Wafer prober having an emissive display inspection system and method of use

An inspection system (20) has an image capture device (10) that is mounted onto a wafer prober (15) for the electrical verification of electronic components (60) having an emissive display (61). The image capture device (10) includes a lens (31) that collects the image generated by the emissive display (61). The image is passed to mirrors (36,37) which redirect a portion of the image into a pickup device (41). The emissive display (61) is partitioned into subregions (62-65) to facilitate the capturing of the image. As the image of each of the subregions (62-65) is collected by image capture device (10), the other subregions (62-65) are deactivated.

BACKGROUND OF THE INVENTION 
This invention relates, in general, to electronic components and, more 
particularly, to apparatuses for inspecting electronic components that 
have an emissive display. 
A new generation of electronic components combines an integrated circuit 
with an emissive display. These electronic components are used in a 
variety of applications such as wireless communication devices. For 
example, an emissive display can be used on a paging device to display 
information sent to the person holding the paging device. The emissive 
display typically consists of a sequence of individual pixels that are 
arranged in an array. Each pixel has a varying intensity and represents a 
dot in the emissive display. Preferably, each pixel can be generated by a 
light emitting diode (LED) or similar device. 
One problem with the fabrication of electronic components that have 
emissive displays arises in the final testing process. Before the 
electronic component is sent to a customer, the electronic component must 
be tested to verify that each pixel in the emissive display is operating 
properly. This is generally done by placing the electronic component under 
a camera that has a resolution, which is equal to or greater than the 
resolution of the emissive display. A sequence of known test patterns is 
then generated in the emissive display. The patterns of the emissive 
display are captured by the camera and analyzed to determine if the 
captured image of the emissive display matches the known pattern. 
As technology evolves, the density of pixels in emissive displays generally 
increases. To accurately capture an image generated by an emissive 
display, the resolution of the camera must also be improved. This is 
typically done by upgrading the camera in the testing apparatus with a 
more expensive camera that has the required resolution. 
Hence, a need exists to provide an inspection system that can be used on 
emissive displays that have varying resolutions. It would be advantageous 
if the inspection system did not require replacement of a camera as the 
resolution of the emissive displays varies and could be used to test 
emissive displays that are of different sizes or configurations.

