U.S. patent application number 11/964744 was filed with the patent office on 2008-09-04 for arrangement and method for focusing a multiplane image acquisition on a prober.
This patent application is currently assigned to SUSS Micro Tec Test Systems GmbH. Invention is credited to Juliane Busch, Ulf Hackius, Joerg Kiesewetter, Michael Teich.
Application Number | 20080212078 11/964744 |
Document ID | / |
Family ID | 39695740 |
Filed Date | 2008-09-04 |
United States Patent
Application |
20080212078 |
Kind Code |
A1 |
Teich; Michael ; et
al. |
September 4, 2008 |
ARRANGEMENT AND METHOD FOR FOCUSING A MULTIPLANE IMAGE ACQUISITION
ON A PROBER
Abstract
The invention relates to a system and a method for capturing
images in a prober. According to the invention, the surface of a
test object is illuminated in succession with light of a first,
second and third color; and an image capturing device records a
gray scale image of the surface; and a composite image is produced
from the three gray scale images by means of an image evaluating
device. The object of the invention is to qualitatively improve the
image capturing, in order to raise the positioning accuracy by
means of an improved display, as a result of which, finely
structured test objects can be used. This object of the invention
is achieved in that the lighting device is designed as a unit,
which can be controlled by the image evaluating unit and which
produces at least three colors and which exhibits at least one
light emitting diode (LED) as the lighting means.
Inventors: |
Teich; Michael; (Moritzburg
OT Friedewald, DE) ; Hackius; Ulf; (Dresden, DE)
; Busch; Juliane; (Dresden, DE) ; Kiesewetter;
Joerg; (Thiendorf OT Sacka, DE) |
Correspondence
Address: |
HESLIN ROTHENBERG FARLEY & MESITI PC
5 COLUMBIA CIRCLE
ALBANY
NY
12203
US
|
Assignee: |
SUSS Micro Tec Test Systems
GmbH
Sacka
DE
|
Family ID: |
39695740 |
Appl. No.: |
11/964744 |
Filed: |
December 27, 2007 |
Current U.S.
Class: |
356/73 ;
356/406 |
Current CPC
Class: |
G02B 21/26 20130101;
G02B 21/06 20130101; G02B 21/365 20130101; G02B 21/32 20130101;
G02B 21/244 20130101 |
Class at
Publication: |
356/73 ;
356/406 |
International
Class: |
G01N 21/00 20060101
G01N021/00; G01N 21/25 20060101 G01N021/25 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 2006 |
DE |
10 2006 062 297.9 |
Jan 9, 2007 |
DE |
10 2007 002 097.1 |
Claims
1. System for capturing images in a prober comprising a movement
device; a clamping fixture mounted on said movement device for
receiving a test object; probe needles to make contact with the
test object; holding devices for the probe needles; a clamping
plate arranged above the clamping fixture and on which the holding
devices are mounted and which has a viewing aperture which visibly
exposes a surface of the test object; and an image capturing device
mounted over the viewing aperture connected to an image evaluating
unit and provided with a lighting device, the lighting device
produces a light beam, directed on the surface of the test object,
wherein the lighting device comprises a unit controlled by the
image evaluating unit and produces at least three colors and
includes at least one light emitting diode (LED) as a lighting
source.
2. System as claimed in claim 1, wherein the at least one LED
comprises a tricolor LED which produces in a controlled manner a
light in three colors.
3. System as claimed in claim 1, wherein the lighting device
contains three LED's, each of which produces light of a different
color.
4. System as claimed in claim 1, wherein the at least one LED
produces light in colors red, green and blue.
5. System as claimed in claim 1, wherein the image capturing device
comprises a video camera having a switching output, outputs a
shutter signal at a shutter time and is connected to the image
evaluating unit so as to control on times of the at least one
LED.
6. System, as claimed in claim 5, wherein the video camera
comprises a black and white camera that records gray scales.
7. System as claimed in claim 1, wherein the image capturing device
includes an objective lens adjusted by a motor and controlled by
the image evaluating unit so as to correspond to the control of the
lighting device.
8. System as claimed in claim 7, wherein the objective lens is
provided with a piezo drive.
