Methods of forming magnetic memory cells, and methods of forming arrays of magnetic memory cells

Methods of forming a magnetic memory cell are disclosed. The method comprises forming a magnetic cell core material over a substrate, wherein forming the magnetic cell core comprises forming a first magnetic region over the substrate, forming a tunnel barrier material over the first magnetic region, and forming a second magnetic region over the tunnel barrier material. A temperature of at least one of the substrate or a wafer stage underlying the substrate is maintained at a temperature below about 0° C. and the magnetic cell core material is exposed to at least a first beam comprising one of an ion beam or a neutral beam comprising ions or elements of at least one noble gas to remove portions of the magnetic cell core material. Related magnetic memory cells and methods of forming an array of memory cells are also disclosed.

TECHNICAL FIELD

Embodiments disclosed herein relate to methods of forming semiconductor structures including magnetic materials. More particularly, embodiments of the disclosure relate to methods of forming STT-MRAM semiconductor structures, methods of forming magnetic memory cells, to methods of forming related arrays of magnetic memory cells, and to related magnetic memory cells.

BACKGROUND

Magnetic Random Access Memory (MRAM) is a non-volatile computer memory technology based on magnetoresistance. One type of MRAM cell is a spin torque transfer MRAM (STT-MRAM) cell, which includes a magnetic cell core supported by a substrate. The magnetic cell core includes at least two magnetic regions, for example, a “fixed region” and a “free region,” with a non-magnetic region in between. The free region and the fixed region may exhibit magnetic orientations that are either horizontally oriented (“in-plane”) or perpendicularly oriented (“out-of-plane”) relative to the width of the regions. The fixed region includes a magnetic material that has a substantially fixed magnetic orientation (e.g., a non-switchable magnetic orientation during normal operation). The free region, on the other hand, includes a magnetic material that has a magnetic orientation that may be switched, during operation of the cell, between a “parallel” configuration and an “anti-parallel” configuration. In the parallel configuration, the magnetic orientations of the fixed region and the free region are directed in the same direction (e.g., north and north, east and east, south and south, or west and west, respectively). In the “anti-parallel” configuration, the magnetic orientations of the fixed region and the free region are directed in opposite directions (e.g., north and south, east and west, south and north, or west and east, respectively). In the parallel configuration, the STT-MRAM cell exhibits a lower electrical resistance across the magnetoresistive elements (e.g., the fixed region and free region). This state of low electrical resistance may be defined as a “0” logic state of the STT-MRAM cell. In the anti-parallel configuration, the STT-MRAM cell exhibits a higher electrical resistance across the magnetoresistive elements. This state of high electrical resistance may be defined as a “1” logic state of the STT-MRAM cell.

Switching of the magnetic orientation of the free region may be accomplished by passing a programming current through the magnetic cell core and the fixed and free regions therein. The fixed region polarizes the electron spin of the programming current, and torque is created as the spin-polarized current passes through the core. The spin-polarized electron current exerts torque on the free region. When the torque of the spin-polarized electron current passing through the core is greater than a critical switching current density (Jc) of the free region, the direction of the magnetic orientation of the free region is switched. Thus, the programming current can be used to alter the electrical resistance across the magnetic regions. The resulting high or low electrical resistance states across the magnetoresistive elements enable the read and write operations of the STT-MRAM cell. After switching the magnetic orientation of the free region to achieve the parallel configuration or the anti-parallel configuration associated with a desired logic state, the magnetic orientation of the free region is usually desired to be maintained, during a “storage” stage, until the STT-MRAM cell is to be rewritten to a different configuration (i.e., to a different logic state).

Switching of the magnetic orientation of the free region of a magnetic memory cell including a magnetic tunnel junction (“MTJ”) may be affected by the tunnel magnetoresistance (“TMR”). The TMR of a MTJ is a function of the resistance between an upper electrode and a lower electrode between which the MTJ is disposed, in the high electrical resistance state and the low electrical resistance state. Specifically, the TMR measures the difference between a cell's electrical resistance in the anti-parallel configuration (Rap) and its electrical resistance in the parallel configuration (Rp) to Rp(i.e., TMR=100·(Rap−Rp)/Rp). Thus, the TMR is equivalent to the change in resistance observed by changing the magnetic state of the free layer. Generally, a MTJ with a homogeneous crystal structure (e.g., a bcc (001) crystal structure), having few structural defects in the microstructure of its magnetic material, has a higher TMR than a MTJ with structural defects. A magnetic memory cell with high TMR may have a high read-out signal, which may speed the reading of the cell during operation. A higher TMR is preferred for a reliable read operation as it will generate a larger signal difference between the on and off states of the cell. In other words, the higher the TMR, the more sensitive the device, and the easier to distinguish between logic states of an associated magnetic memory cell.

Patterning of magnetic memory cells often includes reactive ion etching (RIE), which may introduce chemical damage to such memory cells. Reactive ion etching may include exposing the magnetic memory cell to one or more gases including halogen-based ions, hydrogen ions, oxygen ions, or other reactive gas components that may undesirably react with the magnetic materials and a tunnel barrier material of the magnetic memory cells. Undesired reactions between the magnetic materials or the tunnel barrier material and reactive gases may affect the crystal structure of the magnetic material cell and undesirably alter properties of the magnetic memory cell.

