Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1997-12-24
2001-09-04
Mintel, William (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S310000, C257S532000, C257S533000, C257S534000, C257S535000, C438S393000, C438S394000, C438S395000, C438S396000
Reexamination Certificate
active
06285050
ABSTRACT:
FIELD OF THE INVENTION
The invention relates in general to maintenance of a stable power supply voltage on integrated circuits (IC's), including high-frequency microprocessors. In particular, the invention is directed to the addition of highly reliable thin film capacitors made within the wiring levels of the integrated circuit, and connected to the power supply wiring levels. The added thin film capacitors function as decoupling capacitors, and they act to minimize fluctuations in the power supply voltage level.
BACKGROUND OF THE INVENTION
In prior production integrated circuits, such as microprocessors, frequencies have been in the 100-400 megahertz (MHz) range. In general, those processors are densely populated by logic and memory devices, and there is little spare area available for other functions, e.g., decoupling capacitors. Prior art decoupling capacitors are implemented as Metal-Insulator-Semiconductor (MIS) structures integral to the silicon bulk, as described by Grzyb in U.S. Pat. No. 5,656,834. Historically, in the pre-gigahertz regime, MIS capacitors are added to dataflows as an afterthought, using whatever spare area is available after the main logic design is complete, wherever that spare area happens to be.
This haphazard historical approach to decoupling capacitance is sufficient for stabilizing the power supply voltage, Vdd, when the processor frequency is less than a few hundred MHz. In future designs done in the gigahertz (GHz) regime and beyond, more decoupling capacitance will be needed, and the proximity of that capacitance to the devices that are switching is much more important. That is, in the GHz regime, a haphazard approach to capacitance is not acceptable: a relatively high capacitance is required, and it must be present in a proximate and regular way throughout the logic and memory dataflows.
From a power perspective, an ideal IC would use 100% of its area for decoupling capacitance and current distribution, and none of its area for logic or memory. From a logic and memory perspective, an ideal IC would have 100% of its area used for logic and memory, and no area spent on the overhead of capacitors, which serve no function insofar as computation goes. In U.S. Pat. No. 5,366,931, Kim attempts to satisfy this contradiction using a structure in which the entire back side of the chip is used for decoupling capacitance.
SUMMARY OF THE INVENTION
The present invention describes a new approach. Specifically, the present invention is an integrated circuit chip comprising a silicon layer of integrated circuits, the requisite metal layers to provide the required interconnection, and a separate set of thin film (TF) layers above the silicon and metal layers. This is a Metal-Insulator-Metal (MIM) structure. The TF layers are used to implement TF capacitors that can be connected to the aforementioned metal layers in a manner that provides adequate capacitance, C, that is physically close to all logic and memory devices on the chip.
In addition, the present invention is a method of fabricating the aforementioned apparatus.
Note that TF layers can be made using materials that have large dielectric constants, hence C can be very large—much larger than the capacitance resulting from use of the residual silicon wafer level as was done previously. Also, C can be located mere microns (instead of millimeters) from the active transistors in such an IC, and so C can act as a localized supply of charge to stabilize Vdd. Finally, TF capacitors have no impact on the physical layout of the logic and memory dataflows, i.e., implementing TF decoupling capacitors greatly simplifies the physical layout because it can be done independently (or subsequently).
Decoupling capacitors made on a silicon wafer level have a Metal Insulator Semiconductor (MIS) structure, where the semiconductor is the silicon wafer itself, and the insulator is SiO2, which has a dielectric constant of about 3.9. When made in TF form in accordance with the present invention, C has the Metal Insulator Metal (MIM) structure, and the insulator can be a high dielectric constant thin film dielectric (TFD). The high dielectric constant TFD enables C to be of order 10-100 times larger than the MIS capacitance.
In addition, the insulator can comprise more than one layer made of different materials so as to create a highly reliable structure. In any capacitor, the capacitance is inversely proportional to the thickness of the insulator. Therefore, it is desirable to make the insulator as thin as possible to obtain a large capacitance. However, thin insulators are prone to developing short-circuits with age and use, and therefore are a cause for reliability concerns.
In the current invention, we describe thin insulators comprising a plurality of layers, at least one of which is used for its high dielectric property, and at least one of which is used because of its imperviousness to punch-through (short circuits).
Therefore, it is an object of the present invention to enable high density microprocessors to operate with very stable power supply voltage Vdd at frequencies in the gigahertz regime and greater. Specifically, this is done by using added decoupling capacitance fabricated within the thin film metal wire levels of the IC. This added decoupling capacitance has the Metal Insulator Metal (MIM) structure, and the insulator can be a high dielectric constant thin film dielectric (TFD), which enables very high capacitance per unit area.
Another object of the present invention is to place the MIM capacitors very close to the active circuits, e.g., within 1-10 microns in a preferred embodiment.
It is a further object of one embodiment of this invention to use all of the available Si substrate area for logic and memory elements so that no Si area is used for decoupling capacitors.
It is still another object of this invention to make the thin film decoupling capacitors in a very reliable structure by forming the capacitor dielectric in a plurality of layers (e.g., two or three or more layers), rather than a single layer. Thus, the thin film capacitors of the present invention combine two important features: reliability and a very high capacitance per unit area by means of high dielectric thin film layers.
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“MOCVD BaSrTio3for ≧1-Gbit DRAMS” Solid State Technology, 07/97, p. 235, S. M. Bilodeau et al.
Emma Philip George
Gates Stephen McConnell
Hwang Wei
F. Chau & Associates LLP
International Business Machines - Corporation
Mintel William
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