9. Method for capturing images in a prober, wherein a surface of a
test object is illuminated in succession with light of a first,
second and third color; and an image capturing device records three
gray scale images of the surface; and a composite image is produced
from the three gray scale images by an image evaluating device,
wherein the light of each color is produced by an LED; and on times
are controlled so as to correspond to the image capturing
device.
10. Method as claimed in claim 9, wherein the light is produced by
a tricolor LED.
11. Method as claimed in claim 9, wherein the light is produced by
at least one LED.
12. Method as claimed in claim 9, wherein red, green and blue are
selected as the first, second and third colors.
13. Method as claimed in claim 11, wherein the gray scale images
are produced with a video camera, which exhibits a readiness to
shoot only during shutter frames, which follow sequentially and are
limited in time; and a shutter start signal is produced at the
beginning of each shutter frame; and the at least one LED is/are
controlled as a function of the shutter start signal in such a
manner that the at least one LED is/-are switched on for a period
of time within a shutter frame, thus producing a different color
for each successive shutter frame.
14. Method as claimed in claim 13, wherein the time period for
switching on the at least one LED is equivalent at most to a length
of the shutter frame.
15. Method, as claimed in claim 14, wherein the time period for
switching on the at least one LED is shorter than the shutter
frame.
16. Method, as claimed in claim 14, wherein the ratio of the on
time of an LED to a shutter frame ranges from 1:1 to 1:100.
17. Method, as claimed in claim 14, wherein, when the at least one
LED is/are switched on, the at least one LED is/-are operated with
a diode current that is higher than an allowable continuous diode
current.
18. Method, as claimed in claim 9, wherein a focusing signal
corresponding to each color is produced and sent to the image
capturing device; and prior to each on time, the image capturing
device is focused, according to the color.
19. Method, as claimed in claim 9, wherein, when the test object is
moved in relation to the image capturing device, the composite
image is shown as a gray scale image.
20. Method, as claimed in claim 9, wherein the test object is
illuminated with white light or with a fast sequence of light
flashes of the first, second and third colors within a shutter
frame.
Description
[0001] The invention relates to a system for capturing images in a
prober, which is provided with a movement device and a clamping
fixture for a test object; and said clamping fixture is mounted on
said movement device. Furthermore, the prober exhibits probe
needles, which can make contact with the test object; holding
devices for the probe needles; and a clamping plate, which is
arranged above the clamping fixture and on which the holding
devices can be mounted and which exhibits a viewing aperture, which
visibly exposes the surface of the test object. The system for
capturing images is provided with an image capturing device, which
is mounted above the viewing aperture and which is connected to an
image evaluating unit and which is provided with a lighting device,
which produces a light beam, directed on the surface of the test
object.
[0002] The invention also relates to a method for capturing images
in a prober. According to this method, the surface of a test object
is illuminated in succession with light of a first, second and
third color; and an image capturing device records a gray scale
image of the surface; and a composite image is produced from the
three gray scale images by means of an image evaluating device.
[0003] It is known from the U.S. Pat. No. 4,875,991 to use black
and white cameras to produce a color image. Said cameras record
images that are produced in succession with lighting that is
filtered or composed of a plurality of different colors. Hence, for
example, the red lighting gives a gray scale image; and a blue
lighting gives a gray scale image; and a green lighting gives a
gray scale image; and then these images are assembled to form one
color image. This solution has the advantage that in each case the
total resolution of the camera can be utilized, because only one
gray scale is to be determined of each pixel. If pixels, which were
recorded in all three colors simultaneously, were to be used, only
one-third of the resolution would be available. This prior art
describes that the object is illuminated in succession with light
of red, green and blue color. The lighting means that were
available at the time of this patent application consisted of
filament lamps.
[0004] The illumination with the light of the respective color
takes place over a period of time that is independent of the period
of time in which the camera captures the image. Usually cameras
capture the image only during the time that the shutter is
open--the so-called shutter time. However, the lighting device
illuminates the object irrespectively of this shutter time.
[0005] Even though the said patent document does not describe the
use of such a three-part production method of color images for
probers, such a practice does exist in probers.
