US4854710A
Expired / Lapsed
US
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Method and apparatus for evaluating surface and subsurface features in a semiconductor
Assignee: Therma Wave Inc
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Filing: 1987-07-23
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Granted: 1989-08-08
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Expires: 2007-07-23
Abstract
Abstract A method and apparatus are disclosed for evaluating surface and subsurface features in a semiconductor sample. In operation, a periodic energy source is applied to the surface of the semiconductor sample to generate a periodic electron-hole plasma. This plasma interacts with features in the sample as it diffuses. The plasma affects the index of refraction of the sample and the changing plasma density is monitored using a radiation probe. In the preferred embodiment, the radiation probe measures the plasma induced periodic changes of reflectivity of the surface of the sample to yield information about the sample, such as ion dopant concentrations, residue deposits and defects.
Inventors
- 👤 Jon Opsal
- 👤 Allan Rosencwaig
- 👤 Walter L. Smith
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 13:37
CPC Classifications
G; G01; G01R; G01R31/00; G01R31/26; G01R31/265; G01R31/2656; G01N; G01N21/00; G01N21/17; G01N21/171
Claims Analysis
Total Claims: 38
Claim 1
Independent Claim
160 words
An apparatus for evaluating surface and subsurface conditions in a semiconductor sample comprising: a periodic excitation source for supplying energy to the surface of the sample sufficient to create an electron-hole plasma having a density sufficient to cause changes in the optical reflectivity of the sample; a probe for emitting a beam of radiation of a fixed wavelength selected to allow focusing in the micron range; means for focusing the radiation probe beam to a radius in the micron range and for directing the focused probe beam within a portion of the surface of the sample which has been periodically excited in a manner such that said probe beam is reflected; means for monitoring the modulated intensity changes in said reflected probe beam resulting from the variations in the optical reflectivity of the sample due principally to the presence of the electron-hole plasma; and means for processing the measured intensity changes of the reflected probe beam to evaluate the sample.
Claim 2
Independent Claim
160 words
An apparatus for evaluating surface and subsurface conditions in a semiconductor sample comprising: a periodic excitation source for supplying energy to the surface of the sample sufficient to create an electron-hole plasma having a density sufficient to cause changes in the optical reflectivity of the sample; a probe for emitting a beam of radiation of a fixed wavelength selected to allow focusing in the micron range; means for focusing the radiation probe beam to a radius in the micron range and for directing the focused probe beam within a portion of the surface of the sample which has been periodically excited in a manner such that said probe beam is reflected; means for monitoring the modulated intensity changes in said reflected probe beam resulting from the variations in the optical reflectivity of the sample due principally to the presence of the electron-hole plasma; and means for processing the measured intensity changes of the reflected probe beam to evaluate the sample.
Claim 3
Dependent Claim
31 words
An apparatus as recited in claim 1 wherein said probe beam is directed toward the center of the area on the surface of the sample which has been the periodically excited.
Claim 4
Dependent Claim
14 words
An apparatus as recited in claim 1 wherein the monitoring means includes a photodetector.
Claim 5
Dependent Claim
47 words
An apparatus as recited in claim 1 wherein the processing means function to compare the monitored changes of the probe beam with predetermined changes of the probe beam associated with a known reference sample whereby variations in surface and subsurface conditions in the sample can be monitored.
Claim 6
Dependent Claim
34 words
An apparatus as recited in claim 1 further including a means for rastering the sample with respect to both the excitation source and radiation probe such that a two dimensional evaluation can be made.
Claim 7
Dependent Claim
16 words
An apparatus as recited in claim 1 wherein said probe beam is defined by a laser.
Claim 8
Dependent Claim
21 words
An apparatus as recited in claim 1 further including a means for controlling the modulation frequency (ω) of the excitation source.
Claim 9
Dependent Claim
47 words
An apparatus as recited in claim 7 wherein the modulation frequency (ω) of said excitation source is set such that the period between cycles is less than the time (τ) required for electron-hole pairs to recombine (ωτ greater than 1) whereby critically damped plasma waves are generated.
Claim 10
Dependent Claim
35 words
An apparatus as recited in claim 8 wherein changes in the probe beam are monitored as the modulation frequency (ω) of the energy source is varied to provide information about subsurface characteristics of the sample.
Claim 11
Dependent Claim
40 words
An apparatus as recited in claim 9 wherein monitored changes in the probe beam are compared with predetermined changes of the probe beam associated with a known reference sample whereby variations in subsurface conditions of the sample can be monitored.
