Measuring and testing – Volume or rate of flow – Thermal type
Patent
1992-09-30
1994-10-11
Goldstein, Herbert
Measuring and testing
Volume or rate of flow
Thermal type
156633, 156657, G01F 168, H01L 21306, B44C 122
Patent
active
053536380
DESCRIPTION:
BRIEF SUMMARY
STATE OF THE ART
The invention relates to a method for constructing a micromechanical sensor.
In connection with customary methods, the sensors formed out of a wafer are separated from the wafer by sawing. The lateral boundary walls of the sensor elements being created in the course of this are oriented perpendicular to the wafer surface. Assembly of micromechanical sensor elements takes place by gluing, soldering or glass-sealing on a substrate, depending on the nature and the material of the sensor element and substrate. The electrical connections for the sensor elements are bonded to metal strips located on the exterior.
ADVANTAGES OF THE INVENTION
The method in accordance with the invention has the advantage that the sensor element is already essentially separated from the wafer by means of anisotropic etching during the structuring process, except for bridges, which maintain the sensor element in a defined position during the manufacturing process. In this connection, it is advantageous that the lateral boundary walls of the sensor element being created form defined angles in respect to the wafer surface, depending on the crystal orientation of the wafer, and are very smooth. Also, an essential advantage of the method lies in the opportunity to perform structuring of the sensor elements, for example by membrane etching, in the same process step.
A second wafer is structured in such a way that an opening is created into which the sensor element fits exactly. The exactness required for creating the dimensions of the sensor element and the opening can be attained in a particularly simple manner with silicon wafers of the same crystal orientation by anisotropic etching, because the crystallographic actualities can be advantageously used in the course of this. For some uses it is particularly advantageous to place the sensor element in the opening of the second wafer in such a way that a homogeneous surface is created, which does not have steps in the transition from the sensor element to the second wafer. This is attained in an advantageous manner in that the sensor element is structured out of a first wafer, which has the same thickness as the second wafer, from which the opening is structured. If the opening extends completely through the second wafer and if the sensor element has the same thickness as the wafer, it is easy to realize a homogeneous surface in a simple manner by means of providing appropriate longitudinal and width dimensions. This method can be used particularly advantageously in connection with the manufacture of micromechanical air mass sensors. In this case, homogeneous laminar flow over the sensor surface is required. Steps, even in the range of some 10 .mu.m, create turbulence which has disruptive effects on the measuring signal. It is possible with the aid of the assembly method in accordance with the invention to produce a sensor surface having the required homogeneity.
DRAWINGS
Exemplary embodiments of the invention are illustrated in the drawings and explained in detail in the following description.
FIG. 1 shows a top view of a wafer section following structuring.
FIG. 2 shows a section through a structured wafer prior to insertion of a sensor element, and
FIG. 3 is a top view of a sensor.
DESCRIPTION OF THE EXEMPLARY EMBODIMENT
In FIG. 1, a wafer is designated by 25, from which sensor elements 10 of the same type have been structured, on which the electronic switching elements have been placed and one of which will be described below by way of example. The sensor element 10 has three resistors 14, 15 and 16 on its surface, which will be described in detail in the course of the description of FIG. 2. When using crystals with (100)- or (110)-crystal orientation, it is possible to create the structures common in micromechanics, such as paddles, tongues or diaphragms, advantageously by means of anisotropic electrochemical etching. Because the manufacture of chips containing electronic switching elements entail very high costs, it is attempted to produce as many chips as
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Goldstein Herbert
Robert & Bosch GmbH
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