[0006] In general, probes are used to test components, in
particular semiconductor components, for their operational function
and the impact that physical parameters have on them. To this end,
the prober generally consists of a movement device, for example, an
X-Y cross-table, which can also perform slight rotary motions in
order to correct the position. This movement device has a clamping
fixture--a so-called chuck. Hence, the test object can be mounted
on this clamping fixture. Above the clamping fixture is a clamping
plate, which is provided with a feed-through and viewing aperture.
At this stage holding devices for the probe needles can be mounted
on this clamping plate, for example, by means of vacuum holders, so
that the probe needles can extend through the feed-through and
viewing aperture and make an electric contact at the corresponding
points on the object to be tested, thus measuring the object to be
tested for its electrical properties.
[0007] There also exist solutions with so-called probe cards, where
the probe needles are mounted, as the probe card needles, securely
on the probe card; and then the probe card is placed securely in
the clamping plate.
[0008] Basically the objects to be tested have to be positioned in
relation to the tips of the probe needles. To this end, a vertical
motion of the movement device usually brings about a separation
between the object to be tested and the probe needles. Then the
movement device moves the clamping fixture and, thus, the object to
be tested in such a manner that another test object or another part
of the test object comes to rest below the tips of the probe
needles. Thereafter, an additional vertical motion places again the
object to be tested into contact with the tips of the probe
needles. As a rule, this positioning operation is controlled by an
image capturing device, for example, a video camera, which is
mounted above the viewing aperture. The image capturing device
photographs the surface of the object to be tested, which in turn
is passed to an image evaluating device. Then with the image
evaluating device it is possible to control with suitable analysis
programs the movement device so accurately that the tips of the
probe needles come to rest directly over the corresponding contacts
on the test object; and the measuring process can begin.
[0009] At this stage it is known to use a tricolor image capturing
process in such probers. In this case light emitting diodes (LED's)
are used as the lighting devices. These LED's also emit light
during the entire period that is provided for capturing a gray
image of a certain color. Therefore, the LED has the task of
illuminating for a relatively long period of time. Correspondingly
the diode current must be set in such a manner that it matches a
maximum continuous diode current. On the one hand, the relatively
long term usage of an LED does not have a significantly negative
impact on the service life of the LED. On the other hand, only
average luminance can be achieved with a continuous diode
current.
[0010] Therefore, for the above reasons, the object of the
invention is to qualitatively improve the image capturing in a
prober, in order to raise the positioning accuracy by means of an
improved display. As a result, it will be possible to use finely
structured test objects.
[0011] This object of the invention is achieved with a system,
wherein the lighting device is designed as a unit, which can be
controlled by the image evaluating unit and which produces at least
three colors and which exhibits at least one light emitting diode
(LED) as the lighting means.
[0012] Controlling the LED by means of the image evaluating unit
makes it possible to control the LED in such a manner that it
illuminates for such a period of time that is adequate to produce a
proper image of the test object. For example, it will be possible
to switch on the LED for a very short period to time, thus avoiding
motion blur.
[0013] One embodiment of the invention provides that the LED is
designed as a tricolor LED. This tricolor LED is constructed in
such a manner that when suitably driven, it can produce a light in
the three colors.
[0014] Another embodiment of the invention provides that the
lighting device contains three LED's, each of which produces light
of a different color. The use of three separate LED's makes it
possible, inter alia, to arrange them spatially in such a manner
that they are separated from each other, thus exploiting the
spatially induced lighting effects.
[0015] It is desirable to render the generated color image in fast
colors, for which reason the three colors red, green and blue are
chosen, in that the three LED's or the tricolor LED's produce these
three colors. However, it is also possible, in principle, to use
intentionally other colors, for example, in order to show the fine
structures with a higher definition. In this case it is just as
possible to use ultraviolet light as it is to use infrared
light.
[0016] Another advantageous embodiment of the invention provides
that the image capturing device is designed as a video camera,
which exhibits a switching output, which outputs a shutter signal
at a shutter time. The switching output is connected to the image
evaluating unit in such a manner that the image evaluating unit
controls the LED or the LED's as a function of the occurrence of
the shutter signal. Thus, it becomes possible for the camera to
initiate the targeted control of the LED. In this way it is
possible to realize, in particular, shorter operating times of the
LED, for example, with higher diode currents, and, thus, achieve, a
kind of flash. As a result, motion blurs can be eliminated.
