Patent Application
20110108792
This disclosure relates generally to the field of phase change memory (PCM) fabrication.
Phase-change memory (PCM) is a type of non-volatile computer memory. PCM stores data in cells comprising a phase change material, which can be switched between two distinct states, i.e., crystalline and amorphous, with the application of heat. The phase change material may be deposited and patterned to form individual PCM cells. However, as PCM cells become smaller, it becomes difficult to pattern the cells using etching techniques such as reactive ion etching (RIE), as RIE may change the chemical makeup of the phase change material within a region of about 10 nm from the feature's edge, which may preclude following the scaling road map since the damaged region would constitute all the material in left in the cell for small dimensions.
Alternately, a small amount of phase change material may be deposited in a small hole, or via, to form an individual PCM cell. Chemical vapor deposition (CVD) and atomic layer deposition (ALD) methods may be used to deposit the phase change material. However, these methods may produce polycrystalline phase change material with crystals larger than the size of the via hole, which may not properly fill the via hole, or amorphous phase change material which may form voids and loose contact with an electrode located at the bottom of the via hole upon crystallization, as the phase change material may shrink as it changes from the amorphous state to the crystalline state.
In one aspect, a method for fabricating a phase change memory (PCM) cell includes forming a dielectric layer over an electrode, the electrode comprising an electrode material; forming a via hole in the dielectric layer such that the via hole extends down to the electrode; and growing a single crystal of a phase change material on the electrode in the via hole.
In one aspect, a phase change memory (PCM) cell includes an electrode comprising an electrode material; a dielectric layer over the electrode; a via hole in the dielectric layer; and a single crystal of a phase change material located in the via hole, the single crystal contacting the electrode at the bottom of the via hole.
In one aspect, a phase change memory (PCM) array comprising a plurality of cells, each cell including an electrode comprising an electrode material; a dielectric layer over the electrode; a via hole in the dielectric layer; and a single crystal of a phase change material located in the via hole, the single crystal contacting the electrode at the bottom of the via hole.
Additional features are realized through the techniques of the present exemplary embodiment. Other embodiments are described in detail herein and are considered a part of what is claimed. For a better understanding of the features of the exemplary embodiment, refer to the description and to the drawings.
Referring now to the drawings wherein like elements are numbered alike in the several FIGURES:
Embodiments of systems and methods for formation of single crystal phase change material are provided, with exemplary embodiments being discussed below in detail.
A single crystal of a phase change material may be grown on an electrode inside a via hole, filling the via hole and preventing void formation between the phase change material crystal and the electrode. The single crystal phase change material may be formed using CVD or ALD methods. The electrode material and the CVD/ALD precursors used to form the phase change material may be chosen such that the precursors used to form the phase change material react with the electrode material, and selective crystalline growth of the phase change material occurs directly on the electrode. The phase change material may also be selected such that the precursors do not react with a dielectric layer in which the via hole is formed. In some embodiments, the electrode may comprise tungsten (W) or titanium nitride (TiN), and the phase change material may comprise a combination of germanium (Ge), antimony (Sb), tellurium (Te) or selenium (Se).
A phase change material has a typical crystal size that will vary depending on the material and temperature on which the crystal is grown. In a via hole larger than the typical crystal size for a chosen phase change material, electrode material, and temperature, a poly crystal may be formed, which may not properly fill the via hole. However, in a via hole smaller than the typical crystal size for the chosen phase change material and electrode material, a single crystal may be formed. Therefore, the via hole may be formed such that it is smaller than a typical crystal size of the chosen phase change material when that phase change material is grown on the chosen electrode material at a chosen temperature. For instance, for Ge2Sb2Te5(GST) deposited by CVD inside a via of a 200 nm CD with a W bottom electrode, at about 300° C., the typical crystal size is about 80 nm. For similar conditions, the typical crystal size for GeTe is about 120 nm.
In block 102, dielectric layer 502 is formed by a conformal deposition, as shown in cross-section 500 of
In block 103, via holes 601 and via hole collars 602 are formed in dielectric layer 502, as shown in cross-section 600
In block 104, a phase change material 701 is deposited in the via holes 601, as shown in cross-section 700 of
In block 105, the surface comprising nitride 204 and polycrystalline phase change material 702 is polished, as is shown in cross-section 800 of
In block 106, oxide layers 1001 and electrical conductor layers 1002 are formed, as is shown in PCM cross-section 1000 of
The technical effects and benefits of exemplary embodiments include formation of relatively small PCM cells while preventing void formation between the phase change material and the electrodes that comprise the PCM cells within the switching region.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.
