Manufacturing process for thin film bulk acoustic resonator (FBAR) filters

• US 20040172798A1
• Filed: 03/07/2003
• Published: 09/09/2004
• Est. Priority Date: 03/07/2003
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Avago Technologies Wireless IP Singapore Pte Limited (Broadcom, Inc.)
• Inventors: Ruby, Richard C., Bradley, Paul D., Larson, John D.
• Granted Patent: US 7,275,292 B2
• Time in Patent Office: Days
• US Class Current: 29/25.35
• CPC Class Codes: H03H 2003/0471 of a plurality of resonators at different frequencies
• CPC Class Codes: H03H 3/02 for the manufacture of piezoelectric or electrostrictive resonators or networks H03H3/08 takes precedence
• CPC Class Codes: H03H 3/04 for obtaining desired frequency or temperature coefficient
• CPC Class Codes: H03H 9/02149 of ageing changes of characteristics, e.g. electro-acousto-migration
• CPC Class Codes: Y10T 29/42 Piezoelectric device making
• CPC Class Codes: Y10T 29/49002 Electrical device making
• CPC Class Codes: Y10T 29/49005 Acoustic transducer
• CPC Class Codes: Y10T 29/49155 Manufacturing circuit on or in base
• CPC Class Codes: Y10T 29/49156 with selective destruction of conductive paths

Abstract

Method for fabricating an acoustical resonator on a substrate having a top surface. First, a depression in said top surface is generated. Next, the depression is filled with a sacrificial material. The filled depression has an upper surface level with said top surface of said substrate. Next, a first electrode is deposited on said upper surface. Then, a layer of piezoelectric material is deposited on said first electrode. A second electrode is deposited on the layer of piezoelectric material using a mass load lift-off process.

Claims

1. A method for fabricating an acoustical resonator on a substrate having a top surface, said method comprising steps of:

a) generating a depression in said top surface;

b) filling said depression with a sacrificial material, said filled depression having an upper surface level with said top surface of said substrate;

c) depositing a first electrode on said upper surface;

d) depositing a layer of piezoelectric material on said first electrode;

and

e) depositing a second electrode on said layer of piezoelectric material using a mass load lift-off process.

2. The method of claim 1 further comprising:

depositing a passivation layer for protecting the second electrode.

3. The method of claim 1 further comprising:

a reverse mass load process that includes the step of depositing conductive material;

depositing an AlN layer;

applying a mass load layer;

applying a photoresist layer over at least one shunt resonator;

etching the mass loading layer and AlN layer to form the second electrode leaving the mass loading layer over the shunt resonator.

4. The method of claim 1 wherein the step of depositing a first electrode on said upper surface comprises the steps of:

depositing a seed layer;

depositing a conductive material;

applying a patterned mask; and

etching the conductive material and seed layer in accordance with the patterned mask to form a bottom electrode.

5. The method of claim 1 wherein the step of depositing a second electrode on said layer of piezoelectric comprises the steps of:

depositing conductive material;

applying a mass load pattern;

depositing a mass load;

lifting off the mass load;

applying a patterned mask; and

etching conductive material in accordance with the patterned mask to form the second electrode.

6. The method of claim 1 wherein the step of depositing a second electrode on said layer of piezoelectric comprises the steps of:

depositing conductive material;

applying a mass load pattern;

depositing a mass load;

lifting off the mass load;

depositing a hard mask layer;

etching the hard mask layer;

etching the conductive material in accordance with the hard mask to form the second electrode.

7. The method of claim 1 further comprising the steps of:

etching the piezoelectric layer.

8. The method of claim 4 further comprising the steps of:

applying a lift-off pattern;

depositing lift-off conductive material for bond pads;

lifting off the conductive material leaving bond pads; and

releasing material from swimming pool.

9. A method for fabricating an acoustical resonator on a substrate having a top surface, said method comprising steps of:

generating a depression in said top surface;

filling said depression with a sacrificial material, said filled depression having an upper surface level with said top surface of said substrate;

depositing a first electrode on said upper surface;

depositing a layer of piezoelectric material on said first electrode;

depositing a second electrode on said layer of piezoelectric material by employing a mass load lift-off process; and

removing said sacrificial material from said depression.

10. The method of claim 9 wherein the step of depositing a first electrode on said upper surface comprises the steps of:

depositing a seed layer;

depositing a conductive material;

applying a patterned mask;

etching the conductive material and seed layer in accordance with the patterned mask to form a bottom electrode.

11. The method of claim 9 further comprising:

depositing a passivation layer for protecting the second electrode.

12. The method of claim 9 wherein said sacrificial material comprises a material chosen from the group consisting of PSG, BPSG, spin-on-glass, polyvinyl, polypropylene and polystyrene.

13. The method of claim 9 wherein said step of filling said depression comprises the steps of:

depositing a layer of said sacrificial material over said depression;

planarizing said deposited layer; and

polishing said planarized layer.

14. The method of claim 11 further comprising the step of providing a layer of an electrically insulating material on the surface of said substrate and depression prior to depositing said layer of sacrificial material, said electrically insulating material preventing a diffusion of elements in said sacrificial material from diffusing into said substrate.

15. The method of claim 9 wherein said first electrode comprises molybdenum.

16. The method of claim 9 wherein said layer of piezoelectric material comprises AlN.

17. An acoustical resonator comprising:

a buffer layer;

a first electrode formed on the buffer layer;

a second electrode formed with a lift-off process; and

a layer of piezoelectric material sandwiched between said first and second electrodes.

18. The acoustical resonator of claim 17 wherein said first electrode comprises molybdenum.

19. The acoustical resonator of claim 17 wherein said layer of piezoelectric material comprises AlN.

20. The acoustical resonator of claim 17 further comprising a substrate having a cavity in a surface thereof, said first electrode bridging said cavity.