[0017] Another embodiment of the invention provides that the video
camera is designed as a black and white camera that captures gray
scales. Thus, it is possible to include gray scales in the imaging
matrix of the video camera at each pixel of the imaging matrix. As
a result, the highest possible geometric resolution for a given
camera chip is achieved. Then the high geometric resolution can be
totally utilized to display the color, so that a high resolution
color image can be produced by means of a method that uses such a
black and white camera.
[0018] In optical lens systems the optical dispersion, i.e. the
refraction of the light as a function of the wavelengths of the
light, produces a chromatic aberration, i.e. an imaging error of
the optical lens system that can manifest itself in, inter alia,
blurring.
[0019] The inventive use of LED's supplies a relatively
monochromatic light or, even better, a light in a very narrow
spectrum. As a result, the chromatic aberration errors are reduced
in accordance with the Abbe definition. Hence, the images are
sharper, because the focus can be adjusted in an optimal manner to
the wavelength of the light. Furthermore, there is the advantage
that a partial color image--for example, the blue color image--can
be recorded, in order to target a high resolution. The blue image
is the image that is illuminated with the shortest wavelength.
Hence, images with the highest definition are possible. That is,
the gray image, which is produced with the blue lighting, can be
better evaluated, for example, for a geometric analysis. Another
advantage lies in the ability to use images with the best contrast.
To this end, one selects the image of the partial color images with
the best contrast in order to use it then for further
evaluation.
[0020] Even if the chromatic aberration error can be largely
reduced by means of the invention, it is still possible to detect
some blurring as a consequence of the chromatic aberration errors.
Usually the objective lenses for rendering a color image that is as
sharp as possible are set to three spectral colors (apochromates).
That is, in these three spectral ranges these objective lenses
usually deliver sharp images. However, these three spectral ranges
do not have to match the spectral lines of the colors, produced by
the LED's--in particular, not the spectral lines of red, green and
blue. In order to use commercially available objective lenses (for
the purpose of increasing the cost efficiency), whose chromatic
adjustment lies perhaps in other color ranges, another embodiment
provides that the image capturing device has an objective lens,
which can be adjusted by means of a motor and which can be
controlled by the image evaluating unit so as to correspond to the
control of the lighting device. In an advantageous further
development the objective lens can be driven by a piezo drive.
[0021] Such an adjustability of the objective lens makes it
possible to set the focus to correspond to the color of the
respective LED that is emitting light at the moment. Thus, it is
guaranteed that each chromatic aberration error can be eliminated.
In addition, it is possible to use very economical objective lenses
that perhaps do not require any chromatic adjustment at all.
[0022] The problem, on which the invention is based, is solved by a
method, wherein the light of each color is produced by an LED; and
the operating times can be controlled to correspond to the image
capturing device. Thus, for example, it is possible to switch on
the LED exactly in the shutter frame of the image capturing device.
Similarly other targeted operating times--that is, operating times
that deviate from the shutter frame--are also possible.
[0023] An advantageous embodiment of the invention provides that
the light is produced by means of a tricolor LED. Such a tricolor
LED exhibits a low spatial coverage and must, therefore, be brought
relatively close to the test object or is very easy to integrate
into a lighting device of the microscope, where the illuminating
light is coupled into the beam path of the objective lens.
[0024] As an alternative, it may be desirable that the light is
produced by means of each LED. As a result, a spatial distribution
of the generated light is possible.
[0025] In principle, all possible colors from ultraviolet to
infrared for illuminating the test object are possible. It is
advisable to select, depending on the application, a suitable color
configuration. It has proven to be advantageous to select the
colors red, green and blue, in order to represent fast colors.