Claim 12
Independent Claim
153 words
A method for evaluating surface and subsurface conditions in a semiconductor sample comprising the steps of: supplying periodic energy to the surface of the sample to excite electrons and create an electron-hole plasma having a density sufficient to cause changes in the optical reflectivity of the sample; focusing a radiation probe beam to a radius in the micron range and directing the focused probe beam on a portion of the area on the surface of the sample which has been periodically excited in a manner such that the probe beam is reflected, said probe beam being of a fixed wavelength selected to allow focusing in the micron range; monitoring changes in the modulated intensity of the reflected probe beam resulting from the changes in the optical reflectivity of the sample due principally to the presence of the electron-hole plasma; and processing the monitored intensity changes of the probe beam to evaluate the sample.
Claim 13
Independent Claim
153 words
A method for evaluating surface and subsurface conditions in a semiconductor sample comprising the steps of: supplying periodic energy to the surface of the sample to excite electrons and create an electron-hole plasma having a density sufficient to cause changes in the optical reflectivity of the sample; focusing a radiation probe beam to a radius in the micron range and directing the focused probe beam on a portion of the area on the surface of the sample which has been periodically excited in a manner such that the probe beam is reflected, said probe beam being of a fixed wavelength selected to allow focusing in the micron range; monitoring changes in the modulated intensity of the reflected probe beam resulting from the changes in the optical reflectivity of the sample due principally to the presence of the electron-hole plasma; and processing the monitored intensity changes of the probe beam to evaluate the sample.
Claim 14
Dependent Claim
30 words
A method as recited in claim 11 wherein said radiation probe is directed towards the center of the area on the surface of the sample which has been periodically excited.
Claim 15
Dependent Claim
47 words
A method as recited in claim 11 wherein during said processing step, the changes of said probe beam are compared with predetermined changes of the probe beam associated with a known reference sample, whereby variations in the surface and subsurface conditions in the sample can be monitored.
Claim 16
Dependent Claim
47 words
A method as recited in claim 11 further including the step of setting the modulation frequency (ω) of the periodic energy source such that the period between cycles is less than the time (τ) required for electron-hole pairs to recombine whereby critically damped plasma waves are generated.
Claim 17
Dependent Claim
38 words
A method as recited in claim 14 further including the step of monitoring changes in the probe beam as the modulation frequency (ω) of the energy source is varied to provide information about subsurface characteristics of the sample.
Claim 18
Dependent Claim
45 words
A method as recited in claim 15 further including the step of comparing the measured changes in the probe beam to predetermine changes of the probe beam associated with a known reference sample, whereby variations in the subsurface conditions of the sample can be monitored.
Claim 19
Dependent Claim
28 words
A method as recited in claim 11 further including the step of rastering the sample with respect to the probe and energy beams to permit a two-dimensional analysis.
Claim 20
Independent Claim
163 words
An apparatus for evaluating surface and subsurface conditions in a semiconductor sample comprising: an intensity modulated laser energy beam for supplying energy to the surface of the sample sufficient to create an electron-hole plasma having a density sufficient to cause changes in the optical reflectivity of the sample; a laser probe for emitting a beam of radiation of a fixed wavelength selected to allow focusing in the micron range; means for focusing the radiation probe beam to a radius in the micron range and for directing the focused probe beam within a portion of the surface of the sample which has been periodically excited in a manner such that said probe beam is reflected; means for monitoring variations in the modulated intensity of said reflected probe beam resulting from changes in the optical reflectivity of the sample due principally to the presence of the electron-hole plasma; and means for processing the measured intensity changes of the reflected probe beam to evaluate the sample.
Claim 21
Independent Claim
163 words
An apparatus for evaluating surface and subsurface conditions in a semiconductor sample comprising: an intensity modulated laser energy beam for supplying energy to the surface of the sample sufficient to create an electron-hole plasma having a density sufficient to cause changes in the optical reflectivity of the sample; a laser probe for emitting a beam of radiation of a fixed wavelength selected to allow focusing in the micron range; means for focusing the radiation probe beam to a radius in the micron range and for directing the focused probe beam within a portion of the surface of the sample which has been periodically excited in a manner such that said probe beam is reflected; means for monitoring variations in the modulated intensity of said reflected probe beam resulting from changes in the optical reflectivity of the sample due principally to the presence of the electron-hole plasma; and means for processing the measured intensity changes of the reflected probe beam to evaluate the sample.
Claim 22
Dependent Claim
30 words
An apparatus as recited in claim 18 wherein the probe beam is directed towards the center of the area on the surface of the sample which has been periodically excited.
Claim 23
Dependent Claim
14 words
An apparatus as recited in claim 18 wherein the monitoring means includes a photodetector.
