Semiconductor device manufacturing: process – Coating of substrate containing semiconductor region or of... – Insulative material deposited upon semiconductive substrate
Reexamination Certificate
1999-04-01
2001-03-20
Booth, Richard (Department: 2812)
Semiconductor device manufacturing: process
Coating of substrate containing semiconductor region or of...
Insulative material deposited upon semiconductive substrate
C427S248100, C427S255391, C427S255394, C427S569000
Reexamination Certificate
active
06204204
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The invention relates in general to the field of chemical-vapor deposition of a material layer, and more particularly to chemical vapor deposition of tantalum-containing barrier layers with an organometallic precursor for microelectronic device applications such as semiconductor chip interconnect diffusion barrier and memory chip capacitor electrode layers.
BACKGROUND OF THE INVENTION
As semiconductor integrated circuit device feature sizes shrink, high-performance and reliable interconnect technology using copper-based metallization becomes increasingly important. However, copper interconnect technology faces a number of important process integration and manufacturing challenges. For instance, copper diffuses relatively rapidly through many materials, including both metals and dielectrics, particularly, at temperatures above ~300° C. In a typical device, copper diffusion into the inter-metal dielectric (IMD) such as silicon dioxide results in current leakage between adjacent metal lines (i.e., line-to-line leakage) and degradation of Inter-level dielectric (ILD) breakdown field. If copper diffuses through the IMD and the pre-metal dielectric (PMD) into the device transistor region, device performance and reliability degrade significantly and the device may become nonfunctional. In addition, copper is prone to corrosion and generally must be passivated to maintain its electrical conductivity characteristics.
Difficulties with the forming of copper interconnects have lead to the development of barrier materials that separate the copper metallization regions from vulnerable device regions. These barrier materials hinder the diffusion of copper into the vulnerable regions. Effective barrier materials generally must possess several characteristics. One important characteristic is a low diffusion coefficient for copper. Copper tends to diffuse during thermal cycling, such as thermal cycling experienced by a substrate during multilevel metallization processes, as well as during actual device operation under applied electric fields. Thus, barrier materials must generally remain thermally stable, including good structural stability so that the barrier remains effective during processing. Another important characteristic for a barrier material is that it generally must provide good adhesive interfaces for supporting deposition of copper on the barrier. Thus, the barrier material should have excellent adhesion to its underlying layer, such as oxide or low-k dielectric underlying layers, and provide excellent adhesion to a copper layer deposited on the barrier material. Further, the barrier should provide a good nucleation surface to promote <111> texture in the overlying copper layer such as overlying layers deposited by CVD, PVD, and/or electrochemical deposition (ECD).
Another important barrier characteristic is low electrical resistivity and via contact interface resistance. For instance, if a barrier is deposited between an underlying copper metal line and an overlying copper via plug, then the barrier should provide minimal increase of resistance for transmission of electric current between the underlying metal line and the via plug. As an example, amorphous barriers of refractory metals typically exhibit good diffusion barrier properties but also typically increase resistance between overlying and underlying copper layers in excess of acceptable levels. This increase is likely due to the relatively high resistivity of the barrier layer.
Another important characteristic of a barrier material is that its deposition should occur with good step coverage in high-aspect-ratio device features such as the dual-damascene trench and via structures. Barrier thickness on feature sidewall and bottom surfaces should be comparable to barrier thickness in the field, and barrier structure should be invariant with wafer topography. As an example of the importance of good step coverage, consider deposition of a barrier with a minimum thickness of 75 Å needed to prevent copper diffusion. If deposition of the barrier is accomplished with 25% step coverage, then a barrier thickness of 300 Å is needed to insure that a minimum thickness of 75 Å is accomplished throughout the interconnect structure. By comparison, if step coverage of the barrier is 75%, then a minimum barrier thickness of 75 Å can be accomplished with barrier deposition of a thickness of 100 Å over the field region.
In an attempt to meet the requirements for copper metallization barriers, a number of advanced barrier materials have been developed to supplant traditional barriers used for aluminum and tungsten metallization, such as TiN and TiW. For instance, Ta, TaN, NbN, WN
x
and ternary barriers such as TiSiN, TaSiN, WSiN, and WBN all support copper metallization with varying degrees of success. However, these materials are generally deposited with physical vapor deposition (PVD) which provides limited step and bottom coverage, putting the usefulness of these (PVD) barrier materials in doubt as device dimensions continue to shrink.
SUMMARY OF THE INVENTION
Therefore a need has arisen for an effective method for depositing a barrier material which provides improved step coverage of the material on device structures to achieve uniform, conformal, and symmetric deposition of the material in terms of barrier thickness and microstructure.
A further need exists for a method for depositing a barrier material with minimal electrical resistivity.
A further need exists for a method for depositing a barrier material which provides good adhesion to underlying and overlying material layers and which provides a good nucleation surface for supporting deposition of copper in an overlying copper layer.
In accordance with the present invention a method for depositing a refractory metal nitride barrier, such as a tantalum-based barrier, is provided that substantially reduces disadvantages and problems associated with previously developed methods for depositing interconnect metallization barrier materials. An organometallic precursor having a refractory metal, such as tantalum, titanium, molybdenum, niobium, and tungsten, is dissolved in an inert, low viscosity, high molecular weight, and low volatility solvent. The precursor solution is then vaporized and flowed over a substrate having device formations to allow thermal or reactive decomposition of the precursor for deposition of tantalum or a tantalum-containing barrier on the substrate.
In one embodiment, a precursor for depositing TaN, such as PEMAT or PDEAT sold by ATMI, is dissolved in an organic solvent having a generally heavy molecular weight, such as a molecular weight of greater than 90. Other characteristics of the organic solvent may include a boiling point substantially similar to the boiling point of the precursor, such as a boiling point at one atmosphere that falls within 50% of the precursor boiling point at one atmosphere. The ratio of solvent to precursor in the precursor solution may be adjusted to a level that establishes the viscosity of the precursor solution substantially to that of the solvent and further that increases the precursor solution liquid flow rate for a given deposition thickness by an order of magnitude. For example, a TaN precursor, such as PEMAT, is dissolved in a solvent, such as octane, to provide a 10% precursor solution. In addition to octane, other potentially useful solvents include heptane, decane and toluene. Substantial precursor dilution enhances flow rate control required for the deposition of thin barriers.
In another embodiment of the present invention, the electrical resistivity of the tantalum-containing barrier is reduced by flowing a reactive gas with the vaporized precursor solution over the substrate during deposition of the tantalum-containing barrier. The reducing gas may be energized via a plasma discharge. For example, reactive gases such as NH
3
, SiH
4
, metal hydrides and metal halides (eg., WF
6
) help to reduce the resistivity of a TaN barrier. These gases eliminate or
Bubber Randhir S.
Moslehi Mehrdad M.
Paranjpe Ajit P.
Velo Lino A.
Baker & Botts L.L.P.
Booth Richard
CVC Products Inc.
Pompey Ron
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