[0026] Another practical embodiment of the invention provides that
the gray scale images are produced with a video camera, which is
ready to shoot only during shutter time periods (shutter frames),
which follow sequentially and are limited in time. In the case of
such a camera, a shutter start signal is produced at the beginning
of each shutter frame. This shutter start signal is usually emitted
by the video camera by way of the switching outputs. The LED or the
LED's is/are now controlled as a function of the shutter start
signal in such a manner that they are switched on for a period of
time within a shutter frame, thus producing one color per each
sequential shutter frame.
[0027] As a result of this control process, sequences of images are
produced that represent in succession an image in a different
color. After three images, the representation with the first color
repeats. Of course, there is also the option of selecting a
different timing that, for example, excludes the one or the other
shutter frame for capturing an image, if this appears to be
practical.
[0028] Another advantageous embodiment of the method provides that
the time period for switching on the LED(s) is equivalent at most
to the length of the shutter frame. Therefore, it is possible to
switch on the LED's during the entire respective shutter frame.
During other periods of time, when, for example, data are
transferred from the video camera to the image evaluating unit, the
LED's are switched off.
[0029] However, in a very advantageous embodiment this inventive
method makes it also possible to select a period of time for
switching on the LED(s) that is shorter than the shutter frame. The
shorter the on time, the lower the risk of a motion blur. In
particular, it is possible to select the ratio of the on time of an
LED to a shutter frame so that it ranges from 1:1 to 1:100. At a
high ratio--for example, 1:100--the short illumination of the LED
acts like a light flash. In this case stroboscopic effects can be
used. That is, the image is captured only for a short flash period,
thus with high definition. If the object moves, a new flash occurs
at a later point in time, thus producing a sharp image, so that no
motion blurs occur.
[0030] The needles are usually moved in probers. In the image
display the needles are shown as black and white objects or as
black objects. If images can be captured at a fast frame rate (that
is, the image refresh in each frame, that is, in the red, green and
blue frame), then the display of the moved black needle is always
sharp. The image refresh of the composite color image--that is, the
color image composed of red, green and blue--does not exhibit any
drawbacks, because the color of the underlying substrate does not
change over time. Hence, the image of the moved object that is of
interest--that is, the needle--is always sharp.
[0031] Another embodiment of the invention provides that, when the
LED(s) is/are switched on, they are operated with a diode current
that is higher than the allowable continuous diode current. This
feature is achieved in that the LED is switched on only for a short
period of time during the shutter frame. If during continuous
operation the diode current is limited due to the thermal effects,
then, as a consequence of the short on time, a significantly higher
diode current can be selected, since this action will not lead to
any thermal effects or, in the event that it does, said thermal
effects can be ignored. The higher diode currents significantly
improve the light intensity of the LED, which in turn also aids in
generating a light flash.
[0032] In addition to the fact that the luminance is increased, it
has also been demonstrated that the short-term actuation of the LED
also results in a prolonged service life. This feature is achieved
in that the LED is switched on only during the shutter time or
during a portion of the shutter time and is switched off during the
camera transfer time. Consequently the on time is significantly
shorter than the off time, a feature that results in the said
extension of the service life.
[0033] In addition, it is possible to exploit another advantage
that commercially available video cameras offer. The cameras
themselves can transmit either a lower image resolution or smaller
image sections. The lower image resolution or the smaller image
sections reduce the amount of time for transmitting the image from
the camera to the image evaluating unit, so that the camera is more
quickly available again for shooting. This means that the LED's are
more quickly available again for illumination purposes. According
to the known state of the art, the light source would have to be
switched on for such fast image sequences. In the case of a single
lighting source with filter systems that are switched on in
succession, the dynamic limits of a higher frame rate would soon be
reached with certainty.
[0034] Another embodiment of the invention provides that a focusing
signal corresponding to each color is produced and sent to the
image capturing device. Prior to each on time, the image capturing
device is focused, according to the color, by means of this
focusing signal. This feature makes it possible to adjust the
objective lens, for example, by means of an attached computer in
such a manner that the objective lens is in optimal focus for the
switched on light flash of an LED. Since the color sharpness may be
corrected by means of a piezo drive, there is, in principle, the
possibility of using more economical objective lenses. Thus, it is
possible to dispense with the use of relatively expensive
apochromates--that is, the objective lenses are optimized in three
spectral ranges--and, instead, to use achromates--that is, the
objective lenses are optimized in only two spectral ranges.
