Patent Application
20070049029
This invention relates to etching of ferroelectric material formed with metal electrodes, and specifically to a method of stack etching a ferroelectric/electrode stack without re-depositing etched electrode material.
During etching of a PCMO layer and a platinum electrode in contact with the PCMO layer, which is generally a sputter etching process, platinum re-deposition frequently occurs. As the PCMO layer is directly in contact with the platinum layer, e.g., as in the case of a platinum bottom electrode, over etching of the PCMO for a hole will redeposit platinum on the PCMO sidewalls. This is also the case when the bottom electrode is formed of other metals, such as iridium, rubidium, iridium oxide, and YxBa2Cu3O7-x (YBCO). The redeposited metal provides a conductive path between a top electrode and the bottom electrode. This is essentially a short circuit, and is not desired, and must be avoided for proper memory operation.
U.S. Pat. No. 6,534,871, of Maa et al., granted Mar. 18, 2003, for Device including an epitaxial nickel silicide on (100) Si or stable nickel silicide on amorphous Si and a method of fabricating the same; and U.S. Pat. No. 6,720,258, to Maa et al., granted Apr. 13, 2004, for Method of fabricating a nickel silicide on a substrate.
A method of etching a top electrode/ferroelectric stack using an etch stop layer includes preparing a substrate; forming a first layer of a first dielectric material on the substrate; forming a bottom electrode in the first layer of a first dielectric material; depositing a first, etch stop layer of a second dielectric material on the first layer of a first dielectric material and the bottom electrode, including forming a hole in the first layer of the second dielectric material exposing a portion of the bottom electrode; depositing a layer of PCMO material on the first layer of the second dielectric material, and extending through the hole to the bottom electrode; depositing top electrode material on the PCMO material to form a top electrode/PCMO stack; stack etching the top electrode and PCMO material, stopping at the level of the etch stop layer; depositing a second layer of a second dielectric material on the first layer of the second dielectric material and encapsulating the top electrode and PCMO material; etching the second layer of the second dielectric material to form a sidewall about the top electrode and PCMO material; depositing a second layer of the first dielectric material; smoothing the second layer of the first dielectric material by CMP; depositing a third layer of the first dielectric material; etching contact holes through the layers of the first and second dielectric material to the bottom and top electrodes; and metallizing the ferroelectric stack.
It is an object of the invention to prevent re-deposition of an electrode metal following an etching process on a PCMO stack.
This summary and objectives of the invention are provided to enable quick comprehension of the nature of the invention. A more thorough understanding of the invention may be obtained by reference to the following detailed description of the preferred embodiment of the invention in connection with the drawings.
FIGS. 2 to 4 depict successive sections through a PCMO stack during practice of the method of the invention.
The present invention improves on techniques developed in the art of stack etching and in the art of damascene etching. In the stack etching prior art, the etch is completed on the bottom electrode. In the present invention, the etch is completed on a dielectric, such as silicon nitride. This dielectric may include such materials as SiO2, TiO2, HfO2, ZrO2 or TaO2. Titanium or TiN may also be deposited onto the dielectric and may be used as an etch stop. The dielectric, titanium or TiN formed on the dielectric, is patterned prior to PCMO deposition.
In the prior art damascene process, the thickness of the dielectric must be thick enough to act as a CMP stop, e.g., a typical thickness is about 230 nm. However, given a dielectric layer of this thickness, dishing occurs, reducing the PCMO thickness at the center of the active area. As a result of providing such a CMP stop, and as a result of subsequent dishing, the dielectric thickness must be greater than would otherwise be require to practice the method of the invention. Cusping of the sputtered PCMO occurs due to shadowing of the edges of a dielectric hole, or process window, as the sputtered material impinges the process window during the deposition process, resulting in gaps in the sputtered material along the sidewalls of the process window. In the present invention, a relatively thin dielectric, having a thickness of between about 30 nm to 50 nm, is deposited and a process window, or hole, is made therein. Cusping is minimized because of the thinness of the material in which the hole is formed, e.g., as previously noted, the state of the art method required a CMP stop layer having a thickness greater than 200 nm, compared to the 30 nm to 50 nm thickness of the CMP stop layer using the method of the invention, which also minimizes re-deposition of etched electrode material. Thus the 30 nm to 50 nm thickness of the CMP stop layer is critical to the method of the invention.
The method of the invention is depicted generally at 10 in
Turning to
As shown in
Thus, a method of etching a TE/FE stack using an etch stop layer has been disclosed. The thickness of the dielectric 2 etch stop layer is significantly less than that which would be required using convention stack etching or damascene processes. It will be appreciated that further variations and modifications thereof may be made within the scope of the invention as defined in the appended claims.
