US5959731A
Expired / Lapsed
US
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Optical micrometer for measuring thickness of transparent substrates based on optical absorption
Assignee: Virginia Semiconductor Inc
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Filing: 1997-10-29
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Granted: 1999-09-28
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Expires: 2017-10-29
Abstract
Abstract Techniques and systems for measuring absolute thickness, the total thickness variation, and electric resistivity of a semiconductor substrate in a nondestructive optical fashion. Optical absorption is used to measure the absolute thickness of a semiconductor substrate with a light source and a photo transceiver. The thickness is determined by comparing the amount of absorption to a calibrated amount. Both the absolute thickness and total thickness variation of the substrate can be measured based on light absorption using an imaging device. The invention can be used to directly image and measure localized features formed on micro machined substrates. The resistivity of a substrate sample can also be measured by using an alternating electrical signal.
Inventors
- 👤 Stephen H. Jones
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 12:17
CPC Classifications
G; G01; G01B; G01B11/00; G01B11/02; G01B11/06
Claims Analysis
Total Claims: 21
Claim 1
Independent Claim
218 words
A system for characterizing semiconductor substrates by using electromagnetic radiation, comprising: a sample holder having a support surface for holding a substrate which has a first surface and a second opposite surface; a light source, disposed relative to said sample holder and configured to produce a first substantially monochromatic light beam at a first discrete wavelength to illuminate the first surface of the substrate, wherein said first discrete wavelength is selected so that said light beam is partially absorbed by the substrate and partially passes through the substrate as a transmitted beam; a single light receiver, disposed relative to said sample holder to receive only said transmitted beam and to produce an electrical signal indicative of an intensity of said transmitted beam; and an information processing device, connected to said light receiver to receive said electrical signal and configured to process said electrical signal to produce thickness information of the substrate, wherein said information processing device is configured to store a first set of predetermined and calibrated absorption-thickness data of light absorption at said first discrete wavelength as a function of thickness of a first set of substrate standards formed of a semiconductor material substantially identical to the substrate, and each of said first set of substrate standards has a different thickness value within a first thickness range.
Claim 2
Independent Claim
218 words
A system for characterizing semiconductor substrates by using electromagnetic radiation, comprising: a sample holder having a support surface for holding a substrate which has a first surface and a second opposite surface; a light source, disposed relative to said sample holder and configured to produce a first substantially monochromatic light beam at a first discrete wavelength to illuminate the first surface of the substrate, wherein said first discrete wavelength is selected so that said light beam is partially absorbed by the substrate and partially passes through the substrate as a transmitted beam; a single light receiver, disposed relative to said sample holder to receive only said transmitted beam and to produce an electrical signal indicative of an intensity of said transmitted beam; and an information processing device, connected to said light receiver to receive said electrical signal and configured to process said electrical signal to produce thickness information of the substrate, wherein said information processing device is configured to store a first set of predetermined and calibrated absorption-thickness data of light absorption at said first discrete wavelength as a function of thickness of a first set of substrate standards formed of a semiconductor material substantially identical to the substrate, and each of said first set of substrate standards has a different thickness value within a first thickness range.
Claim 3
Dependent Claim
54 words
A system as in claim 1, further comprising a resistivity-sensing module operable to measure electric resistivity of the substrate, said module including two metal probes located at two different locations in a close proximity of said substrate and applying a RF signal across said two probes to generate a signal indicative of the resistivity.
Claim 4
Dependent Claim
103 words
A system as in claim 1, wherein: said light source is operable to produce a second substantially monochromatic light beam at a second discrete wavelength; and said information processing device is configured to further have a second set of predetermined and calibrated absorption-thickness data of light absorption at said second discrete wavelength as a function of thickness of a second set of substrate standards that are made of the same semiconductor material as the substrate, each of said set of substrate standards having a different thickness value within a second thickness range which is at least partially different from said first thickness range.
Claim 5
Dependent Claim
28 words
A system as in claim 3, wherein said first discrete wavelength is within the visible spectral range and said second discrete wavelength is within the IR spectral range.
Claim 6
Dependent Claim
57 words
A system as in claim 1, wherein said light receiver includes a light sensing array operable to capture an image of at least a portion of the substrate illuminated by said first light beam and said information processing device processes said image to produce information on thickness and thickness variation of said illuminated portion in the substrate.
Claim 7
Dependent Claim
34 words
A system as in claim 5, wherein said information processing device further includes a frame grabber operating to digitize said image to obtain a substrate thickness map of said illuminated portion of the substrate.
Claim 8
Dependent Claim
15 words
A system as in claim 5, wherein said light sensing array is a CCD array.
Claim 9
Dependent Claim
20 words
A system as in claim 1, wherein said information processing device includes a computer which analyzes results of light absorption.
Claim 10
Dependent Claim
35 words
A system as in claim 1, further comprising a resistivity sensing module disposed relative to said sample holder and configured to measure electrical resistivity of the substrate by applying a RF signal to the substrate.