[0035] Another embodiment of the method provides that, when the
test object is moved in relation to the image capturing device, the
composite image is shown as a gray scale image. This feature
largely eliminates by optical means a blurring of the colors (as
could be the case during a color production of the composite image
from three partial images, which follow chronologically in
succession, in the individual illumination colors--especially
during relatively long data processing periods.
[0036] As an alternative or in addition, the color blurring can be
avoided in that, when the test object is moved in relation to the
image capturing device, the test object is illuminated with white
light or with a fast sequence of light flashes of the three colors
within a shutter frame. This procedure always produces images that
correspond to the same color and, thus, renders the temporal
differences between the sequential partial images ineffective.
[0037] As a result of the above reasons, the advantageous inventive
method for capturing tricolor images can be carried out especially
when the test object is stationary; and during times of relative
motion, at least one colored display of the composite image is
avoided.
[0038] The invention is explained in detail below with reference to
one embodiment.
[0039] FIG. 1 depicts an inventive prober in an embodiment with
probe needles.
[0040] FIG. 2 depicts an inventive prober in an embodiment with a
probe card.
[0041] FIG. 3 is a sectional drawing of an inventive image
capturing device; and
[0042] FIG. 4 depicts the control of the inventive system,
according to the inventive method.
[0043] As shown in FIG. 1, a prober 1 comprises an X-Y cross table
2 as a movement device. The X-Y cross table 2 is disposed in a
housing 3. A clamping fixture 4 is mounted on the X-Y cross table.
In this case the clamping fixture 4 can be rotated by an angle
.PHI.. The clamping fixture 4 serves to receive a test object 5.
The test object 5 may be, for example, a semiconductor wafer, on
which there are a plurality of semiconductor chips, which in turn
exhibit individual contact pads. In order to test the test object
5, probe needles 6 make contact with said test object. An external
test circuit (not shown in detail) makes contact, for example, with
the contact pads of a semiconductor wafer, as the test object.
Therefore, said contact pads are driven with electric signals; and
in this way their reaction is determined.
[0044] One end of the probe needles 6 is fastened in probe holders
7. Hence, on the one hand, the probe holders serve to hold the
probe needles and, on the other hand, to fine position the probe
needle in relation to the test object. In order to fasten the probe
holders 7, there is a clamping plate, a so-called probe holder
plate 8. The probe holders 7 can be vacuum mounted on this probe
holder plate 8 and are, thus, fixed in place.
[0045] The probe holder plate 8 is provided with an aperture 9. On
the one hand, this aperture 9 exposes at the top the surface 10 of
the test object 5 for observation. On the other hand, it is
possible for the probe needles 6 to extend through this aperture 9
from the top side of the probe holder plate 8 as far as to the test
object 5.
[0046] An image capturing device 11 is mounted above the viewing
aperture 9 in the probe holder plate 8. This image capturing device
11 comprises a microscope 12 with a lighting device 13 and an
objective lens 14 and a video camera 15. The video camera 15 is
connected to an image evaluating unit 16. The image evaluating unit
16 in turn comprises a computer with suitable analysis
software.
[0047] FIG. 2 shows a design that is analogous to the design
described in FIG. 1. The major distinction between the two
embodiments lies in the use of a probe card 17 in FIG. 2, instead
of individual probe needles 6 with separate probe holders 7. This
probe card 17 exhibits its own probe card needles 18 and is held in
the aperture 9 by means of a probe card adapter 19.
[0048] The image capturing unit, as depicted in FIGS. 1 and 2, is
enlarged once again in FIG. 3 and shown as a sectional drawing.
[0049] For focusing purposes, the objective lens 14 is provided
with a microscope objective lens focusing unit 20. This microscope
objective lens focusing unit comprises a piezo drive (not
illustrated in detail), which is made of a quartz that changes
geometrically on applying a voltage; and, as a consequence of this
geometric change, the objective lens 14 is adjusted in its focusing
distance. At this stage the microscope objective lens focusing unit
20 is connected to the image evaluating unit 16, so that owing to
the software, which is installed in the image evaluating unit 16,
the microscope objective lens focusing unit 20 can adjust the focus
of the objective lens very quickly to correspond to the images to
be captured (to be explained below).
