Selection of wavelengths for end point in a time division multiplexed process
The present invention provides a method for establishing endpoint during an alternating cyclical etch process or time division multiplexed process. A substrate is placed within a plasma chamber and subjected to an alternating cyclical process having an etching step and a deposition step. A variation in plasma emission intensity is monitored using known optical emission spectrometry techniques. A first wavelength region is selected based on a plasma emission from an etch by product and a second wavelength region is selected based on a plasma emission from a plasma background. A ratio of the first wavelength region to the second wavelength region is computed and used to adjust the monitoring of an attribute of a signal generated from the time division multiplex process. The alternating cyclical process is discontinued when endpoint is reached at a time that is based on the monitoring step.
1 . A method of establishing endpoint during a time division multiplex process comprising the steps of:
subjecting a substrate to the time division multiplex process;
selecting a first wavelength region based on a plasma emission from an etch by product;
selecting a second wavelength region based on a plasma emission from a plasma background;
computing a ratio of said first wavelength region to said second wavelength region;
monitoring an attribute of a signal generated from the time division multiplex process;
adjusting said monitoring step based on said ratio of said computation step;
processing said adjusted attribute of the periodic signal generated from the time division multiplex process using an envelope follower; and
discontinuing the time division multiplex process at a time based on the processing step.
2 . The method of claim 1 wherein said attribute is plasma emission intensity.
3 . The method of claim 2 wherein said monitoring step further comprising monitoring a plurality of regions of plasma emission intensity.
4 . The method of claim 3 wherein said plurality of regions of plasma emission intensity are chosen using a statistical method.
5 . The method of claim 4 wherein said statistical method further comprising factor analysis.
6 . The method of claim 5 wherein said plurality of regions of plasma emission intensity are chosen using an off-line analysis.
7 . The method of claim 6 wherein said off-line analysis further comprising spectra differencing.
8 . The method of claim 3 wherein said monitoring step further comprising performing mathematical operations on said multiple regions of plasma emission intensity.
9 . The method of claim 1 wherein said attribute is plasma impedance.
10 . The method of claim 1 wherein said processing step further comprising using a plurality of peak detect algorithms.
11 . The method of claim 10 wherein said plurality of peak detect algorithms are processed in parallel.
12 . The method of claim 10 wherein said plurality of peak detect algorithms are reset sequentially in a round robin fashion.
13 . The method of claim 12 wherein said reset further comprising a clock period that is at least half the process period of the time division multiplex process.
14 . The method of claim 1 wherein said processing step further comprising post processing of an extracted amplitude detection signal.
15 . The method of claim 14 wherein said post processing is digital signal processing.
16 . The method of claim 15 wherein said digital signal processing comprises a filter.
17 . The method of claim 16 wherein said filter is an infinite impulse response filter.
18 . The method of claim 16 wherein said filter is a finite impulse response filter.
19 . A method for establishing endpoint during a time division multiplexed process, the method comprising the steps of:
a. etching a surface of a substrate in an etching step by contact with a reactive etching gas to removed material from the surface of the substrate and provide exposed surfaces;
b. passivating the surface of the substrate in a passivating step during which the surfaces that were exposed in the preceding etching step are covered by a passivation layer thereby forming a temporary etching stop;
c. alternatingly repeating the etching step and the passivating step;
d. selecting a first wavelength region based on a plasma emission from an etch by product;
e. selecting a second wavelength region based on a plasma emission from a plasma background;
f. computing a ratio of said first wavelength region to said second wavelength region;
g. analyzing an intensity of at least one wavelength region of a plasma emission through the use of an envelope follower algorithm;
h. adjusting said analysis step based on said ratio of said computation step; and
i. discontinuing the time division multiplexed process at a time which is dependent on said analysis step.
20 . A method of establishing endpoint during a time division multiplex process comprising the steps of:
subjecting a substrate to the time division multiplex process;
selecting a first wavelength region based on a plasma emission from an etch by product;
selecting a second wavelength region based on a plasma emission from a plasma background;
computing a ratio of said first wavelength region to said second wavelength region;
monitoring an attribute of a signal generated from the time division multiplex process;
adjusting said monitoring step based on said ratio of said computation step;
processing said adjusted attribute of the periodic signal generated from the time division multiplex process using a peak-hold and decay algorithm; and
discontinuing the time division multiplex process at a time based on the processing step.
21 . The method of claim 20 wherein said attribute is plasma emission intensity.
22 . The method of claim 20 wherein said processing step further comprising using a linear decay algorithm.
23 . The method of claim 20 wherein said processing step further comprising using a non-linear decay algorithm.
24 . The method of claim 20 wherein said processing step further comprising post processing of an extracted amplitude detection signal.
25 . The method of claim 24 wherein said post processing is digital signal processing.
26 . The method of claim 25 wherein said digital signal processing comprises a filter.
27 . The method of claim 26 wherein said filter is an infinite impulse response filter.
28 . The method of claim 26 wherein said filter is a finite impulse response filter.