Title: Schottky diode
Abstract: A Schottky diode has a Schottky junction formed by a thin metal layer and/or metal silicide layer at the top side of a doped well in a semiconductor body or substrate. In contrast to the fabrication of low-impedance contacts on CMOS wells, a metal, to be precise titanium in the preferred embodiment, is applied not to a highly doped contact region but to the lightly doped semiconductor material of the doped well, for example an HV well for the fabrication of high-voltage transistors.
Patent Number: 6,885,077 Issued on 04/26/2005 to Dietl, et al.
| Inventors:
|
Dietl; Josef (München, DE);
Taddiken; Hans (München, DE)
|
| Assignee:
|
Infineon Technologies AG (Munich, DE)
|
| Appl. No.:
|
619012 |
| Filed:
|
July 11, 2003 |
Foreign Application Priority Data
| Jan 11, 2001[DE] | 101 01 081 |
| Current U.S. Class: |
257/486; 257/109; 257/485 |
| Intern'l Class: |
H01L 027//09.5 |
| Field of Search: |
257/109,485-486
|
References Cited [Referenced By]
U.S. Patent Documents
| 3508125 | Apr., 1970 | Ertel et al.
| |
| 4292643 | Sep., 1981 | Kellner et al.
| |
| 4835580 | May., 1989 | Havemann et al.
| |
| 4871686 | Oct., 1989 | Davies.
| |
| 4874714 | Oct., 1989 | Eklund.
| |
| 4956688 | Sep., 1990 | Honma et al.
| |
| 5030930 | Jul., 1991 | Sugai.
| |
| 5200664 | Apr., 1993 | Sugai.
| |
| Foreign Patent Documents |
| 198 24 417 | Dec., 1998 | DE.
| |
| 1 539 784 | Feb., 1979 | GB.
| |
| 60022357 | Feb., 1985 | JP.
| |
| 2000174293 | Jun., 2000 | JP.
| |
Primary Examiner: Wilson; Allan R.
Attorney, Agent or Firm: Greenberg; Laurence A., Stemer; Werner H., Mayback; Gregory L.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation of coepending International Application No.
PCT/DE01/04906, filed Dec. 27, 2001, which designated the United States, and was
not published in English.
Claims
1. A Schottky diode, comprising:
a semiconductor body having a top side;
a weakly-conductive doped well formed in said semiconductor body;
a metallic layer on said well for forming a Schottky junction with lateral edges
delimiting said Schottky junction, said lateral edges being at least one of curved,
ramified, and rimose;
said metallic layer being at least one layer selected from the group of thin
layers consisting of:
a liner of a contact hole filling extending in a dielectric layer covering said
top side,
a metal silicide layer, and
a liner on said metal silicide layer; and
a contact region being highly doped for a low-impedance contact connection and
having a lateral boundary in said doped well, said lateral boundary having one
of a lattice-shaped structure, a finger-shaped structure, a comb-shaped structure,
an irregularly curved edge, a ramified edge, and a rimose edge.
2. The Schottky diode according to claim 1, wherein said lateral edges of said
Schottky junction and said lateral boundary of said highly doped contact region
facing said Schottky junction have a constant distance therebetween.
3. The Schottky diode according to claim 1, wherein said doped well is selected
from the group consisting of a high-voltage n-type well and a high-voltage p-type
well of a CMOS technology.
4. The Schottky diode according to claim 1, further comprising:
a further doped well containing said doped well and being doped for an opposite
sign of electrical conductivity than said doped well; and
a further highly doped contact region provided on said further doped well and
having the same sign of conductivity as said further doped well.
5. The Schottky diode according to claim 1, wherein said metal layer has a finger-shaped structure.
6. The Schottky diode according to claim 5, wherein said contact region is finger-shaped
and is intermeshed in a comb-shaped manner with the metal layer.
7. A Schottky diode, comprising:
a semiconductor body having a top side;
a dielectric layer covering said top side and having a contact hole formed therein;
a contact hole filling disposed in said contact hole;
a weakly-conductively doped well formed in said semiconductor body;
a metallic layer on said well for forming a Schottky junction with lateral edges
delimiting said Schottky junction, said lateral edges being at least one of curved,
ramified, and rimose, said metallic layer being selected from the group of layers
consisting of:
a liner of said contact hole filling,
a metal silicide layer, and
a liner on said metal silicide layer; and
a contact region being highly doped for a low-impedance contact connection and
having a lateral boundary in said doped well, said lateral boundary having one
of a lattice-shaped structure, a finger-shaped structure, a comb-like structure,
an irregularly curved edge, a ramified edge, and a rimose edge.
