GB1583156A

GB1583156A - Device for scanning an object with a light beam

Info

Publication number: GB1583156A
Application number: GB1786977A
Authority: GB
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1976-04-28
Filing date: 1977-04-28
Publication date: 1981-01-21
Also published as: DE2718711A1; JPS52132851A; JPS607764B2; DE2718711C2

Description

(54) DEVICE FOR SCANNING AN OBJECT WITH A LIGHT BEAM (71) We, CANON KABUSHIKI KAISHA, a Japanese Company of 30--2, 3-chome, Shimomaruko, Ohta-ku, Tokyo, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a scanning device for scanning an object having a flat reflection surface and a further reflection surface which is inclined with respect to the flat reflection surface, the device being particularly useful for observing alignment marks on masks and wafers as a step in a process for manufacturing semiconductor elements such as transistors and integrated circuits (IC and LSI).

Alignment of the mask and wafer of an IC or LSI has generally been done by moving either the mask or the wafer in a plane parallel to the other until the alignment marks on both of them come to a predetermined positional relationship. In processes for manufacturing IC elements it is necessary to position the wafer very accurately for the printing of patterns thereon and to do this the alignment marks on both the mask and the wafer must be observed. Automatic positioning devices are known for carrying out the desired alignment, these comprising the so called "bright field observation" type in which the reflected light from the flat reflection surface is observed and the socalled "dark field observation" type in which the light reflected from the inclined surface is observed. The present invention is concerned with dark field observation of the object.

A known positioning device of the dark field observation type is described in Britishpatent No. 1,549,727. This device is described in more detail later with reference to Figures 1 and 2 of the drawings. Briefly, it comprises a device for illuminating the entire surface of the object and then focussing the light reflected from the flat surface at a filter. The filter is arranged to intercept light reflected from the flat surface while transmitting light reflected from the inclined surface for detection by a photoelectric detector.

In this known device, although the entire surface of the object is illuminated, only a small part of the illuminating light is transmitted to the detector. The system is therefore not particularly efficient.

According to the present invention, there is provided a device for scanning with a light beam an object having a flat reflection surface portion and a further surface portion inclined relative to the flat portion, comprising: a telecentric lens for transmitting light to, and receiving light from, said surface portions; means for directing a light beam into the telecentric lens and for repeatedly angularly deflecting the beam about a point substantially where the focal plane of said telecentric lens intersects its optical axis, whereby the beam is repeatedly scanned across the object; a filter for receiving light reflected from said reflection surfaces after such light has passed back through the telecentric lens, and positioned to intercept said reflected light when the beam is incident normally on said flat surface portion but not when it is incident on said further surface portion; and a light detector positioned to receive light not intercepted by the filter.

Instead of scanning the image at the image plane as in the known device and hence deriving an output determined only by the small proportion of the total light beam present in the instantaneous scanning position, the device according to the present invention scans the object surface by scanning the entire beam across the surface, thus, in principle at least, enabling the amount of detected light to be the whole beam, when reflection is occurring from the inclined surface portion.

Some embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figures 1 and 2 are respectively schematic diagrams of the light scanning device of a dark field type as disclosed in the above mentioned patent; Figure 3 is a schematic diagram showing an optical layout of a first embodiment of the present invention; Figure 4 is a schematic diagram of a main part of the optical system shown in Figure 3 for the purpose of explanation; Figure 5 is a schematic diagram showing an optical layout of a second embodiment of the present invention; Figure 6 shows a sight, as through a microscope, of the scanning pattern in accordance with the second embodiment of the present invention shown in Figure 5; Figure 7 is a schematic diagram showing an optical layout of a third embodiment of the present invention; and Figure 8 is a schematic diagram showing an optical layout of a fourth embodiment of the present invention.

Figures 1 and 2 show the optical layout of a known observing device of the dark field type which is described in detail in British Patent No. 1,549,727. In Figure 2, reference numeral 1 designates an object having a flat reflection surface 2 and an inclined reflecting surface 3. A telecentric lens 4 is positioned with its optical axis perpendicular to the flat surface 2 of object 1. An aperture shown in heavy lines is positioned at the front focal plane 5 of the lens 4. The entrance pupil of the lens is positioned in the focal plane and its diameter corresponds to the diameter of the aperture 5.

