In-situ spectroscopy for monitoring fabrication of integrated computational elements

Patent metadata

Field	Value
Publication number	US-9727052-B2
Application number	US-201414414653-A
Country	US
Kind code	B2
Filing date	Feb 14, 2014
Priority date	Feb 14, 2014
Publication date	Aug 8, 2017
Grant date	Aug 8, 2017

Abstract

Technologies are described for monitoring characteristics of layers of integrated computational elements (ICEs) during fabrication using an in-situ spectrometer operated in step-scan mode in combination with lock-in or time-gated detection. As part of the step-scan mode, a wavelength selecting element of the spectrometer is discretely scanned to provide spectrally different instances of probe-light, such that each of the spectrally different instances of the probe-light is provided for a finite time interval. Additionally, an instance of the probe-light interacted during the finite time interval with the ICE layers includes a modulation that is being detected by the lock-in or time-gated detection over the finite time interval.

First claim

What is claimed is:

1. A method comprising:
receiving, by a fabrication system, a design of an integrated computational element (ICE), the ICE design comprising specification of a substrate and a plurality of layers, their respective target thicknesses and complex refractive indices, wherein complex refractive indices of adjacent layers are different from each other, and wherein a notional ICE fabricated in accordance with the ICE design is related to a characteristic of a sample;
forming, by the fabrication system, at least some of the layers of a plurality of ICEs in accordance with the ICE design;
sequentially illuminating, by a measurement system associated with the fabrication system, the formed layers with instances of probe-light provided by the measurement system, the instances being spectrally different from each other within a measurement spectral range, such that each of the instances of the probe-light illuminates the formed layers for a finite time interval;
detecting, by the measurement system for each of the instances of the probe-light, a modulation of probe-light that interacts with the formed layers;
generating, by the measurement system, a spectrum of the probe-light interacted with the formed layers over the measurement spectral range from a set of values of the detected modulations corresponding to the instances of the probe-light; and
adjusting, by the fabrication system, said forming based on the generated spectrum.

2. The method of claim 1 , further comprising generating the modulation of the instances of probe-light that interacted with the formed layers prior to said illuminating the formed layers.

3. The method of claim 2 , wherein the instances of the probe-light are modulated with an optical chopper.

4. The method of claim 3 , wherein the optical chopper is placed within an optical path starting at an optical source that emits the probe-light and ending at the formed layers.

5. The method of claim 3 , wherein the optical chopper comprises one of a shutter or an acusto-optic modulator.

6. The method of claim 2 , further comprising emitting, by an optical source that spans the measurement spectral range, the probe-light as a train of pulses, wherein the instances of the probe-light are modulated by the train of pulses.

7. The method of claim 2 , wherein the formed layers are at rest, while performing said detection is performed, relative to a location where the modulated instances of the probe-light illuminate the formed layers.

8. The method of claim 2 , further comprising:
receiving, by an interferometer of the measurement system, probe-light provided by an optical source that spans the measurement spectral range; and
for each optical path difference of a plurality of optical path differences of the interferometer, providing, by the interferometer, an instance of the probe-light associated with the optical path difference.

9. The method of claim 8 , wherein each of the optical path differences is maintained at least for a duration of the finite time interval.

10. The method of claim 8 , wherein the measurement system associated with the fabrication system comprises an FTIR spectrometer.

11. The method of claim 8 , wherein said detecting is synchronized with the modulation and is performed using a lock-in detector referenced by the modulation.

12. The method of claim 11 , wherein the finite time interval during which each of the modulated instances is detected comprises a specified number of time constants of the lock-in detector.

13. The method of claim 12 , wherein the specified number of time constants of the lock-in detector is between five and ten.

14. The method of claim 11 , further comprising for each optical path difference of a plurality of optical path differences of the interferometer, detecting, by the lock-in detector, the modulation of the instance of the probe-light that interacted with the formed layers as a lock-in detector signal corresponding to the optical path difference.

15. The method of claim 14 , wherein said generating the spectrum of the probe-light that interacted with the formed layers over the measurement spectral range comprises
fitting a set of values of lock-in detector signals corresponding to the plurality of optical path differences to obtain an optical path difference dependence of the detected modulation, and
processing the obtained optical path difference dependence of the detected probe-light to generate the spectrum.

16. The method of claim 15 , wherein said processing the obtained optical path difference dependence of the detected probe-light comprises Fourier transforming the obtained optical path difference dependence of the detected probe-light.

17. The method of claim 2 , further comprising:
receiving, by a monochromator of the measurement system, probe-light provided by an optical source that spans the measurement spectral range, wherein the monochromator includes a wavelength selector and an output port; and
for each relative orientation of a plurality of relative orientations between the wavelength selector and the output port of the monochromator, providing, by the monochromator, an instance of the probe-light associated with the relative orientation.

18. The method of claim 17 , wherein each of the relative orientations between the wavelength selector and the output port of the monochromator is maintained at least for a duration of the finite time interval.

19. The method of claim 17 , wherein
said detecting is synchronized with the modulation and is performed using a lock-in detector referenced by the modulation, and
the method further comprises for each relative orientation of a plurality of relative orientations between the wavelength selector and the output port of the monochromator detecting, by the lock-in detector, the modulation of the instance of the probe-light that interacted with the formed layers as a lock-in detector signal corresponding to the relative orientation.

20. The method of claim 19 , wherein said generating the spectrum of the probe-light that interacted with the formed layers over the measurement spectral range comprises
fitting a set of values of the lock-in detector signals corresponding to the plurality of relative orientations between the wavelength selector and the output port of the monochromator to obtain a wavelength selector orientation dependence of the detected probe-light, and
processing the obtained wavelength selector orientation dependence of the detected probe-light to generate the spectrum.

21. The method of claim 20 , wherein said processing comprises correlating the plurality of relative orientations between the wavelength selector and the output port of the monochromator with corresponding wavelengths of the measurement spectral range.

22. The method of claim 1 , further comprising generating the modulation of the instances of probe-light that interacted with the formed layers by periodically moving the formed layers in-and-out of a beam spot of the instances of probe-light, such that the modulation corresponds to timing of the periodic motion.

23. The method of claim 22 , further comprising:
receiving, by an interferometer of the measurement system, probe-light provided by an optical source that spans the measurement spectral range; and
for each optical path difference of a plurality of optical path differences of the interferometer, providing, by the interferometer, an instance of the probe-light associated with the

Assignees

• Halliburton Energy Services Inc

Inventors

• Price James M
• Nayak Aditya B
• Perkins David L

Classifications

• G01N21/8422

  Investigating thin films, e.g. matrix isolation method · CPC title

• G01J3/28 Primary

  Investigating the spectrum (using colour filters G01J3/51) · CPC title

• B29D11/0073

  Optical laminates · CPC title

• G01N2021/8438

  Mutilayers · CPC title

• G01N21/31

  Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry {(G01N21/72 takes precedence)} · CPC title