The invention is in the field of semiconductor fabrication processes and, more particularly, semiconductor fabrication processes that employ silicide processing.
The formation of metal-silicides on semiconductor regions of a metal oxide semiconductor (MOS) transistors is well known. Typically, a metal layer is deposited over a wafer topography that includes exposed silicon regions and dielectric regions. The wafer is then heated in an inert ambient. Where the metal layer is in contact with silicon, the metal reacts with the silicon to form a silicide (e.g., nickel silicide or cobalt silicide). Where the metal contacts dielectric, no reaction occurs. The unreacted metal portions are then selectively removed with an etch process.
Silicides are usually formed on the source/drain regions and the polysilicon gate electrode of a transistor. In many cases, the fabrication process includes forming extension spacers on sidewalls of the gate electrode. The extension spacers smooth the resulting topography and provide a means for displacing the source/drain implant from the edges of the transistor gate electrodes, which is desirable in short channel devices. Extension spacers are frequently fabricated from silicon nitride. A liner oxide is usually formed before depositing the silicon nitride to provide a stress buffer between the silicon nitride and the silicon substrate. When exposed portions of the liner oxide (those portions not underlying the extension spacer) are removed prior to depositing the silicide metal, concave notches may form in exposed ends of the liner oxide. During subsequent processing, these notched ends can promote the formation of unintended silicide “strings” (also referred to herein as silicide stringers) that can provide a short circuit or conductive path between neighboring device elements. It would be desirable to implement a silicide process that suppressed or otherwise prevented the formation of silicide stringers without substantially altering the well known silicide processing sequence.
The present invention is illustrated by way of example and not limited by the accompanying figures, in which like references indicate similar elements, and in which:
Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve the understanding of the embodiments of the present invention.
Disclosed herein is a semiconductor fabrication process that prevents or removes silicide stringers that may occur when an extension spacer is formed on a liner oxide. In such processes, portions of the liner oxide overlying source/drain regions and gate electrode regions are exposed following extension spacer formation. To enable a subsequent silicide process, these portions of the liner oxide are dipped off in HF or otherwise removed. Removing exposed portions of the liner oxide may form notched extremities. Silicon may accumulate in these extremity notches during subsequent processing. The accumulated silicon may then be converted to conductive silicide that forms a conductive stringer traversing the length of the liner oxide extremity notch. Preventing the formation of these notches is achieved by etching back the extension spacer after silicide formation. The spacer etch back etches the notched extremity sufficiently to expose the stringer. Additional processing is then performed to remove the stringer. This stringer removal processing may include, as an example, bombarding the notched extremity with an inert species such as argon.
Turning now to the drawings,
A gate module 110 has been formed overlying semiconductor layer 104. Gate module 110 includes a conductive gate electrode 112 over a gate dielectric layer 114. A liner dielectric layer 116 covers an upper surface of semiconductor layer 104 and gate electrode 112. Extension spacers 108 have been formed adjacent sidewalls of gate electrode 112. Extension spacers 108 are in contact with liner dielectric layer 116.
Gate electrode 112 is preferably a heavily doped polycrystalline silicon (polysilicon) and gate dielectric 114 is preferably a thermally formed silicon dioxide. In other embodiments, gate electrode 112 may include a metal portion of TiN, TaSiN, tungsten, and other suitable metal materials. In some embodiment, gate dielectric 112 may be a high k dielectric (a dielectric having a dielectric constant greater than approximately 4.0). Suitable high k materials include metal oxide compounds such as hafnium oxide as well as suitable metal silicate, and metal nitride compounds.
Liner dielectric layer 116 is preferably a deposited silicon oxide film and extension spacers 108 are preferably silicon nitride. In other embodiments, however, alternative dielectric materials may be used for liner dielectric layer 116 and extension spacers 108. Source/drain regions, extension regions, halo implant regions, lightly doped drain regions, and the like may be formed in semiconductor layer 114 through conventional ion implantation processing. These implanted impurity distributions are omitted from the drawings for the sake of clarity.
The cross section of
Exposing areas of semiconductor layer 104 and gate electrode 112 requires removing exposed portions of liner dielectric layer 116 (i.e., portions not covered by spacer 108). For embodiments in which liner dielectric layer 116 is a silicon oxide layer, the preferred technique for removing exposed portions of liner dielectric layer 116 is dipping wafer 101 in an HF solution according to well known processing. The removal of exposed portions of liner dielectric layer results in the formation of a liner dielectric structure 126 (
Wet etching the exposed portions of liner dielectric layer 116 may unintentionally and undesirably etch portions of dielectric 126. The detail view of
Referring now to
In the preferred implementation, metal layer 130 is deposited with a physical vapor deposition (PVD) and, more specifically, with a radio frequency (RF) sputter deposition process. RF sputtering is well known technique for depositing a variety of thin films, especially metal and transition metal films. RF sputtering processes typically include a pre-clean step in which the wafer is cleaned by sputter etching and/or plasma etching. If a sputter clean is used, silicon atoms in semiconductor layer 104 may be sputtered (dislodged) and some of these sputtered atoms in the vicinity of extremity notch 120 may be unintentionally “deposited” on the sidewalls within notch 120 and thereby form an unintended silicon stringer 122, which is depicted in the detail view of
Referring to
The fabrication processing described herein includes processing to remove silicide stringer 132 from wafer 101. The stringer removal processing may include etch processing, sputter or other PVD processing, or a combination thereof. Referring to
In the embodiment depicted in
In an embodiment exemplified by the detail view of
In the depicted embodiment, the spacer etchback process produces a convex profile 127 at the edge of the resultant dielectric structure 126. To achieve this result, the preferred etchback process is a dry etch process that prevents the formation of a new concave surface during the etch back. If the etchback process produced a concave surface, it may be possible for sputtered silicide to get re-trapped inside that concavity thereby resulting in the formation of stringers that the etchback was originally intended to eliminate.
Referring to
In the foregoing specification, the invention has been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. For example, the depicted embodiment uses a semiconductor on insulator (SOI) wafer 101. In other embodiments, however, conventional silicon bulk wafers are compatible with the stringer removal processing described. As another example, transistor 150 as depicted in the
Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or element of any or all the claims. As used herein, the terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
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6541328 | Whang et al. | Apr 2003 | B2 |
6767777 | Joyner et al. | Jul 2004 | B2 |
20040211992 | Joyner et al. | Oct 2004 | A1 |
20070224808 | Chang et al. | Sep 2007 | A1 |
Number | Date | Country | |
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20090093108 A1 | Apr 2009 | US |
Number | Date | Country | |
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Parent | 11226826 | Sep 2005 | US |
Child | 12244413 | US |