[0050] The lighting device 13 couples the light for illuminating
the surface 10 of the test object 5 into the beam path of the
objective lens by means of the semi-reflective mirror 21. In so
doing, the light for illumination purposes is produced by means of
an LED 22. This LED 22 is designed as a tricolor LED, that is, it
exhibits connectors, by means of which on applying a voltage to the
LED, different colored light--in this case preferably red, green,
and blue--can be produced in accordance with the selection. This
light travels now over a condenser lens 23 into the beam path 24 of
the objective lens. Thus, this illumination becomes effective on
the surface 10 of the test object 5.
[0051] Furthermore, the beam path 24 travels to the video camera
15. At the camera the image is converted into electric signals by
means of a suitable image capturing matrix, which is not
illustrated in detail. The electric signals in turn are fed back to
the image capturing device 11. The image is captured in this camera
during image capturing periods--so-called shutter frames 25--which
are shown in FIG. 4a. In the interims 26 between the shutter frames
25 the image data--the images--that had been recorded in the
shutter frames 25 are then transmitted. The beginning and the end
of the shutter frame 25 is also transmitted by means of the
connection 27 between the video camera 15 and the image evaluating
unit 16. Thus, it is possible for the software in the image
evaluating unit to drive the LED 22 in such a manner that the LED
is switched on for a short period of time during the shutter time
periods. Therefore, the software does not have to apply continuous
voltage to the LED, thus not emitting light continuously. As a
consequence, it is possible that only short-term thermal stresses
on the semiconductor transition regions to the LED will occur. For
this reason the LED's are driven with a higher diode current. On
the one hand, the result is a higher light efficiency during the on
time; and, on the other hand, the service life of the LED 22 is
extended. As FIG. 4b shows, the LED 22 is switched on in succession
in the individual colors red, blue and green. That is, during the
first shutter frame 25, the LED 22 is switched on in order to
produce a red color. During the second shutter frame 25 the LED 22
is switched on in order to produce a blue color; and finally during
the third shutter frame the LED is switched on in order to produce
a green color. Then the procedure is repeated again by switching on
the LED in order to produce a red color.
[0052] In this way the images in the individual shutter frames are
transmitted in a different color of the three colors. Then, inside
the image evaluating unit 16 the three color images are put
together to form one color image. In so doing, the images in the
individual colors can be transmitted as gray scale images, to which
when producing the images, the original colors are allocated; or
when intentionally misrepresenting the color external colors may
also be allocated. Since the objective lens 14 exhibits an
aberration error, as explained in connection with the description
of the state of the art in the introductory part, it is desirable
to use the microscope objective lens focusing unit 20 to focus the
objective lens 14 in accordance with the color, which has been
produced by the lighting device 13. As FIG. 4c shows, the
microscope objective lens focusing device 20 is sent a varying
adjustment voltage. As a result, the adjustment of the objective
lens 14 is optimal with respect to the respective color of the LED
23 that is used.
[0053] During a movement, especially during fast motions of the
object to be imaged, the color in the display of the composite
image blurs due to the illumination which occurs in chronological
sequence. This color blurring is also dependent on the respective
processing speed during the production of the composite image. In
order to approach such a blurring of the color, it is desirable to
suspend the color image production of the composite image during
such a movement process and, instead, to realize a pure gray scale
rendering of the composite image.
LIST OF REFERENCE NUMERALS
[0054] 1 prober 2 X-Y cross table 3 housing 4 clamping fixture 5
test object 6 probe needle 7 probe holder 8 probe holder plate 9
aperture 10 surface of the test object 11 image capturing device 12
microscope 13 lighting device 14 objective lens 15 video camera 16
image evaluating unit 17 probe card 18 probe card needle 19 probe
card adapter 20 microscope objective lens focusing device 21
semi-reflective mirror
22 LED
[0055] 23 condenser lens 24 beam path 25 shutter frame 26 space 27
connection between the video camera and the image evaluating
unit
* * * * *