Ion beam etching (IBE) is a potential alternative for patterning of MRAM cells. However, conventional ion beam etching may damage the relatively thin materials of the magnetic materials of the memory cells. At conventional ion beam etching energies (e.g., about 200 eV), noble gases and other ion sources included in the ion beam may implant into the magnetic material, often several monolayers into an exposed surface of the magnetic material. The implanted materials may distort a crystal structure and induce lattice distortion in the magnetic materials, which may negatively alter the magnetic properties of the magnetic materials and associated memory cells. For example, intermixing and diffusion of elements of the ion beam and of adjacent materials in the magnetic stack may reduce one or more of a coercitivy (Hc), a magnetism, or a tunnel magnetoresistance (TMR), and may increase a resistance (i.e., an increased switching current, Jc), of the magnetic memory cell.

In addition, materials of the magnetic cell structure may exhibit a relatively low vapor pressure and may not, therefore, be carried out of an etch chamber during or after patterning. Accordingly, such materials may resputter (e.g., redeposit) on sidewalls of memory cell stack structures being patterned during the etching process. The resputtered material may be electrically conductive and cause an electrical short between adjacent memory cells and between, for example, upper and lower electrodes of the same memory cell.

DETAILED DESCRIPTION

The illustrations included herewith are not meant to be actual views of any particular systems or magnetic memory cells, but are merely idealized representations that are employed to describe embodiments herein. Elements and features common between figures may retain the same numerical designation except that, for ease of following the description, for the most part, reference numerals begin with the number of the drawing on which the elements are introduced or most fully described.

The following description provides specific details, such as material types, material thicknesses, and processing conditions in order to provide a thorough description of embodiments described herein. However, a person of ordinary skill in the art will understand that the embodiments disclosed herein may be practiced without employing these specific details. Indeed, the embodiments may be practiced in conjunction with conventional fabrication techniques employed in the semiconductor industry. In addition, the description provided herein does not form a complete process flow for manufacturing semiconductor devices, magnetic cell cores, or magnetic memory cells, and the semiconductor devices, magnetic cell cores, or magnetic memory cells described below do not form complete semiconductor devices, magnetic cell structures, or magnetic memory cells. Only those process acts and structures necessary to understand the embodiments described herein are described in detail below. Additional acts to form a complete magnetic memory cell including the magnetic cell cores described herein may be performed by conventional techniques.

According to embodiments disclosed herein, a magnetic memory cell including a magnetic cell core may be formed by beam etching with an ion beam, a neutral beam, or combinations thereof. A stack of magnetic materials may be formed (e.g., patterned) with a first beam at a temperature below about 0° C. (e.g., such as below about −50° C.) to form the magnetic cell core. The first beam may comprise at least one noble gas (e.g., neon, argon, krypton, xenon, or combinations thereof) and, in some embodiments, may further include at least one oxygen-containing gas. The at least one oxygen-containing gas may include at least one of oxygen, ozone, nitric oxide, nitrous oxide, nitrogen dioxide, carbon monoxide, carbon dioxide, or combinations thereof. After patterning the magnetic memory cell, sidewalls of the magnetic memory cell may be exposed to at least a second beam comprising at least one oxygen-containing gas and, in some embodiments, at least one noble gas, the second beam having a lower energy and a different beam angle than the first beam. The second beam may oxidize at least a portion of sidewalls of the magnetic memory cell. Forming the patterned magnetic memory cell at a temperature below about 0° C. may substantially reduce or eliminate an amount of intermixing between magnetic materials and adjacent tunnel barrier materials. In addition, forming the magnetic memory cell at a temperature below about 0° C. may substantially reduce or eliminate an amount of diffusion and intermixing of beam elements (e.g., the at least one noble gas, the oxygen-containing gas, or both) into the materials of the magnetic materials. Magnetic memory cells formed according to the embodiments described herein may exhibit improved crystal structures (e.g., symmetry) and improved magnetic properties (e.g., increased TMR, reduced resistance, reduced switching current density Jc, etc.).

FIG. 1is a simplified cross-sectional view of an array100of magnetic memory cells150according to embodiments of the disclosure. The magnetic memory cells150each include a magnetic cell core101disposed over a substrate102. The magnetic cell core101may be disposed between an upper electrode136and a lower electrode104. The magnetic cell core101may include a magnetic region and another magnetic region such as, for example, a “fixed region”130and a “free region”132, respectively. A tunnel barrier material126may be disposed between the fixed region130and the free region132. The fixed region130, the free region132, and the intervening tunnel barrier material126may form a magnetic tunnel junction.

The substrate102may include a base material or other construction upon which components, such as those within magnetic memory cells, are formed. The substrate102may be a semiconductor substrate, a base semiconductor material on a supporting substrate, a metal electrode, or a semiconductor substrate having one or more materials, structures, or regions formed thereon. The substrate102may be a conventional silicon substrate or other bulk substrate including semiconductor material. As used herein, the term “bulk substrate” means and includes not only silicon wafers, but also silicon-on-insulator (“SOI”) substrates, such as silicon-on-sapphire (“SOS”) substrates or silicon-on-glass (“SOG”) substrates, epitaxial layers of silicon on a base semiconductor foundation, or other semiconductor or optoelectronic materials, such as silicon-germanium (Si1-xGex, wherein x is, for example, a mole fraction between 0.2 and 0.8), germanium (Ge), gallium arsenide (GaAs), gallium nitride (GaN), or indium phosphide (InP), among others. Furthermore, when reference is made to a “substrate” in the following description, previous process stages may have been utilized to form material, regions, or junctions in the base semiconductor structure or foundation.

