Piezoeletric wet etch process with reduced resist lifting and controlled undercut

A method of forming a microelectronic device, comprising the steps:

• providing a structural member;
• forming a lower contact layer comprising platinum over the structural member;
• forming a layer of piezoelectric material comprising primarily lead zirconium titanate on the lower contact layer;
• forming an upper contact layer comprising on the layer of piezoelectric material;
• forming a top contact mask over the upper contact layer;
• removing the upper contact layer, where exposed by the top contact mask, with a plasma etch process using chlorine radicals, oxygen radicals and argon, to form a top contact on the layer of piezoelectric material;
• exposing a top surface of the layer of piezoelectric material, where exposed by the top contact, to an overetch process comprising a plasma process using chlorine radicals and oxygen radicals, the plasma process being substantially free of argon;
• exposing the top surface of the layer of piezoelectric material, where exposed by the top contact, to an oxygen plasma, the oxygen plasma removing the top contact mask;
• exposing the top surface of the layer of piezoelectric material, where exposed by the top contact, to an oxygen plasma over-ash process for 50 seconds to 100 seconds;
• forming a piezoelectric element mask on the layer of piezoelectric material, extending past the top contact;
• thermally baking the piezoelectric element mask at 180° C. to 190° C. for 45 minutes to 90 minutes;
• baking the piezoelectric element mask at 200° C. to 250° C. while exposing the piezoelectric element mask to UV radiation for 90 seconds to 150 seconds;
• removing at least a portion of the layer of piezoelectric material, where exposed by the piezoelectric element mask, by a first wet etch comprising an aqueous solution of 4.5 percent to 5.5 percent NH4F, 1.1 percent to 1.3 percent HF, and 16.5 percent to 19.5 percent HCl, wherein a ratio of the HCl to the HF is maintained at a value of 14.5 to 15.5;
• removing the aqueous solution of the first wet etch by an agitated rinse process;
• exposing the layer of piezoelectric material to a second wet etch comprising an aqueous solution of 4.5 percent to 5.5 percent NH4F, 1.1 percent to 1.3 percent HF, and 16.5 percent to 19.5 percent HCl, wherein a ratio of the HCl to the HF is maintained at a value of 14.5 to 15.5;
• removing the aqueous solution of the second wet etch by a rinse process;
• removing the piezoelectric element mask by an ash process;
• forming a bottom contact mask over the top contact and the piezoelectric element, extending partway onto the lower contact layer;
• removing the lower contact layer, where exposed by the bottom contact mask, to form a bottom contact;
• and
• removing the bottom contact mask.

A method of forming a microelectronic device, comprising the steps:

• providing a structural member;
• forming a layer of piezoelectric material above the structural member;
• forming a top contact on the layer of piezoelectric material;
• exposing a top surface of the layer of piezoelectric material, where exposed by the top contact, to an oxygen plasma;
• forming a piezoelectric element mask on the layer of piezoelectric material, extending past the top contact;
• thermally baking the piezoelectric element mask;
• baking the piezoelectric element mask while exposing the piezoelectric element mask to UV radiation;
• removing at least a portion of the layer of piezoelectric material, where exposed by the piezoelectric element mask, by a first wet etch comprising an aqueous solution of 4.5 percent to 5.5 percent NH4F, 1.1 percent to 1.3 percent HF, and 16.5 percent to 19.5 percent HCl, wherein a ratio of the HCl to the HF is maintained at a value of 14.5 to 15.5;
• removing the aqueous solution of the first wet etch by an agitated rinse process;
• exposing the layer of piezoelectric material to a second wet etch comprising an aqueous solution of 4.5 percent to 5.5 percent NH4F, 1.1 percent to 1.3 percent HF, and 16.5 percent to 19.5 percent HCl, wherein a ratio of the HCl to the HF is maintained at a value of 14.5 to 15.5;
• removing the aqueous solution of the second wet etch by a rinse process;
• and
• removing the piezoelectric element mask.