US4953982A — Method and apparatus for endpoint detection in a …

Claim 1

Independent Claim 131 words

A method for endpoint detection in a semiconductor wafer etching system comprising the steps of: making multiple scans of a semiconductor wafer surface along a substantially identical path with a narrowly focussed beam of radiant energy and detecting a reflected portion of said beam; firstly analyzing said reflected portion to determine a preferred parking spot on a preferred flat area of said surface, said preferred flat area having a minimum transverse dimension greater than a spot size of said beam, said step of firstly analyzing said reflected portion including analyzing a region of a first scan and a corresponding region of a second scan; parking said beam at said preferred spot; and secondly analyzing said reflected portion of said beam to determine when said preferred flat area has been etched through.

Claim 2

Independent Claim 131 words

A method for endpoint detection in a semiconductor wafer etching system comprising the steps of: making multiple scans of a semiconductor wafer surface along a substantially identical path with a narrowly focussed beam of radiant energy and detecting a reflected portion of said beam; firstly analyzing said reflected portion to determine a preferred parking spot on a preferred flat area of said surface, said preferred flat area having a minimum transverse dimension greater than a spot size of said beam, said step of firstly analyzing said reflected portion including analyzing a region of a first scan and a corresponding region of a second scan; parking said beam at said preferred spot; and secondly analyzing said reflected portion of said beam to determine when said preferred flat area has been etched through.

Claim 3

Dependent Claim 36 words

A method as claimed in claim 1 wherein said step of firstly analyzing said reflected portion includes analyzing a series of regions of said first scan and a corresponding series of regions of said second scan.

Claim 4

Dependent Claim 27 words

A method as claim in claim 1 wherein said step of secondly analyzing said reflected portion includes comparing an actual etching curve with a projected etching curve.

Claim 5

Independent Claim 170 words

A method for finding a preferred parking spot for a laser beam of a laser beam interferometer comprising the step of: making multiple scans along a scan path on the semiconductor wafer surface with a narrowly focussed laser beam and detecting a reflected portion of said beam; analyzing said reflected portion of said beam to determine a preferred parking spot within a preferred flat area having a minimum transverse dimension which is larger than a spot size of said laser beam, wherein said analyzing said reflected portion of said beam develops a set of data values for each of said multiple scans including a plurality of data values taken within said preferred flat area, thereby minimizing the effects of transistors and steps on said semiconductor wafer surface which may surround said preferred flat area, said analyzing said reflected portion of said beam further including the step of comparing a first subset of data values of first scan S1 to a corresponding first subset of data values of second scan S2.

Claim 6

Independent Claim 170 words

A method for finding a preferred parking spot for a laser beam of a laser beam interferometer comprising the step of: making multiple scans along a scan path on the semiconductor wafer surface with a narrowly focussed laser beam and detecting a reflected portion of said beam; analyzing said reflected portion of said beam to determine a preferred parking spot within a preferred flat area having a minimum transverse dimension which is larger than a spot size of said laser beam, wherein said analyzing said reflected portion of said beam develops a set of data values for each of said multiple scans including a plurality of data values taken within said preferred flat area, thereby minimizing the effects of transistors and steps on said semiconductor wafer surface which may surround said preferred flat area, said analyzing said reflected portion of said beam further including the step of comparing a first subset of data values of first scan S1 to a corresponding first subset of data values of second scan S2.

Claim 7

Dependent Claim 26 words

A method as claimed in claim 4 wherein said first subsets are compared to find the minimum difference S1S2 min between any two corresponding data values.

Claim 8

Dependent Claim 84 words

A method as claimed in claim 5 wherein a second subset of scan S1 is used to calculate a factor S1 max corresponding to the maximum difference between any two data values within said second subset of scan S1, and wherein a second subset of scan S2 is used to calculate a factor S2 max corresponding to the maximum difference between any two data values within said second subset of scan S2; wherein said second subsets are not necessarily different from said first subsets.

Claim 9

Dependent Claim 38 words

A method as claimed in claim 6 wherein a relative value R is calculated as follows: R=S1S2 .sub.min -[S1.sub.max +S2.sub.max ] where if R<0 then R=0; where said relative value R represents the relative desirability of said spot.

Claim 10

Dependent Claim 35 words

A method as claimed in claim 7 wherein a plurality of R values are calculated for scans S1 and S2, the maximum of which corresponds to a quality factor Q for scans S1 and S2.

Claim 11

Dependent Claim 33 words

A method as claimed in claim 8 wherein more than one pair of scans are compared to determine a plurality of Q values, the maximum of which corresponds to said preferred parking spot.

Claim 12

Independent Claim 133 words

A method for endpoint detection in a semiconductor wafer etching system comprising the steps of: parking a beam of radiant energy on a spot of a semiconductor wafer surface; detecting a reflected portion of said beam to determine an actual etching curve; and analyzing said reflected portion to determine when said surface at said preferred spot has been etched through by comparing said actual etching curve to a projected etching curve, wherein endpoint is detected when a series of points on the actual etching curve are of a greater magnitude than a corresponding series of points on said projected etching curve by at least a predetermined fraction of the difference between the magnitude of a prior peak value of said actual etching curve and said series of points on said projected etching curve.

