Semiconductor device manufacturing: process – Coating of substrate containing semiconductor region or of... – Insulative material deposited upon semiconductive substrate
Reexamination Certificate
2000-08-17
2002-11-12
Everhart, Caridad (Department: 2825)
Semiconductor device manufacturing: process
Coating of substrate containing semiconductor region or of...
Insulative material deposited upon semiconductive substrate
C438S780000, C438S789000
Reexamination Certificate
active
06479404
ABSTRACT:
BACKGROUND OF THE INVENTION
TECHNICAL FIELD
The invention relates to semiconductor devices and components and, specifically, to methods for forming gate dielectrics for semiconductor devices and components.
ART BACKGROUND
Dielectric materials are a key aspect to the performance of semiconductor devices. As devices become smaller, and the need for higher performance becomes greater, the thickness of the dielectric layers in semiconductor devices is decreasing. At the same time, the need for dielectric materials with a dielectric constant greater than that of the most common dielectric material, SiO
2
, is increasing. Also, as the thickness of the dielectric layer in semiconductor devices decreases, the need for materials that do not leak charge even when the layer of the dielectric material is very thin (e.g. less than 100 Å) is increasing.
However, not all dielectric materials form acceptable, thin dielectric layers for use in semiconductor devices and components. Semiconductor devices have certain performance requirements such as efficiency, power of operation, etc. The properties of the layer of dielectric material directly effect device performance. For example, if the thin dielectric layer allows too much current to pass through it (this unwanted current is referred to as leakage current), then the resulting device or components will not meet the desired performance requirement. Since the leakage current through the gate dielectric of a MOSFET (metal-oxide-semiconductor-field-effect-transistor) indicates the insulation properties (resistance and reliability) of the dielectric, a gate dielectric layer through which the leakage current is too high indicates that the resistance and reliability of the dielectric layer is too low.
The interface state density between the dielectric layer and the underlying semiconductor interface also affects device performance. The interface state density degrades the current drive (current across the channel) and the reliability of MOSFETs and MIS(metal-insulator-semiconductor) FETs. Thus, if the interface state density is too high, then the resulting device or component will not meet the desired performance requirement.
Consequently dielectric materials that form thin dielectric layers with acceptable leakage characteristics and other properties are sought.
SUMMARY OF THE INVENTION
The present invention is directed to a process for fabricating a semiconductor device. In the process, a single crystal semiconductor substrate is provided. The substrate typically has structures such as device channel regions, and field oxide regions formed therein. The gate dielectric is then formed on the substrate. The gate dielectric is either a metal oxide, a metal silicate or both. A metal silicate material has the general structure (MO
2
)
x
(SiO
2
)
y
, wherein M is a metal, Si is silicon and O is oxygen. The relative mole fractions of these elements in the metal silicate are represented by x and y. Therefore, the sum of x and y is equal to 1. It is advantageous if the mole fraction of the metal oxide (x) is about 0.05 to about 0.8. It is advantageous if the mole fraction of the metal oxide is about 0.05 to about 0.5. The present invention contemplates metal oxides and metal silicates that contain one or more metals.
The dielectric materials of the present invention are advantageous because they are thermodynamically stable on silicon even when exposed to the high temperatures (i.e. over 800° C.) that are intrinsic to MOSFEIT fabrication. A stable material will maintain structural and chemical “integrity” because it does not react with the substrate. A structurally stable material does not undergo a phase change (e.g. from amorphous to polycrystalline) after formation. For example, Ta
2
O
5
is not suitable because it reacts with silicon at 700° C. to form a tantalum-silicon-oxygen interface layer. Such an interface layer is undesirable because its thickness and composition are not controllable. In the process of the present invention, the undesirable interface layer is not formed, and the metal oxide or metal silicate formed on the substrate is stable.
The gate dielectric is formed on a prepared silicon substrate surface. The prepared surface has either a very thin (i.e. less than about 1.5 nm) oxide or silicon oxynitride layer formed thereon, is a hydrogen-terminated surface, or, advantageously, a clean silicon surface. The cleaned surfaces are formed using techniques well known to one skilled in the art.
The dielectric layer is formed on the prepared surface of the silicon substrate. The deposition conditions are selected to favor the formation of the metal silicate or metal oxide over the formation of silicon dioxide (SiO
2
). Specifically, gaseous precursors that favor the formation of the metal silicate over silicon oxide are selected.
The gate dielectric layer is formed by chemical vapor deposition (CVD). In the CVD process, a first precursor (referred to as the inorganic precursor) is provided as the source for the metal component of the metal oxide or metal silicate. The first precursor has at least one metal-containing compound. If the dielectric layer is a metal silicate, the inorganic precursor has a silicon-containing compound in addition to a metal-containing compound. The silicon-containing compound is the source for silicon in the metal silicate. Thus, when the dielectric material is a metal silicate, it is contemplated that the first precursor is either one compound that is the source for both metal and silicon or two compounds (one being a metal source and the other being a silicon source). A second precursor (referred to as the organic precursor) is provided as the source for the oxygen in the dielectric layer.
The metal is any metal or combination of metals suited for forming a metal oxide or metal silicate dielectric layer. It is advantageous if the dielectric material has a dielectric constant of at least about 10. Examples of metals that form metal oxides and metal silicates with sufficiently high dielectric constants include zirconium, hafnium, lanthanum, yttrium, tantalum, aluminum, cerium and titanium. The metal-containing compound is selected to provide reaction kinetics that favor the formation of metal oxide or metal silicate on the silicon surface. Specifically, it is advantageous if the temperature at which the metal-containing compound decomposes is higher than the deposition temperature. Candidate metal compounds have decomposition temperatures at least above 200° C. It is advantageous if the precursors have a decomposition temperature above the deposition temperature so that the reaction by which the dielectric is formed is adequately controlled. Examples of suitable metal compounds include metal tetrachlorides (e.g. hafnium tetrachloride) and metal alkoxides (e.g. zirconium t-butoxide). For the metal alkoxides, it is advantageous if the alkyl moiety has no more than six carbon atoms to ensure that the metal alkoxide has a suitably high volatility.
The silicon containing compound, if present, is a silicon precursor such as tetraethyl orthosilicate (TEOS), silane or dichloro silane. Such precursors are well known to one skilled in the art and not discussed in detail herein. It is advantageous if the decomposition temperature of the silicon-containing compound is also above the deposition temperature.
As previously noted, the organic precursor is the source for oxygen. The organic precursor serves to catalyze a reaction with the inorganic precursor and with the surface of the silicon substrate to form the dielectric layer. However, the reaction does not favor the formation of SiO
2
. Thus, the present invention affords an advantage over prior art processes where SiO
2
is formed along with the metal oxide or metal silicate. This is because, in prior art processes, oxygen species such as O
2
favor the formation of SiO
2
. Examples of suitable organic precursors include alkyl oxides, alkyl phosphine oxides, alkyl sulfoxides and heterocyclic oxides. The alkyl moieties have 1-3 carbon atoms (e.g. methyl, ethyl and propyl
Steigerwald Michael
Wilk Glen David
Agere Systems Inc.
Botos Richard J.
Everhart Caridad
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