One or more lower intermediary regions106may optionally overlie the lower electrode104. The lower intermediary region106, if included, may be configured to inhibit diffusion of species between the lower electrode104and materials overlying the lower electrode104. The lower intermediary region106may include a conductive material such as one or more of copper, tantalum, titanium, tungsten, ruthenium, tantalum nitride, or titanium nitride.

A seed material108may overlie the lower intermediary region106. In some embodiments, the seed material108directly overlies and contacts the lower intermediary region106. In other embodiments, the seed material108directly overlies and contacts the lower electrode104. The seed material108may comprise one or more of tantalum, ruthenium, titanium, or platinum. In some embodiments, the seed material108comprises tantalum, platinum, and ruthenium. In some such embodiments, the seed material108may comprise distinct regions of each of the tantalum, platinum, and ruthenium. In yet other embodiments, the seed material108may include a mixture of two or more of tantalum, ruthenium, titanium, or platinum.

The fixed region130may overlie the seed material108. In some embodiments, the fixed region130directly overlies and contacts the seed material108. The fixed region130may include a first magnetic portion120over seed material108, a coupling material122over the first magnetic portion120, and a second magnetic portion124over the coupling material122. The first magnetic portion120and the second magnetic portion124of the fixed region130may include a fixed magnetic orientation, as indicated by arrows121. The fixed magnetic orientation may be north, south, east, west, etc. The fixed magnetic orientation of the first magnetic portion120and the second magnetic portion124may be the same or may be different.

In some embodiments, the fixed region130may include one or more magnetic materials and, optionally, one or more non-magnetic materials. By way of nonlimiting example, the fixed region130may be configured as a synthetic antiferromagnetic including a sub-region of ruthenium or tantalum adjoined by magnetic sub-regions. The magnetic sub-regions may include a material including cobalt, and at least one of palladium, platinum, or a combination thereof, a CoFeB material, or combinations thereof. As used herein, the term “CoFeB material” means and includes a material comprising cobalt (Co), iron (Fe), and boron (B) (e.g., CoxFeyBz, wherein x=10 to 80, y=10 to 80, and z=0 to 50). A CoFeB material may or may not exhibit magnetism, depending on its configuration (e.g., its thickness). In some embodiments, the fixed region130may include at least one of cobalt, iron, or nickel and may further include at least one non-magnetic material such as boron, zinc, aluminum, titanium, ruthenium, tantalum, silicon, silver, gold, copper, carbon, or nitrogen. By way of nonlimiting example, the fixed region130may include CoFe or NiFe and may further include boron.

In other embodiments, the first magnetic portion120includes a superlattice structure and the second magnetic portion124includes another superlattice structure. Referring toFIG. 2, in some such embodiments, the first magnetic portion120and the second magnetic portion124may include alternating portions of a magnetic material117and a conductive material119. The conductive material119may enable the magnetic material117to exhibit a perpendicular anisotropy (i.e., a vertical magnetic orientation). The conductive material119may include at least one of platinum, palladium, nickel, or iridium. In some embodiments, the magnetic material117includes cobalt and the conductive material119includes platinum. AlthoughFIG. 2depicts six regions of the magnetic material117and six regions of the conductive material119in the first magnetic portion120, the magnetic portion is not so limited and may include any number (e.g., one, two, three, four five, etc.) of alternating regions of magnetic material117and conductive material119.

Referring back toFIG. 1, the coupling material122may directly overlie and contact the first magnetic portion120. The coupling material122may include ruthenium, rhodium, or a combination thereof.

The second magnetic portion124may directly overlie and contact the coupling material122. The second magnetic portion124may include the same materials and may be substantially the same as at least a portion of the first magnetic portion120. In some embodiments, the second magnetic portion124includes a material including cobalt and at least one of palladium or platinum.

In yet other embodiments, the fixed region130may include an antiferromagnetic material adjacent to a ferromagnetic material. The antiferromagnetic material may include at least one of PtMn, IrMn, MnO, MnS, MnTe, MnF2, FeCl2, FeO, CoCl2, CoO, NiCl2, NiO, or Cr. In other embodiments, the antiferromagnetic material may include one or more of ruthenium, rhodium, palladium, osmium, iridium, platinum, gold, or silver. The ferromagnetic material may include at least one of CoFeB, Fe, Co, Ni, Gd, Dy, CoFe, NiFe, MnAs, MnBi, MnSb, CrO2, MnOFe2O3, FeOFe2O3, CuOFe2O3, MgOFe2O3, EuO, or Y2Fe5O12.

A tunnel barrier material126may overlie the fixed region130. The tunnel barrier material126may be disposed between the fixed region130and the free region132. In some embodiments, the tunnel barrier material126directly overlies and contacts the free region130. The tunnel barrier material126may include a non-magnetic (e.g., a magnetically insulative) material including oxide materials and nitride materials such as magnesium oxide (MgO), aluminum oxide (Al2O3), titanium dioxide (TiO2), titanium nitride (TiN), aluminum nitride (AlN), or other oxide or nitride materials. In other embodiments, the tunnel barrier material126may include an electrically conductive, non-magnetic material, such as materials used in spin valve structures.

