Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Physical stress responsive
Patent
1995-10-31
1998-07-28
Dutton, Brian
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Physical stress responsive
H01L 2144, H01L 21465
Patent
active
057862354
DESCRIPTION:
BRIEF SUMMARY
This application is a 35 U.S.C. 371 application PCT/DE94/00505, filed on May 5, 1994.
BACKGROUND OF THE INVENTION
The invention relates primarily to the improvement of the SGFET (suspended-gate field-effect transistor) as a gas sensor, but it also has other possible applications, such as the production of microscopic capillaries and micromechanical membranes. The prior art relevant to structuring with the aid of masks during vapor deposition is disclosed in prior art references Austrian Patent 241,536, German Patent 027,798 and U.S. Pat. No. 4,469,719.
In the SGFET (U.S. Pat. No. 4,411,741), the sensitive layer can be deposited either electrochemically or by physical methods (German Patent 3,834,189) such as sputtering or vapor deposition. Since the sensitive layer must be situated between the gate and the channel of the transistor, other processing steps such as the production of the gate or the etching of the spacer follow the application of the sensitive layer by physical methods. These steps may alter the sensitive layer, or only a few materials are compatible with these subsequent steps. This narrows down the choice of the sensitive layer considerably.
SUMMARY OF THE INVENTION
The object is to produce an integrable SGFET whose chemically sensitive layer is not altered by any further processing step.
In general terms the present invention is a process for producing a suspended-gate field-effect transistor. A gate oxide is applied to a substrate which comprises a source region, a drain region and a channel disposed in between. A first silicon nitride layer, a silicon dioxide layer, a second silicon nitride layer and a metal layer are applied to the gate oxide. The metal layer and the second silicon nitride layer are structured using a photoresist procedure such that a mask is produced. A cavity is formed beneath the mask by etching the silicon dioxide layer in an etching process which attacks silicon dioxide selectively with respect to silicon nitride and metal. A chemically sensitive layer is deposited underneath the mask. The deposition of the chemically sensitive layer takes place from different directions so that a surface-wide coating takes place underneath the mask. The mask forms, a gate electrode or membrane, a functional component of the suspended-gate field-effect transistor.
In an advantageous development the mask is closed during the deposition of the layer.
Another embodiment of the present invention is also a process for producing a suspended-gate field-effect transistor. A gate oxide is applied to a substrate which comprises a source region, a drain region and a channel disposed in between. A first silicon nitride layer, a silicon dioxide layer, a second silicon nitride layer and a metal layer are applied to the gate oxide. The metal layer and the second silicon nitride layer are structured with the aid of a photoresist procedure so that a mask is produced. A cavity is formed underneath the mask by etching the silicon dioxide layer in an etching process which attacks silicon dioxide selectively with respect to silicon nitride and metal. A chemically sensitive layer is deposited underneath the mask. The deposition of the chemically sensitive layer takes place from different directions so that a coating over the entire area takes place underneath the mask. The mask is closed by a deposition. The mask forms, as gate electrode or membrane, a functional component of the suspended-gate field-effect transistor.
Advantageous developments of the present invention are as follows.
A grid is used as the mask.
A layer with honeycomb structure is used as the mask.
Part of a gas sensor is used as the coated area.
The sensitive layer of a gas sensor is used as the coated area.
A part of a gas sensor whose principle of measurement is based on a change in work function during gas adsorption is used as the coated area.
The area on which the layer is deposited was already structured.
Sensitive elements, such as conductivity or capacity structures, have already been produced on the area on which the lay
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Eisele Ignaz
Flietner Bertrand
Lechner Josef
Dutton Brian
Siemens Aktiengesellschaft
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