Patent Application
20080179689
Disclosed embodiments herein relate generally to the manufacture of semiconductor devices, and more particularly to semiconductor devices and related methods of manufacturing having a protective layer for decreased silicide stringer or encroachment during metal salicide formation.
As technology in products and equipment continues to become more complex, the use of integrated circuit (IC) devices in these products and equipment is basically essential. In addition, consumers and manufacturers alike have continued to desire smaller product size, which requires a continued decrease in overall IC chip size. As a result, the large-scale integration of circuit components, such as transistors and capacitors, has become a necessity for decreased overall size, but increased device performance. Thus, semiconductor device improvements have been largely accomplished by reducing device feature size to the point where currently micron and sub-micron device features are being used, and predictions for future device sizes do not foresee an end to the trend of ever smaller and denser devices.
Along with desired reductions in device size, and thus increased chip densities, comes a required reduction in device power consumption that imposes the use of decreased device feature lengths. This is because, as a general rule, device speed varies inversely with device feature length, while power consumption increases approximately with the square of the device feature length. Thus, feature sizes currently being employed are in the micron and sub-micron or 0.13 um range where it is expected that the feature size of 0.65 nm will become a common in the near future.
Field Effect Transistors (FETs) are at this time used extensively in Ultra Large-Scale Integration (ULSI) applications. FETs are formed using gate electrodes, usually made of polysilicon, over a gate oxide, and adjacent source/drain regions surrounding the gate oxide to define the channel of the device. Silicides are typically employed in the source/drain regions, and over the gate electrode, to improve the electrical connection between the parts of the transistor and metal interconnects dispersed throughout the IC chip to connect circuit components. These contact pads are typically comprised of a metal silicide formed by reacting a deposited metal with the silicon it is deposited over.
Metal silicide has been employed to provide the electrical contact between parts of the semiconductor devices and these metal interconnects primarily because of the reduced contact resistance and sheet resistance provided by metal silicide. Self-Aligned metal silicide contact structures, commonly referred to as “salicide” structures, are often used in the formation of Metal Oxide Semiconductor (MOS) transistor structures to minimize contact resistance. In one known salicide process for a MOS transistor, source and drain regions are formed aligned to a gate electrode structure and/or any sidewall spacers that may be present. A blanket metal layer is deposited so that silicon, at the upper surface of source, drain and gate regions, is in contact with the metal. The wafer is then heated (“annealed”) to a temperature to undergo a reaction and form a metal silicide. The sidewall spacers serve to prevent bridging of the gate silicide region with either the source or drain silicide regions. When no silicon is available from the sidewall spacers or other areas of the device structure, no silicide forms thereon. After the metal silicide is formed, the unreacted metal is then removed, and regions of metal silicide are revealed. After removal of the metal not reacted to form a silicide, a second, higher temperature silicide anneal step is often employed to stabilize the silicide regions formed and to provide the lowest possible silicide resistivity.
However, as device geometries become smaller, the separation (spacing) between devices also becomes smaller. As a result, salicide “stringers” become an increasingly serious problem. Specifically, stringers can form at the corner of the sidewall spacers and the salicide source/drain areas if RF sputtering is employed in the pre-salicidation cleaning process, and can detrimentally affect device performance. For example, as active regions are formed closer together to improve device spacing, and thus the isolation regions, such as shallow trench isolation (STI) structures, are made more compact (e.g., less than 0.2 microns wide), silicide stringers from adjacent source/drain regions might be connected at the STI structures, and therefore cause salicide short-circuits between adjacent devices. While alternative pre-clean methods may be employed, such processes often require expensive, dedicated equipment. While some process alterations or optimization can help alleviate the stringer problem, often stringer formation cannot be eliminated through such means, and yield loss results from electrical problems caused by such stringers.