Assume that a point light source is disposed at the centre of the focal plane 5 (see Fig. 2).

Since the point source is disposed in the focal plane, the rays passing through the telecentric lens 4 become parallel with the optical axis of the telecentric lens and impinge on both flat reflective surface 2 and inclined reflective surface 3. The image of the point light source is formed by the light A which is reflected from the flat reflecting surface 2 and travels back along the same path to the centre of the focal plane. The light B reflected by inclined surface 3, on the other hand, does not travel back along the same light path.

Hence the light B never passes the centre of the focal plane. Thus, if a light absorbing member having the same size as the light source is positioned at the centre of the focal plane, the light A is absorbed and the light B passes through, so that the observer can see only the inclined surface.

The known optical system using this principle is shown in more detail in Figure 1.

The object 1, lens 4 and aperture are positioned as in Figure 2. The illuminating optical system 6 forms a secondary light source image at the focal plane 5 by reflection from semi-transparent mirror 7. The image of the light source is smaller than the pupil diameter of lens 4.

A relay lens 8 forms an image of the object 1 on scanner 9 (broken lines in Figure 1 denote the light path). The scanner 9 has a slit opening and moves in a direction transverse to the optical axis, causing light reflected from different parts of the object 1 to pass through the slit in sequence.

A lens 10 forms an image of the pupil of lens 4 at a light intercepting plate or filter 11. A light converging lens 12 directs light passing through filter 11 to a photo electric detector 13. The filter 11 has an annular opening surrounding a central light blocking portion conjugate with the central point of focal plane 5. Consequently that light reflected from flat surface 2 of the object, which appears to originate from that central point, is intercepted by the filter and only light reflected from the inclined surface 3 passes through the opening in the filter to be detected by detector 13.

In this known optical system, which may be referred to as the "dark field detection system", the entire object is illuminated but only a small portion of the illuminating light, i.e. that reflected by the inclined surface, is actually detected. This results in a relatively low efficiency.

In the devices of the present invention, to be described in more detail below, instead of spreading the illuminating light over the whole object at once, it is concentrated in a small spot or slit of light which is projected onto the object surface, and then scanned across it. The light is concentrated at the position being detected at any one time and if this position corresponds to an inclined part of the surface the intensity of the light transmitted to the detector will be of the order of the intensity of the illuminating light spot. The detection efficiency is therefore increased.

The size of the light spot can be controlled by using a collimator lens of long focal length in conjunction with a light source so as to converge the light. Alternatively, a laser beam may be used as the light source to provide a small spot.

Figure 3 shows a first embodiment of an optical system according to the present invention using a parallel plate type scanner.

An opening 20 in the form of a slit or a spot is located in the light beam from a light source. The opening 20 is in a conjugate relationship with the object 1 relative to lenses 4 and 22. A parallel plate scanner 21, which is of the type which causes the light beam from opening 20 to move sideways but parallel to the optical axis is positioned next to the opening 20.

A relay lens 22 directs light travelling parallel to the optical axis to the centre of focal plane 5, where this plane intersects the optical axis. In other words, the rear side focal plane of lens 22 coincides with the focal plane 5 of telecentric lens 4. The function of lens 22 can be seen more clearly with reference to Figure 4. The opening 20 is located at the front side focal plane of lens 22. A light beam 23 after passing through scanner 21 is shifted sideways as the scanner rotates but the principal ray remains parallel to the optical axis since the incidence angle is equal to the transmitted angle (a property of the parallel plate scanner). Beam 23 is shown in three different scanning positions.

It can be seen that in all scanning positions, because the beam is effectively emitted from the focal plane of lens 22, it becomes a parallel beam after passing through the relay lens 22. Also, because the displacement of the beam is parallel at scanner 21, and rear side focal plane of lens 22 coincides with focal plane 5, the position at which the beam crosses focal plane 5 remains constant during scanning, so that the beam displacement is converted to a deflection about a fixed point in the centre of focal plane 5.

The F-number of the light beam 23 (controlled by a lens) is larger than the F-number of the relay lens so that the diameter of the incident light beam at focal plane 5 is less than the diameter of the pupil in that plane.

It is possible to make use of Figure 2 again in explaining how beam 23 is reflected from the object. On the left of Figure 2 the rays A can be regarded as the principal rays of scanning beam 23 when the scanning beam 23 is in two different scanning positions.

