Method for manufacturing BAW resonators on a semiconductor wafer
A method for manufacturing a wafer on which are formed resonators, each resonator including, above a semiconductor substrate, a stack of layers including, in the following order from the substrate surface: a Bragg mirror; a compensation layer made of a material having a temperature coefficient of the acoustic velocity of a sign opposite to that of all the other stack layers; and a piezoelectric resonator, the method including the successive steps of: a) depositing the compensation layer; and b) decreasing thickness inequalities of the compensation layer due to the deposition method, so that this layer has a same thickness to within better than 2%, and preferably to within better than 1%, at the level of each resonator.
1. A method, comprising:
forming a Bragg mirror on a substrate, the forming of the Bragg mirror including:
forming a first conductive layer having a temperature coefficient of acoustic velocity of a first sign;
forming a compensation layer on the first conductive layer, the compensation layer having a temperature coefficient of acoustic velocity of a second sign that is opposite to that of the first sign; and
decreasing thickness inequalities of the compensation layer at least until the compensation layer has a thickness variation less than 2%; and
forming a piezoelectric resonator on the compensation layer, the forming of the piezoelectric resonator including:
forming a first electrode on the compensation layer;
forming a piezoelectric layer on the first electrode; and
forming a second electrode on the piezoelectric layer.
2. The method of claim 1 wherein the forming of the Bragg mirror includes:
forming a first dielectric layer on the substrate;
forming the first conductive layer on the first dielectric layer;
forming a second dielectric layer on the first conductive layer; and
forming a second conductive layer on the second dielectric layer.
3. A method, comprising:
forming a stack of layers on a semiconductor substrate, the forming of the stack of layers including:
forming a Bragg mirror on the substrate, the Bragg mirror including:
a first conductive layer on the substrate;
a first dielectric layer on the first conductive layer;
a second conductive layer on the first dielectric layer; and
a second dielectric layer on the second conductive layer, the first and second conductive layers having a temperature coefficient of acoustic velocity (TCV) of a first sign;
depositing a compensation layer on the second dielectric layer of the Bragg mirror, the compensation layer having a TCV of a second sign that is opposite to that of the first sign; and
decreasing thickness inequalities of the compensation layer at least until the compensation layer has a thickness variation less than 2%; and
forming a piezoelectric resonator on the compensation layer, the forming of the piezoelectric resonator including:
forming a first electrode on the compensation layer;
forming a layer of a piezoelectric material on the lower electrode; and
forming a second electrode on the layer of the piezoelectric material.
4. The method of claim 3 wherein decreasing thickness inequalities includes decreasing the thickness inequalities until at least the compensation layer has less than a 1% variation in thickness.
5. The method of claim 3 wherein decreasing thickness inequalities includes decreasing by ion etching of overthicknesses of the compensation layer caused by the depositing.
6. The method of claim 3 wherein an upper layer of the Bragg mirror and the compensation layer are a single layer of a same material.
7. The method of claim 3 wherein the compensation layer includes silicon oxide.
8. The method of claim 3 wherein the first and second electrodes includes molybdenum.
9. The method of claim 3 wherein the layer of piezoelectric material includes aluminum nitride.
10. The method of claim 3 wherein the first and second conductive layers each have a first acoustic impedance and the first and second dielectric layers each have a second acoustic impedance smaller than the first acoustic impedance.
11. The method of claim 10 wherein the first and second conductive layers are tungsten and the first and second dielectric layers are silicon oxide.
12. The method of claim 3 , further comprising forming a frequency adjustment layer on the resonator, the frequency adjustment layer having a thickness capable of compensating for a frequency shift due to manufacturing dispersions.
13. A method, comprising:
forming a Bragg mirror, including:
forming a first dielectric layer on a substrate;
forming a first conductive layer on the first dielectric layer;
forming a second dielectric layer on the first conductive layer; and
forming a second conductive layer on the second dielectric layer;
forming a temperature compensation layer on the second conductive layer of the Bragg mirror; and
decreasing thickness inequalities of the temperature compensation aver at east until the compensation layer has a thickness variation less than 2%; and
forming a piezoelectric resonator on the temperature compensation layer, the forming the piezoelectric resonator including:
forming a first electrode on the temperature compensation layer;
forming a piezoelectric material layer on the first electrode; and
forming a second electrode on the piezoelectric material layer.
14. The method of claim 13 further comprising forming a frequency adjustment layer on the second electrode of the piezoelectric resonator.
15. The method of claim 13 wherein the temperature compensation layer has a temperature coefficient of acoustic velocity (TCV) of a first sign and the first and second conductive layers of the Bragg mirror have a TCV of a second sign that is opposite to the first sign.