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US 6,639,673 B1Granted
Surface coating measurement instrument and apparatus for determination of coating thickness
AssigneeCommonwealth Scientific and Industrial Research Organisation
InventorsChristopher Hayes Freund, Roger Pryce Netterfield, Monty Glass
Life of this patent
Estimating the term…
Abstract
An apparatus (10) and method for measuring the average thickness of a non-uniform coating (110) on a rough surface (40) are disclosed. A source of light (20) of substantially a single wavelength is directed at a coated surface (40) under investigation. The light reflected (5) from the surface (40) is incident on two or more photodetectors (70), which measure the intensities of different polarisation states. A processing means (90) is provided to calculate the average coating thickness from the measured polarisation state intensities.
Claims9
Apparatus for measuring the average thickness of a non-uniform coating on a rough surface, comprising:
- a source of light of substantially a single wavelength, which is to be directed at a coated surface being examined;
- at least one polarising beam splitter receiving light reflected from said coated surface to produce a pair of orthogonal reflection components at 0° and 90° to the plane of incidence of said light source;
- at least two photodetectors for measuring the intensities, D1 for 0° and D2 for 90° of said orthogonal reflection components;
- and
- processing means coupled to the photodetectors that determines a variable ψ by the calculation:
- ψ = arctan ( D2 D1 ) 1 / 2
- and subtracts a predetermined zero offset from ψ and multiplies the result by a predetermined slope factor to give a measure of average thickness of said coating.
4 more elements
Apparatus for measuring the average thickness of a non-uniform coating on a rough surface, comprising:
- a source of light of substantially a single wavelength, which is to be directed at a coated surface being examined;
- at least one polarising prism beamsplitter receiving light reflected from said coated surface to produce a pair of orthogonal reflection components at ±45° to the plane of incidence of said light source;
- at least two photodetectors for measuring the intensities, D3 for +45° and D4 for −45° of said orthogonal reflection components;
- and
- processing means coupled to the photodetectors that determines a variable ω by the calculation:
- ω = 2 arctan ( D3 D4 ) 1 / 2
- and subtracts a predetermined zero offset from ω and multiplies the result by a predetermined slope factor to give a measure of average thickness of said coating.
4 more elements
Apparatus for measuring the average thickness of a non-uniform coating on a rough surface, comprising:
- a source of light of substantially a single wavelength which is to be directed at a coated surface to be examined;
- a first polarising beam splitter receiving light reflected from said coated surface to produce a first pair of orthogonal components at 0° and 90° to the plane of incidence of said light source;
- a second polarising beam splitter receiving light reflected from said coated surface to produce a second pair of orthogonal components at ±45° to the plane of incidence of said light source;
- at least four photodetectors for measuring the intensities, D1 for 0°, D2 for 90°, D3 for +45° and D4 for −45°, of said first and second pairs of orthogonal reflection components;
- and
- processing means that:
- (a) determines a variable ψ by the calculation ψ = arctan ( D2 D1 ) 1 / 2 ;
- (b) determines a variable ω by the calculation ω = 2 arctan ( D3 D4 ) 1 / 2 ;
- (c) determines possible thickness values for each of ψ(Tψn) and ω(Tωn) from predetermined tabulated values, wherein Tψn and Tωn are thickness values;
- and
- (d) determines the average thickness of said coating for the values of Tψn and Tωn that substantially match.
8 more elements
A computer program, storable in and executable by a computer to determine the average thickness of a non-uniform coating on a rough surface comprising:
- instructions for digitizing a plurality of electrical signals indicative of respective 0° and 90° intensities (D1, D2 respetively) of polarization states of a beam of light of substantially a single wavelength reflected off a location or a sample, said intensities being with reference to the plane of incidence of said beam;
- instructions for determining a variable ψ by performing the calculation ψ = arctan ( D2 D1 ) 1 / 2 ;
- and
- instructions for subtracting a predetermined zero offset from ψ and multiplying the result by a predetermined slope factor to give a measure of thickness of said coating.
