maxima of the composite intensity, and generating a second electrical signal which is phase shifted from the first electrical signal by 90°
;(d) processing said first and second electrical signals to obtain a count of the number of maxima or minima of the composite intensity; (e) timing the period between successive changes in the count of minima or maxima and inverting the value of the period to establish the frequency of the maxima or minima; and (f) computing the etch depth and the etch rate in accordance with the number of maxima or minima, and the frequency, respectively, of the composite intensity. - View Dependent Claims (2, 3, 4, 5)
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6. An appartatus for automatically measuring the depth and rate of etching of an article comprising:
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means for directing a beam of light towards the article, formed of a substrate having a light transmissive layer, causing a first beam to be reflected from the light transmissive layer and a second coincident beam to be reflected from the substrate therebeneath, the beams interfering because of a path length difference therebetween, causing the composite intensity of the reflected interfering beams to exhibit periodic maxima and minima as the path length difference changes during etching of the light transmissive layer; means for detecting the composite intensity of the reflected interfering beams during etching and for providing an output signal which varies accordingly; means coupled to said detecting means and being responsive to the output signal thereof for generating first and second electrical signals, said first electrical signal changing in state in response to a minima or maxima of the composite intensity of the beams and said second electrical signal being phase shifted 90°
from said first electrical signal;means for processing said first and second signal to obtain a count of the number of minima or maxima of the composite intensity; means for timing the period between successive changes in the count of the minima or maxima and inverting the value thereof to establish the frequency of the minima or maxima; and means for computing the depth and rate of etching of the article in accordance with the count of the number of minima or maxima and the frequency thereof, respectively. - View Dependent Claims (7, 8, 9, 10, 11)
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12. A method for automatically measuring the rate and depth of ething of an article comprising the steps of:
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directing light towards the article, formed of a substrate having an overlying light transmissive layer, to cause a first beam of light to be reflected from the substrate and a second, coincident beam to be reflected from the light transmissive layer thereabove, the coincident reflected beams interfering because of a path length difference therebetween causing the composite intensity of the beams to exhibit periodic maxima and minima as the path length changes during etching of the light transmissive layer; detecting the composite intensity of the reflected beams during etching; obtaining the derivative of the composite intensity and generating a first electrical signal which changes state in response to the zero-crossing of the derivative of the composite intensity; obtaining the integral of the derivative of the composite intensity and producing a second electrical signal which changes state in response to the zero-crossing of the integral of the derivative of the composite intensity; processing the first and second signals to obtain a count of the number of minima or maxima of the composite intensity; timing the period between successive changes in the count of the minima or maxima and inverting the value of the period to establish the frequency of the mizima or minima; and computing the etch rate and depth in accordance with the number of minima or maxima and the frequency, respectively, of the composite intensity. - View Dependent Claims (13, 14)
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Specification