Device and method for testing sensitive elements on an...

Semiconductor device manufacturing: process – With measuring or testing – Electrical characteristic sensed

Reexamination Certificate

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C324S765010

Reexamination Certificate

active

06607929

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a device and method for testing sensitive elements of the surface of an electronic chip.
More and more electronic chips are being used as an analysis support and/or an information collector in the fields of biological or chemical analysis, or for measuring physical quantities. The electronic chips have for this purpose on their surface a plurality of sensors, receivers or microsystems, hereinafter referred to as “sensitive elements”. The sensitive elements are, for example, electrodes which can be immersed in a fluid to be analyzed. These electrodes are then selectively covered with a lining layer sensitive to a given chemical or biological compound. In some cases, the chips can also have means for selectively addressing the sensitive elements in order to apply thereto an electrical potential or for making individual electrical measurements on these elements.
The present invention finds applications in particular in checking the correct functioning of electronic chips equipped with electrodes and in checking the quality of the sensitive lining layers which cover the electrodes.
PRIOR ART
The accompanying
FIG. 1A
is a schematic section of an electronic chip having electrodes.
The chip has a substrate
10
with a plurality of electrodes. For reasons of clarity only four electrodes are depicted in the figure, these electrodes bearing respectively the references
12
a,
12
b,
12
c
and
12
d.
A chip may, however, have a large number of electrodes. The electrodes have a bottom layer
13
made from a material such as titanium, for example, covered with a top layer
15
of a metal such as gold or platinum.
In order to confer on the electrodes their function of biological or chemical sensor, they are provided with a layer of reactive material or a material able to interact with the biological material. These materials may include electrically conductive polymers. By way of example, a modified polypyrrole can be used as a biologically sensitive layer.
All the electrodes can be covered with the same material or can be selectively covered with different materials sensitive to different compounds. By way of illustration of the use of chips equipped with electrodes, for the analysis of chemical or biological substances, reference can be made, for example, to documents (1) and (2) whose references are indicated at the end of the present description. Document (3), also referenced, relates more generally to the machining of silicon and the manufacture of sensors.
Returning to
FIG. 1A
, it can be seen that the electrodes
12
on the chip
10
are electrically connected to input/output terminals
14
, only one of which is shown. The electrical connection is shown schematically by a dot and dash line
16
.
Where the chip has a small number of electrodes, each electrode can be respectively connected to a particular input/output terminal associated with it.
However, as shown in
FIG. 1A
, the connection between the electrodes and the input/output terminals can also be effected by means of multiplexer circuits
18
.
The multiplexer circuits enable addressing to take place from a small number of input/output terminals to several hundreds of electrodes on the surface of the chip.
In the sense of the present description, addressing means the putting of at least one electrode (or other sensitive element) in electrical connection with at least one input/output terminal. The addressing of an electrode makes it possible not only to apply a voltage or signal to it by means of one or more input/output terminals but also to make electrical measurements on this electrode.
To effect addressing, that is to say to select a certain number of electrodes, the input/output terminals are connected to external electronic control devices, not shown, for example by connection means
20
, shown in outline.
In
FIG. 1A
, it can be seen that the top metal layer
15
of the electrode
12
d
has a porosity
23
able to allow a fluid to come into contact with the subjacent bottom layer
13
of the electrode.
Moreover, during the manufacture of the electrodes, residues of material may remain on the surface of the chip. For example, residues of lacquer used during operations of forming etching masks may remain.
Such residues, marked in
FIG. 1A
with the references
24
a,
24
c
and
24
d,
may partly cover an electrode, which is the case with the electrode
12
a,
cover it completely, which is the case with the electrode
12
c,
or remain in a region with no electrodes, which is the case with the residue
24
d.
As mentioned previously, the electrodes on a chip, intended for the analysis of biological or chemical environments, are covered with a layer of material which confers on them their sensitivity to a given chemical compound or biological substance.
The lining of the electrodes on the chip in
FIG. 1A
is illustrated by FIG.
1
B. It can be seen that the electrode
12
b
in
FIG. 1B
is covered with a sensitive layer
22
b,
for example made of conductive polymer. The sensitive layer
22
b
covers the entire surface of the electrode. The sensitive layer can be formed by selective deposition methods or possibly electrochemically by selectively applying an appropriate electrolysis current to each electrode which is to be lined.
It can be seen, on the other hand, for the electrode
12
a,
that the material of the sensitive layer
22
a
covers only part of its surface not encumbered by the residue
24
a.
Thus the covering of the electrode
12
a
is not homogeneous.
For the electrode
12
c,
it can be seen that the residue
24
c
which covers the entire surface prevents the formation of a sensitive layer.
Finally, it is apparent that the electrode
12
d
in
FIG. 1B
has been partly destroyed during the lining step.
The bottom layer
13
of this electrode, by not being correctly protected by the top layer
15
, because of the porosity
23
, has undergone deterioration caused by the agents or fluids used for the lining of the electrodes. Thus the electrode
12
d
is unable to make analysis measurements.
Electrodes such as the electrode
12
a
or
12
c
which either have no sensitive layer or are equipped with a layer which only partially covers their surface, lead to erroneous analysis results.
Moreover, a residue such as the residue
24
d,
visible in
FIGS. 1A and 1B
, even if it does not directly interfere with the formation of a sensitive layer, risks interfering with the analysis measurements made on the adjacent electrodes.
All the probable faults mentioned above are liable to prevent the functioning or interfere with the functioning of a certain number of analysis electrodes on a chip.
Similar problems are posed also for chips equipped with other sensitive elements such as micromechanical elements, whose functioning may also be disturbed by residues of material or by defects caused during the manufacturing processes.
In the field of micro-electronics, a certain number of tests designed to check the correct functioning of electronic chips are known.
Amongst these tests there are notably conductimetry tests and visual tests.
Conductimetry tests consist essentially of moving movable conductive spikes on the surface of the chip in order to put them in contact with conductive elements on this chip and check the passage of a measuring current.
However, in an application to analysis chips, electrical tests with movable spikes do not make it possible to detect the electrodes which are certainly covered with a lining layer but for which the lining layer has a lack of homogeneity or porosities, or covers only part of the electrode, as in the case of the electrode
12
a
in FIG.
1
B.
In addition, electrical tests with movable spikes offer a resolution which makes it difficult to use them for chips where the electrode pitch is less than 50 &mgr;m.
In addition, the movable test spikes moved on the surface of the chip risk locally breaking a layer of residue covering an electrode and locally coming into contact with the subjacent electrode. In this case, a measuring current may

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