BRIEF DESCRIPTION OF DRAWINGS
The accompanying figures which is incorporated in and form part of the specification, further illustrate the present invention and, together with the detailed description of the invention, serve to explain the principles of the present invention.
FIG. 1 illustrates a block diagram of a pressure sensor in accordance with the present invention; and
FIG. 2 illustrates a flow diagram for a process of fabricating a flow sensor in accordance with features of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Pressure sensors are typically made by growing an N-type epitaxy layer on a P-type substrate. After dicing the wafer into individual die, the N-type epitaxy is exposed around the edge of the silicon die and under certain conditions this edge can come in contact with the conductive elastomeric seal. The conductive elastomeric seal is typically contacted to the top and/or bottom side of the silicon die, but under adverse conditions this seal can become wrapped around the edge of the die and can short out the topside contacts to the N-type epitaxy because the epi is actually biased up to the supply voltage.
As shown in FIG. 1, a P-type isolation region 130 is fabricated together with sensor diaphragm 105 and associated circuitry 115 on the silicon pressure sensor wafer 100 using a mask around the edge of an N-type material sensor die 110 and in contact with the P-type substrate 120, which then makes the edge of the die (P-type). The present inventors have found that if a new edge of the die 120 is instead made with P-type material, that will create a back-biased diode with the substrate 120, then shorting of a conductive elastomeric seal (when used), with the N-type die material 110 can be eliminated. Shorting is eliminated because P-diffusion already exists as an isolation region around the edge of the N-type epitaxal region of the die, while in contact with the P-type substrate 120. It should be noted that FIG. 1 is of a single pressure sensor die after fabrication and dicing and that the fabrication process described above is for a silicon wafer that would contain a plurality of devices in a manner common to those familiar with wafer processing. A new mask enables matching material use and elimination of shorting of conductive seals (not shown) with pressure sensor components. Typically isolation diffusion is conducted to keep the edge of the wafer from having problems during etching.
Referring to FIG. 2, a flow diagram of process steps for making a pressure sensor having a conductive elastomeric seal that prevent shorting with the die is shown. First, as shown in Block 210, a p-type wafer is provided; then as shown in Block 220, an n-type epitaxy is grown on the wafer. With these steps, a silicon wafer is fabricated by starting with a p-type substrate wafer and growing an N-type epitaxy layer on the substrate. Then, as shown in Block 230, a mask adapted for achieving isolation diffusion by using P-type material in the so-called streets of the die pattern is obtained. Finally, as shown in Block 240, isolation diffusion using P-type material is accomplished around the edge of the die using the mask to thereby cause patterning around the edge of the die. This step creates the isolation layer using a P-type doping material. To complete processing of a pressure sensor wafer fabricated in the foregoing manner, the wafer is then diced or sawed into individual pressure sensor dies as shown in Block 250. Then as shown in Block 260, each die is then packaged into a housing with a conductive elastomeric seal. With the resulting die design, incorporating a patterned insulator around the edge of each die, shorting is preventable.
The embodiments and examples set forth herein are presented to best explain the present invention and its practical application and to thereby enable those skilled in the art to make and utilize the invention. Those skilled in the art, however, will recognize that the foregoing description and examples have been presented for the purpose of illustration and example only. Other variations and modifications of the present invention will be apparent to those of skill in the art, and it is the intent of the appended claims that such variations and modifications be covered. The description as set forth is not intended to be exhaustive or to limit the scope of the invention. Many modifications and variations are possible in light of the above teaching without departing from the spirit and scope of the following claims. It is contemplated that the use of the present invention can involve components having different characteristics. It is intended that the scope of the present invention be defined by the claims appended hereto, giving full cognizance to equivalents in all respects.
Patent Application
20070289387