Another problem with conventional processes is that such semiconductor device structures are vulnerable to silicide “encroachment.” More specifically, silicide encroachment can result in short-circuiting between source/drain regions and the well. Additionally, encroachment can occur under the sidewall spacers and into the spacer oxide liner over the source/drain and channel regions, particularly when an oxide undercut at the base of the sidewall spacers and/or on top of the STI are formed before salicide formation. Regardless of how a silicide stringer or encroachment occurs, the result is typically leakage in corresponding areas of the semiconductor device(s), and often short-circuiting of the device(s) as discussed above. Accordingly, what is needed are techniques for forming salicide regions on semiconductor devices, while reducing or eliminating silicide stringer and/or encroachment.
Disclosed herein are various embodiments of techniques for preventing silicide stringer or encroachment formation during metal salicide formation in semiconductor devices. The disclosed technique involves depositing a protective layer, such as a nitride or other dielectric layer, over areas of the semiconductor device where metal silicide formation is not desired because such formation detrimentally affects device performance. For example, excess Si surface/residue exposed outside the dielectric layer coverage due to spacer liner oxide undercut or STI loss during process, is protected from reacting with metal deposited to form metal silicide in certain areas of the device. As a result, silicide stringers or encroachment in undesired areas is reduced or eliminated by the protective layer when the salicidation occurs.
In one embodiment, a method of manufacturing a semiconductor device in accordance with the disclosed techniques includes forming device features on a semiconductor substrate, depositing a protective layer over the device features, and removing portions of the protective layer to expose at least one of the device features while leaving the remaining device features covered. In addition, such a method also includes depositing a metal layer over the at least one exposed device feature and remaining portions of the protective layer, and forming a metal silicide in the at least one exposed device feature by reacting portions of the metal layer with silicon in the exposed device feature. During metal silicide formation, the protective layer prevents portions of the metal layer from reacting with silicon in the covered device features. In addition, this embodiment of the method also includes removing non-reacted portions of the metal layer after silicide formation.
In another embodiment, a semiconductor device constructed according to the disclosed principles comprises device features formed on a semiconductor substrate, and a protective layer exposing at least one of the device features and covering the remaining device features. In addition, such a semiconductor device comprises metal silicide formed in the at least one exposed device feature by silicon located therein reacting with a deposited metal, wherein the protective layer isolates the covered device features from the deposited metal. The protective layer prevents any silicon present in the covered device features from reacting with the deposited metal, and thus keeps metal silicide from forming in those protected areas.
For a more complete understanding of the principles disclosed herein, and the advantages thereof, embodiments are illustrated by way of example in the following figures in which like reference numbers indicate similar parts, and in which:
In the illustrated embodiment of
The device 100 also includes a gate oxide 160 formed under the gate electrode 130 and over the channel region defined between the LDDs 150 (only one LDD 150 is shown). In addition, dielectric (e.g., nitride or oxynitride) sidewall spacers 170 (only one is illustrated) have been formed on the sides of the gate electrode 130, to electrically insulate the gate electrode 130 during device operation. Then, in accordance with the disclosed principles, a protective dielectric layer 180 is shown deposited over the entire structure of the device 100, as well as over the STI structure 120. In this embodiment, the protective layer 180 is a nitride layer 180 that has been deposited over the area before salicide regions (discussed below) have been formed on the device 100. In other embodiments, however, the protective layer 180 may be an oxide and/or oxynitride layer.
After depositing the protective layer 180, a dry etch may be performed to remove specific portions of the protective layer 180 and thus expose areas S1, S2 of the device 100, which will have salicide regions formed therein. To etch the protective layer 180, any conventional technique where the etching parameters may be carefully controlled may be employed. More specifically, vertical and horizontal control of the dry etch process is carefully managed so that openings in only the desired areas of the protective layer 180 are formed. Regardless of the type of removal technique employed, portions of the protective layer 180 are left in (and therefore protecting) specific areas of the device 100 that are often subject to silicide stringer formation and/or encroachment. This protection is discussed in further detail below, with reference to the formation of the salicide regions. Moreover, although the remaining portions 180a of the protective layer 180 are illustrated as block-shaped, it should be understood that these portions 180a may take on any shape, while still providing the protection described herein.
