Active solid-state devices (e.g. – transistors – solid-state diode – Physical configuration of semiconductor – Groove
Reexamination Certificate
2002-10-15
2004-09-28
Munson, Gene M. (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Physical configuration of semiconductor
Groove
Reexamination Certificate
active
06798042
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a diode and a method for fabricating it. The invention relates, in particular, to a PIN diode. Diodes of this type are used, for example, in discrete circuits for switching radio frequency signals.
Diodes are used as rectifiers and switches in many areas of electronics and are offered commercially in various configurations. Applications as switches in the radio frequency range require diodes with a low blocking capacitance (C
T
) for an applied reverse-biased voltage, and a low forward resistance (r
f
) for a forward-biased voltage, which leads to low attenuation in the forward direction and high insulation in the reverse direction. One quality feature for PIN diodes is the product C
T
*r
f
.
The blocking capacitance of a diode, C
T
, is composed of an area capacitance, C
A
, and a fringing capacitance, C
P
. The area capacitance is dominant in large-area diodes. It is determined by the surface area and also the thickness of the depletion layer of the diode, which forms for a given voltage between the regions of different conductivity. Furthermore, the blocking capacitance is determined by the material of the semiconductor substrate or the relative permittivity of the semiconductor material. In the case of silicon, the relative permittivity is relatively high, with ∈=12.
The fringing capacitance encompasses all of the capacitances of a diode that cannot be assigned to the area capacitance. Examples of this are capacitances that are determined by the supply line and contact-making areas. The fringing capacitance is dominant primarily in small-area diodes.
The forward resistance can be minimized primarily by using short paths in the semiconductor substrate. This is achieved e.g. by the current, which enters from the front side through the diffusion layer, emerging again on the rear side of the semiconductor substrate. The rear side of this substrate has previously been thinned.
The PIN diodes have become established in the radio frequency range right into the GHz range (e.g. the diode family BAR-63 from Infineon Technologies AG). The active region of these diodes essentially includes three regions, a highly doped diffusion region of a first conduction type, a quasi intrinsic region with no doping or only very low doping and a highly doped region of a second conduction type. In the case of these diodes, the thickness of the depleted region is given essentially by the thickness of the intrinsic region, since the intrinsic region is completely depleted of free charge carriers even at very small voltages on account of the low doping. A relatively thick intrinsic region makes it possible to produce diodes that have very low blocking capacitances even at small voltages.
FIG. 5
is a cross sectional view taken through a prior art rotationally symmetrical planar PIN diode
10
. The figure shows the semiconductor substrate
1
, which has a p-conducting substrate region
3
and an intrinsic substrate region
5
. The intrinsic substrate region
5
is generally realized by an undoped or only weakly doped epitaxial layer. The intrinsic region
5
is non-conducting and therefore acts as a kind of dielectric between the n-conducting diffusion region
7
and the p-conducting region
3
. Furthermore, the diode has a rear side contact
17
, which is preferably realized by a gold-arsenic layer, so that the rear side serves as a second contact of the diode. In order to minimize the resistance of the diode, the rear side of the semiconductor substrate is thinned.
The total capacitance of the diode is given by the sum of the area capacitance C
A
and the fringing capacitance C
P
, which are both depicted diagrammatically in FIG.
5
. If the diode area is small, then the influence of the fringing capacitance must increasingly be taken into account. The fringing capacitance C
P
in
FIG. 5
is relatively large, since the dielectric constant is essentially prescribed by the depleted silicon, which has a high dielectric constant (∈=12).
In order to reduce the fringing capacitance C
P
, so-called mesa diodes are often used for applications in radio frequency technology.
FIG. 6
shows a cross sectional view taken through a rotationally symmetrical mesa PIN diode
30
. In this case, due to the mesa structure, the fringing capacitance C
P
is significantly reduced in comparison with the diode shown in
FIG. 5
, since in the trench
20
, air is prescribed as the dielectric, and air has a low dielectric constant (∈=1). The trench is covered by a trench oxide layer
22
and a nitride layer
24
lying on the latter, so that the silicon surface is passivated in the trench. The blocking capacitance of the diode typically lies below 400 fF.
For the same resistance in the forward direction, mesa PIN diodes make it possible to realize capacitances in the reverse direction that are approximately 15% smaller than the capacitances that are possible with a planar diode. A further advantage of a mesa PIN diode resides in the shorter turn-off time. This can be attributed to the fact that, as a result of the lateral delimitation of the charge carriers, during the switch-off, no charges can be removed from the edge region of the diode, as is the case with a planar diode.
However, the diode shown in
FIG. 6
has the disadvantage that, for a given thickness of the intrinsic region, the junction capacitance is downwardly limited by the size of the electrode
9
that is required for contact-making. The area of the electrode
9
cannot be arbitrarily reduced, since later it is necessary to apply a bonding wire or another terminal connection on this area. This bonding wire or terminal connection connects the diode e.g. to a housing PIN. Conventional bonding methods require a bonding bearing area of about 10,000 &mgr;m
2
or more. This generally has the consequence that the size of the diffusion region
7
also cannot be reduced, since the contact-making area required for a microwelding connection must maintain a minimum size. Since the size of the electrode
9
is prescribed by the area required for contact-making, e.g. by a bonding wire, the reduction of the blocking capacitance of the diode is limited by this area. A further disadvantage is that, in the case of small diodes and thus also small contact-making areas, e.g. a bonding base of a bonding wire can reach across the contact area and can damage the insulating layers
22
and
24
even in the event of very small misalignments.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a diode and a method for producing the diode which overcomes the above-mentioned disadvantages of the prior art apparatus and methods of this general type.
In particular, the object of the invention is to provide a diode having a desired, i.e. minimum, blocking capacitance even in the case of a predetermined minimum bonding area. Furthermore, the diode is intended to have the typical switching behavior of a mesa PIN diode.
With the foregoing and other objects in view there is provided, in accordance with the invention, a diode that in particular can be used for applications in radio frequency technology, including: a semiconductor substrate having a surface, a first region of a first conductivity type, a second region of a second conductivity type, and a depletion region between the first region and the second region being formed when the diode is operated in a reverse direction; at least one electrode configured on the surface of the semiconductor substrate, the first region having an area being directly electrically connected to the electrode; at least one trench formed in the semiconductor substrate; and insulation configured on the surface of the semiconductor substrate. The trench limits the depletion region that is formed when the diode is being operated in the reverse direction. The insulation limits the area of the first region that is directly electrically connected to the electrode.
The diode has the advantage that the extent of the depletion region,
Ahrens Carsten
Gabl Reinhard
Peichl Raimund
Greenberg Laurence A.
Infineon - Technologies AG
Mayback Gregory L.
Munson Gene M.
Stemer Werner H.
LandOfFree
Pin diode and method for fabricating the diode does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pin diode and method for fabricating the diode, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pin diode and method for fabricating the diode will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3192229