Claim 11
Independent Claim
254 words
A system for characterizing semiconductor substrates based on light absorption, comprising: a sample holder having a support surface for holding a substrate which has a first surface and a second opposite surface; a light source, disposed relative to said sample holder and configured to produce a substantially monochromatic light beam at a discrete wavelength to illuminate at least a portion of the first surface of the substrate, wherein said discrete wavelength is selected so that said light beam is partially absorbed by the substrate and partially passes through the substrate as a transmitted beam; a single light sensing array having a plurality of sensing elements, disposed relative to said sample holder to receive only said transmitted beam and to produce an electrical image of the illuminated portion of the substrate, wherein said electrical image represents an intensity distribution across said transmitted beam to indicate light absorption by the illuminated portion; and an information processing device, connected to said light sensing array to receive said electrical image and configured to store a first set of predetermined and calibrated absorption-thickness data of light absorption at said first discrete wavelength as a function of thickness of a first set of substrate standards formed of a semiconductor material substantially identical to the substrate, wherein each of said first set of substrate standards has a different thickness value within a first thickness range and information processing device operates to compare said electrical image to said first set absorption-thickness data to produce a thickness map and image of the substrate.
Claim 12
Independent Claim
254 words
A system for characterizing semiconductor substrates based on light absorption, comprising: a sample holder having a support surface for holding a substrate which has a first surface and a second opposite surface; a light source, disposed relative to said sample holder and configured to produce a substantially monochromatic light beam at a discrete wavelength to illuminate at least a portion of the first surface of the substrate, wherein said discrete wavelength is selected so that said light beam is partially absorbed by the substrate and partially passes through the substrate as a transmitted beam; a single light sensing array having a plurality of sensing elements, disposed relative to said sample holder to receive only said transmitted beam and to produce an electrical image of the illuminated portion of the substrate, wherein said electrical image represents an intensity distribution across said transmitted beam to indicate light absorption by the illuminated portion; and an information processing device, connected to said light sensing array to receive said electrical image and configured to store a first set of predetermined and calibrated absorption-thickness data of light absorption at said first discrete wavelength as a function of thickness of a first set of substrate standards formed of a semiconductor material substantially identical to the substrate, wherein each of said first set of substrate standards has a different thickness value within a first thickness range and information processing device operates to compare said electrical image to said first set absorption-thickness data to produce a thickness map and image of the substrate.
Claim 13
Dependent Claim
40 words
A system as in claim 10, wherein said information processing device includes a frame grabber operable to digitize said electrical image and a microprocessor operable to process said digitized image to obtain a substrate thickness map of the illuminated portion.
Claim 14
Dependent Claim
54 words
A system as in claim 10, further comprising a resistivity-sensing module operable to measure electric resistivity of the substrate, said module including two metal probes located at two different locations in a close proximity of said substrate and applying a RF signal across said two probes to generate a signal indicative of the resistivity.
Claim 15
Dependent Claim
24 words
A system as in claim 10, further comprising a beam collimating device disposed relative to said light source to substantially collimate said light beam.
Claim 16
Dependent Claim
48 words
A system as in claim 10, further comprising a positioner configured to control a relative translational position of said sample holder relative said light sensing array in a plane substantially perpendicular to said light beam and operable to select a desired portion of the substrate for thickness mapping.
Claim 17
Dependent Claim
35 words
A system as in claim 10, further comprising a resistivity sensing module disposed relative to said sample holder and configured to measure electrical resistivity of the substrate by applying a RF signal to the substrate.
Claim 18
Dependent Claim
25 words
A system as in claim 10, wherein said light source comprises a laser, a light-emitting diode, or a white light source having a bandpass filter.
Claim 19
Dependent Claim
124 words
A nondestructive method for measuring thickness and thickness variation of a substrate, comprising: providing an optical beam at a discrete wavelength to which the substrate is partially transparent; illuminating the substrate with said optical beam to produce a transmitted beam which has a transmission intensity distribution profile indicative of a spatial profile of light absorption of the substrate; determining thickness distribution profile of the substrate according to said absorption profile by using a set of predetermined and calibrated absorption-thickness data of light absorption at said discrete wavelength as a function of thickness of a set of substrate standards that are made of the same semiconductor material as the substrate, wherein each of said substrate standards has a different thickness value within a thickness range.
Claim 20
Dependent Claim
124 words
A nondestructive method for measuring thickness and thickness variation of a substrate, comprising: providing an optical beam at a discrete wavelength to which the substrate is partially transparent; illuminating the substrate with said optical beam to produce a transmitted beam which has a transmission intensity distribution profile indicative of a spatial profile of light absorption of the substrate; determining thickness distribution profile of the substrate according to said absorption profile by using a set of predetermined and calibrated absorption-thickness data of light absorption at said discrete wavelength as a function of thickness of a set of substrate standards that are made of the same semiconductor material as the substrate, wherein each of said substrate standards has a different thickness value within a thickness range.
Claim 21
Dependent Claim
27 words
A method as in claim 17, wherein the substrate is processed to have micro features and said thickness distribution profile effects an image of said micro features.
References Cited (Backward Citations)
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