Description
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a Schottky diode that can be fabricated in the
context of a CMOS process.
If a metal layer is applied as a surface contact to a weakly electrically conductively
doped semiconductor material, a layer that is enriched or depleted with respect
to charge carriers forms in an edge region—adjacent the metal—of
the semiconductor material, depending on the type of materials used. In the case
of a depletion edge layer, this metal-semiconductor contact thus obtained has properties
that are comparable to a pn junction in semiconductor material. Such a diode-like
metal-semiconductor contact was investigated by W. Schottky and is therefore referred
to as a Schottky diode.
The Schottky diode has a reverse direction, characterized by high resistance,
and a forward direction, in which the Schottky diode can be operated depending
on the polarity of the applied voltage. Although the Schottky diode does not have
the blocking capability of a conventional diode with pn junction, it is nonetheless
distinguished by a small forward voltage. Therefore, there is a need for Schottky
diodes in CMOS technology as well, specifically in the application in high-frequency
circuits. However, it is difficult to fabricate Schottky diodes in the context
of a CMOS process because the available semiconductor layers are generally doped
too highly for a Schottky diode.
In the context of a CMOS process, for the fabrication of transistors, wells that
are doped complementarily to one another are fabricated in a usually p-conducting
semiconductor body or substrate. The n-doped wells are disposed in the semiconductor
material of the substrate, while the p-doped wells are disposed in the n-doped
wells. The volumes occupied by the doped wells extend in each case as far as the
top side of the substrate. At the upper edges of the interfaces of the wells, that
is to say at the top side of the substrate, insulating regions are formed by oxidation
of the semiconductor material or as so-called STI regions (shallow trench isolation),
and isolate the wells from one another at the top side of the substrate. For an
electrical connection of a well, a metal contact is applied, which is preferably
formed by a contact hole filling (via), that is to say a metallic filling of a
contact hole (via hole) etched out in a dielectric layer above the well. In order
to obtain a low-impedance junction between the metal of the contact and the semiconductor
material, the contact is applied to a highly doped contact region that is formed
in the well and has the same sign of the conductivity.
U.S. Pat. No. 4,874,714 to Eklund describes a method for fabricating a lateral
Schottky diode in the context of a CMOS process. A silicide-semiconductor junction
as Schottky diode on weakly n-doped semiconductor material is isolated from a low-impedance
metal-semiconductor contact by a spacer on the top side of the semiconductor body.
German published, non-prosecuted patent application DE 198 24 417 A1 describes
an integrable Schottky diode in which a low-impedance n-conducting layer is present
within an n-type well, which layer is provided with a Schottky contact and is surrounded
by a guard ring. The Schottky contact is configured as a ring around a central
pn junction. Japanese patent application JP 2000174293 reveals that titanium silicide
on semiconductor material is suitable for forming a Schottky diode.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a Schottky diode that
overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices
of this general type and that has an improved structure that can be realized without
significant additional outlay in the context of a CMOS process.
With the foregoing and other objects in view, there is provided, in accordance
with the invention, a Schottky diode including a semiconductor body, a weakly conductively
doped well, a thin metallic layer, a contact region, and a layer or a metallic
silicide layer. The semiconductor body or substrate has a top side. The weakly
conductively doped well is formed in the semiconductor body or substrate. The thin
metallic layer on the well is for forming a Schottky junction with lateral edges.
The lateral edges are at least one of long, greatly curved, irregularly curved,
ramified, and rimose. The contact region is highly doped for a low-impedance contact
connection and has a lateral boundary in the doped well and a lattice-shaped structure,
a finger-shaped structure, a comb-like structure, an irregularly curved edge, a
ramified edge, or a rimose edge. The Schottky diode also includes one of a liner
of a contact hole filling introduced into a contact hole in a dielectric layer
covering the top side, a metal silicide layer disposed between the liner 7
and the doped well 2, and a liner on the metal silicide layer.