Claim 13

Independent Claim 133 words

A method for endpoint detection in a semiconductor wafer etching system comprising the steps of: parking a beam of radiant energy on a spot of a semiconductor wafer surface; detecting a reflected portion of said beam to determine an actual etching curve; and analyzing said reflected portion to determine when said surface at said preferred spot has been etched through by comparing said actual etching curve to a projected etching curve, wherein endpoint is detected when a series of points on the actual etching curve are of a greater magnitude than a corresponding series of points on said projected etching curve by at least a predetermined fraction of the difference between the magnitude of a prior peak value of said actual etching curve and said series of points on said projected etching curve.

Claim 14

Dependent Claim 229 words

A laser interferometer endpoint detection system comprising: beam forming means adapted to produce a narrowly focussed beam spot, said beam forming means including a laser source adapted to produce a laser beam, beam expanding means positioned in the path of said laser beam and adapted to produce an expanded laser beam, and beam focussing means positioned in the path of said expanded laser beam and adapted to produce a focussed laser beam; scanning means coupled to said beam forming means and adapted to scan said beam spot across a surface of a semiconductor wafer in discrete steps; detection means responsive to a reflected portion of said beam spot which is reflected from said semiconductor wafer, said detection means including a photodetector and detection optics separate from said beam focussing means for focussing said reflected beam on said photodetector; environmental isolation means for isolating said beam forming means and said detection means from said semiconductor wafer; and control means having an input coupled to said detection means and having an output coupled to scanning means, said control means being operative to cause said scanning means to scan across a preferred flat area which is wider than said beam spot plus one discrete step, said control means being further operative to develop an endpoint detection signal when the output of said detection means indicates the cessation of a characteristic etching curve.

Claim 15

Dependent Claim 229 words

A laser interferometer endpoint detection system comprising: beam forming means adapted to produce a narrowly focussed beam spot, said beam forming means including a laser source adapted to produce a laser beam, beam expanding means positioned in the path of said laser beam and adapted to produce an expanded laser beam, and beam focussing means positioned in the path of said expanded laser beam and adapted to produce a focussed laser beam; scanning means coupled to said beam forming means and adapted to scan said beam spot across a surface of a semiconductor wafer in discrete steps; detection means responsive to a reflected portion of said beam spot which is reflected from said semiconductor wafer, said detection means including a photodetector and detection optics separate from said beam focussing means for focussing said reflected beam on said photodetector; environmental isolation means for isolating said beam forming means and said detection means from said semiconductor wafer; and control means having an input coupled to said detection means and having an output coupled to scanning means, said control means being operative to cause said scanning means to scan across a preferred flat area which is wider than said beam spot plus one discrete step, said control means being further operative to develop an endpoint detection signal when the output of said detection means indicates the cessation of a characteristic etching curve.

Claim 16

Dependent Claim 54 words

A laser interferometer endpoint detection system as claimed in claim 11 wherein said beam forming means further includes optical isolation means disposed between said laser source and said beam expanding means along said path of said laser beam, whereby said optical isolation means minimizes reflection of said laser beam back to said laser source.

Claim 17

Dependent Claim 19 words

A laser interferometer endpoint detection system as claimed in claim 12 wherein said optical isolation means includes polarizing means.

Claim 18

Dependent Claim 186 words

A laser interferometer endpoint detection system comprising: beam forming means adapted to produce a narrowly focussed beam spot; scanning means coupled to said beam forming means and adapted to scan said beam spot across a surface of a semiconductor wafer; detection means responsive to a reflected portion of said beam spot which is reflected from said semiconductor wafer; environmental isolation means for isolating said beam forming means and said detection means from said semiconductor wafer, said environmental isolation means including window means disposed between said beam forming means and said semiconductor wafer and adapted to thermally isolate the beam forming means side of said window from the semiconductor wafer side of the window, said window means including a plurality of spaced-apart panes; and control means having an input coupled to said detection means and having an output coupled to said scanning means, said control means being operative to cause said scanning means to scan across a preferred flat area, said control means being further operative to develop an endpoint detection signal when the output of said detection means indicates the cessation of a characteristic etching curve.

Claim 19

Dependent Claim 186 words

A laser interferometer endpoint detection system comprising: beam forming means adapted to produce a narrowly focussed beam spot; scanning means coupled to said beam forming means and adapted to scan said beam spot across a surface of a semiconductor wafer; detection means responsive to a reflected portion of said beam spot which is reflected from said semiconductor wafer; environmental isolation means for isolating said beam forming means and said detection means from said semiconductor wafer, said environmental isolation means including window means disposed between said beam forming means and said semiconductor wafer and adapted to thermally isolate the beam forming means side of said window from the semiconductor wafer side of the window, said window means including a plurality of spaced-apart panes; and control means having an input coupled to said detection means and having an output coupled to said scanning means, said control means being operative to cause said scanning means to scan across a preferred flat area, said control means being further operative to develop an endpoint detection signal when the output of said detection means indicates the cessation of a characteristic etching curve.

Claim 20

Dependent Claim 26 words

A laser interferometer endpoint detection system as claimed in claim 14 further comprising heating means for heating at least the pane closest to said semiconductor wafer.

Claim 21

Dependent Claim 26 words

A laser interferometer endpoint detection system in claim 14 wherein said environmental isolation means further comprises enclosure means at least partially enclosing said beam forming means.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1993-09-03	1994-03-05	1994-09-04	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1997-09-03	1998-03-05	1998-09-04	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2001-09-03	2002-03-05	2002-09-04	$7700.00	Window Closed / Lapsed

Method and apparatus for endpoint detection in a semiconductor wafer etching system

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