Appeal No. 95-3557
Application No. 07/833,417
diffusing a boron (i.e., “p-type”) dopant into a monocrystalline silicon substrate 50 to form rim
area 20 surrounded by first 51 and second 53 undoped regions (Fig. 4A; col. 6, lines 7-20) to a
thickness (i.e., “x-y”) from 1 to 20 µm, e.g., approximately 15 µm (col. 6, lines 24-30),
forming polycrystalline silicon layer 34 either on dielectric layer 40 or, if the dielectric layer 40 is
not used, spanning at least portions of both the doped area 20 and the undoped area 51 of the
substrate to provide support for the device after etching, typically to a thickness (i.e., “y”) of 8000 D,
i.e., 0.8 µm, (Fig. 4B; col. 6, lines 60-66), and doping the polycrystalline silicon layer with phosphorus,
boron, arsenic or other common silicon dopants by diffusion or ion implantation to enhance its electrical
conductivity (col. 6, line 66 - col. 7, line 5),
providing additional insulating and metal layers and electronic circuitry on top of the
polycrystalline silicon layer 34 to complete a thermocouple sensing assembly (Figs. 4C-4E; col. 7, lines
6-48), and
selectively etching away undoped areas 51 and 53 of the substrate 50, but not doped rim 20 or
any of the layers formed on the front side of the sensor, e.g., with an ethylenediamine-pyrocatechol
(EDP) and water etch (col. 7, lines 48-53). Controlled time etch-stop (col. 3, lines 40-46; col. 8, lines
1-16) and electrochemical etch-stop techniques (col. 3, lines 47-57; col. 8, lines 17-29) are also
described as alternative etches to the above diffused boron etch-stop technique.
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Last modified: November 3, 2007