Because its apparent source remains at the same central point in focal plane 5, the principal ray is always incident perpendicular to object 1 and consequently is reflected back along its path of incidence when it strikes the flat surface portion. Because the beam 23 incident on lens 4 is parallel and object 1 is at a focal plane of lens 4, the whole beam after reflection passes along the same path through focal plane 5 as it did on its way towards lens 4 and is also at that point a parallel beam.

The light then enters the detection optical system 10, 11, 12, 13 (which correspond with the similarly numbered components in Figure 1) by means of a beam splitter 7.

Focal plane 5 and the light intercepting plate or filter 11 are conjugate relative to lens 10.

So, even though the beam is being scanned, its light always falls on the central blocking portion so long as the beam is reflected back along its incidence path at object 1, i.e. it is incident on the flat surface of object 1.

However, when in the course of scanning the principal ray of the beam strikes the inclined surface of the object it does nor return along its original path, as indicated at B in Figure 2, and neither does the rest of the beam. Thus the beam does not pass back through the centre of the focal plane 5 and therefore is not incident on the central blocking portion of filter 11, but instead passes through the filter and is incident on the detector 13, which indicates the presence of an inclined surface portion when the beam is in that particular scanning position.

When the scanning beam is in the form of a spot, the shape of the light beam to be filtered or intercepted at plate 11 is a spot.

The filter may therefore have a transmitting portion of ring shape. When the scanning beam is in the form of a slit, a filter having a slit shaped intercepting portion may be placed at 11. The shape of the filter is therefore dependent on the shape of the scanning beam.

In Figure 5 the optical system of Figure 3 is shown applied to an automatic aligner for an integrated circuit (IC). For a mask and wafer to be two dimensionally aligned at least two alignment marks should be obser- ved. Only one such mark is shown in this illustration for simplicity.

Another optical system identical to that shown on the right hand side in Figure 5 would in practice be located at the left hand side of the drawing. Scanner 36 is constructed so that it may be used by both optical systems. The number of scanners may be increased, depending on the number of observation points.

The light source comprises a laser 31, a laser of lmW or less being sufficient for the purpose since the output of the laser can be converted to a photo electric signal with high efficiency. The laser beam is expanded by beam expander 32, but this component is not essential and in some cases it may not be necessary to expand the beam. The laser beam is focussed on slit or spot aperture 35 by mirror 33 and lens 34. If 35 is a slit, lens 34 should preferably be of cylindrical form, while it can be an ordinary spherical lens if 35 is a spot. The F-number of this lens is arranged to provide the necessary restriction on the beam diameter as described with reference to Figure 4 above Next in the light path is located a transmission type scanner 36 which is a glass block. The rotational axis of this scanner is arranged to pass through the intersection point of the optical axes of the optical systems, as indicated in the drawing, and is normal to the drawing. Thus three optical systems can be used, only one of which is shown in full. Slit or spot openings 35 for each of the systems are shown. The optical system shown corresponds to channel X, and the optical systems of channels Y and Z, which are identical to that of channel X, are partly omitted. The light from single source 31 may be split by a beam splitter for use by all three channels.

Light scanned by the scanner passes through an image rotator 37 before it reaches a lens 39 (corresponding to the lens 22 in Figure 3). Assume, for example, that the nonnal of the three mirror surfaces constituting the image rotator 37 of the channel Y (enclosed by dotted lines) is disposed at a position rotated by 45 degrees about a rotational axis PP. The light which has passed through the channel X is scanned within the plane of the drawing across the surface of the object (the numerals 41 and 42 each carrying an alignment mark). On the other hand, however, the light which has passed through the channel Y is scanned in the direction normal to the drawing sheet. That is, as shown in Figure 6, light from the channel X and light from the channel Y move relative to each other, as shown by the arrows in the drawing, viewed as though within the sight of a microscope, with the conseqence that two-dimensional discrepancy between the marks on mask and wafer 41 and 42 can be detected. When the member 35 is in slit form, the direction of the slit should preferably be set in such a manner that it is perpendicular to the scanning direction.

In Figure 5, reference numerals 38 designate beam splitters, and numeral 40 refers to the telecentric objective lens equivalent to lens 4 in Figure 3.