The free region132may overlie the tunnel barrier material126. The free region132may be homogeneous, or may include more than one sub-region. The free region132may include a magnetic material exhibiting a switchable magnetic orientation, indicated by arrows131, during use and operation of the memory cell. The switchable magnetic orientation may be switched between a parallel configuration and an anti-parallel configuration by the application of a current or applied field to the magnetic cell structure100.

In some embodiments, the free region132may be a conventional free region (i.e., a magnetic region including different materials than the first magnetic portion120, the second magnetic portion124, and the coupling material122). In other embodiments, the free region132may include the same materials as each of the first magnetic portion120and the second magnetic portion124of the fixed region130. However, the free region132is not so limited and may include other suitable magnetic materials that exhibit a switchable magnetic orientation.

One or more upper intermediary regions134may optionally be disposed over the free region132. The upper intermediary region134, if included, may be configured to inhibit diffusion of species between the upper electrode136and underlying materials during operation of the memory cell. The upper intermediary region134may include a conductive material (e.g., one or more materials such as copper, tantalum, titanium, tungsten, ruthenium, tantalum nitride, or titanium nitride) that may form a conductive capping region. In other embodiments, the upper intermediary region134may also include an insulating material such as MgO, Al2O3, TiO2, or combinations thereof.

The upper electrode136may overlie the upper intermediary region134. The upper electrode136may include copper, tungsten, platinum, palladium, titanium, tantalum, nickel, titanium nitride, tantalum nitride, tungsten nitride, polysilicon, a metal silicide, a metal alloy, or combinations thereof. In some embodiments, the upper electrode136includes the same materials as the lower electrode104.

An oxide material140may overlie sidewalls of the magnetic memory cells150. In some embodiments, the oxide material140may be electrically insulative. The oxide material140may extend from the upper electrode136to a surface of the substrate102. In other embodiments, the oxide material140may overlie only the tunnel barrier material126and the magnetic materials of the fixed region130and the free region132. In some such embodiments, the oxide material140may extend from a portion of the fixed region130to a portion of the free region132and may not, therefore, extend over, for example, the lower electrode104, the lower intermediary region106, the seed material108, the upper intermediary region134, or the upper electrode136.

The oxide material140may comprise a metal oxide of a material over which the oxide material140is disposed. Stated another way, if the oxide material140is disposed over a lower electrode104comprising titanium, the metal oxide material over the lower electrode104may comprise a titanium oxide (e.g., TiO2). As another example, the oxide material140may comprise a metal oxide of a metal (e.g., a magnetic material) at portions overlying the free region130and the fixed region132and may comprise an oxide or an oxygen rich material at portions overlying the tunnel barrier material126.

Accordingly, the oxide material140may comprise one or more different compositions along the sidewalls of the magnetic memory cells150, depending on a composition of the material over which the oxide material140is disposed. In other words, portions of the oxide material140overlying each of the lower electrode104, the lower intermediary region106, the fixed region130, the tunnel barrier material126, the free region132, the upper intermediary region134, and the upper electrode136may differ depending on a composition of such components of the magnetic memory cell150.

The oxide material140may have a thickness between about one monolayer and about ten percent of a width W of the magnetic memory cells150. In some embodiments, the width W may be between about 20 nm and about 40 nm, such as about 25 nm. In some such embodiments, the oxide material140may have a thickness between about one monolayer and about 4 nm, such as between about 1 nm and about 3 nm, although the disclosure is not limited to such thicknesses.

Although the magnetic memory cells150ofFIG. 1are illustrated as “bottom-pinned” memory cells (i.e., memory cells in which the fixed region130is disposed under the free region132), the magnetic memory cells150may comprise “top-pinned” memory cells. In some such embodiments, a relative location of the free region132and the fixed region130may be switched. In other words, the free region132may be located closer to the substrate102than the fixed region130.

The magnetic memory cells150ofFIG. 1may be formed by forming and patterning a stack of magnetic materials with ion beam etching (IBE) (also referred to as ion beam sputtering or ion beam milling), neutral beam etching (NBE) (also referred to as neutral beam milling), or a combination thereof.FIG. 3is a simplified schematic of an etching tool300that may be used to pattern a plurality of magnetic memory cells, according to embodiments of the disclosure. The etching tool300may comprise a beam machine, such as an ion beam etching tool (also referred to as a sputter etching tool, an ion beam milling tool, or an ion beam reactor) or a neutral beam etching tool (also referred to as a neutral beam milling tool or a neutral beam reactor), although the disclosure is not so limited. A source gas308may enter the etching tool300through a source gas inlet310. A gas outlet324may operably couple an operating chamber305of the etching tool300to a vacuum chamber to evacuate outlet gases, indicated by arrow326, from the chamber305. In some embodiments, the etching tool300is operated at vacuum pressures. Such etching tools are known in the art and, therefore, are not described in detail herein.

The etching tool300may be configured to provide a beam302comprising an ion beam, a neutral beam, or both accelerated at a substantial velocity toward a substrate304disposed on a wafer stage306(which may also be referred to as a wafer table or a chuck). The beam302may comprise ions or elements of the source gas308. The substrate304may comprise, for example, a stack of materials to be patterned to form the array100(FIG. 1) of magnetic memory cells150(FIG. 1).

