Ion beam etching utilizing cryogenic wafer temperatures

A method of etching a substrate for forming a spin-torque-transfer random access memory (STT-RAM) device, the method comprising:

• receiving the substrate in a reaction chamber, the substrate comprising (i) a bottom electrode layer, (ii) an etch stop layer positioned over the bottom electrode layer, (iii) a first magnetic layer positioned over the etch stop layer, (iv) a tunneling dielectric layer positioned over the first magnetic layer, (v) a second magnetic layer positioned over the tunneling dielectric layer, and (vi) a patterned mask layer;
• performing a first ion beam etching operation to define features on the substrate,
• the first ion beam etching operation comprising exposing the substrate to ion beams to etch through at least the second magnetic layer, the tunneling dielectric layer, and the first magnetic layer, and
• wherein during the first ion beam etching operation, a substrate support is maintained at a temperature between about 10° C. and about 120° C.;
• performing a second ion beam etching operation to narrow the features on the substrate,
• the second ion beam etching operation comprising exposing sidewalls of the features to ion beams and preferentially depositing a first material in regions etched during the first ion beam etching operation, and
• wherein during the second ion beam etching operation, the substrate support is maintained at a temperature between about −70° C. and about 10° C.

An ion beam etching apparatus for etching a substrate while forming a spin-torque-transfer random access memory (STT-RAM) device, the apparatus comprising:

• a reaction chamber;
• an ion beam generator;
• a substrate support configured to heat and cool a substrate;
• a controller having instructions to etch the substrate by:
• receiving the substrate in the reaction chamber, the substrate comprising (i) a bottom electrode layer, (ii) an etch stop layer positioned over the bottom electrode layer, (iii) a first magnetic layer positioned over the etch stop layer, (iv) a tunneling dielectric layer positioned over the first magnetic layer, (v) a second magnetic layer positioned over the tunneling dielectric layer, and (vi) a patterned mask layer;
• performing a first ion beam etching operation to define features on the substrate,
• the first ion beam etching operation comprising exposing the substrate to ion beams to etch through at least the second magnetic layer, the tunneling dielectric layer, and the first magnetic layer, and
• wherein during the first ion beam etching operation, a substrate support is maintained at a temperature between about 10° C. and about 120° C.;
• performing a second ion beam etching operation to narrow the features on the substrate,
• the second ion beam etching operation comprising exposing sidewalls of the features to ion beams,
• wherein the second ion beam etching operation is performed at a lower ion energy than the first ion beam etching operation, and
• wherein the first and/or second ion beam etching operation result in formation of conductive material on exposed portions of the tunneling dielectric layer and/or in the tunneling dielectric layer;
• and
• performing a conductive material mitigation operation to mitigate the conductive material formed on or in the tunneling dielectric layer during the first and/or second ion beam etching operation,
• wherein mitigating the conductive material comprises either removing the conductive material or rendering the conductive material less conductive,
• wherein the conductive material mitigation operation comprises exposing the substrate to ion beams,
• wherein the conductive material mitigation operation is performed at a lower ion energy than the second ion beam etching operation, and
• wherein during the conductive material mitigation operation, the substrate support is maintained at a temperature between about −70° C. and −10° C.