Semiconductor device manufacturing: process – Introduction of conductivity modifying dopant into... – Diffusing a dopant
Reexamination Certificate
1998-12-18
2001-03-20
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Introduction of conductivity modifying dopant into...
Diffusing a dopant
C438S003000, C438S240000
Reexamination Certificate
active
06204158
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to metal oxide ceramic films used in integrated circuits (ICs). More particularly, the invention relates to preventing a mobile specie in a metal oxide ceramic film from adversely impacting a semiconductor device incorporating the metal oxide ceramic film.
BACKGROUND OF THE INVENTION
Metal oxide ceramic materials have been investigated for their use in ICs. For example, metal oxide ceramics that are ferroelectrics or are capable of being transformed into ferroelectrics are useful due to their high remanent polarization (2Pr) and reliable long-term storage characteristics. Non-ferroelectric metal oxide ceramics, such as superconductors, have also been investigated.
Various techniques, such as sol-gel, chemical vapor deposition (CVD), sputtering, or pulsed laser deposition (PLD), have been developed for depositing ferroelectric films on a substrate. Such techniques, for example, are described, for example, Budd et al., Brit. Ceram. Soc. Proc., 36, p107 (1985); Brierley et al., Ferroelectrics, 91, p181 (1989), Takayama et al., J. Appl. Phys., 65, p1666 (1989); Morimoto et al., J. Jap. Appl. Phys. 318, 9296 (1992); and co-pending U.S. patent applications Ser. No. 08/975,087, titled “Low Temperature CVD Process using B-Diketonate Bismuth Precursor for the Preparation of Bismuth Ceramic Thin Films for Integration into Ferroelectric Memory Devices,” U.S. Ser. No. 09/107,861, titled “Amorphously Deposited Metal Oxide Ceramic Films,” all of which are herein incorporated by reference for all purposes.
Metal oxide ceramics are often treated with a post-deposition thermal process at a relatively high temperature in order to produce resulting materials with the desired electrical characteristics. For example, some Bi-based oxide ceramics such as strontium bismuth tantalate (SBT) are thermally treated by a “ferroanneal.” The ferroanneal converts the as-deposited films into the ferroelectric phase. After the as-deposited films are converted into the ferroelectric phase, the ferroanneal continues, growing the grain size (e.g., greater than about 180 nm) of the films in order to achieve a good remanent polarization. Other types of metal oxide ceramics can be deposited as ferroelectrics. For example, lead zirconium titanate (PZT) is often deposited at relatively higher temperatures, such as greater than 500° C., to form an as-deposited film with a ferroelectric perovskite phase. Although the PZT is generally deposited as a ferroelectric, a post-deposition thermal process is often still needed to improve its electrical characteristics.
Typically, the metal oxide ceramic materials contain a mobile specie which easily diffuses into other regions of the IC. Diffusion of the mobile specie into other regions can have a detrimental effect on the performance and functionality of the IC. For example, in the case of Bi-based oxide ceramics, the diffusion of Bi into other regions of the IC can alter stress, cause shorts and/or alter the electrical properties of the diffusion regions of devices, thus adversely impacting functionality of the IC.
In view of the foregoing discussion, it is desirable to prevent unwanted diffusion of a mobile specie from a metal oxide ceramic material.
SUMMARY OF THE INVENTION
The invention relates to reducing or minimizing diffusion of an excess mobile specie from a metal oxide ceramic into unwanted regions of a device. In accordance with the invention, a scavenger layer is provided above the metal oxide ceramic layer. The scavenger layer reacts with the excess mobile specie, preventing it from diffusing into, for example, the substrate,
In one embodiment, a substrate is provided. The substrate is prepared to include, for example, a partially formed semiconductor device. A metal oxide ceramic is deposited on the prepared substrate. The metal oxide comprises, in one embodiment, a Bi-based metal oxide that can be transformed into a ferroelectric.
A pre-anneal is performed to form nuclei of the ferroelectric phase in the metal oxide layer without causing substantial diffusion of the excess mobile specie. The pre-anneal is performed at about 650-700° C. for about 10-30 minutes.
In one embodiment, a scavenger layer is formed over the metal oxide ceramic layer. The scavenger layer comprises a material which reacts with the excess mobile specie. In one embodiment, the scavenger layer comprises Ti or TiO
2
. After the scavenger layer is formed, an anneal is performed to grow the grains of the metal oxide ceramic in order to achieve the desired electrical characteristics. The substrate is annealed at, for example, 700-800° C. for about 5-30 minutes.
The anneal also cause the excess mobile specie to diffuse out of the metal oxide ceramic and react with the scavenger layer. The reaction consumes the excess mobile specie, preventing it from diffusing into other regions of the device.
A conductive layer is formed over the scavenger layer. The conductive layer serves as an electrode from which an electric field is applied to the metal oxide ceramic.
In another embodiment, the scavenger layer is removed by etching or chemical mechanical polishing (CMP) prior to forming the top electrode. Alternatively, the scavenger layer could be formed over the top electrode. The scavenger layer can be removed or left on as part of the device, depending on the nature of the scavenger layer subsequent electrical properties and their affect on device performance.
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U.S. application No. 08/975,087, Hintermaier et al., filed Nov. 20, 1997.
U.S. application No. 09/107,861, Hintermaier et al., filed Jun. 30, 1998.
Budd et al., “Sol-gel processing of lead titanate (PbTiO3), lead zirconate (PbZrO3), PZT and PLZT thin films” Brit. Ceram. Soc., Proc., vol. 36, p. 107, 1985.
Brierley et al., “The growth of ferroelectric oxides by MOCVD” Ferroelectrics, vol. 91, p. 181, 1989.
Takayama et al., “Preparation of epitaxial Pb(ZrxTi1−x)O3thin films and their crystallographic, pyroelectric, and ferroelectric properties” J. Appl. Phys., vol. 65, 1989, p. 1666.
Hideo Kidoh et al., “Preparation of Pb(Zr, Ti)O3 Films on Si Substrate by Laser Ablation” Jpn. J. Appl. Phys., vol. 31, 1992, pp. 2965-2967.
Masuda et al, “Mechanism of Stoichiometric Deposition of Volatile Elements in Multimetal-Oxide Films Prepared by Pulsed Laser Ablation” Jpn. J. Appl. Phys. vol. 35, 1996, pp. 237-240.
William S. Rees, Jr.,Editor, Rees, “CVD of nonmetals” (1996) ISBN 3-527-29295-0.
Baum Thomas H.
Desrochers Debra A.
Hendrix Bryan C.
Hintermaier Frank S.
Roeder Jeffrey F.
Advanced Technology & Materials Inc.
Le Dung A
Nelms David
Whitman Robert A.
Zitzmann Oliver A. M.
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