US 20050074933 A1
A lower electrode may be covered by a protective film to reduce the exposure of the lower electrode to subsequent processing steps or the open environment. As a result, materials that may have advantageous properties as lower electrodes may be utilized despite the fact that they may be sensitive to subsequent processing steps or the open environment.
1. A method comprising:
forming a lower electrode;
covering the lower electrode with a protective layer such that said protective layer is formed directly over said lower electrode; and
forming a phase change material over said lower electrode.
2. The method of
defining a singulated opening;
forming a cup-shaped phase change material in said opening; and
forming a thermally insulating material in the cup-shaped phase change material.
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This invention relates generally to electronic memories and particularly to electronic memories that use phase change material.
Phase change materials may exhibit at least two different states. The states may be called the amorphous and crystalline states. Transitions between these states may be selectively initiated. The states may be distinguished because the amorphous state generally exhibits higher resistivity than the crystalline state. The amorphous state involves a more disordered atomic structure. Generally any phase change material may be utilized. In some embodiments, however, thin-film chalcogenide alloy materials may be particularly suitable.
The phase change may be induced reversibly. Therefore, the memory may change from the amorphous to the crystalline state and may revert back to the amorphous state thereafter, or vice versa, in response to temperature changes. In effect, each memory cell may be thought of as a programmable resistor, which reversibly changes between higher and lower resistance states. The phase change may be induced by resistive heating.
In some embodiments, the cell may have a large number of states. That is, because each state may be distinguished by its resistance, a number of resistance determined states may be possible, allowing the storage of multiple bits of data in a single cell.
A variety of phase change alloys are known. Generally, chalcogenide alloys contain one or more elements from Column VI of the periodic table. One particularly suitable group of alloys is the GeSbTe alloys.
A phase change material may be formed within a passage or pore through an insulator. The phase change material may be coupled to upper and lower electrodes on either end of the pore.
One problem that arises with existing lower electrodes is that some suitable lower electrode materials that have advantageous properties cannot be used because they may be adversely affected by necessary subsequent processing steps or upon exposure to the open environment. Among the advantageous attributes of the lower electrode material is good electrical contact to phase change materials and effective resistive heating to promote more efficient phase change programming.
Thus, there is a need for better designs for phase change memories that may be manufactured using more advantageous techniques.
A pore may be formed above the lower electrode 14 between the lower electrode 14 and the top electrode 28. The pore may include a tapered, cup-shaped phase change material 18 covered by a similarly shaped barrier layer 20. A fill insulator 22 may fill the central portion of the barrier 20 and the phase change material 18. An etch stop layer 24 underlies a barrier layer 26 that in turn underlies the top electrode 28.
A technique for forming the memory cells 10, according to one embodiment, may involve initially forming the lower electrodes 14 on a substrate 12 using conventional patterning and deposition techniques, as shown in
The lower electrode 14 may be formed over the base layer 42 if utilized. Finally, a protective film 40 may be formed over the electrode 14. The lower electrode 14 may be any of a variety of conductive materials including carbon. The protective film 40 may be chosen from a variety of insulating materials including SiO2, Si3N4 or Al2O3. In general, the protective material may also be any material in the form SixNy, where x and y represent the stoichiometry and an advantageous stoichiometry is where x is equal to three and y is equal to four.
The base layer 42, lower electrode 14 and a protective film 40 may be formed sequentially. Advantageously, the lower electrode 14 and the protective film 40 are formed in situ, for example in the same deposition chamber without venting back to atmosphere.
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The imposition of the insulator 22 over the phase change material 18 reduces upward thermal losses. Thermal losses may result in the need for greater programming currents to obtain the same programming effect.
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In accordance with some embodiments of the present invention, a wider selection of lower electrode 14 material is made available by providing a technique for limiting the exposure of the lower electrode 14 to other process steps or to the open environment. As a result, a purer, less contaminated lower electrode 14 may be achieved in some embodiments, achieving more consistent, predictable device operation.
While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.