# US 10,319,899 B2 · Method of forming a semiconductor device

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- Number: US 10,319,899 B2
- Document ID: US10319899B2
- Status: Granted
- Kind: B2
- Application number: 15/669,309
- Filed: 2017-08-04
- Published: 2017-11-23
- Granted: 2019-06-11
- Earliest claimed: 2014-06-30
- Assignees: Texas Instruments Incorporated
- Applicants: Texas Instruments Incorporated
- Inventors: Neng Jiang; Xin Li; Joel Soman; Thomas Warren Lassiter; Mary Alyssa Drummond Roby; YungShan Chang
- Web page: https://patentgrep.com/patent/US10319899B2

## CPC

- H10N 30/082: by etching, e.g. lithography
- H10N 30/03: Assembling devices that include piezoelectric or electrostrictive parts
- H10N 30/04: Treatments to modify a piezoelectric or electrostrictive property, e.g. polarisation characteristics, vibration characteristics or mode tuning
- H10N 30/074: by depositing piezoelectric or electrostrictive layers, e.g. aerosol or screen printing
- H10N 30/8554: {Lead-zirconium titanate [PZT] based}
- H10N: ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR

## 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% NH4F, 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 NH4F, HF, and HCl.

## Claims

### Claim 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 using an etch chemistry;
exposing the microelectronic device to an agitated rinse process;
exposing the layer of piezoelectric material to a second wet etch comprising the etch chemistry; and
removing the piezoelectric element mask.

### Claim 2 (depends on 1)

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

### Claim 3 (depends on 1)

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.

### Claim 4 (depends on 1)

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.

### Claim 5 (depends on 1)

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.

### Claim 6 (depends on 1)

The method of claim 1, wherein the etch chemistry comprises 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.

### Claim 7 (depends on 1)

The method of claim 1, wherein the agitated rinse process is selected from the group consisting of:
a deionized water (DI H2O) rinse with nitrogen bubbling;
a deionized water (DI H2O) rinse with ultrasonic power applied to the DI H2O; and
a deionized water (DI H2O) rinse which is stirred by a stirring mechanism.

### Claim 8 (depends on 1)

The method of claim 1, wherein the agitated rinse process comprises a DI H2O spray rinse.

### Claim 9 (depends on 1)

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

### Claim 10 (depends on 1)

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

### Claim 11

A method of forming a microelectronic device, comprising the steps:
forming a layer of piezoelectric material over a substrate;
exposing a top surface of the layer of piezoelectric material to an oxygen plasma;
forming a piezoelectric element mask on the layer of piezoelectric material;
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 using an etch chemistry;
exposing the microelectronic device to a rinse process;
exposing the layer of piezoelectric material to a second wet etch comprising the etch chemistry; and
removing the piezoelectric element mask.

### Claim 12 (depends on 11)

The method of claim 11, wherein the layer of piezoelectric material comprises primarily lead zirconium titanate.

### Claim 13 (depends on 11)

The method of claim 11, wherein thermally baking the piezoelectric element mask comprises baking at 180° C. to 190° C. for 45 minutes to 90 minutes.

### Claim 14 (depends on 11)

The method of claim 11, wherein the etch chemistry comprises an aqueous solution of NH4F, HF, and HCl.

### Claim 15 (depends on 11)

The method of claim 11, wherein the etch chemistry comprises 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.

### Claim 16 (depends on 11)

The method of claim 11, wherein the rinse process is an agitated rinse process selected from the group consisting of:
a deionized water (DI H2O) rinse with nitrogen bubbling;
a deionized water (DI H2O) rinse with ultrasonic power applied to the DI H2O; and
a deionized water (DI H2O) rinse which is stirred by a stirring mechanism.

### Claim 17

A method of forming a microelectronic device, comprising the steps:
forming a layer of piezoelectric material over a substrate;
forming a piezoelectric element mask on the layer of piezoelectric material;
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 (NH4F), 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 NH4F, HF, and HCl;
removing the aqueous solution of the second wet etch by a rinse process; and
removing the piezoelectric element mask.

### Claim 18 (depends on 17)

The method of claim 17, wherein:
the first wet etch comprises 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; and
the second wet etch comprises 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.

### Claim 19 (depends on 17)

The method of claim 17, wherein the agitated rinse process is selected from the group consisting of:
a deionized water (DI H2O) rinse with nitrogen bubbling;
a deionized water (DI H2O) rinse with ultrasonic power applied to the DI H2O; and
a deionized water (DI H2O) rinse which is stirred by a stirring mechanism.

### Claim 20 (depends on 17)

The method of claim 17, wherein the layer of piezoelectric material comprises primarily lead zirconium titanate.