Patent Application
20060042938
The present invention relates to sputter targets and, more particularly, to improved sputter target materials which provide magnetic data-storing thin films with optimized grain size and grain-to-grain separation when reactively sputtered in the presence of oxygen.
The process of sputtering is widely used in a variety of fields to provide thin film material deposition of a precisely controlled thickness with an atomically smooth surface, for example to coat semiconductors and/or to form films on surfaces of magnetic recording media. In the reactive sputtering process, a cathodic sputter target is positioned in a vacuum chamber partially filled with a chemically reactive gas atmosphere, and is exposed to an electric field to generate a plasma. Ions within this plasma collide with a surface of the sputter target causing the sputter target to emit atoms from the sputter target surface. Material which has been sputtered off of the target chemically reacts with the reactive species in the gas mixture to form a chemical compound which forms the desired film on the surface of the substrate.
Conventional magnetic recording media typically comprise several thin film layers which are sequentially sputtered onto a substrate by multiple sputter targets. As illustrated in
Grain refinement and grain-to-grain microstructural separation of magnetic materials are key in the construction of discrete magnetic domains with little cross-talk and a high signal-to-noise ratio (SNR). Various materials have been utilized as additives to cobalt (Co) based alloys, to improve this grain size reduction and separation, including chromium (Cr), boron (B) and tantalum (Ta). More recently work has begun to include dielectric materials, which effectuate the formation of “granular media,” or materials with a granular microstructure in which nano-scale magnetic grains are encapsulated in an insulating matrix. Despite these enhancements, however, conventional materials have been unable to produce a data-storing thin film with sufficiently small grain size and sufficiently large grain-to-grain separation to keep up with the ever increasing demands of data storage.
As the refinement of magnetic thin film media approaches the limits of magnetic dipole stability, it is increasingly desirable to develop materials with small grain sizes and sufficient grain-to-grain separation such that each grain is not magnetically influenced by neighboring grains in the medium. In particular, it is desirable to provide a sputter target material which can be reactively sputtered to form a granular medium with optimized grain size and grain-to-grain separation.
The present invention solves the foregoing problems by providing a sputter target material for reactively sputtering a granular medium with optimized grain size and grain-to-grain separation characteristics.
According to one aspect, the present invention is a sputter target composed of a ferromagnetic alloy having a base metal. The sputter target is further composed of X1, a metal having an atomic diameter of less than 0.266 nm and an oxidation potential greater than that of the base metal.
The base metal of the ferromagnetic alloy of the sputter target is iron (Fe), Co, or any other ferromagnetic metal. In one arrangement, the base metal is Co, and the ferromagnetic alloy is further composed of Ta, platinum (Pt), or PtCr. In a second arrangement, the base metal is Fe, and the ferromagnetic alloys is further composed of Ta or Pt.
Considering that it is a function of the oxide material in the magnetic recording medium to act as an insulating and anti-magnetic barrier to grain-on-grain interactions, the features of the present invention include that X1 is more quickly diffused to grain boundaries during sputtering and is more easily oxidized than other matrix materials. These features are further effectuated when X1 has an atomic radius of less than 0.18 nm and an oxidation potential greater than −1.0 eV.
It is to be understood that the word “greater,” when referring to “greater oxidation potential,” indicates a more negative charge, measured in eV. For instance, an oxidation potential of −2.7 eV (Mg) is greater than that of −2.3 eV (Pm).
X1 is selected from the list of Al, Ba, Be, Ca, Cd, Ce, Cr, Cs, Dy, Er, Eu, Ga, Gd, Hf, Ho, K, La, Li, Mg, Mn, Na, Nb, Nd, Pm, Pr, Rb, Sc, Sm, Sr, Ta, Th, Te, Th, Ti, V, Y, Zn, and Zr. Additionally, the sputter target material is composed of more than 0 atomic percent and less than fifteen atomic percent X1.
According to a second aspect, the present invention is a method for manufacturing a magnetic recording medium. The method includes the step of reactively sputtering in the presence of oxygen a sputter target composed of a ferromagnetic alloy having a base metal, and X2, a metal having an atomic diameter of less than 0.266 nm and an oxidation potential greater than that of the base metal.
According to a third aspect, the present invention is a magnetic recording medium having a substrate and a data-storing thin film layer formed over the substrate. The data-storing thin film layer is composed of a ferromagnetic alloy having a base metal, and an oxide of X3, a metal having an atomic diameter of less than 0.266 nm and an oxidation potential greater than that of the base metal.
X3 is selected from the list of Ba, Be, Ca, Cd, Ce, Cr, Cs, Dy, Er, Eu, Ga, Gd, Hf, Ho, K, La, Li, Mg, Mn, Na, Nb, Nd, Pm, Pr, Rb, Sc, Sm, Sr, Ta, Th, Te, Th, Ti, V, Zn, and Zr.
