Piezoeletric wet etch process with reduced resist lifting and controlled undercut

Patent metadata

Field	Value
Publication number	US-9755139-B2
Application number	US-201514738847-A
Country	US
Kind code	B2
Filing date	Jun 13, 2015
Priority date	Jun 30, 2014
Publication date	Sep 5, 2017
Grant date	Sep 5, 2017

Abstract

A microelectronic device containing a piezoelectric thin film element is formed by oxidizing a top surface of a piezoelectric layer with an oxygen plasma, and subsequently forming an etch mask containing photoresist on the oxidized top surface. The etch mask is conditioned with an oven bake followed by a UV bake. The piezoelectric layer is etched using a three step process: a first step includes a wet etch of an aqueous solution of about 5% NH 4 F, about 1.2% HF, and about 18% HCl, maintaining a ratio of the HCl to the HF of about 15.0, which removes a majority of the piezoelectric layer. A second step includes an agitated rinse. A third step includes a short etch in the aqueous solution of NH 4 F, HF, and HCl.

First claim

What is claimed is:

1. A method of forming a microelectronic device, comprising the steps:
providing a structural member;
forming a lower contact layer over the structural member;
forming a layer of piezoelectric material on the lower contact layer;
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 ultraviolet (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 ammonium fluoride (NH 4 F), hydrofluoric acid (HF), and hydrochloric acid (HCl);
exposing the microelectronic device to an agitated rinse process;
exposing the layer of piezoelectric material to a second wet etch comprising an aqueous solution of NH 4 F, HF, and HCl;
removing the aqueous solution of the second wet etch by a rinse process; and
removing the piezoelectric element mask.

2. The method of claim 1 , wherein the layer of piezoelectric material comprises primarily lead zirconium titanate.

3. The method of claim 1 , wherein removing the upper contact layer comprises forming a plasma with chlorine-containing gas, oxygen and argon over the top surface.

4. The method of claim 1 , comprising an overetch process after removing the upper contact layer and before exposing the top surface of the layer of piezoelectric material to the oxygen plasma, wherein the overetch process comprises forming a plasma with chlorine-containing gas and oxygen over the top surface, the plasma of the overetch process being substantially free of argon.

5. The method of claim 1 , comprising an over-ash process after exposing the top surface of the layer of piezoelectric material to the oxygen plasma and before forming the piezoelectric element mask, wherein the over-ash process exposes the top surface of the layer of piezoelectric material to the oxygen plasma after the top contact mask is removed for 50 seconds to 100 seconds.

6. The method of claim 1 , wherein the piezoelectric element mask comprises negative photoresist.

7. The method of claim 1 , wherein thermally baking the piezoelectric element mask comprises baking at 180° C. to 190° C. for 45 minutes to 90 minutes.

8. The method of claim 1 , wherein baking the piezoelectric element mask while exposing the piezoelectric element mask to UV radiation comprises exposing the piezoelectric element mask to at least one of a low intensity UV source with power densities from 80 milliwatts/cm 2 to 108 milliwatts/cm 2 and a high intensity UV source with power densities from 225 milliwatts/cm 2 to 280 milliwatts/cm 2 while heating the microelectronic device to 200° C. to 250° C., for 90 seconds to 150 seconds.

9. The method of claim 1 , wherein:
the first wet etch comprises an aqueous solution of 4.5 percent to 5.5 percent NH 4 F, 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; and
the second wet etch comprises an aqueous solution of 4.5 percent to 5.5 percent NH 4 F, 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.

10. The method of claim 1 , wherein the agitated rinse process comprises a deionized water (DI H 2 O) rinse with nitrogen bubbling.

11. The method of claim 1 , wherein the agitated rinse process comprises a deionized water (DI H 2 O) rinse with ultrasonic power applied to the DI H 2 O.

12. The method of claim 1 , wherein the agitated rinse process comprises a deionized water (DI H 2 O) rinse which is stirred by a stifling mechanism.

13. The method of claim 1 , wherein the agitated rinse process comprises a DI H 2 O spray rinse.

14. The method of claim 1 , wherein removing the piezoelectric element mask is performed with an ash process.

15. The method of claim 1 , wherein the top contact layer comprises a layer of platinum.

16. The method of claim 1 , wherein the bottom contact layer comprises a layer of platinum over an adhesion layer.

17. The method of claim 1 , comprising:
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.

18. The method of claim 1 , wherein the step of removing the top contact mask is free of a wet clean.

19. 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 NH 4 F, 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 NH 4 F, 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

Assignees

• Texas Instruments Inc

Inventors

• Jiang Neng
• Li Xin
• Soman Joel
• Lassiter Thomas Warren
• Roby Mary Alyssa Drummond
• Chang Yungshan

Classifications

• H01L41/1876

  Electricity · mapped topic

• H01L41/332 Primary

  Electricity · mapped topic

• H10N30/082 Primary

  by etching, e.g. lithography · CPC title

• H10N30/03

  Assembling devices that include piezoelectric or electrostrictive parts · CPC title

• H10N30/8554 Primary

  Lead-zirconium titanate [PZT] based · CPC title