In accordance with a further object of the invention, the lateral edges of the
Schottky junction and the lateral boundary of the highly doped contact region facing
the Schottky junction have a constant distance therebetween.
In accordance with a further object of the invention, the doped well is a high-voltage
n-type well or a high-voltage p-type well of a CMOS technology.
In accordance with a further object of the invention, the Schottky diode includes
a further doped well and a further highly doped contact region. The further doped
well contains the doped well and is doped for an opposite sign of electrical conductivity
than the doped well. The further highly doped contact region is provided on the
further doped well and has a same sign of conductivity as the further doped well.
In accordance with a further object of the invention, the Schottky diode includes
the metal silicide layer and has a finger-shaped structure.
In accordance with a further object of the invention, the contact region is finger-shaped
and is intermeshed in a comb-like manner with the metal silicide layer.
The Schottky diode according to the invention has a Schottky junction formed
by a thin metal layer and/or metal silicide layer at the top side of a doped well
in a semiconductor body or substrate. In contrast to the fabrication of low-impedance
contacts on CMOS wells as described in the introduction, a metal, to be precise
titanium in the preferred embodiment, is applied not to a highly doped contact
region but to the lightly doped semiconductor material of the doped well, for example
an HV well for the fabrication of high-voltage transistors.
The thin metal layer is preferably formed by a so-called liner which, in the
case of a contact hole filling, serves as a barrier against outdiffusion of the
semiconductor material into the metal and for improving the adhesion property of
the contact on the semiconductor material. This liner is present as a thin layer
on the semiconductor material or, in an alternative embodiment, on a likewise thin
metal silicide layer above the semiconductor material. The electrical connections
of the Schottky diode are formed by contact hole fillings on the top side of the
substrate or by leads in the substrate.
The operating properties of the Schottky diodes are essentially governed by the
current flow parallel to the surface of the substrate and are improved by fabricating
the lateral edges of the Schottky junction such that they are as long as possible,
in particular greatly curved: i.e. longer than a simple straight edge. The electrical
connection to the lightly doped well via the highly doped contact regions is preferably
effected in such a way that there is an essentially constant distance between the
edge of the Schottky junction formed by the liner or the metal silicide layer and
a lateral edge—facing the Schottky junction—of the highly doped contact
region. The metal silicide layer and the highly doped contact region may, in particular,
be patterned in a finger-shaped manner and be intermeshed with one another in a
comb-like manner.
The Schottky diode according to the invention is described in more detail below
using the examples illustrated in FIGS. 1 to 5.
Other features that are considered as characteristic for the invention are
set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in
a Schottky diode, it is nevertheless not intended to be limited to the details
shown, since various modifications and structural changes may be made therein without
departing from the spirit of the invention and within the scope and range of equivalents
of the claims.
The construction and method of operation of the invention, however, together
with additional objects and advantages thereof will be best understood from the
following description of specific embodiments when read in connection with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 2 are fragmentary, diagramatic sectional views of embodiments of
a Schottky diode according to the invention,
FIG. 2 being a section taken along line II—II in FIG. 3;
FIGS. 3 and 4 are fragmentary, plan views of the embodiment shown in FIG. 2,
FIG. 3 being a section taken along line III—III in FIG. 2; and
FIG. 5 is a fragmentary, plan view of a third embodiment of a Schottky diode.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the figures of the drawings in detail and first, particularly
to FIG. 1 thereof, there are shown doped wells
2,
3 that are formed
in a semiconductor body or substrate
1 and are disposed one in the other.
In this case, the substrate
1 is a p-conducting substrate, and the doped
wells are a lower high-voltage n-type well HVn and a high-voltage p-type well HVp
embedded therein, as are customary in the case of a CMOS process for the corresponding
components. For the electrical connection of the inner doped well
2, at
least one contact region
4 is present which is sufficiently highly doped,
p
+-doped in this example, for a low contact resistance.
In this case, the doped well
2 is disposed in a further doped well
3,
in which the semiconductor material is doped for the opposite sign of the conductivity,
in this case n-conducting. In this example, for an electrical connection, the further
doped well is provided with at least one highly doped contact region
5 having
the same sign of the conductivity (n
+-doped) and permits shielding of
the Schottky diode with respect to the substrate
1. The upper edges of the
doped wells
2,
3 are provided with insulating regions Ox. The substrate
1 in this case has a contact region
6 for electrical connection that
is p
+-doped.
