Ferroelectric capacitor and process for its manufacture

Details Ferroelectric capacitor and process for its manufacture Ferroelectric capacitor and process for its manufacture

2002-11-29

2004-08-31

Dinkins, Anthony (Department: 2831)

Electricity: electrical systems and devices

Electrostatic capacitors

Fixed capacitor

C361S306300, C361S321100, C361S321500, C361S302000, C361S303000

Reexamination Certificate

active

06785119

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method of patterning capacitors, more particularly for the fabrication of ferroelectric capacitors (FeRAMs) which find application in a number of devices including non-volatile memories and for high-k dynamic random access memories (DRAMs). Ferroelectic capacitors have the advantage that they are able to switch quickly and can be fabricated on a single VLSI chip. They also have the endurance of DRAM, the fast read/write times of SRAM and the non-volatility of flash.
BACKGROUND OF THE INVENTION
Conventionally, an FeRAM is manufactured by depositing a ferroelectric film, such as lead zirconate titanate (PZT), strontium bismuth tantalum oxide (SBT), bismuth lanthanum titanium oxide (BLT) or strontium ruthenium oxide (SRO) on a first, planar, electrode film, and forming a second electrode film over the ferroelectric layer. The second electrode layer and the ferroelectric film are then etched using a reactive ion etch method, after which the first electrode film is etched using a similar method. The result is a number of stacks comprising a first and second electrode film sandwiching the ferroelectric film.
After etching of the individual FeRAM capacitor structure, it is conventional to form an encapsulation (CAP) layer of Al
2
O
3
to prevent diffusion by H
2
and O
2
into the structure. This layer is formed by a sputtering process. The basic FeRAM elements are ideally formed with very deep sidewalls. The sputtering method of forming the CAP layer has the disadvantage of low coverage of steep sidewalls of FeRAM elements. Whilst this problem could be solved by forming the CAP layer by atomic layer deposition (ALD), it would require use of expensive specialist equipment.
It would be desirable to improve the uniformity of the sidewall coverage without using ALD.
SUMMARY OF THE INVENTION
The present invention forms a thicker Al
2
O
3
cap layer, preferably by sputtering and then etching back providing a more uniform coverage without the use of ALD.
According to a first aspect of the present invention a capacitor is formed using a method comprising the steps of:
forming a ferroelectric capacitor element on a substrate;
forming a CAP layer over the ferroelectric capacitor element; and
etching the CAP layer to a more uniform thickness.
For the avoidance of doubt, reference herein to “forming a ferrorelectric capacitor element on a substrate” includes the possibility of one or more intermediate layers being formed between the capacitor element and the substrate.
According to a second aspect of the present invention a capacitor comprises:
a substrate layer;
a matrix of ferroelectric capacitor elements including a first electrode layer substantially fixed relative to the substrate, a second electrode layer, and a ferroelectric layer sandwiched between the first and second electrode layers;
a shoulder layer extending from the substrate to the matrix; and
a CAP layer etched to have substantially constant thickness covering sides of the matrix extending beyond the substrate.
In most preferred embodiments, the CAP layer is Al
2
O
3
. Also, in most preferred embodiments, it is formed by sputtering. However, it could instead of Al
2
O
3
be SiN, Ti-Oxide, HPO2 or ZrO2, for example. The average thickness of the CAP layer on top of the device (above the second electrode) before etching is preferably from 10 nm to 100 nm, more preferably from 30 nm to 40 nm.
The CAP layer May for example be etched-back using a reactive ion etching (RIE) method. Such a method for etching electrically conductive and electrically insulating materials is well known.
Preferably, after etching, the average thickness of the CAP layer on top of the device is from 5 nm to 30 nm.
Further uniformity and integrity of the CAP layer structure can be obtained by depositing a further layer of the same material over the etched primary CAP layer, for example to an average thickness of from 5 nm to 30 nm, preferably from 10 to 15 nm.
According to a second aspect of the present invention, there is provided a capacitor formed in accordance with the method of the first aspect of the present invention.


REFERENCES:
patent: 6211542 (2001-04-01), Eastep et al.
patent: 6492673 (2002-12-01), Fox et al.

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