Claim 24
Dependent Claim
48 words
An apparatus as recited in claim 18 wherein the processing means functions to compare the monitored changes of the probe beam with predetermined changes of the probe beam associated with a known reference sample, whereby variations in the surface and subsurface conditions in the sample can be monitored.
Claim 25
Dependent Claim
34 words
An apparatus as recited in claim 18 further including a means for rastering the sample with respect to both the excitation source and the radiation probe such that a two-dimensional evaluation can be made.
Claim 26
Dependent Claim
21 words
An apparatus as recited in claim 18 further including a means for controlling the modulation frequency (ω) of the excitation source.
Claim 27
Dependent Claim
43 words
An apparatus as recited in claim 23, wherein the modulation frequency (ω) of said excitation source is set such that the period between cycles is less than the time (τ) required for electron-hole pairs to recombine whereby critically damped plasma waves are generated.
Claim 28
Dependent Claim
39 words
An apparatus as recited in claim 24, wherein changes in the probe beam are monitored as the modulation frequency (ω) of the laser energy beam is varied to provide information about the surface and subsurface characteristics of the sample.
Claim 29
Dependent Claim
40 words
An apparatus as recited in claim 25, wherein monitored changes in the probe beam are compared with predetermined changes of the probe beam associated with a known reference sample, whereby variations in subsurface conditions of the sample can be monitored.
Claim 30
Dependent Claim
39 words
An apparatus as recited in claim 18 wherein said focusing means includes a lens and wherein both said modulated laser energy beam and said probe laser beam are focused normal to the surface of the sample through said lens.
Claim 31
Independent Claim
160 words
A method for evaluating surface and subsurface conditions in a semiconductor sample comprising the steps of: directing a periodic laser beam at the surface of the sample having an input energy sufficient to excite electrons and create an electron-hole plasma having a density sufficient to cause changes in the optical reflectivity of the sample; focusing a laser probe beam to a radius in the micron range and directing the focused probe beam on a portion of the area on the surface of the sample which has been periodically excited in a manner such that the probe beam is reflected, said probe beam being of a fixed wavelength selected to allow focusing in the micron range; monitoring changes in the modulated intensity of the reflected probe beam resulting from the changes in the optical reflectivity of the sample due principally to the presence of the electron-hole plasma; and processing the monitored intensity changes of the probe beam to evaluate the sample.
Claim 32
Independent Claim
160 words
A method for evaluating surface and subsurface conditions in a semiconductor sample comprising the steps of: directing a periodic laser beam at the surface of the sample having an input energy sufficient to excite electrons and create an electron-hole plasma having a density sufficient to cause changes in the optical reflectivity of the sample; focusing a laser probe beam to a radius in the micron range and directing the focused probe beam on a portion of the area on the surface of the sample which has been periodically excited in a manner such that the probe beam is reflected, said probe beam being of a fixed wavelength selected to allow focusing in the micron range; monitoring changes in the modulated intensity of the reflected probe beam resulting from the changes in the optical reflectivity of the sample due principally to the presence of the electron-hole plasma; and processing the monitored intensity changes of the probe beam to evaluate the sample.
Claim 33
Dependent Claim
30 words
A method as recited in claim 28 wherein said radiation probe is directed towards the center of the area on the surface of the sample which has been periodically excited.
Claim 34
Dependent Claim
47 words
A method as recited in claim 48 wherein during said processing step, the changes of said probe beam are compared with predetermined changes of the probe beam associated with a known reference sample, whereby variations in the surface and subsurface conditions in the sample can be monitored.
Claim 35
Dependent Claim
47 words
A method as recited in claim 28 further including the step of setting the modulation frequency (ω) of the periodic laser beam such that the period between cycles is less than the time (τ) required for electron-hole pairs to recombine whereby critically damped plasma waves are generated.
Claim 36
Dependent Claim
39 words
A method as recited in claim 31 further including the step of monitoring changes in the probe beam as the modulation frequency (ω) of the periodic laser beam is varied to provide information about subsurface characteristics of the sample.
Claim 37
Dependent Claim
28 words
A method as recited in claim 28 further including the step of rastering the sample with respect to the probe and energy beams to permit a two-dimensional analysis.
Claim 38
Dependent Claim
34 words
A method as recited in claim 28 further including the step of focusing the periodic laser beam and the probe laser beam normal to the surface of the sample through the same optical element.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1992-08-07 | 1993-02-06 | 1993-08-08 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1996-08-07 | 1997-02-06 | 1997-08-08 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2000-08-07 | 2001-02-06 | 2001-08-08 | $7700.00 | Window Closed / Lapsed |