This invention relates, generally, to the field of semiconductor devices and more particularly to metal-insulator-metal (MIM) capacitors in semiconductor devices.
One type of capacitor used in integrated circuits is a planar metal-insulator-metal (MIM) capacitor. A planar MIM capacitor includes a MIM dielectric between a top plate electrode and a bottom plate electrode. MIM capacitors are commonly used in decoupling and bypass applications.
Generally, a planar MIM capacitor may be unreliable and subject to premature breakdown when integrated over copper using a typical backend damascene process integration because of defects in the inter-level dielectric (ILD) between the copper and the planar MIM capacitor. Defects arising from, for example, topography, roughness, grain instability, and oxidation of the copper have all been variably identified as causes of the reliability failures. To avoid such issues, the MIM layout has been excluded from directly overlaying copper structures. Unfortunately, this can be a severe penalty against available on-chip MIM area; thus limiting the capacitance which can be created for decoupling and bypass applications. Thus, a need exists to control defects in a MIM capacitor when formed over copper.
The present invention is illustrated by way of example and not by limitation 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.
Generally, the present invention provides, a method for forming a semiconductor device having a planar MIM capacitor. The planar MIM capacitor is formed over one or more metal interconnect layers. Each of the metal interconnect layers is isolated by an inter-level dielectric (ILD) layer. The capacitor has a bottom plate electrode and a top plate electrode. An insulator is formed between the plate electrodes. Prior to forming the first plate electrode a first insulating layer is deposited over the metal of an interconnect layer. The first insulating layer is planarized using a chemical mechanical polish (CMP) process in order to remove a portion of defects such as those transferred from the underlying metal. A second insulating layer is then deposited over the planarized first insulating layer to remove an additional portion of defects such as smaller defects caused by the CMP process. The bottom plate electrode is formed over the second insulating layer. An insulator which functions as the capacitor dielectric is formed over the bottom plate electrode. Finally a top plate electrode is formed over the insulator.
By planarizing the first insulating layer and depositing a second insulating layer over the first insulating layer, a surface with substantially fewer defects is formed over metal than exists in current practice. Thus, the planar MIM capacitor has reduced premature insulator breakdown due to defects and is therefore more reliable.
An ILD layer 14 is deposited on the semiconductor substrate 12. The ILD layer 14 can be any combination of layers of dielectric material formed by any process. For example, it may be silicon dioxide (SiO2), carbon-doped silicon oxide (e.g. SiCOH), tetraethyl orthosilicate (TEOS), boron/phosphorus doped TEOS (BPTEOS), silicon rich oxynitride (SRON), plasma-enhanced nitride (PEN), phosphosilicate glass (PSG), silicon carbon nitride (SiCN), or silicon rich oxide (SRO). Preferably, the ILD layer 14 is deposited to a thickness of between about 4000 to 10,000 Angstroms using plasma enhanced chemical vapor deposition (PECVD). A first conductive layer 16 is formed over the ILD 14 using physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), electroplating, the like, and combinations of the above. In a preferred embodiment a first conductive layer 16 is predominately copper. However, in other embodiments, the first conductive layer 16 can be aluminum or an aluminum-copper alloy. Also, the first conductive layer 16 may be formed of multiple layers of materials. For instance in copper inlaid metallization schemes, diffusion barriers comprising tantalum or tantalum nitride are often formed prior to forming a copper layer.
A second ILD layer 18 is formed on the conductive layer 16 followed by a second conductive layer 20 using the same materials as described above for the first ILD layer 14 and the first conductive layer 16. In the illustrated embodiment two interconnect layers are illustrated. In other embodiments, there may be as few as one interconnect layer or more than nine interconnect layers. The conductors of the interconnect layers are connected to each other and to the circuits on the substrate 12 as needed using contacts formed through vias, such as contacts 22 and 24.
Generally, in a planar MIM capacitor, the top plate electrode is smaller than bottom plate electrode. Therefore, the top plate electrode defines an active area for the capacitor, which should be as defect free as possible for high reliability. However, for relatively large planar MIM capacitors, the top and bottom plate electrodes are of similar size.
In accordance with the illustrated embodiment, large area planar MIM capacitors of approximately one square centimeter or more can be formed on an integrated circuit (IC). In one embodiment, the planar MIM capacitor may cover 50 percent or more of the integrated circuit, and in another embodiment, substantially the entire surface of the integrated circuit. Also, the planar MIM capacitor can have a relatively high capacitance density of more than 10 fF/μm2 using low, medium, or high K insulators deposited by conventional methods such as ALD, CVD, PVD, and the like.
The embodiment described as shown in the figures is a planar MIM capacitor formed just below the final interconnect layer. However, those skilled in the art will realize that the planar MIM capacitor may be formed anywhere above the substrate 12. For example, the planar MIM capacitor may be formed below the first interconnect layer, above the final interconnect layer, or anywhere in between. There are related structures, not explicitly shown in the figures, which are generally always present on-chip as essential parts of the IC interconnect circuitry.
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.
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 MIM capacitor could be formed using a damascene integration. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention.
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Number | Date | Country | |
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20060292815 A1 | Dec 2006 | US |