1 more element
A computer program, storable in and executable by a computer to determine the average thickness of a non-uniform coating on a rough surface comprising:
- instructions for digitizing a plurality of electrical signals indicative of respective +45° and −45° intensities (D3, D4 respectively) of polarization states of a beam of light substantially a single wavelength reflected off a location or a sample, said intensities being with reference to the plane of incidence of said beam;
- instructions for determining a variable ω by performing the calculation ω = 2 arctan ( D3 D4 ) 1 / 2 ;
- and
- instructions for subtracting a predetermined zero offset from ω and multiplying the result by a predetermined slope factor to give a measure of thickness of said coating.
1 more element
A computer program, storable in and executable by a computer to determine the average thickness of a non-uniform coating on a rough surface comprising:
- instructions for digitizing a plurality of electrical signals indicative of respective 0°, 90° +45° and −45° (D1, D2, D3, D4 respectively) of polarization states of a beam of light of substantially a single wavelength reflected off a location or a sample, said intensities being with reference to the plane of incidence of said beam;
- instructions for determining a variable ψ by performing the calculation ψ = arctan ( D2 D1 ) 1 / 2 ;
- instructions for determining a variably ω by performing the calculation ω = 2 arctan ( D3 D4 ) 1 / 2 ;
- instructions for determining possible thickness values for each of ψ(Tψn) and ω(Tωn) from predetermined tabulated values, wherein Tψn and Tωn are thickness values;
- and
- instructions for determining the average thickness of said coating for the values of Tψn and Tωn that substantially match.
3 more elements
A method for measuring the average thickness of a non-uniform coating on a rough surface, comprising the steps of:
- performing a calibration operation on a non-coated sample of said rough surface to derive an offset value;
- performing a calibration operation to determine a slope factor representing the variation of thickness with a reflectance measure;
- directing a source of light of substantially a single wavelength at a coated surface being examined;
- causing reflected light components to be split into a pair of orthogonal reflection components at 0° and 90° to the plane of incidence of said light source;
- measuring the intensities D1 for 0° and D2 for 90° of said orthogonal reflection components;
- determining a variable ψ by the calculation:
- ψ = arctan ( D2 D1 ) 1 / 2 ;
- and
- calculating a measure of average thickness of said coating by subtracting said zero value from ψ and multiplying the result by said slope factor.
6 more elements
A method for measuring the average thickness of a non-uniform coating on a rough surface, comprising the steps of:
- performing a calibration operation on a non-coated sample of said rough surface to derive an offset value;
- performing a calibration operation to determine a slope factor representing the variation of thickness with a reflectance measure;
- directing a source of light of substantially a single wavelength at a coated surface being examined;
- causing reflected light components to be split into a pair of orthogonal reflection components at ±45° to the plane of incidence of said light source;
- measuring the intensities D3 for ±45° and D4 for −45° of said orthogonal reflection components;
- determining a variable ω by the calculation:
- ω = 2 arctan ( D3 D4 ) 1 / 2 and ;
- calculating a measure of average thickness of said coating by subtracting said zero value from ω and multiplying the result by said slope factor.
5 more elements
A method for measuring the average thickness of a non-uniform coating on a rough surface, comprising the steps of:
- (a) performing a calibration operation by:
- (i) directing a source of light of substantially a single wavelength at a coated sample of said rough surface having a known thickness of coating;
- (ii) causing reflected light components to be split into pairs of orthogonal reflection components at 0°, 90°, +45° and −45° to the plane of incidence of said light source;
- (iii) measuring the intensities D1 for 0°, D2 for 90°, D3 for +45° and D4 for −45° of said orthogonal components;
- (iv) determination a variable ψ by the calculation:
- ψ = arctan ( D2 D1 ) 1 / 2 ;
- (v) determining a variable ω by the calculation:
- ω = 2 arctan ( D3 D4 ) 1 / 2 ;
- and
- (vi) repeating steps (i) to (v) for a range of known thicknesses of coating and tabulating said respective values of ψ and ω;
- (b) performing steps (i) to (v) but for a coated sample of unknown thickness;
- (c) determining possible thickness values for each of ψ(Tψn) and ω(Tωn) from said tabulated values, wherein Tψn and Tωn are thickness values;
- and
- (d) determining the average thickness of said coating for the values of Tψn and Tωn that substantially match.
11 more elements
Dependencies are inferred from the claim text.