US4995939A
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Method and apparatus for determining the layer thickness of semiconductor layer structures
Assignee: RESEARCH INSTITUTE FOR TECHNICAL PHYSICS HAS 1325 BUDAPEST PF 76 HUNGARY
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Filing: 1988-05-04
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Granted: 1991-02-26
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Expires: 2008-05-04
Abstract
Abstract In a process for determining the layer thickness of semiconductor layer structures, a sample of a multilayer semi-conductor (4) is placed in contact with an electrolyte (2) then subjected to anodic etching during which the depth of etching is determined by integration of the current. During etching, the sample (4) is also excited by an electric signal and the real component of the admittance and hence the conductance of the probe at the frequency of excitation is determined, the extreme values of this component are analyzed, and the values of the depth of etching corresponding to these extremes, which characterize the junctions between the layers of the sample (4) tested, are determined. The installation for implementing the procedure contains a cell (1) filled with electrolyte (2) in which is immersed a graphite electrode (5), a saturated calomel electrode (6), and a platinum electrode (7) surrounding the surface of the sample (4) subjected to etching, electrodes (8,9) neither of which touch the surface of the sample (4) subjected to etching, a potentiostat (13) which is connected to the calomel electrode (6) and the direct current source (12), the current integrator (14), which receives the etching current intensity signal, a generator (15) which emits a periodic signal between the sample (14) and the metal electrode, and the measurement element (16) for measuring the conductance of the sample (4).
Inventors
- 👤 Gyorgy Ferenczi
- 👤 Katalin Erdelyi
- 👤 Maria Somogyi
- 👤 Janos Boda
- 👤 Gyorgy Fule
- 👤 Gabor Aszodi
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-31 16:43
CPC Classifications
G; G01; G01B; G01B7/00; G01B7/02; G01B7/06; G01N; G01N27/00; G01N27/26; G01N27/416; G01N27/42
Claims Analysis
Total Claims: 15
Claim 1
Independent Claim
137 words
A method for determining the layer thickness of semiconductor layer structures, in which a multilayer semiconductor sample is examined, comprising the steps of contacting a surface of said sample with an electrolyte, anodically etching said surface using an etching current, determining, during the etching process, the actual etching depth, by integrating said etching current, said sample being excited by a periodic electrical signal while said sample is being etched and measuring a response to said periodic signal in a manner such that at the frequency of the exciting signal a real component, comprising the conductance of the admittance, of the sample is measured, wherein the extreme values of said component are examined and the etching depth data associated with said extreme values are recorded, said extreme values defining the transitions of the examined layers of the sample.
Claim 2
Independent Claim
137 words
A method for determining the layer thickness of semiconductor layer structures, in which a multilayer semiconductor sample is examined, comprising the steps of contacting a surface of said sample with an electrolyte, anodically etching said surface using an etching current, determining, during the etching process, the actual etching depth, by integrating said etching current, said sample being excited by a periodic electrical signal while said sample is being etched and measuring a response to said periodic signal in a manner such that at the frequency of the exciting signal a real component, comprising the conductance of the admittance, of the sample is measured, wherein the extreme values of said component are examined and the etching depth data associated with said extreme values are recorded, said extreme values defining the transitions of the examined layers of the sample.
Claim 3
Dependent Claim
25 words
A method as claimed in claim 1, wherein said sample is an n-type sample and said periodic electric signal is produced by means of light.
Claim 4
Dependent Claim
19 words
A method as claimed in claim 1, wherein said etching process is carried out continuously during the whole measurement.
Claim 5
Dependent Claim
16 words
A method as claimed in claim 1, wherein said surface of the sample is uniformly etched.
Claim 6
Dependent Claim
25 words
A method as claimed in claim 1, wherein said periodic electric signal is a sine signal having a frequency between 500 Hz and 10 kHz.
Claim 7
Dependent Claim
23 words
A method as claimed in claim 1, wherein said etching process is carried out by a current between 1 μA and 100 μA.
Claim 8
Dependent Claim
41 words
A method as claimed in claim 1, wherein said exciting signal is coupled between a platinum electrode immersed in said electrolyte and at least two electrodes with sharp-pointed ends pressed to a surface of the sample other than said etched surface.
Claim 9
Dependent Claim
41 words
A method as claimed in claim 7, wherein before measurement is started, an electric discharge is provided between said sharp-pointed electrodes and said sample, whereby the material of the sharp end of said sharp-pointed electrodes is slightly alloyed in said sample.
Claim 10
Independent Claim
181 words
An apparatus for determining layer thickness of a multilayer semiconductor structure comprising a cell filled with an electrolyte, a carbon electrode immersed in said electrolyte, a saturated calomel electrode immersed in said electrolyte, a metal electrode also immersed in said electrolyte and being positioned so as to surround an etched surface of a sample to be etched, a pair of additional electrodes for contacting at least one surface of the sample not exposed to said electrolyte, said carbon electrode and said pair of additional electrodes cooperating so as to establish a direct current voltage for anodically etching the sample a potentiostat coupling an adjustable potential between said carbon electrode and said sample, the potentiostat being connected to said calomel electrode and to a direct current source, a current integrator for receiving a signal representing an etching current, a generator for exciting the sample with a periodical signal by coupling said periodical signal between said metal electrode and said sample and a unit measuring the response of said sample to the periodical excitation, wherein said measuring unit is a conductance measuring unit.
Claim 11
Independent Claim
181 words
An apparatus for determining layer thickness of a multilayer semiconductor structure comprising a cell filled with an electrolyte, a carbon electrode immersed in said electrolyte, a saturated calomel electrode immersed in said electrolyte, a metal electrode also immersed in said electrolyte and being positioned so as to surround an etched surface of a sample to be etched, a pair of additional electrodes for contacting at least one surface of the sample not exposed to said electrolyte, said carbon electrode and said pair of additional electrodes cooperating so as to establish a direct current voltage for anodically etching the sample a potentiostat coupling an adjustable potential between said carbon electrode and said sample, the potentiostat being connected to said calomel electrode and to a direct current source, a current integrator for receiving a signal representing an etching current, a generator for exciting the sample with a periodical signal by coupling said periodical signal between said metal electrode and said sample and a unit measuring the response of said sample to the periodical excitation, wherein said measuring unit is a conductance measuring unit.
Claim 12
Dependent Claim
20 words
An apparatus as claimed in claim 9, wherein said conductance measuring unit comprises a lock-in amplifier and a phase-sensitive amplifier.
Claim 13
Dependent Claim
39 words
An apparatus as claimed in claim 9, wherein the output of said conductance measuring unit is connected to a first input of a signal processing unit that has a second input coupled to an output of said current integrator.
Claim 14
Dependent Claim
23 words
An apparatus as claimed in claim 11, wherein said signal processing unit comprises a plotter for drafting an etching depth versus conductance diagram.
Claim 15
Dependent Claim
13 words
An apparatus as claimed in claim 9, wherein said metal electrode comprises platinum.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1994-02-25 | 1994-08-27 | 1995-02-26 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1998-02-25 | 1998-08-27 | 1999-02-26 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2002-02-25 | 2002-08-27 | 2003-02-26 | $7700.00 | Window Closed / Lapsed |