Optics: measuring and testing – Shape or surface configuration
Reexamination Certificate
2002-04-19
2004-06-22
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
Shape or surface configuration
C356S613000
Reexamination Certificate
active
06753971
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method of determining geometrical structures on or in a substrate on which diffraction of light occurs, as well as a method of determining parameters of the materials present on or in a substrate, whereby geometrical structures that lead to diffraction of light are present in or on the substrate.
Substrates having structures are, for example, optical storage media (CD, CD-R, DVD, CD-RW, DVD-RW, DVD-R, MO/MD, etc.), which are provided with channels, so-called grooves, for the recording, reading and/or erasing of data, and the geometries of which, such as depth, width and spacing, differ for the various types of media and are manufacturer specific. On the structured substrates, preferably blanks of polycarbonate, where for the manufacture of the optical storage media various layers having different refractive and/or absorption indices, and varying layer thicknesses, are applied, so that the desired optical, thermal, electrical, and mechanical properties of the storage medium result. Methods for the measurement of thicknesses of continuous layers are known and are described, for example, in DE 197 39 794 A, which originates from the same applicant, and in the documents mentioned there, as well as in U.S. Pat. No. 5,963,329. However, with the known method it is not possible to determine the various thicknesses that are present over the substrate surface, in other words, to determine a lateral change in layer thickness perpendicular to the direction of the build-up of the layer.
It is therefore an object of the present invention to provide a method that enables not only the determination of thicknesses of continuous layers, but also of geometrical structures on or in a substrate. It is a further object of the present invention to provide a method for determining parameters of the materials present on or in a substrate.
SUMMARY OF THE INVENTION
The stated object is realized with a method of determining geometrical parameters on or in a substrate, on which diffraction of light occurs, by the following method steps:
Measuring reflection and/or transmission light intensity values of the diffracted light as a function of the wavelength,
Calculating the reflection and/or transmission light intensity values using an iteration model in which are incorporated the individual layer, structure and/or material parameters, and
Modifying the parameters until the measured and calculated values coincide to the greatest extent possible.
In this connection, the layer, structure and/or material parameters vary over the surface of the substrate, are segmented in a lateral direction, and the layer, structure and/or material parameters of the individual segments are determined.
With the inventive method it is possible to measure not only the surface structures, such as grooves or channels, that are present in a substrate, but also the geometrical structures of coatings and layers of various materials that are applied to the substrate. For example, it is possible with the inventive method to also determine segmentations that are present at right angles to the direction of the build-up of a layer, in other words, lateral structures, such as are present, for example, with information-carrying substances of one time writable CD's (CD-R). As a consequence of the inventive measures, by amplitude and/or inphase overlapping of all partial waves to simulate the optical spectra, and by variation of the geometrical parameters to determine these parameters such that the measured and modulated spectra coincide optimally, it is possible to also locally determine layers that are present or applied over the substrate with varying layer thicknesses. Since the spectra react very sensitively to changes of the thicknesses of thin layers, for example in the nanometer range, the precision of the inventive method is accordingly high. The inventive method furthermore operates in a non-destructive manner and without the necessity for preparing samples, as is the case with conventional methods.
Pursuant to the inventive method, in a first method step the reflection and/or transmission light intensity values of the diffracted light are measured as a function of the wavelength. In this connection, it is particularly advantageous to measure the diffracted light of zero order of diffraction, although the diffracted light of higher orders of diffraction can also be evaluated for this measurement.
With the inventive method the determination of the geometrical dimensions of the structures in and/or on the substrate is particularly advantageous. In this connection, the geometrical structures are preferably determined by the thicknesses of the layers applied to the substrate.
Pursuant to a particularly advantageous embodiment of the invention, the local structures on the substrate surface are determined. As a result, it is possible to locally determine lateral segmentations or differences in relief over the surface of the substrate.
For the case where the structures on the substrate continuously vary over the substrate surface it is particularly advantageous pursuant to a further embodiment of the invention if at least these regions of continuously varying structures are segmented by the formation of polygons, and the structures of the individual polygonal segments are determined. In this way, it is also possible with the inventive method to determine, for example, inclined or rounded surface portions by dividing the structures into a resolution of segments or cells, whereby the precision of the determination of the structure is selectable by means of the fineness of the resolution. The structure of such a multi-component sectioning is thus sensed by suitable resolution with cells of any material, thickness, depth and/or width.
The structures that possibly also vary at least partially continuously over the surface of the substrate are preferably formed by layers that are applied to the substrate. In this connection, it is particularly advantageous if the inventive method is utilized for regulating the structure formation in a manufacturing process. This means that the determined data is input into a closed control loop of a production unit for the respective determination or fixing of the adjustment values. The inventive method is thus preferably used “inline” in a manufacturing process.
It is, of course, also possible to use the inventive method for the measurement of structures of substrates and of substrate layers applied thereon, and hence for the determination of the quality of multi-component structures or media, in other words, for the “offline” control.
Pursuant to a particularly advantageous embodiment of the inventive method, the reflection and/or transmission light intensity values of the diffracted light are simulated as a function of the wavelength for the in, formation of desired optical target data. Thus, instead of the measurement of the light intensity values, the inventive method also enables the simulation of desired optical target data and hence the fixing, in other words a structure design, of the structure that is to be applied to a substrate, for example a multi-component system in the case of optical storage media.
Pursuant to one advantageous embodiment of the invention, the substrates are blanks for data storage media, whereby the structures are embodied as channels in the blank, and the structures that are applied to the blank are formed of layers of information-carrying substances, so-called dyes. The layer thicknesses, the so-called segmentations, that vary over the surface of the substrate, result, for example with one-time writable CDs (CD-R), in that the dye-layer thickness in the grooves is greater than the thickness between the grooves, in the so-called land regions, since in the case of this storage media the groove depth is very great, for example in contrast to the groove depth with the CD-RW.
The inventive method is, of course, not limited to use in conjunction with optical storage media and the manufacture thereof. For example, it is also v
Becker R W
Pham Hoa Q.
R W Becker & Associates
Steag ETA-Optik GmbH
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