As in conventional salicide formation techniques, the metal layer 190 is blanket deposited over the source/drain region 140, the gate electrode 130, and also on the remaining portions 180a of the protective layer 180. A first rapid thermal anneal (RTA), as indicated by arrows A1, is then performed on the device 100 to cause the deposited metal layer 190 to react with silicon molecules present in areas in contact with the metal layer 190 in order to form metal silicide. In exemplary embodiments, the first RTA is performed at a temperature of about 200° C.-400° C. for a time period of about a few seconds to a few minutes. Of course, other temperatures and time periods may also be employed that are beneficial to the formation of metal silicide on the device 100.
In addition, in accordance with the disclosed principles, the portions 180a of the protective layer 180 that remain over certain portions of the device 100 structure after the dry etch performed above serve to protect areas of the structure that typically suffer from silicide stringers and/or silicide encroachment occurring during salicide formation that may affect device performance. One specific area protected by the portions 180a is area 210 of the substrate 110 that is exposed at the perimeter of the recessed STI structure 120.
The typical processing steps results in the corner of the STI structure 120 becoming recessed below the top surface of the substrate 110. In conventional approaches, when the salicide regions 195 are formed, the deposited metal 190 intended to react with the silicon in the desired areas (e.g., the source/drain regions 140 and the gate electrode 130) may inadvertently react with these areas 210 of the substrate 110, thus allowing the excess metal silicide to form over the STI corner 120 (deep salicide formation or encroachment). Such encroachment occurs when metal used to form the metal silicide diffuses from the top of STI to the exposed Si corner. This might cause junction leak and device failure.
Another area of the device 100 structure that may be protected by the remaining portions 180a of the protective layer 180 illustrated in
However, in accordance with the principles disclosed herein, the remaining portions 180a of the protective layer 180 proximate to this area 220 of the device 100 serves to resist or prevent such silicide encroachment and/or stringer issues. Thus, to address the problems of stringers and encroachment, these portions 180a are left protecting this area 220 so that silicon will not inadvertently react with the metal layer 190. Furthermore, if an oxide undercut is performed on the device 100, the remaining protective portions 180a serve to “fill in” the undercut portions in order to reduce or prevent exposure of portions of the substrate 110 in the area 220 near the corner of the sidewall spacer 170, and thus reduce or prevent metal diffusion under the sidewall spacer 170 during the salicidation process.
After etching portions of the metal layer 190 that have not reacted with silicon-based device features, a second RTA step may be performed, a shown by arrows A2. The second RTA step finalizes the formation of the salicide pads 195 in the device 100 structure and stabilizes the metal silicide therein. As shown in
While various embodiments of the disclosed technique have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the invention(s) should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with any claims and their equivalents issuing from this disclosure. Furthermore, the above advantages and features are provided in described embodiments, but shall not limit the application of such issued claims to processes and structures accomplishing any or all of the above advantages.
Additionally, the section headings herein are provided for consistency with the suggestions under 37 CFR 1.77 or otherwise to provide organizational cues. These headings shall not limit or characterize the invention(s) set out in any claims that may issue from this disclosure. Specifically and by way of example, although the headings refer to a “Technical Field,” such claims should not be limited by the language chosen under this heading to describe the so-called technical field. Further, a description of a technology in the “Background” is not to be construed as an admission that technology is prior art to any invention(s) in this disclosure. Neither is the “Brief Summary” to be considered as a characterization of the invention(s) set forth in issued claims. Furthermore, any reference in this disclosure to “invention” in the singular should not be used to argue that there is only a single point of novelty in this disclosure. Multiple inventions may be set forth according to the limitations of the multiple claims issuing from this disclosure, and such claims accordingly define the invention(s), and their equivalents, that are protected thereby. In all instances, the scope of such claims shall be considered on their own merits in light of this disclosure, but should not be constrained by the headings set forth herein.
