Method of making a silicon based biomedical sensor

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS.
1 & 2, there is shown a prior art biosensor device 10.
The biosensor 10 is typically formed on a silicon substrate 12, and has a pair of leads N1 and N2, which are preferably metal.
The leads N1 and N2 are formed on an insulating layer 14 formed on the surface of substrate 12.
A polymer enzyme layer 16 is formed over the leads N1 and N2.
A polymer overcoat 18 is then formed over the polymer enzyme layer 16.
To use the sensor, a blood sample is placed on the polymer overcoat and the resistance between leads N1 and N2 is measured.
The resistance measurement provides a measure of the blood glucose levels as a result of the interaction between the blood sample and the polymer enzyme.
In order to measure the resistance between the leads N1 and N2, it is necessary to make backside contact with the leads, so as to not disturb the outer surface of the sensor 10.
Referring now to FIG.
3, there is shown a cross-section of a sensor 20 made in accordance with the present invention.
The sensor is formed on a semiconductor substrate 22, which is N-type silicon in the preferred embodiment.
Dielectric layers 23 and 24 are formed on the face and backside of substrate 22, respectively.
Metal leads 26 and 28 contact the substrate 22 through openings in dielectric layer 23.
The leads 26 and 28 are also each connected to a set of interleaved longitudinal contact fingers 27 and 29.
While the sets of fingers 27 and 29 are interleaved, they are not in electrical contact with each other.
A pair of backside contacts 30 and 32 are formed on the dielectric layer 24, and contact the substrate 22 through contact holes in dielectric layer 24.
In the preferred embodiment, dielectric layers 23 and 24 are oxide, but could also be other dielectric material.
Backside contact 30 is in ohmic contact with metal lead 26 through a conductive region 34.
Conductive region 34 extends through substrate 22 and is preferably formed by diffusing a P-type dopant through substrate 22