Patent Application
20110272287
This invention relates to the method of obtaining optimized magnetic orientation and undercut free patterning of magnetic films by a double etching approach, and particularly to a method of patterning magnetic devices and sensors by double etching.
Magnetic materials can be made to have preferred magnetic orientation induced by applying an external magnetic field during deposition. The deposition method includes but not limited to electrodeposition or physical vapor deposition. Obtaining a uniform and large enough field across large dimensions, such as 200 mm or 300 mm wafers, is one of the major challenges associated with building magnetic devices on 200 mm or 300 mm wafers. The shape anisotropy of a small patterned area demands additional field strength requirement in additional to the field requirement of a blanket symmetric film due to the demagnetization effect. By depositing a blanket film, or a film close to blanket continuity, the preferred magnetic orientation can be induced with a smaller magnetic field, which is more attainable and much less expensive.
U.S. Pat. No. 3,853,715 (“Elimination of Undercut In Anodically Active Metal During Chemical Etching”) describes a frame plating methodology to achieve magnetic orientation in a patterned structure. The method employed includes depositing a blanket seed layer, putting on frame resist for patterning, plating up the structure, block resist patterning to protect the structure, chemically etching away the rest, and stripping the resist. However, a drawback with this approach is the seed layer under the thin frame serves as a path for undercut during chemical etching of the remaining materials. The consequence of the undercut easily destroys the whole pattern by lifting the resist frame and etched away the wanted structure. The undercut also restricts the minimum dimension that can be built in this approach to be millimeters.
Accordingly, the present invention relates to an improved method, which includes double etching for manufacturing a device pattern, eliminates undercut issue, provides a reliable process to build devices ranging from nanometer size to tens of centimeters size range
In accordance with the invention, the method includes in a series of steps patterns a magnetic structure by putting down a layer of dielectric as the substrate (step 1), depositing a thin adhesion layer and a thin seed layer (step 2), putting thin resist frame to pattern the structure (step 3), depositing up the structure and the field area (step 4), stripping the resist frame (step 5), etching the seed layer and the adhesion layer exposed below the resist frame down to the dielectric surface by sputter etch or reactive ion etch (step 6), etching the field magnetic materials by electrolytic etching where the device structures are typically isolated from the field (step 7), and etching the seed layer and adhesion layer in the field by sputter etch, and/or reactive ion etch (step 8).
Specifically, an aspect of the method of patterning magnetic devices and sensors by double etching includes:
The above steps are repeated for building structures with multiple layers.
A more complete appreciation of the disclosure and many of the attendant advantages will be readily obtained, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings.
Etching step 7 uses electrolytic etching, which uses electrical current to dissolve the unwanted film in a sodium chloride solution, which does not attack the desired device structure due to electrical isolation of the device structure and the unwanted magnetic film in the field.
This invention discloses a few major improvements over the existing methodology. More specifically, it patterns a magnetic structure by:
The above steps are repeated for building structures with multiple layers.
In a preferred embodiment, suitable substrates may include but they are not limited to: silicon, quartz, glass, sapphire, metal, gallium nitride, gallium arsenide, germanium, silicon-germanium, indium-tin-oxide, alumina (Al2O3), and plastic. The substrate may be rigid or flexible.
In another preferred embodiment, the dielectric layer may be silicon oxide, silicon oxynitride, low-k dielectric, and a polymer such as a polyimide, or resist
In another preferred embodiment, the thin adhesion layer may include but it is not limited to Ta, TaN, Ti, TiN, Cr, and combinations of thereof.
In another preferred embodiment the seed layer may include but is not limited to Ni, Co, Fe, Cu, Ru, Rh, Zn, Ag, Au and the alloys thereof. The seed layer is typically deposited to a thickness from about 5 nm to about 500 nm. The layer may be deposited by PVD, CVD, ALD or by electroless deposition techniques
In another preferred embodiment, the electroplating can be carried out using an anode such as Pt, Ti or other soluble metals such as Ni, Co, Fe, Cu and the alloys thereof, and a cathode, which is the wafer substrate to be plated with a conductive seed layer.
In another preferred embodiment, the electroplating is generally carried out employing a current density of about 1 to about 100 milliamps/cm2, more typically about 1 to about 50 milliamp/cm2 and even more typically about 5 to about 20 milliamps/cm2. Also, the electroplating is generally carried out at temperatures of about 10° C. to about 80° C.
The general dimensions for electroplating are between about 10 nm and about 10 cm. The aspect ratio is from about 0.5 to about 10.
In another preferred embodiment, the etching of adhesion layer and seed layer may include conventional dry etching for example, sputtering, reactive ion etching, ion beam etching and/or plasma etching.
The electrolytic etching utilizes an electrical current to dissolve the electrically connected metal film, with the metal film being the anode, and a counter electrode of Pt, Ti, Cu, Ni, steel, or other conductive materials being the cathode. A typical electrolytic etch solution is sodium chloride with pH range of −1 to 3. The etching solution provides sufficient conductivity, and can be made to be aggressive toward the specific metal dissolution. Any other desired chemical may be used for the etching treatment.
Obviously, numerous modifications and variations of the disclosure are possible in light of the above disclosure. It is therefore understood that within the scope of the appended claims, the disclosure may be practiced otherwise than as specifically described herein.
