Method for creating double bragg mirror for tight frequency reference control

Patent metadata

Field	Value
Publication number	US-11146230-B2
Application number	US-201916553518-A
Country	US
Kind code	B2
Filing date	Aug 28, 2019
Priority date	Aug 28, 2019
Publication date	Oct 12, 2021
Grant date	Oct 12, 2021

Abstract

A method for creating a double Bragg mirror is provided. The method comprises providing a wafer having a plurality of bulk acoustic wave (BAW) devices at an intermediate stage of manufacturing. A first dielectric layer is deposited over the wafer. A plurality of as-deposited thicknesses of the dielectric layer are determined, each as-deposited thickness corresponding to one BAW device from the plurality of BAW devices. A corresponding trimmed dielectric layer over each of the BAW devices is formed by removing a portion of the dielectric layer over each of the BAW devices, with a thickness of the removed portion determined from a corresponding as-deposited thickness and a target thickness. A Bragg acoustic reflector that includes the corresponding trimmed dielectric layer is formed over each of the BAW devices.

First claim

The invention claimed is:

1. A method of manufacturing a semiconductor device comprising the steps of:
providing a wafer having a plurality of bulk acoustic wave (BAW) devices at an intermediate stage of manufacturing;
depositing a dielectric layer over the wafer;
determining a plurality of as-deposited thicknesses of the dielectric layer, each as-deposited thickness corresponding to one BAW device from the plurality of BAW devices;
forming a corresponding trimmed dielectric layer over each of the BAW devices by removing a portion of the dielectric layer over each of the BAW devices, a thickness of the removed portion determined from a corresponding as-deposited thickness and a target thickness; and
forming over each of the BAW devices a Bragg acoustic reflector that includes the corresponding trimmed dielectric layer.

2. The method of claim 1 , wherein thickness nonuniformity of the dielectric layer within a production wafer is reduced by the trimming.

3. The method of claim 1 , further comprising measuring a post-trim thickness of the dielectric layer over each of the plurality of bulk acoustic wave devices after trimming the dielectric layer.

4. The method of claim 1 , wherein removing a portion of the dielectric layer is performed using ion beam milling.

5. The method of claim 1 , wherein an amount of the dielectric layer removed is different for each bulk acoustic wave device.

6. The method of claim 1 , wherein the dielectric layer comprises silicon dioxide.

7. The method of claim 1 , wherein trimming the dielectric layer provides a variance of less than ±3000 parts per million of the target thickness over the plurality of bulk acoustic wave devices.

8. The method of claim 1 , further comprising pre-trimming the plurality of BAW devices prior to depositing the dielectric layer, the pre-trimming limiting a variance of a pre-trim resonant frequency to ±3000 ppm.

9. The method of claim 1 , further comprising separating the plurality of bulk acoustic wave devices from the wafer.

10. A method of manufacturing a semiconductor device, comprising the steps of:
providing a substrate;
forming a lower Bragg acoustic reflector over the substrate, the lower Bragg acoustic reflector having alternating layers of a low-acoustic impedance material and a high-acoustic impedance material;
forming a lower electrode over the lower Bragg acoustic reflector;
forming a piezoelectric structure over the lower electrode;
forming an upper electrode over the piezoelectric structure;
depositing a first layer of an upper Bragg acoustic reflector over the upper electrode, the first layer having a first thickness;
comparing the first thickness with a predetermined thickness of the first layer;
removing a portion from an exposed surface of the first layer;
depositing additional layers of the upper Bragg acoustic reflector over the first layer.

11. The method of claim 10 , wherein the predetermined thickness is substantially equal to one quarter the wavelength of a fundamental resonant frequency of an associated BAW device.

12. The method of claim 10 , wherein the upper Bragg acoustic reflector is a first upper Bragg acoustic reflector, and further comprising determining the first thickness over a plurality of upper Bragg acoustic reflectors located over the substrate, the plurality including the first upper Bragg acoustic reflector.

13. The method of claim 10 , wherein the removing includes ion beam milling.

14. The method of claim 12 , wherein the removing includes removing a different amount of the first layer over each of the plurality of upper Bragg acoustic reflectors.

15. The method of claim 10 , further comprising determining a thickness of the first layer after the removing and before depositing the additional layers.

16. The method as recited in claim 10 wherein the semiconductor device is a BAW resonator.

17. The method as recited in claim 16 wherein the BAW resonator is a solidly mounted resonator (SMR).

18. The method of claim 17 , further comprising trimming the solidly mounted resonator prior to depositing the first layer.

19. The method as recited in claim 12 , further comprising separating the first upper Bragg acoustic reflector from the plurality of upper Bragg acoustic reflectors after depositing the additional layers.

20. The method as recited in claim 10 , wherein the first layer comprises silicon dioxide.

Assignees

• Texas Instruments Inc

Inventors

• Dellas Nicholas S
• Goodlin Brian
• Jackson Ricky

Classifications

• H10P14/69215

  the material being a silicon oxide, e.g. SiO2 · CPC title

• H10H20/841

  Reflective coatings, e.g. dielectric Bragg reflectors · CPC title

• H10H20/814

  having reflecting means, e.g. semiconductor Bragg reflectors · CPC title

• H03H3/02 Primary

  for the manufacture of piezoelectric or electrostrictive resonators or networks (H03H3/08 takes precedence) · CPC title

• H03H2003/025

  the resonators or networks comprising an acoustic mirror · CPC title