The photo electric detection system for channel X consists of members 43, 44, 45 and 46, in which 43 is the lens for forming an image of the pupil or focal plane of lens 40 at a stopper or filter 44, 45 denotes a light converging lens, and 46 represents a photo detector. The functioning of this photo electric detection system is the same as explained in relation to Figure 3, hence no further explanation of this will be given A further beam splitter 38 may be inserted as shown by a dotted line in Figure 5 to provide a beam for scanning a different part of the mask and wafer.

Figure 7 illustrates another optical system similar to that shown in Figure 5. In this embodiment, the optical axis of the objective lens 40 is normal to the drawing sheet so as to be able to observe the mask 41 and the wafer 42 positioned within a plane parallel with the drawing sheet. With this optical system, two image rotators 36 can be used.

Although a single image rotator would be sufficient, two image rotators are used in this embodiment to correct the light path length.

The function of the optical system is exactly the same as that shown in Figure 5, with like parts having like reference numerals, hence it is not explained in detail.

In Figures 5 and 7, an optical system for direct observation by eye and the light source for this observation may be provided, if necessary. The provision of such a system can easily be allowed for by inserting a beam splitter in one part of the light path, or by changing a mirror 33 to a beam splitter, and it is therefore not illustrated. In the constructions shown in Figures 5 and 7 it is essential that the image rotator be present.

However, by improving the alignment mark on the mask and wafer in some way, the discrepancies in both X and Y directions can be detected at once by unidrectional scanning.

In such a case, since the scanning operation can be performed in a single direction, the image rotator is not required, nor is it necessary to introduce the beam in two channels with respect to each viewing position.

Figure 8 shows a different embodiment with a scanning optical system of the type which causes the scanning beam to rotate about one point on the scanner as the centre of deflection, for example, using a scanning device such as a rotatory polygonal mirror or a galvano mirror. A reference numeral 50 designates a laser beam, in the path of which a beam expander or a converging or diverging lens may be inserted, if necessary. This component is not shown for simplification.

Numeral 51 refers to a lens for converging the laser beam, and 52 refers to one surface of a rotary polygonal mirror. Numeral 53 designates a field lens disposed at a converging point X of the beam due to the lens 51. The point X is moved perpendicularly with respect to the optical axis by the rotation of the rotary polygonal mirror 52. The size of the spot at the point X is determined by the F number of the light beam as in turn determined by the lens 51. Numeral 54 denotes a relay lens, and 4 refers to a telecentric object lens as in previous embodiments. Numeral 5 represents a focal plane of lens 4.

The part of the system composed of various members from the beam splitter 7 up to and including the light detector 13 is the same as that shown in Figure 3, hence explanation of this part is omitted.

The characteristic in this type of scanning system is that, when the principal light ray of the scanning beam is projected into the relay lens 54, it is no longer parallel to the optic axis. Accordingly, merely locating the focal plane of the telecentric object lens 4 on the focal point of the relay lens as in Figures 3 to 7, is not sufficient for separation of light reflected from the flat and inclined surfaces and a different arrangement is required. In order that the beam may be directed perpendicularly to the flat reflecting surface during scanning, the beam reflecting position, which is a substantially unmovable point on the rotatory polygonal mirror, is utilized. That is, since the position of reflection of light projected onto the rotatory polygonal mirror fluctuates to so small a degree that it can be regarded as a substantially unmovable point, this point is focussed on the centre of focal plane 5 of the objective lens by the use of the field lens 53 and the relay lens 54. In this way, the object surface can be scanned, while the beam position in the focal plane of lens 4 is main tained unmovable. The focussing point X of the beam due to the lens 51 is arranged to be conjugate with the object surface, with respect to lenses 4 and 54, as shown by the solid lines in the Figure. Consequently, the power of the lens 51 to be used can be pri marily decided from the size of scanning spot to be used in scanning the object surface, and the diameter of the incident laser beam.

In general, since the diameter of the scanning spot is normally larger than the.diffraction limit of the objective lens, the diameter of the incident laser beam on the focal plane is smaller than the diameter of the pupil of the objective lens with the result that the filtering method as shown in Figures 3 to 7 becomes feasible.

The scanning of the object surface with a light beam and detection of the scanned light beam in a dark field according to the present invention is an improvement over conventional methods since detected light quantity is improved, as is the-SN ratio and polarity of signal.. The present invention has wide varieties of applications, not only in automatic alignment devices for integrated circuit manufacture, but also in other fields such as size measurement, curve tracking, and so forth.

