Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Responsive to non-optical – non-electrical signal
Reexamination Certificate
1998-06-30
2004-12-21
Fourson, George (Department: 2823)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Responsive to non-optical, non-electrical signal
C428S620000, C148S033300, C438S052000, C438S053000
Reexamination Certificate
active
06833570
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a structure including an insulating part in a massive substrate and a method of producing such a structure.
Such structures find applications in the field of micro-electronics for the manufacture of integrated circuits, certain parts of which must be insulated and free from parasitic effects such as parasitic capacitive effects.
The structures also find applications in the field of micro-mechanics for the production of sensors such as accelerometers or pressure sensors, as well as the creation of actuators. In the case of an accelerometer, the insulated part of the structure is, for example, constituted by a seismic mass for measuring accelerations.
DISCUSSION OF THE BACKGROUND
For the production of sensors such as pressure sensors or accelerometers, widespread use is made of SOI type structures. These structures comprise a thin surface layer of silicon separated from an underlying layer of silicon by an embedded silicon oxide layer. The thin layer of silicon is locally freed from the underlying layer. It can then constitute, for example, the membrane of a pressure sensor or, when it is suitably formed, the seismic mass of an accelerometer. Reference may be made to this subject in documents (1) and (2), the references for which are given at the end of this description.
The surface layer can also be formed in such a way that an actuator is produced. Actuators produced according to micro-machining methods are described in documents (3) and (4), the references for which are also given at the end of this description.
The embedded oxide layer has the role of supporting the structure formed in the thin surface layer. This aspect is apparent in particular, in document (2) relating to an accelerometer.
However, because of its small thickness, the electrical or mechanical insulation provided by the insulatinq oxide layer can prove to be insufficient.
In particular, parasitic capacitance phenomena can be induced between the deep underlying layer of silicon and the surface layer of silicon.
These phenomena can affect, in a negative way, the measurements of an accelerometer or those of another sensor that operates according to a capacity measurement principle.
Another disadvantage of SOI type structures and of devices produced from these structures is associated with their cost.
SUMMARY OF THE INVENTION
The aim of this invention is to provide a structure with an electrically insulating part, the production of which is not expensive and which does not have the limitations mentioned above.
Another aim is also to provide a structure with an insulating part which is nearly not subject to parasitic capacity effects, and can be used for the production of a sensor. An aim of the invention is also to provide a method of producing such a structure.
In order to achieve these aims mentioned above, the invention has the more precise objective of a structure comprising a first part and at least one second part, electrically insulated from the first part, the first and second parts each being formed in the same wafer of material, said first and second parts each having substantially one and the same thickness, extending substantially in one and the same plane, and having at least one mutually adjacent edge, and, the adjacent edges of the first and second parts being separated by a spacing. Conforming to the invention, the structure comprises, in addition, at least one joint of insulating material, arranged in the spacing, to make the first and second parts integral, the joint being in mechanical contact with at least a portion of each wafer and extending substantially over the entire thickness of the wafers.
The joint of insulating material has a double function. The first function is to provide electrical insulation between the first and second parts. It should be noted that the quality of the electrical insulation can be adapted by making use of the width of the spacing, and hence the width of the joint, as well as the material used to form the joint. A second function of the insulating joint is to maintain the cohesion of the structure by making the first and second parts integral. In particular, the joint allows the wafers to be held with their principal faces substantially in one and the same plane.
Although the structure thus obtained can be linked to a suitable support structure, the second insulated part can be sufficiently far from the support or separated from the first part to prevent capacitive effects, if these are not desired.
On the other hand, in other applications, the adjacent edges of the first and second parts can be configured in such a way and arranged sufficiently close that a variable capacity is formed.
The measurement of this capacity and of its variations then allows the determination of any possible displacement between the first and second parts. This aspect, that permits the production of an accelerometer or an actuator, is described in greater detail in a subsequent part of the description.
According to one advantageous aspect, the first and second parts can have complementary shapes. The spacing between the parts is then substantially uniform.
The first and second parts can be simply wafers placed side by side, obtained by cutting a substrate into two parts along a line. However, according to a variant, the second part can be a portion of a wafer of material, cut in the wafer of material forming the first part, in accordance with a specific pattern.
In the text that follows, reference is only made to one single first part and one single second part. It is however possible to design the structure with one first part and a plurality of second parts, mutually insulated and insulated from the first part. In particular, it is possible to cut in the wafers of material forming the first part, a plurality of portions of wafers which then form a plurality of second parts of the structure.
In accordance with the envisaged applications and in particular for the production of sensors such as, for example, an accelerometer or an actuator, the material of the wafer forming respectively the first and second parts of the structure can be chosen to be non-insulating. By non-insulating material, one understands a semi-conductor or conductor material.
By way of example, the material is chosen from among the following semi-conductor materials AsGa, Si, SiC, the following metals Au, W. Ti, Cr, Al, Fe, Ni, Mo and alloys of these metals.
Another objective of the invention is a method of producing a structure comprising a first part and at least one second part, co-planar with and electrically insulated from the first part. The method includes the following steps:
a) cut a substrate wafer in order to define in the wafer, a first and a second part, at least one portion of the substrate, called the holding portion and linking the first and second parts, being preserved at the time of cutting,
b) substitution of an insulating holding joint, linking at least one portion of the first and second parts over substantially their entire thickness, at said holding portion of substrate connecting the first and second parts of substrate.
By substitution of an insulating holding joint, at said holding portion of substrate connecting the first and second parts, one understands, either the putting into place of said joint and the removal of the portion of substrate, or the transformation of the portion of holding substrate into an insulating joint.
The method of the invention can be implemented in accordance with several possibilities.
According to a first possibility, step a) comprises the formation of at least one cut in the substrate wafer, that goes right through and separates for the main part, the first and second parts. Step b) then comprises the filling of the cut with an insulating material forming the holding joint between the first and second parts, and the removal of the portion of the holding substrate linking the first and second parts.
One may consider that the cut that goes through separates, for the main part, the first and second parts of
Blanc Henri
Brun Jean
Danel Jean-Sebastien
Vincent Fabrice
Fourson George
Garcia Joannie Adelle
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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