The source gas308may be exposed to a stream of high-energy electrons between a cathode312and at least one anode314in a plasma region316of the etching tool300. In some embodiments, the electrons may ionize the source gas308to a high-energy state with a positive charge in the plasma region316. An optically aligned grid318may be configured to substantially collimate and direct the beam302toward the substrate304. In some embodiments, the beam302may pass through a neutralizer filament320prior to contacting the substrate304. In some embodiments, the wafer stage306may be negatively grounded and the beam302(which, in some embodiments, may comprise positively charged ions) may be attracted to the wafer stage306. Material from surfaces of the substrate304may be removed from the substrate304responsive to exposure to the beam302.

The wafer stage306may include a rotating member322configured to rotate the wafer stage306and the substrate304during use and operation of the etching tool300. In some embodiments, the wafer stage306may be configured to rotate such that a beam angle between the substrate304and the beam302may be between about 0° and about 90°, wherein a beam angle of 0° refers to a substantially perpendicular beam302relative to a major surface of the substrate304and a beam angle of about 90° refers to a beam302that is substantially parallel to major surface of the substrate304.

The etching tool300may be configured to control a temperature of the wafer stage306, the substrate304, or both. By way of nonlimiting example, the wafer stage306may be cooled with one or more of an ice bath, liquid carbon dioxide, liquid nitrogen, backside gas cooling (e.g., such as with helium gas), or other method of cooling the wafer stage306and substrate304. The etching tool300may be configured to maintain a temperature of the wafer stage306and the substrate304below about 0° C., such as below about −50° C., below about −100° C., below about −150° C., below about −200° C., or below about −250° C. during use and operation thereof.

FIG. 4AandFIG. 4Billustrate a method of forming the array100of magnetic memory cells150ofFIG. 1. The method may include forming a stack400of materials over a substrate402. A lower electrode material404may be formed over the substrate402. A lower intermediary region material406may, optionally, be formed over the lower electrode material404. A seed material408may be formed over the lower intermediary region material406and a fixed region material430may be formed over the seed material408. The fixed region material430may include a first magnetic portion material420, a coupling material422, and a second magnetic portion material424. A tunnel barrier material426may be formed over the fixed region material430and a free region material432may be formed over the tunnel barrier material426. An upper intermediary region material434may be formed over the free region material432and an upper electrode material436may be formed over the upper intermediary region material434. Each of the substrate402, the lower electrode material404, the lower intermediary region material406, the seed material408, the fixed region material430, the tunnel barrier material426, the free region material432, the upper intermediary region material434, and the upper electrode material436may comprise the same materials described above with reference toFIG. 1and each of the substrate102, the lower electrode104, the lower intermediary region106, the seed material108, the fixed region130, the tunnel barrier material126, the free region132, the upper intermediary region134, and the upper electrode136, respectively. The first magnetic portion material420and the second magnetic portion material424may exhibit a fixed magnetic orientation, as indicated by arrows421, and the free region material432may exhibit a free magnetic orientation, as indicated by arrows431.

Each of the lower electrode material404, the lower intermediary region406, the seed material408, the fixed region material430, the tunnel barrier material426, the free region material432, the upper intermediary region material434, and the upper electrode material436may be formed by conventional techniques, such as one or more of atomic layer deposition (ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD), plasma enhanced chemical vapor deposition (PECVD), low pressure chemical vapor deposition (LPCVD), or other film deposition processes.

Referring toFIG. 4B, portions of the stack400(FIG. 4A) may be removed to form an array100′ of patterned magnetic memory cells150′. Portions of the lower electrode material404, the lower intermediary region material406, the seed material408, the fixed region material430, the tunnel barrier material426, the free region material432, the upper intermediary region material434, and the upper electrode material436may be removed to pattern a plurality of magnetic cell cores401. As described above, in some embodiments, the stack400(FIG. 4A) may be patterned by one or both of ion beam etching (IBE) or neutral beam etching (NBE). In some embodiments, at least the fixed region material430, the tunnel barrier material426, and the free region material432may be patterned by IBE or NBE.

FIG. 5is a simplified flow diagram illustrating a method500of forming the array100,100′ (FIG. 1,FIG. 4B) of magnetic memory cells150,150′ (FIG. 1,FIG. 4B). The method500comprises act502including disposing a substrate on a wafer stage of an etching tool, the substrate including the stack400(FIG. 4A) of materials; act504including maintaining a temperature of the wafer stage, the substrate, or both below about 0° C.; act506including introducing a source gas into the etching tool to form a first beam having a first composition comprising at least one noble gas; act508including exposing the substrate to the first beam to remove portions of the materials and form an array of magnetic memory cells; act510including altering a composition of the source gas to form a second beam having a second composition comprising at least one oxygen-containing gas; and act512including exposing the array of magnetic memory cells to the second beam while maintaining the temperature of the wafer stage, the substrate, or both below about 0° C. to form an oxide material on sidewalls of the magnetic memory cells.

Act502includes disposing a substrate on a wafer stage (e.g., wafer stage306(FIG. 3)) of an etching tool (e.g., etching tool300(FIG. 3)). In some embodiments, the substrate may be substantially similar to the stack400described above with reference toFIG. 4A.

Act504includes maintaining a temperature of the wafer stage, the substrate, or both below about 0° C. By way of nonlimiting example, the wafer stage may be maintained at a temperature between about 0° C. and about −273° C., such as between about 0° C. and about −250° C., between about 0° C. and about −50° C., between about −50° C. and about −100° C., between about −100° C. and about −150° C., between about −150° C. and about −200° C., or between about −200° C. and about −250° C. In some embodiments, the temperature may be below about 0° C., such as below about −50° C., below about −100° C., below about −150° C., below about −200° C., or below about −250° C.

