Active solid-state devices (e.g. – transistors – solid-state diode – Schottky barrier – Specified materials
Reexamination Certificate
1998-12-28
2001-02-06
Wilczewski, Mary (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Schottky barrier
Specified materials
C438S575000, C438S581000, C438S583000
Reexamination Certificate
active
06184564
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to schottky diodes and, more specifically, to a novel process for their manufacture in which the barrier height is adjusted to a desired value.
Schottky diodes and processes for their manufacture are well known. For example, U.S. Pat. No. 4,206,540 and its divisional U.S. Pat. No. 4,408,216, as well as U.S. Pat. Nos. 4,398,344 and 4,849,199 and application Ser. No. 08/701,847, describe processes for the manufacture of a schottky diode in which a palladium and/or platinum silicide barrier is used as the schottky barrier to a silicon substrate.
An important characteristic of the schottky diode is its barrier height or turn-on voltage, sometimes called its knee voltage. Another important characteristic of a schottky diode is its hot reverse leakage current. Typically, low hot reverse leakage currents are desirable, such as five milliamperes per square millimeter at 125° C.
The known processes for the manufacture of a schottky diode typically attain a barrier height or knee voltage that is fixed and which cannot be changed by the respective process.
For example, a known process for the manufacture of a schottky diode includes a molybdenum to silicon barrier which allows for variations in the resistivity and thickness of epitaxial layer in the upper surface to obtain a targeted blocking voltage and to allow for variations in the die dimensions for targeted current and heat dissipation ranges. The knee voltage for this process is fixed at 0.30 volts.
Another known process for forming a schottky diode uses an ultra-thin palladium-diffused layer formed in the upper surface of the epitaxial layer and upon which a molybdenum film is applied. Such a process is described in U.S. Pat. Nos. 4,206,540 and 4,408,216. The process also allows for variations in the epitaxial layer of resistivity and thickness and attains a targeted blocking voltage with allowed variations and die dimensions for targeted current and heat dissipation ranges. The knee voltage attained using this process is similarly fixed at 0.36 volts.
Though a 0.30 volt or 0.36 volt knee voltage is suitable for many applications, other applications optimally require a schottky diode having other knee voltages and thus require design compromises to use one of the above schottky diodes.
It is therefore desirable to have a process for the manufacture of a schottky diode in which the barrier height can be tailored to the optimal level suitable for a respective application.
SUMMARY OF THE INVENTION
The present invention provides for a schottky diode having a palladium silicide on silicon barrier in which the barrier height is adjusted by adding a small quantity of another metal during the deposition of the palladium. The added metal raises or lowers the barrier height of the device.
In accordance with the invention, a schottky diode device and a process for its manufacture includes a silicon body. A metal silicide layer is formed atop at least a portion of the surface of the silicon body and forms a schottky barrier to the silicon body. The metal silicide layer is comprised of palladium and of a small quantity of another metal. The choice of added metal is determined based on a desired value of the barrier height of the schottky diode. A contact metal is formed atop the upper surface of the metal silicide layer.
The added metal may be either nickel or platinum, with the barrier height being greater than an ordinary palladium silicide device when the metal is platinum and less than an ordinary palladium silicide device when the metal is nickel.
In accordance with another aspect of the invention, a field oxide layer is grown or deposited atop a surface of an N− epitaxially deposited silicon layer formed atop a more heavily doped body portion. An annular window is opened in the field oxide layer, and a P+ guard ring is formed in the silicon layer in the annular window. A portion of the field oxide is located within a region enclosed by the annular window is removed. A barrier metal layer is deposited in the manner described above and is sintered with a portion of the silicon layer contacted thereby to form a silicide schottky barrier to the silicon located beneath the silicide. A contact metal is formed atop an upper surface of the metal silicide and silicon schottky barrier and is connected to the guard ring.
A major advantage of the invention is that a range of barrier heights and knee voltages are attained using one basic process in which only change is the choice of metal added to the palladium silicide to silicon junction to attain a barrier height that is less than or greater than that attained using a pure palladium silicide barrier.
Another advantage of the invention is that the junction is buried and is thus more forgiving of variations of the surface chemistry and processing. Thus, the process is very reproducible in a production environment.
As a further advantage, the process of the present invention produces a high yield of schottky diodes.
Moreover, when a higher barrier height device is formed using the present invention, the process need
15
not generate a corresponding higher forward voltage drop.
The higher barrier height device has, at higher current levels, a better dynamic impedance so that the device has a lower V
ON
than known devices.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.
REFERENCES:
patent: 4063964 (1977-12-01), Peressini et al.
patent: 4206540 (1980-06-01), Gould
patent: 4398344 (1983-08-01), Gould
patent: 4408216 (1983-10-01), Gould
patent: 4692991 (1987-09-01), Gould
patent: 4864378 (1989-09-01), Tsaur
patent: 5888891 (1999-03-01), Gould
Goodwin David
International Rectifier Corp.
Ostrolenk Faber Gerb & Soffen, LLP
Wilczewski Mary
LandOfFree
Schottky diode with adjusted barrier height and process for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Schottky diode with adjusted barrier height and process for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Schottky diode with adjusted barrier height and process for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2594494