Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
2000-08-07
2002-11-12
Ver Steeg, Steven H. (Department: 1755)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192110, C204S192150, C204S192200, C204S298040, C204S298060, C204S298080, C118S7230AN, C118S7230MP, C427S162000, C427S255700, C427S402000
Reexamination Certificate
active
06478931
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to the fabrication of multilayer structures, and more particularly an improved physical-vapor deposition apparatus and method of use (and structure produced therefrom) for intra-layer modulated material deposition and assist beam.
BACKGROUND OF THE INVENTION
It is well known in the prior art to utilize RF or DC magnetron sputter deposition systems for fabrication of thin film devices such as magnetic recording sensors and storage media. Such sputter deposition systems, commonly referred to as “plasma sputtering deposition,” are characterized by crossed electric and magnetic fields in an evacuated chamber into which an inert, ionizable gas, such as argon, is introduced. The gas is ionized by electrons accelerated by the electric field, which forms a plasma in proximity to a target structure. The crossed electric and magnetic fields confine the electrons in a zone between the target and substrate structures. The gas ions strike the target structure, causing ejection of atoms that are incident on a workpiece, typically a substrate on which it is desired to deposit one or more layers of selected target materials.
In the prior art conventional plasma sputtering deposition systems, relatively low operating pressures are utilized. This results in high translational energy atom and ion fluxes incident upon the substrate. This flux introduces manufacturing process difficulties, as device thicknesses become increasingly smaller. In particular, high levels of interfacial roughness and/or mixing are observed.
It is known in the prior art to utilize ion beam sputter deposition in certain applications to overcome some of the difficulties encountered with conventional RF/DC sputter techniques. Several aspects of ion beam sputter deposition, commonly referred to as “ion beam deposition” (IBD), differ from conventional plasma sputter processes and provide significant advantages. For example, (1) the use of a lower background pressure results in less scattering of sputtered particles during the transit from the target to the substrate; (2) control of the ion beam directionality provides a variable angle of incidence of the beam at the target; (3) a nearly monoenergetic beam having a narrow energy distribution provides control of the sputter yield and deposition process as a function of ion energy and enables accurate beam focusing and scanning; (4) the ion beam is independent of target and substrate processes which allows changes in target and substrate materials and geometry while maintaining constant beam characteristics and allowing independent control of the beam energy and current density; (5) a second inert gas ion beam can be directed at the substrate to provide ion assisted deposition.
However, while the conventional IBD process has achieved much success, this conventional process also suffers from unacceptable high levels of interfacial roughness and interlayer mixing.
Also known in the prior art is to utilize molecular beam epitaxy (MBE) process to achieve physical-vapor deposition apparatus, as illustrated in U.S. Pat. No. 5,976,263 to Poole and U.S. Pat. No. 5,951,767 to Columbo the contents of which are incorporated herein by reference. In MBE, metal atoms are thermally evaporated and condensed onto a substrate. The atoms have low translational energies (~kT, where k is Boltzmann's constant and T is the absolute temperature) of <0.1 eV. During deposition, atomic assembly needed to form a high quality interface structure occurs by thermally activated diffusion on the grow surface. In conventional MBE, this thermally activated diffusion causes the grown films to suffer rough and interdiffused interfaces.
Several important applications, including giant magneto-resistive (GMR) exchange biased spin-valves thin-film read heads, photonic components, and semiconductor heterostructures, use multi-layer material stacks to perform various electronic, photonic signal processing and data storage functions. For instance, anti-reflection coating (ARC) films and dielectric optical filters utilize alternating layers of dielectric oxides with controlled thickness and roughness. Another application that uses multilayer material structures is the magnetic data storage industry. For instance, giant magneto-resistive (GMR) thin-film read head and magnetic random access memory (MRAM) concepts use multilayered material structures comprising stacks of non-magnetic conductive, ferromagnetic, and/or insulating material layers as thin as 10 to 30 Å (Angstrom).
In 1987, the giant magneto-resistive or GMR effect was discovered. GMR materials, usually consisting of at least two magnetic nanostructure entities separated by a nonmagnetic spacer. They display a large change of resistance upon the application of a magnetic field. GMR materials have a larger relative resistance change and have increased field sensitivity as compared against traditional anisotropic magneto-resistive or MR materials, such as Ni80Fe20 films. The improved relative resistance change and field sensitivity of GMR materials and related magnetic sensing elements allow the production of sensors having greater sensitivity and signal-to-noise ratio than conventional sensors. Thus, for instance, data storage systems using GMR read sensors can read data in smaller bit areas as compared to conventional read head devices. However, material stacks for fabricating GMR sensors generally use 6 to 8 layers of 4 to 6 different materials, as compared to the MR material stacks, which usually have only 3 layers of materials such as permalloy layers with Soft Adjacent Layers (SAL). Thus, creating material stacks for GMR read sensors generally requires more processing steps, including more complicated equipment and fabrication techniques for high-yield manufacturing of high-performance GMR thin-film heads.
In order to meet its goals for improved storage density, industry has turned to exchange biased spin-valve GMR thin-film read heads. Spin-valve GMR read heads are comprised of multi-layer depositions of 10 to 100 angstrom thick material films having precise thickness and microstructure control as well as extremely cohesive interface control at each interface of a multi-layer spin-valve GMR stack. Each spin-valve GMR stack must have good crystalinity in conjunction with abrupt and smooth material interfaces with minimal interface mixing to ensure proper GMR response and to establish excellent thermal stability. Essentially, GMR stacks may require controlled deposition of metallic multilayers which comprise ultrathin films as thin as about 5 to 10 atomic monolayers.
Another application for GMR materials is magnetic random access memories (“MRAM”), which are monolithic silicon-based nonvolatile memory devices presently based on a hysteretic effect in magneto-resistive or MR materials. MRAM devices are beginning to be used in aerospace and military applications due to their excellent nonvolatile memory bit retention and radiation hardness behavior. However, the MRAM devices can be easily integrated with silicon integrated circuits for embedded memory in a host of future applications in cell phones, personal computers, microprocessors, personal digital assistants (PDAs), etc. The implementation of GMR materials, such as spin-dependent tunnel junctions, could improve the electrical performance of MRAM devices to make MRAM devices competitive with semiconductor DRAM and flash EPROM memory devices. However, the performance of MRAM memory depends on precise control of layer thickness values and the microstructures of various thin films in a GMR stack of thin metallic films. Thickness fluctuations and other interface or microstructural variations in thin metallic layers can cause variation in MRAM device performance.
Similar difficulties can occur with periodic laminated multi-layer structures, such as laminated flux guide structures of iron, tantalum and silicon di-oxide.
As such, GMR materials have significant technological importance because they can be used to develop highly sensitive magnetic
Quan Junjie
Wadley Hadyn N. G.
Zhou Xiaowang
Decker Robert J.
University of Virginia Patent Foundation
Ver Steeg Steven H.
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