Act506includes introducing a source gas into the etching tool to form a first beam having a first composition comprising at least one noble gas. The source gas and, therefore, the first beam may comprise a neutral beam comprising at least one noble gas, such as at least one of neon, argon, krypton, or xenon or an ion beam comprising ions of at least one noble gas, such as ions of neon (Ne+), argon (Ar+), krypton (Kr+), or xenon (Xe+). In some embodiments, the at least one noble gas may also include helium (He+). In some embodiments, the at least one noble gas comprises or consists essentially of argon.

In some embodiments, the source gas may include at least one noble gas and at least one oxygen-containing gas. The oxygen-containing gas may comprise an oxidizing gas. The oxygen-containing gas may comprise one or more of oxygen (O2), ozone (O3), nitric oxide (NO), nitrous oxide (N2O), nitrogen dioxide (NO2), carbon monoxide (CO), or carbon dioxide (CO2), or other oxygen-containing gas. In some embodiments, the oxygen-containing gas comprises oxygen (O2).

The oxygen-containing gas may constitute between about 0 volume percent and about 100 volume percent of the source gas, such as between about 0 volume percent and about 60 volume percent, between about 0 volume percent and about 40 volume percent, or between about 0 volume percent and about 20 volume percent of the source gas. In other embodiments, the source gas may comprise or consist essentially of the oxygen-containing gas. In some such embodiments, the source gas may be substantially free of the at least one noble gas.

Act508includes exposing the substrate to the first beam to form an array of magnetic memory cells. The wafer stage, the substrate, or both may be maintained at a temperature below about 0° C. while the first beam contacts surfaces of the substrate and removes at least a portion of the stack400(FIG. 4A) of materials. In some embodiments, a plurality of magnetic memory cells may be patterned with a source gas comprising or consisting essentially of one or more noble gases. In other embodiments, the magnetic memory cells are patterned with a source gas comprising one or more noble gases and one or more oxygen-containing gases. In yet other embodiments, the magnetic memory cells are patterned with a source gas comprising an oxygen-containing gas.

An incident energy of the first beam may be greater than about 200 eV. In some embodiments, the beam energy of the first beam may be between about 200 eV and about 1,000 eV (about 1 keV), such as between about 400 eV and about 800 eV, or between about 500 eV and about 700 eV.

In some embodiments, an angle of the first beam (i.e., a beam angle) may be maintained between about 0° and about 45° while patterning the substrate. Stated another way, the beam angle of the first beam may be between about substantially perpendicular to a major surface of the substrate and about 45° with respect to the major surface of the substrate.

Act510may include altering a composition of the source gas to form a second beam having a second composition comprising at least one oxygen-containing gas. The composition of the source gas may be selected to comprise one or more oxygen-containing gases including at least one of oxygen, ozone, nitric oxide, nitrous oxide, nitrogen dioxide, carbon monoxide, or carbon dioxide, or other oxygen-containing gas. In some embodiments, the source gas may comprise or consist essentially of the oxygen-containing gas, such as oxygen (O2). In other embodiments, a composition of the source gas may include at least one oxygen-containing gas and at least one noble gas.

In some embodiments, the oxygen-containing gas may constitute between about 1 volume percent and about 100 volume percent of the source gas, such as between about 1 volume percent and about 25 volume percent, between about 25 volume percent and about 50 volume percent, between about 50 volume percent and about 75 volume percent, or between about 75 volume percent and about 100 volume percent of the source gas. A remainder of the source gas may comprise the at least one noble gas. Accordingly, in some embodiments, the source gas comprises between about 0.1 part and about 10 parts of the oxygen-containing gas for every about 1 part of the noble gas, such as between about 0.1 part and about 0.2 part, between about 0.2 part and about 0.5 part, between about 0.5 part and about 1 part, between about 1 part and about 2 parts, between about 2 parts and about 5 parts, or between about 5 parts and about 10 parts of the oxygen-containing gas for every about 1 part of the noble gas.

Act512includes exposing the magnetic memory cells to the second beam while maintaining the temperature of the wafer stage, the substrate, or both below about 0° to form an oxide material on sidewalls of the magnetic memory cells. In some embodiments, the temperature is selected to be substantially the same as the temperature described above with reference to act504. In other words, the temperature may be between about 0° C. and about −273° C., such as between about 0° C. and about −250° C., between about 0° C. and about −50° C., between about −50° C. and about −100° C., between about −100° C. and about −150° C., between about −150° C. and about −200° C., or between about −200° C. and about −250° C.

The second beam may comprise one or more of a neutral beam or an ion beam comprising the oxygen-containing gas, or the oxygen-containing gas and at least one noble gas. A beam energy of the second beam may be less than a beam energy of the first beam. The second beam may have a beam energy between about 10 eV and about 200 eV, such as between about 10 eV and about 50 eV, between about 50 eV and about 100 eV, or between about 100 eV and about 200 eV. Accordingly, the beam energy of the second beam may be less than about 200 eV, such as less than about 100 eV, or even less than about 50 eV.