DETAILED DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a reduced isometric view of an inspection system 20 that is used 
to test electronic components having an emissive display. Inspection 
system 20 includes a wafer prober 15 such as any wafer handler commonly 
used in the semiconductor industry. Wafer prober 15 positions and stores 
individual wafers as they undergo an electrical testing process. This 
testing process verifies the electrical performance of the electronic 
components while the electronic components are still in wafer form. Wafer 
prober 15 is operated by a control panel 21 that is used to specify the 
type of wafers loaded into wafer prober 15 and the test program that is to 
be used for the testing process. A wafer 22 is shown in FIG. 1, which 
contains a plurality of electronic components, each having at least one 
emissive display in accordance with the present invention. 
Inspection system 20 also includes an image capture device 10 that mounts 
to wafer prober 15 by a post 23 or some other suitable means. A control 
device 50 controls the operation of image capture device 10 during the 
testing operation. Control device 50 also controls the operation of the 
electronic components being tested by passing control signals to the 
individual electronic components on wafer 22. The control signals are 
generated by control device 50 and are passed to the device under test 
(DUT) through wafer prober 15 to activate the emissive display of each 
component. Image capture device 10 captures the images generated by each 
individual emissive display that is on wafer 22. A more detailed 
description of how the images are captured will be provided shortly. 
FIG. 2 is an isometric view of image capture device 10. The image 
(indicated in FIG. 2 by an arrow 32) generated by an emissive display 61 
on an electronic component 60 first passes through a lens 31. Lens 31 is a 
photographic enlarger lens that has a flat field and a high resolution. 
After the image passes through lens 31 (indicated in FIG. 2 by an arrow 
33), it is directed towards mirrors 36 and 37. Mirrors 36 and 37 are 
positioned or tilted by mirror controls 38 and 39, respectively. Mirror 
controls 38 and 39 can be servo motors, galvanometers, electrical 
actuators, pneumatic actuators, or hydraulic actuators. Mirror controls 38 
and 39 are used to select the portion of the image coming out of lens 31 
(arrow 33) that is to be redirected into a pickup device 41. In other 
words, not all of the image generated by emissive display 61 is redirected 
towards pickup device 41. Instead, mirrors 36 and 37 are rotated to select 
only the portion of the image generated by emissive display 61 and lens 31 
that is to be captured by pickup device 41. Control signals are sent to 
mirror controls 38 and 39 to position mirrors 36 and 37, respectively, to 
select the portion of the image that is to be captured. 
The selected image (indicated in FIG. 2 by an arrow 35) is then captured by 
pickup device 41. Preferably, pickup device 41 operates using industry 
defined standards such as the RS170 standard. For example, pickup device 
41 can be a solid state charge coupled device (CCD) style camera. Such 
cameras have low noise, geometric linearity that is constant across the 
array, and are sensitive to the wave lengths generated by emissive display 
61. 
Lens 31, mirrors 36 and 37, and pickup device 41 are all mounted to a body 
40 to provide image capture device 10. Image capture device 10 also has a 
hole 30 that is used to mount body 40 to wafer prober 15. 
FIG. 3 is a block diagram of the control device 50 used to control the 
operation of image capture device 10 of FIG. 2. Control device 50 has two 
control lines 56 and 57 that provide control signals to mirror controls 38 
and 39 (see FIG. 2). These control signals are labeled in FIG. 3 as 
CONTROL1 and CONTROL2 and are used to direct the position of mirror 
controls 38 and 39, respectively. Control device 50 has a control line 59, 
labeled DUT.sub.-- CONTROL, which is used to pass the necessary signals to 
the electronic component under test and operate the emissive display as 
needed. Control device 50 also has an input line 58, which is labeled 
VIDEO.sub.-- INPUT in FIG. 3. VIDEO.sub.-- INPUT represents the image 
(FIG. 2, arrow 35) from the emissive display under test that is captured 
by pickup device 41. 
Due to the possibility of noise in either image capture device 10 or the 
image generated by emissive display 61 (see FIG. 2), signal processing is 
performed to ensure that an accurate image is captured. This signal 
processing is performed by a microprocessor or microcontroller that 
typically has a central processing unit (CPU) 51 and a memory 52 that is 
either external or internal to CPU 51. 
Each image that is captured by pickup device 41 is an array of pixels. For 
purposes of illustration, the array of pixels is arranged in "I" rows and 
"J" columns, where "I" and "J" are integers. Therefore, each pixel can be 
identified as P.sub.I,J corresponding to the pixel in the Ith row and Jth 
column. Each pixel (P.sub.I,J) has an light intensity value labeled 
I.sub.I,J at each pixel location. 
In the preferred embodiment, it is assumed that noise is dark and thus has 
a low intensity value. To generate the image that is captured by image 
capture device 10 (see FIG. 2), several images (1 to n, where n is an 
integer) are stored in memory 52 and a composite image is generated by CPU 
51 on a pixel by pixel basis from the stored images. Each pixel in the 
composite image is assigned the intensity value of the largest intensity 
value (I.sub.I,J) of all the images at the same location. Thus, each pixel 
in the composite image is determined by the expression: 
EQU (P.sub.I,J)=MAX(Image.sub.1 (P.sub.I,J), Image.sub.2 (P.sub.I,J), . . . , 
or Image.sub.n (P.sub.I,J)) 
It should also be understood that image capture device 10 can operate where 
noise has the brightest intensity. In this case then, each pixel would be 
the minimum intensity value of from all the images: 
EQU (P.sub.I,J)=MIN(Image.sub.1 (P.sub.I,J), Image.sub.2 (P.sub.I,J), . . . , 
or Image.sub.n (P.sub.I,J)) 
Once a composite image is generated, control device 50 uses an output line 
53 to pass the image, labeled in FIG. 3 as VIDEO.sub.-- OUTPUT, back to 
inspection system 20. Inspection system 20 performs a comparison of the 
captured image to a predicted or known image to determine if the emissive 
display currently under evaluation is operating properly. 
FIG. 4 is an enlarged top view of electronic component 60 and is provided 
to illustrate an example of how emissive display 61 is tested in 
accordance with the present invention. Emissive display 61 is divided into 
subregions, namely subregion 62, subregion 63, subregion 64, and subregion 
65. Each subregion 62-65 represents a portion of emissive display 61 that 
is captured by image capture device 10. Preferably, emissive display 61 is 
partitioned such that each subregion 62-65 does not overlap any adjacent 
subregion 62-65 and are exclusive relative to each other. This prevents a 
defect in the emissive display that happens to be near the intersection of 
two adjacent subregions 62-65 from being counted twice as a defect. 
FIG. 5 is a flow chart representation of a process of capturing an image 
from emissive display 61 (see FIG. 4) using image capture device 10 (see 
FIG. 2). The process begins with box 80. Mirror controls 38 and 39 are 
adjusted so that only the portion of the image from emissive display 61 in 
subregion 62 is passed to pickup device 41. 
Control device 50 generates control signals and passes them to electronic 
component 60 through wafer prober 15. The control signals are intended to 
activate only the portion of emissive display 61 in subregion 62 (box 81). 
At the same time, control signals are sent to electronic component 60 to 
deactivate subregions 63-65. 
Control device 50 operates image capture device 10 and captures several 
images (n images) of subregion 62 (box 82). Preferably, the sampling rate 
of subregion 62 occurs at a slightly lower frequency than the operation of 
pickup device 41 to prevent the optical illusion of a bar across the 
image. For example, similar optical illusions occur when the image of a 
computer monitor is seen on a television screen. Once several images, 
preferably 3 to 10 images, are captured, a composite image is generated 
(box 83) using the process described earlier where each pixel of the image 
is either the brightest or darkest pixel from the images stored during the 
sampling. 
After the composite image for subregion 62 is generated, mirror controls 38 
and 39 are manipulated as needed to adjust mirrors 36 and 37 so that image 
capture device 10 only captures the image generated from subregion 63 of 
emissive display 61. The image of subregion 63 is then generated in the 
same manner (boxes 80-83) and this process is repeated until the image of 
each subregion 62-65 of emissive display 61 is captured (box 84). Once the 
entire image of emissive display 61 is captured, it is sent to inspection 
system 20 (see FIG. 1) to determine if the electronic component is 
operating properly (box 85). 
One advantage of image capture device 10 is that an optical directional 
means (mirrors 36 and 37) is positioned between lens 31 and pickup device 
41. This allows pickup device 41 and image capture device 10 to remain 
still during the testing of an emissive display. This configuration also 
allows a portion of the image of an emissive display to be captured even 
if the emissive display has a resolution that is higher than that of 
pickup device 41. 
Therefore, a variety of emissive displays can be tested using the same 
image capturing device. As the resolution and size of emissive displays 
increases, the same image capturing device can be used by simply 
partitioning the emissive display into smaller subregions. This obviates 
the need to replace pickup device 41 with one having a higher resolution 
as the resolution of emissive displays improves. This not only saves the 
expense of the pickup device, but also simplifies the manufacturing 
operation as the same image capturing device can be used for products that 
have emissive displays of different sizes. The present invention also 
provides for the generation of a composite map from several stored images 
to eliminate noise in either the image capture device or the emissive 
display under test.