Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2001-11-29
2004-08-24
Pham, Long (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S629000
Reexamination Certificate
active
06781184
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an integrated circuit having a hydrogen barrier layer to protect elements containing metal oxide materials from degradation in integrated processes utilizing or producing hydrogen, and in particular to specific materials for use in such barrier layers, specific structures for such barrier layers, and processes for making such materials and structures.
2. Statement of the Problem
Metal oxides have been used in integrated circuits, particularly memories. For example, ferroelectric compounds possess favorable characteristics for use in nonvolatile integrated circuit memories. See U.S. Pat. No. 5,046,043 issued Sep. 3, 1991 to Miller et al. A ferroelectric device, such as a capacitor, is useful as a nonvolatile memory when it possesses desired electronic characteristics, such as high residual polarization, good coercive field, high fatigue resistance, and low leakage current. Lead-containing ABO
3
-type ferroelectric oxides such as PZT (lead titanate zirconate) and PLZT (lanthanum lead titanate zirconate) have been studied for practical use in integrated circuits. Layered superlattice material oxides have also been studied for use in integrated circuits. See U.S. Pat. No. 5,434,102 issued Jul. 18, 1995 to Watanabe et al. Layered superlattice material compounds exhibit characteristics in ferroelectric memories that are orders of magnitude superior to those of PZT and PLZT compounds and also exhibit dielectric constants that make them useful for DRAMS. See, for example, U.S. Pat. No. 5,519,234 issued May 21, 1996 to Paz de Araujo et al. Integrated circuit devices containing ferroelectric elements are currently being manufactured. Nevertheless, the persistent problem of hydrogen degradation during the manufacturing process hinders the economical production in commercial quantities of ferroelectric memories and other IC devices using the layered superlattice material and other metal oxide compounds with the desired electronic characteristics.
A typical ferroelectric memory device in an integrated circuit contains a semiconductor substrate and a metal-oxide semiconductor field-effect transistor (MOSFET) in electrical contact with a ferroelectric device, usually a ferroelectric capacitor. A ferroelectric capacitor typically contains a thin film containing ferroelectric metal oxide located between a first, bottom electrode and a second, top electrode, the electrodes typically containing platinum. During manufacture of the circuit, the MOSFET is subjected to conditions causing defects in the silicon substrate. For example, the CMOS/MOSFET manufacturing process usually includes high energy steps, such as ion-mill etching and plasma etching. Defects also arise during heat treatment for crystallization of the layered superlattice material at relatively high temperatures, often in the range of from 500° C. to 900° C. As a result, numerous defects are generated in the single crystal structure of the semiconductor silicon substrate, leading to deterioration in the electronic characteristics of the MOSFET.
To restore the silicon properties of the CMOS/ MOSFET, the manufacturing process typically includes a hydrogen annealing step in which defects, such as dangling bonds, are eliminated by utilizing the reducing property of hydrogen. Various techniques have been developed to effect the hydrogen annealing, such as a forming-gas anneal (“FGA”). Conventionally, FGA treatments are conducted under ambient conditions in a H
2
—N
2
gas mixture between 350° C. and 550° C., typically around 400° C. to 450° C., for a time period of about 30 minutes. In addition, the CMOS/MOSFET manufacturing process requires other fabrication steps that expose the integrated circuit to hydrogen, often at elevated temperatures, such as hydrogen-rich plasma CVD processes for depositing metals and dielectrics, growth of silicon dioxide from silane or TEOS sources, and etching processes using hydrogen and hydrogen plasma. During processes that involve hydrogen, the hydrogen diffuses principally through the top electrode to the layered superlattice material, but also from the side edges of the capacitor, and reduces the oxides contained in the ferroelectric material. The absorbed hydrogen also metallizes the surface of the layered superlattice material by reducing metal oxides. As a result of these effects, the electronic properties of the capacitor are degraded. After the forming-gas anneal (FGA), the remnant polarization of the ferroelectrics is very low and no longer suitable for storing information or the dielectric properties are degraded. An increase in leakage currents also results. In addition, the adhesivity of the layered superlattice material to the upper electrode is lowered by the chemical change taking place at the interface. Alternatively, the upper electrode is pushed up by the oxygen gas, water, and other products of the oxidation-reduction reactions taking place. Thus, peeling is likely to take place at the interface between the top electrode and the layered superlattice material. In addition, hydrogen also can reach the lower electrode, leading to internal stresses that cause the capacitor to peel off its substrate. These problems are acute in ferroelectric memories containing layered superlattice material compounds because these oxide compounds are particularly complex and prone to degradation by hydrogen-reduction.
A related problem encountered in the fabrication of ferroelectric and other metal oxide devices is the stress arising in and between the different circuit layers as a result of the manufacturing processes. The products of the hydrogen reduction reactions cause an increase in the total volume of the metal oxide element. As a result, the material exerts an upward pressure on the layers above it.
Several methods have been reported in the art to inhibit or reverse hydrogen degradation of desired electronic properties in ferroelectric oxide materials. Oxygen-recovery annealing at high temperature (800° C.) for about one hour results in virtually complete recovery of the ferroelectric properties degraded by hydrogen treatments; but the high temperature oxygen anneal itself may generate defects in silicon crystalline structure, and it may offset somewhat the positive effects of any prior forming-gas anneal on the CMOS characteristics. Also, if hydrogen reactions have caused structural damage to the ferroelectric device, such as peeling, then a recovery anneal is not able to effectively reverse the damage.
To reduce the detrimental effects of the hydrogen heat treatment and protect the ferroelectric metal oxide element, the prior art also teaches the application of hydrogen barrier layers to inhibit the diffusion of hydrogen into the ferroelectric material. The barrier layer is typically located over the ferroelectric element, but it can also be located below and laterally to the sides of the element.
Hydrogen degradation is also a problem in complex metal oxides used in nonferroelectric, high-dielectric constant applications in integrated circuits. Hydrogen reactions cause structural damage, as described above for ferroelectric oxides, and cause degradation of dielectric properties. Examples of metal oxides subject to hydrogen degradation include barium strontium titanate (“BST”), barium strontium niobate (“BSN”), certain ABO
3
-type perovskites, and certain layered superlattice materials, such as strontium bismuth tantalate (“SBT”). Hydrogen barrier layers are, therefore, also used to protect nonferroelectric, high-dielectric constant metal oxides.
A problem associated with utilizing a recovery anneal of an integrated circuit substrate with a hydrogen barrier layer is that the high temperatures employed during the recovery anneal can cause grain growth in the hydrogen barrier layer, thereby changing the amorphous nature and electrical properties of the hydrogen barrier layer. A further problem is that the use of a hydrogen barrier layer in connection with a metal layer, such as aluminum, is that the metal layer cannot with
Celinska Jolanta
Joshi Vikram
McMillan Larry D.
Paz de Araujo Carlos A.
Solayappan Narayan
Patton & Boggs LLP
Peralta Ginette
Pham Long
Symetrix Corporation
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