To its advantage, the present invention provides a granular medium with an insulating and anti-magnetic barrier to grain-on-grain interactions. If is another feature and advantage of the present invention to provide a magnetic recording medium with an improved signal-to-noise ratio.
In the following description of the preferred embodiment, reference is made to the accompanying drawings that form a part thereof, and in which is shown by way of illustration a specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and changes may be made without departing from the scope of the present invention.
Referring now to the drawings in which like reference numbers represent corresponding parts throughout:
The present invention is an enhanced sputter target material which can be reactively sputtered to form magnetic data-storing thin films having granular media with optimized grain size and improved grain-to-grain separation.
The base metal of the ferromagnetic alloy of the sputter target is Fe, Co, or any other ferromagnetic metal. In one arrangement, the base metal is Co, and the ferromagnetic alloy is further composed of Ta, Pt, or PtCr. In a second arrangement, the base metal is Fe, and the ferromagnetic alloys is further composed of Ta or Pt.
It is a function of the oxide material in the magnetic recording medium to act as an insulating and anti-magnetic barrier to grain-on-grain interactions. As such, the features of the present invention include that X1 is more quickly diffused to grain boundaries during sputtering and is more easily oxidized than other matrix materials. In this regard, the metals of Table 1 are to be considered as primary candidates for oxides in effective granular magnetic media. These features are further effectuated when X1 is selected from the metals of Table 1 combining the greatest oxidation potential (<−1.0 eV) and lowest atomic diameter (<0.18 nm).
*in eV
†in Ångstroms
Additionally, the sputter target material is composed of more than 0 atomic percent and less than fifteen atomic percent X1.
In more detail,
It is to be understood that
In
In step 410, the process begins. In step 420, a sputter target is provided, and is disposed inside of a sputtering chamber. The sputter target is composed of a ferromagnetic alloy having a base metal. The sputter target is further composed of X2, a metal having an atomic diameter of less than 0.266 nm and an oxidation potential greater than that of the base metal. The sputtering chamber is a vacuum chamber in which a reactive plasma can be contained, and in which both sputter targets and substrates can be disposed.
In step 430, a substrate is provided, and is disposed inside of the sputtering chamber. The substrate is positioned so as to accumulate a thin film during the sputtering process. In step 440, the gaseous atmosphere, comprising both a non-reactive gas species and oxygen, is introduced into the sputtering chamber to form a partial vacuum.
In step 450, the gas species in the sputtering chamber are excited to create a plasma. The gas species are excited by applying a voltage difference between the substrate and the sputter target. In step 460, the material of the sputter target is deposited as a granular medium onto the substrate. This deposition is the result of the sputter target being bombarded by energetic ions of the sputtering gas species in the plasma, such that molecules from the sputter target are ejected from its surface. Molecules of X2 which are ejected react with the oxygen molecules in the plasma to form oxide groups. Both these oxide groups and the ejected molecules of the ferromagnetic alloy, are not in a state of thermodynamic equilibrium, and will therefore tend to condense back into their solid phase upon colliding with any surface in the sputtering chamber. The substrate, being such a surface, therefore accumulates a thin film of the desired material during the sputtering process. In step 470, the process terminates.
In more detail, magnetic recording medium 500 includes non-magnetic substrate base 501, seed layer 502, at least one underlayer 504, at least one interlayer 505, data-storing thin film layer 506, and lubricant layer 508. The data-storing thin film layer 506 on magnetic recording medium 500 is composed of a ferromagnetic alloy, the ferromagnetic alloy having a base metal, and an oxide of X3, where X3 is a metal having an atomic diameter of less than 0.266 nm and an oxidation potential greater than that of the base metal. In an alternate arrangement, magnetic recording medium 500 omits seed layer 502, underlayer 504, interlayer 505 and/or lubricant layer 508.
Considering that it is a function of the oxide material in the magnetic recording medium to act as an insulating and anti-magnetic barrier to grain-on-grain interactions, features of the present invention include that X3 is more quickly diffused to grain boundaries during sputtering and is more easily oxidized than other matrix materials. In this regard, the metals of Table 2 are to be considered as primary candidates for oxides in effective granular magnetic media. These features are further effectuated when X3 is selected from the metals combining the lowest atomic diameter (<0.18 nm) and greatest oxidation potential (<−1.0 eV).
*in eV
†in Ångstroms
Additionally, the magnetic recording medium is composed of more than 0 atomic percent and less than fifteen atomic percent X3.
The invention has been described with particular illustrative embodiments. It is to be understood that the invention is not limited to the above-described embodiments and that various changes and modifications may be made by those of ordinary skill in the art without departing from the spirit and scope of the invention.
