Active solid-state devices (e.g. – transistors – solid-state diode – Integrated circuit structure with electrically isolated... – Passive components in ics
Reexamination Certificate
1999-10-22
2003-05-20
Loke, Steven (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Integrated circuit structure with electrically isolated...
Passive components in ics
C257S537000, C257S510000, C257S513000, C257S516000
Reexamination Certificate
active
06566732
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an integrated high voltage resistive structure on a semiconductive substrate, and more specifically to a serpentine integrated resistive structure on a semiconductive substrate having a first type of conductivity opposite to that of the semiconductor substrate.
BACKGROUND OF THE INVENTION
Embodiments of the invention relate in particular, but not exclusively to a resistive structure at high voltage to be integrated on a semiconductive substrate together with power devices and the following description is made with reference to this field of application with the sole objective of simplifying its disclosure. Discussion of steps or processes well known to those skilled in the art has been abbreviated or eliminated for brevity.
As is well known, high voltage resistive structures which are integrated on a semiconductive substrate find ample use in the application field for power devices formed as integrated circuit, for example VIPower devices.
VIPower devices integrate on the same chip a region on which the power devices are formed (power region) and a region on which signal devices are formed (signal region). In some applications, it is necessary to arrange, inside the signal region, a division of the substrate voltage. This can be provided by using a resistive structure connected between the substrate and a control region of the signal device. This resistive structure will therefore be subjected to the substrate voltage Vs which as is well known, in devices of the VIPower type, can reach elevated values of up to 2KV, hence the term resistive structure or high voltage resistance HV.
In
FIGS. 1 and 2
the electrical diagrams of two examples of possible applications of the high voltage resistive structures are shown.
In
FIG. 1
for example, a first circuit structure C
1
is shown comprising a bipolar component Q
1
of the NPN type connected in series on the emitter region to a first terminal of the resistance R
1
. A Zener diode D
1
is connected, in inverted polarization, between the base terminal of the component Q
1
and a second terminal of the resistance R
1
. A high voltage resistance R
HV
is connected between the collector region and the base region of the component Q
1
.
When a current I
1
flows through the resistance R
HV
, the component Q
1
switches on and drives a low voltage circuitry BT connected to an emitter region of the component Q
1
. The current which flows through the resistance R
HV
obviously depends on the substrate voltage Vs and on the value of the resistance itself.
In
FIG. 2
, a second circuit structure C
2
is shown comprising two circuit branches
1
a
and
2
a
having a common node A. The first branch
1
a
comprises a Zener diode chain D
2
, D
3
and D
1
connected to the base region of a first bipolar component Q
2
, which is polarized by a resistance R
2
. The second branch
2
a
comprises a resistance R
3
connected in series to the emitter region of a second bipolar component Q
3
, which is controlled by a battery Vb. A high voltage resistance R
HV
is then connected to node A.
In this configuration the voltage value on node A can be used as a reference value for permitting conduction on branch
1
or on branch
2
, depending on the value of Vz of the Zener chain, of the Vb battery voltage as well as from the other components present in the circuitry. In this case, the resistance R
HV
is used simply as a voltage divider.
In both examples, the voltage of substrate Vs applied to the resistance R
HV
, as said before, can reach elevated values. The voltage divider used as a driver signal for the linear region (circuit C
2
), and also the current which flows through the resistance HV (circuit C
1
), assumes values which must be comparable and therefore not above the maximum voltage of the well inside which the signal circuitry is integrated, and therefore of the maximum current foreseen for a determined circuit structure. This means that the resistance R
HV
must have a resistive value such as to permit the division or the current required by the driving circuitry as foreseen by the circuit structure used.
This resistance value can also be in the order of some M&OHgr; and in any case not less than a few tens of K&OHgr;.
A first known technical solution for the formation of resistive structures with high resistive values foresees forming doped regions having a high resistivity on a semiconductive substrate.
Though advantageous in many respects, this first solution has various problems, in particular, when forming regions of high resistivity, fairly high area dimensions are required for the die.
Another solution of the prior art foresees the formation of long resistive structures which, according to the area used, minimize the dimensions of silicon occupied thanks to a particular layout.
One layout embodiment according to the prior art is shown in FIG.
3
. In particular, in a substrate
1
′ of N type a serpentine region
2
′ of P type is formed. This type of layout, nevertheless, cannot be used for the resistive structure at high voltage, because it would occupy a fairly large area of silicon. This is due to the size of the depletion region
3
′, outlined in
FIGS. 3 and 4
, that is inversely proportional to the concentration of dopant (and therefore directly proportional to the resistive value), during inverted polarization of a portion of doped silicon and therefore the size of this depletion region is very important in the resistive structures R
HV
.
Even if the high voltage resistive structures can be integrated by using the more resistive layers used in the technology, VIPower devices capable of supporting elevated voltages necessarily have an elevated resistivity of the substrate, in varying degrees of size bigger than the more resistive layers available with current technological processes. This means that layouts which tend to optimize area availability of silicon on chips such as that of
FIG. 3
, have the problem of pinch-off phenomenon.
In particular, the depletion regions of two or more parallel branches of the resistive structure come into contact, as illustrated on the right side of
FIG. 4
, with subsequent alterations in the values of the resistive structure itself and therefore of the functioning of the circuitry of which it is a part.
In order to overcome this problem, it is necessary in the design phase of the layout for the high voltage resistive structure that the distance between the various branches of the serpentine resistive structure which face each other in parallel, should be more than the total of the widths of the depletion regions which belong to each branch. This means that the branches of the resistive structure subjected to a high voltage must be set apart according to the drop in voltage on the resistive structure itself.
As a consequence of this, the layout in
FIG. 4
, in the case of a high voltage resistance structure, takes the form shown in
FIG. 5
with considerable dimensions of silicon areas.
Furthermore, the high voltages placed on the resistive structure, would require border structures, capable of protecting the more pressing regions against premature breakdowns from the high voltages. Metal field plates or rings with a high resistive structure are used for example in this case, which anyway tend to further increase the area of silicon occupied.
In order to reduced the lateral depletion region between the various branches of the resistive structure, a known technique enriches the layer intended for integration of the resistive structure itself. Nevertheless this solution reduces the capability of the device to hold the voltage, in that in order to obtain a reduction of the widening of the depletion region it would be necessary to have a concentration of dopant in the surface region which would be very high.
The same considerations made above can also be repeated in the case in which the high voltage resistive structure is integrated around the region at high voltage which surrounds the device. In this way, especially if the device occ
Carlson David V.
Jorgenson Lisa K.
Loke Steven
SEED IP Law Group PLLC
STMicroelectronics S.r.l.
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