The beam angle of the second beam may be between about 45° and about 90°, such as between about 60° and about 85°, or between about 70° and about 80°. In some embodiments, the beam angle of the second beam may be different than the beam angle of the first beam. Without wishing to be bound by any particular theory, it is believed that selecting the source gas of the second beam to comprise the oxygen-containing gas and selecting the beam angle of the second beam to be between about 45° and about 90° may facilitate forming an oxide material (e.g., the oxide material140(FIG. 1)) on sidewalls of the magnetic memory cells.

After forming the oxide material140, the substrate may include an array100of magnetic memory cells150, each magnetic memory cell150comprising a magnetic cell core101, and an oxide material140on sidewalls thereof, as described above with reference toFIG. 1. Forming the oxide material may substantially reduce a likelihood of the magnetic memory cell150shorting between the lower electrode104(FIG. 1) and the upper electrode136(FIG. 1). By way of comparison, magnetic memory cells formed according to conventional patterning processes may include a resputtered conductive material on sidewalls of material stacks. The resputtered conductive material may electrically connect an upper electrode and a lower electrode and cause shorting therebetween. Forming the oxide material140according to embodiments of the disclosure may include forming an electrically insulative oxide material from an electrically conductive material.

Accordingly, in some embodiments, a method of forming a magnetic memory cell comprises forming a magnetic cell core material over a substrate, forming the magnetic cell core material comprising forming a first magnetic region over the substrate, forming a tunnel barrier material over the first magnetic region, and forming a second magnetic region over the tunnel barrier material. A temperature of at least one of the substrate or a wafer stage underlying the substrate is maintained at a temperature below about 0° C. and the magnetic cell core material is exposed to at least a first beam comprising one of an ion beam or a neutral beam comprising ions or elements of at least one noble gas to remove portions of the magnetic cell core material.

Accordingly, in other embodiments, a method of forming an array of magnetic memory cells comprises forming a stack of magnetic materials comprising a first magnetic material over a substrate, a tunnel barrier material over the first magnetic material, and at least a second magnetic material over the tunnel barrier material and exposing the stack of magnetic materials to a first beam comprising at least one noble gas at a beam angle between about 0° and about 45° while maintaining a temperature of the substrate or a wafer stage on which the substrate is disposed below about 0° C. to remove portions of the stack and form a plurality of magnetic memory cells.

Accordingly, in yet other embodiments, a method of forming an array of memory cells comprises disposing a substrate including a stack of magnetic materials over the substrate on a wafer stage of an etching tool, maintaining a temperature of at least one of the substrate or the wafer stage below about 0° C., and exposing the stack of magnetic materials to a first beam comprising at least one noble gas and having a first beam energy to form magnetic memory cells over the substrate. The substrate is exposed to a second beam comprising at least one oxygen-containing gas and having a second beam energy lower than the first beam energy.

Forming the magnetic memory cells150,150′ (FIG. 1,FIG. 4B) at substrate and wafer stage temperatures below about 0° C. and with the source gases described above may form magnetic memory cells exhibiting improved magnetic properties. By way of nonlimiting example, one or more of a coercivity, a resistance of the magnetic tunnel junction, a TMR, a switching current density, or other property of the magnetic memory cells may be improved compared to when the magnetic memory cells are patterned at temperatures above about 0° C., such as at temperatures of about 25° C. By way of nonlimiting example, the magnetic memory cells150,150′ may exhibit a TMR between about 100% and about 200%, such as between about 100% and about 150%, or between about 150% and about 200% while magnetic memory cells formed by conventional methods may exhibit a TMR up to about 100%.

The magnetic memory cells150,150′ may exhibit a homogeneous crystal structure substantially free of any crystal lattice mismatch. For example, the fixed region130(FIG. 1), the free region132(FIG. 1), and the tunnel barrier material126(FIG. 1) may each comprise a varying purity across a width (W) thereof with an increasing purity extending in a direction away from exposed portions thereof and toward, for example, a laterally central portion of the magnetic cell core101(FIG. 1). In some embodiments, the materials of each of the fixed region130, the tunnel barrier material126, and the free region132may exhibit a purity varying between about 95 percent and about 99 percent proximate sidewalls thereof to about 100 percent at a depth between about 1 nm and about 2 nm from the sidewalls. Stated another way, each of the fixed region130, the tunnel barrier material126, and the free region132may include a varying concentration of a component of the first beam or the second beam (e.g., argon, oxygen, etc.) with an increased concentration proximate the sidewalls. In some embodiments, a concentration of the at least one noble gas or the at least one oxygen-containing gas may vary from between about 1×107atoms/cm3and about 1×108atoms/cm3at a region proximate the sidewalls to about 0 atom/cm3at a depth between about 1 nm and about 2 nm from the sidewalls. In some embodiments, the magnetic memory cells150,150′ may exhibit a varying degree of lattice mismatch across a width thereof with a higher degree of lattice mismatch proximate the sidewalls and a reduced amount of lattice mismatch in a direction toward the laterally central portion of the magnetic cell core101. In some embodiments, the magnetic memory cells150,150′ may exhibit substantially no lattice mismatch at about 1 nm or about 2 nm from the sidewalls.