Two main ways of causing correct deflection of the beam have been disclosed. In one, the light beam is shifted sideways but remains parallel to its original direction, during scanning. This may be achieved by means of a rotating parallel flat plate such as- a transmitting type rotatory polygonal prism, or a vibrating type parallel flat plate as used in a photo-electric microscope, for example. The principal ray remains parallel to the optical axis during scanning, and this is converted to the desired angular deflection about a fixed point in focal plane 5 as described for example with reference to Figures 3 and 4.

Alternatively the scanner may be a rotating reflection mirror such as a galvano mirror or polygonal mirror, for example. In this case the point of reflection of the light beam on the mirror remains substantially the same but its angle with respect to the optical axis varies as the mirror rotates. This fixed reflection point, about which the beam is deflected, could in principle be located in focal plane 5. If this is not practical, then the reflecting point on the mirror (which is substantially constant) is brought into a mutually conjugate relationship with the centre of the focal plane 5 by means of a suitably arranged optical system. This ensures that the principal light beams impinging on the object are perpendicular to the flat reflecting surface, so that light reflected from this surface travels back along the same path and can be stopped at the filter. A device using this type of scanning system has been described above in more detail with reference to Figure 8.

In both types of scanning system the arrangement is effectively such that the deflect tion point of the beam is located, actual!y or optically, at the point of intersection of the focal plane and the optical axis.

WHAT WE CLAIM IS;- 1. A device for scanning with a light beam an object having a flat reflection surface portion and a further surface portion ip dined relative to the flat portion, comprising: a telecentric lens for transmitting light to, and recieving light from, said surface portions; means for directing a light beam into the telecentric lens and for angularly deflecting the beam about a point substantially where the focal plane of said telecentric lens intersects its optical axis, whereby the beam is scanned across the object; a filter for receiving light reflected from said reflection surfaces after such light has passed back through the telecentric lens, and positioned to intercept said reflected light when the beam is incident normally on said flat surface portion but not when it is incident on said further surface portion; and a light detector positioned to receive light not intercepted by the filter.

2. A device as claimed in claim 1, wherein an optical system is interposed in the path of reflected light from the telecentric lens to the filter and said focal plane and said filter are at substantially conjugate positions relative to said optical system.

3. A device as claimed in claim 2, wherein said optical system forms in the plane of said filter an image of the pupil of the telecentric lens, which pupil lies in said focal plane, and the filter comprises a light intercepting element smaller than said pupil image.

4. A device as claimed in claim 2, wherein said filter is positioned in said focal plane.

5. A device as claimed in claim 4, wherein the filter comprises a light intercepting element which is smaller than the pupil of said telecentric lens, which pupil lies in said focal plane.

6. A device as claimed in any preceding claim, wherein the means for angularly deflecting the light beam comprises means for shifting the light beam transversely parallel to itself and an optical system for converting said shift to an angular deflection about said point.

7, A device as claimed in claim 6, wherein said converting optical system is a lens system having its optical axis parallel with the beam and having a focal plane coin

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

focussed on the centre of focal plane 5 of the objective lens by the use of the field lens

53 and the relay lens 54. In this way, the object surface can be scanned, while the beam position in the focal plane of lens 4 is main tained unmovable. The focussing point X of the beam due to the lens 51 is arranged to be conjugate with the object surface, with respect to lenses 4 and 54, as shown by the solid lines in the Figure. Consequently, the power of the lens 51 to be used can be pri marily decided from the size of scanning spot to be used in scanning the object surface, and the diameter of the incident laser beam.

In general, since the diameter of the scanning spot is normally larger than the.diffraction limit of the objective lens, the diameter of the incident laser beam on the focal plane is smaller than the diameter of the pupil of the objective lens with the result that the filtering method as shown in Figures

3 to 7 becomes feasible.

The scanning of the object surface with a light beam and detection of the scanned light beam in a dark field according to the present invention is an improvement over conventional methods since detected light quantity is improved, as is the-SN ratio and polarity of signal.. The present invention has wide varieties of applications, not only in automatic alignment devices for integrated circuit manufacture, but also in other fields such as size measurement, curve tracking, and so forth.

