Camera.

Moiré methods are based on that two regular structures such as line grids are placed with approximately equal lattice constants for superimposing optical means. The applied or aufprojizierte on the specimen object grating is imaged on a reference grid. Deformations of the object grating by topographic properties result in the plane of the reference grid characteristic moire lines.

From IBM Technical Disclosure Bulletin Vol. 25 No. 1, pages 357-358 (1982) is known to image the object grating located on the specimen on a physical grid. The resulting in this image plane moire lines are recorded by means of a second image by a CCD camera receiver. This second image of the Moiré lines could also be done by any other camera or on a photographic film.

The second figure brings considerable intensity losses with itself, which require a very high illuminance at the object. This is just very difficult or complicated and expensive to implement in large-area specimens, so that the prior art allows only small-scale samples or low resolution.

One solution is the direct use of a CCD image sensor as a reference grid. The row or column structure of the sensor array can be used directly as a lattice structure of a reference grid. The resulting moiré images are not affected by intensity losses, so that a large test surface can be considered, but they allow only a low resolution, which is caused by the small number of rows / columns in the CCD image sensors. Such CCD sensors allow a few hundred lines. Although an interconnection of several CCD image sensors increases the line number of the reference grid, but requires a technically more complicated and slower read-out operation of the image obtained.

Starting from this prior art, the invention aims to provide a camera of the aforementioned type, which has a high resolution and a large field.

This object is achieved by the features of the characterizing part of the main claim.

By applying the reference grid as additional physical grid structure directly in the image plane in which the moire lines are recorded for processing, the only additional intensity losses are those that are caused by the non-transparent part of the applied grid. With a 1: 1 - rectangular amplitude grating, the light attenuation is thus only 50%. A technically possible in thin film processes lattice constant of a few micrometers, the number of be on the generation of moire structure volved grid lines from a few hundred to several thousand lines increases. An upper limit of the usable line number is then only in the quality of the CCD camera lens used.

In an advantageous embodiment of the invention, a use of the image guide on the image plane of a conventional CCD image sensor in the way that the entrance plane of the image guide in the image plane of the object imaged grating comes to rest. An application of the reference grid on the entrance plane of the image guide brings the advantages mentioned above with simultaneous detachment of the CCD image sensor chips from the manufacturing process of the reference grid with it, in the then only the technically easier to handle image conductor is coated and patterned.

Further embodiments of the invention are subject of the subclaims.

Embodiments of the invention will become apparent from the drawing. Show it:<ul><li>Fig. 1 is a schematic perspective view of a section of the CCD image sensor according to a first embodiment of the invention,</li><li>Fig. 2 is a perspective view of a CCD camera with a CCD image sensor according to the invention and </li><li>FIG. 3 is a perspective view of a section of the image guide for a CCD image sensor according to a second embodiment of the invention.</li></ul>

Fig. 1 shows in perspective view a detail of a first embodiment of the invention. shown schematically is a charge coupled light detector matrix which is hereinafter briefly referred to as a CCD image sensor 1, which is connected via connecting wires 2 with a carrier plate 3rd The CCD image sensor 1 is constructed in its image plane 4 of 5 pixels in rows and columns 6, are being drawn to the clarity of FIG. 1 only four columns 6. The CCD image sensor has, as usual, on each of several hundred rows and columns. 6

When picked up by the pixels 5 image is passed through contact feet 7 to an image processing circuit, in which form the columns 6 of the image sensor 1 in a projection moiré method, for example, in a projection moiré method for large-scale topography measurements of a device under test, a grid wherein the object grid is on the sample surface.

As Fig. 1 shows schematically, directly a reference grid 8 of alternating transparent and non-transparent strip is applied to the image Level 4. An advantageous technique for applying a reference grating 8 in the form of a rectangular amplitude grating in the usual SiO₂-protection layer of the CCD image sensor 1 in the image plane 4 consists in the application of thin film processes - such as evaporation or sputtering - and subsequent photolithographic patterning. In the thin-film processes chromium / chromium oxide may be used as well adhering and patternable materials.

With these processes, lattice constants are also possible in the range of 1 to 5 microns so that when a size of the image plane 4 of the CCD image sensor 1 of approximately 10 x 10 mm² a grid line number from 2000 to 10,000 is obtained, of which in Fig. 1 for simplification only a few are drawn.

The number of grid lines 9 is substantially greater than the number of columns 6 of the CCD image sensor 1 in order to obtain a small lattice constant for the reference grating 8, and unwanted Moiré appearances by superposition of the reference grid 8 with the grid of the column 6 of the image sensor 1 to avoid. For this purpose, three grid lines are 9 per pixel 5 sufficient in column 6 of the image sensor 1, wherein the reference grid 8 to increase that number are preferably diagonally applied to the column 6 of the image sensor. 1 However, the mentioned Moire phenomena occur at any angle of the reference grid 8 to the column 6 of the CCD image sensor. 1

Fig. 2 shows a CCD camera 10, in which the CCD image sensor 1 is built in the image plane of the camera. The quality of the lens 11 of the CCD camera 10 is limited by its lateral resolution during the imaging of the object grating on the reference grating 8, the maximum usable number of lines that are in the range of 20 grid lines per pixel 5 in the column 6 of the CCD image sensor 1 ,

To take the advantage of a single figure, the reference grating 8 in optically close to the image plane 4 must be located where the moire lines are recorded for processing. This problem may be also solved as shown in FIG. 3 in accordance with a second exemplary embodiment in that the reference grating 8 is applied to the entrance plane 12 of an image guide 13, the rear side 14 is in direct contact with a conventional CCD image sensor 1. Fig. 3 shows the portion of the image guide 13, the length of which may be any of the incidence plane 12 for rear side 14.

In addition to the condition that the number of grid lines 9 must be greater than the number of column 6 of the CCD image sensor 1, the image guide 13 must be chosen such that the number of transmission fibers 15 is greater than the number of the pixels 5 of the CCD is image sensor. 1 The preparation of the reference grid 8 produced by the method mentioned in the first embodiment, in which case there is an advantage that does not need to be engaged in the manufacturing process of the CCD image sensor. 1

The grid lines of the reference grid 9 8 have been shown schematically for illustrative reasons in FIGS. 1 and 3 as parallel lines at intervals of the same width. The extent indicated rectangular amplitude grating can also be replaced by a sinusoidal grating or by one another extending between 0% and 100% in the transparency function following grid. The grid lines 9 can also be curved in the longitudinal direction along the grating plane. Further, the ratio of the distance of the grid lines can to their width and not 1: 1 is selected. Then height measurements of curved surfaces can be improved by the creation of simpler moiré images.