Overhanging Separator for Self-Defining Discontinuous Film

This invention is directed to semiconductor films and the manufacture of the same, more particularly to a self-defining discontinuous film, and most particularly to a capacitor employing a self-defining electrode.

Stacked capacitor structures using high-dielectric materials such as (Ba,Sr)TiO.sub.3 (BST) require noble metal electrodes, such as platinum, which are very difficult to pattern using conventional semiconductor processing such as reactive ion etching (RIE), ion beam etching, or chemical-mechanical polishing (CMP). Therefore there is a need for a capacitor structure which does not require a separate patterning step to define both electrodes.

For purposes of this invention, the term "oxide" layer is used generally to refer to a layer of silicon dioxide, and the silicon dioxide may be undoped or doped, for example, with boron, phosphorous, or both, to form for example borophosphosilicate glass (BPSG), and phosphosilicate glass (PSG). The silicon dioxide layers may be grown or deposited by conventional techniques.

It is therefore an object of the present invention to provide a capacitor structure which does not require a separate patterning step to define the electrodes.

It is a further object to provide a structure which is useful for forming a discontinuous film in one process step.

It is a further object to provide such a structure which is feasible for routine manufacturing.

In accordance with the above listed and other objects, a discontinuous film structure on a surface which may be a substrate, with an underlying layer on the surface having a first opening formed therein, a separator layer on the underlying layer having a second opening formed therein, and the second opening overlying the first opening such that the separator layer overhangs the underlying layer. A discontinuous-as-deposited film is formed on the separator layer, with the discontinuity substantially in register with the second opening. The structure is made into a stacked capacitor with the discontinuous film being the bottom electrode, by forming a continuous dielectric layer on the bottom electrode and a continuous top electrode layer on the dielectric layer.

These and other features, aspects, and advantages will be more readily apparent and better understood from the following detailed description of the invention, in which:

FIGS. 1a-1f are sectional views of the processing steps to manufacture the capacitor structure; all in accordance with the present invention.

The present invention is described herein in the context of a stacked capacitor merely as a specific example, and is not meant to limit applicability of the invention to such. Those skilled in the art will understand that the invention is broadly applicable to any structure or method in which it is desirable to have a self-defining discontinuous film structure with a separator layer overhanging an underlying layer and a discontinuous-as-deposited film formed on the separator layer.

In FIG. 1a, a substrate 100 with a contact region 102 has formed thereon a layer of oxide 104. Note that for certain applications of the capacitor structure to be formed, other circuit elements such as word line and bit line contacts may be fabricated prior to and below the capacitor, within substrate 100 or oxide 104. Oxide 104 has been patterned by forming a hole extending down to contact region 102. A conductive material, for example in-situ doped polysilicon, tungsten, titanium, or various silicides including tungsten and titanium silicides, was then deposited for example by low pressure chemical vapor deposition (LPCVD) followed by planarization to form plug 106. Note that contact area and plug 106 are not required for all applications of the structure.

In FIG. 1b, underlying layer 108 is deposited, followed by separator layer 110. Layers 108 and 110 are patterned to form an opening down to oxide 104, and underlying layer 108 is then recessed with respect to separator layer 110 for example by a selective wet etch in FIG. 1c. Underlying layer 108 may be formed from any material which is selectively etchable with respect to separator layer 110, oxide 104, and plug 106. For example, underlying layer 108 may be an insulator such as an oxide or nitride, with separator layer 110 a nitride or oxide.

With overhanging separator 110 complete, formation of the stacked capacitor can begin as shown in FIG. 1d. A bottom electrode layer 112 is deposited in a single process step for example by a sputter process, physical vapor depostion, or ion beam deposition which may be made more directional for example by collimation. Bottom electrode 112 may be for example Pt, Ir, Pd, or IrO.sub.2 and is preferably a noble metal or noble metal oxide for high dielectric constant capacitor applications. It is important to note that bottom electrode layer 112 is discontinuous, and that the discontinuity is caused by the arrangement of separator 110 and underlying layer 108. Layer 112 can also be characterized as non-patterned, or discontinuous-as-deposited. Even though some electrode material will be deposited within the opening, adjacent capacitors are prevented from shorting together. Thus the bottom electrode is self-forming or self-defining.

FIG. 1e shows the dimensions of the self-defining discontinuous film structure. Optimally, for a non-directional deposition process for layer 112, separator layer 110 overhangs underlying layer 108 by at least twice the thickness T of layer 112. Underlying layer 112 optimally has a thickness greater than or equal to the underhang, or 2T. For a directional process, these dimensions may be smaller, for example half the non-directional values.

The capacitor is completed in FIG. 1f by depositing a dielectric layer 114 followed by a top electrode layer 116. Layers 114 and 116 are deposited by sputtering or CVD, for example. Dielectric 114 is any suitable capacitor dielectric, and is preferably a high-dielectric constant material (i.e. with a dielectric constant over 20) such as (Ba,Sr)TiO.sub.3 (BST). Top electrode 116 is preferably from the same group of materials as bottom electrode 112.

In summary, a capacitor structure is provided which does not require a separate patterning step to define the bottom electrode. More generally, a structure is provided which is useful for forming a discontinuous film in one process step, and is thus feasible for routine semiconductor manufacturing.

While the invention has been described in terms of specific embodiments, it is evident in view of the foregoing description that numerous alternatives, modifications and variations will be apparent to those skilled in the art. Thus, the invention is intended to encompass all such alternatives, modifications and variations which fall within the scope and spirit of the invention and the appended claims.