Two main ways of causing correct deflection of the beam have been disclosed. In one, the light beam is shifted sideways but remains parallel to its original direction, during scanning. This may be achieved by means of a rotating parallel flat plate such as- a transmitting type rotatory polygonal prism, or a vibrating type parallel flat plate as used in a photo-electric microscope, for example. The principal ray remains parallel to the optical axis during scanning, and this is converted to the desired angular deflection about a fixed point in focal plane 5 as described for example with reference to Figures 3 and 4.

Alternatively the scanner may be a rotating reflection mirror such as a galvano mirror or polygonal mirror, for example. In this case the point of reflection of the light beam on the mirror remains substantially the same but its angle with respect to the optical axis varies as the mirror rotates. This fixed reflection point, about which the beam is deflected, could in principle be located in focal plane 5. If this is not practical, then the reflecting point on the mirror (which is substantially constant) is brought into a mutually conjugate relationship with the centre of the focal plane 5 by means of a suitably arranged optical system. This ensures that the principal light beams impinging on the object are perpendicular to the flat reflecting surface, so that light reflected from this surface travels back along the same path and can be stopped at the filter. A device using this type of scanning system has been described above in more detail with reference to Figure 8.

In both types of scanning system the arrangement is effectively such that the deflect tion point of the beam is located, actual!y or optically, at the point of intersection of the focal plane and the optical axis.

WHAT WE CLAIM IS;- 1. A device for scanning with a light beam an object having a flat reflection surface portion and a further surface portion ip dined relative to the flat portion, comprising: a telecentric lens for transmitting light to, and recieving light from, said surface portions; means for directing a light beam into the telecentric lens and for angularly deflecting the beam about a point substantially where the focal plane of said telecentric lens intersects its optical axis, whereby the beam is scanned across the object; a filter for receiving light reflected from said reflection surfaces after such light has passed back through the telecentric lens, and positioned to intercept said reflected light when the beam is incident normally on said flat surface portion but not when it is incident on said further surface portion; and a light detector positioned to receive light not intercepted by the filter.
2. A device as claimed in claim 1, wherein an optical system is interposed in the path of reflected light from the telecentric lens to the filter and said focal plane and said filter are at substantially conjugate positions relative to said optical system.
3. A device as claimed in claim 2, wherein said optical system forms in the plane of said filter an image of the pupil of the telecentric lens, which pupil lies in said focal plane, and the filter comprises a light intercepting element smaller than said pupil image.
4. A device as claimed in claim 2, wherein said filter is positioned in said focal plane.
5. A device as claimed in claim 4, wherein the filter comprises a light intercepting element which is smaller than the pupil of said telecentric lens, which pupil lies in said focal plane.
6. A device as claimed in any preceding claim, wherein the means for angularly deflecting the light beam comprises means for shifting the light beam transversely parallel to itself and an optical system for converting said shift to an angular deflection about said point.
7, A device as claimed in claim 6, wherein said converting optical system is a lens system having its optical axis parallel with the beam and having a focal plane coin

cident with the focal plane of the telecentric lens.
8. A device as claimed in any one of claims 1 to 5, wherein the means for angularly deflecting the light beam is means which converts a stationary incident bean into an angularly deflecting output beam.
9. A device as claimed in claim 8, in which the point of deflection of the beam by the deflecting means is located at a position, relative to an optical system, which is conjugate with said point in the focal plane of the telecentric lens.
10. Apparatus for positioning an object having a flat reflection surface portion and an alignment mark which includes a further surface portion inclined relative to said flat portion, and including a scanning device as claimed in any preceding claim for detecting the position of the alignment mark.
11. Apparatus as claimed in claim 10, for positioning an object having a plurality of such alignment marks and including a respective such scanning device for scanning the alignment marks in different scanning directions to detect their positions in the respective directions.
12. Apparatus as claimed in claim 11, wherein a single beam deflecting means is common to two or more of said devices.
13. A device for scanning an object, substantially as herein described with reference to Figures 3 and 4 of the accompanying drawings.
14. A device for scanning an object, substantially as herein described with reference to Figures 5 and 6 of the accompanying drawings.
15. A device for scanning an object, substantially as herein described with reference to Figure 7 of the accompanying drawings.
16. A device for scanning an object, substantially as herein described with reference to Figure 8 of the accompanying drawings.