By way of contrast, magnetic memory cells formed by conventional methods may include an increased concentration of impurities and at greater depths than those described above and may, therefore, exhibit a greater amount of crystal lattice mismatch and reduced magnetic properties. Without wishing to be bound by any particular theory, it is believed that forming the magnetic memory cells150,150′ at a temperature below about 0° may substantially reduce an amount of diffusion of impurities in each of the fixed region130, the tunnel barrier material126, and the free region132and may substantially reduce a degree of lattice mismatch thereof. By way of nonlimiting example, magnetic memory cells formed according to the methods described herein may exhibit less than about one-half a lattice damage of a magnetic memory cell formed by conventional methods. For example, magnetic memory cells formed by conventional methods may exhibit a damage in a lattice structure of the magnetic materials and tunnel barrier materials up to a depth of at least about 5 nm from exposed sidewalls thereof while, in some embodiments, magnetic memory cells formed according to the methods described herein may not exhibit lattice damage beyond about 2 nm from exposed sidewalls thereof. In some embodiments, magnetic memory cells formed according to the methods described herein may exhibit a TMR up to about 50% greater than a TMR of a conventional magnetic memory cell. In some embodiments, magnetic memory cells formed according to the methods described herein may exhibit a resistance between electrodes (e.g., between the lower electrode104(FIG. 1) and the upper electrode136(FIG. 1)) that is about one-half a resistance of a conventional magnetic memory cell. In some embodiments, the magnetic memory cell may be reduced from about 10 kΩ to about 5 kΩ.

The magnetic memory cells and arrays of magnetic memory cells formed according to the methods described herein may exhibit an improved performance. For example, magnetic memory cells formed according to the methods described herein may exhibit a reduced likelihood of device failure, such as by shorting (e.g., between the upper electrode136(FIG. 1) and the lower electrode104(FIG. 1). By way of comparison, up to about 10 percent of magnetic memory cells formed according to conventional methods may fail while less than about 0.0010 percent of magnetic memory cells formed according to the methods described herein may fail. Without wishing to be bound by any particular theory, it is believed that formation of the oxide material140(FIG. 1) substantially reduces a likelihood of shorting of the magnetic memory cells150(FIG. 1).

Accordingly, in some embodiments, a magnetic memory cells comprises a magnetic cell core comprising a first magnetic region over a substrate, a tunnel barrier material over the first magnetic region, and a second magnetic region over the tunnel barrier material. The magnetic memory cell further comprises an oxide material over sidewalls of the magnetic cell core, wherein the magnetic cell core exhibits a homogeneous crystal structure with an increasing purity in a direction toward a laterally central portion of the magnetic cell core.

FIG. 6is a graph illustrating each of a TMR and an overall resistance of a magnetic tunnel junction formed (e.g., patterned) at different temperatures. For example, when the magnetic tunnel junction is formed at lower temperatures, the magnetic tunnel junction exhibits an increased TMR and a reduced resistance, as illustrated in the upper left portion of the graph. By way of contrast, and as illustrated in the lower right corner of the graph, when formed at relatively higher temperatures, the magnetic tunnel junction exhibits a reduced TMR and a higher resistance.

FIG. 7is a graph illustrating an amount of source gas diffusion as a function of diffusion depth in a substrate at different patterning temperatures (e.g., room temperature, −20° C., and −100° C.). As illustrated, a material being patterned may include a lower concentration of diffused source gases when the material is patterned at lower temperatures compared to when the material is patterned at higher temperatures. In addition, source gases may diffuse only to shallower depths in materials patterned at lower temperatures.

Without wishing to be bound by any particular theory, it is believed that at temperatures below about 0° C., a reduced amount of elemental diffusion and intermixing between adjacent materials of the magnetic tunnel junction occurs. In addition, at lower temperatures, an amount of diffusion of source gases from a beam into a material being patterned is substantially reduced.

FIG. 8AandFIG. 8Billustrate magnetic tunnel junctions800,800′ patterned at a temperature above about 0° C. and at a temperature below about 0° C., respectively. As illustrated inFIG. 8A, the magnetic tunnel junction800patterned at a temperature above about 0° C. exhibits a distorted crystal structure (e.g., a lattice mismatch) in each of a first magnetic material802, a second magnetic material806, and a tunnel barrier material804between the first magnetic material802and the second magnetic material806. The magnetic tunnel junction800may exhibit a distortion in the crystal structure of the tunnel barrier material804up to a depth D1measured from a sidewall808of the magnetic tunnel junction800. In addition, the magnetic tunnel junction800may include an increased concentration of etchant gases810(e.g., oxygen atoms, argon atoms, etc.) dispersed therein.

By way of contrast, and referring toFIG. 8B, the magnetic tunnel junction800′ formed according to embodiments of the disclosure (i.e., patterned at temperatures lower than about 0° C.), may be substantially free of crystal defects in each of a first magnetic material802′, a second magnetic material806′, and an intervening tunnel barrier material804′. The magnetic tunnel junction800′ may not exhibit a lattice mismatch in any of the first magnetic material802′, the second magnetic material806′, or the tunnel barrier material804′. In addition, the magnetic tunnel junction800′ may be substantially free of diffused etchant gases810in the crystal structure thereof.

Accordingly, forming the array100of magnetic memory cells150(FIG. 1) at a temperature below about 0° C. may increase magnetic properties of the magnetic memory cells150. In some embodiments, elements from the fixed region130(FIG. 1) may not substantially diffuse and intermix with elements of the tunnel barrier material126(FIG. 1). Similarly, elements of the free region132may not substantially intermix with elements of the tunnel barrier material126. Accordingly, interfaces between the fixed region130and the tunnel barrier material126and between the free region132and the tunnel barrier material126may be substantially free of intermixed elements and may be distinct.