Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Physical stress responsive
Reexamination Certificate
1998-11-06
2001-03-27
Picardat, Kevin M. (Department: 2822)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Physical stress responsive
C438S050000, C438S051000
Reexamination Certificate
active
06207470
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a pressure-measuring device equipped with a resonating element.
More specifically, the invention relates to a method for manufacturing a pressure-measuring device for measuring absolute, relative or differential pressure.
The pressure-measuring device that can be manufactured using the method according to the invention is, for example, of the type described in Italian patent application No. MI96A002268, filed in the name of the same applicant as the present application, the disclosure of which is incorporated herein for reference.
It is known that pressure-measuring devices can be prepared by suitably machining wafers of semiconductor-based materials.
In particular the technologies currently known and referred to as “silicon micromachining” are widely used for manufacturing sensors using silicon as the base material.
It is known that such micromachining technologies are very similar to those used for the production of microelectronic circuits. With a single process, it is possible to machine a considerable number of devices that are identical to one another with significant advantages in terms of production costs.
Micromachining generally comprises technologies such as thin layer deposition (a few microns thick) of semiconductor materials and their derivatives or metal materials, extremely precise photolithographic techniques (resolutions of less than one micron), selective removal of semiconductor material through the action of suitable chemical agents, bonding techniques on separate layers.
It is known from the literature that “silicon micromachining” technologies can be divided into two main categories known as “bulk micromachining” technologies and “surface micromachining” technologies.
The former refers to the possibility of obtaining monocrystalline structures by machining both sides of a wafer of semiconductor material, whereas the latter refers to machining performed on one side of the wafer only. “Bulk micromachining” technologies have been developed from crystal machining and are therefore highly consolidated. “Surface micromachining” technologies, on the other hand, are highly innovative compared to the former and make it possible to manufacture smaller microstructures (one order of magnitude smaller). They also offer the considerable advantage of easier machining and greater potential for integrating the structures produced with microelectronic circuits made in the same chip of semiconductor material.
The manufacture of pressure-measuring devices generally involves a number of manufacturing difficulties as described hereinafter, especially when high performances are required.
In the first place, the high number of manufacturing process phases makes the manufacture of the pressure sensor costly. Moreover, the devices of known type are often based on polysilicon and quartz and their mechanical performances are not optimal. Also, in most cases, both sides of the wafer are subjected to very critical machining steps, thus complicating the manufacturing process.
SUMMARY OF THE INVENTION
The main aim of the present invention is therefore to provide a method for manufacturing a pressure-measuring device, based on a resonating element, that is capable to give high performances.
As part of this aim, one object of the present invention is to provide a method for manufacturing a pressure-measuring device that makes it possible to integrate the resonating element of the device with the diaphragm to which the pressure is applied.
Another object of the present invention is to provide a method for manufacturing a pressure-measuring device, that enables the production in batches of the device.
Another object of the present invention is to provide a method for manufacturing a pressure-measuring device by which it is possible to produce three-dimensional structures using either technologies for machining on both sides of the wafer or technologies for machining on a single side.
A further object of the present invention is to provide a method for manufacturing a pressure-measuring device in which the resonating element operates under a high vacuum and is protected from overrange pressure pulses.
Yet another object of the present invention is to provide a method for manufacturing a pressure-measuring device in which the machining for making the resonating element is performed on one side of the wafer only.
A further though not the last object of the present invention is to provide a pressure-measuring device that is highly reliable and relatively easy to manufacture at competitive costs.
This task, as well as these and other objects that will appear more clearly hereinafter are achieved by a method for manufacturing a pressure-measuring device comprising a diaphragm of semiconductor material having a resonating element fixed thereto, said diaphragm being exposed to the pressure of a process fluid. The method of the present invention is characterised by the fact that it comprises the following phases:
i) machining a multilayer semiconductor material to obtain a diaphragm having on the upper side a resonating element,
ii) machining a semiconductor material having one or more layers to obtain a support having a pressure port for the flow of the process fluid;
iii) making a bond between the lower side of said diaphragm and the upper side of said support.
The present invention is a combination of silicon and bulk micromachining technologies. This solution is particularly advantageous compared to the prior art, because it allows to perform the most critical machining steps working on a single plane even performing a three-dimensional structure.
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ABB Kent Taylor S.p.A.
Josif Albert
Modiano Guido
O'Byrne Daniel
Picardat Kevin M.
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