In this example, the electrical connection of the Schottky diode is realized
by
contact hole fillings
8,
9 introduced into contact holes KL in a dielectric
layer
11 covering the top side
20 of the component. The contact hole
fillings presuppose the application of a thin metal layer as liner
7. This
liner
7 is present at the boundary between the contact hole fillings
8
and the doped well
2 as Schottky junction and between the contact hole fillings
9 and the highly doped contact regions
4,
5,
6 with
the function that is known per se from CMOS processes. To form the Schottky diode,
there may additionally be a metal silicide layer
10 between the liner
7
and the semiconductor material of the doped well
2.
FIG. 2 illustrates an alternative exemplary embodiment, in which the Schottky
diode is formed on a high-voltage n-type well HVn in a p-conducting substrate
1.
In this case, the contact regions
4 of the doped well
2 are doped
in a highly n-conducting manner. The configuration of the contact hole fillings
8 with which individual portions of the Schottky diode are formed is modified
here relative to the configuration in the exemplary embodiment in accordance with
FIG.
1. The reference symbols designate parts corresponding to those in
FIG.
1.
The lateral edge of the Schottky junction is preferably constructed to be as
long as possible. It is therefore favorable if, given the presence of the metal
silicide layer
10, the edge thereof is patterned to the greatest possible
extent in the layer plane. It is advantageous, moreover, if the lateral boundary
of the contact regions
4 disposed in the doped well
2 has a similar
structure, so that power is supplied to the Schottky junction all around at an
approximately equally small distance (d).
FIG. 3 illustrates a plan view of the structure in accordance with FIG. 2 in
the position marked there. It can be seen from this that, in this exemplary embodiment,
the contact region
4 is contiguous with the doped well
2 and forms
a lattice. Strips of the metal silicide layer
10 are disposed between the
portions of the lattice. The thin liners and contact hole fillings introduced into
the contact holes form contacts X on the contact region
4 and on the metal
silicide layer
10. The contacts on the metal silicide layer
10 form
individual portions of the Schottky diode.
FIG. 4 illustrates an exemplary embodiment with the structure of the exemplary
embodiment of FIG. 3, with the difference that the metal silicide layer
10
is omitted and the Schottky junction is formed by the liner on the lightly doped
semiconductor material.
FIG. 5 illustrates a further preferred structure of the Schottky diode according
to the invention in a plan view. In this case, the metal silicide layer
10
is patterned in a finger-shaped manner. This structure is applied and embedded
into the doped well
2 at the top side of the semiconductor body or substrate.
In this case, the highly doped contact region
4 is preferably likewise of
finger-shaped construction and intermeshed in a comb-like manner with the metal
silicide layer
1.
In this exemplary embodiment, a lead
18, which is part of the patterned
metal silicide layer
10, is preferably provided for the electrical connection.
Current can be fed into the contact region
4 within the semiconductor material
via a likewise highly doped further lead
19, which merges with the contact
region
4. The leads
18,
19 may be routed to another part of
the electronic circuit to which the Schottky diode belongs as a component, or,
in a similar manner to the exemplary embodiment in accordance with FIG. 1, be provided
with metallic contacts at the top side. In the latter case, the leads are preferably
provided with suitable extensions as contact areas on which the metallic contacts
are applied.
The distance between the edge of the metal silicide layer
10 and the contact
region
4 is approximately uniformly small at all points in the case of the
finger-shaped structure owing to the boundaries—running parallel to one
another—of the metal silicide layer
10 and of the contact region
4. The lateral edge of the metal silicide layer
10 and, preferably
at a small distance therefrom that is the same at all points, also the edge of
the associated contact region may instead be constructed such that they are irregularly
curved, ramified or rimose. If the metal silicide layer is absent, the same applies
correspondingly to the edge of the Schottky junction formed by the liner and the
contact hole filling on the semiconductor material of the doped well.
The edge of the junction acting as a Schottky diode should always have the longest
possible overall length. The metallic layer of the Schottky diode may be a thin
metal layer, in particular a liner of a contact hole filling, or a metal silicide
layer or a liner on a metal silicide layer. In all the exemplary embodiments, the
metal that is appropriate for the Schottky junction is preferentially titanium;
a metal silicide layer is titanium silicide in this case.
*
